investment casting: what would happen if...

Folks,
If I...
--invest a flask with my sprued art and
--burn out the wax as usual and
--then place the button upwards in the oven and then
--put gold or silver casting grain in the button with some flux and then
--cranked the temperature to the point where the metal melted and then
--let it sit for a while and then moved it into
--a vacuum chamber as for vacuum casting and pulled a vacuum through the
bottom or sides

....would I get a good result?
....and would this work well with very thin castings that are hard to do
otherwise?

just wondering,
PW

On Thu, 01 Jun 2006 18:37:14 -0700, in rec.crafts.jewelry "Paul Wilson"
wrote:

Folks,
If I...
--invest a flask with my sprued art and
--burn out the wax as usual and
--then place the button upwards in the oven and then
--put gold or silver casting grain in the button with some flux and then
--cranked the temperature to the point where the metal melted and then
--let it sit for a while and then moved it into
--a vacuum chamber as for vacuum casting and pulled a vacuum through the
bottom or sides

...would I get a good result?
...and would this work well with very thin castings that are hard to do
otherwise?

just wondering,
PW

First, the normal way to handle thin, hard to cast models is to raise the
temperature of the mold, as well as giving the metal itself a higher "superheat"
(the difference between the melting point of the metal, and the somewhat higher
temp (usually by 50 to 100 degrees for gold) that one heats the metal to for
casting is called a superheat.) If your sprues are good, you can cast almost
anything once you've got the temps right. But you'll be better off melting the
metal seperately, and pouring it into the mold with the vacuum assist while you
pour. For even better filling ability, cast with a centrifuge, rather than
vacuum assist. Upper size limits on the flask size can be a problem however.

While this is theoretically possible as a general method, doing it just the way
you describe will not work. Standard casting investments should not be heated
above about 1350F or the gypsum based materials acting as binders will start to
break down. The result is a very course surface, breakaways, and an intensely
oxidized surface, since the breakdown of the investment releases sulphur
compounds. In short, it makes a mess. And if this isn't enough, the slow
heating in air that you'd be doing, even with a bit of flux added, likelywill
give you really crappy metal. Also, once the metal melted in the sprue cup,
it would flow down, pretty much without the vacuum. If the investment were that
hot, the metal would have all the time in the world to fill the mold. But cast
that hot, you'd have a crappy casting. This might work a bit better ifyou
used a phosphate bonded investment such as is used for platinum. But these
investments cure to a much denser material, less gas permiable, so your vacuum
pull would tend to be ineffective. It's part of why platinum is usually cast in
centrifugal equipment.

Now that you've got those negative thoughts out of the way, though, here's how
you can do pretty much the same thing, but have it work reasonably well. It's
based on an ancient method of casting employed by a number of peoples in
Camaroon and Ghana. The Ashante people are especially well known for their fine
craftmanship with these methods, which have been used for centuries, bothwith
gold castings, and brass, etc. Filligree castings of surprising delicacyand
complexity are possible with these methods, all using very low technology
methods.

The model is wax, usually beeswax, but can be your usual casting waxes. Sprues
are designed for a full gravity pour, no vacuum assist, and extend from the
model up to a hemisphere which will become the bottom half of a combined sprue
button and melting crucible. Instead of investment, the model is coated with
several layers of a mix of clay and organic material. I don't recall theexact
mixes needed from memory, but searching the web, or the Ganoksin.com web site's
archives of the Orchid list should find articles on Ashante casting (lookfor
articles by Paulette Werger, or by the renowned swiss jeweler and teacherwho
brought the method to the attention of western jewelers, (Including teaching it
to Ms Werger) Max Frohlich.

The initial layer of clay over the wax has a high organic material content
(often finely chopped straw), and subsequent layers have more clay. The model
is thus coated with several layers to build up a shell, much the same as in
modern ceramic shell casting (who's materials might also be used for this. Not
sure.) Upon burnout, the organic material forms carbon in the mold cavity,
which results in nicely deoxidized castings, and it's burning out also gives the
mold sufficient gas permiability so trapped air is not a problem. The mold at
this point now looks a bit like a dumbell, with the blob encasting the model
connected by a narrowed neck to the area that will become the sprue cup.

