Every machine is inseparable from bearings. What role does the bearing play and how is it classified?

Today we will talk about several key points of bearings that we must master in mechanical design! Bearing is an important part of contemporary mechanical equipment. Its main function is to support the mechanical rotating body, reduce the friction coefficient during its movement, and ensure its rotation accuracy. According to the different friction properties of moving elements, bearings can be divided into two categories: rolling bearings and sliding bearings. Among them, the rolling bearing has been standardized and serialized, but compared with the sliding bearing, its radial size, vibration and noise are larger, and the price is also higher. According to the direction of load bearing, bearings can be divided into radial bearings (bearing radial loads, also known as radial bearings), thrust bearings (bearing axial loads) and radial thrust bearings (bearing radial and axial loads at the same time, and called radial thrust bearing).

1 Sliding bearing Sliding bearing: a bearing that works under sliding friction. Sliding bearings work smoothly, reliably and without noise. Under the condition of liquid lubrication, the sliding surfaces are separated by the lubricating oil without direct contact, which can greatly reduce the friction loss and surface wear. ▲The part of the sliding bearing shaft supported by the bearing is called the journal, and the part that matches the journal is called the bearing bush. In order to improve the friction properties of the bearing surface, the layer of anti-friction material cast on its inner surface is called a bearing lining. The materials of the bearing shell and bearing bush are collectively referred to as sliding bearing materials. Sliding bearing applications are generally under low speed and heavy load conditions, or operating parts where maintenance and lubricating oil are difficult. Sliding bearings can be divided into radial (radial) sliding bearings and thrust (axial) sliding bearings according to the direction of the load.

1.1 Radial Sliding Bearings Sliding bearings bearing radial loads. The part of the shaft supported by the bearing is called the journal, the part that matches the journal is called the bearing bush, and the part of the bearing bush made into a full cylinder is called the bearing bush of the bushing. The half is called the bearing housing. The cover and the seat are connected by studs, and the joint surfaces of the two are positioned by a stop or a pin, and spacers of different thicknesses can be placed to adjust the bearing clearance.

1.2 Thrust sliding bearing is a sliding bearing that bears the axial thrust and restricts the axial movement of the shaft. Thrust bearings whose two friction surfaces are completely separated by a fluid film are divided into hydrodynamic thrust bearings and hydrostatic thrust bearings, which are suitable for high and medium speed operation. Thrust bearings whose two friction surfaces cannot be completely separated by a fluid film work under boundary lubrication and are only suitable for low-speed operation. 2 Rolling bearing Rolling bearing is a precise mechanical element that reduces the friction loss by changing the sliding friction between the running shaft and the shaft seat into rolling friction. Rolling bearings are generally composed of four parts: inner ring, outer ring, rolling elements and cage. The function of the inner ring is to cooperate with and rotate with the shaft; the function of the outer ring is to cooperate with the bearing seat and play a supporting role; the rolling elements are evenly distributed between the inner ring and the outer ring by means of the cage, Its shape, size and number directly affect the performance and life of the rolling bearing; the cage can make the rolling elements evenly distributed, prevent the rolling elements from falling off, and guide the rolling elements to rotate for lubrication.

2.1 Basic Types of Rolling Bearings 2.2 Codes of Rolling Bearings GB/T272-93 specifies the composition and representation of rolling bearing codes. The rolling bearing code consists of the front code, the basic code and the rear code, which represent the content and the order of arrangement, see the table below. 2.3 Types of rolling bearings The size, direction and nature of the load on the bearing are the main basis for selecting the bearing type. (1) Load size and nature: ball bearings should be used for light and medium loads; roller bearings should be used for heavy loads or impact loads. (2) Load direction: For pure radial load, deep groove ball bearings, cylindrical roller bearings or needle roller bearings can be selected. For pure axial loads, thrust bearings can be selected. That is, when there is radial load and axial load, if the axial load is not too large, deep groove ball bearings or angular contact ball bearings and tapered roller bearings with a small contact angle can be selected; if the axial load is large , these two types of bearings with larger contact angle can be selected; if the axial load is large and the radial load is small, the thrust angular contact bearing can be selected, or the radial bearing and the thrust bearing can be used together. 2.4 Calculation criteria for rolling bearings When determining the bearing size, necessary calculations should be made for the main failure modes of the bearing. For bearings in general operation, the main failure mode is fatigue pitting corrosion, and the life calculation should be carried out according to the basic dynamic load rating. For bearings that do not rotate, oscillate or rotate at extremely low speed (n≤10 r/min), the main failure mode is plastic deformation, so the strength calculation should be carried out according to the rated static load. 3 Precautions for the use of bearings 3.1 The lubrication of the bearings must be selected according to the season and region, and the lubricating oil must be selected according to the regulations. Lubricating oil (grease) should be added regularly. The quantity and quality of the lubricating oil in the oil bath or the oil pool of the pressure lubrication system should be checked, supplemented and replaced in time. The pressure lubrication system should have sufficient oil supply. If the oil pressure is abnormal, it should be checked and dealt with in time. 3.2 Working conditions of bearings Bearing damage is mainly identified by abnormal working conditions. Unstable operation and abnormal running noise may be caused by excessive wear of the sliding bearing, melting of the alloy, falling off of the alloy, or wear of the rolling surface of the rolling bearing, which makes the radial clearance too large. Heavy operation and abnormal temperature rise may be due to the sliding bearing alloy falling off, alloy scratching, dry friction caused by poor contact between the bearing bush and the bearing seat, etc.; or the rolling surface of the rolling bearing is damaged. Such as metal peeling, cracking, ablation (that is, high temperature annealing, the color is purple-black), the bearing is too tight and the lubrication is poor, etc., should be checked and dealt with in time. 3.3 Check the integrity of the bearings When performing regular maintenance on the machine, the integrity of the bearings should be carefully checked. If the bearing bush is damaged or the clearance exceeds the allowable limit, it should be rebuilt; if the rolling bearing is damaged, the looseness should be replaced; the oil circuit of the lubrication system should be cleaned and smooth.