Screw and barrel of the two parts work quality, plasticizing of materials, products quality and production efficiency, have important influence. Their work quality and the manufacturing precision of two parts, assembly clearance. Heavily damaged when the two parts, the output of extruder falls, you should arrange for screw and barrel of the maintenance.
One, the screw and barrel of the damage reason
1, the screw rotation inside the barrel, friction material with both the screw and barrel of the surface of the work gradually wear: screw diameter reduced gradually, the barrel inner hole diameter increase gradually. In this way, the matching of the screw and barrel diameter clearance, with the gradual wear and tear of the a little bit more. , 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. Results decreased extruder production. This phenomenon and make the material stay in the barrel time increased, the material break down. If it is polyethylene, decomposition of hydrogen chloride gas is used to strengthen the corrosion of the screw and barrel.
2, material such as calcium carbonate and filling material such as glass fiber, can speed up the screw and barrel of the wear and tear.
3, because the material does not have uniform plasticizing, metal object or a mixed in the material, to rotate the screw torque force suddenly increases, the torque beyond the ultimate strength of the screw, the screw twist off. This is a kind of unconventional accident damage.
Second, the restoration of the screw
1, twist off the screw should be in accordance with the actual diameter of barrel, according to the new screw and barrel of the normal clearance to outside diameter deviation of manufacturing.
2, wear threads of the screw diameter to reduce the surface after treatment, thermal spraying alloy, and then via grinding to size. This approach generally have professional spraying plant, repairing cost is still relatively low.
3, in the wear of the screw thread part of surfacing welding alloy. According to screw the wear degree of surfacing welding 1 ~ 2 mm thick, then grinding screw to size. The wear resistant alloy by C, Cr, Vi, Co, W and B material composition and so on, to increase the screw's ability to resist wear and corrosion resistance. Professional welding plant to the processing fee is very high, in addition to the special requirements of the screw, rarely used.
4, to repair the screw can also be used surface hard chromium plating method, chromium is wear resistance and corrosion resistance of metal, but the hard chromium layer is easy to fall off. Three, the barrel of the repair of barrel inner surface hardness is higher than the screw, it's more damage than the screw later. Scrapping is the inside diameter of barrel diameter increases due to time wear. The repair method is 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, barrel diameter by machining renovation to casting alloy, thickness between 1 ~ 2 mm, then processed to 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. So for these two parts after the wear and tear of repair or replacement of new parts, must be comprehensive analysis from the point of view of economy. If repair costs lower than the cost of a new screw, decided to repair, this is not necessarily the right choice, the repair cost and update the cost comparison, is just one aspect. Take another look at using screw time cost and after repair and update the ratio of cost and update the screw use time. USES the ratio of small program just economy, is the right choice.
4, the screw and barrel manufacturing materials manufacturing screw and barrel, the current domestic commonly used materials have 45, 40 cr and 38 crmoala. Imported extruder screw and barrel manufacturing materials, commonly used alloy steel has 34 craini7 and CrMoV9. The material yield strength 900 mpa. After nitriding treatment, in more than 1000 hv hardness, wear resistance and good corrosion resistance.