The manufacturing industry has used various methods to bring together a rubber and a metal part. One could either have a one coat formulation or a two coat formulation. And the decision solely depends on the end use. For critical applications, the manufacturer may choose a two coat method of adhesion.
Let’s look at the two coat method.
The two coat method involves (1) a primer layer and (2) an adhesive coat. The primer layer improves the adhesion to the metal item. A primer has another role to play – that of being resistant to corrosion and certainly to heat. The primer applied on the metal forms a film with cross-linking resins and fillers. A topcoat for adhesive is applied to the primer layer. The primer to metal bonding causes adsorption of the primer layer on the metal. The primer to adhesive bonding creates adhesion between the layers. The layers are organised progressively thereby decreasing in modulus between the layers allowing for gradual change in stiffness between the metal and the elastomer.
The rubber-metal bonding depends on the type of elastomer in use, the preparation of the surface, the quality of the primer as well as the adhesive and the moulding type.
How do you choose the right elastomer for bonding?
Elastomer is selected on the basis of the performance of the material, mixing ability, processing ability and moulding ability. Most bonding requirements are met with natural rubber, styrene-butadiene rubber, polychloroprene, butyl rubber, isoprene and polybutadiene. The choice of the elastomer depends on the end objective of the bonded material in terms of strength, chemical resistance, heat resistance, fluid resistance, process requirements, etc.
The testing of the performance of rubber-metal bonding is done as per the ASTM D 429-14. This testing defines eight specimen types and methods for evaluation as also the types of failures in the adhesion of the two materials.
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