Single row angular contact ball bearings

Single row angular contact ball bearings can accommodate axial loads acting in one direction only.

Under radial loads a force acting in the axial direction is produced in the bearing, and this force must be counteracted. Consequently the bearing is normally adjusted against a second bearing.

Normally SKF single row angular contact ball bearings have one high and one low shoulder.

Some bearings, particularly those of Diameter Series 8 and 9, have an inner ring with two high shoulders as in a deep groove ball bearing. The low shoulder on one or both rings enables a large number of balls to be incorporated in the bearing, thus giving the bearings a relatively high load carrying capacity. They are of non-separable design.

The contact angle a is 40�, designation suffix B, for the most common sizes. For larger bearings contact angles of 25� and 30� are the most common, designation suffixes AC and A respectively.

SKF single row angular contact ball bearings are produced in two versions

• basic design bearings (not universally matchable) � can only be used for arrangements with single bearings
• bearings for universal matching.

The larger sizes are produced exclusively as universally matchable bearings.

Basic design bearings

Basic design single row angular contact ball bearings are intended for arrangements where only one bearing is used at each bearing position. They have Normal tolerances concerning bearing width and standout of the rings. Therefore, they are not suitable for mounting directly adjacent to each other.

Bearings for universal matching

Bearings for universal matching are specifically manufactured so that when mounted in random order, but immediately adjacent to each other, a given internal clearance or preload and/or an even load distribution will be obtained without the use of shims or similar devices, refer to the section “Internal clearance and preload”. Universally matchable bearings carry a designation suffix to indicate the internal clearance (CA, CB, CC) or preload (GA, GB, GC) of a set of two, prior to mounting.

When ordering, it is necessary to state the number of individual bearings required and not the number of sets.

Paired mounting is used when the load carrying capacity of a single bearing is inadequate (tandem arrangement) or when combined or axial loads act in both directions (back-to-back and face-to-face arrangements).

When arranged in tandem (fig) the load lines are parallel and the radial and axial loads are equally shared by the bearings. However, the bearing set can only accommodate axial loads acting in one direction. If axial loads act in the opposite direction, or if combined loads are present, a third bearing adjusted against the tandem pair must be added.

Tandem arrangement

The load lines of bearings arranged back-to-back (fig) diverge towards the bearing axis. Axial loads acting in both directions can be accommodated, but only by one bearing in each direction. Bearings mounted back-to-back provide a relatively stiff bearing arrangement that can also accommodate tilting moments.

Back-to-back arrangement

The load lines of bearings mounted face-to-face (fig) converge towards the bearing axis. Axial loads acting in both directions can be accommodated, but only by one bearing in each direction. This arrangement is not as stiff as the back-to-back arrangement and is less suitable for the accommodation of tilting moments.

Face-to-face arrangement

Bearings for universal matching can also be beneficial in arrangements with single bearings. Most bearings are SKF Explorer and as such have higher precision, increased carrying capacity and speed capability.

Bearings with inch dimensions

Single row angular contact ball bearings with inch dimensions for the aftermarket also belong to the SKF standard assortment. The dimensions of these bearings follow the British standard BS 292:Part 2:1982. This standard has subsequently been withdrawn in 1997 as a consequence of metrication. It is recommended not to use these inch bearings for new bearing arrangement designs.

Design The design of inch angular contact ball bearings (fig) conforms to that of the metric standard bearings with the exception of the contact angle, which is only 20� instead of 40� for the metric bearings. Due to this design feature, inch bearings cannot support the same heavy axial loads as similarly sized metric bearings, but can operate at higher speeds.

The assortment of SKF inch angular contact ball bearings comprises some popular bearings in ALS and AMS series for shaft diameters from 7/8 to 5 inches.

Cages Depending on the size, SKF inch single row angular contact ball bearings are equipped as standard with one of the following cages:

• Injection moulded window-type cage of glass fibre reinforced polyamide 66, ball centred, designation suffix P (fig).
• Machined window-type brass cage, ball centred, designation suffix M (fig).

Tolerances and internal clearance Inch bearings are manufactured to Normal tolerances, according to Standard BS 292:Part 2:1982.

The internal clearance in single row angular contact ball bearings is only obtained after mounting and is dependent on adjustment against a second bearing, which provides axial location in the opposite direction.

SKF Explorer class bearings

High performance SKF Explorer angular contact ball bearings are shown with an asterisk in the product table. SKF Explorer bearings retain the designation of the earlier standard bearings, e.g. 7208 BECBP. However, each bearing and its box are marked with the name “EXPLORER”.

