The Way That I Cast : Lost Wax Process- Part 6

Last time I discussed the most basic casting set-up that I could think of, that was likely to create successful results. I also mentioned the biggest problem with this system – your model is destroyed in the process.

The biggest question about casting that you really need to ask yourself is “Is this something that I want to do just once, or twice, or is this something that I want to be able to continue to do for the foreseeable future?” And along with this question is another important issue – “Do I feel that I have to do all the parts of the casting process myself? Or can I “farm out” some, or most, of the process to a professional?”

So what sort of options do we have? Well, the first thing that comes to mind is to solve the problem of destroying your model yourself. You can make a mold of the model so that you have the option of making copies of the model if you want to make more items, or if the casting process fails. There are a lot of very user-friendly Room Temperature Vulcanizing compounds out there that do not require any special equipment. I have more complex equipment, but I still often use RTV compounds to make molds. Here are a couple of my molds.

RTV molds

What if you really enjoy the idea of making the model, but you really are just not up to doing the casting yourself? Well there are reputable companies in the US that will take your model and cast it for you. They will generally want to make a mold of the model as insurance against a failed casting. You can arrange to receive the mold yourself, along with the cast piece, or have them archive the mold. Be sure to understand all of the costs, who owns the mold, and whether they archive it, or you get it back.

I do not recommend sending a model “offshore” to places like Pakistan or China. Factories in these areas usually specialize in large quantity production. They often own the molds, and you may not get your master back. Your legal recourse if you are not pleased with the results, is limited, and you will have to pay import fees. I do know people who have their business production done off-shore. The Pakistani company is casting bronze pieces and their minimum order is 1000 of the same pieces. I was not impressed with their quality. The Balinese company is casting silver. They will cast much smaller numbers of items, but still not ones and twos, and their quality is very good.

But back to getting work done in the US. As long as you understand the fees and rules you should be fine. Taking this to the extreme, there are shops that will do custom casting, from design to finish. The most technologically savvy shops will have computer design capabilities that will use 3D printers to create the original model. I have seen them in action, and it is amazing. Small shops may also be willing to do wax models and cast very limited quantities.

I hope that this blog gives you some ideas about your casting options.

The Way That I Cast: Lost Wax Process Part 4

Last time we created the actual molds that are used for casting, and we poured the molten metal into them. But what happens now? Well, they need to be quenched.

Quenched? Yes. The metal needs to be cooled down the rest of the way so that it can be handled, and it needs to be removed from the plaster in the flask. Quenching accomplishes both of these things at the same time. Here is a picture of my high tech quenching arrangement. I have a bucket of water sitting up on a metal stool. The still hot flask (in the tongs) is lowered into the bucket of water. Sizzle, spit, steam and it all happens. The forceps in my other hand are used to remove the still warm metal from the flask. I set it aside into another smaller container of water while I clean the flask.

quench and reveal

There is always some plaster left in the flask, so I scrape it out with a putty knife and throw it into the other bucket that you can see next to me on the floor. The flask is then scrubbed with a wire brush, rinsed and put on the floor to dry.

flasks drying

And here they are drying! Meanwhile the newly cast piece is sitting in a small container (an old cooking pot) full of water. It is now cool to the touch, and this is what a typical one looks like.

newly cast buttons

Once I am done casting it is time to begin making these messy looking blobs into something worthy of being put in my shop. This picture shows the basic process. First the pieces, in this case buttons, are cut off of their sprues. This process often requires that the metal has to be cut apart in stages so that none of the buttons are damaged. Then the sprues are set aside to be cleaned and the buttons are given an initial tumble to remove any remaining investment and reveal any surface imperfections. Any flawed buttons go into the sprue pile to be recycled later. The remaining buttons are sanded, polished, inspected, and touched up until they look like this.

smaller button picture

The sprues are then cleaned and polished to remove all traces of investment and metal oxides. They are then dried and put away for later use.

I thought it was important to include a lovely picture of me in all of my pouring safety gear. Quite the fashion statement!

full kit

So for those wishing to replicate this major fashion statement…Starting at the top we have a full face shield to prevent burns from splashing molten metal and boiling water. Under that shield we have a high quality particle dust mask. The process of quenching the flasks can put quite a bit of fine particulate silicon into the air, which is very bad for your lungs. The blue jacket with leather sleeves is a welding jacket – doesn’t catch on fire easily and protects from an assortment of hot things. Leather welding apron and gloves complete the ensemble. What you can’t see is loose fit cotton jeans and high top leather boots.

Next time: How I Got Started Casting

The Way That I Cast: Lost Wax Process Part 3

Last time we created a mold by using a wax model and investment. But is it really a mold that we can pour molten metal into yet? Nope! We now need – Heat, Heat, and More Heat!

Right now the investment is still soft and it still contains waaay too much water to be anywhere near molten metal. Most of the wax has been melted out by the dewaxer, but the investment now needs to be hardened, the remaining wax needs to be burned away, and any remaining moisture in the investment needs to be driven off. The way this is accomplished is by placing the flasks into a burnout oven and cooking them for hours. Here is a picture of my burnout oven.

burnout oven

And yes, 947 is the temperature in the oven. This is actually the low end of the temperature cycle, the temperature at which the flasks are held, at the end of the burn-out cycle while they are waiting to be cast. The high temperature portion of the cycle varies, depending on exactly the type of investment that is used, but it is often around 1300 degrees Fahrenheit. The burnout cycle starts slowly, at about 200 degrees and gradually increases. By the time it is at 700 degrees we open all of the windows and doors in the Studio to let the fumes out. Burning casting wax is a truly nasty smell, and not good for you. By the time the cycle is finished and we are at the holding temperature, about eight hours later, the smell is gone and there is no more wax residue left in the flasks. They are now officially molds!

Once the end of the casting cycle is coming to an end it is time to start melting the metal. I have two electric melting furnaces, a small one that uses a removal crucible, and a bigger one, which is called a “tilt and pour” This just means that you pick up the entire furnace and pour the molten metal directly from the furnace into the flasks.  In either case I have to preheat the graphite crucibles in the furnaces, add the new casting grain and the old metal that I am re-melting, and wait. If you peek into the furnace while it is heating, this is what 1980 degrees Fahrenheit looks like.

recently recharged furnace

Once the metal has melted completely, I start bringing the flasks out of the burn-out oven one at a time. The flask is placed on the silicone pad on the vacuum machine, the vacuum is turned on, and the molten metal is poured into the flask. And this is what it looks like.

big furnace pour

The vacuum machine is actually pulling air out of the bottom of the flask, which helps produce better castings. The flasks are removed from the vacuum machine and set aside to cool. Here is a picture of three flasks cooling on a metal cart. They are sitting next to my small furnace.

small Furnace with flasks

This is a great picture because it really shows how you can see what temperature the metal is by its color. The right hand flask is yellow because it is the hottest. The almost black metal on the left is ready for the next step in the process.

Next Time – What Happens Now That We Have Poured the Metal?