Self-aligning ball bearings

Description

Self-aligning ball bearings are double-row bearings with two raceways at the inner ring and a joint concave raceway in the outer ring. This design allows for swiveling at various angles, and the bearings of this type are not affected by a slant between shaft and housing. For this reason, they are well suited to arrangements of bearings in which major shaft deflections or misalignments are to be expected.

Dimensions/standards

In self-aligning ball bearings, the main dimensions are standardized according to ISO 15 (Radial bearings – boundary dimensions), DIN 616 (Roller bearings – boundary dimensions) or DIN 630 (Radial self-aligning ball bearing – double row).

The dimensions of the self-aligning ball bearings with wide inner ring are manufactured according to the standard DIN 630-2, withdrawn without replacement in 1993.

Tolerances

SLF produces self-aligning ball bearings with standard tolerance (PN) according to DIN 620-2 (Roller bearing tolerances – tolerances for radial bearings) and ISO 492 (Radial bearings – dimensions and tolerances). Please specifically request different tolerance classes or special tolerances.

Bearing design types

SLF offers self-aligning ball bearings with cylindrical and tapered holes in the 12, 22, 13 and 23 series. In bearings with a tapered hole, the taper ratio is 1:12.

Self-aligning ball bearings can be swiveled out of the center position by approx. 4°. In sealed bearings, the maximum angle is 1.5°.

In some large-sized self-aligning ball bearing types, the balls slightly protrude laterally; this feature must be considered when dimensioning the surrounding components.

Bearings with wide inner ring

The self-aligning ball bearings in the 112 and 113 series are made with a wide inner ring. Attachment is done using dowel pins that engage with the axial groove at one side of the inner ring. In these two bearing series, the bearing hole has a J7 tolerance.

Clearance

For standard, we deliver self-aligning ball bearings according to DIN 620-4 (Roller bearing tolerances – radial clearance) and ISO 5753-1 (Roller bearings – clearance – radial clearance) in the clearance class CN. We can also supply design types in other clearance classes upon request.

Clearance tables:

Cage

Self-aligning ball bearings can be designed with fiberglass reinforced polyamide 66 with the designation suffix TV, as well as with a solid brass cage (suffix M). We can also supply individual self-aligning ball bearing types with sheet metal cage (J) upon request.
Self-aligning ball bearings with cages made of fiberglass reinforced polyamide 66 (TVP) are suitable for continuously increasing temperatures up to 120 °C. In case of oil lubrication, additives contained in the oil may reduce the operational life of the cage, if the temperature is greater than 100 °C over a longer period.

Working temperature

SLF-self-aligning ball bearings with a maximum outer diameter up to 240 mm are standard stabilized in size (S0), meaning that they are subjected to heat treatment to make them usable up to a working temperature of 150 °C. At more than 240 mm outer diameter, the self-aligning ball bearings are standard stabilized in dimension (S1), meaning that they are subjected to heat treatment to make them usable up to a working temperature of 200 °C. However, as a rule, the maximum working temperature is not limited by the dimensional stability of the bearing rings and balls. Frequently the limitation is the cage, lubricant, or sealant. For the necessary detailed information, see the corresponding chapters. If you are uncertain or have specific questions regarding the maximal temperature our bearings withstand, don’t hesitate to contact the SLF team.

Greasing/lubrication & sealing

Sealed self-aligning ball bearings (bearings in the 22 … and 23 series) are equipped with contacting sealing on both sides (2RS). They are also standard filled with a high quality lithium-saponified roller bearing grease (bearings with D≤62mm) or a high-performance grease-EP-grease (bearings with D>62mm) based on an age-resistant mineral oil.
It is possible to use these bearings at temperatures from -20 °C to max. 110 °C for short periods. When doing this, please note that the operational life of the grease is reduced at a constant temperature >70 °C. In cases like these we recommend special grease customized for the application.

Dimensioning

Dynamic equivalent load

For lifetime calculation, in the case of a combined load, insert an equivalent radial load. It is to be determined as follows:

\(\)
$$P = F_r + Y_1 * F_a$$ for $$\frac{F_a}{F_r} \leq{e}$$
$$P = 0,65 * F_r + Y_2 * F_a$$ for $$\frac{F_a}{F_r} > e$$
P dynamic equivalent load at radial and axial load [kN]
Fr radial dynamic load [kN]
Fa axial dynamic load [kN]
e, Y1, Y2 factors according to bearing table [-]

Static equivalent load

To estimate the static load safety factor with a combined load, determine the equivalent radial load as follows:

\(\)
$$P_0 = F_{0r} + Y_0 * F_{0a}$$
P0 static equivalent load [kN]
F0r radial static load [kN]
F0a axial static load [kN]
Y0 factor according to bearing table [-]

Static load safety factor

For statically loaded self-aligning ball bearings, always inspect the static load safety factor S0 in addition to the nominal lifetime L (L10h).

\(\)
$$S_0 = \frac{C_0}{P_0}$$
S0 static load safety factor [-]
C0 static load rating [kN]
P0 static equivalent load [kN]

Required minimal load

To avoid slippage between elements in contact, the self-aligning ball bearings must be sufficiently loaded. A minimal radial load in the order of magnitude of

\(\)$$P > \frac{C_0}{100}$$

has been shown to be necessary.

Mostly the radial load resulting from the weight of the components run on bearings combined with the external forces is higher alone than the minimal load required. Should this value not be met, contact an SLF application technician.