Homebrew PCBs

Hello,
I'm wondering it its possible to seal the shaft from a very low 
RPM (< 20 RPM) electric motor (stepper maybe), enough so its 
protected from splashes of etchant. Of course a suitable plastic 
sleeve will be needed on the metal shaft so no metal is exposed. 
A quick google search showed a typical commercial waterproof 
motor will use two shaft seals and design to run ten meters under 
sea water.
I'm thinking even if etchant doesn't get inside the motor housing 
then fumes might, and so could possible corrode the steel.
Any thoughts ?

Adam Seychell wrote:
> Hello,
> I'm wondering it its possible to seal the shaft from a very low 
> RPM (< 20 RPM) electric motor (stepper maybe), enough so its 
> protected from splashes of etchant. Of course a suitable plastic 
> sleeve will be needed on the metal shaft so no metal is exposed. 
> A quick google search showed a typical commercial waterproof 
> motor will use two shaft seals and design to run ten meters under 
> sea water.
> I'm thinking even if etchant doesn't get inside the motor housing 
> then fumes might, and so could possible corrode the steel.
> Any thoughts ?
> 
   No point in over-engineering this, use a $5 stepper and throw it away 
as needed.  Less than 20 RPM likely won't even matter if the bearings 
corrode, and there's little else inside.  If you still want some 
protection, take a plastic bag of the right type and pull it up the 
shaft and it'll stretch and conform to the shaft.  You should be able to 
get an inch of cover on the shaft this way.  Then cut off the rest of 
the bag, and pull another piece up the shaft a bit.  Tear a hole so it 
then rides up the shaft, having a quarter inch or so of plastic pressing 
against the shaft and on top of the first piece, and the rest of the bag 
goes around the motor.  Not exactly high tech but enough that it'll be 
likley to outlive both of us.

Alan

--- Adam Seychell <adam_seychell@...> wrote:
> Hello,
> I'm wondering it its possible to seal the shaft from
> a very low RPM (< 20 RPM) electric motor (stepper
> maybe), enough so its protected from splashes of
> etchant.

Yes:

2.) 60+ minute polyester resin, which is also known as
epoxy, is both water, gasoline, fecl and hcl proof
(Just to name a few). I've used this in many
applications as a chemical barrier. It's effective,
cheap and lasts longer than anything else I've found.
I have appliations where it has literally lasted 10
years. This soltion is great for metal, plastic or
anything else you can think of. This is a high
friction solution.  

It's done like this:

A.) Clean the area to be protected with 0000 steel
wool and Ajax or comet. Wipe this stuff off really
well with a rag and some h20. 

B.) Dry with 100% denatured alcohol and a clean paper
towl. Be sure the area is TOTALLY clean. This is
vitally important.

C.) Protect the area you do NOT want any epoxy or
lagur with petroleum jelly.

D.) Apply 3 coats in very thin layers with a bush. Let
each coat dry over night (24 hours at least) before
applying the next coat. Rough each coat up with 0000
steel wool (Clean again with denatured alcohol and
leave no debre) before applying the next coat.
Anything over three coats will not provide additional
protection and could mechanically bind whatever your
protecting if you apply too much.

E.)  If a sleave or anything else is going to be in
contact with the area you have applied the protective
coat, and this sleave or whatever it is will be
subject to friction, apply a liberal coat of petroleum
jelly between the area you protected and the sleave. 


This is a well known, tried and true solution for
protection from chemicals in industrial, military and
aviation enviroments

Best regards

Marvin Dickens
Alpharetta, Georgia

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--- Adam Seychell <adam_seychell@...> wrote:

> I'm thinking even if etchant doesn't get inside the
> motor housing 
> then fumes might, and so could possible corrode the
> steel.

Adam, 

For whatever reason I did not read this part of your
post. I think you are guaranteed a fine micro mist of
etchant (Just like in a hot shower) inside the etching
machine. The only answer that I see as viable (But not
practical...) is to totally disassemble the motor and
apply protectant to every part that is suspect. If
possible, I would attempt to figure out how to mount
the motor outside and away from the etchant.

