Research On Online Monitoring Technology For Metal Debris In Lubricants

Metal wear swarf in lubricating oil can effectively reflect the health status of mechanical friction subsets in aero-engines.The real-time online monitoring of lubricating oil metal wear debris is of great significance for the wear status assessment and early fault warning of aero engines.The online monitoring technology of lubricating oil wear swarf based on electromagnetic induction principle realizes the online monitoring of ferromagnetic and non-ferromagnetic metal wear swarf through the difference of electromagnetic characteristics of wear swarf materials.However,there are still problems of leakage detection,false detection,and too single monitoring index in practical application.Based on these problems the following research work is carried out in this paper:(1)The formation mechanism of aero-engine abrasive swarf and the mechanism of action between abrasive swarf and sensors are analyzed.(2)The motion model of metal particles in the slip oil pipe is constructed by Comsol liquid-solid coupling module.The effects of wear debris shape,slip oil speed and viscosity on the motion pattern of abrasive debris were analyzed.It was found that the circular debris kept turning over when moving in the oil pipeline,but the radial position was basically unchanged.The radial position of square-shaped and long strip-shaped debris will change when following the oil movement,and gradually approach the pipe wall along with the turning,and the closer to the pipe wall,the faster the turning speed.When the oil flow rate is between 0.5m/s and 2m/s,the rectangular-shaped debris gradually approach the pipe wall with the flip,and when the oil flow rate drops to 0.05m/s,the debris gradually approach the pipe wall.The slower the oil flow rate is,the more the number of weeks the debris are turned over in the horizontal pipe at the same distance.When the oil viscosity is high,the wear debris movement is accompanied by turning and gradually approaching the pipe wall,and when the viscosity decreases,the wear debris gradually approaches the pipe wall,and the lower the viscosity,the faster the speed of approaching the pipe wall.And as the viscosity of the oil decreases,the frequency of debris turning gradually decreases.(3)The influence law of different shapes and postures of the abrasive debris on the output signal of the sensor is analyzed.Through simulation and experimental analysis,it is found that for non-spherical debris,the output voltage varies under different postures of the same debris,with the angle between the bottom surface and the centerline of the sensor varying from 0° to 90° for flaky debris,and with the angle between the long axis direction and the centerline of the sensor varying from 0° to 90° for long debris,the output voltage caused gradually becomes smaller.The larger the ratio between the diameter and thickness of the flake and the larger the ratio between the length and diameter of the long strip,the larger the difference in the sensor output voltage caused by the change in attitude.The reason for the variation is that when the magnetic field direction is constant,the change in attitude of the non-spherical debris causes a change in the demagnetization factor of the debris,which affects the magnetization effect.The eddy current effect also changes with the change of attitude.When the debris rotates in the monitoring area of the sensor,the sinusoidal voltage signal output from the long strip and the round debris will be distorted,and the larger the L/D ratio of the long strip and the larger the diameter to thickness ratio of the round debris,the greater the distortion of the waveform.And the waveform distortion caused by the long strip of debris is larger than that of the round debris.The degree of distortion of the output voltage signal can be used to simply classify the shape of abrasive debris,which enriches the monitoring index of the inductive wear debris sensor.(4)The effect of the simultaneous presence of double abrasive debris in the sensor monitoring interval on the output signal is analyzed.Through simulation and experimental analysis.Finally,it is found that for two debris with ferromagnetic or nonferromagnetic properties,the output voltage increases when both debris are on one side of the sensor monitoring interval at the same time,and decreases when both debris are on both sides of the sensor monitoring interval.For two debris,one is ferromagnetic and the other is non-ferromagnetic,the output voltage decreases when both debris are on one side of the sensor,and increases when both debris are on both sides of the sensor.The aliasing signal is analyzed by controlling the space between the two grinding debris.A feature extraction method was proposed for the aliasing signal caused by double wear debris.The number of wear debris was determined by the time length of the aliasing output signal,and the size of the front and back wear debris was determined by the first and last peak of the aliasing signal.It can effectively improve the problem of missing the number of grinding debris and reduce the monitoring error of the size of grinding debris.