Subject: Re: Pulling a vacuum

From: [email-masked] (Christopher McDowell)
Date: 29 Sep 1994 20:49:50 GMT

John W Bottoms ([email-masked]) wrote:
: Slightly off topics...but, I'm trying to cast some small parts 
: in silicone rubber and need to pull a vacuum to get the air
: bubbles out of the mixture. I'd like a low-tech solution so
: I'm open for suggestions. Is there a hand-held pump thingy I

	How about the old water-in-the-can-on-the-stove-then-into-the-bucket
-of-water trick. i.e., put a fairly strong metal (NOT GLASS!) container on the
stove with a bit of water in the bottom.  Make/get a lid with a hose going to
your mold.  Once the steam starts flowing out, connect the hose to the mold
and put the can into some cold water. voila - instant vaccum.
	Don't know if it'll work, but The vaccum this develops could be 
fairly substantial.  Disclaimer - please don't kill yourself.
--

	  ** ***		
	** *** **		Christopher S McDowell
	**** ****		Mfg. Eng. BU
	   \  /			Bmed. Eng RPI
	    ||		
	    ||		Trees.  Cool.
      ______||____

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From: [email-masked] (bob prohaska)
Date: 30 Sep 1994 01:07:31 GMT

It turns out that a  refrigeration compressor makes a rather
decent single stage vacuum pump; One can probably be found
at no cost from an appliance shop. Rotary pumps will probably
have less windage and so will give a slightly better base pressure,
but either is likely to be good enough.

bob
gary preckshot ([email-masked]) wrote:
: In article <[email-masked]>, [email-masked] (John W
: Bottoms) wrote:
: > 

: [....vacuuming silastic....]

: This is a real problem because silicone casting rubber is about the gooiest
: stuff you can imagine, and it attracts bubbles from light years.  Yes, a
: brake bleeding pump works, but your hand gets real tired.  We've done it
: (wife & me) by mixing the silastic in a 3" diam, 1/4 wall acrylic tube
: sealed at each end with a 1/4" plate covered with neoprene rubber.  When
: you suck it down, the force makes the seal.  However, we got real tired of
: squeezing the little pump, so we got a surplus GAST 2 cyl pump that was
: originally used to pressurize card readers.  I replumbed the pump to make a
: 2-stage vacuum pump, which pumps down to 28" Hg.  Works fine, but watch out
: for the silastic bulge.  When you pull it down, it comes up like insane
: bread dough rising, about 3 - 4X size.  If you're not careful, it climbs
: up, into your pump line, and through your pump.  A filter is recommended.

: Try C&H surplus, Pasadena CA for surplus pumps.

---

From: [email-masked] (John W Bottoms)
Date: Thu, 29 Sep 1994 19:54:25 GMT

Slightly off topics...but, I'm trying to cast some small parts 
in silicone rubber and need to pull a vacuum to get the air
bubbles out of the mixture. I'd like a low-tech solution so
I'm open for suggestions. Is there a hand-held pump thingy I
can get to do this?

I saw a vacuum resealer for food advertised on TV but I was half
away because it was an info-mercial at 3:00 in the morning. Anyone
know a source for these things?

-johnbottoms (Concord, MA)

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From: [email-masked] (James Kirkpatrick)
Date: 29 Sep 94 14:42:10 MDT

In article <[email-masked]>,
[email-masked] (John W Bottoms) writes:

|>Slightly off topics...but, I'm trying to cast some small parts 
|>in silicone rubber and need to pull a vacuum to get the air
|>bubbles out of the mixture. I'd like a low-tech solution so
|>I'm open for suggestions. Is there a hand-held pump thingy I
|>can get to do this?

Haven't tried this personally, but consider the hand-pump available
in auto supply stores (and Wal-Mart) that is used for bleeding brake
lines.  A friend indicated it was a pretty good vacuum pump, if you
don't mind using a little muscle.  If the enclosure can be made only
slightly larger than the work, there should not be too many cubic
inches to deal with.

Be reminded that an imploding enclosure can be quite unpleasant, and
plan accordingly.

If you find a nice solution, you might let us know!

Jim

---

From: [email-masked] (gary preckshot)
Date: 29 Sep 1994 23:49:11 GMT

In article <[email-masked]>, [email-masked] (John W
Bottoms) wrote:

[....vacuuming silastic....]

