Help me heat up a powder coating oven (made out of an old steel cabinet)

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curtis73
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The long story is, I'm building a powder coating oven out of an old steel cabinet. The process is to coat an item with powdered color, then heat it to about 400F to melt the coating on (in case you're not familiar with the process). There is more to it than that, but for the sake of this discussion, that's all we need to know. Skip to the end for the short story.

I'm going back and forth on using primarily radiant heat vs convection, but I wonder how much it will matter in the long run. I'm going to run some ideas past you and can you "grade my essay?"

First, the cabinet in question:
1700238933482.png


The bottom is yet to be skinned, and obviously the doors are off. The whole thing will be insulated inside with a 1" rigid fiberglass board, and the outside will have 4" of rockwool or fiberglass batt insulation. I've drawn red lines in the corners which was my first idea - using four, 4' long IR halogen heating elements. The idea was to heat the part more than the air which should be more efficient as opposed to heating the very poorly-conducting air and relying on convection... which was my second idea. Using traditional household oven elements near the bottom of the sides to heat the air to convection-heat the parts.

My real thought here was that using a radiant heat source would be more efficient - that is to say, I could achieve my target curing temperature on the coated part with fewer BTUs or watts expended, but before I can start mathing out how much output I need, I need to know just how much (relatively speaking) the difference will be between convection vs radiation.

For example, here are some heating elements I've been considering.

Traditional electric oven heating elements (primarily convection):
1700239415776.png

Traditional LPG grill burners (primarily convection):
1700239710560.png

IR-emitting halogen elements (primarily radiant):
1700239522148.png

LPG catalyst radiant heaters (primarily radiant):
1700239596703.png


My real question is this: All of the above elements will produce both radiant and convective heat.... but in what ratios? Is the radiant halogen 90% radiant and 10% convecting, or 60/40? What about the oven element? I know it will offer some radiant energy, but how much?

The reason I need to know is because there is a requirement to pretty accurately control the heat of the entire piece being coated. I can't have one end reaching 450 degrees F while the other end is only 350.

My brain is telling me that I either need to do a whole bunch of smaller IR so I can bathe the whole part, or a few large hot things so I can heat the AIR to my temperature and (with the help of air circulation) make sure all of the air in contact with the part is doing the job of evenly heating. But I don't want to mess up and put a bunch of convective heaters in the bottom only to find out that their radiant heat is greater than anticipated and thereby scorching the bottom of the parts

If any of that made sense, great. If not, the short story is:

Let's say you needed to use that above cabinet to evenly heat something to 400 degrees. How would you do it?
 
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  • #2
curtis73 said:
The long story is, I'm building a powder coating oven out of an old steel cabinet. The process is to coat an item with powdered color, then heat it to about 400F to melt the coating on (in case you're not familiar with the process).
I see them doing this on these restore an old piece of equipment Youtube videos. Now I want one
curtis73 said:
I need to know just how much (relatively speaking) the difference will be between convection vs radiation.

I know nothing of these matters but one thing sticks out for me:

curtis73 said:
The reason I need to know is because there is a requirement to pretty accurately control the heat of the entire piece being coated. I can't have one end reaching 450 degrees F while the other end is only 350.
Seems to me, your steel cabinet is not wll suited to this, being long in one dimension and quite short in another. You're asking for hot spots and cold spots. It means that you're going to need to use a bunch of smaller heat sources in there and it's going to be pretty awkward to get them all equidistant from the target.

That's all I got.
 
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  • #3
Most people on YouTube [re]use kitchen oven elements. I like this video:



Even Eastwood uses them (with fans) in their own product:



These guys don't even use ovens! The latter even do it outside! So, if this is for personal projects, you might be overthinking it.



 
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  • #4
curtis73 said:
My real question is this: All of the above elements will produce both radiant and convective heat.... but in what ratios? Is the radiant halogen 90% radiant and 10% convecting, or 60/40? What about the oven element? I know it will offer some radiant energy, but how much?
"400 F?" Any higher, and heat transfer/port is primarily radiative; lower, it's conduction/convection. You're going to have "surface emissivities," Ch. ? of Rohsenow & Hartnett, giving you fits.
 
  • #5
DaveC426913 said:
I see them doing this on these restore an old piece of equipment Youtube videos. Now I want oneI know nothing of these matters but one thing sticks out for me:


Seems to me, your steel cabinet is not wll suited to this, being long in one dimension and quite short in another. You're asking for hot spots and cold spots. It means that you're going to need to use a bunch of smaller heat sources in there and it's going to be pretty awkward to get them all equidistant from the target.

That's all I got.
I agree. The main point of this cabinet was that I have a van roof rack that I want to coat. If I break it down into its smallest piece, it's still 68 inches. The cheapest quote for pro powdercoating I got was nearly $2400. The way I see it, I put $300 into this, coat the rack, maybe do a set of wheels, and I have what I want for a $2100 savings. Then maybe I coat a buddy's wheels in exchange for a case of root beer, and even if I throw the cabinet in a dumpster, I'm ahead two grand and a case of root beer. (Welcome to my mind)
 
  • #6
DaveC426913 said:
Seems to me, your steel cabinet is not wll suited to this, being long in one dimension and quite short in another. You're asking for hot spots and cold spots. It means that you're going to need to use a bunch of smaller heat sources in there and it's going to be pretty awkward to get them all equidistant from the target.