After thorough drying, the mold is placed "cup down" into a charcoal fired
furnace (you can make one with some fire brick lining a steel pail). Supplied
with ordinary charcoal or coke as fuel, with a blower for air into the bottom
(hair dryer). The resuling furnace type can be quite hot, actually. Some
hobbyists have built versions of this type of furnace that can melt cast iron...
But I digress.

Anyway, the mold is burned out in this manner, removed from the furnace and
allowed to cool. now the required metal, sufficient for both the castingand
it's sprues, is placed in the cup area, and more clay is added, building up
around the cup to fully enclose it. In the end, you have a mold with twofully
closed dumbell ends. At one end is the hollow mold cavity left by the burned
out wax. At the other is the larger hollow cavity enclosing the raw metal, with
the two areas of course connected by the sprue structure. Again, the mold is
allowed to fully dry.

Now the mold is placed with the metal containing end down, again in the furnace.
Heating proceeds until the mold is hot enough that the metal is known to be
melted. This will be evidenced, especially with brass, by the evolution of
fumes from the molten metal which color the flame coming from the furnace, as
well as by the visual temperature of the mold. During melting, organic material
in the clay, which formed carbon upon heating, means the melting metal isbeing
melted while fully enclosed in a carbon containing mold cavity. It's thus being
melted in a finely reducing atmosphere, easily the equal of that found incostly
graphite crucibles in electric melting furnaces. The difference of course is
that one melting setup costs a bunch of money and uses lots of electricity,
while the other is built from stuff dug from the riverbank (clay), straw from
the fields, an old bucket, and some charcoal for fuel.

When one is sure the metal is properly melted within it's cavity, castingis
done by removing the mold from the furnace, and simply inverting it as one might
do to start an hourglass. The mold cavity will be slightly cooler than the
melting area, since it was higher up in the furnace (often not fully within the
furnace), but it will be hot enough so the metal does not freeze too quickly.
The result, in any case, is that the metal has plenty of time to fill themold
via just gravity, all while still enclosed in a fully reducing atmosphere. The
mold can be allowed to cool for a while until one is sure it's cool enough so
that one can break the mold apart to retrieve the casting. I don't recall if
this is best done just by breaking it, or by quenching (not sure if quenching a
mud clay mold wouldn't make a big mess...)

While the addition of the organic material tends to create slightly higher
surface roughness in the castings done this way, the overall quality attainable
is quite high, and the high mold temps during casting allow filling of very
delicate forms. Some of the examples Dr. Frohlich showed when he visited my
graduate school class back in '87 to demonstrate this, were things I don't think
I could cast by our normal methods. Many made of very thin wax wires barely
touching each other wound into coils and filigree forms. Or the lacy bead made
of strands of wax, weblike, forming a fully hollow bead. It was made by
building up the wax model over a round core of the clay mold material, which was
then left to be part of the mold itself for casting.

Anyway. it's an interesting method. But don't try it with standard casting
investment. You need a higher temp material.

Peter

Peter W.. Rowe, wrote:
On Thu, 01 Jun 2006 18:37:14 -0700, in rec.crafts.jewelry "Paul Wilson"
wrote:


Folks,
If I...
--invest a flask with my sprued art and
--burn out the wax as usual and
--then place the button upwards in the oven and then
--put gold or silver casting grain in the button with some flux and then
--cranked the temperature to the point where the metal melted and then
--let it sit for a while and then moved it into
--a vacuum chamber as for vacuum casting and pulled a vacuum through the
bottom or sides

...would I get a good result?
...and would this work well with very thin castings that are hard to do
otherwise?

just wondering,
PW


First, the normal way to handle thin, hard to cast models is to raise the
temperature of the mold, as well as giving the metal itself a higher "superheat"
(the difference between the melting point of the metal, and the somewhat higher
temp (usually by 50 to 100 degrees for gold) that one heats the metal to for
casting is called a superheat.) If your sprues are good, you can cast almost
anything once you've got the temps right. But you'll be better off melting the
metal seperately, and pouring it into the mold with the vacuum assist while you
pour. For even better filling ability, cast with a centrifuge, rather than
vacuum assist. Upper size limits on the flask size can be a problem however.

