Powdercoating cabinet sorta build thread

At first I wondered if I got a short to ground at a burner, but that would only allow that specific element try to heat off 120V, but they were all glowing.  Latent heat or still powered, I don't know.  The other thing is, if I got a short to ground, trying to pull 9000w through one leg would have tripped the breaker, yes?

Pulled it apart.  Gotta be a faulty SSR.

Turn on the oven (with the box open... totally safe).  I verify I'm getting 12v from PID to SSR.  Output of the SSR goes to 246v.  Elements get hot.  Once it gets up to temp, the signal light turns off, 12v signal stops from the PID like it should, but I'm still getting 246v out of the SSR.  Fortunately they're cheap.

Solves that.  Not carryover heat or latent heat, it's still sending juice.

Anyone know of a better replacement?  All of the ones on Amazon seem to be the same $15 thing.  If I could find one for $30 that doesn't suck, I'll consider it.

In reply to Curtis73 (Forum Supporter) :

Have you checked the amperage rating of the SSR you're using?  9000W / 246 V = 36.6 A +/-    I'd make sure that you're using something rated for 50 A at 240 V if you can.

In reply to 11GTCS :

On paper, I calculated using 240v which came out to 37.5A so I used a 40A.  I figured with the 246V actually getting to the SSR it might be a little lower amperage and thought I was safe.  I didn't actually test the ohms of the burners because I figured whatever they measure goes out the window when they're glowing red.

So it is possible that the SSR's 40A rating was optimistic, or possible that the actual wattage of the burners is a tad high.  The interesting part is that even after running the oven for 45 minutes today, the SSR wasn't even warm to the touch, but I also admit that I don't know what voodoo happens inside.

Ordered a new brand/style rated for 60A

Got the new relay today along with some 250v LED indicator lights that I can use to monitor when the SSR outputs to the burners.

... and then promptly wired up the relay and accidentally put the primary on the secondary and vice-versa.  The fireworks were beautiful.

Fortunately, the PID seems to be undamaged, but my ego is pretty bruised.  I laughed at my goof and sent for a replacement SSR.

Facing a hard truth.  The oven works great for smaller pieces that only occupy minimal height in the cabinet.  I did a test today with a piece of square aluminum tubing, as well as one of the pieces of the roof rack (the main reason I built this cabinet).

I set the oven to 350F and put the pieces in.  I periodically checked on their temps.  The bottom of the pieces was getting to 390-400F, and the tops were never getting past 300-ish.  I replaced the perforated steel heatsink/diffusers with solid 22 ga sheet and it didn't help.  I tried circulator fan on and off and it didn't seem to help. I think I need to move the burners, which means a complete disassembly and that sucks.  I can't imagine getting a quality coating if I have nearly 100 degrees difference top to bottom.  I guess I put more faith in convection and the circulation fan than I should have.  Seems like the radiant heat blasting the bottom is a poor choice.

I could move the side burners up, but I think if I have multiple items in the oven, the outer ones will block radiant heat from getting to the middle parts.  I suppose I could move the side ones to the back in the middle, but then I might have too much heat blasting the middle of the part.

Where would you put the burners?  Any other suggestions?

I'd probably go with 3 burners straight up the back and as wide as you can find. Then line your doors with a reflective coating to bounce the heat back.

That's kind of what I was thinking, because that will even out the radiant heat, but the convective heat might make the top hotter.

Worth a shot.

OTOH, you have apparently created an alternate universe where heat does *not* rise.  so you got that goin' for you.  which is nice.

In reply to AngryCorvair (Forum Supporter) :

I've ripped a hole in the space-time continuum.

In reply to Curtis73 (Forum Supporter) :

If the convective heat is making the top too hot, you can always vent it. 

If the radiant heat is too much, you could also set it up with a gear drive top so you could slowly spin your part to spread out the heat. An old rotisserie motor should do the trick. That is assuming it's not too wide.  

