Subject: How To Pull Vacuum?

From: [email-masked] (John Earle)
Date: 6 Dec 1996 21:58:32 GMT

Hi and thanks for reading this posting.  I am working on a small
project to pot (embedd) some electronics in an epoxy and once
the mixture is stirred up it's full of air bubbles - the data sheets
say to pull a vacuum on the mixture - I assume this is with some sort
of inverted bell jar or something.  Anyone got any experiencee with this
sort of procedure and if so, where would I go to scare up some
equipment "a la cheap" to rig up a small setup?

Maybe those little venturi based gadgets hooked to the compressor would 
work? then again - perhaps it would take all day...

Anyway, any help people can provide would be much appreciated.

---

From: [email-masked]
Date: 7 Dec 1996 14:43:33 GMT

Cole Palmer sells a lexan vacuume jar and base cheap <$100. Any small
vacuum pump will do for your application. Oil type are best and can be
found used for about $200. The venturi model might work as well.

---

From: Jay Hayes <[email-masked]>
Date: Fri, 06 Dec 1996 23:51:13 -0800

> Anyway, any help people can provide would be much appreciated.

John,

Depending on how much open time your potting compound has(the time you
have to mix and work with the mixture before it starts to gel), and the
volume you need to evacuate, you will probably need a decent vacuum
pump.

I mix a lot of resins and use a (real) 1/3 HP rotary vane vacuum pump
and 12" bell jar. I bought them from a lab supply about fifteen years
ago and they are indespensible for processing some of the resins. It
cost a few hundred for the set-up but it paid for it self in no time.

I've used asperator type eductor vacuum generators, refrigerator
compressor conversions and reversed air compressors. None can compare to
the real thing. This is especially true if you are working with fast
reactions like urethanes and or high viscosity materials like silicones.
If you don't pull a good vacuum fast your mix may set while it is
frothing. If your use is limited you can use a vacuum tank to help speed
up your pull down. Used vacuum pumps are also an option.

The quality of the bell jar is really important too! Mine is molded
Lexan. I shutter to think what would happen if a glass jar imploded
while soneone was standing next to it. For safety sake don't skimp here.

Hope this helps,

Jay

---

From: Michael Hanz <[email-masked]>
Date: Mon, 09 Dec 1996 10:13:00 -0800

If you're trying to minimize cost, don't forget the big vacuum pump 
sitting in the garage...the family car.  You can pull a 20" vacuum from 
it any day of the week (unless you have a racing engine.)  All you need 
is a long hose and a way to get to the intake manifold.  I've used it for 
everything from evacuating A/C systems to "debubbling" epoxy and it seems 
to work just fine.  Maybe not ideal, but it's cheap!

---

From: [email-masked] (George Butts)
Date: Mon, 09 Dec 96 15:07:06 GMT

I don't think you want MUCH vacuum for this purpose.  I use the back end of an 
old paint sprayer, the intake side.  The "tank" is the bottom and gasket from 
a Nesco pressure cooker.

This cooker is the type which has a domed top with a little "spigot" on which 
you place a round weight.  In regular use the weight jiggles when up to 
pressure.  The little spigot is perfect to slip on the vacuum hose.

Immediately, I saw the casting syrup was viscous enough that the air was slow 
to release and foamed up all over the tank... so I replaced the (metal)regular 
lid with a 1/2in thick square of Lexan plastic.  Lexan can be drilled and 
tapped nicely.  Thru this new lid, I installed a standard lab gas-cock as an 
exhaust fitting for the vacuum hose.  Then, I could see what was happening 
inside.  Promptly, I saw the "fix" for the frothing was to put another lab 
gas-cock to let me moderate the pressure.  Then, I saw the air feeding in the 
second opening impinged on the syrup which, in my work, was VERY helpful to 
break the rising foam.  I could also insert a few drops of surface foam 
breaker in stubborn cases thru this intake port.

If you can't watch the process and moderate the foam-up problem, you risk 
damage to pulling some of the froth into the vacuum system...  not too swell!
Cost?  Lexan is not cheap.  Nesco cooker with gasket is "free" from our 
kitchen when I can get it out from under certain watchful eyes.  The paint 
sprayer is from (about) 1955 and very useful for small pressure work (up to 
30lbs) in our shop.  Now it's useful for vacuum work also, but that's not it's 
proper use and I don't know how newer/other sprayers would respond to using 
its air intake end.  This sprayer intake is threaded so I just put it to use 
with little to lose.

