Last night I finally got around to using the "Chicago Electric" powdercoating setup I bought at HF a couple of months ago. It was on sale, like $60, and others have reported satisfactory results with it. I had some problems, though, and wondered if anyone has any ideas to help.

The problem was that the powder delivery was very erratic. Whenever I pulled the trigger or jiggled the gun the tiniest bit, a huge blast of powder would come out. Huge. I'd say, 1/16" or so of powder would splat out onto the work. After the huge splurt, the powder would come out in a reasonable manner, and go right where it was supposed to. Gradually, though, the fog would get thinner and thinner, and I'd have to shake the gun a tiny bit. This produced another huge splurt, then another interval of acceptable flow. To get by, I had a scrap metal shield that I kept in front of the work until the splurt was over, then moved out of the way during the intervals of acceptable operation. It works, but it's tedious and messy.


The instructions say to either use 10-15 psi regulated at the compressor, or to use the regulator screw on the gun itself. I'm using the shop at my work, and the compressor is off in a different room that I don't have a key for. So I bought a cheapo HF regulator that I screwed onto the gun, and before loading it with power, tried to test the operation. With the trigger pulled, I could - barely - regulate the pressure, but as soon as I released the trigger, the pressure would climb to line pressure. The POS Chinese regulator wasn't regulating. Then, based on the instructions, I removed the regulator and tried regulating the air with the screw built into the gun. No way of knowing the pressure, but from the sound I could hear the rate of flow and trim it to something reasonable. In any case, the air flow is smooth and steady.

Any tips or suggestions ? The obvious thing to try is buy a non-crap regualtor. But has anyone had luck using the metering screw in the gun itself ? My hunch right now is that maybe I had the air flow too slow. How rapidly should the powder coat the work ?

TIA, Jeff

p.s. I'm off skiing tomorrow; won't be back until Tues.

Jeff if you didn't do it the first thing to do is shake the powder really well before loading the gun. Powder settles down when it sits and will pack into a semi- solid chunk. Moisture is obviously an enemy as is proper air flow. I'm not sure how the cheapo units werk but on the proffesional units the pickup tube supplies air flow to the box of powder to keep it loose and free flowing. If the H.F. unit has such a feature check it as well. Hope this helps.

Shake the powder - good idea ! In fact, the powder came in a plastic bottle that screws directly onto the gun, so it never even got transferred.

I haven't really poked around much, so I can't say for sure how the gun works. The bottle screws onto it and there's a J-shaped tube that pokes into the bottle. In operation the bottle is upside down, the mouth of the J points downwards. I don't know if the air flows through the bottle or just down the barrel. Anyway, thanks for the tip. I'll try shaking the powder up for my next attempt.

Scott is right about shaking the powder.

The powder should spray out pretty evenly. What you're describing isn't normal. Might be you have a defective gun... after all, it is HF.

Were you spraying powder during high humidity? I've found that can cause problems.

My hunch is that humidity wasn't the issue. Once the powder came out, it seemed to have a very "dry" feel/look to it. And during the "good intervals, it did make a nice fine fog. I was working indoors (under a good exhaust hood) in a climate-controlled building.


Right now, I'm thinking the shaking idea will fix it; I'm certain that the powder wasn't shaken or agitated in any way, except for turning the bottle upside down once after it attached to the gun. Also, it could be that b/c the powder was compacted and the very first splurt of powder was such a suprise, that I backed off the air and wasn't really using enough flow. Stay tuned...

Pics of the finished job, or pics of the mess ?

The parts I coated were an oil pan and splash tray from a Subaru EG33 that I reworked (shortened) for putting in my 914 one of these days. The coating is black, so it's real hard to see anything at all in the pics. Here's one with contrast and gain cranked up fairly high. What can I say ? It's black. I missed a few spots on the inside, and they really stand out in the picture. I originally wasn't gonna coat the inside, and did it after the pan was hanging in its curing position, so some angles were tricky. For curing I used a catalytic propane heater and some sheets of scap metal set up behind the part as reflectors. (Sorry, no pics). The heat wasn't super-even, so I kept rotating and adjusting the parts/heater during curing. A proper oven would pobably be much more uniform.

Click to view attachment

Hey, that was picture # 666 for my camera. Coincidence ? I don't think so...

Here's a pic looking down into the pan, with the splash tray in place. Again, major contrast/gain tweaking. The splash tray was the first piece I coated. Towards the rear (top of pic) got less heat during curing, and came out more glossy than the rest. Also, I made several attempts on the tray (wiping it off w/ a paper towel), and it wasn't coated super -evenly, so you can see some bumps. I have no idea why the bottom of the pan (seen through pick-up tube opening) looks so white in the pic; in reality it is a nice, even black.

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More than likely you didn't get a full cure on the part. I don't know what the cure schedule was for your perticular powder, but typically if there are areas with more gloss than others, then the cure was not completed.

You may want to run some test parts prior to running real parts to play around with application and curing.

If you take some MEK on a Q-tip and rub it on the "shiny" spots, the paint will come off. (This is a rub test with a generic solvent. Rub Test kits should be available from the powder manufacturer.)

The shaking of the powder just prior to pulling the trigger may help. The use of a fluidizer really helps keep the powder loose.

To cure parts like that pan, I would shoot for a lower temp for a longer time (to get the metal temp more consistant without burning the powder).