As usual, I am of no practical help, but it occurred to me recently that you could heat a powdercoated workpiece by attaching a wire to each end and applying a low-voltage, high current source, with a controller linked to a thermosensor in close contact with the workpiece.  Bound to be much more efficient than heating a space and putting the workpiece in the space.  Just use the piece as the heat source.

Crazy, like a fox.  I know!

I would run the elements up the back wall. You will run into finish/gloss variations, as well as not curing, with that much temp differential top to bottom.

My day freed up so I moved the burners up the back wall.  It's still not perfect, but I'm at least within 20 degrees over the whole 6' pieces, so I think I can deal with that.  I'm going to make a call to Prismatic and find out more about the powder I bought... ask how hot is too hot, can I go 350 for a longer time, etc.

I also might try creeping up on the temp.  I could put the pieces in and set it for 300, then let it hang there a bit, then repeat at 350, then 400.  That might give more time for the heat to wick out in the part.

1988RedT2 said:

As usual, I am of no practical help, but it occurred to me recently that you could heat a powdercoated workpiece by attaching a wire to each end and applying a low-voltage, high current source, with a controller linked to a thermosensor in close contact with the workpiece.  Bound to be much more efficient than heating a space and putting the workpiece in the space.  Just use the piece as the heat source.

Crazy, like a fox.  I know!

In all the crazy powdercoating methods I have seen on the googles, I never saw that one.  It would probably work.

Maybe you could lay the cabinet on its side or back? Less convection column to deal with?

Is there any way to spin the part?  I'm thinking of having the hanger turn so a long skinny part at least sees even heat on all sides.  20 F degrees top to bottom is pretty close.

A super-size hot dog roller grille?

VolvoHeretic said:

Maybe you could lay the cabinet on its side or back? Less convection column to deal with?

I have no way of suspending the part from the other end without disturbing the powder.  It has to hang vertically.  I can't lay it on its side and still be able to open the doors, and if I lay it on its back, I have no where to hang anything because the door will be facing up.

Convection seems to be the least of my worries.  It seems like the bulk of the heating is from radiation.

JoeTR6 said:

Is there any way to spin the part? 

Not without some serious engineering

Curtis73 (Forum Supporter) said:

JoeTR6 said:

Is there any way to spin the part? 

Not without some serious engineering

I should have said "Not without some serious engineering.... hold my beer."

Curtis73 (Forum Supporter) said:

JoeTR6 said:

Is there any way to spin the part? 

Not without some serious engineering

As suggested above. Rotisserie motor, $18 on amazon. 

Add one of these...

And a bit of this with a collar and a hook...

That would be super helpful for some items.  I'll have to look into it.  I should also test temps on the front and back of the pieces I'm doing for this roof rack... see if the back side is getting hotter than the front.  The aluminum part with holes in it is 1/8" thick, and the base is 1/4" thick, so I don't imagine much trouble evenly heating through, but worth a check.

I also need to come up with an idea for suspending other kinds of parts.  Right now I have a piece of all thread going across the top with some S-hooks which was a quick solution to suspending the roof rack pieces, but it won't work for heavy things like wheels or a motorcycle frame.  Don't want a one-trick pony.

I use stainless picture hanging wire from the orange box store to hang light weight stuff. For rims, I have some loops with about a 4" long section of 1/4-20 thread. Hang them by the valve stem hole with the loop toward the middle of the rim. The 4" long ones give you something to grab onto when moving them into the oven.

In reply to jgrewe :

I've been stocking up on various eyebolt sizes for that very thing.

Here's what I'm thinking for heavier things.  I think I'll build a rectangle that sits in the bottom with two uprights that fit in the back corners of the cabinet.  Then I can slip-fit some tubing sections over the uprights with arms (maybe shelf brackets) that can swing out. 

Another way could be to have a "peg" in the bottom and a conduit clamp at the top of the tubes which would let me eliminate the rectangle frame at the bottom.  Either one would be removable for max space potential

 Quick and dirty drawing: