How com­pa­nies pre­vent assem­bly dam­age to rub­ber seals

Many design­ers come from the met­al sec­tor and have lit­tle expe­ri­ence with elas­tomers. There­fore, they can hard­ly assess how the mate­r­i­al behaves in prac­tice. This some­times leads to problems.

For exam­ple, the design some­times over­es­ti­mates the elas­tic­i­ty of rub­ber. It there­fore pro­vides too lit­tle space in the hous­ing for the seal (“When in doubt, the mate­r­i­al will give”). How­ev­er, this com­pres­sion expos­es the seal to per­ma­nent pres­sure, which leads to mate­r­i­al fatigue and fail­ure over time. The com­po­nent in which the seal is inte­grat­ed can also be dam­aged by the pres­sure, for exam­ple by bending.

Sim­i­lar prob­lems can occur with O‑rings if they are not the right size for the appli­ca­tion. For exam­ple, if the seal is too small and has dif­fi­cul­ty fit­ting over a pipe, it will be under per­ma­nent ten­sion. Rub­ber can stretch, but even­tu­al­ly the mate­r­i­al will fatigue and crack.

Anoth­er source of error is the pro­duc­tion-relat­ed tol­er­ances of elas­tomers. In prin­ci­ple, rub­ber can­not be man­u­fac­tured as pre­cise­ly as met­al. There are always small devi­a­tions from the tar­get val­ues, but these are sig­nif­i­cant­ly high­er than is usu­al in the met­al sec­tor. For this rea­son, design­ers should always allow for suf­fi­cient buffers when rub­ber mold­ed parts are to be installed. Oth­er­wise, seals that are at the upper end of the tol­er­ance range can be squeezed off.

Sharp edges also pose a risk. If a seal is stretched over such an edge, it can eas­i­ly be dam­aged. This applies both to assem­bly-relat­ed fric­tion effects (e.g. when the gas­ket is pushed into posi­tion) and to crush­ing that only occurs over time. Here, on the one hand, the design must coun­ter­act and avoid cor­re­spond­ing geome­tries or round off edges. On the oth­er hand, the assem­bly should take spe­cial care and watch out for pos­si­ble dam­age to the seal.