Screw is an important part of injection molding machine. Its function is to transport, compact, melt, mix and pressure plastics. All this is accomplished by the rotation of the screw in the barrel. When the screw rotates, the plastic will cause friction and mutual movement to the inner wall of the barrel, the bottom surface of the screw groove, the screw edge advancing surface and the plastic and plastic.

The advance of plastics is the result of this combination of motion, and the heat generated by friction is also absorbed to increase the temperature of plastics and melt plastics. The design structure of the screw will directly affect the degree of these effects.

The screw of injection molding machine works under high temperature, high pressure, high mechanical torque and high friction environment for a long time, and the loss is inevitable. Even though the screw of the injection molding machine has undergone various surface treatments, from quenching to nitriding, boronizing to base spraying, to double-alloy splashing, it seems that the quality of the injection molding screw itself has been improved a lot.

But in actual production, why is the life difference so big? Some factories can use the same injection molding machine screw for 8 years, and some can only use it for 2 months. What is the gap between the same injection molding machine screw and iron.

Screw segment description

Generally, the screw of injection molding machine can be divided into feeding section, compression section and homogenizing section (also called metering section).

Note: The ratio of three segments of different screws is different, the screw groove depth is different, and the transition form of screw bottom diameter is different)

(1) Description of feeding section: the depth of screw groove in this section is fixed, and its function is to be responsible for preheating and plastic solid conveying and extrusion. It must be ensured that the plastic begins to melt at the end of the feeding section.

(2) Description of compression section: this section is the depth of the screw groove of the reducing screw, and its function is the melting, mixing, shearing compression and pressurized exhaust of plastic raw materials. The plastic will be completely dissolved in this section, and the volume will be reduced. The design of compression ratio is very important.

(3) Description of homogenization section: this section is the fixed depth of screw screw groove, and its main functions are mixing, melt conveying and metering. It must also provide sufficient pressure to maintain the uniform temperature of melt and stabilize the flow of melt plastic.

The key to the life of injection molding machine screw is use and maintenance. The following use and maintenance principles can be used for reference:

1) When the injection molding machine is started, the injection molding shall be fully preheated. After the barrel reaches the preset temperature, Φ Keep the temperature below 60mm for another 15 minutes. After the above 30 minutes, start the motor to start the screw related action.

2) The material and screw should match. Especially for corrosive materials and hard materials, such as PVC, flame-retardant materials and glass fiber materials, professional screw shall be used, and ordinary screw shall be avoided.

3) If ordinary machine corrosive materials are used, they must be cleaned and replaced with stable materials such as HDPE and HIPS at the first time after use.

4) If the ordinary machine occasionally uses glass fiber material, be sure to use high material temperature, low screw speed and low back pressure, and remember.

5) No matter what kind of material, try not to use the lower temperature limit for production. For example, PC material can be produced at 250 ℃ and ABS material can be produced at 185 ℃. However, it is not good for screw because it requires large torque and is seriously worn. At the same time, if the lower limit must be used, the lower screw speed should be used.

6) If the machine is shut down for more than half an hour each time, the blanking port shall be closed, the material in the material barrel shall be cleaned, and thermal insulation shall be set.

7) Avoid foreign matters falling into the barrel and damaging the screw and barrel. Prevent metal chips and sundries from falling into the hopper. If processing recycled materials, magnetic hopper shall be added to prevent iron chips from entering the barrel.

8) Make sure that the plastic in the barrel is completely melted when using anti-slipping, so as not to damage the parts of the transmission system when the screw moves backward.

9) Avoid screw idling and slipping.

10) When using new plastic, clean the residual material of the material barrel. When using POM, PVC, PA+GF and other materials, reduce the degradation of raw materials as much as possible, and wash them with ABS and other nozzle materials in time after shutdown.

11) Avoid mixing POM and PVC into the barrel at the same time, which will react at the melting temperature and cause serious industrial problems

accident.

12) When the temperature of the molten plastic is normal but it is found that the molten plastic has black spots or discoloration, check whether the rubber screw check ring seat (through the rubber ring and meson) is damaged.