The process of annealing is commonly used for improvement of machinability; improvement of mechanical or electrical properties; or increase in stability of dimensions. Plastic is one material that is heated in an annealing oven. During the machining of plastic parts residual stresses are induced. These stresses can affect the material strength and cause reduced wear resistance and cracking. To prevent this, plastics are heated in an annealing oven. Annealing heats the plastic to just below its transition temperature for a prescribed period of time. Wisconsin Oven manufacturers plastic tempering and plastic annealing ovens in both batch and conveyor styles.
Annealing Process Stages
The three stages of the annealing process are: recovery, recrystallization, and grain growth.
Stage 1: Recovery
Recovery results in softening of the metal through removal of primarily linear defects called dislocations and the internal stresses they cause. Recovery occurs at the lower temperature stage of all annealing processes and before the appearance of new strain-free grains. The grain size and shape do not change.
Stage 2: Recrystallization
This stage of the annealing process is where new strain-free grains nucleate and grow to replace those deformed by internal stresses. If annealing is allowed to continue once recrystallization has completed, then the third stage of the process occurs.
Stage 3: Grain Growth.
Grain growth is the third stage in the annealing process and it happens when annealing is allowed to continue after stage two is completed. In this stage, the microstructure starts to coarsen and may cause the metal to lose a substantial part of its original strength. However, this can be regained with hardening.
When plastic is molded or machined,internal stresses are induced. These residual stresses can cause localized weakness, reduced resistance to wear and chemicals, and other undesirable physical properties. To relieve these residual stresses, plastics are annealed, or stress relieved
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