Gaskets and seals materials

Sealants. Gaskets, and Beads. All gaskets or beads are required to be at least 3/8 inch wide with a Shore "A" durometer hardness of 50 and conform to ASTM Specification C509-84 (Cellular Elastomeric Preformed Gasket and Sealing Material). 

Table XV Chemical resistance of commonly used elastomer gaskets and sealing materials...

Solvent/fume leak- Maintain integrity of gaskets and seals age from casing, gaskets compatible with process materials joints resulting in loss of heck mating faces for corrosion/unevenness, containment. particularly on clad components ... 

Silicones. Silicones are useful where high temperature resistance or compatibility with silicone components such as molded seals are needed. Silicone firewall insulation materials and silicone gaskets and seals are bonded with silicone rubber adhesives. 

Minor parts that are not identified (sueh as nuts, springs, washers, gaskets, and keys) shall have eorrosion resistance at least equal to that of speeified parts in the same environment. Gasket or seal material between the shaft and the shaft sleeve under the paeking or meehanieal seal shall be verified by the vendor as being satisfaetory for the serviee conditions. 

Resistance. The pump should be inert to the various solvents, buffer salts and solutes to which it will be exposed in general use. In the vast majority of applications, stainless steel is used for metallic parts that contact the mobile phase, and this is perfectly acceptable. Elsewhere in the pump, resistant minerals such as sapphire or ruby are used for the pistons and in valve components subject to hard wear, and materials such as PTFE (Teflon ) are used for gaskets and seals. 

The widest usage of these materials within the chemical process and pharmaceutical industries is for gasket and sealing applications, linings, flexible tubing, electrical insulation, and drive belts. 

Silicone elastomers are noted for high temperature and oxidative stabihty, low temperature flexibility, good electrical properties, and high resistance to weathering and oil. They are used in wire and cable insulation and surgical implants and as material for gaskets and seals. 

Gaskets and seals form a thin, protective intermediate layer of material between two surfaces. Often there is a significant difference between the modulus of elasticity and the CTE of the materials being gasketed or sealed. 

The use of EPDM rubbers for the manufacture of automobile and truck tires has not been successful, mainly because of poor tire cord adhesion and poor compatibility with most other rubbers. However, EPDM rubbers have become widely accepted as a moderately heat-resisting material with good weathering, oxygen, and ozone resistance. They find extensive use in nontire automobile applications, including body and chassis parts, car bumpers, radiator and heater hoses, weatherstrips, seals, and mats. Other applications include wire and cable insulation, appliance parts, hoses, gaskets and seals, and coated fabrics. 

The major use of Buna-S is in the manufacture of automobile tires, although Buna-S materials are also used to manufacture conveyor belts, hoses, gaskets, and seals against air, moisture, sound, and dirt. 

Polymers and elastomers are usually sp>ecified by proprietary name. Use of ASTM specifications and standard descriptions is not common. When evaluating materials for gaskets and seals, obtain a sample of the actual product to make a test specimen. Do not use a generic material, since the details of composition and manufacture can have a significant imp>act on performance. 

The compatibility of CFC-alternatives with the internal plastic parts of many pieces of equipment is a concern. In many applications, parts such as the 0-rings, gaskets and seals will need to be changed to other polymer materials that are not affected by the new materials. This can only occur after large quantities of CFC-altematives are available for extensive customer testing. 

It also has been noted that many of the currently used dispersing agents are not compatible with these newer materials used in valves. The gaskets and sealing compounds used in metered-dose valves present compatibility problems to the formulator however, other gaskets have been developed and were found to be satisfactory. Several of the critical properties of these newer propellants are shown in Table 19.7. 

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