The screw of injection molding machine plays an important role in plasticizing quality. It has the functions of conveying, melting, mixing, compression, measurement and exhaust, which is the key factor affecting the plasticizing quality.So how to choose the screw of the standard is particularly important, below, give you a few important parameters for your reference.
1. Screw diameter (D) is related to the amount of injection required: injection volume =1/4* * * *D2*S (injection stroke) *0.85;
2. The diameter (D) of the screw is inversely proportional to the maximum injection pressure, which is directly proportional to the plasticizing capacity;
3. Be responsible for the transportation, pushing and preheating of plastic, and ensure the preheating to melting point;
4. Suitable length of crystalline plastics (such as POM and PA);Non-crystalline materials (such as PS, PU, ABS);Minimum heat sensitivity (e.g. PVC);
5. Responsible for the mixing, compression and pressure exhaust of plastics, through which the raw materials of this section are almost completely fused, but they are not necessarily uniformly mixed;
6. When the plastic melts gradually, the volume of the spiral groove must be reduced correspondingly to reduce the geometrical volume of the plastic; otherwise, the material pressure is not solid, the heat transfer is slow, and the exhaust is poor.
7,Compression section generally accounted for more than 25% of the screw working length, but the nylon screw accounted for about 15% of the section, high viscosity, high fire resistance, low conductivity, additives, such as plastic screw accounted for about 40%, PVC screw can be accounted for 100% of the proportion, lest produce intense shear heat.
8, measuring long mixing effect is good, is too long, easy to melt thermal decomposition stay too long, too short, easy to make uneven temperature, generally about 20% proportion, ensure that all plastic melt and uniform temperature, mixing evenly;
9. Thermal sensitive plastic, such as PVC, should not stay too long to avoid thermal decomposition.
10, feed screw groove depth the deeper, the larger the throughput, but need to consider the screw strength, metering screw groove depth is shallow, the plasticizing fever, mixing performance index is higher, but the measuring screw groove depth is too shallow shear heat increase, authigenic heat increases, the temperature is too high, cause plastic discoloration or burnt, especially bad for heat-sensitive plastic.
It can be said that the screw is the heart of the injection molding machine, the quality of the screw determines the quality of the products.