Steam Casting Lessons by Don Norris
Don Norris has been kind enough to let me post his free online steam casting class here at the Heap. Don teaches silver casting online and through seminars. He has an excellent free course on steam casting. All six lessons can be viewed from the links below. I have tried his method and it works. I will include a page with pictures of what I have done so far and an example of how to do it as soon as I find some time. Don has a great website with loads of useful information, check out what he has to show you! You can find Don's website here. http://users.frii.com/dnorris/
Kind of Interesting Stuff You Might Want To Know That Will Make Casting Easier
Before we start this whole process, I want explain my basic understanding the mechanics of casting metal and the physics (basic natural laws) that affect the castings. If you like, you can call them "Don's Principles of Casting". I believe these will help you understand why we have to do certain things to get consistent good castings. At the bottom of the page, make sure to follow the link to instructions for building your own steam caster.
Don's First Principle of Casting
You Have To Have A Mold. In other words, you cannot usually just pour metal into the air and have it make something useful. Of course, if you were high enough, you could pour metal in to the air and it would solidify, probably into small balls before it hit the ground. The air and air pressure would actually be your mold. Or, if you could pour it in to space, without gravity, it might be really interesting and make some neat jewelry. If you pour molten metal into water, the water becomes the mold. You could just look for an interesting place (be conscious of safety), pour the metal in it or on it, and you might get an interesting casting. Whatever you pour the metal on, or in, becomes the mold. So, Don's Principle of Casting #1: You have to have a mold.
Don's Second Principle of Casting
Something Has To Force The Metal Into The Mold. In other words, metal will not jump out of whatever you melt it in and magically fill the mold. The only forces that I can think of that are used for casting art metals for jewelry and sculptures are: gravity, vacuum, centrifugal (or spinning), steam, and pressure. I would like to discuss each briefly.
Gravity is one of the oldest forces used for casting, for all the "natural reasons". We all know what gravity is, right? Well, I do not. Yes, I understand that it is a law of nature, but I truly do not think we know all there is to know about gravity and why it acts as it does. For casting, let me just say that the force of gravity pulls metal down towards the mass of the earth just as it pulls everything "down" towards the mass of the earth. This seems overstated, but if you are gravity casting, it is very difficult to make the metal run horizontally or against the force of gravity. However, when I teach sand casting, I routinely prove that you can make the metal flow up against the forces of gravity, but that may be a whole different article. Types of gravity casting are: sand, RTV, natural, water, cuttle bone, fire brick, charcoal block, and bean casting. (I plan to write a full article on each.)
Vacuum casting is a little more difficult to understand. Consequently, I divide it into two different categories based on types of vacuum casters--one that most small volume jewelers and craftspeople use, and one that high volume casters use. I will be the first to admit that I am not familiar with the latter. These casters are very expensive (in the thousands and tens of thousand of dollars). I believe that the expensive high volume casters may actually use the force of a vacuum to cast the metal, but the small vacuum casters that are under $1,000.00 do not use the force of vacuum to actually cast the metal. Now, before the manufacturers of these machines or all of you vacuum casters out there get too excited, please read my explanation carefully. I believe that in the large casting machines the mold is placed in a chamber, and an actual vacuum is created in this chamber; so a true vacuum is created in the chamber and the mold. The molten metal is then allowed to fill this vacuum, and vacuum casting occurs. However, on the small vacuum caster the mold sets on top of the caster. A vacuum is not created in the mold, it is created inside the caster. I always use the bell jar to create more vacuum. Then just as the metal is poured in to the mold, a switch is moved so that the vacuum creates a suction action that "sucks" the metal into the mold. If I am wrong about this, let me know, but please be very specific about it. I believe that it is not the force vacuum that actually casts the metal in to the mold, but the force of suction that does the casting. BUT, the real force of the suction is air pressure, not the vacuum. In other words, the small vacuum caster builds up a vacuum (void of air and air pressure) within the caster and/or the bell jar. The mold is placed on top of a small hole on top of the caster, and as the metal is poured, a lever is moved. The air pressure outside the mold tries to equalize, as it always does, so the air attempts to rush into the vacuum. It has to go through the mold (investment) as it does this. As the metal is poured into the mold, it gets in the way of the air. The air pushes it into the mold.
Am I right or am I wrong? Any physics or science teachers out there? My science teacher always taught me that if it were not for air pressure and the vacuum that we formed in our lungs, that we could not "suck" our favorite drinks through a straw.
- Special note: At high altitudes there is less air pressure there for less sucking action. This makes it more difficult to "vacuum" cast at high altitudes.
I live in Estes Park at about 8000 feet above sea level--a lot higher than Mile High Denver. This is why I say vacuum casting sucks. It sucks the metal into the mold. I also, believe that gravity has a lot to do with this kind of casting. Think about it; if it was truly the metal trying to move in to a vacuum, we could set the caster on it's side and the metal would move toward the vacuum. I want to be very careful here to make sure that everyone knows that I own two of these small vacuum casters and would not want to be without them. I use them for vacuuming my investment to remove bubbles.
Centrifugal or spinning creates a force that is somewhat hard to understand, too. I know there is a natural law about this, but I really do not understand it myself. We all know that when we were kids we could grab our little brother's legs and spin really quick, around and around, and he would spin out and fly around in a circle. Then, we could let him go and crash him in to the wall. Weren't those days fun? I miss that! Well, that is how centrifugal and spin casters work.
These are actually two different kinds of casters. A spin caster is a casting machine that is motor driven, has large rubber molds and usually is used to cast pewter. The molds are spun and the pewter is poured in to a center hole in the mold. As it enters the mold, the centrifugal force pushes (or pulls, I'm not really sure) the metal to the outer edge of the rubber molds and in to the cavities. The molds are spun until the metal cools and freezes.
