Powdercoating cabinet sorta build thread

Decided to start a new thread.  I'm building a powdercoating cabinet.  It may only get used for this one project, but I anticipate it being a cheap enough build that it's going to save me lotsa money.

Some of you know about my whining surrounding my aluminum roof rack that has been sitting around for 1.5 years.  I'm scared to paint it, and powdercoating was going to be stupid expensive.  So instead, I just came here to ask way too many questions about stuff I still don't understand.  I decided to youtube some powdercoating videos.

Fast forward to now.  After cleaning and remodeling the shop, I was left with a surplus steel cabinet

It's 18"D x 36"W x 72"H.  Unfortunately, with the base being up several inches, it wasn't going to fit the longest piece of the roof rack I want to coat.  Free height inside is 65", and the longest piece of the rack is 68".  I decided to cut the bottom out and make a 12" extension.  I just whipped up an ugly thing from an old bed frame.  I'll skin it with sheet metal from the shelves.

So this is as far as I've come.  Let's crowd-source some ideas.  I already  have some great ideas from the Powdercoating - Bad Ideas Only thread, so now that I've made my choice of bad ideas, I figured I'd make a new thread.

I've had suggestions of gas and electric.  My next steps (once I finish welding up the extension) is to insulate and add the heating.  I saw some stuff on the intarwebs that suggested gas doesn't leave a nice finish because of the water vapor involved.  Any truth to that?

Insulation:  I was going to put duct board inside and wrap the outside with fiberglass batts, but duct board is only rated to 250 degrees, and batts will be hard to attach to the outside.  I suppose I could put some steel studs on the outside and then some kind of skin.  Luan would be a cheap and easy option I suppose.  Thoughts?

How many watts/BTUs would you put in it?  My only 240v outlet is a 20A circuit, so I can only go to about 4500W unless I rewire it, which isn't a terrible prospect since it's only about 4' away from the panel.

Let's powdercoat some schtuff.

Insulation: extra high temp sheeting from McMaster (p/n 93315K71) used for kiln insulation and thin with very high heat resistivity.

Link: kiln insulation

Other versions may work too. I demonstrated this stuff to Dusterbd13 with a propane torch  getting one face to glowing red and grabbing it within seconds. I used it as home made glass-pack packing material. It could be supported on the inside walls with safety wire or similar methods.

I always thought it would be cool to make a modular cabinet setup that you could size as required for the job. I have zero experience with powder coating anything myself- I'll be watching closely. 
 

What about rock wool or mineral high temp insulation applied to the outside and wire mesh (maybe even as simple as chicken wire?) to secure it. To make it look.  You could build a simple box around the outside of that as well- I'd think some high temp insulation applied to the inside of that would work as well to keep the wood from catching. I'd think an electric oven element would be a no brainer and inexpensive with the right temp controller. I used these (similar) on my home brewing setup  

PID controller

Any cheap pizza ovens around ?

may be good for heating elements etc
 

In reply to Teh E36 M3 :

Electric oven elements would work and they're cheap, but I'm a bit concerned with how many I'll need.  Most of them are in the 3000-4000W area.  I know it takes about 15 minutes to heat up the oven in my stove to 400, I'm just concerned that a volume this big might need way more juice than one.  Many of the videos I see of DIY coating ovens are smaller than this and they have three more more oven burners.

In reply to Teh E36 M3 :

I found a video where I guy did a modular-type setup.  He made small-ish (like 2' x 2') panels with steel studs, steel sheet inside and out, and fiberglass in the cavity.  He would just set them on his workbench and connect them all together.

Your suggestion for just rockwool on the outside makes sense.  I was thinking that insulation inside would pay big dividends in not having to lose as much heat soak to the walls, and it might, but it's a trade-off for interior space.

stafford1500 said:

Insulation: extra high temp sheeting from McMaster (p/n 93315K71) used for kiln insulation and thin with very high heat resistivity.

Link: kiln insulation

Other versions may work too. I demonstrated this stuff to Dusterbd13 with a propane torch  getting one face to glowing red and grabbing it within seconds. I used it as home made glass-pack packing material. It could be supported on the inside walls with safety wire or similar methods.

That insulation isn't too cost prohibitive, either.  As with any insulation though, the R-value kinda sucks unless you go thick.... and then you're subtracting interior volume.

I don't see why you couldn't use a gas burner for heat, just don't vent the products of combustion into the cabinet.  Use some sort of heat exchanger that moves them through without mixing with the air in the cabinet.

I ordered some BBQ gasket tape to try and close up any gaps around the doors, but that's further down the road.

