Magnetic Particle Inspection of Odd Shaped Parts

These parts also need to be magnetized in two directions perpendicular to each other.

In order to magnetize these parts, we have developed a double-head machine, wherein two pairs of head & tail tocks perpendicular to each other are used to magnetize the part.

The field generated by both pairs is circular in nature, but the two fields are perpendicular to each other.

Calculation of headshot current is done as per the formula given in ASTM standards.

Head Shot Current = 20 X Diameter (in mm)

In the above formula, the diameter should be taken as the maximum distance between any two points along the length of the part.

A tailor-made bench-type machine is used to perform magnetic particle testing on such parts. The part is placed on the machine by using specially designed fixtures. A pneumatically operated arrangement is used to clamp the part from all four ends. Pneumatic clamping ensures that there is no sparking when a high current is passed through the part. The use of braided copper pads is also recommended to eliminate arcing sparks.

 

Multidirectional magnetization is a special technique employed to identify defects in all orientations within a single examination. This stands in contrast to the combined magnetization shot utilized in traditional machines, which doesn’t align with ASTM standards. This technique proves effective in identifying both longitudinal and transverse cracks within one examination.

In this machine, multidirectional magnetization is used so that defects in all directions can be detected in one shot.

Testing Procedure for conventional machines

• Clean up & dry the part’s surface before inspecting.
• The part is placed on the fixture.
• Now apply a magnetic solution bath to the part.
• Press the ‘Cycle Start’ button.
• The part automatically gets clamped from all sides.
• Stop the flow of the bath.
• Now, the current passes through the part in multidirectional mode.
• It shows up on the digital metering unit.
• The part automatically gets de-clamped.
• Inspect the front surface of the part under UV light for all defects.
• Take out the part & place it on the grills.
• Inspect the back surface of the part under UV light for all defects.
• Demagnetize