Abstract: The 1 #, 2 #, and 3 # oil transfer pumps at Xingang Station of Dalian Company are multi-stage horizontal split pumps, with pump model KDY790-77 × 3. The pump main bearing is a sliding bearing (TFH75-04/05), and is equipped with angular contact ball bearing to balance the residual axial force. Sliding bearings have stable, reliable, and noise free operation. Under liquid lubrication conditions, the sliding surface is separated by the lubricating oil without direct contact, which can greatly reduce friction loss and surface wear. The oil film also has a certain degree of vibration absorption ability. However, sliding bearings require high installation accuracy, and incorrect installation can cause problems such as bearing heating and vibration. Therefore, how to install and maintain the sliding bearings correctly 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 bearing pads, are divided into radial bearing pads and thrust bearing pads. And the KDY790-77 at Xingang Station of Dalian Company × The bearing pads of Type 3 oil pump are radial bearings. The following will explain the precautions for installation and maintenance of this bearing pad.
I. Installation of sliding bearings
Sliding bearings are generally used under conditions of low speed and heavy load. The installation considerations for sliding bearings are as follows:
1. The installation of sliding bearings should ensure that the journal rotates flexibly, accurately, and smoothly in the bearing hole. Due to the hassle of maintaining sliding bearings, it is important to ensure that the bearings are completely installed correctly and without errors during installation. Ensure that the bearings can operate normally without errors.
2. Pay attention to the smoothness of the oil circuit and ensure that it is connected to the oil tank. When scraping and grinding, the points on both sides of the oil groove should be soft to form an oil film, and the points on both ends should be uniform to prevent oil leakage. In the later maintenance, it is necessary to facilitate the addition of lubricating oil. Easy to maintain.
3. The bearing shell and bearing seat hole should be scraped tightly, and the split surface of the bearing shell should be 0.05-0.1mm higher for easy compression. When pressing in the integral bearing shell, it is necessary to prevent deviation and fix it with a set screw. If the bearing deviates during installation, it can cause poor operation, cause deformation of the shaft, and damage mechanical equipment.
4. Pay attention to cleanliness, and any parts that may show oil stains during the repair and debugging process must be cleaned and oiled after repair. Before installing the bearings, it is necessary to clean them to ensure that the sliding bearings are clean. Even small impurities can cause damage to the bearings.
5. During the use of sliding bearings, it is necessary to regularly check for lubrication, heating, and vibration issues. In case of heating, smoking, jamming, abnormal vibration, noise, etc., timely inspection should be carried out. If a series of faults occur, analysis should be conducted, and corresponding measures should be taken based on the specific situation analyzed. Try to avoid unnecessary damage.
II. Inspection and maintenance precautions for sliding bearings:
1. Inspection of bearing shells
(1) Measurement items for disassembly of radial bearing pads: bearing pad tightening force, top clearance, side clearance, and symmetry of side clearance; The contact between the lower bearing and the shaft diameter and the degree of wear of the bearing black gold; Roundness of shaft diameter and surface roughness; The cleanliness level and oil quality test results of the oil system; Other inspection items (clearance and wear of the labyrinth sealing ring, adjustment of the contact between the pad iron and the bearing seat, etc.).
(2) Inspection items for radial bearing shells: The bearing alloy is free of defects such as detachment, cracks, sand holes, and air holes; The contact angle contact area between the shaft diameter and the bearing pad; Adjust the fit between the pad iron and the bearing seat; Check whether the joint surface of the bearing pad is flat, whether there are burrs or deformations.
(3) Inspection and treatment of bearing shell detachment: The inspection method for bearing shell detachment is to soak the bearing shell in kerosene for a while, remove and dry it, place clean paper on the joint or apply white powder to the joint, and then squeeze the bearing shell with black gold by hand. If there are oil stains on the paper or white powder, it indicates that the bearing shell detachment is caused; If one of the following defects is found after the inspection of the bearing bush, it must be recast: the clearance between the bearing bush is too large, the alloy thickness cannot be further scraped, and there are large areas of sand holes, pores, impurities, and detachment cracks in the black gold.
2. Repair of bearing shells
(1) Radial bearing bush repair and scraping:
Check the contact between the radial bearing shell and the bearing seat and bearing gland; If the manufacturer has no clear regulations on the contact angle, the contact angle should be taken as 60-70 degrees;
The contact point shall not be less than 3 points per square centimeter, and no contact points are allowed to appear on other parts of the bearing shell after leaving the contact surface;
Oil pocket (oil port): When lubricating oil enters the oil pocket, the oil immediately disperses, increasing the oil flow channel, which is conducive to the formation of oil film and cooling of the bearing. For Babbitt alloy bearing shells, deep scraping should be carried out. 3-5 deep oil pits should be scraped at the bottom of the bearing shell. Generally, the depth of the oil pit should reach 0.3-0.4mm, and the clearance and size of the oil pit should be 8mm × 8mm is better. The oil grooves on both sides of the bearing shells should also be scraped simultaneously, but they can be shallower than the bottom, generally 0.25-0.3mm is more ideal. In addition, great attention should be paid to the surface roughness of the bearing shells during scraping and grinding, especially after deep scraping of oil pits. It is necessary to use a soft cloth or towel to polish the surface of the bearing shells smooth and clean, and to remove the sharp edges generated during scraping with the scraper;
Transition line: Refers to the boundary between the contact area and the non-contact area. The boundary should be clear, but steps are not allowed. The junction between the oil pit and the tile surface should also have a smooth transition.
