The basic working principle of the injection molding machine can be understood as the plastic material is uniformly plasticized in the cylinder, and then the injection molded product is obtained through injection, liquid filling, pressure holding, and cooling. Under the action of the barrel screw of the injection molding machine, the granular plastic stored in the funnel continuously moves along the screw groove. Due to the combined action of the heating outside the barrel and the shear of the barrel screw of the injection molding machine, the plastic is continuously heated and softened, forming a viscous flow state of the melt, and the melting force of the screw head pushes the screw back. Adjust the screw oil return speed by changing the screw back pressure (working oil return resistance), change the plastic flow state in the screw groove of the injection molding machine barrel, and achieve the purpose of controlling the plasticization performance of the plastic.
Commonly used materials and material requirements for barrel and screw of injection molding machine:
Commonly used and common materials for the barrel and screw of an injection molding machine are No. 45 steel, 40Cr, nitrided steel, and 38CrMOAl. The following describes the performance requirements of these materials one by one, as follows:
1. No. 45 steel is relatively cheap, cost-effective, and has good processing functions. The only shortcoming is: poor wear resistance and corrosion resistance.
2. The function of 40Cr is stronger than that of No. 45 steel, but we must often coat it with a layer of chromium to improve the corrosion resistance and wear resistance of the barrel and screw of the injection molding machine. However, it has higher requirements for the chromium plating layer. If the plating layer is too thin, it is easy to be worn, and if it is too thick, it is easy to peel off. After peeling, it will accelerate its corrosion. Therefore, it is currently used less.
3. The comprehensive functions of nitrided steel and 38CrMoAl are relatively excellent, and their application functions are also relatively extensive. Generally, the nitride layer reaches 0.4-0.6 mm. However, the ability of this material to resist corrosion is relatively low, and the price is relatively expensive.
The barrel screw of the injection molding machine is operated under high temperature, certain corrosion, strong wear and large torque. Therefore, the barrel screw of the injection molding machine must meet the following requirements:
1. High temperature resistance, no deformation under high temperature;
2. Wear resistance and long life;
3. Corrosion resistance, the material is corrosive;
4. High strength, can accept high torque and high speed;
5. Has a good cutting function;
6. After heat treatment, the residual stress is small, and the thermal deformation is small.