Why the gas generation in injection molds?

Reasons why injection molds generate gas when manufacturing products

① In the feeding system, the material carries gas or there is air in the cavity. Besides, during the forming process, the gas is not discharged from the runner and cavity in time.
② The resin is not sufficiently dried and contains water, which evaporates into water vapor at the injection temperature.
③ The injection temperature is higher and the plastic will decompose to produce gas.
④ Some additives in the resin are easy to volatilize or react chemically to generate gas. For example, when thermosetting plastics are formed, not only does the plastic contain water and volatile components, but also a polycondensation reaction occurs during the curing process to produce condensation water and low-molecular volatile gases.
⑤ Residual gas is in the resin.

Consequences of the mold poor venting

① The gas is subjected to great compression and generates back pressure, which increases the resistance of mold filling flow of molten material, and prevents the molten plastic from filling the mold normally and quickly. In this case, the mold cavity cannot be filled completely and the plastic does not have clear edges.
② There are obvious flow marks and weld marks on the products, which leads to reduce the mechanical properties of the products.
③ After the gas is compressed, it will penetrate into the plastic inner layer, causing silver streaks, voids, loose structure, delamination and other surface quality defects.
④ After the gas is compressed in the cavity, the heat is generated to rise the local temperature of the plastic. And then, the plastic melt will decompose and discolor, and even burned and carbonized.

⑤ Poor venting will reduce the filling speed and increase the cycle of product forming, especially for high-speed injection molding, which leads to reduce productivity seriously.