introduction to magnetism
Basic properties of MagnetsEvery magnet is made up of a north and south pole. If two north pole are set near each other they will repel each other and the same goes for two south poles. If you place a north pole near a south pole they will attract each other.
If you cut a magnet in half it will become two magnets both with a north and south pole. This is the key feature to magnetic particle testing.
A permanent magnet is a piece of metal that has been magnetized and retains is magnetic properties. The dipoles creates a magnetic field which exert forces on moving charged particles such as tiny pieces of iron.
Electric current through a loop generates the same magnetic field as a permanent bar magnetic. This is what is actually used to do magnetic particle testing.
If there is a break in the magnet it creates a flux leakage and creates a new set of dipoles that attract each other and magnetic particles.
![CrackInField](CrackInField.jpg)
Magnetic Particle Testing
Magnetic particle testing uses electric current to create a magnetic field through a material. Once the magnetic field is established tiny iron particles are dusted over the area. If the material has a crack within the magnetic field it acts the same as a break in a magnet and creates a new dipole point which attracts the iron flakes. This creates a deviation in the normally observed magnetic field making the crack visible to the naked eye, even if it is slightly below the surface of the material.
![MT](mt.jpg)
This process of testing materials is extremely useful for detecting imperfections in welds.