What is a sliding bearing
What is a sliding bearing?
Sliding bearing is a bearing that works under sliding friction. The sliding bearing works stably, reliably and without noise. Under the condition of liquid lubrication, the sliding surface is separated by the lubricating oil without direct contact, which can also greatly reduce the friction loss and surface wear, and the oil film also has a certain vibration absorption ability. However, the starting friction resistance is large. The part of the shaft supported by the bearing is called the journal, and the parts matching the journal are called the bearing bush. In order to improve the friction properties of the bearing surface, the antifriction material layer cast on its inner surface is called bearing lining. The materials of bearing bush and bearing liner are collectively referred to as sliding bearing materials. The application of sliding bearing is generally under the condition of high speed and light load.
Main characteristics of sliding bearing
Common sliding bearing materials include bearing alloy (also known as babbitt alloy or white alloy), wear-resistant cast iron, copper based and aluminum based alloys, powder metallurgy materials, plastics, rubber, hardwood and carbon graphite, polytetrafluoroethylene (Teflon, PTFE), modified Polyoxymethylene (POM), etc.
The sliding bearing absorbs and transmits the force between the relative moving parts to maintain the position and positioning accuracy of the two parts. In addition, it also converts the directional motion into rotary motion (such as reciprocating piston engine).
Composition and structure of sliding bearing
The sliding friction occurs when the sliding bearing works; the size of the sliding friction mainly depends on the manufacturing accuracy; and the size of the friction of the sliding bearing mainly depends on the material of the sliding surface of the bearing. Generally, the working surface of the sliding bearing has self-lubricating function; the sliding bearing is divided into non-metallic sliding bearing and metal sliding bearing according to the material.
Non metallic sliding bearings are mainly plastic bearings, which are generally made of engineering plastics with better performance; more professional manufacturers generally have engineering plastics self-lubricating modification technology, and carry out self-lubricating reinforcement modification on engineering plastics through fibers, special lubricants, glass beads, etc. to achieve certain performance, and then use modified plastics through injection molding processed into self-lubricating plastic bearings.
At the beginning of the 21st century, the most commonly used metal sliding bearing is the three-layer composite bearing. This kind of bearing generally takes the carbon steel plate as the substrate. First, a layer of spherical copper powder is sintered on the steel plate through the sintering technology, and then a layer of PTFE lubricant of about 0.03mm is sintered on the copper powder layer. The main function of the middle layer of spherical copper powder is to enhance the bonding strength between the steel plate and PTFE However, it also plays a certain role in bearing and lubrication.
Manufacturing materials of sliding bearings
1) Metal materials, such as bearing alloy, bronze, aluminum based alloy, zinc based alloy, etc
Bearing alloy: bearing alloy, also known as white alloy, is mainly an alloy of tin, lead, antimony or other metals. Due to its good wear resistance, high plasticity, good running in performance, good thermal conductivity, good glue resistance and good adsorption with oil, it is suitable for heavy load and high speed. The strength of bearing alloy is small and the price is expensive. It must be cast on the bearing bush of bronze, steel strip or cast iron A thin coating is formed.
2) Porous metallic materials (powder metallurgy materials)
Porous metal material: porous metal is a kind of powder material with porous structure. If it is immersed in lubricating oil, the micropores will be filled with lubricating oil and become oil-bearing, which has self-lubricating performance. Porous metal material has small toughness and is only suitable for stable non impact load and medium and small speed.
3) Non metallic materials
Bearing Plastics: commonly used bearing plastics include phenolic plastics, nylon, polytetrafluoroethylene, etc. plastic bearings have high compressive strength and wear resistance, can be lubricated with oil and water, and also have self-lubricating performance, but their thermal conductivity is poor.
Damage and prevention of sliding bearing
Damage of sliding bearing
During the operation of sliding bearing, the contact between journal and bearing bush will produce friction, resulting in surface heating, wear and even “bite”. Therefore, in the design of bearing, sliding bearing materials with good antifriction shall be selected to manufacture bearing bush, appropriate lubricant and appropriate supply method shall be adopted to improve the bearing structure to obtain thick film lubrication.
