Burn Out
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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.
I fold them in half, making four wires
and twist them together at the fold
This makes what I call a "quad pod"
I cut these four 18 gauge wires off to about 1/4 inch
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.
Burn Out
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.
Cut a thick wire coat hanger apart and bend it into a handle. Bend it in half, and then in half again
About three inches from the loose ends, bend them at a 90 degree angle, then bend them back again to the center
Bend them down straight again
Put the loose ends through the pot, put the handle tight, and bend the loose end at 90 degrees again inside the pot. Spread the handle a little and you are all set.
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.
Caution: the kiln and the wire handle are hot enough to burn you!
After two hours of burn out, it is ready to cast, which will be covered in Steam Casting #6 - Casting.