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The difference between high-speed bearings and ordinary bearings-analyze the selection standard of suitable preset pressure and heat generation of bearings

The difference between high-speed bearings and ordinary bearings-analyze the selection standard of suitable preset pressure and heat generation of bearings


Introduction to the difference between high-speed bearings and ordinary bearings

For each bearing, it has its own limit speed, the speed of the bearing is mainly limited by the temperature rise caused by frictional heating inside the bearing. When the speed exceeds a certain limit, the bearing will be burnt and cannot continue to rotate, or even the bearing will be stuck.

So, we are rotating the appropriate bearing type according to the rotational speed of the bearing, so we need to choose the requirements of the bearing. In some applications other factors are more important than limit speed. Such as: low speed, reciprocating swing, etc.

The limit speed of the bearing refers to the boundary value of frictional heating and continuous rotation without burning. Therefore, the limit speed of the bearing depends on the type, size and accuracy of the bearing, the lubrication method, the quality and quantity of the lubricant, the material and type of the cage, the load condition and other factors.

The limit speed given by the bearing manufacturer generally refers to the highest speed that can be achieved under the agreed conditions: for example, the bearing tolerance is 0; the bearing clearance is 0 groups; the bearing load is 10% of the rated load; the lubrication and cooling conditions are normal; Bearing radial load, thrust bearing only bears axial load; the temperature of the outer ring does not exceed 100°C.

The speed range required for the application helps determine which bearing to use. Most bearing manufacturers' product catalogs provide the limiting speed value of the product. Practice has proved that it is best to work at a speed lower than 90% of the limit speed.

1. Select the bearing category according to the speed

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

b. In the case of the same inner diameter, the smaller the outer diameter, the smaller the rolling body, and the smaller the centrifugal inertia force added to the foreign raceway by the rolling body, it is suitable for high-speed work. Therefore, on highways, bearings with a smaller outer diameter in the same diameter series should be selected. If a bearing with a smaller outer diameter is used and the load carrying 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 great influence on the bearing speed.

Solid cages allow higher speeds than stamped cages, and bronze solid cages allow higher speeds.

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

Ball bearings are available for low speed applications.

Factors Affecting Bearing Speed

Factors affecting the limit speed of the bearing include the magnitude of the applied load, the direction of the stress, the type of lubricant, the amount of lubricant, the bearing manufacturing accuracy, the bearing tolerance class and the bearing clearance.

Also, lubricants may be superior to other properties, but are not suitable for high speed rotation.

The factors of bearing limit speed are related to bearing type, load, precision, size, lubrication, clearance, cage and cooling conditions. However, the most important factor is the allowable operating temperature or lubricant of the bearing material.

General high-speed bearings refer to bearings with speeds up to 60 meters per second. The high speed, medium speed and low speed of the bearing are not determined by the rotational speed but by the linear speed. A small bearing can turn tens of thousands of times without moving, and it is not considered a high-speed bearing, and a large bearing with a few hundred turns is considered a high-speed bearing. Among sliding bearings, hydrostatic bearings, hydrodynamic bearings, gas hydrostatic bearings, and gas dynamic pressure bearings are all suitable for high-speed rotation.

High-speed bearings and ordinary bearings: installation fit and adjustment of high-speed bearings

1. The fit and clearance of high-speed bearings Since high-speed bearings must meet the requirements of high-precision bearings and high-temperature bearings, when considering their fit and clearance, the following two points should be taken into account:

(1) Dimensional change and hardness change when rising from normal temperature to high temperature;

(2) Force system change and shape change caused by centrifugal force at high speed.

In short, under the condition of high speed and high temperature, it is difficult to maintain the precision and working performance of the bearing from the selection of fit and clearance.

In order to ensure the raceway deformation after the bearing is installed, the interference fit of the small angular contact ball bearing cannot be too large, and the centrifugal force at high speed and thermal expansion at high temperature can offset the normal pressure of the mating surface. Or make the mating surface loose, so the interference must be carefully calculated under the premise of considering the above two factors. The effective interference at normal temperature and speed may be invalid for high-speed bearings.

If the calculation result is too contradictory (usually only at ultra-high speeds), only double lubrication measures using the under-ring lubrication method and the static pressure lubrication method are adopted, and this solution may cause the dmn value of the bearing to break through 3 million mark.

Thermal expansion at elevated temperatures, or against the normal pressure of the mating surfaces. Or make the mating surface loose, so the interference must be carefully calculated under the premise of considering the above two factors. The effective interference at normal temperature and speed may be invalid for high-speed bearings.

When considering the clearance of high-speed bearings, not only the above factors must be considered, but also the influence of the thermal elongation of the shaft on the clearance should be considered. It is required that the bearing has the best clearance under the working condition, that is, at the working temperature, and this This kind of clearance is formed under the state of precise alignment of the centers of the ball grooves of the inner and outer rings. Since high-speed bearings strive to reduce relative sliding and internal friction, it is best not to adjust the clearance of ball bearings by displacing the inner and outer rings in the axial direction.

When considering the fit interference and clearance of the bearing, it is necessary to pay attention to the characteristics that the material becomes soft and easy to deform at high temperature, and the possibility of permanent deformation caused by multiple temperature changes from normal temperature to high temperature.

2. Requirements for host related parts

High-speed bearings require the rotary system where the bearing is located to undergo precise dynamic balance. The shaft and seat hole where the bearing is installed should have a higher dimensional accuracy and shape accuracy than the general requirements. The verticality, and when considering these issues, it is also necessary to pay attention to the high speed factor and high temperature factor when the bearing is running.

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

(Longteng, the world's great power, comes out of Dongfang Tengda Tianxia Longteng three types of self-aligning roller bearings Liu Xingbang CA CC E MB MA)

Analyze the selection criteria and heat generation of ball bearings for proper preset pressure

The so-called surface pressure means that when the preset pressure is applied to the ball bearing, the contact part of the ball and the track groove is deformed to form an elliptical contact area, and the vertical component force (rolling force) generated on the contact part of the ball and the track groove body load) divided by the area of the ellipse.

The radius of the major axis of the ellipse formed on the contact surface between the ball and the track groove of the ball bearing is a, and the radius of the minor axis is b, then the area of the ellipse is S=лab. In addition, if the component force perpendicular to the contact area is set to Q, side pressure = Q/S. The unit is usually in the form of MPa.

The selection criteria of the surface pressure are as follows: When considering the factors of noise and life

(1) When the service life exceeds 10,000 hours, the preset pressure should be below 800MPa.

(2) When the service life is 5,000 to 10,000 hours (general grade products), take the preset pressure of about 1,000 MPa.

(3) When the service life is less than 5,000 hours (emphasis on rigidity), take the preset pressure of about 1500MPa.

If the material is high-carbon chromium steel, the surface pressure exceeds 2700MPa, and plastic deformation will begin. Therefore, even if the load is short-term, if the load equivalent to the average surface pressure of 2700MPa is applied, although the bearing will not be damaged, it is recommended to keep the applied load below 1600MPa from the viewpoint of safety.

The heat generated by the rotation of the ball bearing is due to the encapsulation of an excessive amount of high-viscosity grease. The viscous grease is stirred during rotation and generates heat due to stirring resistance. The countermeasure is to reduce the filling amount of grease, or replace it with guide grease, etc.

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