What determines the screw of injection molding machine?

1. The screw diameter (d) is related to the requested injection volume: injection volume = 1 / 4 * π * D2 * s (injection stroke) * 0.85;

2. The screw diameter (d) is inversely proportional to the highest injection pressure and directly proportional to plasticization;

3. Crystalline plastics should be long (such as POM, PA); amorphous materials (such as PS, PU, ABS); thermal sensitivity is the shortest (such as PVC);

4. In charge of mixing, compression and pressure exhaust of plastics, almost all materials in this section are melted, but not necessarily evenly mixed;

5. Be responsible for the transportation, extrusion and preheating of plastics, and ensure the preheating to the melting point

6. If the metering section is too long, the mixing effect will be good; if it is too long, the melt will stay for too long and break down; if it is too short, the temperature will be uneven, generally accounting for 20% of the control proportion, so as to ensure that the plastics are fully melted, the temperature is even and the mixing is even;

7. When the plastic melts gradually, it is necessary to reduce the volume of the screw groove to correspond to the decrease of the geometric volume of the plastic. Otherwise, the material pressure is not solid, the heat transfer is slow and the exhaust is poor;

8. Generally, the compression section accounts for more than 25% of the working length of the screw, but the nylon section accounts for about 15%, the plastic screw with high viscosity, fire resistance, low conductivity and high additive accounts for 40%, and the PVC screw can account for 100%, so as to avoid severe shear heat.

9. PVC and other thermosensitive plastics should not stay for too long to avoid thermal decomposition. A shorter measuring section can be used;

10. The deeper the feed screw groove is, the larger the delivery volume is. However, it is necessary to consider the screw strength. The shallower the metering screw groove is, the higher the plasticization heating and mixing function index is. However, if the metering screw groove is too shallow, the shear heat increases, the autogenous heat increases, and the temperature rise is too high, forming the plastic discoloration or burning, which is especially unfavorable to the thermosensitive plastic.

Screw is the heart of injection molding machine, the quality of screw determines the quality of injection molding products, so it is necessary to choose a good screw.