That's all I got.
I don't disagree. The primary purpose for this is that I want to coat a van roof rack. Broken down into its components, the longest pieces are 68" long, but only about 6" wide. The cheapest quote I got for pro powdercoating was nearly $2400 (which, ironically, exceeds the value of the van it goes on).

The way I see it is this: If I put $300 into this contraption and only coat this one roof rack, I'm $2100 ahead. Then if I coat some wheels later, and maybe do a set of a friend's wheels for a couple hundred bucks, I could throw this thing in the dumpster (I wouldn't) and I will have spent nothing but got the outcome I want. (yes, this is how my brain works)
 
  • #7
jack action said:
Most people on YouTube [re]use kitchen oven elements. I like this video:



Even Eastwood uses them (with fans) in their own product:



These guys don't even use ovens! The latter even do it outside! So, if this is for personal projects, you might be overthinking it.




I can use kitchen elements, and I may do that. The problem is getting the amperage/wattage I need to achieve and maintain temp. This box is 10 times the size of a household oven. Actual interior dimensions are 18" D, 36" W, and 80" H, or approximately 30 cu ft.

I looked into all kinds of ways to use radiant heat like those last two videos. What they don't explain is how the resulting finish is arguably very weak. It's more than just melting stuff on, there is evidently a period where it's supposed to hit 450F to outgas, then spend 20 minutes between 350 and 400F to properly flow and bond. Definitely worth a shot, and I should try some small test pieces. I've never powdercoated so I am no expert, I'm only coughing up stuff I've read on the always-correct interweb. Thanks for the suggestion, and I'll give that a shot.
 
  • #8
Ok, so given this feedback (thank you all so far), another idea popped into my head. What if I were to find oven elements that were straight and install them like the red lines in the first picture? Then it wouldn't really matter if the primary energy transfer were radiative or convective (provided I can move the air enough without disturbing the pre-cured powder.)

I haven't had any luck finding straight oven elements, but I should think I could find them somewhere.

Like this, but not bent to fit in an oven....
1700252080223.png
 
  • #9
curtis73 said:
I can use kitchen elements, and I may do that. The problem is getting the amperage/wattage I need to achieve and maintain temp. This box is 10 times the size of a household oven. Actual interior dimensions are 18" D, 36" W, and 80" H, or approximately 30 cu ft.
The Eastwood oven in my previous post is 4X4X6 (96 cu.ft.) and from their website requires 240 VAC, 39 A, and 9360 W for their 3 elements to heat up to 400°F in under 15 minutes.
 
  • #10
jack action said:
Most people on YouTube [re]use kitchen oven elements. I like this video:
I did want to mention, though... That eastwood video has a great nugget of info that might be helpful in my mathing. They mention that it has 3 elements that put out 35,000 BTUs (assuming total, not each). That's roughly 10,264W, which is about 43A at 240V.

That's a benchmark I can use. I was looking at keeping my circuit to 40A, so I might install three elements at around 3000W each which will keep me within the 40A realm. Since my cabinet is roughly a third the size and likely won't be as well insulated, it might work based on a really large ballpark
 

FAQ: Help me heat up a powder coating oven (made out of an old steel cabinet)

How can I safely convert an old steel cabinet into a powder coating oven?

To safely convert an old steel cabinet into a powder coating oven, you'll need to ensure that the cabinet is structurally sound and free of rust. Install proper insulation to maintain heat and prevent energy loss. You'll also need to install a heating element that can reach the necessary temperatures for powder coating (typically between 350°F and 450°F) and a thermostat to regulate the temperature. Ensure proper ventilation to avoid any buildup of fumes.

What type of heating element should I use for the powder coating oven?

The most common types of heating elements for DIY powder coating ovens are electric coil heaters or infrared heaters. Electric coil heaters are relatively easy to install and can provide consistent heat. Infrared heaters are also effective and can heat objects directly without significantly heating the air around them. Make sure the heating element you choose can reach and maintain the required temperature for powder coating.

How do I ensure even heat distribution inside the oven?

To ensure even heat distribution inside your powder coating oven, you should install a fan or blower to circulate the hot air. This helps to maintain a consistent temperature throughout the oven. Additionally, placing the heating elements evenly around the interior and using reflective materials on the walls can help distribute the heat more uniformly.

What safety precautions should I take when building and using the powder coating oven?

Safety is paramount when building and using a powder coating oven. Ensure all electrical connections are secure and insulated to prevent short circuits or electrical fires. Use high-temperature resistant materials for insulation and sealing. Always have a fire extinguisher nearby and ensure the workspace is well-ventilated. Regularly check for any signs of wear or damage to the oven components and repair them promptly.

How can I control the temperature accurately in my DIY powder coating oven?

To control the temperature accurately in your DIY powder coating oven, install a digital thermostat with a temperature probe. Place the probe in a location where it can accurately measure the internal temperature without being directly exposed to the heating element. The thermostat will allow you to set and maintain the desired temperature, ensuring consistent curing of the powder coating.

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