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  #51  
Old 06-26-2006, 03:29 PM
Arrow Arrow is offline
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Re: Bronze Clay?

The process is sintering: powdery metals become a coherent mass by heating without melting.

Quite different from casting molten bronze. More closely related to ceramics.

The link Mark Pilato provided explains the general process:
http://www.cisp.psu.edu/pdf/NL-Fall05.pdf
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  #52  
Old 06-26-2006, 04:05 PM
mark pilato mark pilato is offline
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Re: Bronze Clay?

Hi Reka -sounds crazy but true and yes it does just sit and wait. mind you it is surrounded by a dense powder that helps hold it up wile it is brought to temperature. Thats the beauty of it. think on it for a wile check out the links I gave above. This is the process of the future of bronze and I cant wait to see what people will do with it, its beyond imagination. Glass, Stainless,bronze and who knows, maybe something altogether new. I plan on putting it in hands of artists to see what can be done. It is a dream you know, to sculpt bronze and have it come out exactly the way you like. I have sculpted my whole life and i have never seen anything like it. Its beautiful,simple and clean. If you scroll up you can read about others that used the pilato process and were very pleased. So jump on man its a crazy ride and maybe it will be you who shows us all something fresh- never seen before. You can weld plus patina and i bet if you were to see a piece done by this method you would say "dam thats a good cast". So say you have your rubber mold and you pour this material in the same way you would a wax, then after it has cooled you take out and clean seam line and here the kicker you sculpt the bronze, find deeper undercuts clean edges and create new forms, then to the kiln were the magic happens and wala a finished bronze- no cups -no vents- no shrinkage -no sand or foreign material- I could go on and on. Again sorry about spelling I am dyslexic so this stuff take me a little longer then most.
All the best,
Mark

Last edited by mark pilato : 06-26-2006 at 04:34 PM.
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  #53  
Old 06-27-2006, 01:17 AM
dawn dawn is offline
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Re: Bronze Clay?

It sounds unbelievable! Mark, are you really going to share it with all of us here? I know how hard for it is for people to share information like this with others for free, especially when it cost you so much time and effort and money and when probably no one had shared their information with you for free when you were in your process of experiment. Your informatin is definitely valuable. For sharing such valuable information with others, it makes you a truly respectable person that we rarely seen today.

I started doing sculpture only for a few years and yes, I had only cast two of my pieces in bronze because I can't afford it. Therefore I tried all those "fake" procedures like resins, cold-cast stuff, etc. I also hand cast a few pewter at home. So, your invention would be something changing my life. I can't wait to hear more and thank you with all my heart.
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  #54  
Old 06-27-2006, 09:17 AM
mark pilato mark pilato is offline
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Re: Bronze Clay?

I have done a lot in my life when it comes to helping people and although it's my gift I always feel that I am receiving much more. I also believe like so many, that when you do something good for someone it makes the world a better place. I volunteer teaching people with disabilities and I have seen true miracles when it comes to the power of art and what lives in our hearts. My latest sculpture Ascent is my gift to the families of 9/11. It took three years and I cried a lot in that time. I saw things I would never want to - ever. But do you know what I found - Love. Some would say it was crazy to give it away and they did, I was offered crazy money for it. but for me there was no other way. I learned more in that three years then my whole life. I saw things in the form that were not there before. I traveled to places deep inside me and found new meaning in my life and i am a better person for it. I met heros talked with Families who's stories move me greatly and the most amassing thing my sculpture has helped heal. What more could I ask. So when it comes to sharing a process that would help so many. That may help an artist express ones self and help with in there career and maybe even bring something into the world that is new never seen before. What is money when it comes to this. I know how hard it is, I have been there. I support my family with my art. Its always hard but I live the life and I love it. Its not fun trying to come up with money for the foundries and when your a sculptor its hard to make a living without them. So I know what this will do for so many. As for worrying about what other would do or not do, that takes to much time and we all know what is right. So do good and try not to let others bring you down.
Check out the link
Quick Time
http://www.pilatostudios.com/pages/s..._qt_large.html
windows media
http://www.pilatostudios.com/pages/s..._wm_large.html

All the best,
Mark
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  #55  
Old 06-27-2006, 11:26 AM
dawn dawn is offline
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Re: Bronze Clay?