A centrifugal caster (sometimes called a broken arm caster) uses this same force, but with a little angle. The mold is placed on an arm that is hinged in the middle and is cocked at a 90 degree angle. When the caster melts the metal, he releases this arm that has been wound up and is driven by a spring, and the arm begins to swing in a circular motion. As it does, the half of the arm that has the metal and the mold on it swings out straight. The centrifugal action causes this. Within the first half turn, the arm has snapped fully straight, and this action throws the metal (by centrifugal force) into the mold. The caster is left spinning for a few minutes to allow the metal to cool and freeze solid. The actual casting is done instantly. Centrifugal casting actually uses a force that is stronger than gravity. It is really important to understand this point. Remember swinging the bucket of water over your head? The centrifugal force actually was greater than gravity and kept the water in the bucket. Interestingly enough, this is how the first centrifugal casting was done. In Egypt, thousands of years ago, centrifugal casting was done just that way. A rope was tied onto a mold, the metal was poured in to the mold, and a very dumb person swung the mold around and around his head until the metal cooled and froze. Even more interesting is that most platinum is cast just like that today. Oh, not by a very dumb person, but by a vertical centrifugal casting machine.
Pressure casting is used in large companies for casting what I call industrial metals--metals like high tech alloys and metals like magnesium, so I will not discuss this method much. I really don't know that much about this method. (I do know that some of these casting machines use a powdered metal and a screw to build up the pressure. As the powder is squeezed, it is melted and then released into the mold).
The only reason I mention it here, is that now and again you will read or hear about a pressure caster built with a bicycle air pump. It always sounds like a Rube Goldberg type of machine, over engineered for what it does. Basically, the pump is used to build up air pressure in a chamber, the metal is melted or poured on top of the mold. The pressurized "caster" is then placed tightly on top of the mold, and the air pressure is released. The air pressure tries to equalize again, and it rushes out of the chamber through the mold. The metal gets in the way of this air pressure and is pushed into the mold. I am sure it works, but if you are not a machinist the caster itself can be hard to make.
Steam pressure is fairly easy to explain and even easier to use. It is definitely cheaper to use than any of the other methods. Steam is created when water, and most liquids, are heated to a temperature at which they turn in to a gas. When water turns in to a gas, it expands. I almost believe that steam might be the most powerful force in nature, after nuclear power. It is hard to beat the force of the sun and a good old atom bomb. By the way, the sun is just too far away to use its nuclear force, and even a small nuclear bomb would probably wake the neighbors. So, I ruled both out for casting purposes.
But STEAM! Man is it powerful! If you doubt this, just remember, the force of some volcanoes. Those explosions are not usually caused by some ignition of an explosive, like dynamite or gas. I believe that most, like Mount Saint Helens, is caused by the steam built up by the ground water being heated by the extreme temperatures of the magma. Again, if I am wrong, science teachers let me know. In any case, we have all heard the terrific stories of pressure cookers exploding, old steam engines blowing up, and sinking steam ships blowing up when the water hit the boilers. The best proof is that the steam engine in old locomotives created enough power, not only to pull cars full of tons of supplies and goods to every part of this country, it literally had the power to build this country. So, even though, we all know what steam pressure is, I hope to explain how a steam caster uses this force to cast metal.
It is important to know that when steam is created, it is a force that is expanding in all directions. It must be controlled. Unlike all the other forces used to cast, steam does not follow a definite direction. To use it, we must find a way to control this force and direct it into the mold, so that as the metal gets in it's way, it is forced in. For now, just understand that we will heat water to the point that it turns in to a gas, steam, in a small contained space. We only give the steam one way out of this contained space and that is through the mold. We melt the metal on top of this mold so that the steam, in its attempt to escape, pushes the metal down into the mold.
These methods all have their place in the metal working world, and later articles will expand upon some of them. For now, let us return to the principles of casting.
Don's Third Principle of Casting
All Metals Do Not Cast The Same. It is important that you know the basics of metals. I taught metals for most of my 13 years as a junior high school teacher. Then the last three years, I taught art. I teach all my classes as a metals teacher, not an art teacher. I believe that if you understand metals--how they melt, bend, react to heat and oxygen, and all that boring stuff, the better silversmith and silvercaster you will be.
The next installment of the steam casting class will be how to build your own Steam Caster.
Building A Steam Caster
Materials You Need
- $ 1.00 1 empty tuna can (mix the tuna with mayo and eat it with crackers while reading the rest of this steam casting info).
- $ 1.00 1 six inch piece of broom handle or one inch dowel.
- $ 1.00 1 roll of paper towels (you need 3 towels but you can use the rest to clean up your tuna and crackers mess.)
- $ 0.10 1 sheet metal screw #10 by 1 inch.
- $ 8.50 1 box of 10 gauge wax sprue wire (can be ordered from Rio Grande , 1-800-545-6566, part # 700-742.
- $ 2.00 1 package of children's clay or cheap sculpting wax or a roll of aluminum foil.
- $ 1.00 1 small tall narrow can of tomato paste.
- $ 2.00 1 small one package of Satin Cast 20 from Rio Grande # 702-099/1 or local supplier.
- $ 2.00 1 wax pattern, either carve one yourself or purchase one from a supplier.
Building The Caster
- Cut a 6 inch piece off an old broom handle or any other old round handle that you might have around the house, or buy a 1 inch diameter dowel rod from the hardware store and cut off 6 inches of that. This is the handle for your steam caster.
- Drill a small 1/8 inch hole in the center of the cut (flat) end. Be careful drilling this hole. The use of a vise to hold the handle would be good, but if you do not have a vise use a c-clamp to hold it down to a table while you drill it. If you do not have a c-clamp, have a real trusting friend (and I find that getting them drunk first is helpful) to hold it for you. Really, it is not that dangerous, but caution should be used so that the dowel does not begin spinning during the drilling process.
- Drill or punch a hole into the center of the empty tuna can bottom. Put the #10 by one inch sheet metal screw through this hole so that it is sticking out the bottom of the can. The head of the screw is in the can.
- Screw the can on to the end of the dowel. The hole that you drilled into the handle will keep it from splitting. Be sure to tighten the screw.
- Tear up three paper towels into approximately 2 inch pieces. Soak these in water and pack them into the can. Pack them in as tightly as possible. (You can even use another can that is slightly smaller than the tuna can to help you pack it tightly. Just pack the paper towels in to the tuna can, then turn it over and press it down on the smaller can until no more water can be squeezed out.) It is important that no more water can drip out of the caster. The paper towels should be damp now, not soaked and dripping.
What is spruing?
