Modern Technology Of Rubber & Allied Industries

Contents

1. Modified Carbon Black As Reinforcing Filler For Sbr
Abstract, Introduction, Materials, Preparation Of Modified Carbon Black, Rubber Compounding And Vulcanization Characteristics, Testing, Carbon Black Modification, Formulation Of Carbon Black (Cb) For Modification, Rubber Compounding, Mix Formulation Of Rubber Compounds, Processing Behavior, Cure Characteristics, Effect Of Modified Carbon Black On Curing Behavior In Sbr Vulcanizates, Tensile Properties, Bound Rubber, De Mattia Crack Growth And Abrasion Resistance, Effect Of Modified Carbon Black On Mechanical Properties In Sbr Vulcanizates, Goodrich Heat Build Up, Conclusion

2. Butyl Inner Tube Processing
Introduction, Manufacture Of Butyl Rubber, Butyl Inner Tube Processing, Mixing Of Inner Tube
Compound, Open Mill Mixing, Finalization, Straining, Extrusion, Valving, Splicing, Chilling, Forming, Vulcanization, Inspection, None Buffing Type Bicycle Tube Valve Base Compound, Innertube Valve Base (No Adhesive Type), Typical Pad Cement, Pad Cement For Adhesion Of Valve Base To Tube, Key Statements

3. Advances In Mixing Line Equipment
Tsr Development And Description, Hopper Section, Smooth Material Flow, Tsr Operation And Control, Continuous, Start/Stop, Common Problems Associated With Conventional Mill Line Equipment, Stock Temperature Reduction Through Tsr, Effective Cooling, Fixed Clearance Screw, Low Power And Heat Generation, No Pusher Required, Reduced Labor/Compact Design, Summary, Multiple Program Controller - Mp - 100/A, Summary Of Advanced Functions, Mp 100 Control Scheme, Benefit To Users, Mp 100 Function, Setting Of Mix   Procedure Sequences, Set Timing Of Material Charge And   Discharge, Setting Of Various Alarms, Announce Finish Of Mix Step, Possible Combinations, Set Mixing Data, Set Daily   Production Schedule, Actual Mix Data Record, Actual Mix Data Storage, Display Of Real Time Operating Data-Running Screen, Test Mixing, Mixing Results Report, Compound List, Utility, Battery Back-Up, Input/Output Of Analog Signals,   Control For Weighing And Conveying Equipment, Data Input By Separate Personal Computer, Communication With Host Computer, Summary, Hardware Requirements

4. Continuous Production Of Rubber Profiles - State Of Extrusion Line Technology
Systems For Continuous Extrusion Of Profiles, Systems For Vulcanization, Applications, Conclusion

5. Semi-Permanent Mould Release Agents
Introduction, Conventional Mould Releasants, Semi-Permanent Mould Releasants (Mono-Coats), How To Use Semi-Permanent Releasants, Precaution, Experiences With Indian   Rubber Moulders, Summary

6. Vulcanization And Vulcanizing Agents (Part-I)
Introduction, Vulcanization, The Effect Of Vulcanization On Vulcanizate Properties, Vulcanizing Chemicals, Sulphur And Sulphur Containing Cross-Linking Agents, Sulphur, Sulphur Donor, Non-Sulphur Vulcanization, Peroxide Vulcanization, Vulcanization By Phenolic Resin, Vulcanization By Metal Oxide, Vulcanization Using Quinone Dioxine, Radiation Vulcanization

7. Vulcanization And Vulcanizing Agents (Part-Ii)
Introduction, Requirement Of An Accelerator, Classification Of Accelerators

8. Rubber Injection Moulding & Product Evaluation
Injection Moulding, Types Of Injection Units, Variations In   Injection Moulding Techniques, Injection Compression Moulding (Icm), Injection-Transfer Moulding (Itm), Advantages, Dis-Advantages, Machine Controls And Process Variables,   Optimum Utilisation For Maximising Production, Selection Of Machine, Space Available In The Mould, Shot Volume, Internal Cavity Pressure, Production Per Hour, Calculation Of Cycle Time, Production Evaluation, Conclusions, Approximate Output Figures Based On Estimated Cure Times For The Production Of Engine Mountings On A 250 Tonne Machine

9. An Introduction To Physical Testing Of Rubber And The Equipment Used For Evaluation Of These Characteristics
Hardness, Resistance To Abrasion, Resistance To Repeated Flexing, Resistance To Permanent Set, Resilience, Resistance To Ageing, Specific Gravity

10. Calenders And Calendering Process/Technology For Rubber Industry
Introduction, Calendering Concept, Calendering Equipments, Comparison Of Roll Dimensions Of Double Poured And Chilled Cast Iron Material, Calender Accessories, Feeding Systems, Comparison Of Mill Feeding And Extruder Feeding System, Alternate Methods Of Calendering, Calender Roll Temperature For Processing Of Different Elastomers,     Developments, Conclusion

11. Improved Bonding Strength Of Selected Fibre With Chloroprene Compound
Introduction, Experimental, Results, Discussion, Conclusion, Dipping Conditions Used For Different Natural And Man-Made Fibres, Formulation (Parts By Weight) Or Compounds Used In The Present Study, Physico-Mechanical Properties Of Non-Rhs, Rhs & Rhs+Compounds, Relative Evaluation Of Non-Rhs, Rhs And Rhs+Silane Bonding Systems On Adhesion For Cords With Cr-Compound, Unaged, Heat-Aged And Water-Aged T-Pullout Adhesion Test Results On Undipped/Dipped Cords With Different Type Of Bonding Systems

