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The self-aligning ball bearing was invented by SKF. It has two rows of balls and a common concave sphered raceway in the outer ring. The bearing is consequently self-aligning and insensitive to angular misalignments of the shaft relative to the housing. It is particularly suitable for applications where considerable shaft deflections or misalignment are to be expected. Additionally, the self-aligning ball bearing has the lowest friction of all rolling bearings, which enables it to run cooler even at high speeds.

SKF produces self-aligning ball bearings to several designs. These are

  • open bearings of the basic design
  • sealed bearings
  • open bearings with an extended inner ring.
Basic designThe basic design self-aligning ball bearing is available with a cylindrical bore or, in certain size ranges, with a tapered bore (taper 1:12).

Large self-aligning ball bearings in the 130 and 139 series originally developed for specific applications in paper mills, can be used in any application where low friction is preferred over high load carrying capacity. These bearings are provided with an annular groove and lubrication holes in the outer ring and lubrication holes the inner ring.

The balls of some bearings in the 12 and 13 series protrude from the sides of the bearing. The overall width, T, of these bearings (over the balls) is provided in the product tables and should be considered when designing the associated components of the bearing arrangement.

Sealed bearings

SKF self-aligning ball bearings are also available in a sealed version with contact seals at both sides - designation suffix 2RS1 (fig 1). These sheet steel reinforced seals are made of oil and wear-resistant acrylonitrile-butadiene rubber (NBR). The permissible operating temperature range for these seals is 40 to +100 C and up to +120 C for brief periods. The seal lip contacts a smooth chamfer on the inner ring with light pressure.

Sealed self-aligning ball bearing, design 2RS1

Sealed bearings are lubricated as standard with a grease with a lithium thickener, that has good rust inhibiting properties and other characteristics according to the table.

SKF sealed self-aligning ball bearings are available with a cylindrical bore. Some sizes are also available with a tapered bore (taper 1:12).

NoteSealed bearings are lubricated for life and require no maintenance. They should not be heated above 80 C before mounting and should not be washed.

Bearings with an extended inner ring

Self-aligning ball bearings with an extended inner ring are designed for less demanding applications using commercial grade shafting. The special bore tolerance enables easy mounting and dismounting.

Self-aligning ball bearings with an extended inner ring are axially located on the shaft by means of a pin or shouldered screw, which engages in a slot at one side of the inner ring and also prevents the inner ring from turning on the shaft.

When two self-aligning ball bearings with an extended inner ring are used to support a shaft, they should be positioned so that the inner ring slots either face each other, or are at the outboard positions of the bearings. If this is not the case, the shaft is axially located in one direction only.

Permissible speedsThe permissible operating speeds for self-aligning ball bearings with an extended inner ring depend less on the common criteria like heat generation or cage stability and strength, but are more influenced by the manner in which the bearings are located on the shaft. Therefore, the product table contains only limiting speeds valid for location on shafts according to h8 tolerances.

Bearings on sleeves

Adapter and withdrawal sleeves are used to secure bearings with a tapered bore onto cylindrical shaft seats. They facilitate bearing mounting and dismounting and often simplify bearing arrangement design.

Adapter sleeves are more popular than withdrawal sleeves as they do not require axial locating devices on the shaft. That is why only adapter sleeves are shown together with suitable bearings in the product table.

Self-aligning ball bearing on an adapter sleeve, smooth shaft

Self-aligning ball bearing on an adapter sleeve, stepped shaft

Self-aligning ball bearing on a withdrawal sleeve

SKF adapter sleeves are slotted and are supplied complete with lock nut and locking device. The adapter sleeves for use with sealed self-aligning ball bearings are equipped with a special locking washer that has a protrusion on the side facing the bearing, in order to prevent the seal from being damaged. These sleeves are identified by the suffix C.

Adapter sleeve with a special locking washer for sealed self-aligning ball bearings

Self-aligning ball bearing kits

To facilitate procurement and to provide the correct bearing/sleeve combination, SKF offers the most popular self-aligning ball bearings together with the suitable adapter sleeve as a kit.

Self Aligning Ball Bearing Kit

Mounting can easily be performed with the help of the SKF lock nut spanner set TMHN 7.

The range of these kits is shown in the table.

