Single Direction Thrust Ball Bearings

SKF single direction thrust ball bearings consist of a shaft washer, a housing washer and a ball and cage thrust assembly. The bearings are separable so that mounting is simple as the washers and the ball and cage assembly can be mounted separately.

Smaller sizes are available with either a flat seat surface on the housing washer (fig 1) or a sphered seat surface (fig 2). Bearings with a sphered housing washer can be used together with a sphered seat washer (fig 3) to compensate for misalignment between the support surface in the housing and the shaft. Sphered seat washers are available from SKF but must be ordered separately.

Single direction thrust ball bearings, as their name suggests, can accommodate axial loads in one direction and thus locate a shaft axially in one direction. They must not be subjected to any radial load.

In addition SKF also offers polymer thrust ball bearings, shown in the section “Engineering products – Polymer ball bearings”.

Double direction thrust ball bearings

SKF double direction thrust ball bearings consist of one shaft washer, two housing washers and two ball and cage thrust assemblies. The bearings are separable so that mounting is simple. The various parts can be mounted separately. The housing washers and ball and cage thrust assemblies are identical to those of the single direction bearings.

Smaller bearings are available with either a flat seat surface on the housing washers (fig 4) or with a sphered seat surface (fig 5). Bearings with sphered housing washers can be used together with sphered seat washers (fig 6) to compensate for misalignment between the housing and shaft. The sphered seat washers are available from SKF, but must be ordered separately.

Double direction thrust ball bearings can accommodate axial loads acting in both directions and can thus serve to axially locate a shaft in both directions. They must not be subjected to radial load.

Dimensions The boundary dimensions of SKF thrust ball bearings with flat or sphered housing washers conform to DIN 711:1988 and DIN 715:1987. The dimensions of the bearings with flat housing washers conform to ISO 104:2002.

The values given for the height H1 for bearings with sphered housing washer(s) are valid only for SKF bearings with SKF washers.

• Single direction
• Single direction, sphered housing washer
• Double direction
• Double direction, sphered housing washers

Tolerances SKF thrust ball bearings are made to Normal tolerances as standard. Some single direction bearings with flat housing washer are also available with increased accuracy to tolerance class P6 or tolerance class P5 specifications. Contact SKF for availability before ordering.

Normal, P6 and P5 tolerances are in accordance with ISO 199:1997.

Misalignment Thrust ball bearings with flat housing washers cannot accommodate any misalignment between the shaft and housing or angular misalignment between the support surfaces in the housing and on the shaft.

The bearings with sphered housing washers are generally used with sphered seat washers and can compensate for initial misalignment between the support surfaces in the housing and on the shaft (fig 7).

Demo

Cages Depending on the bearing series and size, SKF thrust ball bearings are fitted as standard with one of the following cages (fig 8)

• a pressed steel cage, no designation suffix (a and b)
• a one-piece machined brass cage, designation suffix M (c)
• a one-piece machined steel cage, designation suffix F (d)
• a two-piece machined brass cage, designation suffix M (e).

Minimum load To achieve satisfactory operation, thrust ball 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 forces of the balls and cage(s), 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 balls and raceways.

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

where

Fam = minimum axial load [kN]

A = minimum load factor (see product data)

n = rotational speed [r/min]

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, particularly when the shaft is vertical, together with external forces, generally exceeds the requisite minimum load. If this is not the case, the thrust ball bearing must be preloaded, e.g. by springs.

Equivalent dynamic bearing load

P = Fa

Equivalent static bearing load

P0 = Fa

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

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