Wednesday, July 21, 2010

Powder Coating

Update2: Description, Schematics and boards

Update: added some more details

So over the last few months I have built a number of powder coating guns as well as a powder coating oven. I'm trying to make something better than the $60 harbor freight gun, from what I have read the HF gun tends to not give consistent powder output and struggle with multi coat.

Mark I:
This gun was inspired by this design
The overall design was pretty much the same; I used an old toaster oven to bake it. It worked ok, but the voltage was too low to get good powder adhesion on additional coats, and it was hard to clean and didn't put out a consistent powder flow.

Mark-I ghetto gun

BMW E36 caliper support brackets (before and after)

Mark II:
The second prototype moves the high voltage electronics into a separate unit; I also added previsions for a variable voltage supply, solenoid controlled air supply, and a separate powder chamber. Results were pretty good.  Its still very much a prototype, for the next revision I'm moving things around and sending PCBs to be made.

Main Power Supply and Control system

The system as I use it; lots of hours on it now.

Here is a picture of the power supply; There are three stages; a generic 110VAC to 36VDC 3A power supply; Provisions for an adjustable stage (36V to 10-32VDC 3A); High voltage step-up stage (10-32VDC to ~25KV done in the switching power supply section)

The AC-DC input stage is built around a standard toroid step down transformer; full bridge rectification and capacitor bank. The supply is controlled by a switch on the front.

The adjustable stage is currently not implemented; instead I have simply added a 12VDC regulator used for supply of the switching section of the HV supply and for the actuator control. In the next revision I will be adding the variable voltage control using a standard adjustable regulator (LM317) with pass transistors to provide additional current. This stage is controlled via a relay which is controlled by a switch on the gun.

The high voltage step up stage is basically a switching power supply driving a flyback transformer out of a CRT computer monitor. The frequency and pulse-width of the drive circuitry is tuned to match the transformer. I set the duty cycle to 20% and adjusted the frequency until maximum output was observed (by measuring arc length). A 555 timer was used for pulse generation; it feeds a IRF240 power mosfet which drives the primary winding of the transformer. The primary winding was made by wrapping 8 turns of 14 gauge transformer wire around the ferrite core of the transformer.

The flyback transformer is directly connected to the tip on the gun via 50KV high voltage wire bought off ebay.

The air supply is set via an adjustable regulator on the front of the chassis; after the regulator the air is connected to a solenoid which is activated by a switch on the gun.

Flyback and air control

The regulator air supply is fed to a powder container; it feeds at the bottom of the container in order to fluidize the powder; the powder then travels to the gun.

Third itteration of the powder pot; this one is quite solid and works very well

The gun its self is very simple it is simply PVC fittings which allow for attachment of various nozzles. The nozzles were purchased from powder by the pound (they're cheap ~$12 so It was easier to buy rather than build).  I've added a switch to the gun (not pictured) which switches on the HV and air.

When it all comes together I have had some pretty good results; powder attraction is much better than with the Mark-I gun and powder flow is more consistent. Multiple layers work well (tested up to three layers so far).

Powder coatingis great; but the hard part is getting a big enough oven to cook the parts in. I ended up building my own oven from sheet metal and steel studs. Since I wanted to keep costs low I used left over bits from various projects and friends and family. It turned out pretty good; it doesn't look like much but it heats up quickly and holds its heat well.

Oven; inside dimensions 2' x 3' x 4'
240V 30A

30A contactor for controlling the elements

Auto Tuning PID temperature controller for driving the contactor

Some formerly brass trim from my fireplace (ready to be cooked)
For temperature control; the elements are fed by 240V at 30A; they are connected via a electrical contactor which is controlled by a auto-tuning PID temperature controller.


Powder Coating System Mark-III:

I've started building the MK-III version of my powder coating system. Here is the plan.

- Move to larger 19" rack mount chassis
- Provisions in chassis for second regulator and PSI gauge for future addition of powder pump.
- Adjustable low voltage DC supply in chassis, all HV moved to gun
- Switching supply and AC fly back mounted on gun
- 5x Voltage multiplier on gun to bring output voltage up to 100KV for large number of coats
- Use custom PCB for switching supply;
- New Gun cabling using circular connectors


lumberjack said...

Excellent project.

Have you drawn up an electrical schematic? If so, I'd love to see it.

Scott Gibson said...

I didn't draw up a schematic; it kind of grew organically. I'm working on a schematic for the next iteration of the design. I should be able to post something shortly.

Anonymous said...
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Andres Sanabria said...

Congratulations, you project is very nice, I want to make it, thanks for share us information. Greetings from Colombia

11andrey54 said...

Where can I see an electrical schematic and drawing the gun with the size dimensions? Or is it a commercial secret? Please, publish your drawings!

Scott Gibson said...

New schematic and diagrams here:

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Ashley said...

I like your blog its nice.

James Norris said...

Thanks for the article. I was looking for something more along the lines of powder coatings in Chicago area, but I decided to give your article a look over and I really enjoyed it. Keep up the great work.

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I need to finish mdf tables. I was reading on Can someone tell me whether powder coating mdf would be a better idea.

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luis ortiz said...

hello love your ideas, would you sell one of this units if so ho much?

Aaron Bert said...

Hi, nice post. You have got great ideas. I can now do metal coating at my home.

Ashley said...

This post is really informative and thanks a lot for sharing. Its a great start up for those new to powder coating. Keep up the good work.

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Sean Castle said...

This is an amazing post, really cool to see that you made your own powder coating gun. I have been powder coating at home for a couple of years and my next step is to build a larger oven very similar to what you built. I also have a blog on powder coating:

Keep up the good work.

wheel specialist said...

Excellent job. keep it up

steve job said...

Powder coating is definitely superior manner of painting several products, mainly metals employing dry powder.

Jeypi Burac said...

Tanks for sharing your thoughts Its been weks since I'm seaching for this kind of blog. It really help to realize what should I do with the powder coating equipment I will choose to buy. Well my father want to build his own power coat services in our town and where looking for good stories or reviews.

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Thank you for sharing this article! Well I'm really looking for good reviews about powder coating supplies. I'm looking for a good brand and where to buy the best supply.

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Anonymous said...

Very impressive. Would you be interested in building a control unit that just has a power supply and adjusts the output voltage from 0-100kv? Similar units cost at least $300 and are hard to find. The unit wouldn't need to control air flow, just the voltage range and the high voltage cascade would be contained in the gun. I don't know enough about electronics to build one myself, but you seem capable enough.

Integra Doors said...

This is amazing. It reminds me of when I first starting dabbling in the powder coating world. Is this just a hobby for you?

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I admire what you have done here. I like the part where you say you are doing this to give back but I would assume by all the comments that this is working for you as well.
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