Thermal Insulation Materials

Hi,
I'm looking for some advice to help me specify a suitable thermal insulation material for a test rig I'm building as part of my research
at Cardiff University.
I need to insulate the sides of a rotating disk, used in the test rig. The disk is made from steel, and I need to apply an insulating ring to both faces of the disk, in order to reduce heat losses in a controlled manner.
The rings would be around 75mm outside diameter, 65mm inside diameter, and at least 4mm thick (although this dimension is still to be finalised. I would envisage atttaching the ring to the disk using some form of high temperature adhesive, although a mechanical means of attachment may be possible.
The disk reaches temperatures of up to 300 degrees C, and the ambient temperature within the test chamber is around 80 to 100 degrees C. The insulation material would be subjected to no mechanical loads, but would be rotating with the disk at up to 12000 rpm. In addition, the insulating material would be subjected to a combination of oil sprays and oil mist, from the lubrication system. The oil is a synthetic traction fluid.
I would also need to machine some shallow grooves into the material, to accommodate various sensors which are attached to the disk.
Has anyone got any ideas?
Cheers
Alastair Clarke
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12000 rpm will place the insulating rings under substantial tensile stress.
It will greatly ease your problems if the insulating rings can be placed inside steel(or other high tensile strength) hoops at the outside edge of the disk. This will put the insulation in compression rather than in tension & simplify everything. Such a hoop should have little or no effect on convective heat loss and if polished will decrease radiation heat loss.
The metallic tensile hoop should not contact the steel disk directly to avoid that heat flow path. Can you cast an insulating refractory ring in place on the disk's edge such that the ring is a larger outside diameter than the disk? That would thermally decouple the hoop from the disk.
Or perhaps a stainless wire surrounding each of top & bottom rings?
Dave
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Dave,
I think we could use the stainless wire idea - what sort of materials would be suitable for the actual insulator?
Cheers
Alastair
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Alastair wrote:

HOW insulated ? Do you have any numbers ?
Steve
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Steve Taylor wrote:

Given that these disks are very small, what about just a fibrous insulating panel, like the ones that are used in gas fires, we bought a four foot square panel of it from Sheffield Insulation (www.sheffins.com ?) The material is exceptionally light and wouldn't present too much load to the bearings in your machine.
Steve
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Alastair wrote:

The 300C number more or less rules out polymers. Something like a glass foam block from a building supply place could probably be machined crudely using carbide or diamond tools. I'd certainly put a steel band around the outside to keep it from coming apart at 12k rpm. You'd also have to dynamically balance it--if the rotation axis isn't one of the principal axes of the assembled disc, you're going to have a very exciting time. Static balancing isn't enough--that just ensures that the centre of mass lies on the rotation axis.
And I'd certainly put the whole thing inside a steel box before I got it anywhere near 12k rpm.
Cheers,
Phil Hobbs
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On 6 Oct 2005 05:42:53 -0700, in sci.materials "Alastair"

maybe his site could be of interest http://www.aerogel.com /
martin
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Here are some possibilities to start with that meet at least the temperature requirements:
Calcium Silicate Boards Polyimide Sheets Millboard Moldable High-Temp. Alumina Boards Calcium Silica Fiber Blankets Ceramic Fiber Blankets Amorphous-Silica Blankets Ceramic Fiber Strips
Found these by going to McMaster-Carr's web site, http://www.mcmaster.com/ and looking under "Thermal Insulation" (bottom right of their home page). When you click on that you'll see the first sub-category, "Thermal Insulation Sheets". Other insulation subcategories are listed across the top.
Hopefully this helps some.
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www.cotronics.com
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Heeheehe.. can you beat vacuum? Line the walls with a heat mirror, and charge the walls, disc, and lubricant so that nothing touches beyond the workroom.
-Aut
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Autymn D. C. wrote:

Yes, you can beat vacuum. The problem with vacuum insulation is that its effectiveness decreases strongly with temperature, and is independent of thickness, because the transport is radiative. A thick layer of Styrofoam is much better insulation than the same thickness of vacuum--at room temperature, the crossover point is something like 1 cm thickness. Of course, you can improve vacuum by putting in intermediate layers of reflective material, as in superinsulated dewars. This tends to be hard to do really well, because it's next to impossible to bake out a superinsulated dewar thoroughly.
Cheers,
Phil Hobbs
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Phil Hobbs wrote:

I should have said, "with a wall emissivity of 1, the crossover point is around 1 cm at room temperature". Silvering helps a lot, perhaps moving the crossover to 20 cm or a bit further.
Cheers,
Phil Hobbs
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Phil Hobbs wrote:

Uh, what's the difference between putting Stryofoam in contact with the disc, and using it to line the vacuum?
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Autymn D. C. wrote:

The thermal conductivity of an ideal gas is independent of pressure, until the vacuum becomes very good. Getting a good vacuum requires eliminating materials that outgas--polymers being among the worst. A piece of nylon or styrofoam is as bad as having a ham sandwich in your vacuum chamber.
Besides, putting a piece of closed-cell styrofoam in a vacuum would probably make it explode into tiny, tiny chunks. I'm not trying it in my vacuum systems, that's for sure.
Cheers,
Phil Hobbs
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