FAQs – Magnetic Yokes

 What is a Yoke and when would you use one?

A magnetic Yoke is a portable device for detecting surface and sub-surface cracking in any ferro-magnetic material. Magnaflux EMEAR Yokes handle the most demanding inspection jobs with ease; their portability makes them ideal for in-plant inspection and repair of welds, automotive components, steel and grey iron castings, and many other applications.

 What types of Yoke does Magnaflux manufacture?

Magnaflux manufactures several types of Yoke under two different ranges.

In the Magnaflux range:

  • Y1 – an extra-lightweight AC electromagnetic Yoke
  • Y6 – a lightweight AC electromagnetic Yoke
  • Y7 – an AC/DC lightweight Yoke
  • Y8 – a battery powered DC Yoke

In the Tiede range:

  • TWM 220N – a lightweight AC electromagnetic Yoke.
  • TWM 42N – a lightweight AC electromagnetic Yoke; 42V.

The Magnaflux and Tiede Yokes differ in construction: the Magnaflux Yokes come with adjustable legs and pole pieces; the Tiede Yokes utilise separate legs and pole pieces.

 How can I check the performance of my Yoke?

You can check the performance of your Yokes with a  lift test using standard test weights as follows:

  • DC test – 18 Kg test weight – Y8, Y7 (DC mode). Can also be used with the electromagnetic Yokes when attached to a DC source such as a battery. If the Yoke lifts the 18 Kg test weight, it is OK to use.
  • AC test – 4.5 Kg test weight – Y1, Y6, Y7 (AC mode). If the Yoke lifts the 4.5 Kg test weight, it is OK to use.

More information on this test can be found in the Y6 lift test operating instructions.

 What is the difference between using AC and DC when using a Yoke?

Several current forms can be used in magnetic particle inspection. Alternating current (AC) is used to detect surface defects, whereas rectified current and direct current (DC) are used when defects are likely to be sub-surface.

The ability to detect sub-surface defects and the limit of the defect is a contentious subject. This depends on many factors, not least of which is the test environment itself. For example, defects detected within a laboratory set-up on an ideal specimen will almost certainly not relate to a welder’s findings on-site in the middle of winter. Coupled with this, the size and orientation of a sub-surface defect can potentially have a major effect because the flux leakage on the surface will be present as a broad outline. This may not be easily detectable against the background.

 Can I convert an AC electromagnetic Yoke into a DC Yoke?

Yes; if you attach the cable of the Yoke to a 12V DC battery, you can make an AC Yoke into a DC Yoke. It can then be used to detect sub-surface defects.

 What is the correct orientation for a Yoke when looking for defects?

The correct orientation for a Yoke is perpendicular to the direction of the defects. Place the Yoke onto the surface of the test piece so that the defect is at 90° to the lines of force.

 Are all Magnaflux Yokes certificated and CE marked?

Yes, all Magnaflux Yokes are certificated and carry the CE marking. They all carry a unique serial number for identification purposes.

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