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CHAPTER 4a - MPI (Part 4,5,6,7) - Coggle Diagram
CHAPTER 4a - MPI (Part 4,5,6,7)
If iron particles are sprinkled on a cracked magnet, the particle will be attracted to & cluster not only at the poles at the end of the magnet but also at poles of the edges of cracks
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Steps:
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If there is any defect on/near the surface present, the defect will create a leakage field
After the component is magnetized, the iron particles (dry/wet) are applied to the surface of the magnetized components/parts
Particles will be attracted & cluster at the flux leakage field which forms a visible indications that NDT officer can detect
Magnetism
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Magnetic poles have never been detected in isolation, but always occur in pairs (dipole)
A dipole is an object which have a magnetic pole on one end & secondly, an equal but opposite magnetic pole on the other
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The source
of Magnetism
All matter is composed of atoms & atoms are composed of protons, neutrons & electrons
The protons & neutrons are located in the atom's nucleus. Electron - constant motion around the nucleus
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A magnetic field is produced whenever electrical charges is in motion. The strength of this field is called the magnetic moment
When the electrons (electric current) are flowing through the conductor, a magnetic field form around it (conductor)
Diamagnetic, Paramagnetic
& Ferromagnetic Materials
In most atoms, electron occur in pairs (electron in a pair spin in opposite direction)
So, when electron are paired together, the opposite spin will cause their magnetic field to cancel each other
Therefore, no net magnetic field exists. Alternately, materials with some unpaired electron will have a net magnetic field & will react more to an external field
Diamagnetic
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Diamagnetic materials are slightly repelled by a magnetic field & the material does not retained the magnetic properties when the external field is removed
In diamagnetic materials all the electron are paired so there is no permanent net magnetic moment per atom
Diamagnetic properties arise from the realignment of electron path under the influence of external magnetic field
Most elements in the periodic table including, copper, silver & gold are diamagnetic
Paramagnetic
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These materials are slightly attracted by a magnetic field and the material does not retained the magnetic properties when the external field is removed
Paramagnetic properties are due to the present of unpaired electron & from the realignment of the electron path caused by the external magnetic field
Paramagnetic materials, include magnesium, molybdenum, lithium & tantalum
Ferromagnetic
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They exhibit a strong attraction to magnetic field & are able to retain magnetic properties after external force have been removed
Ferromagnetic materials have some unpaired electron, so their atoms have a net magnetic moment
Magnetic domain:
- number of atoms moment (10^12 to 10^15)
- aligned parallel so that magnetic force within the domain is strong
When a ferromagnetic material is in the unmagnetized state, domains are nearly randomly organized, the net magnetic field = 0
When a magnetizing force is applied, the domains become aligned which produce a strong magnetic field within the component
Iron, nickel, cobalt are examples of ferromagnetic materials components with these materials are commonly inspected using MPI