Magnetic Particle Inspection of Connecting Rods

The connecting shaft 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 connecting rod.

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 the maximum diameter of the connecting rod.

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 connecting rod.

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

Testing Procedure for conventional machines

• Clean up & dry the connecting rod’s surface before inspecting.
• The connecting rodis placed on the fixture.
• Now apply magnetic solution bath to the connecting rod.
• Press the ‘Cycle Start’ button.
• The connecting rod automatically gets clamped.
• Stop the flow of bath.
• Now, the current passes through the connecting rod.
• It shows up on the digital metering unit.
• The connecting rod automatically gets de-clamped.
• Inspect the connecting rod 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 connecting rod under UV light for transverse defects. Rotate on Rollers

Testing Procedure for Multidirectional machines

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