May 16, 2020

The solutions to the serious plastic molded parts appearance sink mark with the boss

Sometimes due to defects in mold manufacturing, the appearance shrinkage of the injection molded part at the position of the cylinder (injection pin) is difficult to solve regardless of the adjustment of the machine. Even if it is reluctantly solved, the injection molded parts are already flashing.

There are two main reasons for the serious sink of the injection pin.

1, The injection pin is too short or too thin, so that the plastic parts of the injection part at the root of the injection pin are too thick (such as greater than 4mm, and the wall thickness of the other parts of the injection part is only 2mm), the shrinkage problem is inevitable, and the thicker the more difficult It can’t be solved even by adjusting the machine. This is the case in most cases in production.

2, The injection pin is too long, so that the wall thickness of the injection molded part and the end of the injection pin is too thin (for example, less than 0.3mm), resulting in a very low thermal strength of the plastic parts here. When the injection molded part is demoulded, the injection pin is drawn out, and a vacuum is formed inside the hole of the injection pin, and the atmospheric pressure outside will dent the appearance of the injection molded part, which is similar to the recession.

Therefore, before solving the problem of shrinkage, the injection part should be cut open and observed. It is found that the position of the injection part is too thick. Generally, it is not thicker than the wall thickness of the injection part, and the injection pin should be lengthened until the shrinkage disappears; if found The recessed position is too thin (usually not less than 0.5mm), the injection pin can be shortened with a grinder, and the recessed problem can be solved.

In addition, spraying a demoulding agent on the injection pin can also be used as an auxiliary means to enhance the effect of improving the recession. Because the demoulding agent can cool the injection pin, the cooling effect at this location is enhanced, thereby reducing the degree of shrinkage, and at the same time, it can prevent the formation of a vacuum when the top tube is ejected, because the release agent will produce a little gas.

Contact one of our Technical Specialists today for assistance at suzubintech@gmail.com. We will be happy to review your design and provide you with recommendations.

Injection Molding, Plastic Mold Case, Plastic Molding Design, Plastic Parts
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