1. Measures taken in the design and manufacture of the machine to reduce the wear of the screw and barrel

The geometry of the screw is designed according to the specific application. If the operating conditions are normal and meet the operating requirements, it should be able to achieve gentle processing of different materials and a long service life of the screw and barrel. In order to reduce the wear of the screw and barrel, corresponding measures have been taken in the design and manufacture of the machine. Through continuous improvement, the geometric design of the screw can be adapted to different, newer and higher requirements.

2. Measures to be taken to reduce the wear of the screw and barrel in terms of process parameters and operations

(1) Packing

In order to reduce the production cost of PVC pipes, profiles and pellets, calcium carbonate is increasingly used in formulations. The wear caused by calcium carbonate is mainly abrasive wear, especially when the addition amount is large (>8 parts), the wear will be very serious. The quantity and quality of calcium carbonate have a great influence on the degree of wear.

Unreasonable amount of lubricant added in the formula (excessive amount of external lubricant, such as organic wax or stearic acid) will slow down the plasticization process and accelerate the wear process.

The above points should be paid attention to when using, and the damage to the equipment should be minimized.

(2) Processing of recycled materials

For the guided rotating twin screw, the material is conveyed in the axial direction, similar to the situation of a pair of calendering rollers (calendering effect). The screw is subjected to upward and outward forces, and the screw is pushed to the barrel, causing the screw and barrel to wear. This is a common phenomenon, but it is more prominent when processing materials. It is conceivable that the above-mentioned force is proportional to the size of the recycled material (hard particles) and the particle size is the main factor affecting the degree of wear of the screw and barrel. The larger the particles, the more severe the wear. When processing recycled materials, the particle size of recycled materials should be as small as possible.

(3) Processing of hard PVC pellets

The particle size of the pellets has basically the same effect as the particle size of the recycled materials. The main difference between the two is that the shape and size of the pellets are more uniform than the recycled materials, and the "hard particle effect" brought by the similar density and geometric shape is basically the same. Therefore, the particle size of the processed pellets should also be as small as possible.

Good plasticization of the material can reduce any unfavorable factors that cause the screw and barrel to wear to a minimum. Therefore, all measures that can promote and optimize the degree of plasticization of materials are worth recommending and adopting. The following points are important:

1) The extruder should always be in a good state of maintenance, especially the temperature control function of the plasticizing unit should be normal. In order to ensure this condition, thermocouples, temperature controllers, heating fins, heat transfer pumps and heat exchangers should be checked regularly, and the above components should be repaired and replaced if necessary. Only when all the functions of the extruder are normal and the temperature of each point can be accurately set, the high quality of the product and the long-term service life of the screw and barrel can be obtained.

2) The formula must be selected correctly, including lubricants, and appropriate blending. Avoid using excessive external lubricants, especially when stearic acid is used for coating. As mentioned earlier, excessive external lubricant affects plasticization. Poor plasticization is easy to detect. In most cases of poor plasticization, the powder will be sucked out through the vent.

3) The screw should be filled as much as possible to ensure the best function.

4) The temperature distribution should be set so that the material in the area where the exhaust hole is located can reach the required degree of plasticization, because if the density in the exhaust area is too low, the powder will be sucked out from the exhaust hole.

5) The torque of the main drive should be as large as possible. The high torque indicates that the plasticization of the extrudate is good, even if the torque reaches 95%, it will not cause any damage to the extruder.