DIY powder coating



Amazing what crap poses and passes as science these days. Holding headphones near the implants of 100 people to see how many malfunction is an experiment a dim adolescent could do if she could recruit enough implanted fools to assist.
The safe limit specified by one ICD mfr for static (DC) B-field is 1 millitesla, and B-fields are easily measured.
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wrote:

I'm thinking E-field (volts per meter), not H field. The current is microamperes. But it's a DC field so I'm probably being over-conservative. The voltage is typically developed by a Villard cascade or Cockcroft-Walton multiplier, both of which usually have enough capacitance in the string to not have much ripple.
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Existential Angst wrote:

I'll try to answer this as brief as possible. First just so you have some background I spent 14 years working in a coating plant that did both liquid and powder coating. Did every job in the place over the years from hanging parts on the lines to supervisor including driving the trucks to P/U and deliver the parts.
First powder coating as a process is not hard to do. The trick to the entire process is really simple. THE PART MUST BE CLEAN!!!! After that it's a cakewalk. Well maybe a few minor items are a PIA but money can fix those.
First your talking aluminum. I would rather coat my tongue than aluminum BUT... First off - How long do you want the coating to last? With aluminum this is the BIG problem. Aluminum Oxide forms VERY fast. This is what causes the coating to fail. So you need to come up with a cleaning method to remove it. In the plant we used a 5 step process, First a simple degreasing bath, then through a 4 stage wash rig. First stage rinsed off the panels with PURE water. Then into an acid wash and rinse then a phosphate bath. Then through a quick rinse and into the drying side of the oven. From there they could be handled WITH CLEAN COTTON GLOVES. Touch the part or let it get dirty and you start over.
Next you hang the parts. The easy way is to drill a hole or holes and use a steel wire to hang the part. Any tapped holes or unpainted areas get masked off (Just about anything that is easy to remove can be used, IF you remove it before curing the powder)
Now you coat the parts. Here you need a powder gun, The cheap guns work BUT if you plan on doing many of these items hit an industrial auction and get a REAL powder gun, Graco, Sames, Norton all make good machines. Make sure you get the COMPLETE unit, should be the control head, and a fluidized hopper you put the powder in, plus the gun itself and the cables and color hose.
Powder to match the characteristics you want. This can get interesting due to all of the different ones out there. ANY color you like can be made, from Clear to Black, High Gloss to dead flat, Textures, Hammertone, Mixed colors, Metallics, Candies, you name it and it's out there.
Powder booth to contain the over spray and reclaim the unused CLEAN powder. (easy to make one for the parts you list out of cardboard or light tin)
The racking for the parts, This can range from a single wire to a complete conveyor system. For many folks the common bakers rack with steel wheels works well.
The oven. This is the part that kicks most people in the guts. "any oven can be used" Well yes/NO First you need an oven that holds the internal temp at the cure point within a few degrees for 20-40 minutes. The common home gas oven doesn't do that very well. An electric beats it hands down. Then you need a way to vent any smell/fumes (yes curing powder does STINK). For the parts you have the easy way out would be an oven built out of tin with electric oven elements and fiberglass insulation with a shell of tin. OR you could go with infrared heaters and a simple insulated tunnel.
As for the process itself.
Hang and clean the part. OR clean it and handle it GENTLY while you hang it up.
