So lately I’ve been looking for ways to improve the quality of my
castings, mostly with respect to porosity. I’ve been casting the same
way for years with reasonably good success, but I’ve always felt like
I’m spending too much time fixing pits.
Currently I’m using a VIC9 vacuum casting unit with oxy/propane
torch. I burn out in a small neycraft furnace with a rio kiln minder.
I’ve always felt that the torch is the hardest variable to control,
so I’ve had my eye on a kerr electromelt.
Does anyone have any experience with these things? I usually only
cast 15~30 grams of gold or silver at a time, and was curious if
something like this would be a good fit for me.
Hi Matt, Personally I find an electromelt hand furnace a little
cumbersome. It seemed like I had to overheat the metal to get a good
pour. I feel likewith a torch i can see when the metal is just
right, I let it go until it’s fluid, give it a pinch of flux, heat
it an extra 5 seconds, making sure it moves like mercury, and then
let it go. I sort of hate to say this “out loud” but I almost never
have any pitting. I have about a 9 hour burn-out cycle that slowly
ramps up and holds at 450F for an hour (the temp that most wax
ignites) and then slowly ramps up and holds at 1350F for 2 hours,
then ramps down to 1000F for casting (I have a couple of other temp
holds in there, but those are the important three). I was having
some issues with pitting in white gold casting a few years ago. I
saved the list of suggested remedies from several sources (including
Orchid). I’m attaching that below. I hope it helps! Mark
First, as far a identifying the problem. The consensus seems to be
that what we have is shrinkage rather than gas pits.
It was said that gas pits tend to be more spherical and are usually
found throughout the casting, while shrinkage usually occurs in
heavyareas, has spongy pores that are really small tears.
Suggested remedies;
Sprue from thick to thin, your objective being that youwant a
homogeneous and smooth flow rate. Spueing from thin to thick
willnearly always cause problems.
Keep your flask temperature for white gold as low as possible to
get good fill with your machine (700-900was suggested, but that
depends on the type of machine).
Try to reuse less than 30% of white gold in castings. There were
some good suggestions on how to reuse a greater percentage and how
to super clean the buttons for reuse.
Regularly calibrate your kiln. Using ceramic cones is an
inexpensive and reliable method.
Use a fairly substantial button with white gold.
Cast heavy and light weight white gold castings separately so you
can adjust your flask temperature down further for the heavier
castings and a little higher for the lighter ones.
Let the flask soak at the casting temperature for a couple of
hours to insure that its at that desired temp inside the flask.
Keep you initial burnout stages long and at a fairly low
temperature to soak the flask well and remove all of the wax like a
dewaxer would do. - Keep you crucibles clean in an effort to remove
any contaminates that inadvertently found there way there.
If possible, it’s better not to cast in your polishing area. It is
a likely source of contaminates.
One thing to consider is that the electro-melts. Are great but when
you have very small amounts of metal in them it is harder for them
to control the temp of the metal. They work better when you are
melting several ounces at a time. It is easier to regulate the temp
of the metal that way.
Phillip Scott
Technical Support
Rio Grande
1.800.545.6566
An electromelt does help improve the metal temp when pouring. The
other advantage of using an electromelt is, the crucible burns and
therefore helps reduce the amount of air that reaches the metal as
it melts. The disadvantage is using an electro-melt for small loads
of metal. Smaller loads are harder to read the metal temperatures.
For best results, you should use these with over an ounce of metal
in them.
Any time you can remove one variable such as over heating your metal
with atorch, you can rule that out as a possible cause of the
casting defects.
I would love to talk with you and see if there are any other changes
that you could help reduce or eliminate some casting defects and
improve your casting quality. We would also be happy to look at some
of the casting defectsto see if we can isolate where the issues may
be.
We would be happy to go over anyone’s casting processes with them to
see ifwe can help improve their casting quality. Give us a call at
1.800.545.6566 and ask for Tech support.
Best regards,
Phillip Scott G. G
Technical Support
Rio Grande
1.800.545.6566
An electromelt does help improve the metal temp when pouring. The
other advantage of using an electromelt is, the crucible burns and
therefore helps reduce the amount of air that reaches the metal as
it melts.
Any time you can remove one variable such as over heating your metal
with atorch, you can rule that out as a possible cause of the
casting defects.
I would love to talk with you and see if there are any other changes
that you could help reduce or eliminate some casting defects and
improve your casting quality.
We would be happy to go over anyone’s casting processes with them to
see ifwe can help improve their casting quality. Give us a call at
1.800.545.6566 and ask for Tech support.
Best regards,
Phillip Scott G. G
Technical Support
Rio Grande
1.800.545.6566
There are many things that can contribute to porosity. Poor spueing,
inadequate burn out and/or mold temperature to high.
I have been vacuum casting using an Electro-Melt for at least 30
years. I use both the 30 and 100 ounce unit.
The big advantage of using an automatic furnace is consistency in
melt temperature. Once you determine the best setting for the melt
temperature that setting of temperature can be achieved with each
pour.
One problem with the electric melt furnaces is the time it takes to
achieve the required temperature. It can take up to 45 minutes to
melt the metal to pouring temperature. The advantage to the
controller unit is you set the temp an let it heat up without
supervision.
Another problem is the cost. The cost of an electric type furnace
may not be justified unless you are doing a lot of casting.