..good luck, gtb  

In article <[email-masked]>, [email-masked] (John 
Earle) wrote:
|
|Hi and thanks for reading this posting.  I am working on a small
|project to pot (embedd) some electronics in an epoxy and once
|the mixture is stirred up it's full of air bubbles - the data sheets
|say to pull a vacuum on the mixture - I assume this is with some sort
|of inverted bell jar or something.  Anyone got any experiencee with this
|sort of procedure and if so, where would I go to scare up some
|equipment "a la cheap" to rig up a small setup?
|
|Maybe those little venturi based gadgets hooked to the compressor would 
|work? then again - perhaps it would take all day...
|
|Anyway, any help people can provide would be much appreciated.
|
|

*---------------------*
* George Butts, KC8T
* Laurie Butts, N8CKI
* [email-masked]
*---------------------*

---

From: Bob Stout <[email-masked]>
Date: Mon, 09 Dec 1996 07:49:03 -0800

> Anyway, any help people can provide would be much appreciated.

Actually, you can get a bell jar assembly and a small hand pump (similar
to those for pulling a vacuum in auto repair) from Edmund Scientific.
Shouldn't be more than $100.00. Works well for your application (been
there, done that).

Bob Stout

---

From: [email-masked]
Date: 9 Dec 1996 21:16:03 GMT

>to work just fine.  Maybe not ideal, but it's cheap!

This is the *really* neat thing about NGs. What a clever idea, $1.00 for
hose from Home depot.

Peter
Still learning.

---

From: [email-masked] (Andy Dingley)
Date: Sun, 08 Dec 1996 11:30:00 GMT

The moving finger of [email-masked] (John Earle) having
written:

>[vacuum degassing epoxy]

You're fortunate in that you don't need a vacuum here, just a pressure
reduced from that in the bubbles. It's nothing like the quality of
vacuum you'd need for laser work.

You can do this with a fridge compressor from an old fridge. They're
not the greatest vacuum pumps, but they'll work well enough for this,
so long as you only use a small volume belljar.

Belljars shouldn't be made of glass, unless they're the genuine
article and in good condition. Even then they need to be carefully
sealed against a flat plate with proper vacuum grease. Glass belljars
should be covered in a wire mesh cover, in case of implosions.

Another belljar alternative is a domestic pressure cooker. You remove
the weight fitting and use it for a vacuum connection, and invert the
rubber safety valve. If it uses a "V" seal, that will need replacing
by a length of O ring (the V is designed to seal against internal
pressure, not external).

Another alternative is the ubiquitous surplus shop - vacuum pumps turn
up pretty regularly.

--
Andy Dingley                          [email-masked] 

ISO9000 :- A technique for perfectly managing the development
of a software product so inflexible and hidebound as to be 
completely useless.

---

From: "J. M. Reid" <[email-masked]>
Date: Mon, 09 Dec 1996 17:27:08 -0700

> > the mixture is stirred up it's full of air bubbles - the data 

Whoa!  A really good vacuum will cause enough bubbling to really foul up
your source!  On top of that it will vaporize the hardener so what is
left won't set.

The cheapest source of vacuum is an aspirator.  A device that fastens
onto a foucet and uses the venturi effect to pull suction on a side
arm.  They are available in metal from Scientific Supply houses.  Our
local TArget stor has plastic ones in a waterbed filler kit for about
$5.00

Of couser, the family car is still good, but proyect it with a liquid
trap:  a jar with inlet and outlet tubes epoxied to the lid so liquid is
trapped there.

cheers

j.m. Reid

---

From: [email-masked] (Jonathan M. Elson)
Date: 10 Dec 1996 19:18:36 GMT

Michael Hanz ([email-masked]) wrote:
: If you're trying to minimize cost, don't forget the big vacuum pump 
: sitting in the garage...the family car.  You can pull a 20" vacuum from 
: it any day of the week (unless you have a racing engine.)  All you need 
: is a long hose and a way to get to the intake manifold.  I've used it for 
: everything from evacuating A/C systems to "debubbling" epoxy and it seems 
: to work just fine.  Maybe not ideal, but it's cheap!

