ISO 281:2007

Overview

ISO 281:2007 - Rolling bearings - Dynamic load ratings and rating life - defines standardized methods for calculating basic dynamic load ratings and rating life for rolling bearings. The standard covers bearings made from commonly used high‑quality hardened bearing steel, of conventional design, and produced according to good manufacturing practice. It provides methods to compute the basic rating life (life at 90% reliability), the modified rating life (accounting for different reliabilities and operating conditions), and the basic dynamic radial/axial load ratings used in life prediction.

Key Topics

• Basic dynamic load rating (Cr, Ca): definition and calculation for radial and axial bearings; the load a bearing can theoretically endure for a specified reference life (document gives the established reference of one million revolutions for the dynamic rating definition).
• Basic rating life (L10): life associated with 90% reliability under conventional operating conditions and good manufacturing quality.
• Modified rating life: methods to adjust life predictions for:
  • different reliability levels (extended to 99.95%),
  • lubrication condition (viscosity ratio, film parameter),
  • contaminated lubricant (contamination factor),
  • bearing fatigue load limit and other system factors.
• Dynamic equivalent load: converting complex/load-varying conditions into an equivalent constant radial or axial load for life calculations.
• Limits and exclusions: ISO 281:2007 does not cover effects of wear, corrosion or electrical erosion and is not applicable where rolling elements run directly on shaft/housing surfaces unless those surfaces are fully equivalent to raceways.
• Symbols and definitions: standardizes terminology (life, reliability, fatigue load limit, roller geometry, contact angle) and symbols used in calculations.

Applications

ISO 281:2007 is used by:

• Bearing manufacturers for rating tables and product data.
• Design and mechanical engineers for bearing selection, load and life estimation in machinery (gearboxes, motors, conveyors, automotive and industrial equipment).
• Reliability and maintenance engineers for service-life forecasting, preventive maintenance planning, and risk assessment.
• Procurement and standards specialists to specify bearing performance and acceptance criteria.

Practical uses include bearing selection based on expected loads and operating conditions, estimating service intervals, comparing bearing types, and assessing the impact of lubrication and contamination on bearing life.

Related Standards

• ISO 76 - Rolling bearings: Static load ratings
• ISO 5593 - Rolling bearings: Vocabulary
• ISO 15241 - Rolling bearings: Symbols for quantities
• ISO/TR 8646, ISO/TR 1281 series - Explanatory/technical background
• ISO/TS 16281 - Advanced life calculations (clearance and misalignment effects)

Keywords: ISO 281:2007, rolling bearings, dynamic load rating, rating life, basic rating life, modified rating life, reliability, lubrication, contamination, fatigue load limit.