What is the basis for the selection of the barrel screw


First, the screw diameter (D) 1. In general, the screw […]

First, the screw diameter (D)
1. In general, the screw diameter D is inversely proportional to the high injection pressure of zui, and is proportional to the plasticizing power.
2. Correlation with the required injection volume: injection volume = 1/4 * π * D2 * S (injection stroke) * 0.85;
Second, the measurement section
1, PVC and other heat-sensitive plastics should not stay too long, so as to avoid thermal differentiation, a shorter metering section or no metering section.
2. The length of the metering section is good, and if it is too long, the melt will stay too long and the heat will be differentiated. If it is too short, the temperature will be uneven.
3, generally account for 20'25% of the screw working length, to ensure that the plastic is fully melted and the temperature is average, mixing average;
Third, the compression section
1. Responsible for the mixing, compression and pressurized exhaust of plastics. The raw materials through this section have been almost completely melted, but they will be evenly mixed;
2, generally accounted for more than 25% of the screw working length, but the compression section of nylon (crystalline material) screw accounted for about 15% of the screw working length, 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% of the screw working length, so as to avoid severe shear heat.
3. In this area, the plastic gradually melts, and the volume of the screw groove must be correspondingly reduced to correspond to the reduction of the volume of the plastic. Otherwise, the material pressure is not real, the heat transfer is slow, and the exhaust gas is poor;
Fourth, the feed screw groove depth, metering groove depth
1. The deeper the depth of the feeding groove, the larger the conveying volume, but the screw strength should be considered. The shallower the measuring groove depth, the higher the plasticizing fever and the inclusion function index, but the metering groove depth is too shallow. Increased heat, self-generated heat increases, temperature rise is too high, causing plastic discoloration or charring, especially helium in heat sensitive plastics;
2. The measurement groove depth = KD = (0.03 '0.07) * D, D increases, then K selects a small value.
Fifth, the conveying section
1. Responsible for the transportation, pushing and preheating of plastics, which should be preheated to the melting point;
2, crystalline plastics should be long (such as: POM, PA) amorphous materials (such as: PS, PU, ​​ABS), heat-sensitive zui short (such as: PVC).