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.
Sliding bearing has the advantages of stable, reliable and noise free operation
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 is also necessary to convert directional motion into rotary motion (such as reciprocating piston engine).
Composition structure editing and broadcasting
Sliding friction occurs when sliding bearing works; The magnitude of sliding friction mainly depends on the manufacturing accuracy; The friction of sliding bearing mainly depends on the material of bearing sliding surface. The general working surface of sliding bearing has self-lubricating function; Sliding bearings are divided into non-metallic sliding bearings and metal sliding bearings according to materials.
Non metallic sliding bearings are mainly plastic bearings, which are generally made of engineering plastics with better performance; Professional manufacturers generally have the self-lubricating modification technology of engineering plastics. They carry out self-lubricating and enhanced modification of engineering plastics through fibers, special lubricants, glass beads and so on to achieve certain performance, and then use the modified plastics to process into self-lubricating plastic bearings through injection molding.
At the beginning of the 21st century, the most commonly used metal sliding bearing is the three-layer composite bearing. This kind of bearing is generally based on carbon steel plate. A layer of spherical copper powder is sintered on the steel plate through 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 steel plate and PTFE. Of course, it also plays a certain role of bearing and lubrication during work.
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. When it is used, it must be cast on the bearing bush of bronze, steel strip or cast iron to form a thin coating.
2) Porous metal materials (powder metallurgy materials)
If the oil is immersed in porous metal, it will become a kind of porous lubricating material, which will be filled with oil. Porous metal materials have low toughness and are 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. They can be lubricated with oil and water. They also have self-lubricating performance, but their thermal conductivity is poor.
Editing and broadcasting of injury and Prevention
During the operation of the sliding bearing, the contact between the journal and the bearing bush will produce friction, resulting in surface heating, wear and even "bite". Therefore, when designing the bearing, the sliding bearing material with good antifriction should be selected to manufacture the bearing bush, appropriate lubricant and appropriate supply method should 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: the spectral analysis found that the concentration of iron was abnormal. There were many submicron particles of iron in the ferrogram, and the water content or acid value of lubricating oil exceeded 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 tile 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 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 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 other conditions.
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 that the volatile acid of insulating paint at a certain temperature, humidity, metal corrosion and protection, the formation of corrosive substances, and the corrosion damage of channel sliding bearing.
The service life of sliding bearing is closely related to manufacturing, assembly and use. Every link must be made in order 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 did not strictly follow the requirements of cleaning and antirust procedures and oil seal antirust packaging to carry out antirust treatment on the coating machine bearing parts in the processing process and the finished coating machine bearing products after assembly. 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.
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 the bearing steel of the coating machine decreases again and again, the material of the bearing steel of the coating machine 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. At present, the sources of bearing steel of coating machine used by 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 antirust treatment. In addition, the hot weather and the violation of rust prevention regulations by production workers also exist.
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.
There are many kinds of plain 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 blade 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 the inner diameter surface, which is usually called bearing lining, so 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 the 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.
Production method editing and broadcasting
Repair welding, shaft sleeve insertion, pitting and other methods are generally adopted for sliding bearing wear in China. However, when the shaft is made of 45 steel (quenching and tempering treatment), if only surfacing treatment is adopted, the 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 material of the shaft is HT200, cast iron welding is not ideal. Some enterprises with high maintenance technology 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 less 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.
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 supplied with oil.
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 rotating speed is low, the grease with small cone penetration should be selected, otherwise, the grease with large cone penetration should be selected. High speed bearings shall be lubricated with grease with smaller cone penetration and good mechanical stability. In particular, the viscosity of the base oil of the grease should be lower.
(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.
2. 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 circumferential speed of the journal 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 circumferential speed of the journal 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 and at the temperature of 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.
3. Lubrication cycle of lubricating grease for sliding bearing:
Occasional 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; The shaft speed is more than 200R / min, and the lubrication cycle is once per shift.
Continuous operation, working temperature 40-100 ℃: shaft speed < 200R / min, lubrication cycle once per shift; The shaft speed is more than 200R / min, and the lubrication cycle is twice per shift.
The journal and 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 research 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 the 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 the sliding bearing with speed higher than 500r / min, the contact angle is 60 °, and for the sliding bearing 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
(every 25 days) × Contact points on 25 mm area)
Below 100 3 ~ 5
More than 2000 and more than 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 editing and broadcasting
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 the machine 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 vibration caused by unbalance, shaft deflection and edge load, overload, etc. cause bearing Babbitt fatigue rupture. 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.