ISO 15312:2018 PDF

Overview

ISO 15312:2018 - Rolling bearings - Thermal speed rating - Calculation - defines the thermal speed rating for oil-bath lubricated rolling bearings and specifies calculation principles to determine this parameter. The thermal speed rating is the shaft or washer rotational speed at which heat generated by bearing friction equals heat emitted through the bearing seating under defined reference conditions. The standard applies to standard-design bearings (or designs that are frictionally equivalent). Thrust ball bearings are excluded.

Key topics and technical requirements

• Definition of thermal speed rating and its role as a thermal limiting criterion (mechanical/kinematic limits are outside its scope).
• Reference conditions - fixed conditions used for calculations:
  • Reference temperature (outer ring/housing): 70 °C; ambient: 20 °C.
  • Reference lubrication: oil-bath up to the center of the lowest rolling element; mineral oils without EP additives with kinematic viscosities of 12 mm²/s (ISO VG 32) for radial bearings and 24 mm²/s (ISO VG 68) for thrust roller bearings.
  • Reference load: 5% of basic static radial load rating C0r for radial bearings, and 2% of basic static axial rating C0a for thrust roller bearings.
• Heat-emitting reference surface area (Ar) - specified formulas per bearing type (radial, tapered, thrust cylindrical/needle, thrust spherical) to represent conduction areas through shaft and housing.
• Reference heat flow density (qr) - empirical q values provided (e.g., 0.016 W/mm² for radial and 0.020 W/mm² for thrust where ΔT = 50 °C) and curves for scaling with larger Ar.
• Calculation principle - energy balance: frictional heat generated at the thermal speed rating equals heat emitted. Frictional losses are decomposed into load-independent and load-dependent components using coefficients f0r and f1r (mean values and guidance in Annex A). Annex B gives explanatory notes; Annex C covers grease-reference conditions chosen to match oil-bath thermal ratings.

Applications and practical value

• Determine maximum operating speeds limited by bearing heating in motors, gearboxes, machine spindles and high-speed rotating equipment.
• Compare bearing types and sizes for high-speed suitability using a consistent thermal criterion.
• Assist in bearing selection, lubrication specification, and thermal management (shaft/housing design, heat dissipation area).
• Useful for OEM design engineers, bearing manufacturers, tribologists, reliability/maintenance engineers and standards authors.

Related standards

Normative references cited by ISO 15312:2018 include ISO 76, ISO 1132‑1, ISO 5593, ISO 5753‑1, and ISO 15241, which cover load ratings, terminology, internal clearance and symbols.