ISO 31657-4:2025

Overview

ISO 31657-4:2025 specifies permissible operational parameters - given as guide values - for calculating selected multi‑lobed and tilting‑pad hydrodynamic plain journal bearings under steady‑state conditions. The standard supports safe start‑up/run‑down behavior, avoidance of thermal and mechanical overloading, and selection of bearing clearances and lubricant-related limits. It complements ISO 31657‑1 (calculation methods) by defining empirical limits and practical guide values used in bearing design and verification.

Key topics and technical requirements

• Operational guide values for start‑up and run‑down: Guidance to ensure the operational characteristic (lubricant film thickness h) remains safely above permissible minima during transient conditions. The standard provides empirical guide values and limiting curves linking sliding speed and specific bearing load at the transition to mixed friction. Notably, the circumferential speed at transition to mixed friction is recommended not to exceed 2 m/s under normal run‑down.
• Minimum lubricant film thickness and transition criteria: Methods and figures relate minimum film thickness to journal/bearing surface roughness, misalignment and deformation. These values determine required lubricant cleanliness and filtration.
• Avoiding thermal and mechanical overload: Temperature‑dependent maximum admissible lubricant film pressures are given for common bearing material groups (lead, tin and copper alloys). The standard notes that pressure limits depend on operating temperature and bearing construction (e.g., composite layer thickness).
• Bearing clearance and profile guidance: Guidance on selecting clearance, profile factor or gap ratio to balance guiding accuracy, cooling and load capacity. The standard states relative clearance should account for shaft diameter and rotational speed, and gives formulas and charts for optimization.
• Lubrication and ageing considerations: Multi‑lobed and tilting‑pad bearings are typically forcibly fed; lubricant circulation time and thermal loading affect lubricant ageing and selection.

Applications and users

ISO 31657-4:2025 is intended for:

• Bearing designers and mechanical engineers designing hydrodynamic plain journal bearings (multi‑lobed and tilting‑pad)
• Rotating machinery OEMs, tribologists, maintenance and reliability engineers who assess start‑up/shut‑down safety, bearing life and lubrication systems
• Specification writers and procurement teams requiring standardized guide values for performance verification and acceptance testing

Practical uses include verifying design calculations from ISO 31657‑1 against permissible limits, selecting clearances and lubricants, specifying filtration and hydrostatic jacking for critical start/stop conditions, and preventing thermal/mechanical overload.

Related standards

• ISO 31657‑1:2025 - Calculation methods for multi‑lobed and tilting‑pad journal bearings
• ISO 31657‑2 / ‑3 - Characteristic values for multi‑lobed and tilting‑pad bearings
• ISO 4381 / 4382 / 4383 - Material standards for bearing alloys

Keywords: ISO 31657-4, plain bearings, hydrodynamic plain journal bearings, multi-lobed bearings, tilting‑pad bearings, permissible operational parameters, lubricant film thickness, bearing clearance, start‑up run‑down, bearing load.