Motion & Control No. 4 — 1998 42

NSK’s spherical roller bearing line-up has included thestandard CD type with pressed-steel cages and the high-capacity H type with plastic cages.

However, NSK recently introduced EA spherical rollerbearings which have the advantages of both types and,moreover, incorporate performance improvements makingthem the next generation of spherical roller bearings.

This article presents NSK’s new EA spherical rollerbearings.

1. Design Concept of EA Bearings

The newly conceptualized and designed interior of EAbearings (Photo 1) offers outstanding features which fulfillthe exacting requirements of today’s industry. (Patented inthe U.S.A., the U.K. and Germany. Patent pending inJapan.)

Fig. 1 compares the interior designs of EA and CDspherical roller bearings.

2. Features of EA Bearings

(1) High Capacity and Long LifeIn CD bearings, a guide ring controls roller movement.

However, this function in EA bearings is assumed by thecage, thus allowing the omission of the guide ring. Theoptimum design of the cage and inner and outer ringsprovides space for larger and more rollers. As a result, theload capacity is increased 10 to 20% and the bearing life isextended 30 to 80%.

Fig. 2 compares the load capacities of EA and CDbearings.

New Products

EA Spherical Roller Bearings

Photo 1 EA spherical roller bearing

EA bearing(NSK Patented)

CD bearing(NSK conventional design)

High load capacity• Larger roller size and increased roller quantity

Reduced heat generation and high limiting speed• Effective roller control by the center flanges of cages (guide ring function performed by cage)• Roller end face guided by cage protrusion

High-strength and low-wear cage• Well-balanced design• Roller-guided

Outer ring

Roller

Cage

Guide ring

Inner ring

400

300

200

100

22211 22212 22213 22214 22215 22216 22217 22218 22219 22220

Bearing numbers

Dyn

amic

load

rat

ing,

kN

EA

CD

Fig. 2 Dynamic load ratings of 222XX Series

Fig. 1 Bearing interior design comparison

43 Motion & Control No. 4 — 1998

(2) Low Temperature Rise and High Limiting SpeedThe cages for both rows, which contact and support each

other at the back face of the center flanges, have theirrotation maintained and guide the roller end faces withsupport from the flanges. The clearance tolerance of thecage is specified to be small so that the motion of therollers is precisely controlled and heat generation isminimized even without the guide ring used in previoustypes.

Due to the above and the optimum design of the rollersand outer and inner rings, the temperature rise of EAbearings is minimal. As a result, the limiting speed isgreatly increased compared to conventional sphericalroller bearings.

Fig. 3 compares the limiting speeds of EA and CDbearings. (3) High-strength and Low-wear Cage

Effectively using the space vacated by the guide ring, astrong and well-balanced cage was created throughdetailed study of optimum cage design using structuralanalysis. A severe test of the strength of these cages hasshown their toughness and durability.

Fig. 4 shows EA and CD cage strength test results.The high accuracy and resulting drastic reduction in

cage wear of these roller-guided pressed cages was madepossible by improvements in press processing technology. (4) High-temperature Specifications

Special heat treatment for the outer and inner rings isstandard and the bearing can be used up to 200°C.

The maximum operating temperatures are as follows:EA ··········································200°CCD ··········································120°CH ·············································120°C

3. Conclusion

New EA spherical roller bearings are tough, high-capacity bearings which were created incorporatingadvanced analysis technology, press processingimprovements, and severe evaluation tests. As a result,the bearings represent the next generation of sphericalroller bearings for CD and H-type replacements. Massproduction of these bearings is under way at NSK as welook to increase their sales in various industries.

22211 22212 22213 22214 22215 22216 22217 22218 22219 22220

6000

5000

4000

3000

2000

Bearing numbers

Lim

iting

spe

ed, r

pm

EA

CD

Fig. 3 Limiting speed of 222XX Series with oil lubrication

NSK CD-1

CD-2

NSK EA-1

EA-2

EA-3

0 2 4 6 8 10

0.15

0.15

5.5

9.5

6

Test bearing: 22220

Cycles until cage failure, × 106

Shock acceleration: 180 GRadial Load: 19 600 N (2 000 kgf)

Fig. 4 Results of cage strength test