Hi, new to this forum, posting a question about graphite crucibles/ 1 kilo electric melter & sterling silver-
I have been having issues with my pour for a few months, usually using anti fire scale silver from Rio. I just casted with all new grain and still got a strange button. Holding temp for electric melter was at 1740, I used a substantial amount of silver (150g) gave it a good stir with the rod to make sure it was all melted, closed the melter for another minute, then when pouring into flask the majority of the silver came out molten but the end of it came out chunky.
My crucibles (from Rio) have been breaking down pretty fast- I’ve casted around 35 times and have 4 crucibles that are basically not usable anymore, just started on my 5th. I try to mitigate this breaking down by not opening the electric melter too much (once to check and stir and once to pour) I leave the crucible in the melter to cool down slowly, and I don’t leave it on any longer than it needs to be.
I can see two possible issues.
Either you have changed your Silver or it is somehow fouled.
And/or the temperature control of your furnace is not calibrated correct at this time.
Has this gotten progressively worse?
I have continued using the anti firescale silver from Rio Grande- I did a test with the yucky bits, surprisingly the casting came out good & white but the button was horrendous (see pics below)
The picture from my original post was all new casting grain in a newly bought (used twice prior to this casting) crucible
My electric furnace is fairly new (around 6 months old) and has a digital temp screen that I have holding around 1740 degrees Fahrenheit
And yes, this problem has progressively gotten worse
Maybe have a check on the temperature probe.
Do you have a secondary system you can use to verify the temperature?
Handheld IR meter or such?
Are there a calibration system for the furnace, check the user manual.
I don’t have anything to test it with…
In your opinion do you think the metal isn’t hot enough or too hot? If it is indeed a problem with the electric melter temperature
I’m not sure, the chunky nature looks like it’s not hot enough,
but then again the grainy almost oxidized surface hints to too hot.
Does the manual say anything regarding calibration?
Nothing in particular, it’s very straight forward
Maybe reach out to the seller?
Yes I did, will see what they say and post here if any good info is given. Thank you
You are welcome, and keep us posted.
What a mystery you’ve got here?
First, I’ve never used a DeOx Sterling alloy in an electro melt furnace. I don’t know if there’s any tricks to it? I would definitely contact Rio Grande Technical Support (where you bought the metal from) and share with them what you shared with us, including these very clear pictures. The folks at Rio Grande technical support are awesome!! Probably it’s something simple, like adjusting the temperatures on your flask and/or crucible.
Sorry that I can’t be more help, but please keep us posted and let us know what Rio Grande says.
Do you know what the alloy metals are in the De Ox silver? I primarily use Continuum silver that is alloyed with palladium and some other proprietary metals. I was told by the guys that invented the stuff to not use a carbon stir rod in the molten metal. I’m curious to see what the metallurgists at Rio have to say about this.
My first post here since I feel I am in a unique position to help.
I also melt in an electric kiln with graphite crucibles. I used rio anti-firescale for about a year and had the exact same issues. I have heated the leftover slaggy bits to nearly 3000⁰ and it still doesn’t melt, just kind of turn to a gummy ball. No idea what it is. I’ll save you the trouble of calling them - their tech support will just recommend flux and stir, which doesn’t work. I have since moved on to alloying my own anti-firescale, de-ox alloy from UPM’s recipe for S57. You can buy the Legor master grain from Rio and mix with fine silver, or set up an account with UPM to order grain. I now get flawless castings and no slaggy loss, no firescale and my pieces resist tarnish pretty well.
Interesting that yours doesn’t re-melt… mine does. And the castings usually are very clean- aside from the button.
Still waiting to hear back- what I find fascinating is that for 2 years I was casting 1x a week at school with virtually the same set up, same anti firescale metal, similar wax etc, and this was NOT a problem. The only thing that was different was the electric melter- it was airtight and a true tilt & pour unit- we were able to pick it up and pour with the crucible still in the machine.
The one I purchased through Rio is roughly 15 lb, very big, and as much as I try to readjust the top it will not lay completely flat when the crucible is in.
I had someone reach out privately saying that they also have this problem- they think that not pouring fast enough is causing the metal to start to freeze at the bottom.
Suggestion was to stop pouring when you see the mold has filled with metal.
I will try this next time I cast and post another picture afterwards here.
Thanks Monothic! Excellent news that you’re getting such good results with making your own de-ox alloy!
One that might be helpful to try? Some folks who cast with an electro-melt furnace, keep a torch on the metal as it’s being poured into the mold. The idea is to help keep the metal in an oxygen-free atmosphere while it’s being poured into the mold.
Because this adds in more to juggle with vacuum casting, having an assistant is very helpful with this.
Something to consider trying.
Another thing to try is capping the crucible with a graphite disc to help prevent any air from getting inside. I cut the bottoms off of old crucibles for this purpose. You do have to flick off the lid onto a safe surface right before pouring, but it has served me well. It didn’t seem to have any effect on the leftover slag from Rio’s AF silver, though.
As for going through crucibles quickly, I am not sure if they will be compatible with an electromelt, but I put my crucibles in the ceramic holder for induction systems. It makes the crucibles last a lot longer.