How to use screw barrel of injection molding machine correctly

Each plastic has an ideal plasticizing processing temperature range, and the barrel processing temperature should be controlled to be close to this temperature range.

The granular plastic enters the barrel from the hopper, and it will first reach the feed section. Dry friction will inevitably occur in the feed section. When these plastics are insufficiently heated and unevenly melted, it is easy to cause increased wear on the inner wall of the barrel and the surface of the screw. Similarly, in the compression section and the homogenization section, if the melting state of the plastic is disordered, it will also cause increased wear.

The speed should be adjusted properly. Because some plastics are added with reinforcing agents, such as fiberglass, minerals or other fillers. The friction of these substances on metal materials is often much greater than that of molten plastics.

In the injection of these plastics, if the high speed is used, the shear force on the plastic will be increased, and the reinforcement will produce correspondingly more shredded fibers. The shredded fibers contain sharp ends, which cause wear The force is greatly increased. When inorganic minerals glide on the metal surface at high speed, its scraping effect is not small. Therefore, the speed should not be adjusted too high.

To remove debris in plastic. Generally speaking, the fresh plastic purchased from the original factory does not have any debris, but after transportation, weighing, drying, color mixing, especially adding recycled raw materials, it is possible to mix debris. It is as small as metal dust, as large as a heating ring nut paper clip, and even a series of warehouse keys, which have been mixed into the barrel. This damage to the screw is self-evident (the barrel will of course also be damaged at the same time) ), Therefore, a magnet holder must be installed to strictly manage and monitor the feeding.

The moisture contained in the plastic has a certain effect on the wear of the screw surface. If the plastic does not remove all the water before injection molding, when the residual water enters the screw compression section, it will form “steam particles” with high temperature and pressure that are melted and mixed in the molten plastic before the injection process. From the chemical section to the head of the screw, these “steam particles” are relieved of pressure and expanded during the shot process, like fine hard particles of impurities, which produce friction and damage to the wall surface.

In addition, for certain types of plastics, under high temperature and pressure, moisture may become a catalyst that promotes the cracking of plastics, producing harmful impurities that can attack the metal surface. Therefore, the drying work before plastic injection not only has a direct relationship with the quality of the parts, but also affects the working life of the screw.