Mark,

I hope more and more people are like you, willing to give a helping hand. Like in this site, people and willing to share informations and their experience. I think it is one of the best site I've ever visited.

BTW, I can't open you PDF link. When could we expect to watch your movie? Please kindly explain each procedure as clearly as possible in your movie as some of us , well, at least me, are quite inexperience even with kiln firing .

Dawn
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  #56  
Old 06-27-2006, 11:55 AM
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HappySculpting HappySculpting is offline
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Re: Bronze Clay?

Quote:
Originally Posted by mark pilato
I traveled to places deep inside me and found new meaning in my life and i am a better person for it.
Yes, I'm just getting a glimpse of the kind of guy you are and all of this giving will give to you in return with lots of happiness. You have a beautiful life right now as I can see by the videos- blessed with a wonderful art partner and the cutest kids. Wish you all the best and thanks for sharing this process with us so generously.

Dawn- I was prompted to download Quick Time "Active X" in order to view the first video. These videos are so professional looking. I can see Mark is multi-talented to say the least. There are other videos on his site that show the whole process of him sculpting the "Ascent" that he donated as a 9/11 monument. I need to go back and watch the rest now.

~Tamara
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Last edited by HappySculpting : 06-27-2006 at 12:26 PM.
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  #57  
Old 07-01-2006, 08:30 AM
mark pilato mark pilato is offline
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Re: Bronze Clay?

Hi I think this may help - I found it on an old web site for Aesthetic Materials. The Fired Bronze Process was invented by Dr. Rand German, Penn State researcher and expert in the field of powdered metals, and Mark Pilato, bronze sculptor. Together they have explored and perfected the process of creating exquisitely detailed, solid bronze sculptures using powdered metals, binders, and sintering.

In this new (patent-pending) process, a proprietary feedstock of powdered metal and binders are mixed into a liquid, which is poured into a rubber mold of the piece to be produced. The mixture is allowed to solidify then the green piece is removed from the mold. (Green pieces can also be carved directly from molded blocks of the mixture.) After molding or carving, the piece is inspected, chased, and prepared for firing.

The firing method used in The Fired Bronze Process is known as sintering, within which the metal particles are heated to a temperature high enough to cause the particles to fuse with one another but not to melt. During the sintering process, the binders holding the green piece together evaporate leaving a piece that is solid bronze -- identical in appearance to foundered bronze. This process is faster, more energy efficient, and less damaging to the environment.

Because the piece can be chased in the green state, little (if any) post-sintering chasing is required. There are no runners or sprues attached to the piece, and surface detail will match the quality of the original mold. Green pieces can be welded, if required. Sintered bronze has excellent surface smoothness and accepts all patina finishes. The process causes shrinkage of about 5%.

Currently, the maximum height of pieces that can be made through The Fired Bronze Process is about 20"; however, the company continues its research and development, which will continue to increase the size of pieces manufactured.

The company employs artisans skilled in the production of rubber molds, and will also accept artists' molds, subject to satisfactory inspection.
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  #58  
Old 07-01-2006, 12:02 PM
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Re: Bronze Clay?

Thanks Mark. Can this bronze clay be purchased somewhere? I know that the link that you gave on this showed a website but are they out of business now?

~Tamara
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  #59  
Old 07-01-2006, 02:40 PM
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Re: Bronze Clay?

If you like forming this type of maleable material --which can be fragile when finished-- I would like to suggest that you consider working in wax. A microcrystaline or something similar for bronze casting. I say this because most clay forms are not typically large and wax does have some similar properties without the negative qualities (dry, brittle,delicate) as you work it. Wax can be worked on anywhere and when cast is a durable finished product.

Working smaller means you can find an independent foundry guy or maybe a local art school sculpture department that could make casting in metal affordible.

