I agree with Gavin, and where ther's water marks, there's free
investment getting included in the gold producing sulphur dioxide
gassing. I'd like to know the alloy you're using, is it one of the newer
silicon alloys? Just in case it is, I think you need to raise all your
temperatures about 100 F (metal and flask) and let the flask cool for 15
minutes before quenching. Silicon gold alloys need to be superheated to
avoid prorosity, weird huh? Got that last bit of info from Stuller.
Gavin Gilmore wrote:
Thomas Williams wrote:
I am probably goingt back the basic problem of spruing and I am sure it is
something I am overlooking.. But here is the problem. Picture if you will a
flat oval shaped peice of wax. About 1mm in thickness and about 1 inch from
the top of the oval to the bottom..
Now that we have pictured this. I can tell you that I am using a flat sprue
going straight into the peice from the side. so the srpue is as thick as the
actual wax itself. I taper the srue outwards slightly at the point where it
connects to the peice. I am putting these peices on the tree at about a 45
The problem is two fold. First of all sometimes when they fill and most
always do. You can see the path that the metal has taken into the peice. Now
there will be what appear to be stains on the metal where this path has shown.
These stains are actually cracks. You can litterally break the peices in two.
This only happens with gold though... Second of all . when they don't crack
they get a heavy textured feel right at the point where the sprue is
attatched. However at the opposite end of the sprue the metal is very smooth
like it should be.. This textured look actually ends up to be porosity that
cannot be chased away either..
Here is my burnout info.. And yes I use a full burnout cycle, I try not to
rush anything. As I have heard alot of people do.
1 hour at 300, 1.5 hours at 600, 2.5 hours at1350, then at least an hour or
more at the casting temp which is usually about 975 to 1000 on the thin stuff.
I should note that this only happens on thin flat peices that I am casting. I
rarely ever have problems with rings or heavier type peices..
Now that I have probably really confused you all I will let you try to help
if you will...
thanks in advance.
What you describe sounds like water marks from mixing too much water
in your investment try making it thicker once and see if this
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