Dimensions The boundary dimensions of SKF single row angular contact ball bearings are in accordance with ISO 15:1998.

Tolerances Basic design SKF single row angular contact ball bearings for single mounting are produced to Normal tolerances. Standard design universally matchable bearings are manufactured to better than Normal tolerances.

SKF Explorer angular contact ball bearings are manufactured only as bearings for universal matching with P6 dimensional accuracy and P5 running accuracy.

Large bearings having an outside diameter of approximately 400 mm and above have dimensional accuracy to tolerance class Normal and running accuracy to tolerance class P6 as standard.

The values for tolerances correspond to ISO 492:2002.

Internal clearance and preload Internal clearance in single row angular contact ball bearings is only obtained after mounting and is dependent on adjustment against a second bearing, which provides axial location in the opposite direction.

SKF universally matchable bearings are produced in three different clearance and preload classes each. The classes for bearing sets with clearance are

• CA – smaller than Normal axial clearance
• CB – Normal axial clearance (standard)
• CC – larger than Normal axial clearance.

Bearings to clearance class CB are standard, or for some larger bearings class G clearance. The availability of bearings to other clearance classes can be obtained from matrix 1. SKF universally matchable bearings with clearance can be combined in sets of any number of bearings.

The classes for bearing sets with preload are

• GA – light preload (standard)
• GB – moderate preload
• GC – heavy preload.

Bearings to GA class preload are standard (matrix 1). Bearings with preload can only be paired in sets of two bearings, in contrast to the SKF universally matchable bearings with clearance, as otherwise the preload would increase.

The values for the clearance classes are provided in table 1 and table 2. The values for the preload classes are given in table 3.

The values apply to unmounted bearing sets, arranged back-to-back or face-to-face, and in case of clearance to zero measuring loads.

Misalignment Single row angular contact ball bearings have only limited ability to accommodate misalignment. The permissible misalignment of the shaft relative to the housing that will not produce inadmissibly heavy additional forces, depends on the operating clearance in the bearing, bearing size, internal design and the forces and moments acting on the bearing. Because of the complex relationship between the influencing factors, it is not possible to quote any values that are universally valid.

For bearings mounted in sets, particularly those with small axial internal clearance mounted in a back-to-back arrangement, misalignment can only be accommodated by increased ball loads, which will create cage stresses and a reduction in bearing service life. Any misalignment of the bearing rings will also lead to increased running noise.

Influence of operating temperature on bearing material SKF angular contact ball bearings undergo a special heat treatment. When fitted with a steel, brass or PEEK cage, they can operate at temperatures of up to +150 �C. Cages Depending on the bearing series and size, SKF single row angular contact ball bearings are fitted as standard with one of the following cages

• an injection moulded window-type cage of glass fibre reinforced polyamide 66, ball centred, designation suffix P (fig)
• an injection moulded window-type cage of glass fibre reinforced polyetheretherketone (PEEK), ball centred, designation suffix PH (fig)
• a pressed window-type brass cage, ball centred, designation suffix Y (fig)
• a machined window-type brass cage, ball centred, designation suffix M (fig).

The available SKF standard assortment is shown in matrix 1. If bearings with a PEEK cage are required other than listed, please consult SKF.

Bearings having a pressed window-type steel cage, designation suffix J (fig), or a machined window-type steel cage, designation suffix F (fig), may also be available. Please check availability prior to ordering.

Note Bearings with polyamide 66 cages can be operated at temperatures up to +120 �C. The lubricants generally used for rolling bearings do not have a detrimental effect on cage properties, with the exception of a few synthetic oils and greases with a synthetic oil base, and lubricants containing a high proportion of EP additives when used at high temperatures.

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

Speed ratings for bearing pairs

For bearings arranged in pairs, the reference speeds provided in the product table are approximately 20% lower than the reference speeds for single bearings.

Load carrying capacity of bearing pairs

The values for basic load ratings and fatigue load limits given in the product table for bearings for paired mounting are valid for the bearing pair.