Forget about editions and make unique pieces. Potentially you might sell some and they will pay for themselves or even allow you to eventually upgrade your scale. I have friends who trade castings with a commercial foundry to cover all the casting expence of the process for both iron and bronze.
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  #60  
Old 07-01-2006, 03:40 PM
mark pilato mark pilato is offline
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Re: Bronze Clay?

Thats a great idea fused - i have traded for castings, I have also sold work for the price of two castings so I would have one to sell, this way the collector is getting a great deal and I am also able to sell one. sometimes I also put a price on work like 5,000 plus casting cost and I have the client pay the foundry direct this way they are not shocked when confronted with a huge amount. One of a kind wax is a really great way to go also. I like sculpting wax in hot water then freezing it so I can sand and make hard edges. Also Try mineral spirits with drywall paper. Tamara the process is not being used right now as far as I know but you may want to try and contact the person on this link and see if anyone is working on it. Tell her you are an artist and talked to me and could she send you a more detailed look at it all. Who knows maybe she will send you everything.
good luck
http://www.cisp.psu.edu/pdf/NL-Fall05.pdf

Last edited by mark pilato : 07-01-2006 at 04:05 PM.
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  #61  
Old 07-02-2006, 11:22 AM
dawn dawn is offline
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Re: Bronze Clay?

Mark, I can't open your PDF file.

Are you still planning to share the technique with us by making a movie?

Dawn
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  #62  
Old 07-02-2006, 12:01 PM
mark pilato mark pilato is offline
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Re: Bronze Clay?

yes I am planning on making video and sharing for free. , I have to finish sculptures for clients plus a new chess set etc, etc, so it will be some time. I have to make sure that I give all the info so i have been trying to get hold of the other scientists to see if they have any info they would like too share. try this - The persons name I mentioned above for you to contact is Sharon Elder at The Center for Innovative Sintered Products at Penn state her E-mail is cisp@psu.edu I know that when I left my team was working on a small scale kiln that was very economical to use. You may want to ask about this also. Good Luck, Back to the studio to grind away.
Mark
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  #63  
Old 07-07-2006, 04:11 PM
sparklemachine sparklemachine is offline
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Re: Bronze Clay?

Wow. This stuff is great. Can't wait to try working with it...
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  #64  
Old 07-31-2006, 10:01 AM
dawn dawn is offline
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Re: Bronze Clay?

I sent an e-mail to Sharon Elder a few weeks ago and another e-mail to Mark Pilato. No reply from either one so far. I wonder if the story ends here.
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  #65  
Old 07-31-2006, 10:22 AM
mark pilato mark pilato is offline
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Re: Bronze Clay?

sorry guys, I am very bussy finishing work to suport my family I have ten sculptures that have to be finished so I can put food on the table, maybe Sharon is on vacation until the school year starts again. Have you reached Rand German? I am sure if you try a little harder you will get your anwers, maybe call Penn State and Talk to Sharon directly. Call Penn State ask for Sharons #. When I get the time which will not be for some time I will share. Sorry I have not e -mailed I am in Vermont for two weeks swimming and fishing with my family. Then I go back to the studio to sculpt sculpt sculpt.
all the best,
Mark
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  #66  
Old 08-01-2006, 12:25 AM
dawn dawn is offline
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Re: Bronze Clay?

Sorry about pushing you. I am just too excited about this new technique to be cooled down. I really want to introduce this technique to HK as I believe many sculptors here could by benefited. Till you have time to share, I'll wait patiently
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  #67  
Old 09-10-2006, 10:33 AM
DanielUCM DanielUCM is offline
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Re: Bronze Clay?

It has been really interesting to follow this thread! I keep getting surprised at how all you people here readily supply hard to come by advice and information to each-other! I was myself thinking of trying to do some liquid-phase sintering with kopper and tin powder mixed with some binder when I found this thread and realised that this Pilato-process appears to be cleaner and better. I for one would have had a hard time to figure out to use aluminum-oxide to encapsulate the sculpture.

