[GreenKeys] GreenKeys Digest, Vol 82, Issue 27

[John Nagle]

On 11/30/2010 9:01 AM, greenkeys-request at mailman.qth.net wrote:
>> GreenKeys mailing list
>>  I am fairly certain the decomposing parts are polyurethane. In the
>>  early 1970s, it was considered a miracle material and used for an
>>  incredible number of applications. It worked very well, but no one
>>  apparently know of it's instability. The best recording tapes of that
>>  day used it in the binder  to hold the oxide coating to the base,
>>  these tapes are totally unusable about 95% of the time today. I have
>>  cleaned the gook out of a couple UGC-74s and substituted rubber tubing
>>  for the covering. The decomposition is greatly accelerated by heat and
>>  humidity, and tends to occur without warning over a short time.
>>  "Gumout" brand choke and carburetor cleaner did a good job getting the
>>  goo off everything. It won't dissolve it immediately all the time, but
>>  loosens it's grip on surfaces so it can be peeled off. It is one of
>>  the nastiest things you can imagine to get off skin and it stains
>>  clothing permanently. Do it outdoors away from any ignition sources,
>>  and wear old clothing and gloves.
>>  Bruce Gentry     KA2IVY

    Plastic stability was a major issue from the era of Bakelite to
the 1980s.

    I'm impressed with the materials choices in the Model 15.
Everything has held up well.  The machine is mostly steel,
of a good grade.  (That's not a given for 1930s steel.)
There are almost no rubber parts.  Where energy needs to be
absorbed, it's dumped into a spring and released slowly, as with
the insanely complex carriage return stop air cylinder.  The wire 
insulation has lasted because it is General Electric Deltabeston
felted asbestos wire with a silk or cotton exterior braid, the top
of the line in 1920s insulation technology.  (Don't strip that
wire; otherwise it's supposedly OK if undisturbed.)  Teletype
avoided the bad materials of the era - varnished cambric
insulation, pot metal, Bakelite, cast rubber, cast iron, and
soft woods.

    Incidentally, it is possible to return yellowed plastic cases,
as on the Model 33, to their original white.  The yellowing is
from bromine migrating to the surface, and there are
techniques involving hydrogen peroxide and UV light to remove it.

				John Nagle