Paul P wrote in message
...

wrote in message
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On Apr 11, 10:10 am, "N_Cook" wrote:
Another old piece of kit this week. Steel case with a bakelite closure
that
was a devil to separate. Metal not rusted and I'm assuming steel does
not
shrink over decades.

Catalin shrinks as Alan suggests - for two reasons. First, the water
entrained when froming the piece dissipates - this happens pretty
quickly. Then additional water and formaldehyde starts to outgas, this
is a gradual process taht depends on climate and temperature, but is
continuous to a greater or lesser degree until ultimately the material
will crumble altogether.

Bakelite uses a much different process although it is essentially the
same material as catalin (thermosetting phenolic resin) but it is
twice-formed and uses some sort of aggregate including colorants, wood
flour (again as Alan suggests), carbon-black, glass powder and fibers
and any of many other sorts of things. *Depending on the aggregate* it
is very dimensionally stable over time and under most conditions,
hence its favor for electrical parts exposed to harsh conditions, and
so forth.

White metal will expand, crumble or crack over time depending on its
composition and environment. Most other pure metals or alloys are
diminsionally stable excepting expansion and contraction for due to
temperature - although some alloys of steel will expand under certain
kinds of radiation - which if they exist in your home to that extent,
you are dead already. Some types of glass will turn purple with age,
some say due to ultra-violet, some say due to cosmic rays as it will
turn purple whether inside or out. Pick whichever you choose.

Peter Wieck
Melrose Park, PA

At the risk of sounding gross, what is the type of plastic that smells
like......vomit?

Paul P




And while at it , what glue, or whatever, breaks down over decades to give
the small of rotted horse manure, not fresh, maybe referred to as a
"caproic" (goaty) smell . You open up some kit and there is that small that
can saturate the workroom for hours before it dissipates.