need help with vacuum casting

"sbright" wrote in message
...
Hi folks.

I'm having some trouble with my castings lately. They aren't forming
completely.

[Did these same castings work previously, or are these different?]

I'm using a kilnminder to burn out, slow cycle up to 1350
degrees and then back down to 1000. Should I raise the temp?

[Not the ultimate temperature, that would be too hot. Investment starts
deteriorating above 1350F. But you might pour the flasks hotter,
particularly if the castings are very thin, and you're casting gold.]

I'm not sure
if the wax is completely burned out but after 12 hours I figured it would
be.

[I'd think so too.]

I think my sprues are wide enough. I try to make them at least as wide
as the pattern. One last thing is that I'm using filtered water from a
water cooler. I had better luck when I was using distilled water but I
have
a tough time believing that's the problem.

[Try it again with distilled water and see if it works any better. I've
heard of stranger things. It could be that the minerals in the water are
affecting the porosity of your mold. But I'd suspect your metal temperature
(too cool) or your vacuuming practice (too late) more than anything to do
with the investment.]

To many factors to keep
experimenting. If anybody has any ideas let me know. Thanks in advance.

-Stanley

[There are a lot of variables in casting, but short shots point to either
not enough heat in the metal, or not enough suction from the vacuum. Changed
the oil lately?]

Andrew Werby
www.unitedartworks.com

Andrew Werby wrote:
"sbright" wrote in message
...
Hi folks.

I'm having some trouble with my castings lately. They aren't forming
completely.

[Did these same castings work previously, or are these different?]

I'm using a kilnminder to burn out, slow cycle up to 1350
degrees and then back down to 1000. Should I raise the temp?

[Not the ultimate temperature, that would be too hot. Investment
starts deteriorating above 1350F. But you might pour the flasks
hotter, particularly if the castings are very thin, and you're
casting gold.]

I'm not sure
if the wax is completely burned out but after 12 hours I figured it
would be.

[I'd think so too.]

Wax changes to smut at temperatures over 300 °C and change again to
CO2 and H2O at temperatures over 480°C and Oxygen (some fresh air
in the kiln).

So theoretical every temp beween about 500°C and 780°C (investment
start to get destroyed at higher temp) ist working to clean the flask.

It is a good idea to look at the main channel. It there is a bright glow, this
should be ok.

I think my sprues are wide enough. I try to make them at least as
wide
as the pattern. One last thing is that I'm using filtered water
from a water cooler. I had better luck when I was using distilled
water but I have a tough time believing that's the problem.

[Try it again with distilled water and see if it works any better.
I've heard of stranger things. It could be that the minerals in the
water are affecting the porosity of your mold. But I'd suspect your
metal temperature (too cool) or your vacuuming practice (too late)
more than anything to do with the investment.]

Sorry, never I could remark that the quality of water could have any
influence to this effect.

Only if the used water contains solutet gases, it happens, that small
gasbubbles are on the surface of wax and so You get small metal
shots at the surface.
One time heat the water, short before boiling and then cooling down
will remove this problem.


To many factors to keep

True

experimenting. If anybody has any ideas let me know. Thanks in
advance.

-Stanley

[There are a lot of variables in casting, but short shots point to
either not enough heat in the metal, or not enough suction from the
vacuum. Changed the oil lately?]

Grommets could be broken.

Good luck :-)
--
Heinrich Butschal
Gutachten, Projektmanagement
www.butschal.de

Casting update. (Don't laugh)

As I was melting the gold to pour into my 1150 degree flask, I noticed it
bubbled. Then I noticed it boiled. Then small pellets started flying out
of the crucible. As I took the torch away, it was cherry red, but hardened
almost immediately. I know you're not supposed to use old gold, but I
wasn't given much choice. I now think that my process is OK, but the gold
has a contaminant. I think its lead. Actually, I'm quite sure it's lead.
I'll have to refine this batch of gold and try again with new. Thanks for
all of your help.

-Stanley


"Heinrich Butschal" wrote in message
...
Andrew Werby wrote:
"sbright" wrote in message
...
Hi folks.

I'm having some trouble with my castings lately. They aren't forming
completely.

[Did these same castings work previously, or are these different?]

I'm using a kilnminder to burn out, slow cycle up to 1350
degrees and then back down to 1000. Should I raise the temp?

[Not the ultimate temperature, that would be too hot. Investment
starts deteriorating above 1350F. But you might pour the flasks
hotter, particularly if the castings are very thin, and you're
casting gold.]

I'm not sure
if the wax is completely burned out but after 12 hours I figured it
would be.

[I'd think so too.]

Wax changes to smut at temperatures over 300 °C and change again to
CO2 and H2O at temperatures over 480°C and Oxygen (some fresh air
in the kiln).

So theoretical every temp beween about 500°C and 780°C (investment
start to get destroyed at higher temp) ist working to clean the flask.

It is a good idea to look at the main channel. It there is a bright glow,
this
should be ok.

I think my sprues are wide enough. I try to make them at least as
wide
as the pattern. One last thing is that I'm using filtered water
from a water cooler. I had better luck when I was using distilled
water but I have a tough time believing that's the problem.

[Try it again with distilled water and see if it works any better.
I've heard of stranger things. It could be that the minerals in the
water are affecting the porosity of your mold. But I'd suspect your
metal temperature (too cool) or your vacuuming practice (too late)
more than anything to do with the investment.]

Sorry, never I could remark that the quality of water could have any
influence to this effect.

Only if the used water contains solutet gases, it happens, that small
gasbubbles are on the surface of wax and so You get small metal
shots at the surface.
One time heat the water, short before boiling and then cooling down
will remove this problem.


To many factors to keep

True

experimenting. If anybody has any ideas let me know. Thanks in
advance.

-Stanley

[There are a lot of variables in casting, but short shots point to
either not enough heat in the metal, or not enough suction from the
vacuum. Changed the oil lately?]

Grommets could be broken.

Good luck :-)
--
Heinrich Butschal
Gutachten, Projektmanagement
www.butschal.de