A, the shaft repair
The repair of shaft generally includes the repair of central hole, journal, thread, keyway and spline shaft, the crack and fracture of shaft and the straightening of bent and deformed shaft.
1, central hole repair
As the positioning benchmark of shaft parts, the central hole should be inspected and repaired first. Remove oil stain and corrosion from the center hole; If the hole wall of the central hole is not seriously damaged, especially the conical surface of the central hole is slightly damaged, it can be trimmed with a triangular scraper or assorted oilstone. If the conical surface of the center hole wall is deformed and can't match the conical surface of the tip, the shaft can be installed on a lathe, aligned according to the journal or other reference datum, and trimmed with a center drill of the same size; The center hole that has not been used or trimmed for a long time should be ground with grinding paste through cemented carbide blades, which is especially important for shafts that need finishing.
2. Repair of worn journal
The common methods to repair worn journal are: repair according to the predetermined repair size, surfacing repair, chromium plating repair, iron plating repair and bonding repair. In the process of surfacing repair, geometric errors should be eliminated by machining before surfacing. In order to ensure sufficient machining allowance, the size of the journal after surfacing should be 2-3 mm larger than the nominal size of the journal. The important journal can be repaired by chromium plating when the wear is small (generally less than 0.4mm). Iron plating repair is a low cost and low pollution repair method. The coating thickness can reach 65438 0.5 mm, and the hardness can reach HB550-650. This is a hopeful process.
3, the repair of the thread on the shaft
There are several ways to repair the thread on the shaft, such as retightening, reforming and welding repair. When the thread damage is small, it can be re-fastened by die or turning and tightened as much as possible to prevent the fit from being too loose; The transformation method is to change the original damaged thread into non-standard thread, but the matching parts must also be replaced; Welding repair method is to turn the damaged thread first, overlay a layer of metal with welding repair method, and then turn it again according to the original thread size.
4. Repair of keyway on shaft
When the keyway has only small dents, burrs and slight wear, it can be trimmed with a fine file and oilstone. In case of serious wear or deformation and key rolling, the keyway can be enlarged or re-grooved in another place. If necessary, the damaged keyway should be welded and repaired before re-slotting. When enlarging the keyway, it must be noted that the enlarged keyway is still symmetrical about the central axis. Re-slotting must consider whether the structure or strength of the shaft allows it.
5. Repair of spline shaft
When the wear of the spline is small, the spline can be partially annealed first, then the middle of the top of the key tooth is split with a chisel with sharp edge and squeezed to both sides, then the split seam is repaired with electric welding, and finally turning, spline grinding and heat treatment are carried out, as shown in figure 1. When the spline wears heavily, a layer of metal with the same material as the shaft can be surfacing on the worn tooth side, and the original size and accuracy can be restored after turning, milling, grinding and heat treatment. When surfacing welding, measures should be taken to minimize shaft deformation caused by welding.
6, shaft fracture and broken repair
When there is a crack on the important officer, clean the crack part and groove, and then preheat the repair welding. After welding, the butt weld and surrounding metal should be heated to 500-600℃ immediately, tempered by slow cooling to eliminate welding stress, and finally machined to restore the size. Broken shaft can be repaired by butt welding, thread tightening and cylindrical pin insertion. The diameter of the threaded hole and pin hole is 0.35-0.4 times of the shaft diameter, and its depth should be determined according to the structure of the shaft, generally not less than 20mm ... When repairing the cracks on the shaft and welding the broken shaft, the welding material should be correctly selected, and welding should be carried out in strict accordance with the welding process parameters, preheating before welding and heat treatment after welding. When the source of accessories is sufficient, the method of replacing the shaft should be mainly adopted.
7. Straightening of bending deformation shaft
The bending deformation of shaft parts is generally repaired by straightening. The specific straightening processes are: pressure straightening, flame straightening and stretch straightening. The extension method is only applicable to shafts with small journal, small deformation and no surface quenching.
Second, the bearing repair
1, repair of sliding bearing
There are two kinds of common sliding bearings: integral bearing and split bearing. Generally speaking, the integral sliding bearing can be repaired by replacing the bushing and the fitter boring, reaming or scraping, or by plastic deformation, that is, reducing the length and inner diameter of the bushing. The repair of split sliding bearing can be divided into two types: the repair of thin-walled bushing and the repair of thick-walled bushing. Thin-walled bushings are often used for high-speed and high-precision parts, such as engine crankshaft journal bearings and connecting rod big end bearings. When the thin-walled bushing is slightly worn, it can be repaired by removing the thin gasket between the two pairs of joint surfaces of the bearing and scraping the journal. Common matching methods for replacing thin-walled bushings. When matching, the accuracy of the bearing seat hole should be checked first, and then the bushing should be selected according to the journal size after grinding. The cutting surface of the bushing should be 0.025-0.05 mm higher than the cutting surface of the bearing seat to ensure that the excircle of the bushing fits closely with the inner wall of the bearing seat hole. Thick-walled bushings are often used in small and medium-sized construction machinery. The hole diameter can be reduced by reducing the gasket between the mating surfaces of two bushings or by filing the mating surfaces and then scraping them according to the journal to meet the mating requirements.
2. Repair of rolling bearing
Rolling bearings are rarely repaired after wear and damage. Generally, new bearings of the original model should be replaced. But some cases can also be repaired: tapered roller bearings can reduce bearing clearance by adjusting compression nuts or adding (subtracting) gaskets; When the fit between bearing inner ring and journal or the fit between bearing outer ring and bearing hole is loose, the bearing outer ring or bearing hole can be repaired by electroplating, but it has lost its interchangeability since then.
