From: Adam Seychell <ASeychell@vet.com.au>
Newsgroups: sci.chem
Subject: melting NaOH
Date: Wed, 30 Aug 2000 15:09:35 +1000

	I need to strip the baked enamel coating off copper winding wire. This
is for home use. Stripping the enamel is only done few centimeters from
the end so electrical connection can be made. I have bundles of thin
wires made up of as many as 100 strands. Somewhere on a newsgroup I read
that dipping in molten NaOH will remove the enamel, but when I tried
this I have trouble containing the salt. My iron crucible rusts in
minutes and CO2 from the gas flame reacts with the liquid NaOH forming a
solid Na2CO3 crust over top. Other than that it strips the enamel is
seconds leaving clean copper wire.

I could change to electrical heating, use stainless steel construction,
and minimize air exposure by using a small opening in the top just
enough to poke the wire through. Is this how its normally done ?

Adam

From: B.Hamilton@irl.cri.nz (Bruce Hamilton)
Newsgroups: sci.chem
Subject: Re: melting NaOH
Date: Fri, 01 Sep 2000 18:18:05 GMT

Adam Seychell <ASeychell@vet.com.au> wrote:

>	I need to strip the baked enamel coating off copper winding wire. This
>is for home use. Stripping the enamel is only done few centimeters from
>the end so electrical connection can be made. I have bundles of thin
>wires made up of as many as 100 strands. Somewhere on a newsgroup I read
>that dipping in molten NaOH will remove the enamel,
>...
>I could change to electrical heating, use stainless steel construction,
>and minimize air exposure by using a small opening in the top just
>enough to poke the wire through. Is this how its normally done ?

Certainly molten caustic is an excellent remover of enamel, I once worked
in a paint shop that had a 400 gallon mild steel, high-temp-steam heated
( around 320C, IIRC ), bath of sodium hydroxide - worked very well.
Problems were disposal of spent solution and high energy use, so it was
replaced with a methylene chloride bath with an alkaline water cover layer
followed by various jets to dislocate the paint and clean the surface.

The advantage of molten caustic is that it cleans to the metal
surface so you don't have to use additional processes to remove
any residual organic film before soldering.

I really don't believe that it's suitable for casual home use
without good ventilation, but if you are using one regularly,
you could set up an electrical heating system - being careful
to ensure that you heat from the outside of the tank to avoid
splattering. Aside from the various hazards - heating a solid
block of caustic to molten temperatures quickly requires care
- you need a large tank with a relatively small surface area
good insulation, excellent ventilation, located well away from
any water.

I suspect that you may find the quickest solution is to burn the
enamel off in a neutral or reducing flame followed by rapid
quenching to force the resulting carbon from the wires. You then
may have to reheat and allow to cool slowly ( in air ) to anneal
the wire again.

I suspect solvent-based enamal strippers will be slow and require
additional treatment to make the surface easy to solder without
using agrressive/corrosive fluxes.

        Bruce Hamilton

Date: Sat, 02 Sep 2000 16:00:24 +1000
From: Adam Seychell <aseychell@vet.com.au>
Newsgroups: sci.chem
Subject: Re: melting NaOH

Bruce Hamilton wrote:

> Adam Seychell <ASeychell@vet.com.au> wrote:
>
> >    I need to strip the baked enamel coating off copper winding wire. This
> >is for home use. Stripping the enamel is only done few centimeters from
> >the end so electrical connection can be made. I have bundles of thin
> >wires made up of as many as 100 strands. Somewhere on a newsgroup I read
> >that dipping in molten NaOH will remove the enamel,
> >...
> >I could change to electrical heating, use stainless steel construction,
> >and minimize air exposure by using a small opening in the top just
> >enough to poke the wire through. Is this how its normally done ?
>
> Certainly molten caustic is an excellent remover of enamel, I once worked
> in a paint shop that had a 400 gallon mild steel, high-temp-steam heated
> ( around 320C, IIRC ), bath of sodium hydroxide - worked very well.
> Problems were disposal of spent solution and high energy use, so it was
> replaced with a methylene chloride bath with an alkaline water cover layer
> followed by various jets to dislocate the paint and clean the surface.
>

Hi Bruce,

Molten NaOH is a fantastic remover, fast, leaves behind bright clean copper that
can be soldered straight away. In fact I have a another heated bath containing
molten solder. after the NaOH dip it goes into water, followed by solder dip. I
once tried methylene chloride paint remover (gel type) but had no success.

>
> I really don't believe that it's suitable for casual home use
> without good ventilation, but if you are using one regularly,
> you could set up an electrical heating system - being careful
> to ensure that you heat from the outside of the tank to avoid
> splattering. Aside from the various hazards - heating a solid
> block of caustic to molten temperatures quickly requires care
> - you need a large tank with a relatively small surface area
> good insulation, excellent ventilation, located well away from
> any water.

