Plastics Blow Oven

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Simple Oven for Blowing Bubble Canopies from Acrylic Sheet.


MRMAINT62 wrote 04/05/2018 at 06:55 point

Thank you for responding. How much does it usually cost you to purchase all the parts to create the heat for your set-up.

I understand the need for even heating, and I was wondering if you think the element from the oven would do a proper job if used in the bottom of the oven you build with the concrete blocks?

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Michael Barton-Sweeney wrote 04/05/2018 at 18:21 point

I don't know the exact cost because I've had most of the parts lying around. The main costs would be the CMUs, the bricks, the MDF, the silicone, the air compressor and then the heating element that you use and the acrylic. CMUs and bricks are around a dollar or two a piece. The MDF is probably around $20, and you can use silicone caulk I, if you make Oogoo. Kanthal wire is pretty cheap (about $5-10 for 50 feet). Depending upon what you already have, the cost of building the oven could be very inexpensive. You might even be able to get the acrylic for free if you look around and talk to a framer.

I think the heating element in an oven would work fine. Most residential ovens run at 220V, but it shouldn't be a problem to run the element at 110V. I don't know how much current yours will draw, but I would imagine that it would be around 10-15A or below. You also usually have a choice of heating elements in an oven to salvage (bake, broil and convection), so you could pick the one that works for you. 

Now that I think about it, convection might even work without taking it out of the oven like your earlier suggestion—I think that most convection elements in residential ovens have air vents on the back panel, so if you did flip the oven upside down, they would be on the bottom and might be able to move the air around to get even heating. 

I'm not sure how well it would work, but it's worth looking into, if you already have a residential oven and want to hack around before getting the other parts. I don't think the built-in oven controller will be too helpful if you flip it upside down (the temperature sensor will most likely be on the bottom), and you also have a fixed oven size, but other than that, it seems like a pretty reasonable way to go.

If you have any luck, share your work! I'd love to see what you make.

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MRMAINT62 wrote 04/06/2018 at 05:29 point

I don't have any immediate projects, but I may just dream one up to have a reason to try this out!

I noticed you have a RC plane in your hand in your pic. How long have you been flying RC? I have a number of planes but seldom get out to fly them. I think I like to build them more than fly them...

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Michael Barton-Sweeney wrote 04/08/2018 at 00:37 point

Hi Mr. Maint! Yes, I'm into RC gliders. I also spend a lot more time building them than flying, mainly because mine always crash :) I've been making them since I was a kid. Almost all of mine are balsa (tissue or monokote), and a big goal of mine has been to get more sophisticated about plastics, so I can build them better.

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MRMAINT62 wrote 04/05/2018 at 01:12 point

Since your heat range requirements are that of a standard common oven, why not buy a used one for $50.00 (or get one free on Craig's List) that has a large glass window for viewing. Drill a small hole in the center of the glass. Epoxy your air fitting to the outside and weld (or screw) quick clamps (metal as they will be on the heated inside of the oven) around the edges of the glass. make a metal ring for the blowing window that the clamps can align with, cover the inside of the oven door glass with your silicone mixture, and now you can preheat the oven, open the door to the oven, install the plastic sheet against the glass. Put the frame against the plastic sheet, lock the clamps (using thick gloves), close the door, flip the oven on it's back to have the forces of gravity even across the sheet, wait till the plastic is to temperature, connect the air hose fitting, turn on the air pressure, turn the oven to the anneal temp and have a slick set-up with all the heat regulating hardware already built in! You could remove the burners and use one of those circuits to run an exhaust fan to deal with removing fumes to the outside.

If you like my suggestions, please let me know...

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Michael Barton-Sweeney wrote 04/05/2018 at 02:09 point

Hi Mr Maint!

I have a hacked residential oven in my shop that I use for other stuff (it's great!). I haven't used it to blow plastic because it seemed harder to solve the problems of getting the air line inside and making it heat evenly, than to just build a simple top-loading oven out of CMUs.

I'm not very good at drilling through glass, so I would probably just replace the oven door with my own lid, if I was going to use the residential oven on it's back. But my hunch is that in either orientation (right side up or on it's back) that it wouldn't heat evenly, because the heating elements wouldn't be symmetrical to the bubble.

Building the oven out of CMUs is also handy, because it means that you can easily change the oven volume and scale it up.

Regardless, that's a good suggestion about trying a residential oven. They are fantastic and cheap. I'd like to see more oven hacks!

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