Spherical roller bearings

01

Check load, life and allowable misalignment

NTN-SNR's spherical roller bearing catalogue gives the ISO 281 nominal life L10 = (C/P)^n with n = 10/3 for roller bearings, at 90% reliability, in millions of revolutions (or × 10⁶ ÷ 60N for hours). The equivalent dynamic load is P = Fr + Y1·Fa when Fa/Fr ≤ e, and P = 0.67Fr + Y2·Fa when Fa/Fr > e, with e, Y1 and Y2 from the bearing tables. It recommends not exceeding Fa/Fr = 0.3, a minimum radial load of 0.01 C0 to avoid roller slip, and static safety factors fs = C0/P0 of 1.5–3 for severe, 1–1.5 for normal and 0.5–1 for undemanding conditions. [1]

On misalignment, NTN-SNR allows a tilt of 0.5° under normal conditions where C/P exceeds 10, with a constant misalignment and rotating inner ring; a rotating outer ring or variable misalignment reduces this, and at low loads the tilt may reach 2°. It adds that below the ISO 281 fatigue load limit Cu a high-quality bearing can achieve a practically infinite life when lubrication and cleanliness are favourable. [1]

SKF's 21308 EKW (40 × 90 × 23 mm, tapered 1:12 bore) lists C = 107 kN, C0 = 108 kN, fatigue load limit Pu = 12 kN, e = 0.24, Y1 = 2.8, Y2 = 4.2, reference speed 7,000 r/min, limiting speed 9,500 r/min and mass 0.75 kg. [2]

Editorial calculation: with Fr = 8 kN and Fa = 0.8 kN on the 21308 EKW, Fa/Fr = 0.1 ≤ e, so P = 8 + 2.8 × 0.8 = 10.24 kN and C/P ≈ 10.4, just inside NTN-SNR's C/P > 10 condition for 0.5° tilt. L10 = 10.45^(10/3) ≈ 2,494 million revolutions, or about 41,600 hours at 1,000 rpm. [1] [2]

NASA's tutorial on rolling bearing life prediction (E. V. Zaretsky, NASA/TP-2013-215305/REV1, 2016) puts that catalogue life in context. It reports that 98% of 51 field and test ball and roller bearing sets reached lives equal to or greater than those predicted by the Lundberg-Palmgren equations with life adjustment factors; that roller bearings in 64 turboprop gearboxes showed a load-life exponent of 5.2; and that the ANSI/ABMA and ISO exponent of 10/3 is not reflective of modern roller bearings and will underpredict their lives. It also warns that a fatigue limit significantly overpredicts life over normal operating Hertz stresses, noting that ISO 281:2007 with a fatigue limit would give a life approaching infinity, so the practical risk becomes undersizing the bearing. [3]

Editorial calculation: for the 21308 EKW example at C/P ≈ 10.45, the ISO exponent of 10/3 gives L10 ≈ 2,490 million revolutions, while NASA's field exponent of 5.2 would give about 199,000 million — an 80-fold spread from the exponent alone, which is why a quotation should state the life method and whether Pu was used. [3] [2]

For condition monitoring of large bearings, a 2025 Politecnico di Torino study validated a multibody vibration model on its test rig for bearings of 280 to 420 mm outside diameter, which applies independent radial and axial loads of up to 200 kN through hydraulic actuators. The test bearing was an SKF 22240 CCK/W33 spherical roller bearing with a 200 mm bore, a 1:12 tapered bore and a 360 mm outside diameter; inner-race, outer-race and roller defects 2 mm in diameter and 0.5 mm deep were machined with a carbide drill, and the reported runs used a 124.8 kN radial load at a 710 rpm shaft speed. The model reproduced the characteristic inner- and outer-race fault frequencies, while amplitudes differed from the measurements; the authors did not simulate above 1,000 rpm. [4]

Editorial note: the 22240 CCK/W33 designation follows the same code pattern as the K (1:12 taper) and W33 (lubrication groove and holes) suffixes described above; when ordering for a monitored machine, give the supplier the bearing's speed and load so that fault frequencies can be calculated from its internal geometry. [4] [1]

Give the supplier the radial and axial loads (steady and peak), speed, required life and reliability, misalignment or shaft deflection, operating temperature, lubrication method, contamination, and the shaft and housing fits or mounting arrangement.

02

Choose internal clearance, bore and cage

NTN-SNR supplies bearings to ISO 492 normal precision with internal radial clearance to ISO 5753, tabulated separately for cylindrical and tapered bores. For an 80–100 mm bore, cylindrical-bore clearance is 60–100 µm for Normal and 100–135 µm for C3, while tapered-bore clearance is 80–110 µm for Normal and 110–140 µm for C3. Its designation codes K for a 1:12 taper and K30 for a 1:30 taper, and C2 to C5 for clearance groups smaller or larger than standard. [1]

For cages, NTN-SNR's ULTAGE (suffix E) designs use a drawn steel cage (EA), a glass-fibre reinforced polyamide cage (EG15) that must not be used above 150 °C, or a machined brass cage (EM) for the harshest applications; the steel is stabilised for use up to +200 °C, and outer-ring lubrication groove and holes are coded W33 or D1. NTN-SNR notes that 55% of bearing faults are due to lubrication defects. [1]

SKF describes its spherical roller bearings as self-aligning, carrying heavy loads in both directions, and usable in a modular system with housings, sleeves and nuts. [2]

03

Compare what suppliers offer

The suppliers linked to this page list spherical roller bearings; their cards link to the pages reviewed.

Ask any supplier for the full designation decoded (series, bore type, cage, clearance, lubrication features), the basic dynamic and static load ratings and fatigue load limit, e and Y factors, speed ratings, tolerance class, steel and heat treatment, and inspection or test records.

04

Trace the bearing parts

This is a functional reference built from the sources cited; it is not one maker's specification.

05

Fill the specification fields with values for your shaft

A spherical roller bearing quotation needs values for your application. The table explains each field, gives published values where a reviewed source states them, and says what to obtain from the supplier.

06

Send the load, speed and mounting data together

Paste it into your enquiry below or into an email to a maker, then replace every bracket.

Loads: [radial; axial; peak]
Speed and life: [rpm; required L10 or hours]
Misalignment: [angle or shaft deflection]
Mounting: [cylindrical or tapered bore; sleeve; fits]
Conditions: [temperature; lubrication; contamination]
Bearing: [clearance group; cage; seals]

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