Porous Aerostatic Thrust Bearing Key Technologies

With high precision and free from friction and pollution, aerostatic bearing is one of the essential elements of the precision and ultra-precision facilities.As the precision and ultra-precision technologies are developing in leaps and bounds, continuous improvements are also required in the stiffness, accuracy and stability of aerostatic bearings.Compared with conventional orifice compensated aerostatic bearings, porous aerostatic bearings have better load capacity, damping and stiffness, which has already attracted the attention and interest of scholars at home and abroad. And research on the measurement of porous material permeability as well as methods of calculating and measuring the static performances of porous aerostatic bearings are the very difficult spots and challenges of this field. This article is just developed around such front question, aiming to explore how to measure the permeability of porous material, and how to calculate and measure the static performances of porous aerostatic bearings. The main missions of the paper are as follows:(1)This paper has founded the mathematical model and proposed a measuring method for the permeability of isotropy porous graphite, taking into account the compressibility of gas and the existence of inertial loss when gas is flowing through porous media. It has also set up the experimental facility, measuring the volume flow values under different supply gas pressures, and the viscous permeability and inertial permeability of the tested porous graphite have been calculated according to this series of data. Moreover, this kind of measurement has been approved to be feasible by test results.(2)Based on the actual working conditions of aerostatic bearings and some reasonable assumptions, it has expounded the mathematical models of the static performances for entire porous compensated gas bearing and partial porous compensated aerostatic bearing using three-dimensional fundamental fluid governing equation.(3)This paper has carried out three-dimensional numerical simulation for entire porous compensated aerostatic bearing and partial porous compensated gas bearing with C.F.D. software FLUENT, analyzing how the restrictor structure parameters, the characteristic parameters of porous media and the parameters of operating condition influence the static performances of porous aerostatic bearings.And the curve of load capacity and stiffness variation with gas film thickness has been produced. Meanwhile, the design suggestions for the two kinds of aerostatic bearings have also been summarized. (4) This paper has conducted other experiments on the self-designed measuring platform, measuring the static performances of all the three compensated kinds of aerostatic bearings. And the measurement has also turned out to be practical through comparison between the simulation and experiment results.Both the results indicate that when the gas film thickness is distributed in the scope of 3μm and 5μm, the static stiffness value of the entire porous graphite aerostatic bearing can be more than 70 N/μm if the porous graphite restrictor is one with the viscous permeability of 7.877×10-15 m2, with the thickness of 10 mm,and with the diameter of 45mm, with the pressure supply of 0.5MPa. Compared with the static stiffness values of orifice compensated aerostatic bearing and partial porous compensated gas bearing with the same diameter of working surface, the entire porous aerostatic bearing has shown higher static stiffness, it has the bright application prospects.To sum up, it has provided the significant support to the application of porous graphite aerostatic bearings through research on the measurement of porous graphite permeability and analysis on the static performances of porous aerostatic bearings.