How fire-resistant is hardie backer?  I was thinking about that for skinning the base instead of sheet metal.  It has an R-value of a 0.13 which isn't great, but probably better than 22-ga sheet steel.

californiamilleghia said:

Any cheap pizza ovens around ?

may be good for heating elements etc

I do have a PCI auctions warehouse about 20 miles from me.

I think you're right about needing a lot of burners. First off you'll need to bring the oven up to about 50º above the curing temp to degass the item being 'coated. Secondly, after you get the oven to the target curing temp, let's say 350 or so. After you open the door you'll lose all your heat. Then put the part in that could be 300º colder than the inside of the cabinet, sucking more heat. Now the burners come on high to get the oven to temp. Let's assume the burners are on the bottom. Would you risk burning the powder on the bottom of the part as the burners go to full output for a long period of time to get the top of the box to temp?  Maybe have the burners mounted on the back wall???

Just thinking out loud. I 'coated a lot of stuff, but the largest thing I did was an LS oil pan. I used rigid foam insulation to make a 'dog house' to set on the opened door of the oven. That doghouse area was 10-15º cooler than the inside of the oven. But being much smaller than your volume, the temps were able to even out fairly easy.

In reply to DrBoost :

Just thinking out loud. I 'coated a lot of stuff, but the largest thing I did was an LS oil pan. I used rigid foam insulation to make a 'dog house' to set on the opened door of the oven. That doghouse area was 10-15º cooler than the inside of the oven. But being much smaller than your volume, the temps were able to even out fairly easy.

*************

You just have to have some pictures to share, for science.

And to Curtis, don't forget about the paint burning off of your cabinet.  That will not be a good thing smoke wise.  I hope you do this outside.

In reply to Noddaz :

Yes, outside.  I have a covered loading dock and the oven is on casters (as of about an hour ago).  Wheel it out, plug it in.

Got the extension put on and the bottom cut out today.  And I put the world's worst casters on it, because cheap.

DrBoost said:

I think you're right about needing a lot of burners. First off you'll need to bring the oven up to about 50º above the curing temp to degass the item being 'coated. Secondly, after you get the oven to the target curing temp, let's say 350 or so. After you open the door you'll lose all your heat. Then put the part in that could be 300º colder than the inside of the cabinet, sucking more heat. Now the burners come on high to get the oven to temp. Let's assume the burners are on the bottom. Would you risk burning the powder on the bottom of the part as the burners go to full output for a long period of time to get the top of the box to temp?  Maybe have the burners mounted on the back wall???

 

Just thinking out loud. I 'coated a lot of stuff, but the largest thing I did was an LS oil pan. I used rigid foam insulation to make a 'dog house' to set on the opened door of the oven. That doghouse area was 10-15º cooler than the inside of the oven. But being much smaller than your volume, the temps were able to even out fairly easy.

I'm very grateful that you're thinking out loud.  I have a lot to learn.

So... what if I were to make it a tanning booth?  Put some IR radiant heating elements in the four corners instead of lining the sides with oven burners?  Then it's not 90% convection and 10% radiant, it's more like 70% radiant and 30% convection.  I suppose I would have to put my temp sensor on the part and not in the oven if that were the case.  I have a feeling I could easily make the part way hotter than the air in short order.

And what if I steal some glass from an oven door to make a window into which I can shoot a laser thermo to monitor the part temp?

Is it possible to put the part in a cold oven and let them both get up to temp together, or do I need to start with a hot oven?

I've always preheated the oven to 450 F, then back the temperature down to 400 F once the parts are in there.  If you are quick at hanging the stuff, the temperature shouldn't go much below 400 F.  I would use electric heating elements.  Radiant heat would work, but may be harder to keep uniform across a longer part.

In reply to Curtis73 (Forum Supporter) :

So when can GRMers start stopping by with a 12 pack and spend the day powdercoating at Curtis Casa de Berkley St?

So here is mine. Metal studs,sheet metal and rockwool insulation. The window, that is missing after the last move, was a basic two pane one that came out of an oven I scrapped. Now its just a piece of sheet metal.

The rack has wheels that roll only one way and it comes out and rides on its own cart with castors.

Here is the burner. That short piece above it is stainless that I've heated up and flared a bit to help it hold onto the flame. It can be slid up and down the burner a little bit to tune the flame. It sits outside the oven held up by a few pairs of vice grips and fires into a 9" diameter piece of HVAC pipe. That is a 0-60psi regulator.