12. Low Pressure Hydraulic Rubber Hose
Introduction, Applications, Product Uses & Applications, Market Survey, Present Status Of The Industry, Present Manufacture Of Rubber Hoses In Small Scale Sectors, Process Of Manufacture, Machinery Requirement For Hose Manufacture, Miscellaneous Equipment, Processing, Reinforcing Fabrics & Nettings, Plies, Process Flow Diagram For Manufacturing Rubber Hose, Addresses Of Machinery Suppliers, Addresses Of Raw Material Suppliers, Plant & Machinery Suppliers (Rubber Glazing), Suppliers Of Raw Materials (Rubber Glazing), Plant Economics, Land & Building, Plant & Machinery, Other Fixed Assets, Fixed Capital, Working Capital Requirement/Month, Salary & Wages/Month, Utilities & Overheads, Total Working Capital/Month, Cost Of Project, T.C.I., Cost Of Production/Annum, Turn Over/Annum, Rate Of Return, B.E.P.

13. Rubber Rollers
Introduction, Market Survey, Production Of Rubbers, Import Of New Rubbers, Bis Specification, Dimensions Of Key Type   Rubber Rolls, Dimension On Slip-On Type Rubber Rolls, Physical Properties, Method Of Manufacture, Process Flow Sheet For Rubber Roller, Suppliers Of Plant & Machineries, Suppliers Of Raw Material, Plant Economics, Land & Building, Plant & Machinery, Other Fixed Assets, Fixed Capital, Working Capital Requirement/Month, Salary & Wages/Month, Utilities And Overheads, Total Working Capital/Month, Cost Of Project, Total Capital Investment, Cost Of Production/Annum, Turn Over/Annum, Rate Of Return, B.E.P.

14. Latex Rubber Condoms
Requirements (Properties), Packing & Marking, B.I.S. Specification, Market Survey, Present Manufacturers, Process Of Manufacture, Packaging Machine Manufacturers, Manufacturers & Supplier Of Raw Materials, Suppliers Of Rubber Condoms Plant (Latex), Plant Economics, Land And Building, Plant & Machinery, Other Fixed Assets, Fixed Capital, Working Capital Requirement/Month, Salary & Wages/Month, Utilities And Overheads, Total Working Capital/Month, Cost Of Project, Total Capital Investment, Cost Of Production/Annum, Turn Over/Annum, Rate Of Return, B.E.P.

15. Cycles Tyres And Tubes
Introduction, Market Survey, Present Manufacturers Of Cycle Tyres & Tubes, Selection Of Rubbers For Specific Applications, Manufacturing Process Of Tyres & Tubes, Flow Diagram For The Manufacture Of Cycle Tyres & Tubes, Suppliers Of Machinery, Suppliers Of Raw Materials, Suppliers Of Accessories For Rubber Goods Cotton Tyre Cord, Plant Economics, Land & Building, Plant & Machinery, Other Fixed Assets, Fixed Capital, Working Capital Requirement/Month, Salary & Wages/Month, Utilities And Overheads, Total Working Capital/Month, Cost Of Project, Total Capital Investment, Cost Of   Production/Annum, Turn Over/Annum, Rate Of Return, B.E.P.

16. Coir Foam (Rubberised Coir)
Introduction, Characteristic Properties And Uses, Bis Specification, Market Survey, Manufacturing Process, Embedding Of Coir Fibers, Combing, Levelling, Present Manufacturers, Process Flow Sheet, Plant Machinery & Equipment, Suppliers Of Rubber Chemicals, Plant & Machinery Suppliers, Plant Economics, Land & Building, Plant & Machinery, Other Fixed Assets, Fixed Capital, Working Capital Requirement/Month, Salary & Wages/Month, Utilities And Overheads, Total Working Capital/Month, Cost Of Project, Total Capital Investment, Cost Of   Production/Annum, Turn Over/Annum, Rate Of Return, B.E.P.

17. Rubber Band
Introduction, Properties, Uses And Applications, Formulations And Compounds Of Rubber, Market Positon With Future Demand, Present Manufacturer Of Rubber Bands, Process Of Manufacture, Process Details, Manufacturing Process, Process Flow Diagram, Storage Vessels, Raw Material Suppliers, Machinery Suppliers, Plant Economics, Land & Building, Plant & Machinery, Other Fixed Assets, Fixed Capital, Working Capital Requirement/Month, Salary & Wages/Month, Utilities And Overheads, Total Working Capital/Month, Cost Of Project, Total Capital Investment, Cost Of Production/Annum, Turn Over/Annum, Rate Of Return, B.E.P.

18. Rubber Reclamation Unit
Introduction, Tread Tyre Building Rubber, Tread Width And Curvature, Uses, Application And Advantages, Market Survey, Demand Position, Supply Position, Bis Specification, Process Of Manufacture, Flow Diagram Of Rubber (Tyre) Reclamation, Tread Tyre Building, Process Flow Chart Tread Rubber Making, Present Manufactures Of Rubber Reclaim Unit, Suppliers Of Plant And Machinery, Suppliers Of Raw Materials, Plant Economics, Land & Building, Plant & Machinery, Other Fixed Assets, Fixed Capital, Working Capital Requirement/Month, Salary & Wages/Month, Utilities And Overheads,     Total Working Capital/Month, Cost Of Project, Total Capital Investment, Cost Of Production/Annum, Turn Over/Annum, Rate Of Return, B.E.P.

