Self-aligning ball bearings are particularly suitable:
- if there is skewing between the outer and inner ring (for the compensation of angular misalignments) ➤ section
- for bearing arrangements with high radial loads ➤ section
- for higher speeds on account of their point contact, than barrel roller bearings with line contact
- where bearings with the above-mentioned characteristics are expected to run more quietly and at lower temperatures, even at high speeds
Self-aligning ball bearings: speed comparison with barrel roller bearings, compensation of misalignments
nG = limiting speed
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Design variants
Self-aligning ball bearings are available as:
- bearings of basic design ➤ Figure
- bearings with extended inner ring and locating slot ➤ Figure
- bearings with adapter sleeve ➤ Figure
- bearings with ball projection ➤ Figure
Bearings of basic design
The outer ring has a curved raceway
Self-aligning ball bearings are double row, self-retaining radial ball bearings, which are part of the group of self-aligning bearings. The outer ring has a single concave raceway for the two rows of balls. As a result, the bearings permit the compensation of static and dynamic angular misalignments (skewing between the inner and outer ring) within certain limits ➤ section. The inner ring has two formed raceway grooves in which the rolling elements run. Solid cages made from polyamide PA66 or brass are used ➤ Table.
The bore is cylindrical or tapered
Bearings of basic design are supplied with a cylindrical bore; self-aligning ball bearings of series 12, 13, 22 and 23 are also available with a tapered bore ➤ Figure.
Bearings with a tapered bore have a bore taper of 1:12 and the suffix K ➤ Table.
Self-aligning ball bearings of basic design
Fr = radial load
Fa = axial load
Self-aligning ball bearing with cylindrical bore, open
Self-aligning ball bearing with tapered bore, open, bore taper 1:12
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Bearings with extended inner ring and locating slot
Suitable for simple bearing arrangements
Self-aligning ball bearings of series 112 have an extended inner ring with cylindrical bore on both sides and a slot on one side of the inner ring ➤ Figure. These bearings are particularly suitable for simple bearing arrangements with conventional shafts. Due to the bearing bore tolerance J7, mounting and dismounting of this type is very simple. The slot is used to locate the bearings in an axial direction by means of a grub screw; ➤ Figure.
Self-aligning ball bearing with extended inner ring and locating slot
Fr = radial load
Fa = axial load
Locating slot
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Bearings with adapter sleeve
Ready-to-fit bearing mounting kits facilitate the ordering and mounting of self-aligning ball bearings
Complete bearing mounting kits are also available for use in locating self-aligning ball bearings with a tapered bore onto a cylindrical shaft journal. These units comprise the bearing, slotted adapter sleeve, tab washer and locknut (series 12..-K + H, 13..-K + H, 22..-K + H, 23..-K + H, 22..-K-2RS + H) ➤ Figure. Adapter sleeves allow bearings to be located on smooth and stepped shafts. The adapter sleeves must also be stated when placing the order. Ordering example ➤ Figure.
Self-aligning ball bearings with adapter sleeve
Fr = radial load
Fa = axial load
Self-aligning ball bearing, open
Self-aligning ball bearing, lip seal on both sides
Adapter sleeve
Locknut
Tab washer
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Bearings with ball projection
The dimension C1 must be observed
In some self-aligning ball bearings with a brass cage (bearings with the suffix M), the balls project to a certain extent at the sides ➤ Figure.
The projection is marked C1 in the product tables. This must be taken into consideration when defining the dimensions for the adjacent parts.
Self-aligning ball bearing with ball projection
C1 = ball projection
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Suitable for high radial and low axial loads
In addition to high radial forces, self-aligning ball bearings also support low axial forces from both directions ➤ Figure to ➤ Figure. Due to the point contact with which the rolling bearings are in contact with the raceways, the radial load carrying capacity of the bearings is lower than for barrel roller bearings with line contact.
Axial load carrying capacity of bearings with adapter sleeve
Where bearings with adapter sleeves are located on a smooth shaft without a fixed stop (e. g. rigid shoulder), their axial load carrying capacity is dependent on the friction between the shaft and the sleeve.
If there is any doubt about the axial load carrying capacity of the location method, please consult Schaeffler.
