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What are the effects of gas discharge in injection molds?

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Gas is often produced in injection molds, which may be related to the following points:

a. The air in the pouring system and mold cavity.

b. Some raw materials contain moisture that has not been dried out, which will vaporize into water vapor at high temperatures.

c. Because the temperature is too high during injection molding, some unstable plastics will decompose and produce gas.

d. Some additives in the plastic raw materials volatilization or mutual chemical reaction generated gas.

At the same time, the cause of the unsmooth exhaust also needs to be found as soon as possible. The poor exhaust of injection mold also brings trouble to plastic parts.

The main manifestations of unsmooth exhaust are as follows:

a. During the injection molding process, the melt will replace the gas in the mold cavity. If the gas is not discharged in time, the melt filling will be difficult, resulting in insufficient injection amount and the mold cavity cannot be filled.

b. The gas excluded will form high pressure in the cavity and penetrate the interior of the plastic at a certain degree of compression, resulting in quality defects such as holes, pores, thin tissue, and silver lines.

c. Because the gas is highly compressed, the temperature in the cavity rises sharply, which causes the surrounding melt to decompose and burn, making the plastic parts appear local carbonization and burning. It mainly appears at the confluence of the two melts and the flange of the gate.

d. The gas exclusion is not smooth, so the melt speed into each cavity is different, so it is easy to form flow marks and fusion marks, and reduce the mechanical properties of plastic parts.

e. Due to the obstruction of the gas in the cavity, the filling speed will be reduced, the molding cycle will be affected, and the tax efficiency will be reduced.

Here is the position of the bubble distribution in the common plastic parts:

a. The bubbles generated by the accumulated air in the mold cavity are usually distributed on the opposite part of the gate.

b: The bubbles produced by decomposition or chemical reactions in plastic raw materials are distributed along the thickness of the plastic parts.

c: The bubbles generated by the residual water gasification in the plastic raw materials are irregularly distributed on the entire plastic part.

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