Some of the most common compounds include silicone, fluorosilicone, viton (fluoro-elastomer), neoprene, nitrile (Buna-N), hypalon, EPDM, SBR (red rubber), FDA white nitrile, polyurethane and natural rubber.
Rubber washers come in varying degrees of hardness which are indicated by numbers between 30 (softest) and 90 (hardest). The thicknesses of rubber washers usually range between 0.031″ to 0.375″.
The size of rubber washers is determined by measuring outside diameter (the outer-most edge) and inside diameter (the center hole). Outside diameters range from around 0.125″ to 2.984″ and inside diameters range from approximately .094″ to 2.859″.
Rubber washers can be fabricated by compression or injection rubber molding depending on the intended application. Injection molding is the process by which molten plastic is injected into an appropriately shaped mold cavity.
The process begins with a collection of raw rubber material that is heated to a liquid state. Once molten, the rubber is injected into a cavity that, in the case of rubber washer fabrication, is shaped like the outline of a washer.
The rubber fills the cavity and takes its shape. It is then allowed to cool and harden, at which point it has become a finished rubber washer. The washer can then be prepared for shipment to customers or sent for additional processing if necessary.
Compression molding is similar to injection molding; the difference is that while the plastic is in the mold cavity, pressure is applied to the plastic to ensure contact with all of the contours of the mold.
Both injection and compression molding are widely used, though injection molding is generally considered to produce more uniform products.