Aluminium Extrusions - Technical Design Guide
February 21, 2017 | Author: oliviamaslinuta | Category: N/A
Short Description
Download Aluminium Extrusions - Technical Design Guide...
Description
/
Page blank in original
ALUMINIUM EXTRUSIONS —
a technical design guide
i;c
Forfree, objectiveadviceon allmatters relating to aluminium extrusions contact: TheShapemakers Information Service Broadway House Calthorpe Road Birmingham
B151TN Tel: 021 4562276 Fax: 021 4562274
ALUMINIUM EXTRUSIONS —a
technical design guide
PUBLISHED BY THE SHAPEMAKERS —the information arm of the UK Aluminium Extruders Association
'I
©TheShapemakers Broadway House Calthorpe Road Birmingham B151TN
DISCLAIMER
This book is intended for use by technically skilled personnel. The use of the information contained herein by suchtechnicallyskilled personnel, is at the risk of the user. While all reasonable skill and care hasbeen exercised in the preparation of this book, there are no warranties, express or implied, as to the accuracy or completeness of this work,either by the author or the publisher, both ofwhom deny responsibility or liability for any results obtainedor damagescaused as a consequenceofthe usethereof .The publisher and the authorhereof grantno licence withthis book and disclaim all liability for suitability, practicability, infringement of property rights of third parties or non-conformance with anycodes, standards or regulations.
ACKNOWLEDGEMENT TO BSI Extracts from British Standards are reproduced with the permission of BSI. Complete copies ofthe Standards canbe obtained by postfromBSI Sales, Linford Wood, Milton Keynes, MK14 6LE. First published October1989 Reprinted July 1991
Printed in Great Britain by St Edmundsbury Press Ltd Bury St Edmunds, Suffolk
VI
Reprinted August 1994
PREFACE to the 1994 reprint — by Howard Spencer
Since this manual was originally published, British Standards havepublished a new aluminium structural code, BS 8118 1991, whichsupersedes BS CP118 1969: — —
Part 1: Code of Practice for Design Part 2: Specification for Materials, Workmanship and Protection
There is at presenta change-over periodwhere both design codes are valid, but at some time in the future BS CP118 will be withdrawn. This new code is intended to bring aluminium structural design into line with othermetals and also with European standard codes, which will simplify future preparation of an overall European structural code for aluminium.
I intend here to give users ofthe manual averybrief outline of how the new codes will affect the use of aluminium. It is impossible to go into too much detail. Those requiring additional information should refer to the codes themselves, available from British Standards (see address below). The New Code The new code is based around a new design approach, based on the principle of 'limitstatedesign'. Thisprinciple is concerned with ensuring that anygivenstructure cancarry the loadsand forces placed upon it withoutfailure, up to a pre-determined limit. The factored resistance of a structure must therefore never be less than the factored loading. The following equation can be applied: Y12R = Y4S
R
S
= overall resistance factor = calculated resistance = overall loading factor = maximum design load
The resistance is calculated from the effective sectional properties, the limiting stressand a material and connection factor. The loading effectisfactored fortypeof load, i.e. dead load, imposed load, wind load and temperature induced forces. The new code also covers the calculation of elastic instabilities. Aluminium sections with verywide, thinelements are susceptible to local buckling underhigh compressive stresses. The relevantcalculations have been simplified in the new code by adopting a classification system based upon a factored relationship between the width or depth of the element and the thickness. Three categories are listed for moment resistance — compact, semi-compact and slender. For compact sections,
I
no further check is required as theywill not suffer fromlocal buckling. (For example, afl the sections listed in BS 1161 "AluminiumStructural Sections" are compact.) Semi-compact resistance is obtained by using the quoted limiting stress of the material. Sections defined as slender, however, are assessed on the basis of a reduced effective wall thickness and the extent of the reduction can be obtained from a seriesofcurves. Only the compact and slender categories are allowed when calculating the axial resistance of struts. Therecommendation fordeflection levels hasnot changed, but a word of caution is included in the specification against imposing too tight a standard on aluminium structures when the particularapplication does not merit it. The section on welding has been greatly extended from that in the original code. Guidance is provided on the design of weldstaking intoaccount the strength ofthe weld metal and a partial reduction in strength in the heat affected zoneof the parent metal. The limiting stressesfor both filler and parent metal are given with factorsfor designing butt and lap joints for both traverse and longitudinal welds. Adhesively bonded joints are only recommended for secondary stressed connections. The factored resistance of a bonded joint can be calculated from an expression containing a failing standard, obtainedfromtesting, and a material connection factor for bonded joints, If validated test data is available, it can be used in the joint resistance expression.
The section on fatigue has also been greatly extended, incorporating information fromboth UK and European research. The tablesfor both welded and non-welded structures contain detailed sketches illustrating the typeof construction, direction of stress, fluctuation and possible cracklocations. Thetables are based upon BS 5400 Part 10: Bridges and give the classification for a range of structural detail. Full supporting data including mathematical formulae relevanttothe design calculationsand curvesused in the codeare setout in the appendices of the new codeand can be used to assistcomputer aided design.
All references in the manual to BS CP1 18 now apply to BS 8118 and, as the new code does not cover permissible stress levels, table 3.2 and figure 3.3 are not applicable. Tables 3.4 and 6.11 have also been modified as the standard elastic modulus for all wroughtaluminium alloysis now 70,000 N/mm2 Reviewing the worked examples given in the manual, the pedestrian balustrade (pages 113—122) results in marginal modifications to some sections whenworkedto the new code but gives similar overall results. In the case of the unloading ramp, however (pages 111—112) there could be a slight saving in the thickness of the section when meeting the new code. The column example (pages 123—125)refers to alloy2014AT6 which is no longer astandard material inthe newcode. Although it can be used, the limit statestresses would have to be established and, in this case, the sectionthicknesswould haveto be slightly increased.
VIII
Competently used, the old code should still give an acceptable level of design. It should be noted, however, that if the calculations are to be officiallyapproved then only the new code is valid. Furthermore, the up-dated information in the new code can result in a more economical structural useof the material. Codes referred to: BS 8118 Part 1: BS 8118 Part 2:
Codeof Practice for Design 1991 Specification for Materials, Workmanship and Protection 1991
These are available from:
Sales Dept, BSI, Linford Wood, Milton Keynes, MK14 6LE, or any HMSO.
ix
INTRODUCTION
Aluminium is a highly versatile, light and strongmaterial whichcanbe produced in a varietyofalloysandextruded intoan almost infinite number ofshapes. Thispowerful combination of factors enables the user to be more innovative and facilitates costeffective design. Comprising 8% of the earth's crust, aluminium is a plentiful resource. It is a modern material, first used in commercial production in 1886. Since then, the list of applications has grown immensely. Now, designers working in a whole range of different sectors, including generalengineering, construction, transport, packaging and consumer products, are reaping the benefits gained by using aluminium extrusions.
The Shapemakers was established by the Aluminium Extruders Association (AEA) in 1984 to provide independent guidance on all matters relating to extruded aluminium. Representing the UK's top extrusion companies, The Shapemakers is ableto drawupon thesecompanies' considerable resources and expertise. This technical design guide contains a wealth of information on aluminium itself, as well as giving details on the extrusion process, fabrication and finishing. Also included is a comprehensive design section, which outlinesthe important design considerations and shows a number ofworked examples.
Forreasonsofclarity, onlysix alloys have been incorporated intothemainbody of the manual. These have been carefully selected to illustrate the various uses of alloys — from general purpose to high strength. Additional alloys are listed in the appendices. For details of the availability of anyalloy listed in this manual, please contact the Shapemakers Information Service in Birmingham, Tel: 021 4562276. The AEA would like to thank The Shapemakers' technical consultant, Howard Spencer, forall his workin compiling thisdesign guide. Aspecial thanksalsogoesto TheShapemakers' members, Hugo Ravesloot, Jim Peach and Chris Forman.
Derek Phillips Chairman of The Shapemakers
CONTENTS
PRINCIPLES OF EXTRUSION
1
MATERIAL SPECIFICATIONS
25
MECHANICAL PROPERTIES
33
DURABILITY
45
SURFACE FINISHING
55
FABRICATION
63
CONDUCTIVITY
87
TEMPERATURE
93
FIRE
97
CARE AND CONTROL
101
DESIGN
105
GLOSSARY OF TERMS
127
APPENDICES
133
ALUMINIUM EXTRUSIONS —
a technical design guide
SECTION 1 - PRINCIPLESOF EXTRUSION
CONTENTS Title
Page No.
EXTRUSIONPROCESS Direct Extrusion IndirectExtrusion Hollow Sections
4
EXTRUDABILITY Extrusion Ratio Shape Factor
7 7 7
SIZE
8
THICKNESS
8
4 5 6
SLOTS
10
SECTION CLASSIFICATION
11
CORNERS
11
TOLERANCES
12
List of Figures Fig No.
Title
1.1
TheDirect ExtrusionProcess
1.2
TheDiffering Operating Principlesof Direct
Page No. 4
and IndirectExtrusion
5
1.3
Extrusion of a Hollow Section
6
1 .4
Thick to Thin Transitionsin Extrusion Cross Section
10
1.5
PressureHinge
10
1.6
SlotAspect Ratios
10
1.7
Standard Section Types
11
Listof Tables No.
Title
1.1
Shape Factor Value
8
1.2
A Guide to MinimumThickness
9
1.3
Toleranceson Diameter of Round Bar Intendedfor use on Automatic Lathes
12
Toleranceson Widths Across Flats of HexagonalBar forthe Manufactureof Nut & Bolts
13
Toleranceson Diameter of Round Bar in the Controlled StretchedCondition
13
1.4
1.5
Page No.
2
List of Tables (contd.) No
Title
1.6
Toleranceson Diameter or Width Across Flats of Bars for General Purposes and on Width of Solid or Hollow RegularSections
14
Angular Tolerancesfor ExtrudedRegul&Sections
15
1.8
PermittedCorner Radii
15
1 .9
Toleranceson Wall Thicknesses of ExtrudedRound Tube (classes A, B and C).
16
Toleranceson Thicknessof Bars and Regular Sections
17
Toleranceson Open End of Channelsand L Beams
18/19
1 .7
1.10
1.11
1.12
1.13
1 .14
1.15
1 .16
1 .17
Page No.
Tolerances on the Outside Diameter of All Extruded Round Tube and on the Inside Diameter of Class A and Class B Extruded Round Tube
20
Toleranceson Thicknessof Hollow Sections (classes A and B)
21
Toleranceson Straightnessfor ExtrudedBar, RegularSections and Extruded RoundTubes
22
Toleranceson Length for All Materials Suppliedin Fixed Cut Lengths
23
Tolerances on Concavity and Convexityfor Extruded Solid and Hollow Sections
23
Toleranceon Twist for Extruded Solid and Hollow Sections
24
3
EXTRUSIONPROCESS
Direct Extrusion The direct extrusion processcan be clearly seen in the schematicdiagram in Fig. 1.1. Cylindrical aluminium alloy billets of cast or extruded manufacture are heated to between4500and 500° before being loaded into a container and the billet squeezed through a die orifice using ram pressuresof up to 68OMPa. The die is supported by a series of back dies and bolsters so that the main press load is transferred to a front platen.
Ram cross head Stem
Liner
Die slide
Dummy block Platen
Container
Billet Die
Backer
Sub bolster Extruded section
Fig. 1.1 - The Direct Extrusion Process
4
On leavingthe die the temperatureof the section is more than 500°C and with heat treatable afloys the quenching, or solution heat treatment, takes place in the production line. Thiscanbe bywater bath, water spray or forced-draughtair, with the latter being particularly useful for thin sections. The approximatetemperaturedrop during the traverse of the quench box is 250°C. To avoid distortion care hasto be exercised in handling sections with extreme aspect ratios and large variations in thickness.
Afterextrusionthe section is guided downthe table by a puller on to a slatted moving belt. Modern Pullers are based on linear motor s,stemsand operateon tables up to 40 metres long. On completion of an extruded length, the section is sheared at the press end and lifted from the slatted table by eccentric pivoted arms. It is then transferred by a walking beam or multi-belttransfertable to the stretcher bay where it is given a controlled stretch to straighten and remove minor mis-alignments.The section is then taken and cut to ordered lengths on high speed tungsten carbide tipped saws.
If the material is requiredin the solution heat treated condition (T4) it is released at this stage. If the full strength aged material (T6) is required, it is given a precipitation treatment before release. In the caseof the T5 temper,there is limited cooling atthe press exit and the material goes directly to precipitationtreatment. Indirect Extrusion In the traditional direct methodof extrusion,as described above, the die is stationary and the press ram applies pressure on to the billet. In the indirect method,the ram carriesthe die and appliespressureon tothe stationarybillet, inthe oppositedirection of extrusion.There can be variationto this basic concept,but in every case the billet remains stationary in relationto the container,thereby keepingfriction loss to a bare minimum. See Fig. 1.2. Die
Extrusion Billet
Die
Extrusion
Indirect extrusion Die
Billet
Fig. 1.2 - The DifferingOperatingPrinciplesof Directand Indirect Extrusion
5
HollowSections A bridgeor 'port-holedie' is usuallyusedto makehollowsections.Asolid billet isforced, under pressure,through acompositedietoolthatfirstdividesthe metal intotwo or more separate streams which then flows down under the bridge to be pressure welded together and emerge, as an extruded section,through the orifice formed betweenthe mandrel nose and the outer section shape which hasbeen cut in the die. See Fig. 1.3. Any sample taken across the section would show an integralmaterial quality with no reductionofstrength in the weld areas. Inspectionmethodsare usually by destructive test samplingin line with that laid down by the British Standards for scaffold tubing in specificationBS 1139. Productionmethodsfor this kind of section are wellestablished and extruders will be pleased to advise on the feasibility of producing any hollow section.
Some caution must be exercised, howeverwherethin hollowsections are required in thestronger alloys,particularlyfromthebridgeorport-holeproductionmethods.Hollow sections are usually produced in these alloys by using centre mandrelsthat are not connectedtothedie but are passedthrough a boredor piercedhole inthecentre ofthe billet and eitherconnectedorsupportedby the press rod. In this type of production,the metalflow aroundthe mandrelis not interruptedandthereare no extrusionweld planes inthe section. Theremaybesome restrictionintheavailabilityofthis type ofproduction and in the range of sectionsobtainablefrom it. As the standardoftolerances may also be wider further informationand advice should be sought from the extruderforstrong alloy hollow sections.
area
Pressure
Mandrel nose
Bridge
Fig. 1.3 - Extrusionof a Hollow Section 6
EXTRUDABILITY Aluminium alloys offer a wide range of performance characteristics and important amongst these is its extrudability. Linked with modern die-making facilities and traditionalexpertisethe metal offersa virtuallyunlimitedvarietyof sectionshapes. The feasibilityof any extrusionhasboth technicaland commercialconsiderationsand most extruders use a numberof methodsto evaluateextrusioncomplexity. These methods are usually based upon a combinationof extrusiontheory and experience.
ExtrusionRatio Extrusion ratio isthe valueobtained bydividingthe cross-sectionarea ofthe extrusion billet bythe cross-sectionarea of the extrusionto be produced. It dependsvery much on the size and type of press available and is a factor that can only be considered by the extruder. Optimumextrusion ratiosfordirect extrusionare usuallybetween30 and 50.
With lowvaluesof 7or under,there isvery littleworkingofthe materialduringextrusion. This gives a correspondingdrop in mechanicalpropertiesand the possibilityof coarse grain bands. Values of 80 and above require high breakthroughpressureswhich are likely to cause die distortion and possible breakage. In some casesthe extrusionratiocanbe improvedby usinga multi-holedie. Inthecase of indirectextrusionmuch higherextrusionratios are possiblebecauseofthe relatively low frictional force developed in the system. Shape Factor
The resistanceof a sectionto extrusioncan be influencedby the shapefactor. This is the relationshipbetween the periphery and cross-sectionareaof the section being extruded. It is usualforextrudersto modifytheshapefactor value, interms of extrusion weight, by dividingthe peripheryby the cross sectional area and multiplyingby .0027. The shape factor of a proposed extrusion is usually compared with that of a similar existing extrusionto obtain a measureof extrudability. This is not a precise method, however, as any large difference in wall thickness canalter the ratio substantially. In general, the higherthe value the moredifficult the extrusion and the more limitedthe alloy choice thereby restrictingsome high strength alloys. Table 1 .1 sets out some general values which can be used for reference.
7
Table 1.1 - Shape FactorValues
SectionType
CCD mm
Thickness mm
Shape Factor
L
142
2.5
300
L
70
1.5
500
112
5.0
152
O
142
solid
15
O
70
solid
30
©
50
3.0
247
©
50
1.5
494
ltiiiiiil
210
3.0
190
210
2.0
285
140
2.0/6.0
183
40
2.0/1.5
430
I
Iii 11J II SIZE
The sizeofanextrudedshape is determinedbythediameterof thecircumscribingcircle (CCD) required to enclose the cross-section. The maximumCCD for any die size is governed by the need to keep an unbroken structural ring aroundthe die orifice.The minimumwidth ofthat ring can vary from 20 mm on an averagesize solid dieto 60 mm or more on dies for large hollow sections. Most averagesectionsfit intoCCDs below 155 mm with a medium range of 250 mm and very large sections up to 400 mm. The section, should, as far as possible, be distributedaroundthe centre of the CCD. In anyextrusion,metalflow is slowertowardsthe outsideedge ofthe dieso the placing of thicker parts of the sectionaway fromthe centre results in a more even metal flow. THICKNESS Factorsthat dictatethickness are influencedbysection shape,alloy, dieface pressure, extrusionspeed and section stability duringsolution heattreatment and post-extrusion handling. Ageneral guide to minimumthickness isgiven in Table 1.2 which is based on 6063 material.
8
Table 1.2 - A Guideto Minimum Thickness
E E
I0) 0)
r
C-)
0)
0)
200
50
250
300
C C D in mm
a)
b)
Values for 6082 should be increasedby 25% Thesethickness - GCDratios representaveragevaluesbased upongood working practice.
c) d)
The values up to 1 .25 mm thick are for small specialised presseswith very high die face pressurelevels. When ratios below those shown are required contact extruders.
The extrusionprocess will toleratevariations in sectionthicknessbut it is importantto avoid abrupt change. Acceptabletransition betweenthicknessescanbe obtained by using radii or blendingcurves, see Fig. 1 .4. Short spans of local thinning can also be
incorporatedin most sections. This is a useful methodof introducingpressurehinges in section elementswhichwillbedeformedduring subsequentfabrication,see Fig. 1 .5. 9
p p
Radius
Fig. 1.4 - Thick to Thin Transitionsin ExtrusionCross-Section
I Thin hinge
/
—
Fig. 1.5 - PressureHinge
SLOTS The formationofslots,or open boxchannels,in asection requiresafinger or box spigot to be retainedon the die. As it is not possibleto reinforcethese spigots, which actas local cantileversunder extrusion pressure,a practical limitmust be placed on the size and type of slots available. Fig. 1.6 detailsthe normal methodofcalculatingslot aspect ratios althoughwhere gaps are below 3 mm these ratiosare evenfurther reduced. The maximum ratios are 3:1. Higher valuesare possible,particularly in 6063 alloy. Screw ports and bolt slots are detailed under these headings in section 6 Fabrication.
— Gap
— Depth
___
_____ =—
—
Area Aspect Ratio =
Aspect Ratio
Gap2
Fig. 1.6 - Slot Aspect Ratios.
10
Depth
Width
Width
SECTION CLASSIFICATION There arethreestandardtypesof section - solid,semi-hollowand hollow. Thefirstand last are self-explanatory.Semi-hollowdescribesthose solid sectionswhich have open box recesseswith aspect ratios (depth/width)less than three. In general,the tooling and productioncosts increasewith section categoriesfrom solid to semi-hollowand then hollow.
Solid
Semi-hollow
Hollow
Fig. 1.7 - Standard SectionTypes CORNERS
All corners are normally broken by a radius but where absolutely necessary,sharp cornerscanbe incorporatedin asection either internallyor externallybut the life of the die and thespeedofextrusionare both markedlyreduced.Suchcorners also introduce problems where paintedfinishes are specified, introducingobvious sight lines. The breakingof the corners,even by 0.5 mm radii is helpful in overcomingthese problems but for ideal extrusion conditions, radii should be related to the overall size of the section. Table 1.8 sets out preferredvalues.
11
TOLERANCES Tolerance levels for regular sectionsare laid down in BS 1474, howeveras the bulk of extrusions are non-standardthey are not covered in the standard. The extrusion industry regards BS 1474 as a target level and is preparedto accept if for all general business,apart from verythin or complexsections which will bethe subject of special enquiry. Closertolerancescanbeobtainedfor some sectionsbut, again,this isamatter betweencustomer and extruder.
In line with most productionmethods,tolerancesare necessaryto cover variationsin the actual process and wearing of toolsand dies. Most tolerances are quoted as plus or minus around a datum value but, if required, unilateral tolerance can be obtained, either all positiveor all negative. It is essential, however, to agree this requirement before die manufacture is commenced as the dimensional datum of the die will be altered.
Alltolerancesshouldbe measuredat 160G. This isparticularlysignificantforthelength tolerancesof long bars.
