Several important geometric parameters of the extruder screw


1, screw diameter (D) a, related to the required inject […]

1, screw diameter (D)
a, related to the required injection volume:
Injection volume = 1/4 * π * D2 * S (injection stroke) * 0.85; b, in general, the screw diameter D is inversely proportional to the highest injection pressure, and is proportional to the plasticizing ability.
2. Conveying section
a, responsible for the transportation of plastic, pushing and preheating, should ensure preheating to the melting point;
b, crystalline plastics should be long (such as: POM, PA) amorphous materials (such as: PS, PU, ​​ABS), the heat sensitivity is the shortest (such as: PVC).
3, the compression section
a. Responsible for the mixing, compression and pressurization of plastics. The raw materials through this section have been almost completely melted, but not necessarily uniformly mixed. b. In this area, the plastic gradually melts and the volume of the groove must be reduced accordingly. Corresponding to the decline of the geometric volume of the plastic, otherwise the material pressure is not real, the heat transfer is slow, and the exhaust gas is poor;
c, generally accounted for more than 25% of the screw working length, but the compression section of the nylon (crystalline material) screw accounts for about 15% of the screw working length, high viscosity, fire resistant
Plastic screw, such as sex, low conductivity and high additive, accounts for 40% 50% of the screw working length, and PVC screw can account for 100% of the screw working length, so as to avoid intense shear heat.
4, metering section
a, generally accounted for 2025% of the screw working length, to ensure that the plastic is fully melted and the temperature is uniform, evenly mixed;
b. The length of the metering section is good for mixing. If it is too long, the melt will stay too long and cause thermal decomposition. If it is too short, the temperature will be uneven. c. The heat-sensitive plastics such as PVC should not stay too long to avoid thermal decomposition. , can use shorter metering segments or do not meter segments.
5, feed screw groove depth, metering groove depth
a. The deeper the depth of the feed screw groove, the larger the conveying volume, but the screw strength should be considered. The shallower the metering groove depth, the plasticizing heat and the higher the mixing performance index, but the metering groove depth is too shallow. The heat increases, the self-generated heat increases, and the temperature rise is too high, causing plastic discoloration or charring, especially for heat-sensitive plastics;
b. Metering groove depth = KD = (0.03.07) * D, D increases, then K selects a small value.