1. Partial welding repair method for tile lining
Partial welding repair may be considered for bearing shells with the following defects.
1) The newly poured bearing shell is overall good, but there are local defects such as air holes, sand holes, scars, etc.
2) Old bearings with worn bushings, mismatched geometric shapes, and local cracks and scars.
1.1 Repair process
(1) Cleaning of old lining alloy: For locally damaged lining that does not expose the bearing shell, use a scraper to clean the damaged alloy surface to expose the metallic luster. Then clean with a 10% alkaline solution at a concentration of 70-100 degrees Celsius for 5-10 minutes to remove fat, and then rinse with hot water at 70-100 degrees Celsius to remove residual alkali.
For the bushing with exposed bearing skin, first clean the damaged area of the alloy with a scraper or file to expose the metallic luster. Alternatively, the alloy residue can be melted off with a flame, and then the surface dirt, rust, and alloy fragments of the lining can be removed with a wire brush, especially the groove part, which should be carefully cleaned.
After cleaning, use a 10% -15% hydrochloric acid or sulfuric acid solution for 10-15 minutes for acid washing and rust removal. Then, rinse off residual acid with hot water at 70-100 ℃, and degrease with a 10% alkaline solution at 70-100 ℃ for about 10 minutes. Finally, rinse off residual alkali with hot water at 70-100 ℃.
The preparation of flux and welding rod requires that the flux can remove impurities from the alloy surface during welding, protect its surface from the influence of surrounding media, and make the welding surface have good wetting properties. Secondly, during welding, the flux can precipitate tin components in the chemical reaction process, forming a 0.03-0.04mm tin containing transition layer, ensuring that the solder rod droplets are firmly bonded to the welding surface.
Common flux formulas:
Zinc oxide 50%
Ammonium oxide 15%
Tin chloride or tin oxide 30%
Sodium fluoride 5%
Mix the above drugs in proportion and mix with water to make a thin paste.
In addition, there is another solder formula:
Zinc oxide 10%
Tin (II) chloride 20%
Purified water 60%
Mix the above three drugs into a solution. Ready to use, cannot be stored.
Welding rods can be made of Babbitt alloy (or black gold) with the same or similar composition as the base metal, with a diameter of 5-10mm. The type of welding gun depends on the size of the repair welding area of the liner, and generally uses sizes 150-250.
1.2 Welding repair process
1) Preheat. Use neutral flames. The oxygen pressure should not exceed 0.29MPa, and the ratio of oxygen to acetylene gas should be 1:3. Preheating should be done evenly and slowly to make the surface of the liner gray (about 200 ℃).
Apply solder flux. Apply solder evenly on the surface to be repaired with a brush, and heat it to a white color. At this point, the repair can be carried out. If the heating turns gray, it indicates that the temperature is too low and needs to be preheated again. If the solder falls off as round beads on the repair surface and cannot be coated with solder, it indicates that the surface temperature is too high.
Welding. When welding, use left welding, with the electrode 6-10mm away from the surface of the liner and moving up and down. The distance between the nozzle and the surface of the liner and the welding rod should be 5-10mm, and the nozzle should swing left and right to take care of the two rows of interfaces.
The sharp corners should be welded first, as they are prone to overheating, generating bubbles and affecting quality. Arc transition is required, and flames should not heat the metal for a long time. After each weld, continuous welding can be performed, but flux should be applied immediately to prevent thermal cracking. Single layer and multi-layer soldering can be performed, and each layer needs to be cleaned with water and re coated with solder flux after soldering. Weld bead width 5-10mm, thickness 2-3mm. The welding allowance can be taken as 2.5-3.5mm, and the scraping allowance is 0.1-0.5mm.
4) Post weld inspection and precautions during construction
① Require fine grain size of the alloy after welding, without the formation of dendritic crystals due to overheating.
② No inclusions, bubbles, tile edges and sharp corners, and high welding quality at both ends.
③ No oxidation or overheating phenomenon.
④ When welding, the temperature should not be too high or too low.
