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Double Row Tapered Roller Bearings

Double row tapered roller bearings can carry heavy loads and are stiff. They are suitable for the accommodation of combined (radial and axial) loads and can locate a shaft axially in both directions with a given axial clearance or a given preload. Their main use is in gearboxes, hoisting equipment, rolling mills and machines used in the mining industry, e.g. tunnelling machines.

SKF double row tapered roller bearings are produced in two configurations and in several different designs:

  • The TDO configuration (fig); bearings of the TDO configuration have one double row outer ring (cup) and two inner rings with roller and cage assembly (cones).
  • The TDI configuration (fig) which comprises one double row inner ring with two roller and cage assemblies and two outer rings.

Both these configurations are produced in several different designs.

Bearings of the TDO configuration

Bearings of the TDO configuration have one double row outer ring, or cup, and two inner rings with roller and cage assembly, or cones (fig). Normally these bearings have an intermediate ring between the two cones. They are thus ready-to-mount units as adjustment of the axial clearance or preload has already been made at the production stage. In these bearings the cones are arranged back-to-back so that the load lines diverge towards the bearing axis. By virtue of this the bearings enable relatively stiff arrangements to be made which can accommodate considerable tilting moments.

These arrangements may be either locating or non-locating. For non-locating arrangements the axial displacement must take place between the outer ring and the housing bore. Those bearings having a blind hole or locating slots in the outer ring are particularly suitable for mounting with a loose fit in the housing as a cylindrical pin which engages the hole or slot can be used to prevent the outer ring from turning in its seat. To enable axial displacement of these bearings in the housing it is recommended that the pin should have a smaller diameter than the hole.

SKF double row tapered roller bearings of the TDO configuration are generally produced in the designs described in the following. Basically these designs differ in cage design or whether provision is made for relubrication or an intermediate ring is positioned between the inner rings.

TDO designBearing with intermediate ring and pressed window-type steel cages (fig).

TDO.1 designBearing with intermediate ring, pierced rollers and pin-type steel cages (fig).

TDO/NA designBearing with matched inner rings which abut each other, with pressed window-type steel cages (fig).

TDO/Z designBearing with intermediate ring and pressed window-type steel cages, protected by shields of sheet steel on both sides (fig).

TDOS.1 designBearing with steep contact angle and intermediate ring, pierced rollers and pin-type steel cages. For applications where the axial load is heavier than the radial load (fig).

TDOSN.TN9 design Bearing with steep contact angle, matched inner rings, injection moulded segment cages of polyamide 66. For applications where the axial load is greater than the radial load (fig).

Bearings of the TDI configuration

Bearings of this configuration (fig) have a double row inner ring with two roller and cage assemblies (double cone) and two outer rings (cups). The two rows of rollers are arranged face-to-face. Normally an intermediate ring is arranged between the two outer rings. This ring is dimensioned so that a certain axial clearance or preload will be obtained.

The bearings are eminently suitable for locating bearing arrangements and are produced by SKF with a cylindrical bore; some sizes are also produced with a tapered bore. For bearing arrangements where the bearings are to be mounted with a loose fit on the shaft or journal, special designs are supplied by SKF. To counteract the disadvantage of a loose fit on the shaft the inner ring turns on its seat, which can cause damage to the bearing and the seat these special bearings have a helical groove in the bore and/or lubrication grooves in the side faces of the bearing rings (fig). These grooves enable lubricant to be efficiently supplied to the sliding contact surfaces.

Bearings having a large contact angle are a special design of the TDI configuration (fig). These bearings have a particularly high axial load carrying capacity and are used primarily as thrust bearings in rolling mill applications. As they are mounted with a loose fit on the roll neck and only subjected to purely axial load, the inner ring has one or more notches in one or both side faces to permit it to be secured and prevent it from turning on its seat. Depending on the application the bearings are supplied with or without an intermediate ring between the two outer rings. They can also be supplied as self-retaining units with a retention sleeve over the outer rings (fig).

These self-retaining bearing units with retention sleeve are characterised by high load carrying capacity and simple handling compared with conventional bearings. The outer rings are integrated in the sleeve. The deformation of the outer rings normally resulting from heavy axial loads is considerably reduced by this means and as a consequence the stress distribution in the rolling contacts is more favourable leading to longer life. The axial internal clearance is determined by the sleeve. Preloading by means of springs is not needed. The arrangement design is simplified and thus more economic and mounting is also easier.

SKF produces double row tapered roller bearings of the TDI configuration mainly in the designs described in the following.

