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Cause and influence of mold air trap

 Wednesday, 18 August 2021

Injection mold is a technical work, and exhaust is also a more important problem, because hot gas is easy to be generated during molding  ,If it is not discharged from the mold cavity in time, it is easy to affect the product quality. Therefore, exhaust during injection mold is also a more strict work.
Source of air trap ,

(1) Air is left in the mold cavity itself;
(2) Some raw materials contain water that has not been removed by drying and evaporate into steam at high temperature;
(3) Gas produced by high temperature decomposition of some unstable plastics during injection molding;
(4) Some additives are volatile gases produced in plastic materials or through mutual chemical reactions.

2. Hazards of poor exhaust ,If the injection mold does not exhaust the air in time, it is easy to cause some damage to the quality of the product. Generally, there are the following manifestations:

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 lead to difficulty in filling the melt, resulting in insufficient injection and unable to fill the cavity;
(2) Under a certain degree of compression, the removal of unobstructed gas will form high pressure in the cavity and penetrate into the plastic, resulting in quality defects such as pores, voids, tissue thinning and cracking;
(3) Since the gas is highly compressed, so that the temperature in the cavity rises sharply, so that the surrounding melting decomposition, burning plastic parts and partial burning carbonization phenomenon. It is mainly found in the confluence of two molten grid flanges;
(4) Due to the poor gas emission, the melt velocity entering each cavity is different, which is easy to form flow marks and melt marks, and reduce the mechanical properties of plastic parts;
(5) Due to the obstruction of gas in the cavity, the filling speed is reduced, the forming cycle is affected, and the efficiency of tax collection and management is reduced.

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