Appropriate housingsSelf-aligning ball bearings with a cylindrical bore or with a tapered bore on adapter sleeve can be mounted in a variety of housings:

  • SNL plummer block housings in the 2,3, 5 and 6 series.
  • SNL plummer block housing, series 2, 3, 5 and 6

  • SAF pillow (plummer) block housings for inch shafts.
  • SAF plummer block housing

  • TVN plummer block housings.
  • TVN plummer block housing

  • FNL flanged housings.
  • FNL flanged housing

  • 7225(00) flanged housings.
  • 7225(00) flanged housing

Bearings with an extended inner ring can be mounted in specially designed housings:

  • TN plummer block housings.
  • TN plummer block housing

  • I-1200(00) flanged housings.
  • I-1200(00) flanged housing

Detailed information on housings can be found in the catalogue "Bearing housings".

DimensionsThe boundary dimensions of SKF self-aligning ball bearings, with the exception of those with an extended inner ring, are in accordance with ISO 15:1998. The dimensions of the bearings with an extended inner ring follow DIN 630, part 2, withdrawn in 1993.

TolerancesSKF self-aligning ball bearings are manufactured as standard to Normal tolerances, except the bore of the bearings with extended inner ring, which is produced to tolerance JS7.

The values of the Normal tolerances are in accordance with ISO 492:2002.

Internal clearanceSKF self-aligning ball bearings are produced as standard with Normal radial internal clearance and most are also available with the greater C3 clearance. Many bearings can also be supplied with the smaller C2 clearance or the much greater C4 clearance.

Bearings in the 130 and 139 series have C3 radial internal clearance as standard.

Bearings with an extended inner ring have a radial internal clearance which lies in the C2 + Normal range.

Clearance values are provided in the table and are in accordance with ISO 5753:1991. They are valid for unmounted bearings under zero measuring loads.

Misalignment

The design of self-aligning ball bearings is such that angular misalignment between the outer and the inner rings can be accommodated without any negative effect on bearing performance.

Demo

Guideline values for the permissible angular misalignment between outer and inner rings under normal operating conditions are provided in the table. Whether these values can be fully exploited depends on the bearing arrangement design and the type of seal used.

Bearing Cages

Depending on the bearing series and size, SKF self-aligning ball bearings are fitted as standard with one of the following cages

  • one-piece pressed steel cage, ball centred, no designation suffix
  • One-piece pressed steel cage

  • two-piece pressed steel cage, ball centred, no designation suffix
  • Two-piece pressed steel cage

  • one-piece or two-piece injection moulded snap-type cage of glass fibre reinforced polyamide 66, ball centred, designation suffix TN9
  • Cage of polyamide 66

  • one-piece or two-piece injection moulded snap-type cage of polyamide 66, ball centred, designation suffix TN
  • Cage of polyamide 66

  • one-piece or two-piece machined brass cage, ball centred, designation suffix M or no suffix (large size).
  • Machined brass cage

Note Self-aligning ball 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 bearing arrangements, which are to be operated at continuously high temperatures or under arduous conditions, it is recommended to use bearings with a pressed steel or machined brass cage.

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

Axial load carrying abilityThe ability of a self-aligning ball bearing mounted on an adapter sleeve on smooth shafts without an integral shoulder to carry axial loads, depends on the friction between the sleeve and shaft. The permissible axial load can be approximately determined from

Fap = 0,003 B d

where

Fap = maximum permissible axial load [kN]

B = bearing width [mm]

d = bearing bore diameter [mm]

Minimum loadTo achieve satisfactory operation, self-aligning 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, 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 load to be applied to self-aligning ball bearings can be estimated using

Pm = 0,01 C0

where

Pm = equivalent minimum load [kN]

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

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 self-aligning ball bearing must be subjected to an additional radial load, for example, by increasing belt tension or by similar means.

Equivalent dynamic bearing load

P = Fr + Y1Fa when Fa/Fr = e

P = 0,65 Fr + Y2Fa when Fa/Fr > e

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

Equivalent static bearing load

P0 = Fr + Y0Fa

Values of Y0 can be found in the product tables.

Supplementary designationsThe designation suffixes used to identify certain features of SKF self-aligning ball bearings are explained in the following.

DesignationBearing Features
C3Radial internal clearance greater than Normal
EOptimized internal design
KTapered bore, taper 1:12
MMachined brass cage, ball centred
2RS1Sheet steel reinforced contact seal of acrylonitrile-butadiene rubber (NBR) on both sides of the bearing
TNInjection moulded snap-type cage of polyamide 66, ball centred
TN9Injection moulded snap-type cage of glass fibre reinforced polyamide 66, ball centred
VE294Annular groove and six lubrication holes in the inner ring


Self-aligning ball bearings | Mounting bearings with a tapered bore

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