While this is theoretically possible as a general method, doing it justthe way
you describe will not work. Standard casting investments should not beheated
above about 1350F or the gypsum based materials acting as binders will start to
break down. The result is a very course surface, breakaways, and an intensely
oxidized surface, since the breakdown of the investment releases sulphur
compounds. In short, it makes a mess. And if this isn't enough, the slow
heating in air that you'd be doing, even with a bit of flux added, likely will
give you really crappy metal. Also, once the metal melted in the sprue cup,
it would flow down, pretty much without the vacuum. If the investment were that
hot, the metal would have all the time in the world to fill the mold. But cast
that hot, you'd have a crappy casting. This might work a bit better if you
used a phosphate bonded investment such as is used for platinum. But these
investments cure to a much denser material, less gas permiable, so yourvacuum
pull would tend to be ineffective. It's part of why platinum is usually cast in
centrifugal equipment.

Now that you've got those negative thoughts out of the way, though, here's how
you can do pretty much the same thing, but have it work reasonably well. It's
based on an ancient method of casting employed by a number of peoples in
Camaroon and Ghana. The Ashante people are especially well known for their fine
craftmanship with these methods, which have been used for centuries, both with
gold castings, and brass, etc. Filligree castings of surprising delicacy and
complexity are possible with these methods, all using very low technology
methods.

The model is wax, usually beeswax, but can be your usual casting waxes.Sprues
are designed for a full gravity pour, no vacuum assist, and extend fromthe
model up to a hemisphere which will become the bottom half of a combined sprue
button and melting crucible. Instead of investment, the model is coated with
several layers of a mix of clay and organic material. I don't recall the exact
mixes needed from memory, but searching the web, or the Ganoksin.com web site's
archives of the Orchid list should find articles on Ashante casting (look for
articles by Paulette Werger, or by the renowned swiss jeweler and teacher who
brought the method to the attention of western jewelers, (Including teaching it
to Ms Werger) Max Frohlich.

The initial layer of clay over the wax has a high organic material content
(often finely chopped straw), and subsequent layers have more clay. The model
is thus coated with several layers to build up a shell, much the same as in
modern ceramic shell casting (who's materials might also be used for this. Not
sure.) Upon burnout, the organic material forms carbon in the mold cavity,
which results in nicely deoxidized castings, and it's burning out also gives the
mold sufficient gas permiability so trapped air is not a problem. The mold at
this point now looks a bit like a dumbell, with the blob encasting themodel
connected by a narrowed neck to the area that will become the sprue cup.

After thorough drying, the mold is placed "cup down" into a charcoal fired
furnace (you can make one with some fire brick lining a steel pail). Supplied
with ordinary charcoal or coke as fuel, with a blower for air into the bottom
(hair dryer). The resuling furnace type can be quite hot, actually. Some
hobbyists have built versions of this type of furnace that can melt cast iron...
But I digress.

Anyway, the mold is burned out in this manner, removed from the furnaceand
allowed to cool. now the required metal, sufficient for both the casting and
it's sprues, is placed in the cup area, and more clay is added, building up
around the cup to fully enclose it. In the end, you have a mold with two fully
closed dumbell ends. At one end is the hollow mold cavity left by the burned
out wax. At the other is the larger hollow cavity enclosing the raw metal, with
the two areas of course connected by the sprue structure. Again, the mold is
allowed to fully dry.

Now the mold is placed with the metal containing end down, again in thefurnace.
Heating proceeds until the mold is hot enough that the metal is known to be
melted. This will be evidenced, especially with brass, by the evolution of
fumes from the molten metal which color the flame coming from the furnace, as
well as by the visual temperature of the mold. During melting, organicmaterial
in the clay, which formed carbon upon heating, means the melting metal is being
melted while fully enclosed in a carbon containing mold cavity. It's thus being
melted in a finely reducing atmosphere, easily the equal of that found in costly
graphite crucibles in electric melting furnaces. The difference of course is
that one melting setup costs a bunch of money and uses lots of electricity,
while the other is built from stuff dug from the riverbank (clay), straw from
the fields, an old bucket, and some charcoal for fuel.

