Insulation for heat die

[bigben2k]

Been going over matweb.com and McMaster, and I'm looking for opinions on these materials, for constructing the insulating box, around the heat die:

#1-Polypropylene
McMaster p/n 8742K18
1/2" thick

Off hand, it looks a little too soft, and the operating temperature may fall outside of what I'll have


#2-Garolite
McMaster p/n 8491K95 (CE grade)
Operating temps are fuzzy: "Highest Operating Temperature
Above +100° F and Above +212° F".
Only 1/8" thick.


Keep in mind that I am still considering applying a vacuum, to further isolate the heat die.

[RoboTech]

Sorry, I've been away for awhile (work, fall weather, etc...)

I would not use polypropylene or any other plastic for that matter (UHMW, PE, etc.) Teflon would be OK if you have lots of $$$

Phenolic is good for direct contact with the thermal die - it can take reasonable temps and is structurally rigid (it looks like wood in the pics of my early therm die sim). I am planning to use ceramic fiber insulation (poor man's Space Shuttle Thermal Tiles). I have various scraps of 1/8", 1/4" paper, 1/2" board and roll insulation left over from old projects. Glass wool or fiberglas insul could be used as "filler" between the therm die sim block and outer housing. Just some ideas... :)

Ceramic insulation

http://www.cotronics.com Great for insulating the thermal die assembly
>Flexible Ceramics >Blankets, Boards, Moldable sheets, Papers

[bigben2k]

Thanks for the reply, and welcome back!

Ok, so who's got a source for this "phenolic resin"? Maybe I'm not quite Googled out, but getting there!

Ceramic insulation, eh? I'll need something to rest between the copper mass of the die, and whatever wall I use, just for the structural aspect of it, because I'm pretty sure that I'm going to go with the vacuum. Let's see what the catalog and datasheet has to say...

I'm also going to spec out o-ring materials, to properly seal whatever material I end up using. Gotta run the vacuum test first, and determine the pressure.

[RoboTech]

Phenolic looks like wood but is made by impregnating paper, canvas, linen, or woven glass with thermoset resin. There are different types or grades depending on what reinforcing material is used. You may see it in some older switch gear - it is primarily used as an electrical insulator but has good mechanical properties and it is machinable. It's a fair thermal insulator as well and can withstand temps up to 250~280F.

Check with a local plastics supply house. For more info see: www.usplastic.com

I plan to use pieces of phenolic as insulating structural members between the therm die body and outer housing, filling the cavity with ceramic insulation. I may also cap my therm die sim with a plate of phenolic, which will provide a rigid, insulated deck for mounting waterblocks and heatsinks.

Hopefully I will be able to devote more time to projects this winter as the weather closes in.

Vacuum sounds interesting but sorta over-kill to me for dealing with secondary losses. I would think the challenges of sealing and insulating around the exposed die surface would negate any slight advantages. Even with vacuum you still need some kind of structural support, which might conduct far greater losses than what you would save using vacuum vs. a more conventional insulation???

Anyway, sounds interesting and good luck... :)

[bigben2k]

Thanks for the info.

Yeah, I first have to determine the resulting air pressure that I can achieve, then I suppose that I could compare its insulating property against various materials, and see which one comes out on top. It might be more of an effort, but it's all enjoyable, and I do appear to have more time on my hands than the resources to build this, so I don't mind doing lots of research and testing.

Right now I'm "venting" my frustrations on the blower shroud. ;)

Regardless, I'll still need something to support the heat die, structurally, and I still have to solve how I'm going to mount anything on top of it, without compromising the insulation. I want something rock solid, but without any metal elements that contact the inside air (aka vacuum).

I'll post a diagram shortly, of the rough idea I have.

Did you catch the latest about JoeC's alignment solution?

I also have to take a serious look at measuring the flatness (another OC article).

