Feman Tooling Co.,Limited
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Several Common Problems and Solutions of Plastic Injection Parts

Ⅰ. Reasons and solutions for deformation of plastic injection parts


An injection molded part is shaped like a cavity but is a twisted version of the cavity shape.


1. Possible reasons for the problem


(1) Bending is due to excessive internal stress in the injection molded part.


(2) The mold filling speed is slow.


(3) Insufficient plastic in the mold cavity.


(4) The plastic temperature is too low or inconsistent.


(5) The plastic injection parts are too hot when ejected.


(6) Insufficient cooling or inconsistent temperature of moving and fixed molds.


(7) The structure of the plastic injection parts is unreasonable (for example, the reinforcing ribs are concentrated on one side, but far apart).


2. Remedy


(1) Reduce the injection pressure.


(2) Reduce the forward time of the screw.


(3) Increase cycle time (especially cooling time). Immerse in warm water (38°C) immediately after ejection from the mold (especially thicker plastic injection parts) to slowly cool the plastic injection parts.


(4) Increase the injection speed.


(5) Increase the plastic temperature.


(6) Use cooling equipment.


(7) Appropriately increase the cooling time or improve the cooling conditions to ensure that the mold temperatures of the movable and fixed molds are consistent as much as possible.


(8) Improve the structure of plastic parts according to the actual situation where permitted.


Ⅱ. Common problems that should be paid attention to in the injection molding process of transparent plastic injection parts


Due to the high light transmittance of transparent plastics, the surface quality of plastic products must be strictly required, and there should be no defects such as streaks, pores, whitening, halo, black spots, discoloration, and poor gloss. Equipment, molds, and even product design, must pay great attention and put forward strict or even special requirements.


Secondly, since most of the transparent plastics have high melting point and poor fluidity, in order to ensure the surface quality of the product, a higher temperature is often required, and the process parameters such as injection pressure and injection speed should also be finely adjusted, so that the plastic injection can be filled with the mold, It will not generate internal stress and cause product deformation and cracking.


Therefore, strict operation should be carried out in terms of raw material preparation, equipment and mold requirements, injection molding process and raw material processing of products.


Ⅲ. Common problems of color difference control of plastic injection parts


Chromatic aberration is a common defect in injection molding. There are many factors affecting color difference, involving raw resin, color masterbatch, mixing of color masterbatch and raw materials, injection molding process, injection molding machine, etc.


Ⅳ. Adjust the process parameters of plastic injection parts(temperature/pressure/speed/position)


The measurement and control of temperature is very important in injection molding. While making these measurements is relatively simple, most injection molding machines do not have sufficient temperature pick-up points or lines. On most injection molding machines, the temperature is sensed by a thermocouple. A thermocouple basically consists of two different wire tails joined together. If one end is hotter than the other, a tiny electrical signal will be generated; the more heated, the stronger the signal.

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