Subject: Re: Powder coating

From: [email-masked] (Alan Frisbie)
Date: 10 Aug 95 11:25:42 PDT

> [email-masked] (Gale Carlisle) wrote:

>>	The electrostatic gun and paint pump unit are quit expensive,
>>	about $5000 for the smaller unit, and I am not sure of the cost
>>	of the oven, of which should be not much trouble to make. 

I had a wild idea that sort of follows this thread.   I needed
to spray paint some pieces of wire mesh (1" openings).   With
the huge ratio of empty space to material, there was a tremendous
waste of paint.   Electrostatic spraying came to mind.

My idea was to connect a high voltage (5-10 KV at very low current)
power supply (from an old laserdisk player) to the work, with the
other lead attached to the can of spray paint.   I would then stand
on large insulating blocks, have a friend turn on the power, and
spray away.   I never got a chance to try this, but am interested
in what you think about this idea (besides the fact that I am
crazy as a loon).

--  Alan E. Frisbie               [email-masked]
--  Flying Disk Systems, Inc.
--  4759 Round Top Drive          (213) 256-2575 (voice)
--  Los Angeles, CA 90065         (213) 258-3585 (FAX)

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From: [email-masked] (James Kirkpatrick)
Date: 11 Aug 95 10:23:39 MDT

In article <[email-masked]>, [email-masked] (Alan Frisbie) writes:

|>I had a wild idea that sort of follows this thread.   I needed
|>to spray paint some pieces of wire mesh (1" openings).   With
|>the huge ratio of empty space to material, there was a tremendous
|>waste of paint.   Electrostatic spraying came to mind.
|>
|>My idea was to connect a high voltage (5-10 KV at very low current)
|>power supply (from an old laserdisk player) to the work, with the
|>other lead attached to the can of spray paint.   I would then stand
|>on large insulating blocks, have a friend turn on the power, and
|>spray away.   I never got a chance to try this, but am interested
|>in what you think about this idea (besides the fact that I am
|>crazy as a loon).

If I tried this, I'd probably make sure one side of the HV was grounded,
and use that side for the paint sprayer (and hence your body).  This would
eliminate the need for the insulating blocks and hake things a bit safer.
Definitely use a low current source, though there has to be some current
used via the transfer of the charged paint globs.  If the source is too
low-current, even a fine paint mist may look like a short and drop the
voltage to something useless.  Not sure which polarity is best, either!

Jim

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From: [email-masked] (Jens)
Date: Fri, 11 Aug 1995 12:03:41 GMT

Some corrections re my previous post ....
apparently you need 8 to 10 kv per inch of air between the gun and the
part. In other words if you are 10 inches away from the part you would
need approx 100kv of charge. I have a book in front of me that showes
a 30-100kv DC supply with a 20 to 200 micro amp capacity.
Film thickness is controlled by voltage.
Also, if you are spraying a liquid, the solvents must be chosen with
electrical characteristics in mind .. being polar enough to accept a
charge from the ionized air but not so polar that they absorb too much
charge.
Also, under safety considerations, it is stated that you must watch
against accidental arc creation (various sources listed) and be
extremely cautios that the booth is vented enough to avoid explosive
gas mixtures.

This info is from "Understanding paint and painting processes' by
Gerald L. Schneberger

I was thinking about taking the high voltage of a TV CRT - being
around 20 to 30 kv or so. Based on this latest info, I think I will
forget about trying to rig up something temporary.

PS.: as far as powder coating is concerned, there is a method where a
hot part is dipped into a fluidized (powder suspended in soft air flow
- sort of like quicksand) powder bed and the powder adheres and melts
onto the hot part - no high voltage involved. I could not find any
info on cost of the fluidized bed system. Also, I would think colour
changes in such a system would be a real pain if it is a larger bed.

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From: [email-masked] (Jens)
Date: Fri, 11 Aug 1995 03:47:01 GMT

>waste of paint.   Electrostatic spraying came to mind.

Well what a coincidence - that is exactly what I am trying to coat

>--  Los Angeles, CA 90065         (213) 258-3585 (FAX)

That is exactly what a commercial powder spray applicator does. You
will need 10 kv and you need to make shure that current is limited.
The current needs to be adjustable I think based on the carrying
capacity of your paint (some materials hold and transfer a charge
better than others).
I taked to some suppliers of powder spray equipment and the bottom
line is that for about 4000 US minimum you get the spray applicator
with a feed hopper and nothing else. It seems to me that somebody is
making an awful lot of money somewhere because the principal of
applying the paint is so simple. I can't see the equipment being that
costly (unless the liability insurance of such gear drives up the
price).
I think I will try to put a system of that nature together and see if
it works. A 10KV supply is easily constructed.

PS.: loons are a lot crazier than that :)