Detailed introduction
27
2018
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07
How to choose a good quality injection molding machine screw
How to choose the screw of injection molding machine?
Injection molding machine plasticizing screw with conveying. To melt. Mix. Compression. Metering and exhaust functions. plays a very important role in plasticizing quality. It is the key factor affecting the quality of plasticization. The screw has several crucial parameters that affect the plasticizing quality. General in accordance with the following principles. selection of injection molding machine screw:
1. Screw diameter (D)
A. related to the required injection volume: injection volume = 1/4 * π * D2 * S (injection stroke) * 0.85, B. generally speaking. The screw diameter D is inversely proportional to the maximum injection pressure. It is proportional to the plasticizing ability.
2. Conveying section
a. Responsible for plastic transportation. Push and preheat. Preheating to melting point should be ensured, B. crystalline plastic should be long (e.g. POM.PA) followed by amorphous material (e.g. PS.PU.ABS). Shortest thermal sensitivity (e. g. PVC).
3. Compression section
a. responsible for plastic mixing. Compressed and pressurized exhaust. The raw material through this section has been almost completely melted. but not necessarily uniformly mixed, B. in this area. The plastic melts gradually. The volume of the screw groove must decrease accordingly. to correspond to the decrease in the geometric volume of the plastic. Otherwise, the material will not be pressed. Slow heat transfer. Poor exhaust, c. generally accounts for more than 25% of the working length of the screw. However, the compression section of the nylon (crystalline material) screw accounts for about 15% of the screw working length. High viscosity. Fire resistance. Low conductivity. High additives such as plastic screw. 40% // 50% screw working length. PVC screw can account for 100% of the working length of the screw. to avoid intense shear heat.
4. Measurement section
A. generally accounts for 20 // 25% of the working length of the screw. Ensure that the plastic is all melted and the temperature is uniform. The mixing is uniform, B. the metering section is long, and the mixing effect is good. Too long is easy to make the melt stay too long and produce thermal decomposition. Too short is easy to make the temperature uneven, c.PVC and other heat-sensitive plastics should not stay too long. to avoid thermal decomposition. A shorter metering section or no metering section can be used.
5. Feed groove depth. Metering groove depth
a. The deeper the feed groove depth. the greater the transport volume. But need to consider the screw strength. The shallower the depth of the metering screw groove. The plasticizing heat. The higher the mixing performance index. However, if the depth of the metering groove is too shallow, the shear heat increases. Increased autogenous heat. The temperature rise is too high, causing discoloration or scorching of the plastic. Especially not conducive to heat-sensitive plastics, B. metering groove depth = KD =(0.03/0.07)* D. D. increase. Then k chooses a small value.
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