When one is sure the metal is properly melted within it's cavity, casting is
done by removing the mold from the furnace, and simply inverting it as one might
do to start an hourglass. The mold cavity will be slightly cooler thanthe
melting area, since it was higher up in the furnace (often not fully within the
furnace), but it will be hot enough so the metal does not freeze too quickly.
The result, in any case, is that the metal has plenty of time to fill the mold
via just gravity, all while still enclosed in a fully reducing atmosphere. The
mold can be allowed to cool for a while until one is sure it's cool enough so
that one can break the mold apart to retrieve the casting. I don't recall if
this is best done just by breaking it, or by quenching (not sure if quenching a
mud clay mold wouldn't make a big mess...)

While the addition of the organic material tends to create slightly higher
surface roughness in the castings done this way, the overall quality attainable
is quite high, and the high mold temps during casting allow filling of very
delicate forms. Some of the examples Dr. Frohlich showed when he visited my
graduate school class back in '87 to demonstrate this, were things I don't think
I could cast by our normal methods. Many made of very thin wax wires barely
touching each other wound into coils and filigree forms. Or the lacy bead made
of strands of wax, weblike, forming a fully hollow bead. It was made by
building up the wax model over a round core of the clay mold material, which was
then left to be part of the mold itself for casting.

Anyway. it's an interesting method. But don't try it with standard casting
investment. You need a higher temp material.

Peter

For a possible source of ceramic slip and info, try;
http://home.c2i.net/metaphor/index.html

Carl


--
to reply, change ( .not) to ( .net)

Paul Wilson wrote:
Folks,
If I...
--invest a flask with my sprued art and
--burn out the wax as usual and
--then place the button upwards in the oven and then
--put gold or silver casting grain in the button with some flux and then
--cranked the temperature to the point where the metal melted and then
--let it sit for a while and then moved it into
--a vacuum chamber as for vacuum casting and pulled a vacuum through the
bottom or sides

...would I get a good result?

No!

...and would this work well with very thin castings that are hard to do
otherwise?

No!

--
Abrasha
http://www.abrasha.com

On Thu, 01 Jun 2006 22:20:23 -0700, in rec.crafts.jewelry Sean
wrote:


Very good tips Peter, and I can finally post something that isnt an
advert (:
You could try the above method using the investment casting process or
use the same principle with second flask containing the metal melting
void that locks onto the first flask.

Well, no, investment won't work for this, at least not standard jewelers casting
investment that we usually use with gold and silver. The reason is just as I
explained at the beginning of the posting, before distracting everyone with a
description of Ashante casting. The sulphate bonded (gypsum) investments
start to break down above about 1350F to 1400F.. You cannot heat an investment
mold much hotter than this before you totally muck it up, and any metal cast
into it too. So while you can use investment for the mold cavity, you cannot
furnace melt the metal in the stuff. Plus it would be difficult to construct
the fully enclosed crucible cavity around the unmelted metal with investment,
since it's liquid. The Ashante method uses clay, which is easily formed into
such a bowl shaped lid to top the initial bottom cavity, thus enclosing the
metal.

Also, the organic componants mixed with the clay, that burn to carbon during the
process are quite important in keeping the metal clean during melting andduring
casting. investment, at least by itself, doesn't offer that advantage, though
one could always add something like charcoal or graphite powder to the
investment mix.

If you're doing this with investment, I think you're still better off melting
the metal seperately, and pouring it into the mold. And frankly, even the most
difficult to fill mold will likely not have a problem filling if the moldis at
1350 or 1400 F., assuming the metal is properly melted, and the model is
properly sprued, etc.

The whole advantage to Ashante casting is the totally simple technology and
simple cheap materials. Using investment means suddenly you're back to the
higher tech needs of a material that needs to be poured into a flask, andall
that jazz. Pick a method and use it, don't try to mix it up. You'll just end
up with a *******ized method that won't work as well as either of it's
"parents".

The thing to remember here is that casting thin sections, while more difficult
than thicker simpler pieces, is certainly not all that hard to do with
conventional vacuum assist lost wax investment casting. We, and many other
manufacturers do it all the time. This bit about trying to melt the metal in
the sprue cavity in the kiln is an interesting question, perhaps, but notany
potential improvement over what already works well, many times per day, for
hundreds or more of jewelers. If just a working process is needed, go with what
works. Ashante casting also works, though it's more fuss and bother, timewise,
to do. But the real reason to use it is the interesting exploration intothis
significant historical method. Not because it's somehow so much better.It
has it's advantages, yes, but it's drawbacks too (surface detail/quality is not
as good as with investment casting).

