科创中国

As the two most important indexes of bearing raceway,surface roughness and roundness have significant influence on bearing noise.Some researchers have carried out studies in this field,however,reason and extent of the influence of raceway surface geometric characteristics on bearing running noise are not perfectly clear up to now.In this paper,the raceway of 6309 type bearing's inner and outer ring is machined by floating abrasive polishing adopting soft abrasive pad.Surface roughness parameters,arithmetical mean deviation of the profile Ra,the point height of irregularities Rz,maximum height of the profile Rmax and roundness f of raceways,are measured before and after machining,and the change rules of the measured results are studied.The study results show that the floating abrasive polishing can reduce the surface geometric errors of bearing raceway evidently.The roundness error is reduced by 25%,Rmax value is reduced by 35.5%,Rz value is reduced by 22%and Ra value is reduced by 5%.By analyzing the change of the geometrical parameters and the shape difference of the raceway before and after machining,it is found that the floating abrasive polishing method can affect the roundness error mainly by modifying the local deviation of the raceway's surface profile.Bearings with different raceway surface geometrical parameter value are assembled and the running noise is tested.The test results show that Ra has a little,Rmax and Rz have a measurable,and the roundness error has a significant influence on the running noise.From the viewpoint of controlling bearings'running noise,raceway roundness error should be strictly controlled,and for the surface roughness parameters,Rmax and Rz should be mainly controlled.This paper proposes an effective method to obtain the low noise bearing by machining the raceway with floating abrasive polishing after super finishing.

Extensive studies on rotor systems with single or coupled multiple faults have been carried out. However these studies are limited to single-span rotor systems. A finite element model for a complex rotor-bearing system with coupled faults is presented. The dynamic responses of the rotor-bearing system are obtained by using the rotor dynamics theory and the modern nonlinear dynamics theory in connection with the continuation-shooting algorithm(commonly used for obtaining a periodic solution for a nonlinear system) for a range of rub-impact clearances and crack depths. The stability and Hopf instability of the periodic motion of the rotor-bearing system with coupled faults are analyzed by using the procedure described. The results indicate that the finite element method is an effective way for determining the dynamic responses of such complex rotor-bearing systems. Further for a rotor system with rub-impact and crack faults, the influences of the clearances are significantly different for different rub-impact stiffness. On the contrary, the influence of crack depths is rather small. The instability speeds of the rotor-bearing system increase due to the presence of the crack fault. The results obtained using the new finite element model, presented for computation and analysis of dynamic responses of the rotor-bearing systems with coupled faults, are in accordance with measurements in experiment. The formulations given can be used for diagnosis of faults, vibration control, and safe and stable operations of real rotor-bearing systems.

Durning the design process of hydrostatic rotary worktable,the processing and assembly tolerance,(the offset of worktable and the gap of the oil film's thickness)is ignored.But it will cause that the real bearing of oil pocket deviates from the initial design value,and then the performance of rotary worktable will be reduced significantly.Up to now,no effort is found toward the research of influence of the processing and assembly tolerance on the performance of the rotary worktable.So the hydrostatic oil film is assumed as the elastomer in this paper,and then the bearing capacity of the oil pocket is studied with and without the mass offset of the worktable by taking an expression between the bearing capacity and the oil film's thickness of the oil pocket as the deform compatibility equation.The influence of the processing tolerance of the oil sealing belt's gap on the bearing capacity of the oil pocket is analyzed.In the light of the liquid hydrostatic worktable of Gantry Moving Milling Center using on the scene,the oil pocket's pressure of the worktable is tested using Rotary Worktable Test System under the circumstance of the mass offset of the worktable and the gap tolerance of the oil sealing belt,and then the equivalent offset of worktable,the average pressure of the oil pocket and the actual thickness of the oil film are analyzed respectively.The test results show that the bearing capacity component of the oil pocket caused by G is consistent,and the component caused by M is relative to the position of the oil pocket.When the oil sealing belt's gap is larger than the theoretical value,the bearing capacity of the oil pocket is smaller than the others;whereas the bearing capacity of the oil pocket is larger than the others.The maximum and minimum equivalent offsets are 0.256 4 mm and 0.047 5 mm,respectively,and the average oil pocket pressure varies from 0.345 MPa to 0.460 MPa,the maximum and minimum value of the actual oil film thickness are 109.976?m(No.7 oil pocket)and 93.467?m(No.10 oil pocket),respectively.The research results can be used to detect the offset of the worktable and the actual thickness of the oil film under processing and assembly tolerance,and provides a basis way for detecting the processing and assembly tolerance of rotary worktable signing reasonably of Gantry Moving Milling Center.