⑤ Solder flux is toxic, and ventilation should be ensured during operation to prevent poisoning.
2. Repair method of recast alloy for sliding bearings
2.1 Preparation before casting alloy
When the tile lining is severely detached from the tile bottom and the alloy damage on the tile lining surface cannot be repaired by local welding, the bearing clearance wear is too severe, and the gasket on the joint surface cannot be adjusted for recovery. When the alloy quality cannot guarantee the safe operation of the bearing, it is necessary to consider re casting the alloy for repair. Generally, bearings with cyclic lubrication have a radial clearance of 0.25% -0.4% of the shaft neck.
Melt off the old tile lining alloy and preserve it. Use a wire brush to remove oxides and dirt from the bottom surface of the tile, giving it a metallic luster. Then use a 10% -15% sulfuric acid solution to remove rust, and rinse twice with hot water. At this time, carefully inspect the bottom of the tile for defects such as cracks. After passing the inspection, evenly apply a layer of zinc oxide solution on the casting surface of the tile bottom. Heat it in the oven to 200-250 degrees, remove it, and then apply a layer of zinc oxide solution while hanging tin. The thickness of the tin layer is 0.1-0.2mm, the thinner the better. The surface of the tin layer should be bright. If there is a dark color, the tin layer needs to be re hung.
A silicon steel sheet or a thin iron Flat noodles not adhering to the alloy shall be padded at the joint surface of the upper and lower tiles. Its width shall be such that its inner side can contact the surface of the tile core, and its outer side is aligned with the tile skin. When installing the tile core, it is necessary to keep the center of the tile core concentric with the center of the closed bearing shell. Also, seal the oil pipe ring groove and return hole with yellow mud. Finally, tighten the bearing shell with a clamp.
Select sufficient bearing alloy blocks according to the size of the bearings and melt them in the furnace. The number of alloy blocks should not be less to prevent rework caused by insufficient casting. The melting temperature of the alloy should not be too high or too low. If there is no measuring instrument, several layers of newspaper strips can be inserted into the melted alloy, and after 1-2 seconds, when the newspaper turns dark yellow, it indicates that the heating temperature of the bearing alloy is appropriate. If it appears black or yellow black, it indicates that the alloy temperature is too high. During the melting process of the alloy, dry wooden strips should be used to continuously stir the alloy solution to ensure even distribution of alloy elements.
Preheat the clamped bearing shells, cores, and plates in the oven at 250 ℃, and do not burn them directly with fire. Place the preheated tile on the dry board and align the tile core. Wrap the outside of the tile with molding sand.
2.2 Casting Bearing Alloy
Remove the molten alloy from the slag and inject it into the bearing shell chamber. When one-third to two-thirds of it is injected, use an iron rod to quickly crush the alloy solution that has not yet solidified inside the bushing, so as to completely eliminate the gas inside the alloy. When casting alloys, if leakage is found, it should be quickly blocked with yellow mud.
To prevent the alloy from being oxidized during solidification, the surface of the alloy solution can be uniformly covered with red charcoal to extend the cooling time, prevent oxidation, and thus avoid the alloy from becoming brittle and producing sand holes after solidification.
During the casting process of alloys, it is important to pay attention to temperature control. When casting alloys, the action should be rapid.
2.3 Quality inspection after casting
After casting the bearing alloy, the casting quality should be checked. The surface of the cast alloy should present a dark silver or silver yellow color, without any purple or dark yellow spots. The surface of the alloy should be free of sand holes and cracks. The alloy has no detachment from the tile bottom phenomenon (can be judged by sound). The surface roughness of the cast alloy is Ra2.5 or Ra12.5. When checking the cross-section of the gate, there should be a fine-grained crystal structure and no rough crystals.
2.4 Bearing Machining
After passing the inspection, the cast bearing shell should be leveled before being processed on the upper bed to align the tile mouth and the joint. If there are positioning pins, they should be inserted. In order to facilitate the adjustment of bearing clearance in the future, 5-10 pieces of 0.02-0.05mm purple copper skin should be inserted into the joint. Finally, remove the dirt on the surface of the bearing shell and machine it on the lathe.
