Back-up Ring
A washer-like device of a relatively hard, tough material installed in the gland on the downstream side of the seal to prevent seal extrusion into the diametrical gap while under pressure.
Bench Test
A laboratory test approximating product service conditions.
Bending Modulus
The measure of applied force required to bend a material a given distance around a specified radius. A measure of material elasticity (stiffness).
Bleeding
A film or beads formed by such compound components as plasticizers that have migrated to the surface of rubber products because of incompatibility with the base elastomer and/or the compound ingredients.
Blemish
A surface mark or deformity.
Blisters
A raised spot on the seal's surface created by an internal void, or air-filled pocket.
Bloom
A milky surface discoloration caused by the migration of certain compound components (such as antiozonants) to the rubber's surface after molding or storage. The waxy film serves as a protective coating shielding the part from oxidation. This discoloration does not adversely affect material performance.
Bond
The mechanical or chemical force that holds an elastomer to some other object. Mechanical bonding includes component interference and no molecular cross bridging between the elastomer and substrate, whereas chemical bonding involves contact adhesives with heat and pressure to adhere an elastomer to a primed surface.
Break-Out
The force required to overcome initial seal to gland surface adhesion, when part movement is intermittent. A common term used to describe one form of friction.
Brittleness
Tendency to crack upon physical deformation at low temperature.

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