Barrel screw has several critical parameters affecting […]
Barrel screw has several critical parameters affecting the plasticizing quality, generally in accordance with the following principles to choose the barrel screw:
I. Screw diameter (D)
1, in general, screw diameter D is inversely proportional to the maximum injection pressure, and is proportional to the plasticizing ability.
2, and the required injection volume: injection volume =1/4*π*D2*S (injection stroke) *0.85;
Two, measurement section
1, PVC and other heat-sensitive plastics should not stay too long to avoid thermal differentiation, can be used in a short measuring section or do not measure the section.
2, the measuring section is long, the mixing result is good, too long is easy to make the melt stay too long and thermal differentiation, too short is easy to make the temperature is not average;
3, generally account for 20'25% of the working length of the screw, to ensure that all plastic melting and average temperature, average mixing;
Three, compression section
1. Responsible for mixing, compression and pressurized exhaust of plastics. The raw materials have nearly all melted through this section, but there will be average inclusion.
2, generally account for more than 25% of the working length of the screw, but nylon (crystalline material) screw compression section accounts for about 15% of the working length of the screw, high viscosity, fire resistance, low conductivity, high additives and other plastic screw, accounted for 40%'50% of the working length of the screw, PVC screw can account for 100% of the working length of the screw, so as to avoid severe shear heat.
3. In this area, the plastic is gradually melting, and the volume of the spiral tank must be reduced accordingly, so as to reduce the volume of the corresponding plastic, otherwise the material pressure is not solid, the heat transfer is slow, and the exhaust is poor;
4. Depth of feeding screw groove, measuring screw groove depth
1, feed the deeper the screw groove depth, the greater the throughput, but need to consider the strength of the screw, measuring the depth of the screw groove is shallower, the higher the plasticization fever, inclusion function index, but measuring the depth of the screw groove is too shallow shear heat increase, self-generated heat increase, the temperature rise is too high, causing plastic discoloration or burning, especially bad for heat sensitive plastics;
2. The depth of measuring screw groove =KD= (0.03'0.07) *D, and the value of K is small if D increases.
V. Conveying section
1, responsible for plastic transportation, extrusion and preheating, should ensure preheating to melting point;
2, crystalline plastic should be long (such as: POM, PA) amorphous materials (such as PS, PU, ABS), the shortest heat sensitivity (such as: PVC).