2022-01-07 News Views 999
Diesel engine connecting rod crankshaft journal and connecting rod between the big end of the installation of sliding bearings, because its shape like tiles, so called connecting rod bearing. The gap between the connecting rod crankshaft journal and the connecting rod bearing is fit, so that when the crankshaft rotates, the oil can form an oil film on the friction surface, thus reducing the friction and wear of the crankshaft journal. The inner surface of the bearing bush is cast with a layer of friction reduction alloy layer, which often occurs in the use of alloy layer melting, peeling, scratching, wear beyond the limit and other faults, so that the normal relationship between the journal and the bearing is destroyed, serious will occur burning tile holding shaft failure, sometimes will cause crankshaft fracture and accidents. The damaged bearing bush to be replaced, the connecting rod bearing bush replacement installation repair method is analyzed.
1. Common defects of connecting rod bearing bush
(1) bearing bush alloy melting. It refers to the phenomenon that the diesel engine crankshaft bushing is damaged or high temperature makes the bushing and crankshaft journal sintered (holding shaft), resulting in the normal operation of the engine. Burning tile is one of the common faults of diesel engine. Before burning tile, there are the following warnings: the engine smoke, oil pressure drop, there is a significant sense of effort, speed quickly reduced, the crankcase vent smoke white, and a "haw" dry friction sound. In this case, the engine should be shut off immediately and the crankshaft should be turned to avoid holding tile. Although the diesel engine with burning tile can be repaired, its normal technical condition is difficult to recover.
(2) the bearing bush alloy falls off. The fatigue crack and even fall off of the alloy surface due to the effect of alternating load on the bearing bush.
(3) bearing bush alloy scratch. Bearing scrape caused by metal abrasive particles in lubricating oil or burr on the edge of the shaft neck oil hole, and will accelerate the wear of the shaft neck and bearing.
(4) Alloy wear. Journal and bearing wear is inevitable, resulting in an increase in the gap between the two, when the gap increases to a certain extent, a lot of oil will leak from now on, resulting in low oil pressure, which will accelerate their wear, serious there will be bearing noise.
2. Replacement assembly of connecting rod tile
The matching clearance between connecting rod bearing and connecting rod journal of diesel engine must meet the requirements. The gap is too large, the lubricating oil is easy to leak, it is not easy to establish the oil film, so that the poor lubrication, wear and tear; Journal and bushing produce knock, damage crankshaft or connecting rod bushing. The gap is too small, the lubricating oil into the amount of less, wear and tear, and even can produce bite burning tile accident. If the matching clearance of the bearing bush is found to be beyond the use standard, it is necessary to replace the new tile. At present, small high-speed diesel engines often use thin wall bearing bush has two categories: one is the wall thickness of 3 ~ 6mm, reduce the thickness of running-in alloy layer is 0.5 ~ 1.5mm; The other is the wall thickness of 0.9 ~ 3mm, and the thickness of reduced running-in alloy layer is 0.25 ~ 0.75mm. Thin-walled tiles are generally not repaired, but replaced. When replacing them, attention should be paid to the following tasks:
(1) The connecting rod bearing bush should be replaced in a complete set, and the size should be corresponding to the size of the connecting rod journal. The connecting rod bushes are interchangeable. Connecting rod and connecting rod cover are machined in pairs and are not allowed to be replaced. The connecting rod cover is positioned on the connecting rod by positioning lip, and the positioning lip groove on each connecting rod is on the same side.
(2) the upper and lower tiles are respectively installed in the connecting rod big head and connecting rod cover, and the positioning lip on the bearing bush should be accurately embedded in the corresponding positioning groove.
(3) take a piece of soft metal sheet or soft wire, put it between the bearing and the journal, when put should pay attention to be perpendicular to the horizontal line between the bearing and the journal. Tighten the tile cover at a certain torque, and then take out the metal sheet or wire to measure its thickness, which is the clearance of the bearing bush.
(4) When installing connecting rod bolts, make a comprehensive inspection of connecting rod bolts and confirm that the bolts are qualified and can be used.
3. Repair
The wear and damage of lead-copper alloy bearing bush generally cannot be repaired, but the defects of white alloy bearing bush, such as cracks and peeling, can be repaired according to the degree of damage:
(1) welding repair. The following problems should be paid attention to when using oxyhydrogen welding: (1) the selection of electrode material should be consistent with the chemical composition of bearing bush alloy. (2) Determine the welding repair part and clean it with a scraper around it. The bearing bush is heated to 160 ~ 180℃ before welding. (4) when welding, the bearing bush shall be welded properly rotated, so that the welding is repaired everywhere in the lowest level position. Welding repair sequence should be from the middle to both sides of the jump welding. ⑥ After welding, the scraper should be scraped flat.
(2) boring of connecting rod bearing bush. Is to use the boring tile machine for boring. Bending and distortion of connecting rod should be checked and corrected before boring. When boring, we should find the right center, a boring amount is not too large, to prevent lava, and strictly control the connecting rod big head, small head center distance must be within the specified range. After boring, roundness and cylindricity should not be greater than 0.02mm, and alloy layer thickness should meet the requirements. And the center line parallelism of connecting rod bushing and bearing bush shall not exceed 0.05mm in the length of 100mm.
(3) repair and scraping of connecting rod bearing bush. Specific methods and steps are as follows:
① Put the crankshaft on the special bracket.
② Apply a thin layer of red lead oil or other colored paint on the surface of the connecting rod journal, and then install the connecting rod to the journal in the correct position and direction, gradually tighten the connecting rod bolts evenly, and tighten them to rotate the connecting rod with a little resistance.
③Rotate the connecting rod several times, then loosen the bolt, remove the connecting rod, observe the contact between the bearing surface and the journal, if the color point is not uniform and at both ends, the application of a scraper to scrape the color point.
④When repairing and scraping, hold the connecting rod or bearing bush cover with the left hand (or clamp it on the bench vice), flat the scraper with the right hand, and scrape the scraper from the outside to the inside with the force of the wrist. Repair scraping scraping direction to constantly change, the first scraping direction and bearing bush line into 30°, the second scraping direction and axis should also into 30°, but towards the other side. Scraping force should be appropriate, too much ripple. After scraping for several times, when the gap is a little larger, the application of hand swinging connecting rod, using its own gravity and the centrifugal force generated by the rod body for research, to ensure that the bearing bush scraping is round and positive, after scraping should be at both ends of the bearing bush scraping garbage trough.
⑤ After scraping the bearing bush, the contact point is required to be evenly distributed, the contact area with the journal should not be less than 75%, the roundness and cylindricity of the bearing bush should not exceed 0.02 ~ 0.03mm, and the gap should be within the range of the assembly gap specified in the specification. In the actual maintenance, the amount of wear is very small, and with the gap and in the required range of the old bearing, the triangular scraper can be used to scrape the surface abrasion and corrosion, the scraping amount should be as small as possible, in order to ensure the correct matching of the shaft and bearing.