I actually experimented with some pre-alloyed 89% copper, 11% tin, powder mixed with mikro-wax to see if it could actually work. I just made a flattened blob of the mix and put it in the aluminum oxid. I used a simple gas-powered furnace and used the steel-container as temperature indicator. The result was a somewhat solid piece of bronze. Since the environment was not full of nitrogen the pieces were heavily oxidised with a lot of scaling and slagg (not sure of the English word?). Beneath all of that was however a thin core of solid bronze, I guess the environment was better on the inside. It was not possible to break the piece with your bare hands, although one of the two pieces made was slightly bent.

Has anyone understood the part about what kiln/furnace to use? Mark: you say that the kiln is a nitrogen-charged furnace? What about the "second hand vacuum furnace" that you mentioned in one of your earlier posts as distinct from the "kiln with computer"? Did you mean that it is only one owen needed, a nitrogen-powered vacuum furnace that is computer operated?

Mark: are you sure its all right to contact those you have worked with earlier? Has anyone here had any luck contacting them recently?
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  #68  
Old 03-29-2007, 01:06 PM
mark pilato mark pilato is offline
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Re: Bronze Clay?

Hi all, its been along time since i posted on this topic, but I have some good news, I tracked down Rand German the man him self. He is excited in working with artists again on this, and he asked me to share his e-mail with you. so e-mail him tell him why you want it and see how you can be apart of this exciting process. Good luck, Rands E-mail german@cavs.msstate.edu
and all the best,
Mark

Last edited by mark pilato : 03-29-2007 at 03:24 PM.
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  #69  
Old 03-29-2007, 03:28 PM
mark pilato mark pilato is offline
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Re: Bronze Clay?

I changed the e-mail in the last post so make sure you got the right one.
all the best,
Mark
Randall M. German
CAVS Chair Professor of Mechanical Engineering
Director, Center for Advanced Vehicular Systems
Mississippi State University
P. O. Box 5405
Mississippi State, MS 39762-5404

email german@cavs.msstate.edu

Last edited by mark pilato : 03-29-2007 at 05:23 PM.
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  #70  
Old 03-29-2007, 05:39 PM
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le granfred le granfred is offline
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Re: Bronze Clay?

Hello

In France, when we wish to create a replica of a work of art, we mix bronze powder with a sturdy acrylic compound that we stamp in a rubber mold. When it is hard it is possible to think of different finishes such as patina. It looks just like a genuine bronze. But it is not as posh and valuable. To us it is junk.
Genuine bronze is matchless to true collectors, nevertheless, this new process is most interesting.
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  #71  
Old 03-29-2007, 05:52 PM
mark pilato mark pilato is offline
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Re: Bronze Clay?

this is the real thing, its bronze not power mixed with acrylic, when its done chase it weld it patina it, the only difference is you get all the detail, and you cut out most of the steps. not snake oil. Step into the future read the thread.
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  #72  
Old 03-29-2007, 06:02 PM
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le granfred le granfred is offline
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Re: Bronze Clay?

Ok

I went through this thread. And I see the interest of the process.
I wondering if it would not be possible to get the same result with a plasma torch projecting liquid bronze with high speed on the inner part of a ceramic mold just like paint.

you said: "With this process i could complete a chess set from the rubber mold to finished bronze in 3 days and give it to a scientist when I was done and he or she would say it's cast. how is that possible to take a three week process and shrink it down two three days."

my answer is that provided I have the original chess set, I bet I can do the same work in three or four days too, using traditionnal ceramic shell casting. It is very easy in fact. And with the original scale. I have my own way.

Last edited by le granfred : 03-29-2007 at 06:15 PM.
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  #73  
Old 03-29-2007, 08:01 PM
mark pilato mark pilato is offline
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Re: Bronze Clay?

