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Unread postAuthor: jrrdw » Wed Nov 09, 2011 6:59 pm

Yes, that's the one.
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Unread postAuthor: Technician1002 » Thu Nov 10, 2011 10:20 am

D_Hall wrote:Makes sense and sounds sexy as hell, but I'm not sure that level of complexity is required. Also can't do the thermal blankets and such that you mention later in your post. There are visual requirements as well. If my specimen is hiding beneath a blanket, the camera can't see it.
.


The blanket is not placed inside the chamber. It is wrapped on the outside and the power is adjusted to match the heat loss while running. It would be like taking a house and embedding a heating element inside the insulation in the walls so the walls produce exactly as much heat as is lost through the R value of the insulation and wall. The result is the outside walls on the inside exactly match the inside temperature with no cold spots on the walls, windows, doors, etc. By knowing the R value of the walls and the BTU heat loss of the wall, the energy added can be set to the loss value resulting in very low temperature gradients inside regardless of the outside temperature. The thermal blanket is nothing more than oven insulation with an embedded heating element that wraps on the outside of a chamber.

We use the ones like shown on this site between the insulation and the chamber. You can order them in custom sizes and wattages. Coupled with a custom controller, they work very well.

http://www.durexindustries.com/products/electric-heaters/flexible-heaters/silicone-rubber-heaters/?gclid=CJqu092urKwCFQRShwod9iYH_w
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Unread postAuthor: D_Hall » Thu Nov 10, 2011 12:03 pm

Technician1002 wrote:The blanket is not placed inside the chamber. It is wrapped on the outside and the power is adjusted to match the heat loss while running.

Oh. Sorry, my bad. I thought you were talking about something internal to the chamber to wrap around the specimen.

Interesting.

Only potential issue I see there is the base of the oven in this case can't be wrapped. Still, I see the utility.

Will definitely look into!
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Unread postAuthor: Technician1002 » Thu Nov 10, 2011 1:33 pm

A blanket can be laid inside the chamber on the bottom to provide heat at the same rate heat leaves the bottom of the oven to provide low internal temperature gradient. A thermocouple can lay on top of the blanket to set the top surface of the heat blanket to the desired internal temperature so all heat generated is just the heat lost out the bottom. For this to be effective, the bottom must be all the same relative thermal mass and R value to prevent cold and hot spots. We typically set chamber temperatures to +- 0.1 C.
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Unread postAuthor: D_Hall » Thu Nov 10, 2011 3:28 pm

Technician1002 wrote:A blanket can be laid inside the chamber on the bottom to provide heat at the same rate heat leaves the bottom of the oven to provide low internal temperature gradient. A thermocouple can lay on top of the blanket to set the top surface of the heat blanket to the desired internal temperature so all heat generated is just the heat lost out the bottom. For this to be effective, the bottom must be all the same relative thermal mass and R value to prevent cold and hot spots. We typically set chamber temperatures to +- 0.1 C.

It won't be. Not much I can do about it either.
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Unread postAuthor: jrrdw » Thu Nov 10, 2011 4:00 pm

You are limited to a one time test with this exact built oven?
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Unread postAuthor: D_Hall » Thu Nov 10, 2011 5:15 pm

jrrdw wrote:You are limited to a one time test with this exact built oven?

The ovens are disposable, yes.

Sand is used as much because it stops fragments as because it's a dirt cheap (literally!) insulator that can handle high temps. Basically, one of our sidelines is research into how items of interest handle non-optimum environments like...oh... say being in a compartment on a ship while there's a fire in the next compartment.
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Unread postAuthor: POLAND_SPUD » Thu Nov 10, 2011 8:09 pm

items of interest
does it involve some gizmos that make O2 and H from water ? :D
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Unread postAuthor: Fnord » Thu Nov 17, 2011 9:15 pm

Giving this one final go since I don't think there is a solid solution yet.

This design isn't elegant but it should work. Not a pre-built solution by a long shot, but could be assembled fairly quickly from scrap if nothing else.

The whole unit stays in the oven.
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Attachments
fan.GIF
The 'radiator' for this would just be a drum of hydraulic oil with a pump stuck in it.

One possible issue is the fluid slowing the magnet rotation down... could be solved by making a disk shape out of it.

The motor will need to be attached to the container wall obviously.
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Unread postAuthor: USGF » Fri Nov 18, 2011 1:10 am

Gents,

The USG powder coating, thermoforming and heat treating pizza oven has a small shaded pole motor driving a long 3/16 diameter stainless shaft. On the end there is a 4" aluminum fan blade purchased from Grainger. The shaft has a bearing close to the fan, the other end is supported by a small coupling on the motor. We run this oven at 400 ° F all the time. The little high temp plastic bearing needs .015" extra clearance because the plastic seems to swell when it gets hot.

Otherwise works great. The shaft is pretty hot (150 °) close to the coupling but the motor is not affected. We ran the temp up to 600 degrees once to see if it would take it. The aluminum blade got so weak it flew apart. Had to buy a new blade and install.

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