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Crane rotary reducer bearing seat repairing method
After prolonged use of a LTM1180 truck-mounted crane, issues such as excessive heat, unusual noise, and oil leakage were observed in the bearing areas of the rotary pinion within the rotary reducer. Upon inspection, it was discovered that the bearing had suffered severe wear and fracture, with its outer ring having detached. The housing of the rotary reducer is constructed from cast steel, which has limited weldability and is prone to defects like white joint structures, porosity, and cracks during welding. The two bearing housing holes are designed for 3524 and 3526 type bearings, respectively, with tight tolerances of (215+0.01)mm and (260+0.01)mm.
When the crane operates, the bearing housing experiences vibration and shock, requiring the material of the seat hole to have moderate hardness, along with good impact and vibration resistance. Three repair methods were considered for the housing: welding, nesting, and partial replacement.
The welding method involves cleaning the housing, boring the seat hole to increase its diameter, preheating the housing to approximately 400°C, and then heating the seat hole to red hot (around 900–950°C). A copper alloy electrode is used to weld the area to a specified thickness, followed by slow cooling in an oven or using an infrared heater. Finally, the surface is machined back to the original design size. This method offers improved impact and vibration resistance, with stable quality and longer service life. However, it is complex, time-consuming, expensive, and may lead to peeling after repair.
The nesting method involves cleaning the bearing hole, enlarging it by 8–10 mm using a boring machine, inserting a cast steel insert with an interference fit, and securing it in place before machining to the required size. This approach is simpler, cheaper, and faster, but the gap between the insert and the shaft can be problematic—too small may cause overheating, while too large could result in bearing slippage.
The partial replacement method involves mapping the damaged bearing area, machining a new bearing housing from a stronger material, removing the old housing, and replacing it with the new one. The connection is made via threading, and any necessary reinforcement is welded. This method ensures a more durable and reliable repair. Despite the advantages of the other two methods, they were deemed unsuitable for this specific application due to their limitations. Therefore, the partial replacement method was chosen, using high-manganese steel such as Mn13, 40Mn18Cr3, or 50Mn18Cr4. Although these materials have low initial hardness, they exhibit excellent toughness and plasticity, and can achieve HBW500 hardness after processing.
After implementing the partial replacement method, the repaired bearing was reinstalled, and the rotary reducer functioned properly during testing.