To coat it the part gets grounded to a ground strip through the hanging wire. The powder goes out of the hopper and picks up a positive electrostatic charge when it goes through the charging section of the gun (usually at the very exit point). The powder goes through the air and settles on the part due to the different charges.
This is the point where the pro gun beats all the home guns. CONTROL, both in the powder stream, speed of discharge, amount of electrostatic charge (the typical Sames gun we used put a 150KV charge on the powder, if you got it close to a ground it would throw a 4" arc!!!) and powder coat mil thickness. Rule of thumb is that the higher the charge the better the powder sticks, BUT it also will apply the powder THICKER, which isn't good. This is where the controls come in. On a good gun you can adjust the entire process.
YES you can cause all the same things with powder that you can do with liquid, gobs stuck in the paint, dirt, bugs, runs, drips. BUT prior to you actually curing that powder you can do one thing you cannot do with ANY liquid paint, REMOVE THE PROBLEM. Simply grab a VERY filtered air line and blow the powder off the part and recoat. (once you get the hang of it you can even do spot touch-ups, blow off JUST the offending item and even create paint designs with just the air gun.
Now you have a clean part, hanging on a wire, with a nice even coat of powder on it. PERFECT. OOPS you sneezed....
OK you didn't sneeze this time... Believe it or not it takes a LOT of force to knock that charged powder off that part if you use a good gun.
Now you transfer the part to the rack and GENTLY roll it into your oven. OR transfer the part to the rack until you have enough coated to fill the oven (you want room between parts if they move some but not a lot)
The oven will be PRE-HEATED to the cure temperature. Open the door, load the oven and close the door. WHY pre-Heat? Because you want those parts to come up to temp FAST so the powder cures properly and bonds to the aluminum. Remember that metals expand when heated, if the powder is already starting to gel as the expansion occurs it will move with the part. If the powder isn't starting to gel and the part expands you get micro-fissures in the paint that let air/moisture in. NOT a good thing. Now for cooling you let them cool together. The powder will again follow the metal. It will actually stay in a semi-plastic state for quite a while when it is warm.
DO NOT TOUCH THE WARM PARTS!!!
Use the hanging wires to move them out of the oven to cool. Why not leave them in the oven till it cools? Because powder CAN also be over cured. Just like baking cookies, there is a point where the dough softens, flows out and sets. Then they start to brown. If you leave them in too long what happens? You get CHARCOAL COOKIES... Powder does almost the same thing at a molecular level. Properly cured powder will move with the substrate, I have taken .020 test panels, coated them, bent them over. Flattened the bend down with a mallet and not had the coating fail on properly cured powder! OVER cure that same powder and it will flake off and fail.
You asked about spraying hot parts as well. YES you can do that and we did that a lot on HEAVY cast parts or on parts where the customer needed a specific thickness of coating for another purpose. For instance the E-One company ( http://www.eone.com/sewer_systems/intro/index.htm ) had us coating the pump housings and parts inside many of the sewage grinder pumps they built. They wanted a VERY thick coat that would then get machined flat and used as a gasketing surface. This kept all of the cast iron housing covered and made those pumps last. To give them the proper coat we would clean the parts and then pre-heat them up to cure temperature. Then spray on the powder to build up the thickness. The heated parts would instantly cause the powder to begin curing and then we baked them a while longer till we reached a full cure.
This process also works on porous items like cast aluminum or iron because it out-gasses the part and allows the powder to gel without having gas bubbles in the coating. On 1/4" it isn't needed.
ANY more questions?
--
Steve W.

