Casting , models and molds

Jewelry Discussion
1 
   I'm looking for anyones expertice on burnout of green
carving wax and mold making. I realize this is quite a large
area so I will attempt to narrow this down to specifics.  Dan,
I hope your there.

  1. What is your de-wax and burnout cycle? Does it differ for
    injection wax?

  2. Does it make any difference if you remove the wax from the
    oven ( via wax tray ) before going to red heat ( i.e.smoke)?

  3. What is the most succesfull metal to cast in terms of less
    porosity, etc?

  4. What is the most successful size flask ( I have a ney
    centrifuge) to assure a better casting for the model you just
    spent two weeks carving?

  5. What is your favorite mold rubber? I’m a tad lost on the
    many differences of rubbers ( although I can recommend a great
    prophylactic )- no shrink, silicon,latex etc. I find the silicon
    gives a great finish o n the wax yet loses on the flexibility of
    the mold. Does a super shiny wax model a better casting make?

  6. What is your favorite injection wax?

Here I’m really in a jungle.

  1. When is one supposed to dust the mold with talc and when to
    spr ay with silicon? It is my understanding that vent lines are
    supposed to be kept open with talc and that silicon should not-
    to prevent them from clogging. Fair enough, but I can’t see how
    the parting lines wouldn’t accumulate this gunk after every
    subsequent talcing and spraying of silicon. Also, after I dust
    the mold and shoot about 4 waxes until the models start coming
    out clean, I get about 2 good waxes before I nee d to dust the
    mold and repeat the process. Is this " normal "? Any replies are
    greatly appreciated, Peter Slone
2

Dear Stephanie & Peter Sloan,

Yes, it's quite a major question you've asked. One could write

not one but several books on the subjects you asked. But no one
will because it’s too time consuming.

I can offer you some answers, however.

For the differences between different mold rubbers, please
check out our web site at: http://www.castaldorubber.com It’s an
exhaustive treatment of the subject with 100’s of pages,
technical articles, descriptions, etc.

Why do your silicone rubber molds lose flexibility? Perhaps you

need a better silicone mold rubber. Please send me your shipping
address and I’ll send you a free sample of a really good
silicone mold rubber. You’ll like it.

As for powder and silicone spray, well, you are not alone in

your confusion.

The silicone spray is used to release the wax casting from the

rubber. It should be sprayed into the mold cavity as needed, but
sparingly and infrequently. (Not needed for silicone rubbers, as
these are self-releasing.)

	Powder is not used for release of the wax. If it is used for

this purpose it will need to be re-applied frequently, will gunk
up the mold, and will degrade the surface finish and reproduction
of details. So don’t do it. Powder is used solely to keep the air
release vents in the mold open to help the wax fill the mold.
(Neither air release vents nor powder are needed if you are using
a vacuum wax injector.)

Flask size is entirely dependent on the size of what you put

into it. There is no " most successful " size. I’m no expert
here- you need to talk to an experienced caster. Or your
investment supplier.

Hope I’ve been helpful

Michael Knight
Castaldo

F.E. Knight, Inc., 120 Constitution Blvd., Franklin, MA 02038 |
508/520-1666 FEKnight@ziplink.net |

3

hello Peter and Stephanie, In answer to your casting questions.

  1. carved waxes… i never steam them out… carving wax begins
    melting in the 250+ degree range .these waxes have a fair amount
    of plastic additives and the nature of these waxes is to expand
    before melting out.Many times steaming will weaken the investment
    around the piece and cause problems. Better to put them in your
    oven at about 250degrees so the wax/plastic begins to melt out
    before expansion. doing this will not harm your regular injection
    wax or investment that has been steamed out.

  2. removing the wax tray does not hurt anything… however, you
    said before going to “red hot”. I would never crank the heat up
    like that… use a digital programmer if you are going to
    cast… save yourself a lot of grief…and realize that you don’t
    have to watch the oven anymore. The reason i say this is that the
    investment you will be casting into will suffer “thermal Shock”
    if you bring the heat up to quickly… follow the
    recommendations of the investment manufacturer.You risk getting
    cracked investment, blowouts ,finning and all sorts of agravation
    including loosing that wax you just spent 2 days carving if you
    bring the heat up too quickly.

  3. We don’t have a problem casting any metal… the trick is
    determining the proper flask temperature and the proper metal
    temperature for the item being cast.(also, we don’t use
    centrifugal casting at all .Serves no purpose)We use a simple
    flat plate vacuum casting table attached to a 29.9" vaccuum
    pump… also, I am the inventor of the paper vaccum liner
    available from The contenti co.(800-343-3364) . This liner
    increases the vaccumm potential of your flask by quite a bit (
    better than most perforated flask). Melting is done with a
    propane (barbecue grill tank) and oxygen torch. You know the
    metal is perfect when you see a mirror surface with no dirt on
    top… do not overflux… or underflux… just clean the
    metal.

  4. flask size: I use flasks from 2x2 to 6x12 depending on
    quantities etc. for models, i prefer using a 2 1/2 x3 or a 2
    1/2 x4 it is important to cover the top of the last wax by at
    least 3/4 " with investment. 1" coverage is best. (by the way,
    you can make your own vacuum caster and run it off your investing
    pump).

  5. Mold Rubber: I use Contenti supplies Red silicone(heat cured)
    I developed this rubber for the contenti co in 1980 while i
    worked for them as a designer/engineer. All the major suppliers
    now sell their own versions of this rubber and they all work.
    Guesswein and Rio also have a good selection. Castaldo also has
    good rubber so check out the price by the pound and see who is
    the least expensive. A shiny wax does give a superior cast
    surface .

  6. My primary injection wax is kerr aqua or nyc … kerr
    plastowax is also good for longevity. kerr greenwax is good for
    some carving. there are other brands available which i do use,
    but kerr is very reliable, which makes it easy to recommend.

  7. Dusting and spraying your molds: There is usually no reason to
    do both dusting and spraying . If dusting, get a couple old socks
    and put fine Italian Talc in the socks(heavy cotton socks work).
    seal the top of the sock with a rubber band.Now, when you tap
    the sock lightly against the mold, you only get the finest talc
    on the mold. If spraying… spray from roughly 12 " LIGHTLY.
    molds need to be properly vented to the outside of the mold. all
    prongs need to be vented.

I hope this helps… If you need molds, i make them for between
$20- $30 Best wishes for a Merry Chrismas and a Happy New Year.

Dan Grandi
http://www.racecarjewelry.com