Bronze Clay

Here is a very fascinating thread by some sculptors about bronze clay. Bronze clay, or bronze wax is a mass of bronze powder particles held together with some kind of binder. The material is either hand shaped or shaped in a mold and then sintered in a oxygen-free or vacuum furnace. (Sintered = fused, like a clay pot from a kiln.)

Details:
[www.sculpture.net]

I think this has applications to RepRap; there are a number of ways we can use this techniqe. I'll discuss them after I finish reading the thread (and get some sleep).

Edited 1 time(s). Last edit at 12/16/2007 05:43AM by SebastienBailard.

There is an interesting article in the new issue of Art Jewelry Magazine. It appears that in July the Rio Grande Company, who makes jewelry making supplies will be introducing a new material similar to the currently available precious metal clays, but in bronze rather than gold or silver.

PMC is a material composed of gold or silver particles suspended in a binder. The material can be worked like playdough, allowed to dry and then fired at high heat. The result is a solid metal object. The base material can also be thinned to produce a more flowable product with a longer drying time but is otherwise identical.

While extrudable PMC always seemed like a possibility for use with RepRap, the fact that it was only available in gold and silver (which are not the best structural metals) and was even more expensive than the metals themselves made it seem like a marginal material at best.

Bronze however is an excellent material for a lot of uses. From the reviews given in the mag it seems that producing an extrudable paste is no problem, so it becomes possible to imagine extruding pieces that fire down to be bushings, bearings, wear plates, rivets, springs, etc. The final bronze is described as 89% copper, 11% tin (a fairly standard bronze formula) and "similar" in strength, density, and electrical conductivity to cast bronze. Prices were not given, but the material will be sold in ounces, rather than grams as is the case with PMC. The base material shrinks by about 25% when fired, but this is uniform and does not alter the shape of the object created, preserving even fine details. The final object might be slightly more porous than normal bronze, but this would actually be a virtue for lubricated parts like bushings or bearings. The dried or leatherhard material can be worked easily before firing to add or subtract details. Firing requires a pottery type kiln as the temperatures must be slowly raised over several hours to to 1550 degrees F (844 C) and held for several more hours before cooling.

Anyway I'm cross posting this to the General board in case anyone wants to talk about this stuff in terms of how materials like this can be integrated into RepRap overall, but I thought I would post it here so we can talk about this stuff in a more technical way.

BDolge, I've merged your thread with an older post on the subject. Read the sculpture.net stuff, it is fascinating.

Thanks Sebastien,
The sculpture.net article is interesting, but definitely a different material. Unfortunately the Art Jewelry Mag folks are very stingy with their web content so I can't link to any content but I will type stuff up as it becomes relevant. The material reviewed in Art Jewelry is definitely easier to handle than the stuff on sculpture.net. The new material is fired by burying it in activated charcoal in a sealed stainless steel container and then fired by raising the temperature in increments of several hundred degrees per hour until the final holding temp is reached. After several hours at that temp the item is cooled and is ready to use. That's it- no N2 tanks, no alumina powder, no flammable outgassing. So I think this is a definite advance in terms of making it widely available. While I generally prefer DIY materials there are exceptions and this may be one.

Someone on the general board mentioned problems with working PMC clays in the leatherhard state; this is true, they require careful handling, But the reviewers mentioned that this material was able to be bent 45 degrees without breaking and could be whittled with an exacto knife as well as sanded and worked with a dremmel type tool.

Also there were concerns expressed about shrinkage. PMC clays with similar shrinkage have been used successfully for some time. The shrinkage is uniform and predictable. Lots of people make items to fit around existing stones or other materials or make rings to exact sizes so I imagine these issues can be addressed.

There is an interesting article in the new issue of Art Jewelry Magazine.
--------%<----SNIP----%<----
(EDIT: This post duplicate's BDolge's earlier post before. I've merged the two threads, and will archive this thread in the Fabrication forum when it goes inactive.)

Edited 1 time(s). Last edit at 06/01/2008 11:22PM by SebastienBailard.

Odd, I could have sworn I'd heard of bronze clay before.

My other half uses silver clay for various little jewellery type things. Observations: its harder to work with than you might expect... it isn't like normal clay. The dried metal clay is extremely fragile for example, and you'd want to be pretty careful doing further work on it.

It should extrude easily; indeed you can buy syringes of the silver clay for making filaments or whatever. Support material choice might be tricky (but isn't it always?), as you want something that can survive being baked in an oven to dry, but something that won't cause problems when you fire the end result.

