In-situ repair of the half shaft of a bulldozer

A TY220 bulldozer produced by our company's Yellow River Engineering Machinery Factory suddenly experienced severe oil leakage at the left drive wheel during operation. After disassembling the left final transmission box, it was found that the half shaft head thread of this bulldozer that had been in use for seven years was completely damaged, the drive sprocket and the splines of the wheel hub were severely worn, the sprocket bearing was damaged, and the first-stage shaft gear failed. Judging from the condition of the left final transmission box, the right final transmission box also needed to be disassembled for inspection. After disassembly, it was confirmed that the degree of damage was basically the same as that of the left one.

The cause of the sudden oil leakage at the drive wheel is: the failure of the drive sprocket bearing causes the drive sprocket to be skewed, and the floating oil seal is damaged due to the large axial force it bears, which in turn leads to leakage.

After inspection, it was found that all the dimensions of the half shaft of the bulldozer were intact and there was no bending. If only one half shaft was scrapped due to the damage of the shaft head thread, the loss would be too great. As the half shaft is the core component of the final transmission part, the market price of one half shaft is approximately 4,000 to 5,000 yuan. According to relevant standards, the press-fitting force of this shaft is 400 to 500kN. Due to the effects of rust and silt, the compressive force is approximately 1000kN. As we want to continue using this shaft, if we adopt the method of pressing out and repairing the thread, although the repair quality is reliable, the risk is relatively high. This is because welding needs to be applied to the half shaft to find the larger force-bearing point. If the operation is not careful, it may cause the half shaft to bend and deform, resulting in its scrapping. Moreover, after pulling out the half shaft for repair, it needs to be pressed in again, which is a cumbersome and complex process, time-consuming and labor-intensive. After comparison, it was decided to carry out in-situ welding repair.

The thread of the half shaft head only serves to fasten the half shaft cone sleeve, thereby pressing the sprocket bearing. The gears in the final transmission box are all spur gears and basically do not generate axial force. Therefore, it is theoretically feasible to repair the thread of the shaft head by welding.

Use a cutting torch to remove the damaged threaded part on the right side of the tool withdrawal groove on the half shaft. Then, process a new shaft head according to the original shaft head size and install a newly purchased lock nut to protect the processed shaft head thread during welding. In addition, a 45° single-sided bevel should be made on the welding surface and aligned with the half shaft. Under the premise of ensuring the coaxiality of the new shaft head and the half shaft, spot welding should be carried out first, and then the 506 electrode should be used for welding. The current should be adjusted to between 130 and 140A. If the current is too large, it will cause undercutting and damage to the thread. If the current is too small, the workpiece will not be penetrated, and the welding quality cannot be guaranteed. Select a 3.2mm diameter electrode and perform symmetrical circumferential welding to control welding deformation. As the size of the repaired half shaft has been extended by 10mm compared to the original size, an additional 10mm thick gasket needs to be processed and installed on the half shaft, and a gasket for the bearing cover also needs to be processed. The rest of the installation methods remain unchanged.

After three months of use, this machine has been operating normally all along. Practice has proved that the in-situ repair method of the half shaft of a bulldozer not only saves time and effort, but also can save a large amount of money. This method is more suitable for projects with few devices and tight schedules, and can win a lot of precious time for the project.