Magnetic Particle Inspection
magnetic particle inspection equipment is designed for use in
laboratory or production environment. The most common stationary
system is the wet horizontal (bench) unit. Wet horizontal units
are designed to allow for batch inspections of a variety of components.
The units have head and tail stocks (similar to a lathe) with
electrical contact that the part can be clamped between. A circular magnetic field is produced with direct magnetization.
The tail stock can be moved and locked into place to accommodate
parts of various lengths. To assist the operator in clamping the
parts, the contact on the headstock can be moved pneumatically
via a foot switch.
Most units also have a movable coil that can be moved into place
so the indirect magnetization can be used to produce a longitudinal
magnetic field. Most coils have five turns and can be obtained
in a variety of sizes. The wet magnetic particle solution is collected
and held in a tank. A pump and hose system is used to apply the
particle solution to the components being inspected. Either the
visible or fluorescent particles can be used. Some of the systems
offer a variety of options in electrical current used for magnetizing
the component. The operator has the option to use AC, half wave
DC, or full wave DC. In some units, a demagnetization feature
is built in, which uses the coil and decaying AC.
inspect a part using a head-shot, the part is clamped between
two electrical contact pads. The magnetic solution, called a bath,
is then flowed over the surface of the part. The bath is then
interrupted and a magnetizing current is applied to the part for
a short duration, typically 0.5 to 1.5 seconds. (Precautions should
be taken to prevent burning or overheating of the part.) A circular
field flowing around the circumference of the part is created.
fields from defects then attract the particles to form indications.
the coil is used to establish a longitudinal magnetic field within
the part, the part is placed on the inside surface of the coil.
Just as done with a head shot, the bath is then flowed over the
surface of the part. A magnetizing current is applied to the part
for a short duration, typically 0.5 to 1.5 seconds, just after
coverage with the bath is interrupted. (Precautions should be
taken to prevent burning or overheating of the part.) Leakage
fields from defects attract the particles to form visible indications.
wet horizontal unit can also be used to establish a circular magnetic
field using a central conductor. This type of a setup is used
to inspect parts that have an open center, such as gears, tubes, and other
ring-shaped objects. A central conductor is an electrically conductive
bar that is usually made of copper or aluminum. The bar is inserted
through the opening and the bar is then clamped
between the contact pads. When current is passed through the central
conductor, a circular magnetic field flows around the bar and
enters into the part or parts being inspected.