what is the force and strength of the screw of the injection molding machine?

Update:24 Aug 2021

The injection molding machine injects molten plastic into the mold, and the product becomes the product after cooling. It has a wide range of uses. Depending on the plastic, the place of use is also different. The injection molding machine is the most used processing machine in the plastics processing industry. Not only a large number of products can be directly produced by the injection molding machine, but it is also the key equipment that constitutes the injection stretch blowing process. So what is the force and strength of the screw of the injection molding machine?

Screw injection molding machine consists of 4 parts: injection device, clamping device, hydraulic drive and electrical control system. The injection device is composed of a barrel, an injection molding machine screw, a nozzle, a hopper, a metering device, a screw transmission device, an injection molding cylinder, and an injection seat moving cylinder. Its main function is to melt and plasticize the plastic uniformly, and then inject a quantitative amount of molten material into the injection mold under a certain pressure and temperature. Mold clamping device is also called mold clamping device. It is composed of a clamping cylinder, a movable template, a fixed template, a clamping mechanism, a tie rod, and a safety gate of a demoulding device. Its main function is to ensure that the mold is opened and closed according to the prescribed procedure and speed, and that there is sufficient clamping force to close the mold tightly.

When the screw of the injection molding machine is matched with the main shaft of the reduction box with a longer cylindrical surface, the screw of the injection molding machine can be used as a cantilever beam with one end fixed. The force state of the screw of the injection molding machine during the extrusion process can simplify the force of the screw: its own weight G; the torque M required to overcome the resistance of the material; the axial force P generated by the pressure of the material. The screw is generally scrapped due to long-term wear and the gap between the screw and the barrel is too large and cannot be extruded normally. However, there are also examples of damage caused by improper design or operation caused by working stress exceeding the strength limit. Therefore, the screw should also meet certain strength requirements. The dangerous section of the screw of the injection molding machine is generally at the smallest thread root diameter in the feeding section.

For the case of a floating connection between the tail of the screw and the main shaft of the reduction box, because the screw of the injection molding machine is floating in the barrel, the bending stress caused by the weight of the screw is equal to zero, so the calculation is only based on the compressive stress and shear stress of the screw. Because the bending stress caused by the weight of the screw is very small (the screw is full of materials), even in the former case, it can be omitted, so the two methods are actually the same. There is also a pure twist to estimate the screw diameter.

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