Thats cool, i have been casting work for over twenty years I had my own foundry and I'm some what of an expert when it comes to casting bronze in the lost wax process. let me know if I missed something, First you cast a wax from the rubber mold, if you are not going direct one of a kind, then you clean or sculpt the wax, then you sprue and gate the wax then you create a ceramic shell mold incasing the wax, then you burn out wax from the shell then you melt the bronze at the same time you heat the now empty ceramic shell, then when the bronze is at temp you pour bronze into mold that you have placed red hot on the pour floor or in the sand vats, then when cool,you brake out shell, bead blast or sand your preference, cut cups and vents off then you chase the bronze. well there is a lot more steps within these steps but thats it in a nut shell. As you and anyone who as ever cast bronze knows the casting is very rarely perfect, at the least you have positive to chase out and most of the time you are satisfied because its a dam good casting. okay with this process you poor the bronze plus binder into the rubber, clean it up, sculpt it , so nice, no skipping, chases like soft soap stone, sand it, use small detail tools, very clean edges. after you like your piece put it into the kiln in a can with powder around it, no shell no dry time no sprues no vents no brake out, then you set the computer and the next day its done, exactly the same as when you put it in but solid bronze. about five minutes to clean up and polish a little more if you want a mirror finish, weld it what ever same as a cast piece then a patina and your done. maybe it can be done as fast cast but you would be hustling, as for selling a sculpture that has been done in this process well i have sold work for 18,000 done this way and the collectors love the fact that its done in the pilato process. The reason I am sharing this process is because I know when it gets in the hands of some artists there will be no stopping it. its so fresh and so much more can be learned who knows what materials people will try using, who knows what idea's will come, and the coolest part its affordable so we will not have to brake the bank to cast our work. the pieces bellow were done this way they took about five minutes to chase after they came out of the kiln. the last one took 4 hours because of polish. anyway this was way to hard to write, good luck, and
all the best,
Mark
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  #74  
Old 03-30-2007, 03:29 AM
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le granfred le granfred is offline
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Re: Bronze Clay?

Yes it is a wonderful process.
And it works wonders.
I wish I could use it in France as I think it is completely unheard of.
What is to be done to get it?
I am most interested.
Congratulations to an outstanding guy.
Look forward to learning more.
All the best
Fred

Last edited by le granfred : 03-30-2007 at 04:21 AM.
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  #75  
Old 04-08-2007, 01:54 AM
Burkhard Burkhard is offline
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Re: Bronze Clay?

This is my first post on this board – apologies that it’s so long!

I came across this thread a couple of days ago and was interested because I tried to see if it was possible to make bronze PMC about a year ago (I was stunningly unsuccessful). Then got really excited that someone had solved the problems and even got it as far as a commercial venture – wow!. Followed by immediate disappointment that the company went out of business. But if one group of people can do it then it can be resurrected and if needs be, reinvented. I’m sort of hoping that there are enough interested people here that we can resurrect the technology between us. I’d love to say I’ve got the method to work and here’s how, but sorry no. Haven’t gotten further than re-commissioning my old kiln, ordering some bronze powder and doing some background reading and musing.

I’ve put some of this info down “on paper” for my own use, but in case people here are interested, I thought I’d post the stuff I’ve got so far. Excuse the style if it sounds stilted, too much like a lecture, and contains stuff others have already mentioned in this thread - I haven’t had time to edit it properly.

DISCLAIMER #1: Why do I think I can add anything to this thread? A long time ago (sometime last century) I got a PhD in chemistry and since then have been doing research in chemistry related fields for last 25 or so years (Sculpting for the last 15 years). However, I am NOT an expert in the sintering of metals or the process described by Mark Pilato so I make no guarantee that anything I say here is mistake-free. In fact, I can almost guarantee that I've made some mistakes.

DISCLAIMER #2: The following is a current “best guess” reverse engineering of what the “Pilato Method” entails. This is based on the comments that Mark made in this forum, the links to the “CISP Fall 2005” newsletter article that Mark supplied a link to and the patent (PCT WO99/54075 “Powdered material rapid production tooling method and objects produced therefrom” Inventors German, Weaver, Thomas, Atre, Griffo) which I think is the original patent referred to in the CISP article. However, this patent does not describe the actual “Pilato method”. As far as I could see the “Pilato method” has not been patented directly (and would be difficult to patent given the prior patenting art). I don’t claim that this is the actual method used or that anything described here will give the results that Mark described, or that it will actually work!

