Rolling bearings generally consist of bearingrings， inner ring and outerring， rolling elements that roll on the raceways of the rings， and a cage that surrounds the rolling elements as seen in Figure 13-3. The rolling elementsare classified according to their shapes. Intoballs， cylindrical rollers， needlerollers， tapered rollers， and barrel rollers as shown in Figure 13-4.
The rolling elements' function is to transmit the force acting on the bearing from one ring to the other. For a high load carrying capacity it isimportant that as many rolling elements as possible， which are as large aspossible， are accommodated between the bearing rings. Their number and size depend on the cross section of the bearing. It is just as important for load ability that the rolling elements within the bearing are of identical size.Therefore， they are sorted according to grades. The tolerance of one grade
1 2
3 4
1 Outer ring, 2 Inner ring, 3 Rolling element, 4 Cage
is very slight. The generatrices of cylindrical rollers and tapered rollers have a logarithmic profile. The center part of the generatrix of a needle roller isstraight， and the ends are slightly crowned， this profile prevents edge stres-sing when under load.
The bearing rings comprise of an inner ring and an outer ring to guide therolling elements in the direction of rotation. Racewaygrooves， lips， and inclined running areas guide the rollers and transmit axial loads in transverse direction as seen in Figure 13-5. .ylindrical roller bearings and needle rollerbearings， which need to accommodate shaft expansions have lips only on one bearing ring and are commonly known as floating bearings.
The functions of a cage are to keep the rolling elements apart so that theydo not rub against eachother， to keep the rolling elements evenly spaced foruniform load distribution， to prevent rolling elements from falling out of separable bearings and bearings that are swiveled out and to guide the rolling elements in the unloaded zone of the bearing. The transmission of forces is not one of the cage's functions.
.ages are classified into pressedcages， machinedcages， and mouldedcages. Pressed cages are usually made of steel， but sometimes ofbrass， too. They are lighter than machined metal cages. Since a pressed cage barelycloses the gap between inner ring and outerring， lubricant can easily pene-trate into the bearing.
Figure 13-5. Raceway groves and lips for typical roller bearings. (Courtesy FAG bearings.)
Machined cages of metal and textile laminated phenolic resin are madefrom tubes ofsteel， light metal or textile laminated phenolic resin， or castbrass rings. To obtain the required strength，large， heavily loaded bearings are fitted with machined cages. Machined cages are also used where lip guidance of the cage is required. Lip-guided cages for high-speed bearings are in many cases made of light materials such as light metal or textile laminated phenolic resin to keep the forces of gravity low.
Molded cages using injection molding techniques can realize designs with an especially high-load carrying capacity. Injection molding has made it possible to realize cage designs with an especially high-load carrying capacity. The elasticity and low weight of the cages are of advantage whereshock-type bearingloads， great accelerations and decelerations as well as tilting of the bearing rings relative to each other have to be accommodated. Polyamide cages feature very good sliding and dry running properties.
There are a number of special rolling bearing designs and some series of cylindrical roller bearings without cages. By omitting the cage the bearing can accommodate more rolling elements. This yields an increased loadrating，but， due to the increased friction， the bearing is suitable for lower speeds only.
.oad ratings. The load rating of a bearing reflects its load carrying capacity and is an important factor in the dimensioning of rolling bearings.It is determined by the number and size of the rolling elements， the curvatureratio， the contactangle， and the pitch circle diameter of the bearing. .ue to the larger contact area between rollers and raceways the load ratings of roller bearings are higher than those of ball bearings.
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