Sunday, December 28, 2008


Some new High Temperature (Ceramic) Materials for Thermoplastic Extruders

Greetings all,

This is my first post to the builders' blog, so I'll keep it short. I've had some success with a new (to me at least) ceramic cement. I was able to reverse engineer (i.e. RTFM) the components of a commercial high-temperature cement and buy them in quantity, for a lower price. The binder is sodium silicate (which Viktor had already experimented with), the thermally-conductive filler is zirconium silicate powder. Both of these are available from ceramics/glaze suppliers, at lower cost than buying from a chemical supply business. More detail is available in my new blog.
Photographs are (for now at least) online in a picassa album
(I'm not having any luck embedding the photos in my blog; please bear with me as a beginning blogger. Please let me know if either of the above links give you problems.)

-- Larry Pfeffer
ursine @t gmail d0t c0m

Hi Larry,
Interesting work. The way I add pictures to a blog is simply to click on the picture icon. It puts up a dialog box which allows me up upload a picture from disc. That then automatically gets added to a Picasa album, one for each blog I contribute to.

For some reason the picture always appears at the start of the article rather than where the cursor is so it has to be cut and pasted.

The size and resolution defaults to about half what I desire so I usually switch to the HTML view, remove the height and width attributes, and change s400 to s800 in the file name.
Damn! That's brilliant work, Larry!
Interesting research.

However, why not use normal fireplace cements?

I bought a 530 gram tube for about 5 euros at a local hardware store. I haven't used my extruder much yet, and it's a bitsfrombytes model, which surrounds the cement and nichrome wire with an external copper tube to avoid thermal erosion of the cement, but so far it seems to work well.

There was a few different variants. I first got one that expanded when heated, intended for fireproofing doorframes etc, but later found this one that doesn't seem to expand, and can take up to 1250 degrees Celsius (the brand is Bison fire place sealant, but there are others). It's pretty fine-grained, and dries to a hard, dark gray solid.

It's intended for fireplaces, stoves, ovens and similar, so it would seem to match our usage profile quite well (repeated heating, no expansion or contraction desired ).

Maybe I mixed things up, but I seem to recall reading that fireplace cement becomes fragile after a while. (Though you point out that there are many kinds, some of which expand -- and probably get more friable in the process.) I have a tube of high-temperature gasket compound that I should try also, but I wanted to be more in control, and try for better heat conductivity.

It may not be the perfect solution, but its a step forward. In any case, the idea of getting materials from clay/ceramics suppliers can't hurt and may well help.

-- Larry
I agree with Larry, it is inherently more RepRapy (RepRapish?) to have the ability to make parts from raw materials when possible. I may not be able to find (or afford) JB Weld or Bison fireplace sealant but zirconium and sodium silicates may be available or scroungeable or I may be able to devise/select a workable substitute based on that knowledge. The more ways there are to build a RepRap the more RepRaps get built and vice-versa.
Brian, et al,

I haven't tried this yet, since I have more Sodium Silicate than I think I'll ever need, but....

I *think* the silica Gel dessicant packets that one sometimes sees in spices or electronics packages is hardened SS. It may need something alkaline to get it to dissolve. I'm not sure whether drain cleaner is pure enough. (Be careful handling chems if you try this!)

Unfortunatly, I'm somewhat leery of re-mailing these materials. SS could leak, and the ZS is a fine, white powder -- something that the authorities could go *nuts* over, even if ziplocked and labelled.
After what the TSA did to Vic's Darwin, I have diminished faith in "The Authorities" especially when "unusual" things are in transit.

Aluminum oxide (which somebody else suggested as a filler) is available as an abrasive. I don't know about pricing or min. orders, though.


-- Larry
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