Rubber Lining Specification

Unless test coupons are produced alongside the lining, the only method of testing the vulcanisation state is with a hand hardness meter. A Shore A or IRHD meter is used for soft rubber linings and a Shore D meter for ebonites. The usual specification is that the hardness has to conform to 5° of the specified hardness. There is no quantitative non-destructive test for the strength of the bond between the lining and the substrate and so such tests are usually carried out in the laboratory on a sample prepared from the materials used. 

The decision to retrofit or install new filters is influenced by plant-specific factors such as the condition of the existing filters, compatibility of the filters to retrofit, availability of space within the plant, etc. Bayer s analysis of the costs and benefits of the retrofit compared to the investment in new filters did not show a clear favourite either decision could be justified. With regard to the rubber lining, gaskets, hydraulic system etc., the Kellys were in very good condition. Because of this, the decision was made to retrofit two of the filters and to use them in a separate brine circuit for the new electrolysers, with a second circuit feeding the amalgam plant. 

The most practical tests specifically followed for rubber lining are hardness test, spark test and immersion test. Hardness test is invariably the most frequently prescribed test for rubber lining quality by clients, though it is an inadequate test. The term hardness is a vague one the different expressions such as "Scratch Hardness","Cutting Hardness" "Abrasion Hardness" etc. illustrate that different concepts of hardness exist. 

A complete check against all rubber lining details on customer drawings and specifications should be made to ensure the rubber lining has been applied to the proper areas and with the correct gauge stock. 

Though a standard norm or absolute reference value is not available for comparison in any of the international standard specifications and the technical and research publications with respect to the chemical resistance properties of rubber, liquid immersion tests certainly provide relative and useful data with which the suitability of anticorrosive rubber lining compounds can be assessed with a fair degree of accuracy. For this reason manufacturers and applicators of rubber lining resort to tests under simulated conditions instead of accelerated ageing immersion or swelling tests. 

If temperatures are not specified in the specification, the immersion tests have to be carried out at room temperature. The volume of the immersion liquids should be adequate enough to immerse the sample of rubber. The test should be carried out in the absence of direct sunlight to avoid atmospheric oxidation. Test pieces from cut samples or counter samples from the finished rubber lining compound have to be buffed smooth. 

The materials handled in the bins are 20% solid by weight and have a flow of 2.9 tons of water per hour and 178 litres/minute of pulp. The size of the material is 100 to over 325 BS specification mesh. Maximum acid concentration is 20% hydrochloric acid. The temperature in the system is 60 °C. A 6 mm thick natural rubber lining of shore hardness 50 on the Shore A scale is used to protect the equipment against the abrasive environment as well as the corrosion effects of hydrochloric acid. 

A number of specifications and codes of practice are followed throughout the world for rubber lining, the major ones being from the ASTM, the BS Specifications, the German Institute for Standardisation (DIN) and the Japanese Industrial Standards (JIS) which give exhaustive information on rubber lining procedures, testing methods and code of practice. 

ASTM D2240-05 [4] deals with the procedure for rubber lining and equipment. ASTM D429-03el [5] deals with adhesion to rigid substrates. The Annual Book of ASTM Standards Part 38 Section 09 [6, 7] is a useful reference for rubber products, industrial specifications and related test methods. 

Rubber lining is a specialist operation and should only be entrusted to competent, established companies who are continually developing lining material systems to keep ahead of the requirements of the process industries. Full consultation should always be held, prior to the final design stage, to ensure that the most-cost effective material specification is employed. 

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