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De-Ox ster casting problem
Has anyone out there found a cure for rings cracking at the sprue when using
the De-ox sterling silver alloys. I found a piece of info on the United Metals website that suggested a "lighter" investment mix as it would be "not" as strong as the mud I usually mix. I like the de-ox for its anti firescale property's, but the shank cracks ( from hairline to complete cracked shanks at the sprue ) are a big problem. So far I have tried ................. Regular sterling silver casting grain no problems. Then comes the fun part.. switch to De-Ox grain and the problems start. The lighter investment mix mentioned. 15{ normal} & 20 & 30 minute wait times before quenching the flasks. At the 30 minute mark, there is almost no boil-off so I dig out the tree with a screwdriver Adding 2 extra sprues to the ring, pain in the *ss to clean up and no help either. I am using a kerr electro-melt with the built in temp controller so over-temp is not a problem. Casting temp is 1950 F per Rio Grande catalog. With the usual 50/50 mix of new grain to sprue/button. Flask temp is 1000 F for heavy stuff, 1100 F for medium stuff and 1200 F for the fillagree type stuff. Kerr Satin-cast 20 is investment. My normal set-up is standard investment procedures with 1 hour setup, De-wax in pre-boiling dewaxer, and into a pre-warmed kiln, ramp up temp 1400 and down to casting with the usual times for heat soak prior to casting. Thanks in advance ! Mark |
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Mark wrote:
Has anyone out there found a cure for rings cracking at the sprue when using the De-ox sterling silver alloys. I found a piece of info on the United Metals website that suggested a "lighter" investment mix as it would be "not" as strong as the mud I usually mix. I like the de-ox for its anti firescale property's, but the shank cracks ( from hairline to complete cracked shanks at the sprue ) are a big problem. So far I have tried ................. Regular sterling silver casting grain no problems. Then comes the fun part.. switch to De-Ox grain and the problems start. I am not shure what is your "de-ox". I suggest it is borax or boric acid. In that case I have an explanation. 1. The grain is hydrophilic and so it contains normally a percentage of water. 2. Silver and Gold alloys are able to dissolve enormous contents of Hydrogen. Quite a lot of books are writing that silver dissolves an enormous content of oxygen. This is possible, however I mentioned in my praxis and in different tests, more evidence for soluted hydrogen. Now, if you put your grain on top of the melted silver, the held water will get separated in nascending Oxygen and nascending Hydrogen. My experience is, that the nascending Hydrogen will be immediatly absorbed by the fluid metal. When the metal is cooling down and building new crystels, there is less absorbing potential, so the gas will build vapor locks. There are some solutions wich will work: Roast your grain one time in the oven with a little bit over 280 °C or put your grain into your melting pot before the silver is fluid, never on top of the fluid metal. If there is some alloy ruined by soluted gas, melt it severeal times and pour it in a iron form under some fire on the surface. So the gas bubbles, witch have no place between the crystals will have some time to get out by the fluid surface. In most cases three times is enough. Alternatively you might use "degassing flux" You find some more description how to use at my homepage he http://www.butschal.de/werkstatt/solution.html -- Heinrich Butschal Forschung und Entwicklung, Goldschmiedemeister http://manufactury.butschal.com |
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