Joe Wilkinson
Bartlett Bearing Company, Inc.
Gastonia, North Carolina
There are many reasons for the use of precision grade bearings. The selection of type and size are specific to the application. Some of the determining factors are load ratings, both radial and axial, operating speeds, temperature and the degree of accuracy during operation.
Bearings are made to exacting tolerances and are rated in various levels of accuracy. These standards were established by the Annular Bearing Engineers’ Committee (ABEC) for the American Bearing Manufacturers Association which has been the benchmark in the industry since the early 1900s.
The ABEC scale classifies different accuracy and tolerance ranges into classifications 1, 3, 5, 7 and 9. These classifications or grades are issued to a bearing after a series of vigorous measuring and testing procedures have been completed.
With higher ABEC grades, an increase in running accuracy, speed and performance can be achieved.
Flexibility in pairs
Spindle bearings make up a large percentage of the super precision bearings used in the machine tool industry. Typically they are single row angular contact ball bearings that run in pairs. This bearing by itself can only carry thrust load in one direction.
But when mounted in pairs, in either a DF face-to-face (a) or DB back-to-back (b) configuration, they are capable of carrying radial, axial or a combination of loads in any direction. They can also be used in DT tandem (c) to accept heavier axial loads in one direction. Notes of the configuration should be made on the job card prior to disassembly.
The line in between the contact points of the raceways and ball is called the contact angle. As the degree of contact angle goes up, the axial load carrying capability increases.
Keep in mind that limiting speeds are reduced when load ratings are increased. Angular contact bearings are available in various degrees of contact angle. The standard offering of super precision grade bearings for the machine tool industry are 15°, 25° and 30°.
Longer life with proper care, handling
As with all types of ball and roller bearings, the intended designed life can be achieved with proper care and handling. These practices are even more critical when using super precision machine tool bearings. The shaft and housing fits vary from one ABEC grade to another. Care should be taken to ensure that you are referencing the correct tolerances for your specific precision grade. The cleanliness of your hands, gloves, tools and workspace is paramount. Contamination of the bearing and/or lubricant is one of the leading causes of premature bearing failure.
Super-precision bearings used in conjunction with proper mounting practices, along with the correct shaft and housing fits for the specific ABEC grade, will allow your customer to achieve.
- Greater accuracy
- Higher running speeds
- Longer life
- Better product reliability
- Lower overall operating cost
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