(1) Cracks caused by residual stress of plastic injection mould
Residual stress is mainly due to the following three conditions, namely overfill, ejection, and metal inserts. As the crack generated in the case of excessive filling, the solution can be mainly started in the following aspects:
(1) Since the pressure loss of the sprue is small, if the cracks are mainly generated near the sprue, the multi-point distribution gate, side gate, and shank gate can be considered instead.
(2) On the premise of ensuring that the resin does not decompose or deteriorate, appropriately increasing the resin temperature can reduce the melt viscosity and improve the fluidity, and at the same time, the injection pressure can be reduced to reduce the stress.
(3) Under normal circumstances, when the mold temperature is low, it is easy to generate stress, and the temperature should be appropriately increased. But when the injection speed is high, even if the mold temperature is lower, the stress can be reduced.
(4) Too long injection and pressure holding time will also generate stress, shorten it appropriately or perform several pressure holding switching effects
When demoulding is pushed out, due to the small demoulding slope, the roughness of the car parts mould and the punch, the pushing force is too large, resulting in stress, and sometimes even whitening or cracking around the pushrod. The cause can be determined by looking closely at the location of the crack
(2) Cracks caused by external stress
The external stress here is mainly due to the stress concentration caused by the unreasonable design, especially at the sharp corners.
(3) Cracks caused by the external environment
Chemicals, water degradation caused by moisture absorption, and excessive use of recycled materials will deteriorate physical properties and cause cracks.