Maintenance techniques for several parts in construction machinery

1. Emergency repair of dry thin-walled cylinder liner

A Komatsu WA420 loader from our company has been working in the field for a long time. The cooling water used in the engine contains more minerals. In addition to the negligence of the maintenance of the cooling system filter, the engine crankcase has cavitation in the II cylinder. The thin-walled cylinder liner is also cavitation, and a hole of Φ2mm size appears, which causes the crankcase oil sump to enter the water. Considering that the aircraft was purchased in 1992, the crankshaft, camshaft and cylinder of the engine have reached or are close to the limit of use. It is worthless to invest a lot of money for repair, but the wear of the cylinder liner and piston of the engine still conforms to the technology. Standard, no burning oil and black smoke, and the engine is working properly, the fuel consumption is not significantly increased, the hydraulic system and the chassis part can still be used continuously, and it is obviously more efficient than the domestic similar machinery. To this end, we transferred the original cylinder liner to 180 degrees, and blocked it with AB glue at the cavitation of the crankcase, and then reassembled the engine. The operation again showed normal operation. With this lesson, I worked fine later. With this lesson, management and maintenance personnel attached great importance to the maintenance of the cooling water filter in later work. It has been a year since the repair, and the machine is still in use.

2. Repair of engine cylinder head deformation

Our two Japanese Kawasaki KLD85Z loaders have warped deformation of the engine cylinder head due to long-term work under high temperature, high pressure, heat load and alternating load. The cylinder head gasket is damaged from the waterway mouth, causing the combustion chamber pressure to drop. Insufficient engine power and water from the radiator.

The cylinder head gasket was changed twice in succession and was washed out after one month of use. After dismantling, it was found that the cylinder block and the cylinder head were deformed. The flatness error of the cylinder block is 50μm, which also meets the technical requirements, but the flatness error of the cylinder head reaches 0.20mm, which is the main reason for the cylinder head to be damaged.

The repair method we used is that, since there is no concave shape on the cover, it is not necessary to consider the change of the combustion volume (the change of the volume of the combustion chamber should not be greater than 4% of the original volume), and the cylinder is machined by plane milling. Cover plane; a copper pad is installed at the waterway opening of the cylinder head and the cylinder joint surface (the thickness of the copper pad is 1.2 times the thickness of the waterway port recess), instead of the rubber seal ring on the cylinder head gasket, and then the cylinder head gasket is installed. At the same time, the cylinder head bolts are reinforced by the method of first tightening and then tightening. The engine repaired by this method does not have a failure of the flush cylinder mat.

3. Welding repair of bulldozer frame

After the SH320 bulldozer has been used for 6 years, the two frame bolts have been broken due to long-term bending moments and torques in different directions. In addition, they have not been discovered in time, resulting in the breakage of the frame arm into two sections. Because it is difficult to repair, and know that even if you buy old parts, you have to pay more than 10,000 yuan. For this reason, we decided to use welding technology to repair. The specific method is to first install the broken bolt according to the original shape, assemble the trolley frame, weld the crack first, then remove and pull it back to the workshop, use the bracket to frame 30cm, and use charcoal fire within 1m around the crack. Warm (to prevent local heat deformation), so that it reaches about 120 °C, then cut the V-shaped groove with acetylene flame gas, so that the groove depth reaches 3/4 of the arm thickness, and then carry out welding. The welding process is as follows: DC arc welding machine, reverse connection method (welding piece connected to the negative electrode), J507 electrode (heated to 100 °C before use), the diameter of the welding rod is Φ3.2mm, and the welding current is adjusted according to the arcing condition. After welding, the stress is removed (heated to 200-300 ° C slow cooling) and repaired. After welding, the installed machine shows that the quality is in full compliance with the requirements. The machine has been in use for 10 months and is working properly. Wear-resistant electrode

4, T815 type dump truck wearing parts repair

Our company has 30 sets of Czech-made T815 self-cylinder cars. It has been found in several years of use that due to the localization of the chassis part of the car, the chassis quality can not meet the construction requirements, and some accessories often have a malignant break, bringing the user Great economic losses. After a long period of exploration, we have welded and repaired the wearing parts of the machine (such as steel plate lugs, steel plate clamps, spring steel plates and semi-axle bushings), and achieved good results. At the time of welding, please pay attention to: use DC arc welding machine, J506 welding rod, pre-weld preheating, post-weld insulation, eliminate local thermal stress and prevent stress concentration.

5, loading mechanism power

Processing and repair of piston cylinder

The double-line gas-assisted hydraulic brake system is often used on the loader. This type of brake system is also used on a KLD85Z loader. Due to long-term use, once, the brake booster suddenly fails during use. The cause of the fault is that the inner cavity of the booster hydraulic cylinder is corroded by the brake fluid for a long time, which causes the rubber cup to wear and fail.

After inquiry, this product has no domestic parts, and the import price is 12,000 yuan. Obviously, if you buy it, it is not economically economical. We found that the rubber cup in the BJ2020 Jeep Clutch Repair Kit is similar in size to the cup of the machine, except that the outer diameter is slightly smaller. After analyzing the size of the piston cavity, it is considered that the piece can be completely processed by lathe; the machining is fast and small infeed to reduce the roughness of the inner cavity; when the tool is fed, the tool holder is adjusted to 2-3 degrees to make the inner wall have a certain inclination; It is set according to the outer diameter of the cup and is 0.4-0.5 mm smaller than its original size. After careful measurement and processing, it can be used normally after repair.