Cylindrical Roller Thrust Bearings

Cylindrical roller thrust bearings are suitable for arrangements that have to support heavy axial loads. Furthermore, they are relatively insensitive to shock loads, are very stiff and require little axial space. As standard they are available as single direction bearings and can only accommodate axial loads acting in one direction.

Cylindrical roller thrust bearings are simple in form and design and are produced in single row (fig 1) and double row (fig 2) designs. The bearings in the 811 and 812 series are mainly used where thrust ball bearings have insufficient load carrying capacity.

The cylindrical surface of the rollers is slightly relieved towards the ends. The resulting contact profile virtually eliminates damaging edge stresses. The bearings are of separable design; the individual components can be mounted separately.

Components For applications where

• the faces of adjacent machine components can serve as raceways and slim bearing arrangements are required or
• other combinations of cylindrical roller and cage thrust assembles and washers are required, e.g. with two shaft or housing washers,

it is possible to order the components

• cylindrical roller and cage thrust assemblies K (fig 3)
• shaft washers WS (fig 4)
• housing washers GS (fig 5)

separately, see product table.

Raceway washers of the LS series (see section “Needle roller thrust bearings – Bearing washers”) may be used for bearings in the 811 series both as shaft and as housing washers where accurate centring of the washers is not needed or where low speeds are involved.

Double direction bearings

Double direction bearings can easily be assembled by combining appropriate shaft washers in the WS 811 series or housing washers in the GS 811 series with two cylindrical roller and cage thrust assemblies in the K 811 series and a suitable intermediate washer with internal centring (fig 6) or external centring (fig 7).

These intermediate washers should have the same quality and hardness as the bearing washers. Recommendations for intermediate washer dimensions will be supplied on request. Guideline values for the dimensional, form and running accuracy are provided in the section “Design of associated components”.

Dimensions The boundary dimensions of cylindrical roller thrust bearings correspond to ISO 104:2002.

Tolerances Cylindrical roller thrust bearings are produced to Normal tolerances as standard. Larger bearings are also available with increased accuracy to tolerance class P5 specifications.

The Normal and P5 tolerances are in accordance with ISO 199:2005.

The cylindrical roller and cage thrust assemblies and the shaft and housing washers are produced to the tolerances listed in table 1. The values for the deviations of the various ISO tolerance grades are provided in table 2. The rollers of one assembly have the same grade; the diameter variation is max. 1 �m.

Misalignment Cylindrical roller thrust bearings cannot tolerate any angular misalignment between the shaft and housing, nor any errors of alignment between the support surfaces in the housing and on the shaft.

Cages Depending on the bearing series and size, SKF cylindrical roller thrust bearings are fitted with the following cages

• an injection moulded cage of polyamide 66, designation suffix TN (fig 8)
• a machined brass cage, designation suffix M (fig 9).

Note Cylindrical roller thrust bearings that incorporate a polyamide 66 cage can be used at operating temperatures of up to +120 �C. The cage properties will not be affected by the lubricants normally used for ball and roller bearings, with the exception of some synthetic oils or greases with synthetic base oils and lubricants containing a high proportion of EP additives when used at elevated temperatures.

For bearing arrangements, which are to operate at continuously high temperatures or under otherwise difficult conditions, it is recommended that bearings fitted with metallic cages be used.

For detailed information about the temperature resistance and the applicability of cages, please refer to the section “Cage materials”.

Minimum load To achieve satisfactory operation, cylindrical 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 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 load to be applied to cylindrical roller thrust bearings can be estimated using

where

Fam = minimum axial load [kN]

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

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 cylindrical roller thrust bearing must be preloaded, e.g. by springs or a shaft nut.

Equivalent dynamic bearing load

P = Fa

Equivalent static bearing load

P0 = Fa

Supplementary designations

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

Design of associated components The support surfaces in the housing and on the shaft must be at right angles to the shaft axis and should provide uninterrupted support for the bearing washers across the whole extent and width of the raceways (fig 10).

Suitable tolerances for shafts and housings which are known to provide satisfactory radial guidance for the individual thrust bearing components can be found in table 3.

Cylindrical roller and cage thrust assemblies are generally guided radially on the shaft in order to obtain the lowest possible sliding speed against the guiding surfaces. At high speeds radial guidance must be provided on the shaft and the guiding surface must be ground.

Raceways on the shaft and in the housing Raceways on the shaft and in the housing should have the same hardness and surface finish as normally used for bearing raceways, if the load carrying capacity of the cylindrical roller and cage thrust assemblies is to be fully exploited. Details about suitable materials as well as surface hardness and surface finish can be found in the section “Raceways on shafts and in housings”.

Cylindrical roller bearings | Single row cylindrical roller bearings | Double row cylindrical roller bearings | Multi-row cylindrical roller bearings | Single row full complement cylindrical roller bearings | Double row full complement cylindrical roller bearings | Multi-row full complement cylindrical roller bearings | Split cylindrical roller bearings

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