How to solve the cracking problem in plastic shell processing?
When we process plastic shells, some problems often occur, one of which is cracking. As we all know, the main cause of cracking is stress deformation, and stress is mainly divided into residual stress, external stress and stress deformation caused by the external environment. Therefore, to solve the cracking problem in plastic shell processing, the injection mold factory must start with solving stress.
1. Cracking caused by residual stress
Residual stress is mainly caused by the following three situations, namely overcharging, demolding and metal inlay. For the cracks generated by the injection mold factory under overcharging, the solution can be mainly in the following aspects:
Since the pressure loss of the sprue is small, if the cracks mainly occur near the sprue, the injection mold factory can consider using multi-point distribution gates, side gates and handle gates. On the premise that the resin does not decompose or deteriorate, appropriately increasing the resin temperature can reduce the melt viscosity, improve fluidity, and reduce the injection pressure, thereby reducing stress. Generally, stress is easy to occur when the mold temperature is low, and the temperature should be appropriately increased. However, when the injection speed is high, even if the mold temperature is low, the stress can be reduced. Moreover, if the injection holding time is too long, stress will be generated, so it is best to shorten it appropriately or switch the holding time. Non-crystalline resins, such as AS resin, ABS resin, PMMA resin and other crystalline resins, such as polyethylene, polyoxymethylene, etc., are prone to residual stress and should be paid attention to.
2. Cracking caused by external stress
The external stress here is mainly caused by unreasonable design of the injection mold factory, especially at sharp corners.
3. Cracking caused by the external environment
Chemicals, water degradation due to moisture absorption and excessive use of recycled materials will deteriorate physical properties and cause cracking.