PNEUMATIC HIGH SPEED SPINDLE WITH AIR BEARINGS Terenziano RAPARELLI, Federico COLOMBO and Rodrigo VILLAVICENCIO Department of Mechanics, Politecnico di Torino Corso Duca degli Abruzzi 24, Torino, 10129 Italy (E-mail: terenziano.raparelli@polito.it) ABSTRACT This article describes different experimental tests performed on a pneumatic spindle with gas bearings in order to evaluate its maximum rotational speed and stability. In particular the rotor unbalance response, the power losses calculated from deceleration tests, the thermal transient due to viscous losses are calculated and analyzed. KEY WORDS Pneumatic Spindle, Air Bearings, Feed hole, Thermal transient INTRODUCTION These applications are related both to high precision devices, e.g. for measuring machines, both to high speed rotating machines, e.g. high speed spindles for operations of finishing or drilling. During the last fifty years the use of no contact air bearings in rotating ma- chines has been the object of interest by part of the researches in order to obtain bearings that support ro- tational speeds out of the range of conventional ball bearings [1]. Limitations on the maximum rotational speed are represented by centrifugal forces and by the well-know whirl instability of gas bearings. Nevertheless gas bear- ings enable to reach higher rotational speeds than rolling bearings, compared at the same diameter. Focusing the attention on the high rotational speeds, a broad spectrum of applications demand the use of gas bear- ings, in manufacturing industry (high speed machin- ing, printed circuit boards drilling, micro-milling and wafer dicing) and not only (high speed compressors and turbines). In the first case the high speed is aimed to obtain high quality surface finishing or the correct tangential cutting speed with micro-tools; in the sec- ond case it is due to a reduction of the dimensions of the turbomachines. The drawbacks of pneumatic bearings can be summa- rized in the following phenomena: the air-hammer [4], the unstable whirl [5][6], the relative low damping. All these problems must be solved to design such systems and obtain a stable operation of the rotor to contain its dynamic runout. 527 Proceedings of the 8th JFPS International Symposium on Fluid Power, OKINAWA 2011 Oct. 25-28, 2011 2B4-4 Copyright © 2011 by JFPS, ISBN 4-931070-08-6