YIKES!  Not only is this now illegal, but haven't you heard what happens
when you decompose Freons by combustion?  You get HydroChloric Acid,
HydroFluoric acid, and maybe even Phosgene!  When evacuating an A/C system,
you always get Freon residues, at least from refrigerant dissolved in the
oil!
>From  your address, I think I live far enough away to be safe, but I'm
worried for your neighbors.
						Jon

---

From: [email-masked]
Date: 10 Dec 1996 23:18:19 GMT

In article <[email-masked]>, [email-masked]

>worried for your neighbors.

That's the second curiously quaint response I have read from you Jon. May
I suggest you *read* the questions and *think* about them before shooting
>from  the hip, lip or fingers.

Peter

---

From: Janos ERO <[email-masked]>
Date: Wed, 11 Dec 1996 15:34:00 GMT

> to work just fine.  Maybe not ideal, but it's cheap!

Please! Don't do this with a car equipped with a regulated catalythic converter. 
After a few actions you probably have to replace the converter. 

Janos Ero

---

From: Regis Galbach <[email-masked]>
Date: 6 Dec 1996 22:44:30 GMT

Try looking for a used jewelry vacuum caster.  New ones can run as low as 
$450 so maybe you can find a cheap used one.   These pull about 
26 microns.

Regis

---

From: [email-masked] (Robert Galloway)
Date: 10 Dec 1996 11:08:03 -0700

You might check with refrigeration suppliers/servicemen for a used vacuum 
pump.  The pumps used to evacuate a refrigerations system reach about the 
same vacuum as laboratory pumps do.

rhg

In article <[email-masked]>,

---

From: [email-masked]
Date: Fri, 06 Dec 1996 23:01:05 -0500

> Anyway, any help people can provide would be much appreciated.

Having done what your about to tackle, a few suggestions.

1. Put the ingredients in a container that will give you the largest
surface area you can get a vacuum on. ie: use a bowl in place of a
coffee cup if you can.
2. Only fill the container 10 to 25 % until you determine how much
outgasing you are going to get from the encapsulating material. It can
bubble up a considerable amount before the outgasing is complete. (many
times is original volume)
3. Have a valve that will allow you to relieve the vacuum quickly.
4. Make sure the material you are outgasing will not damage the vacuum
pump, you might need some sort of trap/filter or special oil for the
vacuum pump.
5. I've seen some operations that use the vacuum generated from the
suction line of an old refrigerator compressor. (cheap but effective)

Oh one last thing, when you mix the material try to avoid
whiping/beating it like you were making whip cream, try to fold the
resin and catalyst. Yea, I know it sounds a little strange but it makes
a big difference as to how much air gets entrapped in the material. 

good luck 
pht

---

From: Michael Hanz <[email-masked]>
Date: Tue, 10 Dec 1996 19:49:51 -0800

> : sitting in the garage...the family car.
>

That's a fair comment, and one should always be thoughtful about the systems one
evacuates.  It does highlight the problem of being brief and offering help as opposed
to two pages of qualifiers, however.  You will note that I did not advocate it - just
reflected experience with it.  To bring some balance to the issue, one would always use
a vacuum pump to evacuate a fully loaded system when it needs a compressor replacement
or the like and the refrigerant needs to be recycled.  You would obviously not use the
automotive method there.  Since Jon wasn't aware, I'll only comment that all my
applications were with systems that had been totally open to the air before
evacuation...folks brought them to me because they didn't know what to do next.  The
last time I used it for an A/C system was about five years ago, so I think I'm safe from
a legal standpoint.  BTW, I'm not totally ignorant of the byproducts of combustion, so I
always did it on a breezy day out near the barn.  Today I did warn my neighbor a couple
of miles down the road he should start looking for signs of ill health.  He said he
would, just as soon as he got home from his 2 hour commute through the smog alert.  The
cows HAVE been acting strangely lately, come to think of it...but it might be the
X-Files they like to watch on Sunday night.

But the comment is a good one, and I support it - every situation needs some thought,
and next time I suggest an idea to the NG I'll properly caveat all the things one should
NOT do with it.

