Society of Automotive Engineers.
Premature curing of compounded rubber stock during processing or storage, with the potential for adversely affecting material flow and plasticity during subsequent shaping and curing processes.
Any device used to prevent the passage of a fluid (gas or liquid) or fine particles.
The potential degradation of seal performance capabilities due to exposure of seal elastomers to stressful environmental factors during storage. Proper packaging and storage conditions help to avoid this problem.
Shore A Hardness
Durometer reading in degrees of rubber hardness as measured on a Shore A gauge. Scale is 0-100, with higher numbers indicating greater hardness.
(1) All rubber materials shrink to some extent during molding. This is normal and should be taken into consideration (by individual polymer shrink rates) when designing rubber parts. (2) Decreased seal volume due to exposure to adverse environmental factors. Can be an indication of plasticizer extraction from system chemicals.
Size, Actual
Actual dimensions of a molded article (including manufacturing tolerances).
Size, Nominal
Basic dimensions of a part from which plus and minus tolerances are developed to account for the range of actual dimensions expected during manufacturing.
Specific Gravity
The weight of a given volume of any substance compared with the weight of an equal volume of water. Specific Gravity is used as a comparison tool to determine the relative density of seal materials, helping to identify base polymers and certain compounds.
Spiral Failure
Generally found on long stroke, hydraulic piston seals, spiral failure results when certain segments of the o-ring slide, while other segments simultaneously roll. At a single point on its periphery, the o-ring gets caught on an eccentric component, or against the cylinder wall, causing twisting and development of 45 degree angle, surface cuts.
Sprue Marks
Raised or recessed marks on the surface of a molded rubber part created by the removal of extra cured material left at the inlet (gate) of the mold by the sprue (pouring nozzle) of the molding machine.
Compression of the o-ring between the two mating surfaces comprising the walls of the cavity or “gland” into which the seal is installed. Squeeze may be either of two types: Axial - squeezed on the top and bottom o-ring surfaces, as in face seals. Radial - squeezed on the inner and outer o-ring surfaces, as in piston or rod seals. Squeeze helps to assure a leak-resistant seal.
Stack Up Tolerance
The summation of sealing system tolerances.
Static Seal
A gasket type application where the seal is contained within two non-moving gland walls, as in face seals.
Deformation per specified area unit of material due to applied force (stress).
Applied force per specified area unit of material.
Increased seal volume caused by exposure to adverse operating conditions, such as exposure to oils, fluids, heat, and the like.


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