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In Search of Thermal Isolator Material

09/12/2009 9:53 AM

Hello All,

I'm in the process of building a DIY Solar thermal system and have run into yet another road block. I'm wondering if anyone in this forum may have some recommendations they could share with me in solving this perplexing problem.

I am looking for some sort of material to use as a thermal isolator to place in-between the copper holddown clips utilized for anchoring down a copper heat manifold pipe and the underlying steel-framing. The temperature of the glycol-water mixture within the manifold pipe will most likely reach about 350 degrees F, so what ever material I choose also has to be heat resistive as well, ie, not melt before my eyes. Whatever material that is chosen has to be relatively inexpensive, easy to drill through (for self-tapping sheet metal screws), and easy to fabricate.....which means it has to be easy to cut, saw, mill and machine, etc. Basically, I need to make thermal and heat resistive shims or washers. I was thinking of using some sort of readily obtainable plastic, but I'm afraid that most plastic would either melt or crumble from prolonged exposure to the high temps my system would be generating. I also have considered using some sort of ceramic washers or shims, but drilling through them would be highly impractical, plus I don't want to buy extremely expensive drill bits I'll use only a few times. I have all sorts of cobalt and HSS bits to use in my industrial grade drill press, but none of them will make a dent in any of the ceramic materials I have tested them on. So much for ceramics, unless someone has a good handle on where to buy inexpensive or industry surplus diamond-tipped bits in the USA!!!! LOL

I want to ask the opinion of the folks here about a material I was considering on using. I was brainstorming (hahaha!) last night about what type of material I could employ in my gizmo, and I think may have hit upon a possible solution: Would a high quality two-part resin epoxy cast into some sort of shim meet my specs? If so, what sort of thickness should I cast them? The approximate contact area of a simple copper holddown clip (obtained from the local plumbing supply store) is 2 x 1-inch squared. I envision the clips with shms would be spaced @ 24-inches o.c. anchoring down a 1 1/4-inch or 1 1/2-inch Type L copper pipe manifold. The heat bulb connections from the encapsulated solar collector tubes will be spaced along the manifold pipe @ 4-inches o.c.

Any suggestions and help would be greatly appreciated. TIA, and please have a great weekend!!!!

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#1

Re: In Search of Thermal Isolator Material

09/12/2009 11:53 AM

You don't like Rulon?

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#3
In reply to #1

Re: In Search of Thermal Isolator Material

09/12/2009 12:09 PM

Hello TVP45,

Actually I would love to use Rulon in my application, but I cannot find anyone around here that sells it to the general public. I looked over the product and it fills the bill in many ways, so to speak!!!!

Seems like the local supply houses around here (and there's a limited amount of them) that I've called this morning will only sell directly to Contractors that have accounts with them. Ohhh bummer....I may have to expand my search northward to the Capital District come monday when everyone is open. Calling places on a Saturday morning looking for this stuff severely limits my options I'm afraid.

Do you know of a company somewhere on the WWW where I can buy it directly using my credit card or Paypal??? TIA!!!!

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#6
In reply to #3

Re: In Search of Thermal Isolator Material

09/12/2009 1:09 PM
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#2

Re: In Search of Thermal Isolator Material

09/12/2009 12:07 PM

An epoxy might work, but................generally, any temperature above 150C will begin to hasten the decomposition of the polymer. That's why multilayer PCB's are brown and not green as single layer boards are. Repeated thermal cycling at elevated temps.

Here's a thought. Get some Hi Temp (two part if available) silicone(it will be filled with iron oxide and will be red.) Coat some glass cloth squares with the silicone and make a "layup" using however many layers of glass you need to achieve the desired thickness. If using RTV from a tube you may want to do just a couple of layers at a time to facilitate proper cure. Press between two plates to remove some of the air. Let cure. You will be able to trim to size with a razor knife. Spent cartridge brass makes a good punch if sharpened slightly at the lip, if you need holes and don't have cork borers. Don't flex the cured parts too much as they will de-laminate if you try to bend excessively.

I hope this makes sense.

Good Luck.

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#4
In reply to #2

Re: In Search of Thermal Isolator Material

09/12/2009 12:31 PM

Hello lynlynch,

I think you may have hit upon a good idea here.

Umm, when you say to incorporate a glass fabric into the matrix, do you mean to use a woven fiberglass cloth/fabric? If so, I think that's a great idea and it would be easy to make too! Also, fairly inexpensive and readily available, and if I screw up it'd be easy to start over again....trial and error will be name of the day! LOL

I think I could make a series of identical molds using some sort of pins sticking out of the molds that would be coated with a mold release agent. I think that'd be easier than using a spent brass bullet cartridge to make the screw pilot holes. I do have a bottle of mold release agent located somewhere on my workshop bench. I use it for whenever I make resin parts for my scaled plastic military aircraft models.......hmmmmmmm good idea! I think this will work for me, and not cost an arm and a leg.....my "Better Half" has begun to drag out the good 'ole trusty financial calculator lately over concerns of my spending way too much on this project! Ummm, nothing like the penny pinchers and paper pushers to throw an Engineer/tinkerer off track!! *LOL*

Thanks!!!!!

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#5
In reply to #4

Re: In Search of Thermal Isolator Material

09/12/2009 12:47 PM

woven fiberglass cloth/fabric? Yes.

If you can find a two part (addition reaction cure) silicone, no release agent will be required because it has no adhesive qualities (without priming) like the adhesive sealants in the tube. Hence the caution about excessive flexing, which would not apply to adhesive/sealants.

