ECONOMICAL APPROACH TO O-RING SEAL DESIGN.

For bores and grooves involving O-ring seals, typical recommendations are for dimensional tolerances on the order of plus or minus 0. 001 in. and for surface finishes not to exceed 32 mu in. rms. There is, however, a design approach that lessens the need for tight specifications. It applies specifically to static radial seals with external grooves. The method overcomes the need for close tolerances and smooth finishes by taking advantage of the elasticity inherent in O-ring materials. Reliability and long life are ensured through close control of both the stretch experienced by the ring as it is snapped into a groove and the squeeze to which it is subjected when inserted in a bore. Application of this method permits dimensional tolerances of plus or minus 0. 005 in. and surface finishes of 125 mu in. rms for bore and groove. Tolerances and finishes of this order eliminate the need for many of the manufacturing operations that are costly for mass-produced products.