(1) The raw material gas or air entrained in the feed s […]
(1) The raw material gas or air entrained in the feed system exists in the cavity. During the molding process, the gas in the runner and cavity was not discharged in time.
(2) The resin is not dry enough and contains water. At the injection temperature, the water evaporates into water vapor.
(3) The injection temperature is high, and the plastic decomposes to produce gas.
(4) Certain additives in the resin will volatilize or undergo chemical reactions to generate gas (for example, when forming thermosetting plastics, the plastic itself not only contains moisture and volatile components, but also condensation reaction occurs during the curing process to generate condensate Water and low molecular weight (volatile gas), residual gas in the resin.
Consequences of poor bmc mold exhaust:
(1) The gas is greatly compressed to generate back pressure, which increases the resistance of the molten material to the filling flow, hinders the normal and rapid filling of the molten plastic, and prevents the bmc mold cavity from filling the mold, resulting in unclear plastic edges.
(2) There are obvious flow marks and weld seams on the product, and the mechanical properties of the product are reduced.
(3) After compression, the gas will penetrate into the internal plastic layer and cause surface quality defects such as silver streaks, pores, loose tissue and peeling.
(4) After compressing the gas in the cavity, heat is generated, the temperature of the plastic increases locally, the molten plastic decomposes and changes color, and even burns and carbonizes.
Poor exhaust will reduce the mold filling speed and increase the molding cycle (especially high-speed bmc molds), which seriously affects production efficiency.