Overview
ISO/TR 20051:2020 - Spherical plain bearings - Derivation of the load rating factors - is a Technical Report that provides the supplementary background and rationale for the load-rating factors referenced in ISO 20015. Rather than specifying new limits, this TR explains how the factors used to calculate static and dynamic load ratings for spherical plain bearings are derived from contact load distribution, geometry and material considerations. It clarifies the assumptions, symbols and integral formulations (Formulas 1–42) used to obtain the load-rating factors for different bearing types.
Key topics
- Purpose and scope
- Background information supporting the derivation of load-rating factors in ISO 20015.
- No normative references; intended as explanatory guidance for manufacturers and engineers.
- Bearing types covered
- Radial spherical plain bearings
- Angular contact thrust spherical plain bearings
- Angular contact radial spherical plain bearings
- Technical content & symbols
- Detailed symbol list (contact area A, diameters D/S, contact angle τ, effective widths C and μ, clearance parameter ε, manufacturing factor k, etc.).
- Load distribution functions p(θ,φ), axial and radial contact-stress functions p_a, p_r and related dimensionless functions g(·).
- Integral expressions that relate distributed contact stress to radial and axial load ratings (basis for Formulas (1)–(42)).
- Load-rating factors and calculation
- Derivation of factors f, f0, fr, fa (for static/dynamic, axial/radial ratings) as functions of geometry, material and manufacturing quality.
- Guidance on using nominal sizes, effective contact width μ, manufacturing tolerance factor k, and parameters such as ε and τ in engineering calculations.
- Annex
- Informative Annex A includes typical factor values for steel/steel contacting surfaces.
Applications
- Bearing manufacturers - to justify and derive product-specific load-rating factors consistent with ISO 20015.
- Design and mechanical engineers - to calculate or validate static and dynamic radial/axial load ratings when selecting spherical plain bearings for machines, automotive joints, hydraulic cylinders, linkages and heavy equipment pivots.
- Procurement and specification authors - to understand how manufacturer-supplied load ratings are derived and to set requirements in specifications.
- Test laboratories and quality engineers - to interpret manufacturer data, assess manufacturing accuracy impact (k factor), and compare bearings from different suppliers.
Related standards
- ISO 20015 - Primary standard for calculation of static and dynamic load ratings for spherical plain bearings; ISO/TR 20051 provides the derivation background and explanatory material that complements ISO 20015.
Keywords: ISO/TR 20051:2020, spherical plain bearings, load rating factors, ISO 20015, radial spherical plain bearings, angular contact thrust, axial load rating, dynamic load rating, bearing manufacturers.