Peter

Peter W.. Rowe, wrote:
On Thu, 01 Jun 2006 18:37:14 -0700, in rec.crafts.jewelry "Paul Wilson"
wrote:

Folks,
If I...
--invest a flask with my sprued art and
--burn out the wax as usual and
--then place the button upwards in the oven and then
--put gold or silver casting grain in the button with some flux and then
--cranked the temperature to the point where the metal melted and then
--let it sit for a while and then moved it into
--a vacuum chamber as for vacuum casting and pulled a vacuum through the
bottom or sides

...would I get a good result?
...and would this work well with very thin castings that are hard to do
otherwise?

just wondering,
PW

First, the normal way to handle thin, hard to cast models is to raise the
temperature of the mold, as well as giving the metal itself a higher "superheat"
(the difference between the melting point of the metal, and the somewhat higher
temp (usually by 50 to 100 degrees for gold) that one heats the metal to for
casting is called a superheat.) If your sprues are good, you can cast almost
anything once you've got the temps right. But you'll be better off melting the
metal seperately, and pouring it into the mold with the vacuum assist while you
pour. For even better filling ability, cast with a centrifuge, rather than
vacuum assist. Upper size limits on the flask size can be a problem however.

While this is theoretically possible as a general method, doing it justthe way
you describe will not work. Standard casting investments should not beheated
above about 1350F or the gypsum based materials acting as binders will start to
break down. The result is a very course surface, breakaways, and an intensely
oxidized surface, since the breakdown of the investment releases sulphur
compounds. In short, it makes a mess. And if this isn't enough, the slow
heating in air that you'd be doing, even with a bit of flux added, likely will
give you really crappy metal. Also, once the metal melted in the sprue cup,
it would flow down, pretty much without the vacuum. If the investment were that
hot, the metal would have all the time in the world to fill the mold. But cast
that hot, you'd have a crappy casting. This might work a bit better if you
used a phosphate bonded investment such as is used for platinum. But these
investments cure to a much denser material, less gas permiable, so yourvacuum
pull would tend to be ineffective. It's part of why platinum is usually cast in
centrifugal equipment.

Now that you've got those negative thoughts out of the way, though, here's how
you can do pretty much the same thing, but have it work reasonably well. It's
based on an ancient method of casting employed by a number of peoples in
Camaroon and Ghana. The Ashante people are especially well known for their fine
craftmanship with these methods, which have been used for centuries, both with
gold castings, and brass, etc. Filligree castings of surprising delicacy and
complexity are possible with these methods, all using very low technology
methods.

The model is wax, usually beeswax, but can be your usual casting waxes.Sprues
are designed for a full gravity pour, no vacuum assist, and extend fromthe
model up to a hemisphere which will become the bottom half of a combined sprue
button and melting crucible. Instead of investment, the model is coated with
several layers of a mix of clay and organic material. I don't recall the exact
mixes needed from memory, but searching the web, or the Ganoksin.com web site's
archives of the Orchid list should find articles on Ashante casting (look for
articles by Paulette Werger, or by the renowned swiss jeweler and teacher who
brought the method to the attention of western jewelers, (Including teaching it
to Ms Werger) Max Frohlich.

The initial layer of clay over the wax has a high organic material content
(often finely chopped straw), and subsequent layers have more clay. The model
is thus coated with several layers to build up a shell, much the same as in
modern ceramic shell casting (who's materials might also be used for this. Not
sure.) Upon burnout, the organic material forms carbon in the mold cavity,
which results in nicely deoxidized castings, and it's burning out also gives the
mold sufficient gas permiability so trapped air is not a problem. The mold at
this point now looks a bit like a dumbell, with the blob encasting themodel
connected by a narrowed neck to the area that will become the sprue cup.

