Injection Must Learn Knowledge Points

- Dec 18, 2018-

3. Exhaust


Some plastics need to be vented in the shooting tank during injection molding to allow the gas to escape. In most cases these gases are only air, but they may be melted moisture or monomolecular gases. If these gases are not released, the gas will be compressed by the melt and brought into the mold, which will expand and form bubbles in the product. To remove the gas before it reaches the nozzle or mold, reduce or reduce the diameter of the screw root to decompress the melt in the shot cylinder.


Here, the gas can be discharged from holes or holes in the shooting tank. The diameter of the screw root is then increased and the melt of the volatiles is directed toward the nozzle. The injection molding machine equipped with this facility is called a vented injection molding machine. Above the vented injection molding machine, there should be a good smoke eliminator for the flammable burner to remove potentially harmful gases.

4. Increase the role of back pressure

In order to obtain a high quality melt, the plastic is uniformly heated or melted and thoroughly mixed. Use the right screw to properly melt and mix, and have enough pressure (or back pressure) in the shot cylinder to achieve mixing and thermal consistency. Increasing the resistance to oil return creates back pressure in the firing tank. However, the screw takes longer to reset, so there is more wear and tear in the injection molding machine drive system. Keeping back pressure as much as possible, isolated from the air, also requires a consistent melt temperature and mixing level.