6.RUBBER COMPOUNDING TECHNOLOGY-FINAL.ppt

RUBBER COMPOUNDING TECHNOLOGY

SUDHA.P DEPUTY DIRECTOR(RIDT) RUBBER TRAINING INSTITUTE DEPARTMENT OF TRAINING RUBBER BOARD KOTTAYAM-686 009

[email protected] Mob: 94964 13731

RUBBER COMPOUNDING

COMPOUND It is a homogenous mixture of ingredients used in a particular product manufacture such that the properties of most of the ingredients are unchanged in the final product whereby providing a defined set of mechanical properties. COMPOUNDING It is the science of selecting and combining elastomers and additives to obtain physical and chemical properties for a finished product.

RUBBER COMPOUNDING OBJECTIVE 1. To secure certain properties in the finished product to satisfy the service requirements. 2. To attain processing characteristics necessary for efficient utilization of available equipment. 3. To achieve desirable properties and processability at the lowest cost. The most important factor in compounding is to secure an acceptable balance among demands arising from the above three criteria.

MAJOR OBJECTIVES OF COMPOUND DEVELOPMENT PROCESS REQUIREMENT  Proper mixing (Incorporation, dispersion, distribution and plasticization)  Viscosity/process safety (ML1+4, MS)  Stickiness and tackiness  Shaping (Calendering, Extrusion, Assembling and Moulding) COMPOUND PROPERTY REQUIREMENT  Hardness  Stress-Strain properties (TS, EB, M-100, M-300, tear)  Abrasion resistance  Hysteresis & set properties  Resistance to cut growth, fatigue, flex cracking

MAJOR OBJECTIVES OF COMPOUND DEVELOPMENT RESISTANCE TO DEGRADATION    

Heat, Oxygen, Ozone Flame Liquids Light

MISCELLANEOUS PROPERTY REQUIREMENTS  Low temperature flexibility  Electrical properties  Permeability  Contact with food stuff and drugs  Bonding to metal & textiles  Swelling  Other specific requirements

CLASSIFICATION OF COMPOUNDING INGREDIENTS 1. 2. 3. 4. 5.

6. 7. 8. 9. 10.

Elastomers Vulcanizing Agents (curatives) Accelerators Activators and Retarders Antidegradants (Anti-oxidants, Antiozonants, Protective waxes ) Processing aids (Peptisers, Lubricants, Release Agents) Fillers (carbon black, non-black materials) Plasticizers, Softeners and Tackifiers Colour pigments Special Purpose Materials (Blowing Agents, Deodorants, etc.)

COMPOUND DESIGN DESIGN REQUIREMENTS  SERVICE REQUIREMENTS/VULCANISATE PROPERTIES  PROCESSABILITY  ECONOMICS DESIGN BASED ON  CUSTOMER SPECIFICATION/REQUIREMENTS  COMPETITOR'S SAMPLE  DEVELOP A NEW PRODUCT

POLYMER SELECTION CRITERIA               

Cost Ease of mixing Strength requirements Modulus or stiffness requirement Abrasion resistance requirement Elongation requirement Oil resistance requirement Low temperature requirement Fatigue requirement Tack Set of stress relaxation Service temperature Dynamic properties (hysteresis, damping resistance) Flammability Chemical resistance

POLYMER SELECTION

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SHOULD HAVE THOROUGH KNOWLEDGE ABOUT POLYMER PROPERTIES REFER STANDARD SELECTION CHARTS/COMPARATIVE CHARTS BLENDS OF POLYMERS PROCESSABILITY FACTOR-suitability for the processes and methods adopted COST FACTOR AVAILABILITY OF DATA ON POLYMER GRADES, PROPERTIES, START UP FORMULATIONS ETC.

