If, during the machining process, significant material is removed, annealing is recommended to relieve machined-in-stress and minimize possibility of premature part failure.
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Why Annealing Plastics
All extruded stock shape plastics are compressed through a profile die when extruded. The compression that occurs in the material is not relieved because the plastic "sets up" as soon as it comes out of the die and it remains in this compressed or highly stressed state. This high stare stress will cause four problems if not addressed:
- Materials will tend to warp or distort
- Physical properties will be different than published data (usually lower)
- Material may crack
- Finished part dimension may change
In order to eliminate these problem extruded products are annealed. Annealing is a stress relief process, which occurs when the material is exposed to heat (air or fluid) above its glass transition point, which allows the material to "decompress" back to a relaxed state. Annealing is important if you want a quality, finished part out of your stock shape.
Annealing/Stress Relieving Procedure for Acetal
- Place parts in air circulating oven such that air can circulate around them
- Heat oven to 300 degrees Fahrenheit at a maximum rate of 20 degrees Fahrenheit per hour
- Hold oven temperature at 300 degrees Fahrenheit 30 minutes plus 15 minutes for every 1/8" of cross section
- Cool oven to 150 degrees Fahrenheit over 15 hours with a maximum cooling rate of 10 degrees Fahrenheit per hour
- Turn off oven and allow to cool to room temperature before removing parts
Notes
This information is only to assist and advise you on current technology knowledge and is given without obligation or liability.
