The Real World of Magnet Wire Tests

A look into the history of developing devices to detect bead and HVC faults in magnet wire.

In 1975, I was demonstrating some equipment at a magnet wire plant along the Ohio River . After what I thought was a spellbinding presentation of the state-of-the-art laser equipment for measuring diameter, my audience yawned and asked if I knew what a bead was. I said no and was then told to pinch the moving coated wire between my fingers so that I could feel the surface texture. Intermittently, I felt little pimples whizzing through my fingers and was told that those were beads, and that was their real interest. Forget the laser diameter gauge. Could we come up with a way to detect these beads online? Of course I said yes (with my fingers crossed).

Define, Detect & Eliminate Beads

It turned out that the term "these beads" was as close to a bead definition as we could arrive at given the infinite number of shapes and orientations that were possible. What really mattered was how it felt to an operator's fingers and that feeling was virtually impossible to describe with numbers. Equipment is designed using numbers and we had none.

Not wanting to start a project on this basis, we elected to pass, for the time being. As it turned out, for 18 years.

Fast forward 20 years to the shipment of the first Lear Engineering bead detection system for 12 lines using computer-aided analysis and fancy graphics, still, with no formal and accepted description of what we were detecting. Our customer still had no better definition than touch nor did the various users of the magnet wire.

A successful approach resulted from utilizing principles first commonly used many decades ago in phonograph records and playback equipment with appropriate modernization and modifications.

Five years later (the year 2000), the system has been very successful across a broad spectrum of the magnet wire industry around the world. Users report great gains in the operator's ability to make bead free wire due to the immediate feedback of surface quality information.

One lesson from the above is to conclude, in this case, that it was much easier to design a product that did the job than to create a world accepted standard for dimensionally defining a bead. Try to imagine how long this might take. Is this the real world of test equipment design? Please read on.

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