Extruder Screw Barrel
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extruder screw barrel
The screw barrel has the conveying, melting, mixing, compression, metering and exhaust functions. It plays a very important role in the quality of plasticization. It is a key factor affecting the quality of plasticization.
There are several critical parameters which effect the quality of plasticization. Normally we choose the injection molding machine screw barrel according with the following principles:
1, screw diameter (D) :
a, related to the required injection quantity: injection volume = 1 / 4 * π * D2 * S (injection stroke) * 0.85;
b, in general, screw diameter D and maximum injection pressure is inversely proportional, and proportional to the plasticizing capacity;
2, conveying section
a, to be responsible for conveying, pushing, compressing and preheating the plastic, the plastic temperature shall be guaranteed to the melting point;
b, the screw of crystalline plastics should be long (eg: POM, PA) ; the following by amorphous materials (such as: PS, PU , ABS) , the shortest heat-sensitive (eg: PVC) .
3, compression section
a, to be responsible for plastic mixing, compressing and exhausting, through this section of the raw materials shall have been almost completely melted, but not uniformly mixed completely;
b, In this region, the plastic shall be gradually melted, the spiral groove volume shall be decreased corresponding to the decline in the volume of plastic geometric, otherwise, the material pressure can be reached the point, heat exchanged is slow, and the exhaust vented is bad;
c, usually accounts for more than 25% of the working length of screw, but the nylon (crystalline material) of the compression screw section is about accounted for 15% of the screw working length, high-viscosity, fire resistance, low conductivity, high-additives such as plastic screw, accounting for 40%--50% screw working length, PVC screw can account for 100% screw working length to avoid the fierce heat of the shear.
4, measurement section:
a, usually accounts for 20%--25% screw working length to ensure that all the molten plastic as well as temperature uniformity, mixing evenly;
b, the more measurement section, the better the compounding effect, but too long, the material will be easy to decompose because of the too high temperature, but too short, the material will be easy to make the temperature non-uniform.
c, PVC and other heat-sensitive plastic should not stay too long in order to avoid thermal decomposition, the measurement section can be shorter or not to be used.
5, the screw groove depth for feeding, the depth of spiral groove for measurment:
a, the deeper the feeding groove, then the greater the throughput, but considering screw strength, the shallower the depth of the measuring groove, then the higher the plasticizing fever and the mixed Performance Index, but too shallow that the the depth of measuring spiral groove cutting-heat will be increased, since the heat increased, temperature is too high, causing discoloration or burning plastic, in particular, is not conducive to heat-sensitive plastic.
Standards of Injector cylinders and screw barrel
The size of cylinder and screw injection machine
25-38000KN clamping force
30g-50000g shot weight
according different plastic material choice different
screw and nozzle
Single screw barrel of extruders and injection machine with
Extruder cylinder / sctew size15-360mm
According different matertal and plastic product to design different screw with compress rate and L/D and form
According different matertal and plastic product to design different cylinder with exhaust system and IKV force load system