- 1. Tile surface corrosion: abnormal concentration of non-ferrous metal elements is found by spectral analysis; There are many sub micron wear particles composed of non-ferrous metals in the spectrum; The water content and acid value of lubricating oil exceed the standard.
- 2. Journal surface corrosion: abnormal iron concentration is found by spectral analysis. There are many submicron particles of iron in the ferrogram, and the moisture or acid value of lubricating oil exceeds the standard.
- 3. Journal surface strain: there are ferrous cutting abrasive particles or black oxide particles in the ferrogram, and there is tempering color on the metal surface.
- 4. Fretting wear of pad back: abnormal iron concentration is found by spectral analysis. There are many iron components, submicron wear particles, abnormal moisture and acid value of lubricating oil in the ferrogram.
- 5. Bearing surface strain: cutting abrasive particles are found in ferrography, and the abrasive particles are composed of non-ferrous metals.
- 6. Tile surface spalling: many large-scale fatigue spalling alloy wear particles and layered wear particles are found in the ferrography.
- 7. Bearing bush burning: there are many large-size alloy abrasive particles and ferrous metal oxides in the ferrography.
- 8. Bearing wear: due to the metal characteristics of the shaft (high hardness, poor concession) and other reasons, it is easy to cause adhesion wear, abrasive wear, fatigue wear, fretting wear and so on.
Prevention of sliding bearing damage
Prevention of paint rust: paint rust is characterized by a sealed motor. At first, the motor sounds good, but in the warehouse for a period of time, the motor becomes very abnormal sound, and the bearing is seriously rusted. Many manufacturers will be regarded as the problem of front bearing. The main problem is the volatile acid of insulating paint, metal corrosion and protection at a certain temperature, humidity and corrosion The formation of corrosive substances causes corrosion damage to the channel sliding bearing.
The service life of sliding bearing is closely related to manufacturing, assembly and use. Each link must be made to make the best bearing for national operation, so as to prolong the service life of bearing.
- 1. In the process of producing coating machine bearings, some enterprises do not carry out anti rust treatment on the coating machine bearing parts in the processing process and the finished coating machine bearing products after assembly in strict accordance with the requirements of cleaning and anti rust procedures and oil seal anti rust packaging. For example, the turnover time of the ferrule in the turnover process is too long, and the outer circle of the outer ring is in contact with corrosive liquid or gas, etc.
- 2. The quality of antirust lubricating oil, cleaning kerosene and other products used by some enterprises in production can not meet the requirements of process and technology regulations.
- 3. As the price of coating machine bearing steel drops again and again, the material of coating machine bearing steel decreases gradually. For example, the content of non-metallic impurities in steel is high (the increase of sulfur content in steel reduces the corrosion resistance of the material itself), metallographic structure deviation, etc. the sources of coating machine bearing steel used by current production enterprises are miscellaneous, and the steel quality is fish dragon mixed beads.
- 4. The environmental conditions of some enterprises are poor, the content of harmful substances in the air is high, and the turnover site is too small to carry out effective anti rust treatment. In addition, there are many phenomena such as hot weather and production workers violating anti rust regulations.
- 5. The anti rust paper, nylon paper (bag) and plastic cylinder of some enterprises do not meet the requirements of anti rust packaging of bearing oil seal of rolling coating machine, which is also one of the factors causing corrosion.
- 6. The turning allowance and grinding allowance of sliding bearing ring of coating machine in some enterprises are too small, and the oxide scale and decarburization layer on the outer circle can not be completely removed is also one of the reasons.
Classification of sliding bearings
There are many kinds of sliding bearings:
- ① According to the direction of bearing load, it can be divided into radial (centripetal) sliding bearing and thrust (axial) sliding bearing.
- ② According to the type of lubricant, it can be divided into 7 categories: oil lubricated bearing, grease lubricated bearing, water lubricated bearing, gas bearing, solid lubricated bearing, magnetic fluid bearing and electromagnetic bearing.
- ③ According to the thickness of lubrication film, it can be divided into thin film lubrication bearing and thick film lubrication bearing.
- ④ According to the bearing material, it can be divided into bronze bearing, cast iron bearing, plastic bearing, gem bearing, powder metallurgy bearing, self-lubricating bearing and oil bearing.
