Research On Thermal-Vibratory Stress Relief Process Of Welding Escalator Drive Spindle

The escalator drive spindle is the core transmission component of the escalator drive system.Its function is to transmit the power of the motor to the escalator which raises the passengers up.As the usage of escalators increases,accidents of escalators frequently occur.According to the accident investigation report,the accident happened partly because of the fatigue failure caused by welding residual stress at the welding joint of the escalator drive spindle.For the sake of poor effectiveness,high energy consumption,heavy pollution of the traditional stress relief process,this thesis proposes a new thermal-vibratory stress relief(TVSR)process combining the feature of thermal stress relief(TSR)and vibratory stress relief(VSR),which is of great significance to the fatigue problem of escalator drive spindle.Based on the theoretical analysis,numerical simulation and experimental research,the influence and mechanism of TVSR was studied and the parameters invovled were optimized in this thesis.The major research contents and conclusions are as follows:(1)Based on ANSYS,using life-and-death element technology,the numerical simulation of the welding process of the driving spindle was established and the distribution of the welding residual stress was analyzed.The results show that the tangential tensile stress on welding seam,as well as the tangential and radial tensile stress on the welding toe,account for the major part of the stress field of the entire welding joint.The hole-drilling method was used to detect the residual stress of the the drive spindle welding sample.The results of the numerical simulation were compared with the test results.The results show that the test values of residual longitudinal,lateral and equivalent stress were basically consistent with the numerical simulation results,which means that the as-welded stress model can be used as an effective stress model for subsequent research.(2)Through ANSYS free modal analysis and constrained modal analysis,the best excitation point and supporting point were obtained and the optimal vibration frequency was acquired.The effective vibration force range was calculated based on the result of harmonic response analysis;The numerical simulation models of VSR and TVSR were established by dynamic transient analysis and thermal-structural coupled transient analysis respectively.Three sets of vibration force parameters and four sets of temperature parameters were studied.The results show that when the temperature is constant,the stress relief rate is positively correlated with the vibration force and is close to a linear relationship;When the vibration force is constant,the stress relief rate is also positively correlated with temperature.However,over the range of 25℃~150℃,the relief rate increases rapidly while over the range of 150℃~200℃,the increase rate of the relief rate slows down obviously;When the vibration force is4 KN and the temperature is 200℃,the average stress relief rate and the peak-stress relief rate are highest.(3)Through the numerical simulation,the torsional TVSR process was explored and the results show that when the temperature parameter is 200℃,the effect of torsional TVSR using maximum vibration force is better than that of the TVSR using maximum vibration torque.(4)Based on the simulation results,reasonable equipments were selected and the TVSR test platform was built up.Using maximum allowed vibration force,the influence of the heating temperature on the effect of TVSR were studied based on residual stress detection method and vibration characteristic curve evaluation method.The results show that residual stress relief rate of TVSR is much higher than that of the VSR,and the stress relief rate also increases with the increase of heating temperature,which is consistent with the results of simulation.Comparing the vibration characteristic curve of the samples before and after VSR and TVSR,the results show that the resonance frequency shifts to the left and the amplitude of peak acceleration rises.And the change trend of the vibration curve is consistent with that of the residual stress detection,which verifies the effectiveness of TVSR and vibration characteristic curve evaluation method.Finally,taking into account the energy consumption and time cost,150℃ was selected as the optimal heating temperature.