RHPB7918X2TADUMSuper Precision Angular Contact Ball Bearing Matched Pair – 90 mm ID, 125 mm OD, 18 mm Width, 15° Contact Angle, Medium Preload, ABEC 7

Product Description

What this part is

RHP B7918X2TADUM matched pair of single-row super-precision angular contact ball bearings, made in the United Kingdom. Bore: 90 mm. Outside Diameter: 125 mm. Overall Width: 18 mm. Contact Angle: 15°. Precision Class: P4, equivalent to ABEC 7 and to BS292 EP7. Number Of Rows: 1 per bearing. Rolling Elements: Balls. Bearing Material: Carbon chrome bearing steel to BS970 534A99/535A99, equivalent to SAE 52100, through hardened. Series: 79, ISO dimension series 19. RHP is an NSK brand.

Decoding the designation

Reading the B-series order code B-7918-X2-TA-DUM-EP7: 7 is a single-row angular contact ball bearing, 9 is ISO dimension series 19, the bore code 18 gives a 90 mm bore, X2 is the 15° contact angle, TA is the outer-ring-guided laminated phenolic resin cage, DU marks a paired unit, M is medium preload and EP7 is the BS292 precision grade. The same bearing is written 7918CTDUMP4 in RHP’s current scheme, where C carries the 15° angle in place of X2.

What these specs mean in practice

Dynamic Load Rating: 41.5 kN per bearing. Static Load Rating: 46.0 kN per bearing. Limiting Speed, oil-air lubrication: 15,400 rpm. Limiting Speed, grease lubrication: 9,500 rpm. Those two figures are for a single bearing under light spring preload. Mounted as a back-to-back medium-preload pair the limiting speeds are multiplied by 0.60, giving 9,240 rpm on oil-air and 5,700 rpm on grease. Face-to-face mounting halves those again. A 15° contact angle favours speed and radial stiffness where a 25° angle favours thrust capacity.

Cage and temperature

Cage Material: Laminated phenolic resin. Cage Type: Outer-ring guided. Maximum Operating Temperature: 120 °C, which is the limit set by the phenolic cage rather than by the rings. The outer-ring-guided design and the low cage mass are what give the range its high speed capability and quiet running.

Preload and stiffness

Preload: Medium. Axial Preload: 740 N for the mounted pair. Axial Stiffness: 156 N/µm. RHP offers exactly four preload grades across this range, extra light, light, medium and heavy. Medium sits one step above the light grade that suits most general spindle work, and buys rigidity at the cost of speed.

Mounting data

Bore Type: Straight. Closure Type: Open. Minimum Shaft Abutment Diameter: 97 mm. Maximum Housing Abutment Diameter: 118 mm. Maximum Outer Ring Abutment Diameter: 120 mm. Chamfer r min: 1.5 mm. Chamfer r1 min: 0.6 mm. Effective Load Centre a: 23.4 mm. Internal Volume: 25.6 cm³. Pitch Circle Diameter Of Lubrication Jets: 102.8 mm. The rings are universally faced, so the pair mounts back-to-back or face-to-face without altering the preload value.

Quantity and configuration

Unit Quantity: 2 Pcs. Arrangement: DU, a universally matched pair. Item Weight: 1.12 kg (2.47 lb) for the pair, 0.559 kg (1.23 lb) each. Bore and outside diameters are matched across the set and the deviation from nominal in microns is marked on each ring face.

Interchange guidance

Cross-references on the same envelope and preload: SKF 71918CD/P4ADGB and FAG B71918C.T.P4S.DUM. The designation is also written B7918X2TADUM, B-7918-X2-TA-DUM-EP7, 7918CTDUMP4 and 71918C. A 7918 at a 25° contact angle shares this 90 x 125 x 18 mm envelope but carries different ratings and speeds, so it is a related size rather than a substitution.