PERIO-MAGNETIC EFFECT ON COLOR COATED MAGNETIC PARTICLES IN MPI

摘要

Perio means around and magnetic effect means magnetic forces on color coated magnetic particles used in magnetic particle testing in NDT magnetic particle are coated with different pigments/colors bound by adhesives/resins to obtain best contrast over various backgrounds. When magnetisation on test object/s is going on along with spray of magnetic particles, there is more pull on magnetic particles and "no" pull on color and adhesives binding them. Magnetic particles always try to aline in direction of magnetic field. These bonded particles are used again and again from re-circulating tanks in units. At some stage color particles/adhesives start to separates out from magnetic particles and do not give good color contrast and do not show defects properly. Application of different methods of current like ac, dc, HWDC etc. For magnetizing objects have different effects to separate bonds of color and magnetic particles, depending on frequencies applied. Moreover, mere mixture of color with magnetic particles have very short life. While loose bonding adhesives gives little good life and good bonding will give better life. Standard test pieces are used. Same type of coated magnetic particles gives different bond-life under different processes of MPI. Study of each testing system with particular magnetic particles requires special set of system.