Eric Stevens wrote:

On Mon, 05 Jul 2004 01:30:53 GMT, Seppo Renfors
wrote:



Eric Stevens wrote:

On Sun, 04 Jul 2004 02:36:09 GMT, Seppo Renfors
wrote:

---- snip ----

And while copper can be welded, in
an inert atmosphere, by melting, it can also be welded at lower temperature
by pressure.

You are wrong, particularly in the case of copper. The power in your
house comes to through a large number of cold welds formed merely by
pressure. This is true irrespective of whether you are supplied via
copper or aluminium cables.

I suspect you snipped the wrong text there! What you left isn't mine.

But then explain how come each strand of a multi-strand cable can
easily be separated from each other - even if very fine strands?

The point is that they have not been forced together under pressure.

If you add enough pressure to distort metal you cause friction and
friction causes heat, the heat is sufficient to "weld" - whatever you
are joining.

Also
electricity uses only the surface of any wire - so it isn't as if it
holds the wire together either.

You are thinking of the 'skin effect' which applies to high
frequencies. You can ignore it for DC of ordinary AC.

You tell that to my brother-in-law and nephew (both electricians), and
they will have a good laugh..... of course it matters for both AC and
DC - it governs the current the cable can carry. I refer you to fuse
wire as an example.

[..]

Ahhhh..... nothing to do with welding at all. You are barking up the
wrong tree - try simple air pressure. Two steel blocks each with a
perfectly smooth surface, and you place those surfaces together - you
can lift the bottom block solely by lifting the top one (momentarily
at least). Air pressure, is what is holding them together. I have a
set of dies made for me by a tool-maker mate that I can demonstrate
exactly that with.

I bet they weren'r of grade 0 or 00 quality. If they were, you
wouldn't want to leave them together overnight.

A reference to a "set of dies" does rather tell you of harsh use - eg
subject to impacts therefor excessively fine tolerances are not
wanted/needed. Further to that the tools are much finer than
commercially bought similar items. They are quite sufficient to
demonstrate the effect.

[..]


--
SIR - Philosopher unauthorised
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The one who is educated from the wrong books is not educated, he is
misled.
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