The relations to single bearings are as follows (valid when the bearings in the pair are mounted immediately adjacent to each other)

• basic dynamic load rating for standard bearings in all arrangements and for SKF Explorer bearings in back-to-back or face-to-face arrangement

C = 1,62 � Csingle bearing

• basic dynamic load rating for SKF Explorer bearings in tandem arrangement

C = 2 � Csingle bearing

• basic static load rating

C0 = 2 � C0 single bearing

• fatigue load limit

Pu = 2 � Pu single bearing

Minimum load To achieve satisfactory operation, angular contact 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, and the friction in the lubricant, 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 load to be applied to single bearings and bearing pairs arranged in tandem (fig) can be estimated using

and for bearing pairs arranged back-to-back (fig) or face-to-face (fig) from

where

Fam = minimum axial load [kN]

Frm = minimum radial load [kN]

C0 = basic static load rating of single bearing, or bearing pair (see product data) [kN]

ka = minimum axial load factor (see product data)

kr = minimum radial load factor (see product data)

? = oil viscosity at operating temperature [mm2/s]

n = rotational speed [r/min]

dm = mean diameter of bearing = 0,5 (d + D) [mm]

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 angular contact ball bearing must be subjected to an additional load. Single bearings and bearing pairs arranged in tandem can be axially preloaded by adjusting the inner or outer rings against each other, or by using springs.

Equivalent dynamic bearing load

For single bearings and bearings paired in tandem

P = Fr when Fa/Fr = e

P = XFr + YFa when Fa/Fr > e

When determining the axial force Fa, reference should be made to the section “Determination of axial forces”.

For bearings mounted in pairs, arranged back-to-back or face-to-face

P = Fr + Y1Fa when Fa/Fr = e

P = XFr + Y2Fa when Fa/Fr > e

Fr and Fa are the forces acting on the bearing pair.

The values for the factors e, X, Y, Y1 and Y2 are bearing dependent and will be found in the product tables.

Equivalent static bearing load

For single bearings and bearings paired in tandem

P = 0,5 Fr + Y0Fa

If P0 < Fr, then P0 = Fr should be used.

When determining the axial force Fa, reference should be made to the section “Determination of axial forces”.

For bearings mounted in pairs, arranged back-to-back or face-to-face

P = Fr + Y0Fa

Fr and Fa are the forces acting on the bearing pair.

The values for the factor Y0 are bearing dependent and will be found in the product tables.

Determination of axial forces When a radial load is applied, the load is transmitted from one raceway to the other at an angle to the bearing axis and an internal axial force will be induced in single row angular contact ball bearings. This must be considered when calculating the equivalent bearing loads for bearing arrangements consisting of two single bearings and/or bearing pairs arranged in tandem.

The necessary equations are provided in table 4 for the various bearing arrangements and load cases. The equations are only valid if the bearings are adjusted against each other to practically zero clearance, but without any preload. In the arrangements shown, bearing A is subjected to a radial load FrA and bearing B to a radial load FrB. Both FrA and FrB are always considered positive even when they act in the direction opposite to that shown in the figures. The radial loads act at the pressure centres of the bearings (see dimension a in the product tables).

Variable R The variable R from table 4 takes into account the contact conditions inside the bearing. The values for R can be obtained from the diagram as a function of the ratio Ka/C. Ka is the external axial load acting on the shaft or on the housing and C is the basic dynamic load rating of the bearing, which must accommodate the external axial load. For Ka = 0 use R = 1

The diagram is valid for bearings of B and BE design, i.e. for a contact angle of 40�. For bearings with other contact angles the equations according to table 4b should be used.

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

Design of bearing arrangements

When designing bearing arrangements incorporating single row angular contact ball bearings, remember that these bearings must either be used with a second bearing (fig) or in sets (fig).

When two single row angular contact ball bearings are used, they must be adjusted against each other until the requisite preload or clearance is obtained, see section “Bearing preload”.

Where bearings for universal matching are used and the bearings are mounted immediately adjacent to each other, there is no need for adjustment. The requisite preload or clearance is obtained by choosing bearings from an appropriate preload or clearance class and by applying suitable fits for the bearings on the shaft and in the housing.

It is important for proper bearing performance and for the operational reliability of the arrangement that the bearings are correctly adjusted, or that the correct choice of preload or clearance has been made. If the clearance of the bearing in operation is too large, the load carrying capacity of the bearings will not be fully utilized; on the other hand, excessive preload will produce more friction and higher operating temperatures, leading to a reduction in bearing service life. It should also be remembered that with single row angular contact ball bearings having a contact angle of 40� (designation suffix B), correct rolling conditions will only be achieved in the bearing when the load ratio Fa/Fr = 1.

Special attention should also be paid to back-to-back and face-to-face arrangements where the axial load acts predominantly in one direction. This creates an unfavourable rolling condition for the balls of the unloaded bearing and can lead to noise, discontinuity in the lubricant film and increased stressing of the cage. Under these conditions, zero operational clearance is recommended and should be attained, for example, by using springs. For additional information contact the SKF application engineering service.

Angular contact ball bearings | Single row angular contact ball bearings | Double row angular contact ball bearings | Four-point contact ball bearings | Other SKF angular contact ball bearings