A minute to understand bearings

First, the basic structure of the bearing

The basic composition of the bearing: inner ring, outer ring, rolling body, cage

Inner ring: often closely matched with the shaft, and rotate together.

Outer ring: often with the bearing seat transition, mainly to support the effect.

The inner and outer ring material is bearing steel GCr15, and the hardness after heat treatment is HRC60~64.

Rolling element: by means of cage evenly arranged in the inner ring and outer ring trench, its shape, size, number are directly affect the bearing load bearing capacity and performance.

Cage: In addition to evenly separating the rolling element, it also guides the rotation of the rolling element and effectively improves the internal lubrication performance of the bearing.

Steel ball: The material is generally bearing steel GCr15, and the hardness after heat treatment is HRC61~66. The accuracy grade is divided into G (3, 5, 10, 16, 20, 24, 28, 40, 60, 100, 200) from high to low according to dimensional tolerance, shape tolerance, gauge value and surface roughness.

There is also an auxiliary bearing structure

Dust cover (sealing ring) : to prevent foreign matter from entering the bearing.

Grease: lubricate, reduce vibration and noise, absorb friction heat, increase bearing service time.

Second, the classification of bearings

According to the friction properties of the moving components are different, bearings can be divided into rolling bearings and rolling bearings two categories. In rolling bearings, the most common are deep groove ball bearings, cylindrical roller bearings and thrust ball bearings.

Deep groove ball bearings mainly bear radial loads, and can also bear radial loads and axial loads together. When only radial load is applied, the contact Angle is zero. When the deep groove ball bearing has too large radial clearance, it has the performance of angular contact bearing and can withstand too large axial load, the friction coefficient of the deep groove ball bearing is small, and the limit rotation speed is also high.

Deep groove ball bearings are the most symbolic rolling bearings with a wide range of uses. It is suitable for high-speed rotation and even very high-speed rotation operation, and it is very durable and does not need frequent maintenance. This kind of bearing has small friction coefficient, high limit speed, simple structure, low manufacturing cost and easy to achieve high manufacturing accuracy. The size range and situation change, used in precision instruments, low noise motors, automobiles, motorcycles and usually machinery and other industries, is the most common type of mechanical engineering bearings. Mainly bear radial load, can also bear a certain amount of axial load.

Cylindrical roller bearing, the rolling body is the centripetal rolling bearing of the cylindrical roller bearing. Cylindrical roller bearing and raceway are linear contact bearings. Large load capacity, mainly to bear radial load. The friction between the rolling element and the rim of the ring is small, which is suitable for high-speed operation. According to whether the ring has a flange, it can be divided into NU\NJ\NUP\N\NF and other single-row bearings, and NNU\NN and other double-row bearings.

A cylindrical roller bearing with an inner or outer ring without a rib, whose inner and outer rings are able to move relative to each other axially and can therefore be used as a free-end bearing. One side of the inner ring and the outer ring has a double rib, and the other side of the ring has a cylindrical roller bearing with a single rib, which can withstand the axial load in the same direction to a certain extent. Steel sheet cages are usually used, or solid cages made of copper alloy. But some of them use polyamide forming cages.

Thrust ball bearings are designed to withstand thrust loads during high-speed operation and are composed of gasket rings with a raceway groove for ball rolling. Because the ring is the seat pad shape, the thrust ball bearing is divided into two types: flat base pad type and aligning spherical seat type. In addition, such bearings can withstand axial loads, but not radial loads.

The thrust ball bearing consists of a seat ring, a shaft ring and a steel ball cage assembly. The shaft ring matched with the shaft, and the seat ring matched with the shell. Thrust ball bearings are only suitable for bearing a part of the axial load, low speed parts, such as crane hooks, vertical pumps, vertical centrifuges, jacks, low speed retarders, etc. The shaft ring, seat ring and rolling body of the bearing are separated and can be installed and disassembled separately.

Three, rolling bearing life

(1) Main damage forms of rolling bearings

Fatigue spalling:

In rolling bearings, the load bearing and relative movement of the contact surface (raceway or rolling body surface), because of the continuous load, the first under the surface, the corresponding depth, the weak part of the crack, and then develop to the contact surface, so that the surface layer of metal flake out, resulting in the bearing can not operate normally, this phenomenon is called fatigue spalling. The final fatigue spalling of rolling bearings is difficult to avoid, in fact, in the case of normal installation, lubrication and sealing, most of the bearing damage is fatigue damage. Therefore, the service life of bearings is usually referred to as the fatigue service life of bearings.

Plastic deformation (permanent deformation) :

When the rolling bearing is subjected to excessive load, the plastic deformation is caused in the rolling body and the rolling to the contact, and the rolling to the surface surface produces a dent, resulting in severe vibration and noise during the running of the bearing. In addition, external foreign particles into the bearing, excessive impact load, or when the bearing is stationary, because of machine vibration and other factors may produce indentation in the contact surface

Wear and tear:

Because of the relative movement of rolling element and raceway and the invasion of dirt and dust, rolling element and rolling to the surface cause wear. When the amount of wear is large, the bearing clearance, noise and vibration increase, and the running accuracy of the bearing is reduced, so it directly affects the accuracy of some main engines.

Fourth, the bearing accuracy level and noise clearance representation method

The accuracy of rolling bearings is divided into dimensional accuracy and rotating accuracy. The precision level has been standardized and is divided into five levels: P0, P6, P5, P4 and P2. Accuracy has been improved from level 0, relative to the usual use of level 0 is enough, according to different conditions or occasions, the required level of accuracy is not the same.

Five, often asked bearing questions

(1) Bearing steel

Commonly used types of rolling bearing steel: high carbon complex bearing steel, carburized bearing steel, corrosion resistant bearing steel, high temperature bearing steel

(2) Lubrication of bearings after installation

Lubrication is divided into three types: grease, lubricating oil, solid lubrication

Lubrication can make the bearing run normally, avoid the contact between the raceway and the rolling surface, reduce the friction and wear inside the bearing, and improve the service time of the bearing. Grease has good adhesion and wear resistance and temperature resistance, which can improve the oxidation resistance of high temperature bearings and enhance the service life of bearings. The grease in the bearing should not be too much, and too much grease will be counterproductive. The higher the speed of the bearing, the greater the harm. Will make the bearing in operation when the heat is large, will be easy to be damaged because of excessive heat. Therefore, it is particularly important to fill the grease scientifically.

Six, bearing installation precautions

Before installation, pay attention to check whether there is a problem with the quality of the bearing, correctly select the corresponding installation tool, and pay attention to the cleanliness of the bearing when installing the bearing. Pay attention to even force when tapping, gently tapping. Check whether the bearings are installed properly after installation. Remember, before the preparation work is completed, do not unpack the bearing to prevent contamination.


Post time: Sep-12-2023