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Ring-A-Day: Bad Sinter

Made this heavy BronzClay ring assuming that I had understood what went wrong previously. The ambient temperature was 47F when I turned the kiln on (it’s cold at Resistor on the weekends), so I added 20 degrees and an hour to the regular program — kinda like baking a bigger bird. Well, it looked good out of the charcoal until I hit it with the brass brusher, or maybe I should say the brass crusher. I quenched it when the temperature was around 500F, so that little bit of moisture combined with the bronze powder to make mud in a thin metal shell.

Back to the drawing board on the kiln controller.


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Ring-A-Day: Broken Shank BronzClay

Seems my PID is having trouble with the proper sintering temperature. I began the polishing by filing the imperfections out of the shank. Then when I attempted to round the ring on the mandrel, the shank split. I sawed off the broken parts to solder it back together, but the sawing exposed a hollow section with unsintered bronze powder inside. Then the ring split at the crown. End of ring.

My best guess is that the kiln is in a room where the ambient temperature is about 30 degrees lower than when the rings were sintering successfully, and the ambient temperature sensor is lowering the programmed temperature. I’ll add 30 degrees or use the AutoTune function again and see if that solves the problem.


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Ring-A-Day: Sand Cast Brass Ring

I’ve collected old brass keys for over 20 years in anticipation of melting them down and casting them one day. Today, I have that power thanks to NYC Resistor and Metalliferous
I got a PID for our kiln and struggled with the translated instructions. Installing and programming the PID would not have been an easy task without help from many knowledgeable members at NYC Resistor. 
The key brass, which is most likely yellow brass (copper 67%, tin 1%, lead 3%, & zinc 35%) is liquid around 1850°F, but pours better, I later found out, around 2050°F. I poured it a little bit cold as you can see inside the shank with the errors.
I didn’t know anything about brass alloys when I started to collect keys. I just wanted to cast something shiny and yellow. There are many copper based alloys to choose from. Each has its own characteristics for pouring, weathering, machining, and applications. Copper is used in jewelry to balance out gold and silver. Rose gold has a high percentage of copper. Sterling is .925 silver and .075 copper for hardness.
It turns out that red brass pours much easier, but it has a higher lead content — which helps it flow better, but is less good for the caster. I’m going to switch to silicon bronze for the rest of the casting exploration phase on recommendation from Steve Chastain in his great two volume series Metal Casting: A Sand Casting Manual For The Small Foundry.
You can pick up your own sand casting kit from Metalliferous and give this a try. You’ll need a kiln or hot torch (i.e. hotter than propane or butane) to melt the metal. I know this because I never got the included casting grain hot with my propane torch.

The wood patern was left over from my laser cut wood rings. When I got the PID working predictably, I looked around for something to cast and this was right there. I may refine it for working with the sand in the future, but there are so many possibilities to explore in pattern making with the laser that refinements are not necessary at the moment.