Early damage form This natural damage is unavoidable during normal use of the bearing due to wear and tear until it eventually loses its ability to work and ends its service life. However, if the bearing is prematurely worn or damaged due to improper adjustment of the engine assembly, poor quality of the lubricating oil or poor use conditions, it is an early damage caused by man. 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, common forms of early damage of sliding bearings are mechanical damage, bearing cavitation, fatigue pitting, corrosion and so on. (1) Mechanical damage The mechanical damage of the sliding bearing refers to the occurrence of different degrees of groove marks on the alloy surface of the bearing bush. In severe cases, metal peeling occurs on the contact surface and large-area disordered scratches occur; in general, contact surface damage and ablation simultaneously exist. The main cause of mechanical damage to the bearing is that it is difficult to form an oil film on the bearing surface or the oil film is seriously damaged. (2) Under the repeated action of the bearing cavitation sliding bearing in the cylinder pressure impact load, the surface layer undergoes plastic deformation and cold work hardening, partially loses the deformation ability, gradually forms the pattern and expands continuously, and then with the wear debris falling off, The loaded surface layer forms a hole. Generally, when cavitation occurs in the bearing bush, the pit first appears, and then the pit gradually expands and causes cracking at the interface of the alloy layer, and the crack spreads in the parallel direction of the interface until peeling off. The main reason for the cavitation of the sliding bearing is that the oil flow is strongly disturbed due to the sudden change of the cross section of the structural elements such as the oil groove and the oil hole, and bubbles are formed in the vacuum region where the oil flow is disordered, and then the bubble collapses due to the pressure rise. eclipse. Cavitation is generally found in the high load area of ​​the bearing, such as the lower bearing of the main bearing of the crankshaft. (3) Fatigue pitting corrosion Bearing pitting corrosion refers to the overheating of the bearing and the excessive bearing clearance due to over-loading of the engine, resulting in fatigue damage, fatigue pitting or fatigue shedding in the middle of the bearing. Most of this damage is caused by overload, excessive bearing clearance, or unclean lubricating oil and foreign matter mixed inside. Therefore, when using, care should be taken to avoid overloading the bearing. Do not operate at too low or too high speed; adjust the engine to a steady state when idling; ensure normal bearing clearance, prevent engine speed from being too high or too low; check and adjust cooling The working condition of the system ensures that the working temperature of the engine is suitable. (4) Bearing alloy corrosion bearing alloy corrosion is generally the area of ​​lubricating oil is not pure, the chemical impurities (acid oxides, etc.) in the lubricating oil cause the bearing alloy to oxidize to generate acidic substances, causing the bearing alloy to partially fall off and form a random Small holes or small pits. The main reason for the corrosion of the bearing alloy is improper selection of lubricating oil, poor corrosion resistance of the bearing material, or rough engine operation and high temperature. (5) There is a slight convex metal surface directly contact between the bearing burning journal and the bearing friction pair to form a local high temperature. In the case of insufficient lubrication and poor cooling, the bearing alloy is blackened or partially melted. This fault is often caused by the over-tightening of the journal and the bearing; the insufficient pressure of the lubricating oil can easily cause the bearing to burn out. (6) Bearings take the outer ring bearing away from the outer circle is the bearing has a relative rotation in the seat hole. After the bearing goes out of the circle, it not only affects the heat dissipation of the bearing, but also causes the alloy on the inner surface of the bearing to ablate, and also causes damage to the back of the bearing and burns the bearing in severe cases. The main reason is that the bearings are too short, the crown is damaged, the processing or installation does not meet the specifications. 2. Preventive measures Early damage to plain bearings is much more common than bearing burnout, so it is important to prevent early damage to the plain bearings. Proper maintenance of the sliding bearing is an effective way to reduce the early damage of the bearing and a reliable guarantee to extend the life of the bearing. Therefore, in the routine maintenance and repair of the engine, attention must be paid to the appearance of the alloy surface, the back end, the end and the edge of the bearing. If there is an abnormality or a sign of excessive wear, it is necessary to carefully identify the cause and take corresponding action. The measures to improve the working conditions of the bearing, pay attention to the prevention of early damage to the sliding bearing. (1) When designing the bearing and improving the design of the manufacturing process or selecting the bearing, the thermal balance of the bearing should be considered to control the temperature rise. Because the bearing works in the friction state, the power consumption is caused by the internal friction (viscosity) of the lubricating oil liquid, which causes the bearing temperature to rise after being converted into heat. The viscosity of the lubricating oil is lowered and the gap is changed, which will soften the bearing of the Babbitt alloy. When the "burning tile hugs the shaft" accident occurred. Therefore, in the structural design, the oil hole is opened from the top of the upper bearing bush (non-load bearing zone) of