On a PWM drive the bearing is part of an electrical circuit. A hybrid bearing with silicon nitride balls takes it out of that circuit. Electric Motors & Drives duty is continuous speed, long grease life and shaft voltages from PWM drives; the material is what decides whether the bearing survives it.
| Industry duty | 1,500–6,000 rpm continuous, up to 20,000 rpm on servo drives |
|---|---|
| Typical media | cooling air, dust, occasional washdown |
| Housing temperature | −20 to +120 °C |
| Material and grade | silicon nitride ceramic (hybrid) — Si3N4 |
| Hardness | 1500 HV |
| Temperature ceiling | 800 °C for the balls, rings limit the bearing |
| Corrosion / chemical | none — inert to water, acids and coolant |
| Relative cost | ≈8–15× of a standard 52100 bearing |
A variable-frequency drive puts a common-mode voltage on the shaft, and the bearing is the lowest-impedance path to earth. The discharge current melts the grease film and craters the raceway, producing the characteristic fluting pattern. Ceramic balls break that path because silicon nitride is an insulator, and their lower mass also cuts centrifugal load on the outer ring, which is what limits a steel ball at 12,000 rpm and above.
| Position | Bearing type | Material / finish | Why it works there |
|---|---|---|---|
| Non-drive end, VFD motor | Deep groove ball | Si3N4 hybrid, 52100 rings, C3, 2RS | Breaks the discharge path; steel rings keep the housing fit and the price sensible. |
| Servo / spindle drive end | Angular contact ball | Si3N4 hybrid, 70xx CD/P4, DB pair | Lower ball mass and lower friction let the pair run at dn values steel balls cannot reach. |
| High-speed blower | Deep groove ball | Si3N4 hybrid, PEEK or phenolic cage | At 20,000 rpm the cage and skidding are the limit; ceramic balls reduce both. |
| Material | Fit here | Choose it when |
|---|---|---|
| Si3N4 | Best fit | Voltage erosion or speed beyond the steel-ball limit, with a grounding ring at the other end. |
| 100Cr6 / 52100 | Workable alternative | If a shaft grounding ring already handles the current, 52100 does the same job for a tenth of the price. |
| M50 | Workable alternative | Heat rather than voltage is the problem — 315 °C ceiling at a fraction of the ceramic cost. |
Yes, and that is the usual arrangement. The hybrid end blocks the current; the other end carries it to earth through the frame. Fit a grounding ring on that shaft as well if the drive is above 30 kW.
The balls do — lower mass, lower friction, less heat generated at the contact. The bearing as a whole runs cooler by 10–20 °C at high speed, which is why preload stays stable.
No better than steel, and slightly worse: the ceramic ball cannot conform, so edge loading concentrates. Fix the alignment first.
Hardness, temperature, corrosion and equivalents for silicon nitride.
Read →Typical duty, recommended types and suffixes for electric motors.
Read →Standard duty — shaft ends and bearing housings in induction motors from 0.75 to 200 kW.
Read →Washdown & food plant — motors on washdown duty in food, beverage and pharmaceutical plant.
Read →Send the position, bore size, quantity and the medium it sees. We reply with the material certificate, clearance class, lubricant and price within 30 minutes on working days.