The difference between high-speed bearings and ordinary bearings

When purchasing rolling bearings, do you suspect that the higher the speed of the bearing, the better it is used? The faster, the more expensive? Is it actually like this? We will provide a detailed explanation of bearing speed and the factors that affect bearing speed in the following content:

For each bearing, it has its own limit speed, which is mainly limited by the temperature rise caused by friction heating inside the bearing. When the speed exceeds a certain limit, the bearing will be burned and unable to continue rotating, or even get stuck. Therefore, we are rotating the appropriate bearing type based on the speed of the bearing, so we need to select the requirements for the bearing. In some applications, other factors are more important than the limit speed. For example, low speed, reciprocating oscillation, etc.

The limit speed of a bearing refers to the boundary value of frictional heating and continuous rotation that does not cause burns. Therefore, the ultimate speed of a bearing depends on factors such as the type, size and accuracy of the bearing, lubrication method, quality and quantity of lubricant, material and type of cage, and load conditions.

The limit speed provided by the bearing manufacturer generally refers to the high speed that can be achieved under agreed conditions: for example, the bearing tolerance is 0; The bearing clearance is 0 groups; The bearing load is 10% of the rated load; Normal lubrication and cooling conditions; Radial bearings only bear radial loads, while thrust bearings only bear axial loads; The temperature of the outer ring shall not exceed 100 ℃.

The speed range required for the application helps determine what type of bearing to use. Most bearing manufacturers' product catalogs provide the maximum speed values for their products. Practice has proven that it operates below 90% of the limit speed.

1. Select bearing category based on rotational speed

a. The limit speed and rotational accuracy of ball bearings are higher than those of roller bearings, so high speed should be given priority in ball bearings.

b. When the inner diameter is the same, the smaller the outer diameter, the smaller the rolling element, and the smaller the centrifugal inertia force exerted by the rolling element on the foreign raceway, making it suitable for high-speed operation. Therefore, on highways, bearings with the same diameter series and smaller outer diameters should be selected. If a bearing with a smaller outer diameter is used and the bearing capacity cannot meet the requirements, the same bearing can be installed or a wide series bearing can be considered.

c. The material and structure of the cage have a significant impact on the bearing speed.

The allowable speed of the solid cage is higher than that of the stamped cage, and the allowable speed of the bronze solid cage is higher.

Deep groove ball bearings, ball bearings, motor bearings, automotive bearings, electric tool bearings angular contact ball bearings;

Rolling bearings can be used in low-speed work environments.

Factors affecting bearing speed

The factors that affect the ultimate speed of bearings include the magnitude of applied load, stress direction, type of lubricant, quantity of lubricant, bearing manufacturing accuracy, bearing tolerance level, and bearing clearance.

In addition, lubricants may outperform other properties, but are not suitable for high-speed rotation.

The factors affecting the ultimate speed of bearings are related to the type, load, accuracy, size, lubrication, clearance, cage, and cooling conditions of the bearings. However, an important factor is the allowable operating temperature or lubricant of the bearing material.

The general high-speed bearing refers to the bearing whose speed reaches 60 Metre per second. The high, medium, and low speeds of bearings are not determined by rotational speed but by linear speed. A small bearing that can rotate for tens of thousands of revolutions is not considered a high-speed bearing, while a large bearing that can rotate for hundreds of revolutions is considered a high-speed bearing. In sliding bearings, hydrostatic bearings, hydrodynamic bearings, aerostatic bearings, and hydrodynamic bearings are all suitable for high-speed rotation.

High speed bearings and ordinary bearings: installation coordination and adjustment of high speed bearings

1. The fit and clearance of high-speed bearings should consider the following two points when considering their fit and clearance:

(1) Changes in size and hardness from room temperature to high temperature;

(2) The changes in force system and shape caused by centrifugal force at high speeds.

In short, it is difficult to maintain the accuracy and performance of bearings in terms of fit and clearance selection under high-speed and high-temperature conditions.

In order to ensure the deformation of the raceway after bearing installation, the interference fit of the small angle contact ball bearing cannot be too large, and the centrifugal force at high speed and thermal expansion at high temperature may offset the normal pressure on the mating surface. Alternatively, to relax the mating surface, the interference amount must be carefully calculated while considering the above two factors. An effective interference amount at room temperature and constant speed may not be effective for high-speed bearings.

If the contradiction in the calculation results is too great (usually only at ultra high speeds), only by adopting a dual lubrication measure of combining underring lubrication and static pressure lubrication, and this plan may cause the dmn value of the bearing to exceed the 3 million mark.

Thermal expansion at high temperatures, or offsetting the normal pressure on the mating surface. Alternatively, to relax the mating surface, the interference amount must be carefully calculated while considering the above two factors. An effective interference amount at room temperature and constant speed may not be effective for high-speed bearings.

When considering the clearance of high-speed bearings, not only the above factors should be taken into account, but also the influence of thermal elongation of the shaft on the clearance. It is required that the bearings have good clearance under working conditions, that is, at working temperature, and this clearance is formed under the precise alignment of the inner and outer ring ball groove centers. As high-speed bearings strive to reduce relative sliding and internal friction, ball bearings should not use the method of relative misalignment of the inner and outer rings along the axial direction to adjust the clearance of the ball bearing.

When considering the fit interference and clearance of bearings, attention should be paid to the characteristics of the material becoming soft and easily deformed at high temperatures, as well as the possibility of permanent deformation caused by multiple temperature changes from room temperature to high temperature.

2. Requirements for host related parts

High speed bearings require precise dynamic balancing of the rotating system where the bearings are located. The parts where the bearings are installed on the shaft and seat holes should have dimensional and positional accuracy higher than general requirements, especially the coaxiality of the bearings and the verticality of the shoulder to the seat hole or journal. When considering these issues, it is also necessary to pay attention to the high-speed and high-temperature factors during bearing operation.

The shaft support system requires both high rigidity and minimal mass. To overcome this contradiction, measures such as reducing surface roughness and improving surface strengthening can be taken to increase the support stiffness, and hollow shafts can be used to reduce system mass.