Spruing is the process of putting your wax pattern on to a wax wire, and attaching the wax wire to a sprue base of some kind. The purpose of this process is to hold the wax pattern up in the air so that when a flask is placed over it and investment is poured into the flask, the wax pattern is covered by the investment.
Wait, wait, wait a minute! What is a wax pattern? What is a sprue base? What is a flask? What is investment? What the heck am I talking about as if everyone knows what these terms and processes are. Sorry! lets go over the terms necessary for all to understand this "Class" on steam casting.
Lost Wax Casting: The process of using a wax pattern of something that you want to cast in metal by making a "ceramic" mold of it, putting this mold in an oven, and burning out the wax pattern. Therefore, the wax is lost! This leaves a cavity in the mold so that metal can be cast into it.
Wax Pattern: The object to be cast. A copy of anything made of wax or any other material that can burn, that is used to cast.
Sprue base: The bottom of a mold that holds the waxes so that they stand up in the flask (can) as the investment (mold material) is poured over them. In commercial casting this is usually a rubber sprue base. See image at right.
Sprue wires: When preparing the mold these are wax wires that hold the wax patterns up from the sprue bases. After burn out, they make the path in the mold for the metal to fill the cavity left by the wax pattern. See image at right.
Investment: A powered material that is mixed with water and then poured into the flask over the wax patterns to form a mold that will withstand the heat and casting procedures. I use Satin Cast 20, because it easy to find.
Crucible: Anything that is used to hold metal while it is being melted.
Getting the mold ready and spruing is very important in any kind of casting, but is the most important step in steam casting. If it is not done correctly, then you probably will not have much success. So, please follow these steps completely and very closely. Nothing is more frustrating than to take time to mold, burn out, and cast something only to get an unrecognizable piece of junk. If you have spent hours carving the item, it is even more devastating.
First, we need a wax pattern. It can be purchased from a wax pattern company through mail order.If you search for wax patterns, several dealers will come up. Or, if you prefer, you can make something. A quick easy method to make a freeform pendant is to carefully melt some wax. Any kind will do, even some crayons or old candle will do.
Melt it in an old spoon and pour it in to some cold water. It will make some interesting patterns. Vary the temperature of the water for different results, swirl the water before pouring in the wax for even different patterns.
After choosing a portion or carving off the unwanted parts, melt a hole with a heated wire (a paper clip will do) where you can insert a jump ring after casting for putting it on a chain. See images to right.
Spruing the wax pattern:
You may want to make a "nudgit". This is a soldering tool/ wax tool that you might want to try. It is patent pending, or at least I am thinking about it, but go ahead a make as many as you like. Take a small wooden dowel about 1/4 inch in diameter, put a rubber thing on one end, put a "T" pin (called a "quilting pin" now and found in the craft section of Walmart) through this rubber end, cut off the sharp point and you have a great wax tool. If you like, you can sharpen it and use it as an pencil!
Sprue the wax pattern by taking a half inch piece of the 8 gauge round wax wire and melting it on to the wax pattern. Attach it to the wax pattern in a place that is easy to clean. Some thought has to be given to positioning the wax pattern so that it will cast. To do this just think of the metal flowing though the wax wire and into the wax pattern in only one direction away from the sprue button.
To make sure that it does not come off when pouring the investment over it, I have a special way to attach it. After the wax pattern has been initially attached, heat your nudgit, and melt a little of the sprue wire and a little of the wax pattern on just one side of the sprue wire. Don't do this all the way around it, only on one side. If you go all the way around, the pattern will likely just drop off. Let it cool completely, and then do the other side of the sprue wire. Then let this cool completely. Note: you can purchase a sticky wax called treeing wax that can also be used for this.
Making the sprue button.
There are two things that will make the difference between a good cast and no cast at all. The first is the size of the sprue button, and the second is the torch that you use to melt the metal. The sprue button is probably the most important, because it, also, becomes the crucible. If it is not large enough, it will not hold all the metal to be melted. If it is too deep, you cannot keep all the metal melted at the bottom of the sprue button, even though a larger torch can solve some of this problem.
Step One: Make a sprue base.
Cut off a large piece of aluminum foil and fold it several times to get it down to a 4" to 4" square and at least 4 layers thick. This is your sprue base.
Step Two: Make a sprue button.
Step Three: Melt some wax on top.
Here are the problems that makes this step so important. Remember some kind of force is needed to push the metal into the cavity of the mold.
- Problem #1: In this case it is steam and we have to control it.
- Problem #2: If the molten metal begins to flow down the sprue wires, before we apply the steam, the surface area of the sprue wires will cool it, and the metal will freeze in place in the sprue wire. Once this has happened it is, I think, impossible to get it melted again (unless it is pewter), because the entire flask would have to be heated to the melting point of the metal being used.
Warning: this is a true story, but is not completely necessary to read for steam casting.
As a college student, I had a job at night to pour lead pigs in a water cooled mold. These pigs were used for a Linotype Machine. The mold was safe because the water ran through it kind of like coolant in an engine. I was told never to have anything to drink in this casting room, so I did not. It was a room about the size of a small bedroom. (10x10).
One night I wanted to test this theory of explosion, so I took a coke with me to work with some ice in it. I had a plan! I poured four pigs of lead (about 100 pounds). I ran to the door, grabbed one small cube of ice, threw it on to the lead, slammed the door, and waited to hear an "explosion!" I heard a little hissing, but no explosion. I was disappointed, until I opened the door. Almost no lead remained in any of the four pigs--the mold was almost empty. BUT, every square inch of that room was covered with shiny splatters of lead. It was beautiful. Then it occurred to me that I was going to get fired, and it would probably even affect my grades if they found out. It was two in the morning and I started scraping! At six in the morning, I had it all cleaned up. If I had stayed in that room, I think it would have killed me. Instead, I got a 25¢ raise for being the first student to clean that room in 20 years! It's the story of my life. I am the luckiest, dumbest guy you'll ever meet!
Moral of the story: You cannot let water drip into the metal that you melt in the top of you flask that is now called the crucible. If it does, it is going to splatter everywhere, and you will probably not get a raise from your significant other for burning holes in you, your clothes, and any other keepsakes in the room. I will talk about this more when talking about the caster. By the way, I was casting pewter into an RTV rubber mold in my garage when I spilled some on the cement floor. It started running along the floor and began to bubble. Remembering my lead pouring incident, I backed away quickly. Sure enough, the moisture in the floor finally turned to steam and blew a golf ball size of cement and some of the pewter into the air!