- ⑤ According to the bearing structure, it can be divided into circular bearing, elliptical bearing, three oil vane bearing, stepped surface bearing, tilting pad bearing and foil bearing.
The bearing bush is divided into split and integral structures. In order to improve the friction properties of the bearing bush surface, one or two layers of antifriction materials are often cast on its inner diameter surface, which is usually called bearing lining. Therefore, the bearing bush has bimetallic bearing bush and trimetallic bearing bush.
Bearing bush or bearing liner is an important part of sliding bearing. The materials of bearing bush and bearing liner are collectively referred to as bearing materials. Because the bearing bush or bearing liner is in direct contact with the journal, the journal part is generally wear-resistant, so the main failure form of bearing bush is wear.
The wear of bearing bush is directly related to the material of journal, the material of bearing bush, lubricant and lubrication state. These factors should be comprehensively considered in the selection of bearing bush material in order to improve the service life and working performance of sliding bearing.
Manufacturing method of sliding bearing
Repair welding, shaft sleeve insertion, pitting and other methods are generally used for sliding bearing wear in China, but the material of the shaft is 45 steel (quenching and tempering treatment), if only surfacing treatment is adopted, welding internal stress will be generated. Under heavy load or high-speed operation, cracks and even fractures may appear at the shaft shoulder. If stress relief annealing is adopted, it is difficult to operate, with long processing cycle and high maintenance cost; when the shaft is made of HT200, cast iron welding is not ideal. Some maintenance technologies are high Enterprises will adopt brush plating, laser welding, micro arc welding and even cold welding. These maintenance technologies often require high requirements and high costs.
The above repair technologies are not common in European, American, Japanese and Korean enterprises. Developed countries generally use polymer composite technology and nanotechnology. Polymer technology can be operated on site, effectively improving the maintenance efficiency and reducing the maintenance cost and intensity.
Problems needing attention in designing sliding bearing
The sliding bearing is in surface contact, so a certain oil film should be maintained between the contact surfaces. Therefore, the following problems should be paid attention to in the design:
- 1. The oil film shall enter the friction surface smoothly.
- 2. Oil shall enter the bearing from the non bearing surface area.
- 3. Do not open the full ring oil groove in the middle of the bearing.
- 4. Such as oil tile, oil ditch shall be opened at the joint.
- 5. The oil ring shall be fully and reliably fed.
- 6. Do not block the filler hole.
- 7. Do not form an oil non flowing area.
- 8. Prevent sharp edges and corners that cut off the oil film.
Sliding bearings can also be lubricated with grease. The following points should be considered when selecting grease:
- (1) When the bearing load is large and the speed is low, the grease with small cone penetration shall be selected, otherwise, the grease with large cone penetration shall be selected. High speed bearings shall be lubricated with grease with smaller cone penetration and good mechanical stability. Special attention should be paid to the lower viscosity of the base oil of the grease.
- (2) The dropping point of the selected grease is generally 20-30 ℃ higher than the working temperature. Under the condition of continuous operation at high temperature, pay attention not to exceed the allowable temperature range of the grease.
- (3) When the sliding bearing works in water or humid environment, calcium base, aluminum base or lithium base grease with good water resistance shall be selected.
- (4) Select lubricating grease with good adhesion.
Selection of lubricating grease for sliding bearing:
- Load < 1MPa, journal circumferential speed less than 1m/s, maximum working temperature 75 ℃, select No. 3 calcium base grease;
- The load is 1-6.5mpa, the journal circumferential speed is 0.5-5m/s, the maximum working temperature is 55 ℃, and No. 2 calcium base grease is selected;
- Load > 6.5MPa, journal circumferential speed less than 0.5m/s, maximum working temperature 75 ℃, select No. 3 calcium base grease;
- Load < 6.5MPa, journal circumferential speed 0.5-5m/s, maximum working temperature 120 ℃, No. 2 lithium grease is selected;
- Load > 6.5MPa, journal circumferential speed less than 0.5m/s, maximum working temperature 110 ℃, No. 2 calcium sodium base grease is selected;
- The load is 1-6.5mpa, the journal circumferential speed is less than 1m/s, the maximum working temperature is 50-100 ℃, and No. 2 lithium grease is selected;
- Load > 5MPa, journal circumferential speed 0.5m/s, maximum working temperature 60 ℃, No. 2 calender grease is selected;
- Calcium sodium base grease should be considered for lubrication in humid environment at 75-120 ℃. In humid environment, when the working temperature is below 75 ℃, there is no no no. 3 calcium base grease, and aluminum base grease can also be used. When the working temperature is 110-120 ℃, lithium grease or barium grease can be used. When centralized lubrication, the consistency should be smaller.
