Detailed information of the hottest sliding bearin

2022-08-05
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Detailed information of sliding bearing

overview

sliding bearing, 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. The oil film also has a certain vibration absorption capacity. But the starting friction resistance is large. The part of the shaft supported by the bearing is called the journal, and the part matching the journal is 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 the bearing liner. The materials of bearing shells and bearing liners are collectively referred to as sliding bearing materials. 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

sliding bearings are generally used in low-speed and heavy-duty working conditions, or in operating parts where maintenance and lubricating oil filling are difficult

principle

according to the working principle of the bearing, it can be divided into rolling friction bearing (rolling bearing) and sliding friction bearing (sliding bearing)

sliding bearing: if a lubricating film can be formed on the surface of the sliding bearing to separate the surfaces of the moving pair, the sliding friction can be greatly reduced. Since the surfaces of the moving pair are not in direct contact, the reaction wear between the implanted biomedical materials and the body can also be avoided. Sliding bearing has large bearing capacity, high rotation precision and anti impact effect of lubricating film. Therefore, it has been widely used in engineering

the formation of lubricating film is the basic condition for the normal operation of sliding bearings. The factors affecting the formation of lubricating film include lubrication mode, relative motion speed of moving pairs, physical properties of lubricants and surface roughness of moving pairs. The design of sliding bearing shall determine the structural type of bearing, select lubricant and lubrication method, and determine the geometric parameters of bearing according to the working conditions of bearing

classification

there are many kinds of sliding bearings

① according to the load bearing direction, it can be divided into radial (radial) sliding bearing and thrust (axial) sliding bearing

② according to the type of lubricant, it can be divided into oil lubricated bearing, grease lubricated bearing, water lubricated bearing, gas bearing, solid lubricated bearing, magnetic fluid bearing and magnetic bearing

③ according to the thickness of lubricating film, it can be divided into thin film lubricated bearings and thick film lubricated bearings

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 bush structure, it can be divided into circular bearing, elliptical bearing, three oil vane bearing, stepped surface bearing, tilting pad bearing and foil bearing

structure

there are many kinds of sliding bearings

① according to the load bearing direction, it can be divided into radial (radial) sliding bearing and thrust (axial) sliding bearing

② according to the type of lubricant, it can be divided into oil lubricated bearing, grease lubricated bearing, water lubricated bearing, gas bearing, solid lubricated bearing, magnetic fluid bearing and magnetic bearing

③ according to the thickness of lubricating film, it can be divided into thin film lubricated bearings and thick film lubricated bearings

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 bush structure, it can be divided into circular bearing, elliptical bearing, three oil vane bearing, stepped surface bearing, tilting pad bearing and foil bearing

materials

1) metal materials, such as bearing alloy, bronze, aluminum based alloy, zinc based alloy, etc

2) porous metal materials (powder metallurgy materials)

3) non metallic materials

among them:

bearing alloy: bearing alloy, also known as white alloy, is mainly tin, lead, antimony or other metal alloys. 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-duty and high-speed situations. The bearing alloy has low strength and is expensive. It must be poured on the bearing bush of bronze, steel strip or cast iron, Form a thin coating

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 materials have small toughness, and are only suitable for stable non impact loads and medium and small speeds

bearing Plastics: common bearing plastics include phenolic plastics, nylon, polytetrafluoroethylene, etc. plastic bearings have high compressive strength and wear resistance. They can be lubricated with oil and water, and also have self-lubricating performance, but their thermal conductivity is poor

fault

sliding bearings will generate friction due to the contact between the journal and the bearing bush during operation, resulting in surface heating, wear and even "seizure". Therefore, in the design of bearings, sliding bearing materials with good friction reduction should be selected to manufacture the bearing bush, appropriate lubricants should be selected and appropriate supply methods should be adopted to improve the bearing structure to obtain thick film lubrication

1. Tile surface corrosion: abnormal concentration of non-ferrous elements was found by spectral analysis; There are many sub micron wear particles composed of non-ferrous metals in ferrography; The water content and acid value of lubricating oil exceed the standard

2. Journal surface corrosion: abnormal concentration of iron element is found by spectral analysis. There are many submicron particles of iron composition in the ferrogram, and the water content or acid value of the lubricating oil exceeds the standard

3. Journal surface strain: there are ferrous cutting abrasive particles or black oxide particles in the Ferrograph, and there is tempering color on the metal surface

4. Fretting wear on the back of the pad: abnormal iron concentration was found by spectral analysis. There were many submicron wear particles in the ferrogram, and abnormal moisture and acid value of the lubricating oil

5. Bearing surface strain: cutting abrasive particles are found in the Ferrograph, 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 Ferrograph

