Making a curing oven out of Commercial Frig

jjjspop · Dec 12, 2017

I picked up a commercial frig from a bar and I plan on making a curing oven. The inside measurements are 26”x56”x54”. I need advice on putting a gas system in to heat it! I can’t decide on natural gas or propane, I have a large propane tank to fuel the oven or a can run a natural gas line from my house. Which one will be cost effective. I welcome all advice from everyone!!
Thanks jjjspop

Hot Rod Grampa · Dec 12, 2017

Buy a cheap tank fill with lp and keep entire operation far away from house or livestock. You are playing with fire, literally, and asking rookie questions. I do not know your level of expertise to be able to offer serious information.

EdT · Dec 13, 2017

Before you worry about exactly how to heat the new "oven" there are a couple of things to be concerned about. Basically, what you have is a metal outer box with, I presume, a metal inner box, insulation in between the two, a door with hinges and latches, some framework, and a bunch of refrigeration stuff that you don't want. Take a look at these things first:
1) What kind of insulation does it have? Since it's a fridge, it's not likely the insulation is going to be good for the temps you will want for a curing oven.
2) What are the door gaskets made from? If they're rubber, they may not work out too well.
3) How hot can you stand the outside to be when it's running? This relates to the space between the inner and outer wall and the insulating value of whatever you end up with in there.
4) Is there any way to take the inner box out of the outer box so you can re-insulate it if required.
5) It's likely that the existing insulation is foamed in place material which will be difficult to remove and may be structural as well.

AFA heating goes, electric is simpler and doesn't explode if you screw up. Can still kill ya if you don't know what you're doing. Gas is harder to control. Some kind of convection fan inside would help maintain a uniform temp throughout the space. The temperature gradient from top to bottom can be pretty large w/o a fan which will give you inconsistent curing of whatever it is you're planning to cure.

sberry · Dec 13, 2017

Get an oven.

jjjspop · Dec 13, 2017

EDT thank you for your information! My plan is to remove the rubber gasket seals and replace it with oven gasket seal. The frig has foam insulation that’s 3” thick, I am going to be adding more insulation on the inside with a new metal liner! The question is how thick of new insulation should I use? The heat source is still up in the air, I’ve heard that gas is cheaper to use and electric is costly! I plan on using a fan in my design to evenly distributed the heat. I’ve read on hear of people using a gas forced air heater by having it on the outside by connecting it with a pipe on the side of the oven. What do you think of heating it that way?

jjjspop · Dec 13, 2017

sberry said:
Get an oven.

An oven is to small for large items I need coated!

Sent from my iPad using Tapatalk

davewo · Dec 13, 2017

I'm no expert, but foam insulation may not be appropriate with such a heat source. Ovens use some type of fiberglass or ceramic blanket with an air gap.

purplezr2 · Dec 13, 2017

davewo said:
I'm no expert, but foam insulation may not be appropriate with such a heat source. Ovens use some type of fiberglass or ceramic blanket with an air gap.

My smoker has foam insulation, no sure what the temp difference is.

I would use an electric source.

davewo · Dec 13, 2017

purplezr2 said:
My smoker has foam insulation, no sure what the temp difference is.

I would use an electric source.

Hmm. I would have never guessed. How hot does a smoker get? I cure my powder coated items at around 450F at the most.

PCustoms · Dec 13, 2017

Bether read through the kidde recall thread before you keep going.

As others have said that foam and enclosure won't be rated for the temperature you need to hit

dogdog · Dec 13, 2017

I think when I was researching for my plans on furnace, I find, a lot of people use kaowool (very pricey) and/or sodium silicate with perlite, or firebricks . They are rated for more than 1800F degs supposedly. and curing oven is only for about 450F. You'll have to make sure your build don't have plastic or anything that can't withstand the temp.

There is an old DIY thread here some guy build an electric heat treatment oven... you might be able to get some inspiration off it... I think if you search oven or SSR (cause he used a commercial temp controller and SSR)

EdT · Dec 13, 2017

I think if there's any kind of foam insulation in the heat barrier you are looking for trouble. For the temps you are looking at, fiber glass insulation would probably work fine. You're not making a furnace for melting metal or forging it so you don't need firebrick or KAO wool. Take a look at the insulation system on an ordinary, free standing kitchen range. They operate in the temp range you are looking at and they won't take your skin off if you touch them while they're operating. I won't pretend to know how thick the insulation should be. You're going to have to figure that out yourself. Same with the kind and implementation of the heating system. If it was me, I'd go with electric because it's so much simpler, but gas may be cheaper to run. Don't know. unless you're planning on running it all the time, I wouldn't think that the operating cost of either method would be a big deal. Ovens are a very developed technology so you will be way ahead if you clone what's already been done rather than trying to invent something. Anyhow, these are all my opinions on the matter and I'm sure you'll hear many more.

Mechtech · Dec 13, 2017

My question is what and how often will you need to cure. (Cure time and environment stability are factors as well)

Do you really need an oven or could you just put them in a small brick room fed with a large propane heater? How important is process control? Is the base material metal would an induction system work?

As far as the fridge goes most polyurethane foams will begin to decompose at around 300F (thermal exposure/no flame) so you would have to completely gut and rebuild it if you wanted to use the case.

Lwel9226 · Dec 14, 2017

What is the inside of the fridge lined with???? If there is any plastic :shocking:

it will melt at the temps that you need.....

LW

EdT · Dec 14, 2017

Go to homemadetools.net. There are a lot of homemade powder coating ovens there. Probably some good ideas.

ovrrdrive · Dec 15, 2017

read this, and then gut all the foam insulation, rubber seals, plastic bits etc out of it and just skip the building steps. Do everything else and what you have should work fine. Personally I'd use electric for an oven that size. After I built mine I didn't even notice a big increase on the electric bill.

What you have won't work in its current form.

http://www.powdercoatguide.com/2014/09/how-to-build-powder-coating-oven.html#.VYth3VI72KV

Brian_WK · Dec 15, 2017

I also say remove the foam and other unneeded refrigeration components once all the foam has been removed use roxul/ mineral wool insulation. Once at temp if well insulated it will use hardly anything for electricity if well insulated.

Electric is the way to go as well. A gas burner in a sealed box won't work it needs oxygen feed and a vent. Electric is also way easier to control the temp to within +/- 5 degrees of set point. Gas is going to be all over the place.

Brian

Making a curing oven out of Commercial Frig

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