Introduction
- Magnet or electrical current creates a magnetic field in part
- Iron fillings align with magnetic field, which disrupts when a crack/defect is present
- Advantages
- Relatively fast and easy
- Part surface preparation is not as critical
- Limitations
- Part must be ferromagnetic
- Ferromagnetic: material that can be magnetized
- Product forms include: castings, forgings, weldments
- can also be performed underwater
- Basic principle
- When a magnet is cracked, a north/south pole pair will form on the crack
- The air gap is not easily permeable to the magnetic field, so it spreads out
- This can be referred to as a flux leakage field, since the field leaks out of the material
Equipment and Materials
- Detection is strongest when magnetic field is orthogonal to defect
- Yoke: a horseshoe-shaped magnet
- Types of portable magnetizing equipment
- Permanent magnets are usually used in underwater and explosive environments, where electromagnets can’t be used
- Electromagnets are popular, but require power
- Prods are electrodes, where an electric current is created in the part that induces a magnetic field
- Arcing is undesirable possibility, check tips for oxide/scale
- Portable coils are electrically powered to induce a longitudinal magnetic field, but require power
- (TODO) Stationary magnetizing equipment is common in lab or production environments
- Particles are either highly visible under white light or ultraviolet light
- UV-A < UV-B < UV-C in terms of safety and harmful effects
- many lights and setups available (TODO)
- Magnetic Field Indicators
- Diagnosing created magnetic field
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Ketos Ring
Testing Practices