ball bearing load rating

Ball Bearing Load Rating

Load Rating

Load ratings for bearings are expressed in Kgf (kilogram force) on this website. That is the force exerted by a mass of 1 kilogram at the Earth's surface. You will often see force expressed in Newton elsewhere. A Newton is defined as the force that will accelerate a mass of one kilogram at the rate of one meter per second per second (or 1 m/s²). Since the force of gravity at the Earth's surface is 9.80665 m/s², 1 Kgf = 9.80665 Newton but, to keep it simple, we say 1 Kgf = 10 Newton.

Dynamic radial load rating

The official explanation for this is... "The dynamic load rating is that constant stationary radial load which 90% of a group of identical chrome steel bearings, with only the inner ring rotating, can endure for one million revolutions before the first signs of fatigue develop". Yes, 1 million revolutions sounds a lot but is it really? If you take a bearing running at 5000 rpm with the max dynamic load applied to it, it will last for 1,000,000 revs divided by 5000 = 200 minutes or 3 hours and 20 minutes!! This should tell you that these figures are used in the calculation of life ratings but bearings should not be subjected to anywhere near such loads in normal application unless you don't expect them to last very long. If long life is required, it is preferable to limit the actual load to between 6% and 12% of a bearing’s dynamic load rating. Heavier loads can be tolerated but life will be shortened. 440 stainless steel bearings will support approximately 80% - 85% of the load figures for chrome steel bearings. Load ratings for thrust bearings are based on the constant axial load endured for 1 million revolutions. 

Static radial load rating

This represents the purely radial load (or axial load for thrust bearings) which will cause a total permanent deformation of the balls or raceway equal to one ten-thousandth of the ball diameter. This may be tolerable for certain applications but not where any smoothness or accuracy is required. Static load ratings for stainless steel bearings are approximately 75% - 80% of the load ratings for chrome steel bearings.

The load capacity of a bearing may be limited by the lubricant. Certain lubricants are only suitable for light loads while others are designed for high load applications. Load ratings are higher for full complement bearings (see Retainer). The axial load capacity of a radial ball bearing can be increased by specifying loose radial play.

Axial load rating

Heavy duty bearing types such as 6200 or 6300 series may take axial loads of up to 50 percent of the static radial load rating. Thin-section deep groove ball bearings can only support axial loads of between 10 and 30 percent of the bearing's static radial load rating due the shallower raceways. Please note, these figures are based on pure axial load. Additional radial loads or moment (misalignment loads) will have an impact on the axial load capacity. To exceed the total recommended limits for combined loads will have a detrimental effect on bearing life.

Ceramic bearing load

The ceramic bearing load is higher than bearing steel type. But due to the fracture toughness, Si3N4 bearing load rating will be 16% of bearing steel bearing load while ZrO2 bearing is 13% of bearing steel bearing. SiC load rating is 11% of bearing steel bearing.