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Casting problems (reply to Jeffrey)


#1

Jeffrey: sorry I haven’t replied to your offer of casting
advice, I get a heck of alot of emails everyday and can barely
keep up with Orchid. I had been having typical casting problems
that so many people have when they start out, though its been
about a year or more now. I don’t cast that often but really love
the process. The main problem is I haven’t found any books that
get very detailed about spruing etc. I only recently discovered
vents. And in a very old book aimed mostly at rock club type
people. I had to cast a size 13 ring (in silver, thats all I can
afford at this point in time) and was pretty scared about it. I
had tried little vents before like adding wire studs here and
there and it didn’t help at all. This time I tried a vent to the
outside of the flask and got my best cast ever. Still some
pitting but very minor. I’m thinking if I had added another vent
it might have come out even better. On smaller pieces I’m
wondering if using blind vents that don’t go outside the flask
will really help or is it best to have a quick exit for the gases
completely outside? I’m using a programmable controller and using
good burnout temps and casting at 800 F so I’m pretty sure my
problems are trapped gas. My last casts were with all new metal
so thats not the problem either. I suppose I could try vacuum
casting at some point since my investment vacuum can do that but
sure want to master centrifugal first before I screw around with
a new ball game. Are there any real good books you know of that
treat this stuff in more detail that you know of? Dave

Art Jewelry for Conscious People
http://www.opendoor.com/stephensdesign/crystalguy.html


#2

Hi,

Three tricks we use in dentistry are:

1.) After the investment sets, scrape the top of the exposed
investment with a lab knife. The smallest particles float to the
top during the vibration process, and literally seal off the
ring. The investment has a micro-porosity to enable any trapped
gasses to be dissipated through the investment.

2.) About 15 minutes before you cast the flask, invert it in
the oven so that the sprue holes are up. This also will let
entrapped gasses escape. Be sure to remember that you
inverted the flask before you place it in the cradle in your
casting machine :slight_smile: or you will think a meteorite landed in your
casting tub! A very expensive meteorite indeed!

3.) A long thin vent of 14ga. sprue wax from the thickest
portion of your pattern down to the sprue former base and
attached low on the base can also be a useful vent.

In dentistry we use a flask liner of some sort of inert mineral
fiber as a liner for the flask ( we used to use asbestos liner).
It comes with the packets of investment right in the case from
the Mfgr. (Jelenko Complete). It allows plenty of venting.
Could you possibly be in gassing your metal? Remember that you
are not trying to set a speed record for how fast you can melt
the metal. The flame, as Bernini said, should “kiss the metal”.
With enough experience, you will be able to tell when the metal
goes from melting point to casting temperature. DON’T BOIL IT!

                                  Skip Meister
                                NRA Endowment and
                                   Instructor
                                @Skip_Meister
                                05/11/9702:17:24