There is no laid-downstandardfor the surface smoothnessor texture of mill finished extruded sections. Table 1.3 - Tolerances on Diameter of Round Bar Intended for useon AutomaticLathes Diameter Over
Up to and
including
mm 10 18
mm 18 30
30 40 60 80
40
100
Plus and minimum toleranceson diameter
+mm
60 80
100 160
±
-mm
0.10 0.13 0.14 0.20 0.30 0.40 0.5% of specifieddiameter 0.05 0.08 0.14 0.20 0.30 0.40
12
Table 1.4 - Tolerances on Width Across Flatsof Hexagonal
Barfor theManufactureof Nuts & Bolts
Width across flats Over
Up to and
Tolerance on width across flats (all minus)
Including mm
mm
-
mm 0.08 0.10 0.13 0.15 0.20
4.0
4.0
19.0
19.0 36.0
36.0
46.0
80.0
46.0
Table 1.5 - Tolerances on Diameter of Round Bar in the Controlled Stretched Condition* Diameter Over
Up to and including
Tolerances on diameter (plusand minus)
mm
mm
+mm
-mm
10 18
18
0.05 0.08 0.14 0.20 0.30 0.40
0.20 0.26 0.28 0.40 0.60 0.80
0.5% of
1.0 % of
specified
specified
diameter
diameter
30 40 60 80 100
30 40 60 80 100 180
* The controlledstretch procedurereducesthe level of any residual stressesin abar and is ideal for machining stock. SpecialTempersT6510 and T6511 refers.
13
Table 1.6 - Tolerances on Diameter or Width Across Flats of Bars for General Purposesandon Width of Solid or Hollow Regular Sections Diameter, width or
width across flats Over
Up to and including
mm
mm
-
3
3
10 18
10 18
30 40 60 80 100
120 140 160 180
200 240 280
Tolerances (see notes 1 and 2)
±mm 0.16 0.20 0.26
30
0.32
40 60
0.40 0.45 0.50 0.65
80
100 120 140
0.80
180
0.90 1.00 1.10
200 240 280 320
1.20 1.30 1.50 1.70
160
NOTE 1: Tolerances in this table apply to solid materialsother than: (a) round bar for use on automaticlathes (see table 1.4) (b) controlledstretchedbar (see table 1.6) (c) hexagonalbars for the manufactureof nuts and bolts (see table 1.5) NOTE 2: Tolerances in this table apply to hollow regular sections having awall thicknessnot less than 1.6mmor3%of the overall width, whichever is the greater. In the case of non-heat-treatedmaterial or 1.6mm or4% oftheoverall width, whicheveris the greater,in the case of heat treated material. The tolerance should be appliedto the width measuredat the corners.
14
Table 1.7 - AngularTolerances for Extruded Regular Sections Nominal thickness of Allowabledeviation from angle thinnest leg (measured at the exUp to and specified Over tremitles of thesection) including mm -
j-
mm 1.6 5.0 -
1.6 5.0
2°
1.5° 1°
Table 1.8- PermittedCorner Radii For square and rectangularsections Minor dimension Over
Up to and Including
mm -
mm 5
5
10
10
25
25 50 120
Radius on corner (max.) mm 0.4 0.8 1.6 2.5 3.0 5.0
50 120 -
I
For regular sections (e.g. angle, channel, I- and - sections) Thicknessof Radius on corner (max.) section mm
mm
Up to and including 5
0.8
Over5
1.5
15
Table 1.9 - Tolerances on Wall Thicknessof Extruded Round Tube (classes A, B and C) (see note 1) Class A
ClassB
Toleranc Wall thickness on mean atany point thickness wall oftube thickness
Class C
Nominal
Tolerano
wall
on mean
(Max.)
(Mm.)
mm
mm
±mm
1.0 1.5
1.20 1.71
2.0
0.15 0.16 0.17
2.23
0.80 1.29 1.77
0.18 0.20
2.5 3.0 4.0
0.18 0.20 0.23
2.74 3.27 4.30
2.26 2.73 3.70
0.22 0.27
5.0 6.0
0.26 0.28 0.31
4.66 5.62 6.57
0.37 0.43
7.0
5.34 6.38 7.43
8.0
0.34 0.40 0.46
8.47
10.0 12.0
10.52 12.61
7.53 9.48
14.0 16.0 18.0
0.53 0.58 0.63
20.0 22.0 25.0
0.68 0.74
NOTE 2:
NOTE3:
NOTE 4: NOTE5:
Wall thickness at any point
wall
thickness
±mm
NOTE 1:
Tolerance on mean
wall
mm
0.81
Wall thickness at any point
-
.
(Max.)
(Mm.)
mm
mm
-
-
1.74
2.27 2.80
3.36 4.42
0.31
thickness
.
(Max.)
(Mm.)
±mm
mm
mm
-
-
1.26 1.73
2.20 2.64 3.58
-
-
0.65 0.70
3.87 4.93
2.13 3.09
6.00 7.09 8.18
4.00
6.73 8.64
-
-
4.51
0.75
0.51
5.49 6.58 7.67
5.42 6.33
0.82 0.89
8.76 10.85 13.03
7.24 9.15
0.94
9.27
11.39
0.56 0.65 0.77
10.97
1.03 1.15
11.36 13.54
10.46
14.71 16.76 18.82
13.29
0.88
12.76 14.66 16.56
1.30 1.40 1.50
12.25
1.00 1.13
15.24 17.34 19.44
15.75
15.24 17.18
20.90 23.00 26.10
19.10 21.00 23.90
1.22 1.35 1.49
21.63
18.38
23.81
20.19 23.00
1.60 1.73 1.88
27.00
4.91
5.82
17.88
14.12
20.00
16.00
22.13 24.32
17.88
27.50
22.50
19.68
BStoleranceclassesA,B and C forround tube denote a descendingorder of tolerancestandard. All classesapplicable to 6063, 6063A, 6082, 6101A, 6463, Only Classes B & C are applicableto 2014A
The tolerances given in this table apply to non-heat-treatedtube ofwall thicknessnot less than 1.6mmor3% ofthe outsidediameter,whicheveris the greater and to heat treatedtube ofwall thicknessnot less than 1.6mmor4% of the outside diameter,whichever is the greater. These toleranceson wall thickness do not apply where tolerances on both outside and inside diameterare required in which case the eccentricity toleranceon the resultantwall should be agreedbetweenthe purchaserand the supplier at the time of the enquiry and order. Mean thicknessisdefinedasthe sum ofthe wall thicknessesmeasuredatthe ends ofany two diameters at right angles, divided by four. The toleranceon the wall thicknessof intermediatenominal wall thickness should be taken as those of the next lower size.
16
—4
034 036 -
032 -
180
240
320
120
180
240
Over
32
060
050
040
036
0
0 28
026
022
020
± mm
065
055
045
039
034
0 30
028
024
022
± mm
6mm up to and up to and including including 6mm 10mm thick thick
3mm
Over
070
060
050
042
0 37
0 33
030
026
-
± mm
10mm up to and including 18mm thick
Over
075
065
055
045
0 40
0 36
032
.
-
+ mm
080
070
060
048
043
0
40
085
075
065
052
50
090
080
070
057
0
-
0 45
-
-
+ mm
-
mm
-
-
-
+
+ mm
-
095
085
075
065
-
.
-
± mm
mm
100
090
082
080
-
.
-
-
105
095
090
-
-
-
-
+ mm
mm
1
10
105
100
-
-
.
-
including including including including including including including including 30mm 40mm 60mm 80mm 100mm 120mm 140mm 160mm thick thick thick thick thick thick thick thick
Over Over Over Over Over Over Over Over 18mm 30mm 40mm 60mm 80mm 100mm 120mm 140mm up to and up to and up to and up to and up to and up to and up to and up to and
NOTE:- For sectionsover 160 mm thick, the toleranceson thickness are thoseshown for comparablewidths (see Table 1.6)
0 30
0 28
80
120
0 26
24
60
80
024
022 0
30
020
018
mm
018
±
016
mm
18
18
10
mm
Over 1.6mm up to and including 3mm thick
30
10
Up
Including
Up to and Including 1.6mm to and thick
Tolerances on specifiedthickness (plus and minus)
60
-
mm
Over
Widthacross flats of bar or width of section
Table 1.10- Tolerances on Thickness of Bars and Regular Sections
mm
10
18
30
40
60
80
100
120
140
160
-
10
18
30
40
60
80
100
120
140
including
3.0 6.0 3.0 6.0 3.0
60 3.0 6.0 -
6 -
3.0
3.0 6.0
3.0
-
3 0
6.0
3.0 6.0
-
6
6 -
6
-
6
-
6
-
6
-
30
1.5
6
1.5
-
mm 1.5 3.0 -
6 0
For 0
-
-
-
-
-
-
-
0.45 0.45 0 43
0.37 0.35
037
-
-
-
-
0.65 0.62 0.59
0.57 0.54
060
0.55 0.52 0.49
0.41
047 044
0.34 0.32
038
0.28 0.26
0.31 0 29 0.28
032
mm
0.23 0 22
+
026
* mm
Up to and up to and over
1.5 3.0
mm
For 0
1.21
1.25
1.11
1.15
1.01
1.05
086
0.90
0.71 0.66
0 75
061
0.70 0 66
0.65 0.61 0 56
053 048
0.57
0.47 0 40 0.36
0.41 0.34 0.30
÷ mm
36 1.30 1
126 120
1.16 1.10
095
1.01
073
0.86 0.80
0.75 0.68
1.52 1.44
134
1,42
32 1.24 1
1.17 1.09
1.02 0.94 0.82
0,77
097 0 89
0.84 0.72
0.70 0 63
081
0 92
0.64
055 0 76
076
0.84
0.55 0.47
070
• -
-
0.68 0.62
0.56 0.46 0.41
• -
* mm
deep
deep + mm
over 40mm up to and including 60mm
ForD over 30mm up to and including 40mm
ForD
23
73 1.61 1
1.63 1,51
1.53 1.41
1.38 1.26
1.11 0.96
1
1.18 1 06 0.91
1.13 1.01 0 86
093 0 78
1.05
74 59
1.94 1.79
1.84 1.69
1
1
59 1.44 1
44 1.29 1.09 1
1.39 24 1.04 1
1 34 1.19 0.99
091
1.11
126
-
-
+ mm
deep
-
mm
For 0 over 80mm up to and including 100mm
• -
+
For 0 over 60mm up to and including 80mm deep
2.15 1.95
1.86
206
1.95 1.76
1.61
1.80
1.46 1.22
165
117
1.41
1.60
1.55 1.36 1.12
-
-
* mm
deep
For 0 over 100mm up to and Including 120mm
76
2.36 2.14
2.26 2.04
2.16 1.94
2.01 1 79
1.35
164
1.86
181 1 59 1.30
1,54 1.26
1
-
-
-'
-
-
-
-
+ mm
mm
2.57 2.31
247 221
2.37 2.11
2.22 1.96
148
2.07 1.81
2.02 1.76 1 43
-
-
-
-
-
-
+
For 0 over 120mm 140mm to and up up to and including including 140mm 160mm deep deep
For 0 over
Inlernalor exte,nai tolerance on open end dimensionfor various deplhs of opening D(pius and minus)
For 0 over 18mm including including 10mm 10mm to and up up to and deep including including 18mm 30mm deep deep
of webor flange
Minimum thickness
Up to and Over
mm
Over
Overall width Wof channelor i-beam
Table 1.11 Tolerances on Open End Channels and L Beams
2.49
2.78
2.39
265
2.58 2.29
2.14
2.43
161
1.99
2.28
-
-
-
-
-
-
+ mm
For 0 over 160mm up to and including 180mm deep
-L (0
320
280
Depth of
280
240 6
-
Open end dlmens!on
-
-
-
-
-
-
-
6
6
-
6
240
-
200
6
-
6
200
-
180
6
6
180
-
160
mm
mm
mm mm
10mm deep
Web
Flonqe
-
-
-
-
31
55 71
Open
1.91
1
151
1
141
1.45
1
1.35
2.00
180
66
160
1
150
56
2
0
14
194
1 82 1.74
1.72 1.64
1.54
1.40 1
162
146
+ mm 71
232
211
191
2 03
181
1.93
1
183
mm
2.40
229
209
2,24
214 199
1.89
204
+
deep
mm
deep +
For D over 80mm up to and including 100mm
For 0 over 60mm up to and including 80mm
Depth of opeeng
+ mm
mm
+ mm +
For 0 over 40mm up to and including 60mm deep
For D over
For D over 18mm 30mm to and to and up up up to and Including Including including 18mm 30mm 40mm deep deep deep
or D For D to and up to and over including IncludIng 10mm
Up
mm
Up to and Over Including
of web or flange
2.66
246
2.26
2 45
2.35 2.16
2.06
225
+ mm
deep
For D over 100mm up to and including 120mm mm
284
264
2.44
2 66
2.34
256
2.24
246
+
deep
For 0 over 120mm up to and including 140mm
0
3.01
281
2 87 261
277 251
241
2.67
+ mm
over 140mm up to and including 160mm deep
For
Minimum thickness internal or external tolerance on open end dimension for variousdepths of opening D (plus and minus)
Over
Overallwidth Wof channel or I-beam
Table 1.11 (continued)
0
3.19
299
3 08 279
298 269
288 259
+ mm
deep
over 160mm up to and including 180mm
For
Table 1.12 - Toleranceson the OutsideDiameter ofAll Extruded Round Tube and on the Inside Diameter of Class A and class B Extruded RoundTube (see note 1)
Outsidediameter, Over
Up to and Including
Tolerance on the actual diameter(see notes 5 and 6)
mm
mm
±mm
±mm
18
0.19 0.23
0.34 0.40 0.45
or inside diameter
12 18 30
30 40
0.25 0.30 0.36
40 50 60
50 60 80
0.45 0.54 0.60
80
300
1%of diameter
Tolerance on themean diameter(see
notes5 and 6)
0.27
314%of
diameter
NOTE 1. For detailsconcerningtheapplicabilityoftolerance class (A or B) to alloy, see 1.9. NOTE 2. The tolerancesare applicableto non-heat-treated tubing ofwallthicknessnotIessthan1.6mmor 3% ofthe outside diameter, whichever is thegreater,and to heat-treated tubing of wall thickness not less than 1.6 mm or 4 % of the outside diameter, whichever Is the greater. NOTE3. In the caseoftubing in straight lengths, the above tolerancelimits are Inclusiveof ovality. NOTE4. Whereatoleranceon wallthicknessisrequired,the toleranceson diameter areto beappliedeithertothe outside diameteror to the Inside diameter, but notto both. NOTE 5. Tolerances on the actual diameter Indicate the amountby which the diameter (inside or outside, as appropriatemeasured in anydirection maydepartfromthespecified diameter. Tolerances on the mean diameter(inside or outside, as appropriate) Indicate the amount by which the mean oftwo diametersmeasured In two directions at right angles in the same plane may depart from the specified diameter.
NOTE6. Thegiventoleranceson the actual diameter do not apply to annealed tube, coiled tube, or tube having a wall thickness less than 2.5 % of outside diameter. The tolerancesoftheseproductsandofcontrolledstretchedtube are subject to agreement between purchaserand supplier.
20
-'
N)
0.48
0.65
.
. -
180
240 320
120 180 240 -
036 041 58
-
075 095
0
0.85 1 05 1 25
0.68
1
1
20 45
0.95
00
mm
1 1
40 80
110
1
-
. 062 0 82
048 058
0.41
048
-
.
-
-
-
* mm
30mm thick
075 -
-
-
0.65
.
055
0.45
036
0.28
-
-
036 045
0.28
022
-
* mm
+ mm
including 1.6mm up to and including 3.0mm thick
Up to and Over
-
0.85 1 00
065 075 0 80
0.54
* mm
3.0mm up to and including 6.0mm thick
Over
mm
00
20 1 40 1
110
1
090 095
-
.
-
40
mm
60 1 80 2 00 1
1.50
145
1
.
-
nm
2 60
240
2.20
2 00
-
-
+
including including including 30mm 10mm 18mm thick thick thick
Over Over 10mm 18mm to and to and up to and up up
6mm
Over
NOTE 2. The tolerancesapply to non-heat-treated sections of wall thickness not less than 1.6 mm or 3% of the overal width, whichever is the greater, and to heat-treated sections of wall thickness not less than 1.6mm or 4% of the overall width, whicheveris the greater.
NOTE 1. For detailsconcerningthe applicabilityof tolerance class (A to B) to alloy, see Note 1 of Table 1,9
0,36
032
60 80 120
0.22 0.28
mm
18mm thick
032
.
+
18mm
Over
-
.
10mm
6.0mm up to and including 10mm thick
Class B
up to and up to and 1.6mm including Including thick
Over
Over
. .
* mm
* mm
30 60 80
026
0.20
+ mm
10 18 30
mm
6.0mm thick
3.0mm thick
Over Up to and Up to and Over 3.0mm Including including 1.6mm 1.6 mm up to and up to and thick including Including
Class A
Tolerances on specified thickness
10 18
mm
Over
Width or widlh across flats
Table 1.13- Tolerances on Thickness of HollowSections(classesA and B(
Table 1.14 - Tolerances on Straightness for Extruded Bar, Regular Sectionsand Extruded Round Tubes (see below) For bars, tubes Temper
Nominal length of bar, tube or section L
or sections
within a circumscribing circle
Over 100
Maximum
S from straightnessof localized kink in any 300 mm length L (metres) portion
(see below)
mm
Up to and including 100
Maximum derivation
m
mm
mm
All tempers
over 0.4
1.5 L
0.6
F
over 0.4
2.0 L
0.8
All other tempers
over 0.4
2.5 L
1.0
NOTE 1. The straightnessis measured by determining the maximum deviation from straightnessSover length1,whenthe bar, sectionortubeis supportedonaflattable such that the deviationis minimizedby Its own mass. NOTE 2. Kink Is measured using a straightedge 300 mm in length(see below). NOTE 3. Tolerances on straightnessfor annealed and controlled stretched materials should besubject toagreement between the purchaserand thesupplieratthe timeofthe enquiryand order.
Localized kink
V
7/ / /
300mm straightedge
/
Bar,tube or section ot length L
///V/ ////4// // /// // / // Maximum
deviation S
Length L
22
Section through tiatness measuring table -
Table1.15 - Tolerances on Length for All Materials Supplied in FixedCut Lengths Diameter, width Tolerances on length for givenlength (plus and minus) across flats or (see notes 1 and 2) overall width Over
Over Up to and Over 1000 mm including 300 mm up to and up to and including including 1000 mm 1500 mm
long
long
Over 1500 mm up to and including 5000 mm
Over Over Over 5000 mm 7000 mm 10000 mm up to and up to and long 7000 mm
10000 mm
long
long
long
including including
mm
mm
jmm
jmm
jmm
jmm
jmm
60
60 100 140 180 240
2.0 2.0 3.0 3.5
2.5 2.5 3.5 4.0 5.0
2.5 3.5 4.0 5.0 6.5
3.5 4.0 5.0 6.5 8.0
4.0 5.5 6.5 8.0 9.5
100 140 180
4.5
jmm 6.5 7.5 8.0 9.5 11.0
NOTE 1. Tolerances on length are measured at a temperature of 16 5 C. Theyprovide for out-of-squareness of cutto the extent of 10. NOTE 2. Total tolerances (i.e. the sum of the plus and minus limits) may be applied unilaterallyby agreement between the supplierand the purchaser.
Table 1.16 - Tolerances on Concavity and Convexityfor Extruded Solid and HollowSections Width
of section W
Maximum allowable deviationD(see figure)
mm
mm
Up to and including 25
0.125
Over25
0.l2Sper2Smm
Coocoolty
increment in width (e.g. for 150 mm width maximumdeviation D permitted is 0.75 mm)
23
Table 1.17- Tolerances on Twist for ExtrudedSolid and Hollow Sections
degrees
3
Under 20
20 up to and including40
degrees
7 5
Over 40 upto and including 80
0.5
Over 80: Lengths upto and including 8000 mm Lengths over 8000 mm
Twist T 24
3
ALUMINIUM EXTRUSIONS —
a technical design guide
SECTION 2- MATERIAL SPECIFICATIONS
CONTENTS
Title
Page No.
ALLOYS
27
TEMPER Solution Heat Treatment PrecipitationHeat Treatment
29 30 30
25
List of Figures Fig No. Title
Page No.
2.1
Temper Cycles
29
2.2
Solubility Diagram
31
Listof Tables No.
Title
2.1
Chemical Composition
27
2.2
Alloy Characteristicsand Uses
28
Page No.
26
ALLOYS High purity aluminium,99.00% and above, hasexcellentdurability together with high thermal and electrical conductivity.It is easily worked and afthoughit can be strengthendby cold working it remains a low stength material.
