Tapered Roller Bearings
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Tapered roller bearings have the rolling elements under the form of frustra of cones. They roll on tapered surfaces which, if extended, converge towards a single point on the bearing axis.
The rollers are guided tangentially by the cage and axially by the big rib of the outer ring, on which they have point contact. As between rollers and raceways there is linear contact, tapered roller bearings can take heavy radial loads. They can also take heavy axial or combined loads, depending on the contact angle caused by the tapered rolling elements. The contact angle is the angle of the outer raceway generatrix.
Tapered roller bearings can be manufactured in the versions : single, double and four row rollers.
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Single row tapered roller bearings are of separable design, i.e. the outer ring and the inner ring with rollers and cage assembly can be separately mounted. These two assemblies are interchangeable.
Tapered roller bearings can be manufactured both in standardized constructive versions with dimensions series 320, 302, 322, 303, 323, 313 and with non-stand-ardized dimensions, mm or inch.
Tapered roller bearings can carry only single direction axial loads. Under pure radial loads, an axial force occurs which is supposed to distance the bearing rings in axial direction. Therefore, tapered roller bearings are generally pair mounted on both ends of the shaft, in X or O arrangements, so that the shaft will be axially located in both directions (table 4). Thus, the optimum clearance in these two bearings can be adjusted.
Single row tapered roller bearings can also be manufac-tured with rib on the outer ring. This design is to be used when the housing cannot be manufactured with shoulder, but only with a passed through bore. In this case, axial location can be provided by the bearing ring.
Paired single row tapered roller bearings
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If tapered roller bearings are pair mounted in X or O arrangements, the load carrying capacity increases and loads can be taken in both directions in the same bearing.
These bearing sets have guaranteed clearance after mounting since the distance rings are mounted between the bearing rings.
certain applications, paired bearings can be delivered with small clearance or lightly preloaded.
Double row tapered roller bearings
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Double row tapered roller bearings are used where load carrying capacity should be greater, loads should be taken in both directions and axial space is smaller than in case of a set of two single row tapered roller bearings.
Double row tapered roller bearings can have the rollers in face- to-face arrangement, double inner ring and two outer rings respectively or the rollers in back-to-back arrangement, i.e. double outer ring and two inner rings.
The first design provides greater stiffness, can take tilting moments and shaft expansions can be compen-sated.
The bearings of the second design can be manufac-tured with tapered bore so that they can be frequently mounted dismounted.
Double row tapered roller bearings can have or not distance rings with lubrication holes, mounted between the simple rings.
In case of bearings with distance rings, the bearing clearance or preload are pre-adjusted; in case of those without distance rings, bearing clearance and preload can and should be adjusted while mounting.
Double row tapered roller bearings with rollers in back-to-back arrangement can also be manufactured in the following two versions:
-with rib on the outer ring; the housing has no shoulder and the bearing is axially-with two seals; this design is used in motor vehicles construction. The bearings are delivered filled with grease and relubrication is not needed.
Dimensions
Tapered roller bearings are manufactured with the fol-lowing dimensions:
-metric dimensions (mm), according to ISO 355;
-inchdimensions;
Misalignment
As between rollers and raceway there is a linear contact, tapered roller bearings have low capacity to compensate for errors of alignment between shaft and housing.
Permissible values of misalignment between shaft and housing are given in table 1, depending on bearing size and load magnitude.
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Tapered roller bearings are generally manufactured to
the normal tolerance class ISO and AFBMA, respectively (for bearings with inch dimensions).
For certain applications (e.g. bearings for machine-tools), they can be also manufactured to tolerance clas-ses P5 and P6X or 3 AFBMA.
At request, they can be manufactured to tolerance class P4.
Single row tapered roller bearings have the outer rings interchangeable with the inner ring – rollers – cage as-sembly (if they have the same mark) and also with bear-ings produced by other companies, according to ISO and AFBMA respectively.
The parts of the two and four row tapered roller bearings are non-interchangeable.
The tolerances for bearings overall dimensions are given in tables on page 24 for tapered roller bearings, both with metric and inch dimensions. Tolerances for mounting chamfer are given in tables on page 41.
Radial and axial clearance
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In case of tapered roller bearings, clearance should be in radial direction, but it is measured and adjusted in axial direction. As tapered roller bearings are dismountable, their clearance is not guaranteed by design and it is adjusted while mounting. Thus, optimum clearance can be obtained for that application.
In case of double and four row tapered roller bearings with distance rings between bearing rings, the clearance is guaranteed and its values are given in table 2. The bearing parts are numbered for each bearing so that the prescribed clearance on each row should be observed while mounting.
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??In case of bearings without distance rings, clearance is adjusted as for single row tapered roller bearings: for DB design – by the inner rings and for DF design by the outer rings. The above specifications are also available for bearings matched in sets.
??The values of the axial clearance can be calculated using the equation:
axial clearance = radial clearance/2tgα
where α is the contact angle.
??In case of certain applications where clearance be-tween shaft and housing should be avoided, tapered roller bearings can also be pre-tightened. This can be adjusted while mounting or is pre- adjusted by distance rings, in case of two or four row tapered roller bearings.
Contact angle
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Contact angle of tapered roller bearings is the angle of the outer ring raceway generatrix. In case of standardized single row tapered roller bearings, this angle can be found in the standard of dimensions (ISO 355 and nation-al standard STAS 3920 respectively). Bearings series 329, 302,322, 303 and 323 have acontact angle between 10? and 17? and those of series 313 have a contact angle of 28? 48′ 39″, so that they can take heavier axial loads. Non-standardized single row tapered roller bearings and also all double and four-row tapered roller bearings have the contact angle between 9? and 30?.
Cages
Small and medium sized tapered roller bearings are generally fitted with pressed sheet cages. Large sized bearings are generally fitted with machined steel or brass cages, with welded pins. In some cases, median or large sized bearings can also be fitted with machined steel or brass cages. In all cases, the cage is guided on rollers.
For small and medium sized bearings, glass fibre rein-forced polyamide
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??Equivalent dynamic radial load can be calculated using the following equations:
-for single row tapered roller bearings:
Pr = Fr, kN, ??? when Fa/Fr e
-for paired bearings and double or four-row tapered roller bearings:
Pr = Fr + Y1 Fa, kN, when Fa/Fr e
??For single row tapered roller bearings, the Fa values can be calculated using the equations in table 4. These equa-tions are available when bearings are mounted so that axial clearance is in fact zero without preloading. FrA and FrB should always be considered as being positive, even if they act in the opposite direction to that in the figure.
??In case of paired bearings and of double or four row tapered roller bearings, Fa and Fr are the loads acting upon the paired bearings or single bearings.
??The values of e, Y, Y1 and Y2 are given in bearing tables
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Abutment dimensions
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The mounting dimensions of tapered roller bearings are given in the bearings tables, for single row tapered roller bearings. These dimensions are also available for bear-ings with ribs and for standardized paired bearings. For the other types of tapered roller bearings, the mounting dimensions should be adapted depending on the cross section size and mounting chamfer.
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