Rubber lining methods

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. 

Several methods are in practice for preparing the metal surfaces before rubber lining such as follows ... 

Design and fabrication of tanks, vessels, piping and other equipment which are required to be protected with rubber lining against corrosion need special consideration in chemical plant construction. Certain features are to be incorporated in the design, and precautionary methods should be taken while fabricating the mild steel equipment to be suitable for rubber lining application. These are discussed below. 

In cases where corner joints are unavoidable while constructing tanks, it is necessary to ensure that there are no air pockets, pits or surface irregularities at weld joints to avoid possibility of air trap between the rubber lining and the metal surface. For this, suitable vent holes are to be provided. A typical method of avoiding air being trapped in weld joints is shown in figures 6.6 A, B, C and D. 

Hot water cures can be used for articles that are not affected by immersion in hot water. This method is useful for thick walled articles and rubber lined equipment and especially most suitable for ebonite compositions. Direct contact with water produces better heat transfer than with hot air or steam. Consequently this system gives less deformation of products during cure. 

No one curing process posesses all the virtues and those which may appear to be most desirable may be rejected on grounds of initial cost and maintenance of the equipment. For example even an autoclave curable rubber lined vessel can be cured in open steam at atmospheric pressure and this method can be adopted while the autoclave is down for repairs and maintenance. 

Test methods for determining chemical resistance of plastics Effects of liquids on rubbers, test method Test method for chemical resistance of protective linings Test method for determining chemical resistance of fiberglass-reinforced thermosetting resin... 

Chemical resistance test for rubber linings by Atlas blind flange test Determination of effects of liquid chemicals on plastics Determination of environmental stress cracking (ESC) by the bent strip method... 

Rubber lining is one of the best known and proven methods employed to protect chemical process equipment against the corrosive and abrasive attacks of the fluids. One of the most important characteristics of both natural rubber and synthetic rubber is the remarkable resistance to corrosive chemicals, fumes, acids, alkalies and other salt solutions. Without protection, corrosion would be so extensive that most products of modern technology could not exist. The variations and large percentages of corrosive impurities have little influence on the rubber lining up to temperatures as high as 100 °C to 120 °C. 

The method for solids transported in slurry form is called hydraulic transportation. Today there are long distance rubber lined pipelines carrying a variety of minerals such as coal, limestone, rock phosphate, copper concentrate, nickel refinery tailings, iron ore concentrates and tailings in various parts of the world. The most important slurry pipelines in operation around the world are given in Table 4.2. 

In the South African mining industry most processes for recovering precious metals, coal, minerals and diamonds are wet methods, involving the suspension of solids in water [1], In the control of such wet abrasive conditions in the pumping of fine particles size slurries, particle size separation in cyclones and in floatation cells, the choice of soft natural rubber lining is the most cost effective. 

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. 

Table 10.1 Minimum adhesion values of rubber lining used in different methods of vulcanisation ...

DISPOSAL AND STORAGE METHODS dilute with the addition of ice water quench or neutralize with chemically basic substance such as lime or soda ash route to sewage plant store in a cool, dry place isolate from strong oxidizers, most metals, organic materials, and alkalies, aqueous solutions should be stored in glass bottles and in rubber-line tankers store anhydrous hydrogen chloride in steel cylinders. 

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