Lear Bead Detector Head

(Background of design)

The reeds would gently tough round wire at four locations (every 90 degrees around the circumference) and accommodate a large range of wire sizes with no adjustments. With wear, however slight and over a long term, this coverage would eventually increase to a full 360 degrees, with initial rapid wear, diminishing exponentially to a much slower wear rate as the contact area between the reed and wire surface increased due to limited profiling.

Desire features of the round wire reed design would include:

1. reed life of approximately 2-3 years
2. easy loading and unloading of the wire into the reeds
3. minimal to no damage done to the surface of the wire
4. capability to operate at high wire surface temperatures
5. high fidelity transfer of wire surface topography characteristics to active elements of the detector. This would require a fairly rigid thin reed which would provide good length resolution along the length of the wire and find closely spaced beads and HVC faults-pinholes.
6. as much surface contact between the reed and wire as possible
7. minimal cost to fabricate the reeds by some means

The material selected to meet the reed life, temperature, and rigidity requirements was ceramic but this choice gave rise to serious concerns of enamel abrasion and shaving.

A proprietary blend was selected that emphasized a rounded leading edge profile as wear related “breakaway” occurred. Extensive controlled testing over a two year period was performed to verify that the wire was not damaged. Extremes of wire speed, diameters, and enamels were included in the tests. Almost all of the testing was done on volunteer customer wire lines followed by periodic microscopic inspection of the enamel.

We now have 14 years of operating experience in many plants all over the world, and have found that all desired reed features were met or exceeded, with average lifetimes of 2-4 years (depending on wire diameter and speed) and without surface abrasions or shaving. For our full Fusions Systems where HVC test are also made using these same reeds, we found that the reeds could be made electrically conductive.

For proprietary reasons, we called the final reed material “Learium”.

The function of the reeds sliding along the surface of the wire is to; a) provide a running measure of the relative smoothness (texture) or graininess (not so smooth) of the enameled surface and; b) to provide an output of larger amplitude when a bead occurs due to the mechanical interaction of the reed with the bead. As said earlier, the long term variations are filtered out and intentionally not recognized as beads.

Sensors that are in surface contact with the reeds convert the reed vibrations into electrical signals. Within the head, these signals are amplified to survive the long trip back to the System Console where they are further amplified and filtered. The System Console will handle up to 12 detectors reporting simultaneously.

Within the PC, the surface signals are compared to bead severity threshold levels which have been keyed into a set-up menu and stored. Many other line parameters such as accumulated wire length have also been stored in order to correlate the bead occurrences to length.

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