Injection molding machine screw plays a decisive role in plasticizing quality. It has functions of conveying, melting, mixing, compression, metering and exhaust, and is a key factor influencing the quality of plasticization. So how to buy the standard screw is also very important, following it, we give you a few important parameters for your reference.
1. The screw diameter (D) is related to the required injection volume: Ejection volume = 1/4*π*D2*S (jetting stroke) *0.85;
2. The screw diameter (D) is inversely proportional to the maximum injection pressure and is proportional to the plasticizing ability;
3. responsible for the plastic transportation, pushing and preheating, should ensure that the preheating to the melting point;
4. crystalline plastics should be long (such as POM, PA); amorphous materials followed (such as PS, PU, ABS); the shortest heat-sensitive (such as PVC);
5. Responsible for the mixing, compression, and pressurization of plastics. The raw materials passed through this stage are almost completely melted, but not necessarily evenly mixed;
6. plastic gradually melting, screw groove volume must be reduced accordingly, in order to correspond to the decline in the geometric volume of plastic, otherwise the material pressure is not true, slow heat transfer, poor exhaust;
7. The compression section generally accounts for more than 25% of the working length of the screw, but this section of the nylon screw accounts for about 15%, plastic screws with high viscosity, fire resistance, low conductivity, high additives and so on account for about 40%, PVC screw can account for 100%. The proportions in order to avoid intense shear heat.
8. the metering section length is good mixing effect, too long is easy to make the melt stay too long and produce thermal decomposition, too short is easy to make the temperature uneven, generally accounting for about 20% ratio, to ensure that the plastic melts all and temperature uniformity, Mix evenly;
9. PVC and other heat-sensitive plastics should not stay too long, so as to avoid thermal decomposition, can use a shorter measurement section;
10. The deeper the depth of the feed screw groove, the greater the amount of transport, but the screw strength needs to be taken into account. The shallower the depth of the metering screw groove, the higher the plasticizing heat and mixing performance index, but the shallower the measuring screw groove depth Heat increases, autogenous heat increases, temperature rises too high, causing discoloration or scorching of plastics, which is particularly detrimental to heat-sensitive plastics.
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 product.