Happy New Year

Make sure you have an air regulator on the gun. I shake my gun while slowly increasing the pressure and soon just a light spray comes out. It's usually about 10 psi. I'm using the Eastwood gun.

If your propblem is powder delivery than you're pressure's worng OR you have moisture in you air lines (regardless of whether the powder *feels* dry coming out). If you don' have a good moisture filter, get one. Especially for powder coating.

Moisture can really cause some erratic problems. I also have the HF gun and was getting the same problems. Once I hook up my air filter it fix the problem. It not the cheapo air filters either. This baby extracts all the moisture. Has an element inside that looks like a roll of toilet paper.
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John you can't get a proper cure that way. The powder MUST be baked within a certain temp range or it will not cure properly. Temp range should be between 400-475 deg. Any lower or higher will cause problems. Higher less so. Lower temp will result in the powder flowing out and looking good, but it will not harden fully and will be easily scratched, chipped etc. Powder is not like paint, the variables can't be changed but so much

in theory with a caveat. RTFM, or read the instructions that come with the powder. I have some powder form Columbia Coatings that specicifies 375 degrees.

Sorry to burst your bubble, but you can definately shoot for the lower limits of the powder for a longer period of time. It's done in the industry all the time to cure irregular parts (or parts with varying thicknesses of metal such as weldments). The key is to get the metal temperature to the cure temperature for the scheduled time.

If one can't slow the conveyor down slow enough at the low end of the temperature range, a lower temperature powder can be chosen (the powder suppliers can even formulate one to work for a given application). Typically, off the shelf powder can be made to work one way or another.

The temperatures are POWDER DEPENDANT. Without the powder curing schedules, you would not know what you are shooting for. You can use "rules of thumb" as you stated, but your results will vary.

If you want consistant surface finish, colors and gloss (especially light ones such as white), then you will definately notice that too hot of an oven will quickly discolor the powder. Overcuring will also have adverse effects on finish, gloss and color.

You left out half of the equation. It's really time AT temperature. The part needs to remain at cure temperature for a given amount of time or the crosslinking will not occur and your powder will not pass a rub test.

We do tesing in our powder application and cure lab for our customers and these are simply facts.

(We sell automated product finishing systems: Ovens, Booths, Application Equipment, Pretreatment, and Conveyors)

is the powder universal to all guns. for example if you have the Eastwood gun are you only able to use the Eastwood brand powder.


just wondering...

thanks

pankopp

Powder can typically be used in any application equipment.

(At least industrial equipment. I don't have much knowledge of the equipment Eastwood or Harbor freight sells).

Thanks for all the info. The glossy area I mentioned was definitely at a lower temperature while curing; it was at the bottom while the part was hangining, and the radiant heat from the propane heater wasn't as intense down there. The second part (the pan itself) was much more even, 'cause I paid a lot more attention to keeping the heat even. My heat setup was pretty half-assed, just a radiant propane heater and some aluminum plates as reflectors. I noticed that the dark steel plate below the parts (welding table top) actually got much warmer than the aluminum. (Higher emissivity, lower conductivity.) So steel plate "reflectors" (i.e., that absorb and re-emit heat) would probably make a much more uniform oven set up.

Also, thanks for the MEK rub test idea.

John part of my job is powder coating, both commercially and most of the time auto/motorcycle parts, and while I agree with you for the most part, in this particular application I don't see an IR light being able to sustain an appropriate temp to be able to cure the pieces. In an oven maybe, but I have personally experienced too low a temp in the oven and poor hardening of the powder. My situation was the controller temp was 100 deg off of the actual temp of the oven. That said we were baking parts at 325 instead of 425. If I understand what you are saying we could have simply increased the bake time to compensate?? If so that would make things a LOT easier. I simply turned the control temp up to 525 to compensate and kept the normal bake time. Do you sell non automated equipment ? I may need to talk to you in the near future !! Yes I have also noticed gloss white really does not like to be jelled then baked, it turns yellowish

Yes we sell Batch Ovens as well as automated ovens. I/R ovens (electric or gas) are definately a viable method of curing out powder.

Some of the testing that we perform at our lab and out in the customers facility is called running a datapaq. A DataPaq is a temperature recorder. Thermocouple probes are placed at different locations of a test part, the part is then placed in the oven (I/R or Convection) for a given amount of time (based on the powder schedule) and then the part is removed.

You can then chart the various temperatures of the probes for the entire time span and watch as they heat up differently. The trick is to get the metal temp up to cure temp for the time required to reach full cure without overheating the powder. Adjustments can be made to an oven (vary the temp in a convection oven, or in the case of IR, one can vary the percentage output of the emitters or in some instances, vary the distance between the part and the emitter).

In the case of home brew powder curing, the best method I have heard of is to obtain an old household oven (the larger and cheaper, the better). The temperature controls are fairly straight forward and can be more easily controlled than I/R space heaters.

You will have to play with emitter output and distance to the part for the I/R space heater thing to work out. I'm sure it can be done, but it would be a lot of work.

The best thing about automated or hand pushed conveyorized powder curing is that the parts are not disturbed much after the application of powder. The powder is fragile until it starts to gel and flow out. Another advantage is that the part never looses being in contact with a good ground.

If you are interested in talking with an application specialist (not me as I am an Engineer), PM me and I'll send you our company contact info.

Back to your regularly scheduled program.