[Rising Knowledge] Is the higher the bearing speed, the better?

2021-08-30 09:55

For each bearing, it has its own limit speed. The speed of the bearing is mainly limited by the temperature rise caused by the friction and heat inside the bearing. When the speed exceeds a certain limit, the bearing will not continue to rotate due to burns, etc. Even make the bearing stuck.

Therefore, we are rotating the appropriate bearing type according to the speed of the bearing, so we need to understand what are the requirements for the speed selection bearing. In some applications, other factors are more important than the speed limit. Such:Low speed, reciprocating swing, etc.

The limit speed of the bearing refersThe limit value that does not generate frictional heat that causes burns and can be continuously rotated.Therefore, the limit speed of the bearing depends on the bearing'sType, size and accuracy, lubrication method, quality and quantity of lubricant, material and type of cage, load condition, etc.various factors.

One

Selection of speed to bearing category

1. Ball bearings have higher limit speed and rotation accuracy than roller bearings,Therefore, ball bearings should be preferred at high speeds.

2. Under the condition of the same inner diameter, the smaller the outer diameter, the smaller the rolling element, and the smaller the centrifugal inertial force of the rolling element on the peripheral raceway during operation, so it is suitable for higher speed Work.Therefore, at high speeds, it is advisable to use the same diameter series of smaller outer diameter bearings. If a bearing with a smaller outer diameter is used and the carrying capacity cannot meet the requirements, the same bearing can be installed again, or a wide series of bearings can be considered.

3. The material and structure of the cage have a great influence on the bearing speed.
The solid cage allows a higher speed than the stamping cage, and the bronze solid cage allows a higher speed.

Generally higher speed work occasions, should choose deep groove ball bearings, angular contact bearings, cylindrical roller bearings;

Tapered roller bearings can be used at lower speeds.

The limit speed of tapered roller bearings is generally about 65% of deep groove ball bearings, 70% of cylindrical roller bearings, and 60% of angular contact ball bearings. The limit speed of thrust ball bearings is low and can only be used for lower speed occasions.

The limit speed given by the bearing manufacturer generally refers to the maximum speed that can be reached under the agreed conditions: for example, the bearing tolerance is level 0; Bearing clearance is group 0; Bearing load is 10% of rated load; Lubrication and cooling conditions are normal; Radial bearing only bears radial load, thrust bearing only bears axial load; Outer ring temperature does not exceed 100 ℃, etc.

The speed range required by the application helps to determine what type of bearing to use. Most bearing manufacturers' product catalogs provide the limit speed value of their products. Practice has proved that it is better to work below 90% of the limit speed.

Factors affecting bearing speed

The factors that affect the limit speed of the bearing include the size of the applied load; the direction of the force; the type of lubricant, the amount of lubricant; the manufacturing accuracy of the bearing is the tolerance level of the bearing and the size of the bearing clearance.

In addition, depending on the type and grade of the lubricant, it may be superior to other properties but not suitable for high-speed rotation.

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

Three

Selection Method of Rolling Bearing Fit

The correct choice of bearing fit has a great relationship to ensure the normal operation of the machine, improve the service life of the bearing and make full use of the bearing capacity.

1. Whether the ferrule rotates.When the inner ring or outer ring of the bearing is working as a rotating ring, a slightly tight fit should be adopted, and the size of the interference should make the mating surface not "crawl" under the working load, because once crawling occurs, the mating surface will Wear, produce sliding, the higher the speed of the ferrule, the more serious the wear. When the bearing is working, if the inner ring or outer ring is a non-rotating ferrule, a looser fit should be selected for easy disassembly and adjustment.

2. Type of load.The ring that bears the local load should choose a loose transition fit or a fit with a small gap, so that the friction torque between the ring raceway drives the ring to rotate, so that the ring is evenly stressed and the service life of the bearing is prolonged.

Four

Other factors affecting bearing fit

1. The influence of working temperature.When the bearing is working, the temperature of the ferrule is higher than that of the matching parts due to the influence of friction heat and other heat sources. The thermal expansion of the inner ring will cause it to loosen its fit with the journal, while the thermal expansion of the outer ring will cause it to tighten its fit with the housing hole.

2. The influence of rotation accuracy and rotation speed.For bearings that bear large loads and require high rotation accuracy, in order to eliminate the effects of elastic deformation and vibration, the use of clearance should be avoided. For the light load bearings of some precision machine tools, in order to avoid the influence of the shape error of the shaft on the bearing accuracy, the clearance fit is often used. It is generally believed that the higher the rotation speed of the bearing, the tighter the fit should be.

3. Conditions for installation and removal of bearings.Considering the bearing installation and disassembly is convenient, it is appropriate to adopt a loose fit, which is particularly important for large and extra-large bearings for heavy machinery. If it is required to be easy to assemble and disassemble and tight fit is required, a separate bearing can be used, or a bearing with a tapered hole in the inner ring, a tightening sleeve and a withdrawal groove can be used.

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