170089832-D3-2-100701-Kiln-Mec-Behav-Patroller.pdf

Kiln Mechanical behavior for Patrollers

Content

1

Thermal Expansion

2

Thermal Expansion effects on the shell

3

Thermal Expansion effects

4

Mechanical crankshaft

Content

1

Thermal Expansion

2

Thermal Expansion effects on the shell

3

Thermal Expansion effects

4

Mechanical crankshaft

Kiln temperature profile > 110°C > 145°C > 180°C > 215°C > 250°C > 285°C > 320°C > 355°C > 390°C > 425 °C

500

Temp: °C

Max Avg Min

450

400

350

300

 Average 250C

250

200

m

150

100

0

10

20

30

40

50

60

70

80

How to evaluate Expansion?

 Expansionmm





 1.2  (

 C   C  T  Final   T  Initial 

100

)  Lengthinitial  ( m )

 At 250°C, a 70 m kiln is 190 mm longer than at 25°C

Temperature must always be taken into account on kilns 

On repair/replacement operations



On adjustments when done in cold conditions

1

Thermal Expansion

2

Thermal Expansion effects on the shell Shrinkage of the tyre on shell Thermal bending

3 4

Thermal Expansion effects Mechanical crankshaft

Shrinkage of the shell into the tyre 





Under tyre shell temperature is greater than tyre average temp. 

In normal operation



.. and more in start-up phase

High risk to shrink the shell at start-up 

too quick preheating



too small cold clearance value

Consequences 

Shell will be deformed permanently



Will possibly lose some bricks



Will probably have some problems of fixation



Will lead to potential shell cracks in the future

Thermal bending Variation of Temperature along kiln Max  Average Min

400 350 300 250

door 

200 150 100 GG

50

Pier

Pier 

Pier 

0 0

8

Why this variation (max/min) of  temperature in a section?

16

24

31

39 is the 47 effect 55 of  What this profile of  temperature?

63

71

Thermal bending Variation of Temperature along kiln 400 350 300 250 200 150 100 50 0 0

8

16

24

Avg. 300 ° C

Length = 12 m

31

39

47

55

63

71

Expansion at 300 ° C = 1.2 x (300-20)/ 100 x 12 = 40 mm Differential = 11 mm

Expansion at 220 ° C = 1.2 x (220-20)/ 100 x 12 = 29 mm Avg. 220 ° C

Thermal bending Variation of Temperature along kiln 400 350 300 250 200 150 100 50 0 0

8

16

24

31

39

47

55

63

71

12m + 40mm

12m + 29mm 

Due to the mass of the kiln, there is still a contact on each pier  





.. but load is lighter at central pier and higher at the other one .. and opposite after half a rotation !

If the thermal bending is very high some tyres could even not touch the rollers!

Thermal bending causes 





 A defect in coating can lead 

To different temperatures on the same section



Then to differential expansion



Then to kiln thermal bending

When the kiln is not properly rotated 

During start-up



During kiln stoppage

When the kiln is not rotated after one incident 

Importance of barring drive!

Thermal bending corrective actions 

Modify process parameters 

to get proper equal coating



Barring drive always to be ready to operate



If too late, shell replacement: Figuil (Cameroon) Example 

Production incident, no barring during 10 min.



Tropical rain (which cools only top of shell)



Kiln bent forever (tyre/roller clearance 25mm)



Need for cut or shell replacement • Cost > 100.000 USD • Stoppage time needed > 10 days

1

Thermal Expansion

2

Thermal Expansion effects on the shell

3

Thermal Expansion effects Girth gear  Kiln bearing liner 

4

Mechanical crankshaft

Girth-gear root clearance increase 



Girth-gear fixed on the shell Example of a 3-pier 4.6 m diameter kiln with pre-heater: Root clearance increases about 6 mm

Clearance

Kiln roller bearing 

Kilns are generally rotating on roller shaft with liners



Few roller bearings because





very high loads and low rotating speed



expensive to design and use

 Are there any limits? 