I'd prefer to stick to the NaOH, my bath is more like 150 ml not 400
gallons. I have a spare 500W heater element used for grills, I could coil
this around a steel pipe containing the molten caustic. Furnace insulating
wool could be wrapped around the hole thing with a final sheet metal
housing. I'm glad I can still use mild steel since it is easier to weld
and work with. Do you know what color the molten caustic was ? was it a
rusty color ?
How much air exposure did the bath get ?
Did you preheat the wire before immersing in the caustic bath ?
I find if the wire is cold then you get a significant about of solidified
NaOH covering the wire. I also found it important to do what 'Uncle Al'
suggested and spread the wire bundle to avoid capillary action of liquid
running up the strands.



>
> I suspect that you may find the quickest solution is to burn the
> enamel off in a neutral or reducing flame followed by rapid
> quenching to force the resulting carbon from the wires. You then
> may have to reheat and allow to cool slowly ( in air ) to anneal
> the wire again.
>

Burning seems to create too much solid carbon deposits and it them
becomes hard to remove it all off each individual strand.

Thanks,

Adam

From: Uncle Al <UncleAl0@hate.spam.net>
Newsgroups: sci.chem
Subject: Re: melting NaOH
Date: Fri, 01 Sep 2000 17:33:27 GMT

Roman A Kresinski wrote:
>
> Since nobody else's taken part I'll venture that '100
> strands' and 'home use' and 'normally done' don't really go
> together.  If I were doing it, I'd just put up with the
> indignity of stripping the wires by hand.  If you've tried
> it with your supply of wire and it's not worth the effort,
> then you're the expert and I believe your assessment of
> the comparison.  Molten NaOH is containable in a porcelain
> crucible for a good while, but it's a real pain, hot &
> terribly corrosive if spilt.  You seem to be a real
> enthusiast, so I'll mention that on an industrial scale
> you'd insulate the product with the fuel for the process.
> If *ever* you try this, and I *do not* personally recommend
> you do, look into the serious safety issues for yourself.

Spread the bundle to prevent capillary rise, soak in
N-methylpyrrolidinone for 10-20 minutes, wipe off loosened varnish.
If you are in a rush, heat the solvent. Solvent-based varnish
strippers are sold.

--
Uncle Al
http://www.mazepath.com/uncleal/
http://www.ultra.net.au/~wisby/uncleal/
 (Toxic URLs! Unsafe for children and most mammals)
"Quis custodiet ipsos custodes?"  The Net!

From: B.Hamilton@irl.cri.nz (Bruce Hamilton)
Newsgroups: sci.chem
Subject: Re: melting NaOH
Date: Sat, 02 Sep 2000 08:01:21 GMT

Adam Seychell <aseychell@vet.com.au> wrote:

> Do you know what color the molten caustic was ? was it a rusty color ?

No. It was a cream-blue colour, as the organics burned off and the
inorganic insoluble material settled out.

>How much air exposure did the bath get ?

Not much, we had good covers to reduce heat loss and caustic fumes.

>Did you preheat the wire before immersing in the caustic bath ?

No - we were stripping paint from metal hangers and appliance fittings,
and the large volume was sufficient for thermal inertia to heat items.

>I find if the wire is cold then you get a significant about of
>solidified NaOH covering the wire.

If you bath is molten, the thermal currents in the caustic should
soon remelt the caustic. If you are getting thermal conduction up the
copper wires you may need to insulate them or push them through a
cover aperture or metal block to speed removal of enamel.

>> I suspect that you may find the quickest solution is to burn the
>> enamel off in a neutral or reducing flame followed by rapid
>> quenching to force the resulting carbon from the wires. You then
>> may have to reheat and allow to cool slowly ( in air ) to anneal
>> the wire again.
>
>Burning seems to create too much solid carbon deposits and it them
>becomes hard to remove it all off each individual strand.

The carbon should be friable not solid, and I've found the quenching
dislodges most, as the copper changes size pretty quickly. However if
it doesn't work for you, then you could use the caustic method, but
be very careful - water and molten caustic can create awesome
explosions, and caustic fumes aren't nice.

If there is any possibly that the work will contain free water,
then you should pre-dry work, as 150 ml of molten caustic will be
splattered around by a few mls of water on submerging work. If
you build an insulated tank, ensure that moisture will not condense
on it and run into the caustic as it cools.

You may also find that any insurance policies on your property are
voided if you aren't complying with local regulations for such
things. Molten salt baths and case hardening compounds have fallen
out of favour here because of OSH and insurance issues.

       Bruce Hamilton