Lubrication cycle of grease for sliding bearing:
- Accidental work, unimportant parts: shaft speed < 200R/min, lubrication cycle once every 5 days; The shaft speed is more than 200R/min, and the lubrication cycle is once every 3 days.
- Intermittent operation: shaft speed < 200R/min, lubrication cycle once every 2 days; Shaft speed > 200R/min, lubrication cycle once a day.
- Continuous operation, working temperature less than 40 ℃: shaft speed < 200R/min, lubrication cycle once a day; Shaft speed > 200R/min, lubrication cycle once per shift.
- Continuous operation, working temperature 40-100 ℃: shaft speed < 200R/min, lubrication cycle once per shift; The shaft speed is > 200R/min, and the lubrication cycle is twice per shift.
Both the journal and the sliding bearing shall be in uniform and fine contact, and there shall be a certain fit clearance.
It refers to the center angle of the contact surface between the journal and the sliding bearing. The contact angle shall not be too large or too small. Too small contact angle will increase the pressure of sliding bearing, and in serious cases, it will cause large deformation of sliding bearing, accelerate wear and shorten service life; If the contact angle is too large, it will affect the formation of oil film and can not get good liquid lubrication.
The experimental study shows that the limit of contact angle of sliding bearing is 120 °. When the sliding bearing is worn to this contact angle, the liquid lubrication will be destroyed. Therefore, the smaller the contact angle is, the better without affecting the compression condition of sliding bearing. From the theoretical analysis of friction distance, when the contact angle is 60 °, the friction torque is the smallest. Therefore, it is suggested that for sliding bearings with speed higher than 500r/min, the contact angle is 60 °, and for sliding bearings with speed lower than 500r/min, the contact angle can be 90 ° or 60 °.
The actual contact between journal and sliding bearing surface can be expressed by the actual contact points per unit area. The more, thinner and more uniform the contact points are, the better the sliding bearing scraping is. On the contrary, the sliding bearing scraping is not good. Generally speaking, the finer the contact points, the more difficult it is to scrape and grind. During production, the contact point shall be determined according to the performance and working conditions of sliding bearing. The data listed in the following table can be used for reference:
|Sliding bearing speed (R/min)||Contact point (Number of contact points per 25×25 mm area)|
|Over 2000||Above 25|
The data in the above table can be used for machines with grade I and II accuracy, and the data in the above table can be halved for machines with grade III accuracy.
Maintenance method of sliding bearing
Damage type, cause and treatment method
The glued bearing is overheated, the load is too large, the operation is improper or the temperature control system fails
- 1. In case of bearing overheating during movement, stop immediately for inspection. It is best to keep the rotor running at low speed or continue to supply oil for a period of time until the bearing bush cools down. Otherwise, the Babbitt alloy on the bearing bush will stick to the journal due to gluing, which is troublesome to repair.
- 2. Prevent insufficient lubricating oil or impurities mixed in the oil and misalignment of rotor installation.
- 3. The bearing bush with light gluing damage can be eliminated by scraping and grinding repair and can be used continuously.
Fatigue rupture Babbitt bearing fatigue rupture is caused by vibration caused by imbalance, shaft deflection and edge load, overload, etc. The quality of bearing maintenance and installation is not high
- 1. Improve installation quality and reduce bearing vibration.
- 2. Prevent partial load and overload.
- 3. Adopt appropriate Babbitt alloy and new bearing structure.
- 4. Strictly control the bearing temperature rise.
The lubricating oil brings large particles of dirt into the bearing clearance and is embedded on the bearing bushing, so that a hard scab will be formed when the bearing is in contact with the Journal (or thrust disc), which will seriously scratch the surface of the shaft during operation. Pay attention to the cleanliness of the oil circuit of the roughened bearing, especially in the maintenance, and pay attention to the cleaning of metal chips or dirt.