TDI designBearing with intermediate ring and pressed steel window-type cages (fig).

TDI.1 designBearing with intermediate ring, pierced rollers and steel pin-type cages (fig).

TDIE designBearing with inner ring extended at both sides, intermediate ring and pressed steel cages. The inner ring extensions are ground and serve as lands for radial shaft seals (fig).

TDIT designBearing with tapered bore, taper 1:12, intermediate ring between the outer rings and pressed steel cages (fig).

TDIS designBearing with large contact angle, intermediate ring between the outer rings and pressed steel cages (fig).

TDIS.1 designBearing with large contact angle, intermediate ring between the outer rings, pierced rollers and steel pin-type cages (fig).

TDIS.2 designSelf-retaining bearing units with large contact angle, outer rings held in a retention sleeve, pierced rollers and steel pin-type cages (fig).

Other bearings of the TDI configuration

If no suitable bearing is found in the product tables, it is recommended to look at whether the standard components of the new SKF four-row tapered roller bearings without intermediate ring can be used to "build" a tailored bearing. For example, from the components of the four-row tapered roller bearing BT4-8004 G/HA1 (fig) it is possible to combine

  • 2 cups (outer rings) OR-BT4-8004-1/HA2 (1)

with

  • 1 double cone (inner ring with two roller and cage assemblies) AJ-BT4-8004 G/HA3 (2)

to form a double row bearings having the dimensions d x D x B = 304,800 x 412,648 x 133,350 mm. This may be advantageous both as regards price and delivery time.

This "building" procedure should primarily be considered if sealed double row bearings are required, although this requires a non-standard inner ring. However, before making the final selection, or in case of doubt, please contact the SKF application engineering service.

Design variantsTo facilitate identification of the various design variants of the TDO configuration (fig) and TDI configuration bearings (fig) letters or combinations of letters are quoted in the product tables under the heading "Design" following the identification of the configuration, e.g. TDO/XDC or TDI/GWIY2. The meaning of the variant identification letters is explained in the following.

DesignationBearing Features
COuter ring with blind hole
DOuter ring with annular groove and lubrication holes (TDO), inner ring with annular groove and lubrication holes (TDI)
D0Outer ring with annular groove and lubrication holes, without intermediate ring
D2Outer ring with annular groove and lubrication holes, intermediate ring with lubrication holes
D3Outer ring with annular groove and lubrication holes, intermediate ring with annular groove and lubrication holes
GHelical groove in bore
NTwo notches at 180 in one side face of inner ring
N1One notch in each side face of inner ring, at 180 to notch in other side face
N2Two notches at 180 in both side faces of inner ring, at 90 to notches in other side face
VBearing with radial shaft seals
WLubrication grooves in side faces of inner and outer rings
WILubrication grooves in side faces of inner ring
WOLubrication grooves in side faces of outer ring
XBearing with retention sleeve
XDOuter ring with lubrication holes
YBearing without intermediate ring
Y2Intermediate ring with annular groove and lubrication holes

DimensionsThe dimensions of double row tapered roller bearings (TDO / TDI) are not standardized by ISO. The dimensions of most of the inch bearings are in accordance with AFBMA Standard 19-1974 (ANSI B3.19-1975). However, this standard has now been withdrawn.

TolerancesSKF double row tapered roller bearings are produced with dimensional accuracy corresponding to

  • Normal tolerances for metric bearings and
  • Normal tolerances for inch bearings

except the bearing width T.

The running accuracy of all bearings is to tolerance class P5 specifications

The Normal and class P5 tolerances for the metric bearings conform to ISO 492-2002. The values of the Normal tolerances for inch bearings follow tolerance class 4 according to ANSI/ABMA Standard 19.2-1994. The ISO Standard 578:1987, which also covered this tolerance class for inch bearings was withdrawn in 1997.

Internal clearanceSKF double row tapered roller bearings of the TDO and TDI configurations generally have an axial internal clearance which is appropriate to a given application. The bearing components must, however, be mounted in the prescribed order.

Double row tapered roller bearings having a clearance other than that of the basic design are identified by a C followed by a three or four-figure number which gives the mean axial internal clearance in m.

MisalignmentAngular misalignments of the outer ring(s) relative to the inner ring(s) of double row tapered roller bearings can only be accommodated by force between the rollers and raceways. This causes appreciably higher bearing loads and should be avoided. If misalignments cannot be ruled out and if the application permits, the TDI configuration bearings with their rows of rollers arranged face-to-face are not so stiff as the TDO bearings, and should be used.