Self-aligning ball bearings compensate dynamic and static angular misalignments
Due to the concave rolling element raceway in the outer ring, self-aligning ball bearings are capable of angular adjustment. As a result, they permit skewing between the outer and inner ring within certain limits, without causing damage to the bearings, and can thus compensate misalignments, shaft deflections and housing deformations.
Permissible adjustment angle
With a rotating inner ring, self-aligning ball bearings can swivel up to 4° from their central position
Under normal operating conditions and with a rotating inner ring, self‑aligning ball bearings can swivel up to 4° from their central position, whereas sealed bearings can swivel up to 1,5°. The extent to which these values can be used in practice is, however, essentially dependent on the design of the bearing arrangement.
If the outer ring rotates or the inner ring undergoes tumbling motion, the angular adjustment facility is considerably smaller. In such cases, please consult Schaeffler.
Greased bearings are maintenance-free
Sealed self-aligning ball bearings are lubricated with a high quality lithium soap grease with a mineral oil base, which has good anti-corrosion characteristics. The grease filling is measured so that it is sufficient for the entire life of the bearing. As a result, these bearings are maintenance‑free.
Do not wash greased bearings out prior to mounting. If mounting is carried out using thermal tools, the bearings should not be heated to a temperature in excess of +80 °C, taking account of the grease filling and seal material. If higher heating temperatures are required, it must be ensured that the permissible upper temperature limits for grease and seals are not exceeded. Schaeffler recommends the use of induction heating devices for heating purposes ➤ link.
Lubrication for ungreased bearings
Open bearings are not greased. They can be lubricated from the end faces using oil or grease.
Compatibility with plastic cages
When using bearings with plastic cages, compatibility between the lubricant and the cage material must be ensured if synthetic oils, lubricating greases with a synthetic oil base or lubricants containing a high proportion of EP additives are used.
Observe oil change intervals
Aged oil and additives in the oil can impair the operating life of plastics at high temperatures. As a result, stipulated oil change intervals must be strictly observed.
Also available with lip seals
Self-aligning ball bearings of series 22 and 23 are also available with contact seals on both sides of the bearing ➤ Figure. The integration of such seals into the bearing provides a compact, economical and reliable solution for the sealing of bearing arrangements. In order that the highest possible sealing effect can still be achieved with minimum friction, the seal lips are in contact with the ground opposing running surface of the inner ring under light pressure. The sealing material used is the proven, oil-resistant and wear-resistant elastomer material NBR. Sealed self-aligning ball bearings have the suffix 2RS ➤ link.
Sealing can be achieved in the adjacent construction, if the bearings are open
In the case of unsealed bearings, sealing of the bearing position must be carried out in the adjacent construction. The sealing system should reliably prevent:
- moisture and contaminants from entering the bearing
- the egress of lubricant from the bearing
Speeds in the product tables
The product tables give two speeds for most bearings:
- the kinematic limiting speed nG
- the thermal speed rating nϑr
Limiting speeds
The limiting speed nG is the kinematically permissible speed of the bearing. Even under favourable mounting and operating conditions, this value should not be exceeded without prior consultation with Schaeffler ➤ link.
The values given in the product tables are valid for oil lubrication in the case of bearings without seals and for grease lubrication where bearings are supplied greased and with seals.
Values for grease lubrication
For grease lubrication, 85% of the value stated in the product tables is permissible in each case.
Reference speeds
nϑr is used to calculate nϑ
The thermal speed rating nϑr is not an application-oriented speed limit, but is a calculated ancillary value for determining the thermally safe operating speed nϑ ➤ link.
Bearings with contact seals
For bearings with contact seals, no speed ratings are defined in accordance with DIN ISO 15312:2004. As a result, only the limiting speed nG is given in the product tables for these bearings.
Schaeffler Noise Index
The Schaeffler Noise Index (SGI) is not yet available for this bearing type ➤ link. The data for these bearing series will be introduced and updated in stages.
Limiting values
The operating temperature of the bearings is limited by:
- the dimensional stability of the bearing rings and rolling elements
- the cage
- the lubricant
- the seals
Possible operating temperatures of self-aligning ball bearings ➤ link.
Permissible temperature ranges