A robot joint rarely turns: it oscillates through a few degrees, millions of times, under a preload that must not change. Robotics & Automation duty is high cycle count, oscillating motion and zero tolerance for play; the material is what decides whether the bearing survives it.
| Industry duty | very high duty cycle, small oscillating displacements and stiffness demands |
|---|---|
| Typical media | clean air, occasional grease starvation at reversal points |
| Housing temperature | 0 to +60 °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 duty cycle in a robot is unusual: small displacements, high frequency, and a load that reverses at the same contact point. That combination starves the contact of lubricant and brinells a raceway long before the rating life is reached. Thin-section 52100 rings are used because the joint envelope is fixed and the stiffness has to come from the ring and the preload, not from the section.
| Position | Bearing type | Material / finish | Why it works there |
|---|---|---|---|
| Joint reducer output | Crossed roller bearing | 52100 thin-section, crossed roller, preloaded | Stiffness in a small section; preload removes play. |
| Harmonic drive flexspline support | Deep groove ball | 52100 thin-section, 2RS | Supports the flexspline with minimum section height. |
| Linear axis carriage | Linear guideway | 52100 rail and block, preloaded | Moment stiffness with recirculating balls. |
| Wrist joint | Deep groove ball | 52100 thin section, sealed for life | Light load, small envelope. |
| Material | Fit here | Choose it when |
|---|---|---|
| 100Cr6 / 52100 | Best fit | Standard joints where stiffness and envelope dominate. |
| Si3N4 | Workable alternative | Very high cycle rates where grease life, not load, ends the bearing. |
| 440C | Workable alternative | Cleanroom or washdown robots where a rust particle is a defect. |
Because the rating assumes rotation. In a joint the contact is loaded at the same spot repeatedly, the film never reforms, and brinelling or wear precedes fatigue.
It increases stiffness and reduces life. A joint is usually preloaded for accuracy, and the life calculation has to include that.
Crossed roller for moment stiffness in a compact section; thin-section ball for lower friction and cost where the moment is smaller.
Hardness, temperature, corrosion and equivalents for 52100 chrome steel.
Read →Typical duty, recommended types and suffixes for robotics.
Read →Cleanroom & washdown — cleanroom, pharmaceutical and food-handling robots.
Read →High cycle, no grease — high-cycle joints and vacuum or cleanroom axes where grease life limits the design.
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.