VULCANIZING AGENTS TYPE

COMMON USE

Sulphur or Sulphur bearing materials

Natural Rubber, Isoprene, SBR, Butyl, Poly Butadiene, EPDM, Nitrile

Organic Peroxides

Urethane, Silicone, Chlorinated Polyethylene, PVC/Nitrile

Metallic Oxide

Polychloroprene, Chlorosulphonated Polyethylene, Polysulphide

Organic Amines

Acrylic, Fluorocarbon, Epichlorohydrin

Phenolic Resins

Butyl

CURING SYSTEM Selection of curing system is based on:    

Base polymer Processing conditions Curing conditions Service requirement

Base polymer  

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Saturated rubber – peroxide e.g. EPR with DCP Unsaturated rubber-peroxide, sulphur/accelerator & resins, e.g. EPDM with DCP, NR with sulphur accelerator, IIR with Resin Special Polymers – Metal oxide, Dioxime, Resin e.g. CR with ZnO/MgO

ACCELERATORS An accelerator is usually a complex organic chemical which takes part in the vulcanization, thereby reducing the vulcanization time considerably- Organic amines & its derivatives . It also improves the properties. Its action may be: slow-

eg. Guanidines, Diphenyl guanidine (DPG) Di ortho tolyl guanidine(DOTG)

medium-

eg. Thiazoles,

Mercapto benzo thiazole (MBT) Di benzthiazyl di sulphide) (MBTS)

fast ( ultra)- eg. Thiurams, Tetramethyl thiuram monosulphide (TMTM) Tetramethyl thiuram di sulphide (TMT)

Dithiocarbamates, Zinc diethyl dithiocarbamate (ZDC) Zinc dibutyl dithiocarbomate(ZDBC)

Delayed-action fast- eg. Sulfenamides Cyclohexyl benzthiazyl sulfenamide (CBS) Dicyclohexyl benzthiazyl sulfenamide (DCBS) Morpholino thio benzthiazylsulfenamide (MOR) Tertiary butyl benzthiazyl sulfenamide (TBBS)

CURING SYSTEM (Contd..) Accelerator Activator  

ZnO and Stearic acid for sulphur cure system TAC for peroxide cure system

Processing condition    

Type of processing equipment used Temperature build up during processing Extent of rework usage Rheological property requirement

Curing conditions    

Type of the product Method of curing employed Temperature of curing Flow requirement during curing

CURING SYSTEM (Contd..)

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Service Requirements Service temperature Duration of exposure Mechanical property requirement. Dynamic property requirement Ageing behaviour and permanent set requirements. Special property requirement.

FILLERS •

Fillers are materials used to extent the range of physical properties, to reduce compound cost, modify the processing properties and to influence the chemical resistance of the compound. The effect of a filler on rubber depends on• structure • particle size • surface area • geometrical characteristics

FILLERS Reinforcing Type

Extending Type

Carbon Black (listed in order of increasing particle size)

N220 (ISAF) N330(HAF) N550 (FEF) N762 (SRF-LM) N990 (MT)

Non-black

Silica Zinc Oxide Magnesium Carbonate Aluminium Silicate Sodium Aluminosilicate Magnesium Silicate Calcium Carbonate Barium Sulfate Aluminium Trihydrate Talc and Soapstone

• • • • •

•

reinforcing carbon blacks non- reinforcing carbon blacks reinforcing non- black semi reinforcing non- black non- reinforcing non- black Reinforcing carbon blacks     

Furnace black SAF – Super Abrasion Furnace ISAF – Intermediate Super Abrasion Furnace CF - Conductive Furnace SCF - Super Conductive Furnace

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HAF

-

High Abrasion Furnace (Low structure and high structure)

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FF

-

Fine Furnace

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FEF -

Fine Extrusion Furnace

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GPF -

General Purpose Furnace

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SRF -

Semi Reinforcing Furnace

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Thermal Black MT - Medium Thermal • • •

•

Channel black EPC Easy Processing Channel Reinforcing Non- black Precipitated silica and fumed silica Semi Reinforcing Non-black aluminium and calcium silicates high styrene resins phenolic resins

Fillers Selection is based on • Reinforcement • Cost • Processing requirement • Colour requirement • Service requirement • Any other special requirement

Compound Designing – Hardness phr required for 1 unit increase in Hardness

Polymer Hardness

NR

SBR

CR

NBR

37-40

39-41

41-43

42-44

2

1.6

1.5

Ppt. Silica

3

3.3

2.2

Calcium silicate

5

4.1

4.5

Hard clay

7.9

5.6

5.0

Soft clay

6.6

8.4

5.0

Whiting

Compound Designing – Hardness Contd.