The service life of rolling bearings is closely related to correct installation, reasonable use and maintenance.
Third, gear repair
The repair methods of gears include reversing method, meshing method, gear ring replacement method, plastic deformation method and welding repair method.
Many gears are often driven in one direction, thus causing unilateral wear. When the structure is completely symmetrical, directly turn to 180. It can be used after installation. If it is asymmetric, the gear can be annealed first, then the asymmetric part is cut and welded to the other side of the gear, and then the gear is heat treated.
For gears with small load and low speed, when individual teeth are seriously damaged, the root of bad teeth can be processed into trapezoidal grooves on milling machine or planer, and the gear blank can be pressed into the grooves with certain tightness, then welded or fastened with pins, and finally the correct tooth profile can be repaired on milling machine with forming milling cutter.
To replace the gear ring, first anneal the gear, close all the gear teeth, then press a gear ring, then fasten it with welding or pins, and finally carry out heat treatment.
Plastic deformation method: after the gear is heated to 800-900℃, it is put into a tooth mould to produce plastic deformation, and the metal in other parts is extruded to the worn surface of the gear, and then heat treatment is carried out after shaping.
Grind the cracked part of gear teeth with a fine grinding wheel to remove the incomplete fatigue layer, and then repair it by surfacing. When welding and repairing, the gear should be immersed in water and then annealed first. For carburized steel gears, 20 or 45 steel wire can be used for gas welding, or low hydrogen covered electrode can be used for repair. After welding, the tooth profile should be trimmed by machining or manual template, and finally it should be reheated and polished with oilstone or abrasive. Cracks in rims, spokes and hubs can be repaired by welding, riveting and bonding.
Fourth, the repair of box parts.
The box parts are generally castings made of gray cast iron, malleable cast iron, nodular cast iron and cast aluminum. The damage of box parts includes deformation, cracks, hole wall damage of fasteners on the box, wall wear damage of bearing holes on the box, loose fastening of split face or end cover sealing surface of the box, cracks in protruding parts of the box, etc. The deformation, cracks and other damages of the box parts have great influence on the working performance of the box and the parts installed and connected to the box.
The influence of box deformation on mechanical properties includes: the relative position accuracy (center distance of holes, parallelism and verticality of axes) between gears and shafts installed in the box is destroyed, and the wear and load of these parts are doubled, resulting in noise, vibration and heat, reduced transmission efficiency and increased energy consumption; The assembly relationship of the box relative to other related parts changes, such as the connection and installation position of the input shaft and the output shaft changes, which affects the assembly accuracy of the whole machine; The mating surface of the box itself and other sealing surfaces are uneven, resulting in oil and gas leakage due to poor sealing after assembly.
The influence of cracks in box parts on box performance: oil leakage and air leakage at cracks; Cracks at the edges of holes or boxes directly affect the interference or assembly size of pipe fittings; Cracks reduce the stiffness and strength of the box, and the box breaks due to the continuous expansion of cracks.
1, maintenance sequence of box parts
The key to ensure the repair quality of box parts is to ensure that the size and relative position of each part are repaired after the box parts are repaired. However, some repair methods, such as welding repair, often make the box body deform again, so when repairing the box body, it should be carried out in a reasonable order in order to eliminate the deformation to the maximum extent.
Commonly used maintenance sequence is:
(1) welding repair: preheat the workpiece before welding repair, and the welding heat during welding will cause deformation of the workpiece, so it should be arranged in the previous process.
(2) Bonding repair, because some adhesives also need to be heated and solidified during bonding, which may also cause deformation of the workpiece.
(3) Repair the machining datum and detect the deformation.
(4) fitter repair, plastic processing and sleeve processing.
2. Repair of box parts
(1) crack repair. Cracks can be repaired by fitter, welding, bonding and other methods, but no matter what method is used to repair cracks, lobes must be drilled at both ends of cracks to prevent cracks from expanding. At the same time, the oil and scale near the crack must be removed. Bench repair is mainly used to repair cracks in unimportant parts, and the common methods are side plate reinforcement or button anchorage. When welding box parts, welding process parameters should be strictly followed, and measures such as "thermal stress relaxation" should be taken to reduce stress and prevent deformation.
(2) Repair the hole in the box. When the hole on the box is worn or other internal surface damage occurs, it can be repaired by restoring the matching accuracy between the shaft or bearing and the hole. When the hole wall is not worn much, the hole wall or journal and bearing outer ring can be repaired by chromium plating; When the wear is serious, replace or repair the bushing for some holes with bushing by inserting sleeve. When repairing the hole, it should be considered together with the overall forming of the box, that is, the parallelism error between the center distance and the center line of the hole should be considered.
(3) Plastic processing of the box. Plastic processing of boxes is a kind of fine processing. It is required to ensure the machining accuracy and cut as little metal as possible. Because the plastic machining allowance of the box is quite small, and the original machining positioning benchmark can not be used because of deformation. Therefore, when selecting the positioning datum for plastic processing, it is necessary to select the key parts of the box, such as the central axis of the hole, as the positioning datum to trim the original processing positioning datum, and then use the trimmed positioning datum for positioning. Generally, the machining allowance of box forming can only be obtained by using the dimensional deviation of the previous machining process or by appropriately borrowing an unimportant dimensional tolerance belt in the dimensional chain. When the joint surface of the box is not tightly sealed, it is often caused by plane warping caused by box deformation. Generally speaking, repairs can be carried out by scraping, grinding or fitter drilling.