8/3/2019 2848-Types of Bearings

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Types of bearingsGEOMETER discusses the various types of bearing

in common use and gives examples of their use

BEARINGS A R E T H E m e a ns by

which shafts are located,enabled to carry loads and

transmit power. Ail machinesnecessarily employ them and allengineers must possess some know-ledge of their design, construction,lubrication, adjustment, etc.

Every bearing must perform one oftwo functions, or a combination ofboth: (1) carry radial loads, as a

journal bearing; (2) take end loads, asa thrust bearing; (3) take both journaland thrust loads.

In some applications, usually of aheavy nature, where both kinds ofloads are encountered, a bearing ofeach type (1 and 2) are fitted, thoughcertain types of bearings combine thefunctions naturally. These are theplain conical and taper types, cup-and-cone ball bearings, standard journalball bearings (l/3 of journal load asthrust) and taper roller bearings.

For a simple purpose, the ordinary

Common types of ball-bearings

M O D E L E N G I N E E R

plain journal bearing can be simplya drilled hole, though a reamed holeis preferred for superior accuracy andsurface finish. Replacement when wearoccurs can be made by bushing thehole A, the bush being the actualbearing and, if required, this can bein some more suitable metal than thehousing.

To locate a shaft endwise, the bushcan be flanged as is usually the casefor crankshaft bearings. In someinstances, where speed of rotation issecondary, no special provision isnecessary to take quite heavy thrusts-other than a flange on the shaft.The screw of a vice B is a commonexample.

The halved (split-and-bolted) bear-ing, C, whether provided with brassesor a white-metal lining, admits ofinitial fitting and later adjustment toaccommodate wear. In this connec-tion, there may be shims in the joint

(steel or brass foil in thicknesses from0.0015 in. upwards), removal of oneor more of which closes the halves toreduce running clearance.

Conical bearingsBetween-centre turning on a lathe

furnishes the most common exampleof a conical bearing, D, though thesame type is used on older lathes fortreadle and countershaft bearings.Here the bearing is a hard pad in theend of the shaft, and the pointedadjusting screw is hardened too and

fitted with a lock-nut.More substantial bearings of thistype are used for the spindles of olderand precision lathes E. Locknutsadmit of regulating the adjustmentfor the spindle to turn freely wtthoutshake. Solid spindles can have asingle ball thrust, though hollowspindles require a thrust in the formof a ring with a number of balls. Aseparate thrust is essential with thistype of bearing for lathe use-toprevent seizing.

Ball bearings

Ball (and roller) bearings possessan advantage over plain types in thatrolling is substituted for slidingaction-reducing friction and obviat-ing the tendency to seize present on

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A selection of typical plain bearings

occasion. Disadvantages are all partsof the bearing must be hard and pointor line contact involves heavy unit

loading. Chipping or scarring ofrunning members can occur.Such bearings, however, can carry

both journal and thrust loads whereneither is too heavy. Commonexamples are cycle wheel bearings F ,and bottom bracket bearings G.On wheel bearings, the cups arepressed in the hubs, one cone is fixedon the spindle and the other adjust-able. On bottom bracket bearings,the cones are formed on the spindle,one cup is fixed, and the other ad-,justable-held by a locknut.

Cups are filled with balls, (avoid

wedging) and grease to hold them isessential for assembly. Complete newsets of balls must be used, not a mix-ture of old and new, as old may beundersize. Cycle head races furnishexamples of thrust types H, thesebeing adjustable from the top-heldby a locknut.

The typical ball bearing or racewhich cannot be dismantled is shownat I. This consists of inner and outermembers and a ring of balls locatedin a cage. A wide range of standardsizes provides for many applications.Outside diameters, bores and widths

are held to close dimensions, andhousings and shafts are made to lightpush or driving fits, to obviaterotation other than in the bearingitself.

22 DECEMBER 1955