NR

SBR

IIR

CR

PBR

NBR

EPDM

Black

ASTM Dsgn

DBP

1.5

1.8

1.3

1.2

2.2

1.7

2.4

SAF

N110

113

1.7

2.0

1.5

1.3

2.5

1.9

2.7

ISAF

N220

114

1.9

2.3

1.7

1.5

2.8

2.1

3.0

HAF

N330

102

2.3

2.8

2.1

1.8

3.4

2.6

3.7

FEF

N550

119

2.5

3.1

2.3

2.0

3.8

2.9

4.1

GPF

N660

90

2.8

3.4

2.5

2.2

4.2

3.2

4.5

SRF

N774

70

2.1

2.6

1.9

1.7

3.2

2.4

3.4

HAFLS

N326

72

SOFTENERS 

Processing aids A softener is an ingredient that : 1. speeds up the rate of polymer breakdown 2. helps to disperse the other compounding ingredients 3. helps to reduce nerve within the compound 4 can impart building tack 5. improves the processing properties and modify the final compound properties 6. adjusts the compound cost and reduce power consumption during processing

Mineral petroleum oils  They are available from petroleum industry. paraffinic naphthenic aromatic  Plasticizers They are of the synthetic type , used where mineral oils are not compatible with the rubber dibutyl phthalate -DBP di isobutyl phthalate-DIB di octyl phthalate - DOP *Factices They are vulcanized vegetable oils used as plasticizers to get smooth compound in extrusion (brown) & to reduce abrasion resistance in products like erasers (white) 

PROCESSING AIDS COMPOSITION

EXAMPLE

FUNCTION

Activated Dithiobisbenzaldihide

Pepton 44

Peptizer for NR

Xylyl Mercaptans

RPA-3

Peptizer for NR,IR,SBR and NBR.

Low-molecular-weight polyethylene

A-C Polyethylene 617A

Release agent, Lubricant

Calcium Oxide

Desical P

Desiccant

Aliphatic-naphthenicaromatic resins

Strucktol 60NS

Homogenizing agent for all elastomers.

Paraffin wax

Release agent, lubricant

Polyethylene glycol

Carbowax PEG3350

Activator for silica, lubricant

Petroleum hydrocarbon

Petrolatum

Release agent, lubricant

PROCESSING AIDS

Selection is based on      

Nature of polymer Solubility parameter Viscosity requirement Filler dispersion Processing requirement Any other special requirement

ANTI-DEGRADANTS- They are agents added to rubber to improve ageing properties, resistance to oxygen, ozone, alkali, acid, chemicals etc TYPE

EXAMPLE

STAINING

Hindered Phenol

2,6 Di-t butyl p-cresol

None to slight

Hindered Bis-phenols

Anti-oxidant 2246

None to slight

Hindered Thiobisphenols

Santowhite Crystals

Slight

Hydroquinones

2,5 di(tert-amyl) hydroquinone

None to slight

Phosphites

Tri(mixed mono and di-nonylphenyl) phosphite

None to slight

Diphenylamines

Octylated diphenylamine

Slight to moderate

Naphthylamines

Phenyl-alpha-naphthylamine

Moderate

Quinolines

Polymerized 2,2,4, tri-methyl 1,2-dihydroquinoline

Slight to moderate

Carbonyl-amines condensation product

Reaction product of diphenylamine and acetone

Considerable

Para-phenylene diamines

Mixed Diaryl-p-phenylene diamines

Considerable to severe

ANTI-DEGRADANTS Selection is based on        

Type of protection desired Environment in which the product is exposed. Chemical activity Persistence (volatility and extractability) Nature of end use Discolouration and staining Toxicology Cost