Traditional model for calculating performance parameters of a fix-pad journal bearing leads to heavy workload,complicated and changeable formulae as it requires deriving various geometric formulae with different bearing types such as circular journal bearing,dislocated bearing and elliptic bearing.Considering different pad preload ratios for non-standard bearing,traditional model not only becomes more complicated but also reduces scalability and promotion of the calculation programs.For the complexly case of traditional model while dealing with various fix-pad journal bearings,unified coordinate system model for performance calculation of fix-pad journal bearing is presented in the paper.A unified coordinate system with the bearing center at the origin is established,and the eccentricity ratio and attitude angle of axis relative to each pad are calculated through the coordinates of journal center and each pad center.Geometric description of fix-pad journal bearing is unified in this model,which can be used for both various standard bearing and non-standard bearing with different pad preload ratios.Validity of this model is verified with an elliptical bearing.Performance of a non-standard four-leaf bearing with different pad preload ratios is calculated based on this model.The calculation result shows that increasing preload ratio of the pad 1 and keeping that of the left three pads constant improves bearing capacity,stiffness and damping coefficients.This research presents a unified coordinate system model unifies performance calculation of fix-pad journal bearings and studied a non-standard four-leaf bearing with different pad preload ratios,the research conclusions provides new methods for performance calculation of fix-pad journal bearings.

Axial-grooved gas-lubricated journal bearings have been widely applied to precision instrument due to their high accuracy, low friction, low noise and high stability. The rotor system with axial-grooved gas-lubricated journal bearing support is a typical nonlinear dynamic system. The nonlinear analysis measures have to be adopted to analyze the behaviors of the axial-grooved gas-lubricated journal bearing-rotor nonlinear system as the linear analysis measures fail. The bifurcation and chaos of nonlinear rotor system with three axial-grooved gas-lubricated journal bearing support are investigated by nonlinear dynamics theory. A time-dependent mathematical model is established to describe the pressure distribution in the axial-grooved compressible gas-lubricated journal bearing. The time-dependent compressible gas-lubricated Reynolds equation is solved by the differential transformation method. The gyroscopic effect of the rotor supported by gas-lubricated journal bearing with three axial grooves is taken into consideration in the model of the system, and the dynamic equation of motion is calculated by the modified Wilson-θ-based method. To analyze the unbalanced responses of the rotor system supported by finite length gas-lubricated journal bearings, such as bifurcation and chaos, the bifurcation diagram, the orbit diagram, the Poincaré map, the time series and the frequency spectrum are employed. The numerical results reveal that the nonlinear gas film forces have a significant influence on the stability of rotor system and there are the rich nonlinear phenomena, such as the periodic, period-doubling, quasi-periodic, period-4 and chaotic motion, and so on. The proposed models and numerical results can provide a theoretical direction to the design of axial-grooved gas-lubricated journal bearing-rotor system.

Bearing ring is the crucial component of bearing. With regard to such problems as material waste, low efficiency and high energy consumption in current process of producing large bearing ring, a new process named "casting-rolling compound forming technology" is researched by taking the typical 42CrMo slew bearing as object. Through theoretical analysis, the design criteria of the main casting-rolling forming parameters are put forward at first. Then the constitutive relationship model of as-cast 42CrMo steel and its mathematical model of dynamic recrystallization are obtained according to the results of the hot compression experiment. By a coupled thermal-mechanical finite element model for radial-axial rolling of bearing ring, the fraction of dynamic recrystallization is calculated and recrystallized grains size are predicated. Meanwhile, the effects of the initial rolling temperature and feed rate of idle roll on material microstructure evolution are analyzed. Finally, the industrial rolling experiment is designed and performed, based on the simulation results. In addition, mechanical and metallographic tests are conducted on rolled bearing ring to get the mechanical parameters and metallographic structure. The experimental data and results show that the mechanical properties of bearing ring produced by casting-rolling compound forming technology are up to industrial standard, and a qualified bearing ring can be successfully formed by employing this new technology. Through the study, a process of forming large bearing ring directly by using casting ring blank is obtained, which could provide an effective theoretical guidance for manufacturing large ring parts. It also has an edge in saving material, lowering energy and improving efficiency.