Sliding bearing refers to a bearing that works under sliding friction. Sliding bearings work smoothly, reliably and without noise. It is generally used in low-speed and heavy-load conditions, or in operating parts where maintenance and lubricating oil are difficult. It is mainly divided into two categories: integral bearing and split bearing. The repair method can be selected according to the following classifications:

 

Integral bearing

(1) When the bearing hole is worn, it is generally repaired by replacing the bearing and machining the bearing hole by boring, reaming or scraping; it can also be repaired by plastic deformation, that is, by shortening the bearing length and reducing the inner diameter.

 

(2) After the inner hole of the bearing without the bearing bush is worn, it can be repaired by the bushing method, that is, the bearing hole is enlarged, pressed into the processed bushing, and then trimmed according to the journal to make it meet the matching requirements.

 

Split bearing

(1) Replacement of bearing bushes generally need to be replaced with new bearing bushes under the following conditions:

Severe burnout, large tile burnout area, and large wear depth cannot be saved by scraping and grinding;

The bearing alloy of the bushing is thinned to the limit size;

The bearing bush is broken or severely cracked;

Serious wear and tear, the radial clearance is too large and cannot be adjusted.

(2) Accidents where scraping and grinding bearings are scratched or severely glued (burning tiles) during operation are often seen.

(3) Adjusting the radial clearance The bearing increases the radial clearance due to wear, resulting in oil leakage, vibration, and accelerated wear.

(4) Reduce the contact angle and increase the size of the oil wedge. As the operating time increases, the wear of the bearing increases gradually, causing the journal to sink and the contact angle to increase, which deteriorates the lubrication conditions and accelerates the wear.

(5) Repair welding and surfacing welding For bearings that are worn, scratched, broken or otherwise defective, repair welding or surfacing welding can be used to repair them.

Use flat chisel, scraper and other tools to clean the parts that need repair welding, so that the surface is free of oil, residue, impurities, and the luster of the metal is exposed;

Select the same material as the bearing material as the electrode, and use gas welding to repair the bearing. The thickness of the welding layer is generally 2-3mm, and the deeper defects can be repaired with multiple layers;

When the repair welding area is large, the bottom of the bearing can be immersed in water for cooling, or intermittent operation, leaving cooling time;

After repair welding, it needs to be reprocessed. Partial repair welding can be repaired by manual trimming and scraping. Larger area repair welding can be cut on the machine tool.

 

 

(6) Re-casting the bearing bushing For the sliding bearing with severe wear and failure, repair welding or surfacing welding can no longer meet the requirements. At this time, it is necessary to re-cast the bearing alloy, which is a very common repair method.

Do the preparations before pouring, including necessary tools, materials and equipment, such as: fixtures and plates for fixing bearing bushes, bearing alloys of the same grade as required by the drawings, tin powder and tin rods for tin hanging, and melting of bearing alloys. Heating furnace, crucible containing bearing alloy, etc.

Before pouring, the old bearing alloy on the bearing bush should be melted off. You can bake it with a blowtorch, or you can put the old tile into the crucible for melting the alloy to melt the alloy.

Check and correct the tile back so that the inner surface of the tile back is free of oxides and is silver-gray; the geometry of the tile back meets the technical requirements; the tile back is expanded before pouring to ensure that the cooling shrinkage after pouring is good with the tile seat fit.

Clean, degrease, decontaminate, rust, and dry the bearing bush to keep it clean before tinning.

 

Hanging tin, including dissolving zinc in hydrochloric acid solution of zinc chloride on the surface of the tile lining, preheating the tile lining to 250 ~ 270 ℃; once again evenly coating a layer of zinc chloride solution, sprinkle some chloride The ammonium powder is formed into a thin layer; the tin bar or tin rod is filed into powder with a file, and evenly sprinkled on the surface of the treated tile lining, the tin is melted on it when heated to form a thin, uniform and bright Tin clothes; if there are light yellow or black spots, it means that the quality is not good and needs to be re-hanged.

 

Melt the bearing alloy, including preheating the bearing lining; select and prepare the bearing alloy; melt the bearing alloy, and sprinkle a layer of crushed charcoal on the surface of the alloy, with a thickness of about 20mm, to reduce the oxidation of the alloy surface, pay attention to control the temperature, neither Too high, but not too low. Generally, the pouring temperature of tin-based bearing alloys is 400 to 450 °C, and the pouring temperature of lead-based bearing alloys is 460 to 510 °C.

 

When pouring bearing alloy, it is best to preheat the tile lining to 150-200 ℃ before pouring; the pouring speed should not be too fast, and it should not be interrupted, but should be carried out continuously and evenly; the pouring temperature should not be too low to avoid the occurrence of blisters; Slag, remove the charcoal and slag floating on the surface of the machine tool.

 

Quality inspection, analyzing and judging defects through fracture, if the quality does not meet the technical requirements, it cannot be used.

 

(7) Plastic deformation method Plastic deformation method can also be used to repair bronze bushings or bearing bushes, mainly including upsetting, compression and correction.

 

The upsetting method is to use a metal mold and a mandrel to center, pressurize on the upper mold to reduce the inner diameter of the shaft sleeve, and then add its inner diameter.

The shaft sleeve is put into the mold by the compression method, and the inner and outer diameters of the shaft sleeve are reduced through the mold under the action of pressure. The reduced outer diameter is restored to the original size by metal spraying, and then processed to the required size. size.

The correction method combines the two half-bearing bushes, and after fixing, presses them into an oval shape on a press, and then cuts the joint surfaces of the half-bearing bushes to a certain thickness, so that the inner and outer diameters of the bearing bushes are reduced, and the outer diameter is sprayed with metal. Repair and rework to the required size.