About the Selection of Rolling Bearings

1. Carrying capacity

We mentioned before that rolling bearings can be divided into ball bearings and roller bearings. The classification is based on the different shapes of rolling bodies.

Generally speaking, under the same dimensions, the bearing capacity of roller bearings is 1.5-3 times that of ball bearings, so when there is a large load or impact load, we can give priority to roller bearings.

However, when the diameter is less than or equal to 20mm, the carrying capacity of the two is similar, and the price of ball bearings is cheaper than roller bearings, so we give priority to ball bearings.

2. The speed cannot exceed the limit speed

The high speed of the rolling bearing will increase the temperature between the friction surfaces, resulting in high temperature. In this case, the lubrication of the two metal surfaces fails, and the rolling elements will undergo glue failure.

Glue phenomenon: the two surfaces in contact with each other will be stuck together. As a result of relative sliding, the bonded part may be torn, thus forming scars on the surface along the sliding direction.

We say that the maximum allowable speed of rolling bearings under certain load and lubrication conditions is called the limit speed.

When designing, if the speed of the rotating shaft is known, when choosing a rolling bearing, we must make its limit speed greater than the speed of the shaft, so that the rolling bearing is safe.

The limit speed of the rolling bearing can be found in the mechanical design manual.

3. Allowable range of angular deviation

Bearing due to installation errors or shaft deformation will cause the inner and outer ring centerline relative tilt. The tilt angle is called the angular deviation.

If the angular deviation is too large, it can even affect the normal operation of the shaft. At this time, you can choose self-aligning bearings, such as self-aligning ball bearings or self-aligning roller bearings.

The outer ring raceway of the self-aligning bearing is a spherical surface centered on the bearing center, so it can be self-aligning.

Angular deviation is not allowed for thrust ball bearings and needle roller bearings.

Thrust ball bearings can only bear axial load, load direction line must coincide with the axis.

If there is an angular deviation, the thrust ball bearing will be severely damaged.

The rolling body of the needle roller bearing is in line contact with the outer ring, which is the most sensitive to the axis deflection, so it is necessary to avoid using it in the case of axis deflection.

4. Angular contact radial bearings should exist in pairs, not alone

Here angular contact to the heart bearing generally refers to the tapered roller bearings and angular contact ball bearings.

When the shaft is in contact with the bearing, the angular contact radial bearing will produce additional axial force due to the existence of the contact angle, so it is generally used in pairs.

There are two ways to install: formal and reverse.

The formal installation means that the narrow sides of the two outer rings are opposite, and the reverse installation means that the wide sides of the two outer rings are opposite.

5. Lubrication method

The lubricant of the rolling bearing may be grease, lubricating oil, or a solid lubricant.

In general, rolling bearings are lubricated with grease.

Grease lubrication is not easy to lose grease, so it is easy to seal and maintain, and a filling grease can run for a long time.

The advantage of oil lubrication is that it has lower frictional resistance than grease lubrication and can dissipate heat. It is mainly used for bearings with high speed or higher working temperature.