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Busted crucible in electromelt


#1

help!

I think I turned up the heat too high on the electromelt because a
chip broke off the rim of the graphite crucible. I thought, ok, no
big deal, and kept on melting stuff. However, when I went to pour
and touched my tongs to the crucible to hold it in place, it shorted
out. I tried resetting the power, to no avail. I went ahead and
poured the silver into the flask I had waiting, figuring that even
with the power off for a couple of minutes it would still be hot
enough and it was. That flask was my best one of the afternoon, with
all eight elements coming out perfectly – thank goodness!

I let the electromelt cool and tried to figure out what was
happening. When I used tongs to lift out the crucible, half of it
came out and I saw that the bottom of the electromelt had the
remaining half of the crucible with a hunk of hot silver in it. I
tipped it over onto a flameproof surface, not wanting the silver to
solidify in the electromelt. So, I dumped out the broken crucible
with the silver. However, I can’t tell what is at the bottom of the
hole now. It looks to me like solidified molten metal, but I thought
I had gotten it all out.

So, how do I go about figuring out what is at the bottom of the
hole? Do I have

to replace the lining to the crucible as well as the crucible? The
whole machine? I just bought it this summer – eek!

Thanks
Carina Rossner
carinarossner.com


#2

I would recommend that if you’re unsure of what you are doing seek a
service centre. Taking an expensive piece of equipment and not
knowing what’s going on will void any warranty.

Ask where you bought the unit from, especially if the unit is new.

Sounds like the crucible was either flawed, not correctly tempered,
or just old.

I know a little bit about how electric melters work, but even I
wouldn’t touch a new device that was still under warranty.

Regards Charles A.


#3

Carina & All,

I have had the same Kerr electromelt since 1980. The only problem I
have had is that I left it on high once and forgot about it. It was
like a nuclear melt down with the core burning out. I bought a
replacement heating element and replaced it. It still works like a
champ. I kept the old element and will try to laser weld the wire
that fried to see if it still works. This Kerr brand electromelt is a
well made unit. I can melt 240 dwt at a maximum.

Here are a few observations:

Temperature maximum is 2000 f. I go to 2100 on a rare occasion. You
risk the core melt down over that. I cast bronze and deox sterling at
1950 f routinely.

Each metal should have its own crucible. There is a little bit of
metal that sticks to the inner wall of the crucible so you cannot mix
different metals or you will contaminate the pour.

You judge the health of the crucible by the top rim. As they get
older it slowly wears off. I have never had one break in the middle.

I do not cast white gold in it. You have to overheat the metal to
get it to flow and I prefer to spin cast white gold anyway. Quality
for me is better that way.

There is one structural difference in the melting crucible you
should know. Inside at the bottom it is either flat or shaped like a
doughnut. This is the area that is the closest to the temperature
sensor. The flat ones are a bit easier to stir when the molten metal
is fluxed, stirred and poured.

The crucible does not come out for pouring the Kerr electromelt
unit. When you open the lid the power is shut off. Using the carbon
rod to keep the crucible in the unit for pouring is the safest and
most successful way to pour.

Best regards,
Todd Hawkinson
www.southeastmn.edu/jewelry


#4
Sounds like the crucible was either flawed, not correctly
tempered, or just old. 

Charles, These crucibles are not like the graphite clay ones you are
used to. They are machined from a rod of pure graphite and do not
need tempering as there is no moisture in them. They are however
fragile which is why it is not recommended to lift them out of the
furnace while in use as you can very easily break one. My best guess
is that the OP possibly dropped too large a piece of metal into the
crucible from a height or packed the metal in in such a way that the
crucilble was fractured by the expanding metal. But it is really
hard to say without being there to watch the event.

James Binnion
James Binnion Metal Arts


#5

Thank you all for your advice and support. Here is what I have
learned so far:

The electro-melt I bought was used (though I thought not too much).
I had never seen a new one before, so I did not realize that my
crucible was very worn and thin. I suspect that crucibles that tend
to slide out when you tip the electro-melt over are worn down and too
thin and need replacing - so rather than figuring out a way to hold
it in place with tongs, replace it!

The molten metal did fry the thermocouple and the only way to get it
all out was to break up a bit of the insulating mantle around the
heating coils in the heating element. While I researched ways to
repair the mantle with heat-resistant cement and other forms of
insulation, Kerr told me that once the coils have been exposed and
come into contact with any metal, they are done for. BTW, the Kerr
representative emailed me back within minutes of my submitting my
question to Kerr via email – at 9pm PST and he is in NJ! Talk about
fabulous service!!!

So, now I face the dilemma of buying a replacement heating element
and thermocouple and putting this old one back together (approx
$350), buying a new one with a year warranty for about $650, or
seeing if one of you generous souls wants to sell an extra one that
you have lying around your shop for somewhere in between these
amounts. Anyone interested in cleaning house and selling an
electro-melt?

I know that I should be able to just melt the silver in a crucible
with a torch to cast, but the thought of getting that all together in
that short time between when the flask comes out of the kiln, etc
totally intimidates me. I guess I should watch some videos of you
masters doing it and get some guts. I really like using the
electro-melt, though - it makes casting so easy!

Special thanks to Ray who emailed me a manifesto about having the
right to fix things myself and gave me the proverbial kick in the
pants to take the thing apart and figure out how it works and what
exactly it needed.

Carina Rossner
carinarossner.com


#6
These crucibles are not like the graphite clay ones you are used
to. They are machined from a rod of pure graphite and do not need
tempering as there is no moisture in them. 

Yuck, pure graphite, never liked the stuff myself, got memories of
the graphite carving room at the aluminium extrusion plant. :frowning: CIA


#7

Just a comment. You might find it beneficial to let the unit heat
for another 5 minutes after it reaches pour temperature. The upper
ring of the crucible will not be at the same temperature as the
metal. It will cool the metal slightly when it is poured.

When I first starting using my Electro Melt many years ago I was
using scrap sheet silver that had bead blank punched out. I would
fold up the scrap as much as I could then add more scrap as the first
charge melted. Castings went well.

The I started using casting pellets. I would pour as soon as the
metal reached pour temperature. I was getting some castings that
looked like the metal was not high enough. I would get a run of metal
solidified from the ring of the crucible at the end of the pour.

I use the large Electro Melt and pour several flasks at at time. I
let the Electro Melt set for around 5 minutes after each pour.

Lee Epperson