Created on:2022-03-19 10:16

Causes and measures of oil leakage of hydrostatic motor oil seal of Dongfeng 4 diesel locomotive

Causes and measures of oil leakage of hydrostatic motor oil seal of Dongfeng 4 diesel locomotive

1. Introduction

Dongfeng 4B and 4C locomotives have been in full load and high-speed operation for a long time, the leakage failure rate of hydrostatic motor oil seal has increased significantly, and the hydrostatic motor oil seal has frequent oil leakage and failure, resulting in the continuous increase of maintenance workload. At the same time, the hydrostatic oil leaked from the hydrostatic motor oil seal adheres to the surface of the cooling section, fan blade, roof shutter and hydrostatic oil pipe under the action of the high-speed rotating fan, which seriously affects the internal cleaning of the locomotive cooling room. As the cooling section is polluted by oil, the dust in the air is easy to stick to the section. As it is located in the western region, there is a lot of sand and dust in the air, which soon forms a layer of oil on the surface of the cooling section, which seriously affects the heat dissipation of the locomotive. With a large amount of oil leakage at the oil seal, the hydrostatic motor cannot rotate normally due to lack of oil in the hydrostatic system, which is prone to serious faults such as high oil-water temperature of the locomotive, piston cylinder pulling of the diesel engine, oil pressure drop, action of water temperature relay, action of oil pressure relay, unloading and shutdown of the locomotive, resulting in machine failure and temporary repair, which has a great impact on the quality and operation safety of the locomotive.

2. Cause analysis

The ZB732 hydrostatic motor is used on DF diesel locomotive. It is composed of shaft, front pump body oil seal, gland, end cover, oil seal, rear cover, port plate, oil cylinder body, spindle ball sleeve, spring, spring seat, pressing plate, connecting rod, piston and mandrel. The skeleton oil is encapsulated in the bearing seat, and the bearing is below the oil seal, The function of oil seal is to prevent hydrostatic oil leakage of lubricating bearing. The oil seal is a skeleton structure with steel rings inside and black rubber on the outside. The black rubber is close to the outer surface of the main shaft. If there is a gap between the black rubber and the main shaft, the hydrostatic oil will leak from this gap. This phenomenon is the oil seal leakage fault. The main causes of hydraulic motor oil seal leakage are as follows:

(1) Oil seal. The skeleton oil seal is the only seal outside the spindle of ZM732 hydrostatic motor. Through the inspection and analysis of the inside of the oil seal, it is considered that the rubber part of the skeleton oil seal in contact with the main shaft plays a main sealing role, and most of the oil seal leakage is the leakage of hydrostatic oil between the oil seal and the main shaft. Due to the poor quality of the existing oil seal and the poor high temperature resistance of the oil seal rubber, the oil seal rubber ring is easy to soften and expand under the action of high temperature for a long time, so that the inner ring of the rubber oil seal can not always stick closely to the shaft diameter, resulting in a gap between the shaft and the shaft diameter, resulting in oil leakage. Due to oil leakage, the wear of the skeleton oil seal increases continuously after long-term application. When the wear reaches a certain degree, the spring inside the skeleton oil seal is in direct contact with the main shaft, the spring is worn off, and the main shaft of the hydrostatic motor grinds out a groove along the circumference, resulting in a large loss of hydrostatic oil. At the same time, the rubber part in contact with the skeleton oil seal and the sealing end cover plays a secondary sealing role. The inside of the skeleton oil seal is a steel skeleton. During the installation of the skeleton oil seal, if the steel skeleton is deformed due to improper operation, it is easy to cause that the outer rubber surface of the oil seal is not close to the inner circumference of the end cover, so that the hydrostatic oil leaks through here.

(2) Axis. When the hydrostatic motor works, the maximum oil pressure is more than 14MPa. In order to make the oil seal work well, the inner diameter of the skeleton oil seal is required to be smaller than the outer diameter of the main shaft to ensure the oil sealing pressure of the oil seal. Through the measurement and analysis of the main shaft size of the locomotive hydrostatic motor used on the line, it is found that although the shaft diameter of many hydrostatic motors is within the size limit, in most cases, after long-term high-speed and heavy-duty operation, the wear and thinning size of the main shaft is close to the lower limit. In this case, it is easy to cause the small oil sealing force of the oil seal, so that the oil seal of the hydrostatic motor leaks.