This is a real problem because silicone casting rubber is about the gooiest
stuff you can imagine, and it attracts bubbles from light years.  Yes, a
brake bleeding pump works, but your hand gets real tired.  We've done it
(wife & me) by mixing the silastic in a 3" diam, 1/4 wall acrylic tube
sealed at each end with a 1/4" plate covered with neoprene rubber.  When
you suck it down, the force makes the seal.  However, we got real tired of
squeezing the little pump, so we got a surplus GAST 2 cyl pump that was
originally used to pressurize card readers.  I replumbed the pump to make a
2-stage vacuum pump, which pumps down to 28" Hg.  Works fine, but watch out
for the silastic bulge.  When you pull it down, it comes up like insane
bread dough rising, about 3 - 4X size.  If you're not careful, it climbs
up, into your pump line, and through your pump.  A filter is recommended.

Try C&H surplus, Pasadena CA for surplus pumps.

---

From: [email-masked] (Paul Amaranth)
Date: 30 Sep 1994 12:36:35 GMT

>I'm open for suggestions. Is there a hand-held pump thingy I

If you can find an old bicycle pump that can be disassembled, you can
take it apart and reverse the sealing cup.  You might have to fiddle
with the valves too, but it should pull enough vacuum for your purpose.

If you have compressed air available, you can get a vacuum device
that runs off of that; I think Harbor Freight sells one of those.

-- 
Paul Amaranth  Manager User Services - office: (810) 370 4541 (also voicemail)
               (e-mail)     [email-masked]         
   Mosaic page: http://www.acs.oakland.edu/links/amaranth/amaranth.html

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From: [email-masked] (Carl F. Ijames)
Date: Fri, 30 Sep 1994 21:53:17 GMT

> : I'm open for suggestions. Is there a hand-held pump thingy I

You could try a water aspirator pump.  This is a nozzle that screws onto a
sink faucet (or you could adapt it to the end of a garden hose) with a
vacuum port on the side.  Decent vacuum, no moving parts or oil, and very
rugged.  Probably costs $15 from a scientific supply house, or visit the
chemistry building at your local university and see if they have any
laying in a junk pile from a previous remodeling.
Carl Ijames     [email-masked]

---

From: [email-masked] (gary preckshot)
Date: 30 Sep 1994 23:48:53 GMT

In article <[email-masked]>, [email-masked]
(Carl F. Ijames) wrote:

[request for vacuum pumping advice]

> You could try a water aspirator pump.

Carl and others have suggested various pumps in apparent ignorance of the
dimension of the pumping problem.  At a minimum, you need 27" Hg vacuum
maintained for about 5 minutes, and it helps to cycle the vacuum up and
down to break the bubbles.  28" is better, and I'd really like to use 29". 
Silastic is incredibly sticky, and the bubbles don't want to come out. 
It's because of this that we went to motorized pumping.  If you do this
more than once, you get real tired of squeezing the plier grip of the brake
bleeder, and I can imagine any other manual pump.  You also need to keep
pumping, because there's leakage.

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From: [email-masked] (Ford Falcon)
Date: Fri, 30 Sep 1994 18:00:11 GMT

Paul Amaranth ([email-masked]) wrote:
: In article <[email-masked]> [email-masked] (John W Bottoms) writes:
: >Slightly off topics...but, I'm trying to cast some small parts 
: >in silicone rubber and need to pull a vacuum to get the air
: >bubbles out of the mixture. I'd like a low-tech solution so
: >I'm open for suggestions. Is there a hand-held pump thingy I
: >can get to do this?

Three thoughts.

1.  You can use the compressor from an old fridge to draw a faily high 
vacuum.  I have used this kind of set up to vacuum out air conditioning
systems.

2.  You can make a vacuum by T-ing in a small tube into a faucet stream.
This depending on the water flow can also draw a vacuum.  If you need
more details on this let me know.

3.  Try a centrifuge (sp?).  Use to cast some small rubber molds and used
a can attached to the end of a chain and whirled the thing around by hadn
to eliminate any bubbles.

Hope this helps.

James

[email-masked]

-- 
                                             [email-masked]

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From: [email-masked] (Carl F. Ijames)
Date: Sat, 1 Oct 1994 23:31:35 GMT

> pumping, because there's leakage.

