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Electrocoating

02/16/2014 11:44 AM

Hi again! I am exploring the idea of using the electrostatic paint principle for spray coating some metal parts. As my budget is quite tight, searching around I found an old transformer used for neon lights with an output of 75K Volts. My idea is to put the part to be sprayed inside an acrylic box, to connect the neg lead to it, fill an aerography spray gun with the coating material, connect the + lead to the nozzle and see what happens. The spray gun will also be contained inside the box, being fixed by an appropriate (isolated) holder. I´d love to hear your comments!

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#1

Re: Electrocoating

02/16/2014 12:28 PM

Just off hand, I'd say that you are creating an explosion hazard.

I used to do electrostatic painting, and the paint that really worked well, was specially formulated to carry a positive charge, and the viscosity had to be perfectly measured with a Zahn cup. There's more involved in the equipment, than just throwing a charge on some paint, also.

They came out with electrostatic airless machines, but unless there have been vast improvements since I tried them...they suck.

Unless this is really easy to try, and just about free, I wouldn't bother.

I know you can't import stuff, but before I put all of that effort into something that may not probably won't work, I would see if anyone in your area does powder coating...same concept, but a much tougher finish. I don't think it's very expensive.

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#2

Re: Electrocoating

02/16/2014 1:59 PM

I'd look at Powder coating - Wikipedia, the free encyclopedia

As the name implies, no liquids to bother with.

Many materials can be used. Epoxies are very popular and tough.

Then there's dip coating, or fluidized bed coating.

Powder Coating Process | Electrostatic and Fluid Bed Coating ...


I have used a vibrating table and a cup to dip coat parts with epoxy.


This is far and away better than spraying, depending on the size of the parts.

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#3

Re: Electrocoating

02/16/2014 3:26 PM

This hobby type powder coat gun quotes a voltage of 11k, your 75k might be a bit over the top.

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#7
In reply to #3

Re: Electrocoating

02/17/2014 12:56 PM

I think the OP might have mis-read the spec plate on the transformer. I've never come across a neon light transformer with a 75kV output. Plenty with 7.5kV output which might just work with the 11kV powder coat gun. Most neon light transformers I've seen run between 5kV and 15kV.

Cheers !

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#8
In reply to #7

Re: Electrocoating

02/17/2014 5:07 PM

Hi Sir Robin, this is the first time I deal with these transformers. Just repeated what the owner of the used transformer said. I have checked this info by calling a manufacturer, confirming you are right about the output! Thanks a lot.

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#4

Re: Electrocoating

02/16/2014 8:05 PM

The process I actually want to do is to apply a chemical compound on a metal rod using the principles of the electrostatic painting. This is a purely experimental job, and only will know if it works after doing some metallographic tests and electron beam microscopy to which I have access to. The spray coating systems I have read about in the internet use a 100 KV source, but as Nigh mentioned, there are some hobby type gadgets working with only 1/10 of this voltage. Probably any high voltage in that range will do. As the attraction of the particles will be lower with less KV it will probably just be a matter of trial and error to determine the best distance between the anode ant the cathode for optimal coverage. You mentioned the explosion hazard, which is something not to underestimate, but working on an open environment, with very small amounts (1 millilitre) of the solution to be sprayed will not make a bigger explosion than a firecracker, should it happen. We are in summer now and air is quite humid (about 50 to 70% RH), so I am concerned about which a safe distance between electrodes might be in order to prevent the occurrence of a voltaic arch that may damage the nozzle of the aerography spray gun to be used. Is it necessary to ground the pos lead of the HV source after disconnecting it from the mains before accessing the parts I will work with?

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#5
In reply to #4

Re: Electrocoating

02/17/2014 4:55 AM

I have one of the powder coat guns shown in my previous post & the instructions tell you to always discharge the gun by touching it on whatever you hang the workpiece on before removing the component.

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#6
In reply to #5

Re: Electrocoating

02/17/2014 8:46 AM

thanks!

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#9

Re: Electrocoating

02/19/2014 2:15 PM

r&ddoc-

As very strong words of CAUTION, that is 75kv that is being "played" with. As several prior to this have stated, that is a lot of voltage and enough to do a very fine job of killing. In fact it is way higher than what is used in the prison electrocution chairs.

If you were to connect wires with round metal spheres on one end of each and the other ends to the terminals of the transformer you will initially obtain a spark at least 1" long. Once the spark gets going you can separate them even more and still maintain the spark. 75KV is what it takes to break down the air between two metal balls and create a spark. Sort of reminds one of Frankenstein's Monsters!

When properly installed in a neon light system this voltage is insulated very carefully to avoid problems. "As my budget is quite tight" usually does not promote safe innovation and equipment. Often times safety is one of the first things compromised for $$$ sake.

Please reduce the voltage down to a level that is not in excess and no more than necessary. Is your life worth the risk? The members of CR4 would hate to lose you and have your obituary posted on this thread. "RIP, Here lays a CR4 member who lived his life to the point that it was shocking".

Good Luck, Old Salt

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#10
In reply to #9

Re: Electrocoating

02/20/2014 7:11 AM

Hello old salt,

I really appreciate and share your concern about safety when dealing with any kind of energy. It is true that many choose doing unsafe stuff when their budget gets thight, but it is not my case. The HV transformer I have been looking at has an output of 0,2A; and my idea is to operate it in an isolated & safe environment. So far I feel I have more chances of being hit by a meteorite than getting electrocuted by my transformer! Kind regards!

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Users who posted comments:

Brave Sir Robin (1); kramarat (1); lyn (1); Nigh (2); old salt (1); r&ddoc (4)

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