For more general use, alloying elements are introduced, producingmaterialsthat retain the general characteristicsof pure aluminium but have greater structure strength (refer to Table 2.2). In the extrusion industry, the alloys most widely used throughoutthe world are in the InternationalStandards 6000 series, to which the British Standards alloys also conform.The main alloying constituents in this series are silicon and magnesium(refer to Table 2.1). Table 2.1 - Chemical Composition
ALLOY
COMPOSITION (%)
BS 1474 SI
6063
0.200.450.60 0.35 0.10 0.10 0.90 0.10
-
0.10 0.10 0.05 0.15
REM
6063A
0.30- 0.150.600.60 0.35 0.10 0.15 0.90 0.05
-
0.15 0.10 0.05 0.15
REM
6082
0.700.40- 0.601.30 0.50 0.10 1.00 1.20 0.25
-
0.20 0.10 0.05 0.15
REM
6101A
0.300.70 0.40 0.05
-
-
-
-
0.03 0.10
REM
6463
0.200.450.60 0.15 0.20 0.05 0.90 -
-
0.05
-
0.05 0.15
REM
0.90 0.50 5.00 1.20 0.80 0.10 0.40 0.25 0.20 0.05 0.15
REM
*
0.502014A
Fe
Cu
Mn
-
Cr
Others Each Total
(1987)
Mg
0.400.90
3.90- 0.40- 0.20-
* 6101A comformsto BS 2898
** T + Zr
27
NI
Zn
TI
Al
0.15-
Table 2.2 - Alloy CharacteristIcs and Uses
BS
CHARACTERISTICS
TYPICAL USES
6063
Suitable for intricate extruded sections ofmid-strength. Forms well in T4 condition. High corrosion resistance. Good surface finish.
Themost widely usedalloy. Architectural
A stronger version of 6063 but retaining mostofthat alloy'sgood
Road and rail transport, general engineering, ladders and light structures.
6063A
surface finish and formability. 6082
The recommended alloy for
structural purposes with good strengthand generalcorrosion resistance.
members i.e. glazing bars and window frames; windscreensections, roadtransport.
Road and rail transport, scaffolding, bridges, cranes and heavy structures.
Busbar,electrical conductorsand fittings
6101A The best combination of electrical and mechanical conductor properties with conductivity of 55% of the InternationalAnnealed Copper Standard.
6463
Based on high purity (99.8%) aluminium, this alloy was developed to respond well to chemical or electro-chemical brighteningor anodizing. It has excellent formability.
2014A A high strength alloy with moderatecorrosion resistance.
Motor car trim and other applications requiringa bright finish.
Structures, aerospace,general engineering.
28
TEMPER
Thepropertiesof alloysinthe6000 and2000range canbeimprovedby heattreatments after extrusion. These alloys, although available in the F, "as manufactured", condition, are more usually produced in one of the followingthree tempers:T4
-
T5
-
precipitationtreated (artificiallyaged)
T6
-
solutionheat treatedand precipitationtreated (fully heattreated)
solution heat treated
T5 PRECIPITATION
___________
SOLUTION
HEAT TREATMENT (AGEING)
EXTRUSION_F (QUENCHING)
: F
Fig. 2.1 TemperCycles
The current procedure for producingthe T4temper is usually 'on-line". An extrusion, emerging from the die at about 500°C, is rapidly cooled by air, water spray or water immersion, depending upon the section shape and extrusion speed. The temper, although strongerthan in the F condition, is stillof relatively low strengthand, with its high elongationvalue, it is an excellent choicewheresevere forming is required. Some natural ageing or hardening will occur which will, in some alloys, curtail the time available forforming.
For thin sections a strongertemper, T5, is available. T5 is given greater strengthby carrying out precipitation treatment without any solution heat treatment. This is provided by heatingthe materialup to about 180°C and soakingfor several hoursin an oven.
29
The final and strongest temper available (without the applicationof cold work) is T6 which combines both the solution heat treatment and the precipitationtreatment. The relationship between mechanical properties and heat treatment of a range of aluminiumalloyswasfirst discoveredbyWilm in 1906. Overtheyears,theprocesshas been developed with improvementsand innovations being introduced which have helped to make the "heattreated" alloys the most widely used extrusion materials in
the world.
in recent years, much greater use has been made of reheat treatment following low temper or heat inducedfabrication operations such as bending and welding. This is a property of aluminium that is well worth considering at the design and material selection stage of fabricated components.
It is not the purpose of this manual to deal with detailed metallurgical aspects of aluminium and its alloys,but the followingsimplifiedexplanationof heat treatmentmay be of background interest:The thermal treatment consists of two phases: a)
b)
solution heat treatment precipitation heat treatment
Solution Heat Treatment Thechemical constituentsofaluminiumalloys are to agreateror lesserextent soluble in aluminium. The degreeofabsorptionvaries with the amount and typeofconstituent andtemperature. The higherthetemperature,the greaterthe amount dissolved. Fig. 2.2 shows a typical solubility diagram where, at temperaturesabove point A , (the Solvus temperature) the atoms are in solid solution and designated by the prefix "solute". These atom phases ofconstituentsare thus dissolved in solid solution and a rapid temperaturedrop,throughquenching,willpreventthe solute atomsfrom diffusing out of solution. This condition, however, is not totally stable and a natural ageing will take place, varying from several days to several weeks depending upon the alloy. Duringthe ageing processa fine dispersionof clustersofsolute atomswilloccur. The final stable condition is defined as T4 temper. PrecipitationHeat Treatment The precipitationheat treatment process, also known as artificial ageing, speeds up and greatly increases the rate of precipitationand fine dispersion of the constituent atoms,which are distributed in clusters over the whole matrix. Thealloy will nowtend to resist material dislocation, resultingin a marked improvementin both strengthand hardness, usually to a level well above that obtained by natural ageing.
30
Liquid
Liquid
- solid
0 U)
CU
0 U)
E
U) I—
Solid
5 % Constituent
Figure 2.2 - Solubility Diagram
31
Page blank in original
ALUMINIUM EXTRUSIONS —
a technical design guide
SECTION 3- MECHANICAL PROPERTIES
CONTENTS
Title
Page No.
INTRODUCTION
35
STRESS Axial Loading
36 38
STIFFNESS
41
HARDNESS
43
FATIGUE
43
33
Listof Figures Page No.
Fig No.
Title
3.1
Yield Point
36
3.2
Typical Stress Strain Curves
37
PermissibleCompressive Stresses in Struts
39
RelationshipBetween Hardness Number and Tensile, Yield Strengths
42
FatigueCurves For Some Aluminium Alloys (Rotating CantileverTests)
44
3.3
3.4
3.5
List of Tables Page No.
No.
Title
3.1
Propertiesto BS 1474
35
(1987)
3.2
PermissibleStresses
38
3.3
EffectiveLengths of Struts
40
3.4
Moduli of Elasticity
41
34
INTRODUCTION
A wide range of mechanicalproperties is availablefrom aluminiumand its alloys with
the level of performancevarying withthe degreeof alloying and temper. The property range forthe more generally availablecommercial alloys is given in Table 3.1. Table 3.1 - Propertiesto BS 1474(1987) ALLOY TEMPER
MAX THICKNESS
0.2% Ps
mm
N/mm2
16
200 150 25 150
T4 15 T6
25 25 25
Fe) T4 T5
6063
6063A
Fe) T4 15
6082
%ELONGATIONb)
5.65y'
50
mm
13 16
12 14
110 160
100 130 150 195
8 8
7 7
90 160 190
150
14 8 8
12
200 230
12
7 7
200
-
150
120 230 255
110 190 270 295
13 16
8
8 7
6 20a)
T6
70
ULT. STRESS N/mm2
-
14
T6
-
170
200
10
8
T4 T6
50 50
75
6463
160
125 185
16 10
-
14 T6
20a) 20a)
230 370
370 435
11
2014A
10 6
6lOlAd)
a) b)
C)
d) e)
7
Thicker sections are possible and give higher mechanicalproperties. For details contact extruder. Theelongationisobtainedfrom atensiletestsampleon which agauge length is markedpriortotesting. Thegauge length is specified,being either 50 mm long or 5.65 cross-sectionalarea. (So) The properties of aluminiumvary with temperatureoutside an approximate rangeof-50°Cto+80°C. They willincreaseat lowtemperaturesand decrease at high temperatures. Thevalues vary with the alloy, seeTable 8.2. Alloy 6101A conformsto BS 2898. Values given for F condition are not specifiedproperties in British Standards and are given for informationonly.
/
35
STRESS Aluminiumdoes not exhibit a yield point. Stress/strainbehaviouris similar to that of a numberof othermetals,includingsome alloy steels. It is necessary,therefore,toadvise a recognisablepoint of departure from elastic to plastic behaviour. In the method chosen, the stress level registeredat 0.2%. Permanentstrain is regardedas the yield point. Theyield point can be obtainedfrom thestress/straincurve bydrawingtheoffset of O.2% strain parallel to the elastic line for the alloy under consideration. The 0.2% proofstress can be read atthe pointof intersectionofthe two lines, seeFig.3.1. Alloy curves will have a different point of departurefor each temper condition.
200
/ / 0.2
Ordinate
E E
z 0, CO
U)
/
/
/ 20
NB. for reasons of clarity the alloy curve is exaggerated
/ 0.50
0.60
% Strain
Fig. 3.1 - Yield Point
36
0.70
2014A T6
500-
Mild Steel 400
/
——
//
E
z
300-
//'7
6082 T6
/
a,
/
ci)
'—'—I
(I)
200-
100-
0
I
I
5
10
I
15 %
20
Strain
Fig. 3.2 - Typical StressStrain Curves
37
Table 3.2 - PermissibleStresses
ALLOY
TEMPER
AXIAL e)
BENDING
N/mm2
N/mm2 Pbt Pbc
SHEAR
BEARING
N/mm2
N/mm2
Pt
Pc
s
6063
15
62
69
37
117
106
6063
T6
87
96
52
139
81
6082
16
139
154
83
222
61
2014A
T4
135 124
153 142
81
239
71
2014A
16
154d)
108
278
49
20 154d) 224
Pt AXIAL TENSION Pc AXIAL COMPRESSION Pbt BENDING TENSION PbcBENDING COMPRESSION s SLENDERNESSRATIO AT EULER BLEND POINT SEE FIG. 3.3 a) b) C)
d)
e)
Permissible stress levels are laid down in BS CP1 18 TheStructural Use of Aluminium". 6063 values are applicableto 6101A and 6463. 6063A is a new alloy, not yet allocateda value but from experienceit should be slightly in excess of 6063 values (8%). Arbitrarily reducedvalues to allow for inferior crack-propagationresistance. Applies only when buckling is notthe criterion.
AxIal Loading
Foraxial loading,incolumnsand struts,the permissiblecompressivestress isobtained by inserting the appropriate slendernessratio into the alloy/tempercurves given in Fig. 3.3, and using the effective length factor from Table 3.3.
38
CM
E E
z'a CM
a) (1)
a)
>
U)
(a a)
0. E
0 0
a)
.0
0) 0) E a)
100
1
A Slenderness Ratio Fig. 3.3 - PermissibleCompressive Stressesin Struts =
K!.
K L r
= = = =
slendernessratio end fixity factor (effective length)
r
=
A
= =
whore
also
spaninmm radius of gyration of section in mm
inertia cross sectional area 39
Table 3.3 - EffectiveLengthsof Struts End Condition
Effective Length
ofStrut
Effectivelyheldin position and restrained in direction at both ends
0.7 L
Effectivelyheldin positionat both ends and restrainedin directionat one end
0.85 L
Effectivelyheldin positionat both ends, but not restrainedin direction
L
Effectivelyheldin position and restrained in direction at one end and partially restrainedin direction but not heldin position atthe other end Effectivelyheldin position and restrained in direction at one end, but not held in position or restrainedat other end
1.5 L
2.0 L
NOTE. L is the length of strut betweenpoints of lateral support.
Theextensive range of shapes and, over the last few years, the ability of the industry to producethinner extrusions hasencouragedthe use of slendersections. Because of low aspect ratios (width/depth)and high elementthickness ratios (width/thickness) of the thinner extrusions they require examination for possible modes of elastic instability. The modesoffailure listedbeloware particularlyrelevanttothin-walledopen sections of asymmetricalshape in aluminium alloys. a) b) C)
Torsional warping Lateral instability Local buckling
All thefactors are influencedbythe shapeand dimensionsofthe section and, whilst (a) and (b) are also relevantto span, (C) is not. Althoughsafe valuesare oftenquoted in simpletermsforaspect and elementthickness ratios,theyare not entirely reliableand should not be used. Ifthere is anydoubt about the robustnessof asection in theformoffailures list above,it shouldbechecked, using appendicesF, G, H and Kin BS CP 118- TheStructuralUseofAluminium".Thedesign approach uses equivalent slenderness ratios in conjunction with alloy compression curves. The strut curves in Fig. 3.3 can be used for torsional warping but will give pessimistic values for lateral instability and local buckling, where the equivalent slendernessratio falls on thestraight line partsofthegraphs: See BS CP1 18 Fig. 2 for modifiedcompression curves suitable for solving lateral instabilityand local buckling.
40
STIFFNESS The stress/strain relationshipis given by Hooke's Law which states that intensity of stress is proportionaltostrain. Thisisapplicabletoaluminiumalloys toa leveljustbelow the 0.2% proof stress, the slope ofthe line being obtained from: Table 3.4 - Modull of Elasticity E
=
ALLOY
Stress Strain
where E is the modulusof elasticity MODULUSOF ELASTICITY E N/mm2
6063 6063A 6082 6101A 6463 2014A
65,500 65,500 68,500 65,500 65,500 72,000
These values are approximately one third of that of mild steel, 210,000 N/mm2. Aluminium under elastic bending will therefore give deflectionsthree times greater than those obtained from mild steel under similar loading conditions. This is not true for self weight loadingwherethe light weightofaluminiumcounteractsthe effect ofthe lower elastic modulus of aluminium. The advantage to be obtained from a low modulus are greater impact absorption with shock loads and lower imposed stress levels from movement in static structurescaused by temperaturevariationor support settlement.The modulusof elasticitywill vary with temperature,see Table 8.2. In applicationswhere deflection is the controlling design factor, the performance of aluminium can be dramatically improvedby utilising the advantagesof the extrusion process to position materialsstrategicallyaround the section. The geometric properties can also be increasedby small additionsto section depth. This modification applies to all materials but can be more readily incorporated into extrudedaluminium sections. Examplesare given in Section 11, Design.
Therelationshipbetweenlateral and longitudinalstrain,within the elastic limit, isgiven by Poisson's Ratio which, for aluminium alloys, is usually 0.34.
41
35
30
Tensile
x E E
z
Relationshipbetween hardnessnumberand tensile strength for magnesium- silicide alloy extrusions in the artificially aged condition
25
-c
0)
c
Yield
20
)2)
(0
D
.; (0 C
a
15-
10
I-
(1/6063 T5 & T6 F
6063A
j"1
Brinell
6082 T6 •1
i'•
T6
45 055 6065 707580 85 9095100105110
Vickers Rockwell
'F' 46 51 56 61
66 71 76 82 87 92 98103 109115
54 61 67 71 76 79 82 85 87 89 91
-
'E' 68 72 77 80 83 86 88 90 92 94 96 Rockwell 'B' 47 55 62 - - -I - 12 23 32 39 45 50 55 60 63 66 Rockwell 'K' Rockwell
I
Webster
I
15253441485358826670737678 5 7 9 10 11 12 13131414—151515161616—1717
—
Hardness number HARDNESS TESTER SETTINGS Rockwell
Brinell
lOmm.Steel ball penetrator - 500kg.load Vickers Diamond penetrator - various loadings
1.6mm
Rockwell
'B'
Steel ball penetrator - lOOkg.load
'K'
3.2mm Steel
Rockwell 'F' 1.6mm Steel ball penetrator - 6Okg.load Rockwell 'E' 3.2mm, Steel ball penetrator - lOOkg.load
Webster Model
ball penetrator - l5Okg.load
'B'
Note: Asthistable shows, a hardnessvalue covers a range of stress levels and must not therefore be used to give precise measurementsof strength.
Fig. 3.4 - Relationship Between Hardness Number and Tensile, Yield Strengths 42
HARDNESS
The surfaces hardnessof aluminium alloys can be assessed by most of the general methods of measurement,Brinell, Vickers and Webster etc. The accuracy of the results canvary, particularlywith those methodsthat usemanual pressureto obtain the surface indentation. Thetrendto relatemechanicalpropertiesto hardnessvaluesis nottobe recommended as there is no accurate constant relationship. The curves shown in Fig. 3.4 are for general guidanceonly and indicatethat there are given rangesof stress levels foreach hardnessvalue. FATIGUE Aluminium is similar in its fatigue behaviourto other non-ferrous metals in that the stress/cyclecurves nevertotally flatten out. An arbitrary maximumendurancelevel is therefore imposed,. usually 50 million cycles. Curves are drawn up for alloy and temper groups against semi-rangeof stress levels (see Fig. 3.5). Fatigue curves are usuallybased upon actualtestresultsfrom Wohler typebeam machineswhich subject the specimensto sinusoidal reversedbending. Theresults are generally plotted for high cycle applications,above 1 O cycles, and any high strain/low cycle applications should be discussed with the extruder. The surface finish and geometric aspects of components, particularly joints, can influenceperformance. Shot blasting of the surface can improve fatigue resistance, whilstnotchescan reduceit. Withweldedconnections,itis usualto obtainbetter results from butt joints than those which are lapped and continuous welds give a superior performance to that of intermittent welds. Some data based upon nine different classifications of structural componentsis given in BS CP1 18.
43
300-
270-
240-
210E E
z a
180-
a
0 a
a, 150C C,,
E
120-
90-
60 -
i0
106 i07 Endurance (cycles)
108
Similar results are obtained for alloy 6082T6
Fig. 3.5- Fatigue Curvesfor Some AluminiumAlloys (Rotating CantileverTests) 44
ALUMINIUM EXTRUSIONS —
a technical design guide
SECTION 4- DURABILITY
CONTENTS
Page No.
Title INTRODUCTION
47
ATMOSPHERIC
47
CHEMICAL
49
MATERIALS Bi-MetaIlic
49 49 53 53 53
Wood InsulatingMaterials Concrete
45
Listof Figures Fig No.
Title
4.1
6082 T6 Alloy (Mill Finish) ExposureGraph (1)
48
6082 T6 Alloy (Mill Finish) ExposureGraph (2)
48
4.2
4.3
4.4
Page No.
Principleof Galvanic Reaction
49
Typical Bi-metallic ConnectionsBetween Aluminium and Steel
52
Listof Tables 4.1
Electro-ChemicalSeries
50
4.2
Guide to Bi-metallic Corrosion Effects at Junction of Aluminium and Other Metals
51
46
INTRODUCTION Aluminiumand its alloys have, in general,excellentdurabilityand corrosionresistance. Like most materials, however,their behaviourcan be influenced by the way in which they are used. In this section the manner in which aluminium respondsto various environments and design situations is reviewed with advice on use in specific applications. ATMOSPHERIC Aluminium's naturalaffinitywith oxygen resultsin theformation of an oxide layer when exposedto air. The resultingfilm is generally50Ang thick, extremely hard,chemically stable, corrosion resistantand adheres stronglyto the parent metal surface, producing an integrated material. Once formed, it prevents further oxidisation and, if damaged in any way, will reform, oxygen availability permitting. The only practical reason for removingthis film is to facilitate anodizingor welding. In the firstinstance, a thicker, morecontrolled deposition of the oxide layer can be carried out and in the latter case, the oxide film would be a deterrentto good metal fusion.
The behaviour under atmospheric exposure can therefore be described as selfstifling. If the surface layer is pitted by any of the air-borne pollutants usuallyfound in industrialor marine atmospheres,such as sulphuric acid and sodium chloride,the resultingchemical reaction producesa larger volume of powderedcorrosionproduct than the volumeof the original pit, thereby sealingoffthe surfaceof the aluminiumand inhibiting any further corrosive reaction. In general,the ratio of corrosion productto pit volume is 240:1. With time, existingpits, which are usuallyof ashallow hemisphericalshape,are sealed and the rate of formation of new pits is reducedso that eventuallyall reaction can be assumed to have ceased. This processcan bedescribed as weathering,forthe depth of pittingis extremelysmall. Thelevel of pollutionofcourse will determinethe general appearance,which will appear to be a soft blueish-greycolour in ruralareas and dark grey to black in industrial areas. Regular maintenanceand washing down should prevent the permanentdiscolourationfrom industrial pollutants. Anodized surfaces, however,will retain their original appearancefor a much longer period, providing that regular maintenanceis carried out. See Section 10. For the purposes of assessment,the various types of environmentalconditionsare divided into 3 categories: a)
RURAL
b)
MARINE
c)
INDUSTRIAL
47
E E
1)
D
Marine Industrial 0.
Rural
3-
6
Exposuretime
Fig. 4.1
- years
- 6082 T6 Alloy (Mill Finish) ExposureGraph (1)
The exposure trialson which Fig. 4.1 is based also provided samples for testing the mechanicalpropertiesofthematerials. As canbeseen inFig. 4.2there isvery littledrop in these properties, even afterprolonged exposure of 12 years. In both figures, the graph line isvirtually horizontaland thereforedurabilityand mechanicalpropertiescan be assumed to have reachedstable conditions.
stri:l
i::
0
6 8 Exposure time - years
10
Fig. 4.2- 6082 T6 Alloy (MillFinish) ExposureGraph (2) 48
12
CHEMICAL The behaviourof aluminium alloys in contact with a wide range of chemicals is welldocumentedarid requestsfor specific information can usually be dealt with by your material supplier. In general,corrosion of aluminiumonly occurs to anygreat degree where the ph is be'ow 3 or above 9, i.e. under strongacidic or alkalineconditions. is thereforenecessaryto knowthe concentrationofthechemical underconsiderationand also thetemperatureat which it will operate, as in some casesthetemperaturecan be the major considerationby alteringthe normal behaviourpattern.
t
MATERIALS When aluminiumwill be in contactwith other materialsunder wet or moist conditions, it is necessaryto check whether some form of protectionis required.
