Thermal insulation sheets?

[knotlogic]

I'm not sure which section of the forums should go in - it might be a technical question, but it isn't really about electronics:

Could anyone recommend a thermal insulation material that comes in the form of flexible sheets?  And also a source for purchasing small quantities? (Say a few A4 or A3 sheets worth.)  It's for a project at work.

I've done searches on Digi-Key and RS, which recommended 3M Flame Barrier products and Nomex Type 410 paper respectively.  Thing is, looking at the datasheets, both these products are marketed as electrical insulators, and just happen to have low (< 0.2 W/mK) thermal conductivity.

Is there something like a flexible form of mica sheets on the market?  A teardown of the Yihua 858D type hot air stations has something like what I might be looking for wrapped around the heating element.  I just don't know what exactly it is (and what to search for).

The application is to insulate heatsinks that run up to 150 deg C that are near PVC.

[Marco]

This thin enough? (Shouldn't hit the heatsink so the reflective barrier can do some work.)

[NiHaoMike]

Take a look at insulation tape used for HVAC work.

[aargee]

Some 3D printers use standard silicone jackets over the hotend to keep the heat in, maybe that's an option?

[knotlogic]

This thin enough? (Shouldn't hit the heatsink so the reflective barrier can do some work.)

Probably not...  Here's more information on the design:  It's a heat exchanger for heating a stream of air for a one-off project.  Two heatsinks clamped back to back over a set of heating elements, and the assembly is dropped into a short length of PVC pipe and air passed over it.  So the insulation material has to a) be thin in order to fit in the space available, b) insulate the PVC from the hot heatsink, and c) provide a surface for the heatsink to sit on.

The air coming out only needs to be 50-60 deg, but to get that the heatsink needs to be hotter (up to 150 apparently).  Honestly I'm not happy about using the PVC pipe, but we're constrained for options.

aargee, NiHaoMike, thanks.  I'll look into that.

[Marco]

Does it hit the pipe because you don't want to build some standoffs to prevent it or because you're really running out of the mm of space to achieve it? The latter seems implausible. Given the application even a couple mm of airgap is better than any insulation which could fill those mm's.

Create some superstructure to keep the heatsink away from the pipe before you try to insulate anything ...

[Gregg]

A simple heat shield may be the best and easiest solution.  Some thin aluminum (about 0.5mm should be ok but might need to be a little thicker to suit) rolled into a cylinder that fits inside the PVC with 3 to 5mm clearance all around; this can be formed around a piece of pipe or something smaller than the inside of the PVC because it will tend to spring out larger around.  The edges can be overlapped and held by very small machine screws with nuts; several more screws can be used to space the aluminum more or less evenly from the PVC.  If I were making this in the US, I would go to a building store and get some aluminum roof flashing material. 
The heat source should be suspended inside the aluminum offset from the fasteners that keep the aluminum heat shield away from the PVC.  If the temperature of the heat source is quite high, some sheet mica between the heat shield and the heat source may be needed.
There MUST be air flow between the heat shield and the PVC pipe for this to work.

[rhb]

Why not woven fiberglass cloth?  It's easy to find.  Wrap a piece of aluminum foil between two layers of glass cloth.

 I'd suggest using CPVC instead of PVC.  It has more strength at elevated temperatures.

[knotlogic]

Does it hit the pipe because you don't want to build some standoffs to prevent it or because you're really running out of the mm of space to achieve it? The latter seems implausible. Given the application even a couple mm of airgap is better than any insulation which could fill those mm's.

Create some superstructure to keep the heatsink away from the pipe before you try to insulate anything ...

Implausible, but that is actually the case.  The outermost fins of the heatsink are actually trimmed to get the assembly to fit in the pipe.  It's not a perfect fit, so there's some space to work with.  I could take a hacksaw to the fins to get more space, but if possible I'd like to explore other options first.

What might be a good material for a supporting superstructure?  It would need to be heat resistant, and in our case, non-magentic.  Oh, and easy to work with and cheap since we have no proper workshop and the budget is.... thin. (The joys of academia...  )  I was looking at ceramic standoffs but I haven't figured out how to cut or mount them yet.

If the temperature of the heat source is quite high, some sheet mica between the heat shield and the heat source may be needed.
There MUST be air flow between the heat shield and the PVC pipe for this to work.

Isn't mica a thermal conductor?  Which is why it's used when attaching TO-220 type packages to heatsinks?  Only I've come across things like this which claims to be a thermal insulator.

Also, this.  If that's a thermal insulator that might be what we're looking for.  If it's not...

I'll look into CPVC, but finding "specialist" materials locally is hard.  I once asked the local office of an international plastics supplier about availability of rods in various materials, particularly acetal.  I was told they had none of what we were looking for in stock, only POM.

