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2022 October the Fourth week UNIM Technical Knowledge: Common faults and diagnosis methods of urban metro vehicle gearbox

As one of the most important components of the bogie system, the gear box is used to transmit the torque generated by the motor through the coupling and drive the wheels to transmit the traction of metro vehicles. Because of the particularity of its function and structure, the gearbox is the component with the highest failure rate in the bogie, and its performance directly determines the application performance of the bogie.

 

The phenomenon of oil leakage of the subway gearbox is one of the common gearbox failure modes. The main reasons are as follows: oil leakage of the closing surface, oil leakage of the bearing seal, oil leakage of the end cover vent, oil leakage of the oil filler and oil drain, etc. The oil leakage and seepage of various components of the gearbox will not only affect the working condition of the surface of each component, but also reduce the lubricating capacity of other small parts inside the gearbox, thus increasing the temperature rise, causing serious wear of internal parts, and finally causing damage to other relevant components of the gearbox. Therefore, it is of great practical significance to do a good job in analyzing the causes of oil leakage in the subway gearbox and taking some relevant measures to solve this problem.

 

1. Principle and composition of gearbox

There are two types of metro vehicles, which are divided into motor cars and trailers. The vehicle without power is a trailer, and the motor car with power is used to transfer energy. The motor car is suspended with a traction motor and gearbox. The motor car drives the traction motor to rotate by receiving the electric energy transmitted by the pantograph, and mainly realizes the transformation and transmission of kinetic energy through electric transmission. As a speed change mechanism, the gearbox converts the higher speed of the traction motor into the appropriate wheel set speed, thus driving the subway vehicle forward. The driving gear box for metro vehicles is located at the bottom of the power car body, with one end suspended on the axle and the other end suspended on the frame. In the high-speed operation of the train, the impact of the track directly acts on the gearbox.

 

2. Gearbox lubrication mode

When metro vehicles are running on the main line, due to the complex working conditions of the line, the bogie is frequently subject to vibration and impact from the track. In order to improve the performance of the gearbox and ensure the service life of the components in the gearbox, reliable lubrication and sealing measures must be taken in the design process. The lubrication method of the bearing and gear of the gearbox drives the flow of lubricating oil in the gearbox through the rotation of the gear to generate splash oil mist for lubrication, that is, the "splash lubrication method", which acts on the mating surface between the gear and the gear and other parts of the gearbox to achieve cooling and lubrication of the gearbox. There is an oil pointer on the lower gearbox, which has two horizontal lines above it, representing the highest and lowest oil levels respectively. Under normal working conditions, the oil level must be kept between the two lines indicated by the maximum oil level and the minimum oil level.

 

3. Common faults and solutions of gearbox

(1) Labyrinth seal failure

Labyrinth seal failure may be caused by the following reasons: during the design and manufacturing process of the gearbox, due to poor design or assembly quality of the labyrinth seal, the assembly tolerance of the gearbox labyrinth seal and other parts is too large, and the oil and gas at the labyrinth seal are easy to leak out; Filling too much lubricating oil into the gearbox will cause the oil level to exceed the upper scale mark, and high oil level will cause oil and gas to escape from the labyrinth. The specific solutions are as follows: drain a proper amount of gearbox lubricating oil, adjust the oil level to near the mid scale line, clean the external surface of the gearbox polluted by oil and gas, and regularly observe the gearbox oil level. If the oil level drops significantly or drops obviously, remove the gearbox output end cover for internal inspection, use special equipment to detect the size and fit tolerance, and replace the sealing structure and O-ring.

 

(2) Closure surface fault

The following reasons may be responsible for the failure of the box closing surface: improper assembly of the box closing surface (improper assembly of sealant or O-ring), nonstandard application of sealant, and the sealant does not cover the entire joint surface area, which may lead to the leakage of lubricating oil from the gap; During gear box assembly, before adjusting the clearance of intermediate stage bearing, sealant is applied on the closing surface of the box, but the bolts on the joint surface are not tightened. After the clearance adjustment is completed, some sealant may have hardened. When all the bolts on the joint surface are tightened later, the sealant cannot be squeezed and spread evenly, resulting in gaps or missing points in some areas, which leads to the leakage of lubricating oil. The specific solutions are: clean and assemble in strict accordance with the maintenance specifications, apply sealant on the box surface, adjust the bearing clearance and ensure that all bolts are tightened according to the regulations, select the sealant model according to the relevant requirements and apply it according to the specifications.

 

(3) Oil pointer position fault

The position failure of oil pointer may be caused by the following reasons: seal failure or poor installation; Cracks on the glass plate caused by foreign objects hitting or mistakenly spraying cleaning agent on the glass cover plate. The specific solutions are: when the oil level does not drop, observe regularly; If there is no obvious oil leakage, it shall be replaced during normal maintenance; If the oil level drops obviously or there is obvious oil leakage, replace it immediately.

