Author Topic: Adventures in powder coating  (Read 3545 times)

Offline kvom

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Adventures in powder coating
« on: June 23, 2018, 06:12:05 PM »
As I mentioned in another thread, a builder I talked with at Cabin Fever has given up painting his models in favor of powder coating.  Based on seeing the results he achieves, I decided to follow suit, and will be using powder coating on my current Muncaster grasshopper build.

What do I need to powder coat?  There's any number of Youtube videos, but basically you need a powder coat "gun", the powder, a source of compressed air, and an oven hot enough to melt the powder.

For the gun, I'm buying one from a friend.  It's an Eastwood dual voltage model:

https://www.eastwood.com/dual-voltage-hotcoat-powder-gun.html

The idea is that you attach an electric lead from the gun to the piece to be coated, and an attractive electric field is created.  The air pressure blows powder towards the work where it sticks.  Then the work is placed in an oven hot enough to melt the power (350-500F).  Once the powder "flashes" to liquid it then needs to cure for several hours.

Powders come in a full array of colors and textures.  I bought several bottles of different shades of grey and black to test on aluminum and steel.  Once you know the color you want you can buy powder in bags at a cheaper price per ounce than the bottles.

For the oven, you shouldn't do this in your kitchen or in any oven to be used for cooking.  Today I found a GE double wall oven advertised for $60 by a couple renovating their house. 



I'll have to do some wiring to use the 220V welding receptacles in the shop.



My plan is to wire a 6-50P plug to the existing oven wire and then buy a premade extension cord.

My buddy has a similar setup.  He has the top oven set to 500F to quickly flash, and then the lower at 350 or so to cure.  Makes for faster work when doing a lot of parts at one time.  The powder may flash at 350F too, meaning any solf solder joints won't detach.  Obviously the lower the oven temp the longer the cure time.


Offline kvom

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Re: Adventures in powder coating
« Reply #1 on: June 25, 2018, 08:08:36 PM »
Got the plug wired to the oven, and the extension cord came today.  I was happy to see that the oven came alive when plugged into the welder outlet.

Offline bent

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Re: Adventures in powder coating
« Reply #2 on: June 25, 2018, 08:29:19 PM »
Looks pretty neat, even if the equipment to run it is kinda expensive.  A local powder coater has said he would let me run parts through his line, as long as I was ok with whatever color they were running for production that day; the price he quoted wasn't bad considering.

Offline kvom

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Re: Adventures in powder coating
« Reply #3 on: June 28, 2018, 10:54:12 PM »
First test today.  I used the Eastwood "cast iron" powder on two small pieces of aluminum (Mic6 and 6061), with one setting on the other.  The Mic6 had the blanchard grinding marks and the 6061 typical endmill tool marks.  After baking, the finish on both pieces was the same with the tool marks completely covered.  The finish is very slightly textured

In addition, the two pieces were glued together by the melted powder at the join edges, and more securely than I can break apart using my hands.  I'll see if a hammer will do the job with what level of force needed.  This may well be a quite useful means of attaching metal parts without fasteners.


Offline Vixen

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Re: Adventures in powder coating
« Reply #4 on: June 28, 2018, 11:29:19 PM »
That sounds like a very tough material which sticks really well to the substrate.
What is the film thickness of the powder coating? Is it like a 'rattle can' spray paint finish or a thicker coating?

Mike
It is the journey that matters, not the destination

Sometimes, it can be a long and winding road

Offline bent

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Re: Adventures in powder coating
« Reply #5 on: June 29, 2018, 04:34:10 PM »
It will depend on the powder formulation, but typically several mils.

Offline Vixen

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Re: Adventures in powder coating
« Reply #6 on: June 29, 2018, 04:40:33 PM »
It will depend on the powder formulation, but typically several mils.

