A Home Bronzecasting Foundry

Stuff for melting pewter, zinc and aluminum.
Stuff for casting any metal.
                         METAL MELTING:
  Great casting metals are pewter, aluminum and bronze.  Pewter melts at
460 F, aluminum melts at 1200 F and silicon bronze melts at 2100 F.
  Pewter can easily be melted in a cast-iron pan or pot on a propane camp
stove. Zinc (pennies) and aluminum can be melted in the same ironware on the
camp stove with a little help from a common propane torch also heating the
metal from above. Melting bronze requires a high-temperature firebrick
foundry, a big propane torch and a graphite crucible.
   Good ironware for melting pewter and aluminum on the propane stove is the
Lodge 3SK fry pan or 2MP2 sauce pot. Be sure to use high-temperature barbecue
mitts. We also made extension handles that slip on the pan handles when ready
to pour.  The extensions are removed after pouring and stay cool.
   The first "sculpture" cast was half of a seashell cast in zinc from
pennies.  We sprayed Pam on the shell and just pushed it straight into wet
plaster.  After the plaster set and dried thoroughly, the shell was removed.
The zinc casting came out surprisingly well-detailed.
   We next pushed the seashell into ordinary silicone caulking.  This left a
perfect impression, but can only be used for wax or low-melting-point alloy,
not pewter. We tried several different two-part RTV silicone rubber kits for
direct casting of pewter in a highly-detailed, flexible mold. Good investment
(high-temperature plaster) is needed for casting bronze.
   We tested a Harbor Freight propane blowtorch, #36346, in a loose-chimney-
brick furnace. There was an opening left in the bottom for the burner and a
hole was left in the top for a vent. The cast-iron crucible sat on the upper
edges of 1" wide chimney bricks which were on their edges and inside the 2"
wide wall bricks.  The loose bricks all sat on kiln shelf halves which sat on
cement blocks.  The bottom opening for the flame was 3 1/2" square.
   The torch puts out 500,000 BTUs.  The gas orifice is .059".  The valve
adjusts the idle flame.  The trigger opens the gas flow for full fire.  But
the valve can also be set to full fire.  Our pyrometer showed that the
temperature was highest, 2150 F, at a point 11"-13" from the end of the
burner.  So that is where the crucible MUST be located.
   When the bronze melts, we turn off the torch, remove the lid and pour a
pinch of borax in the crucible with a long tea spoon in an extension handle.
Turning the gas back on will re-light the torch.  After a few minutes, we
check for lumps and stir with a carbon rod in the extension handle. Finally,
add a piece of clear glass to the mix to sequester all the impurities. Always
turn the gas off when taking off the lid or even when looking into the vent.
It will re-light by itself on the hot crucible when turned back on.
   The crucible and molten bronze are white-hot when ready to pour, like
being too close to a roaring fireplace, so be dressed for it. And some fluxed
bronze will cling to a cast iron crucible, so not all of it will pour out.
It's best to have a true graphite crucible.  We manageed to get  our first
good 2-lb ingot using this simple chimneybrick furnace.
   Next, true firebricks were arranged into a loose-firebrick furnace for
the best and quickest-heating system.  When leaks open up as the furnace is
fired up and the bricks expand, we just push them shut with the crucible
tongs.  Later, we added a steel outer shell to the side and back walls which
is held on by its own spring force. The bottom layer of firebricks sit in a
steel box pan.
Our first firebrick/propane foundry.
Inside the assembly.
  The lowest four and a half firebricks lie flat on top of a 13" kiln shelf.
Seven full bricks and one cut to 6" are used for the walls.  The side flame
opening is 3" wide.  Two firebricks and two halves of chimney bricks form the
lid.  The lid vent is 3 & 1/2" long.
   The kiln shelf can rest on concrete blocks or on a steel table.  The
graphite crucible sits on a kiln shelf shard inside.  The lid bricks are
clamped in a steel frame.  The Lodge 27C2 cornbread mold is great for ingots.
Armil makes great insulating firebricks. Salamander makes the best crucibles.
Castable-refractory knifesmith's forge, tongs & books.
   The firebrick foundry or one made of castable refractory can also be used
as a blacksmith's forge for wrought-iron work and knifemaking.  Flat springs,
edger & mower blades and files all make good knife blades.
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                    OUR BEST SCULPTURE SYSTEM:
   This process consists of a 2-part RTV silicone rubber mold poured into a
plaster "mother first" mold. (Usually the mother is made after the RTV rubber
mold.) The original piece needs to be made of fired clay and painted with
a thin coat of Vaseline for a mold release. (Non-porous masters do not need
any release agent.) Install a support rod in the master that will be where the
pouring opening will be. Or attach a support bracket with double-stick foam
mounting tape.