Best regards


Marvin Dickens
Alpharetta, Georgia  USA


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Your suggestion about sealing metal parts with polyester resin 
was useful nevertheless. I should of mentioned that I wanted to 
run a stepper motor inside the etch chamber to drive the conveyer 
assembly directly. The motor will be housed in a sealed PVC 
enclosure (made from section of 90 mm diameter PVC storm water 
pipe and a press fit end cap) The motor's plastic shaft will exit 
one side of the PVC enclosure and pass through two rotary seals 
before being exposed to the chamber atmosphere. I bought a couple 
of oil seals (Nitrile rubber, 8 mm ID) to try out. You are right, 
about etchant mist. When I tested the nozzle and pump I used a 5 
liter bucket and directed the nozzle to the bottom. When it was 
running a fine aerosol of etchant was forming all around the 
bucket, and you couldn't stand near it or you'll choke :)

The only reason I'm trying to put the motor inside and mounted 
directly on the conveyer assembly is because it will greatly 
simplify its design and construction than trying to drive it 
externally.




mpdickens wrote:

> --- Adam Seychell <adam_seychell@...> wrote:
> 
> 
>>I'm thinking even if etchant doesn't get inside the
>>motor housing 
>>then fumes might, and so could possible corrode the
>>steel.
> 
> 
> Adam, 
> 
> For whatever reason I did not read this part of your
> post. I think you are guaranteed a fine micro mist of
> etchant (Just like in a hot shower) inside the etching
> machine. The only answer that I see as viable (But not
> practical...) is to totally disassemble the motor and
> apply protectant to every part that is suspect. If
> possible, I would attempt to figure out how to mount
> the motor outside and away from the etchant.
> 
> Best regards
> 
> 
> Marvin Dickens
> Alpharetta, Georgia  USA
> 
> 
> =====
> Registered Linux User No. 80253
> If you use linux, get counted at: 
> http://www.linuxcounter.org
> 
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> Do you Yahoo!?
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>

--- Adam Seychell <adam_seychell@...> wrote:

> When it was 
> running a fine aerosol of etchant was forming all
> around the 
> bucket, and you couldn't stand near it or you'll
> choke :)

micro particulant misting... Great for some apps, but
pretty much sucks when corrosive or otherwise
dangerous chemicals are involved. However, I have been
giving this some thought in that I thought it was
going to be an issue.

The micro particulate mist is airborne for two
reasons. It has a strong electrical charge (For a
liquid of it's compostion) and it is close to the
weight of air. The electrical charge is our friend and
is going to help us get rid of the mist and the weight
issue is really a non-issue (As far as impeding the
removal of the mist) because the mist is not lighter
than air. 

The electrical charge was created at moment the
etchant was forced through the plumbing and spray
nozzles at a high pressure/speed. Further,  this is a
common problem in industrial environments that utilize
high pressure and spray nozzles. There are two ways to
fix the problem.  You either reverse the electrical
charge of the micro mist at the nozzle (In this case,
depending on the material(s) that compose the nozzle,
this may not be practical) or you put a plate made of
metal that is corrosive resistant in the etch tank and
give it a strong postive charge (Some apps have a
plate on each wall of the tank). The micro mist will
quickly move to the plate and deposit itself on to
it's surface. It's actually pretty neat to watch...


Best regards


Marvin Dickens
Alpharetta, Georgia  USA

=====
Registered Linux User No. 80253
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--- In Homebrew_PCBs@yahoogroups.com, mpdickens <md30022@y...> wrote:

> 2.) 60+ minute polyester resin, which is also known as
> epoxy, is both water, gasoline, fecl and hcl proof
> (Just to name a few). I've used this in many
> applications as a chemical barrier. It's effective,
> cheap and lasts longer than anything else I've found.
> I have appliations where it has literally lasted 10
> years. This soltion is great for metal, plastic or
> anything else you can think of. This is a high
> friction solution.  

Polyester resin and epoxy are two very different things. And are not
equally effective to all solvents.

However, since this is not structural it doesn't matter so much if it
softens as long as it doesn't swell enough to crack or fall off.

Steve