Multiparameter eddy-current NDT method for quality control of thin sheet, multilayer products and coatings

摘要

For quality control of multilayer, thin-sheet metal products with dielectric layers and their defects evaluation it is proposed to implement multimeter eddy-current method of electrophysical and thermal-physical products' parameters measuring that provides sheet thickness measurement as well. The radio pulses generator via exciting winding of the eddycurrent & thermal transducer (ECTT) induces whirling currents and generates thermal field in the examined product; informative parameters of eddy currents and thermal field are measured by relevant transducers, i.e. eddy-current and thermal. Based on revealed patterns of those parameters changes developed are methods of selective measurements of: conductivity, thermal diffusivity, metal sheet thickness and delaminations between product' metal and dielectric parts. The thermal diffusivity evaluation is based on measurement of velocity of temperature change in time and along the product surface; the temperatures measured at the moment of rectangular pulse impact end and one measured at the steady state mode are used for estimation of ratio of thermal diffusivity to sheet thickness; based on induced parameters of ECTT' windings measured are conductivity, dielectric coating' thickness and metal sheets integrity i.e. defects presence. In the paper presented are block diagrams and algorithms of the proposed eddy-current & thermal testing method as well as scheme of device for selective NDT of thickness, thermal diffusivity and conductivity of thinsheet metal products (coatings) and composite materials. Also shown are functional layout and structural diagrams of instruments: -) for examination of delaminations and adhesion quality in multilayer thin-sheet metal products with dielectric layers; -) for detection of flaws relevant to integrity evaluation, metal plates thickening, internal corrosion, erosion and other types of defects.