Except that POM - polyoxymethylene - IS acetal. 

A colleague has suggested silicone sheets, and another says he might have some insulation tape used for their equipment.  So that's more options to look at.

[macboy]

...
Is there something like a flexible form of mica sheets on the market?  ...

Mica has long been used as an electrical insulator and thermal conductor for mounting power devices to heat sinks.

[rhb]

CPVC is what is required by code for the hot water supply lines.  Available anywhere that sells PVC. 

An alternate proposal.  Wrap plain fiberglass insulation around a piece of CPVC, then wrap that with a sheet of aluminum flashing secured in place with SS hose clamps.  That's all local builder's supply store stuff.  You can usually split a fiberglass bat into thinner pieces with a bit of practice.

[T3sl4co1l]

Try looking for fiberglass felt or paper?

https://www.mcmaster.com/#fiberglass/=1bu872j as an example, but you'd probably want something cheaper. Doesn't even need to be fiberglass really, plenty of cheap organic fibers are just fine at 150C.  Maybe check the hardware store, or craft store even?  Or automotive?

Tim

[BravoV]

Wonder if the banned asbestos sheet still one of the best insulating material ?

[Kevman]

https://www.summitracing.com/parts/the-14610?seid=srese1&cm_mmc=pla-google-_-shopping-_-srese1-_-thermo-tec&gclid=EAIaIQobChMI0e75zdfV2QIV3UsNCh1RSwduEAQYAyABEgKJEvD_BwE

or

https://www.eastwood.com/x-mat-sound-deadening-material-5pc-12x12.html

?

Another option is to get pipe insulation for the next size down from your pipe and push it into the pipe. They have a tendency to be thick, but remember that you're only get so much insulation for so much thickness. If you use too thick insulation and smoosh it its R value plummets.

[TerraHertz]

http://agaus.com.au/product-category/thermal-insulation/

Not much use to you since they are in Australia. But it may give you some ideas, and maybe there are equivalents near you.

[FrankE]

Aerogel?
Polyiso?
That cement board that replaces asbestos-cementboard?

[CatalinaWOW]

A bit outside the box, but your space constraints seem to be inside the pipe.  If you have room outside why not buy some of those cheap PVC tinker toys and expand to the next larger size pipe for the heat exchanger section.  You then have room for fiberglass batting, glass foam, a glass structure (most university chemistry departments have someone who can make small glass items in no time), or many other options.

Barring that you might want to think about how much thermal barrier you can make in a space a few thousandths thick.  The thermal resistance will be proportional to area divided by thickness with thickness being a really small number.  The remedy is to make the contact area small.  This converts most of the conducting material to the gas in your heat exchanger, which probably has thermal conductivity as low as the materials you will have access to.  Then arrange the points of contact to minimize gas flow as much as possible to eliminate physical transport (convection like flows).  Something like a glass fiber wound in a helix around the heat exchanger.  Finally make the surfaces reflective to reduce radiative transfer.  The heat sink ends can be polished.  You probably don't want to polish the sides of the fins, both because it is difficult and because it will reduce functionality as a heat exchanger.  Making the inside of the PVC reflective is harder, but someone in your physics or chemistry department should be able to flash coat it in gold, silver or aluminum.  The latter two should be cheap, and even gold wouldn't be that bad for these dimensions.

[thermistor-guy]

One option would be to use an "Engineering plastic" like PPS, in sheet form.

https://www.professionalplastics.com/PPS_Film
" PPS (Polyphenylene Sulfide) film is an impact-modified, unreinforced extrusion grade. PPS offers high tensile elongation, unusual flexibility and ductility...".

https://www.quadrantplastics.com/fileadmin/quadrant/documents/QEPP/EU/Product_Data_Sheets_PDF/AEP/Techtron_HPV_PPS_PDS_E_28042011.pdf

PPS is good for 200 deg. C. However, it's thermal conductivity may be a little high, at roughly 0.3 W/mK depending on formulation. I use PPS washers from Digi-Key for mounting certain power components.

Plastics suppliers could advise you on the right plastic for your application:
https://www.professionalplastics.com/professionalplastics/ThermalPropertiesofPlasticMaterials.pdf

A second option is to use a synthetic rubber from Raytech Italy:
http://www.nexusparts.com/raytech-magic-rubber
https://uk.rs-online.com/web/p/potting-compounds/7031228/

This is a two-component cross-link cured rubber, indefinite shelf life, good to 200 deg. C. You mix the two components, then pour it into a mold. In your case, the mold would be the bottom of a large flat container, so you can make your own sheets of whatever thickness you want, and cut to shape. Cure time is about 15 minutes.

I've used the Raytech product as well, and it's quite useful.

[T3sl4co1l]

Teflon is a pretty good insulator, a few layers of tape wrapped around a form would do.

Tim