Abstract: The 1 #, 2 #, and 3 # oil pumps at Dalian Company's Xingang Station are multi-stage horizontal open pumps with a pump model of KDY790-77 × 3. The main bearings of the pumps are sliding bearings (TFH75-04/05) and are equipped with angular contact ball bearings to balance residual axial forces. Sliding bearings have smooth, reliable, and noise free operation. Under liquid lubrication conditions, the sliding surface is separated by lubricating oil without direct contact, which can greatly reduce friction loss and surface wear. The oil film also has a certain ability to absorb vibrations. However, sliding bearings require high installation accuracy, and incorrect installation can lead to problems such as bearing heating and vibration. Therefore, how to correctly install and maintain the sliding bearings is the key to the normal operation of the oil pump.

Keywords: oil pump sliding bearing; Installation; maintain; early prevention

Sliding bearings, also known as bushings, are divided into radial bushings and thrust bushings. The KDY790-77 × 3 oil pump bearing of Dalian Company's Xingang Station is a radial bearing. The following will explain the precautions for the installation and maintenance of this bearing.

1. Installation of sliding bearings

Sliding bearings are generally used under low-speed and heavy load conditions. The following are the precautions for installing sliding bearings:

1.1 The installation of sliding bearings should ensure that the journal rotates flexibly, accurately, and smoothly in the bearing hole. Due to the complicated maintenance of sliding bearings, it is necessary to ensure that the installation of the bearings is completely correct and error free during installation. Ensure that the bearings can operate normally without any errors.

1.2 Pay attention to the smooth flow of the oil circuit and connect it to the oil tank. When scraping, the dots on both sides of the oil groove should be soft to form an oil film, and the dots on both ends should be even to prevent oil leakage. It should be easy to add lubricating oil during later maintenance. Beneficial for maintenance.

1.3 The bearing shell and bearing seat hole should be scraped and pressed firmly, and the cutting surface of the bearing shell should be 0.05-0.1mm higher to facilitate compression. When the integral bearing is pressed in, it should be prevented from tilting and fixed with set screws. If the bearing deviates during installation, it will cause poor operation, deformation of the shaft, and damage to mechanical equipment.

1.4 Pay attention to cleanliness. During the process of repairing, scraping, and debugging, any parts that may have oil stains should be cleaned and oiled after scraping. Before installing bearings, they must be cleaned to ensure that the sliding bearings are clean. Even tiny impurities can cause damage to the bearings.

During the use of sliding bearings, lubrication, heating, and vibration issues should be regularly checked. If there is heating, smoking, jamming, abnormal vibration, sound, etc., it should be checked in a timely manner. If a series of faults occur, analysis should be carried out, and corresponding measures should be taken according to the specific situation analyzed. Try to avoid causing unnecessary damage.

2. Precautions for inspection and maintenance of sliding bearings:

（1） Bearing shell inspection

1.1 Radial bearing disassembly measurement items: bearing tightness, top clearance, side clearance, and side clearance symmetry; The contact between the lower bearing and the shaft diameter, as well as the degree of wear of the black gold on the bearing shell; Axis roundness and surface roughness; The cleanliness of the oil system and the results of oil quality testing; Other inspection items include the clearance and wear of the labyrinth seal ring, adjusting the contact between the shim and the bearing seat, etc.

1.2 Radial bearing shell inspection items: The bearing alloy has no defects such as detachment, cracks, sand holes, and air holes; The contact angle contact area between the shaft diameter and the bearing shell; Adjust the fit between the shim and the bearing seat; Whether the joint surface of the bearing shell is flat, and whether there are burrs or deformations.

1.3 Inspection and treatment of bearing shell detachment: The inspection method for bearing shell detachment is to soak the bearing shell in kerosene, let it sit for a moment, then remove it and dry it. Place clean paper on the joint or apply white powder to the joint, and then squeeze the bearing shell detachment by hand. If there are oil stains on the paper or white powder, it proves that the bearing shell detachment; If any of the following defects are found during the inspection of the bearing shell, it must be recast: excessive clearance between the bearing shells, inability to continue scraping and grinding the alloy thickness, large areas of sand holes, air holes, impurities, and detachment cracks in the black gold.

（2） Bearing maintenance

1.1 Radial Bearing Scraping:

Check the contact between the radial bearing shell and the bearing seat, as well as the bearing cover;

If the manufacturer has no clear regulations on the contact angle, the contact angle should be set at 60-70 degrees;

The contact point shall not be less than 3 points per square centimeter, and contact points are not allowed to appear in other parts of the bearing after leaving the contact surface;

Oil pit (oil port): When lubricating oil enters the oil pit, the oil disperses and increases the oil flow channel, which is conducive to the formation of oil film and cooling of the tile. For deep scraping of Babbitt alloy bearings, scrape 3-5 deep oil pits at the bottom of the bearing. Generally, the depth of the oil pits should be 0.3-0.4mm, and the gap and size of the oil pits should be 8mm × 8mm. Both sides of the bearing shell should also scrape the oil grooves at the same time, but it can be shallower than the bottom, generally 0.25-0.3mm is more ideal. In addition, when scraping and grinding bearing shells, great attention should be paid to the surface roughness of the bearing shells, especially after deep scraping of oil pits. The surface of the bearing shells must be polished smooth with a soft cloth or towel, and the knife spikes generated during the scraping process should be removed;

Transition line: refers to the boundary between the contact area and the non-contact area, requiring a clear boundary but not allowing steps. The junction between the oil pit and the tile surface should also have a smooth transition.

