What Is The Bearing Speed?
Bearing speed is one of the most important factors affecting bearing temperature rise. The maximum allowable speed of the bearing, i.e. the limit speed, decreases with the increase of the bearing diameter series and width series. The limit speed NLIM value of various types and sizes of bearings is listed in the bearing samples or design manuals. The test conditions are equivalent dynamic load P < = 0.1C (C is the basic rated dynamic load). The cooling conditions are normal and the maximum allowable speed of bearings with Class 0 tolerance. However, since the limit speed is mainly limited by the temperature rise during operation, the limit speed in the sample cannot be considered an absolutely insurmountable limit.
From the requirements of working speed on the bearing, the following points can be determined:
(1) The ball bearing has a higher limit speed and rotation accuracy than the roller bearing. Therefore, the ball bearing 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 element, and the smaller the centrifugal inertia force applied by the rolling element on the foreign raceway during operation, so it is suitable for working at higher speed. Therefore, at high speed, the bearing with a smaller outer diameter in the same diameter series should be selected. If a bearing with a small outer diameter is used and the bearing capacity cannot meet the requirements, the same bearing can be installed in parallel, 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 rotational speed than the stamped cage, and the bronze solid cage allows a higher rotational speed.
The speed of the bearing exceeding 12000 revolutions per minute should be considered a high-speed range. In addition, the temperature that an ordinary bearing can withstand depends on the deformation of the cage. For example, if the cage is deformed at 100 degrees and the bearing is jammed, the temperature that the bearing can withstand is 100 degrees.
The rotation speed of the bearing is mainly limited by the temperature rise caused by the friction heat inside the bearing. When the rotation speed exceeds a certain limit, the bearing will not continue to rotate due to burns. The limit speed of the bearing refers to the limit value of continuous rotation without generating friction heat causing burns. 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 the lubricant, the material, the type of the cage, the load conditions, and other factors.
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; The bearing clearance is 0 group; The bearing load is 10% of the rated load; Lubrication and cooling conditions are normal; The radial bearing only bears the radial load, and the thrust bearing only bears axial load; The outer ring temperature shall not exceed 100 ℃.
The factors affecting the bearing limit speed include the magnitude of the applied load; Force direction; Type and quantity of lubricant; The manufacturing accuracy of the bearing is the tolerance grade of the bearing and the clearance size of the bearing.
In addition, the lubricant may be superior to other properties but not suitable for high-speed rotation according to its type and brand.
The speed range required for the application helps to determine what type of bearing to use. The product catalog of most bearing manufacturers provides the limited speed value of their products. The practice has proved that it is better to work under 90% of the limit speed.
(1) The ball bearing has a higher limit speed and rotation accuracy than the roller bearing. Therefore, the ball bearing 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 element, and the smaller the centrifugal inertia force applied by the rolling element on the foreign raceway during operation, so it is suitable for working at higher speed. Therefore, at high speed, the bearing with a smaller outer diameter in the same diameter series should be selected. If a bearing with a small outer diameter is used and the bearing capacity cannot meet the requirements, the same bearing can be installed in parallel, or a wide series of bearings can be considered.
(3) The material and structure of the cage have a great influence on bearing speed. The solid cage allows a higher rotational speed than the stamped cage, and the bronze solid cage allows a higher rotational speed.
Generally speaking, deep groove ball bearing, angular contact bearing, and cylindrical roller bearing should be selected under the working conditions of high speed; Tapered roller bearings can be used in low-speed working conditions. The limit speed of tapered roller bearing is generally 65% for deep groove ball bearing, 70% for cylindrical roller bearing, and 60% for angular contact ball bearing. The limit speed of the thrust ball bearing is low, and it can only be used in the case of lower speed.