(3) Hydrostatic oil magnetic filter. In order to ensure that the hydrostatic oil in the hydrostatic motor is clean and reduce the failure of the hydrostatic motor, DF diesel locomotive is equipped with a hydrostatic oil tank. There is a magnetic filter in the hydrostatic oil tank, which is used to absorb impurities in the oil. Because the impurities in the oil will wear the spindle surface of the hydrostatic motor and the inner surface of the sealing rubber ring, resulting in surface scratch failure and oil leakage of the oil seal. Through practical use, it is found that the hydrostatic motor shaft is seriously worn due to many impurities in the hydrostatic oil, resulting in more oil leakage of the oil seal.

3. Measures

Through the analysis of the structure of relevant components of the hydrostatic motor, it is found that since the main shaft of the hydrostatic motor is connected with the cooling fan through keys and fastening bolts, and the connection is far from the upper bearing of the main shaft of the hydrostatic madane, due to the imbalance of the blades of the cooling fan, the blades will inevitably produce periodic radial vibration under high-speed rotation, This vibration will inevitably increase and decrease the distance between the shaft and the oil seal periodically and instantaneously. Therefore, from the analysis of structural principle, it is impossible to make the oil seal of hydrostatic motor completely leak free. Our current focus is how to minimize the oil leakage through technical improvement. Through theoretical research and a large number of experiments, the following specific improvement measures have been taken.

(1) Double oil seal structure is adopted. Change the single oil seal structure of hydrostatic motor and adopt double oil seal structure, as shown in Figure a. Through actual measurement, it is found that the distance between the original oil seal cover of single oil seal and the cooling fan is enough to accommodate the oil seal end cover of double oil seal. Therefore, the crude oil seal end cover is technically transformed into an oil seal end cover that can install two oil seals, so that the double oil seal can seal the oil, and its oil sealing effect is significantly improved than before. Moreover, the inner diameter of the double oil seal end cap is the same as that of the original single oil seal end cap, which is convenient for normal replacement in maintenance.

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(2) Strictly limit the size of the hydrostatic motor shaft. The size of the hydrostatic motor shaft shall be strictly limited. The shaft diameter of the new shaft must be close to the upper limit. Those whose shaft diameter is close to the lower limit shall not be used as much as possible, so as to avoid oil leakage due to small oil seal force caused by small shaft diameter.

(3) Strictly implement the maintenance process. Strictly implement the maintenance process. When installing the oil seal, the maintenance workers shall strengthen the inspection. Once the outer circle of the oil seal is uneven and there is a gap with the end cover, the oil seal shall be replaced immediately. In addition, when installing the oil seal, the force should be light and uniform. It is strictly prohibited to knock on one side and load and unload savagely, so as to avoid the deformation of the steel framework and oil leakage.

(4) Modify the maintenance scope. The maintenance scope is modified. The original cleaning of magnetic filter during 4 minor repairs is changed to cleaning and replacing hydrostatic oil during 3 minor repairs, so as to reduce the oil leakage caused by the serious wear of impurities in hydrostatic oil on the shaft surface of hydrostatic motor.

(5) Pay attention to cleaning during maintenance. Pay attention to the cleaning during maintenance. When replacing the hydrostatic pump, hydrostatic motor, safety valve, temperature control valve and oil pipe, workers must pay attention to the cleaning of the operation process, especially after the pipeline welding repair, the internal welding slag must be cleaned to prevent external impurities from entering the hydrostatic oil and damaging the sealing effect of the oil seal.

Through a large number of loading tests, after taking the above treatment measures, especially after the hydrostatic motor oil seal is changed from the previous single oil seal to the double oil seal structure, the number of repairs due to the leakage of the hydrostatic motor oil seal is reduced by 60% compared with the previous, and the failure of the leakage of the hydrostatic motor oil seal is effectively controlled. Machine failure, temporary repair and preparatory repair are greatly reduced, which saves a lot of human, material and financial resources, reduces the maintenance cost of the locomotive, improves the quality of the locomotive and ensures the normal operation of the locomotive.

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