After thorough drying, the mold is placed "cup down" into a charcoal fired
furnace (you can make one with some fire brick lining a steel pail). Supplied
with ordinary charcoal or coke as fuel, with a blower for air into the bottom
(hair dryer). The resuling furnace type can be quite hot, actually. Some
hobbyists have built versions of this type of furnace that can melt cast iron...
But I digress.

Anyway, the mold is burned out in this manner, removed from the furnaceand
allowed to cool. now the required metal, sufficient for both the casting and
it's sprues, is placed in the cup area, and more clay is added, building up
around the cup to fully enclose it. In the end, you have a mold with two fully
closed dumbell ends. At one end is the hollow mold cavity left by the burned
out wax. At the other is the larger hollow cavity enclosing the raw metal, with
the two areas of course connected by the sprue structure. Again, the mold is
allowed to fully dry.

Now the mold is placed with the metal containing end down, again in thefurnace.
Heating proceeds until the mold is hot enough that the metal is known to be
melted. This will be evidenced, especially with brass, by the evolution of
fumes from the molten metal which color the flame coming from the furnace, as
well as by the visual temperature of the mold. During melting, organicmaterial
in the clay, which formed carbon upon heating, means the melting metal is being
melted while fully enclosed in a carbon containing mold cavity. It's thus being
melted in a finely reducing atmosphere, easily the equal of that found in costly
graphite crucibles in electric melting furnaces. The difference of course is
that one melting setup costs a bunch of money and uses lots of electricity,
while the other is built from stuff dug from the riverbank (clay), straw from
the fields, an old bucket, and some charcoal for fuel.

When one is sure the metal is properly melted within it's cavity, casting is
done by removing the mold from the furnace, and simply inverting it as one might
do to start an hourglass. The mold cavity will be slightly cooler thanthe
melting area, since it was higher up in the furnace (often not fully within the
furnace), but it will be hot enough so the metal does not freeze too quickly.
The result, in any case, is that the metal has plenty of time to fill the mold
via just gravity, all while still enclosed in a fully reducing atmosphere. The
mold can be allowed to cool for a while until one is sure it's cool enough so
that one can break the mold apart to retrieve the casting. I don't recall if
this is best done just by breaking it, or by quenching (not sure if quenching a
mud clay mold wouldn't make a big mess...)

While the addition of the organic material tends to create slightly higher
surface roughness in the castings done this way, the overall quality attainable
is quite high, and the high mold temps during casting allow filling of very
delicate forms. Some of the examples Dr. Frohlich showed when he visited my
graduate school class back in '87 to demonstrate this, were things I don't think
I could cast by our normal methods. Many made of very thin wax wires barely
touching each other wound into coils and filigree forms. Or the lacy bead made
of strands of wax, weblike, forming a fully hollow bead. It was made by
building up the wax model over a round core of the clay mold material, which was
then left to be part of the mold itself for casting.

Anyway. it's an interesting method. But don't try it with standard casting
investment. You need a higher temp material.

Peter

Very good tips Peter, and I can finally post something that isnt an
advert (:
You could try the above method using the investment casting process or
use the same principle with second flask containing the metal melting
void that locks onto the first flask.

Paul hasn't mentioned exactly how large or thin his casting is going to
be which would help.

A coloidal silica/zircon flour investment slurry would do the job
admirably but it sets like concrete when fired and one would have to be
very careful removing it aftercast.

Also a lot can be said for just plain gravity casting, the beauty of
this is you can inspect your mould prior to pouring, metal cleanliness
can be better controlled and given the right sprueing and venting is
employed you would be at surprised at the thin walls it can achieve.

regards Sean

Peter W.. Rowe, wrote:
On Thu, 01 Jun 2006 22:20:23 -0700, in rec.crafts.jewelry Sean
wrote:

Very good tips Peter, and I can finally post something that isnt an
advert (:
You could try the above method using the investment casting process or
use the same principle with second flask containing the metal melting
void that locks onto the first flask.

Well, no, investment won't work for this, at least not standard jewelers casting
investment that we usually use with gold and silver. The reason is just as I
explained at the beginning of the posting, before distracting everyone with a
description of Ashante casting. The sulphate bonded (gypsum) investments
start to break down above about 1350F to 1400F..