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Steve W. wrote:

Very good write up. I would make one addition. Use a good respirator when working with the powders. They are toxic until they are cured. Cheap dust masks don't cut it. Use a vacuum to clean up the area if not recycling powder overspray. Same goes for your clothes.
Thats why a booth is used as a controlled area. Powder goes back into the can or into the filter.
Also, if you make your own oven, check the cure temperature of the powder you plan to use. Harbor Freight powders need a cure temp of 400 degrees F for 20 minutes after powder glosses over.
Good luck
Jim Vrzal Holiday, Fl.
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Steve W. wrote:

Nope. You just convinced me not to bother with trying to powder coat aluminum (specially in a marine enviornment where it really matters).
Stainless, Gunner!
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cavelamb wrote:

Powder would work OK but that first step of cleaning the part is the problem part. We did a LOT of marine parts for a couple of the big outfits as well as http://www.taylormadeproducts.com/ (hatches and window frames)
It can be done but not with the low end stuff.
--
Steve W.

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Steve W. wrote:

No, this is a fitting that has a pin that fits into a socket on deck.
I suspect powder coating will get chipped, and in a salt water environment aluminum would corrode away rather quickly.
I've never had the chance to machine stainless - or any steel for that matter. I've whittled aluminum with a mill though, and could make what I needed. So the idea of making parts from stainless is kind of over the top for me. I honestly don't know how hard it is to do, or how long it would take. But if I have the choice - all other things being equal...
Like Forest Gump always said, "One less thing to worry about".
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Stainless isn't too bad to machine, depending on thge alloy. However, I woudln't be surprised if the best stainless for marine use is harder to machine. The problem with SS is that machining it work hardens it. You want to be more agressive with it than aluminum, which might tax your machine tools. Carbide helps a lot because it doesn't care so much that the work is hardened.
Doug White
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wrote:

You got it.
Gunner
"Aren't cats Libertarian? They just want to be left alone. I think our dog is a Democrat, as he is always looking for a handout" Unknown Usnet Poster
Heh, heh, I'm pretty sure my dog is a liberal - he has no balls. Keyton
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Steve W. wrote:

Powder coating without spray gun, charges, or oven:
I watched a CalTrans crew today repaint street markings in front of an intersection. They laid down metal stencils, then used a weedburner type torch to heat the asphalt inside the letter cutouts. Then white powder was dusted over the stencil.
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Two: Is there an exam? Do I get college credit? :) Good post.
Why does the oxide of aluminum cause problems for powder coating? It's electrical conductivity is much lower than aluminum (mebbe even an insulator?), but that shouldn't affect the static electricity effect, unless alum oxide in fact affects that as well.
Speaking of alum oxide/powder coating, I guess that's why god invented anodizing. Which is another option.
That was cool, machining the powder coat itself! Super-neat! Some creative engineers, on that one!
--
EA

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Existential Angst wrote:

The insulating properties are not the problem. It is that the oxide coating acts as a contaminant and prevents a good bond between the powder and material. Then the paint fails. Same problem with chrome plating on aluminum.

Yup, and it's a better one for some applications.

They picked up that trick from one of our other customers. Small outfit called GE Turbine Systems. We coated ALL of the shaft seals used on the various turbines they made for about 10 years. In that case we used a special powder that provided insulation properties for the shaft.
We also did some parts for Raymond Corp. (fork lift parts) Those were interesting. The powder was a special high temp cured nylon blend. Cure temp was 650 degrees. Those parts had to be preheated, coated then cured. ALL of this had to be done HOT. These were done in a batch oven. You would hang the parts, let them get HOT, then open the oven door, grab a couple parts, close the door, spray them, open the door, then hang them back up. Repeat until you finished the batch. These parts and items like the seals and some medical items we did were done by two people. We also were the ones who taught all the other sprayers the ropes and did all the gun maintainance as well.
AHH the good old days.....
--
Steve W.

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I can see Al2O3 being a problem for chrome plating, which depends on where materials fall in the chemical "emf series", but it is less clear why such a stable compound, useful in its own right, could not be powder coated. Surely Al2O3 can be *painted*, right? Epoxied? Glued?
Seems to me it should be powder coat-able, which is, in essence, a kind of melted polymer/paint? Not argering, just thinking out loud.
From what you describe, it seems like there are various chemical configurations for powder coats beyond simple pigments, for different applications/properties -- none for oxided alum, or even anodized alum?
--
EA



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Existential Angst wrote:

The oxide forms a layer on the aluminum which acts almost like you coated the part with some dust prior to coating. The way the powder bonds is interesting.

There are literally thousands of different chemical blends for powder coating. For instance lets say you desire a flat black coating 1 mil thick. What UV stability do you need? Will the part be inside or outside? What final surface finish do you wish, smooth, pebbled, sand textured? Does the coating need to be temperature resistant?, How many degrees? What temperature will the substrate withstand and for how long? What wear characteristics do you need? Electrical Characteristics? Gloss retention? Fade resistance?
These are just a few things that you decide prior to making the blends. All of them have to be determined PRIOR to producing the powder. They cannot be changed later, Unlike a liquid paint which you can add a pearl or a flatting agent or a gloss additive or whatever.
--
Steve W.

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Eastwood ( http://www.eastwood.com/hotcoat-powder-coating.html ) also has a good line of hot coat guns and powder. Their forums helped me out quite a bit when I first started too.
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or try here http://www.caswellplating.com/index.html
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