US 4,931,731 AGranted

Magnetic particle inspection apparatus with enhanced uniformity of magnetization

OwnerWilliam C. Jenksinventor

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Abstract

A ferrous metal inspection device particularly for elongated parts provides high intensity DC magnetic fields in each of two modes contemporaneously. One mode is generated by passing a DC current axially through the part to be inspected and the other is generated by a separate DC current passing through a pair of electromagnet coils positioned one at each axial end of a part to be inspected. Magnetic field lines are thereby generated in a pair of mutually orthogonal planes. Control and polarity of the two direct currents is effected by controlling the phase of conduction of separate corresponding silicon controlled rectifiers. The part to be inspected is drenched with a mixture of fine ferrous particles in a liquid vehicle. Solenoid wound coils connected in series or parallel are placed, one at each end of the part and a third coil surrounds the part circumferentially, thereby producing two substantially orthogonal magnetic fields. The ferrous particles of any orientation define flaws in the part being tested, for visual evaluation.

Claims11

Dependent claims

A magnetic inspection system for detecting flaws in ferrous metal parts, comprising:

first means for passing a first pulsating direct current axially through a part to be inspected thereby generating a corresponding first magnetic field associated with said part;
second means for generating a second magnetic field generally orthogonal with respect to said first magnetic field, said second means including a pair of solenoid-wound first electromagnets adjacent to said part to be inspected, one of said first electromagnets being adjacent at each end of said part, said first electromagnets being energized by a second pulsating direct current;
third means comprising circuits connected from a three-phase alternating current source for supplying said first and second pulsating direct circuits, from first and second phases of said three-phase source, respectively, the pulses of said first and second direct currents being phase displaced from each other because of the inherent phase relationship among the phases of said alternating current source;
fourth means associated with said third means for independently controlling the magnitudes and polarities of said first and second pulsating currents to achieve a predetermined balance between said first and second magnetic fields;
and
fifth means for bathing said part to be inspected in a fluid vehicle containing finely powdered magnetizable particles, thereby to exhibit a characteristic visual pattern of said particles under the influence of said magnetic fields at the location of any flaw in said part.

3 more elements

In a wet process magnetic inspection system in which an elongated magnetizable part to be inspected is bathed in a fluid vehicle carrying fine magnetizable particles and longitudinal and circular mutually orthogonal fields are applied thereto, the combination comprising:

first means including an AC power source of more than one phase, a first network of SCR elements responsive to one phase of said power source for full wave rectification of said power to provide a first pulsating DC current connected to pass axially through said part to produce said circular magnetic field about said elongated part;
second means including first and second electromagnetics positioned one adjacent each end of said elongated part to produce a net longitudinal magnetic field within said elongated part in response to current in said electromagnets;
third means including a second network of SCR elements responsive to a second phase of said AC power source for full-wave rectification thereof to provide a pulsating DC current to said second means electromagnets to generate said longitudinal magnetic field in said elongated part;
and
fourth means for controlling the phase angle of conduction of said SCR elements to independently control the magnitude and polarity of said pulsating DC currents produced by said first and third means to control the corresponding magnitudes of said circular and longitudinal magnetic fields extant contemporaneously but with phase offset corresponding to the phase offset between phases of said AC power source.

2 more elements

Dependencies are inferred from the claim text.