Double row angular contact ball bearings
SKF double row angular contact ball bearings correspond in design to two single row angular contact ball bearings but take up less axial space. They can accommodate radial loads as well as axial loads acting in both directions. They provide stiff bearing arrangements and are able to accommodate tilting moments.
SKF produces double row angular contact ball bearings in several designs depending on size and application. These are described in the following and include
- basic design bearings (fig)
- sealed bearings (fig)
- bearings with a two-piece inner ring (fig)
- large bearings for heavy engineering applications with two-piece inner or outer ring
The standard range is shown in matrix 1. The matrix is also valid for bearings in the 52 A and 53 A series, which have the same performance characteristics and dimensional features (except for the width of size 5200).
Basic design bearings
SKF double row angular contact ball bearings with the designation suffix A have optimized internal geometry and do not have filling slots. The advantages are
- universal applicability,
- high radial and axial load carrying capacity in both directions,
- quiet operation.
The bearings have a 30° contact angle (24° for 54 A series) and the ball sets are in a back-to-back arrangement.
Bearings with filling slots are available in the 52 E and 53 E series. They also have a 30° contact angle, except for 5205 E and 5203 E that have 25°.
Basic design bearings that are also available with seals or shields may, for manufacturing reasons, have seal recesses on inner and outer rings (fig).
The most common basic design bearings can also be supplied with shields or seals (matrix 1). Bearings in the 32 A and 33 A series are filled with a high-quality NLGI class 3 grease with a lithium thickener and are marked with the designation suffix MT33. This grease has good corrosion inhibiting properties and can be used at temperatures between –30 and +120 °C. The base oil viscosity is 98 mm2/s at 40 °C and 9,4 mm2/s at 100 °C.
Bearings in the 52 and 53 series use a mineral oil based high-temperature grease with a polyurea thickener. The operating temperature range of this grease is –30 to +140 °C. The base oil viscosity is 115 mm2/s at 40 °C and 12 mm2/s at 100 °C.
SKF Energy Efficient angular contact ball bearings use a synthetic oil based low-friction grease with a lithium thickener. The operating temperature range of this grease is –40 to +140 °C. The base oil viscosity is 25 mm2/s at 40 °C and 4,9 mm2/s at 100 °C.
Sealed bearings are lubricated for life and are maintenance-free. They should not be washed or heated above 80 °C before mounting.
Bearings with shields
Bearings with shields, designation suffix 2Z, are produced in two different designs. The sheet steel shields used in smaller bearings form a narrow gap with the land of the inner ring shoulder (fig). Larger bearings as well as all SKF Explorer bearings have recesses in the inner ring side faces into which the shields extend (fig).
Shielded bearings are primarily intended for applications where the inner ring rotates. If the outer ring rotates there is a risk that grease will be lost from the bearing once it reaches a certain speed.
Bearings with seals
Bearings with seals, designation suffix 2RS1, use a acrylonitrile-butadiene rubber, sheet steel reinforced seal that fits against a recess in the inner ring side face (fig). The lip of the seal exerts a light pressure against the inner ring for a positive seal. The periphery of the seal engages in a recess in the outer ring to provide a good sealing. The permissible operating temperature range for these seals is –40 to +100 °C and up to +120 °C for brief periods.
Grease may be lost from sealed bearings at the inner ring under extreme operating conditions, e.g. at high speeds or at high temperatures. For applications where this could be a disadvantage, special design steps should be taken to prevent this. For additional information please contact the SKF application engineering service.
Bearings with two-piece inner ring
In addition to the basic design bearings, double row angular contact ball bearings are also available with a two-piece inner ring. These bearings incorporate a large number of large balls and have a high load carrying capacity, especially in the axial direction.
Bearings in the 33 D series
Bearings in the 33 D series (fig) have a 45° contact angle, a special internal clearance and can support heavy axial loads in both directions. The bearings are separable, i.e. the outer ring with ball and cage assemblies can be mounted independently of the inner ring halves.
Bearings in the 33 DNRCBM series
Bearings in the 33 DNRCBM series (fig) have a 40° contact angle and a snap ring groove with snap ring in the outer ring, enabling simple and space-saving axial location in the housing. They have been designed specifically to operate under the conditions pertaining in centrifugal pumps, but can also be used in other applications. These bearings are non-separable.
SKF large double row angular contact ball bearings were originally designed for the axial location of the rolls of finishing mills and wire rolling mills which are supported in cylindrical roller bearings. They are eminently suitable for the high speeds and relatively small axial forces encountered in these applications, but are also suitable for other applications, for example in heavy engineering, where shafts rotating at high speeds require radial support and have to be located axially with a small play.
Depending on size the large double row angular contact ball bearings have a two-piece inner or outer ring. They are of non-separable design.
Bearings with two-piece inner ring (fig, fig) have load lines which diverge towards the bearing axis (ball rows arranged back-to-back) and a 40 or 32° contact angle. They enable relatively stiff bearing arrangements to be made which can also support tilting moments.
The load lines of bearings having two-part outer rings (fig) converge towards the bearing axis (face-to-face arrangement). The contact angle is 40°. The face-to-face arrangement of the ball rows makes the bearings less stiff than those with a back-to-back arrangement, but they are less sensitive to minor misalignment.
SKF Explorer class bearings
High performance SKF Explorer angular contact ball bearings are shown with an asterisk in the product tables. SKF Explorer bearings retain the designation of the earlier standard bearings, e.g. 3208 ATN9. However, each bearing and its box are marked with the name "EXPLORER".
