Maintenance skills for several parts in construction machinery

Emergency repair of dry thin-walled cylinder liners

One of our company's Komatsu WA420 loaders, due to long-term fieldwork, the cooling water used by the engine contained a relatively high amount of minerals. Coupled with the neglect of the maintenance of the cooling system filter, cavitation occurred at Cylinder II of the engine crankcase, and at the same time, the thin-walled cylinder liner was also eroded, resulting in holes of Φ2mm in size, which led to water entering the crankcase oil pan. Given that this machine was purchased in 1992, the crankshaft, camshaft and cylinder block of the engine have reached or are close to their service limits. It is no longer worthwhile to invest a large amount of money in repair. However, the wear of the cylinder liner and piston of the engine still meets the technical standards, with no oil burning or black smoke emission. Moreover, the engine is working normally and the fuel consumption has not increased significantly. The hydraulic system and chassis parts can still be used, and their efficiency is significantly higher than that of similar domestic machinery. For this reason, we rotated the original cylinder liner by 180 degrees and sealed the cavitation areas in the crankcase with AB glue. Then, we reassembled the engine and ran it again, which showed that it was working normally. After this lesson, the work went on normally later. After this lesson, both the management and maintenance personnel attached great importance to the maintenance of the cooling water filter in their subsequent work. It has been a year since the repair, and the machine is still in use.

2. Repair of deformed engine cylinder heads

Two of our company's Kawasaki KLD85Z loaders from Japan have seen their engine cylinder heads warp and deform due to long-term operation under high temperature, high pressure, thermal load and alternating load. The cylinder gasket was damaged at the water passage opening, resulting in a drop in combustion chamber pressure, insufficient engine power and water leakage from the radiator water filling port.

I replaced the cylinder gasket twice in a row, but each time it was worn out after one month of use. After disassembly and inspection, it was found that both the cylinder block and the cylinder head had deformed. The flatness error of the cylinder block is 50μm, which still meets the technical requirements. However, the flatness error of the cylinder head reaches 0.20mm. This deformation is the main reason for the damage of the cylinder gasket.

The repair method we adopted was that since there was no combustion chamber concave shape on the machine cover, there was no need to consider the change in the combustion volume (the change value of the combustion chamber volume generally should not exceed 4% of the original volume), and the cylinder head plane was machined by the planar milling method. A purple copper gasket (1.2 times the thickness of the concave platform at the water passage opening of the joint surface between the cylinder head and the cylinder block) was installed to replace the rubber sealing ring on the cylinder gasket. Then, the cylinder gasket was installed, and at the same time, the cylinder head bolts were tightened by cold tightening first and then hot tightening. The engine repaired by this method has never had the fault of over-hitting the cylinder gasket again.

3. Welding repair of the bulldozer frame

After six years of use, the frame of the SH320 bulldozer was subjected to the long-term effects of bending moments and torques in different directions. The bolts of the two brackets broke, and due to the failure to detect it in time, the small arm of the frame broke into two sections. As it was difficult to repair and we learned that even buying old parts would cost over 10,000 yuan, we decided to use welding technology for the repair. The specific approach is as follows: First, reinstall the broken bolts in their original state, then assemble the trolley frame. Spot weld the crack first, then remove it and pull it back to the workshop. Support it up by 30cm. Within a 1-meter radius around the crack, heat it with charcoal fire (to prevent local deformation due to heat) to around 120 ℃. Then, use acetylene flame to cut out a V-shaped bevel. Make the groove depth reach three quarters of the arm thickness, and then carry out the welding. The welding process is as follows: A DC arc welding machine is used, with the reverse connection method (the workpiece is connected to the negative pole), J507 electrode (heated to 100 ℃ before use), and the electrode diameter is Φ3.2mm. The welding current is adjusted according to the arc initiation situation. After welding, stress relief is carried out (heat to 200-300℃ and cool slowly), and then grinding treatment is performed. The installation and use after welding indicate that the quality fully meets the requirements. This machine has been in use for 10 months and is working normally. Wear-resistant electrode

4. Welding repair of vulnerable parts of T815 dump truck

Our company has a total of 30 T815 self-cylinder trucks made in the Czech Republic. During several years of use, it was found that due to the localization of the chassis part of this vehicle, the chassis quality could not meet the construction requirements, and some parts often suffered malignant fractures, causing huge economic losses to users. After long-term exploration, we have carried out welding repair on the vulnerable parts of this machine (such as steel plate lifting lugs, steel plate clamps, spring steel plates and half shaft sleeves, etc.), achieving good results. When welding, pay attention to: Use a DC arc welding machine and J506 electrodes. Preheat before welding and keep warm after welding to eliminate local thermal stress and prevent stress concentration.

5. Loading mechanism power unit

Machining and repair of piston cylinders

Double-pipe air-assisted hydraulic braking systems are widely used on loaders. One of our company's KLD85Z loaders also adopts this braking system. Due to long-term use, once, the brake booster suddenly failed during operation. The cause of the fault was found to be: the inner cavity of the hydraulic cylinder of the booster was corroded by the brake fluid for a long time, resulting in pitting, which caused the rubber cups to wear out and fail.

After checking, there are no domestic parts for this product, and the import price is 12,000 yuan. Obviously, it would not be economically viable to purchase. We found that the rubber cups in the clutch repair kit of the BJ2020 jeep are similar in size to those of this machine, only with a slightly smaller outer diameter. After re-analyzing the size of the piston cavity, it is believed that this part can be fully processed by a lathe. Adopt rapid and small feed rate processing to reduce the roughness of the inner cavity; When making the cut, adjust the tool rest by 2 to 3 degrees to create a certain slope on the inner wall. The inner diameter is determined based on the outer diameter of the leather bowl and is 0.4 to 0.5mm smaller than its original size. After careful measurement and processing, it can be used normally after repair.