What determines the quality of the screw of the injection molding machine?


1. The screw diameter (D) is related to the requested i […]

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 maximum injection pressure, and proportional to the plasticizing ability;

3. The crystalline plastic should be long (such as POM, PA); the amorphous material is second (such as PS, PU, ​​ABS); the heat sensitivity is the shortest (such as PVC);

4. Responsible for the mixing, compression and pressurization of plastics. The materials passing through this section are almost completely melted, but they may not be evenly mixed;

5. Responsible for the transportation, pushing and preheating of the plastic, and ensure that it is preheated to the melting point;

6. If the metering section is long, the mixing effect will be good. If it is too long, it will cause the melt to stay too long and cause thermal screw barrel for injection molding machine decomposition. If it is too short, it will easily cause uneven temperature, which generally accounts for 20% of the dominant ratio to ensure that the plastic is fully melted and the temperature is uniform. Uniform mixing;

7. The plastic gradually melts, and the volume of the screw groove must be reduced accordingly to correspond to the decrease in the geometric volume of the plastic, otherwise the material will not be compacted, the heat transfer will be slow, and the exhaust will be poor;

8. The compression section generally accounts for more than 25% of the operating length of the screw, but this section of the nylon screw accounts for about 15%. The plastic screw with high viscosity, fire resistance, low conductivity, and high additions accounts for 40%, and the PVC screw can account for 100%. To avoid severe shear heat.

9. Heat-sensitive plastics such as PVC should not stay for too long to avoid thermal decomposition, and a shorter measurement period can be used;

10. The deeper the feed groove depth, the greater the delivery volume, but the strength of the screw needs to be considered. The shallower the metering groove depth, the higher the plasticizing heating and mixing function index, but the shallow metering groove depth means shearing Heat increases, self-generated heat increases, and the temperature rise is too high, resulting in plastic discoloration or scorching, which is particularly unfavorable for heat-sensitive plastics.