We need to talk about this here, because we need to control the steam, and the size and shape of the sprue button (now the crucible) will do it for us. If the moist part of the caster touches the molten metal first, it will create steam mixed with the metal, and it will try to explode in all directions. We want the steam to force the metal in one direction: down and into the mold. This is relatively easy to do.
Solving problem #1.
Make the spure button deep enough to hold all the metal after it has been melted, so that the metal is below the top of the flask and the investment. This way, when the caster is pressed on to the flask, only the top of the investment hits the moist material in the caster. This does two things:
- It seals the chamber where the metal is melted so the steam cannot escape, and
- It creates steam in the air pocket above the molten metal.
This steam does not have anywhere to go but through the mold, and it pushes the molten metal down into the mold as it does, thus, casting the piece. Therefore, we need the sprue button deep enough to allow about a 1/4 of an inch above the metal after it is melted. However , if it is too deep, it will be nearly impossible to get all the metal melted because the investment will constantly cool it.
This is the portion of the investment that touches the moist part of the caster and creates the steam. (not the metal!)
Solving problem #2.
Because the metal is melted on top of the flask with the sprue button acting as the crucible, we have to devise a way to keep the molten metal from entering the mold too soon. Then, as we melt the metal, it does not prematurely run down in to the sprue wire and "freeze". This happens because of the surface temperature of the investment cooling the metal. When this happens, the metal will block the sprues and prevent any further casting. To prevent this, we will use something called "surface tension." As with most of what I do and teach with metal, I try to use the laws of nature and physics to help me. Surface tension is a great one to use. An example of surface tension is a drop of water sitting on a pile of dirt as a perfect drop, without getting absorbed into the dirt. Then, you touch it, and it quickly disappears and mixes with the dirt. Or, I think, it is like the drop of oil on top of the water which will not mix. Then you add soap, it acts as a surface tension reliever, and the oil mixes with the water?
Anyway, if the metal is melted on top of large holes made by the sprue wires, it may flow into them too soon and freeze. If we make small holes, by using small sprue wires, the metal will sit on top of these holes and surface tension will keep the metal from flowing down in to the sprues too early. Then, when we apply the steam pressure it forces the metal down through the sprue wires and into the mold. Problem solved, I hope.
Attaching the wax pattern to the sprue base.
It is now time to attach the wax pattern to a sprue button, but before that, we need to prepare it to create the surface tension that we need.
Split the 8 gauge wire into two forks on opposite ends of the wax pattern. This is the quickest way to do this that I have found. You could twist four 14 or 18 gauge wires together to form a "quad pod," and then attach it to the end of the sprue wire if you like. It takes more time and patience. I have also been informed that using a small 1/4 inch piece of sheet wax for this purpose works too. I will investigate this at a later time and let you know. The information is in the October, 1998 issue of Rock and Gem. It sounded like a good article.
Attach the split ends to the sprue base carefully. If you do not do this carefully, you will end up with large holes leading to the sprue wires. I found that by heating my nudgit and gently melting the wax on the sprue button, and then quickly putting the sprue wires into the melted wax works the best.
You can not go back and remelt this area. Doing this will only lead to making a mess and enlarging the sprue wire openings. Once this is successfully accomplished, you are finished spruing! We are now ready to "invest." Investing will be covered next. Put away your sprued wax pattern in a safe cool place until then.
Investing is the process of making a "ceramic" mold of the waxes. Once you have done this, the waxes can be burned out, leaving a cavity in this ceramic mold so that the metal can be forced in to it. Remember, I am trying to teach this class with the idea of using the least amount of equipment and at the lowest cost.
Investment is the dry white powdered mold material that when mixed with water, dries to make a hard "ceramic" mold. This special investment is necessary to withstand the high temperature of burning out the wax. Plaster of Paris can not be used for investment. It will crack and fail during burn out. Follow the safety instructions that will come with the investment.
Step One: Prepare Flask For Investing.
Step Two: Measure The Water.
Fill a can the same size as the flask being used with water. I recommend that this water should be distilled bottled water or tap water that has been sitting for about a week. I just use an old milk jug for storing this water with the cap off. Pour this water into a small mixing bowl large enough to hold at least twice the volume of the flask.
Step Three: Measure the Investment.
Most investment companies recommend that you mix investment at the ratio of one part water and two parts investment by weight. To measure the investment without an accurate small scale use this method. Dry the can used to measure the water thoroughly and fill with investment, heaping the investment over the top of the can. I use Satin Cast 20, because it is available locally. I have used R&R Investment in the past, and many other casters have recommended using it. I believe that you will have less bubble problems with R&R. R&R's phone number is 419/865-9497 or fax at 419/865-9997. Satin Cast can be purchased in small quantities (and large) from the Rio Grande Company at 1-800-545-6566.
Step Four: Pour the Investment Into The Water.
I know this seems too simple to be a separate step, but it is how you pour it into the water that is very important. Pour the investment down one side of the bowl, tipping the bowl if necessary. The reason this is important is that, if you just dump the investment into the bowl, and the water covers the investment, it will trap air in the investment. This will not only cause bubbles, but also clumps in the investment (just like gravy clumps, yak!). By pouring it down the side of the bowl the water can seep into the investment from the bottom and force the air out through the dry powder. You will be able to watch the air come up.
Step Five: Repeat Step 3 and Step 4.
This will give you the approximate mixture for two parts investment to one part water.
Step Six: Mix The Investment.
I had a friend that would follow the above steps and never stir the investment at all. He would just pour it into the flasks. He would pour the investment into the water and just wait until it was completely absorbed. It worked great for him! I just cannot seem to be that patient! (It's a character flaw, I know, but one of my smaller character flaws!) I stir the investment with a plastic spoon to insure it is mixed well and to get a feel for the consistency. I used to do this with my hands, it really gave me feel for the consistency, but dried my hands terribly. It did give me a sense of being more of an "artist," though! Stir slowly so that you do not add bubbles to the investment. You just want to make sure it is mixed thoroughly.
Step Seven: Add more investment if needed.
