Numerical Validation of Designed Aerostatic Bearing and Experimental Study with the Effect of Surface Roughness on its Performance

Abstract

Aerostatic bearing is an ultra-precision component that uses spindle surrounded by a thin film of air. The advantage of air lubrication is that it is frictionless as the viscosity of air is less and it is easily available. Due to its high accuracy, the demand of these components is very high in electronic, instrumentation, healthcare and other manufacturing or processing industries. The development of aerostatic bearing is mainly focused on better design and optimization techniques which leads to improvements in performance. This study is focused on the experimental determination of the effect of roughness parameter on the performance of the aerostatic journal and thrust bearing. In order to achieve this target, the aerostatic bearing is designed based on theoretical analysis available in the literature review on the improvement in performance of the aerostatic bearing with the geometrical parameters. The design is numerically investigated by simulation of airflow in ANSYS Fluent with computational fluid dynamics (CFD) module. The model of aerostatic bearing for the journal and thrust bearings are analyzed based on boundary conditions of fluid flow within the orifice and clearance. The results from the simulation are validated by the results generated for pressure distribution in previous researches. After the validation of the model, the manufactured components are assembled to the analyze the variation in radial and axial loads acting on the spindle with the spindle displacement (1-5μm) in the direction of the load at supply pressures (3-6bar) in the clearance of 30μm. In order to analyse the effect of roughness parameter, the value of average surface roughness of bearing and spindle surfaces are improved with cylindrical grinding and MR fluid-based finishing method. For each roughness reduction technique, the variation in axial and radial load acting on the spindle are determined with variation in spindle displacement. The experimental results showed that for journal bearing at 5µm displacement in spindle, the average change in load capacity due to improvement in roughness values is found to be 0.68N. Similarly, the effect of roughness on thrust bearing at same parameters on the average change in load carrying capacity is evaluated as 2.0N. The results determined for the surface finish parameter gives the experimental proof for the effect of surface characterization on the load carrying capacity of the aerostatic journal and thrust bearing. The current study on the aerostatic bearing is effective for the applications such as drives in production machines where the friction and surface properties are the major parameters of performance and efficiency.