the bearing to introduce the lubricating oil from the non-load bearing zone; the oil groove is opened in the longitudinal or lateral direction around the oil inlet hole on the inner surface of the bearing bush. Conducive to the uniform distribution of lubricating oil on the journal to control the temperature rise. According to the working condition of the bearing, the bearing material must have the following properties: small friction coefficient; good thermal conductivity, small thermal expansion coefficient; strong wear resistance, corrosion resistance and anti-adhesive ability; sufficient mechanical strength and plasticity. Therefore, the bearing material can be selected from babbitt. Babbitt alloy works well under stable load, but it is prone to cavitation under unsteady load, so it is not suitable for use in high-power engines. High-tin lead-based alloys and low-tin-lead-based alloys have higher strength and hardness, stronger fatigue resistance and cavitation resistance, and are better used in high-power engines. In recent years, foreign countries have used physical vapor deposition sputtering method to plate 20% tin-containing aluminum alloy or pure tin plating on the copper-lead bearing surface nickel grid, which is very effective. In addition, the full-circle oil groove bearing bush is changed to a semi-circular oil groove or a partial oil groove bearing bush, which not only improves the lubrication state of the engine sliding bearing, but also improves its bearing capacity. (2) Improve the maintenance and assembly quality of the bearing, improve the quality of the bearing's hinge, ensure that the back of the bearing is smooth and spotless, and the positioning bump is intact; its own opening amount is 0.5-1.5mm, which can ensure the self-elasticity of the bearing after assembly. It fits tightly with the bearing housing hole; each end of the upper and lower bearing bushes installed in the bearing housing should be 30-501μm higher than the bearing seat plane. The high output can ensure that the bearing cap bolt is tightly tightened according to the specified torque. Cooperate, produce sufficient friction self-locking force, the bearing will not loosen, the heat dissipation effect is good, and the bearing ablation and wear can be prevented; the working surface of the bearing can not be measured by the scraping method to reach 75%-85% contact impression, and should not be scraped. The matching clearance between the bearing and the journal is required. In addition, the assembly should pay attention to check the machining quality of the crankshaft journal and bearing, strictly implement the repair process specification, prevent the installation from being improper due to improper loading method, and the torque of the bearing bolt is not uniform or does not meet the requirements, resulting in bending deformation and stress. Concentration, leading to early damage to the bearing. (3) Reasonable selection and filling of lubricating oil In the process of use, lubricating oil with small surface tension of oil film should be selected to reduce the impact of oil flow when the formed bubble collapses, which can effectively prevent bearing cavitation; lubrication The viscosity grade of the oil should not be increased arbitrarily to avoid increasing the coking tendency of the bearing; the lubricating oil surface of the engine must be within the standard range, and the lubricating oil and refueling tools must be cleaned to prevent any dirt and water from entering, while ensuring the engine parts. Sealing effect. Pay attention to the regular inspection and replacement of lubricating oil; the place where the lubricating oil is added should be free from pollution and sand, and prevent the intrusion of all pollutants; the lubricating oils of different qualities, different viscosity grades and different types of use are forbidden to be mixed, before the lubricating oil is filled. The precipitation time should generally not be less than 48h. (4) When properly using and maintaining the engine-mounted bearings, apply the specified grade of cleaning oil to the moving surfaces of the shaft and bearings. After the engine bearing is installed, the fuel switch should be turned off before starting for the first time. The engine is idling several times with the starter. When the engine oil pressure gauge is displayed, turn the fuel switch on and off, and set the throttle to the low speed position to start the engine. Perform operation observation. The idle running time should not exceed 5 minutes. After the new machine and the overrun, the running-in operation of the engine running-in period is prohibited. During the running-in period, it is forbidden to work for a long time in the sudden increase of the load and the high-speed state; after the engine is finished for a long time and full load, it cannot be immediately In the case of shutdown, the engine must be operated at no-load and low-speed for 15 minutes before the machine can be shut down, otherwise the internal heat will not be able to escape. Strengthen the cleaning and maintenance work of the oil filter and crankcase ventilation device, and replace the filter element in time according to the instructions; ensure the normal operation of the engine cooling system, control the normal temperature of the engine, prevent the radiator from "opening the pot", and strictly prohibit the cooling water. Car; correctly select fuel, accurately adjust the valve phase and ignition timing, etc., to prevent the engine from burning normally; timely check and adjust the technical status of the crankshaft and bearing.
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Composite PP Biaxial Geogrid With Nonwoven Geotextile
Biaxial Geogrid With Nonwoven Geotextile, Extruded Plastic Geogrid Nonwoven Geotextile, Bx Geogrid Welded Nonwoven Geotextile
Feicheng Lianyi Engineering Plastics Co., Ltd , https://www.lianyigeosynthetics.com