Wear and scratch due to impurities, foreign matters and dirt mixed in the lubricating oil, improper maintenance method, incorrect installation, improper use and maintenance and lax quality control.
- 1. Clean the journal, oil circuit and oil filter, and replace the clean lubricating oil meeting the quality requirements.
- 2. Equipped with repaired bearing bush or new bearing bush.
- 3. If the installation is found to be misaligned, it shall be aligned in time.
- 4. Pay attention to the maintenance quality.
Cavitation erosion due to unreasonable bearing structure (unreasonable oil stain on the bearing), shaft vibration, steam bubble formed in the oil film, steam bubble rupture, vacuum generated on the local surface of the bearing bush, causing small pieces to peel off and cavitation damage.
- 1. Increase the oil supply pressure.
- 2. Improve the shape of bearing bush oil groove and oil groove, and modify the edge or shape of the groove to improve the shape of oil film streamline.
- 3. Reduce bearing clearance and shaft center shaking.
- 4. Replace more suitable bearing bush materials.
Due to poor insulation or poor grounding, or static electricity, electric corrosion forms a certain voltage between the journal and the bearing bush, penetrates the oil film between the journal and the bearing bush and generates electric sparks, which makes the bearing bush into pits.
- 1. Check the insulation of the machine, and pay special attention to whether the wires of some protective devices (such as thermal resistance, thermocouple, etc.) are well insulated.
- 2. Check the machine grounding.
- 3. If the damage after electric corrosion is not too serious, the bearing bush can be scraped.
- 4. Check the journal. If there are electric corrosion pits on the journal, polish the journal to remove the pits.
National standard for sliding bearings
- 1. GB/T14910-1994: sliding bearings – technical requirements for thick walled multilayer bearing liners
- 2. GB/T16748-1997: sliding bearings – compression testing of metallic bearing materials
- 3. GB/T18323-2001: Dimensions and tolerances of sintered shaft sleeves for sliding bearings
- 4. GB/T18324-2001: sliding bearing copper alloy sleeve
- 5. GB/T18325.1-2001: sliding bearings fatigue strength in testing machine and practical application under hydrodynamic lubrication
- 6. GB/T18326-2001: Plain Bearings metal multilayer materials for thin wall sliding bearings
- 7. GB/T18327.1-2001: Basic symbols for sliding bearings
- 8. GB/T18329.1-2001: sliding bearings ultrasonic nondestructive testing of bonding strength of multilayer metal sliding bearings
- 9. GB/T18327.2-2001: application symbols for sliding bearings
- 10. GB/T18844-2002: terms, characteristics and causes of damage and appearance change of sliding bearings
- 11. GB/T21466.3-2008 hydrodynamic journal bearings under steady state conditions circular journal bearings Part 3: Allowable operating parameters
- 12. GB/T21466.1-2008 hydrodynamic journal bearings under steady state conditions cylindrical sliding bearings Part 1: calculation process
- 13. GB/T21466.2-2008 hydrodynamic journal bearings under steady state conditions circular journal bearings Part 2: functions used in calculation
- 14. GB/T7308-2008: tolerances, structural elements and inspection methods for sliding bearings with or without flange Thin-walled bearing shells
- 15. GB/T10447-2008: sliding bearings – semicircular thrust washers – Elements and tolerances
- 16. GB/T10446-2008: sliding bearings – full circle thrust washers – Dimensions and tolerances
- 17. GB/T2889.1-2008 sliding bearings – terms, definitions and classification – Part 1: design, bearing materials and their properties
- 18. GB/T23893-2009: classification and marking of thermoplastic polymers for sliding bearings
- 19. GB/T23895-2009: quality assurance of Thin-walled bearing shells of sliding bearings selection and assembly of reducing the range of bearing clearance
- 20. GB/T18325.3-2009: sliding bearings – bearing fatigue – Part 3: flat strip test of metal multilayer bearing materials
