Thermal Insulator Material?

[raynerd]

Hi Guys,
Does anyone have any suggestions as to a reasonably priced thermal insulating material. Something that can be machined. I`m basically going to make a piece of brass very hot, then I need to then insulate this piece from the rest of the assembly so that as little as possible heat is transfered and the rest of the assembly stays cool.

I believe PEEK is suitable for the job but not easy to get hold of and quite expensive. Would PTFE be another option? - but I believe goes quite soft when hot. I`ll be getting this up to near 200degC.

PEEK is currently used for the commerical items on sale so I guess this may be a wasted question as I`m sure research has been done! I just wanted to check if anyone had other recommendations.

Chris 

[David Jupp]

For PTFE, be very sure of maximum temperature -> it decomposes to very nasty fumes above 350 C (so probably OK at temperatures you mention).

Machinable ceramics ? 

Aerogel with something else to give mechanical support ?

If using PEEK, be aware that dimensions can change slightly when it is 'annealed' - you might want to carry out final machining after a heat cycle or two.

[philf]

Hi Guys,
Does anyone have any suggestions as to a reasonably priced thermal insulating material. Something that can be machined. I`m basically going to make a piece of brass very hot, then I need to then insulate this piece from the rest of the assembly so that as little as possible heat is transfered and the rest of the assembly stays cool.

I believe PEEK is suitable for the job but not easy to get hold of and quite expensive. Would PTFE be another option? - but I believe goes quite soft when hot. I`ll be getting this up to near 200degC.

PEEK is currently used for the commerical items on sale so I guess this may be a wasted question as I`m sure research has been done! I just wanted to check if anyone had other recommendations.

Chris

Hi Chris,

How good a thermal insulator does it need to be?

Is this for your RepRap?

I have pieces of PEEK, machineable ceramic and even Vespel (polyimide - good for 300 deg. C - mega expensive if you have to buy it). Providing the piece isn't massive you're welcome to raid my stock.

Unfilled PTFE isn't very stable if you need something not to move. I think that at 200C even PEEK will soften - there is a glass filled version but I think mine is unfilled.

Cheers.

Phil.

[Lew_Merrick_PE]

Chris,

Do you really need to machine it?  There are a number of castable ceramic insulating materials that are reasonably inexpensive and will provide you with thermal conductivities many times better (lower) than any plastic.  Have you looked at various types of wood?  It seems to me that I have used red oak for holding things that were fairly hot -- though I don't remember the temperatures involved (300°C = 572°F for those of us who think that way).  There is a requirement for construction timbers to withstand a 1000°F input for some specific (which I do not remember off the top of my head) time under the American Fire Protection Association Code used in American building codes.  This is called the hot wire ignition test under the AFPA code.  Most non-resinous, well dried timbers pass this test.  ???

[ChrisC]

I take it from the description that you are looking for insulation for a RepRap hot end.  PEEK works well for load bearing components, and lasts well at 250 deg C.  You can buy PEEK bar from RS, but it is expensive; the trick is to use as small a piece as possible.  PTFE is normally used as a low friction liner inside the Hot end, it is fine at 250 deg C, but as others have noted it is very hazardous if you heat it to decomposition point, it generates Hydrogen Fluoride.  I have found that PTFE is next to useless when used for load bearing, it quickly deforms.  It is ok in compression, such as between two metal plates.  Machinable ceramics would be ok, but they make PEEK look cheap!

If you want to avoid using PEEK take a look at some of the more modern hot end designs.  The newest Makerbot hot end and the Huxley hot end (see the RepRap wiki)  both use a short length of stainless steel tube as a thermal barrier, one end in the heater block, the other into a heatsink.

The design of the hot end seems to makes a huge difference to the performance of the Reprap.  I would suggest you have a look at a number of the published designs on the RepRap wiki and www.thingiverse.com.

Chris


Chris