Fabrication And Performance Control Of Aerostatic Bearings Based On Porous Ceramics

Aerostatic bearing is a type of sliding bearing with gas as lubricating medium,which uses the pressure accumulated by compressed air in bearing clearance to support the bearing.The bearings have been widely applied in precision machining,precision detection,aerospace and other fields due to the advantages of high motion accuracy,long service life,no pollution and low friction loss.Porous aerostatic bearings have better bearing capacity,stiffness and stability.Porous ceramic material is considered to a better material as the porous restrictor for aerostatic bearing due to its unique structural characteristics,which is one of the research hotspots in the field of bearing in recent years.Aiming at the frontier topic,the aerostatic bearing based on porous ceramic was devised and prepared.The theoretical model of static characteristic of the bearing was established.Fluent was used for simulation calculation.A static characteristic experimental platform was built to test the static characteristics of the bearing.The main research contents are as follows:In this study,a structural design and preparation scheme of porous ceramic based aerostatic bearing was proposed.Based on the principle that the gas flow in porous restrictor follows Darcy’s law and the flow in bearing clearance satisfies the principle of Navier-Stokes equation,a theoretical model of porous aerostatic bearing was established.The theoretical equation for calculating the static characteristics of porous aerostatic bearing was derived.Porous alumina ceramics were prepared by solid phase sintering method with alumina as raw material and polystyrene microspheres as pore-forming agent.The effects in the particle size of pore-forming agent on the microstructure and mechanical properties of porous alumina ceramics were explored.The results show that the larger the particle size of pore-forming agent,the larger the pore structure,but the lower the mechanical properties.With 20 wt.%of PS50,the optimum porous alumina ceramic achieved a porosity of 11.8%,an average pore size of 17.8μm,and a bending strength of 150.4 MPa.Porous alumina ceramic was used as the restrictor of aerostatic bearing.Both simulation and experiment proved that optimizing the pore structure of ceramics can improve the bearing capacity of bearings.The porous Si C ceramic prepared by reactive sintering,with a porosity of 25.8%and a pore size of 20.55μm,was used as the restrictor to fabricate the aerostatic bearing.Through the permeability experiment,it is found that the ceramic has good permeability,which reaches to 2.78×10^-13mm².The static characteristics of bearings were simulated by using the fluid dynamics simulation software Fluent.The pressure distribution and velocity distribution of the gas in the porous medium and the gas film gap were analyzed.The bearing capacity,static stiffness and gas flow rate of the bearing were solved.At the same time,the factors affecting the static characteristics of porous aerostatic bearings were explored.The influence of working condition parameters and porous medium characteristic parameters on the static characteristics of the bearings with the change of gas film clearance is analyzed.The experimental platform for the static characteristics of the bearing was constructed to research the static characteristics of the porous ceramic-based aerostatic bearing.The experimental results were compared with the Fluent simulation results to verify the accuracy of the simulation calculation.