C31-670-KMB bearing: complete specifications & equivalents
The C31-670-KMB 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 | SKF |
| 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 | brass |
| Basic dynamic load rating C | 11800 kN |
| Basic static load rating C0 | 21200 kN |
| Fatigue load limit Pu | 1290 kN |
| Reference speed (thermal) | 380 rpm |
| Limiting speed (mechanical) | 500 rpm |
| Operating temperature | -40 to +120 °C |
| Mass | 1300000 g |
| Manufacturer designation | C 31/670 KMB |
| Standard | ISO 15 |
| Catalog version | SKF PUB BU/P1 17000/1 EN (Oct 2018), ch. 10.1 CARB toroidal roller bearings |
| Last verified | 2026-09-27 |
Source: catalog reference (SKF PUB BU/P1 17000/1 EN (Oct 2018), ch. 10.1 CARB toroidal roller bearings) · extracted 2026-09-27
Parameters extracted from the official SKF Rolling Bearings catalogue (SKF PUB BU/P1 17000/1 EN (Oct 2018), ch. 10.1 CARB toroidal roller bearings); SKF® and SKF Explorer® are trademarks of AB SKF, used here for identification only — mpnbase is not an authorized SKF distributor. Boundary dimensions are ISO 15 interchangeable; current production values may differ, verify at skf.com.
Dimensions in inches & C3100-series range
| Bore d | 26.378 in |
|---|---|
| Outer diameter D | 42.913 in |
| Width B | 13.228 in |
| ISO bore code | — |
| Radial section height (D−d)/2 | 210 mm |
| Smallest bore in C3100-series | 100 mm |
| Largest outer diameter in C3100-series | 1580 mm |
| Width range across C3100-series | 52–462 mm |
| Bore position in C3100-series (smallest first) | 25 of 28 |
| Bore above smallest C3100-series size | 570 mm |
Cross references & equivalents
| Equivalent model | Brand | Match level | Note |
|---|---|---|---|
| C31-670-MB | SKF | full Dimensions and internal design equivalent — standard interchange. | Same 670×1090×336 mm ISO 15 envelope and equivalent catalogue C/C0; C 31/670 MB is the cylindrical-bore MB inner-ring-guided brass-caged execution of this size — boundary dimensions interchangeable, only mounting and cage execution differ. |
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 C31-670-KMB model number is decoded
For long shafts that grow thermally, SKF supplies C 31/670 KMB: the toroidal rollers allow the 670 mm inner ring to displace axially without induced thrust, while still accommodating shaft deflection like a spherical bearing. SKF builds the CARB order number from size plus execution: the bare number C 31/670 is the brass-caged cylindrical-bore bearing, K (or K30) makes the bore tapered for sleeve mounting, and the cage/seal letters follow — here KMB. CARB bearings locate neither radially nor axially: the inner ring can walk axially inside the outer ring over the catalogue-listed axial-displacement range (s), so shaft thermal growth disappears as thrust rather than preloading the 670 mm seat. Speed planning separates the 380 r/min thermal reference from the 500 r/min mechanical limiting speed. The full-complement V executions carry more load but list no thermal reference speed; the brass-caged executions run faster and cooler at light load. Seat tolerances follow the ISO 15 recommendation for the heavy-loaded position — the 1090 mm outer ring typically takes a loose housing fit to preserve float, and the rings must be supported across their full faces.
Typical equipment & failure modes
Common applications
- continuous-caster guide rolls and slab-caster segments under heat growth
- vibrating screen exciters fitted with the VE240 tolerance execution
- long fan and kiln main shafts where the free end must float without thrust load
- heavy industrial gearbox layshafts used as the non-locating position
Known failure patterns
- roller-end and flange smearing after lubricant starvation at the long roller contacts
- thermal preloading when a shaft is located at both ends and growth has nowhere to go
- PA66 cage (TN9) softening when the sustained temperature passes the polymer limit
- electrical erosion of raceways on VFD-driven shafts without grounding or insulation
- oil starvation at the sliding contact zones of large spherical roller thrust bearings on forced-feed trips
Selection pitfalls — read before you substitute
- At 670 mm bore the 1300 kg mass and 336 mm width make seating geometry dominant: sphered-washer seats and oil flow must be verified in place, not just on the drawing.
- The quoted 11800/21200 kN ratings belong to this exact execution (C 31/670 KMB); VE240 vibrating-screen variants and sealed 2CS/2NS variants have their own figures even at the same envelope.
- Do not block the axial displacement in the drawing: housing covers, labyrinth rings and snap rings must leave the catalogue float (s) free, or the bearing silently becomes a poorly located fixed bearing.
- Tapered-bore K executions mount on adapter sleeves (1:12) and K30 on withdrawal sleeves (1:30) — the 670 mm bore changes the sleeve family, and the drive-up procedure differs accordingly.
- Reference and limiting speeds are different limits: the 380 r/min reference speed is the thermal criterion under load, the limiting value is the mechanical ceiling; observe the reference under load unless the arrangement calculation says otherwise.
- The 11800/21200 kN ratings and 1300000 g mass are SKF catalogue values transcribed from ch. 10.1 of PUB BU/P1 17000 (PDF table page 868); mounting data — axial displacement (s) and seating details — appears in the running text because the structured record carries the boundary envelope only.
Frequently asked questions
Which dimensions does the C 31/670 KMB have?
A C 31/670 KMB measures 670 mm bore × 1090 mm outside diameter × 336 mm width (26.378 × 42.913 × 13.228 in). From SKF catalogue PUB BU/P1 17000: dynamic C 11800 kN, static C0 21200 kN, fatigue limit Pu 1290 kN, reference speed 380 r/min, limiting speed 500 r/min, mass about 1300000 g.
What does C 31/670 KMB mean in SKF part numbering?
C marks CARB; 31 the dimension series; the size code gives 670 mm bore; KMB is the execution (tapered 1:12 bore for adapter (H) sleeve mounting, machined inner-ring-guided brass cage (MB)). The envelope follows ISO 15 and matches spherical roller bearing outlines, but the functions differ.
Why is C 31/670 KMB used opposite a spherical roller bearing?
The spherical bearing locates the shaft and takes thrust; the CARB bearing at the other end self-aligns but floats, absorbing thermal expansion without inducing axial load. The pair is standard on paper machine drying cylinders and long caster rolls.
Is the C 31/670 KMB sealed?
No, it is an open execution relying on the housing seals; relubrication follows the groove/hole features of the size.
Reviewed & verified by the MPN Base engineering desk against source catalog SKF PUB BU/P1 17000/1 EN (Oct 2018), ch. 10.1 CARB toroidal roller bearings on 2026-09-27. Read our editorial & correction policy.