Why does the processed plastic shell crack?

Author: MULAN - Plastic Molding Manufacturer

When we deal with plastic housings in injection molds, we often encounter some problems, the more common of which is cracking. As we all know, the main cause of cracking is stress deformation, and stress is mainly divided into residual stress. Stress deformation caused by external stress and external environment.

Therefore, in order to solve the cracking problem in the processing of plastic shells, the injection mold factory must start from solving the stress. 1. Cracks caused by residual stress. Residual stress is mainly caused by the following three situations, namely overfilling, mold release and embedded metal parts.

The injection mold factory produces streaks when the filling is too much. The solution mainly starts from the following aspects: due to the small pressure loss of the sprue, if the injection mold factory mainly cracks near the sprue, multi-point distribution can be considered Point the gate. Side gate and handle gate methods; on the premise that the resin does not decompose and deteriorate, properly increasing the resin temperature can not only reduce the melt viscosity and improve fluidity, but also reduce the injection pressure to reduce stress; generally speaking, when the mold temperature When it is low, it is easy to produce stress, and the temperature should be increased appropriately. However, when the injection speed is high, even if the mold temperature is low, the generation of stress can be reduced; if the injection and holding time are too long, stress will also occur.

Appropriate shortening or secondary pressure switch is good; non-crystalline resin, such as AS resin. ABS resin. PMMA resin and other crystalline resins, such as polyethylene and polyoxymethylene, are prone to residual stress and should be paid attention to.

2. External stress caused by cracking. The external stress here is mainly due to the stress concentration caused by unreasonable design, especially at the sharp corners. 3. Cracking caused by external environment.

chemical. Water degradation due to moisture absorption, as well as excessive use of recycled materials can deteriorate the substance and cause cracking.