Externally Pressurized Gas Journal Bearings with Asymmetric Gas Supply (Verification of Availability of Gas Pressure Control using a Small Size Test Rig)

Abstract

Externally pressurized gas journal bearings with an asymmetric gas supply mechanism have been developed by authors. This bearing has a large load capacity compared with conventional symmetric gas supply bearings because low and high pressurized gases are supplied to loaded and counter-loaded side bearing surfaces, respectively. It has been proposed that this type of bearing has advantageous characteristics applicable for use in a general purpose X-ray computed tomography scanner gantries. The adaptation of this gas bearing to the device can conceivably contribute to an improved performance by increasing the rotational speed and decreasing the operating noise. This is effective for higher precision scanning and for reduction of the level of stress on a patient. Numerical calculations of this bearing were conducted and the resulting characteristics were compared with those of a conventional symmetric supply gas journal bearing. The effectiveness of the bearing for this application was demonstrated by conducting rotation tests using a small size test rig. The rotor generates centrifugal force by the rotation. The bearing diameter and length were 60 and 120 mm, respectively. The test bearing was operated under several supply gas pressure controlled conditions. The rotor vibration amplitude can be decreased by supply pressure control under generating the centrifugal force condition. The amplitude increased under conventional symmetric gas supply conditions with an increase in rotational frequency. Therefore, effectiveness and safeness of the bearing was experimentally verified. The gas flow rate decreased under controlled supply pressure conditions compared with conventional supply pressure conditions.