Bi-Metallic When dissimilar metals are coupled together in the presence of moisture, there is a likelihood of a galvanic reaction in which one metal will corrode see, (Fig. 4.3). In this situation an electrolytic couple is formed in which a current flows from the less noble metal,acting as an anode, tothe morenoble metal,acting as acathode,with corrosion concentratedon the less noble metal. This behaviouris usually consistent with the relative placings in the electro chemical series, see Table 4.1.
Corrosion Electrons
—
ri 1
+
Positive ions
2
Electrolyte Cathode
Anode
Corrosion cell
Fig. 4.3 - Principleof Galvanic Reaction
49
Base or less noble metal Noble metal
Theseverityofthe galvanicactionalso dependsonthe degreeof separation,electrical resistanceofthe metalpath, conductivityofthe solution and the arearatio betweenthe two dis-similar metals. In practice, however, reaction between the metals can be avoided by insulatingthem from each other with an electrically inert non-abosrbent barrier. An excellent exampleof this kind of connection is between the aluminium super-structure and steel decking on ships. Reference can be made to B.S. publication PD 6484 - 1984.
Table 4.1 - Electro-Chemical Series
BASE
Magnesium Zinc Aluminium Cadmium
Mild Steel Cast Iron Lead Tin
Nickel Brasses Copper Bronze Monel Silver solders (70% Ag. 30% Cu) Nickel
Stainless Steel (Type 304) Silver Titanium
NOBLE
Graphite Gold Platinum
50
PASSIVE
Table 4.2 - Guideto Bi-metallicCorrosion Effects at Junction of Aluminium and Other Metals Metals Coupled With
AluminiumOf
Bi-metallic Effect
Aluminium Alloy Gold.platinum, rhodium,silver.
Attackacceleratedin mostenvironments
Copper,copperafloys. irwnersion.silver solder
Attack acceleratedin mostatmospheres to aluminiumand itsand conditionsof total
Soldercoatingson steel orcopper
Attack acceleratedattheinterfacein severeor moderateatmospheresand underconditionsof total immersion,
Nickel,nickelalloys
Attackacceleratedin marineand industrial atmospheresand conditions of total irmtersionbutnot in mildenvironments,
—_____________
—---
Steel,castiron
Attackacceleratedin marineand industrial atmospheres and conditionsof total immersion butnot in mildenvironments.
Lead,tin
Attackacceleratedonlyin severeenvironments, such asmarineand some indiatrial.
I
These metals,and especiallythoseat thetop of thelist are generallycathodicto aluminiumand its alloys,whichtherefore suffer preferential attack when corrosion occurs.
Tin zinc plating (80/20)onsteel
Attackacceleratedonlyin severeatrrspheres and condtionsof total Immersion.
Pure aluminiumand alloysnot containing
Whenaluniniumis alloyedwith appreciableamountsof copper becomesmoe nobleand when alloyedwith appreciable amountsof zinc itbecomesless noble. Inmarineor industrial atmospheres orwhen totallyimmersed,alunnium alloysuffers acceleratedattackwhen Ingood electricalcontactwith another aluminiumalloy that containssubstantialcopper,such ax wroughtalloys2024 and 2014and castalloysLM 4-M and BS L92. Thealuminium-zincalloys,being less noble,areused ascladdingfortheprotectionof thestrongeraluminuimalloys,
Cadmium
No acceleration ofattack on cadmiumexcept infairlysevereatmospheresin contactwith an aluminiumalloy containingcopperand under conditionsof total immersion,
Zinc and zinc alloys
Attackon zinc acceleratedin severeenvironments such as marineand industrial and under conditionsof total immersion,
si,stantialadditions of copperorzinc
Magnesiumand magnesiumbase alloys
Titanium
Attackonmagnesiumacceleratedinsevere environments such asmarineand industrialand underconditionsof total immersion,
Thesemetalsare generallyanodicto aluminiumand suffer attackwhen corrosion occurs,thereby protectingthe aluminium,
Attackonalurntnium may alsobe accelerated.
Not manydata available,but attackon alurTinium is knownto beacceleratedin severemarineand industrial conditionsand when immersedin seawater.
Stainlesssteel (18 8. 18/8/2and
/
13%, Cr)
Chromiumplate
Noacceleration ofattack on aluminiumin moderate atmospheres, butattack maybeaccelerated inseveremarineand industrial atmospheres and underconditionsof total irrynertion.
—-
Noacceleration ofattack on aluminiumwhen plating is not less than 0.0025 mmthick. except insevereatmospheres; alsoprovldedthe preliminarynickelcostingus in accordancewith requirements of BS 1224.
51
These metalsform protectivefilms that tend to reduce bi-metalliceffects. Where attackoccurs thealuminiumbase materialsuffers.
Bulb plate stiffener
Aluminium
plating
between Steel bracket and 150mm mm. Steel foundation bar
A
Inside
Outside
Inside
Outside
)
Treatment as for A but with plate lapped to inside of foundation bar.
C
Steel rivets
B
Aluminium plate lapped to joggled steel flat bar. Galvanised steel bolts with insulating washers and ferrules. Treatment otherwise as for A.
C
Figure 4.4 - Typical Bi-metallicConnectionsBetween Aluminium and Steel 52
Wood In dry conditions there is usually no reaction on the aluminium but if the wood is unseasonedor in damp conditions,it should be coated with aluminiumor bituminous paint. Invery aggressive environments(immersion)anon-absorbentinsulatinggasket should be fitted as with bi-metallicjoints. Where timber is treated with preservative advice should be obtained from your aluminiumsupplier.
Insulating Materials In the unusual event of insulatingmaterials becoming saturated, some protection of the aluminium would be necessary for, apart from the possibility of attack from leached-outchemicals, some poultice corrosion could occur, activatedmainly by the reduced availabilityof oxygen. Protectioncan be afforded by using an inert barrier. Concrete Under perfectly dry conditions,aluminium buried in concrete would need no protection. In practice,however, such conditionsare rarely achievedtherefore it is recommendedthat in all cases the contact areaofthe aluminiumis coated with a bituminous paint. In no circumstancesshouldthe steel reinforcementused in concretebe allowed to come in direct contact with the aluminiumas this will result in a bi-metallicreaction which in turn could cause spalling of the concrete.
53
Page blank in original
ALUMINIUM EXTRUSIONS —
a technical design guide
SECTION5- SURFACE FINISHING
CONTENTS Page No.
Title
INTRODUCTION
57
PRE-TREATMENT
57
ANODIZING SpecificationFactors for ArchitecturalType Anodizing Chromic Acid Anodizing Hard Anodizing
57
PAINTING Electrophoretic Electrostatic Paint Performance
61 61
55
59 61 61
61
62
List of Figures Fig
No.Titie
5.1
AnodizingProgramme
58
5.2
Depositionof Colouring
59
Page No.
Listof Tables 5.1
Suitabilityfor Anodizing
60
5.2
Paint Performances
62
56
INTRODUCTION One ofthe most importantconsiderationsrelatingto surfacefinish is the need to have a sound and permanent bond between any applied film or coating and the parent material. In this respectaluminiumand its alloys are particularlysuitable, providingas theydo integralbondingwith anodizingand excellentpaintkeys when suitablyetched and de-greased. PRE-TREATMENT The surfacetextures on aluminium,like those on other metals, will be visible through all but the thickest coating so it is as well to considerthis aspect before deciding on the final surfacetreatment. Where positive relief features are required, like ribbing or serrations,these can be easily incorporated into the extrusion shape. The usual cycle for pre-treatmentincorporatesa de-greasingdip, followed by a rinse and then an etch dip. The make-up and chemical concentrationof this etch can be varied to produce a range of surfacesthat will affect the final appearanceof an anodizedfinish. These canbe graded from the natural metal appearance,through a light grey satin finish to a darker grey frosted appearance. Specialisedsurface finishes can be applied,such as chemical brightening,mechanical polishing, scratch brushing and shot or vapour blasting. The special finishes extend from bright reflective polished surfaces, through to heavy peened rough textures. Aluminiumprovidesan excellentsurfacefor paint. Afterdegreasing,alight etchis used followed, when necessary,by a chemicalconversioncoatingto improvethe paint key even further. All ofthese services are available directly or indirectlythrough extrusionsuppliers. In general the level of concentrationof pre-treatmentchemicals makesthem unsuitable for manual non-dip application. ANODIZING Anodizing is a controlled surface oxidisation by immersion in an electrolyte, usually dilutesulphuricacid. A lowvoltage,high amperagedirect current is passedthroughthe metal, using the aluminium as the anode and a hard, non-corrodingoxide film builds up on the surface of the aluminium. A less dense layer is subsequentlyformed in which there are capillary pores. These pores provide the meansfor further oxidisation, building up the thickness from the base. This film is an integralpart of the metal and is not an applied coating.
57
ProTreatment
Degrease
OPTIONAL TREATMENTS Mechanically Polish
Chemically
Metallic Colour
Brighten
Organic Colour
Scratch Brush
Vapour Blast Rinse
r
r
Shot Blast Light Etch Etch
Rinse
I
I
Anodize I
Natural Finish
Seal I
FIg. 5.1 - Anodizing Programme
Afterthe actual anodizingoperation, the surface film is porous and in a conditionto accept colouring agents, if required. If a natural aluminiumfinish is desired then the material proceedsdirectly tothe final tankwhich is usuallyboilingwater. Thechemical reaction of immersion seals the pores against further moisture penetration,giving a hard, weather resistingsurface.
Wherecolour is required, thechoice lies betweenthose obtainedfrom organicdies, as used with textiles, and those obtainedfrom metallicsalts. Theformergives a rangeof primarycolours,whilstthe latterofferscolours varyingfrom greythrough umbertodark brown and black. As will be seen from Fig. 5.2the organic dies tend to remain at the top and the metallic salts at the bottom of the surface pores.
58
l7nm
25 micron (25,000nm) H Ratio d
= 1500:1
Natural
Organic dies
Metallic salts
Fig. 5.2 Deposition of Colouring SpecificationFactorsfor ArchitecturalType Anodizing British Standardslay downspecificationsto govern thequality of anodizing. BS 1615coversgeneral anodizedcoatings in aluminiumand BS3987 covers external architecturalapplications. Europeanstandardsare covered by the Qualanod quality control scheme.
The average thicknesses readily available are usually designated in AA values, the figures conformingdirectly to the film thickness in microns.
M 5
Applications Furniture and other indoor products. Also used with chemically brightened material where a thicker coating would tend to reduce reflectivity.
101 155
Internal applicationslikely to have more robust handlingsuch as hand-railingand internalpartitions.
25
All external applicationssuch as windowframes etc.
59
c)
The mostappropriateextrusion alloysfordecorativeand architectural anodizing are in the 6063 range. Other alloys canbe anodizedbutthe finish cannot be guaranteed to meet the requirements of British Standards architectural specifications.
Table 5.1 - Suitability For Anodizing
*
Alloy
Natural
Colour
Brightened
Protective
6063
V
V
G-V
V
6063A
V
V
G-V
V
6082
F
F
F
G
6463
V
V
E
V
2014A
F
F
U
G
*This also includes "hard"anodizing E = excellent V = very good G = good F = fair U = unsuitable d)
In componentanodizing,the heat affectedzone ofwelded orbrazed joints will show somecolour variationfrom that on the rest ofthesection. This can vary fromslightly darker tone to averydark grey oreven black if a siliconfiller wire is used in brazing.
e)
There can be slight variation in colour between production batches, so top and bottom colour limits should be agreed with the anodizer. This is particularlyso where cast and wrought componentsare concerned,because an exact colour match is rarely possible due to the markeddifference in the chemical composition of the two materials.
f)
Electrical contact is extremely important between the loading bars and the aluminium section during anodizing. It is obtained by jigging with nonmetallicclamps. Thecontact areas, however, do not anodizeor colour and willtherefore leavea light-colouredarea even on naturallyanodized material. Non-visible surfacesshould be shownondrawings sothat the clamps can be placed in the best possible position. If all surfacesare visible, then an extra 50 mm should be allowedat eachendofthe bar forclampings,which can be cutoff after anodizing. 60
ChromicAcid Anodizing The original commercially developed anodizing process used chromic acid as the electrolyte.The procedureis similarto that employedwith sulphuricacid but the bath temperatureis higher.The resultantfilm is softer and thinner (max. 10 microns) but for equal thicknessesitoffers morecorrosionresistancewhich makesit idealforaggressive industrialenvironmentswhere the relatively soft surface is no disadvantage.As the chromicacid is passivewithaluminium,itisalso recommendedlorfinished components where there are laps or crevices which could retainelectrolyte.
Hard Anodizing Hard anodizingis a lowtemperatureoperation,usingconsiderablyhighervoltage than other anodizingprocesses.The relatively rough surfaceproduced is extremelydense and hard and is available up to 125 micronsthick. The film is normally left unsealed but can be waxed or treated with mineraloil. In either case, the abrasion resistance is very high, comparingfavourablywith that of tooled steel and chromiumplate. Hard anodizedfilms have good electrical insulationpropertiesand their excellent corrosion resistance and durability make them ideal for use even in aggressiveenvironments. PAIN11NG
Aluminium rarely needs to be paintedfor protectionbut where colour is necessaryon aesthetic grounds a number of high-quality paints and methods of application are available.Thesurfacepresentedby aluminiumis idealforcoatingwhenthecorrect pretreatmentiscarriedout. As mostcoatingsare appliedbycommercialcoatingcompanies, the basic pre-treatmentsare usuallyvariedtosuit their particularpaintformulationsand methods of application. In general, the oxide film is removed and the material degreased,etchedand rinsed.This is adequatepreparationfor electrophoreticpaints but thereis an additionalchemicalconversioncoatingwhich isthen appliedforelectrostatic application. Electrophoretic
Thepre-treatedworkpiecesare madeanodicand dippedinto electricallychargedpaint tanks. This ensuresthat the paint is attractedto the metal surfaceand deposited in an even coating.Afterrinsing,thematerial passesthroughstoving ovensatapproximately 160°Cforadurationof 15 minutes.Duringthis operationthepaint isfused and strongly bonded to the aluminium. Electrostatic Afterpre-treatment,the workpieces are passed through an electrostatic field during which time paint, in theform of wet or powderparticles,is sprayed on to the surfaces. Theworkpiecesare then transferredto atunnel oven where they are stoved at 200°C for 10 minutes. 61
Paint Performance Comparing paint surfaces and their respective performance is always somewhat subjective,neverthelessTable5.2 attemptsto providegeneralised information.Paint and coating companies are always pleased to advise on the best system of application. For all paints and systems, sharp corners provide a challenge in that either a metal or a shadow line appears,depending upon the thickness of the paint. This can be avoided by following good extrusion design although for paint the minimum recommendedcorner radius is 1mm. Table 5.2 - Paint Performances PAINT
Acrylic
Method of
Mean Colour Thickness Range Application (Microns)
Surface Texture
Electro-
Gloss Level
Colour Fastness
Hardness Inside Groove
Post
Coating
Painting Fabrication
V. good
Good
25
White
Smooth
70%
Moderate
Hard
60-80
Wide
Slightly Textured
20%-
Good
93%
Moderate Shallow Channels
Polyphorec urethane (WetBath) Polyester
Electrostatic
Range
(Powder Spray) PVF2
Electrostatic
Excellent
Only
30-100
Small
(a)
Range
25(a)
Wide
V.good
(Powder Spray)
Fluoro- ElectroCarbon
static
Smooth
9%70%
Excellent
Moderate
Moderate
Smooth
9%90%
Good
Hard
V. good
Range
(Wet Spray) Acrylic ElectroPolyesterstatic
25
Full Range
(Wet Spray)
(a) Suitable formulti-coat applications Further information is available from: Aluminium Coating Association Broadway House Calthorpe Road Birmingham B15 1TN
62
ALUMINIUM EXTRUSIONS — a technical
design guide
SECTION6- FABRICATION
CONTENTS
Titles
Page No.
BENDING MachineTypes Alloy/Temper Shape Factors Tube Bending
65 65 67 67 69 70 70
Springback
Lubrication MACHINING
70 72 73 74
Routing Drilling
Sawing JOINING Welding
75 75 79
JointDesign
81
Screwing Crimping
82 83 85 86
Riveting Bolting
Adhesives
63
Listof Figures Fig No.
Title
Page No.
6.1 6.2
Bending Methods Routing (Profilingand
65/66 72 73 74 77 78
Facing) 6.3
6.4 6.5 6.6
6.7 6.8 6.9 6.10 6.11 6.12
Drills Types of Saw TIG Welding MIG Welding RecommendedDiameters of ScrewGrooves LongitudinalScrew Grooves Crimping Blind Rivets Self-Piercing Rivets Clench Rivets
81
82 82 83 84 84
Listof Tables No.
Title
6.1 6.2 6.3 6.4 6.5 6.6
Bending Characteristics Minimum Bend Radii (1) Minimum Bend Radii (2) Minimum Bend Radii (3) Minimum Bend Radii (4) Minimum Root Radii R in Terms of Tube Diameter Basic Saw Tool Data Process Capacity RecommendedFiller Alloys for Welding Parent Metal Combinations Edge Preparationand Fit Up forTiGand MIG Permissible Stress Levels
6.7 6.8 6.9
6.10 6.11
Page No.
64
67 68 68 69 69 71
74 76
79 80 81
BENDING There are several types of torming machinesuitablefor bending aluminium sections. Thechoicedepends uponthe class ofsection, whethersolid open or hollow;the range of support tooling available; the alloy and the temper. Machine Types Bending may be carried out by four main methods, as shown in Fig. 6.1. The three roll bender has a centralmoveablerollerwhich is graduallydepresseduntil the desired radius is obtained. The point bender has a similarmethodof operation,the load either being appliedgraduallyorimpacted. Theroll and point methodsof bendingare usually applied to robust sections. In the wrap and the mandrel benders, it is possible to provide formers and other support tools which enable tighter radii to be obtained and minimise the amount of buckling.
As the name implies,the stretchformer putsthe section into tension and then, moving laterally,wraps it arounda former: this method reducesthe likelihoodof compression failure. As well as the above basic machines, a number of specialist benders are available, such as the rotating disc, which is suitable for tube bending.
-Former
Wrap Bender
I
Clamp
Guide
Draw Mandrel Bender
Former Moves Around Section
Section Moves Around Former
Fig. 6.1 - Bending Methods 65
Section Bending Roll Fixed Position Drive Rolls
Three Roll Bender
Bending Point
Fixed Position Drive Points
Three Point Bender
L
Stretch Former
FIg.6.1 - BendingMethods(continued) 66
Alloy/Temper
Heattreated aluminium alloys in the T6 conditionhave relatively short plastic ranges with proof-stress/ultimate-stressratiosof0/86: 1 and minimumelongationvaluesof7% - 10%. Althoughthese values do notprovidethe whole pictureof ductileperformance, theygive a reliableindicationof bendability. Where bending is aprimary requirement, it is usualto use materialinthe T4 solutiontreated condition. Theplastic stress range ratios are then improvedto0.6:1 with minimumelongationvaluesof between14%and 16%. Theslowrateof natural ageing in the 6000 series alloys does not appreciably affect the bending characteristics,except in the most severe bending cases. Bending at raised temperatures is not usually recommended as the mechanical propertieswould be affected. It is possibletocarry out post-bendingheattreatmenton T4 temper materialthat will increase its propertiestowards those of the T6 condition. Care should be exercisedwith thin sections as some distortioncould occur underthis treatment. Table 6.1 - Bending Characteristics
Alloy
Temper
Bending Index
6063
T4 T6
V
6063A
G
14 T6
G
6082
T4 T6
G F
G = good
6101A
T6
G
F=fair
6463
T4 T6
G
2014A
V
V=verygood
V
G
14 T6
F
Shape Factors The complexityof shapesavailablein aluminiumalloys makes it verydifficultto provide information to cover every situation. By considering the behaviour of the various elements of the shape in relationto the bending axis it is possible to predictthe most likely modeoffailure when bent throughtoo tight a radius. In most cases,the neutral axis of the section and the bending axis almostcoincide butthis is nottrueforstretchforming where, becauseof longitudinaltension,the bending axis is assumedto move outside of the section. 67
Thefollowing tables give minimum bend radii for section elements under the various forms of bending stresses. Radii values are to the neutral axis and are given in multiplesof y.
y is the maximumdistancefrom outerfibres of the element to the neutral axis ofwhole section. t is thickness of element. Flange denotes shaded element parallelto the plane of bending. Web denotes shaded element vertical to the plane of bending.
Theuse of support tooling in the bucklingmodescan reduce the minimum radiibelow the levels shown in the tables. Theextent of the reduction depends upon the typeof tooling used. Table 6.2 - Minimum Bend Radii (1)
y t
1
2
4
8
12
Alloy
Temper
6063
T4
O.7y
0.7y
O.8y
2.Oy
3.5y
T6
O.8y
0.By
l.4y
3.Sy
7.Oy
T4
2.5y
2.5y
2.5y
3.Oy
5.Oy
T6
2.5y
2.5y
2.5y
3.5y
7.Oy
6082
=1
Table 6.3 - Minimum Bend Radii (2) y
t
2
3
4
6
Alloy
Temper
6063
T4
l.Oy
3.5y
8.Oy
20.Oy
T6
l.Oy
4.Oy
1O.Oy
20.Oy
T4
l.8y
4.Oy
1O.Oy
20.Oy
T6
l.8y
5.Oy
1O.Oy
25.Oy
6082
WEB TENSILE
L
L WEB BUCKLING
C1
68
F1
Table 6.4
- Minimum Bend Radii (3) FLANGE
FLANGEWIDTH THICKNESS
4
8
Alloy
Temper
6063
14
7.Oy
8.Oy
T6
10.Oy
lO.Oy
14
8.Oy
Boy
T6
10.Oy
lO.Oy
6082
TENSILE
Table 6.5 - Minimum Bend Radii (4) FLANGE WIDTH THICKNESS
FLANGE 4
8
J
Alloy
Temper
6063
T4
5.Oy
8.OY
T6
8.Oy
20.OY
T4
7.Oy
l2.Oy
16
8.Oy
2O.Oy
6082
N.B.