OTHER MATERIALS 

Peptizers : They speed up the rate of polymer break down and also control the speed of breakdown, decreasing nerve within the compound and shrinkage during subsequent processing. penta chloro thiophenol Renacit VII

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Retarders : They help to increase the scorch time (premature vulcanization) but do not interfere with the vulcanization

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cyclohexyl thiophthalimide (CTP) Santogard PVI

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Stiffeners : Stiffeners are used to improve the plasticity of the compound in very small quantities. dihydrazine sulfate

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Flame retardants Chemicals which can improve the flame retardency of the compound highly chlorinated paraffins and waxes, antimony oxide, aluminium oxide and selenium

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Colors and pigments They provide esthetic look and appearance for the product [organic and inorganic] Tackifying agents

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They are useful in providing tackiness to the compound. wood rosin, coumarone resins, pine tar.

Blowing agents  They are materials which provide either open or closed cell structure by producing CO2 or nitrous gases during vulcanization  dinitroso pentamethylene tetramene (DNPT)  azocarbonamide (ADC)  baking soda (sod.bicarbonate)

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Bonding agents They facilitate adhesion between rubbers, fibers, fabrics, metals chemlok, resorcinol – formaldehyde- latex for dipping of nylon cords in tyre manufacture Reordants They are basically perfumes added to mask odors of rubber during processing and service life of rubber. Bactericides / fungicides to resist microbial agents

STEPS OF COMPOUND DEVELOPMENT Modification of existing compound with respect to   

Cost/price Processing Performance

New compound development          

Set specific objectives (properties, processing, price etc) Select best polymer Study test data of existing compounds Survey compound formulations. Choose starting formulation. Develop compound in the laboratory to meet objectives. Estimate cost of the compound. Evaluate processability in factory Use compound to make a product sample. Test product sample against performance specification.

The mix        

Rubber Vulcanizing agent Accelerator/s Activator Antidegradents Fillers Softner Other materials when necessary

100 0.3 - 3.5 0.5 – 1.5 2.5 – 5.0 1-2 As required

5 - 10 As required

STAGES OF PRODUCT DEVELOPMENT Compound Design, Lab Evaluation, Shop floor processing trials (mixing, moulding,extrusion, calendaring, fabrication of product, curing, etc ), Analysis of feedback , Compound Modification (if reqd.), Testing of processing properties and of finished product, Field trials, Validation of manufacturing process.

:

MIXING 

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Compound properties & batch to batch consistency depends on :  Compounding formulation design,  Raw materials Quality,  Effects of Further Processing,  Rework blending (Rework Quality & Quantity)  Rubber processing equipments available & their condition. The knowledge of Raw Materials used & their behavior during mixing and further processing is essential

MIXING

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Mixing Process is the base of Rubber Product Manufacturing Technology. The success of subsequent processing & finished product quality depends entirely on the quality & batch-to-batch consistency of the mixed compounds. ‘Mixing’ deals in deciding: What equipment to use (speeds, pressures, temperature, time cycles, procedures, etc. to blend the selected compounding ingredients into a properly mixed compound. How to achieve High Degree of Dispersion and batch to batch consistency.

MIXING • Mixing process can be sub-divided into three stages : 1) Feeding ingredients to mixer (correct quantities at correct times at correct temperature.), 2) Actual Mixing of the ingredients, 3) Discharge of mixed compound and its shaping, cooling, packaging and storage for the next process.

38

MIXING Five main steps involved in the Mixing Operations : 1.

