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

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

2. Measures to reduce the wear of the screw barrel in the process parameters and operation

(1) Packing

In order to reduce the production costs of PVC pipes, profiles and granules, calcium carbonate is increasingly used in formulas. The wear caused by calcium carbonate is mainly due to abrasive wear, especially when the amount of addition is large (>8 parts). The amount and quality of calcium carbonate have a great influence on the degree of wear.

The amount of lubricant added to the formulation is unreasonable (external lubricants such as organic wax or stearic acid are added too much) will slow down the plasticization process and accelerate the wear process.

The above points should be taken into consideration when using and minimize the damage to the equipment.

(2) Recycled materials processing

For guided twin screws, the material is conveyed in the axial direction, similar to the case of a pair of calendering rolls (calendering effect), the screw is subjected to an upward and outward force, and the screw is pushed toward the barrel causing the screw and the barrel to wear. This is a common phenomenon, but it is even more prominent when processing materials. It can be imagined that the above-mentioned force proportional to the size of the regrind (hard particle) particle is the main influence factor of the degree of wear of the screw barrel. The larger the particles, the more severe the degree of wear. When processing regrind, the regrind size should be as small as possible.

(3) Processing of hard PVC pellets

The particle size of the granules is basically the same as the effect of adding back the material size. The main difference between the two is that the pellets are more uniform in shape and size than the recycled materials, and the "hard particle effect" brought about by the similar density and geometry 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 cause any adverse effects on the wear of the screw barrel to be minimized. 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. In particular, the temperature control function of the plasticization unit should be normal. In order to ensure this condition, thermocouples, temperature controllers, heaters, heat transfer pumps, and heat exchangers should be inspected on a regular basis. Repairs and replacements of the above-mentioned components should be made when necessary. Only when all the functions of the extruder are normal and the temperature at each point can be accurately set, can the high quality of the product and the long service life of the screw barrel be obtained.

2) The recipe must be properly selected, including lubricants, and appropriate blending should be performed. Excessive external lubricants should be avoided, especially when coated with stearic acid. As already mentioned, external lubricants have an excessive effect on plasticization. Poor plasticization is easy to find. In most cases of poor plasticization, the powder will be sucked through the vent.

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

4) The temperature distribution should be set so that the required degree of plasticity can be achieved in the area where the exhaust hole is located, because the density of the material in the exhaust area is too low to suck out the powder from the exhaust hole.

5) The main drive torque should be as large as possible. The high torque indicates that the plasticization of the extrudate is performing well, and even if the torque reaches 95%, there will be no damage to the extruder.