List of DURACON® POM grades

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6. Molding Characteristics

6.3 After-shrinkage and Dimensional Change Due to Moisture Absorption

6.3.1 After-shrinkage and Annealing

Fig. 6-10 Relationship between wall thickness and after-shrinkage (mold temperature: 30°C)	Fig. 6-11 Relationship between wall thickness and after-shrinkage (mold temperature: 80°C)
Fig. 6-12 Relationship between wall thickness and after-shrinkage (mold temperature: 120°C)	Fig. 6-13 Relationship between treatment time and after-shrinkage

If allowance for after-shrinkage is limited by the performance requirements of a product, mold temperature and annealing conditions should be determined in consideration of these relations. Namely, one of the following two methods must be adopted:

• Mold at a high mold temperature
• Mold at a low mold temperature and anneal at a temperature suitable for the highest service temperature.

The purpose of annealing is to relieve residual stress and to improve dimensional stability as described above. With general purpose moldings, annealing is rarely applied. When aiming to eliminate residual stress through annealing, the following points apply:

• 145-150°C is suitable for the annealing temperature.
• Annealing is not applied to metal-inserts moldings.
• The standard annealing time is approximately 30 minutes for a wall thickness of 2-3 mm.

6.3.2 Dimensional Change Due to Moisture Absorption

Fig. 6-14 Relationship between environment conditions and water absorption

Fig. 6-15 Relationship between water absorption and dimensional change