The investment should be the consistancy of heavy cream or thick pancake batter. I find that with the great investments that are mentioned above, this is not as important as you may think. I have had students, both teenagers and adults, mix their investments with the constancy of 2% milk! They still got a good cast! I have had them also mix and pour it like molasses and still get a good cast. I have never had a flask blow out the bottom. I guess I may have been lucky over all these 25 plus years, but I think it is just the improvements in the investment. If you do mix it too thick, you are taking the chance of trapping large bubbles in and on the wax patterns that will cast as large "balls" on the finished casting. I add this extra investment by sprinkling it over the top and letting it soak in, then stir gently.
Note: A word or two about bubbles and debubblerizers. There is a debate about whether you should use debubblerizers or not. I do not recommend any one method over the other. Use debubblerizers if you wish, and just follow their directions. You can also make your own debubblerizers by mixing "green soap" with isopropyl alcohol (rubbing alcohol from the drug store, not denatured alcohol from the hardware store). Green soap can be ordered from most large drug store chains. I have mixed it at many different ratios and did not notice any differences in how it worked. Most casters and debubblerizers recommend that you spray or paint on the debubblerizer and let it dry before pouring the investment. I like to spray it on, because I have had students break waxes while painting it on. Again I have had students that let it dry, and I have students that forgot to spray it on in time to let it dry. So, they sprayed it on just before they poured. Both got good results.
Another method that you always hear about that I have never personally found to work, is painting investment on to the waxes before you pour. I have never been able to get the investment to easily "paint" on to the surface of slippery, smooth wax! It also took too much of my time, and you risk breaking the wax or breaking the wax off the sprue.
The new investments actually have debubblerizers contained within them. So, I just follow the steps below, without worrying about bubbles.
Step Eight: Pour investment into the flask.
I pour the investment down one side of the flask, while gently tapping the side of the flask with the plastic spoon, that I used to stir the investment. I pour down the one side for two reasons. If you pour directly onto the wax, you could break the wax pattern or break it off the sprue wire. I also pour down the side to eliminate the possibility of trapping air bubbles in and on the waxes. As you pour the investment down one side, and tap gently with the spoon, the investment flows to the bottom of the flask and flows up and around the waxes. As it slowly fills the flask from the bottom it pushes the air up and out, hopefully not trapping in air bubbles. Tapping the flask with the spoon helps "vibrate" the investment into all the detail of the wax pattern, and gently shakes air bubbles off the patterns. I had one student in her eighties who swore that after the investment was poured, she would tap the flask fairly hard three times. She just poured in the investment, then tapped it three times, and only three times. She told me she never had any bubbles. I have tried this and I never got any bubbles, either. I think what happens is that any bubbles that may be attached to the waxes are shaken off during this process. Even though they may only move off the waxes a fraction of and inch and are "frozen" into the investment, they do not cast. Even if they are still just barely touching the wax they will make a bubble that is easily cleaned off. Sometimes, they will just "twist" off the casting with pliers.
Important Note: I pour the investment just one quarter of an inch (1/4) over the top of the waxes. I feel that this will allow the air to escape faster out of the mold cavity. I have also filled the flask to the top to see if it made a difference and still got good castings. Again, these new investments are designed so that the air flows through them easily.
Step Nine: Let The Flask Set Up.
Do not move the flask at all after you have poured the investment. Leave it sit for about a half hour. Most investment will get hard (set up) with in seven to ten minutes depending on the temperature of the water used for mixing the investment. Then I take a t-pin and scratch my initials and a note of what is in this flask into the top of the investment.
Note: The process of the investment getting hard or "setting up" is a chemical reaction, not a drying action. This is important to know, because if you see the that investment has "set up" it still contains a lot of moisture. If not allowed to dry for a time, this moisture could turn to steam during the burn out process. The steam could expand and break and crack the investment, ruining the mold. This could be really bad if you spent hours carving the wax.
Step Ten: Let the flask dry.
How long should the flask dry? I don't know! Ask 12 casters and you will get at least 10 answers, and all of them are probably right. Again, these new investments are so good you can do almost anything you want to do without too much worry about how it is going to effect the casting. To prove this I offer the following examples. Once, I had a junior high student invest his wax pattern, let it set up and put it into a hot kiln (at least 1300 degrees). When I realized what he had done, I called the entire class over and explained again why this was just going to ruin his cast and his wax that he spent a week carving! Less than a hour later we cast it, and he got a good cast. There was a lot of flashing because the investment did crack, but it did not "explode" in the kiln as we have all heard. He cut and filed the flashing off, polished the ring, and is probably still wearing it. Every time he looks at that ring, he probably thinks to himself, "That Mr. Norris sure didn't know what he was talking about!"
I have also read that you should not wait too long to burn out the flask. There is something about it that makes it best to have a little moisture in the investment when beginning the burn out. It is supposed to turn to steam, push against the wax and help the wax pull cleanly away from the walls of the mold. I really do not know how it can do that. The investments are so porous anymore that air can easily pass through it. Steam always travels the path of least resistance through the investment. I do not believe that it can push against the wax. In any case, I always let my flasks dry over night, but not because of any concern for the investment. I just invest in the afternoon and cast the next morning. For students that come to class once a week, they invest one week and we cast the next week. We have no problems with burn out or casting! One school year ended, and I had several flasks left that we invested and did not cast. So, after three months of summer, I cast them to see what was in them and got good castings. I decided to experiment with the time a flask could sit before casting. I invested two flasks, dated them, and cast one about a year later and got a good cast. I forgot about the second flask for almost two and a half years (2 1/2 years). I burned it out as usual and cast it. I got good casting just as if I had invested it the day before.
So, I believe the drying time should be somewhere, between at least two hours (four would be better), and two years. I will not argue with anyone that has their perfect drying time! If it works for them, it is perfect!
Step 11: Take The Flask Off The Sprue Base.
We are now ready for the Burn Out. The next class will cover this process.
Let's Get Started
Before we discuss burn out I need to backtrack a little and cover a couple of things that I left out earlier. I apologize for these omissions. Remember that I am writing this Online Class for everyone, but especially for those who are beginning and have no equipment or supplies. I am teaching it for everyone to use the least amount of equipment and supplies. This is especially true when it comes to building a kiln.