BUCKLING
Where flanges have bulbs greater than 3t thick they can be bent to radii 60%
of those shown in the table. Tube Bending The recommendedmethodsof tube bending are wrap and draw mandrel. Although threepoint bendingcan be used,there is lesscontrolparticularlywiththin-walledtubes in the stronger alloys and tempers. Aluminiumtubes can be readily bent but, like all materials,there are limitsand thekey to successfulbendingisto understandthem and take appropriateaction at both the design and fabrication stages. Failure modesare, once again,tensiletearing and compressionbuckling butthere are in-between situations where wrinkling, necking and flattening can occur without causingfracture ofthetube. To preventthese surfacedefectsor to restrictthem to an acceptable level, the tubes can be filled with sand, springs or low melting materials such as Wood's metal. 69
Theseare allestablishedmethodsofprovidinginternalsupportwhich,together withthe use of external groove formers and followers,provide the maximum level of bending control. Table 6.6 shows the minimumrootradiifor a rangeof tube sizes based upondiameter! wall thickness ratios, alloys and tempers but ignoringflattening. Sprlngback Althoughthedegreeofspringbackcanbecalculatedforaspecific sectionthathas been bent around a given radius,it involvesa lengthy process. The more usual method of establishing springback is to carry out trials prior to a production run. Generally, sectionswhich are symmetricaland havethe majorportion oftheir material awayfrom the neutral axis exhibit less springbackthan a heavy centred cruciform section or an asymmetricalT-bar.
Lubrication Frictionbetweenthesurfacesof steelformingtoolsand the natural surfaceoxideof the aluminiumcreatesthe need to lubricateboth work and tools. This helpsto reducetool wear and prevent damageto the surfacefinish ofthe formed parts. Dependingupon toolshape,sectionsize andalloy,thelubricantscommonlyusedincludemineraloil, lard oil, proprietarywater soluble compounds and waxes. MACHINING Aluminium alloys are amongst the most machinable metals and can be cut at high speeds. Two basic properties influencethe machiningoperation: a)
the high co-efficient of linear expansion of aluminium.
b)
the friction generated betweensmall tools and aluminium.
The problems associatedwith the above characteristicscan easily be overcome by using a combined lubricantand coolant. Machines normallyfound in a workshopare suitable for use on aluminium. The best results are obtained with relatively high speeds and it is frequently found that woodworkingmachinescan be employedfor machining,providingthey have sufficient power and rigidity. High speed steel tools may be used on all the aluminium alloys. Plain carbon steels may also be used for short runs buttheydo not have sufficient life for quantity production. For long productionruns tungsten carbide tips are recommended but even these toolswould require regular resharpeningparticularly when used with anodized material. A chip breaker should be used on alloy 6082 for high speed operations to avoid the formation of long spiral swart.
70
Table 6.6 - Minimum Root Radii R In Termsof TubeDiameter
MATERIAL DESIGNATION
CHARACTERISTICCURVE
AND TEMPER
WRAP
MANDREL
B B
B B
C
C
F T4 T6
B
B
C D
C D
6101A T6
C
C
6063
6082
F T4 T6
4U -
30
30
C
tr o
o
20
10
Ill S
20
-
S 15
——--———-
lEt
2D
———-
3D
4D
5
lD
50
Minimum Root RodS In Terms Of lobe Diomneter
2D
3D
71
5D
Minimum Rout Rods In Terms Of Tube Diameter
Mandrel Bend
Wrap Bends
4D
Where extensive removalof metal is to becarried out, there is alwaysthe possibilityof distortion occurring. Machining practiceswill also affect the amount of distortion that takes place. Coolingand lubricationshould be generous but even so, over-tightened chuckscould add tootherstressesoccurringthroughthermalexpansion. Ifthere is any doubt, the material suppliershould be consulted. Routing One ofthebest methodsofmachiningaluminiumis byrouting. This resemblesa milling operation, giving a good surface finish, as fine as 0.75 micron,and can be used with spindle speeds up to 24,000 rpm. The high operating speed, in conjunctionwith low loading,ensures smooth, easy controlwhich is essentialwhen followingthe contours of a complextemplate. See Fig 6.2.
Helix angle
Radial rake
Primary clearance
CUlliNG SPEED
FEED
HELIX
RADIAL
rn/mm
rn/mm
ANGLE
RAKE
Profiling 600-2100
Up to 6 Reduced
CLEARANCE
speeds
Facing:
Upto 6000
necessary with increase in work thickness
5-7°
25°
Fig. 6.2 - Routing(Profiling and Facing) 72
5-10°
Drilling As with other aluminiummachiningoperations,drilling can be carriedout atveryhigh speeds. Specialmachinesfor usewith small diameterdrills work at 80,000 rpm, most drilling operations, however, are carried out at more modest speeds. The cutting performanceot adrill is influencedby its peripheralspeedand this shouldbetaken into account when deciding upon the spindle speed for a given drill diameter. Drills should be inspectedregularly to ensure that they keep their bright finish and polishedflutes to ensure rapid chip removal and prevent build-up. When necessary, thedrills should be regroundwithcare beingtaken to ensurethatthechisel edgeretains itscorrect lengthandtheweb atthedrill point does notthicken. Shouldthickeningoccur therewill be increased end pressureon the drill with the possibilityof drill breakage. When drilling deep holes, particularlyof large diameter,excessiveheat is generated and if not dissipatedby the coolant, hole contractioncould take place.
TOOL ANGLE
DRILL ELEMENT PointAngle,H
118°
Helix AngIe
20 - 25°
ClearanceAngle, 0
12 - 20°
Flutes
Polished
Web Thickness
Thiner than that used for other metals
Fig. 6.3 - Drills
73
Sawing Modernsawsused inthefabricationofaluminiumsectionsgiveclean, virtuallyburr-free cuts providedthatthe correcttooth size and rotationspeed are used and theteeth kept sharp. This is particularlyso for tungsten carbidetipped blades which are in general useforaluminium. Thistypeofblade gives excellentresultsonthe hardsurfaceof preanodizedsections. Feedwill vary with the type of saw, section size, alloy and temper butshouldneverbebelow 0.05mm per tooth. When cuttingthin sections,itis advisable to havetwo or moreteeth engaging at the same time. Table 6.7 sets out basic tooldata. Thelower speed range is recommendedfor high speed steel blades and the higher range for tungsten carbide tipped blades. It is always advisable to use a cutting fluid. Segmental teeth High speed steel Top clearance Top clearance
Top rake
Th
Depth of
Depth of
gullet
gullet
Fig. 6.4 - Typesof Saw Table 6.7 - Basic Saw Tool Data Type of Blade Saw & Size
Teeth Cutting Pitch Gullet Speed
Blade Material
m/min
mm
Circular 250-460 dia High Speed x Steel 2.3-3.7 thick Circular 5601220 Segmental dia Inserted x Carbide 64-12.7 thick Tips
mm
Depth mm
8.5-13
1500 to 2400
Hollow to Ground 12.7
6.4
1200
coarse
to
25-50
4500
12.7breaker 57 teeth Chip-
74
Top Rake
Angles Clearances Side Top
Handfeed: 12-18° 20-30° Powerfeed: 15-24° 25-35° Handfeed: 5-12° 7-9° Powerfeed: 10-20° 5-7°
1-2°
1.2°
JOINING Aluminium alloys can beconnected in avariety ofways. Theusual methods, all wellestablished,are welding, riveting,bolting, screwing,corner crimpingand glueing (but aluminium alloys have also been explosivelybonded to other materials)..
The combination of material flexibility and the extrusion process enables mating sectionsto be manufacturedin a range coveringboth permanentand releasabletypes of sliding, rolling or straight clip connections. Detailsof this type of joining are given under Section 11, Design. Welding Aluminium welding is a widely accepted method of fabrication, with no shortage of competent personnel in the engineering and manufacturingindustries. There are several methodsavailable,the basic ones being Tungsten Inert Gas (hG) and Metal InertGas (MIG). As the titles suggest,both are inert gasshieldedsystems where the weld area is shrouded from the air to prevent the reformation of an oxide film. Preparation Cleanlinessand the removalof theoxide film are most important. The proposedweld areas has to be de-greased, using white spirit or acetone and the joints wiped dry. Adequate ventilation must be provided for any solvents used but is particularly applicableto industrialcleaning solvents, such as carbontetrachlorideetc. After degreasing the joint is deaned, using stainless steel wire brushes or a chemical etch cleanerto removethe oxide film. Welding should be carried out as soon as possible afterwards. Carborundumwheels are not recommendedas grit particlescanbecome embedded in the surfacecausing contaminationof the completed weld. Filler wire is cleaned by wiping with wire wool; pre-packed spool wire is supplied in a clean condition. Tungsten Inert Gas In the tungsten inert gas (TIG) process,the arc is struck betweenthe workpieceand
a non-consumabletungsten electrode. The filler wire is fed independently. Although mechanisedTIG is available the process is more widely used as a manual system where close controloftheweldingconditionscan be readily maintained. The resulting welds are usuallyof good appearanceand penetration,particularlywhere no backing plate is available. Fig. 6.5 shows a schematiclayout of atypical TIGsystem and Table 6.8 shows the thickness range.
75
Metal Inert Gas
In the metal inert gas (MIG) process, the arc is struck betweenthe workpieceand a consumable electrode which is constantly fed from a wire spool. The arc is selfadjusting and takes into account small movements of the torch. Penetration and appearanceare not so easyto control as in the TIG system, althoughthe addition of pulsed arc equipment will improve the penetrationand reduce the need for backing plates. Fig. 6.6shows a schematiclayoutofatypical MIGsystemand Table 6.8shows the thickness range. Small spool hand guns, sometimes called fine wire, are also available with MIG systems. These dispense with the need for long wire feed leads thereby increasingthe areaof work accessible from the base unit. Table 6.8- ProcessCapacity
PROCESS
PARENT METAL THICKNESS I Max. Mm (mm) (mm)
EQUIPMENT Item Compositeunit (350A) Transformer(350 A) H.F. orSurge Injector unit Suppressor Welding Torches
TIG 1.2
Compositeunit (250 A)
MIG 0.5 kg
1.6
MIG 5kg
NOTES:
9.5 (1)
4.8
withWire Feed unit and Welding Gun for 1 lb Spool
8.0 (2)
Compositeunit (350 A)
withWire Feed unit and Welding Gun for 10 lb spool
None
(1)
Althoughthe TIG processcanweld thicker material, for economicreasons it is not normallyused for aluminium over 9.5 mm thick.
(2)
In theory there is no upper limit for 'one-pound'MIG, but it is more economicalto use 'ten-pound MIG for material over 8.0 mm thick.
'
76
NOTES 1
CompositeTIG welding units include all the necessaryauxiliaries: argon and watershut-offvalves are usually controlledby solenoids, although they may be manuallyoperated.
2
The main power cable, fuseand torch can be air-or water-cooled.
Fig. 6.5 - TIG Welding 77
Dry Bobbin Flowmeter Pressure Reducing Valve
Pressure Gauge
Wire Feed Unit
Workpiece
4
NOTES
Voltage pick-up lead for 'one-pound' MIG.
1
The a.c. supply is 11OV for 'one pound'MIG and 220V tot 'ten-pound'
5
The main power cable and gun of 'ten-pound MIG can be watercooled.
6
Arc Voltage in MIG Welding Proceduresis measuredwitha voltmeterconnected between the contact tube and the workpiece.
MPG welding. 2
CompositeMIG welding units have the contactorand control box built in.
3
The filler wire feed unit is integral withthe gun in 'one-pound' MIG and independentof it in 'ten-pound MIG Systems.
Fig. 6.6 - MPG Welding 78
Filler Wire 6063 and 6082 alloys can be readilywelded to awide rangeofotheraluminiumalloys. Table 6.9shows the preferredweld filler wire in bold print. An alternative,where given canbe usedwhen the finished componentis to be anodizedand a close colour match is required betweenthe weld area and the parent metal. Alloy 2014A is not shown in the table as this alloy is not recommended for welding using the TIG and MIG processes.
Table 6.9 - Recommended Filler Alloys for Welding Parent Metal Combinations PARENT ALLOY
6063 6082
1050a
4043 5356
3103
4043 5356
5083
5356
5251
5356
5454
5356
6061
6063 6082
4043 5356
Alloy 2014A is Not Recommendedfor FusionWelding
Joint Design Good joint design encompassesboth the practicalitiesof thewelding processand the structuralrequirementsofthejoints in service. Theedgepreparationwill depend upon the typeofjoint, butt or lap, thickness of materialto be joined and the weldingprocess to be employed. Table 6.10 shows typical edge preparation for both TIG and MIG processes.
Thestrength of welds is covered by BS CP118 which gives permissiblestress levels for both 6063 and 6082 alloys in both butt and filled applicationssee Table 6.11. The reduction in strength from the 0.2% proof stress levels is very marked, allowing for 79
Table 6.10 - Edge Preparation and Fit Up for Tig and Mig THICKNESSt MIG
TIG
n
g
(1) NOMINAL
MAXIMUM
ROOT
GAP
GAP
(mm)
(mm)
FACE (mm)
a
-
0.8c
Nil
Nil
-
-
-
1.2c 1.6c 4.8c
Nil Nil Nil 1.6
Nil
1.6 1.6
3.2c 4.8c 3.2p 8.0
6.4c
-
Nil 1.6
0.8
3.2
1.6
60 60 60 75
2.4 4.8
0.8 1.6
2.4 3.2 6.4 2.4
Nil
g
4iit
6.4c
Nil
12.7 15.9
-
Nil Nil
0.8 0.8
1.6 1.6
90 90
-
1.6 2.4 6.4
Nil Nil Nil
Nil 0.8 1.6
-
-
6.4p
-
1.6
3.2
0.8
60
9.5
-
Nil
0.8
0.8
60
-
1.6 -
Nil
8.9
Nil Nil Nil
0.8 1.6
-
-
25.4
-
Nil Nil Nil
1.6 1.6 1.6
3.2 4.8 6.4
60 60 60
-
0.8
Nil
Nil
-
-
-
1.2c 2.4c
Nil Nil
Nil
-
-
-
1.6
Nil Nil
-
-
3.2 4.8
3.2 4.8 12.7 19.0
3.2c
1) MinimumThicknessof ParentMetal
0.8
Nil 0.8
80
DETAIL
$
4.8 1.6
4.8P -
JOINT
INCLUDED ANGLE (deg.)
jj I
HL
g
r Li
[JJ flu
n
p= PermanentBacking Plate c=TemporaryBacking Plate
g
contingenciesinthe weldingprocessand the reducedpropertylevels of theweld heat affectedzones. Themost cost effectiveway ofdesigningwelded structures,therefore, is to keepthe weldedconnectionsclearof maximumstress points, as far as possible. Table 6.11- PermissibleStressLevels BUTT WELDED JOINTS & REDUCEDHAZ.
ALLOY
FILLET JOINTS (WELD METAL)
TENSION COMPN TRANSVSL LONGITL 6063
31
19
54
31
6082
51
31
54
31
PermissibleStressesfor Table WeldedJoints in N/mm2 HAZ = Heat affected zone Screwing The ease with which aluminiumalloys canbe drilled orpunched and the incorporation of screws ports or channels in extrusions has encouragedthe useof stainless steel self-tappingscrews asthe standardmethod of joining, particularlyin the window and door industries. The stainless steel threads bite into the aluminium to give a very positiveconnection. A typical patio door will use two self-tappingscrews per kilogram of aluminium section used. Screw ports are rarely fully closed as the use of 300 degree ports, (Fig. 6.8), gives a very marked improvementin extrudabilitywith very little loss in pullout strength. The dimensional accuracy of the port diameter is very important and all extruders have standardbore dimensionsfor each screw size. It is advisableto contact extruders at the die design stage and where possibleprovide samplescrews. Screw —
—
__
1.78mm
(mm) N
..
....
\\
Size
\
6 8
60°
/ // I /
10
12 14
Screw Dia. (mm) 3.45 4.17 4.88 5.59 6.25
Screw Groove Int. Dia. (mm) 3.20 3.56 4.32 5.03 5.74
FIg 6.7 - Recommended Diameters of Screw Grooves 81
Theuse of longitudinalscrew grooves, (Fig. 6.8), is not so widespreadbut thecorrect combinationof slot width and screw size can ensure high pullout values. Some care is necessary if self-tapping screws of triangulated cross-section are used as full engagementof threads may not be possible on both sides ofthe groove. Advice from the extruder is recommended.
Li Fig. 6.8 - LongitudinalScrew Grooves Crimping
In this method of corner connection,the extrusion has a built-in channel recess and afterthe sections have been mitred,thecrimpingangle isfitted and thejointassembled and heldin a rigidjig. Two pressureprongsthen upsetthesectionflange intothe corner angle, producingavery stableframe assembly,see Fig 6.9. Most crimped corners rely onmechanicalconnections,but, if required,aslowsettingadhesivecan beusedtoseal the corners and providesome extra strength. Crimpingis most likely to befound in the door and window industrybut is applicableto anycomponent orform of constructionwhere mitredcorners are used.
Crimping flange
Fig. 6.9 - Crimping 82
Riveting Aluminiumcanberivetedwith aluminiumrivets, which are usuallydrivencold. As there is atendency for these to work hardenduringthe processtheyshould be closed with the minimumnumberofblows. It is advantageousto use a long stroke hammer,asize larger than would be used with equivalentdiameterhot steel rivets. Therivets should be drivensquare, not rolled round theedges. Largerdiameterrivets(over 12 mm.)can have pre-formedend recess points to assist initialforming. Poweroperated squeeze riveters are ideal for aluminiumas the heads are formed in a single stroke. Where aluminium is to be riveted to steel structures, the faying (contact) surfaces should betreated with azinc-chromateprimerand broughttogether whilestill wet. Hot driven steelrivets should be used but these must be given at least one coat of primer in way of the aluminium, after driving and cooling. Blind Riveting This form of joining is well established and uses rivets of tubular constructionwhich enablethe workto becarriedoutfrom one side only. This isparticularlyattractivewhere accesstothe reverseside is difficult. Only one operator is required and there is choice of setting tools - pneumatic,hydraulicor hand held. Thereare a numberof proprietary systems available,in diametersupto6.5 mm. Rivetlengthsare availableforcombined joint thickness of up to 13 mm. Furtherdetails are availablefrom rivet manufacturers.
ELE Mandrel breaks and falls free
Setting tool Clinching mandrel
Fig. 6.10 - Blind Rivets
83
Self-Piercing Riveting
This is a relatively new developmentwhich canbe usedon combined thicknesses of up to 6.5 mm.
T Max.
L = 9.5mm 1=6.5mm S = 5.0mm Countersunk
Fig. 6.11 - Self-PiercingRivets Clench Riveting
A numberofproprietaryfasteningsystemsusethegripof threadedboltswiththeclosing mechanismof clench riveting. Fig. 6.12 showsatypicalpin and collet assembly. The bolts are closedfromone side in asimilar mannerto blind riveting, althoughaccess to the non-closing side is necessary to install the rivet. The collet deforms around the threaded pinbefore the pin breaksoff atthe waistedneckunder a pre-determinedload. As well as the advantage of ease of installation, these fastenings have excellent vibration resistance.
Fig. 6.12 - Clench Rivets
84
Bolting Inthismethodoconstructionstainlesssteel,aluminiumor mildsteelboltscan be used. If stainlesssteel to 18/8 specificationis used, no extraprotectionis used andthe bolts can be used in the conventionalmanner. The best aluminiummaterials are 6082 and 2014A but the latter will need painted protection in heavy industrial and marine environments. Alloy 2011 is a widely used and available bolt material but would certainly need protection in any external application. In the case of mild steel bolts, galvanizedsteel washers MUST be fitted. All boltsare best used in close-fitting holes and the appropriate tolerance levels will be found in BS CP118. Where possib'e, controltorque levels shoudbe specifiedfor aluminium bolts and the indiscriminate use of "tommy bars' is an unacceptable practice. In line with good bolting practice, no part of the threaded portion should be within the thickness of the joint flanges. The extrusion processallowscaptive bolt head slots to be built intothe extrusion. The bolt can be positioned anywhere along the slot, thus requiring hole accuracy in one dimension only. The internal width of the slot should be dimensioned to suit the maximum width of the boithead across flats thereby locking the bolthead against turning when tightening up the nut. See Fig. 11.3
85
Adhesives This methodofjoining hasfound favour inthe high-techindustries,i.e. electronicsand aero-spacewhere product cleanlinessand close fabricationcontrol were alreadywellestablished practices. In more recent years, adhesives tolerant of imperfect joint conditions have been developed and have been taken up, particularly by transport, engineering and even structural industries. In general, bonding systems still require clean etched surfaces; some respond to unsealed,anodizedor conversioncoatedsurfaces. The range of adhesivesavailable covers cold, impact or heat curing together with single or two-part mixes. Each has its own characteristicand therefore advice on suitabilityfor any specific application should be sought from adhesive manufacturers.
