RHP7211ETSUMP4Super Precision Angular Contact Ball Bearing 55x100x21 mm, 25° Contact Angle, Phenolic Cage, ABEC 7, Medium Preload, Single Universally Ground, Medium 72-Series Section

Product Description

Part identity

RHP (now NSK) 7211ETSUMP4 super precision angular contact ball bearing, single row. Brand: RHP. Designation: 7211ETSUMP4. Base number: 7211E. Series: 72 (ISO dimension series 02). Bore code: 11. Contact angle: 25°. Precision class: P4 (ISO class 4, ABEC 7, RHP EP7). Preload: medium (M). Grouping: SU, single universal. Closure: open. Number of rows: 1. Rolling elements: balls. Harmonization code: 8482.10.50.

Dimensions

Bore d: 55 mm. Outside diameter D: 100 mm. Width B: 21 mm. Ring chamfer r min: 1.5 mm. Second chamfer r1 min: 1.0 mm. Design units: metric. Mass: 0.603 kg (1.33 lb). Bearing material: through-hardened carbon chrome bearing steel to BS970 534A99 / 535A99, equivalent to SAE 52100.

Load ratings and speeds

Basic dynamic load rating Cr: 50 500 N (50.5 kN). Basic static load rating C0r: 38 000 N (38.0 kN). Limiting speed with oil/air lubrication: 20 000 rev/min. Limiting speed with grease lubrication: 12 400 rev/min. Both speed figures are for a single bearing under spring preload with the inner ring rotating.

Preload and stiffness

Axial preload for a medium-preload pair in the 72-series 25° range at bore code 11: 1 180 N. Axial stiffness for the same pair: 255 N/µm. Speed factor for a back-to-back pair at medium preload: 0.60 of the single-bearing figure; a face-to-face pair is reduced by a further 50 per cent; a spring-loaded tandem pair carries a factor of 0.95.

Mounting data

Effective load centre a: 28.6 mm. Abutment diameters: d1 min 64 mm, D1 max 91 mm, D2 max 94 mm. Internal free volume: 27.8 cm³. Pitch circle diameter for lubrication jets dT: 72.0 mm. Maximum recommended operating temperature for a laminated phenolic resin cage: 120 °C. Recommended shaft fit at P4 in this diameter range: +3 to −2 µm, a mean 3T interference. Recommended housing fit at P4 for a locating position: +5 to −2.5 µm, a mean 5C clearance.

Designation breakdown

7 is a single-row angular contact ball bearing. 2 is RHP dimension series 02, the ISO 72 medium section. 11 is the bore code for 55 mm. E is the 25° contact angle in the RHP scheme, corresponding to A5 in NSK’s. T is the outer-ring guided laminated phenolic cage, written TR in full. SU is single universal grouping. M is medium preload. P4 is precision grade 4.

Cage and contact angle

Cage type: machined one-piece, outer-ring guided. Cage material: laminated phenolic resin. The material and design suit high rotational speed and quiet running, and the cage’s own porosity retains lubricant. A 25° contact angle places more of the ball load in the thrust direction than the 15° C angle of the same size, giving higher axial load capacity and greater axial stiffness at a lower limiting speed — the 15° 7211C runs to 23 000 rev/min on oil/air against 20 000 for this bearing.

Universal face control

The inner and outer rings are the same width and the relative positions of the faces are adjusted at manufacture so that a predetermined preload force exists once the bearing is clamped against a partner of the same designation. A universally faced bearing therefore mounts back-to-back or face-to-face at the same preload value with no shims and no grinding, and shares load equally in tandem. Back-to-back (DB) mounting produces the highest radial and moment stiffness; face-to-face (DF) accommodates shaft-to-housing misalignment; tandem (DT) shares thrust in one direction between two bearings. The high point of radial runout is marked by a small circle or burnished spot on the inner ring face, and a V line on the outer ring outside diameter marks the direction of the contact angle.

Applications

Machine tool spindles, milling and turning centres, grinding heads, precision gearboxes, rotary tables, high-thrust precision shafts, and test rigs.

Cross-reference guidance

NSK designation for this bearing: 7211A5TRSUM P4. Timken/Fafnir world number 3MM211WI CR, where 3MM denotes a 25° contact angle and CR a phenolic outer-land-riding cage; MM-prefixed Fafnir numbers normally carry P4S tolerance. Related designations elsewhere: SKF 7211 ACDGC/P4A (medium preload; the GB version is light preload) and FAG B7211-E-T-P4S-UM. Search forms carried on this record: 7211E-T-SUM-P4, 7211 E T SUM P4, 3MM211WICRDUM, B7211X3TADUMEP7. The 15° 7211C bearing shares the 55x100x21 mm envelope with a different contact angle, load rating and speed capability.