Deciding How Much Silver You Will Need:
In most kinds of casting it is important to know how much metal you need to cast with. The easiest way I have found to do this is to weigh the wax pattern and sprue, and multiply its weight by 11 (some say 13). Therefore, if a wax weighs 1/2 a gram, then the silver would weigh about 5.5 (5 1/2) grams. This creates some problems for beginners. Most waxes weigh less than a gram, and if you are multiplying by 11 you need to be fairly accurate in weighing. So, you need to be able to weigh in tenths of a gram. Most scales that you can buy at a discount, hardware, or department store are not that accurate. In fact most gram scales are not that accurate. Example: if you weigh a wax pattern on a cheap scale that only weighs in grams, you have to guess if a wax weighs one half, one, one and half, or two grams. The amount of metal could be 5.5 grams (about 1/5 of an ounce), 11 grams (about 1/3 ounce), 17 grams (over 1/2 ounce), or 22 grams. It becomes just a guess.
Of course if you have a good triple beam, electronic or balance scale there is no problem
If you do not have a good scale this is one solution.
One solution I have always heard suggested is to fill a glass or other container with water to the brim. Put your wax and sprue wire in the water. The water is supposed to leak over the edge of the glass. Then take out the wax, and this leaves space in the glass. The next step would be to fill with the metal until the water is at the brim again. Sounds really easy! Problem is though, when I first started to teach steam casting, I tried this method. I did not get good results. We tried the method with the same wax six times. Then we weighed the silver with my triple beam gram scale and got 6 different amounts of silver. Again, this method turned out to be not very accurate, but maybe good enough for steam casting. I find that I can "guess" at how much I need just as good as this method. Try and see if it works for you.
Once you have the amount of metal needed for your wax pattern, I always recommend that you then add a least another ten percent (10%) for extra metal for the sprue button.
All of the above is why I forgot to mention it before. If you will follow my instructions for this class, this all will be taken care of as we go. You will learn that one of the most important aspects of steam casting is the kind of torch that you will use to melt the metal. I am teaching this Online Class for those who do not have any torch, and I recommended that they purchase the $10.00 torch from the hardware store. This torch limits what you can cast. With this torch I recommend that you only cast one or two rings at a time.
Therefore, if you make the sprue base the size and shape I demonstrated in spruing, the question of how much metal will take care of itself.
I recommend that you do not go out and buy a scale just yet. Let this Steam Casting process make you enough money first.
More about spruing!
In my attempt to keep this class as simple and as cheap to do as possible, I forgot to include some other information about spruing. The method that I discussed and pictured will work fine.
I also use and recommend the following for spruing for steam casting.
The question of the size of the sprue is very important!
I have tested 10, 12, 14, 16, and 20 gauge sprues to see which gave the best results. The 10 and 12 gauge wires were just too large, and the silver entered the wires and froze. The 14 and 16 gauge worked well most of the time, but if the flask was accidentally jarred or moved in anyway during the melting process, it resulted in no cast. The 18 gauge seemed to work fine, but is frustrating to work with. I think it worked the best out of all I tried. The 18 gauge worked better with pewter too. The 20 gauge was just too small to work with and did not let the metal cast fast enough. I usually use 16 or 18 gauge wax wire. I take two lengths about 1 inch long.
Then I attach them to the sprue base as described earlier. I cut off the twisted end at about 1/8 inch. These four 18 gauge wires are about the size of an 8 gauge sprue wire when combined. This end is attached to the wax pattern. Remember, I am trying to teach this for people who have no experience, equipment or supplies. This is why I think when casting for the first time you should just use the 8 gauge sprue wire and split it in half. It is easy to do and works for most small castings.
Another note about spruing. At one point I made a mold of the "quad pod" above. Then I could just make as many as I wanted. I have lost that mold, but may make another one. If I do I will make them available on my web site.
If you have a kiln, great, because almost any kiln can work for casting. Even a ceramic kiln used for pottery and ceramics will work fine. If you do not, then we will make one. A lot of fun and jokes have been leveled at the idea of making a kiln out of a flower pot and a hot plate, but it does work. I have had many, many students use it with great success. I do not believe that the "burn out" process is very important when it comes to casting.
Over twenty five years ago, I started casting and read all the books and instructions. I followed all the instructions about burning out at 300 degrees for the first hour, then turned up the kiln for the next hour, and then some more for the next hour, and so on and so on. Every book I read had a different time table. Every article I read had a different opinion according to what book the author had read. Every caster I asked had their own method. In short I began using "my method" with great success. There were two factors in developing my method. One: I taught junior high, and those kids taught me that you could do almost anything during the burn out process without affecting the casting. Two: I began to cast small Mountain Alder "Pine" Cones. I was selling a lot of these cones in solid sterling silver and had to develop a method of casting them so that I got 100 percent of them to cast. I began to cast ten flasks per day, 2 1/2 inches in diameter by 3 /12 inch high. I would sprue 20 to 30 "pine cones" in each flask. So I averaged about 200 "pine cones" per day and I wanted to end up with all 200. I wanted to hit 100 percent! I found that the burn out in this case was the most critical.
My method became simple. I found that burning out the "pine cones" at the highest temperature possible was the most important aspect of reaching the 100 percent mark. I was burning out at well over the 1300 degrees that almost every one recommends. Then it happened, the pyrometer on my kiln burned out because of these high temperatures. It was followed a few days later by the control switch. Because it was a $450.00 kiln, and I wanted to keep using it, I simply wired the kiln directly to the power cord. So, the plug became my on and off switch.
My method became quite simple:
- I loaded the kiln with 10 flasks and plugged it in.
- Two hours later when the kiln was glowing a nice bright red, I cast.
I am still using that kiln and I am still using that method. I know this will upset a lot of casters, but I have found that when I cast the flask as hot as possible, glowing a nice dull red, I always get good castings with no porosity, no excessive fire scale, and nothing but good castings. This is not a vacuum or centrifugal casting class, so I will not cover the reasons why, but I have found that the most of what I have read about burn out just does not agree with my experiences over the past 25 years. If you are a caster, and your method is working for you, keep using it! I personally do not believe one method is better than the other, because I found that it just does not matter. I will cover this more in future online classes about Vacuum and Centrifugal casting.
