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How much is the gap between the screw and the barrel of a single screw device su​itable?

Jan 19, 2018

The combined working quality of the two parts of the screw and the barrel has an important influence on the plasticization of the material, the quality of the products and the efficiency of production. The quality of their work is related to the manufacturing precision and the assembly gap of the two parts. When the two parts are badly worn and the output of the extruder drops, the maintenance of the screw and the cylinder should be arranged.

1. The cause of the damage of the screw and the cylinder

1, the rotation of the screw in the cylinder and the friction between the material and the two will make the working surface of the screw and the cylinder gradually wear away: the diameter of the screw gradually shrinks and the diameter of the bore of the barrel increases. In this way, the diameter gap between the screw and the cylinder is increased with the gradual wear of the two. However, due to the resistance of the front head and the diffuser plate of the barrel has not changed, this increases the leakage flow when the extruded material is advancing, that is, the flow volume increases from the diameter gap to the feed direction. The result makes the production of the extruder drop. This phenomenon also causes the material to stay in the cylinder to increase the residence time and cause the material to decompose. If it is polyethylene, the decomposition of the hydrogen chloride gas strengthens the corrosion of the screw and the cylinder.

screw2-kalshine.png2. The material, such as calcium carbonate and glass fiber, can accelerate the wear of the screw and the cylinder.

3, because the material has no uniform plasticizing, or metal contamination material, so that the rotation of the screw torque suddenly increases, the torque exceed the strength limit of the screw, the screw is broken. This is a kind of unconventional accident damage.

Two, the repair of screw

The broken screw 1, according to the actual diameter of the barrel to consider, made according to new screw diameter deviation of normal clearance and cylinder are given.

2. After the thread surface of the wear screw diameter is reduced, the wear-resistant alloy is heat sprayed and then machined to the size. This method generally has a professional spraying plant repair, the cost is still relatively low.

3. The wear-resistant alloy is surfacing in the thread part of the wear screw. The 1~2mm thickness is surfaced according to the degree of wear of the screw, and then the screw is grinding to the size. The wear-resistant alloys are made up of C, Cr, Vi, Co, W and B materials to increase the wear resistance and corrosion resistance of the screw. The cost of this kind of processing is very high in the professional surfacing plant. In addition to the special requirements, the screw is rarely used.

4, the repair screw can also be coated with hard chromium on the surface, and chromium is also a wear-resistant and corrosion resistant metal, but the hard chromium layer is easier to fall off.

From: Single Screw And Barrel