The exhaust of injection mold is an important problem in mold design, especially in injection molding, the exhaust requirements of injection mold are more strict. (1) Source of gas in injection mold :1) Air in the gating system and mold cavity. 2) Some raw materials contain water that has not been removed by drying. They are gasified into water vapor at high temperature. 3) The gas produced by the decomposition of some unstable plastics due to the high temperature during injection molding. 4) Gases generated by volatilization or mutual chemical reaction of some additives in plastic raw materials.
(2) Hazards of poor exhaust Poor exhaust of injection mold will bring a series of hazards to the quality of plastic parts and many other aspects. The main performances are as follows: 1) In the process of injection molding, the melt will replace the gas in the cavity. If the gas is not discharged in time, it will make it difficult to fill the melt, resulting in insufficient injection volume and unable to fill the cavity. 2) Poor gas removal will form high pressure in the mold cavity and penetrate into the plastic under a certain degree of compression, resulting in quality defects such as pores, cavities, loose tissue, crazing and so on.
The most common way to solve this problem is to slow down the injection time of the first stage. It can provide more time for the emission of air in the mold cavity. However, this can be an expensive proposal. If the injection time of the first stage must be increased from 1 second to 1.5 seconds, what is the cost of the additional production cycle time? There is a better way. Vacuum exhaust can alleviate these problems by immediately expelling air from the mold cavity when filling the cavity. In addition, its unique technology includes: a blowback circuit, which can clean the exhaust pin and reduce the maintenance of the injection molding machine mold.
When using raw materials with excessive moisture and volatile content, a large amount of gas will also be generated, resulting in poor mold exhaust. At this time, the raw materials should be dried and volatiles removed. In addition, in the process operation of the mold system, poor exhaust can be improved by increasing mold temperature, reducing injection speed, reducing flow assistance of the gating system, reducing mold clamping force, and increasing mold gaps.