Keywords: bearings, deep groove ball bearings, angular contact bearings, cylindrical roller bearings, Tapered roller bearings, bearing speed
When choosing bearings, will you wonder: the higher the speed of bearings, the better to use? Faster and more expensive? Today we are going to talk about those things bearing speed...
For each bearing, there is its own limit speed, bearing speed is mainly limited by the temperature rise caused by friction heating inside the bearing. When the speed exceeds a certain limit, the bearing will not continue to rotate because of burns, etc., or even make the bearing stuck.
Therefore, we rotate the appropriate bearing type according to the speed of the bearing, so we need to understand the requirements of the speed selection of the bearing. In some applications, other factors are more important than the limit speed. Such as: low speed, reciprocating swing and so on.
The limit speed of bearings refers to the limit value that does not produce friction heating that causes burns and can be continuously rotated. Therefore, the ultimate speed of the bearing depends on the type, size and accuracy of the bearing, as well as the lubrication mode, the quality and quantity of lubricant, the material and type of the cage, load conditions and other factors.
The limit speed given by the bearing manufacturer generally refers to the highest speed that can be achieved under agreed conditions: for example, the bearing tolerance is level 0; Bearing clearance is 0 group; Bearing load is 10% of rated load; Lubrication cooling condition is normal; Radial bearing only bears radial load, thrust bearing only bears axial load; The outer ring temperature does not exceed 100℃, etc.
The speed range required in the service situation helps to decide 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 under the state of 90% limit speed.
| The selection of rotating speed to bearing category
1. Ball bearings have higher limit speed and rotation accuracy than roller bearings, so they should be preferentially selected at high speed.
2. Under the condition of the same inner diameter, the smaller the outer diameter, the smaller the rolling body, the smaller the centrifugal inertia force added by the rolling body on the outer raceway during operation, so it is suitable for working at a higher speed. Therefore, at high speed, it is advisable to choose bearings with smaller outer diameters in the same diameter series. If a bearing with a smaller diameter and the bearing capacity is not up to the requirements, the same bearing can be installed again, or consider using a wide series of bearings.
3. The material and structure of cage have a great influence on the bearing speed.
Solid cages allow higher rotational speeds than ram cages and bronze solid cages allow higher rotational speeds.
The ultimate 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 ultimate speed of thrust ball bearings is low, and can only be used for low speed occasions.
| Factors affecting bearing speed
The factors affecting the ultimate speed of bearing include the size of applied load; Force direction; The type of lubricant and the amount of lubricant; Bearing manufacturing accuracy is bearing tolerance grade and bearing clearance size.
In addition, lubricants depending on their type and brand may be superior to other properties but not suitable for high speed rotation.
Bearing ultimate speed is related to bearing type, load, accuracy, size, lubrication, clearance, cage and cooling conditions. However, the most important factor is the working temperature or lubricant allowed by the bearing material.
| Selection method of rolling bearing fit
Correct selection of bearing fit is very important to ensure the normal operation of the machine, improve the service life of bearings and make full use of bearing capacity.
1. Whether the ring rotates. When the inner or outer ring of the bearing works as a rotating ring, a slightly tighter fit should be used. The size of the interference should make the mating surface not "crawling" under the working load, because once crawling occurs, the mating surface will wear and slide, and the higher the ring speed, the more serious the wear. When bearing is working, if its inner ring or outer ring is not rotating ring, in order to facilitate disassembly and adjustment, it is advisable to choose a loose fit.
2. Load type. A loose transition fit or a smaller clearance fit should be selected for the local load bearing ring, so that the friction torque between the raceways of the ring drives the ring to rotate, so that the force on the ring is uniform and the service life of the bearing is prolonged.
| Other factors affecting bearing fit
1. Influence of working temperature. When the bearing is working, the temperature of the ring is higher than that of its matching parts due to the influence of friction heating and other heat sources. The thermal expansion of the inner ring will cause the loosening of its fit with the journal, while the thermal expansion of the outer ring will cause the tightening of its fit with the shell hole.
2. Influence of rotation accuracy and rotation speed. In order to eliminate the influence of elastic deformation and vibration, clearance fit should be avoided for bearings with large loads and high rotation accuracy. For light load bearings of some precision machine tools, in order to avoid the influence of shape error and shaft on bearing accuracy, clearance is often used. It is generally believed that the higher the rotation speed of bearings, the tighter the fit should be.
3. Conditions for installing and disassembling bearings. Considering the convenience of bearing installation and disassembly, it is appropriate to use a loose fit, which is particularly important for large and very large bearings used in heavy machinery. If convenient assembly and disassembly are required and tight fitting is required, separated bearings can be used, or bearings with taper holes in the inner ring, fixed sleeves and back groove can be used.
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