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. The common methods are side plate reinforcement or key anchorage, as shown in Figure 4. 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.