Most motor bearings are 52100, and that is not a compromise: the grease-life calculation the motor was rated on assumes this steel. 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 | through-hardened chrome steel — 100Cr6 / 52100 |
| Hardness | 59–65 HRC |
| Temperature ceiling | 120 °C (200 °C stabilised) |
| Corrosion / chemical | none — rusts without protection |
| Relative cost | 1.0× of a standard 52100 bearing |
The bearing in a motor is rarely load-limited. It is grease-life and noise limited, and 52100 is the grade those two limits were written around: a fine, homogeneous structure takes a mirror finish, which keeps the vibration level low, and the through-hardened ring holds its fit on an aluminium end shield without yielding. The material question only becomes interesting when the housing passes 120 °C or the drive puts a voltage on the shaft.
| Position | Bearing type | Material / finish | Why it works there |
|---|---|---|---|
| Drive end (locating) | Deep groove ball | 52100, CN or C3, 2Z / 2RS | Takes the residual axial load from the rotor and any belt pull, and fixes the shaft position. |
| Non-drive end (floating) | Deep groove ball | 52100, C3, one side shielded | Outer ring is free to creep axially, so thermal growth of the shaft does not preload the pair. |
| Large frame, belt drive | Cylindrical roller | 52100, NU type, C3 | Radial capacity for belt pull; NU floats, so no axial load crosses the bearing. |
| Brake motor, tail end | Deep groove ball | 52100, C3, 2RS | Keeps grease in and brake dust out of the raceway. |
| Material | Fit here | Choose it when |
|---|---|---|
| 100Cr6 / 52100 | Best fit | Cost, capacity and noise are all best in class below 120 °C. The default. |
| Si3N4 | Workable alternative | VFD-driven motors where shaft voltage erodes the raceway, or speed × bore beyond the steel-ball grease limit. |
| 440C | Workable alternative | Washdown motors in food plant, where a rust film on the rings would contaminate the line. |
In a locating position the outer ring is stationary and takes the fit load, so the same spot passes under the ball every revolution. Electrical discharge and false brinelling from standstill vibration both show up there first.
Not in a motor with an aluminium end shield. The housing expands more than the steel ring, clearance is lost, and the bearing runs preloaded and hot. Keep the class, or measure the fits and let us recalculate.
They stop the discharge through that bearing, because the ceramic ball insulates the rotor from the frame. The voltage still exists and finds another path, so one hybrid end plus a shaft grounding ring is the reliable combination.
Hardness, temperature, corrosion and equivalents for 52100 chrome steel.
Read →Typical duty, recommended types and suffixes for electric motors.
Read →Washdown & food plant — motors on washdown duty in food, beverage and pharmaceutical plant.
Read →VFD & high speed — VFD-driven motors and high-speed servo spindles where shaft voltage erodes the raceway.
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.