The smaller unit would work best for you.
You can melt enough metal for several pours.
Its best to not fill the crucible to the top. It is a little
difficult topour from a fully loaded crucible.
Let the unit set for about 5 minutes after reaching melt temperature
and between pours. That delay allows the upper part of the crucible
to heat up. Metal will be chilled if it is poured over the cooler
upper ring of the crucible.
You might want to check out Rio Grandes Automatic Melting Furnace.
It is the less expensive but is still pricey.
I don’t recommend the unit that requires removing the crucible to
pour themetal.
I purchased a Kerr Electromelt from Rio last year. Kerr had a free
crucible rebate promotion which I did receive, value $45??
The machine works as expected, although I haven’t really put it
through the paces yet.
Not cheap, but I couldn’t reasonably use a torch in the casting area
I had at the time.
Now that I think about it I bought a Dura-Bull version for a few
hundred cheaper that was very poorly made (loose lid). That one went
back immediately.
The only problem I have with the Kerr is that if you keep the
digital panel facing you, and don’t unplug prior to pouring, the
handle is to the left, requiring that you pour it with the left hand.
I would love to know why. The VIC 12 unit I use for vacuum casting
requires pouring from the right side.
I too would be interested to know if the condition of the hot metal
is better with this type of melting process. I’m sure I will never
use the flame process, so no way to compare.
I have the Rio version of the same unit–LOVE it! I always use it,
even for small castings. Really like it when I’m melting a larger
amounts of bronze for prototypes/mold masters.
I have been considering getting an electromelt—possibly the
Tilt-pour Rio automatic, however, I am concerned about the weight.
It is listed as 13.6 lbs, which I assume is the shipping weight.
However, I have been told that its actual weight is 10 lbs. This
seems like a lot for me to have to lift, and pour with accuracy.
I have small hands and slender wrists not much strength-- and wonder
if it will be too heavy for me?
When one pours with it, does one hold it with just one hand? Or does
one hold the handle in the back with the right hand, and the handle
on the side with the left hand? If, so, that would distribute the
weight, and I might be able to manage it. However, would this result
in the possibility of the crucible falling out? I was told that when
pouring, one should hold the crucible in using the tongs, so that it
cannot fallout, but with both hands holding the electomelt, this
would not be possible.
An alternative would be the Rio furnace that has the removable
crucible, but a friend who has one has advised me against it as she
has problems getting a good pour with it. In fact she is selling
hers and going back to melting with her torch.
An alternative would be the Rio furnace that has the removable
crucible, but a friend who has one has advised me against it as
she has problems getting a good pour with it.
I have a furnace with a removable crucible. I chose it because I
thought it was crazy to try to lift a heavy furnace and try to get a
precision pour. For those who can do it, that’s fine.
I got less-than-great pours until I took a round rasp to the ‘spout’
of the crucible, which is just a very small cut-away on the inside of
the rim. I enlarged it wider and deeper down into the crucible. Now
it pours very well.
I do a test ‘pour’ or two while the crucible is cold and empty to
make sure I have the right clearance and distance to the flask, and
to build up a little muscle memory.
For smaller pours the metal will tend to freeze on me near the end
of the pour, so I make sure to have everything set up just right and
do a fast pour.
As with many other tools, sometimes it just takes a little thought
and practice to get it to do what you want. It will do it, just fine.
I use the one with the removable crucible and like it a lot.
However, I also have another reason for using it. I cast mostly
filigree, so need higher melt temperatures(as well as higher flask
temps) to allow the silver time to flow into all the nooks and
crannies. I’m using vacuum casting, and don’t have any trouble
getting good pours. Don’t know about the heavier one. but I can
imagine it could be more awkward to use than the lighter crucible.
If the top of the furnace is high and the top of the flask is low,
you may tend to start tipping the crucible for the pour before the
bottom of the crucible quite clears the top of the furnace. Outcome,
a spill or a bungled pour.
If the furnace is low and the flask is higher, you can start the
pour as soon as the flask is lifted straight up out of the furnace.
So a good setup is the key to a good pour. Part of the equation is
how tall you are. You don’t want to pour higher than your arm will
comfortable manage. Work it out with a cold setup, run through it a
bunch of times until it is obvious that everything is just right.
When one pours with it, does one hold it with just one hand?
Alma, I have the larger Kerr model and although it pretty much just
collects dust now, I have used it quite a bit in the past. I’m not
sure of the weight, butI used my right hand to pour.
Here are the steps I would follow. When the metal was at the desired
temperature I would seat my flask, turn on the vacuum, unplug the
electromelt cord from the unit to get the cord out of the way, pick
it up with my right hand by the handle, with my left hand I would
pick up my melting dish (melting crucible on a handle) and position
that on an angle with the flat back side facing the pour hole of the
flask to prevent over-splash of the metal (opposite side of the pour,
just acting as a back stop), lift the lid with my right thumb, then
pour.
I never really had much of an issue with the carbon crucible sliding
out, butif it did it would just stop against the back of the melting
dish. It would have no effect on the pour as the metal was out
before the crucible beganto slide.
Personally I prefer to torch and spin rather than vacuum cast, more
because I seem to get consistently good results that way. The
onlytime I vacuum cast and use the hand furnace is when I have a
huge pour, over 60 dwt (that’s huge for me) and that happens very
seldom. Hope that helps. Mark