Influence of operating temperature on bearing materialSKF double row tapered roller bearings are subjected to a special heat treatment so that they may be operated at temperatures up to +150 C without any inadmissible dimensional changes occurring.

CagesThe cages used for SKF double row tapered roller bearings are either

  • pressed steel cages (fig), or
  • steel pin-type cages (fig).

Minimum loadTo achieve satisfactory operation, double row tapered roller bearings, like all ball and roller bearings, must always be subjected to a given minimum load, particularly if they are to operate at high speeds, or are subjected to high accelerations or rapid changes in the direction of load. Under such conditions the inertia of the rollers and cages, and the friction in the lubricant, can have a detrimental influence on rolling conditions in the bearing arrangement and may cause damaging sliding movements to occur between the rollers and raceways.

The requisite minimum radial load to be applied to double row tapered roller bearings can be estimated using

Frm = 0,02 C

where

Frm = minimum radial load [kN]

C = basic dynamic load rating [kN] (see product data)

When starting up at low temperatures or when the lubricant is highly viscous, even greater loads may be required. The weights of the components supported by the bearing, together with the external forces, generally exceed the requisite minimum load. If this is not the case, the double row tapered roller bearing must be subjected to an additional radial load. This is particularly easy to apply with tapered roller bearing arrangements by adjusting the inner or outer rings against each other to give an axial preload.

Equivalent dynamic bearing load

P = Fr + Y1Fa when Fa/Fr = e

P = 0,67 Fr + Y2Fa when Fa/Fr > e

Values of the calculation factors e, Y1 and Y2 can be found in the product tables.

Equivalent static bearing load

P0 = Fr + Y0Fa

Values of the calculation factor Y0 can be found in the product tables.

Comparative load ratingsFor rolling mill applications, load ratings are often used which are not calculated according to ISO 281:1990 but by a different method based on a rating life of 90 million revolutions (500 r/min for 3 000 operating hours). As a direct comparison of these load ratings with ISO load ratings is not possible, even if they are converted for 1 million revolutions (ISO life definition), "comparative" load ratings calculated by the same non-ISO method are given in the product tables for double row tapered roller bearings as these bearings are frequently used in rolling mills.

These comparative load ratings may only be used together with the life and equivalent load equations specified below; they may not be used to calculate an ISO rating life.

Comparative life calculationThe comparative life is calculated using the comparative load rating CF as follows

LF10 = 90 (CF/PF) 10/3

or

LF10h = (CF/PF)10/3 (1 500 000/n)

where

LF10 = comparative rating life [million revolutions]

LF10h = comparative rating life [operating hours]

CF = comparative dynamic load rating to give a rating life of 90 million revolutions [kN]

PF = equivalent dynamic bearing load (for conditions please refer to table 1) [kN]

n = constant operating speed [r/min]

For load cases 1a) and 1b), see table 1, it is necessary to use the load rating for one roller row when using PFL. This load rating (for 1 row) can be obtained from

CF (row) = 0,58 CF (bearing)

Mounting instructionsWhen mounting double row tapered roller bearings the individual bearing components must be mounted in the correct order. The components are identified by a letter (fig). All the components of one bearing are marked with the same serial number so that there is no risk of mixing components if several bearings are to be mounted at the same time.

In the majority of applications in rolling mills, the direction of load is constant on the outer ring, so that only approximately one quarter of the outer ring raceways is under load. For this reason, the side faces of the outer rings are divided into four zones (fig) marked with I to IV. The marks for zone I are additionally joined by a line across the outside surface of the outer ring.

When mounting for the first time it is usual to position zone I in the direction of action of the load. When the chocks are remounted, the outer rings should be turned through 90 so that the next zone is exposed to the load. Detailed mounting instructions will be supplied with the bearing if required.

When mounting smaller TDI-configuration bearings care should be taken to see that the intermediate rings, which are often relatively thin-walled, are not deformed (compressed), for example, when tightening the cover screws. This would lead to too small an axial clearance in the bearing or too high a preload. It is, therefore, recommended that these bearings be fitted into their housing seats, e.g. by providing a spigot in the cover which is appropriate to the bearing width.

If sufficiently experienced personnel is not available for mounting the bearings, it is advisable, particularly if they are large bearings, to contact SKF. SKF service personnel will then quickly and reliably perform the mounting on site.


Tapered roller bearings | Single row tapered roller bearings | Paired single row tapered roller bearings | Double row tapered roller bearings | Four-row tapered roller bearings

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This page is still under construction. All bearing information remains the property and copyright of SKF Group.