Sub Division Of larger lumps & aggregates,

2. Incorporation Of powders or liquids 3. Dispersion Involves reduction of the size of agglomerates, 4. Simple Mixing Involves moving particles from one point to another. 5. Viscosity Reduction By breakdown of the polymer and transforming it to desired viscosity. 39

MIXING • A good Dispersion rating requires :  High Shear Stress (i.e. High mix viscosity),  High Filler Loading,  Polymers of not too low viscosity,  Low Mixing temperatures,  Charging oils at the end of mixing cycle. • During Dispersive mixing, the carbon black agglomerates are broken down to less than 1 micron size. • Dispersion largely depends on shear stress ( a critical value of shear stress is necessary to breakdown the agglomerates below which no dispersion action will take place). 40

Two-Stage Mixing in Internal Mixers • To avoid scorching of compound; a two stage mixing procedure is used. • Stage 1 - carbon black and other non vulcanizing additives are combined with the raw rubber and Higher mixing temperatures up to 160°C are used. [The term Master Batch is used for first stage mixture] • Stage 2 - After stage 1 mixing has been completed, and time for cooling has been allowed; stage 2 mixing is carried out in which vulcanizing agents are added. Lower mixing temperatures 90-100 °C are used. [The term Final Batch is used for second stage mixture]

41

MIXING

42

NR Mastication & Blending NR+SR • Mastication of NR to Optimum Degree and proper blending of Synthetic Rubbers with NR is Very Important . • Ingredients which are difficult to disperse (e.g. hard carbon blacks, Ppt. silica, ZnO, etc) require Higher stock viscosity to disperse well. 

Stock Viscosity Control is achieved through:



Compounding formulation design,



Close temperature control during mixing operations,

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Use of specific sequence for addition of ingredients ,

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Remixing of the stock after cooling. 43

• Raw NR is dry & tough (Mooney Viscosity at 100°C > 80) and has to be masticated to a Workable Level of Mooney Viscosity of 50 to 60. • Most Synthetic Rubbers are produced to a tailored Mooney viscosity (range 50 – 60) and hence ‘Mastication’ is not necessary. •

Keep Lower Mastication Temperatures when a Two-Roll mill is used (say, 60-70°C).

• Viscosity of Masticated NR should be closer to the Synthetic Rubber to be blended with it. • NR-BR blends require higher shear rates for proper blending and hence Banbury / Intermix are more suitable than a mixing mill. 44

EFFECT OF MASTICATION TEMPERATURE ON MOONEY VISCOSITY OF NR MILLING TIME, MIN

MOONEY VISCOSITY (ML1+4 @ 100°C, UNITS) WITHOUT PEPTIZER

WITH PEPTIZER (DBD=0.5 PHR)

@ 70°C

@ 100°C

@ 70°C

@ 100°C

0

95

95

95

95

3

76

85

58

56

6

57

83

40

40

9

47

68

33

28

12 45 START TEMPERATURE, OPEN MILL (TIME = 8 MIN) 70 °C 100 °C INTERNAL MIXER (TIME 4 MIN) 150 °C 160 °C

65 30 24 MOONEY VISCOSITY (ML1+4 AT 100°C), UNITS PEPTIZER = 0 55 75

PEPTIZER = 0.25 42 42

PEPTIZER = 0.5 36 37

90 88

54 48

42 36 45

Mixing Time, Min

Mixer Speed 25 rpm

Mixer Speed 50 rpm

No Peptizer

0.1 Phr PCTP

No Peptizer

0.1 Phr PCTP

ML1+4@100°C

ML1+4@100°C

ML1+4@100°C

ML1+4@100°C

0

90

90

90

90

2

74

69

69

52

4

68.5

60

50

37

6

67

56

42

29

8

65

53

34

-

Note of Mooney viscosity at 10the rapid reduction 61 50 - higher rotor speeds in the presence of chemical Peptizer at a very small dosage.

46

Effects of “Under Mastication” of NR • Lower Mixing Cycles, • High heat build up during mixing and subsequent steps, • Poor extrudability / calendaring properties of the stock, • Excessive shrinkage & dimensional control problems with extrudates / calendared stocks. • Scorchy compounds. • Excessive porosity in extrudates, • Difficulties with ‘Rework’ blending,

47

Effects of “Over Mastication” of NR  Lower shrinkage of extrudates / calendared sheets, • Lower die swell & loss of dimensional control, • Increased curing defects in finished products due to excessive flow and air entrapment, • Compounded sheets stick to each other during storage and sagging of sheets, • Excessive surface tack due to poor green compound strength, • Loss of dynamic, tensile & tear strength properties of the vulcanizate, • Changes in the viscosity of solvent based solutions & loss of surface tack. 48

MIXING

PROBLEMS & REASONS

PROBLEMS

Poor Dispersion

REASONS Batch size not optimized, mixing time is lower, filler addition time not proper, insufficient ram pressure, poor temp. control, poor / inconsistent raw material quality, excessive moisture content in polymer and fillers, under / over mastication of NR.

