Hot Metal: Lost Wax Casting

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How To's

Photo Gallery 2002-2003

Wax Tree In this wax tree the major sprues are wood. The art is fed from the bottom, taking care to minimize turbulence and minimize air bubbles. 4 Investments Here, there are four plaster investments in the burnout kiln.
The kiln Outside view of the kiln. That is a half tube sticking out of the lower observation port. Melted wax from the investment is gathered and sent to flow out that tube. It is then captured in a cup [not shown]. Wax tree Another wax tree. In this case the wax flower on the left has been 'painted' with fine casting plaster. That is done to ensure the investment material penetrates deeply into the recesses of the art.

The art on the right doesn't have deep recesses, so it has less need for pre-investing.
The wax work area This is part of my wax working area. I took a woodburning iron and reduced the power using a light dimmer circuit. It does wonders for attaching sprues. The hot glue gun is also very useful for sprues, mostly wood sprues. Preparing to pour aluminum Preparing to pour aluminum. Bricks and iron skillets are set out to place hot things onto: molds, crucible, furnace lid.
The furnace. The regulator is special for propane. Acetylene regulators only go to 15psi. This one goes to 40.

A fuel hose leads to the homemade burner. It fires into the bottom of the furnace. The red sparker at the mottom middle of the picture is inserted into a hole 120 degrees from the burner. Currently that hold is plugged with ceramic wool.
Tools laid out The crucible holder on the left is custom made to fit the custom steel crucible. The degass applicator is a pipe welded to the end of a steel handle. The claw is a blacksmith project that is useful as both a filter and as a holder. The filter next to it is somewhat flimsy; when molten metal hits it, the expanded steel gets too soft. The crucible holder on the right is versatle, but a bit small for some of our crucibles.
Supplies laid out Thermocouples are inconvenient. They can only be used after thecrucible has been pulled from the furnace. But this means the aluminum is rapidly cooling. Makes it hard to pour at the ideal position. An optical pyrometer would be far better, but they are much more expensive. John relaxes on lawn chair Did we mention it was a hot day? John relaxes on lawn chair.
Using the claw Using the claw to lower more aluminum into the crucible. Pour aluminum Allen pours aluminum into the casting. You should get down low to expose the molten aluminum to as little air as possible. Also pour quickly.
Excess aluminum Allen pours excess aluminum into a muffin tin. The resulting aluminum muffins are a convenient size and pop out of the tin easily. excess aluminum Don't try this with brass/bronze! You will never get it out of the tin. I learned that lesson with this tin. Notice the grass showing thru one of the 'cup's.
All that aluminum is from a 'bleeder'. All of that aluminum came from a bleeder that was placed into this skillet. That shows the value of the skillet. Aluminum spilling onto the grass gets contaminated. Of course, the art in the bleeding investment was a total loss. Using water to remove investment material. Using water to remove investment material. The plaster is so hot that it almost boils away when hit by the water.
A casting Our pouring temperature was close to optimum. The surface on this pour is excellent. Investment material removed.  Shows unburned wood sprues. This used hardwood dowels for the main sprues. The breathing riser was a cooking skewer. A 6 hour burnout was not enough for the wood. Much of the dowel is left. Perhaps because of the striction in flow, the breather doesn't reach the top of the plaster. Or perhaps the aluminum had cooled too much by the time we got to this casting.
Investment material removed. This casting also shows evidence of constrained flow in the incomplete breather tubes.

I used dental investment on these to ensure a good quality surface. The lower object is a rose. The upper is a key.
Soaking the art in vineagar softens the investment material.  You especially need this with dental investment in deep cracks. Investment material is difficult to remove from deep recesses. And dental investment is the most difficult. Soaking in vinegar for a few days softens it greatly.
Breaking away the plaster. Another way to remove the plaster is to break it away. An advantage of this approach is that there is a chance for reuse of the plaster. A disadvantage is that the art may be damaged by the force. Hence I usually use water instead. A flower You can't see it in the picture, but there was a fingerprint visible in the aluminum of this casting.
Pouring muffins Karen watches as I pour excess aluminum into muffins. Mixing plaster When mixing plaster you really want to use gloves. We learned that that stuff eats skin.

