Spherical Roller Thrust Bearings

In spherical roller thrust bearings the load is transmitted from one raceway to the other at an angle to the bearing axis (fig 1). The bearings are therefore suitable to accommodate radial loads in addition to simultaneously acting axial loads. Another important characteristic of spherical roller thrust bearings is their self-aligning capability. This makes the bearings insensitive to shaft deflection and misalignment of the shaft relative to the housing.

SKF spherical roller thrust bearings incorporate a large number of asymmetrical rollers and have specially designed raceways with an optimum conformity. They can therefore support very heavy axial loads and permit relatively high speed operation.

SKF spherical roller thrust bearings are produced in two designs depending on the size and series. Bearings up to and including size 68 identified by the designation suffix E have a pressed steel window-type cage which, with the rollers, forms a non-separable assembly with the shaft washer (fig 2). All other bearings have a machined brass or steel cage which is guided by a sleeve held in the shaft washer bore (fig 3). The shaft washer and cage with rollers form a non-separable unit.

SKF Explorer class bearings

High performance SKF Explorer spherical roller thrust bearings are shown with an asterisk in the product table. SKF Explorer bearings retain the designation of the earlier standard bearings, e. g. 29330 E. However, each bearing and its box are marked with the name “EXPLORER”.

Dimensions The boundary dimensions of SKF spherical roller thrust bearings are in accordance with ISO 104:2002.

Tolerances SKF spherical roller thrust bearings are produced as standard to Normal tolerances as specified in ISO 199:1997. However, depending on bearing size, the tolerances for the total height of

• SKF standard bearings are more than 50% tighter
• SKF Explorer bearings are 75% tighter

than specified by ISO.

Misalignment By virtue of their design, spherical roller thrust bearings are self-aligning, i.e. they tolerate misalignment of the shaft relative to the housing, and shaft deflections during operation (fig 4). Whether the permissible misalignment can be fully exploited depends on the design of the bearing arrangement, the type of seal etc.

Demo

The permissible misalignment is reduced as the load increases. The values indicated in table 1 can be permitted provided there is constant misalignment and a rotating shaft washer. When designing bearing arrangements, it is advisable to contact the SKF application engineering service if the following conditions occur:

• Rotating housing washer combined with misalignment.
• The shaft wobbles in relation to the housing.

Influence of operating temperature on bearing material

All SKF spherical roller thrust bearings undergo a special heat treatment so that they can be operated at higher temperatures for long periods, without the occurrence of inadmissible dimensional changes. For example, a temperature of +200 �C for up to 2 500 h, or for shorter periods at even higher temperatures, is permitted.

Minimum load To achieve satisfactory operation, spherical roller thrust 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 the load. Under such conditions, the inertia forces of the rollers and cage, and the friction in the lubricant, can have a detrimental influence on the rolling conditions in the bearing arrangement and may cause damaging sliding movements to occur between the rollers and raceways.

The requisite minimum axial load to be applied to spherical roller thrust bearings can be estimated using

where

Fam = minimum axial load [kN]

Fr = radial component of the load for bearings subjected to combined load [kN]

C0 = basic static load rating [kN] (see product data)

A = minimum load factor (see product data)

n = rotational speed [r/min]

If 1,8 Fr < 0,0005 C0 then 0,0005 C0 should be used in the above equation instead of 1,8 Fr.

At speeds higher than the reference speed or when starting up at low temperatures, or when the lubricant is highly viscous, even greater minimum loads may be required. The weight of the components supported by the bearing, together with external forces, generally exceeds the requisite minimum load. If this is not the case, the spherical roller thrust bearing must be preloaded, e.g. by springs. For additional information, contact the SKF application engineering service.

Equivalent dynamic bearing load

Normally a spherical roller thrust bearing is arranged so that runouts in the bearing arrangement do not affect the load distribution in this bearing. For a dynamically loaded spherical roller thrust bearing arranged under these conditions, provided Fr = 0,55 Fa

P = 0,88 (Fa + 1,2 Fr)

When runouts in the bearing arrangement affect the load distribution in the spherical roller thrust bearing, provided Fr = 0,55 Fa

P = Fa + 1,2 Fr

If Fr > 0,55 Fa, the SKF application engineering service should be contacted.

Equivalent static bearing load

P0 = Fa + 2,7 Fr

provided Fr = 0,55 Fa. If Fr > 0,55 Fa, the SKF application engineering service should be contacted.

Supplementary designations The designation suffixes used to identify certain features of SKF spherical roller thrust bearings are explained in the following.

three appropriate eye bolts

Design of associated components The abutment dimensions da and Da given in the product table apply for bearing loads up to approximately Fa = 0,1 C0. Where bearings are to be subjected to heavier loads it may be necessary for both shaft and housing washers to be fully supported (da = d1and Da = D1) and for radial support to be provided for the housing washer. For additional information, contact the SKF application engineering service.

For E-design bearings with a pressed steel cage, the housing bore must be recessed (fig 5) to prevent the cage from rubbing against the housing if the shaft should become misaligned. Recommended guideline values for the diameter of this recess are

• D + 15 mm for bearings with outside diameter up to and including 380 mm and
• D + 20 mm for larger bearings.

Lubrication Generally lubrication with oil or grease containing EP additives is recommended for spherical roller thrust bearings.

When lubricating with grease the roller end/flange contacts must be supplied with an adequate amount of lubricant. Depending on the application, this can best be done by completely filling the bearing and its housing with grease, or by regular relubrication.

Because of their internal design, spherical roller thrust bearings have a pumping action that can be taken advantage of, in order to provide circulation of the lubricating oil when

• the shaft is vertical (fig 6) or
• the shaft is horizontal (fig 7).

The pumping action must be considered when selecting lubricants and seals.

For more detailed information about the lubrication of spherical roller thrust bearings contact the SKF application engineering service.

Mounting SKF spherical roller thrust bearings are of separable design, i.e. the shaft washer with cage and roller assembly can be mounted separately from the housing washer.

If bearings of earlier design with a machined cage, where the cage-guiding sleeve also served as a spacer sleeve, are to be replaced by E-design bearings, a spacer sleeve is needed between the shaft washer and the existing abutment (fig 8).

If earlier B-design bearings, which were mounted with a spacer sleeve, are to be replaced, the sleeve must be checked and re-machined if necessary (fig 9). The sleeves must be hardened and should have ground end faces; the recommended sleeve outside diameter is provided for each bearing in the product table.

Detailed instructions for a selected bearing can be found on “skf.com/mount”.

Spherical roller bearings | Open bearings | Sealed bearings | Bearings for vibratory applications | SKF Energy Efficient (E2) spherical roller bearings | Split spherical roller bearings

Bearing terminology | Y-bearings | Deep groove ball bearings | Needle roller bearings | Combined cylindrical roller/taper roller bearings | Cylindrical roller bearings | Angular contact ball bearings | Combined needle roller bearings | Spherical roller bearings | Tapered roller bearings | Thrust ball bearings | CARB� toroidal roller bearings | Cylindrical roller thrust bearings | Angular contact thrust ball bearings | Tapered roller thrust bearings | Needle roller thrust bearings | Track runner bearings | Spherical roller thrust bearings | Indexing roller units | Backing bearings for cluster mills | Other SKF rolling bearings | Bearing accessories | Engineering products | Mechatronics