Common Materials Of Injection Molding Screw Barrel


    Injection Molding Screw Barrel is an important part of injection molding machine. Its role is to transport, compress, melt, mix and apply pressure to plastics. All of this is done by rotating the screws in the cylinder. When the injection screw rotates, the plastic will generate friction and mutual movement between the inner wall of the barrel, the bottom of the screw groove, the advancing surface of the screw edge and the plastic.

    The basic working principle of    injection molding machine can be understood as plasticizing the plastic material uniformly in the cylinder, and then obtaining injection molded products through injection, liquid filling, pressure holding, and cooling. Under the action of the injection screw, the granular plastic stored in the funnel moves continuously along the screw groove. Due to the combined action of the heating outside the barrel and the shear of the injection screw, 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 injection screw groove, and achieve the purpose of controlling the plasticization performance of the plastic.

       Commonly used materials and material requirements for injection screws:

      The commonly used and common injection screw materials are No. 45 steel, 40Cr, nitrided steel and 38CrMOAl. The following describes the performance requirements of these materials one by one, as follows:

       1, 45 steel is relatively cheap, cost-effective, and processing functions are good, the only shortcoming is: poor wear resistance and corrosion resistance.

      2, 40Cr has stronger functions than 45# steel, but we often have to coat it with a layer of chromium to improve the corrosion resistance and wear resistance of the injection screw. 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 wide. 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 injection screw is operated under high temperature, certain corrosion, strong wear and high torque. Therefore, the injection screw must meet the following requirements:

      1, high temperature resistance, no deformation under high temperature;

      2, wear resistance, long life;

      3, corrosion resistance, the material is corrosive;

      4, high strength, can accept large torque, high speed;

      5, has a good cutting function;

       6. After heat treatment, the residual stress is small, and the thermal deformation is small.

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