Ha ha, And that will depend on what you mean by a mil. Is that what we call a thou (of an inch) on the east side of the big pond? :Jester:

Mike
It is the journey that matters, not the destination

Sometimes, it can be a long and winding road

Offline kvom

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Re: Adventures in powder coating
« Reply #7 on: June 29, 2018, 11:52:28 PM »
The thickness depends on the powder and how much you spray.  You can also spray another coat after this one has cured.  In this case, I was testing and put on a fairly light coat.  In fact in the attached pic you can see where I missed a spot or two.  Between the bare spot and the covered I can't detect any difference by feel.  I mic'ed a separate piece of 3/8" Mic6 at .378 and the covered piece showed .379 in a couple of places.  At the join line between the pieces there is a barely detectable ridge of coating that's probably responsible for the strength of the bond.  I gave it some fairly firm blows with a soft hammer without dislodging it.  To be sure of getting them apart I'd try a torch.

Offline bent

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Re: Adventures in powder coating
« Reply #8 on: July 02, 2018, 05:29:02 PM »
Yup, mil=thou, tho I am on the west end of the east side of the pond... :Lol:

Offline Mcgyver

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Re: Adventures in powder coating
« Reply #9 on: July 02, 2018, 05:42:09 PM »
great thread; a topic I'd like to know more about.

What do you do about areas not to be painted?  A resist, mask?  I've been painting a lot lately, what a pita with all the masking!

To our metric friends, mils is how you refer to coating thickness here, you wouldn't encounter someone referring to thous as mils in general shop parlance.


Offline kvom

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Re: Adventures in powder coating
« Reply #10 on: July 02, 2018, 05:59:30 PM »
Masking areas is done with hi-temp silicone tape, which can be had in various widths.  I ordered a 5-roll set on eBay last week with different widths.  For holes I bought a set of silicone plugs of varying dimensions, especially critical for threaded holes.  So no relief vs. painting on the effort to mask.  OTOH if you apply the powder and need to modify the masking it's easy to blow off the powder and start over.

One experiment for this week is to powdercoat some metal with a screw in a threaded hole to see how hard it is to remove the screw afterwards.  One of the videos I've watched shows a fairly large bolt being used to suspend the work in the oven, so for larger screws it's probably easy enough to remove them.

Offline Vixen

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Re: Adventures in powder coating
« Reply #11 on: July 02, 2018, 06:49:09 PM »

To our metric friends, mils is how you refer to coating thickness here, you wouldn't encounter someone referring to thous as mils in general shop parlance.

Over in Europe, we are merticated, therefore measure and specify a coating thickness in 'microns'.

A few of us older engineers still like to work in inch measurements, we were brought up that way. We don't use the term 'mils' over here, it is not our general shop parlance, we would say 'thou' instead. So you will understand why I asked for the clarification.

Cheers

Mike
It is the journey that matters, not the destination

Sometimes, it can be a long and winding road

Offline Mcgyver

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Re: Adventures in powder coating
« Reply #12 on: July 02, 2018, 07:45:01 PM »
. We don't use the term 'mils' over here, it is not our general shop parlance, we would say 'thou' instead.


understood and agreed, same here....I was only clarifying mils is not shop parlance for thous, its a coating thing.  Coatings are spec'd in mills, if you told a machinist the part was a mil big you'd get, well, some sort of look back :)

Offline kvom

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Re: Adventures in powder coating
« Reply #13 on: July 03, 2018, 12:52:19 AM »
Today's little test involved a block of brass in which I had a through threaded 1/2-13 hole.  To that I added a tapped 8-32 hole, then screwed in appropriate screws.  The assembly was then coated and baked with the same "cast iron" powder.



The wire was used to suspend the piece from the oven grate.

As it turned out, both screws were easily removed afterwards,


Offline b.lindsey

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Re: Adventures in powder coating
« Reply #14 on: July 03, 2018, 01:02:38 AM »
What have you seen so far with respect to adherance to sharp edges like the corners of the test blocks. Is is best to have a chamfer or small radiusor does it not matter?

Bill

 

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