How to choose bearings and precautions in use

With the progress and development of society, mechanization has been widely used in production and life. As an indispensable part of the machine, the range of use of the bearing will become wider and wider, as the bearing is used whenever there is a rotation.

Bearings mainly support and reduce friction in the machine, so the accuracy and noise of the bearings are directly related to the use and life of the machine. However, business people often encounter customers who use the best bearings or imported bearings, and the efficiency is not high, which is related to the use and selection of bearings. Some people may say that "the use and selection of bearings is the user's business, I only want what the user wants me to sell." However, as a qualified salesperson, besides mastering the knowledge of its own products, it must be proficient in the use of products, that is, doctor-type sales, and select the best matching bearings according to the performance and use conditions of the user's accessory products. This is the popular professional manufacturing and sales of major companies in the world. This method has also achieved good results since the implementation of the People's Group.

Because of the wide variety of bearing types, the following will focus on the use and selection of the most widely used deep groove ball bearings. Those who wish to know less about bearings can deepen their understanding of bearings.

First, the choice of bearings

1. Selection of bearing model: The bearing model is generally selected by the user's technical personnel according to the service conditions of the supporting product and the bearing load. The business personnel mainly understand whether the actual load of the user is consistent with the selected bearing. If the bearing does not meet the requirements for use, the customer should be advised to re-select the model as soon as possible, but unless the special product is selected on the model, there will be no problem.

2, the choice of bearing clearance: users generally only know what type and grade when buying bearings, rarely ask for the clearance of the bearing, the business personnel must ask about the conditions of use of the bearing, the speed and temperature of the bearing The tolerances are directly related to the choice of bearing clearance. Motors with a speed of 3,500 rpm or less generally use CM clearance. For example, high-temperature high-speed motors require relatively large clearance. After the assembly, the bearing clearance will be reduced due to the increase of the inner hole and the reduction of the outer circle. The reduction of the clearance = the interference amount × 60% (except for the bearing chamber is aluminum). For example, the clearance before the assembly of the bearing is 0.01 mm, and the interference at the time of assembly is 0.01 mm, and the clearance after the assembly of the bearing is 0.004 mm. In theory, the noise and life of the bearing are at the best state when the bearing is at zero clearance, but in the actual operation, considering the temperature rise and other problems, the clearance of the bearing after assembly is preferably 0.002mm-0.004mm.

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6 features of sliding bearing damage

As the world's top bearing imported bearings, such as SKF, NSK and other bearing applications are very extensive. In every industry, the characteristics of its damage are also different. Today we look at the damage characteristics of the engine sliding bearing.

(1) Mechanical damage

The mechanical damage of the sliding bearing means that the alloy surface of the bearing bush has different degrees of groove marks. In severe cases, metal peeling occurs on the contact surface and a large area of ​​random scratches occurs; in general, the contact surface damage and ablation phenomenon exist simultaneously. 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), bearing cave erosion

Under the repeated action of the sliding bearing in the cylinder pressure impact load, the surface layer is plastically deformed and hardened by hardening, and the local deformation loss ability is gradually formed, and the grain is gradually formed and expanded continuously. Then, as the wear debris falls off, a hole is formed in the loaded surface layer. . 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

Bearing fatigue pitting 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 in the interior. 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 and 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

The bearing alloy corrosion is generally the area where the lubricating oil is not pure. The chemical impurities (acid oxides, etc.) in the lubricating oil cause the bearing alloy to oxidize to form an acidic substance, causing the bearing alloy to partially fall off and form irregular micro holes or small concaves. pit. 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.

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