DISCLAIMER #3: As with any process there are inherent dangers and risk. Hence, I do not recommend that anyone tries to repeat these processes. In fact I recommend the opposite – that is, don’t try this. If you hurt yourself, blow yourself up, poison yourself, kill yourself, lose an eye or two, burn yourself or do yourself or your property some other damage, please do not blame me. You have been warned. Some safety issues to consider: Any work with hot objects, kilns, unknown materials at high temperature etc carries safety risks. Also, the “Pilato method” may produce toxic gases such as carbon monoxide. The “Pilato method” may produce flammable and/or explosive gas mixtures.

Background:
The Pilato method uses sintering of bronze particles to produce bronze objects. The method is potentially very useful because it simplifies the traditional, labor intensive, lost-wax bronze casting methods. Depending on how it’s used, it could also free the sculptor from limitations due to the necessity of having to produce moulds i.e. one could work directly in bronze. Does it work? It appeared to, as a company was set up and several customers (apart from Mark) had good experiences with the company. The company no longer exists, so the question is “can the method be reproduced in a non-industrial setting by ye average sculptor?”

Put very simply, in the Pilato method, an object (e.g. a sculpture) is produced using a mixture of wax containing 60-70% bronze powder. The object is then placed in a container and packed with 1-10 times its volume of a very fine powder such as aluminium oxide. The container is placed in a kiln that can be sealed and that has an inert gas (e.g. nitrogen) line inlet and an outlet attached. The temperature in the kiln is slowly raised. As the wax melts, the aluminium oxide absorbs the wax, as the temperature is raised further the wax decomposes. As the process is carried out in an inert gas (i.e. in the absence of oxygen) the wax does not burn in the kiln but decomposes to a mixture of hydrogen gas, carbon (i.e. soot), methane, ethane, propane, butane etc (similar to natural gas or LPG type gas). This flammable gas exits the kiln via the outlet line and is ignited here to prevent build up of flammable gas.

Please note: The mixture of flammable gas produced in combination with oxygen from the atmosphere and high heat from the kiln could lead to explosive gas mixtures. If the burning of the flammable gas mix is carried out in an oxygen poor environment toxic carbon monoxide could also be produced. A very (very) rough calculation says that a kilogram of wax could produce about 300 liters of flammable gas.

The temperature of the kiln is then raised to the sintering temperature of bronze (in article it said about 840C). After cooling, the object is removed from the aluminium oxide powder and is ready to be polished, patinaed etc.

In order for bronzes to be produced by a sintering method, three main problems needed to be solved. Firstly, sintering produces porous objects – how can one increase the density so that the strength, weight and feel of a bronze are obtained? Secondly, metal powders oxidize very rapidly at high temperature. If you heat bronze powder in air you’ll get copper oxide and tin oxide powder not a bronze statue. Thirdly, the bronze powder has to be mixed with a binder in order to form and mould it in its green state (i.e. in its pre-sintered state) – how can one remove the binder if we cannot burn it out in the presence of air/oxygen?

1. Sintering:
Sintering is a process that has been used to produce billions of objects that we use every day. It is mainly used for producing ceramics, everything from sinks to cups to bricks.

In the process, a material that is made up of very fine particles with a binder is formed into a suitable shape. In the case of clay, the binder is usually just water. The material is then heated to a point where the binder is removed and the surface of one particle fuses with the surface of another particle without actually melting.

As an analogy, imagine going into a freezer room and collect a bucket of ice cubes, about an inch wide, placed in bucket. Now take the bucket outside and allow the ice cubes to warm up just enough so that each ice cube has a thin film of water on the outside. Now place the bucket back inside the freezer and allow the thin film of water to freeze again – you have just sintered the ice. You could in principle invert the bucket and de-mould your ice-bucket object. If you did, you would immediately notice how many holes there are left between the ice cubes. This is a consequence of the sintering method – sintering gives porous materials.

