Try resin manufacturers. This from the GE site
LEXAN® resins Anneal LEXAN at 250° F for as short as time as possible to achieve acceptable part performance (30 minutes at temperature 250° F per 1/8 inch thickness). Determine this time by experimenting with actual end-use testing.
The injection molding process generally results in parts with molded-in stresses. These stresses can arise from a number of sources, but key causes include differential flow patterns in the mold, sharp wall transitions, different wall thicknesses, and machining.
Annealing is a secondary operation that can remedy certain stress imbalances. It is accomplished by exposing the part to elevated temperatures for extended periods of time.
Annealing should not be used for glass-filled part, and may cause increased notched sensitivity and reduced chemical compatibility in some parts. Also the extended time needed for cooling can affect manufacturing efficiency and production rates.
Injection molding plastic parts invariably produces molded in stresses. These stresses arise from a number of sources. Differential flow patterns in the mold, sharp wall transitions, different wall thicknesses, and machining all contribute to nonuniform distribution of inherent stresses.
Although annealing reduces stresses, it should not be considered a cure-all for a number of reasons:
Annealing glass-filled parts may not thoroughly relieve internal stress, because they are composites.
Studies show that post-molded heat histories may increase notch sensitivity and reduce chemical compatibility with certain substances. Therefore, the time at temperature should be the minimum needed to achieve acceptable part performance.
The extended periods of time needed for annealing may prevent it from being used economically in actual production.
Review and examine molding procedures and part designfor possible problems before choosing annealing as a solution
Always anneal parts in an air circulating oven and cool them slowly to prevent thermal "shock," as cooling rates may reintroduce stresses into the part causing warping and cracking. To avoid overly rapid cooling rates, cool the parts by turning the oven off until the parts return to ambient temperatures.
hope it helps . . . <b> <i> Louis </i> </b>
Silly Poly Questions <i> Moderator</i>
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[This message has been edited by Louis (Edited: 08/18/01).]