If the bearing shell is accurately aligned on the lathe and the machining size is reasonable, there can be no scraping allowance left. After machining, it can be directly used after local treatment by the fitter. At present, most repair units in China still use the scraping and grinding technology for bearing shells. After processing, in order to remove tool marks and correct geometric shapes, scraping and grinding are still required, so a scraping allowance should be left during machining.
2.5 Open the oil tank
Oil groove on split type bearings with oil rings
Oil groove on split type bearings without oil rings
When opening the oil groove, it is necessary to ensure that the oil groove is not opened at the stressed part of the lower bearing, and the oil groove inside the bearing cannot pass through the edge of the bearing.
2.6 Scraping and grinding of bearing shells
The purpose of scraping and grinding is to form the correct geometric shape on the working surface of the tile lining, and to establish a wedge-shaped oil film in the lubricating oil inside the tile lining during motor operation, so that the shaft neck can operate under the buoyancy of the oil film.
The scraping and grinding of the bearing shell is based on the shaft neck, so it is necessary to inspect the shaft neck for defects in advance. The surface of the shaft neck should be smooth and undamaged, so that when checking the shaft neck deviation and elliptical deviation with a micrometer, it should not exceed 0.025-0.035mm. If there is floating rust on the shaft neck, it should be polished with fine sandpaper and wiped clean with a clean cloth.
Scraping tools must use scrapers, either manual or electric, but do not use fine files or sandpaper to wipe. Require the scraper to be sharp.
Place the lower bearing shell under the shaft neck, apply a thin layer of display agent on the shaft neck (use red lead powder for rough scraping, use No. 22 turbine oil for fine grinding), then turn the wheel to make the protruding part of the bearing liner stick with the display agent, remove the lower bearing, and gradually scrape off the protruding area with the display agent with a scraper. According to the size of the protruding area, the force of the scraper should be determined. The maximum area should be completely scraped off, while the medium area should only scrape off a small piece of the middle protruding part. Small areas can be left untouched for now. First, scrape from one direction. Scrape from another direction until the blade lines intersect and grind. The scraper should form a 30 degree angle with the grinding surface and be scraped along the rounded corner (i.e. the direction of axis rotation) in sequence, without random scraping. To prevent the bearing from scraping off, only the knife marks form a network shape. Spots can only be evenly distributed.
The above operation should be repeated several times and finally refined. At this point, there is no need to use a display agent. Just add a little turbine oil, place the lower tile under the shaft neck, rotate the rotor in both directions 3-5 times, tap the rotor, and lift it to a small height to prevent the shaft from bending. Generally, lift it by 0.4-0.6mm. Remove the bearing shell and determine the weight and direction of the scraper according to the uneven contact on the alloy surface of the bearing shell. Repeat the above operation until the tile lining is in good contact with the shaft neck. Generally, it is required that there should be two or more evenly distributed contact points per square centimeter of the lower tile area within a 60 degree (or 120 degree) arc. The scraping and grinding of the tile is also the same as the above method, requiring at least one contact point per square centimeter of area.
For motors above 600r/min, the contact angle between the bearing and the shaft is 60 degrees. For larger motors with heavy loads, the contact angle should be selected within the range of 90-120 degrees.
After scraping and grinding the bearing, there should be no clear boundary between the contact and non-contact parts of the bearing. When touching the surface of the bearing liner with your hand, you should feel smooth and without steps.
After scraping and grinding the bearing shell, it should be cleaned with gasoline and placed in the bearing seat covered with insulating paper or cloth to prevent dust from falling in.
2024 August 5th Week Marginal Product Recommendation:
Material Specification Sheet–MG-6:
Material specification sheet – MG-6 is Ball and roller bearing steel according to EN ISO 683-17. Ball and roller bearing steel for balls and rollers of any dimension,rings and discs up to 30mm effective thickness.
