Fafnir2MM9120WIDUHSuper Precision Angular Contact Ball Bearing — 100 x 150 x 24 mm, 15° Contact Angle, Phenolic Cage, Duplex Heavy Preload, Open

Product Description

What this part is

A Fafnir 2MM9120WI-DUH super-precision angular contact ball bearing set, supplied as a duplex universally ground pair. Bore is 100 mm, outside diameter 150 mm and each ring width 24 mm. The bore is straight, the bearing is open on both faces, and the cage is machined phenolic. The ISO equivalent size and arrangement is a 7020 C pair. Fafnir is Timken’s super-precision spindle bearing brand.

Decoding the designation

In the Fafnir WI scheme the leading 2MM sets a 15° contact angle, and the MM prefix carries the P4S precision grade, which is ABEC 7/9. The leading 9 in 9120 places the bearing in the ISO 70 light dimension series, giving 7020 as the ISO number; 20 is the bore code, at five millimetres per unit. WI marks the super-precision spindle grind, CR marks the phenolic outer-land-riding cage, DU marks universally ground faces for duplex mounting in any pairing, and the final H sets heavy preload. The preload letters run L light, M medium, H heavy.

What these specs mean in practice

A 15° contact angle sits at the speed end of the angular contact range: it carries less thrust per row than a 25° bearing but runs cooler and faster because the ball orbit is closer to pure radial rolling and centrifugal ball loading disturbs the contact path less. Heavy preload takes the trade the other way, buying axial and radial stiffness and better repeatability of position at the cost of higher running torque and more heat, so it suits a rigid, well-cooled spindle carrying cutting loads rather than a lightly loaded high-speed one. The phenolic cage is light and self-lubricating, which is what makes the high limiting speed of 16600 rpm achievable, and it rides on the outer ring land so oil is carried through the cage pockets. Ratings are 18800 lbf dynamic and 17400 lbf static, with an operating range of −30 °C to 120 °C on oil lubrication.

Quantity and configuration

2 Pcs, supplied as a universally ground duplex pair at heavy preload. Universal grinding means the pair can be arranged back-to-back, face-to-face or in tandem, and the ground offsets deliver the specified preload in any of those arrangements.

Mounting arrangement

Back-to-back mounting gives the widest effective bearing spread and the highest resistance to overturning moments. Face-to-face narrows the spread and tolerates a little more misalignment between the two seats. Tandem stacks both rows to take thrust in one direction with roughly double the axial capacity of a single row. The universal grind on a DU pair supports all three.

Fitting notes

The bearings are open, so lubrication and sealing are provided by the spindle. Rings are ground for a light interference fit on the shaft and a close fit in the housing, and preload is delivered by the ground ring offsets rather than by a spacer, so no shim grinding is required at assembly. The phenolic cage sets the upper temperature limit at 120 °C.

Interchange guidance

SKF 7020 CD/P4ADGC and FAG B7020-C-T-P4S-DUH are the same size, the same 15° angle and the same heavy-preload duplex arrangement, and are direct interchanges. A 3MM9120WI pair is the same envelope at a 25° contact angle and is a related size rather than a substitution, because the change of angle changes the thrust and speed behaviour. A 2MM9120WI-DUL or -DUM pair is the same bearing at light or medium preload and is a different stiffness class.