(2) Grinding and scraping of radial bearing shells:
After disassembling the radial bearing pads, check the wear marks on the upper and lower pads. There should be no contact points on the upper pads. If there are contact points on the upper pads, the cause should be found and the contact points should be eliminated;
If the running-in mark of the lower bearing shell is less than 70% of the standard contact area, consider scraping the bearing shell; Use a scraper to scrape the gray and shiny contact points of the lower bearing, apply red lead, and then conduct contact inspection and grinding. Place the bearing in place, rotate the rotor, and check the contact condition of the bearing again until the scraping is qualified (the contact angle is 60-70 degrees, and the oil inlet wedge angle transitions evenly).
When repairing the bearing pads, the oil blocking edge is not repaired, and the oil blocking edge is also the location for measuring the side clearance.
(3) Treatment of journal defects:
The surface of the journal should be bright, without any scars or rust, and the roundness and cylindricity requirements of the journal should not exceed 0.02mm;
When rust spots, corrosion, scars, and out of roundness appear on the shaft neck, timely treatment should be taken. If the defect has not yet developed to the extent that it needs to be processed by a machine tool, it can be repaired on-site using grinding methods;
(4) Measurement of radial bearing clearance and tightening force:
Top clearance: 1.5-2 ‰ of the journal, with side clearance being half of the top clearance;
Bearing bush tightening force: 0.05-0.15mm.
The top clearance and tightening force of the bearing pad can be measured by pressing lead wire.
(5) Precautions for bearing bush measurement work:
The diameter d of the lead wire should be no less than d/2 after flattening;
The length of the lead wire should not be too long, generally 1/5-1/6 of the length of the bearing pad is appropriate;
When measuring the thickness of the flattened lead wire, attention should be paid to the measurement value at the thinnest point, which is the smallest gap between the equipment mating surfaces. Therefore, when taking the average measurement value, the minimum value should be analyzed, as the minimum 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.
(6) Maintenance suggestions for lubricating oil system:
The lubricating oil system must be clean and take measures to prevent foreign objects;
It is prohibited to use fluffy rags to clean the oil chamber;
Do not wear gloves when in contact with the lubricating oil system;
When installing a new pump with sliding bearings, the lubricating oil should be replaced after running for about 100 hours. In general, the oil should be changed once every 300-500 hours of operation 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） Fuel supply system malfunction and poor oil quality
The oil supply system malfunctions, causing the interruption or partial interruption of lubricating oil, resulting in the melting of bearing alloys due to a 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 is damaged, resulting in semi dry friction and melting of the bearing alloy; The oil temperature is too high or too low.
（2） Problems with bearings and bearing shells
The quality of bearing alloy is unqualified or the casting process is poor, resulting in defects such as pores, slag inclusions, cracks and detachment in the bearing alloy layer; Due to reasons such as unqualified clearance or contact angle repair of bearing shells, poor contact of adjusting pad iron of bearing shells, and incorrect installation position of bearing shells (small top clearance, excessive tightening force of bearing shells), the contact between bearing shells and journal does not meet the requirements, resulting in uneven lubrication and load distribution of bearing shells, causing local dry friction and wear of bearing alloys.
（3） Accidents caused by reasons other than bearings
The equipment vibrates excessively, causing the journal to continuously impact the bearing alloy layer, resulting in white marks and visible cracks on the alloy surface, and then the alloy in the crack zone begins to peel and detach. Cracks cause damage to the oil film, and the detached alloy can block the oil gap, causing the bearing shells to not receive normal lubrication; Due to corrosion caused by axial current, the corrosion occurs on the surface of the journal and alloy. Slightly, the surface loses its metallic luster, and in severe cases, it will electrocorrosion the journal and alloy surface into pitting. If it continues to develop, it will damage the normal contact between the bearing bush and journal; Due to defects such as out of roundness, rough surface, and scratches in the journal, the alloy undergoes 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 burning, it is important to prevent early damage to sliding bearings. Proper maintenance of sliding bearings is an effective way to reduce early bearing damage and a reliable guarantee for extending bearing life. Therefore, in the daily maintenance and repair of oil transfer 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 abnormalities or signs of over half wear, it is necessary to carefully identify the cause and take corresponding measures to improve the working conditions of the bearings, and pay attention to the prevention of early damage to the sliding bearings.
More about Epen E20 Bushing:
E20 is bimetallic bearing material, based on steel backing, and a layer of copper sinter, which is composed of special copper powder with solid lubricants (major ingredient is graphite) dispersed, acts as wear resistant surface and processed through oil-impregnating treatment.
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