86
ALUMINIUM EXTRUSIONS —
a technical design guide
SECTION7- CONDUCTIVITY
CONTENTS
Title
Page No.
THERMAL Thermal Barriers
89 89
ELECTRICAL
90
87
Listof Figures Fig No. Title 7.1
7.2
Page No.
MechanicallyClosed InsulatingWeb
90
Poured Resin InsulatingWeb
90
List of Tables No.
Title
7.1
Thermal Conductivity 0-100°C
90
7.2
Electrical Conductivity
91
Page No.
88
THERMAL Aluminium has a high co-efficientof conductivity. It varies withthe different alloys but the value forpure aluminium is 244 W/m0C. SeeTable 7.1. This propertyis extremely useful whendesigningheat transferproducts,such as radiatorsand electrical heat sink units. It is obviously less attractive in those applicationswhere low heat transfer is required and it is then often necessary to in-corporatecomponents to improve the thermal resistance, e.g. thermally broken window sections. Thermal Barriers This solution to the therma transfer problem has been used in the building and constructionindustriesfor nearlythirty years. During this time, design and manufacturehasbeen refined so that now two majortypes of systems are in general use. In the first, Fig. 7.1, the thermal insulatingweb, or webs, is madefrom strip material nylon, polyamide etc. - fixed into position by mechanical closing of dovetail type channelsinthe aluminiumsections. Twoseparatesections are used enablingdifferent surface finishes or colours to be used. The closing methods vary between rolling, pressingand broaching,dependinguponindividualmanufacturers.Internalbroaching, can only be used in the case of double web sections.
Thesecond systemis frequentlyreferredto as the "pour and cut" method, Fig. 7.2. A specially formulated liquid resin is poured into a semi-closedchannel in the single aluminium section. After the resin has solidified,the connecting aluminiumstrip "a" is cutaway leavingthe thermalbarrier orbarriers. Aswith thefirstsystem, a doubleweb sectioncanbeproduced,inthis case byusingeitheraproprietaryinstantaneousdouble pourmachineor by a two pass procedureon conventionalmachines. Thestructural properties of thermal barrier materials will generally be below those of aluminiumand will varynotonly betweendifferentmaterialsbut alsoover atemperature range of -20°C to +80°C. It is good design procedure,therefore,to keep the thermal barrier materialas close as possible to the neutral axis of thefinal composite section. In practice,this is not always possible and examplescanbe seen in existingwindow systems wherethethermal barrieris offset. Inthese cases it is essentialthat extensive laboratory proving tests are carried out to confirm that the composite section has sufficient strengthand stiffness as wellas thermal performance.
89
Lips Mechanically Closed On Insert Aluminium
Resin Webs
Holding Web Cut Out "a"
Solid Insulating Inserts
Mechanically Closed
Poured Resin
Fig. 7.1 - Mechanically Closed Insulating Web
Fig. 7.2 - Poured Resin Insulating Web
Table 7.1 - Thermal Conductivity
0- 1000C
ALLOY 6063 6063A 6082 2014A
TEMPER
W/m°C
T4 T6 T4 T6 14 T6 T4 T6
* InternationalAnnealed
% IACS
197
50
201
51.1
197
50
201 172
51
184 142 159
43.7 46.7 36.1
39.8
CopperStandard
ELECTRICAL Materials that are good thermal conductors are in general also good electrical conductorsand this is certainlytrueof aluminium. Thecopper/aluminiumratio values for thermal conductivity run virtually parallel to those for electrical conductivity. A special alloy hasbeen developedforelectrical use-6101 A. Thismedium strengthalloy hasexcellent electricalconductivityandgood fabricatingcharacteristics. It isavailable in the T6 temper only. Comparedwith copper, an aluminiumconductorofequal current-carryingcapacitywill have cross-sectionalarea 84% larger but will be only 54% ofthe weight of the copper bar.
90
Table 7.2 - Electrical Conductivity Electrical
Resistivity
Conductivy
ALLOY
(20°C) Microhm
(200C) %IACS
6101AT6
3.133 max.
55.1 mm.
91
Temperature Coefficientof Resistance per°C
0.00364
Page blank in original
ALUMINIUM EXTRUSIONS —
a technical design guide
SECTION8- TEMPERATURE
CONTENTS Title
Page No.
EXPANSION
95
MECHANICALPROPERTIES Creep Melting Point
96 96
93
95
List of Tables No.
Title
8.1
Coefficientof Linear Expansion (200 C - 1000 C)
95
Influence of Temperature on Propertiesas % of 25° C Values
96
8.2
Page No.
94
EXPANSION Although aluminium has a relatively highco-efficientof linear expansion,24x 10-6 per degree Cin its pureform,the low modulusofelasticityenablesthetemperatureinduced stresses to be held at a low level. These are usually two thirds of those induced in a similarsteelstructure. It is still recommended,however,that all long restrained structures likely to be subjectedto temperature variation and particularly those in dark colours are checked out in the design stage. Any excessivestresses can be reduced by fitting simple expansion joints. The general effect of alloying is to reduce the coefficient of expansion and relevantvalues forthe more common aluminiumalloys are shown in Table 8.1. Table 8.1 - Coefficientof LInear Expansion (20°C - 100°C) ALLOY
TEMPER
106/0C
6063
T4 T6
24 23.5
6063A
T4 16
24
6082
T4
23
T6
23
T6 T4
23.5
16
23.5 22 22
6101A
6463 2014A
T4 T6
23.5
24
MECHANICAL PROPERTIES Variation in temperaturealso directly affects the mechanicalproperties of aluminium alloys. At low temperaturesthe structural strength and elastic modulus values are actually increased, whilst at higher temperatures they are reduced. A further important characteristicis that at low temperaturesaluminiumand its alloys show no brittleness which makes them extremely useful in cryogenic applications such as containers for low temperatures liquid gases. The more important properties are given for each of the alloys in Table 8.2. The dotted line inTable 8.2 signifies the maximumtemperatureat which itis recomendedeach alloycancontinuouslybe used. Some official codes will accept highertemperaturesin specific applications- BS5222 "Aluminium PressurePiping" sanctionstemperaturesup to 2000C. Note: special alloys have been developed for high temperatures applications, contact extruders for performancedata and availability.
95
Table 8.2 - Influence of Temperature on Properties as % of 25°C Values
Alloy Temper
Stress
606316 Ult
Temoerature -200 -100 25 100 150
130
0.2% PS 115 608216 Ult 130 0.2% PS 115
2014AT6
Ult
124
0.2% PS 125
200
110 105 110
100 100 100
95 95 95
65 20 65 I 20 70 I 40
105 108 109
100 100 100
95 85 87
44 41
10 10 10 5
L40 191
11
17
10
Modulus
of Elasticity
300
I
110
105
100
100
95
90
70
Creep
At elevated temperatures under the prolonged application of a stress of sufficient magnitude,metalwill"creep"and may eventuallyrupture.This behaviour,the progressivedeformationwithout increasein load, does notenterinto the designconsiderations for structures operating below 100°C but may require study in high temperature applications. When creep is consideredto be adesign factor, moreinformationshould be obtained from the material supplier.
Melting Point As aluminiumapproachesits melting point it does not change colour, so othermeans such as temperature sensitive crayons, must be employed if a visual check on the temperature is required. While pure aluminium has a well-defined melting point of 660°C, aluminium alloys have a meltingrange which, forthe alloys listed in the Table 8.2, varies from 570°Cto 660°C.
96
ALUMINIUM EXTRUSIONS —
a technical design guide
SECTION9- FIRE
CONTENTS Title
Page No.
ALUMINIUMANDFIRE
97
99
List of Tables No.
Title
9.1
BS 476 Fire Test Series
Page No.
98
99
ALUMINIUM AND FIRE ALUMINIUMDOES NOT BURN. It will not ignite. Itwill not add tothe fire load. It will not spread surface flame. Although aluminiummelts at around 620°C, it has athermal conductivityof fourtimes that of steel and a specific heat twicethatof steel. Heat isconducted away faster and therefore agreater heat inputis necessarytobring aluminiumupto agiventemperature than required for steel. In any applicationrequiringa structuralfire resistancemeasured against time, a test certificate is usually necessary. Although aluminiumcomponents have obtained approvals above 30 minutes in tests it is not possibleto make accurate predictions. It is necessary,therefore,to obtain atestapprovalfor eachtypeof application. Where highertime ratings are required, aluminium must be used in conjunction with other conventional fire-resisting materials.
The more usual fire performance requirements for aluminium extrusions can be obtained from the results of the British Standardstestsshown in Table 9.1. Table 9.1 - BS 476 Fire Test Series Part No.
Aluminium Results
Title
*4
Non-CombustibilityTest
Non-Combustible
*5
ignitibility Test
P, not easily ignited
*6
Fire PropagationTest
P. actual index will
*7
Surface Spread of FlameTest
Class 1. Painted surfaces will reduce performancerating
21 1 22 23
Time/Structural Resistance& Insulation Test
vary with thickness
** individual component testing required
99
The BritishStandardfire testsare laid down in BS 476 and define results irrespective of materials. Aluminiumand its alloys achieve the highestpossibleratingsfor parts 4, 5, 6 and 7 and are therefore widely used throughout the construction and other industries where the highest standards of performance are required. Painted surfaces could, however, reduce the levels of performance.
Tests 21, 22 and 23 are used to obtain the performanceof a component or unitfor strength, integrity and insulation, all compared to time against closely calibrated temperature levels. **
It is usualfor aluminium extrusions,in these instances,to be used in conjunction with other materials to obtain resistancetimes in excess of 30 minutes.
*
Indicated highestpossible rating.
100
ALUMINIUM EXTRUSIONS —
a technical design guide
SECTION 10- CARE ANDCONTROL
CONTENTS
Pag No.
Title INTRODUCTION
102
HANDLING
102
STORAGE
102
MAINTENANCE
103
101
INTRODUC11ON
In post-extrusionhandling,every care is taken by extrudersto minimisedamage. It is essential that this "good house-keeping"is continued in customers'works and warehouses. As with other high quality materials,carelessnesscan cause unnecessary rejection, resultingin higher productioncosts. HANDLING The following recommendedpractices should be followed:-
(1) Single lengths should never be pulled longitudinallyfrom the middle of a bundle of aluminium sections as the entrappedend will score adjacent sections. (2) Cleanlinessis very important,particularly with sections to be anodised. Gloves should be worn whenever dealing with this typeof section as the natural oil from the hands can cause finger print corrosion which will become apparent at the etching stage of the process. (3) When lifting by crane, double slings should be used as single slings can cause bending damage particularly with bundles of long, light sections. (4) The sectionsshould always have adequatesupportwhen liftedby a fork-lifttruck. STORAGE Although aluminiumalloys are very resistantto atmosphericcorrosion,certain simple precautionsshould be taken duringtheir storage. All materialsshould be storedaway fromexcessivedustor fumes; particularlywhen portable gas or oil heaters are used, for as wellas pollutantsthese heaters also produce moisture. Storagespacesshould be dry and well ventilated and kept at a constant temperature above 16°C. Any superficial corrosion that occurs on extrusions is usually easily removed by hand cleaning with white spirit. Even the most severe superficial corrosion responds to cleaning with finewire wool and white spirit. The moretroublesomeform of staining is water marking,caused by moisture ingress betweensections that are closely nested, e.g. angle bars. Thiscan occur directly or by condensation. In the latter case, it is possiblefor the moistureto work upwardsby capillary action. Stacking in a self-draining position is therefore no solution. It is, however, easily avoided by spacing the sections and ensuring that moisture can not bridgethe gap. Thestain canbe removedby wire-brushingand chemical treatment. Storage staining and corrosion will not usually have any detrimental effect on the mechanicalproperties of the material.
102
Vertical racks are preferred for storage. If horizontal storage is unavoidable, care should be taken not to overloadracksand to supportlight sections adequatelyto avoid local damage atthe points ot support. Timberrubbing bars should be fitted to steel racksto minimiseabrasion and to avoidspots which could cause condensationunder adverse storage conditions. Racking should be arrangedto facilitate easyinspectionwhich should be carried out at regularintervals. As mostaluminiumalloys look alike, materialsshould be stamped or colour-coded so that different alloys and tempers can easily be identified. This would not be necessary where an alloy or temper is consistentwith a special shape. It is also usefulto mark batches on arrival in store to ensure that they are used in the original delivery sequence. MAINTENANCE Aluminium alloys require little or no maintenanceto retain their original mechanical properties. Without regularcleaning,however,surfacescanbecome stained particularly under prolonged exposure on industrial sites. Mill-finishedaluminium can be cleaned by rubbing down with finewire wool and white spirit. Anodised surfaces are more resistantto staining but, nevertheless,benefit from regular washing down with soapy water. Proprietarycleaners are available for both mill finished and anodised surfaces but should they be used, it is absolutely essential that the manufacturer's instructionsare strictly adhered to.
103
Page blank in original
ALUMINIUM EXTRUSIONS —
a technical design guide
SECTION 11 - DESIGN
CONTENTS Page No.
Title DESIGN PROCEDURE
107
VALUEANALYSIS
107
PRACTICALDESIGN FEATURES
109
WORKEDEXAMPLES UnloadingRamps PedestrianBalustrade
111 111
Columns
105
113 123
Listof Figures Fig No. Title
Page No.
11.1
Steel and Aluminium Beams
108
11.2
Examplesof Solid Section Aluminium
108
11.3
Built-in MechanicalFastener
110
11.4
Advantagesof Aluminium Versus Steel
110
Various Snap Fit Connections
110
11.5
106
DESIGN PROCEDURE
Indesigningasection,itisusualto haveaperformancespecificationsettingoutthetotal requirements of both section and material. This could be part of a much wider specificationfor a completefinished product ofwhich the aluminiumextrusion is only one of the components. The extentand detail requiredfor such a specificationwillvary with the applicationand also within different industries. It is good design practice to have such a "check list" providing, as it does, a target of what needs to be achieved and alogical procedurefor assessingdifferentideas. Acomprehensivelistofdesign considerations is set out in Appendix 1. Rarely will all these factors need to assessed and a moregeneral approach is given in the following flow chart. Idea Performance Specification I Material Selection
4
I
Fabrication
Appearance
I Mechanical
I••
Durability
Properties
I.
Machining
Shape
Strength
Atmospheric Electrical Conductivity
Forming
Surface Finish
Stiffness
Chemical
I
Jointing
Hardness
I.
Unit Special Requirements Cost
.1..
Availability
Unit Weight
Fatigue
VALUE ANALYSIS Although basic materialcost isimportant,itshould be balancedagainstthe overallcost of fabrication and subsequentservice performance. This is particularly relevant to aluminium extrusionswhere shapes can be produced that require little or no further fabrication and the aluminiumalloys availablehave characteristicssuitable for awide range of applications. Aluminium extrusions are usually sold by weight which tends to encouragecomparison with other materials on a straight weight/cost basis. This in unrealistic as compared with steel, allowingfor the lower elastic modulus, aluminium/steelweight ratios of 1 : 2 are easily attained to equal performancespecifications.
107
..
100
145
0L Steel 21.7 kg/M
150
Aluminium 10.6 kg/M
Ag. 11.1 - Steeland Aluminium Beams Thetwo beams in Fig. 11.1 have been designed for equal stiffnessin both xx and yy axes. The strength of the aluminiumbeam is well over twice that of mild steel if alloys 2014A 16 or 6082 T6 are used. It is importantalways to check the actualdeflectionrequirementas in many cases the steel design has been stress based and the corresponding level of deflection is automaticallyaccepted without considerationof the real level required. The economic use of aluminium alloys is not just confined to comparisonswith steel and other materials. The proficient use of extrusions can frequently result in comparisons with other aluminium profiles to obtain the optimum shape. Fig. 11.2 illustratesthe design of solid sectionsto give good strengthand stiffness in both major axes instead of a more expensivehollow section.
ii
[1
ft_
11
Fig. 11.2- Examples of Solid SectionAluminIum
108
Inothercases,the useofstandardstructuralsections is moreappropriate. Two ranges of I beams,channels,Tbars and anglesare available,namelythe speciallydesigned lipped sections conforming to BS 1161 and the range covering structural sections similar to the universalsections used in the steel industry.
in manufacture,the availabilityof sectionsthat require little or no fabrication can be a majorfactor in reducingfinal componentcosts. Thisequallyappliesto site erection
where, apartfrom light weight, the ability to use hiddenfixings can simplify procedure. PRACTICAL DESIGN FEATURES Replace several parts One extrusioncan oftendo thework ofseveral structural shapesjoined togetherand produce a neater, sounder design,at less cost.
Place metal where It is most effective Thus, bulbs,fillets and variationsin thicknesscaneasily be incorporated for structural advantage and local increasesof thicknesscan beintroduced tocounter wear and abrasion orpermittappingofscrews. The two bulbs, and root buteress improve inertia and section modulus values as well as increasing torsional resistance.
Hinge Fits Continuous hinges with built in stop bars plus screw groove forend stops.
Aslidefitwhichallowsone shapetomoveinacirculararc with respecttotheother.
109
Slots, holes and threads for mechanical fasteners can be extrudedas integralfeatures.
Adjustable locking connection.
FIg. 11.3 - Built-in Mechanical Fastener
Typical early steelframe section.
Typical aluminium frame section.
FIg. 11.4- Advantagesof AluminiumVersus Steel
Retractable Cover
Locking Cover
Fig. 11.5 - Various Snap Fit Conections 110
Adjustable Locking
WORKED EXAMPLES
UnloadingRamps Singlelengthsofchannelbar are frequentlyused intandemto unload wheeledvehicles. In the interests of good working practice, they should always be longitudinally and transversely restrained. There are severalwaysof calculatingthe size required. The followingmethodis based upon simple point load bending without any axial component. it is assumed that unloading is always controlled and no unusualdynamic loads will occur.
Slope Q in degrees
Specification. The rampsshould be a maximumweight of 50 kg each. Span 2.5 metres. Operatingangle up to 30 degrees. Maximumvehicle load2.0 tonnes equally shared on fourwheels. Maximumtyre width 200 mm with 25 mm clearance.
Theinitialchoice of sectionsize isgovernedby the final specificationrequirement,that of typewidth and clearance. Channel Section : 254 x 88 x
11
web x 14 flanges (all in mm)
Section properties: Area
5030 mm2
Modulus
Zxx
54620 mm3
Inertia
lxx
3459100 mm4-
Radius of Gyration Weight/metre Alloy
26.2 mm 13.39kg/m 6082 T6
111
Note: as section is used in this plane check with propertytables to confirm the wayx & y axes are given
Asthevehicle isunloadedit movesoutofthe horizontalwith aconsiderable shift in its neutralaxis and the loadingon thefirstsetofwheels increasing. This will be a feature of the individualvehicle. Forthe purposesofthis calculation it is assumedto be 10%, hence Loading.
Maximum individual wheel load
= 1 9640N (2 tonnes) x 1 10 = 5400N 4
100
Bending Stresses. The ramp acts as a simply supported beam and with normal wheelbasedvehicles will have a central load as the worst condition. (Load Case 2.)
M=
WL = 5400N x 2500mm 4
4
Maximum bending moment = 3375000 Nmm Maximum Stress =
3375000= 54620
fbc= 61.8N/mm2
Allowable Stress Levels. See Table 3.2 (From British Standards CP1 18) 6082 T6 alloy Bending
p,
154N/mm2
Deflection
8 =
For 6082 E = 68,900N/mm2 48El
8 =
5400x 2500 48 x 68900 x 3459100
8 =
7.45mm
The deflection/spanfactor =
336 which is well insidethe recommendedvalue of 200
Lateral Instability. It is usuallyadvisableto checkthe ramp for lateral instability. The methodforcalculatingthis canbefound in BS CP1 18. Thecross-tyingofthetwo ramps together with lateral ties will dramatically increasethe resistanceto lateral instability, but in thiscase, with thestronger axis ofthe section acting transversally,instabilitywill not occur.
112
Pedestrian Balustrade Specification. To enclosean external pavedareawithintheconfinesofan officeblock. Therailingsmustmeetthe requirementsofthe appropriateBritishStandardsandwhilst being functional should have an attractive appearance. Low maintenance is also essential. BS 3049 Pedestrianguardrail BS 6180 Protective barriers in and around buildings. In this instance BS 6180 applies. As it isa possible areaof assembly,althoughin anofficedevelopment,two categories of use are applicable. From BS 6180 Table 1 Type 4 Type 7b
Office building Placeof assembly
LOAD FACTORS Tables 2 and 3 from BS 6180 TYPE
4
7b
HORIZONTAL U.D.L. kN/M
INFILL
0.74 1.5
1.0 1.5
IJ.D.L. kN/M2
INFILL MINIMUM POINT LOAD BARRIER HEIGHT
kN 0.50 1.50
mm 1100 800
Access will be controlled and private so that type 4 will apply. Material.
Aluminium alloy 6063 T6 will meet all the requirementsof surfacefinish durability low maintenance
It is also an approved material in BS 6180 and its structuralcharacteristicsare set out in BSCP 118.
