Design And Structural Parameter Optimization Of Compound Throttling Aerostatic Bearing

Aerostatic thrust bearing is widely used in ultra-precision machining and measuring equipment benefits from its advantages of high speed,ultra-precision and negligible friction.However,the rapid development of machining and measuring technologies need the bearing to be high LCC,high stiffness and better stability.Many literatures focused on the restricting techniques because restrictor is one of the crucial components determining the bearing performance.Aerostatic thrust bearing is usually restricted by pocketed restrictor,inherent restrictor,slot restrictor or porous restrictors.However,the bearing with pocketed orifice-type restrictor inclines to produce gas hammer,which seriously affect the bearing stability.Although the bearing with inherently orifice restrictor has better stability,LCC and stiffness of the bearing are low.Aerostatic bearing with slot restrictor has good performance in stiffness and stability.However,it is difficult to be manufactured.Compared with traditional throttling methods,porous throttling has the advantages of high LCC and high stiffness.However,in porous materials,the pore distribution is irregular and uneven,which makes the fluid flow and its boundary conditions very complex.In view of the above problems,this paper designs and studies a compound throttling aerostatic bearing,and mainly completes the following aspects:(1)A compound aerostatic thrust bearing is proposed to fully exploit the characteristics of the bearing with pocketed orifice-type restrictors,non-blocking and high LCC and stability of bearing with porous restrictor.(2)FLUENT software is used to analyze the pressure distribution and the flow field in the gas film of compound throttling aerostatic bearing.Large eddy simulation was used to analyze the stability of compound throttling aerostatic bearing,and its stability and static performance were compared with traditional aerostatic bearing.It is indicated that the bearing with compound restrictors has better stability than that of with multi-orifice restrictor.Moreover,LCC and stiffness of the bearing with compound restrictors are much higher than that of with porous restrictor or that of with multi-orifice restrictor if film thickness is in rational range.(3)The influences of supply pressure,orifice number,orifice diameter,orifice distribution,porous thickness and porous permeability coefficient on the bearing performance are analyzed.Moreover,given the optimal design scheme,the structural parameters of the bearing with the best LCC and stiffness are obtained.(4)Further,the dynamic performance of the bearing is studied.The results show that the dynamic performance of bearings increases first and then decreases with the increase of rotational speed.When the bearing speed reaches 105,000 revolutions per minute,the bearing capacity reaches its maximum.(5)The processing of compound throttling aerostatic bearing was completed.The bearing performance was tested and compared with simulation results.The results show that the experimental results are in good agreement with the simulation results.