Detailed explanation of the sliding bearing

7, Bearing bushings: Ferroalloy more large size alloy abrasive particles and black metal oxide.

Features
The main installation site of plain bearings is bearing bush. Most of the turning equipment used in power plants are plain bearings. Generally, bearing bushings are made of Babbitt alloy. Therefore, the softening point and melting point of bearing bush are relatively low , And the contact area with the shaft is also very large, can carry heavier loads, damping performance is also very good, able to withstand larger impact load, if the lubricant stored in the bottom of the bearing when the need for bad oil driven to Ensure tile surface film formation. Under normal circumstances, the provisions of the temperature of the rolling bearing can not exceed 80 ℃, while the sliding bearings to be lower, the temperature can not exceed 70 ℃.
Design considerations
Sliding bearings are surface contact, so the contact surface to maintain a certain film, so the design should pay attention to the following questions:
1, to make the oil film can smoothly enter the friction surface.
2, the oil should be non-bearing surface area into the bearing.
3, do not make the full ring groove open in the middle of the bearing.
4, such as oil tile, seams open ditch.
5, to make oil ring full and reliable oil.
6, filling hole do not be blocked.
7, do not form the oil does not flow area.
8, to prevent sharp edges and edges cut off the film.
Damage form
Sliding bearings used in the engine are usually divided into two types: one is lining bush-type thin-walled bearings, commonly known as tile bearing bush; the other is bushings, also known as copper sleeve, the shape of a hollow cylinder. Liner watts thin-walled bearings are mainly used to support the engine crankshaft and connecting rod; bush is mainly used to support camshaft journal and piston pin. The following we mainly understand is the lining of thin-walled bearings (bearings) early damage forms and preventive measures.
1. The form of early damage
Bearing in normal use, due to the gradual wear and tear until the last loss of ability to work to end its service life, this natural damage is unavoidable. However, if the engine assembly due to improper adjustment, poor quality or poor conditions for the use of lubricants and other factors lead to premature bearing wear or damage, it is caused by man-made early damage. Early damage not only greatly reduces the bearing life, but also affect the normal operation of the engine.
According to the long-term diesel engine maintenance experience found that the common forms of early damage to sliding bearings are mechanical damage, bearing cavitation, fatigue pitting corrosion and so on.
(1) mechanical damage? Mechanical damage to the plain bearing is the bearing surface of the alloy with varying degrees of groove marks, in serious contact with the metal surface peeling and the emergence of a large area of miscellaneous scratches; under normal circumstances, the contact surface damage and ablation Phenomenon exists at the same time. Mechanical damage caused by the main bearing is difficult to form the bearing surface film or oil film was severely damaged.
(2) bearing cavitation? Sliding bearings in the cylinder pressure impact load) under repeated action, the surface layer of plastic deformation and cold hardening, partial loss of deformation capacity, and gradually form the pattern and continue to expand, and then wear debris off, A hole is formed in the loaded surface layer. When a general bearing pitting occurs, a pit first appears, and then the pit gradually expands and causes cracking at the interface of the alloy layer. The crack propagates along the parallel direction of the interface until it peels off. The main reason for the cavitation of the sliding bearing is that due to the sudden change of the cross section of the structural elements such as the oil groove and the oil hole, the oil flow is strongly disordered, bubbles are formed in the turbulent vacuum area of the oil flow, and then the bubble is destroyed due to the pressure increase, eclipse. Cavitation generally occurs in the bearing high load area, such as crankshaft main bearing on the lower bearing.
(3) fatigue pitting? Bearing fatigue pitting refers to, due to engine overload, making the bearing overheating and bearing clearance is too large, resulting in the central bearing fatigue damage, fatigue, pitting corrosion or fatigue. Most of this damage is due to overload, bearing clearance is too large, or unclean lubricating oil, mixed with foreign matter inside. Therefore, the use should be taken to avoid overload bearing work not too low or too high speed operation; idling engine to be adjusted to a steady state; to ensure normal bearing clearance to prevent the engine speed is too high or too low; check and adjust the cooling System work, to ensure that the engine operating temperature appropriate.
(4) bearing alloy corrosion? Bearing alloy corrosion zone is generally impure, the chemical impurities in the lubricating oil (acidic oxides, etc.) so that the bearing alloy oxidation and generate acidic substances, causing the bearing alloy part of the fall, the formation of no Regular tiny holes or pits. Bearing alloy corrosion is mainly due to improper use of lubricants, bearing material corrosion resistance is poor, or rough engine work, the temperature is too high.
(5) Burn the bearing neck and bearing friction between the minor convex metal surface direct contact, the formation of local high temperature, lack of lubrication, poor cooling, the bearing alloy black or local burning. This failure is often caused by journal and bearing too tight; insufficient oil pressure is also easy to burn bearings.
(6) Bearings take the outer circle? Bearings take the outer circle is the bearing hole in the relative rotation. Bearing away from the outer circle, not only affect the bearing heat, easy to ablate the inner surface of the bearing, but also the back of the bearing damage, burned bearings in severe cases. The main reason is that the bearing is too short, the tenon damage, processing or installation does not meet the specifications and so on.
Preventive measures
Early damage to plain bearings is much more common than bearing burnout, so it is important to prevent early damage to plain bearings. The correct maintenance of plain bearings is an effective way to reduce the early bearing damage, but also to extend the bearing life of a reliable guarantee. Therefore, the daily maintenance and repair of the engine, we must pay attention to bearing the alloy surface, back, ends and edges and corners of the appearance of the shape, if there is abnormal or there are signs of over-wear, it is necessary to carefully identify the cause and take the appropriate Measures to improve the working conditions of bearings, emphasis on the prevention of early bearing damage.
(1) to improve the bearing design and manufacturing process? Design or selection of bearings, bearing heat balance should be considered to control the temperature rise. Because the bearing work in the friction state, due to the internal friction (viscosity) of the lubricating oil caused by power consumption, converted into heat caused by bearing temperature, oil viscosity decreases, the gap changes, the bearing Babbitt will soften, serious Occurs when "burning tile hold axle" accident. Therefore, in the structural design, from the bearing on the top of the bearing (non-bearing area) into the top of the hole, so that the introduction of oil from the non-load-bearing zone; the inner surface of the bushings into the oil hole as the center along the vertical or horizontal open groove, It is beneficial to distribute the lubricating oil uniformly on the journal to control the temperature rise. According to the work of the bearing, bearing materials must have the following properties: low coefficient of friction; good thermal conductivity, thermal expansion coefficient; wear resistance, corrosion resistance and anti-gluing ability; have sufficient mechanical strength and plasticity. Therefore, the pad material optional Babbitt. Babbitt alloy can work well under steady load, but cavitation easily occurs under unstable load, so it is not suitable for high power engine. High tin lead-based alloys and low tin-lead-based alloys have higher strength and hardness, stronger resistance to fatigue and cavitation erosion, and better performance in high-power engines. In recent years, foreign countries have appeared with physical vapor deposition sputtering method on the surface of the copper and lead bearing nickel plated with 20% tin or pure tin plating, the effect is very good. In addition, the whole round grooved oil tank bearings into semi-circular groove or part of the oil tank bearing, so that not only can improve the lubricating state of the engine sliding bearing, but also can improve its carrying capacity.
(2) to improve the quality of bearing repair and assembly? To improve the quality of the bearing hinge to ensure that the back of the bearing smooth without spots, positioning bumps intact; its bounce volume of 0.5-1.5mm, which ensures the assembly of bushings with their own Elastic and bearing hole fit closely; mounted in the bearing seat at both ends of the upper and lower bearing bush should be higher than the bearing seat plane 30-501μm, higher than the amount to ensure that the tightening of the bearing cap bolts bearing torque and bearing Closely with the friction to produce sufficient self-locking force, the bearing will not loose, cooling effect is good, to prevent the bearing ablation and wear; bearing surface can not be used to match the method to reach 75% -85% contact printing as a measure should not Scraping bearings and journal with the gap to meet the requirements. In addition, the assembly should pay attention to check the crankshaft journal and bearing processing quality, strict implementation of repair process specifications to prevent improper installation due to improper installation and bearing bolt torque is not uniform or inconsistent, resulting in bending and deformation Stress concentration, leading to early bearing damage.
(3) The rational selection and filling of lubricating oil? In the course of the oil film to be selected with a small surface tension of oil, so that the collapse of the formation of the oil flow impact of the corresponding reduction, which can effectively prevent bearing cavitation; Lubricating oil viscosity grades can not be arbitrarily increased, so as not to increase the bearing coking tendency; engine oil surface must be within the standard range, lubricating oil and refueling tools must be clean to prevent any dirt and water to enter, while ensuring the engine ministries The sealing effect. Pay attention to regular inspection and replacement of lubricants; refueling places should be pollution-free, no sand, to prevent the intrusion of all pollutants; different quality, different viscosity levels and different types of lubricants prohibited mixing, Precipitation time generally should not be less than 48h.
(4) Proper use and maintenance of the engine? Bearing installation, the shaft and bearing surface should be coated with a predetermined number of clean oil. After the engine bearing is installed, the first start should be closed before the fuel switch, the engine driven by the engine idling a few times, when the engine oil pressure gauge is displayed and then connected to open the fuel switch, and the accelerator set in low-speed position, start the engine Operational observation. Idling time can not exceed 5min. Do a good job of the new machine and after the overhaul of the engine run-in period of operation, in the run-in period forbidden long time in the sudden increase and decrease in load and high-speed work; end of the engine after a long time full load, can not immediately shut down, you must make the engine empty Can be shut down after 15 minutes of low-speed operation, otherwise the internal heat can not be dispersed. ? To strengthen the oil filter, crankcase ventilation device cleaning and maintenance work, according to the instructions required to replace the filter; ensure that the engine cooling system to work properly to control the normal engine temperature, to prevent the radiator "to open the pot" is strictly prohibited without cooling water On the road; the correct selection of fuel, accurately adjust the gas phase and ignition timing, etc., to prevent the engine does not burn properly; timely crankshaft and bearing technology check and adjust the work.
Setup
basic requirements
It is necessary to make the journal and plain bearings even close contact, but also have a certain gap with.
Contact angle
Is the journal and the contact surface of the bearing center of the angle. Contact angle can not be too large nor too small. Contact angle is too small will increase the pressure on the sliding bearings, will result in serious deformation of the sliding bearings in severe cases, accelerated wear and shorten the service life; contact angle is too large, will affect the formation of oil film, not good liquid lubrication. ?
Experimental studies show that the contact angle of the plain bearing is 120 °. When the sliding bearing wear to this contact angle, liquid lubrication will be destroyed. Therefore, under the premise of not affecting the pressure condition of the sliding bearing, the smaller the contact angle, the better. From the theoretical analysis of the friction distance, when the contact angle is 60 °, the friction torque is the minimum. Therefore, it is suggested that for the sliding bearing with the speed higher than 500r / min, the contact angle is 60 ° and the speed is lower than 500r / min. The contact angle can be 90 ° or 60 °.
Contact point
The actual contact between journal and plain bearing surfaces can be expressed in terms of actual number of contacts per unit area. More contact points, the more detailed, more uniform, that the better the sliding bearing scraping research, on the contrary, it means sliding bearing scraping research is not good. In general, the more contact points, the more difficult scratching.