Yokes are the Power Tools for Magnetic Particle Inspection
These handheld electromagnets create a magnetic field in a Steel workpiece.
Particle mobility in a magnetic yoke setup is about allowing the magnetic particles to be free enough to gather at flaws while the magnetic field is applied.
Adequate mobility (especially with an AC yoke) increases the sensitivity and reliability of magnetic particle inspection, leading to more accurate detection of surface-breaking cracks and other discontinuities.
The higher the Particle Mobility the faster, and more reliable, the particle will congregate to a defect or a change in surface profile.
AC Yokes
These fields provide the greatest particle mobility as the frequency of the power simply causes the Particle to vibrate. The polarity at each pole (leg) alternates from positive to negative at the same frequency as the electrical input current of 50 to 60 Hertz (pulses per second).
AC / DC Yokes
The fields provide is identical to those outlined above. The DC Portion from Yokes is a Phase Controlled pulse or rectified AC. The inductance of the Yoke’s Coil and Iron Core is enough that the Field induced into the material is Straight DC, with a slight ‘ripple’ due to the AC input frequency of 50 or 60 Hertz.
Battery Operated Yokes
These yokes take the 12 Volts DC from the Battery and Chops the current, simply turning the field on and off at 125Hz. This Chopping of the electrical supply lowers the effective draw on the battery, thus extending the useful life of a charge. As the chopped current keeps re-energizing the coil, the flat level of the DC curve is interrupted creating a ripple effect that induces some particle mobility.
Permanent Magnetic Yokes
These yokes simply induce a magnetic field into the work piece, almost the equivalent of a full wave DC field. As a result there is no change in the strength or polarity (frequency) of the field, thus there is very low Particle Mobility.
Specialty Yokes
Safety and Premium Yokes
Using a Yoke