A water aspirator pump with the full flow available in a normal sink will
give at least 27" and more likely 28-28.5" Hg.  The ultimate base pressure
is the vapor pressure of water at the outlet temperature, about 15 torr or
29.3" Hg at 70F.  Pumps as long as the water is running.  No, this isn't
as good as a real vacuum pump, but it is a lot cheaper, readily available,
and stands a good chance of working for what may very well be a one-time
project.
Carl Ijames     [email-masked]

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From: [email-masked] (Don Stauffer)
Date: 3 Oct 1994 08:57:22 CDT

>-johnbottoms (Concord, MA)

There is a type of RTV for moldmaking sold with advertisements that it 
does not need vacuum.  I have tried it, as I didn't want complexity of 
having vacuum source.  It works pretty well, I have had only one small 
bubble in about half a dozen molds I have poured.  It is so thick that 
every time I use it I swear it will not work this time, but it settles 
well as it hardens, and as I say, I have had very little problem with 
bubbles.  I am making very small parts for models, and I am amazed at how 
well it holds detail.

Don Stauffer in Minneapolis

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From: [email-masked] (James Foster x2912)
Date: Mon, 3 Oct 1994 15:44:20 GMT

In article <[email-masked]>, [email-masked] (John W Bottoms) writes:
|> Slightly off topics...but, I'm trying to cast some small parts 
|> in silicone rubber and need to pull a vacuum to get the air
|> bubbles out of the mixture. I'd like a low-tech solution so
|> I'm open for suggestions. Is there a hand-held pump thingy I
|> can get to do this?
|> 
|> I saw a vacuum resealer for food advertised on TV but I was half
|> away because it was an info-mercial at 3:00 in the morning. Anyone
|> know a source for these things?
|> 
|> -johnbottoms (Concord, MA)

There were a number of other good suggestions.  One I'd make
is to check used tool shops/pawn shops, etc. for a used vacuum
pump.  I've seen a lot more of them recently since the gov. has
mandated that you have to have a cfc recycling setup if you work
on refrigeration equipment.  Shops that will keep doing this work
have upgraded their stuff and some part timers have probably given
it up.  I got a servicable pump for about $75, which isn't a whole
lot more than the hand vacuum pump I have for automobile testing
cost.

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From: [email-masked] (Les Bartel)
Date: 3 Oct 1994 18:02:03 GMT

> You could try a water aspirator pump.  This is a nozzle that screws onto a

Or visit a waterbed shop.  They often use that type of gizmo to empty the
mattress.  It will likely require some ingenuity to modify for your
application, but then I assume you have an above-average level of
ingenuity, since you are doing casting work.  :-)

 - les

-- 
	Les Bartel               Spec: Specification or Speculation???
  Intergraph Corporation
  Electronics Division
    [email-masked]
      (205) 730-8537

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From: [email-masked] (Don Stauffer)
Date: 3 Oct 1994 08:57:22 CDT

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From: [email-masked] (James Foster x2912)
Date: Mon, 3 Oct 1994 15:44:20 GMT

---

From: [email-masked] (Les Bartel)
Date: 3 Oct 1994 18:02:03 GMT

- les

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From: [email-masked] (Barry Workman)
Date: Thu, 6 Oct 1994 04:50:24 GMT

>Jim

The latest Harbor Freight catalog listed a 29.5 in. vacuum pump
for about $20 or $30.  When I was teaching jewelry making we would
use the compressor out of an old reefer.  Build a table with the
vacuum tube mounted in the base.  put the item to be debubblized
on the table and cover with a bell jar.  You can seal the edges with
plasticine clay.  Turn on the pump and watch the spatters hit the
bell jar.
-- 
    - Barry Workman

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From: [email-masked] (david reid)
Date: Mon, 10 Oct 1994 22:52:26 GMT

In Article <[email-masked]>, [email-masked]
>that runs off of that; I think Harbor Freight sells one of those.

    De-airing silicone rubber?. Try the lateral approach. Chill the rubber
base in the fridge for a while. This will slow the setting cycle. Mix with
the catalyst, a little less than usual, and pour/scrape the mix into
polystyrene cup. Leave it for a bit (an hour or more) (Check a sample for
the setting time under these conditions) Puncture a hole in the bottom of
the cup to run the rubber into the mould. No bubbles. 
Invention/creativity

A mixture of curiousity, necessity, serindipity, persistence and preparedness,in
varying parts.