About Double Row Angular Contact Ball Bearings by arb-Bearings.com

Double Row Angular Contact Ball Bearings are rigid, non-separable radial bearings. They are suitable for high - speed applications and can accommodate both radial and thrust forces including combined loads and tilting moments.
As single row angular contact ball bearings they only accept thrust loads in one direction, they must be used in pairs where a bearing has to be adjusted against another to guide the shaft in the opposite direction.
Angular contact ball bearings transfer the loads acting on the bearing at a certain angle, the so - called "contact" angle from the shaft centre line (see sketch below).
The ability of single row angular contact ball bearings to accommodate thrust loads depends on their contact angle. The higher the angle the better the thrust load capacity.

Due to their universal feature single row angular contact ball bearings are produced in various designs and with different contact angles.
NKE Single Row Angular Contact Ball Bearings are produced with several different contact angles, these contact angles are identified by the following suffixes:

Bearing Suffix              Alpha Angle

A                                    30deg
  
B                                    40deg

C                                    15deg

D                                    25deg
  


Single row angular contact ball bearings of the series 72 and 73 with a contact angle of 40deg (suffix B) are regularly used in the general machinery industry.
Other angular contact ball bearings with different contact angles are mainly used in working spindles of machine tools.
Thus they are also often used with precision tolerance class P4 (ABEC7) up to high precision class P2 (ABEC9) and are frequently called spindle bearings. Single row angular contact ball bearings are frequently used in pairs or. sets where two or more bearings are located side by side.

To retain certain clearances single bearings that are used in pairs have to be matched accordingly. For that reason single row angular contact ball bearings of the series 72 and 73 featuring contact angles of 40deg are available in a variant for use as a single bearing (suffix B) and in a universal matched variant to be used in pairs or sets (suffix BG).
Single row angular contact ball bearings have a very limited ability to accommodate misalignments. Therefore any operating misalignments applied to this bearing type creates additional forces subsequently reducing their service life and, additionally, generates higher running noise levels.
Where individual single row angular contact bearings or pairs of bearings are arranged Face to Face, up to 2 angular minutes misalignment from the centre position does not normally affect the bearings negatively.
However, when arranged in pairs Back to Back or Tandem or as Sets, spindle bearings must not run misaligned.
Tolerances
NKE single row angular contact ball bearings of the series 72 and 73 are produced to normal tolerance class (PN) as standard.

NKE machine tool spindle bearings of the series 719, 70 and 72 are produced to ISO tolerance class P4 (ABEC7) as standard. On order request these bearings are produced to closer tolerances, up to high precision class P2 (ABEC 9).

To retain certain clearances single bearings that are used in pairs have to be matched accordingly. For that reason single row angular contact ball bearings of the series 72 and 73 featuring contact angles of 40deg are available in a variant for use as a single bearing (suffix B) and in a universal matched variant to be used in pairs or sets (suffix BG).
Single row angular contact ball bearings have a very limited ability to accommodate misalignments. Therefore any operating misalignments applied to this bearing type creates additional forces subsequently reducing their service life and, additionally, generates higher running noise levels.
Where individual single row angular contact bearings or pairs of bearings are arranged Face to Face, up to 2 angular minutes misalignment from the centre position does not normally affect the bearings negatively.
However, when arranged in pairs Back to Back or Tandem or as Sets, spindle bearings must not run misaligned.

Cages

The NKE single row angular contact ball bearings, with normal tolerance class are fitted with Pressed Steel cages as standard. Large types and sizes have machined Solid Brass cages (Suffix M) fitted as standard.
Bearings used in Higher Precision or Machine in Tool Spindle applications are normally fitted with either Phenolic Resin (suffix TPA) or machined Solid Brass cages (suffix M).

Some special applications have machined Solid Steel cages (suffix F) or Light Metal Alloy cages (suffix L) fitted as standard.

Internal Clearnace

The axial play of angular contact ball bearings is achieved by adjusting one bearing against another. NKE single row angular contact ball bearings in universal design, with normal bearing mounting fits, are matched in pairs either "Face to Face" or "Back to Back" to give a small axial play.

The "normal" fits are:
Shaft fits: j5
Housing fits: J6

Special clearances

NKE also produce upon request paired single row angular contact ball bearings to customers requirements and specifications.

Bearing pairs (see drawing below)
Single row angular contact ball bearings in universal design, (suffix BG) and spindle bearings are frequently used in pairs or sets. (see arrangements sketch below)
Tandem Arrangement
Single row angular contact ball bearings in a tandem arrangement are used when the actual thrust force exceeds the thrust load capacity of a single angular contact ball bearing. These
thrust forces are accommodated in one direction only and are distributed equally to both bearings.
Single row angular contact ball bearings in tandem arrangement must always be adjusted against another bearing inversely arranged for shaft guidance in the opposite direction.

Face to face arrangement

Thrust forces are accommodated in both directions by each individual angular contact ball bearing.
Bearing pairs arranged face to face do not require a very accurate alignment of the bearing positions due to their relatively small support width (a). On the other hand, these arrangements are suitable to take tilting moments due to their less stiffness.
For bearing pairs arranged face to face temperature increase of the shaft causes a reduction of axial internal clearance or an increase of preloading forces, respectively.

Back to back arrangement

The axial forces are, similar to face to face arrangements, accommodated in both directions by each individual bearing.
Angular contact ball bearings arranged back to back provide a very rigid bearing arrangement due to their large support width (a). They are also able to accept tilting moments.
Bearing arrangements consisting of more than one bearing normally give more accurate bearing positional alignment, this results in optimum load transmission.
Bearing pairs arranged back to back are not able to compensate for misalignments.