Regards,
Michael Hanz

---

From: "Ginsberg Family (Ed Ginsberg KE6BNL)" <[email-masked]>
Date: Mon, 09 Dec 1996 14:34:00 -0800

Don Buchan wrote:
> 
> On 6 Dec 1996, John Earle wrote:
> 
> I like the word Cheap and OBO after the price.:)
> A bell jar and a vacumm sounds like the process you need. When the vacumm
> is released the change causes all the bubbles to collapse.
> I use a gast vacumm pump my brother in law got me of a brewery machine
> and a pressure cooker I bought at a auction sale for $3.00. I use it to
> find out how much gas is in my molten alumuinum before I cast. It creates
> about 25 Hg is short order and that should also be lots for what your doing.
> Hope this helps. Try surplus for vacumm pumps.
> 
> DonI used a ball jar that I silver soldiered a fiiting to the top of and 
would pull a vacumm marinated meat to help the liquid permeate the meat. 
These pumps can be found often at surplus stores.  If you happen by a ari 
conditioning vacumm they are far better if the price is right.  Ed 
Ginsberg  KE6BNL
-- 
1¾

---

From: Don Buchan <[email-masked]>
Date: Sun, 8 Dec 1996 20:48:17 -0600

Don

---

From: Paul Pierce <[email-masked]>
Date: Tue, 10 Dec 1996 16:14:30 -0700

> This is the *really* neat thing about NGs. What a clever idea, $1.00 for

Saw some septic tank pump truckers (operating on a shoestring) who
utilized
manifold vacuum (hope they had a trap on it) to draw sewage out of
septic
tanks...  Like someone just said vacuum is vacuum.

-- 
Paul in AJ AZ  NRA Endowment Member

Checkout the Metal Web News at:
new address (11/23/96)

http://www.ten.k12.tn.us/~wgray

Checkout the FAQ at:
http://PLAINS.UWYO.EDU/%7Emetal/index.html

---

From: [email-masked]
Date: 11 Dec 1996 16:04:11 GMT

In <[email-masked]>, Michael Hanz <[email-masked]> writes:
  <snip>
>evacuates. 

Reminds me of the house vacuum system here at work.  One time some fool
in the lab sucked up a bunch of *ether* into the system.  All the pumps
caught on fire!  

Also, consider that vacuum pumps (surplus, especially) have been *used*
for something - sometimes for pumping systems with toxic mixtures or
by-products of reactions.  Nowadays anybody like Leybold or Veeco
or Balzers who is in the vacuum business views a pump coming in for
rebuild with *extreme* prejudice.  Each pump must have a person
who personally knows what was in it, and will be responsible if a mechanic
gets injured, or they will NOT touch it.

As far as de-gassing goes, my experience is on preparing epoxy potting
compounds, and I believe that anything other than a 2-stage pump
capable of pumping to 10 millitorr will not do the job.  Yes, the epoxy
will foam.  It is supposed to, and you must size the lot to not overflow
the container.  This is the only way to remove all the entrained air - 
for us, this is critical, as we use the epoxy to make cryogenic vacuum
feedthrus.  However, the material properties improve otherwise, as
well, and de-gassing is a straightforward step.

Bell jar, short vacuum hose, small manifold for venting/pumping,
and a 2-stage pump is what is called for here.

Jim

---

From: [email-masked] (Alan Horowitz)
Date: 11 Dec 1996 21:28:01 -0500

Peter,

It might be worth your while to buy somewhat more than a $1.00 hose.
Epoxy in your engine ain't gonna be funny.

---

From: [email-masked]
Date: 12 Dec 1996 20:07:20 GMT

In article <[email-masked]>, [email-masked] (Alan

>Epoxy in your engine ain't gonna be funny.

Might quiet it down some though. <g>

Peter

---

From: [email-masked] (John William Kietzman)
Date: 13 Dec 1996 16:38:33 -0800

Can anybody recommend a supplier of big (14"+ dia.), relatively
cheap bell jars for vacuum use?  I've got a Nalgene rig from
Fisher Scientific, which is about 12" dia. x 15" high jar,
but I now have some things a little bit bigger than that.

Thanks,

John Kietzman

[email-masked]
415 723 0565

Rapid Prototyping Lab
Stanford University

---

From: [email-masked] (Robert Grauman)
Date: Fri, 6 Dec 1996 20:17:21 mountain

>Anyway, any help people can provide would be much appreciated.

