Back to Ganoksin | FAQ | Contact

Electric Furnance


#1

I have just bught an electric furnance, and it seems that I have been
over heating the metal because the porosity I�m getting on my
castings. Do sombody knows the exact casting temperature for sterling,
considering that while you take the crucible out of the furnance and
pour it, the metal would cool off a little. Thank you very much

Gus


#2

Gus! You leave a lot of ?s 1 what kind of mold are trying to pour in
too, sand mold, investment mold or what ? do you have a casting
machine either Vac or Centricfiul ?

Sterling melts at 1640 F but i pour at 1740-1800 after i flux with a
little Borax so i can see a bright shineie metal and also to clean
metal. There is lots of books out there on Silver and Gold Smithing
and one of the better book is ( The complete Metalsmith ) by Tim
McCreight about 12- 15 bucks and you can find in any Rock Shop or
Lapidary Shop also Book Stores can order it for you. OK. Let me know
what you are trying to do and maybe I can help you, also where you
are at. Bill D. In the back woods of East Texax


#3
I have just bught an electric furnance, and it seems that I have
been over heating the metal because the porosity I�m getting on my
castings. Do sombody knows the exact casting temperature for
sterling, considering that while you take the crucible out of the
furnance and pour it, the metal would cool off a little. Thank you
very much 

There is a flask temperature and a metal temperature… I assume you
are asking about the oven/ flask temperature. To answer this question
properly , I would have to know if you are doing Centrifugal casting
or Vacuum casting.Also if the item being cast is heavy,medium,light
weight or filigree.What alloy are you using? Standard 925 or deox
alloyed 925?How Many items are in your flask? What flask
size?Perforated flask or not? If you are doing centrifugal casting,
then your oven temp should be a little lower than if you are doing
vacuum casting. For vaccum casting, a heavy piece can be cast between
750 oF - 900 oF A medium weight item between 950 oF - 1050 oF a Light
item … 1050 - 1150 a very thin filigree item… 1150- 1250 a
piece of paper can be cast at 1300 This is assuming that the metal is
not being overheated If you give me more I can give you
a better , more accurate reply. Daniel Grandi

http://www.racecarjewelry.com (visit the “workshop” on My website) We
do casting, model making,mold making, finishing for people in the
jewelry trade.


#4

Thank you, Im trying to pour on a perforated flask, for vac. I use to
melt with a torch ( butane and oxigen) . Now Im trying to use this
electric furnace (electric melting equipment) with a graphite
crucible. Im at sea level, the pieces are heavy design. But I have
found to have more porosity than when I melt with torch.

Gus


#5

Hi Gus, Porosity usually occurs with too much heat or uneven cooling.
Put the sprue at the thickest part of the wax and turn down the
heat.Good luck.
Tom Arnold


#6

Gus

I just returned from the SantaFe Symposium which is a scientific and
technical conference on jewelry making. One of the papers given there
by Dieter Ott from The Research Institute for Precious Metals in
Germany titled “Metallurgical and Chemical Factors Influencing
Working Conditions” described how the reaction of oxygen in the air
and the graphite in the crucible makes a strongly reducing
environment of carbon monoxide. He went on to say that carbon
monoxide can cause gas porosity because it is absorbed by some
molten precious metals and alloys it is then released upon cooling.
Solution: If you are using a hand held melting furnace you may want
to put a gas (butane propane or natural gas flame over the mouth of
the crucible rather than leaving the lid closed . This will create a
different composition reducing atmosphere and will not contain much
if any carbon monoxide . Another likely cause of porosity is small
amounts of investment that are left on metal that is being reused in
the melt. In a reducing atmosphere the investment will break down and
form metallic sulfides i.e. silver sulfide or copper sulfide in
sterling or gold alloys. These sulfides are not reducible and will
form inclusions that end up as a form of porosity in the cast piece.
If they form on the surface they will show up as pits because they
will dissolve in the water quench or in the pickle otherwise they
will be hard spots in the piece and will cause “comet trails” on the
surface if they are exposed when polishing. Solution: clean reused
metal thoroughly to remove all trace of investment.

Jim


@jbin
James Binnion Metal Arts
4701 San Leandro St #18
Oakland, CA 94601
510-533-5108


#7

Hello everybody Dear JAGMAN you give very good informatins about the
flask’s temperature but there is a divergence between the highest and
the lowest temperature on same items.I want to ask ,if you consider
that the flask looses temperature when you take out of the oven ,so is
this the oven temperature or the flask’s temperature on casting?
Thanks nikiforos legakis


#8

Hello Nikiforos, Yes, I do take into consideration the amount of time
taken to remove the flask from the oven and pour the metal… which ,
in my case is very quick. If you visit my website, Look for "workshop"
on my frontpage and enter the site. You will see a few pages devoted
to simple lost wax casting. Notice that my metal is being melted by
oxy/propane torch and is held in place by a modified microphone
stand.This allows me to bring my metal to almost a complete melt …
then I remove my flask from the oven and place the flask on the
Vacuum casting table.The metal is now ready to pour into the
flask.This operation is done in under 1 minute and due to this
method, there is no real loss of Internal flask temperature . It is to
difficult and cumbersome to have an actual flask temperature on the
table. In past incarnations of my work, i have had flasks with digital
thermocouples removed from ovens and put on a vacuum machine…In the
1st minute + , there is no real temp.loss internally. If you let the
flask sit on the Vaccuum table or in your centrifugal machine and wait
for your metal to melt, you will have problems casting as each time
you melt a different amount of metal, your flask will cool a
different amount of time and your results will Vary from flask to
flask.This is one of the biggest reasons people have a problem
understanding flask temperatures.In any Scientific method, it is
important to develop a method that can be repeated everytime you cast
and for every temperature you cast at.

In my paricular case,(I do a lot of casting for many people) it is
important to be able to receive a wax from a Jeweler who has spent
much time carving the wax and be able to guesstimate the correct flask
temperature and get the casting perfect the 1st time.This is a skill
that requires time and patients to aquire.

Oh, I have also used a modified microphone stand to hold the torch
and melt the metal for the simple centrifugal ,broken arm casting
machines…this fixed a problem that many casters had with those
machines as well. Many Centrifugal casters would place the flask in
the machine and then heat the metal and cast. This would give
uncertain results as the flask temperature would be very different on
each cast flask as the amount of metal and melt time would be
different. Using a torch holder, it allows you to get the metal
almost melted, then install your flask and push your crucible forward
using a tool or a protected hand while using the other hand to hold
the torch on the mic. stand on your metal.This requires a bit of
practice, but i can say that that $15. microphone stand from Radio
Shack was a good deal !!! Hope this helps some of you. Daniel Grandi
http://www.racecarjewelry.com Visit the “workshop” on my web. We do
casting for Jewelers, stores, designers and finishing.