The molding process of the screw and barrel is: first a […]
The molding process of the screw and barrel is: first add granular or powdered plastic into the barrel, and turn the screw and heat the outer wall of the barrel to make the plastic into a molten state, and then the machine closes the mold and moves the injection seat forward to make the nozzle Close to the gate of the mold, and then pass pressure oil into the injection cylinder to push the screw forward, thereby injecting the melt into the closed mold with a lower temperature at a high pressure and a faster speed. After a certain time and Hold the pressure (also known as holding pressure), cool it to solidify and form, then the mold can be opened and the product can be taken out (the purpose of holding pressure is to prevent the backflow of the melt in the cavity, replenish the material in the cavity, and ensure that the product has a certain Density and dimensional tolerances).
The basic requirements of injection molding are plasticization, injection and molding. Plasticization is a prerequisite for realizing and ensuring the quality of molded products, and in order to meet the requirements of molding, injection must ensure sufficient pressure and speed. At the same time, due to the high injection pressure, a correspondingly high pressure is generated in the cavity (the average pressure in the cavity is generally between 20 and 45 MPa), so there must be a sufficient clamping force. It can be seen that the injection device and the clamping device are the key components of the injection molding machine.
The adjustment of the process in the screw and barrel production process is a necessary way to improve the quality and output of the product. Because the injection cycle itself is very short, if the process conditions are not well controlled, there will be an endless stream of waste. When adjusting the process, only change one condition at a time, and observe a few more times. If the pressure, temperature, and time are all adjusted together, it is easy to cause confusion and misunderstanding. If there is a problem, I don't know the reason. There are many measures and means for the adjustment process of the double alloy screw.
Screw and barrel characteristics
1. Wear resistance and long life;
2. High temperature resistance, no deformation under high temperature;
3. Corrosion resistance, the material is corrosive;
4. Good cutting performance;
5. High strength, can withstand large torque and high speed;
6. After heat treatment, the residual stress is small, and the thermal deformation is small.
Repair of screw barrel
(1) When the inner surface of the barrel is not severely worn or scratched, use oilstone or emery cloth to grind and polish on the lathe.
(2) When the inner surface of the barrel is severely worn, check the depth of the wear groove first, and calculate whether there is a heat-treated hard layer on the inner wall of the barrel after the wear layer is removed, and the surface of the inner hole of the barrel can be trimmed. After grinding, the inner surface roughness Ra of the barrel should not be greater than 1.6 um. The tolerance of the hole axis is precision processed according to GB1184-80 level 7. If there is no heat-treated hard layer on the inner surface of the barrel after the mold is repaired, it can be matched with the gold sleeve in the barrel, or centrifugal casting method can be used to cast a layer of cemented carbide on the inner wall of the barrel, which is used after machining and grinding.