ISO 12168-1:2019

Overview - ISO 12168-1:2019 (Hydrostatic plain journal bearings calculation)

ISO 12168-1:2019 defines a standardized calculation method for oil‑lubricated hydrostatic plain journal bearings without drainage grooves operating under steady‑state conditions. The document covers mathematical procedures to determine operational parameters (eccentricity, load‑carrying capacity, stiffness, required feed pressure, lubricant flow, frictional and pumping power, and temperature rise) and supports the design of the lubrication system including restrictor (e.g., capillary) data. Only bearings without oil drainage grooves between recesses are addressed.

Key technical topics and requirements

• Calculation basis and assumptions

  • Uses Reynolds‑equation‑based approximation (Hagen‑Poiseuille for pressure flow; Couette for drag flow).
  • Assumes laminar flow, incompressible Newtonian lubricant, full film lubrication, rigid surfaces and axial parallel clearance.
  • Applicable steady‑state range: relative eccentricity ε ≈ 0 to 0.5; bearing width/diameter B/D ≈ 0.3 to 1.
  • Lubricant feed from a common pump at constant system pressure via linear restrictors (capillaries).

• Primary calculation outputs

  • Load‑carrying capacity and stiffness
  • Lubricant flow rate, pumping power and restrictor sizing
  • Frictional power and total power (optimization of restrictor ratio)
  • Temperatures, viscosities and minimum recess pressures

• Design and boundary conditions

  • Recess pressure assumed constant over recess area.
  • Recess depth typically 10–100× clearance gap height.
  • Guidance to avoid low recess pressure (prevents air entrainment) and to ensure sufficient clearance under maximum load.
  • Annex A: approximation method; Annex B: worked calculation examples.

Practical applications and who uses this standard

• Applications

  • Design, verification and optimization of hydrostatic plain journal bearings for precision machinery (e.g., machine tools, high‑precision spindles).
  • Sizing of lubrication systems (pump pressure and restrictors), energy loss and thermal assessment, and layout of recess geometry.

• Intended users

  • Mechanical design engineers and tribologists working on journal bearings
  • Machine tool designers and rotating‑equipment specialists
  • Standards bodies, testing labs and OEMs requiring consistent calculation methods

Related standards

• ISO 12168‑2:2019 - Characteristic values for calculation of oil‑lubricated plain journal bearings without drainage grooves (normative reference cited by Part 1).

By following ISO 12168‑1:2019, engineers get a consistent, documented method for calculating and designing oil‑lubricated hydrostatic plain journal bearings, improving performance predictability for high‑precision rotating equipment.