Magnetic Particle Inspection of Bell Housing

The bell housing needs to be magnetized in two directions perpendicular to each other.

A circular magnetic field is used to detect longitudinal flaws in the part.

Circular magnetic field is generated by passing a current through the length of the bell housing.

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

Head Shot Current            =        20 X Diameter(mm)

In the above formula, the diameter should be taken as diameter of the base portion.

Longitudinal magnetic field, required for detection of transverse defects is generated by using an encircling coil.

Formula for calculation of coil current

In the above formula, the diameter should be taken as the average diameter of the bell housing.

A horizontal bench type machine is used to perform magnetic particle testing on bell housings. Bell housing is placed on the steady rollers fitted on the head & tailstock of the machine. A pneumatically operated arrangement is used to clamp the bell housing from both ends. Pneumatic clamping ensures that there is no sparking when high current is passed through the bell housing. Use of braided copper pads is also recommended to eliminate arcing sparks.

Testing Procedure for conventional machines

• Clean up & dry the bell housing’s surface before inspecting.
• The bell housingis placed on the steady rollers.
• Now apply magnetic solution bath to the bell housing.
• Press the ‘Cycle Start’ button.
• The bell housing automatically gets clamped.
• Stop the flow of bath.
• Now, the current passes through the bell housing.
• It shows up on the digital metering unit.
• The bell housing automatically gets de-clamped.
• Inspect the bell housing under UV light for longitudinal defects. Rotate on steady rollers.
• Now, again apply bath to the job.
• Press the ‘Cycle Start’ button.
• Stop the flow of bath.
• Now the current passes through the coil.
• It shows up on the digital metering unit.
• Inspect the bell housing under UV light for transverse defects. Rotate on Rollers
• Demagnetize

Testing Procedure for Multidirectional machines

• Clean up & dry the bell housing’s surface before inspection
• Place the bell housing on the steady rollers.
• Now apply a bath to the bell housing.
• Press the ‘Cycle Start’ button.
• The bell housing will automatically get clamped &the Coil will come into position
• Stop the flow of the bath.
• Now the current will pass through the bell housing& the coil in multidirectional mode.
• It will show up on the digital metering unit.
• The bell housing will automatically get de-clamped.
• Inspect the bell housing under UV light for defects in all directions. Rotate on rollers.