, Volume 43, Issue 6, pp 591–600 | Cite as

High-speed electrospindle running on air bearings: design and experimental verification

  • G. Belforte
  • F. Colombo
  • T. Raparelli
  • A. Trivella
  • V. Viktorov


In high-speed machining there are a number of applications in which the spindle is supported by air bearings. This type of bearings has very low friction and wear, resulting in virtually unlimited life. If the system is designed correctly the radial stiffness on the tool is comparable to that of ceramic ball bearings.

A mathematical model of rotor-air bearing system and experimental work on high-speed spindle for machining applications are presented. The model is numerically solved paying special attention to boundary condition of supply ports. The discharge coefficient c d is considered on the basis of experimental findings. The influence of clearance and supply port diameter is discussed for radial bearings and axial thrust bearings. The aim is to find an optimum solution representing the compromise between high stiffness, supply flow and stability.

The prototype of a high-speed electrospindle running on air bearings is described. The rotor, 50 mm in dia. and weighing 7 kg, is designed for 100 krpm. The spindle is driven by a high frequency asynchronous motor featuring closed loop speed control. Experimental stiffness curves are shown at different supply pressure ratings.


Discharge coefficient High-speed spindle Gas bearings Lubrication 



Ratio of critical pressure to admission pressure


Discharge coefficient of supply orifice


Conductance of supply orifice


Diameter of supply orifice


Radial journal center displacement


Film thickness


Journal bearing average radial/axial clearance


\(\sqrt{293/T^{0}}\) temperature coefficient


Length of bearing


Mass of shaft




Port downstream pressure level


Mass flow rate through supply port per unit surface


Radial coordinate


Journal radius


Gas constant, in calculations R 0=287.6 m2/s2 K


h02 modified Reynolds number


Cross-section of supply port




Absolute temperature, in calculations 288 K


Mean velocity components in z- and -direction


Cartesian coordinates


Eccentricity ratio


Dynamic viscosity


Air density in normal conditions


Angular coordinate


Angular velocity of rotor


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Copyright information

© Springer Science+Business Media B.V. 2008

Authors and Affiliations

  • G. Belforte
    • 1
  • F. Colombo
    • 1
  • T. Raparelli
    • 1
  • A. Trivella
    • 1
  • V. Viktorov
    • 1
  1. 1.Dipartimento di MeccanicaPolitecnico di TorinoTorinoItaly

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