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Meccanica

, 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
Article

Abstract

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.

Keywords

Discharge coefficient High-speed spindle Gas bearings Lubrication 

Abbreviations

b

Ratio of critical pressure to admission pressure

cd

Discharge coefficient of supply orifice

cs

Conductance of supply orifice

ds

Diameter of supply orifice

e

Radial journal center displacement

h

Film thickness

h0

Journal bearing average radial/axial clearance

kT

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

L

Length of bearing

m

Mass of shaft

p

Pressure

pc

Port downstream pressure level

q

Mass flow rate through supply port per unit surface

r

Radial coordinate

R

Journal radius

R0

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

Re*

h02 modified Reynolds number

S

Cross-section of supply port

t

Time

T0

Absolute temperature, in calculations 288 K

u,v

Mean velocity components in z- and -direction

x,y,z

Cartesian coordinates

ε

Eccentricity ratio

μ

Dynamic viscosity

ρN

Air density in normal conditions

ϑ

Angular coordinate

ω

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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