Advice needed with LW Casting problem from exp steam caster

Hey all,
Well I'm getting very consistent results lately in castings of pure
silver....unfortunately not in a good way. Very bad pitting, sometimes
holes clear through. Was wondering if anyone here could tell me the most
likely cause by looking at the results.
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In my novice mind I have narrowed it down to two *most* likely causes.
Incomplete burnout or water contamination from steam casting. If you feel
the latter is the most likely cause I'm looking for advice on how to improve
results but still use steam casting...."switch to vacuum" won't help me.
Hope all is well and thanks for any advice.
=B
Reply to
Ben
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You should probably post this on rec.crafts.jewelry. Its hard to tell what's missing or didn't work from the pictures, but I'd work on eliminating some of the variables. Are you using organics (wood, leaves, plastic, etc.) or wax to form your model? Temperatures can range widely using a torch, so make sure your casting metal is at the ideal temperature before you apply the steam pressure. Thats the best I can do without actually having more information. -Mike -Mike
Reply to
mlcorson
It's a moderated group and in my exp on topic posts generally take 24-36 hours to be visible.....
Using wax from Rosenthal, the aqua injection wax chips.
Would you guess not hot enough from the pic?
Let me know if you need more info, appreciate the attempt.
=B
Reply to
Ben
Is the metal that is shiny breaking through the investment? If so the model is too close to the edge of the investment. More distance to to the edge. You need more sprues, but smaller ones in steam casting so the molten metal does not fall in the mold until steam pressure is applied. In other words, the molten metal clings to the top of the mold because it needs the pressure to push the metal down. Make sense? Also, how hot is the mold when you melt the metal? How long does it take to melt it? The mold could cool down enough to be problematic. What kind of investment and what is your process to invest it? Vacuum to remove the air? ? Vibrating the liquid investment? How do you do your burnout? How long?
Reply to
mlcorson
[snip]
No, it's not filling completely or leaves large cavities.
Yes, I've tried with various sprue configs. From 18g x 4 to 12g x 1. This same result happens more than 50% of the time regardless of sprue config.
No pyrometer but when I pull it from the charcoal burnout (answer to below) the stainless flask has been red red/orange for at least two hours. Also it's a 2.5 x 3 inch solid flask.
Using MAPP/Oxy and easily melting 10g pure silver in 20 to 30 seconds.
I thought that could be the issue too and difficult to measure the exact temp by other means than color or steel when I pull it and making sure I cast quickly....maybe.
Satin Cast 20, 100/38 mix per box and vibrating to de-bubble. Not having issues with bubbles in the investment.
Charcoal in one of those charcoal starter things from Home Depot, four hours. It was working well in the past but after I switched waxes this issue started to appear which made me tend to think I wasn't burning hot/long enough(?)
Thanks again for any advice.
Reply to
Ben
Try venting the bottom of the mold. Small vents (sprues going up from the bottom to to the top of the mold) at the far end. Maybe the steam is forcing air or trapping air in the mold. Vents should help the metal go in by providing a place for the displaced air. Investment ok -Maybe, this is hard to ascertain. Could still have bubbles. Doubt it though from what you say. These would not be a large as you have. Burn out ok - Sprues ok, if you avoid the drop down affect. Other than that, I'll have to tag out. Maybe someone else has some ideas.
Reply to
mlcorson

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