113
.r 76x50 Top rail
70x70x2.5 Posts
—30x30x2 Balusters E
—100mm Max Gap
E 0 0
50x54 1lOOmm
1500mm
1500mm
FabricationDetails Main stanchions: Theseare tobesetdirectly into concretefoundations.Thestanchion base overthe areato be bedded intothe ground is to be giventwo coats of bituminous paint.
Topandbottom rails: Theseare to be connectedtothe stanchionsusingbolted lugs. Bolts to be stainless steel to 18/8 specification. Balusters: These are to be slotted intothetop rail and intopunchedslots inthe bottom rail, then welded intoposition on both top and bottom rails. Surface finish: A natural anodized finish is required to AA 25 suitable for external application. This will necessitate the infill panels being anodized as single units. Check availabilityof suitable facilities.
114
SectionDesign Thefollowing sectionshave been drawn upto meet the requirementsof the performance specification.
76
::
70
Rad.: 70
Overallthickness 2.5mm
—I
lop rail
Stanchion
54 2mm
50
Baluster Bottom rail
STANCHION
TOP RAIL
Area
661 mm2
CCD
99mm
Shapefactor 298
Area 585 mm2 CCD 89mm Shape factor 334
BALUSTER
BOTTOMRAIL
Area
215 mm2
CCD
43mm
Area 300 mm2 CCD 74mm Shapefactor 370
Shapefactor 370 115
The CCDs are wellwithin the capacityof most medium sized presses with container diameters of 150 mm. The shape factors are slightly above average,but still acceptable. Thethicknesses have been checked out against Table 1.2 and are within the level required for 6063 material. A further check is necessaryon the top rail forboth the extrudabilityratios of the semienclosedareaand the depth/width ratio of the side channels. 59 mm x 45 mm = 2655 mm2
=
Large recess Gap Area/gap2 ratio
= 31 mm = 2.76: 1
Gap2
= 961 mm2
The section can be classed as a solid and the extrudability is acceptable. Side channels Depth Gap Depth/gapratio
17.5 mm = 3.5 mm = 5:1
This is not acceptable so it is necessary to reduce the outer flange from 20 mm to 13 mm.
The internal depth of the channel is now 10.5 mm Thedepth/gap ratio is now 3 : 1 This is now acceptable and the new top rail section details are as follows: = = =
Area CCD Shape factor
550 mm2 89mm 314
Section Properties STANCHION
-
Area Modulus Z Inertia
TOP RAIL (modified)
-
BOTTOMRAIL
-
I
Area Modulus Zy Inertia ly
Area Modulus Zy* Inertia ly * *effective area values (less slot area) 116
661 mm2 14190 mm3 496680 mm4
550 mm2 11150 mm3 423740 mm4
300 mm2 5650 mm3 152500 mm4
-
BALUSTERS
Area Modulus Z Inertia I
215 mm2 1838 mm3 27600 mm4
Loading
The load is appliedto the stanchionthrough the top rail.
STANCHIONS
740N1M x 1.5M = 111ON
Hence load RAILS
The loadfor the top and bottom rails is the same as thatfor the stanchions. Hence load
BALUSTERS
=
..WL
=
Z
=
=
8Z
=
WI.
=
8Z
Y.L.
4Z
lllONxl500mm 8 x11150mm3 Load Case
=
86.OON/mm2
lllONxl500mm
Two span, simply supported UDL =1886N/mm2
Simply supportedUDL = 36.BON/mm2
8x5650mm3
BALUSTERS f =
Cantilever
14190 mm3
BOTTOM RAIL
f
lllQNxllQOmm Load Case
- YL.
500N
Load Case
TOP RAIL
f
111ON
Central point load
STANCHIONS
f
=
Load Case
=
500N x 100mm
4x1838mm3
117
Simply supported central point load
=
68.OON/mm2
From CP 118 "StructuralUseofAluminium",the allowablestress levelsfor6063 T6 are as follows (see Tables 3.2 and 6.11) Bending
96N/mm2
Shear
52N/mm2
Welded areas Heat affected zones
Bending
31N/mm2
Shear
19N/mm2
Welds (throatarea)
31N/mm2
Assessment of bending stresses. STANCHIONS No welding. Allowablebendingstress 96N/mm2 Section acceptable TOP RAIL Heat affected zone is in maximumbending position. Allowablestress level 31N/mm2. Section acceptable. BOTTOMRAIL Heat affected zone in maximumbending position. Allowablestress level 31N/mm2. Section not acceptable - re-design BALUSTER Heat affected zone clearof maximum bending position. Allowable stress level 96N/mm2. Section acceptable. 54
Redesignof Bottom Rail.
Large bulbs placed at toesof flanges and merged into 2 mm thickness by 45 degrees fillet to ease transition.
Newextrudabilityfactors Area CCD Shape factor
= = =
350 mm2 74mm 335 118
New geometric properties (effectiveless slot area) ModulusZy Inertialy
=
6830mm3 184410 mm4
=
Re-checkbending stress
= lllONxl500mm =30.5Nfmm2
= 8Z
8 x6830
Allowablestress for heat affected zone material from Table 6.11
=
31N/mm2
New section acceptable.
Weld
Weld Strenath Baluster
Thebalustersare slottedintothetopchannelandwelded in position. They stand on the top ofthe bottomchannel web and arewelded intoposition.Thetopweldshold the balusterin the line ofthe top rail and do notdirectlytake the full load. This is also the case at the bottom ofthe balusterand itis reasonable, therefore, to consideronly the bottom rail.
Weld 25mm each side (no transversewelds)
Consideraweld leg lengthof3mm. Thecriticaldimension weld design isthe throat width. It isusual to define this dimensionas afractionof the leg length.
Throat LegI
For 90degreesangle throat factor=0.7.
Weld
Throat width = 0.7 leg length = 2.1 Effectiveweld area = length of weld x throat width
5Ommx2.1 mm=105mm2
Shear load on weld
= QQII
=
250N/mm
=
2.3NImm2
=
19N/mm2
2
Stress in weld
=
QJ
105 mm2 Allowablestress in weld material
With such ahigh safety factor,the balustercan be weldedtothe bottom rail in a similar manner to that at the top, on the longitudinalsides only. Weld strengthacceptable,topand bottomwelds resistingdownwardloadwithtopweld also resistingsideways load. 119
TIG WELDING Electrode dia.
rod dia.
Nozzle Bore
mm
mm
2.4
2.4
Filler
Alt.
Weld speed
mm
Argon flow Llmin
current A
mm/mm
9.5
5.7
110
190
Weld passes
1
No edge preparation and no gap between sections. Filler rod material - 4043 or 5356 This material would give better colour match after anodising Deflections.
STANCHIONS 6
=
Load Case
WL3
=
TOP RAIL =
Load Case WL3
=
BOTTOM RAIL =
BALUSTERS =
lllOx 1500
=
5x1110x15003
LoadCase
1.3 48E1
0.73mm
Simply supported UDL
=
3.93mm
384x65500x 184410
384EI
8
Two span, simply supported UDL
Load Case
=
15.14mm
185 x 65500 x 423740
1 85E1
8
=
1110x11003
3 x 65500 x 496680
3E1
8
Cantilever
=
500x l000
central load Simplysupported =
5.70 mm
48 x 65500x 27600
Allowable Deflection. BS6180sets out a maximumdeflectionstandardof 12 mm but calculatedon the basis of: Aoolied load + wind load
2 120
This requires a wind load assessmentto be made using BS CP3 chapter V "Wind Loading". It is necessaryto know where the installationis to be, as thewind code lays down a map of basic wind speeds related to area and on which the dynamic wind pressure is based. Birminghamand the West Midlandsare in the 44m/sec area. This value is, however,factored for there are other considerations:
Si Topography (site exposure)
i
For urban areas the value is .00. S2 Ground roughnessand height For urban areas the value is 0.56 in this case. S3 ProbabilitylevelsTheprobabilityofthe maximumdesign wind speed being exceeded. Theusualfactor is once in 50 years and the value is 1.00. Wind speed is therefore: 44 x 1.00
x 0.56 x 1.00 = 25 m/s.
Dynamic Pressure = 383N/m2 Total area per panel span of balustrading = 0.59m2 Wind load = 383
x 0.59 = 226N
The worst case is the stanchionwith an actual deflectionof 15.14 mm. Therefore considerthe stanchion. Code BS61 80 requiresthe deflectionto be consideredusing an equivalenttotal load which equals: Basic load
+ Wind load 2
121
And where the resultingdeflection should not exceed: Span between stanchions 125
Equivalentdesign load
=
111ON
+ 226N =
668N
2
Stanchion deflection with load 668N = 9.20 mm Permissibledeflection
= j.QQ =
12mm
125 Stanchion is acceptable.
It is obvious that allthe other sectionswill meet the deflectionstandard. Temperature. In hot sheltered sites thermal expansion should be considered and in general it is preferable to fit expansionjoints in long runs of balustrading. Assumed erection temperature
16°C
*Max surfacetemp. on aluminium 36°C 20°C
Temperature rise
*Thiswillvaryonthe degree of sun and wind as well as onthe colourofthe aluminium.
= 23.5 x
Thermal expansion of 6063
1 061°C
Fit expansion joints at 15 metre intervals Expansion = 23.5 x
=
10-6
x 20°C x 15000 mm
7.1 mm
Stress induced in the rails if this expansion is not relieved can be obtained from: Stress Strain
= =
E
69000M/mm2
x
7.1 mm
=
32.4N/mm2
15000mm
If expansionjoints are not fitted, the 32.4N/mm2stress will be absorbedaxially down the rail. To check the ability of the rail to withstand this stress it will be necessary to calculatethecombined bendingand axial compressionin asimilarmannerto that given 122
inthe columnexamplepage 11.20. The bottom rail, however,is performingvery close to its allowable stress level e.g. 30.5N/mm2 to 31.ON/mm2. Therefore it will not withstandthe extratemperatureinducedstress. Expansionjoints at 15 metre intervals are therefore necessary.
The above proposed design meets all the requirementsof BS 6108 and is therefore acceptable.
Columns a)
An aluminium alloy column, 1 metre long, is fixed and restrained at both ends. The cross section is a 50 mm x 50 mm x 2 mm hollow box and subjectedto a 62 kN concentric load. It is necessaryto confirmthe most appropriate alloy and temper.
Section Properties 384 mm2 5910 mm3 19.6 mm
Section Area Section Modulus Radius of gyration Actual axial stress
f
=
Load
Cross sectional area =
62000 = 161.5N/mm2 384
As the column is rigidly held at both endsthe effective length from Table 3.3
= o.7L = 700 mm X
=
Effective Lenath
Radiusof gyration
=
700 mm = 35.7 19.6 mm
Using this value in the strut curve Fig 3.3 the 35.7 vertical ordinate gives the permissible axial stress for a numberof alloys and tempers. Pc = 163N/mm2 for 2014A T6
A 50 x 50 x 2 mm box hollow in 2014A T6 is acceptable. b)
If the load in the above column is offset by 10 mm, will the column still be strong enough?
Theloadeccentricitywill inducebending stressesas well as axial stressesintothe column.
123
The simplestwayto checkistoconsiderthe axial and bendingstressesindividually and then check against the requirementsof the combined stresses.
Theaxial stressat 161 .5N/mm2 is 99% or the permissiblestress of 163N/mm2so there is obviously no allowance left for bending in the original section. Increasesection size to 70 x 70 x 2.5 mm boxalloy 2014A T6. Section properties 675 mm2 14670 mm3 27.6 mm
Section Area Section Modulus Radius of gyration =
700mm = 25.4 27.6 mm
FromFig. 3.3 25.4 ordinatefor 2014AT6 Givesthepermissiblestress = 177N/mm2 Actual axial stress from concentric load
fc fc
Load Cross sectional area =
f bc f bc
f
= bc
62,000N x 10mm 620,000 N mm Moment
Section modulus =
62.000mm 675mm2
92N/mm2
Induced bendingstress Moment = =
=
= 620.000N mm 14,670 mm3
42.3N/mm2
Permissiblecompressive bending, stress for 2014A 16 from Table 3.2 =
202N/mm2
Individuallythe bending and axial stress levels are within thepermissiblestresses laid down in BS CP 118, but the should be checked against combined stress allowances.
124
For combined bending and axial compression
I bc
+
Pc
must not exceed 1
Pbc(1-J Pe
Where
fPcc 5 bc Pbc
Pe
axial compressivestress permissibleaxial compressivestress compressivestressesdue to bending permissiblebending compressivestress Euler critical stress for buckling
where Pe =
Pe
it2
x 72.400 =
1108N!mm2
25.42
fc
Pc
5 bc Pbc Combined stresses
= = = =
92N/mm2 177N/mm2 42.3N/mm2 202N/mm2
= .52 + .23 < 1 = .75 < 1
New 70 x 70 x 2.5 mm box section in 2014A T6 is within combined stress requirementsin BS CP 118. Further modificationscould be carried out by reducingthe size of the section in order to obtain a moreefficientsolution and thereby approximatingthe combined stress ratios towards unity.
125
Page blank in original
ALUMINIUM EXTRUSIONS —
a technical design guide
GLOSSARY OF TERMS Term
Definition
Ageing
Precipitationfrom solid solution resulting in a change in properties of an alloy, usually occurring slowly at room temperature (natural ageing)and morerapidlyat elevatedtemperatures(artificialageing).
Angularity
Conformity to, or deviation from, specified angular dimensions in the cross sectionof a shape or bar.
Annealing
Thermal treatment intended to soften a metal or alloy hardened by cold work or artificialageing.
Anodizing
An electrochemicalmethod of producing an integral oxide film on aluminium surfaces. See Section 5.
Anodizing
Describes material with characteristics that make it suitable for decorative anodizingaftersuitable preliminary treatment.
Quality Billet
A cast aluminiumproductsuitableforsubsequentextruding.Usually of circular cross-sectionbut also may be rectangular.
Bow
The deviation, in the form of an arc, of the longitudinal axis of a product.
Bright anodizing
A process used to obtain highly reflective and bright anodized
Buffing
A mechanical finishing operations in which fine abrasives are appliedto a metal surfaceby rotatingfabric wheels for the purpose
surfaces using alloy 6463.
of developing a lustrousfinish. Burr
Athin ridgeorroughnessleftby a cutting operationsuch as routing, punching, drilling and sawing.
Chemical brightening
Treatment to improve the reflectivity of a surface.
Circumscribing
(CCD)A circlethatwilljust containthe crosssection of an extrusion, usually designatedby its diameter. 127
circle diameter
Cold work
Plastic deformation of metal at such temperature and rate that strain hardeningoccurs.
Concavity
A concave departure from flat.
Concentricity
Conformityto acommoncentre as, for example, the inner and outer walls of round tube.
Container
A hollow cylinder in an extrusion press from which the billet is extruded.
Conversion coating
Treatment of materialwith chemicalsolutionsby dippingorspraying to increasethe surface adhesion of paint. See Section 5.
Corrosion
Thedeteriorationof a metal bychemicalor electrochemicalreaction with its environment. See Section 4.
Direct extrusion
A process in which a billet in the containeris forced under pressure through an aperture in a stationary die.
Drift test
A routine samplingtestcarried outon hollow sectionsproducedby
bridge or porthole methods, in which a tapered mandrel is driven into the end of the section until it tears or splits. Drawing
The process of pulling material through a die to reduce the size, change the cross section or shape, or work harden the material.
Etching
Theproductionof a uniform mafl finish by controlled chemical (acid or alkali), treatment.
Etching test
Thetreatment of a sample using a chemical reagentto reveal the macro-structureof the material.
Extrusion ratio
The ratio of the cross-sectionalareaof the extrusion container to that of the extrudedsection (or sections in the case of multi-cavity dies).
Fillet
A concave junction betweentwo surfaces.
Flutes
Longitudinalconcavecorrugationswith sharpcusps betweenthem used to break up the surface decoratively.
Free machining An alloy designedto give small broken chips, superiorfinish and/or alloy longer tool life. Full heat treatment
Solution treatment followed by artificial ageing. 128
Grain growth
The coarsening of the grain structure occurring under certain conditionsof heating.
Grain size
The mean size of the grain structure usuallyexpressed in terms of the numberof grains per unit area or as the mean grain diameter.
Hardness
The resistanceof a metaltoplasticdeformationusuallybycontrolled indentation.
Heat treatable
An alloy capable of being strengthenedby suitable heat treatment.
alloy
Homogenization A high temperature soaking treatment to eliminate or reduce segregationby diffusion. Indirect extrusion A process wherebya moving die locatedat the end of a hollow ram is forced against a stationary billet. Mean diameter
The sum of any two diameters at right angles divided by two.
Mean wall thickness
The sum of the wallthickness of tube measureat the ends of any two diametersat right angles, divided by four.
Mechanical properties
Those propertiesof a material that are associatedwith elastic and inelasticreactionwhenforce isapplied,orthatinvolvethe relationship between stress and strain. These properties are often incorrectly referred to as physical" properties.
Modulus of Elasticity
The ratio of stress to corresponding strain throughout the range wherethey are proportional.Also referredto as "Young'sModulus".
Modulus of Rigidity
The ratiooftheunit shearstress,inatorsion test,tothe displacement caused by it per unit length in the elastic range.
Non-heat treatable
An alloy incapable
Ovality
The departureof the cross section of a round tube, bar or wire from
Percentage
The increase in distance between two gauge marks that results from stressing the specimen in tension to fracture.
elongation Physical properties
of being strengthenedby thermal treatment.
a true circle.
The properties,other than mechanical,that pertain to the physics of a material;for example, density, electrical conductivity,thermal expansion. 129
Pitting
Localised corrosion resulting in small pits or craters in the metal surface. See Section 4.
Porthole die
An extrusion die that incorporatesa mandrelas an integral part of itsassembly. Bridgeand spider are specialforms of this typeofdie, which are used to produce extruded hollow products from solid extrusion billets.
Proof stress
The level of stress used to signify the limit of proportionality designated at the point of 0.2% strain for aluminium and it alloys.
corrosion
See Section 3. Quenching
Controlled rapidcooling of a metalfrom an elevatedtemperatureby contact with a liquid, gasor solid.
Residual stress That internalstresswhich is left in afinished productafterfabrication. Sealing
A treatment applied after anodizing to reduce the porosity of the surface.
Segregation
Non-uniform distribution or concentrationof impurities or alloying constituentsthat arises during the solidificationof a billet.
Solution heat treatment
A thermal treatment
Stabilizing
A thermal treatmentto reduce internalstresses in order to promote
Stepped extrusion
An extrudedshapewhosecross sectionchangesabruptly in areaat
Stretching
The straightening of extruded and drawn materials by imparting
Tempers
Stable levels of mechanicalpropertiesproduced in a metal or alloy by mechanical or thermal treatments.
Twist
A winding departure from flatness.
Ultimate tensile strength
The maximum stress which a material is capable of sustaining in tension under a gradual and uniformly applied load.
in which an alloy is heated to a suitable and held for sufficienttimeto allowsolubleconstituents temperature to enterintosolid solutionwheretheyare retainedinasupersaturated state after quenching. See Section 2.
dimensional and mechanical property stability. intervals along its length. sufficient permanentextensiontoremove distortion. Specificlevels of stretching (permanent set) can be imparted to relieve internal stresses.
130
Waterstains
Superficial surface oxidization due to the reaction of water films held betweenclosely adjacentmetal surfacessuch as nested angle sections. The appearancevaries from iridescentin mild cases, to white, grey or black in more severe instances.
ABBREVIATIONS *N
E = Young's modulus of elasticity G = Torsion modulus r = Radius of gyration k = End fixity co-efficient = Slendernessratio 8 = Deflection
=
Newton
= kiloaramme gravity
* P = Pascal = N/m2 = Micron P = Stress suffix - - tension c - compression * iN/mm2 = 1MPa both terms are used to define stress
t
levels
131
Page blank in original
ALUMINIUM EXTRUSIONS — a technical
design guide
LISTOF APPENDICES No.
Title PageNo.
APPENDIX 1
DESIGN CONSIDERATIONS
135
APPENDIX 2
BEAM STRESSAND DEFLECTIONTABLES
139
PREVIOUS B.S. DESIGNATIONS
153
COMPARISONOF NATIONAL SPECIFICATIONS-WROUGHTALLOYS
155
CHEMICALCOMPOSITION LIMITS AND MECHANICAL PROPERTIES
159
APPENDIX 3 APPENDIX 4
APPENDIX 5
133
Page blank in original
ALUMINIUM EXTRUSIONS —
a technical design guide
APPENDIX 1 - DESIGN CONSIDERATiONS
135
Thefollowing list containsmost potentialconsiderationslikelyto arise in the design of aluminium extruded products. ALLOY TEMPER MECHANICALPROPERTIES -
0.2% proof stress Ultimate stress
% elongation Compressive strength Axial loading - column length end fixing load eccentricity Shear stress Bearing stress (jointing) Surface hardness Torsion Fatigue Stiffness SECTION DESIGN
- Size, shape and thickness Production availabilityand section extrudability Geometric properties Weight Tolerance Value engineering
SURFACEFINISH
-
Mill Etched
Shot blasted Anodised - Natural Colour (organic) Colour (metallic) AAthickness Protective anodizing - Colour Paint Electrostatic(Powder Spray or Wet Spray) Electrophoretic(Wet Dip)
136
JOINING
- Welding
-
TIG Filler wire MIGJ
Gas Welding Brazing
Rivetingi Bolting
I
Screwing
-
Bearing strength Choice of fastening material Screw material and size Pull out strengths
Corner crimping Adhesives - Type Strength Applicationdetails FABRICATION
-
Bending
-
Alloy and temper Tooling Twisting Necking
Machir;ing -
Springback Routing Drilling
Sawing TEMPERATURE
- Expansion/Contraction Effect
CONDUCTIVITY
-
on mechanicalproperties
Heat transfer Electrical
DURABILITY
-
Atmospheric
-
Environment -
Chemical
-
Substance Concentration Temperature Design of Bi-metallic connections
Rural Marine Industrial
Compatibility -
FIRE
-
Melting point Non-combusibility
Non-ignitability Fire propogation Surface spread of flame Structuralresistance
137
Page blank in original
ALUMINIUM EXTRUSIONS —
a technical design guide
APPENDIX 2-
BEAM STRESSAND DEFLECTIONTABLES
139
Stresses
Typeof Beam
GeneralFormulafor Stress atany Point
Case 1.- Supportedat Both Ends, TOTAL LOAD W
fjfjjfijf4
Points
Stress at centre,
UniformLoad
2
StressesatCritical
If
s=-
cross-section is
constant, this maximumstress.
