Design and Fabrication Errors of Foil Bearings: A Review

Abstract

Aerodynamic gas foil bearing (GFB) is a self-acting hydrodynamic bearing that used ambient air as a working fluid to carry small turbomachinery with medium load capacity. The compliant structure of foil bearings provides more reliability to a high-speed rotating system. The thin flexible structure of top foil and bump foil assists the foil bearings to accommodate shaft misalignment with better stiffness characteristics. Due to frictional interactions, the GFBs also provide coulomb damping with nonlinear behavior. As a consequence, the complexity of GFBs is increased. With compliant structure, the foil bearings offer many advantages such as the capability to operate at high speed with elevated temperature, longer service life (due to air lubricant), and less operating cost. But there are some limitations of GFBs, i.e., high friction loss at low speed. Due to small and complex structure, the manufacturing process of FBs is large and slightly challenging. As a consequence, many undesirable manufacturing errors are developed in FBs design such as foil thickness error, bump pitch error, and bump height error. This paper reviews the present research related to manufacturing techniques which are used for developing the compliant corrugate shape of foil bearings. These manufacturing techniques are blanking–punching, metal cutting, etc. To overcome these manufacturing errors and make the fabrication process of the FBs with more accurate, heat treatment and quenching process are also used. Currently, the advanced manufacturing technique such as rapid prototyping is used to avoid any error and developing accurate foil bearings.