Permanent magnets are commonly used in magnetic yokes. This refers to a handheld magnetic device used to induce a field in an area between two poles. They can also be electromagnetic yokes. Either kind of magnetic yoke can be used for participle inspection outdoors, in hard-to-reach places, or in remote locations. They can also evaluate whether a weld job is of quality, detecting surface and subsurface cracks and defects in ferromagnetic material.  Magnetic yokes can identify defects in ferromagnetic material, including seams, porosity, tears, inclusions, laps, lack of fusion, welding slaps, grinding cracks, and quenching cracks. Essentially, they can attract particles to the poles; however, if there are no cracks or discontinuities, no particles will be attracted. Note that certain parts may require demagnetization function properly post-testing.

Permanent Magnets Yoke

When using permanent magnets for a yoke, they can be used as single poles or pairs (horseshoe magnet or two bar magnets with fixed spacing). These yokes are also longitudinal; whatever is magnetized is given a north and south pole. Unfortunately, you can’t closely inspect the contact points of the object. Doing so just confuses the mass of particles at the poles.  The primary benefit of yokes made from permanent magnets is that they can retain their applied magnetic field after the active power is removed.  Additional benefits of permanent magnet yokes include: 
  • Portable
  • No electrical source required
  • Compact
Limitations of permanent yoke magnets include: 
  • You can’t change the field strength at will
  • Not sufficient enough field to magnetize large areas
  • Difficult to remove magnetic particles if very strong  

Electromagnetic Yokes

Electromagnetic yokes can also be used to detect defects. The same shape as permanent yokes, their U-shape core is typically made of soft, laminated iron with a coil around the base. Once the current passes through, there is a north and soul pole at both ends of the core.  Advantages of electromagnetic yokes include: 
  • Varied field strength
  • Easier to affix and remove from the part you’re checking
  • Ability to be turned off and on

Apex Magnets & Particle Testing

We like to be aware and up-to-date on all the ways our customers can use our magnets. At the same time, we love to learn from you as well. Sign up for our newsletter to get stories sent straight to your inbox, but never hesitate to contact us and share your own experience.