Created on:2021-09-06 10:32

Construction machinery_ Hydraulic failure of d85a-18 bulldozer

Construction machinery_ Hydraulic failure of d85a-18 bulldozer

The high temperature of the hydraulic system can cause the failure of seals in the system in a short time, the oxidation and deterioration of hydraulic oil and the deformation and damage of some components. A d85a-18 bulldozer (hydraulic system as shown in Figure o) of a company has a sudden sharp rise in the temperature of the hydraulic system during normal use. During the inspection, the oil temperature is as high as 124 ℃ after only 0.5h of operation, far exceeding the normal working temperature (50 ~ 70 ℃).

The fault causes may be strain, seal failure, wear of slide valve, aging of seal and damage of oil pipe. The leakage of various valves, oil seals and oil pipes may be the direct cause of high temperature.

The troubleshooting method and process are as follows.

First, measure the working pressure. The standard working pressure of the machine is 14 ~ 15MPa, and the actual value is 14.2Mpa, indicating that the hydraulic pump works normally.

Second, check the hydraulic cylinder. Mainly check the working conditions of bulldozer lift cylinder 14 and cultivator cylinder 10, that is, lift the bulldozer and cultivator to make the piston rods of the two hydraulic cylinders extend naturally, and the extension speeds are 64mm / 15min and 52mm / 15min respectively. Then the bulldozer and the cultivator are used to support the engine body, turn off the engine, and observe the retraction of the piston rods of the two hydraulic cylinders under the action of the gravity of the engine body. The results show that the speed of the bulldozer cylinder is 84mm / 15min and the speed of the cultivator cylinder is 82mm / 15min, which are within the standard range, indicating that the sealing effect is good.

Third, check. Small copper powder was found. It was preliminarily determined that the oil distribution plate of the pump was strained. After disassembly and inspection, it was found that one oil distribution plate was slightly strained. After grinding and adjusting the clearance, the installation test shows that although the temperature has decreased, it still exceeds 100 ℃ after 0.5h, and the condition has not fundamentally improved.

Fourth, disassembly and inspection. The matching clearance of slide valves in bulldozer lift valve 4, bulldozer tilt valve 6 and cultivator valve 9 was disassembled and checked. The results showed that the clearance between slide valve and valve body was within 0.03 ~ 0.06mm, and there was no obvious scratch and strain, so the possibility of leakage of these three slide valves could be ruled out; Check the safety valve 3, flow check valve 5, check valves 11 and 16, and there is no strain, indicating that there is no leakage; Check the sealing conditions everywhere, and no damage is found.

Finally, check the oil pipe, that is, a metal connecting pipe from bulldozer tilt valve 6 to cultivator valve 9 in the hydraulic oil tank, with O-rings at both ends; In addition, there is a metal connecting pipe from the cultivator valve 9 to the oil filter 2. The seal between it and the valve 9 is a plane seal, and the other end is a rubber ring clamping seal. After careful inspection, the two metal oil pipes are in good condition without sand holes and cracks; There is a flat plate between the oil return pipe and slide valve 9. After careful inspection, it is found that the flat plate is blue locally, but there is no obvious plane deformation during plane inspection. It can be basically concluded that the hydraulic oil temperature is too high due to the oil leakage at these two planes.

In view of the above failure causes, two gaskets were made and installed at the joint of the flat plate, the valve and the oil pipe. The installation test shows that the machine has completely returned to normal.

This fault shows that due to long-term use, the bolts fastening the plate are not the same. When encountering high temperature, the connecting plane of the plate or oil pipe is deformed, so that the original plane can not play a good sealing role, resulting in oil leakage.

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