Technology and Experiments of 42CrMo Bearing Ring Forming Based on Casting Ring Blank

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.

Analysis and optimization of stamping and forming process of bearing outer ring

To address the common issues of wrinkling,tearing,and uneven wall thickness in the actual sheet metal stamp-ing process of the outer ring of needle roller bearings,this study analyzes critical technical indicators such asforming limits,thickness distribution,and principal strains in the forming process in detail.Three-dimensionalmodels of the concave and convex dies were constructed.The effects of different process parameters,includingstamping speed,edge pressure,sheet metal thickness,and friction coefficient,on the quality of the forming partswere investigated by varying these parameters.Subsequently,the orthogonal experimental method was used todetermine an optimal experimental group from multiple sets of experiments.It was found that under the processparameters of a stamping speed of 3000 mm/s,edge pressure of 2000 N,sheet metal thickness of 0.9 mm,andfriction coefficient of 0.125,the forming quality of the outer ring of the bearing is ideal.

Subsurface crack propagation under rolling contact fatigue in bearing ring

The influences of subsurface cracks,distributing along the axial direction,on the rolling contact fatigue(RCF)faliure in a bearing ring are investigated.A realistic three-dimensional model of the bearing ring containing three subsurface cracks is used to evaluate the fatigue crack propagation based on stress intensity factor(SIF)calculations.Moreover,the distributions of the subsurface cracks along the axial direction are varied to study their effects on RCF.The results provide valuable guidelines for enhanced understanding of RCF in bearings.

Microstructure evolution and mechanical anisotropy of M50 steel ball bearing rings during multi-stage hot forging

This study aimed to explore the evolution of flow lines and microstructures of M50-steel bearing ring and the anisotropy of its tensile mechanical properties after Multi-Stage Hot Forging(MSHF) and subsequent spheroidizing annealing(MSHFA). To this end, the present study mainly employed stereo microscopy, Optical Metallurgical Microscopy(OMM), Scanning Electron Microscopy(SEM), and Electron Backscatter Diffraction(EBSD) to characterize and analyze the workpiece at each processing stage of MSHF while performing microhardness measurement and uniaxial tensile experiment to test and analyze the mechanical properties of the workpiece. Macro-structure observation showed that the simulation results of flow lines at each stage were consistent with the experimental results. Microscopic observation showed that, after MSHF, deformation gradually became less significant along the outward radial direction of the bearing ring. After MSHFA,the microstructures of the bearing ring became uniform, whereas primary carbides did not dissolve.The mechanical properties were better in the axial direction(AD) than in the radial(RD) and circumferential directions(CD) after MSHF due to the smaller grain width. After MSHFA, the mechanical properties in the ADs and CDs were better than those in the RDs, which was due to the large cross-sectional area of carbides along the flow-line direction.

Heat Treatment Properties of 42CrMo Steel for Bearing Ring of Varisized Shield Tunneling Machine

The heat treatment properties of 42CrMo steel for bearing ring of varisized shield tunneling machine were investigated by optical microscope （OM）, scanning electron microscope （SEM）, transmission electron microscope （TEM）, and impact tests. The addition of 0.03 wt% C into 42CrMo steel can increase the hardness. But it reduces the impact energy by 46 J because of the appearance of coarser carbides in the matrix and the carbides along the austenite grain boundary. The addition of 0.40 wt% Mn into 42CrMo steel can improve hardenability. However, the toughness of steel is also reduced by 26 J mainly because of the coarsening of carbides and the strengthening of matrix. Both hardenability and toughness of 42CrMo steel can be improved by adding 1.49 wt% Ni and reducing 0.32 wt% Cr. The depth of hardening layer can be raised to 45 mm, and the impact energy at -20 ℃ is 120 J. Thus, it is concluded that a good combination of hardness, hardenability, and toughness of 42CrMo steel can be achieved by alloying with adding some content of C and Ni. Detailed content of C and Ni should be on the requirements of heat treatment properties of steel for bearing ring of varisized shield tunneling machine.

Effects of Floating Ring Bearing Manufacturing Tolerance Clearances on the Dynamic Characteristics for Turbocharger

The inner and outer oil film dynamic characteristic coefficients of floating ring bearings（FRBs） change due to the manufacturing tolerance of the floating ring, journal and intermediate, which leads to high-speed turbocharger＇s vibration too large and even causes nonlinear vibration accident. However, the investigation of floating ring bearing manufacturing tolerance clearance on the rotordynamic characteristics is less at present. In order to study the influence law of inner and outer clearance on turbocharger vibration, the rotor dynamic motion equations of turbocharger supported in FRBs are derived by analyzing the size relations between floating ring, journal and intermediate for the inner and outer oil film clearances, the time transient response analysis for combination of FRBs clearance are developed. A realistic turbocharger is taken as a research object, the FE model of the turbocharger with FRBs is modeled. Under the conditions of four kinds of limit state bearing clearances for inner and outer oil film, the nonlinear transient analyses are performed based on the established FE dynamic models of the nonlinear rotor-FRBs system applied incentive combinations of gravity and unbalance force, respectively. From the waterfall, the simulation results show that the speed for the appearance of fractional frequency is not identical and the amplitude magnitude is different under the four kinds of bearing manufacturing tolerance limit clearances, and fractional frequency does not appear in the turbocharger and the amplitude is minimum under the ODMin/IDMax bearing manufacturing tolerance clearances. The turbocharger vibration is reduced by controlling the manufacturing tolerance clearance combinations of FRBs, which is helpful for the dynamic design and production-manufacturing of high-speed turbocharger.

Effects of Semi-floating Ring Bearing Outer Clearance on the Subsynchronous Oscillation of Turbocharger Rotor

Semi-floating ring bearing（SFRB） is developed to control the vibration of turbocharger rotor. The outer clearance of SFRB affects the magnitude and frequency of nonlinear whirl motion, which is significant for the design of turbocharger. In order to explore the effects of outer clearance, a transient finite element analysis program for rotor and oil film bearing is built and validated by a published experimental case. The nonlinear dynamic behaviors ofrotor-SFRB system are simulated. According to the simulation results, two representative subsynchronous oscillations excited by the two hearings respectively are discovered. As the outer clearance of SFRB increases from 24 ~tm to 60 pro, the low-frequency subsynchronous oscillation experiences three steps, including a strong start, a gradual recession and a combination with the other one. At the same time, the high-frequency subsynchronous oscillation starts to appear gradually, then strengthens, and finally combines. If gravity and unbalance are neglected, the combination will start starts from high rotor speed and extents to low rotor speed, just like a ＂zipper＂. It is found from the quantitative analysis that when the outer clearance increases, the vibration amplitude experiences large value firstly, then reduction, and suddenly increasing after combination. A useful design principle of SFRB outer clearance for minimum vibration amplitude is proposed： the outer clearance value should be chosen to keep the frequency of two subsynchronous oscillations clearly separated and their amplitudes close.