Extruder screw, barrel causes of damage and repair methods

Screw and extruder barrel is the most important part. Quality of their work with the precision of two parts manufacturing, assembly space related. When the two parts wear badly worn extruder production dropped, it should carry out repairs.
Abstract...Articles section First, the causes of damage to the screw and barrel
1, screw in the machine barrel rotation, friction between the two materials and to make screw and barrel work surface gradually wear: Screw diameter gradually reduced, the inner barrel diameter gradually increased. As the cylinder head and manifold resistance has not changed. This increases the material being extruded forward leakage flow, that is, the material directly from the diameter of the gap at the direction of flow of the feed increased, resulting in counter-current phenomenon. Result extruder production dropped. While keeping the material in the machine barrel residence time, resulting in material decomposition. If it is polyethylene, the decomposition of hydrogen chloride gas will be produced on the screw and barrel erosion.
2, the plastics material is not uniform, or a compound mixed with a metal foreign body, so that a sudden increase in screw rotation torque, the torque exceeds the ultimate strength of the screw, the screw is broken.
Second, the screw repair
1, the broken barrel of the screw according to the actual diameter to consider, according to the normal gap and barrel diameter of the screw gives the new manufacturing deviations.
2, the wear of the screw thread surface treatment, thermal spraying wear-resistant alloy, and then by grinding to the required size. This method generally have a professional spray-processing repair, costs are lower.
3, the screw thread part in the wear resistant surfacing alloy. Screw wear welding according to 1-2mm thick, and then grinding capacity of the screw to the desired size. This wear-resistant alloy by the C, Cr, Vi, Co, W and B, material composition, increasing the screw anti-wear and corrosion ability. Professional welding plant for the high cost of this processing, in addition to the special requirements of the screw seldom used.
4, repair the screw can also be hard chrome plated method, chromium is the wear and corrosion-resistant metal, but the hardware layer of chromium is easier to fall off.
Third, the barrel repair
The inner barrel surface hardness is higher than the screw, screw it later than the damage. The scrap is the diameter of barrel wear and increase as long to repair as follows:

       1, due to increase in the diameter of the barrel wear, if there is a certain degree of nitriding layer can direct the machine barrel hole boring, grinding to a new diameter, and then press diameter of the preparation of a new screw.

       2, cylinder bore finishing process by re-casting alloy, thickness 1-2mm, and then finished to the desired size.

       3, under normal circumstances, all of the segments of barrel wear faster, more sections can be repaired by boring holes, adding a nitriding steel bushings, screw diameter of the hole diameter of the light, with the gap left in the normal conduct preparation for processing.

        Also note that the screw and the barrel of these two important parts, one is the slender thread rod, a relatively small diameter and long holes, and their machining and heat treatment processes are more complex, assuring accuracy are more difficult. Therefore, these two parts to repair worn or replaced with new parts, we must do a comprehensive analysis of the economic point of view.

        4, the screw and barrel materials for manufacturing the screw and barrel, currently used materials 45,40 Cr and 38Cr Mo Al A..

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           Peter Huang