Tim Shoppa wrote in message
...
On Apr 11, 7:10 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.

I have found that many of the pot metal castings used for metal parts
on old radios, turntables, etc. have expanded over time.

I was astonished to learn that metal can do that in a timescale
measured in decades.

I'm sure that bakelite and other plastics can change dimension over
time too. Those I have a much easier time understanding, since the
evaporation (sublimation?) rate of the organic chemicals is always
something that I've associated with a timescale of years or decades,
and I know from my experience living in southern california that
exposure to ozone and intense sunlight can accelerate the process
incredibly.

My gut feeling is that just like different pot metal mixes exhibit the
expansion at different rates probably based on whatever they had to
throw in the pot that day, that plastics can vary based on detail of
manufacture too.

Tim.

+++++

The one this week was where the bakelite closure, top panel, was recessed
into the steel back body, so either metal had shrunk or the bakelite had
expanded over 70 years