several sources I have for steam casting use a method of
attaching a round piece of 14 gauge metal wire(no more than 1/2
") from the sprue base to the model. It must be removed, of
course, before burnout. Have you casted this way and what are
the results? Also, one of the books recommends making a little
ball of wax at the bottom of the wax wire leading from the
model, and then attaching a 14 gauge metal wire from the base
to the ball.
It sounds as if both methods would only make one sprue wire
(path for the silver to get the the model). i have found that one
wire is just not enoung path way to get a half ounce or more of
metal forced through it in the small amount of time necessary.
Remember, every casting method used for silver and gold casting
(not as important in pewter casting) depends on forcing the metal
into the mold quick enough to prevent the surface area of the
mold (investment} from freezing the metal before it fill the
mold. I found that one sprue did not work.
The metal wire sounds like a good idea (it would hold the wax
pattern more firmly than wax), but remember that you must depend
on “surface tension” to keep the metal up in the sprue button and
out of the sprue wires until the steam is applied. Thus forcing
the metal down through these small 14 guage sprues wires, in to
the 8 or 10 guage sprue wire and then into the mold made by the
wax pattern. I believe that the simple pulling out of this metal
wire would also pull or break out some of the investment at the
surface of the sprue button (which becomes the crucible). This
allows the molten metal to enter the sprue wire and freeze before
the steam can be applied. I would not want to take the chance of
preparing a wax pattern, spruing it, investing it, and burning it
out only to have it fail because of this problem that is easy to
avoid with wax wires.
I really do not understand the wax ball thing! It sounds as if
the author could only figure that method to get the wax to stick
to the metal wire.
I really appreciate the I would like everyone that
has read, heard, or tried any method different from mine to
please let me know of those differences. I want this Steam
Casting Online Class to be the best, most detailed, mistake proof
class (article) that will ever be written on this subject.
I promise I will pass along all methods and include them in the
“Online Class”. I will also try each method if I think they could
be better than what I am teaching. These two methods just do not
have enough merit for me to try. If any one has used them or
would like to try, I would love to hear from you.
Thanks again!
Don Norris
@Donald_Norris
PO Box 2433 Estes Park, CO 80517
I think the wax ball they are referring to is just a resivuoir
to reduce shrinkage porosity. I don’t use steam casting, but I
almost always use a wax resivuoir when vacuum casting. It helps
tremendously on eliminating porosity. I have a few examples on my
(far from finished web page)
http://home.swbell.net/jwlrymkr/tech.html Great stuff Dan. I
always enjoy reading your posts on alternative methods of
casting. My father once taught a casting workshop and one of the
students used a hibachi to burn out her flasks with and a bicycle
wheel rigged up to a gear with a hand crank for the centrifuge.
Surprisingly, she got fairly good results. Ken Sanders
Hi Ken and all, My 2cents on the subject. Whether you do ashante
casting or you’re using the lastest induction melt pressure
casting unit, spruing accounts for 90 something percent of
porosity problems. If you measure your wax pattern and use a
sprue at each “hot spot” with a sprue that is a couple of tenths
of a millimeter larger that the cross section of the spot you’re
spruing then gather those to a resercoir you will greatly
increase your chances of success. Think of the wax model, the
sprues, the reservoir and the button as a total casting system
instead of focusing merely on the model. The wax model should be
approximately 1/3 of the system. This can be hard for folks on a
budget when you’re casting gold, but porosity can be more
expensive in the long run. J.A.
I think the wax ball they are referring to is just a
resivuoir to reduce shrinkage porosity. I don't use steam
casting, but I almost always use a wax resivuoir when vacuum
casting.
It IS a reservoir. With normal vacuum or centrifugal casting,
the sprue button itself, if the sprue isn’t overly long or thin,
can function as that reservoir. but with steam casting, the main
feed srue is attached to any button remaining by those small 14
guage sprues leading out of the crucible area, thus isolating the
button itself. So if you want an actual reservoir mass attached
to the sprue, it needs to be that additional ball of wax below
those 14 guage multiple sprues. Plus, the larger wax ball makes
it easier to actually assemble those multiple 14 guage wax
wires…
Peter Rowe
Dear All, Here’s my 2 cents about wax spruing.
Not only its is a major factor in wax porosity, but it is
probably THE major factor in casting shrinkage – far more so
than rubber shrinkage.
Thickness, length, number of sprues, placement of sprues and
wax ball reservoirs combined with injection time and dwell time
are some of the factors. In general, to reduce shrinkage you want
the shortest, fattest sprue possible attached to the fattest,
thickest part of the model and shot and held for the longest
possible time.
Michael Knight
F. E. Knight Inc. /CASTALDO RUBBER
F.E. Knight, Inc., 120 Constitution Blvd., Franklin, MA 02038 |
508/520-1666 FEKnight@ziplink.net |