Free-blowing a bulged bubble canopy?

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I don't know why anyone would use any foam as insulation in an oven. If you have a runaway control event the foam will give off toxic gas. Regular pink home fiberglass insulation works great, and is fire proof. I have built half a dozen ovens with it, the biggest one being 8'x8'x24', 2 million BTU!
Using 3 1/2" fiberglass insulation, oven at 400 degrees F, the outside tin wall of the oven is barely above room temp.
 

Pops

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A neighbor built a 4'x4'x8' powercoat oven from 11 gauge steel on the outside and a thinner steel box on the inside with fiberglass insulation between. Full size door on one end with a mono-rail on the center of the inside roof that would extend to the outside the door for loading parts. He did rudder pedals , stick, etc for the JMR for me. Electric stove heating elements and a small circulating fan.
His business was making steel tables that he powercoated. First class work.
 

cluttonfred

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A poor man's solution might be very thin mild steel or aluminum sheet screwed to the inside of a steel 2 x 4 frame with the corners and butts sealed with high temp industrial foil tape (600 degrees F) then insulated with fiberglass and covered in cement backer board.
 

patrickrio

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Awesome information here. Couple questions, you speak as if you have done this before, did you make the whole oven box out of 2" foam, or did you apply the foam to a substrate like plywood? If it is just out of foam, what kind of tape did you use to create the oven box? These questions have to do with what can withstand 300 degrees F. I could see where you could glue the insulation to plywood, plywood is the outside structure, the insulation protects the plywood. But if you just used the rigid insulation, what type of tape would be fireproof?
I built a xps foam box for heat treating baggage and clothing for bedbugs at 120 degrees F for a friend who used to do a lot of trips/hotel stays for work. (he learned the hard way about this....) Built the 3'x4'x6' box in his garage. All I did was tape the foam together with duct tape with no plywood reinforcement. I did use duct tape bands for reinforcement. The floor was the only structural reinforcement used (could be table top also). He used it weekly for many years without needing repair. A poliso or rigid fiberglass insulation box adequate for your temperature will be similar construction as long as they are faced with some material you can tape to. they are plenty rigid if you support below with a table or the floor. I think that for your purposes and for just a few uses, the plywood is just unnecessary expense. worst case, get a few cheap slats or 1x2 boards for support if the box is really big... wood is too expensive now to buy if not necessary.

The poliso brands above in vigilant1's post will work fine. You can also use Owens Corning 703 frk rigid fiberglass like THIS.

You can buy a six sheet box of the faced rigid 703 FRK fiberglass good for up to 450 degrees F HERE. Note, these sheets are 2'x4'x2". The insulation is available at sizes up to 4'x8' from other suppliers.

This construction won't be as PRETTY as what Pops has for powder coating, but it will be cheaper and easier to build.

If you want to powder coat too with the oven you can...

For tape, exterior box is fine with duct tape. Interior, I think the adhesive on duct tape might be too soft when hot, so maybe for the interior you use high temp foil tape like Cluttonfred suggests.

The convection oven mod was different than what you need as I just put soft kiln insulation inside a large convection toaster so that it would reach about double the internal temperature with the same equipment. Then I substituted the PID temp control for the temp control that came inside the convection toaster. The samples I was testing were tin can sized so they fit inside the toaster just fine. I used automated setting PID control because I wanted my test temps to keep +/- 1 degree for the test temperatures from 500 to 900 degrees.

I have not built such a thing specifically for composite curing or acrylic softening, but the above builds are very close. I am recommending a combination of the two which should work fantastic for your purposes. You will use the convection oven for the fireproof/electrical safe portion and build it into a large box made of the rigid poliso or fiberglass. you can use a multi probe cooking thermometer to verify you are getting good circulation around the object after building and can put another fan in the fan circuit if circulation needs to be improved. If you don't have a multi probe cooking thermometer for kitchen and BBQ use already, you should get one anyway because they allow you to cook perfect meat and fish every time.... something like this
 
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patrickrio

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Here is a youtube video of some guy building a large curing oven from rigid insulation. No additional interior or exterior facing or structure needed....

 
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Matthew, The thinner the inner lining the better, less thermal mass/inertia, heats up easier. I used old galvanized roofing tin .020 thick for the bigger ovens, seal nail holes with red silicone. For the smaller windshield oven, 5'x4'x7', I used old aluminum "press plates" .010 thick. No tapes are needed on corners or sheet edges inside the oven. Build the oven at least twice as big as you need for your item, you need the unused space for air circulation.
 

