Common Defects and Control Methods in Plastic Mold
Cracking is a more common form of plastic defects, the main reason is due to stress and deformation caused. Mainly there are residual stress, external stress and external stress generated by the deformation.
(-) residual stress caused by the crack
Residual stress is mainly due to the following three cases, namely, overfilling, stripping and metal inserts caused by the introduction. Plastic Mold As in the case of overfilling caused by cracks, the solution can be mainly in the following aspects:
(1) due to the minimum loss of the gate pressure, so if the cracks are mainly produced in the vicinity of the gate, you can consider switching to multi-point distribution point gate, side gate and handle gate way.
(2) to ensure that the resin does not break down, Plastic Mold not deteriorated under the premise of appropriate to improve the resin temperature can reduce the melt viscosity, improve mobility, but also can reduce the injection pressure to reduce stress.
(3) Under normal circumstances, the mold temperature is relatively easy to produce stress, should be appropriate to improve the temperature. However, when the injection speed is high, even if the mold temperature is low, can also reduce the stress generation.
(4) injection and holding time is too long will produce stress, it should be appropriate to shorten or hold the pressure switch effect is better.
(5) non-crystalline resin, such as AS resin, ABS resin, PMMA resin and other crystalline resin such as polyethylene, POM and other prone to residual stress, should be noted.
When the mold release is introduced, due to the small mold release angle, the mold type glue and the punch mold are rough, the pushing force is too large, Plastic Mold the stress is generated, and the whitening or the rupture phenomenon occurs even around the pushing rod. As long as careful observation of the location of the crack, you can determine the cause.
In the injection molding at the same time embedded metal parts, the most prone to stress, and easy after a period of time after the crack, great harm. This is mainly due to the difference in thermal expansion coefficient between the metal and the resin, and over time, the stress exceeds the strength of the resin material which gradually deteriorates to produce cracks. In order to prevent the resulting cracks, as a result of the experience, Plastic Mold the wall thickness 7 “with the embedded metal outer diameter of the general-purpose polystyrene is basically not suitable for the inserts, while the inserts have the least impact on the nylon due to the glass fiber Resin material thermal expansion coefficient is relatively small, more suitable for embedded parts.
In addition, preheating the metal insert before molding, also has a good effect.
(B) the external stress caused by the crack
Here the external stress, mainly due to unreasonable design stress caused by concentration, especially in the sharp corner of the more attention.
(C) the external environment caused by the crack
Chemicals, moisture absorption caused by moisture absorption, and excessive use of recycled materials will make the physical deterioration, Plastic Mold resulting in cracking.
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