Yes, there is a limit of pressure on a liner 



Special mode of friction, low speed, negative influence

Kiln roller bearing liner Temperature 

Depends on friction -> related to rotation 





Torque liner about Torque motor x (0.03 to 0.05)

Depends on the load -> related to 

Design. (FLS, POLYSIUS, CLE, FCB using approx. same design limit)



Quality of geometry and lubrication







Most of the torque used to lift the material inside the kiln / Very little converted to heat through the shaft/liner contact

 Alignment of kiln tires Shell axis deformation (permanent or thermal)

In case of severe liner overheating, this torque can suddenly increase

Expansion effect on Kiln bearing liner  





When the kiln starts, tyre will heat the roller, then the shaft  After 48 hrs, the shaft diameter will be bigger but the liner support will remain cool (water cooling) The expansion of the shaft will reduce the oil film thickness… and the contact will increase SHAFT (HOT)

SHAFT (COLD)

Contact Surface

Kiln bearing liner overheating cycle Viscosity decreases

Overheating

Shaft diam. increases

More wear 

Less clearance

Less oil

Kiln bearing liner -> Emergency procedures 

Best method = Oil re-circulation with cooling and cleaning 



Small units available on the market with installation on request

In case of small problem, putting the kiln on barring can save you! 

Time to decrease shaft temperature, get proper viscosity back, come out of the vicious cycle



Cool by air roller flank to limit kiln heat transmission to shaft



Oil usage 



The best oil cannot solve contact pattern problems Very thick oil or synthetic oil cannot solve too low clearance between shaft and liner   



Check if this synthetic oil can be mixed with mineral Check if this synthetic oil does not chemically attack any bearing part

put the highest viscosity you can, assuming the real viscosi ty will drop very quickly because of temperature (oil viscosity diagram versus temperature must be known)

Kiln bearing liner -> Musn’t 

Fan cooling: dangerous on bearing 



Housing open = Dust contamination = Be careful!  Are you sure you are cooling the shaft or the housing? (think of  expansion)



Cool the roller flank with water 



Water on roller is dangerous 



Permanent application or heat shock leads to spalling

Use grease or molycot is forbidden 



very dangerous can block the oil pocket, preventing any oil from entering to lubricate liner and shaft

Expansion Conclusion 





Heat is a very important parameter for kiln shell  Attention should be always given to temperatures 

Maximum temperature



But also differential

Mechanical staff must take extreme care in case of kiln thermal bending

Content

1

Thermal Expansion

2

Thermal Expansion effects on the shell

3

Thermal Expansion effects

4

Mechanical crankshaft Misalignment Brick Failure

Kiln Misalignment 

 As an example on 3 piers, a mechanical bend is one tube which is deformed so the 2nd section is rotating when sections 1 and 3 are perfectly set-up in line

Wrong Kiln Alignment 

Wrong alignment of shell at erection due to 

Subcontractor’s lack of know-how



Deformed new or old shells



Not properly chosen shells to be replaced

SHELL ECCENTRICITY OR "CRANKSHAFT" KILN SHELL  AXIS UNDER TYRE

POOR  ALIGNMENT OF SHELLS

Wrong Kiln Alignment effects 



On a poorly aligned 3-station kiln, tire 2 too high by about 10 mm 

Overload = 8 t/mm x 10 mm = 80 t (TC calculation)



Permanent load supported by this tire = 80 t higher than normal

Possible problems (depending on design safety coefficient) on 

Bearing liners overheating



Tyre (wear, holes, crack, …)



Rollers (wear, holes, crack, …)



Shaft crack



Brick failures • Too high load => too high ovality => problem of bricks



Frame cracks



Shell cracks

Brick Failure 





If not followed by stoppage (major cause) Too long run with missing bricks / Too high temperature on the shell with bricks Some indicators 



If the circumference of hot-spot is > 90° of the total, it becomes dangerous for the kiln shape, otherwise it will create only l ocal deformations (but still bad)  Axial hot-spots are less dangerous than radial

Brick Failure effect

Brick Failure effect

Brick Failure effect

Mechanical crankshaft without visual indications 





Possible Since kilns are generally very flexible, you may have a crankshaft but as the kiln deforms during rotation, the deformation is not visible Sometimes kilns are affected by several crankshafts in opposite phases