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Bakelite question
#1
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HH56
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I would like to remove several layers of paint from a piece made of bakelite as safely as possible in order to make a mold casting. Requires getting into the small crevices to bring back the detail and particularly concerned about distorting the piece.

Is there a solvent that will do the job safely with brushing or wiping or even soaking without risk of damage to the structure. At a quick try of wiping, acetone works but want to make sure no underlying damage since some places will be difficult and will take lots of effort. I know from past experience on other less complicated pieces that whatever is in regular brush on stripper paste is not the answer as that softens.

Posted on: 2010/4/19 10:52
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Re: Bakelite question
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Owen_Dyneto
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HH56, I think that's going to be a tricky undertaking. Bakelite is a rather primitive plastic and is the reaction product of the condensation of phenol(s) and formaldehydes(s). By the use of subsitituted phenols and formaldehydes a rather large range of Bakelites can result with a rather large range of physical and chemical properties. Generally they are soluble in alkalis and don't have good organic solvent resistance and these two classes of compounds are common ingredients in paint strippers. I wish I had an answer, but don't - hopefully you've got some sacrificial parts to experiment with. If not, many of today's plastic household light switch cover plates are made of one of the Bakelite formulations and you could consider experimenting with them. I'd think any of the ester solvents (methyl, ethyl, butyl acetates, common components of lacquer thinner) would be very detrimental to the Bakelite; too bad, they're good paint solvents.

Posted on: 2010/4/19 11:01
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Re: Bakelite question
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Caveat first: This is advice rather than experience, but Bakelite is I believe formaldehyde-phenol product. I would expect polar solvents to be more likely to attack it. So be careful with the acetone. I'd try mineral spirits (mostly non-polar) first.

Posted on: 2010/4/19 11:05
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Re: Bakelite question
#4
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HH56
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Thanks everyone for the info but now you have me wondering if the piece is bakelite since a couple of you mentioned old technology. It is the air conditioning vent on the dash of 55-6s. It is black, somewhat brittle and always assumed since it is fairly heavy, not flexible and appears somewhat grainy & rough in a broken area to be bakelite. If not bakelite and anyone has another suggestion would sure appreciate hearing it.

Want to remove the paint from around script & the sharp crease where the finger pull is. The original mold I made some years ago is just too thin, a little indistinct in detail and, I didn't section it correctly for easy removal of finished piece so am starting another.

Posted on: 2010/4/19 12:22
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Re: Bakelite question
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Owen_Dyneto
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Yes, the Bakelites are generally VERY acid resistant, in fact they (a member of the Bakelite family known as novolac resins) are used as the photosensitive mask for semiconductor manufacture - they can resist some of the harshest chemicals around - BUT NOT alkali, that is what they are developed and stripped with.

I suspect the AC vents are not Bakelite, as cast it's parts generally have no flexibility to speak of.

Posted on: 2010/4/19 14:15
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Re: Bakelite question
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bkazmer
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I'm thinking maybe ABS. Fairly rigid, more so after aging and degradation of the rubbery part, easy to mold, and easily painted. Also really crummy solvent resistance!

Posted on: 2010/4/19 14:22
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Re: Bakelite question
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Owen_Dyneto
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Yes, I think ABS (acrylonitrile/butadiene/styrene terpolymer in techno-speak) would have been a very suitable plastic for that application. Someone might check that to see what kind of solvent resistance it has, I don't know off hand.

Posted on: 2010/4/19 14:32
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Re: Bakelite question
#8
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portlandon
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If I remember correctly, alot of the small table top radios of the 30's through the late 40's were made of bakelite. Their knobs were bakelite also. My Admiral table top radio is bakelite with bakelite knobs. Maybe you could find out how they strip them down for restoration.

http://www.antiqueradios.com/forums/

http://www.antiqueradios.com/forums/viewforum.php?f=7

Posted on: 2010/4/19 15:00
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Re: Bakelite question
#9
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portlandon
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Here is an answer from a bakelite radio knob restortation from this post:

LINK

"If the knobs are Bakelite, petroleum solvent stripper will remove the varnish. Like 5F5 or Strip-ease, etc.

If the knobs are some other kind thermoforming plastic then try an organic such as a lye based stripper or drain cleaner.

Orange based strippers are somewhere in between and may soften or craze if it is NOT Bakelite.

Always try a small daub of the stripper on the backside of the knob and leave it long enough to prove suitability.

I would suggest boiling water with Simple Green but that may deform some thermosetting plastics. It would ruin Tenite and craze Bakelite.

Good Luck!

Chas"

Posted on: 2010/4/19 15:10
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Re: Bakelite question
#10
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HH56
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I don't know what it is either anymore but if ABS, then nothing like todays. This piece has no flex and a kind of a hard sharp sound when struck and as mentioned, very brittle and cracks easily.

Whatever it is, I think it might have been at least partially or completely injection molded back then because of the complexity and thin sections. To pour in a mold like I'm doing, has to be done in parts, let cure a bit and turned several ways to get filling. Doubt they would have taken the time to do that in mass production--but lots I don't know about processes so anything including machining is possible. I'll plug away at it.

Posted on: 2010/4/19 15:15
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