When extruding thermoplastic from plastic sheet production equipment, the design of the screw and the structure of the screw and barrel are very important.
If you consider these things in advance, you can ensure the successful completion of the processing of thermoplastic composites. Most screws used for thermoplastic extrusion are mainly used for feeding, plasticizing, and extrusion.
Generally speaking, the feeding part of the screw is used to transport solid particles. Compared with those thermoplastics without fillers, the conveying section of the screw in thermoplastic composites is very different in structure, which is mainly affected by the relative friction coefficient of solid particles.
The following article will explain in detail.
Generally, a very important economic factor that the geometric structure and shape of the screw can affect the plasticizing effect is the volume compression rate, which mainly depends on the continuous change of the volume of the conveying section or barrier section. In addition to the depth of the plasticizing section of the screw, the flow gap at the safety barrier should be fully considered for the barrier screw used in thermoplastic composite building materials.
We must consider the wear of screw and barrel in processing thermoplastic composite structural materials. If the volume compressibility of thermoplastic composite building materials is not optimistic, then there will be obvious wear and tear phenomenon at the root of the screw. Different fillers will cause different wear, which occurs in different development areas of the screw.
The wear caused by such fillers as mica and glass fiber mainly occurs in the feeding section of the screw. Generally, in this case, the wear begins to appear continuously in the third and fourth rings of screw edges and will extend to the third, fourth, and fifth rings of screw edges in the conveying section, especially on the side of the force that is easy to promote the material flow.
Most of the wear occurs in our areas because the screw passes through the resin in these areas as pellets and the composite structure material is close to the outer surface of the pellets, causing serious wear to the unprotected screw root. Once the resin can start to melt, a film produced between the molten resin will lubricate the activities of the area at the root of the ball and screw.
A low-cost method to reduce the wear of the screw root of plastic plate production equipment is to nitrify the screw so that the hardening depth of the root and flow surface can reach 0.015 ー 0.0201 m (1in = 25.4 mm), and the hardness can reach 60RC, but its thickness is only 0.015 ー 0.020 in. At the appointed time, it will slowly disappear like a knife through bread. The problem is that the operator does not know when this will happen unless the screw is regularly pulled out of the extruder and checked. Generally speaking, this kind of wear can be repaired. The only problem is that there are many pinholes where the newly welded material contacts the original nitrided substrate. These pinholes are
caused by nitrogen "boiling" on the metal substrate during welding. At present, there is basically no way to prevent the formation of these pinholes. However, they do not affect the performance of the screw, except for the appearance of the screw.
The specific analysis reasons for screw wear of plastic plate production technology equipment and the methods that can reduce the wear have been systematically explained in detail in this paper. When you use this equipment, you should pay more attention to the maintenance operation in this regard, so as to ensure the operation effect and production quality of the equipment, and timely and effectively solve the wear situation.