1.2 Radial Bearing Scraping:

After disassembling the radial bearing, check the running in marks on the upper and lower bearings. There should be no contact points on the upper bearing. If there are contact points on the upper bearing, investigate the cause and eliminate them;

If the running in mark of the lower bearing shell is less than 70% of the standard contact area, consider scraping the bearing shell; First, use a scraper to scrape the gray and shiny contact points of the lower bearing, apply red lead, and then perform contact inspection and grinding. Place the bearing in place, rotate the rotor, and check the contact condition of the bearing again until it passes the scraping inspection (contact angle of 60-70 degrees, uniform transition of oil inlet wedge angle).

Generally, when repairing the axle tile, the oil blocking edge is not repaired, and the oil blocking edge is also the part for measuring the side clearance.

1.3 Neck Defect Handling:

The surface of the journal should be shiny, without any scratches or rust, and the roundness and cylindricity of the journal should not exceed 0.02mm;

When rust spots, corrosion, scratches, and roundness appear on the shaft neck, timely treatment should be carried out. If the defect has not yet developed to the point where it needs to be machined by a machine tool, it can be repaired on site by grinding;

1.4 Measurement of radial bearing clearance and tightening force:

Top clearance: 1.5 to 2 thousandths of the shaft neck, and half of the top clearance is the side clearance;

Bearing tightening force: 0.05-0.15mm.

The clearance and tightening force of the bearing shell can be measured by pressing the lead wire.

Precautions for measuring the 1.5 bearing shell:

The diameter d of the lead wire should be no less than d/2 after flattening;

The length of lead wire should not be too long, generally 1/5 to 1/6 of the length of the bearing shell is suitable;

When measuring the thickness of flattened lead wire, attention should be paid to the measurement value at the Z-thin point, that is, the Z-small point of the equipment joint surface gap. Therefore, when taking the measurement average, the Z-small value should be analyzed because the Z-small value is often true, while the average value is false;

The placement of lead wires must be in accordance with the actual situation of the equipment.

1.6 Suggestions for maintenance of lubricating oil system:

The lubricating oil system must be clean and measures must be taken to prevent foreign objects;

Do not use cloth with fluff to clean the oil chamber;

Do not wear gloves when in contact with the lubricating oil system;

After installing a new pump with sliding bearings and running for about 100 hours, the lubricating oil should be replaced. Generally, the oil should be changed every 300-500 hours in the future. In special circumstances, the oil should be changed at least once every six months.

3、 Defects and causes of sliding bearings:

（1） Oil supply system malfunction and poor oil quality

The oil supply system malfunctions, resulting in interruption or partial interruption of lubricating oil, causing the bearing alloy to melt due to lack of oil; Poor oil quality, such as excessive acidity, water and impurities in the oil, can cause wear and corrosion of the bearing alloy and shaft diameter. In severe cases, the oil film can be damaged, resulting in semi dry friction and melting of the bearing alloy; The oil temperature is too high or too low.

（2） Bearing and bearing shell issues

The quality of the bearing alloy is unqualified or the casting process is poor, resulting in defects such as porosity, slag inclusion, and crack propagation in the bearing alloy layer; Due to inadequate clearance or contact angle repair of the bearing shells, poor contact of the adjusting pad iron of the bearing shells, and incorrect installation position of the bearing shells (small top clearance, excessive tightening force of the bearing shells), the contact between the bearing shells and the shaft neck does not meet the requirements, resulting in uneven lubrication and load distribution of the bearing shells, causing local dry friction and resulting in wear of the bearing alloy.

（3） Accidents caused by reasons other than bearings

The equipment vibrates excessively, causing the shaft neck to continuously collide with the bearing alloy layer, resulting in white marks and visible cracks on the alloy surface, and then the alloy in the crack area begins to peel off and detach. Cracks cause damage to the oil film, and the detached alloy can block the oil gap, resulting in the bearing shell not receiving normal lubrication; Corrosion occurs on the surface of the shaft neck and alloy due to shaft current. In mild cases, the surface may lose its metallic luster, and in severe cases, the shaft neck and alloy surface may be electrocorroded into pitting. If it continues to develop, it will damage the normal contact between the bearing shell and the shaft neck; Due to defects such as out of roundness of the shaft neck, rough surface, and scratches, the alloy experiences abnormal wear, which damages the integrity of the oil film.

Given the importance of using sliding bearings and the fact that early damage to sliding bearings is much more common than bearing burnout, it is important to prevent early damage to sliding bearings. The correct maintenance of sliding bearings is an effective way to reduce early damage to bearings and a reliable guarantee for extending bearing life. Therefore, in the daily maintenance and repair of oil pumps, attention must be paid to the appearance and shape of the alloy surface, back, end, and edge corners of the bearings. If there are any abnormalities or signs of over half wear, the cause must be carefully identified and corresponding measures taken to improve the working conditions of the bearings, and prevention of early damage to sliding bearings should be emphasized.

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