Mechanical Design Bearing Selection Guide

1、why choose rolling bearings?

Rolling bearings support and guide the rotation or swing of machine components (such as shafts) with minimal friction, and transfer loads between machine components. Rolling bearings have high precision and low friction properties, so high speed can be achieved while reducing noise, heat, energy consumption and wear. These bearings are cost-effective and are typical interchangeable machine parts that meet national or international dimensional standards.

2、How to select rolling bearings? 

There are many kinds of bearings and rich types, there are ultra-small bearings of millimeter level, and there are large bearings of more than 10 meters. When designing mechanical equipment, it is very important to choose bearings suitable for different machines from these many varieties.

How to choose bearings, the following conditions are very important:

Condition 1: Must be suitable for the use of mechanical environment, such as: ambient temperature, humid environment, dusty environment, etc

Condition 2: Must be suitable for the mechanical requirements of the bearing conditions, such as: size, speed, load, vibration, silence and so on

Condition 3: It is relatively easy to buy replacement bearings, which is convenient for mechanical maintenance and inspection, such as: vertical/horizontal installation, coupling/belt/gear transmission, lubrication supplement, etc. 

The main purpose of bearing selection is correct: to reduce mechanical failures, shorten the replacement time of bearings during maintenance, and extend the operating life of machinery.

In order to correctly select bearings, you can roughly follow the following 8 steps to select the right bearing for the equipment:

First: How to choose the bearing type

1、mechanical design, most of the first to determine the size of the shaft to meet the necessary strength, and then select the bearing on this basis.

For example, when the motor is designed, the diameter of the motor shaft is first determined according to the transmission power of the motor.

When the bearing mainly bears the radial (perpendicular to the axis) load, the radial bearing is selected; When the bearing mainly bears axial (in the same direction as the shaft) load, the thrust bearing is selected;

The bearing load is small, choose ball bearings; When the load is large, choose roller bearings. Multi-row roller bearings and full roller bearings have greater load carrying capacity.

When the speed is higher, choose ball bearings; When the speed is low, choose roller bearings, of course, full roller bearing without cage speed is lower.

The difference between a ball and a roller is the way it makes contact with the raceway. The ball makes point contact with the raceway of the inner and outer rings of the bearing. As the load acting on the bearing increases, the contact point becomes an oval area. If the contact area is small, the rolling dust is also small, so that the ball bearing can adapt to high-speed operation, but its carrying capacity is limited.

The roller makes linear contact with the raceway of the inner and outer rings of the bearing. As the load acting on the bearing increases, the contact line becomes a rectangle. Due to the larger contact area and the resulting greater friction, roller bearings can withstand heavier loads but at lower speeds than ball bearings of the same size.

When a bearing bears radial load and axial load at the same time (combined load), if the combined load is small, choose deep groove ball bearings or angular contact ball bearings; If the load is large, choose tapered roller bearings.

When bearing large bilateral axial loads or alternating axial loads, more than two bearings can be combined or multiple rows of bearings can be selected. For example: with diagonal contact ball bearings or paired tapered roller bearings.

2, mechanical design, in addition to determine the bearing diameter according to the size of the journal, we also need to consider the size of the bearing seat, that is, the installation space to consider the bearing. The product catalog of each bearing manufacturer has a bearing main size (inner diameter, outer diameter, etc.) table. Select the type of bearing that can fit into the mounting space according to the size of the shaft or housing. Even for bearings with the same inner diameter, there are a variety of width sizes and outer diameter sizes, from which the suitable bearing can be selected.