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Choosing a melting furnace from Rio Grande


#1

I want to get an automatic melting furnace, from Rio Grande. I would
prefer their tilt and pour model, p. 513 of the 2012 catalog,

http://www.ganoksin.com/gnkurl/1xo

but am concerned about the weight. It is 13.6 lbs, and as I have
small hands and wrists, I am not sure I can manage it. I spoke to
them and they verified that this is the weight of the item, not its
shipping weight.

Therefore, I am considering getting their other model,
which has a removable crucible, and therefore is light weight. The
tongs that it comes with seems flimsy to me.

http://www.ganoksin.com/gnkurl/1xp

If anyone has this model I would appreciate about it. It
is made in Italy.

Thanks for your suggestions. Alma


#2

Alma, I have that exact one from Rio and I love it! I too thought I
wanted the one that poured out, but it was going to be far to heavy
for me to lift and pour. Also, if I’m not mistaken, that crucible
comes out so you must have to hold it in place somehow while
pouring–that just seemed a bit too dangerous for me to tackle. Just
a few notes about the Rio 1-Kilo Furnace:

  1. It takes practice to get used to lifting the crucible out, but
    the tongs aren’t flimsy at all. The crucible has a groove and the
    tongs fit right in them very securely.

  2. I did many “dry runs” before I actually used it and found that it
    is much easier if you grip the tongs with your palm facing the
    ceiling (so gripping underneath the tongs). That way when you lift
    and pour it is a more natural movement. That may seem obvious to
    some, but the first few times I tried it I was gripping from the top
    and had to rotate my arm in quite a bit during pouring–not very
    comfortable.

  3. The folks at Rio told me to add 50 degrees to the casting
    temperature because the actual temperature of the metal is about
    that much less than what the thermostat reads.

  4. The crucible will cool quickly when you lift it out of the
    furnace, so I keep a plumbers torch lit and in contact with the
    mouth of the crucible when going from the furnace to the vacuum
    table. It is just a foot away but the crucible does cool down
    quickly! I had a bad pour the first time because I was using the
    awkward hand placement and did not use the torch to assist.

Hope that helps! :slight_smile:
Beckie


#3

I have the first one and use the tongs to pick up the crucible and
pour (machine too heavy and bulky plus crucible shifts around). Only
downside is that my crucibles don’t last long because of heat shock.
They thin down within 5-10 pours to the point that they don’t rest in
the lip but fall in the furnace.

Thanks
Carina


#4
Only downside is that my crucibles don't last long because of heat
shock. They thin down within 5-10 pours to the point that they
don't rest in the lip but fall in the furnace. 

Not heat shock, the graphite just burns up. Heat carbon up to the
temperature that these metals melt at and the graphite combines with
the oxygen in the air making carbon dioxide. just something you have
to get used to if you use graphite melting crucibles in air.

Jim

James Binnion
James Binnion Metal Arts


#5
Not heat shock, the graphite just burns up. Heat carbon up to the
temperature that these metals melt at and the graphite combines
with the oxygen in the air making carbon dioxide. just something
you have to get used to if you use graphite melting crucibles in
air. 

Interesting, the bilge type crucible I use don’t seem to suffer as
much as this. Mine seem to last for years. Mind you I forgot to
temper a crucible once, and it went boom in my furnace.

Wonder if there’s built in redundancy?

That carbon dioxide does actually help with the melt, so it’s not
all bad.

Regards Charles A.


#6

Is there an option? Another material for the crucibles? Thanks for
clarifying

Carina


#7
Not heat shock, the graphite just burns up. 

Does that make for a reducing atmosphere? Or is it not enough to
make a difference?

Neil A.


#8
Is there an option? Another material for the crucibles? Thanks for
clarifying 

The main reason that they use graphite is it has a very high thermal
conductivity when compared to the ceramics used for other crucibles.
This high thermal conductivity transfers the energy from the heating
elements through the crucible wall rapidly so that the metal melts
quickly. If you were to use a ceramic crucible it will actually act
as an insulator which will mean a very slow melting time which is not
such a good idea. It is the trade off you have to accept for these
small relatively low power furnaces.

Jim

James Binnion
James Binnion Metal Arts


#9
Interesting, the bilge type crucible I use don't seem to suffer as
much as this. Mine seem to last for years. Mind you I forgot to
temper a crucible once, and it went boom in my furnace. 

That is because they are not pure graphite but rather mixture of
equal parts fire clay and graphite. The old name for this mixture is
plumbago. The plumbago crucible is also typically glazed with borax,
this makes it fairly impervious to the actions of the oxygen at high
temperature. The crucibles in these little electric melting furnaces
that we are talking about here are pure graphite so they burn up
fairly quickly.

