ISO 20056-2:2017

Overview

ISO 20056-2:2017 - Rolling bearings: Load ratings for hybrid bearings (Part 2: Static load ratings) specifies methods for calculating static load ratings of hybrid rolling bearings whose rings are made of high‑quality hardened bearing steel and whose rolling elements are silicon nitride (Si3N4). The standard defines calculation procedures, contact stress limits and guideline safety factors for bearings with contemporary materials and manufacturing quality. It is intended for hybrid bearings with ceramic rolling elements having a modulus of elasticity of about 300 000 MPa or higher.

Key topics and technical requirements

• Scope and applicability: Applies to hybrid bearings with steel raceways and Si3N4 rolling elements; for ceramics with lower modulus, ISO 76 rules apply.
• Static contact stress limits: Defines permissible Hertzian contact stresses used to derive the basic static load ratings (e.g., 4 600 MPa for ball bearings and 4 200 MPa for roller bearings in the specified material range).
• Calculation methods: Prescribes formulae for basic static radial and axial load ratings for:
  • radial ball bearings (including self‑aligning)
  • thrust ball bearings
  • radial roller bearings
  • thrust roller bearings Formulae and factors (f, X, Y, Z, etc.) are provided in Clause 5 and supported by Annex A (Hertzian parameters) and Annex B (guide values of f).
• Static equivalent load: Guidance for computing static equivalent radial/axial loads using established factors (Clause 6), consistent with ISO 76 methodology.
• Static safety factor (S0): Recommends guideline S0 values for different operating conditions (Clause 7, Tables 1 & 2) to ensure adequate margin against permanent deformation.
• Informative annexes: Annex A (Hertzian calculations), Annex B (factor guidance), Annex C (discontinuities in calculations), Annex D (material properties/classification).

Applications

ISO 20056-2:2017 is used to ensure reliable bearing selection and safe design where static loading and minimal plastic deformation are critical. Typical applications:

• High‑speed spindles and electric motors where hybrid bearings reduce inertia and improve performance
• Aerospace and defence components requiring lightweight/temperature‑resistant rolling elements
• Machine tools, precision instrumentation and robotics where contact deformation limits affect accuracy
• Automotive and EV drivetrains using hybrid bearings for higher speed capability

Who should use this standard

• Bearing designers and manufacturers
• Mechanical and tribology engineers performing bearing selection and life/safety calculations
• OEMs specifying bearings for equipment design
• Test laboratories and quality assurance teams verifying static capacity

Related standards

• ISO 76:2006 (Static load ratings - general rules)
• ISO 5593 (Rolling bearings - Vocabulary)
• ISO 26602, ISO 3290‑2 (ball material/quality)
• ISO 12297‑2 (roller specifications)

Keywords: ISO 20056-2:2017, hybrid bearings, static load ratings, silicon nitride, Si3N4, rolling bearings, static safety factor, Hertzian contact stress.