19. Auto Tyres, Tubes & Flaps
Introduction, Classification Of Tyres, Bis Specification, Market Survey, Increasing Exports Of Tyre Industry, Estimated Demand For Auto Tyres And Tubes, Present Manufacturers, Selection Of Rubbers For Specific Applications, Composition Of Rubber, Manufacturing Process, Flow Chart For Tyre Manufacturing, Addresses Of Plant & Machinery Suppliers, Addresses Of Raw Material Suppliers, Suppliers Of Accessories For Rubber Goods & Others, Plant Economics, Land & Building, Plant & Machinery, Other Fixed Assets, Fixed Capital, Working Capital Requirement/Month, Salary & Wages/Month, Utilities And Overheads, Total Working Capital/Month, Cost Of Project, Total Capital Investment, Cost Of Production/Annum, Turn Over/Annum, Rate Of Return, B.E.P.

20. Synthetic Rubber
Introduction, Properties Of E.P.D.M., Uses And Application, Bis Specification, Market Survey, Synthetic Rubber - Yearwise Production And Consumption (Metric Tonnes), Price, Present Manufacturer, Manufacturing Process, Process Flow Sheet, Suppliers Of Plant & Machinery, Storage Tank, Pressure Vessels & Reaction Vessels, Raw Material Suppliers, Plant Economics, Land & Building, Plant & Machinery, Other Fixed Assets, Fixed Capital, Working Capital Requirement/Month, Salary & Wages/Month, Utilities And Overheads, Total Working Capital/Month, Cost Of Project, Total Capital Investment, Cost Of   Production/Annum, Turn Over/Annum, Rate Of Return, B.E.P.

21. Hawai Chappals
Introduction, Raw Materials And Their Uses, Bis Specification, Market Position, Production Figures Of Rubber Footwear, Export Statistics Of Rubber Footwear, Manufacturers Of Hawai Rubber Chappals, Manufacturing Process, Manufacture Of Sole Surface, Manufacture Of Sole, Conditions, Formulation, Two Roll Rubber Mixing Mill, Suppliers Of Raw Material, Suppliers Of Other Rubber Chemicals Including Rubber, Suppliers Of Rubber Chemicals Dyes & Pigments, Suppliers Of Plant And Machinery, Plant Economics, Land & Building, Plant & Machinery, Other Fixed Assets, Fixed Capital, Working Capital Requirement/Month, Salary & Wages/Month, Utilities And Overheads, Total Working Capital/Month, Cost Of Project, Total Capital Investment, Cost Of Production/Annum, Turn Over/Annum, Rate Of Return, B.E.P.

22. Rubber Auto Parts
Introduction, Engine Mounting, Types Of Suspension, Component Mountings, Product Uses, Market Survey, Formulations, Shock Absorbers-Nr, Rubber Compounding, Mastication & Mixing, Moulding, Testing & Inspection, Packing, Process Flow Sheet For The Manufacture Of Rubber Auto Parts

23. Rubber Gaskets
Introduction, Uses Of Gaskets, Properties Of Gaskets, B.I.S. Specification, Manufacturing Process Of Rubber Gaskets, Preparation Of Compound, Flow Diagram Of Manufacturing Process, Market Survey Report

24. Rubber Powder From Waste Tyres
Introduction, Properties, Uses, B.I.S. Specification, Market Position, Manufacturing Process, Process Flow Sheet

25. Rubber Belting
Introduction, Uses & Applications, Process Of Manufacture, V-Belts Construction, Finishing, Industrial V-Belts, Future Scope, Bis Specifications, Process Flow Sheet For The Manufacture Of V-Belts

26. Hard Rubber Battery Containers
Introduction, Properties, Uses And Application, B.I.S. Specification, Market Survey, Automotive Batteries, Miscellaneous And Industrial Type Batteries, Process Of Manufacture, Process Flow Sheet Diagram For Manufacture Of     Battery Containers

27. Rubber Floor Mat For Automobiles
Introduction, Uses And Applications, Properties, Market Survey, Moulding Technique, Types Of Moulding Techniques, Manufacturing Process, Production Of Rubber Floor Mat For Automobiles

28. Rubber Plantation - A General Survey
Early History, Rubber Plantation In The East, Guayule Plantation, Nr Production & Estimate, Rubber Plantation On A Commercial Scale, Rubber Plantation & Kerala, Rubber Plantation In The Non-Traditional Areas, Rubber Plantation Exceeds     Target, World Bank Assisted Project, Anticipated Rubber   Consumption, Overall Demand Position By 2000-2001 A.D., Rubber For Earthquake Safety, Rubber - A Multipurpose Material

29. The Rubber Goods Manufacturing Industry
Tyre Industry, Cycle Tyres And Tubes, Footwear, Belt And Beltings, Latex Products, Miscellaneous Rubber Products

30. The Automatic Tyre Industry
Introduction, Production And Demand, Tyre Technology,   Exports, Raw Materials, Is Marks And Retail Price, Leaders In The Industry, Research And Development, Demand Projections Of Tyre Domestic And Export, Tyre Companies At A Glance

31. Raw Materials & Machinery For The Rubber Industry
Styrene Butadiene Rubber, Polybutadiene Rubber (Pbr),   Nitrile Rubber (Nbr), Butyl Rubber (Iir), Ethylene Propylene Rubber (Epdm), Silicone Rubber, V.P. Latex, Reclaim Rubber, Carbon Black, Rubber Chemicals, Blowing Agents, Insoluble Sulphur, Precipitated Silica, Zinc Oxide, Process Oil, Solvents, Stearic Acid, Sulphur, Plasticizers, Pigments, Titanium Dioxide, Mineral Fillers, Tyre Cord And Industrial Fabrics, Rubber Machinery

32. India's Foreign Trade
Chemicals And Allied Products Export Promotion Council (Capexil), Rubber Goods Exports, Export Promotion Councils

33. The Rubber Board
Functions Of The Board, Publications, Other Publications, Rubber Control (Main Features), Registration, Licensing Of Transactions In Rubber, Bench Mark Price, Inter-State Transport Of Rubber, Excise Duty, Submission Of Returns

34. Bureau Of Indian Standards (Bis)
Councils, Isi Certificate Marks Scheme, Iso 9000/Is 14000 Series Standards, Publications, Offices, Origin Of Technical Specifications For Rubber, Standards Published By Bis (Rubber Products And Related Products)

35. Natural Rubber
Latex Preservation, Sheet Rubber, Crepe Rubber, Crepe Rubber, Scrap Rubber, Technically Specified Natural Rubber (Tsnr), Advantages Of Tsnr, Speciality Rubbers, Epoxidized Natural Rubber (Enr), Superior Processing Rubber (Sp), Tyre Rubber, Constant Viscosity & Low Viscosity Nr, Oil Extended Natural Rubber (Oenr), Thermoplastic Natural Rubber (Tpnr), General Purpose Rubber, International Grades For Natural Rubber,

36. Synthetic Rubber
Styrene Butadiene Rubber (Sbr), Polybutadiene (Br), Polyisoprene (Ir), Special Purpose Rubbers, Butyl Rubber (Iir), Bromobutyl (Biir), Chlorobutyl (Ciir), Chloroprene Rubber (Cr), Butadiene Acrylonitrile Copolymers (Nbr), Hydrogenated Nitrile Rubber, Ethylene Propylene Rubber (Epdm) (Epr), Polycrylic Rubber (Acm), Silicone Rubber (Mq), Flurocarbon Rubber (Epm), Chloro Sulphonated Polyethylene (Csm), Polysulphide Rubber (T), Ethylene/Acrylic Elastomer, Poly-Urethane Rubber (Au), Epichlorohyrin (Eco),   Thermoplastic Elastomer (Tp), Propylene Oxide Polymers, Ethylene-Vinyl Acetate (Eva)

37. Reclaim Rubber
Carbon Black

38. Directory Section

39. Cost Calculation

Sample Chapters

BUTYL INNER TUBE PROCESSING

INTRODUCTION

History of Butyl Rubber started a long way back in 1870s when Gorianov and Butlerov and later Otto (1927) polymerized Isobutylene at room temperature in the presence of BF3 and H2SO4 to yield low molecular weight oily polymer of Polyisobutylene. In 1930. Mr. I.G. Farben, a prominent scientist in Germany synthesized high molecular weight polyisobutylene at a very low temperature by homopolymerization (Fig. 1). Though the above polymer showed some unique properties like low gas permeability, outstanding resis-tance to heat, ozone and chemical attack, yet, this was not well accepted in rubber industries due to its inability to be cured by regular sulphur and accelerators because of their saturated hydrocarbon structure. Subsequently, Butyl Rubber was synthesized jointly by W.J. Sparks and R.M. Thomas in 1937 by copolymerization of Isobutylene and Isoprene from Exxon Research and Engineering Company.

By 1937, only Exxon Chemical organization was among the largest in the world with laboratories in Linden (New Jersey), Baton Rouge (Louisiana) and England and its affiliated laboratories were located in Texas and Canada. Since 1937, Exxon Chemical have also developed a number of Isobutylene ranges of products for different applications as well as for improved processabilities and these are :

- Halobutyl (Chlorobutyl and Bromobutyl)

- Star Branch Butyl (SBB)

- Halogenated SBB (CI-SBB and Br-SBB)

- Exxpro

It is interesting to note that the first large batch of Butyl was made in Linden laboratory of Exxon Chemical on a July Sunday afternoon. The conditions under which Butyl was made were :

1. It required extreme cold temperature below - 60oC.
2. It was an explosive type of reaction and took place within a fraction of a second.
3. For synthesizing Butyl rubber, Isobutylene must be at least 95% pure and Isoprene should be at least 92% pure.
4. Friedle Craft Catalyst (Al Cl3/BF3) is a must for the above reaction.
5. Reaction takes place in a suitable media like alkyl halide type of solvent (Methyl Chloride).

The properties of Butyl rubber were summarized as:

1. It holds air 13 times better than natural rubber.
2. It has excellent resistance to ageing, weathering, chemicals, moisture, ozone and heat.
3. It does not bounce at ambient temperature, so that it has greater capacity to absorb shock and vibration.
4. It has excellent tear resistance.

In this article, we shall be dealing with Butyl tube processing technology with respect to compound mixing, straining, extruding tubes, valving, splicing, chilling, forming and finally inspecting the tubes for quality assurance.

MANUFACTURE OF BUTYL RUBBER

Figure 2 shows the chemistry of Butyl polymerisation (a copolymerization of Isoprene and Isobutylene) and Fig. 3 shows the flow sheet diagram of Butyl rubber manufacturing process. This is the most expensive polymerization process known so far.

The feed is a 25% solution of Isobutylene (97-98% purity) and 2-3% Isoprene (more than 99.5% purity) in Methyl Chloride solvent and are cooled to - 100oC in a feed tank in which catalyst (Al CI3, BF3) is already dissolved in Methyl Chloride. The above solution streams are injected continuously into the reactors and the polymerization takes place instantaneously.

Since the above reaction is highly exothermic in nature, cooling is very important and thus liquid ethylene is boiled continuously through cooling coils to keep the reactors set at - 95oC and on completion of polymerization, the slurry is formed with very small particles of Butyl polymer suspended in Methyl Chloride. Occasionally, Butyl film is found deposited on heat transfer surfaces blocking cooling tubes and prevents slurry circulation and as a result, a cyclinical operation is used in which some reactors operate while others are washed with hot solvents to remove fouling.

Typical cycle lasts from 18-60 hours depending on the feed purity, concentration of slurry solid and the rate of production. Recent patents have described the use of block copolymer stabilizing agent to create steric repulsion forces between slurry particles to prevent or slow down the extent of fouling.

After polymerization, the slurry overflows into a flush tank containing hot water. This mixture is vigorously agitated and the diluents and unreached monomers and flushed off and are recovered and recycled. Like all synthetic rubber, Butyl rubber is alo protected with an antioxidant which also helps to prevent breakdown in subsequent high temperature drying and finishing. Zinc Stearate is also added to prevent the polymer flakes from sticking together during the finishing operation. The slurry is then vacuum stripped off residual hydrocarbon. In the finishing operation, the Butyl slurry is de-watered in a series of extruders to bring the water content to 5-10%.

Drying is done in a high pressure extruder where the compressed polymer melt and is forced through a die to form an exploded crumb as the pressure is released. The crumb is air conveyed to an enclosed fluidized bed conveyor, where water vapour is removed and the crumb is cooled prior to baling and packing.

In the above polymerization, the Friedle Craft Catalyst (Al Cl3, BF3) provides extremely high polymerization rate at low temperature. Although the above catalyst systems are not essentially stereo-specific, but the polymeric chain contain a very regular structure due to the symmetrical nature of Isobutylene structure and as a result, Butyl elastomers are self-reinforcing polymers with pure gum tensile strength around 250 kgf/cm2. The abundance of Methyl side-groups in the polymer chains bring about a considerable steric hindrance to elastic movement though its Tg is around - 65oC, close to natural rubber (-70oC), yet its resilience of the vulcanizate is very low, only around 14%. But its densely packed structure definitely causes gas permeability to be very low.

Table 4 shows the different commercial grades of Butyl rubber based on the difference in

1. Mole percent unsaturation
2. Mooney viscosity values

Butyl rubber have typical viscosity average molecular weights of 350,00-450,000 and mole percent unsaturation level (due to Isoprene units) of 0.8 to 2.0. The term "mole percent unsaturation" refers to the number of Isoprene molecules in 100 monomers a molecules in the polymer. Thus, a one mole percent unsaturation Butyl would contain one molecule of Isoprene and 99 molecules of Isobutylene.

Butyl rubber compounder often blends different grades of Butyl polymer to improve following properties :

1. Blend with low mooney grades provide better processability and improve flow of compound.
2. Blend with low unsaturation grade improve ozone resistance.
3. Blend with high unsaturation grade improve heat resistance.

1. All Grades Stabilized With Non-Staining Antioxidant.
2. This Grade Contains No Antioxidant.

As we have already stressed that one of the major properties of Butyl is its low rate of gas permeability and thus this rubber has found major application in inner tube world wide (Table 2). Before Butyl rubber inner tube, natural rubber inner tube was used extensively but the following advantages of Butyl inner tubes have replaced natural rubber inner tubes world wide :

1. Lower fuel consumption
2. Longer tube life
3. Longer tyre life
4. Longer tread life, as a result higher mileage
5. Loss maintenance
6. Safer/Smoother steering (better steering response)
7. Lower risk of blow out.

Figures 4 and 5 are showing excellent air retention properties of Butyl rubber both in static and dynamic conditions. The above benefits considerably outweigh the higher cost of Butyl tubes.

BUTYL INNER TUBE PROCESSING

A flow sheet diagram is described in Fig. 6, which indicates Butyl inner Tube processing stages. In fact, Butyl Inner Tube processing involves all stages from mixing, straining, extruding, valving, splicing, forming, vulcanizing and finally inspecting the tubes for the assurance of quality level. Before we go into details of the above processing stages, we must make a note of the following which must be considered as important factors for processing :

1. Butyl has lower affinity for carbon black because of its low level of unsaturation as compared to General Purpose Rubber (GPR) and as a result, Butyl needs comparatively higher mixing time and shearing forces for better dispersion.
2. Since different carbon black surface area will have different affinity for Butyl Rubber, adequate mixing is required for mixing two different type of blacks.
3. Carbon black with higher surface area will provide better green strength but difficult to get dispersed in Butyl Rubber. If dispersion of above black is inadequate, this can create problem as porous extrusions and blisters in vulcanizate.
4. Mineral fillers are not recommended in inner tube formulation as this cause die plating problem. Down time, scrap and rejections often increase due to the use of mineral fillers.
5. Stearic acid Incorporation is always better, as it minimizes mill sticking and mould sticking problems.
6. P-nitrosoamine derivatives improve fold break-down problem and vulcanizate properties by improving filler-rubber interaction. This, however, needs extended mixing cycle and higher dump temperature of around 180oC.
7. Scorch safety of MBT is better below 130oC over MBTS, as a result, MBT should be preferred in inner tube processing.
8. Scorch control agents in GPR are ineffective in Butyl Rubber compound. Calcium Stearate (1-2 parts) is the most effective retarder in inner tube compounds.
9. The normal range of temperature for curing Butyl inner tube is 150-180oC, however, temperature beyond 180oC does not harm Butyl polymer, rather it provides shorter cure cycle. The temperature co-efficient of vulcanization for carbon black filled Butyl Rubber is around 1.80.