[bigben2k]

Ok, here's a proposed heat die assembly, for everyone's view:
http://www.wbta.us/bigben2k/heat%20die.jpg

[Skulemate]

A vacuum alone won't isolate the heat source entirely, as you will still need some sort of reflective layer inside the outer shell to ward off radiation. Also, you will have to be very careful of thermal bridges forming through your structural supports, which may end up making the vacuum useless. However, if you do insist on using a vacuum, perhaps you could use an air pump to maintain the pressure within the heat die assembly to prevent problems due to bad seals (i.e. run the pump during testing, and shut it off when not in use).

[WAJ_UK]

I'm going to be using the superwool blanket and board from www.rswww.com for insulating my heaters. I thought it looked like pretty good stuff comes in large quantities though. I already have the wool and it looks pretty good and you can mould it into shape quite well

[bigben2k]

Thanks for the tips Skulemate! Yeah, I think I'm going to add a gap between the top of the copper block. Hopefully this ceramic insulation that Robotech mentionned is machineable. Two o-rings...

As for the radiated heat, I could try coating the inside of the vacuum chamber with that thermal blanket stuff, you know, the kind we find in emergency roadside kits? What do you think?

I'm still waiting for the vacuum gauge, and it's hard for me to figure out any kind of preliminary idea as to what my vacuum pump can do right now (it's built into the chiller, and was originally part of a "dryer"). I'm hoping for 10" Hg under atmospheric, but that may be optimistic.


Wa_Juk: Interesting stuff! (You got PM)

Thermal conductivity at mean temperature of: 300°C 0·12W/m.k

[edited out: wrong unit!]

Robotech's linked stuff (the 360) has a thermal conductivity of 0.45 "BTU-in. /Hr. ft^2 deg F" (@500 deg F). Let's see if I can convert that... (anyone?)

[Groth]

1 Btu*in/hr.*ft^2*deg F. = 0.142 W/mK

[bigben2k]

Thanks Groth! ;)

I corrected my above post, because the figure for air was in BTU per hour per square foot per degree F temp difference.

[bigben2k]

To recap...


There's Robotech's ceramic stuff (model 360) at:
0.45 BTU-in. /Hr. ft^2 deg F (@500 deg F)
which converts to
0.0639 W/mK

Then there's WAJ_UK's Superwool board at:
0·12W/m.k (@300 deg C)


Comparatively, air stands at:
0.18 BTU-in. /Hr. ft^2 deg F
which converts to:
0.02556 W/mK


(I'll dig up phenolic resin specs and update this post)

[gone_fishin]

Give it a good coat of paint using this additive. Buy enough to do your house while your at it..........if you feel real froggy your welcome to paint mine too.:D

http://www.hytechsales.com/insulating_paint_additives.html

[bigben2k]

Specs look fine, but the thin application would make it relatively useless, no?

Minimum quantity to order is 1 gallon, which is a paint additive ($18 w/ shipping, not bad). I could coat a few house areas, but I'd still like to see the results in numbers.

Does anyone have any figures for the phenolic resin?

[gone_fishin]

Specs look fine, but the thin application would make it relatively useless, no?

Minimum quantity to order is 1 gallon, which is a paint additive ($18 w/ shipping, not bad). I could coat a few house areas, but I'd still like to see the results in numbers.

Does anyone have any figures for the phenolic resin?


That's ok, do my house and we'll examine it.:D

On a side note the simplicity of refractory cement comes to mind.


Oh, and I'd like to say it looks like business as usual, no real progress in the form of something physical that has been put together by you and presented to the community. Man, I admire your fortitude with nothing to show for it. Kinda like a Timex eh? I would like to say that I am fully qualified to use the term "eh" as it is part of the Finish heritage and slang from which I originate.:D

Which brings me to your WBTA BS.............

Time has passed, show us something or credibillity is weak at best.

[bigben2k]

In time... personal emergencies first: all projects on hold for now (and I was so close to finishing the blower for my case!). Got me some new tools...

But there's nothing stopping anyone from contributing to the WBTA Forums: I put it up, so go ahead, use it. It's not just MY show...