From: SFPhysics@aol.com
Date: Sun Dec 21 2003 - 01:51:36 PST
From: SFPhysics@aol.com Message-ID: <f5.35a848e3.2d16c728@aol.com> Date: Sun, 21 Dec 2003 04:51:36 EST Subject: Metal to Metal cold welding...
Normally metals have a thin crust of oxide and impurities on their surfaces
which will prevent a cold contact weld. Two machined metal surfaces placed
together normally still have only about 1% actual contact area due to microscopic
surface roughness. However two pieces of metal will contact weld if the
clean mating surfaces are very finely polished, matching in shape, and pressed
together in an inert atmosphere. The process relies on electron migration and
crystal lattice connection. Industry uses cold welding for many applications
and found it a problem in nuclear weapons manufacturing and space technologies.
One related modern process is called ultrasonic welding and utilizes an
ultrasonic vibration to push out trapped gas molecules, abrade away surface
impurities, and grind irregularities smooth at the atomic level. The very small
amount of energy applied causes a slight thermal response but still way below the
melting point of the materials. These cold welds are used mostly in the
semiconductor industry where heat would destroy the semiconductors when the pin out
leads are being wired onto the chips.
Happy Holidays to everyone,
Al Sefl
Who has been known to become cold welded to his Lazy Boy Lounger...
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