Magnafluxing - Made Simple

You've heard the term Magnafluxed. To most, it means taking a part and checking it for cracks. Typically, the teardown guy brings a part to the "Mag" unit, wets it down with solution, presses the button a couple of times, then shines the black light on the part, checking it for cracks. The process seems simple enough, but there is much more to inspection than most racers realize.

Magnaflux is actually the name of the company that began building magnetic particle inspection (MPI) equipment in the '30s, and is still the leading manufacturer of the equipment.

The process of magnetic particle inspection is straightforward: An inspector places a part on the bed of the unit, either clamps the part in the contact plates or places it in the coil, wets the part, magnetizes it, then looks at it under a black light. To do the job properly, you must understand the basics of the inspection process and how to find cracks or defects in parts.

Magnetic particle inspection is one of several inspection methods used in the nondestructive testing industry. Other methods are X-ray, ultrasonic, dye penetrant, eddy current, and visual inspection, to name a few. Each inspection method is used to find defects or flaws in components. The method of choice depends on the type of parts being tested and the location and type of defect being sought.

Magnetic particle inspection is only used to test parts made of a ferromagnetic metal, which can be magnetized and retain magnetism. Magnetic particle inspection is capable of finding flaws at the surface and those up to 11/44 inch below the surface of a part.

Magnetic particle inspection is based on the fact that a crack in a magnetized ferromagnetic part creates a small magnetic field on the surface of that part. When iron powder is sprayed onto the part, the field acts as a little magnet to attract the powder to the crack. You may not be able to see a crack, but you are able to see the iron powder collecting at the magnetic field in and around the crack. The iron powder used in wet horizontal units is contained in water or oil bath. In fluorescent inspection, the iron powder is encapsulated in a fluorescent pigment. When the part is sprayed with the solution, the iron dust settles in the cracks and brightly shines when viewed under a black light.

The ProcessThe first step in MPI is magnetizing the part. In this case, only wet horizontal inspection units will be discussed. The unit produces an electric current that flows directly through a part or around a part. Electrical current is measured in units called amperes. When the electrical current flows, a magnetic field is created. When current flows through or around a ferromagnetic part, the part remains magnetized after the current stops flowing. The magnetic field left in a part is called the residual field. The residual field is measured in units called gauss. The material and the size of the part determine the amount of electrical current required to create the magnetic field. Typically, more electrical current (or amperes) is needed to magnetize bigger parts.

Typical wet units have two contact plates and a coil. One of the contact plates moves on a rail, while the other moves in and out by means of a pneumatic cylinder. The first way to magnetize is to place the part between the contact plates, then clamp the part in place by extending the pneumatic plate. When the energize button is pushed, an electrical current flows to one of the contact plates through the part and returns to the unit through the other contact plate. The electrical current that flows through the part creates a magnetic field contained within and around the part.