Screw is an important part of injection molding machine. Its role is to transport, compaction, melt, stir and pressure plastics. All of these are accomplished through the rotation of the screw in the barrel. During the rotation of the screw, the plastic can produce friction and mutual movement between the inner wall of the cylinder, the bottom of the screw, the propeller, and the plastic and plastic. The moving forward of plastic is the result of this combination, and the heat generated by friction is also absorbed to raise the plastic temperature and melt the plastic. The design structure of the screw will directly affect the degree of these effects.
Injection molding machine screw is long time in high temperature, high pressure, high mechanical torque and high grinding environment work, loss is inevitable. Even if the injection molding machine screw has undergone various surface treatment, from quenching to nitriding, boronizing to spraying, to double alloy spraying, it seems that the quality of the screw itself has improved a lot.
But in actual production, why is life so different? The same injection molding machine screw can be used for 8 years, some can only be used for 2 months, also is the injection molding machine screw to make iron gap so big.
Screw section description.
The injection molding machine screw generally can be divided into the charging section, the compression section, the homogenized section (also known as the metering section). (note: the ratio of the three segments is different, the screw groove is different, and the diameter of the screw is different.)
(1) description of feeding section: this segment is deeply fixed, and its function is to preheat and push the plastic solid. It is necessary to ensure 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 tapered screw, and its function is the melting, mixing, shear compression and pressure exhaust of plastic raw materials. The plastic will dissolve completely in this section, the volume will shrink, and the design of compression ratio is very important.
(3) the homogenization section: this section for screw fixed screw groove groove depth, its main function is mixed, melt conveying, metering, must also provide enough pressure, maintain stability of the melt temperature and the flow of the molten plastic.
The key of the screw life of the injection molding machine is the use and maintenance. The following use and maintenance principles are available for reference:
1) when the injection molding machine is started, the injection should be fully preheated. After the cylinder reaches the preset temperature, Φ continue under 60 mm heat preservation for 15 minutes. After 30 minutes, start the motor and start the screw.
2) the material should match the screw. Especially corrosive materials and hard materials, such as PVC, flame retardant materials, glass fiber added materials to use professional screw, avoid common screw.
3) if the common machine USES corrosion material, it will be replaced by the cleaning of the stable materials such as HDPE and HIPS for the first time after use.
4) if the common machine occasionally USES fiberglass, be sure to use high temperature, low screw speed and low back pressure.
5) no matter what kind of material, as far as possible need not temperature limit production, can also make production such as PC material 250 degrees, barely can do ABS in 185 degrees, but the screw is not good, because need large torque, and badly worn. At the same time, if the lower limit problem must be used low screw speed.
6) shut down the feeding port and clean the material inside the feeding tube for more than half an hour, and set up the insulation.
7) avoid the foreign body falling into the material barrel to damage the screw and barrel. Prevent metal debris and debris from falling into the hopper. If the material is processed, magnetic hopper should be added to prevent iron filings from entering the feeding tube.
8) make sure that the plastic in the material tube is completely melted when using the saliva, so as not to damage the parts of the transmission system when the screw is back.
9) avoid the phenomena such as idling and skidding.
10) when using the new plastic, the material should be cleaned. Use POM, PVC, PA+GF and other materials to reduce the degradation of raw materials as far as possible. After shutdown, clean the materials with ABS and other water materials.
11) avoid the mixing of POM and PVC at the same time, which will cause serious industrial accidents at melting temperature.
12) when the melting plastic temperature is normal, and it is found that the molten plastic appears black or discoloration, check whether the rubber screw stop ring (over the rubber ring and muon) is damaged.