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From: "Barry L. Ornitz" <ornitz@dpnet.net>
Subject: Re: Scrubbing Bubbles?
Date: 11 Jun 1999
Newsgroups: rec.antiques.radio+phono

TSchw10117 wrote in message
<19990610221253.00538.00000667@ng-fi1.aol.com>...
>Thank you Phil and Barry! I knew someone would have the answer....Now the
>question is, what does this do to the Bakelite? If clean Bakelite reacts
>this way, it must be leaching SOMETHING from the surface. I personally
>won't try it on an exposed radio cabinet surface.


You are welcome, Terry, but I have not discussed this yet!

Dow's "Scrubbing Bubbles" (I think technically known as Basin, Tub and Tile
Cleaner) contains a small amount of glycol ethers.  These are good solvents
and if the surface has any residual phenol, this will dissolve and turn the
foam brown colored.  However, this is not a very good test.
I can think of several types of plastics that could do this.  However, it
does not hurt the phenolic to use "Scrubbing Bubbles" on it.  The phenol it
removes should not be there anyway.

Also this test relies on the fact that old phenolic plastic must already be
degraded.  If the plastic is new, or has been recently cleaned, the test
will likely not work.  The reason that it works sometimes is that old
phenolic plastic parts in radios were never manufactured very well.
Bakelite is a CHEAP material, and if the phenol and formaldehyde are not
mixed in exactly the right proportions and/or the curing is improperly
done, the finished material will be more likely to degrade with age.
Properly proportioned and cured, Bakelite degrades very little.

Until thermoset polyester and epoxy resins became available in the 1950's,
Bakelite (and closely related melamine resins) were the only thermoset
plastics available.  Bakelite will not melt if heated, and its odor when
heated is extremely distinctive (the phenol).  I really do not understand
why it is so difficult for people to identify.

        73,  Barry L. Ornitz     WA4VZQ     ornitz@dpnet.net





From: "Barry L. Ornitz" <ornitz+U@dpnet.net>
Subject: Re: Glue for bakelite?
Date: 24 Mar 1999
Newsgroups: rec.antiques.radio+phono

Bob wrote in message <36F96324.5A7@erols.com>...
>Could anyone recommend a glue for repairing bakelite?  I'm looking for
>one that is thin enough in consistency to give seamless repairs.  I
>tried Krazy glue but it is ineffective on certain plastics including
>bakelite.  Thanks.


Bakelite, being a thermoset polymer, is not softened by the solvents in
glues.  Thus the only way for the glue to provide strong adhesion is by
mechanical means.  Roughening the surface for gluing therefore helps.
Properly applied the cyanoacrylate glues (super glues) do a great job.  But
the joint will always be weaker than the surrounding Bakelite.  For best
results with cyanoacrylate glues, the two surfaces must mate to very close
tolerances.  Epoxies also work well and can handle larger cracks but the
same caveats apply as to the mechanical adhesion of the joints.

        Dr. Barry L. Ornitz     WA4VZQ     ornitz@dpnet.net




 
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