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? Also
electricity uses only the surface of any wire - so it isn't as if it
holds the wire together either. I think you are confusing something
with "welding".


No it can't. "Pressure" in itself does almost nothing. A loaded
freight train running over a "copper" coin only flattens it and does
nothing else. It is the sudden impact pressure that causes the
molecules to move rapidly, that causes FRICTION, which in turn causes
heat and if sufficient sudden pressure is applied (eg hammer blow to
already hot metal) it CAN melt the material. To "weld" something by
definition requires bringing part of it to a liquid state - ie melted
in the portion being welded.

How do you explain the well known welding at ambient temperatures of
precision slip-gauges made of hardened steel? Leave them in contact
overnight and you will be lucky to get them apart in the morning.

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.

Not knowing what a "slip-gauge" was, I looked it up and they tell the
same story.

http://homepage.tinet.ie/~jcelce/sub...metrology.html
"The measuring faces of Slip Gauges have such a good surface finish
that when you place two gauges together with their measuring faces in
contact, and slide one gauge over the other, they will wring together.
Basically this means that they are almost stuck together, and that
they will not slide off each other easily."

Nothing at all to do with welding.

--
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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