There is a hole in the cross pipe that IIRC is a #59 or #60 drill bit for the propane to flow through.

Stampie said:

In reply to Curtis73 (Forum Supporter) :

So when can GRMers start stopping by with a 12 pack and spend the day powdercoating at Curtis Casa de Berkley St?

Hopefully soon.  Whiskey is also legal tender on Berkley St.

In reply to JoeTR6 :

I was thinking of 4-foot units, but I get what you're saying.  I watched a video with a commercial radiant coating oven and it didn't even have insulation.  I would insulate of course, but I thought I might be able to get the part up to curing temp without having to go through heating the air (slow) which then heats the part (slow)

Like this picture.  I was thinking the red lines could be heating elements or IR radiant elements.

In reply to jgrewe :

I love the pics.  Thanks.  I'm a visual person.

Help me with mathing.  If I use the KISS principle and just do three oven heating elements, I can get about 7500-9000W easily and inexpensively.

8000W x 3.41 = 27,280 BTU
8000W / 240v = 34A

I can rewire the outlet with some 8/3 and add a 40A breaker, not a problem.  It's only about 4' from the panel to the outlet and it's all exposed conduit.

Question is... will it be enough wattage?  I know I can't predict the actual effectiveness of the insulation and my door sealing tape, but do you think that's adequate?

My thought on the radiant heaters is still in my brain, but here's my train of thought on that... correct me if I'm wrong.  Since radiant will heat the part more than the air, I would have to find a way to measure the temperature of the part, not just rely on a thermometer in the oven and time, which means I'll need full coverage to evenly heat the part.  That has proven to be difficult - in gas/ceramic OR electric.  I would end up buying about 12 smallish infrared burner replacements for BBQ grills at $50 a pop to get a full bath of IR on longer parts.

Or am I overthinking it?  Should I just stuff two big infrared propane heaters in the bottom and stop worrying about it?  Maybe even just a big propane grill burner in the bottom?

So confused.  The research I've been doing is dizzying.  jgrewe says he can get up to 230kbtus,(equivalent to  67449W) but another video I saw had a bigger oven than mine with a variable 30-80kbtus from his propane and only ever uses the 30k range to coat. (8798W and 23,460W, respectively)  I'm looking at a third  of that wattage if I go with three oven burners.

So, current ideas on the table.  If there are any pros/cons?  I just seems as though gas provids more punch for your dollar

- 3 oven burners mounted low on the sides for 8000 ish watts.  Heat the air, the air heats the part.
- Expensive IR (either gas or electric) in the four corners hitting the whole length of the part
- Screw it an put a couple propane IR ceramic radiators in the bottom and let the convection and radiation duke it out.

Long story longer, I've narrowed it down to needing anywhere from 7500W up to 80kbtus or as high as 230kbtus.

That's a large range.

DrBoost said:

I think you're right about needing a lot of burners. First off you'll need to bring the oven up to about 50º above the curing temp to degass the item being 'coated. Secondly, after you get the oven to the target curing temp, let's say 350 or so. After you open the door you'll lose all your heat.

I think the fix to that is to put some thermal mass in the oven so that when you open the door you lose the hot air, but you can heat the now-cold air using the mass of the other hot stuff in there without needing to run the burners as hard.

codrus (Forum Supporter) said:

DrBoost said:

I think you're right about needing a lot of burners. First off you'll need to bring the oven up to about 50º above the curing temp to degass the item being 'coated. Secondly, after you get the oven to the target curing temp, let's say 350 or so. After you open the door you'll lose all your heat.

I think the fix to that is to put some thermal mass in the oven so that when you open the door you lose the hot air, but you can heat the now-cold air using the mass of the other hot stuff in there without needing to run the burners as hard.

 

That's not a bad idea.  I had a thought on that.  Now that I've added about 16" to the height of the cavity, there is room for a heat source on the bottom.  One of my ideas was some heavy cast iron grill grates above a couple grill burners.  It was also my main reason for thinking radiant IR heaters, since the heat source IS the temperature, so to speak.  Using IR would mean that less heat escapes when you open the oven.  Convection means that the part's heat source is the air.  Losing a bunch of air opening the cabinet means you lose most of the heat energy you've built up.  Since radiant heats the part itself, opening the door would do less slowing of the heating.  Am I thinking right?

My other thought (since I don't know much about this yet) was to put the parts in a cold oven and let everything get up to temp at the same time, but I don't know if that's a viable method.  At least that way I could use a window to check temps with a laser thermo to tell when they're fully cooked.  Is there a reason (other than cook time) that starting with a hot oven is preferable?