Mixing of Inner Tube Compound

In an internal mixture, the key requirement is the proper dispersion of filler in the rubber. Butyl compound mixing is done in two stages. First stage or Master Batch contains all ingredients except the curatives and in the second stage or Final Batch, only curatives are added. In order to get better dispersion, the use of banbury volume is very important. In case of Master Batch, the normal leading is 10-20% higher than that used for GPR compound. For banbury, it is better to use fill factor between 0.90 to 1.0 for better dispersion of carbon black in Butyl, Butyl/EPDM Rubber. Banbury batch weight is calculated in the following manner :

Batch weight (kg) = Banbury volume (liter) x Fill Factor x Compound Specfic Gravity.

One may remember that the banbury volume indicated by manufacturer is the volume of water having specific gravity 1.0. A banbury, having 50 liter of capacity, fill factor of 1.0 and compound specific gravity of 1.12 shoule have 56 kg of batch weight (50 x 1.12 x 1.0). For a very new banbury, it is desired to keep fill factor around 0.90 because very high batch weight has always adverse effect on dust seals and as a result, optimum batch weight is determined practically around the calculated batch weight which should provide adequate mixing in desired mixing time without affecting dust seals. It is desired that the starting temperature of banbury in kept around 80oC and the dump temperature of Master and Final Batch are kept around 160oC and 105oC respectively. In fact, adequate mixing time will depend on :

1. Type of banbury (2 wing/4 wing chamber)
2. Banbury volume loading
3. Banbury starting temperature
4. Black : Oil ratio in the Master Batch
5. Sequence of loading
6. Dump temperature

There could be a variety of sequences of loading, examples are given below (considering 5' of mixing cycle for 230 liter banbury) :

Butyl Rubber provides less effectiveness for premastication. In open mill mixing, there is no significant reduction in mooney viscosity, but it is worthwhile to premasticate Butyl Rubber either in banbury on in open mill, because with premastication of Butyl, its acceptance of further addition of ingredients become smoother which ultimately provides better dispersion. Premastication in banbury is effective for 30-45 seconds at 80oC which results in reduction in mooney viscosity and provides better homogenization of polymer/filler combination and other ingredients. Very recently, more emphasis has been given for higher productivity and as a result, shorter mixing cycle of 3-3.5 minutes. In such cases, if premastication is difficult, then the polymer is recommended to keep in hot house (60-80oC), which also takes care of improved dispersion particularly at low ambient temperature (winter season in India).

Open Mill Mixing

Open Mill Mixing of inner tube compound is rare in India now but nevertheless it exists particularly for a new plant. Following are the important parameters for Open Mill Mixing :

1. Adjust narrow nip gap for band formation.
2. Maintain friction ratio of Mill 1.25 : 1.0 and temperature of mill around 40oC, which can be done either by passing steam or by rubber mastication without opening water circulation value.
3. Add ZnO and Stearic Acid and allow band formation.
4. Add 50% of black (higher reinforcing black should be added at the begining).
5. Remaining 50% black is added with oil and increase nip gap now to avoid over-mastication and open water circulation full. After mixing is over, sheet out from mill to cool.
6. In case of mill sticking problem, releasing agents such as phosphate esters or methyl hydroxy stearate can be used. Avoid highly loaded mineral filler stock.

Finalization

In general, finalization is done either at intermix or at extruder warm up mill. In banbury, it is desired to fill the banbury to 80-90% of the total master batch weight in order to get better dispersion at safe dump temperature of 100-105oC. There are two sets of mill at extruder viz.

1. Warm up mill
2. Feed mill

Sieved curatives are in warm up mill. In many cases, for better dispersion of curatives and to have clean environment, master batch of curatives are added. For the later case, it is desired to have two sets of master batches, one with sulphur and the other with combination of accelerators.

Straining

Butyl inner tube compounds are strained to remove:

1. Foreign matter
2. Black agglomerates
3. Particles of undispersed rubber.

Both on-line and off-line extrusions are shown in Fig. 1.

Extrusion

It is a continuous process by which the desired profile of the extrudate could be maintained with respect to their dimensions. Extrusion is largely affected by the plasticity of rubber compounds and the rubber compound plasticity has close relation with loading volume of filler and plasticizers and in general, higher loading provides better extrudability. Normally, extruder for inner tube extrusion is equipped with a two-mill operation set up; warm-up mill followed by feed mill to ensure constant quality and the temperature of feed. Preferred feed strip temperature should be 80-90oC and rolling bank on feed mill should be kept as small as possible. Feed mill should also be provided with a blender bar for better mixing particularly when the curatives are added to the warm up mill. Feeding volume of the compound should be adjusted as slightly larger than extruding volume. If feeding volume and extruding volume are same, small variation of take off conveyor speed will provide porosity, blister, non-uniform dimensions of extrudates etc. Conditions for improved feeding are :

1. Constant and force feeding with conveyor/feed roller.
2. Feed stock should not be thick since the thick Butyl stock from feed mill tends to contain more porosity and blister.
3. Keep nip gap of feed mill constant and only change width of the feed strip for different sizes.

The uniformity of extrusion is very important with respect to the splicing of green tubes. There are two types of extrusions.

1. HOT FEED EXTRUSION which is mostly used by Rubber Industries.
2. COLD FEED EXTRUSION, which is being currently used by some modernized plant.

Some guidelines for hot feed extruder feed mill are as follows :

1. Compound auto-feeder is desirable.
2. Always use blend of multiple batches at the autofeeder for uniform dimension of the extrudate.
3. Maintain rolling pencil bank on the feed mill for better dispersion.
4. Monitor addition of rework at a constant ratio of around 10-15%.
5. Fix nip gap of feed mill for all time and maintain change in volume by change in the width of the feed strip of extruder.
6. Maintain constant feed strip for fixed size of the tube.
7. Feed strip temperature should be between 80-90oC.