 

(4) Oil blackening fault

The oil blackening may be caused by the following reasons: the oil blackening may be caused by the running in of new bearings after a period of time; The oxide skin on the replaced new bearing ball that has not been removed may be washed off by oil during operation, resulting in oil blackening; During the maintenance of the gearbox, the running in test run oil is not replaced in time, and the color of the oil will be black after the test run oil is mixed with new oil (with clear color).

 

The specific solutions are as follows: first observe whether the blackened oil deposits in the gearbox are powder or metal fragments. The powder like foreign matters should be caused by poor internal cleanliness of the gearbox. If there are metal fragments, find out the cause, drain oil to flush the gearbox, refill oil, and then continue to enter the gearbox? During the running in test, after the test run, one end of the high-speed shaft of the gearbox shall be lifted while hot to drain the oil in the gearbox as much as possible from the side of the oil filling magnetic plug. The running and commissioning oil shall be replaced regularly during maintenance to ensure the cleanliness of the oil.

 

(5) Oil leakage

Because of the non-contact labyrinth seal structure, oil mist will spill out along the labyrinth seal gap. In the process of overflow, most of the oil mist condenses and returns to the box, and a small part of the oil mist continues to spread outwards. When encountering cold air, the oil mist that spreads outwards will condense on the outer surface of the bearing pedestal and the sealing ring, and combine with the dust in the environment? The accumulated wet ash stains will form and be adsorbed on the surface of the box body: the other part will be condensed in the annular groove of the water outlet, and will be discharged from the water outlet together with the external cooling water vapor after cooling. The liquid sagging marks will form near the water outlet, which may cause the sagging marks to spread when the vehicle is running. In addition, excessive lubricating oil in the gearbox will aggravate the above phenomenon. The specific solutions are as follows: For the parts where the putty has dried, please clean the putty and clean it with cleaning agent, and apply a layer of silica gel on the sealing connection parts and the periphery for sealing. After the gearbox is newly filled with lubricating oil, it must be ensured that the lubricating oil leakage within one oil change cycle will not cause the lubricating oil level in the gearbox to drop from the middle level to below the minimum level. If the lubricating oil level gradually decreases, it cannot meet the normal oil change cycle of gearbox maintenance. In combination with maintenance, appropriate time shall be selected for plugging measures. When the gearbox oil level is below the minimum level, lubricating oil shall be added again.

 

(6) Oil emulsion fault

The gearbox oil emulsion failure may be caused by the following reasons: the main reason is that external dust, dust, moisture, etc. are sucked into the gearbox from the gearbox ventilator or seal, especially when the subway vehicle passes through the tunnel, negative pressure is formed at the gearbox ventilator, and polluting small particles such as dust, dust, moisture, etc. are easy to flow back into the gearbox with the air flow, causing emulsification or blackening of the lubricating oil. The specific solutions are as follows: drain the old oil first, then add 5% of the normal oil for flushing, and then drain it. Add the working oil with normal oil volume to the standard oil level. Under normal conditions, operate for 1~3h, and the oil temperature can reach 40 ℃. Drain all lubricating oil while it is hot within 30min after the gear box is shut down. Then add the working oil again to the standard oil level according to the use and maintenance requirements. During 1~3 months of normal operation, monitor the lubricating oil of the gearbox, take random samples for physical and chemical tests, and ensure that the performance of the lubricating oil meets the operating requirements.

 

4. General fault diagnosis method of gearbox

If the gearbox fails, it needs to be diagnosed in time, and can be quickly located and judged through efficient and scientific diagnostic methods. The general methods for diagnosing gearbox faults are:

Frequency spectrum analysis method: when the gearbox fails, the fault information contained in its vibration signal usually appears in the form of modulation, and the source of the fault problem can be known by demodulating the fault information.

 

Signal analysis method: dynamic signals such as noise, vibration and temperature rise generated by the gearbox in the working process are collected by professional equipment, and the fault is analyzed and diagnosed according to the signal analysis method.

 

Wear analysis method: according to the metal wear theory, through collecting the samples in the gearbox lubricating fluid, testing the kinematic viscosity, water content and metal wear analysis in the lubricating fluid, and judging the source of materials by the wear metal parts per million in the lubricating fluid, so as to determine the state of the lubricating fluid and comprehensively evaluate the oil performance.

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More about UNIM General Gearboxes:

Transmission or gearbox are widely applied in Mechanical Transmission, wind turbines, and also used in agricultural, industrial, construction, mining and automotive equipments. WD high precision deep groove ball bearings, angular contact ball bearings, cylindrical roller bearings and some customized bearings for gearboxes are high speed, low noise and long life.

 

General Gearboxes 

 

Working together with over 20 Chinese leading factories, UNIM relies on China completive industry resources and provides you with the optimum solution. UNIM has over ten-year experience in making conventional bearings, precise bearings and non-standard bearings. UNIM also produces and exports bearing parts (roller, ball, seal, ring and so on), chain, sprocket, pulley and such other machinery parts.

 

 

 


2022-10-21