- 21. GB/T18325.2-2009: sliding bearings – bearing fatigue – Part 2: cylindrical specimen test of metal bearing materials
- 22. GB/T23896-2009: failure mode and effect analysis (FMEA) of sliding bearing thin wall bearing bush in quality assurance design stage
- 23. GB/T18325.4-2009: sliding bearings – bearing fatigue – Part 4: metal multilayer bearing materials – bearing bush test
- 24. GB/T23894-2009: sliding bearings copper alloy inlaid solid lubricated bearings
- GB/t23892.2-2009: sliding bearings hydrodynamic tilting pad thrust bearings under steady state conditions Part 2: calculation function of tilting pad thrust bearings
- 26. GB/T23892.1-2009: sliding bearings hydrodynamic tilting pad thrust bearings under steady state conditions Part 1: Calculation of tilting pad thrust bearings
- 27. GB/T23892.3-2009: sliding bearings hydrodynamic tilting pad thrust bearings under steady state conditions Part 3: allowable values for calculation of tilting pad thrust bearings
- 28. GB/T23891.1-2009: sliding bearings hydrodynamic pad thrust bearings under steady state conditions Part 1: Calculation of pad thrust bearings
- 29. GB/T23891.2-2009: sliding bearings hydrodynamic pad thrust bearings under steady state conditions Part 2: calculation function of pad thrust bearings
- 30. GB/T23891.3-2009: sliding bearings hydrodynamic pad thrust bearings under steady state conditions Part 3: allowable values for calculation of pad thrust bearings
- 31. GB/T2889.4-2011: sliding bearings – terms, definitions and classification – Part 4: Basic symbols
- 32. GB/T27939-2011: quality control technology and inspection of geometric and material quality characteristics of sliding bearings
- 33. GB/T12613.6-2011: sliding bearings – rolled shaft sleeves – Part 6: inner diameter inspection
- 34. GB/T27938-2011: failure and damage terms, appearance characteristics and causes of thrust washers of sliding bearings
- 35. GB/T12613.1-2011: sliding bearings – rolled shaft sleeves – Part 1: Dimensions
- 36. GB/T12613.2-2011: sliding bearings – rolled shaft sleeves – Part 2: test data for outer diameter and inner diameter
- 37. GB/T12613.3-2011: sliding bearings – rolled shaft sleeves – Part 3: lubricating oil holes, oil grooves and oil pockets
- 38. GB/T12613.4-2011: sliding bearings – rolled shaft sleeves – Part 4: Materials
- 39. GB/T12613.5-2011: sliding bearings – rolled shaft sleeves – Part 5: inspection of outer diameter
- 40 Gb/t12613.7-2011: sliding bearings – rolled shaft sleeves – Part 7: measurement of wall thickness of thin-walled shaft sleeves
- 41. GB/T2688-2012: sliding bearings – powder metallurgy bearings – technical specifications
- 42. GB/T28278.1-2012: sliding bearings hydrostatic journal bearings without oil grooves under steady-state conditions Part 1: Calculation of oil lubricated journal bearings without oil grooves
- 43. GB/T28279.1-2012: sliding bearings Hydrostatic Journal Bearings with oil grooves under steady-state conditions Part 1: Calculation of oil lubricated journal bearings with oil grooves
- 44. GB/T28279.2-2012: sliding bearings Hydrostatic Journal Bearings with oil grooves under steady-state conditions Part 2: calculated characteristic values of oil lubricated journal bearings with oil grooves
- 45. GB/T28278.2-2012: sliding bearings hydrostatic journal bearings without oil grooves under steady-state conditions Part 2: calculated characteristic values of oil lubricated journal bearings without oil grooves
- 46. GB/T28280-2012: quality characteristics of sliding bearings calculation of machine capacity and process capacity
- 47. GB/T28281-2012: statistical process control (SPC) for quality characteristics of sliding bearings
- 48. GB/T10445-1989: shaft diameter of sliding bearing integral shaft sleeve
- 49. GB/T12948-1991: destructive test method for bimetallic bond strength of sliding bearings
- 50. GB/T12949-1991: sliding bearings bimetallic shaft sleeves covered with antifriction plastic layers
Source: China Bearing Manufacturer – Yaang Pipe Industry (www.steeljrv.com)
(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)
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