SKF Energy Efficient (E2) bearings
SKF has developed a new, low-friction double row angular contact ball bearing. The SKF Energy Efficient (E2) performance class is characterized by a reduction of the frictional moment in the bearing by a minimum of 30% when compared to a comparable standard SKF bearing. This substantial reduction of the frictional moment was achieved by optimizing the internal geometry of the bearing and applying a new low-friction grease. The bearings are equipped with a shield on both sides and lubricated for the life of the bearing. Due to the reduction of the frictional moment, SKF E2 double row angular contact ball bearings run up to 20 °C (35 °F) cooler than standard bearings. This increases grease life and potentially bearing service life.
SKF Energy Efficient bearings are dimensionally interchangeable with standard bearings – enabling both, easy upgrades of existing applications as well as improving the energy efficiency of new applications. SKF E2 double row angular contact ball bearings are available in the 32 and 33 dimension series.
For more information, refer to the publication SKF Energy Efficient double row angular contact ball bearings - Reduced friction for reduced energy use
The boundary dimensions of SKF double row angular contact ball bearings are in accordance with ISO 15:1998, except for the width of bearing 3200 A.
The dimensions of the snap ring grooves and snap rings conform to ISO 464:1995.
The dimensions of the bearings identified by a Drawing No. are not standardized but those of the rolling mill bearings have achieved international acceptance in the industry.
SKF basic design double row angular contact ball bearings are produced to Normal tolerances as standard. SKF Explorer bearings, SKF Energy Efficient bearings and bearings in the 33 DNRCBM series are produced to tolerance class P6 specifications.
The outer rings of the Drawing No. bearings are also produced to Normal tolerances; the dimensional and running accuracy of the inner rings are to tolerance class P6 or P5. The running accuracy is always at least to tolerance class P6.
The values for tolerances correspond to ISO 492:2002.
SKF double row angular contact ball bearings identified by a series designation are produced as standard with Normal axial internal clearance. They are also available with the greater C3 clearance (matrix 1). Values for the clearance limits are given in table 1. For bearings with smaller C2 clearance, please check availability before ordering.
Bearings in the 33 D and 33 DNRCBM series are produced exclusively with an axial internal clearance according to the values provided in table 1. They are valid for bearings before mounting under zero measuring loads.
Large SKF double row angular contact ball bearings identified by drawing number are produced with special axial internal clearances appropriate to their original application. Values for the clearance limits are given in table 2. They are valid for bearings before mounting and under zero measuring loads.
Misalignment of the outer ring with respect to the inner ring of double row angular contact ball bearings, particularly those with the ball rows arranged back-to-back, can only be accommodated by generating forces between the balls and the raceways. Any misalignment will lead to increased noise in operation and reduced bearing service life.
Influence of operating temperature on bearing material
SKF angular contact ball bearings undergo a special heat treatment. When equipped with a steel or brass cage, they can operate at temperatures of up to +150 °C.
Depending on the bearing series, size and design, SKF double row angular contact ball bearings are fitted as standard with two of the following cages
- an injection moulded snap-type cage made of glass fibre reinforced polyamide 66 (fig), ball centred, designation suffix TN9
- a pressed snap-type steel cage (fig), ball centred, no designation suffix or suffix J1
- a pressed steel crown cage (fig), ball centred, no designation suffix
- a pronged machined brass cage (fig), outer ring centred, designation suffix MA,
- a machined window-type brass cage (fig), ball centred, designation suffix M.
Several bearings are available as standard with a choice of cage design so that bearings with a cage appropriate to the operating conditions can be chosen (matrix 1).
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".
To achieve satisfactory operation, double row 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 cages, 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 radial load to be applied to double row angular contact ball bearings can be estimated using
Frm = minimum radial load [kN]
kr = minimum radial load factor (see product data)
? = oil viscosity at operating temperature [mm2/s]
n = rotational speed [r/min]
dm = mean bearing diameter
= 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 exceed the requisite minimum load. If this is not the case, the double row angular contact ball bearing must be subjected to an additional radial load.
<2>Equivalent dynamic bearing load
P = Fr + Y1Fa when Fa/Fr = e
P = XFr + Y2Fa when Fa/Fr > e
The values for the factors e, X, Y1 and Y2 depend on the bearing contact angle and can be found in the product table.
Equivalent static bearing load
P0 = Fr + Y0Fa
The value for the factor Y0 depends on the bearing contact angle and can be found in the product table.
The designation suffixes used to identify certain features of SKF double row angular contact ball bearings are explained in the following.
|A||No filling slots|
|C||Controlled axial internal clearance|
|C2||Axial internal clearance smaller than Normal|
|C3||Axial internal clearance greater than Normal|
|D||Two-piece inner ring|
|E||Max type bearing, with filling slot|
|HT51||High temperature grease for operating temperature s in the range –30 to +140 °C|
|J1||Pressed snap-type steel cage, ball centred|
|M||Machined window-type brass cage, ball centred|
|MA||Pronged machined brass cage, outer ring centred|
|MT33||Grease with lithium thickener of consistency 3 to the NLGI Scale for a temperature range –30 to +120 °C (normal fill grade)|
|N||Snap ring groove in the outer ring|
|NR||Snap ring groove in the outer ring with snap ring|
|P5||Dimensional and running accuracy in accordance with ISO tolerance class 5|
|P6||Dimensional and running accuracy in accordance with ISO tolerance class 6|
|P62||P6 + C2|
|P63||P6 + C3|
|TN9||Injection moulded snap-type cage of glass fibre reinforced polyamide 66, ball centred|
|2RS1||Sheet steel reinforced contact seal of acrylonitrile-butadiene rubber (NBR) on both sides of the bearing|
|W64||Solid Oil filling|
|2Z||Shield of pressed sheet steel on both sides of the bearing|
Some Drawing No. bearings have the designation prefix BA2B which identifies them as double row angular contact ball bearings.
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