[Collins] FW: [Hallicrafters] Bakelite knob cleaning

Sun, 13 Jan 2002 14:10:32 -0500

Interesting reading for those of us who are interested in polishing Collins
knobs.

David Knepper - W3ST
Publisher of the Collins Journal
Secretary to the Collins Radio Association
CRA website:  http://www.collinsra.com

-----Original Message-----
From: [email protected] [mailto:[email protected]]On
Behalf Of [email protected]
Sent: Sunday, January 13, 2002 9:02 AM
To: [email protected]; [email protected]
Subject: Re: [Hallicrafters] Bakelite knob cleaning

It is important to understand how Bakelite parts are made, what the nature
of
the material is and what happens to it over time. This will help us conserve
what's left and decide on a good approach to make the part presentable
again.
Bakelite was invented in 1907 and is what they call a thermosetting phenolic
resin. It is composed of two entirely different substances (formaldehyde and
phenothalene I think) that react under temperature and pressure to form a
new
material which remains permanently set when formed. After curing it is a
hard, tough and durable substance that is mostly unaffected by temperature,
pressure, and most chemicals (extremes notwithstanding). Usually a filler
material was added to the mix such as wood flour or ground mica among others
before it was poured in the molds. Sunlight is the main enemy of Bakelite
causing its surface to degrade and decompose over time. Many times this
decomposition of the surface is not noticeable right away on a radio that is
about to be cleaned because the knobs have body oils, dirt and other foreign
substances deposited on the surfaces which make them appear shiny as new.
Good Bakelite will be unaffected by the application of most cleaning agents
but decomposed Bakelite will easily wash off with what appears to be a
stream
of brown liquid rinsing off the part. This is usually thought to be nicotine
at first, then when the part has dried it is discovered the part has lost
its
gloss. This is because the glossy surface is gone and the underlying filler
material is now exposed giving the part a dull grainy appearance. It is
generally concluded the part was attacked and made dull looking by the
cleaning agent but this is actually not the case. Here's what happened: When
the resin with the filler was poured in the mold and cured, the curing
process caused a very thin skin of pure resin to form at the surface
resulting in a very high natural gloss. The powdery filler starts just below
this glossy surface. If sunlight and other environmental mechanisms are
allowed to attack this very thin glossy skin over time the filler material
will be exposed when the decomposed resin is washed off resulting in a dull
looking part. No amount of polishing will completely restore the appearance
of the part although with a lot of effort and hand labor using various
automotive compounds and waxes an acceptable compromise can often be
reached.
My personal favorite that seems to nourish the surface back to a pretty good
looking gloss is a furniture wax that contains beeswax called MinWax. Many
other hobbyists recommend painting the part afterwards to restore appearance
but paint is soft and not very durable unless a hardener is added and the
paint cured at high temperature.

Regards, Greg Gore; WA1KBQ

List Administrator: Duane Fischer, W8DBF **for assistance**
[email protected]
---
Hallicrafters Collectors International: http://www.w9wze.org
---
Submissions [email protected]
Subscriptions [email protected]