What are the characteristics of the injection screw of the injection molding machine

The plasticizing screw of the injection screw barrel for injection machine has the functions of conveying, melting, mixing, compressing, metering and exhausting, and plays an important role in the plasticizing quality.
First, several important geometric parameters of the screw:
1, screw diameter (D)
a, in relation to the required injection volume:
Injection volume=1/4*π*D2*S (injection stroke)*0.85;
b, Generally speaking, the screw diameter D is inversely proportional to the maximum injection pressure and proportional to the plasticizing ability.
2, conveying section
a, responsible for the transportation, pushing and preheating of the plastic, and it should be preheated to the melting point;
b, crystalline plastics should be longer (eg: POM, PA), followed by amorphous materials (eg: PS, PU, ​​ABS), and the shortest thermal sensitivity (eg: PVC).
3, compressed segment
a. Responsible for mixing, compressing and pressurized exhaust of plastics. Almost all the raw materials passing through this section have been melted, but they may not be uniformly mixed;
b. In this area, the plastic gradually melts, and the volume of the screw groove must decrease 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;
c, generally account for more than 25% of the working length of the screw, but the compression section of the nylon (crystalline material) screw accounts for about 15% of the working length of the screw, high viscosity, fire resistance, low conductivity, high additives and other plastic screws, accounting for 40% '50% screw working length, PVC screw can account for 100% screw working length, so as to avoid intense shear heat.
4, metering section
a, generally account for 20'25% of the working length of the screw, to ensure that the plastic is fully melted and the temperature is uniform, and the mixing is uniform;
b. If the metering section is long, the mixing effect is good. If it is too long, the melt will stay for too long and cause thermal decomposition. If it is too short, the temperature will be uneven.
c, PVC and other heat-sensitive plastics should not stay for too long to avoid thermal decomposition, and a shorter metering section or no metering section can be used.