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  #1  
Old 03-01-2007, 09:45 AM
andrew avent andrew avent is offline
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Problems melting Bronze

I am currently having problems with melting Silicon Bronze, I appear to be getting a build up of Oxide and as a result the pour resembles tapioca / rice pudding ! Some of the melt is very fluid but a high percentage just will not melt and incorporate itself into the rest. I have tried adjusting the air / gas mix on the burner to ensure that I have a reducing atmosphere in the furnace and I am confident I am achieving the temperatures required although I have not yet built my pyrometer.

Any help would be very welcome.
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  #2  
Old 03-01-2007, 10:11 AM
RWJR RWJR is offline
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Re: Problems melting Bronze

if you preheat a 1/4" steel rod and dip it in the melt, the bronze should drip off the end, until you can get a pyrometer, this is a one way of guessing pour temp. for silcon bronze

Last edited by RWJR : 03-01-2007 at 11:57 AM. Reason: word added
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  #3  
Old 03-01-2007, 10:18 AM
RWJR RWJR is offline
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Re: Problems melting Bronze

http://www.backyardmetalcasting.com/forums/index.php
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  #4  
Old 03-01-2007, 11:02 AM
PTsideshow PTsideshow is offline
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Re: Problems melting Bronze

You didn't say if you are using known alloy shot/ingot or assorted scrap.
99 % of the time you don't need deoxidizers. "Simply melt in a slightly oxidizing atomsphere to 100'F above the desired pouring temp. (pull the heat don't soak) normal melting with clean material requires no flux or deoxidizing treatment.
If the metal is metled improperly (reducing atmosphere) or allowed to asborb oxygen and or hydrogen, it can be deoxidized with phosphor copper as you would with red brass." From casting Brass by CW Ammen and tab books.
CW Ammen seem to be the Moses of small time casting and all of his books are in print some where in the globe. There is a good one out that covers general metal casting that carries his name.
Metal casting made simple McGraw-hill Craftmasters series ISBN 0-07-134246-X
Biggest problem with using all or alot of scrap is the unknown alloy or even if it is what they claim it is. Also if you are using virgin shot or ingots
That they haven't mixed up by somebody else sweeping up and putting it in the wrong container, in the studio.
Check out the link that was in the above post as that is the place for the cutting edge of backyard casting.
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been there done that !
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and standard disclaimers apply. Do not try this at home, use only as directed, No warranties express or implied, for the intended use or suggested uses, Wear safety glasses, closed course, professionals only
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  #5  
Old 03-01-2007, 11:50 AM
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dondougan dondougan is offline
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Re: Problems melting Bronze

It will vary your alloy somewhat for purposes of matching chasing/welding patches later (makes it a little bit yellower), but to increase fluidity try adding a little bit of aluminum or zinc right at the end of the melt (after temp has been reached) before taking the pot out of the furnace. For a 300 lb. pot I usually add about a quarter-pound of aluminum or a bit more (by weight) if using heavier zinc.
Don
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  #6  
Old 03-01-2007, 04:27 PM
andrew avent andrew avent is offline
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Re: Problems melting Bronze

Many thanks to you all

I am using silicon bronze shot from an art foundry suppliers, but I think the large surface area is part of the problem.

I'll try a slightly oxidizing atmosphere. Do you think a pinch of Borax would help ?

The silicon carbide crucible is a v bright orange or yellow when the bronze is molten - I'll try the steel rod trick.

I'll do a melt tomorrow and let you know how I get on.

Cheers
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  #7  
Old 03-01-2007, 05:18 PM
RWJR RWJR is offline
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Re: Problems melting Bronze

how much bronze are you melting? 20lbs should be ready to pour in less than 30 min with with a natural gas , homemade burners. makes a certain sound when it's burns right and gets white inside the chamber. after you scrap the inpurities of the surface the molten looks like a mirror
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  #8  
Old 03-01-2007, 05:42 PM
Max Silver Max Silver is offline
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Re: Problems melting Bronze

This is one of those deals where buying the right metal (or any material) from a known supplier is the most cost-effective way to go. Silicon bronze is used for its very predictable results and no surprises.

Sounds like it either isn't getting hot enough to melt properly, it contains impurities that are causing other chemical reactions or it is not silicon bronze.
I had an experience once where a machine shop owner wanted his filings and scrap melted down and poured into ingots. The stuff acted similarly to what you have described ......incomplete melt with globules and all manner of weird stuff. The aluminum actually seemed to ignite and turned into some solid mass that ruined a crucible.

If you are going to cast your own stuff, you must have (invest in) a good furnace, good metal, a quality handheld pyrometer, sandblaster, tig welder, and in my opinion ........good ceramic shell system for molds. At this point however, you have become more business person than creative artist.

Barring this, it just pays really to use a good foundry and cut your costs where you can...... making your own molds, preparing your own waxes and finishing out raw castings from the foundry. But having a good piece of relatively flaw-free metal is key to a quality finished work of art.
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  #9  
Old 03-01-2007, 06:01 PM
Max Silver Max Silver is offline
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Re: Problems melting Bronze

A follow-up point.........you mentioned junk building up on the surface. Even when melting a good alloy like silicon bronze, which is about 95% copper, 4% silica and 1% trace, you will get some slag on top of your melt. If you are remelting used bronze it will have firescale, dirt, bits of old mold material, etc that will float out to the surface.

You can buy commercial surface cleaners, but just throw some pieces of broken glass (any glass....beer bottle, window glass) onto the surface of the molten metal and it will act as a binder that will trap all the nasty little bits of junk that you would rather not have float into the essential details of whatever you are casting. WEAR PROTECTIVE FACE SHIELD AND OTHER GEAR AS THE GLASS WILL SOMETIMES POP AND COULD POSSIBLY FLY OUT AND HIT YOU.

Just use a skimmer or even a long piece of old metal rod or pipe to skim off the junk just before you pour. Just make sure it doesn't have any moisture on it.
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  #10  
Old 03-02-2007, 07:21 AM
andrew avent andrew avent is offline
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Re: Problems melting Bronze

Thanks again for all your help, I have taken it all on board.
I think that tuning the burner to produce the correct atmosphere inside the furnace will help enormously. The melt last night was much cleaner and quicker - a little over 30 mins for 25 lbs.

Unfortunately the sculptural pieces I am doing for classic yachts do not command sufficient margins to allow for contracting out the castings, and since I have very good facilities here I would like to try to keep it all in-house.

All the best, Andrew
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  #11  
Old 03-02-2007, 07:32 PM
andrew avent andrew avent is offline
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Smile Re: Problems melting Bronze

SUCCESS The castings worked beautifully tonight - very excited at the results - the glass and a tiny pinch of borax worked a treat !

Thank you all very much for your help and advice !

All the best, Andrew
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  #12  
Old 03-02-2007, 11:01 PM
Max Silver Max Silver is offline
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Re: Problems melting Bronze

That is good news. We are fortunate to have these forums to exchange opinions and ideas.
Happy casting...............
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  #13  
Old 03-03-2007, 08:07 AM
PTsideshow PTsideshow is offline
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Re: Problems melting Bronze

Congrats on a sucess
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glen
been there done that !
I am not a lawyer, and never played one on TV!
All the usual
and standard disclaimers apply. Do not try this at home, use only as directed, No warranties express or implied, for the intended use or suggested uses, Wear safety glasses, closed course, professionals only
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  #14  
Old 01-08-2009, 10:52 AM
ara ara is offline
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Re: Problems melting Bronze

glass eh? how interesting..i must try that when i have my furnace running

Whats the science behind it then?

ara
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