磁悬浮轴承系统通常采用滚动轴承作为保护轴承。基于传热学、滚动轴承摩擦学以及转子动力学等理论,建立一种用两个滚动轴承组成的双层保护轴承(Double-decker auxiliary bearing,DDAB)的热学模型,通过建立热传递方程,计算轴承的摩擦热和温度分布,研究DDAB的热学特性。研究内容如下:建立双层滚动轴承(Double-decker rolling bearing,DDRB)的热传递模型,推导热传递阻抗和热传递方程,计算DDRB在普通运转条件下达到热平衡时的温度分布;研究不同结构、载荷、转速、润滑剂粘度、材料属性等参数对轴承温升的影响,并对比其与普通轴承在相同工况下的热学特性;建立试验台,实际测量轴承的温升,研究不同结构形式和润滑参数条件对于轴承热学特性的影响,探讨可以降低发热的主要措施。研究结果表明:DDRB的径向载荷和内圈转速直接影响轴承摩擦力矩的大小进而影响轴承的发热,在相同工况下DDRB比普通滚动轴承的内圈温升要小5%～20%,外圈温升要小10%～30%;结构、润滑剂粘度、材料的热学性能对轴承内外圈温度分布影响较大,润滑剂的填装量在轴承空间的1/3,采用Z形结构、铝制中圈、陶瓷滚动体等可以使轴承在高速运转下获得较好的热学特性和较低的温升。
Thin silver films are deposited by radio frequency magnetron sputtering on glass ceramic at room temperature.Variations of sputtering power,bios voltage and power density are carried out for each deposition,then parts of as-deposited samples are subjected to annealing at 600 ℃ within a vacuum chamber.Structural properties are studied by X-ray diffraction(XRD),scanning electron microscope(SEM)and laser scanning confocal microscope(LSCM).It is shown that structural properties have a strong dependency on sputtering power and annealing temperature.Electrical contact resistance measured by a four point probe instrument is directly affected by the thickness of films.It is also found that the film conductivity,especially in thinner films,is improved by the increasing grain size.Finally,the film adhesion is observed by scratch tests.And the adhesive ability deposited by radio frequency magnetron sputtering shows a better performance than that produced by traditional methods.
In an active magnetic bearing(AMB) system,the catcher bearings(CBs) are indispensable to protect the rotor and stator in case the magnetic bearings fail.Most of the former researches associated with CBs are mainly focused on the dynamic responses of the rotor drops onto traditional single-decker catcher bearings(SDCBs).But because of the lower limited speed of SDCB,it cannot withstand the ultra high speed rotation after rotor drop.In this paper,based on the analysis of the disadvantages of SDCBs,a new type of double-decker catcher bearings(DDCBs) is proposed to enhance the CB work performance in AMB system.In order to obtain the accurate rotor movements before AMB failure,the dynamic characteristics of AMB are theoretically derived.Detailed simulation models containing rigid rotor model,contact model between rotor and inner race,DDCB force model as well as heating model after rotor drop are established.Then,using those established models the dynamic responses of rotor drops onto DDCBs and SDCBs are respectively simulated.The rotor orbits,contact forces,spin speeds of various parts and heat energies after AMB failure are mainly analyzed.The simulation results show that DDCBs can effectively improve the CBs limit rotational speed and reduce the following vibrations,impacts and heating.Finally,rotor drop experiments choosing different types of CBs are carried out on the established AMB test bench.Rotor orbits,inner race temperatures as well as the rotating speeds of both inner race and intermediate races after rotor drop are synchronously measured.The experiment results verify the advantages of DDCB and the correctness of theoretical analysis.The studies provide certain theoretical and experimental references for the application of DDCBs in AMB system.
提出在传统保护轴承外圈加弹性环来提高其在主动磁悬浮轴承(Active magnetic bearing,AMB)系统中的工作性能。为完善转子跌落仿真模型,得到AMB失效前转子准确的运动状态,理论推导得到AMB的支撑动刚度曲线,进而基于有限元分析方法得到转子在其支撑下的模态,并与试验结果进行对比,验证所得刚度曲线的正确性。在刚性转子理论基础上,建立转子在AMB系统中的动力学模型。基于Hertz接触理论,分别建立AMB失效后转子与保护轴承内圈之间的碰撞模型和保护轴承的实时动刚度模型。根据所建立的模型,对不同弹性环支撑刚度阻尼在不同初始转速下跌落后的动力学响应进行仿真计算,并与无弹性环状态下跌落结果进行对比。仿真分析结果表明,选用合适的弹性环有利于降低转子跌落后的振动幅值和碰撞力。分别在不同初始状态下进行跌落试验研究,试验结果与理论分析结果基本相符。
