The relationship between the gas generated during the injection molding process and the mold Causes of gas generation in the manufacture of products

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The Gas And The Mold
Translated By Jasmine HL
The relationship between the gas generated during the injection molding process and the mold
Causes of gas generation in the manufacture of products
① The gas entrained in the material in the feeding system or the original air in the cavity. During
the forming process, the gas in the flow channel and cavity was not exhausted in time.
② The resin is not sufficiently dry and contains water. At the injection temperature, it
evaporates to become water vapor.
③ The injection temperature is high, and the plastic decomposes to generate gas.
④ Some additives in the resin, volatilization or chemical reaction to generate gas (such as
thermosetting plastics, not only the plastic itself contains moisture and volatile components, but
also polycondensation reaction during the curing process, resulting in condensation water and
low molecular volatile gases).
⑤ Residual gas in the resin.
Consequences of poor mold venting:
① The gas is subjected to large compression to generate back pressure, and this back pressure
increases the resistance of the molten material to the mold filling flow, prevents the normal and
rapid filling of the molten plastic, prevents the mold cavity from filling, and causes the plastic
edges to be unclear.
② There are obviously visible flow marks and fusion seams on the product, and the mechanical
properties of the product are reduced.

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③ After the gas is compressed, it will penetrate into the inner layer of the plastic, causing the
plastic to produce surface defects such as silver streaks, pores, loose tissue, and peeling.
④ After the gas in the cavity is compressed, heat is generated and the local temperature of the
plastic rises, and the plastic melt decomposes and discolors, and even burns and carbonizes.
⑤ Poor exhaust, reducing mold filling speed, increasing the molding cycle (especially high-speed
injection molding), which seriously affects production efficiency.