ANSI ABMA 9:2015 pdf free download – Load Ratings And Fatigue Life For Ball Bearings ANSI/ABMA 9:2015
4.2.3 Bearing Types
The f cm factors specified in basic load rating formulae are valid only for those ball bearing configurations specified in section 4.1 above. This standard is not applicable to designs where the rolling elements operate directly on a shaft or housing surface, unless that surface is equivalent in all respects to the bearing ring (or washer) raceway it replaces. This standard is not applicable to instrument ball bearings covered in ANSI/ABMA standards 1 2.1 and 1 2.2.
4.2.4 Lubrication
Basic rating life calculated according to this standard is based on the assumption that the bearing is adequately lubricated. Determination of adequate lubrication depends upon the bearing application. An adequate amount of an appropriate type of lubricant is essential to achieving expected performance. The lubricant must be free of excessive contaminants and of a viscosity level that will provide a film thickness somewhat greater than the rolling contact surfaces’ composite roughness at the operating temperature
(Λ > 1).
4.2.5 Ring Support and Alignment
Basic rating life calculated according to this standard assumes that the bearing inner and outer rings are rigidly supported, and that the inner and outer ring axes are properly aligned. Bearing rings (or washers) must be mounted so that any deformation of rings as a result of mounting compliance is small compared to contact deformation under the applied load.
4.2.6 Internal Clearance
Radial ball bearing basic rating life calculated according to this standard is based on the assumption that only a nominal internal clearance occurs in the mounted bearing at operating speed, load and temperature. Internal clearance may be needed to account for effects of interference fits and thermal gradients; however, excessive clearance will reduce life. Negative clearance will also decrease life and increase friction. Excessive negative clearance may lead to bearing seizure.
4.2.7 High Speed Effects
Basic rating life calculated according to this standard does not account for high speed effects such as ball centrifugal forces and gyroscopic moments. These effects tend to diminish fatigue life. Analytical evaluation of these effects frequently requires the use of high speed digital computation devices and hence, cannot be included herein.
4.2.8 Interference Fits
Interference fits between the shaft and bearing bore, and centrifugal effects of high-speed operation will introduce a tensile hoop stress in the bearing inner ring. This tensile stress reduces bearing life. In addition, a high tensile stress can lead to catastrophic failure by fracture of the race.
4.2.9 Residual Stress
Compressive residual stress that extends into the zone of maximum shear stress will reduce the effective shearing stress beneath the contacting surfaces of the bearing race. This reduced stress can extend bearing life, especially at light load. Compressive residual stress will counter the negative effect of tensile stress and reduce the risk of race fracture. Compressive residual stress can be introduced by use of case-hardened steel or by mechanically cold working the bearing race.
4.2.10 Groove Radii
The load-carrying ability of a bearing is not necessarily increased by the use of smaller groove radii than those specified in sections 4.1 .2 to 4.1 .5, but it is reduced by the use of groove radii larger than those specified.