Variation of start temp., variation in dump time and / or temp. , poor dispersion, Batch to Batch variation in ram pressure, variation in Variations polymer / filler/ oil quality / rework quality, under / over mastication of NR Poor Processability

Compound viscosity not within controlled limits, under / over mastication of NR, Processing temp. not under control, poor

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Manufacturing process 

Unvulcanized rubber, whether natural or synthetic behaves as a viscoelastic fluid during mixing. It is the operation required to obtain a thorough and uniform dispersion of all ingredients called for by the formulae in the rubber

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Machinery 2-roll mixing mill kneader internal mixers Continuous, automatic high speed mixing

2 –ROLL MIXING MILL

KNEADER

Two Roll Mill with stock blender & individual roll drives

53

F 270 Banbury Mixer

K 6A INTERMIX

54

Capacities: Banbury Mixers Torque rating kW / RPM

Banbury Mixer

Mixer Chamber Net Volume, ltr

Approx. Batch Wt * kg

Mixing Speed Range, RPM

Compact Drive

Uni Drive

F 50

50

50

40 - 120

2.2

4.6

13.2

F 80

80

60

30 - 105

3.7

6.3

16.1

F 120

120

90

30 - 90

5.6

9.0

19.5

F 160

160

120

20 - 80

7.5

12.0

30.2

F 200

200

165

20 - 60

8.9

12.7

30.5

F 270

270

202

20 - 60

13.1

24.6

43.0

F 370

414

310

20 - 60

-

37.3

54.0

F 440

438

330

20 - 60

-

-

-

F 620

672

500

20 - 50

-

52.2

110.5

Approx. Machine Weight, MT

( * Fill factor = 75% , S.G. = 1.0 ) 55

Capacities: Intermix Mixer Chamber Net Volume, ltr

Approx. Batch Wt kg

Single Speed

Two Speed

K0

1.8

1.26

76

75 / 150

5,

K1

5.5

3.9

40 / 145

Variable drive

50

K 2

20

14

30

22 / 44

50.

50 / 100

50

K 2A

49

34

33

22 / 44

150 ,

75 / 150

60

K4

91

64

33

22 / 44

220,

50 / 300

98

K5

143

100

33

22 / 443

300,

200 / 400

140

K6

206

144

33

22 / 44

475,

320 / 640

235

K 6A

257

180

33

22 / 44

500,

350 / 700

280

K7

310

217

33

22 / 44

750,

500/1000

310

K8

498

349

33

22 / 44

Intermix

Mixing Speed, RPM

Motor HP 1-Speed , 2-Speed

5 / 10

Machine Weight, MT 5.6 20

-

-

( * Fill factor = 70% , S.G. = 1.0 ) 56

Dry rubber based products Mix and Compound Design For manufacture of dry rubber products, the following minimum process steps are essential  compounding  shaping  vulcanization

MIXING PROCEDURE Weighing compounding ingrediants as per formulation Mastication

Compounding And Homogenisation

Maturation

Prewarming

Blank preparation

DRY RUBBER PRODUCTS MANUFACTURE

RUBBER

COMPOUNDIN G

CHEMICALS

MATURATION

PREWARMING TESTING& QC

MOULDED GOODS

EXTRUDED GOODS

CALENDERED GOODS

MOULDED GOODS

EXTRUDED GOODS

AUTO CLAVE OR OVEN

BLANK PREPARATION

MOULDING (HYDRAULIC PRESS)

CALENDARED GOODS

VULCANISATION

FINISIHING OPERATION AND QUALITY CONTROL

PACKING AND DESPATCH