Rolling-element bearing
One of the earliest and best-known rolling-element bearings are sets of logs laid on the ground with a large stone block on top.
Rolling-element bearings have the advantage of a good trade-off between cost, size, weight, carrying capacity, durability, accuracy, friction, and so on.
Common mechanical components where they are widely used are – automotive, industrial, marine, and aerospace applications.
The rolling element bearing was developed from a firm foundation that was built over thousands of years.
[2] After a long inactive period in the Middle Ages, it was revived during the Renaissance by Leonardo da Vinci, and developed steadily in the seventeenth and eighteenth centuries.
[1] The internal rolling components may differ in design due to their intended purpose of application of the bearing.
The shape allows for more surface area to be in contact adding in moving more weight with less force at a greater distance.
Barrel - Provides assistance to high radial shock loads that cause misalignment and uses its shape and size for compensation.
[7] Needle - Varying in size, diameters, and materials these types of bearings are best suited for helping reduce weight as well as smaller cross sections application, typically higher load capacity than ball bearings and rigid shaft applications.
Each race features a groove usually shaped so the ball fits slightly loose.
Often fewer than half of the total number of rollers carry a significant portion of the load.
The animation on the right shows how a static radial load is supported by the bearing rollers as the inner ring rotates.
Since the rollers are thin, the outside diameter of the bearing is only slightly larger than the hole in the middle.
However, the small-diameter rollers must bend sharply where they contact the races, and thus the bearing fatigues relatively quickly.
[9] This non-locating bearing can be an advantage, as it can be used to allow a shaft and a housing to undergo thermal expansion independently.
Linear motion roller-element bearings are typically designed for either shafts or flat surfaces.
For example, with a stationary (non-rotating) load, small vibrations can gradually press out the lubricant between the races and rollers or balls (false brinelling).
[12] There are three usual limits to the lifetime or load capacity of a bearing: abrasion, fatigue and pressure-induced welding.
In high speed applications, the oil flow also reduces the bearing metal temperature by convection.
The life of a rolling bearing is expressed as the number of revolutions or the number of operating hours at a given speed that the bearing is capable of enduring before the first sign of metal fatigue (also known as spalling) occurs on the race of the inner or outer ring, or on a rolling element.
All information with regard to load ratings is then based on the life that 90% of a sufficiently large group of apparently identical bearings can be expected to attain or exceed.
This model was developed in 1924, 1947 and 1952 work by Arvid Palmgren and Gustaf Lundberg in their paper Dynamic Capacity of Rolling Bearings.
Particularly owing to improvements in the quality of bearing steels, the mechanisms for how failures develop in the 1924 model are no longer as significant.
By the 1990s, real bearings were found to give service lives up to 14 times longer than those predicted.
With all this, GBLM includes the effects of lubrication, contamination, and race surface properties, which together influence the stress distribution in the rolling contact.
[21][22] Even if the 2019 GBLM release was primarily developed to realistically determine the working life of hybrid bearings, the concept can also be used for other products and failure modes.
Balls and rollers, though simpler in shape, are small; since they bend sharply where they run on the races, the bearings are prone to fatigue.
For angular contact bearings nDms over 2.1 million have been found to be reliable in high performance rocketry applications.
Although liquid oxygen is a poor lubricant, it was adequate, since the service life of the pump was just a few hours.
Contamination in the lubricant is abrasive and greatly reduces the operating life of the bearing assembly.
