Bearing Precision and Grades
Bearing precision can be explored from various perspectives—namely, overall errors, or errors that occur within certain restrictions, or through comparison with the equivalent precision metric of their rivals. Bearings grade can be determined by means of a grading system that focuses on defining and evaluating the bearing’s accuracy, surface finishing, and internal clearance. The ultimate grade granted depends on the combination of the bearing’s stiffness and its overall reliability.
Overall Errors
Overall errors can be analyzed from various perspectives. First, radial play, or runout of an inner race, is determined by the tilt and shape of the bearing’s tracks. Radial play is a measure of the bearings ability to resist movement when subjected to radial load. Runout is a measure of the bearings overall stiffness and its ability to absorb shocks.
The size of faulty bearings (too large or too small) is determined by measuring the bearing against a datum point. Size acceptance can also be determined by using a caliper, a device used to measure the distance between two points. The size tolerance must not exceed the specified range.
The parallelism of the bearing’s races is determined by measuring the distance between two points on the same race. Boundary dimensions, or the external dimensions of the bearing, are also strictly monitored. For cylindrical roller bearings, the allowable deviation allows for a maximum inner-ring diameter difference of 0.3 mm in a single row and 0.5 mm in a double-row.
Measurement of inertia and pre-load are additional measures of a bearing’s overall errors. Inertia measures the bearings radial force, or the bearings ability to resist movement when subjected to radial load. Preload measures the initial amount of force required to move the bearing.
Bearing grades
Bearing grades are determined by a system that examines the bearings accuracy and surface finish. The bearings grade is determined by its radial runout, which is measured using a microscope, a micrometer, a snap gauge, or a special gauge. The radial runout should not exceed 0.001 mm.
For ground bearings, surface finish is determined by visual inspection and a comparison to a set of reference samples. A distinction is made between the side of the bearing that faces the load and the side that faces away from the load. The side facing the load must be within the specified grade range.
The bearings internal clearance is determined by two measurements: Radial Clearance and Angular Clearance. Angular clearance is determined by measuring the circumferential running clearance between the inner and outer race, while radial clearance is determined by measuring the movement of the rollers inside the bearing. The bearing grade must ensure that the bearings internal clearance does not exceed the specified range.
The grade of a bearing also relies on its overall reliability. A bearings abrasion rate and lubrication rate are two of the main factors observed in grading. Generally, abrasion rate and lubrication rate must not exceed the specified values.
In conclusion
Bearing precision and grades are important measures of a bearings overall performance and are a measure of its ability to withstand loads and resist shock. Bearings accuracy is determined by measuring overall errors, such as radial errors and size discrepancies. Barings grade is determined by analyzing the bearings radial runout, surface finish, and internal clearance. The overall grade of a bearing is also determined by its abrasion rate and lubrication rate. These are all important measures that must be taken into consideration when selecting the right bearing for a particular application.