2 Betweeneachsupport Stress at centre, andload,
Case 2.- SupportedatBoth Ends, Loadat Center
S= -
If
2Z
is the
-
cross-section
constant, this maximumstress.
is
is the
2
2
For segmentof length
Case 3.- SupportedatBoth Ends, Loadatany Point
a,
5=-x ZI
Stressat load - wa
If
cross-section is
For segmentof length constant, this maximumstress. b,
I
I
ab1
Case 4.- SupportedatBoth Ends, TwoSymmetricalLoads
TId w
w
-
w
S
Way
—-
Between each support andadjacentload,
s=
-z
Between loads,
w
z
140
is the
Stress at each load, andatallpointsbetween, Wa
Deflections
GeneralFormulafor Deflection atany Point
at CriticalPoints
Deflections
Maximumdeflection,at centre,
W(I-)
V3
——
24E11 '12÷x(I-x)J
El
384
Betweeneach supportandload, Maximumdeflection,atload, WI3
4BEl (312-4x2) For segmentoflength a, —
6E11
(I2--b)
For segmentoflength b,
4E7
Deflectionatload, Wa2b2
3E II Let a be the length of the shorter segment and b of the longer one. The maximum deflectionisin the longersegment,at
(12-v2-a2)
bv'jj
Betweeneach supportandadjacentload,
Maximumdeflectionat centre,
y=
=
Way
v=
Betweenloads,
"
Wa
- 6E I f3a (I a) x2)
'312-4a2)
Deflectionatloads
Wa
6E1 (3v(I-v)-a21
141
= v1, and is
(3/-4a)
Stresses
Typeof Beam
Case 5.- Both EndsOverhanging SupportsUnsymmetrically, UniformLoad
GeneralFormulafor Stressatany Point
L2ZL
Foroverhangingendof lengthd, S=
=1
C2Lx
÷d2X(!X)} 2(/-d-c)
Points
Stress at support next Foroverhangingendof endoflength c, length c, Wc2 w X(c-u)2 s— 2ZL Criticalstressbetween isat supports Betweensupports, /2÷ c2- d2 X 2/
TOTAL LOADW
w 2! ÷d-c)
Stressesat Critical
2ZL W
andis
2)
2ZL (C2- X7 Stress at supportnext
endoflengthd,
Ld2
If
2ZL
cross-section
is
constant, the greatest of these three is the maximumstress. If x,>' the stress is 2 - c2 zero at points on both sides of x =Xr
.f
Case 6..- Both EndsOverhanging
Supports, Loadatany Point
ba Between
I
(a+b=I)
Between supports: For segmentoflength a,
s=_x ZI For segmentoflength
b,
S7f
Way
Beyondsupportss=o.
142
Stress atload,
7i Wa!)
If cross-section is constant, this is the maximumstress.
Defiections
GeneralFormulafor Deflectionatany Point
Deflections
at CriticalPoints
For overhangingend of length c, Wv
Deflectionatend c,
24E1L (21(d2÷2c2)
i-6c2u-u2(4c-u)-13J
24E1L (21(d2÷ 2c2)÷3c3-13J
Betweensupports,
Deflectionatend d,
Wx (I -x) I' 24E1L x(I-9+I2--2(d2÷c2)
-
24E1L (21(c2÷ 2d2)÷3d3-131
fd÷ c2(Ix)J}
Thiscase is socomplicatedthatconvenient generalexpressionsforthe critical deflections betweensupportscannotbeobtained.
For overhangingendoflength d,
)24EILt2+2c) ÷6d2w-w2(4d-w)-13J Between supports, same as Case 3. For overhangingend oflength c,
y=
Wabu
For overhangingend oflength d,
Between supports,same asCase 3.
Deflectionatend c,
Wabc
Deflectionatendd,
+ 6EII (I a)
y = - WaLw (1÷ a)
143
Stresses
Type of Beam
General Formulafor
Stress at any Point
Case 7.- Both Ends Overhanging Supports, Single Overhanging Load
Stressesat Critical Points
Between load and Stress at support adjacent support, adjacentto load, WC
W(c - U)
-
Between supports, Wc S=
z If
cross-section is
constant, this is the (I x) maximum stress. Stress is zero at other Between unloadedend support. andadjacentsupport, s
= 0. Case 8.- Both Ends Overhanging Supports, Symmetrical Overhanging Loads
Between each load and adjacentsupport,
s=
w
w
W
Stress atsupports and at all points between,
--(c-u)
Wc
1
Between supports S= W
W
Wc
Case 9.- Fixed at One End,
If cross-section is constant, this is the maximum stress. Stress at support,
Uniform Load
W thi-2
TOTAL LOAD W
-WI
If
cross-section is
constant, this is the maximumstress.
144
Deflections
General Formulafor Deflection
Deflectionsat Critical Points
at any Point
Between load and adjacent support,
Wu
all Wcx
—y
(a + I)
Maximum upward deflection is at
Between supports,
Y=
!.1 3EI
Deflectionat load,
(3cu-u2÷2c!)
x=042265I, and
(I-x)(2I-x)
Wc12
5
15.55E1
Betweenunloadedendandadjacentsupport, Deflectionat unloaded end,
y=
Betweeneach load and adjacent support, =
WcId
Wc/w
Deflections
(3c(I + U) - u2]
Between supports,y
-W-
at loads,
Deflection at center,
2E1 (I-x)
6EI
—
(2c + 3/)
7
Wa!2
The above expressions involve the usual approximationsof the theory of flexure, and hold only for smalldeflections. Exact expressionsfor deflectionsofany magnitudeare as follows:
a
Between supports the curve is circle ofradius __________
Deflectionat centre,
/r - / 2
r=E
Wc
y = V'r2 1/412
/2 (l/2 I-
2-
y= 24E1! -'--—f2! + (2!- x)2]
Maximumdeflection,at end, WI3 8E1
145
x)2
Stresses
Type of Beam
General Formulafor Stress at any Point
Case 10. - Fixed at One End, Load
Stress at support,
at Other
s=
w
wI(
Stresses at Critical Points
W
-y (i-x)
If
cross-section is
constant, this is the maximum stress.
Case 11. - Fixed at One End, IntermediateLoad
Between support and load, S
wI
=
W
Z
Beyondload, s = o.
Case 12. - Fixed at OneEnd,
If
cross-section
is
constant, this is the maximum stress.
Maximumstress at
Supportedat the Other, Uniform Load
TOTAL LOAD W
Stress at support,
wi
point of fixture,y
r
Stress is zero at
S1)r/4Ix) 2Z1
=V4L
Greatest negative stress isatx=6/.Iand
5
9
146
WI
Deflections
General Formulafor Deflectionat any Point
(3!-x)
y
-
Deflectionsat Critical Points
Maximumdeflection,at end,
Betweensupport and load,
Y=
Deflections
(31-x)
at load,
WI3
Maximumdeflection,at end,
Between unloadedendandadjacentsupport, WI2
y=
(3v -I)
(2! ÷ 3b)
Maximumdeflection is at x = 05785I,
and is =
W2 (I -x) 48E
(31- 2x)
Y?I_ 185E
I
Deflection at center,
I
192E
Deflection at point of greatest negative stress,
147
atX=
— us
8
WI3
187E1
Stresses
Type of Beam
General Formulafor Stress at any Point
Stressesat Critical Points
Case 13. - Fixed at One End,
Between point of Maximum stress at Supportedat the Other, Load at Center fixture and load, point offixture, 3 14'! 16 Z s= w lix) Stress is zero at w Between support and x= 3 I
-(3I-
-
load, 16
I
5
s=_T
Case 14. - Fixed at One End, Supported at the Other, Load at
32Z
Z
of
2(n-mx)
Between support and load,
Wab(/÷b) 2/2
s= a2
w[i--(sI-a)]
Greatest
-Wa 2v
2(3Ia)
positive
stress, at point offixture,
/2
V.P(J÷)
Wb
s=
n=aI(I÷b)
Wv
Between point fixture and load,
any Point
m_—(I÷a)(I+b)+a/
Greatest negative stress at center, 5 Wi
Greatest negative stress, at load, Wa2b 2Z13
(3!- a)
If a 0.5858!,maximumdeflectionisbetween load and point of fixture, at 2n
and
Wbn3
'53EIm2I3
Maximumdeflection,at centre,
—
Wx2
24E1! (/-x)2
384E1
149
Stresses
Typeof Beam
GeneralFormulafor Stress atany Point
Case 16.- Fixedat Both Ends,
Stressesat Critical Points
Stress at end next segmentoflength a,
Loadatany Point
Wab2
For segmentoflength a,
Wab2
Wab /2
s=
3(aI-x(I÷2a)]
r2
Stress at end next segmentoflength b, Wa2b Z12
Maximum stress is at
Forsegmentoflength end b,
Tb2(/2) Wa2(/2;f fT
next
shorter
segment.
32(bI V(I+ 2b)j
S
Stress is zero for
a!
=
I÷2b Greatest negative stress,
atload
2Wa2b2
---patCenterof Each
TOTAL LOAD ON EACH SPAN,W
J'I-j) (I/i) 2Z!
Case 18. -
ContinuousBeam,with
TwoEqualSpans, EqualLoads
atCenterofEach w
-
Maximum stress at WI pointA,
Case 17. - ContinuousBeam,with TwoEqualSpans, EqualLoads
-_____
Stress is zero at
x=4I
--
Greatest negative stressisatx=5/5! and is,_ 9 WI
Maximumstress at Between point A and 3 WI A, point load,
s=
w
j-(3I-llx)
Between point B and load,
5iT 150
5
Wv
16
Z
Stress is zero at X
3
Greatestnegative stressatcenterof span 5 WI
----r
Deflections
GeneralFormulafor Deflectionatany Point
Deflections
atCritical Points
Wa
Deflectionatload, For segmentoflength a, 2b2
(2a(I-x)÷I(a-x)]
For segmentof length b,
Letb bethe length ofthelongersegmentand aoftheshorterone. The maximum deflection is in the longer segment,at 2N
V1
= Wv2a2 (2b (I- v) + I(b - v)J
6EJ/3
and is
I(I÷ 2b)2
2Wa2b3
3E
Maximum deflectionisatx=0.5785!, and is WI3
185E1
- Wv2(I-) 48EII —
Deflectionatcenterofspan,
'3/ - 2Xi
Deflectionatpointofgreatestnegative stress, atx
BetweenpointA andload,
I £ 8
is
WI3
187E1
Maximumdeflectionis at v=0.4472!, andis
W y= -j.(9I-11x)
WI3
107.33E1
Betweenpoint Bandload, =
WI3
192EI
Deflectionatload,
wv
9J(3I 2-5v2)
151
L !! El
768
Page blank in original
ALUMINIUM EXTRUSIONS — a technical
design guide
APPENDIX3- PREVIOUSBS DESIGNATIONS
153
PREVIOUS B.S. DESIGNATIONS (PROPERTIESIN IMPERIAL UNITS)
OLD
NEW
B.S. B.S. TEMPER NUMBER NUMBER OLD NEW
50 MM
ON
4.5
8.5
14
T5
7.1
9.7
7
IF
T6
10.4
12.0
7
M
F
7.5
12
TB
14
7.8
12.4
14
TF
16
16.5
19.1
7
TB
T4
HE9
TE
HE9
6063
% ELONG
12
F
HE9
ULT.
STRESS TONS/IN2 6.5
M
HE9
0.2 % PROOF STRESS TONS/IN2
-
HE3O HE3O
1 6082
HE3O
E91E
6101A
TF
T6
11.3
13.3
8
BTRE6
6463
TF
T6
10.4
12.0
9
HE15
2014A
TB
14
15.3
24.7
10
TF
T6
24.7
29
6063A
TB
T4
6.0
10.0
12
6063A
TE
15
10.4
13.3
7
6063A
IF
16
12.6
15.3
7
HE15
6
Thesedesignations andproperties areforguidanceonly. All orders are manufactured to the existing British Standards alloy numbers and tested in metric units.
154
ALUMINIUM EXTRUSIONS —
a technical design guide
APPENDIX 4-
COMPARISON OF NATIONALSPECIFICA11ONS
155
Page blank in original
01
—
Al Cu 4Mg 1
2024
Si Mn
144054
Al
Cu 451 Mn
Pb
1
N61 H20 H9 H30
AIM5IS1Cu Al Mg 0.5 Si
AISi I Mg Mn
55565
6061
6082
2L95;L160;L161; L162
Al Zn 6Mg Cu
7075
DTD 5025: 5104A: 50945
7014
Hi7
DTD0I3O:5120A
7010
Al Zn 4.5 Mg
E6
6463
7020
916
6101A
6063
1452
1451
Al Mg 3.6
5454
5554
N4
Al Mg 2
5251
145
N8
Al Mg 4.5 Mn
5083
5154A
N6
51Mg 5
50565
1441.
Al Mg
142
4047
5005
N21
N31
4043
3105
N3
3.4335 3.4365
A-Z 5G U
3.2315
3.3537
3.3525
33547
3.3555
A-Z 5 G
A-SG M0.7
A-CSUC
A-G 2,5 MC
A-G 2 M
A-C 4.5 MC
A-C 0.6
A-S 12
A-S 5
3.0505
3,0515
Mn
Al Zn Mg Cu 1.5
Al Zn Mgi
1
UN13735
UN17791
UN13571
UN13569
UN16170
Granges SM 6958
144212
Mg
Zn 45Mg
1
1
0.5
Zn 6Mg Cu
Al
Si
Sil Mn Al Mg
Al
Mg 2.7 Mn
Al Mg 5
Al Mgi
Mg 21 Mn
144104
144140
144106
Al Mg 2 UN17789
UN13575
UN17790
U14l13576
UN15764
UN13568
Mg 2 Mn 0.3
Mg 4.5 Mn
Al Mg Si
Al
Al
Al
Al Mg 5
Al Mn 0.5 Mg 0,5
Al
Al
5
1318
1316
— —
2024
2017A
20145
2011
1350
V95
6063
7075
7020
7014
7010
6463
6101A
6082
6061
AD3I
55565
5554
5454
0201
5154A
5083
50585
5005
4547
4043
3105
3103
AD3
AMG3
AK4-1
26185
3103
A-U2GN
Al Mn
Al Cu 4Mg 1.5
Al
Bi
2117
UN13577
LJN13583
144338
Al Cu 6
2031
Al Cu Mg 0.5
Al Cu Mg2
UN13SO1
144355
H16
—
Cu
AlCuMgi
Al
UN16362
A-U 20 3.1305
3,1355
3.1325
3,1255
Al Cu Si Pb
E-Al99,S
A-U2N
A-U4GI
A-U4G
A-U4SG
3.1655
A-U 5 Pb Bi
E-Al
26185
1
1080A
10505
InternationalNumber
2218
Al Mn
AK8
USSR
7L25
2117
Li 10
.
A199.0
A199,5
Switcerland
1200
3.0257
A5/L
144010
144004
144007
Sweden
1199 UN13567
Italy
A4 Al99
A199 5
A99 3.0205
3.0255
WantGermany WerkstottNumber DIN Designation
2218
H12 3L86
2031
Cu 2 Mg
AICu 4Mg Si
20175
Al
H15
Al Cu 4Si Mg
2014A
2L 97, 2L 98, L 109, DTO 5100A
EC1
Al Cu 6 Di Fb
1E
2011
1350
1C
1200
A199
1
AS
IA
A199-5
1080A
1199
A5
lB
A199-S
1OSOA
Franca
FormerNF
FormarBS Designation
Alloy Type as Depicted by Old ISO Number
BS and International
Page blank in original
ALUMINIUM EXTRUSIONS —
a technical design guide
APPENDIX 5-
CHEMICAL COMPOSITION LIMITS AND MECHANICAL PROPERTIES
159
Page blank in original
a)
'1
0_to
0.35
0.20
0.40
0.35
7020
0.10
0.45-
1.001.40
0.50
0.200.60
0.450.90
0.05-
0.401.20
005
0,40-
-
090
0.601.20
090
0,50-
0.35
0,10-
0.10
-
-
025
005
035
120
0.90
0.04-
0.80-
0.401.00
075
0.10
0.15
0.05
0.35-
0.10
0.60
¾
%
Chromium
¾
Manganese Magnesium
-
0.10
-
-
-
-
-
5.00
4.00-
0,25
005
-
0.20
015
0_ia
0.25
0_is
-
%
-
Zinc
¾
Nickel
( INDIVIDUAL PERCENTAGE VALUESOF CONSTITUANTSARE MAXIMUM (2) ALL MECHANICALPROPERTIESARE TYPICAL. BARS (3) TEMPER T6510 APPLIES ONLY TO CONTROLLEDSTRETCHINGOF SOLID
5 00
3.90-
0,50
0.500.90
20i4A
060
0,20-
0.20
0.40
030-
6101A
0.15
0.50
0.70130
6082
6463
0.05
035
070
0.10
0.15-
atO
0.150.40
060
0.60
0.20-
080
0.10
¾
Coppe
0.70
030
0,40-
0.10-
060
%
%
0.30-
iron
Smlioon
0.30-
6063A
6063
6061
6060
Material designation
008-0.25 Zr Ti
0.20 Zr eTi
-
0.15
-
-
. -
0.15
0.10
0.10
0.15
0_to
¾
-
'
-
-
¾
Other restrictions Titanium
________
0.05
0.05
0.05
0.03
0.05
0,05
0.05
0.05
005
¾
Each
0.15
0,15
0,15
0.10
0.15
0.15
0.15
0.15
0.15
¾
Total
—
Rent
Rem.
Rent.
Rem.
Rem.
Rent
Rent.
Rem.
Rent.
¾
Aluminium
T4 T6
T65i0
T6
T4
T4 T6
T6
T5 T6 T65t0
20
20 75
-
25 25
200 150
20
150 200
20 75
50 50
.
190 280
230 250 250 230 370 435 420 390
150
78
170
300 340
370 435 480 465 435
370 390 390
125 185
200
(100) 190 170 270 295 310 280
-
' -
150 200 230
(100) 130 120 150 195 150
-
280
190
190
120 145
90 160 190
70 70 110 160 130
-
.
150 120 200 100 6 230 20 255 ISO 270 200 240
205 200
25
25 25
200 200 150 200 25 150 205
75 150
-
itS
iSO 240
150
Mm.
strength
Max,
5.65 'JSo (rrrin.(
On
-— -
-
-
-
-
170
-
-
-
-
-
-
140
-
-
-
12 10
7 7
7
8 8 7
ii ii
16 tO
10
8 8 S
(13) 16 13
16
8 8
14
8 8 6
(13) 16 13
15
8
16
16 8 8
N/mm' N/mm' N/mm' %
proof stress (mm.)
150 60 150 100 150 150
mm
—
20 7S
-
150
-
-
-
150
-
-
150
T4
F
0
iSO
T4 T5 T6
l,
I
150
5 -
-
-
-
-
-
mm
-
T5 T6
T4
F
0
T65i0
T6
T4
T4 T5 T6
—
(bar) or thickness (tube! section)
and mechanical properties °1 of heat-treatable Aluminium alloy bars, extruded round tube and sections
(Figures in parentheses refer to the notes at the end of this table)
Chemical composition limits
10 8
-
-
-
6
-
-
10
14 9
8
-
8 7
-
(12) 14
14
12
7 7
-
7 7
-
14
(12)
13
7
14
-
¾
(mn.)
On 50 mm
Page blank in original
Aluminiumextrusions are used in a wide variety of engineering and architectural applications. As a strong, light, non-corrosive material which can be extruded into complex shapes, aluminium provides the solution
to a whole range of design problems.
This concise technical guide provides the reader with the
information necessary to design effectively with aluminium extrusions.
It presents brief details on the extrusion
process,
outlines aluminium's material specifications and mechanical properties and covers such design considerationsas conductivity, temperature, fabrication and finishing. The book also contains specific guidance on design procedure, including worked examples, and concludeswith an extensiveglossary.
"It's a true working manual...a
must for every
drawing office which uses or might use aluminium extrusions" Chris Rand, Industrial Technology magazine
"A valuable document...four star rating out of
fve" Andy Pye, Design Engineering magazine
"A much needed source of reference" Roy Woodwarci,Aluminium Industry magazine
Published by The Shapemakers — the information Aluminium ExfrudersAssociation
Aluminium
arm of the
UK
View more...
Comments