1. Reasons for oil leakage of bushing
(1) Structural and processing reasons
1) The shaft seal structure is incomplete.
2) The joint surface between the tile base and the tile cover is deformed,
3) Poor shaft seal design. The gap distance between the two ends of the tile in the tile seat is small, there is no oil return groove, and there is a gap between the two joint surfaces of the oil seal. There is no oil baffle at both ends of the tile.
4) The quality of the oil ring processing is insufficient, and the oil ring is unbalanced: the size does not match.
(2) Reasons for operation and maintenance
1) Excessive filling of lubricating oil. Exceeding the allowable level.
2) The lubricating oil brand does not match.
3) The old sealing coating at the joint between the tile seat and tile cover cannot be cleaned thoroughly.
4) Uneven filling of the new sealing coating, and even forgetting to fill the coating.
5) The sealing gasket is not installed correctly.
6) Poor sealing at the inlet and outlet pipe joints, oil cup, thermometer sockets, and valves.
7) The ventilation system creates a vacuum at the bearing end, and lubricating oil is drawn out from inside the bearing.
2. Analysis of Sealing Characteristics of Sliding Bearings in Imported Motors
(1) Characteristics of Sealing Structure for Japanese Motor Bearings
1) Toshiba Motor Japan
An oil baffle is welded into the bearing seat of the steel plate welding, and inserted into the shaft groove instead of the shaft seal. A baffle is welded around the inner cavity of the tile seat near the mating surface as an oil groove on the mating surface.
One end of the bearing has a fixed oil blocking ring, and the other end has a fixed oil ring for lubrication. Each tile seat is equipped with a thrust tile, which serves as an oil barrier. Its outer diameter is spherical and matches with the tile seat.
There are two types of thrust pads: one-way and two-way. The bearing seat at the load end and mechanical connection of the unit is a two-way thrust pad, which controls axial movement. The remaining tile seats are unidirectional thrust. The two circular roots of the rotating shaft do not have oblique oil slinging grooves, but square oil slinging grooves, and are equipped with oil blocking plates that are inserted into the square oil slinging grooves to provide oil blocking and sealing.
The oil slinging groove is designed for motors with a shaft diameter of 500mm, a groove width of 30mm, and a depth of 15mm. There are two 5mm wide oil slinging rings on the shaft for oil slinging.
The joint surface of the thrust tile and the joint surface of the tile seat are installed at a 45 degree angle offset, so that the two joint surfaces are not on the same line, which plays a role in blocking oil. The bearing oil supply system has high-pressure sleeves for start-up and low-pressure oil for operation.
The fixed oil ring on the shaft is not limited by speed and steering, which can bring oil to the scraper and inject it back into the bushing, and prevent it from continuing to lubricate when the pipeline is cut off.
The design of the tile seat structure is convenient for motor installation, rotor suspension, and unrestricted in the axial direction, making it easy for the coupling stopper to detach. And generally, the motor must have one end of the upper and lower tiles removed in order to detach the coupling and lift out the rotor. During installation, if the two couplings do not match the holes, the couplings can be rotated freely to align, which is beneficial for equipment installation work.
The tile seat oil return indicator is easy to observe and connected by flanges, making it easy to operate and less prone to oil leakage
2) Structural characteristics of Hitachi Electric in Japan:
The bearing sealing structure of a 2500kW motor manufactured by Hitachi in Japan. The tile base and tile bottom are welded components, and 2mm thick brass plates are installed on the shaft seals at both ends of the tile base. There are 3 sets of 3 pieces per set at each end, forming a labyrinth seal ring that fits tightly with the shaft root neck. An air pressure seal is added between the inner sealing rings, and the air comes from the fan of the motor itself and is sent to the space of the sealing rings through the ventilation pipeline; Maintain positive air pressure and seal the oil leakage area. Different from Toshiba motor structure. There are no baffles at both ends of the bushing, and there are oil return grooves and drilled oil return holes on the joint surface of the bushing to control oil leakage.
(2) Characteristics of Siemens motor sealing structure
1) Sealing structure of bearings for general medium-sized motors:
600kW, 1000r/min motor bearing sealing structure. There are two oil slingers at the circular roots on both sides of the shaft diameter that are higher than the shaft neck size, and they are inserted into the return oil grooves at both ends of the bushing to seal the bearing, which is the line of defense against leakage. On both sides of the tile joint surface, two copper baffles are installed as the second line of defense against leakage. This sealing effect is good.
2) Siemens motor bearing sealing special structure
There are no oil slinging grooves or oil rings at the two circular roots of the shaft neck, but a straight smooth surface is connected to the circular root of the shaft shoulder. The two ends of the tile seat are equipped with tile seat shaft seals, which have four brass oil baffles on top, forming a labyrinth seal ring. The brass oil baffle has a blade shape and fits tightly with the shaft surface, without oil leakage.