Test master mounted on a support bracket.
   Wrap the master mummy style with bubble wrap, bubbles in, and secure it
with a piece of tape.  The wrapping should have a thickness of about 1/2" for
a to 6" piece. This will be the RTV mold's wall thickness.
Test master bubble-wrapped and taped.
   Make a minimal plaster tub using a cardboard box lined with aluminum foil.
Pour plaster in and bed the wrapped master in the plaster until half-buried.
Leave the pouring hole open.  Leave the surface of the plaster naturally
uneven, or put some random furrows into it with your finger.  Let this set up
overnight.  Next, pour in the upper plaster .  Let this set for another day.
  Note exactly where the support rod is in reference to the plaster halves.
Mark the depth, the location front to back and side to side, and the angles
from the side and from the front directly on the plaster.  Use a hammer and
screwdriver as a wedge to pry the plaster halves apart. Take the master out
and unwrap it.
   The master now needs to be supported inside the two plaster halves so
that the RTV rubber can flow around it.  Use your previous marks for lining
up the support rod.  Do not let the master touch the plaster anywhere or the
mold will have a hole there.
The master supported in the plaster.
   Open the RTV rubber jar.  Put duct tape around the jar to extend the lip
up 1".  Pour all the catalyst in and stir very slowly for a few minutes,
scraping the sides down and toward the center, trapping as few bubbles as
possible.  Pour the RTV in the plaster halves around the master.  Let the RTV
rubber mold cure for 24 full hours.
   The RTV mold is now removed and cut away from the master along the
outline/parting line using a sharp blade in a hobby knife.  Use one hand to
spread the mold as you cut for easier progress. You might also need to use
the knife to cut off the outer RTV to form a clear band so you can better
see where to cut the RTV down to the artwork on the parting line.
   Dust the RTV halves inside with talc using a brush.  Clap the halves
together to remove excess talc.
  Put one RTV mold half back in the best half of the plaster mother mold.
Put the top RTV mold half onto the other half in the plaster precisely aligned
with it at the seam.  Pour a new plaster top layer.  Look in the pouring
opening to be certain the mold seam stayed mated precisely.  Adjust it if
necessary.  Let the top plaster layer dry overnight.
  Bind the mold assembly with a long spring or folder rubber bands for extra
insurance.  Put the mold assembly in the freezer a few hours before casting.
Pewter is melted in the iron pan or pot on the camp burner just prior to the
pour.
   As soon as all the pewter melts, turn off the gas.  Stir with a long tea
spoon and check for unmelted lumps. Skim off the surface slag. Bring the mold
out of the freezer and put it in a pan or tray in case the halves pop open.
Pour the pewter into the mold. Tap the mold to jar pewter into all crevices.
Pouring the pewter into the RTV mold.
   If the melt puddle is to be the base of the piece, be sure the puddle is
level.  After the pewter cools and hardens, pop open the mold assembly and
remove it. Cut off any seam flashing and bubble bumps, grind any rough places
and wire-brush for the desired finish.  Pits can be filled with pewter chips
and an 80-watt soldering iron.
Akron RTV mold, mother mold and pewter casting.
   Akron can withstand 500 F and so is good for pewter alloys. This particular
casting was done with graphite as a mold release.  But talc is less messy and
they both work well. The color comes from the RTV iself on the first pour.
Some sandblasted pewter castings.
  This is Akron Low-Viscosity RTV rubber. The mold for the RTV mold, and later
the flask for the investment is a welded, heavy steel form.
Three-part RTV mold, flask and wax intermediate.
The mold as it appears when ready for pouring wax.
Brown-wax figure.
Blue-wax figure.
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                       CASTING IN BRONZE:
   If the final piece is to be bronze, the above piece must be cast in wax.
No plaster outer mold is (usually) necessary. Just use several rubber bands to
hold the RTV mold together.  Sometimes straight pins are required at some
stubborn seams.  (Tape will not stick to RTV.)
  It is necessary to attach crayons (without paper) to the wax form to form
vents.  Bronze will not fill a mold as nicely as pewter. The trapped air must
be allowed to escape. In the photo, there is a styro espresso cup that will
serve as the pouring opening.
Sprue and vents sketch.
The sunbather with crayon vents and styro cup.
  There will be a steel rod pushed into the crayon on the head. The rod will
then be pulled out once the investment hardens to form a third vent.
Better-quality waxes used.
Waxes and figures.
  (At left is beautician's facial-hair wax, used to attach crayons.)
