Magnetic Inspection

Front 1

How is local magnetic flux leakage produced?

Back 1

- when a specimen is magnetised the magnetic flux is confined within the specimen
- if there is a surface breaking crack, the filed is distorted and the field lines have to cross the gap
- in the air gap they spreadout hence producing a flux leakage

Front 2

what are the two magnetic inspection groups?

Back 2

- Magentic particle inpection (MPI)
- Magnetic flux leakage (MFL)

Front 3

what are the different methods of magnetising a component?

Back 3

- residual magnetism
- current flow techniques
- magnetic flow techniques
- induced current flow techniques

Front 4

What are the characteristics of the MPI technique?

Back 4

- magnetic particles are either in powerde form or in liquid suspension.
- in ink particles are small (100µm) and with a concentration of about 2%
- powder generally used for rough and hot surfaces. Ink for good, oily, wet, underwater surfaces
- can be automated with CCTV and digital image processing

Front 5

what are the two types of MFL probes?

Back 5

- induction coil sensors
- solid state sensors (such as Hall-effect probes)

Front 6

How does the Hall-effect probe for MFL work?

Back 6

- Hall elements are crystals of specially grown semiconductor material
- when excited by the flow of electric currents they react to the presence of an external magnetic field by developing a voltage across their two parallel faces
- the Hall voltage is proportional to the applied flux density By (i.e. the normal component)

Front 7

How dies the induction coil sensor for MFL work?

Back 7

- farday's law of induction is used which states that a voltage is induced in a conductor or coild of N turns, as it passers through a magnetic field, or as the magnetic flux through it changes
- V=-dNL/dt
- if a DC system is used, probe must be in motion relative to specimen

Front 8

Draw a solid state sensor system

Back 8

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