On one side of the bearing joint surface, there is an oil inlet pipe oil hole, and on the other side, there is a return oil groove in the shape of a collection groove. There are two small square holes under the groove as return oil holes, which allow oil to flow into the lower bearing seat. This allows the oil in the oil collection tank to not only establish an oil film in the bearing, but also allow excess oil to flow back to the lower bearing seat through the holes, reducing the amount of oil return at both ends of the bearing and preventing oil leakage caused by excessive oil return spraying onto the shaft seal of the bearing seat. Alloy baffles are installed at both ends of the bushing. Closely fit with the surface of the shaft. In addition, there are thrust pads on both sides of the bushing to control the axial displacement. The length of the bushing is 0.8 times that of the journal. The tile seat is made of cast iron and has a spherical tile arc. The temperature measuring element is pressed tightly with a spring and the lower tile mouth temperature hole, resulting in a high temperature measurement effect.
(3) Characteristics of Sealing Structure for Motor Bearings in the Former Soviet Union
The bearing sealing structure of the 1500KW bipolar synchronous machine is designed for sealing, and alloy baffles are installed at both ends of the bushing as a leakage prevention measure. In addition, tooth groove shaft seals are installed on both sides of the uranium bearing seat as a second anti slip measure.
3. Improvement measures for bearing sealing device
(1) The groove sealing method for machining grooves on the shaft has caused oil leakage in Soviet and old product motors due to unreasonable sealing structures. When repairing, it can be modified according to the bearing sealing measures of Toshiba Motor in Japan. A groove shaped groove is machined on the shaft, and a baffle is inserted into this groove groove on the tile seat for sealing, which has a good effect.
Operation process:
1) Firstly, create groove shaped grooves on the rotating shaft. Large motors can be operated on the original equipment without the need for machining on a lathe. The method is to use a DC motor to drive the processed rotor to rotate at a speed of 10-50 r/min. Remove the upper tile cover and upper tile from the bearing to be processed, keep the lower tile and oil ring still, use oil ring to lubricate, close the valve of the oil delivery pipeline, and wrap the inlet and outlet oil pipes of the tile seat with cloth. To prevent the cut iron powder from falling into the workpiece, it is necessary to block both sides of the shaft neck with rubber pads or cardboard and press them down. Install a tool holder at the joint surface of the bushing for machining groove shaped grooves, and the machining tool holder can be made using a small tool holder on the lathe. Prevent axial movement during turning, remove the lower tile after machining, clean the iron powder and dirty oil.
When machining grooves on both sides of the journal, the tool should be turned upside down to ensure safety during turning.
2) Remove the lower tile of the unit and support the rotor with spare tiles or wooden blocks. Close the lower tile and send it to the lathe for processing.
3) Design the sealing ring size and cast aluminum parts according to the tile seat and shaft dimensions. When designing dimensions, the displacement should be taken into consideration to prevent the baffle inserted into the slot from rubbing due to shaft displacement. The clearance between the sealing ring and the shaft is selected according to the clearance between the shaft and the tile.
(2) Add oil slinger and sealing ring device on the shaft
Insert a sleeve with an oil slinger onto the shaft, which can bounce the exposed oil back into the sleeve. Install a sealing ring outside the sleeve. For bearing bodies with sufficient space, this method can achieve leak prevention.
(3) Add labyrinth sealing device
A labyrinth sealing device with a simple structure and wide applicability. Due to the small gaps between each part. The length is very long, so it has a greater resistance to oil flow and a better oil prevention effect.
(4) Measures to extend the oil ring groove
To prevent oil ring spillage, extending the local oil ring groove on the upper bushing below the joint surface of the lower bearing can effectively prevent oil spillage. Two thirds of the original tile has oil ring grooves. To prevent oil leakage, the oil ring grooves are extended below the centerline. Add oil ring groove baffle and fix it with screws.
Non scraping technology for sliding bearings
(1). Overview
The traditional machining of split bushings involves turning the Babbitt joint pad into a complete circle, leaving a certain amount of scraping allowance, and then manually scraping and grinding it. This method has long processing time, high labor intensity, and unstable quality, requiring operators to have high operational experience. In order to improve the quality of bearing repair, shorten the repair cycle, and improve working conditions, a new process that does not scratch the bearing can be adopted. Practice has proven that using machining methods is feasible and effective.
(2). Process characteristics
1) Cutting parameter selection: cutting speed of 80~150m/min, cutting depth of 0.02~0.05mm, cutting amount of 0~0.15mm/r.
2) In order to reduce deformation of the bearing during machining. To ensure machining accuracy, specialized fixtures are required. Usually, circular clamps are enclosed with 30mm thick steel plates and made by turning.
3) Use a slightly larger gap than when manually scraping and grinding the bushing. (Generally larger by 0.04-0.05mm).
4) First, use an alloy cutting tool to remove the inner circle of the bearing, but leave a margin of 0.03~0.05mm, and then use a gemstone cutting tool for precision machining. When using a gemstone knife for processing, the roughness is RaO.8 to achieve a mirror finish, and then the oil groove is milled.
5) The precision of machining the geometric dimensions of bushings is higher than manual scraping, so the level of liquid friction lubrication is improved.
6) The surface of the machined bearing increases in contact with the journal, and under certain load conditions, the machined bearing reduces its operating temperature due to the decrease in pressure.
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MG-EPB5Z Plastic Plain Bearings：
MG-EPB5Z Plastic Plain Bearings It is a high load material with excellent low friction factor. Marginal load application is acceptable and it is with good wear resistance both for hard and soft shafts. Continuous working temperature: -100℃～250℃; High load capacity; Higher speed is permissible; Marginal pressure is permissible; Best performance for oscillating movement.
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