Compounding Elastomers for Rubber Lining

Although the inherent chemical resistance of the rubber chosen is quite suitable for the given duty conditions, many a times the bond or adhesion failure is the cause of lining failure. Therefore much care is taken while applying the lining especially at joints, seam, corners and flanges. 

For correct rubber compounding of lining compounds a thorough knowledge and understanding of the following points are vital  

1) The type of rubber basically suited for the service conditions required. 

2) The process by which the product will be manufactured, i.e., by extrusion, moulding, calendering, hand laying and forming. 

3) The complete physical and chemical properties of the compounding ingredients and their reactions with acids and oxidising agents. 

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A number of synthetic rubbers and elastomeric materials have been developed with special characteristics that extend the overall usefulness of the elastomers for corrosion-resistant equipment. In addition, polymers of ethylene and propylene have been developed with elastomeric properties. Like natural rubber, each of these may be compounded in several ways for maximum resistance to specific chemical exposures. Natural rubber and other elastomers are frequently used in combination with brick linings for temperature conditions that are above those allowed for elastomer material alone. They have proved to be excellent membrane linings for such construction. 

Plastics and Elastomers. Common plastics and elastomers (qv) show exceUent resistance to hydrochloric acid within the temperature limits of the materials. Soft natural mbber compounds have been used for many years as liners for concentrated hydrochloric acid storage tanks up to a temperature of 60°C (see Rubber, natural). SemUiard mbber is used as linings in pipe and equipment at temperatures up to 70°C and hard mbber is used for pipes up to 50°C and pressures up to 345 kPa (50 psig). When contaminants are present, synthetic elastomers such as neoprene, nitrile, butyl. 

Just as in the manufacture of sheet natural rubber and the asphaltic sheet linings, the basic material as the sheet lining manufacturer receives it from the plantation (rubber) or from the refiner or importer (asphalt), the manufacturer of the synthetic lining materials will receive his synthetic elastomer, thermoplastic or other basic resin from the company that produces it-and will have to blend it with fillers, stabilizers, plasticizers, and other materials to make a suitable compound which will-as a lining—perform its function satisfactorily under the anticipated conditions, and for an economical length of time. The actual amount of the basic resinous material in the compound may be as low as 70% of the total weight. 

Typical products are elastomer modified heterophasic copolymers (heco), as compounded or reactor TPOs. Talc, typically below 20%, is added for higher stiffness and lower coefficient of thermal expansion (LCTE). The latter is an important condition for zero-gap concepts, in which the bumper follows very closely the line of the body fascia. Now that bumpers painted in body colors have become a standard feature, paint adhesion and enhanced surface finish have become important criteria. These can be influenced by optimizing the polymer structure and rubber content. The recycling aspects are treated in the chapter on Bumper recycling technology in this book. 

Rubber and elastomers are widely used as lining materials for columns, vessels, tanks, piping. The chemical resistance depends on the type of rubber and its compounding. A number... 

Natural rubber is also widely used in nontire applications which account for approximately 30% of the consumption of all rubber as an aggregate (including both natural and synthetic rubber). However, in the nontire sector, natural rubber was about 22% of total rubber consumption in 2012. Many times natural rubber is used as the sole base elastomer in compounds used in automotive bushings, motor mounts, vibration isolators, and dampers. On the other hand, NR is blended with SBR for compounds used in conveyor belts, welding hose covers, braided water hose, laboratory tubing, footwear knee boots, footwear microcellular compounds, footwear boot uppers, tank linings, and play balls. NR/BR blended compounds are used to make conveyor belt cover stocks, shoe soling, and so on. 

Rubber weatherstripping for automotive exteriors is usually produced from compounds based on EPDM. These weatherstrips can be dense (no voids), cellular (closed cell structure), or semidense. Weatherstripping is commonly extruded and cured in a continuous vulcanization unit (CVU). Some new production lines are switching over to thermopiastic elastomers (TPEs), which eliminate the curing step, with a reduction in production costs. 

Chapter 16C Compression, Transfer and Injection Molding of Specialty Elastomers by Dr. Robert W. Keller will give the rubber compounder an excellent view of the considerations necessary in the molding operation in the factory. This is only one aspect of rubber processing, but similar approaches are needed for other processes such as extrusion, calendering, machine, and hand building of hose, belts, rolls, tank, and pipe linings, and so on. 

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