Cracking, including surface cracking, microcracking, top whitening, cracking, and sticking of parts due to sticking of parts, or traumatic crisis, cracking and cracking according to the cracking time. There are mainly the following: The reasons are:
1. Processing:
(1) The processing pressure is too large, the speed is too fast, the more the charge is, the injection, and the holding time is too long, all will cause the internal stress to be too large and crack.
(2) Adjusting the mold opening speed and pressure to prevent the mold from cracking due to rapid and strong pulling of the workpiece.
(3) Appropriately increase the mold temperature, make the parts easy to demoulding, properly lower the material temperature to prevent decomposition.
(4) Prevention of cracking due to welding marks, plastic degradation causing mechanical strength to become low.
(5) Appropriate use of release agent, note that often eliminate the mold surface attached to the aerosol and other substances.
(6) The residual stress of the part can be reduced by eliminating the internal stress by annealing heat treatment immediately after forming.
2. Mold:
(1) Ejection should be balanced. For example, the number of ejector pins, the cross-sectional area should be sufficient, the draft angle should be sufficient, and the cavity surface should be sufficiently smooth so as to prevent cracking due to the concentration of residual stress caused by the external force.
(2) The structure of the parts must not be too thin. Transitions should be rounded as much as possible to avoid sharp corners and stress concentration caused by chamfers.
(3) Minimize the use of metal inserts to prevent internal stress from increasing due to the difference in shrinkage between inserts and parts.
(4) Suitable demoulding air inlets should be provided for deep-bottom parts to prevent the formation of vacuum negative pressure.
(5) The main channel is sufficiently ambassador's spout to release mold in the future and it is easy to demold.
(6) The joint between the main bush and the nozzle should prevent the cold material from dragging and make the product stick to the fixed mold.
3. Materials:
(1) The content of recycled materials is too high, resulting in too low strength of the parts.
(2) Humidity is too high, causing some chemical reactions between plastics and water vapor, reducing the strength and leading to cracking.
(3) The material itself is not suitable for the processing environment or the quality is poor, and the pollution will cause cracking.
4. Machine side:
Injection molding machine plasticizing capacity to be appropriate, too small plasticization can not fully mix and become brittle, will degrade when too large.