The combined work quality of the two parts, screw and barrel, has important influence on the plasticization of materials, the quality of products and the production efficiency. The quality of their work is related to the manufacturing accuracy and assembly gap of two parts. When two parts wear badly and the output of the extruder decreases, the maintenance of screw and barrel should be arranged.
1. Causes of damage to screw and barrel.
1. The screw is rotated inside the barrel, and the friction between the material and the two is gradually worn down on the working surface of the screw and the cylinder: the diameter of the screw is gradually reduced, and the diameter of the inner hole of the cylinder is gradually increased. In this way, the diameter gap between the screw and the cylinder is increased with the gradual wear of the two. , however, because of the barrel in front of the nose and shunt plate resistance has not changed, which adds to the forward extrusion material leakage flow, the material feeding direction from diameter clearance flow has increased. The result is a decrease in the production of extruder. This phenomenon also causes the material to stay in the barrel for more time, resulting in the decomposition of materials. If it is polyethylene, the decomposition of hydrogen chloride gas enhances the corrosion of the screw and cylinder.
2. Materials such as calcium carbonate and glass fiber fill material, can accelerate the screw and cylinder wear.
3. As the material is not plasticized, or mixed with metal foreign material, the torque force of the screw is increased suddenly, and the torque exceeds the strength limit of the screw, causing the screw to twist. This is an unconventional accident.
2. Repair of screw rod.
1. The twisting screw should be considered according to the actual inner diameter of the cylinder, and the outer diameter deviation of the new screw rod should be manufactured according to the normal clearance of the cylinder.
2. After treatment of the threaded surface of the reduced screw diameter, the thermal spraying wear-resistant alloy is then machined to the size. This method generally has professional spraying factory to repair, the cost is relatively low.
3. Weld wear-resistant alloy in threaded part of wear screw. Weld 1~2mm thick according to the degree of screw wear, and then grind the screw to the size. This kind of wear-resisting alloy is composed of C, Cr, Vi, Co, W and B, which increases the resistance of the screw and the corrosion resistance. Professional surfacing factory is very expensive for this kind of processing, except for the special requirement of screw, it is seldom used.
4. The repair screw can also be used for hard chromium plating. Chrome is also a metal with abrasion resistance and corrosion resistance, but the hard chromium layer is easy to fall off.
3. Repair of the cylinder.
The inner surface of the cylinder is higher than the screw, and its damage is later than the screw. The scrap of the cylinder is the diameter of the inner diameter increased due to time wear. Its repair methods are as follows:
1, because wear increases, the diameter of the barrel, if there is a certain of nitriding layer, can be boring, the barrel inner hole directly grinding to a new diameter size, and then according to the diameter of the new screw.
2. The inner diameter of the cylinder is machined and re-cast alloy, and the thickness is between 1~2mm, and then finished to the size.
3, in general, the plane homogenization of cylinder wear faster, but will take 5 ~ 7 d (long) this paragraph by boring nap, match again a nitriding steel bushing, diameter of bore with reference to the screw diameter, stay in normal fit clearance, carry on the processing preparation.
Here, a point underscored by the screw and barrel of the two important parts, one is the slender thread rod, a hole is the relatively small diameter and long, their machining and heat treatment process are complex, precision guarantee are more difficult. Therefore, after the wear of these two parts is repaired or replaced, it must be analyzed comprehensively from the economic perspective. If the cost of repair is lower than the cost of replacing the new screw, it will be decided to repair. This is not necessarily the correct choice. The comparison between the repair cost and the renewal fee is only one aspect. It is also necessary to look at the ratio of the cost of repairs and the use of the screw time to the update cost and the time to update the screw. It is the right choice to adopt a scheme with small ratio.
4. Screw and barrel manufacturing materials.
There are 45, 40Cr and 38CrMoAlA commonly used in domestic materials.
The manufacturing materials of screw and barrel in imported extruder are commonly used in alloy steel with 34CrAINi7 and CrMoV9. The yield strength of this material is about 900MPa. After nitriding treatment, the hardness is above 1000HV, which is both wear-resistant and good corrosion resistance.