1, in order to eliminate some internal stress. In the process of plastic injection molding, due to uneven mixing plasticization, uneven filling speed and uneven cooling, uneven crystallization, orientation and shrinkage are inevitable, which leads to internal stress in production, which leads to the decline of mechanical properties of products during storage and use, and defects such as silver lines or cracks appear on the surface of products. After heat treatment of injection products, the forced frozen molecular chains can relax, and the oriented macromolecular chains turn to random positions, thus eliminating some internal stresses.

2. Improve the crystallinity of crystalline plastic products and stabilize the crystalline configuration, thereby improving the elastic modulus and hardness of products and reducing the elongation at break of products.

3. Not all injection products need heat treatment. For products with flexible molecular chain or low glass transition temperature, such as polyoxymethylene, the internal stress in the products can disappear slowly, and some products have low requirements for use. They may not be subjected to heat treatment.

4, but there are metal inserts, thick-walled products, products with high dimensional accuracy requirements, plastic products with large molecular chain rigidity and internal stress that is not easy to disappear by itself, should be heat treated.

5. The heat treatment method is relatively simple. Put the product in a liquid medium (such as water, mineral oil, glycerol, ethylene glycol, liquid paraffin, etc.) heated at constant temperature. ) or let it stand in a hot air circulating constant temperature oven for a certain period of time, and then slowly cool it to room temperature (if it is cooled too fast, internal stress may be generated again).

6. Different heat treatment conditions should be set for different injection molding products. Generally, the heat treatment should be controlled above the product service temperature 10~20℃ or below its thermal deformation temperature10 ~ 20℃; The cooling rate of thick products is 10℃/h, and that of thin-walled products is 50 ~ 60℃/h; The heat treatment time can be set by experiment according to the principle of long low temperature time and short high temperature time.