For you beginners starting to Steam Cast, I just want you to ignore anything that you have read about expensive kilns, steam wax removal systems, digital controls, lengthy burn out procedures, and exact casting temperatures. This simple method will disprove all of them. However, for more proof that all of the above does not really matter, let me just say that I have had junior high students do everything wrong according to the experts and still get good casts. One student put his flask into a kiln at over 1300 degrees, probably closer to 1500 degrees, because we were casting insects and "pine cones." Even though the flask was poured and set for less than 10 minutes before he put it into the red hot kiln, we cast it at the end of class, and he got a good casting. It had a lot of small "flashing" from the investment cracking due to the wet investment and the high heat, but he cleaned up the ring, polished it, and is probably still wearing it. One day I had a student cast a cold flask, that had been burnt out the day before, and got a good cast. My point is that the kiln we make will work just fine. It looks a little laughable, but it works!
Make a Kiln
Step One: Cover the pot.
Buy a six inch clay flower pot, wrap the out side with aluminum foil, put it over a heat source and you have a kiln! Wrap the pot with several layers of the foil. Some pots will crack because of the heat, and the foil will keep the pot held together. Do not put the foil inside the pot. The "kiln" gets so hot that it will just melt the aluminum.
Step Two: Make a handle for the pot.
Step Three: Make the heat source.
The flower pot is the easy part, the heat source can be the difficult part. For years, I and everyone that I knew of was taught to use an old electric hot plate, or an old popcorn popper that was taken apart to expose the coils. The problem is that the word "old" is the important part. They have the old spiral coiled elements that heat up to a glowing red.
The new hot plates have those modern elements like you find on top of the stove. These flat coils heat up, but rarely glow as red as the old elements. They probably replaced the old coiled elements due to safety factors. The new hot plates just do not do the job. I believe it is because they do not radiate enough heat. They are designed to heat by contact with a pan, to conduct heat, not to radiate heat. The old coils were designed to radiate the heat to the pan. The pans never touched the coils. They were held above the coils by the ceramic part of the hot plate. This radiating heat is what we need to burn out the wax from our flasks. The problem is that the old hot plates are hard to find. I used to go to flea markets and garage sales and buy them for $1.00 or $2.00. Now it is hard to find them at any price. If you can find one, use it. Many years ago, over 20, I put a pyrometer down into the hole of the flower pot, just before I cast, after about two hours of burn out. It read a little over 1300 degrees. I was surprised! I did not believe that it could reach that high of a temperature! It is high enough to burn out and cast with for sure.
In place of the hot plate, I have found that a small propane camp stove purchased at a Target or Walmart works great as well. It does use a lot of propane, but is still a lot cheaper than a kiln. I really like it because I always wanted to teach steam casting at a "tail gater's" rock show, where everyone camps and there is no electricity.
At one of these, a hot plate cannot be used. Steam casting is perfect for these shows. These camp stoves come with bases so use them. I also use the larger, fatter propane bottles to make them more stable. You could make even sturdier stands, but I have never had a problem with knocking over a kiln. When you do this, please use all safety practices necessary not to burn up your house and yourself. I will cover all of these in the "Casting" part of this Online class, or you can check them out in the Online Bean Casting Class.
You will need to put a wire mesh screen over the camp stove to hold the flask and the flower pot. You can buy a small square of steel screen at the hardware store. Even a small mesh steel hardware cloth will do. I stress steel, because the heat generated will melt aluminum.
You now have a kiln that will burn out one or two flasks at a time. It seems to get just as hot as the electric hot plate, and it is a radiating heat. I have used this kiln for about 20 casts with great results. No problems with burn out have occurred.
Note: I had one student that used his kitchen stove with the vent fan turned on. I cannot recommend it, but I thought it was funny. He said it worked fine for one or two rings in a flask and for two flask at a time! I also always wanted to try charcoal in a grill to burn out the flasks. Some day I will try it. If you do, let me know how it worked.
Step Four: Begin burn out.
Take the kiln outside and somewhere safe, so that no children, pets or really stupid adults can play with it or knock it over. I believe it should be on a table. A card table covered with scrap plywood or particle board is great. If it is snowing or raining you can not cast outside. If it is really cold out, you will not get a good burn out. If it is cold out place the kiln outside for the about 1/2 hour. It will burn the wax out and smoke a lot during the first 1/2 hour and then stop smoking. You could then bring it inside your shop or garage. I do not recommend your kitchen or living room, but I have had many students that covered their kitchen table with plywood, did the initial burn out on the porch, and then brought in the kiln.
Place the flask, crucible side down, on top the screen and put the pot over it. Light the camp stove or plug in the hot plate. The kiln will heat up and begin to burn out the wax in about 2 minutes. It will begin to smoke, then the wax can actually drip down and catch fire and burn. This worried me at first. I did not know what that could do if it hit the coils in the hot plate or the flames on the camp stove. I even tried to catch this wax in small jar lids. However, I found that it just did not make any difference. All the flames are contained within the pot and it has never hurt the coils or the camp stove. I just put the flask on and let em' burn, baby.
After about a half hour, it will stop smoking and the bulk of the wax will be eliminated. However, the flask is not hot enough to cast. I recommend that you do not cast for a good hour or so. This extra time allows even the wax that might be trapped in the flask to burn away. I compare this process with a self cleaning oven. It just gets so hot that every thing burns up, turns to ash, then to gasses, and finally disappears. The entire flask, including the center, has to reach a high temperature to accomplish this burn out.
It is also necessary for the flask to be as hot as possible for steam casting so that the surfaces of the investment do not cool and freeze the metal before it enters the mold. The hotter the flask is, the easier and faster it will be to melt the metal in the "crucible" formed by the sprue button.
After two hours of burn out, it is ready to cast, which will be covered in Steam Casting #6 - Casting.
Let's Get Started
After the burn out time of about two hours it is time to cast, but during that two hours we should get everything ready for this process.
