Research On Magnetization Specification For Magnetic Particle Inspection Of Railway Locomotive And Rolling Stock Axles

In the magnetic particle inspection of railway locomotive and rolling stock axles,the rationality of magnetization process is an important factor affecting the quality of magnetic particle inspection.Whether for new axles or in-service axles that have been used for a period of time,efficient and accurate non-destructive testing is an important guarantee to ensure the driving safety.It has been more than ten years since the last revision of the current magnetic particle inspection standard,some of which are inherited from the 1980 s.At present,the axle magnetic particle flaw detector used in China is the composite magnetization of low filling factor alternating current with two ends electrified.The calculation method of magnetization current is mostly empirical formula,and the derivation process of the formula is unreasonable The measurement accuracy of Tesla meter for surface magnetic induction is lack of verification.However,there is a lack of theoretical and Experimental Research on the specific effects of longitudinal magnetization,supersaturation magnetization,demagnetization,electrode clamps and coils on the magnetization effect.The purpose of this paper is to explore the above problems,and then optimize the magnetization specification of magnetic particle inspection for railway locomotive axle.First of all,the development and current situation of common nondestructive testing methods and magnetic particle testing of railway locomotive and rolling stock axles and the research significance of this paper are introduced.Various defects will appear in the process of axle manufacturing and use,and the defect form determines the choice of magnetization current and magnetization mode.Magnetic particle testing is widely used in railway industry because of its intuitive and accurate characteristics.Through the analysis of the existing flaw detection technology,the existing problems in the process are introduced.Secondly,in order to improve the deficiency of the current magnetization specification for axle magnetic particle inspection,a series of experiments were designed and carried out to verify the rationality of the circumferential and longitudinal magnetization specifications.Aiming at the circumferential magnetization,through the comparison of theoretical calculation and measurement results,the irrationality of the current method of measuring the near surface magnetic field of EA4 T axle with Tesla meter is verified;At present,the calculation formula of magnetization current is unreasonable.The magnetic field near the axle end is consistent with the peak value,while the magnetic field at other positions is between the effective value and the peak value;Although the frequency of three-phase half wave and full wave rectifier is higher than that of alternating current,it does not conform to the skin depth calculation formula.The actual skin depth is deeper than that of alternating current,and it has a good disturbance effect on magnetic powder,so it can replace alternating current to magnetize the axle in circumferential direction.For the longitudinal magnetization,with the help of computer simulation calculation and experimental measurement,it is concluded that the demagnetization factor is not uniformly distributed in the magnetized axle of the finite length loose winding magnetizing coil,and the counteracting effect of the demagnetization field on the internal magnetic induction of the workpiece is not uniform,but the two ends are strong,and the middle tends to be flat.Therefore,in order to eliminate the influence of demagnetizing field on magnetization,the optimal length of clamps at both ends of the axle is 20% of the axle length;The influence of the thickness of copper layer of electrode clamp on the longitudinal magnetic flux leakage field of the axle is studied experimentally.The results show that the thickness of 2mm soft copper layer can effectively avoid the bad contact and burn the axle,and the magnetic flux leakage is within a reasonable range.Finally,optimization suggestions are put forward for the current magnetization specification of magnetic particle inspection for railway locomotive and rolling stock axles.