Annealing (stress relief) of machined or semi-finished products is recommended when dimensional stability and freedom of distortion (warping & bowing) of the finished part is desired. Annealing temperatures of 210-310° F (100-160° C) combined with slow cooling will relieve residual stresses, normally caused by non-uniform crystallization during the cooling process. Thicker parts are more subject to residual stresses, since the outside surface cools much more rapidly than the insulated core of the part or billet. Rapid cooling creates an outer shell which restricts shrinking and promotes internal stresses.
In order to properly anneal Gar-Dur® the part should be heated in an oven or a liquid bath containing silicone oil or glycerine. Temperatures above 275-280° F (135-138° C), the crystalline melting range of Gar-Dur® are preferred. Although heating rate is not important (20° F or 10° C/hr above 175° F or 80° C), cooling rate is critical and care must be taken to slowly reduce the oven or bath temperature at 10° F (5° C) per hour until reaching 150° F (65° C). The part should then be wrapped an insulating blanket to permit slow cooling for 24 hours.
Machined parts with narrow tolerances should only be rough machined prior to stress relief. These parts should be fixtured during the annealing process due to shrinkage. Care should be taken not to overheat the machined surface during final machining to eliminate potential distortion and dimensional changes.