Backrind is typified by a longitudinal recess (shaped like a wide-angle “U” or “W”) found at the parting lines on the seal’s O.D. and/or I.D. (see Figure 61). This recess may sometimes exist on the entire circumference of the O-ring. Backrind can result from the thermal expansion of material over a sharp mold edge. It can also be caused by premature curing of the material. (For maximum acceptable backrind, see Table 25.)

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