Sorry Peter, I should have said ceramic shell investment casting
process. It will withstand much higher temps and is regularly used for
high temp steel and copper alloys.
The other process that just came to me is the "Shaw" method, a slurry
mixture of zircon flour, zircon sand and ethyl silicate thats cures in
about 2 minutes with a few drops of hydrolyzed ammonia.
The process is much the sames as investment flask casting.. but again
will withstand much higher temps..this process is particularly good for
casting net and near net steel dies.

You cannot heat an investment
mold much hotter than this before you totally muck it up, and any metalcast
into it too. So while you can use investment for the mold cavity, you cannot
furnace melt the metal in the stuff. Plus it would be difficult to construct
the fully enclosed crucible cavity around the unmelted metal with investment,
since it's liquid. The Ashante method uses clay, which is easily formed into
such a bowl shaped lid to top the initial bottom cavity, thus enclosingthe
metal.

Also, the organic componants mixed with the clay, that burn to carbon during the
process are quite important in keeping the metal clean during melting and during
casting. investment, at least by itself, doesn't offer that advantage,though
one could always add something like charcoal or graphite powder to the
investment mix.

If you're doing this with investment, I think you're still better off melting
the metal seperately, and pouring it into the mold. And frankly, even the most
difficult to fill mold will likely not have a problem filling if the mold is at
1350 or 1400 F., assuming the metal is properly melted, and the model is
properly sprued, etc.

The whole advantage to Ashante casting is the totally simple technologyand
simple cheap materials. Using investment means suddenly you're back tothe
higher tech needs of a material that needs to be poured into a flask, and all
that jazz. Pick a method and use it, don't try to mix it up. You'll just end
up with a *******ized method that won't work as well as either of it's
"parents".

The thing to remember here is that casting thin sections, while more difficult
than thicker simpler pieces, is certainly not all that hard to do with
conventional vacuum assist lost wax investment casting. We, and many other
manufacturers do it all the time. This bit about trying to melt the metal in
the sprue cavity in the kiln is an interesting question, perhaps, but not any
potential improvement over what already works well, many times per day,for
hundreds or more of jewelers. If just a working process is needed, go with what
works. Ashante casting also works, though it's more fuss and bother, timewise,
to do. But the real reason to use it is the interesting exploration into this
significant historical method. Not because it's somehow so much better. It
has it's advantages, yes, but it's drawbacks too (surface detail/quality is not
as good as with investment casting).

Peter

The ashante method sure sounds interesting, and it would be a good match
for ceramic shell casting as its very easy to handle, after wax burnout
a simple crucible shaped piece could easily be attached with some mortar
, it would heat up easier and once the metal melted just invert the lot
an bingo!

Just on a similar topic I have only heard of, not seen, a process used
for casting simple iron railway parts, the moulds are imported from
china or somewhere fully closed and ready to go...they contain a mixture
of metal filings and exothermic power...basically all you do is light a
wick and wait an hour or so until the metal melts and seeps into the
shape..interesting but I wonder how clean the melt would be....maybe its
not critical.

regards Sean

Paul Wilson schrieb:
Folks,
If I...
--invest a flask with my sprued art and
--burn out the wax as usual and
--then place the button upwards in the oven and then
--put gold or silver casting grain in the button with some flux and the=
n
--cranked the temperature to the point where the metal melted and then
--let it sit for a while and then moved it into
--a vacuum chamber as for vacuum casting and pulled a vacuum through th=
e
bottom or sides
=20
...would I get a good result?
...and would this work well with very thin castings that are hard to do=

otherwise?
=20
just wondering,
PW
=20
=20
This is a silly idea. Most of the alloys like to grow their cristals if t=
he=20
have time to.
This alloys are brittle and have shrinkholes.
To avoid this, it is important to cast in a system wich coos down the gap=
=20
between liquidus temperature and solidus temperature as fast as possible.=

With Your system you can=B4t realize that.


Mit freundlichem Gru=DF,
Heinrich Butschal
--=20
Schmuck gut verkaufen und g=FCnstig kaufen http://www.schmuck-boerse.com
Geschichten ber=FChmter Juwelen http://www.royal-magazin.de
Schmuck nach Ma=DF anfertigen http://www.meister-atelier.de
Firmengeschenke und Ehrennadeln http://www.schmuckfabrik.de