  Investment is next coated onto the wax form. Put strips of bronze screening
or wire mesh in the investment for strength.  Let the investment set up and
harden for a full day.
Spooning investment onto the wax form.
  The wax form shown in this photo did not have the proper vents on it, which
we discovered only aftr we cast it.
  The wax must be vaporized out at 1200 to 1300 F.  The foundry torch can be
used with a loose-chimney-brick assembly for this procedure.  We happened to
have an old kiln that we also could use. Both ways do work. The torch must be
constantly monitored. If the investment gets too hot, the mold will be greatly
weakened. The wax smoke comes out of our small molds in about an hour or less.
  Melt the bronze in the firebrick foundry. Wear a welder's jacket, heavy
denim work pants, hi-temp barbecue mitts, heavy boots and a face shield when
pouring the molten bronze!
  The bronze must be at just the right temperature. It should be at the lowest
temperature that will allow it to run off of a steel rod dipped into it. The
pouring lip should be as close to the mold opening as possible.  Pour slowly
so as not to entrap air.
Pouring molten bronze into an investment mold.
The figurine as cast.
The figurine when finished.
Yoga figurine with sprue and vents.
Some yoga figurines cleaned and mounted.
Child's hand in bronze.
    The child's hand was pressed into common plaster, wax was poured in, then
the wax was used to make an open, mesh-reinforced, plaque-type mold.
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Test castings with masters.
   The Buddha and sunbather are pewter cast directly in RTV molds using talc
mold release. The doll's face is a mix of brass and bronze cast in investment
using graphite for the mold release.  The sunbather had several bad castings
before this final one.
Test master, RTV mold halves and one plaster half.
   This is Akron RTV, the best that we have found. It is translucent, so it
is easy to cut the mold on the perfect parting line. It gets bubbles in it,
but few will adhere to the master and form balls that will need to be
removed. A bigger problem is bubbles near the surface. They  will expand
when the hot pewter is poured in and form dimples on the cast piece.  Use
small pewter pieces and a soldering iron to fill the dimples. And/or use a
hobby knife blade to pierce the RTV down to the biggest bubbles so air can
escape.
Castaldo Liquacast mold and low-melt-alloy casting.
   This molding rubber has the look, feel and stretch of overchewed gum. It
is alright for casting wax and low-melting-point alloy, but not for pewter.
Equipment for casting pewter.
STUFF FOR PEWTER CASTING:
      barbecue lighter          plaster mixing bowl    cast iron ingot mold
      cast iron pan or pot      whisk                  Akron RTV rubber kit
      propane camp stove        large spoon            duct tape
      plaster of Paris          talc                   aluminum foil
      pewter ingots             talc brush             a selection of boxes
Equipment for casting bronze.
ADDITIONAL STUFF FOR BRONZE CASTING:
      ice-melter/weed-burner propane torch, propane tank (no regulator)
      (16) firebricks (one cut to 6" and two bricks cut in half)
      (2)  concrete blocks or a steel table
      (2)  1.5" x 1.5" x 14" perforated angle iron for lid/vent clamp
      (2)  1/4"-20 x 13" threaded rods (stainless is best)
      (4) 1/4"-20 wing nuts (stainless is best) and steel washers
      13" diam. kiln shelf, some kiln shelf shards
      #4 graphite crucible
      crucible tongs
      carbon stirring/testing rod
      long tea spoon
      extension handle with clamp screw for spoon and carbon rod
      high-temperature barbecue mitts
      scale, accurate (for mixing investment)
      silicon bronze ingots (Atlas #873 ("Everdur"), 1-800-662-0143)
      Vaseline, brush (used only for Vaseline)
      borax flux (welding supply)
      bronze screen strips, steel mesh and/or toilet-flapper chain
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SUPPLIERS:
 Cement plant: chimney bricks (cheap, but soak up heat and will crack)
 Ceramics store: kiln shelf, kiln shelf shards (lid rests and under crucible)
 KerrLab SatinCast20 is excellent investment. Mix 8 oz. water to 20 oz.
    powder by (exact) weight. (1 to 2.5)  Add powder to water ONLY.  Whisk
    for full 3 minutes. It has an 11- to 13-minute absolute working deadline
    from the point of touching water to stiffening.  But all manipulating
    should stop at 8 minutes.
Connecticut casting supplier.
Get Lo-Vis clear RTV rubber only.
Excellent firebricks.
   (insulating firebrick, 2800 F, density 55, 2.5" x 4.5" x 9", straight)
  Hallmark Metals has lead-free, silver-like MPK pewter. 1-888-467-8000
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Printable casting booklet.