James Binnion
James Binnion Metal Arts


#10
Not heat shock, the graphite just burns up. 
Does that make for a reducing atmosphere? Or is it not enough to
make a difference? 

Yes it does produce a reducing atmosphere, the carbon combines with
oxygen and first makes carbon monoxide which is a strong reducing
agent. It will find an additional oxygen atom and form carbon dioxide
or reduce metallic oxides back to metal. So it scavenges most of the
oxygen it comes in contact with. This keeps the oxygen from getting
to the metal. This is the second benefit of graphite crucibles and is
probably almost as important as graphites high thermal conductivity
to the good results you get with these little furnaces.

James Binnion
James Binnion Metal Arts


#11

Please, also double check with alpha supply. The prices were better
and customer service was Great! (I have no connection to Alpha except
as a satisfied patron)

Elaine “Fresh” needs each and everyone of us to be on the same page.

Thanks God for Keeping those Windows Open!

ME Willig!


#12
Please, also double check with alpha supply. 

There are several companies named Alpha Supply, but the lapidary
supplier has been out of business for two or three years.

Al Balmer
Pine City, NY


#13
That is because they are not pure graphite but rather mixture of
equal parts fire clay and graphite. 

That’s right I use clay graphite crucibles. They are unglased
though.

However I do use a lot of flux with my melting procedure, so maybe
that helps make my crucibles last.

A pure graphite crucible… geez they’d be delicate… wouldn’t want
to drop them :frowning:

Regards Charles A.


#14
A pure graphite crucible... geez they'd be delicate... wouldn't
want to drop them :-( 

Dropping any crucible is a recipe for disaster.

James Binnion
James Binnion Metal Arts


#15
A pure graphite crucible... geez they'd be delicate... wouldn't
want to drop them :-( 

Actually, Charles, they’re pretty sturdy. They’re not molded from
some claylike mix or something. They’re machined from solid blocks.
The stuff is pretty solid and strong, even if they’re soft (they ARE
graphite, after all…) I suppose if you dropped one on a concrete
floor, it might break, but then, so might your graphite/clay types…
The time they get fragile is when, after a fair number of uses, they
get sufficiently burned up to be quite thin, often near the top just
under the thicker edge which you use to pick them up. Full of metal,
picked up in that condition, I once had one break, with the bottom
2/3ds dropping back into the furnace. It didn’t break further or
spill, fortunately, but it did kind of get exciting there for a
moment. As I was melting to pour ingots, rather than a casting, it
was easy enough to just turn the furnace off, wait for things to
cool, and sort it out then…

Peter


#16
 Dropping any crucible is a recipe for disaster.

The clay graphite ones bounce… within reason :wink: CIA


#17
Dropping any crucible is a recipe for disaster. The clay graphite
ones bounce... within reason ;-)

Yes and are you willing to risk having that crucible fracture with a
full load of molten metal from a tiny crack it sustained when being
dropped? I did not mean that the graphite or any crucible was
particularly fragile but the risk of taking a dropped crucible up to
the temperatures and stresses it encounters in use after dropping it
is akin to playing Russian roulette. Crucibles should be treated very
carefully because the things that can happen when a load of molten
metal is inadvertently released due to a broken crucible can be quite
catastrophic.

James Binnion
James Binnion Metal Arts


#18

Well, realizing all the problems with crucibles convinces me that
the best thing for me is to use my torch to melt my metal. Alma


#19

I check my crucibles before I melt, it’s an audio check, just tap it
with a stick. If there’s a fracture in it that may cause issue, you
can hear it (sounds odd but it works).

I have dropped one of the larger crucibles, but only from a height
of about 6 inches, it was empty (hence the within reason) and it’s
fine. The large crucibles are really thick, and quite rugged compared
to jewellery sized crucibles.

I’ve never dropped a small jewellery sized crucible, so I can’t give
you a report on those.

Regards Charles A.


#20
Well, realizing all the problems with crucibles convinces me that
the best thing for me is to use my torch to melt my metal. Alma 

You can look at it like that, but there are some very cool
advantages using crucibles over a torch.

If you use a clay graphite crucible you get a better melt due to the
atmosphere created by the crucible.

You can melt the metal passively, I find it a little less stressful.

When it’s melted, you can pick up the melt and pour. This last part
is dependent on the volume of metal you are melting.

With 250g or less, you may need to apply heat when pouring the
molten metal (I find it works better doing this). With 500g plus you
don’t need heat when pouring. This is what I’ve observed.

I find it more efficient and economical to use a crucible to melt
metal.

Regards Charles A.