"R"

Radial Shaft Seals - Also called grease seals, rotary seals or shaft seals. Made of rubber to seal grease in a housing with a rotating shaft.

Rebound - Rebound is a measure of the resilience, usually as the percent- age of vertical return of a body which has fallen and bounced.

Rebound test - Method of deter- mining the resilient properties of vulcanized rubber, by measuring rebound of a steel ball or pendulum falling from a definite height onto a rubber sample.

Register - The accurate matching of the plates of a mold.

Reinforcing Agent - In rubber compounding, a finely-divided substance or filler which, when properly dispersed in rubber, produces improved physical properties in the vulcanized product, i.e., greater energy of resilience, greater resistance to abrasion, higher modules of elasticity and tensile strength Certain grades of furnace blacks are the most important reinforcing agents for black stocks. For light-colored stocks, calcium silicate, precipitated calcium carbonates, silica and clay are the most commonly used.

Reliability - The probability that an item will continue to function at customer expectation levels at a measurement point, under specified environmental and duty cycle conditions.

Reliability Apportionment

Reproducibility - The variation in the average of measurements made by different operators using the same gage when measuring identical characteristics of the same parts.

Resilience - The property of a material that enables it to return to its original size and shape after removal of the stress which causes the deformation.

Resilience - The energy returned by vulcanized rubber when it is suddenly released from a state of strain or deformation. The returned energy, expressed as a percentage of the original potential energy, is a measure of the resilience. Various rebound testers are used to measure rebound (Bashore, Lupke).

Retarder - Any substance whose presence ill relatively small proportion retard a chemical reaction. Specifically, a substance which when added in small proportion to a rubber compound, retards the rate of vulcanization. An anti-scorching agent; examples, phthalic anydride, salicylic acid.

Reversion - (1) A deterioration of physical properties that may occur upon excessive vulcanization of some elastomers, evidenced by a decrease in hardness and tensile strength, and an increase in elonga- tion; (2) A similar change in proper- ties after air aging at elevated temperatures. Natural rubber, butyl, polysulfides and epichlorobydrin polymers exhibit this effect (extreme reversion may result in tackiness). Most other polymers will harden and suffer loss of elongation on hot air aging.

Reversion - The softening of some vulcanized rubbers when they are heated too long. Usually accompanied by an increase in extensibility, a decrease in tensile strength and a lowering of the stress required to produce a given elongation. Extreme reversion may result in tackiness; the rubbers "revert" to an unvulcanized then to a non-polymeric condition.

Rheology - The science of deformation and flow of matter. Deals with the laws of plasticity, elasticity and viscosity and their connections with paints, plastics, rubber, oils, glass, cement, etc...

Rheometer (Monsanto) - An oscillating disk cure meter used for determining vulcanization charac- teristics of a rubber compound.

Rimseal - A sealing device used on the rim of round plate or rim of a wheel.

Rings - Round sealing devices.

RMS - Root Mean Square - The measure of surface roughness, obtained as the square root of the sum of the squares of micro-inch deviation from true flat.

Rod Seals - Any seal used on the rod of a hydraulic or pneumatic cylinder made from rubber or plastic.

Rollers - A round, flat ring used as a wheel or guide.

Rotary Seals - Seals used on rotating shafts - see lips seals, grease seals, oil seals.

Rotocure - Rotory press.

Roto Glyd - A flat plastic, PTFE or Teflon ring used on a rotatinfg shaft.

Rubber - A material that exhibits elastic properties that allow recovery from large deformations quickly and forcibly. A tough, waterproof substance obtained through polyme- ric synthesis or in natural form from the sap of various species of plants or trees.

Rubber Latex - Colloidal aqueous emulsion of an elastomer.