[Jewelry making - Article 00162] - Re: [Orchid] Bezel Melting Problems

[Peter W . Rowe]

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>        I have to question this, Peter, though I can't remember the
>     last time you were wrong on a technical matter :-).  Charcoal
>     blocks get very hot and because they are a poor conductor of heat,
>     the heat doesn't spread out; it stays close to the heat source and
>     reflects back to the piece being soldered.  So rather than acting
>     as a heat sink, charcoal blocks serve to facilitate the soldering
>     process (unlike most refractory materials). 

    The charcoal blocks not only reflect the heat well, back to the
    metal, but any extra oxygen gets used in actually burning the
    charcoal, making the environment around the metal nicely reducing, so
    things stay cleaner, and in doing that, additional heat is also
    generated by the burning charcoal.  So yes, the charcoal blocks can
    considerably facilitate the process, as you say.  But for that to
    happen, the block has to be reached by the flame.  If the sheet
    metal is sitting right on the block, the area it's sitting on will be
    heated only by the metal, which, though not much, chills the metal,
    and won't cause actual combustion of the block.  Now, certainly as
    the block warms up, it then radiates this heat back to the metal, and
    doesn't cool the metal much.  But you get better heating if you lift
    the metal slightly above the block, so the flame can get underneath
    the metal.  Then the heat from the flame which heats the block
    reflects well into the metal, as well as the flame also heating the
    metal from below.  Try it and compare.  For small pieces, it's not a
    big difference, but as the surface area of the piece your soldering
    on gets larger, it gets quite noticeable.  One alternative to using
    nails or cotter pins that also works is just to cut some grooves in
    the surface of the block, again so that the flame can get underneath
    a bit.  And after a block has been used for a while, it's surface
    gets pitted and rough enough that even without the grooves, you get
    some air space, so then it also works this way. 

Peter


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