Make sure you mix enough plaster. Discontinuities in the investment will cause cracks, which result in metal leaks.
Pouring plaster This is an early tree using a plastic cup. I switched to paper cups because hot glue sticks to them much better. Paper also behaves much better when skewered. As you can see we skewer the cup to hold it until the plaster hardens. Pouring plaster John is pouring plaster around the tree. Plastic water boxes such as this work pretty well. They are usually free. They provide good height, which is important for gravity feed. And the grooves make them easier to lift.
Releasing the bubbles John bangs on the wet plaster mold to encourage bubbles to rise away from the art. This has to be done immediately after the pour before the plaster gels. And it gels very quickly.

Photo Gallery 2004

hauling investments Once the melt is close to ready we remove the investments from the still-hot kiln, and haul them out to the pouring area. That's Dave and me working. lifting investments The plaster of these investments is hot. We can only hold one a few seconds before we have to set it down and take off our welding gloves quickly.
temperature check Dave checks the temperature of the melt using the thermocouple. Unfortunately it is much too high. The guy assigned to watching the melt got distracted. Degass In desparation we use degassing compound to try to recover the aluminum. First Dave measures it.
Degass I dunk the degass material into the melt. View into investment Here is a view into one of the investments. The plaster is also a problem. Notice the cracks. I got the plaster to water proportion wrong when mixing. The result is a powdery investment.
Pour I know this isn't going to be a good casting. But I pour it anyway. Bleeder As expected the investments crack and bleed. Aluminum pours onto the grass, producing lots of smoke.
Opening the investment John sprays water onto the investment to remove the plaster. The casting is a complete disaster. Equipment Here is a layout of some of our equipment.

Photo Gallery 2009

Anna Anna Anna and I attaching artwork to a wax tree.
Dragon Wax trees partially plastered. Dragon [left]. Tux [right]. Tux Tux
We had trouble with wax bonding with this tree. It broke several times and we had to patch it back together. Anna Anna Steam-out
Casting Allen, Anna, and Dave waiting for the aluminum to melt. Anna
Dave Anna and Dave add aluminum to the crucible.

The flower at right shows why I have stopped using wood in the wax trees. The skewer stem didn't burn out completely, resulting in a broken stem.
Anna After burnout the investments are very hot. Anna and Allen pull investments from kiln. Investments are burned out upside-down so that any trapped wax can drip out.

Dave pulls the molten aluminum from the furnace.
We have placed the investments right-side-up into sand lined pans. If there is a bleeder, with aluminum pouring out the side of the investment, the sand will help contain it. Dave pours aluminum. Jerome assists by holding a filter. Dave casting area
casting tree Allen and Anna show the resulting casting tree. casting tree
chasing Tux Kinetic Chicken
check temperature Dave checks temperature with an optical pyrometer as Ken, Allen, and Anna look on.

Anna prepares the degasser. This is a chemical which is mixed in with the aluminum. It scavanges hydrogen from the melt, so that the resulting pour has fewer bubbles.
bleeders We set up walls of bricks with sand ready. The idea was to contain any bleeders from the casting. It appeared to work. I think we will continue to do this in the future.

Ken places the hot investment while Paul stands by to quickly fill the sides with sand. As soon as they do that I will cover it with ceramic wool to insulate it.
hot investment
pour the pour Top view of poured investment. The main aluminum blob is the top of the pouring cup. Aluminum is also visible in the 9 or so air vents. This is a good sign. When I poured the plaster I scratched the plaster with a 'D' to indicate this one is the dragon.
hot investments Once we were fairly confident the aluminum had solidified we moved the hot investment on bricks on top of Salvador [the dolly]. We take it out where we can hose it down. Water on hot plaster tends to break the plaster without damaging the casting. But we poke it with a metal pole to help it along. deplaster
The casting The casting, ready for chasing. This is the process of cutting away sprues and cleaning up any imperfections. Chasing

Last modified 27 Sep 2009