Abstract: The cylinder head gasket was changed twice in succession, and it was washed out after one month of use. After disassembly and inspection, it was found that the cylinder block and cylinder head were deformed. The flatness error of the cylinder block is 50μm, which still meets the technical requirements, but the flatness error of the cylinder head reaches 0.20mm, and this deformation is the main reason for the cylinder gasket being damaged.
1. Repair of engine cylinder head deformation
Two Japanese Kawasaki KLD85Z loaders of our company have warped and deformed their engine cylinder heads due to long-term operation under high temperature, high pressure, thermal load and alternating load. , Insufficient power of the engine and water flowing out of the radiator water inlet.
The cylinder head gasket was changed twice in succession, and it was washed again after one month of use. After disassembly and inspection, it was found that the cylinder block and cylinder head were deformed. The flatness error of the cylinder block is 50μm, which still meets the technical requirements, but the flatness error of the cylinder head reaches 0.20mm, and this deformation is the main reason for the cylinder gasket being damaged.
The repair method we used is that, because there is no combustion chamber concave on the cover, it is not necessary to consider the change of the combustion volume (the change value of the combustion chamber volume should generally not be greater than 4% of the original volume). The cylinder was machined by plane milling Cover plane; a copper pad (the thickness of the copper pad is 1.2 times the thickness of the recess of the water channel opening) is installed at the waterway opening of the interface between the cylinder head and the cylinder block, instead of the rubber seal ring on the cylinder head gasket, and then the cylinder head gasket is installed, At the same time, tighten the cylinder head bolts by first cooling and then tightening. The engine repaired by this method no longer has the problem of overshooting the cylinder head gasket.
2. Emergency repair of dry thin-walled cylinder liner
A Komatsu WA420 type loader in our company has been working in the field for a long time, and the cooling water used by the engine contains a lot of minerals. In addition to the negligence of the maintenance of the filter of the cooling system, the engine crankcase is corroded at the II cylinder. The thin-walled cylinder liner was also eroded, and holes with a size of Φ2mm appeared, causing water to enter the crankcase oil pan. Considering that the machine was purchased in 1992, the crankshaft, camshaft and cylinder block of the engine have reached or are close to the service limit. It is worthless to invest a lot of money to repair, but the wear of the engine's cylinder liner and piston is still in line with technology Standard, no burning oil and black smoke, and the engine works normally, the fuel consumption has not increased significantly, the hydraulic system and the chassis part can still be used, and it is obviously more efficient than similar domestic machinery. To this end, we turned the original cylinder liner 180 degrees, and used AB glue to plug the cavitation of the crankcase body, and then reassembled the engine. Running again showed that it was working properly. With this lesson, it worked fine later. With this lesson in mind, the management and maintenance staff attached great importance to the maintenance of the cooling water filter in the later work. It has been a year since the repair and the machine is still in use.
3. Welding repair of bulldozer trolley frame
After 6 years of use, the SH320 bulldozer has been subjected to bending moments and torques in different directions for a long time, and the two bracket bolts have broken. In addition, it has not been found in time, which has caused the boom of the carriage to break into two sections. Because it is difficult to repair, and at the same time, we learned that even if you buy old parts, it will cost more than 10,000 yuan, so we decided to use welding technology to repair. The specific method is to first install the broken bolts as they are, assemble the trolley frame, spot weld the cracks first, then remove and pull back to the workshop, use a bracket to raise 30cm, and use charcoal fire within 1m around the crack Temperature (to prevent local deformation due to heat), make it reach about 120 ℃, and then cut the V-shaped groove with acetylene flame to make the groove depth reach 3/4 of the arm thickness, and then perform welding. The welding process is as follows: DC arc welding machine, reverse connection method (weld piece is connected to negative electrode), J507 electrode (heated to 100 ℃ before use), electrode diameter is Φ3.2mm, and welding current is adjusted according to arc starting condition. After welding, remove the stress (heat to 200-300 ℃ slow cooling), and carry out grinding treatment. The use of the machine after welding shows that the quality fully meets the requirements. The machine has been used for 10 months and is working normally.
4. Loading mechanism power device
Processing and repair of piston cylinder
Most of the loader adopts double-line air-assisted hydraulic brake system, and this brake system is also used on a KLD85Z loader of our company. Due to long-term use, once, the brake booster suddenly fails during use. The cause of the fault is: the internal cavity of the booster hydraulic cylinder is corroded by the brake fluid for a long time and pits appear, resulting in wear and failure of the rubber cup.
After inquiry, this product has no domestic parts, and the import price is 12,000 yuan. Obviously, it is not economically feasible to purchase. We found that the rubber cup in the BJ2020 Jeep clutch repair kit is similar in size to this machine, except that the outer diameter is slightly smaller. After analyzing the size of the piston cavity, it is considered that this piece can be fully processed by lathes; it is processed with a fast small feed to reduce the roughness of the inner cavity; the tool holder is adjusted 2-3 degrees when feeding, so that the inner wall has a certain slope; the inner diameter According to the outer diameter of the cup, it is 0.4-0.5mm smaller than its original size. After careful measurement and processing, it can be used normally after repair.
5. Welding repair of wearing parts of T815 dump truck
Our company has a total of 30 T815 self-cylinder vehicles made in the Czech Republic. It has been found in several years of use that due to the localization of the chassis of this car, the quality of the chassis cannot meet the construction requirements. Great economic losses. After long-term exploration, we have repaired the machine's wearing parts (such as steel plate lugs, steel plate clips, spring steel plates and half shaft sleeves, etc.), and achieved good results. Note when welding: use DC arc welding machine, J506 electrode, preheating before welding, heat preservation after welding to eliminate local thermal stress and prevent stress concentration.