John

Scientific supply houses, and others, sell a venturi device you
attach to a water faucet.  I have found that they will pull about half
an atmosphere, and have a suprisingly large capacity.  An old
refrigerator compressor will pull 25 to 27 ins. Hg, but they are
slow.  If you use a small chamber, and your potting compound
is slow setting, a refrigerator compressor might do.  I use a
Welch vacuum pump which I obtained rather inexpensively,
and it will pump quite a high vacuum with a reasonable capacity.
I use a commercially available bell jar made of plastic about the
size of a gallon jug, and my pump will bring it down in about 40
seconds.  My experience with epoxies and such is that the
viscosity determines how much vacuum you need.  A very
viscous material usually needs to be pulled to a high vacuum,
and be held there while you vibrate the bell jar plate.  And you
need to hold the vacuum while the material settles back into
place.  If you release the vacuum too soon, the material will
sometimes trap air in the hollows.  A thin material will boil
all the air out quite quickly.  I tried to use some household
RTV to pot something the other day.  I was totally unsuccesful.
The air came out, leaving holes behind which wouldn't till.
Does anyone know how to thin RTV?

		Robert Grauman in Sunny Alberta

---

From: "Randy R. Cox" <[email-masked]>
Date: Sun, 15 Dec 1996 10:12:19 -0600

Robert Grauman wrote:

      <snipped>
>                 Robert Grauman in Sunny Alberta

 <<>> <<>> <<>> <<>> <<>> <<>> <<>> <<>> <<>> <<>> <<>> <<>> <<>> <<>>

If you're talking about silicon rubber out of a caulking tube, or
smaller plastic glue applicator, I use this stuff to paint on clay and
wax models to build very strong rubber mold.  For years I thinned the
first coat with toulene--very noxious stuff.  Then, one day when I was
out of toulene, I tried mineral spirits.  It worked better and without
the noxious side-effects.  Try mineral spirits.

Randy

---

From: [email-masked] (Georgie Stanford)
Date: 10 Dec 1996 00:29:16 GMT

Andy Dingley ([email-masked]) wrote:
: You're fortunate in that you don't need a vacuum here, just a pressure
: reduced from that in the bubbles. It's nothing like the quality of
: vacuum you'd need for laser work.

I've been looking at these posts and pondering the time I wasted $15 
worth of room temperature vulcanizing compound (making molds for lost 
wax) because my vacuum pump wasn't working right and would only pull 27 
lb. of vacuum. It might be worthwhile to look up some local jewelry caster 
and wheedle some vacuum caster time from them so as to watch your 
compound and see when the bubbles come up and break. You could watch the 
vacuum gauge and tell exactly how much pressure you need. 

It may be that you can do with low vacuum that a refrigerator compressor can 
give (I have a friend who works at a fiberglass shop and they regularly vacuum 
bag boat hulls with low vacuum) or it may be your compound will need more 
vacuum than just a refrigerator compressor running backwards. But why 
risk wasting a batch experimenting?

Georgie

---

From: [email-masked]
Date: 11 Dec 1996 17:34:42 GMT

In article <[email-masked]>, Michael Hanz <[email-masked]>
writes:

>But the comment is a good one, and I support it - every situation needs
some
>thought,
>and next time I suggest an idea to the NG I'll properly caveat all the
things
>one should

Scuse me, didn't the original poster want to take air bubbles out of an
epoxy pot mix?

Peter
Amazed at the shifts and jumps in threads.

---

From: [email-masked] (Chuck Sherwood)
Date: 11 Dec 1996 18:09:26 GMT

>After a few actions you probably have to replace the converter. 

I dont think you should do it at ALL !
First consider what you may be sucking into the engine. Will it burn?
Probably. What by products of combustion will be produced? Are they
poisonous? Do you want to send them into the air or breath them?

Also there are other things you can damage other than your catalytic
converter. The O2 sensor comes to mind. They are sensitive and I have
heard stories about O2 sensors being damaged by some gasket compounds,
like RTV, used on intake manafolds.  I believe these stories because if
you read the instruction on RTV they now say they are safe for these type
of applications.

Ok, I'm cautious. I believe in doing it right the first time and not
damaging something that costs so much more that the right tool.

chuck

-- 
--
Chuck Sherwood
[email-masked]

---

From: [email-masked]
Date: 12 Dec 1996 12:05:45 GMT

>worried for your neighbors.

Jon
Lighten up Man!!!!!!!!!!!!!!    The wind in OK dissipates it fast enough,
besides, Freon is too expensive to let any waste.  Just for vacuuming a
new system, it works great.

Cecil in OK   Who makes freon vacuum systems out of refrig compressors.