7. Bearing bush burning: there are many large-size alloy abrasive particles and ferrous metal oxides in the Ferrograph

features

the main installation part of sliding bearings is the bearing bush. Most of the large rotating equipment in power plants are sliding bearings. Generally, the bearing bush is made of Babbitt alloy, so the softening point and melting point of the bearing bush are relatively low, and the contact area with the shaft is also very large. It can carry heavy loads, has good shock absorption performance, and can withstand large impact loads, If the lubricating oil is stored in the lower part of the bearing bush, it needs to be driven by oil damage to ensure the formation of oil film on the surface of the bush. Generally, the temperature of rolling bearing shall not exceed 80 ℃, while that of sliding bearing shall be lower, and the temperature shall not exceed 70 ℃

design considerations

sliding bearings are in surface contact, so a certain oil film should be maintained between the contact surfaces. Therefore, the following problems should be paid attention to during design:

1. The oil film should smoothly enter the friction surface

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. If oil tile is used, oil groove shall be opened at the joint

5. The oil ring shall be fully and reliably supplied

6. Do not block the filler hole

7. Do not form an oil stagnant area

8. Prevent sharp edges and corners that cut off the oil film

damage form

sliding bearings used in engines are usually divided into two types: one is lining thin-walled bearings, which are similar to tiles and commonly known as bearing pads; The other is bushing, also known as copper sleeve, which is a hollow cylinder. Liner thin-walled bearings are mainly used to support the crankshaft and connecting rod of the engine; The bushing is mainly used to support camshaft journal and piston pin. What we mainly know below is the early damage form and preventive measures of lining thin-wall bearing (bearing bush)

1. The form of early damage

during normal use, the bearing gradually wears out until it finally loses its working capacity and ends its service life. This natural damage is inevitable. However, if the bearings are prematurely worn or damaged due to improper engine assembly and adjustment, poor treatment of domestic and foreign investment by lubricating oil quality, poor law enforcement principles between state-owned and private enterprises, large companies and small and medium-sized enterprises, or poor service conditions, it is an early damage caused by human factors. Early damage not only greatly reduces the service life of the bearing, but also affects the normal operation of the engine

according to the long-term experience of diesel engine maintenance, the common forms of early damage of sliding bearings are mechanical damage, bearing cavitation, fatigue pitting, corrosion, etc

(1) mechanical damage the mechanical damage of sliding bearing refers to the groove marks in different degrees on the alloy surface of the bearing bush. In serious cases, the metal peeling occurs on the contact surface and a large area of random scratch occurs; Generally, the contact surface damage and ablation phenomenon exist at the same time. The main reason for bearing mechanical damage is that the bearing surface is difficult to form oil film or the oil film is seriously damaged

(2) bearing pitting under the repeated action of cylinder pressure impact load), the surface layer of sliding bearing will undergo plastic deformation and cold work hardening, locally lose the deformation ability, gradually form wrinkles and continue to expand, and then form cavities in the loaded surface layer with the falling off of wear debris. Generally, when the bearing bush is pitted, the pit first appears, and then the pit gradually expands and causes the crack at the interface of the alloy layer. The crack extends along the parallel direction of the interface until it peels off. The main reason for the cavitation of sliding bearings is that the sudden change of the cross section of structural elements such as oil grooves and oil holes causes a strong disorder of oil flow, forming bubbles in the vacuum area with disordered oil flow, and then cavitation occurs due to the collapse of bubbles due to the increase of pressure. Cavitation usually occurs in the high load area of the bearing, such as the lower bearing bush of the crankshaft main bearing

(3) fatigue pitting corrosion bearing fatigue pitting corrosion refers to the fatigue damage, fatigue pitting corrosion or fatigue falling off in the middle of the bearing due to the overload of the engine, resulting in overheating of the bearing and excessive bearing clearance. This kind of damage is mostly caused by overload, too large bearing clearance, or unclean lubricating oil, mixed with foreign matters. Therefore, during use, attention should be paid to avoid overload of the bearing and do not run at too low or too high speed; Adjust the engine to a stable state when idling; Ensure the normal bearing clearance to prevent the engine speed from being too high or too low; Check and adjust the working condition of the cooling system to ensure that the working temperature of the engine is appropriate

(4) bearing alloy corrosion bearing alloy corrosion is generally caused by the impure lubricating oil. The chemical impurities (acid oxides, etc.) in the lubricating oil oxidize the bearing alloy to form acidic substances, causing part of the bearing alloy to fall off, forming irregular small cracks or pits. The main causes of bearing alloy corrosion are improper selection of lubricating oil, poor corrosion resistance of bearing materials, or rough engine operation and high temperature

(5) there is a small convex metal surface between the bearing burning journal and the bearing friction pair, resulting in local high temperature. In the case of insufficient lubrication and poor cooling, the bearing alloy will be blackened or partially burned. This fault is often caused by the tight fit between the journal and the bearing; Insufficient lubricating oil pressure may also cause

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