Vigilant1

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If the precise temperature of the part is important (e.g. acrylic sheet, epoxy layups, etc), then no matter what you use for heating elements (stove burner elements, heat guns, etc) you'll want to be sure the radiant heat from those elements doesn't directly heat the part. Use reflective foil (2 layers with air in between is best) or whatever else is handy/safe so that the part doesn't "see" the hot elements and is only heated by the circulating air.
 
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jmt1991

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The guys in the one powder coating forum I used to frequent used RockWool insulation for their ovens.
They liked its resistance to fire and heat.
It's not nearly as cheap as the fiberglass, but right now, nothing's cheap.
 

mcrae0104

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The guys in the one powder coating forum I used to frequent used RockWool insulation for their ovens.
They liked its resistance to fire and heat.
It's not nearly as cheap as the fiberglass, but right now, nothing's cheap.
It also comes in boards—handy for an oven.
 

BBerson

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Home Depot has $16 big bags of Perlite in the garden section (volcanic foamed rock). Mix it with cement for a cheap,fireproof, light stucco plastered on OSB board.
I used fiberglass batts last time. The fiberglass binder smokes. Do it outside if not fireproof, the fumes are bad.
 

patrickrio

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for these rigid insulation boards:
XPS is limited by the material itself to 165F
Poliso is limited by the material itself to 350F
Rigid Fiberglass foil faced is limited by the binder used to make it rigid to 450F the plastic faced is limited by the facing temperature to 175F
Foil Faced Rock Wool is limited by the foil facing to 1200F The non foil faced can handle higher and is likely limited by your oven build.
 

Hot Wings

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Mix it with cement for a cheap,fireproof, light stucco plastered on OSB board
Or - just thinking out loud.................
Make your own refractory sheets with some chicken wire in the middle for reinforcement. Perlite in cement can be pretty light and if it works to insulate 2500F for my foundry it should work well enough at plastic forming temps.

Thanks for the HD source. ;) I've only found small bags up this point.............
 

Vigilant1

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You guys are thinking too hard, working too hard, and solving problems that don't exist. Plain old fiberglass, no backing, works perfect and is cheap. I have 30 year old ovens that work as good now as when I built them.:eek:
Loose batt fiberglass can work fine, but it isn't perfect for every task/oven. It's dusty/itchy (so would need an inner facing for use in a paint booth, etc). A lot of folks hate working with it. Also, it's pretty easy to just cut the tapes on a temporary sheet foam oven and store it flat up in the rafters until it is needed again, might weigh just a few pounds. No wood, chicken wire, screws, nails, etc at all.
Unfaced or faced FG can work, too, but I sure wouldn't say any other approach isnt worth doing.
 
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geosnooker2000

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Bump-
Next question is where to source the UV filtering cast acrylic to form windshields and side windows. My hour-long google search has yielded a bunch of sneeze-guards and some companies that don't understand how to organize a website for choosing purchase options (one of them only allowed the purchase of a sample). The one site I found that I knew what I was buying was what I wanted was $180 for a 2x4 sheet of 1/4". Heck, I can come real close to buying actual Piper Cherokee windscreens for that kind of money...
 

Hephaestus

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Next question is where to source the UV filtering cast acrylic to form windshields and side windows. My hour-long google search has yielded a bunch of sneeze-guards and some companies that don't understand how to organize a website for choosing purchase options (one of them only allowed the purchase of a sample). The one site I found that I knew what I was buying was what I wanted was $180 for a 2x4 sheet of 1/4". Heck, I can come real close to buying actual Piper Cherokee windscreens for that kind of money...
Look for local plastics companies. GE paint and plastic and industrial paint and plastic are generally the goto's around my neck of the woods.

Sign shops also tend to have mass quantities of plastic sheet on hand.
 

geosnooker2000

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I ordered cast acrylic from the local window company and got some off brand with no idea what it was.
They didn't care.
Yeah, that's the kind of thing that worries me about sourcing it. It's like when you go to the local ACE hardware and ask the guy "Is this 6061-T6?" and he goes... "dude... it's Aluminum..."
 
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Sourcing is a majour pita, that's why companies have full time purchasing departments, and it's getting worse. I buy from a few suppliers in Toronto, one is Laird Plastics. I called them and they said the closest Laird to you (Geosnooker2000 Somerville TN) is Louisville, KY, or Atlanta, GA . You could call them and ask if they have a closer dealer or one of their customers you could buy from.
 
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