Accounting for all that shrinkage is going to be a bit of a black art when making bearings, I'd say. How much better will bronze bearings made in this way be than HDPE equivalents, do you think? I can't help thinking that for mechanical components, machining is probably the way to go with metal. But as always, feel free to correct me

Note:

This thread should probably be merged with the Bronze Clay thread in the
Fabrication forum:
[forums.reprap.org]


Here's a link to a sculptors forum where they've come up with two different recipes
for bronze clay. There's a fair bit of information there:
[www.sculpture.net]

Ex One can print in various metals, they take orders in STL, but it's pricey.
You may have seen Bathsheba Grossman's art.
[www.bathsheba.com]

Sounds interesting. I like the low-cost approach. It is very contrary to the industry and that's why these things can help future RepRap become very competitive. Of course the quality should be on par as well.

B.t.w. If shrinkage is constant and known (e.g. 25.43% exactly), you should be able to compensate for that and make accurate and even slightly more detailed objects.

On the other hand, it probably takes some care to make sure it is constant: e.g. weigh out larger amounts and do tests, use the rest for a precise job.

---

Regards,

Erik de Bruijn
[Ultimaker.com] - [blog.erikdebruijn.nl]

Re bearings:

A. We might want to take this to the fabricationb forum as it may get somewhat technical but...

B. With PMC shrinkage can be as much as 25% and is consistent and predictable so is easily accounted for. The review of BMC did not mention this as a difference so I assume it was not. Also several items were shown that involved mating BMC components with existing fixed size elements.

C. According to the article BMC was considerably tougher in it's leatherhard state than PMC, able to be bent up to 45 degrees and carved with an exacto knife, Thus an FFF ( Fused Filament Formation) object could be made slightly oversize, finished with hand tools and then fired for a more precise final object. Much easier and safer than machine tooling.

D, Plastic bearings are fine for many uses, but for high speed, high temperature, or high load bearings they will not do. Bronze bushings or babbit metal bearings fill the space between low friction plastic bearings and ultra high speed/tolerance ball and magnetic bearings. Auto engines and drive trains used brass bearings until after WW2.

According to this post:
[www.sculpture.net]
the BMC from Bill Struve (via Rio Grande)
"had about a 20% shrinkage rate and would continue to shrink with subsequent firings."

Apparently it is straightforward to use the activated charcoal method with at least one of the homebrew bronze clay recipes:
[www.sculpture.net]
I find that reassuring as activated charcoal or graphite are more straightforward to deal with than nitrogen or carbon dioxide gas tanks.

Regarding Bathsheba Grossman's metal pieces, those are made by laser-sintering steel particles*, and then dipping the steel mesh in liquid bronze.
* - there's some coating on the steel particles.

I'm wonder how we'd reprap this stuff. The possibilities include
1) Make filament or pellets of bronze powder + binder, and use a heated extruder.

2) Syringe deposition of 'wet' bronze clay.

3) Lay down a layer of bronze powder, squirt down binder, repeat.

4) Make a plastic, elastomer, or jewelry-investment mold with the reprap, and then pour or press in bronze clay.

Ru Wrote:
-------------------------------------------------------
> Support material choice might be
> tricky (but isn't it always?), as you want
> something that can survive being baked in an oven
> to dry, but something that won't cause problems
> when you fire the end result.

Plaster of Paris. When fired in a kiln, it reverts to the original water-soluable stuff.

I'd use jewelry investment instead of plaster of paris. You work it like plaster, it's refractory (heat resistant), so it won't misbehave when you heat it, and it's also water soluble after firing.

When I came across the Rep Rap project over a year ago, I immediately became interested in how to more fully develop its ability to self-replicate. My initial thoughts centered around providing a sustainable energy source, e.g. solar power, or the ability for a Rep Rap machine to print solar cells. So I went looking on the web for things like powdered copper. There are actually some companies that produce copper ink now. I believe that the copper ink is for use in a conventional or modified inkjet printer head. It would therefore make sense to me to be able to first print an ABS PCB board, and then come back on top of it with a powder nozzle or and inkjet nozzle to overlay the copper ink (in however many layers would be appropriate to the desired amp conductivity), and then to swap the nozzle / printer head for the extruder once again and print an encapsulation layer of abs, or some other thermoplastic on top of the copper ink pathways. Has anyone looked into this? Also, if this is feasible, it would seem the logica next step to design something that could recycle copper wire, and perhaps even pennies into a cheap copper ink. It may even be possible to skip the copper ink, and just experiment with copper powder and some form of resin or epoxy that will set when cooled. Thoughts?