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2 Common fault analysis and maintenance 2.1 Rotational failure analysis: The cause of the excavator's rotation weakness may be: excessive oil return resistance, excessive movement resistance of the slewing mechanism and low servo operating pressure; main pump, motor and reversing valve wear, etc. , possible causes:
2.1.1 Pressure-limiting valve damping hole blockage Generally, the setting pressure of the rotary oil circuit is lower than other pressures of the system, mainly related to the rated pressure of the hydraulic motor, and also far lower than the rated pressure of the upper pump, the state of the pressure limiting valve of the rotary oil circuit. It is always open. The constant opening of the pressure limiting valve causes the wear of the valve plug sleeve on the one hand, and the impurity in the oil can block the orifice damping hole on the other hand. After the damping hole is blocked, the opening pressure of the pressure limiting valve is completely determined by the preloading force of the main spool return spring, and the preloading force can only satisfy the friction force and hydraulic power of the spool, and cannot drive the swing motor. .
2.1.2 Filling valve wear and tear valve Due to frequent opening and closing, the deformation and wear between the valve seat and the valve core will occur, and the wear pattern is mainly based on the wear of the valve cone. The worn valve core and valve seat will cause the sealing performance of the circuit in the non-replenishing state (ie, the driving state) to decrease, and the working pressure oil leaks from the replenishing valve, thereby causing the rotation to be weak.
(1) Fault check: First check the working condition of the hydraulic main pump, and observe the load level of the engine under the full-speed state of the boom, which is mainly judged according to the exhaust smoke color and sound of the engine. If the load level can reach 2/3 of the rated power, the main pump works normally. Then operate the rotary device, if the engine load is very low, and the rotation speed is very slow, or even can not be rotated, it can be initially determined that the charge valve and the pressure limiting valve are faulty. (2) Troubleshooting: Disassembling the charge valve and limiting the pressure Valves, such as the valve plug of the charge valve, wear less than 0.3 mm to smooth the valve core to the original taper, or to flatten and polish with a fine boring tool on a drill press or lathe. When assembling, a gasket can be placed on one end of the spool spring as needed. If the amount of wear is greater than 0.3 mm, the charge valve needs to be replaced. Repairing the pressure limiting valve mainly depends on the wear of the pilot valve. The repair method can also be used for emergency repairs and replaced if necessary. To repair the pressure limiting valve, it is necessary to check whether the orifice is unblocked by the light transmission method. If not, use compressed air to blow through. During assembly, if there is no pressure measuring device on site, the adjusting bolt can be left 1~2 buckle outside the lock nut, and then adjusted according to the operation.
For the grinding condition of the valve core, the main reason for the premature wear of the valve core is that the hardness of the valve core is low. It is recommended that the manufacturer appropriately increase the surface hardness of the valve core and change the material of the valve core. The excavator repaired by the above method is used for hundreds of hours, and no fault of rotation is caused again, which ensures the normal operation of the excavator.
2.2 The loose motor is loose. 2.2.1 Fault phenomenon The bolts at the joint between the swing motor and the rotary platform are loose and not firmly combined.
2.2.2 Failure Analysis The mining environment and the force generated by the inertia at the joint are the key factors for the loosening of the swing motor. In general, new excavators rarely have slack motor looseness during use. However, if the swing motor and the swing platform have been dismantled during maintenance, even if the tightening torque of the bolt is not less than the original tightening torque value, the loose motor will be loose.
(1) The joint between the swing motor and the rotary platform is fastened by selecting a bolt of a certain diameter and matching the matched torque. The tightened bolt has sufficient pre-tightening force, and the pre-tightening force makes the joint plane Frictional force is generated to meet the design requirements to resist the impact caused by the excavation environment and inertia, so that the swing motor is not loose.
If the tightening torque when re-installing the swing motor is less than the technical value, the tightening force of the bolt will be reduced, and the friction between the joint planes will be reduced accordingly, so that the swing motor will loosen after the excavator has been working for a period of time. phenomenon.
When the bolt is used repeatedly, its tensile strength will decrease slightly. Although the torque during reinstallation meets the technical requirements, the tensile stress of the bolt will decrease and the pre-tightening force of the bolt will be reduced. Therefore, when reinstalling the swing motor, the tightening torque is 30 to 50 Nm larger than the specified value.
(2) The amount of friction between the joint planes depends not only on the amount of force applied between the planes, but also on the coefficient of friction and the contact area between the planes. Due to the presence of the joint plane oil and debris, the coefficient of friction between the planes is reduced and the contact area is reduced, so that the friction between the flat surfaces after fastening is reduced, resulting in looseness of the swing motor.
(3) The positioning pin between the slewing motor and the slewing platform is not only a positioning function, but the locating pin and the hole are interference fit, which greatly increases the initial resistance of the slewing motor relative to the slewing platform. Reduce the possibility of loose motor rotation. Therefore, when the locating pin is loose, the slewing motor will be loosened.
Analysis and repair of common faults of Hitachi hydraulic excavator
1 Introduction Hydraulic excavator is a multifunctional machine that is widely used in hydropower, mining and other engineering construction. Hitachi series excavators are common brands in hydraulic excavators. Guangdong Hydropower Second Bureau Co., Ltd. has several Hitachi series hydraulic excavators. In the course of use, various faults often occur, which affects the progress of construction. Here, we introduce several common faults of Hitachi series hydraulic excavators, and analyze the causes of the faults from the aspect of construction, and propose solutions and suggestions.