18 5 月, 2024

Manufacturing

Processing Machinery

How to choose the right bearing? These 7 selection principles are indispensable

5 min read

Crushing sand making, construction waste treatment equipment configuration, maintenance knowledge of dry sharing

When selecting bearings, it is based on several important parameters: bearing load, bearing speed, centering requirements, allowable space, bearing mounting and dismounting, tolerance level and price. Bearings mainly play the role of supporting and reducing friction in mechanical equipment, so the precision and noise of bearings are directly related to the stable operation and service life of mechanical equipment.

Generally speaking, the steps for selecting bearings are:

1. according to the working conditions of the bearing, including load direction and type, speed, lubrication, coaxiality requirements, positioning or non-location, installation and maintenance environment, ambient temperature, etc., select the basic type of bearing, tolerance level and clearance;

2. according to the working conditions of the bearing, the force and life requirements, through the calculation to determine the bearing type, or according to the use of requirements, selected bearing type, and then check the life;

3. check the rated load and limiting speed of the selected bearing.
The main considerations for selecting bearings are limiting speed, load capacity, while other factors help to determine the bearing type, structure, size and tolerance grade and clearance requirements.

7 factors to consider when selecting bearings

Various types of rolling bearings have different characteristics and are suitable for different uses in various machines. Under normal circumstances, bear the thrust load when the selection of thrust bearings, angular contact bearings; high-speed applications usually use ball bearings; bear heavy radial load, the selection of roller bearings.

1. The space and position of the machinery occupied by the bearing

In mechanical design, generally determine the size of the shaft, and then, according to the size of the shaft to choose rolling bearings. Usually is a small shaft selection of ball bearings, large shaft selection of roller bearings. However, when the bearings in the direction of the diameter of the machine is restricted, then the selection of needle roller bearings, special light and ultra-light series of ball or roller bearings; when the bearings in the axial position of the machine is restricted, you can choose a narrow or special narrow series of ball or roller bearings.

2. The size, direction and nature of the load on the bearing

Load is the most important factor in the selection of bearings. Roller bearings are used to withstand heavier loads, ball bearings are used to withstand lighter or medium loads, carburized steel or bainite quenched bearings, can withstand shock and vibration loads.
In the direction of the load, bear pure radial load, can choose deep groove ball bearings, cylindrical roller bearings or needle roller bearings. Withstand smaller pure axial load, can choose thrust ball bearings; Withstand larger pure axial load, can choose thrust roller bearings. When bearings bear radial and axial joint load, generally use angular contact ball bearings or tapered roller bearings.

3. Bearing centering performance

When the center line of the shaft and the center line of the bearing housing is different, there is an angular error, or because of the shaft of the two support spacing is large and the rigidity of the shaft is small, easy to bend or tilt, can choose to have a good self-aligning performance of self-aligning ball or roller bearings, as well as external ball bearings. Such bearings in the shaft slightly tilted or bent, can maintain normal work.
Bearing centering performance is good or bad, and its allowable different axial degree related, different axial degree value is bigger, the better the centering performance.

4. Bearing rigidity

Bearing rigidity, refers to the bearing to produce unit deformation of the size of the force required. Rolling bearing elastic deformation is very small, in most of the machinery can not have to consider, but in some machinery, such as machine tool spindle, bearing rigidity is an important factor, generally should be selected with cylindrical and tapered roller bearings. Because these two types of bearings in bearing load, its rolling body and raceway belong to point contact, rigidity is poor.
In addition, various types of bearings can also be preloaded to achieve the purpose of increasing the rigidity of the support. Such as angular contact ball bearings and tapered roller bearings, in order to prevent the vibration of the shaft, increase the rigidity of the support, often in the installation of a certain amount of axial force is applied in advance, so that they are pressed against each other. But the amount of preload must not be too large, otherwise it will make the bearing friction increases, temperature rise increases, affecting bearing life.

5. Bearing speed

Each bearing model has its own limit rotational speed, it is by the size, type and structure and other physical characteristics of the decision, more than this limit will lead to bearing temperature rise, lubricant dry, and even make the bearing stuck. Practice has proved that in the limit speed below 90% of the state work is better.
The limiting speed of grease lubricated bearings is lower than that of oil lubricated bearings, and the way the bearings are supplied with lubricant has an effect on the limiting speed that can be achieved. It must be noted that for grease lubricated bearings, the limiting speed is generally only 80% of the limiting speed when the bearing is used with a high quality recirculating oil system, but for oil mist lubricated systems, the limiting speed is generally 50% higher than for the same basic lubrication system. The design and structure of the cage also affects the limiting speed of the bearing.

6. Bearing play and axial displacement

Normally, a shaft is supported by two bearings at a certain distance from each other. In order to adapt to the shaft and the shell of different degrees of heat rise impact, the installation should be a bearing in the axial fixed, the other bearing so that it can travel on the shaft (i.e., travel support), in order to prevent due to the shaft of the extension or contraction caused by the phenomenon of seizure.

7. Facilitate the installation and dismantling of bearings

Selection of bearing type, also need to consider whether the installation and dismantling is convenient, especially large and very large bearing installation and dismantling is particularly important.
Bearings are important parts of mechanical equipment. Reasonable selection, correct operation and maintenance can effectively improve the performance and service life of bearings and equipment.