The causes of cracking in injection molding products are analyzed

In the process of producing injection molding finished products, plastic molds are prone to some defects, such as cracking, which is a common problem. Why do cracks appear? Today, Xiaobian will give you an answer.

Cracking is a common defect in plastic products of injection molding manufacturers, which is mainly caused by stress deformation. It mainly includes residual stress, external stress and stress deformation caused by external environment.

（1） Cracking caused by residual stress

The residual stress is mainly caused by the following three conditions: excess filling, demoulding and pushing out and metal inserts. As the crack caused by excessive filling, the solution can be mainly started from the following aspects:

(1) Because the pressure loss of the straight gate is small, if the crack mainly occurs near the straight gate, the multi-point distribution point gate, side gate and handle gate can be considered.

(2) On the premise of ensuring that the resin does not decompose and deteriorate, appropriately increasing the resin temperature can reduce the melt viscosity and improve the fluidity. At the same time, it can also reduce the injection pressure to reduce the stress.

(3) Generally, when the mold temperature 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 lower, the generation of stress can be reduced.

(4) Too long injection and pressure holding time will also produce stress, which can be appropriately shortened or switched for several times

(5) Non crystalline resins such as as as resin, ABS resin and PMMA resin are more prone to residual stress than crystalline resins such as polyethylene and polyformaldehyde, which should be paid attention to.

During demoulding and pushing, due to the small demoulding slope and the rough mold glue and punch, the pushing force is too large, resulting in stress, and sometimes even whitening or cracking around the pushing rod. As long as you carefully observe the location of the crack, you can determine the cause.

When inserting metal parts during injection molding, it is easy to produce stress, and it is easy to crack after a period of time, which is very harmful. This is mainly because the thermal expansion coefficients of metal and resin are very different, resulting in stress, and with the passage of time, the stress exceeds the strength of the gradually deteriorating resin material to produce cracks. In order to prevent the resulting cracking, Dongguan machco injection molding factory, as experience, the universal polystyrene with wall thickness of 7 "and the outer diameter of embedded metal parts is basically not suitable for adding embedded parts, and the embedded parts have little impact on nylon. Due to the small thermal expansion coefficient of glass fiber reinforced resin materials, it is more suitable for embedded parts.

In addition, preheating the metal insert before forming also has a good effect.

（2） Cracking caused by external stress

The external stress here is mainly the stress concentration caused by unreasonable design, especially at sharp corners.

（3） Cracking caused by external environment

Chemicals, water degradation caused by moisture absorption, and excessive use of recycled materials will degrade the physical properties and produce cracking.