All the above parameters will ensure extrudate with (i) minimum porosity, (ii) minimum variation in viscosity and scorch and (iii) better dimensional control at a constant rate.

Some operating guidelines for cold feed extruder operators are:

1. Keep extruder barrel filled and use force feed roller to feed extruder.
2. Standardize extruder RPM for each tube size.
3. Keep barrel and screw temperature within 50-60oC and die temperature 110-120oC.
4. The design of die should be such that
1. Crown : base gauge ratio in maintained at 1.5-1.6 : 1.
2. There is smooth entry of extrudate through die and the increase in pressure gradient is maintained optimum.
3. There is no excess injection of talc or dusting ingredients.
5. The speed of feed conveyor, extruder RPM, take-off conveyor and cooling line are to be synchronized.
6. Pulling down extrusion on take-off coneyor should be avoided. It is desired to make different die for different sizes of tubes.
7. Efficient and through cooling is essential.
8. Ensure proper position of bright colored polythylene patches.
9. Rework can be added uniformly on warm up mill upto 10% in BC and PC tubes and 15% in TB and larger tubes. It is important to note that high amount of rework and higher quantity of rework are the potential source of blisters and porocity in cured tubes.

Valving

Butyl tube value can be categorized basically into two groups viz. Auto tube valve and bicycle tube valve. The compound formulations of value should be based on the following parameters for good adhesion and brass stem :

1. Should have low rubber content in the range of 40 to 50%.
2. Should contain large particle size carbon black like SRF-LS, GPF.
3. Should contain adequate level of silica between 10-15 parts.
4. Should contain large quantity of metalic oxide like ZnO and MgO (around 45 parts).
5. Should have less amount of process oil, softness, fatty acid etc.

Valve base compound formulation is shown in Tables 3 and 4 for automotive and bicycle tube respectively. Tables 5 and 6 are showing different formulation for pad cement for adhesion of valve base tube. Tubeless tyre valve base tube. Tubeless tyre valve base is desired to be based on EPDM for better durability.

Consolidation of valve is important parameter in the valving process of inner tube. Importance should be given on the following :

1. To use soft rubber foot (45 Shore A hardness) to cover entire valve stem.
2. Dwell time of rubber foot is important for proper consolidation.
3. Consolidation is done by pneumatic piston for 4-5 seconds.
4. Dwell time of rubber foot and its pressure should be just sufficient to consolidate valve and it should not provide edge lifting problem.

Following are typical valve related problem and their solutions :

Splicing

Splicing problem in most cases is due to non-uniformity in the extrusion rather than problem in the splicing machine. In many cases, rubber compounder starts experimetal work as well by changing oil dose, filler dose, adding resins and by overmixing the compound in order to increase the flow properly but in most cases these causes blister problem due to drop in compound viscosity. In case of splicing machine problem, special attention is to be given to the following parameters :

1. Clamping pressure.
2. Butting pressure.
3. Butting time.
4. Knife blade cutting angle.
5. Knife temperature.
6. Knife cutting and traversion speed.
7. Butting pad hardness (Shore A=65oC).

Following are the important guidelines for the use of universal inner tube splicing machine :

1. KNIFE CURRENT VARIATIONS

Normal current valves for Butyl tubes are low heat 25-30 amps and high heat 55-65 amps. But there is no thumb rule. The above value may change from machine to machine. It may be necessary to readjust after a knife change. Knives are electrically balanced and must be changed in matched pairs. The knives should cut the tubes without excessive smoking and must start to glow red above and below the tube about one-third through the cut. The cut end should show a uniform matt surface along its whole length without smearing or a shiny appearance or a tail at the exit fold. A milled appearance of the cut indicates that the high heat setting is too low and a shiny appearance, on the other hand, indicates that the heat setting is too high (scorchy). A small shiny section at the entry fold indicates that the high heat has been switched on too early and should be retarded. Smearing at the entry fold indicates that the high heat has been switched on too late.

2. Clearance between the Knives and the Rubber Edge

This clearnace controls the overhang after cut. This gap is to be adjusted to 1.0-1.2 mm. This gap should be same for each knife and rubber face, that is, knife has to be properly centralised between the rubber faces. The gap should be checked at the front, rear and middle of the jaws with the jaws opening at the maximum setting.

3. Knife Angle

The knife angle is normally set to 11 +/- 1o to the plane of cut. Cutting angle greater than 12o can result in a wavy cut. On the other hand, cutting angle less than 10o can result in smearing.

4. Alignment of Rubber Clamp Faces

The alignment of rubber clamp faces must be aligned horizontally and vertically to eliminate stepped splice problem. If steps are evident, the rubber jaws should be slimmed so that the steps are eliminated. Absence of slow down process may cause a step even when the jaws are properly aligned.

5. Knife Show Down Points

These are normally selected by moveable slotted fingers on the knife carriage which is operated by appropriate magnetic induction proximity switches. They are moved backward or forward to adjust the slow down points which should be 1.0-1.5 cm before the fold entry or exit points. The upper finger usually adjusts entry slow down. There is a timer that controls the duration of knife slow sped after the initial transition before entering the rear fold. Normally it is set for an engagement of slow speed for 1-1.25 cm after entry.

6. Running Adjustments

Running adjustments are :

1. Clamp width.
2. Clamping pressure.
3. Butting pressure.
4. Butting time.
5. High heat initiation point.

Table 7 gives the specifications for the above running adjustments. It is important to note that the machine will normally require about thirty minutes to reach operating uniformity.