Search GlobalSpec or Google: two part high temp silicones.

Yes molds and pins are certainly good ways to go.

Buy the wife some flowers. That'll throw her so far off she'll forget about the project!

I think you can do this.

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#7
In reply to #5

Re: In Search of Thermal Isolator Material

09/12/2009 3:33 PM

Ahhhhh flowers for the wife.....yes I can yes I can yes I can.....flowers for the wife.....yes I can yes I can yes I can.....flowers for the wife.....yes I can yes I can yes I can.....flowers for the wife.....yes I can yes I can yes I can.....flowers for the wife.....yes I can yes I can yes I can.....flowers for the Mrs. Moosie!!!!!

LMAO

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#16
In reply to #2

Re: In Search of Thermal Isolator Material

09/14/2009 11:03 AM

"That's why multilayer PCB's are brown and not green as single layer boards are. Repeated thermal cycling at elevated temps." Funny; we buy multilayer PCBs by the tens of thousands (we produce medical electronics, ECGs & related, mostly) and they're all green . . . The brown and green boards are in fact made from different materials in the first place, and thermal cycling is not the issue. The brown is SRBP (Synthetic Resin Bonded Paper), and the green is Fire Retardant 4 (FR4), made of fiberglass and epoxy resin. The resin in SRBP is phenolic.

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#17
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Re: In Search of Thermal Isolator Material

09/14/2009 11:36 AM

Thanks for that clairification. I've been wrong all these years.

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#18
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Re: In Search of Thermal Isolator Material

09/14/2009 11:51 AM

Raychem makes one that is actually milky robin's egg blue that is actually a high temp ceramic board material. We used it for high temp downhole electronics back when I was in that biz. We used high temp 18k gold solder from Indium Corp. too for all the connections. It had a controlled CTE so it would not expand and contract with changes in temp. but we found that was only in the x and y axes, the Z (thickness) axis had quite a large CTE by comparison. That led to problems with plated through holes.

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#8

Re: In Search of Thermal Isolator Material

09/12/2009 3:46 PM

Is 350f too hot for some good dry hardwood? A pizza oven gets hotter than that. Is Bakelite or sheet teflon available? Maybe your local electrical and plumbing supply could recommend some insulating standoffs.

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#9
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Re: In Search of Thermal Isolator Material

09/12/2009 4:26 PM

Thanks, I like the idea of using bakelite as well!!!

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#10

Re: In Search of Thermal Isolator Material

09/12/2009 5:41 PM

Try http://www.usplastic.com. They list their PTFE sheets as having a working temp from -20F to +500F.

Their 1/32" PTFE (#45252) in a 24" x 48" sheet is 3.8 cents/sq-inch.

Their 1/16" PTFE (#45253) in a 24" x 48" sheet is 8.0 cents/sq-inch.

I have only used them a few times but we were always happy.

Let us know how it works out,

Bruce

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#11

Re: In Search of Thermal Isolator Material

09/12/2009 10:41 PM

TVP45 and Bruceflorida, many thanks for the links you guys provided! For some reason I must be half blind today and missed your respective postings...mee thinks I didn't drink enough Joe this AM!!! LOL

I want to thank all of you that helped me here today trying to select an adequate material for my 'lil project! I hope I didn't miss thanking anyone. You're a great bunch of guys and gals. I want to let you know that, okay??!!!!

Now I have way too many materials to choose from....don't know where to start evaluating them all, and each is a very good choice for my needs.

Again, many thanks to all!!!! Goodnight, and have a great Sunday!

===Mark, aka Moosie

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#12

Re: In Search of Thermal Isolator Material

09/13/2009 12:12 AM

Ketron

Chemically resistant structural and bearing & wear material for continuous use to 480°F (250°C). Product profile: Excellent chemical resistance. Very low moisture absorption. Inherently good wear and abrasion resistance. Unaffected by continuous exposure to hot water or steam. Ketron® PEEK grades offer chemical and hydrolysis resistance similar to PPS, but can operate at higher temperatures. PEEK 1000 offers steam and wear resistance. This general purpose grade is unreinforced and offers the highest elongation and toughness of all PEEK grades. Meet FDA requirements CFR 21 Section 177.2415 & 177.2416 and ASTM D6262 S-PAEK 0111.

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#13
In reply to #12

Re: In Search of Thermal Isolator Material

09/13/2009 10:09 AM

Many thanks bwire!

Ketron looks like the ideal material to use in my project, but there's one very large hitch about using it: buying a single sheet of this stuff will break my project budget....

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#15
In reply to #13

Re: In Search of Thermal Isolator Material

09/13/2009 3:58 PM

I thought so too but then again if you got a rod; way less cost, and cut the length at the thickness you need of a thermal isolator that would be simpler and more cost effective; less waste. You could drill the end of the rod for the screw size required then cut-off the length as needed.

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#14

Re: In Search of Thermal Isolator Material

09/13/2009 2:02 PM

Red wiring board like that used for electrical panel installation (essentially glass reinforced phenolic board.)

phenolic (linen)

FR4 glass epoxy.

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#19

Re: In Search of Thermal Isolator Material

09/14/2009 12:13 PM

I suppose if you were brainstorming the thought of using layers of gypsum or drywall didn't occurr...seems the most readily available and least expensive option. Spray on some sizing used for ironing clothes to keep dusting to a minimum

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#20

Re: In Search of Thermal Isolator Material

09/14/2009 12:25 PM

If you can switch to machine screw threads there are these.

http://www.mcmaster.com/#screw-insulators/=3mnmpo

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