ISO 7902-3:2020

Overview

ISO 7902-3:2020 - "Hydrodynamic plain journal bearings under steady-state conditions - Circular cylindrical bearings - Part 3: Permissible operational parameters" specifies empirical limits and assessment methods for the operational parameters that ensure reliable tribological performance of circular cylindrical (plain journal) bearings. The standard defines how to evaluate minimum lubrication film thickness, effective waviness, maximum permissible specific bearing load and bearing temperature, and gives guidance on bearing clearance. It complements the calculation procedure in ISO 7902-1 and is intended to prevent wear, mechanical damage and thermal degradation.

Key topics and requirements

• Minimum permissible lubricant film thickness (h_lim):
  • Formula-based determination that accounts for surface roughness (Rz), misalignment and deflection.
  • Empirical tables provide practical h_lim values (typical range ~3 µm to ~18 µm depending on shaft diameter and peripheral speed).
  • Notes on running-in, filtration and material selection to reduce wear risk.
• Effective waviness (h_wav,eff) and limits:
  • Methods (figures and coefficients E, G) to evaluate waviness influence for the most unfavorable shaft position.
  • Procedure to determine maximum permissible effective waviness and absolute waviness.
• Maximum permissible specific bearing load (p_lim):
  • Empirical load limits by bearing material group (examples: Pb/Sn and Cu-based alloys; values typically of order MPa; see Table 3 for material-specific guidance).
  • Guidance on starting loads and when hydrostatic assist may be required.
• Thermal limits (T_lim):
  • Maximum permissible bearing temperatures depend on bearing material and lubricant; tables give empirical values for different lubrication regimes and oil flow ratios.
  • Emphasis on viscosity loss, lubricant ageing (>80 °C) and reduced load capacity at elevated temperatures.
• Bearing clearance (ψ):
  • Provides an empirical sizing approach and a preferred series of mean relative clearances (0.56‰ to 3.15‰) to balance temperature and hydrodynamic performance.
• Practical assessment aids: Figures, worked examples and empirical tables to apply limits in design and verification.

Applications

• Design and specification of hydrodynamic plain journal bearings for engines, gearboxes, turbines, pumps and rotating machinery.
• Bearing selection, tolerance/clearance definition and lubrication system design.
• Condition assessment, maintenance planning and failure prevention (wear, seizure, thermal degradation).
• Use in calculations and simulations that follow ISO 7902-1 for steady-state bearing performance.

Who uses this standard

• Mechanical engineers, bearing designers and tribologists
• Machine manufacturers and component suppliers
• Maintenance and reliability engineers
• Test laboratories and standards/quality personnel

Related standards

• ISO 7902-1 (Calculation procedure for circular cylindrical plain journal bearings) - normative reference.
• Material and bearing-specification standards referenced in the document (e.g., ISO 4381, ISO 4382 series).

Keywords: ISO 7902-3:2020, hydrodynamic plain journal bearings, circular cylindrical bearings, permissible operational parameters, lubrication film thickness, waviness, bearing load, bearing temperature, bearing clearance, bearing design, tribology.