If the clamp width is set too small for the tube, the splice and the adjacent area will be pinched at the folds. Pinching often results in fold breakdown which in turn can lead to thinning in the splice area or splice opening in the forming and curing operations. If the clamp width is set too wide for the tube, it results in mismatched folds or a splice which is not consolidated at one or both the folds. A thinned or pen splice can then result during forming and curing.

There are two clamping pressures, one is applied during cutting and the other (higher pressure) to prevent the movement of the clamp. The clamping pressure should be the lowest which will prevent the tube from moving in the clamps during the cutting and butting operations. It is to be remembered that extrusion thickness control is important for optimum splicing. If there are high variation in the thickness across the tube, higher pressure will be required to ensure that thinner section of tube do not move under butting pressure. This will result in deep imprint on the thicker part and folds may be crushed.

Butting pressure should be that which provides required splice quality with minimum butting time. Splicing quality is also dependent on the plastic flow of the tube compound. Tube compound containing high structure black (GPF, HS) and a blend of high and low surface area (FEF/SRF) provides better flow property and good thickening at the splice which increases with increasing butting pressure at constant time.

Chilling

Chilling increases compound green strength on the splicing zone and thereby minimises splice opening problem during forming operation and weak splice problem after curing. Chilling of the butt splice in the crown area is a must for thick gauge tube above (1.5 mm) but for thin gauge tube (e.g. bicycle tube gauge 1.0 mm), chilling is not a must. If the butt splice is adequate for thin gauge tubes, then chilling of the same might not be essential. Normal chilling time is kept for one cure cycle. Over-chilling and condensate on splice should be avoided.

Forming

This is also called preforming operation in which tube is expanded with compressed air before curing on a performer to about 95% of cured volume. Forming rings or the preformer should not be placed too close to the mould in order to avoid localized heating which may cause thinning problem. Forming rings are normally provided with limit switch so that inflation of the green tube could be restricted to around 95% of the cured volume. Normal forming time is kept to one cure cycle. Excess dwell time in the forming ring as well as the excess inflation should always be avoided to avoid thinning, creasing or punching problems in the mould. Too rapid inflation has always drawback on weak splice or open splice on the forming ring.

Vulcanization

This is the final stage of processing. Before vulcanization, it should be ensured that mould is clean and its vents are not blocked. Inflation of the inner tube in the mould can either be done by hot air or by steam. Too low internal pressure gives rough surface and porocity on the product, too high pressure can give excessive flash and thinning problem. Mould temperature is normally kept between 175-190oC and the internal temperature is normally kept at 10oC less than the mould temperature. Cure cycle for auto tube and bicycle tube are kept 6-9 and 3-5 minutes respectively including blowdown time.

Inspection

This is a vital quality control measure of the product. During inspection, particular attention is to be given in splice, valve and fold regions. During inspection, tubes may be inflated to 1.3 times (particularly for bicycle tyre) to observe crack and other defects. Before storage, tubes are evacuated and packed in sealed polyethylene bags which help to prevent ozone attack during long storage. High vacuum should be voided because this produces high stress on the fold region, which is sensitive to ozone degradation.

KEY STATEMENTS

The key statements of this write up are as follows :

1. In banbury mixing for Master batch, it is worthwhile to use fill factor 0.9 for a new banbury and 1.0 for old one (Banbury batch weight (kg)=Banbury volume (liter) x Fill Factor x Compound specific gravity). Very high batch weight has always adverse effect on Banbury dust seals. For Final Batches, it is desired to fill 80-90% of the total Master Batch weight.
2. Dump temperature of Master Batch should not be lower than 160oC and that for final should exceed 150oC.
3. There is better mixing at banbury starting temperature around 80oC.
4. Butyl Rubber should be premasticated either in banbury or open mill mixing because, with premastication, the acceptance of ingredients increases. In case difficulty in premastication, Butyl is recommended to keep at hot house (60-80oC).
5. Before tube extrusion, inner tube compounds are strained to remove foreign matter, undispersed particles and black agglomerates.
6. In case of mill sticking problem, releasing agents such as methyl hydroxy esters (phosphate esters) can be used and adviced to avoid highly loaded mineral filler.
7. Tube extrusion process should be equipped with two mixing mill sets. Feed mill should be followed by warm-up mill. Uniformity of extrusion along the length of the tube is very important for the quality of splicing.
8. In case of splicing machine problem, special attention should be given on clamping pressure, butting pressure, butting time, knife temperature and its angle, knife cutting and traversing speed, butting pard hardness (Shore A=65o).
9. Chilling increases compound green strength on the splicing zone but chilling is not required for tubes having gauges upto around 1.0 mm (bicycle tube).
10. Preforming operation provides the flow of compound under stretch condition and preforming should be done upto 95% of the cured volume. Excess air pressure and dwell time in the forming operation should be voided.
11. Tube curing mould temperature is kept between 175-190oC and internal steam temperature is kept 10oC less than the mould temperature. Inflation of the inner tube in the mould can either be done by steam or air. Low internal pressure provides rough surface and porocity on the cured product and high inflation pressure will provide excessive flash out and thinning problem.
12. Cure cycle of auto and bicycle cubes are kept between 6-9 and 3-5 minutes respectively including blow down time. Higher the mould temperature, lower is the cure cycle.
13. Inspection of tubes should be based on splice, valve and fold regions. Bicycle tubes are inflated to 1.3 times to observe defects.
14. Before storage, tubes are evacuated and is packed in a sealed polyethylene bag. High vacuum should be avoided since this produces high stress on the fold region, which is sensitive to ozone cracking.