There are two ways of getting around this:

Firstly, increase the temperature to as close to melting point as possible without actually melting the stuff. This is what one does with ceramics – the low-temperature, bisque firing leaves the pots very porous, with low mechanical strength, whereas firing to near the melting point of ceramics at 1300C gives hard, vitreous (glass-like) non-porous ceramics (or if you’ve pushed the temp too high it leaves you with a slumped mess). Down-side of this is that the higher the sintering temp the greater the overall shrinkage of the object. Too much shrinkage will result in distortion of the original object.

Secondly, use a mixture of particle sizes. For instance, if you take another bucket of ice cubes and mix in several handfuls of crushed ice, you can fill in most of the holes left between the large ice cubes. If you sinter the ice in this bucket, you’ll end up with a much denser object, fewer voids. The ratio of large to small particles is important in order to obtain maximum packing density but can be approximately calculated (I’ve got the numbers somewhere but haven’t looked it up at this stage) or can be gotten by experimentation.

The Pilato method makes use of the second point above in order to reduce the porosity to a low 13%. That is, one needs to use a mixture of particle sizes. The low porosity of 13% would make it difficult to tell a sintered bronze apart from a cast bronze just by looking at it and holding it. Presumably one could still use single-size bronze particles, but the resultant bronze would be far weaker than using a mixture.

(By the way, the statement in the CISP newsletter that a scientist would not be able to easily tell a cast and a sintered bronze apart is not true – just measure the density, the sintered bronze will be 13% less dense. Another by the way – using mixtures of particles in order to increase density is not something new invented by the Pilato method, this has been around for a very long time).

2. Sintering bronze – the problem of oxidation

Most people would have heard of PMC – Polymer Metal Clay. PMC comes either as silver PMC or gold PMC. PMC is vaguely similar to clay in its wet state. When dry one can simply heat it with a torch or in a kiln, burn out the binder and sinter it, and voila – a silver (or gold if you’re rich enough) object is created. If you’re a sculptor and have heard of PMC you immediately think “wouldn’t it be nice to have a few kg of this in bronze”.

Alas, life is not that simple. PMC is made up of fine particles of silver (or gold) in a polymer binder (methyl cellulose), with a few additives such as detergent to improve its handling ability, and certain amount of water. Gold and silver are part of a group of metals known as “noble” metals (other metals include platinum, palladium, iridium etc). Gold in particular doesn’t oxidize easily, whereas silver does oxidize but still much slower than metals such as copper, iron tin, etc. In fact silver is just inert enough to be used in PMC whereas copper oxidizes enough that it can’t be used. I had a look at the patents on the PMC stuff to see whether these guys thought they had a trick for doing copper, but couldn’t see anything (doesn’t mean it’s not out there somewhere – patents are deliberately obscure and difficult to read at times).

[Oxidation: reaction with oxygen to form an oxide e.g. iron plus oxygen equals iron oxide commonly known as rust. Air is approximately 21% oxygen, the rest is mainly nitrogen with small amounts of carbon dioxide and various other gases.]

The simple answer is of course to heat in an atmosphere of gas without oxygen e.g. in a nitrogen atmosphere, or even better nitrogen containing 10-20% hydrogen which will reduce any copper oxide back to copper metal. Using hydrogen can be done in the lab but is difficult for the average punter due to hydrogen’s high flammability and because it can form explosive gas mixtures at high temp if there’s a leak in your system and oxygen from the air seeps in. However, if the bronze particles aren’t too small and not too oxidized prior to sintering an inert atmosphere such as nitrogen or argon will suffice to keep the particles from oxidizing.

For the Pilato method this means that you need a kiln with an air-tight door and a steel tube nitrogen inlet going in one side of the kiln and an outlet at the other side of the kiln to let the nitrogen and any other gases produced during the heating out.

