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Casting problem

#1

I have experienced the same problem twice now and wonder as to
its cause. I use a centrifugal caster and vacuum well before
casting. I pour the investment into the flask by pouring slowly
down a wooden rod.

Both times I have cast a ring with a reasonably hollow ( domed )
head. I have calculated the metal needed carefully as I have
done on successful casts. When I remove the cast rings there is
no button and the space (hollow) on the underside of the dome is
full of metal that I assume was for my button. A realmess!

Is it due to the fact that the investment did not fill the
hollow space and air remained there and hence a space for molten
metal existed? How do I avoid (cure) this problem?

Thanks.
Bob

#2

Hi: I protect myself from this problem by coating this surface
with investment ,using a paint brush,before I pour the investment
into the flask.If the pocket is deep i will coat it 3-4 times,
building up the investment before I pour the rest of the
investment into the flask.

GOOD LUCK

                LZ
#3

hi bob,

it sounds like that an air pocket is forming under the dome. try
a different orientation of your wax. sprue from the dome or put
the dome towards 3 or 9 o’clock. i’m assuming that the dome is
oriented at 12 o’clock when your problems occured. as john h.
asked me, ’ are you weighing out yur investment carefully and
measuring your water. a mixture too thick may be worsening the
problem.

best regards

#4

Hi Bob… a simple way to fix this sort of problem is to take a
brush and coat your wax with the investment until you have build
up a shell… Now invest that the way you normally do. Any bubbles
will be on the inside of the investment and not on or near the
wax.

Have a platinum dayJurgen J. Maerz
Manager of Technical Education, PLATINUM GUILD INTERNATIONAL USA

#5

Hi Bob,

You hit it right on the head. It is trapped air. Sprue the
ring from the sides not the bottom of the shank. You can get
away with 8 ga. sprues but pinch the ends down to 12 ga. and
use6 or 8 sprues. The extra thickness will act as a reservoir.
You may also wish to tip the pattern so that the shank is
slightly higher than level and when you pour the investment into
the flask, hold the flask on the vibrator on an angle that will
fill the underside of the ring pattern and then finish pouring
with the flask level. The only alternative is to make a hole in
the top of the pattern and solder it closed. Good luck. If you
have any other problems you can E-mail me and I will try to
help.

Regards,

Skip

                                  Skip Meister
                                NRA Endowment and
                                   Instructor
                                @Skip_Meister
                                10/30/9703:23:01