But first--a word about torches. I am teaching this Online Class for those who would like to do casting at home with as little cost a possible. This is why I am using the inexpensive propane torch that you can usually purchase from Ace Hardware for about $10.00. The type of torch that you use will have the most impact on the success of your castings than any other part of Steam Casting. A better kiln would be nice, but it really will not affect your success that much. The torch you use however, will determine how fast you can melt your metal, and how much you can melt quickly enough to cast. Your success will be determined by how hot the flask is, and how quickly you can get the metal into the mold before it cools. If it is too cool, the metal will freeze as it enters the sprue wires, and the cooler temperature of the surface of the investment cools the metal enough to solidify it before it fills the mold.
or even better, a "Smith Handiheat,". It is the torch that I like the best for silversmithing. They will melt your metal faster and increase your success rate greatly. Even an oxy-acytelene torch can be used, though I usually do not like to use oxygen to melt silver. It will cause more firescale, oxidization and pits in your casting.
The small propane torch will work, but every thing has to been done as directed if you want to get 100% success rate in your casting. So start with this torch, and make enough money to purchase the Smith torch. As I said, it is the torch that I use for silversmithing and silvercasting, and I always recommend it to my silversmithing and silvercasting students.
Step One: Get the caster ready.
Soak the paper towels in the caster, and squeeze the excess water out by pressing the caster down on top of a soup can.
Step 2: Get ready to cast.
Safely Note: Make sure your fire extinguisher is charged. To do this, take a plastic cup, fill it with water, and keep it handy. Also, you should wear goggles or eye protection. (Actually, I recommend an that you prepare to cast doing the following: Put on an athletic cup, knee pads, elbow pads, back brace, lifting belt and body armor. Then cover all this and yourself with tin foil, especially the top of your head. Then put on one of those fire fighters suits [you know the ones that used to made of asbestos until we found that it hunts us down and attacks us.] Put in ear plugs, followed by those ear protector muffs, and a helmet. Protect your hands with welding gloves and put on steel-toed shoes. Put on light filter glasses followed by goggles. Be sure to put on the best air filtering mask that you can find and hook an oxygen mask to that. Be very careful with the oxygen; we are going to use a torch you know. Oh, the tin foil is so that you can't be detected by aliens as you cast. They are always trying to steal this technology.) Final warning: if you do something stupid, you can injure yourself, burn down your house, your neighbor's house, kill the dog, and/or start a small world war. There, I think I have now covered my tail as far as safety. I sure hope so! Proceed at your own risk!
Cover your table with something that will not burn easily. Plywood, particle board, or any thin metal will be fine.
Step 3: Preheat your metal.
Measure out your metal. You want enough to cast the piece, plus enough to leave a large sprue button in the crucible (sprue button formed by the mound of wax). You want this extra metal for the following reasons:
- I always want the sprue button to be larger than the casting because I want it to be the last thing to cool. I want the casting to cool first. This will allow for any shrinkage problems. As the casting cools, it can draw metal from the larger still molten sprue button. I learned that this is very important when I did a lot of sand casting. I found that large reservoirs of metal decreased the shrinkage in the piece being poured.
- A large sprue button will aid in the metal being forced into the mold. It gives the force that every method of casting must use, something to push against. Therefore, the more metal there is, the more force to push the metal into the mold at a pressure that will decrease porosity. Some people recommend building reservoirs between the sprue button and the wax pattern. This is completely unnecessary if you have a large sprue button. In fact this secondary reservoir can increase porosity by increasing the surface area the silver flows over before entering the mold, and by increasing the turbulence of the metal within the mold.
I preheat the metal so that it will take less time to melt it on top of the flask. This will increase your chances of a good cast because it will give the flask less time to cool down. This will help with the problem of the metal cooling as it is forced into the mold, and as it is cooled by the lower temperature of the investment.
Put on your gloves.
Lighting the torch is easy if you do it right. Do it wrong and it scares you, your neighbor, and your teacher! Follow these steps and you will never be afraid of lighting a torch again.
- Light the lighter.
- Place the lit lighter directly under the torch's tip.
- Slowly turn on the torch--very slowly. If you do not know which way to turn the knob to turn on the torch, follow these instructions: Without trying to light the torch, turn the knob both directions, until you can hear the gas come out. Do this several times until you know which way to turn it on. No, it will not fill the room with gas and blow you up, and no, it will not gas you and kill you. The whole tank could empty in to an average room and not blow up or gas you. It will, however, stink. Now, back to the steps.
- While you are turning the torch on with the lighter under the nozzle, a small fluffy flame will appear first. Leave the lighter on, and keep turning on the torch slowly, until this small fluffy flames "jumps" down into the torch and comes back up as a sharp, short flame. The torch is now lit. The next step is to adjust it to flame about 1 1/2 inch long.
- When the metal is melted and forms a puddle, quickly take the torch off the metal, and sprinkle a little borax on to the puddle.
- Quickly reheat the metal and melt it back into a puddle.
Now is when you must go into high gear and move with quick, concise movements. You may even want to practice this part when everything is cold, before you ever turn on the kiln.
Take the torch off the metal, and set it so that it can safely be kept burning, or have someone hold it for you. The metal will cool and solidify into a red hot button.
Step 8: Set down the tongs and use the tweezers to place the red hot button of metal into the sprue button, which is now going to act as the crucible.
I do this so that the metal heats faster and you can direct the flame at the metal that has not melted, while keeping the flask hot with the torch.
Step 10: As you heat the metal with your left hand (if you are right handed, right hand if you are left handed), grab the caster with your right hand and get ready to cast!
You want to do this very quickly and carefully. It needs to come down straight on to the flask. Hold the caster in place for about five seconds or so. Actually the metal is cast in the first split second that the damp towels touch the hot investment and the steam is created.
A small prayer is OK as you wait.
A note about safety: The reason I use a tuna can is that it is deep enough to prevent molten metal from splattering out. As it goes down on the flask the deep sides of the tuna can go down over the sides of the flask. If any metal were to spray out, it would just drop to the side of the flask and on to the brick. No problems!
Step 13: While you are waiting, get a bucket or some relatively large container and fill it with water.
Do not move it top to bottom in the water, or the casting may fall into the bucket. This is not the worse thing you could do though. It just means you will have to go fishing for it in the bucket! I move it side to side carefully. The water will break up the investment and leave the casting in the flask.
Step 16: Clean and polish it as you would any piece of jewelry.
If enough people would like a quick class on cleaning and polishing castings, let me know, and I will do another section on a cheap and easy way to finish your castings.