Research On Distinction Mechanism Of Metal Debris Material And Detection Of Multi-contaminants Based On Multi-parameter Analysis

Oil cleanliness is a key indicator of health status of vessels and marine equipment,and oil contaminants can reflect the wear state,oil oxidation degree and lubricating performance of equipment.Studying oil condition monitoring technology and accurately obtaining information about the type,content and size of contaminants can not only achieve fault location,but also provide an basis for early fault warning and health assessment.This is of great value for fault diagnosis and intelligent maintenance based on multi-source information under big data,and is also of significance for improving the safety of mechanical equipment.Aiming at the problems faced by oil detection technology,such as inability to identify metal debris materials,limited types of detectable contaminants and low sensitivity,this thesis proposed a distinguishing detection method of oil contaminants based on multi-parameter analysis supported by the National Natural Science Foundation of China and other projects.Through comprehensive analysis of the inductance,resistance and capacitance data collected by oil sensor,the high-sensitivity detection and distinction of metal debris,air bubbles and water content in oil are achieved,and the material of metal debris is effectively identified.The main research contents and conclusions are as follows:(1)The detection mechanism of metal particles in non-uniform time-harmonic electromagnetic field is brought into research.First,the magnetization model of metal particles in time-harmonic magnetic field is constructed based on Maxwell equations and Lorentz specifications,and the magnetic vector potential at any point,which generated by metal particles,is obtained.Then the magnetic field distribution model of cylindrical coil in usual medium is established,the formula of magnetic induction intensity at any position is obtained.And the magnetic field distributions of empty coil,built-in magnetic medium coil,and external magnetic medium coil are investigated.Third,the impedance change model of cylindrical coil caused by metal particle is obtained by combining magnetization model and magnetic field distribution model.Fourthly,the intrinsic relationship between particle magnetization coefficient and debris material is revealed,and the action mechanism of magnetic field frequency,magnetic field strength and detection coil structure on impedance change is expounded,which provides a theoretical basis for the material differentiation of metal debris.Finally,the influence of non-uniform magnetic field on detection results is studied,and the signal difference of metal particles passing through coil with various paths is compared.The results show that the impedance change caused by particles along inner hole center path is the largest,while particles along plane center path will generate “double peak”signals.(2)Material distinction of metal debris based on inductance detection is carried out.The difference in particle magnetization coefficient causes different trends in amplitude-size curves,a debris material identification method based on inductance-resistance analysis is proposed.And the relationship curves between inductance/resistance amplitude and particle size for debris with different materials are established.By combining the debris information represented by inductance and resistance signals in relationship curves,the material and size can be judged.The eddy current inside metal particle increases with magnetic field frequency,a debris material identification method based on high and low frequency magnetic excitation is proposed.And a debris sensor with high and low frequency magnetic excitation is designed,the relationship curves between inductance amplitude and particle size for high-frequency and low-frequency units are constructed.By comparing the inductance signals generated by metal particles in two units,material information can be obtained.Detection units with different structures have different sensing capabilities,a debris material identification method based on multi detection units is proposed.A debris sensor with multi detection units is designed by changing coil structure and adding magnetic medium,and the relationship curves between inductance amplitude and particle size for each unit are constructed.By comparing the identification results of debris information under each curve,the particle material can be determined.In addition,this three methods can be combined to increase the difference in amplitude-size curves,thereby further expanding the types of identifiable materials.(3)By integrating the inductance and capacitance principles,the comprehensive detection of multi-contaminants is achieved.The straight-channel and annular-channel sensors with inductance-resistance and capacitance units are designed to detect metal debris,air bubbles and water content.For inductance-resistance unit,research shows that inductance parameter has a stronger detection ability for ferromagnetic metal particles,and resistance parameter has a stronger detection ability for non-ferromagnetic metal particles.Combined with inductance and resistance parameters,straight-channel sensor can detect >16μm iron particles and >60μm copper particles,annular-channel sensor can detect >35μm iron particles and >90μm copper particles.In capacitance unit,air bubbles will reduce capacitance value,generate negative pulse signals,and water will increase capacitance value.A new method for water content measurement using micro-sensor is proposed,which obtains the water content by calculating the capacitance difference between clean oil and oil sample,preventing the interference of solid impurities.The experiment shows that capacitance changes linearly with the bubble volume and water content.Pulse amplitude is used for size measurement,pulse number is used for particle counting,the direction and presence of pulses are used for Particle property differentiation.By analyzing the of inductance-resistance-capacitance signal characteristics,high-accuracy non-crosstalk detection of metal debris,air bubbles and water content can be achieved.(4)Research on sensitivity improvement of oil contaminant sensors is carried out.Planar and solenoid sensors with inductance and capacitance modes are designed.By adding silicon steel,high-gradient magnetic fields are constructed to lower the limit in inductance mode.At same time,the silicon steel sheet and coil are skillfully used as capacitor plates,so air bubbles and water content are measured through mode conversion.Planar inductance-capacitance sensor can detect >30μm iron particles,>90μm copper particles,>160μm air bubbles,and water content.Solenoid inductance-capacitance sensor can detect >55μm iron particles,>115μm copper particles,>170μm air bubbles,and water content.A dual-coil sensor with square channel is designed,which uses two coils,two excitation silicon steel strips,and a external silicon steel strip to build a strong magnetic high-sensitivity region,which achieving detection of >25μm iron particles and >85μm copper particles.