231-670BK bearing: complete specifications & equivalents
The 231-670BK is a ISO 15 radial bearing sized 670 x 1090 x 336 mm (bore x OD x width). Verify dimensions against the official catalog before ordering.
Specification table
| Parameter | Value |
|---|---|
| Brand | NTN |
| Bore diameter d | 670 mm |
| Outer diameter D | 1090 mm |
| Width B | 336 mm |
| Material | GCr15 |
| Seal / shield | open |
| Internal clearance | CN |
| Tolerance class | P0 |
| Cage | steel |
| Basic dynamic load rating C | 12500 kN |
| Basic static load rating C0 | 23600 kN |
| Fatigue load limit Pu | 1400 kN |
| Limiting speed (mechanical) | 230 rpm |
| Operating temperature | -40 to +120 °C |
| Mass | 1210000 g |
| Manufacturer designation | NTN 231/670BK |
| Standard | ISO 15 |
| Catalog version | NTN Ball and Roller Bearings CAT.No.2203E |
| Last verified | 2026-10-01 |
Source: catalog reference (NTN Ball and Roller Bearings CAT.No.2203E) · extracted 2026-10-01
Parameters extracted from the official NTN Ball and Roller Bearings catalogue (NTN Ball and Roller Bearings CAT.No.2203E); NTN® is a trademark of NTN Corporation, used here for identification only — mpnbase is not an authorized NTN distributor. Boundary dimensions are ISO 15 interchangeable; current production values may differ, verify at ntnglobal.com.
Dimensions in inches & 23100-series range
| Bore d | 26.378 in |
|---|---|
| Outer diameter D | 42.913 in |
| Width B | 13.228 in |
| ISO bore code | 31 |
| Radial section height (D−d)/2 | 210 mm |
| Smallest bore in 23100-series | 100 mm |
| Largest outer diameter in 23100-series | 1420 mm |
| Width range across 23100-series | 52–412 mm |
| Bore position in 23100-series (smallest first) | 31 of 36 |
| Bore above smallest 23100-series size | 570 mm |
Cross references & equivalents
| Equivalent model | Brand | Match level | Note |
|---|---|---|---|
| 231-670B | NTN | partial Main dimensions match; tolerances, seals or internal clearance differ. | Same NTN 23100-series envelope, cage and ratings; this is the tapered-bore execution (K, 1:12) of the cylindrical-bore 231-670B — mounting (adapter/withdrawal sleeve or tapered seat, drive-up) differs. Verify shaft arrangement. |
Interchange levels: full standard interchange · partial verify parameters · verify manual confirmation required. Links resolve to the equivalent model's specification page where available.
How the 231-670BK model number is decoded
231/670BK belongs to the 23100 series of NTN spherical rollers: self-aligning, high radial capacity, moderate axial load in either direction. Numbering ties 231/670BK to its envelope and execution: same-number EA versus EM or plain variants share the 670 mm bore but differ in cage and sometimes mass, so they are quoted as separate articles. At 12500 kN C and 1210000 g mass the 23100 series part is built for shock and vibration; the 336 mm-wide ring needs square abutments to keep both rows equally loaded. Pu 1400 kN against C0 23600 kN anchors the contamination derating; for dirty mining duty the adjusted life of 231/670BK moves with cleanliness far more than with small C variations. On vibrating-duty shafts verify the radial clearance class and cage choice at order time; the open 231/670BK leaves sealing and the C3/C4 clearance decision to the application drawing.
Typical equipment & failure modes
Common applications
- steel-mill and heavy crusher main shafts
- mining shovel and dragline swing shafts
- cement-rotary-kiln support and trunnion rolls
- large SAG/ball-mill trunnion and pinion shafts
Known failure patterns
- raceway spalling at the roller ends when misalignment or deflection concentrates the line contact
- machined EM cage wear from inadequate oil film at the cage-guiding surfaces
- roller-end smearing during skidding starts under light load and high viscosity grease
- water-induced pitting in washdown or outdoor duty without effective external seals
- fretting corrosion between adapter sleeve and tapered bore when the drive-up is insufficient
Selection pitfalls — read before you substitute
- At 670 mm bore 231/670BK is normally mounted on adapter/withdrawal sleeves with hydraulic assistance; follow the NTN drive-up angle or oil-injection procedure — manual nut tightening cannot set the multi-tonne seating correctly.
- The D1/W33 groove only helps if the housing has a matching grease passage; mounting a grooved 231/670BK in a solid block with no port wastes the feature and leaves the centre rows under-lubricated.
- Adapter-sleeve mounting requires the correct sleeve series and locknut for the 670 mm shaft; a sleeve sized to bore alone ignores thread, width and the oil-injection option on large K30 seats.
- The D1/W33 groove only helps if the housing has a matching grease passage; mounting a grooved 231/670BK in a solid block with no port wastes the feature and leaves the centre rows under-lubricated.
- Open spherical rollers swallow dust in mining duty; specify labyrinth or taconite seals externally, or the 230 r/min grease rating is lost to abrasive wear long before fatigue.
- The 12500/23600 kN ratings, 1400 kN Pu and 1210000 g mass are NTN Ball and Roller Bearings CAT.No.2203E values for 231/670BK (basic); another maker's same-envelope part revises internal geometry, so re-verify ratings and cage before substitution on vibrating or rated drives.
Frequently asked questions
What are the dimensions and catalogue data of 231/670BK?
231/670BK is an NTN double-row spherical roller bearing to ISO 15: 670 mm bore, 1090 mm OD and 336 mm width (26.378 × 42.913 × 13.228 in). From NTN Ball and Roller Bearings CAT.No.2203E: C 12500 kN, C0 23600 kN, Pu 1400 kN, grease limiting speed 230 r/min, oil 300 r/min, mass about 1210000 g. It is open, with pressed-steel cage (standard execution) and a 1:12 tapered bore.
What is the difference between the K/K30 tapered bore and the cylindrical bore versions?
K denotes a 1:12 tapered bore. 231/670BK mounts on an adapter sleeve (or tapered shaft seat) and is driven up to the specified residual clearance; its cylindrical-bore counterpart in the same envelope and ratings is 231/670B.
What do EA and EM mean on NTN spherical roller bearings?
EA is the NTN standard-capacity/high-capacity execution with a pressed sheet-steel window cage; EM is the high-capacity execution with a one-piece machined brass cage. Both use the optimised symmetric-roller design, but cage identity changes mass, speed behaviour and suitability for duties like vibrating screens, so they are separate order numbers. 231/670BK is the basic execution.
What do D1 and W33 mean on 231/670BK?
231/670BK is listed without a D1/W33 outer-ring groove in 2203E; lubrication is supplied from the ring sides. D1 (NTN spelling) and W33 add the annular groove plus holes and are ordered as distinct suffixed executions of the same envelope.
How much misalignment and axial load can 231/670BK take?
The sphered outer raceway compensates static and dynamic misalignment in the order of 1–2° (verify the exact 2203E figure for the 23100 series); beyond that, load concentrates on one roller row. Load is predominantly radial with a moderate axial share in either direction — 12500 kN C / 23600 kN C0 — but sustained pure axial load is not recommended because it unloads one row.
Reviewed & verified by the MPN Base engineering desk against source catalog NTN Ball and Roller Bearings CAT.No.2203E on 2026-10-01. Read our editorial & correction policy.