Dear Bill, LF Group,
I have a considerable amount of Litz wire recovered from a scrap Decca
loading coil - as has been said, there is more than one type of enamel
used. The newer type (usually orange, red or pink) is self-fluxing, which
is easy, but the type I have is a dark brown enamel that seems impervious
to any chemicals I have tried, including Nitromors and other types of paint
stripper. The alcohol burner method removes it well, but with 729 strands
it is not really practical to burn the insulation off all the strands
without causing a raging inferno! Similarly, the asprin method works to a
degree, but it only cleans some of the strands with thick litz wire, the
residue makes it difficult to repeat the process to clean the remaining
strands, and the smoke generated is horrendous!
The method I have used is to burn the insulation off with a blowtorch - but
to do this without burning away a lot of the strands some care is needed.
First, strip about 70 - 100mm of the plastic sheathing, and un-twist the
end 25mm so that the strands are like a small paint brush. Then, tightly
wrap this end in a strip of copper foil, such as might be peeled off a PCB.
Wrap the strands next to the plastic sheathing in another piece of foil,
and clamp in a metal clamp or vice - this acts as a heatsink to stop the
sheathing melting. Then heat the foil-wrapped end with a blowtorch, taking
care to apply the flame only to the foil, not the strands. The foil gets
red hot, and the enamel burns off with an oily flame. After it has cooled,
unwrap the foil - it looks like the enamel has just turned black, but the
residue can be removed fairly easily by dipping it in water and brushing
gently with a toothbrush, or rubbing the strands together like cleaning a
paintbrush, to leave clean copper. Then it can be tinned in the normal way.
I can't say it is an easy method, but it does work with otherwise
indestructible enamel, and after a few practice runs it gave me
satisfactory results for my loading coil.
Cheers, Jim Moritz
73 de M0BMU
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