An alternative may be to place the object and the aluminium oxide into a separate steel container that has a nitrogen inlet and outlet. The container is then placed inside an ordinary kiln. This would mean that one doesn’t have to try and make a gas tight kiln.

For the average sculptor without access to nitrogen cylinders, gas fittings, tubing etc this may be the most challenging part to set up.

3. Removal of binder.

Speaking strictly from a patent point of view, the above two points aren’t particularly novel, the idea on how to remove the binder without burning it away in an oxygen atmosphere is/was the novel patent-able bit of the Pilato method.

However, this was already disclosed in the patent by German, Weaver, Thomas, Atre, Griffo in 1999, where they used the process to produce far more complex materials, consisting of a ceramic-metal, with a second infiltrated metal, than what is required for sculptures. In patent language this would mean that the Pilato method would be “obvious to those skilled in the art” after reading the original patent, but that the process isn’t actually covered by the patent. The good news is that, if there are no other patents out there, (but I didn’t look that hard), then this could mean that the Pilato process is not covered by a patent and hence available for exploitation/use by anyone.

Anyhow, back to the clever bit – how to get rid of the binder. What the Pilato process does is to use a melt-able material as the binder rather than a non-melting polymer and to pack a “wicking” powder around the object which adsorbs the molten binder. In the Pilato method the binder is simply wax. As the temp is raised the wax is soaked up by the wicking powder and then as the temperature is increased further the wax decomposes to a variety of gases such as hydrogen, methane, ethane, propane, butane etc (similar to natural gas) as well as soot. The decomposition occurs in the wicking powder, not in the bronze particle matrix, hence no problem with the soot contaminating the bronze powder and no chance of the bronze being damaged by internal gas build up. I think Mark Pilato mentioned in one of his posts that a flame is lit under the nitrogen gas outlet in order to safely burn off the decomposition gases.

The wicking powder mentioned in the Pilato method is alumina (aluminium oxide). However, the patent also mentions other ceramic powders can be used as long as the ceramic powder does not sinter at the highest firing temperature used. An important point is that the wicking powder must be fine enough so the wax preferentially is drawn into the wicking powder by capilliary forces i.e. the particles of the wicking powder should be smaller than the bronze particles.

Patent mentions that between 1 to 10 volumes of wicking powder to the volume of the bronze/wax is used.

Additionally, the binder also provides some mechanical stability to the object until the temp is raised to the sintering point. I.e. the wicking powder is packed around the bronze/wax object by “uniaxial tapping” to ensure intimate contact with the bronze/wax and to ensure maximum stability and support. I assume this means that one takes a stick and gently rams the powder around the object from above.


Other Stuff

The time of the firing i.e. wax melting, wax decomposition, metal sintering time is important, however, this will vary depending on the size of the bronze/wax being fired and will probably need to be fine-tuned by trial-and-error.

The foot-vibrator and the vacuum oven are probably used in the first phase where bronze/wax mixture is poured into the silicone mould. Given the amount of bronze powder used, the bronze/wax mixture probably has the consistency of concrete. In order to get a cast with minimal air pockets you ideally want to place the mould on a vibrating table inside the vacuum oven, fill the mould with the bronze/wax mixture and vibrate the whole thing under vacuum while the oven keeps the wax molten. This would give the best packed wax.

(I don’t know whether a foot vibrator would survive in the oven, so it may be easier to heat the mould, add the bronze/wax while vibrating, and then place in vacuum oven? Problem is that if there are any air-bubbles trapped in the bronze/wax you’ll end up with all the bronze/wax coating the inside of your oven as you apply the vacuum! Mmh, I suspect that you do need to stick the vibrator in the oven. Alternatively, the people who pour concrete often simply ram their concrete into moulds, live with imperfections or patch them after demoulding. Biggest danger is of course having a large air bubble trapped inside your bronze/wax object as you heat up the object while it’s still full of wax – could cause the object to crack or bits of it to explode. Once the wax is removed the bronze powder may be porous enough that trapped air can escape if the heating is carried out slowly enough.)

If I get any further I'll let people know.
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