The Reason Why Gas Is Often Discharged In Injection Molds

- Aug 04, 2018-

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

(1) Air in the casting system and mold cavity.

(2) Some materials contain water that has not been dried out, and they vaporize to steam at high temperatures.

(3) Due to the high temperature during injection, some unstable plastics will decompose and produce gas.

(4) Gases produced by volatilization or chemical reaction of certain additives in plastic materials.

2. At the same time, the cause of poor exhaust is also to be found out as soon as possible.The bad exhaust of injection mold also brings troubles to plastic parts.The main performance is as follows:

(1) During the injection process, the melt will replace the gas in the cavity. If the gas is not discharged timely, the melt will be difficult to fill, resulting in insufficient injection volume and the cavity cannot be filled.

(2) If the gas is not free, high pressure will be formed in the cavity, and it will infiltrate into the interior of the plastic to a certain degree of compression, resulting in quality defects such as cavitation, stomata, tissue sparseness and silver grain.

(3) As the gas is highly compressed, the temperature in the cavity rises sharply, causing the surrounding melt to decompose and burn, resulting in partial carbonization and charring of the plastic parts.It mainly appears at the junction of two melts, gate flange.

(4) The gas cannot be removed smoothly, so the melt velocity entering each cavity is different, so flow marks and fusion marks are easy to be formed, and the mechanical properties of the plastic parts are reduced.

(5) Due to the gas obstruction in the cavity, the mold filling speed will be reduced, the molding cycle will be affected, and the tax efficiency will be reduced.

3. Distribution of bubbles in plastic parts

(1) Cavitation bubbles generated by air accumulation in the cavity are usually distributed on the part opposite the gate.

(2) The bubbles generated by decomposition or chemical reaction in the plastic materials are distributed along the thickness of the plastic parts.

(3) The bubbles generated by residual water gasification in the plastic materials are distributed irregularly throughout the plastic parts.