The gas in the injection mold includes not only the air in the cavity, but also the air in the gate and the decomposition gas generated by the plastic melt, and the steam which caused by plastic in high temperatures. During injection molding, these gases should be exhaust in time, otherwise there will be some issues as following:
1. Defects such as flow mark, water mark, and weld marks will be formed on part surface;
3. It is difficult to fill the plastic melt or flash locally;
4. The gas generates high temperature under high temperature and high pressure, causing local carbonization and burnt marks on the product;
5. Reducing the filling speed of the plastic melt, not only the molding cycle is prolonged, but the melt temperature decreases quickly after injection speed dropped, the residual stress will increase, if the injection pressure is increased, and the possibility of warping deformation of the plastic part after demolding will increase, if the material temperature is increased in order to reduce the injection pressure, it will cause the plastic to crack.
Properly making the exhaust slot can reduce the injection pressure greatly, reduce the injection and the holding time, and reduce the clamping pressure, thereby improving the production efficiency, reducing the production cost, and the energy consumption of the machine. For transparent plastic parts or plastic parts with strict surface requirements, we should be careful with the mold exhaust system design.