How to improve the service life of the injection molding machine screw?

Update:23 Jan 2021

Generally, the screw of the injection molding machine has undergone nitriding treatment to increase the surface hardness, that is, to improve the wear resistance. However, if you neglect to cause the injection molding machine screw to work under high temperature, high pressure, high mechanical torque and high friction environment for a long time. The process conditions of the first few factors are required, and the wear caused by friction is inevitable. The cause of wear, if you don't try to reduce wear as much as possible, it will inevitably reduce the life of the screw. In order to ensure the safe and stable production of the injection molding machine screw and prolong its service life, it is necessary to strengthen the maintenance of the injection molding machine screw. The basic contents are as follows:

(1) Each plastic has an ideal plasticizing temperature range. The processing temperature of the barrel should be controlled to make it close to this temperature range. Granular plastic enters the barrel from the hopper and first reaches the feeding section, and then the feeding section Dry friction will inevitably occur. When these plastics are not heated enough and the melting is uneven, 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 becomes uneven , Will also cause increased wear.

(2) The speed should be adjusted properly. Because some plastics add oil strengthening agents, such as glass fibers, minerals or other fillers. The friction of these materials is often much greater than that of molten plastic. When injection molding these plastics, if a high rotational speed is used, while increasing the shearing force to the plastic, it will also cause the strengthening agent to produce more shredded fibers. The shredded fibers contain sharp ends. The wear force is greatly increased. When the non-polar minerals slide on the metal surface at high speed, it has a lot of scraping effect. So the speed should not be adjusted too high.

(3) To inspect the debris in the plastic. Generally speaking, there are no sundries in the original purchased plastic, but after transportation, weighing, drying, color mixing, especially the addition of recycled materials, there may be sundries. As small as metal scraps, as large as hot-ring nut paper clips, and even a bunch of warehouse keys, there are precedents that have been mixed into the barrel. The damage to the screw is indescribable (the barrel is also damaged at the same time), so , Must strictly manage and monitor the feeding.

(4) The water content in the plastic has a certain effect on the wear of the screw surface. If the plastic is not completely drained of water before injection, when the residual water enters the compression section of the screw, it will transform into "steam particles" with high temperature and high pressure melted in the molten plastic. With the advancement of the injection molding machine screw during the injection process, From the chemical section to the screw head, these "steam particles" relieve pressure and expand during the injection process, just like tiny impurity hard particles, which cause friction and damage to the wall.

In addition, for certain types of plastics, under high temperature and pressure, moisture may become a catalyst that promotes the cracking of the plastic, producing harmful impurities that can attack the metal surface. Therefore, the drying work before plastic injection molding not only has a direct relationship with the quality of the parts, but also affects the working life of the screw. As mentioned earlier, in order to extend the working life of the screw, flame hardening and nitriding are usually used. However, because filled plastics and reinforced (glass fiber reinforced) plastics are commonly used daily, and individual plastics themselves are corrosive or highly abrasive, the life of these treated screws is still too short. In recent years, some new ones have been developed. The high-tech approach has greatly improved the situation.

The brief introduction is as follows: Using the plasma transfer method, hard materials such as nickel and cobalt alloys are injected into the plasma arc in powder form, and then melted and coated on the surface of the screw, which becomes a state of metal bonding, which is better than ordinary spraying. More solid. Use ion nitriding instead of gas nitriding, so that nitrogen and the metal on the screw have a chemical effect, forming a thin but uniform and harder coating. Since the cost of ion nitriding treatment is relatively cheap, and its wear life is 2 to 3 times that of commonly used hardening tools, it is often used for screws with smaller diameters. In addition, there is an ion insertion treatment method, the resulting injection molding machine screw has higher hardness and longer life.More about:Nitriding screw barrel Company