We are looking for pin hole sized leaks. Solution should be fast(less
than 5 min.) and low cost..$5 or less. Capital investment can be up to
$750.
We seal styrofoam in clear plastic(4mil) for hot tub covers. Foam can
be up to 4 ft x 8ft and 4 in thick. Sealed with iron on 3 sides, then
all air is sucked out with a vacuum pump. If the plastic has a hole in
it or we don't seal it completely the bag becomes limp & sags as air
enters.
Here is what we have tried. Injected hot air and used a sensitive temp
gauge(.1 deg.) to look for leak. Have to be +-.25in to locate it.
Injected freon and used freon detector used by refrigeration pros. No
success...air is coming into bag. Tried ultra sonic sound device to
detect freq 40-50k hz as air vibrated going through hole. Too big an
area to scan.
Tried rubbing dye into plastic surface, hoping it would go into hole
and show up behind plastic and on white styrofoam. No success. Tried
powder on inside an used compressed air to blow it. It should move if
air goes through hole. No luck. tried to suck it through "the hole"
with a vaccuum hose. Tried magnifying glass without success.
Open to ideas.

---

Request for Question Clarification by krobert-ga on 02 Aug 2003 20:53 PDT

sven1791-ga,

What plastic are you using to wrap the styrofoam in? Do you know the specific type?

krobert-ga

---

Clarification of Question by sven1791-ga on 08 Aug 2003 05:20 PDT

to krobert-ga
I use 4 mil low density polyethylene...common plastic sheeting

sven1791...

Perhaps the injection of an easily detectable gas, in combination
with a detector capable of measuring small changes in the 
concentration of that gas in the atmosphere, in the same way that
methyl mercaptan is added to natural gas in order to be detectable
(by the human nose) in very small quantities. Mercaptan itself is,
perhaps, not the best choice, since detectors are hard to find
(other than one's nose), and the gas is not healthy for employees.
Yet other gases might prove non-toxic and easily detectable.

Would it be possible to attach a valve to seal the hole after the
extraction ... Then, after 5 minutes, to see if a second pump out is
still extracting air?

Can you do the hot air injection trick while the styrofoam-wrapped
unit is in a cold air freezer?  Can you get the styro-sealed-unit into
a walk-in freezer? You will see the hot-air leak as clear as you see
your breath out-of-doors when the air is frigid.

The hot air cold room solution will not work due to a lack of moisture
in the escaping air.  It sounds to me like the hole is small.  The
easiest solution to locate the leak is to use a detergent based liquid
solution.  Reverse the direction on the air flow to inflate the
plastic then simply mop the solution onto the plastic and look for
bubbles at the leak site.  You will need to clean the solution off the
plastic afterwards, but it is certainly less costly and hazardous than
gases, dyes, and other methods.  I would use 1 cup of Joy dish soap to
about 1 gallon of water.

Stephen

You might want to consider switching gears.  Instead of trying to find
pinhole leaks (which can always appear later, even after your testing,
and the customer will blame you for them anyway!), maybe you can solve
the sagging-bag problem even if a leak materializes.

Two possibilities come to mind:

1.  Use "shrinkwrap" type plastics to form a tight, sag-free enclosure
around the styrofoam, or

2.  Use an adhesive to bind the plastic bag to the sytrofoam (or iron
the plastic cover onto the entire block of styrofoam, not just at the
edges).

In either case, the plastic wouldn't sag, even if a pinhole leak were
present.

Is it possible at all to apply  ideas like:
--after sucking out the air place the whole thing in heat room (with
high pressure, perhaps) so that the plastic will lose its elasticity
completely and take the foam's shape , then place it in a  cool or
cooler room
(with high pressure again, perhaps)  ?
--after sucking out the air place the whole thing in heat room (with
high pressure, perhaps) so that the plastic will lose its elasticity
completely and take the foam's shape --while continuing the air
sucking , then place it in a  cool or cooler room (with high pressure,
perhaps)  ?

Hi sven1791-ga, 

It would be very nice if you could address the questions raised by the
opinion below re. my comment above.

"
Subject: Re: Over 1,000 Comments, please! 
From: probonopublico-ga on 04 Aug 2003 23:06 PDT     
Hi, Googel 
 
Many thanks for sharing your idea with me. 
 
I cannot find any bug in your proposition but, with these things, you
never know until you try them out. Even so, the exercise could lead 
to a more elegant solution.
 
But, in terms of the original question, would it be possible to do the
tests within the cost and time parameters set out?
 
Fortunately, I don't have the problem but I am sure that the
Questioner has been given a few things to mull over.
 
Regards 
 
Bryan
"

... and heat could be applied like by vacuum forming  machines?!