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Analysis of the principle of using and maintenance of injection molding machine screw


Analysis of the principle of using and maintenance of injection molding machine screw

Screw is an important part of injection molding machine. Its function is to transport, compact, melt, stir and press the plastic. All of this is done by rotating the screw in the barrel. When the scre
Screw is an important part of injection molding machine. Its function is to transport, compact, melt, stir and press the plastic. All of this is done by rotating the screw in the barrel. When the screw rotates, the plastic will cause friction and mutual movement between the inner wall of the cylinder, the bottom of the screw groove, the advancing surface of the screw and the plastic and plastic. The advance of the plastic is the result of this combination of motion, and the heat generated by friction is also absorbed to improve the plastic temperature and melt the plastic. The design structure of the screw will directly affect the extent of these effects.   
Injection molding machine screw is long time in high temperature, high pressure, high mechanical torque and high friction environment work, the loss is inevitable. Even though the injection molding machine screw has a variety of surface treatment, from quenching to nitriding, boronizing to spray low, to double alloy splashing, it seems that the injection molding to explain the screw itself quality has been improved a lot.
But in actual production, why is life span so different? The same injection molding machine screw plant can be used for 8 years, and some can only use 2 months, the same is the injection molding machine screw to do iron gap is so big?.  
Sectional description of screw
The injection machine screw can be divided into feeding section, compression section and homogenizing section (also called metering section) under the general condition. (Note: the ratio of the three segments of the screw is different, the screw groove depth is not the same, the screw bottom diameter transition form is not the same)
(1) the charging section shows that the groove is deep fixed, and its function is to be responsible for preheating and solid conveying and pushing of plastics. The plastic must be melted at the end of the feeding section.
(2) the compression section shows that this section is the tooth depth of the tapered screw groove, and its function is the melting, mixing, shearing, compression and exhaust of the plastic material. Plastic will dissolve completely in this section, volume will shrink, compression ratio design is very important.
(3) homogeneous section: this section is the fixed screw groove deep ditch, its main function is to melt mixing, transporting, metering, must also provide enough pressure to maintain uniform temperature and melt stability of molten plastic flow.
The key to the service life of injection molding machine screw is to use and maintain. The following usage and maintenance principles are available for reference:
1) injection molding machine start time, injection molding full preheating. After the material barrel reaches the preset temperature, the heat preservation is continued for 15 minutes under 60mm. After 30 minutes, start the motor and start the screw action.
2) material and screw to match. In particular, corrosive materials and hard materials, such as PVC, flame retardant materials, glass fiber reinforced materials to use professional screw, should not avoid ordinary screw.
3) if the ordinary machine with corrosion material must pay attention to use, after the first time with stable materials such as HDPE, HIPS and other cleaning replacement.
4) if the ordinary machine occasionally use glass fiber material, must pay attention to use high material temperature, low screw speed, low back pressure, remember to remember.
5) no matter what kind of material, as far as possible without temperature lower limit production, such as PC material 250 degree can also be produced, ABS can barely do at 185 degrees, but the screw is not good, because the torque is big, and wear seriously. At the same time, if the lower limit must be used, the screw speed should be used at low speed.
6) every time the machine stops for more than half an hour, it is necessary to close the blanking port, clean the inner material of the drum, and set up heat preservation. 7) avoid foreign objects falling into the material cylinder damage screw and cylinder. To prevent metal debris and debris into the hopper, if processing recycling material, it is necessary to add a magnetic hopper to prevent iron filings and other materials into the barrel.
8) when using the anti saliva, it is necessary to determine the complete melting of the plastic in the barrel, so as to avoid the damage of the transmission parts when the screw back.
9) avoid screw idling, slipping and so on.
10) when using new plastics, the remaining material of the cylinder can be cleaned. Use POM, PVC, PA+GF and other materials as much as possible to reduce the degradation of raw materials, after downtime, rinse with ABS and other nozzle materials.
11) avoid mixing POM and PVC at the same time, the reaction will occur at the melting temperature, resulting in serious industrial accidents.
12) when the melting plastic temperature is normal, but continuously found melting plastics appear black spots or discoloration, should check the rubber screw backstop ring seat (apron, meson) damage.