Introduction: Backyard Foundry
The Pandemic of 2020 turned me into a metal caster. This is my journey to create 5 brass plaques for a veterans memorial. For a while now I have been forging and making knives. Soon after the Pandemic started and with extra time on my hands, a friend asked if I could make military plaques for our veterans memorial. I knew that it would not be a "walk in the park" and ended up taking about 6 months to perfect my process.
200 lbs Olivine 120 sand https://seattlepotterysupply.com/
10 lbs Bentonite clay https://seattlepotterysupply.com/
Furnace Here is an example. http://media.nbcmontana.com/Dual-Fuel-Metal-Melt...
Pyrometer (not essential but you need to make sure your metal is hot enough)
Phosphor Copper Shot https://www.budgetfoundrysupply.com/phosphor-copper-shot
The following I made from pictures I found on the internet using mostly found materials.
--Sprue cutter Ingot Molds
Step 1: Making Your Tools
Setting up a foundry can be very expensive if you have to buy all of the supplies. If you want an idea of what things cost you can go to Midwest Technology https://www.midwesttechnology.com/teacher-supplies... They have everything you will need. I will try and explain each of the pictures above in roughly the order they appear.
Tongs You will need lifting tongs for removing the crucible from the furnace. The ones pictured are made from bent rebar and some 1 1/2" x 3/16" flat bar welded together. I designed mine for two people because of the size of my crucible and I think it is a little safer. Then you need a regular set of tongs for feeding the metal into the furnace. These are made of rebar as well. You will need to flatten the hinge area and then bolt or rivet together.
Pouring Shank Again this is made from rebar and flat bar. There are a lot of possible designs, dependent on your crucible. I made mine with a safety latch so the crucible can not fall out when pouring. It also requires two people as stated above.
Safety Gear Hot metal is dangerous. Here is a list of what I consider the absolute minimum: face shield, leather apron, natural fiber clothing, welding gloves and leather shoes or boots. The one thing I would like to add is leather chaps that cover your legs and shoes.
Flask This will hold the sand and your mold. It is an easy-to-build item but it has a few things that need to be included. It needs to be big enough to enclose your pattern as well as room for your sprue, runners, gates and risers. It needs alignment pins to accurately locate the molds. It needs something around the inside to provide mechanical grip for the sand. I used metal staples but it is more common to use half round pieces of wood instead. It needs grab handles for moving. It should be color coded so you don't put it together backwards. You will also need top and bottom boards for lifting, moving and flipping the flask.
Plastic containers You will need plastic storage boxes for your sand and supplies. I have one that holds all of my ready-to-use sand and then several others to hold sand waiting to be processed.
Riddle The riddle can be any shape and needs a screened bottom. I find 1/8" hardware cloth to work best. You can usually find it at a hardware store or a bee supply store. A riddle is used to put facing sand on your pattern so you get a smoother finish and don't get any trapped air pockets.
Rammer This is used for packing the sand inside the flask. I turned mine from a piece of fire wood but it can be made from a variety items. The main features are a round flat face and narrower wedge end. The size will depend on the size of your flask.
Scoop This just moves sand. I made mine from a dowel, piece of plywood and a piece of sheet metal.
Sprue cutter Ideally these are tapered but I use a piece of 1" thin wall stainless tubing I had.
Spoon Yes, a kitchen spoon. They sell fancy ones but I don't really see the point.
Striker This removes excess sand and makes a flat surface on the top and bottom of your flask. It can be a piece of wood or I prefer a piece of angle iron.
Skimming tool I made one with rebar and a round piece of metal with holes drilled in it.
Pyrometer This is not essential but if you are having problems with your mold not filling all of the way, one possibility is that the metal is starting out too cold.
Phosphor Copper Shot This is a must-have item for casting brass. (shown in priority box) This reduces porosity (air bubbles) in the metal and increases fluidity (flows better through the mold cavity). This made a noticeable difference in the quality of my castings.
Talc This is what used to be in baby powder but is now considered toxic but you can still get it as Tire Talc. This will be used as parting dust to allow the pattern to be easily removed from the sand mold.
Step 2: Making Green Sand
Cheap Green Sand
It is very simple to make but requires proper mixing and remixing before every pour. I started out by sourcing my own sand from a sandbar and crushing kitty litter to get powdered bentonite. The Forks Strong plaque was made using that sand and you can see the surface finish is rough. I used a cement mixer, 100 lbs. of sand, 10 lbs. of crushed kitty litter and water. Mix everything dry and then slowly add water. It is better to err on the side of not enough water rather than too much.
Better Green Sand
To achieve finer detail I used 200 lbs. of 120 mesh olivine sand, 12 lbs. of bentonite clay and water. I mixed the sand in a muller which I built myself. You can find plenty of how-to videos online. This works very well and gives improved detail. I made the mistake of adding too much water and bentonite to the mix but fortunately I only mixed half my sand before I tested it so I just added plain sand to get the right consistency. I believe because the olivine is so much finer it requires less bentonite to bind everything together.
Not necessary but sure does a nice job. There are lots of how-to videos online, just search "Homebuilt foundry sand muller"
Step 3: Making the Pattern, Mold and Flask
While the idea is simple, the execution is somewhat more complicated. The basic idea is you dig a hole in sand and pour metal into it. You may have seen people pouring molten metal down ant holes but if you want a result that is less random it has to be planned.
Making the pattern
The first thing you need is a pattern. These can be made from lots of materials; many times they are made from wood. I made all of my patterns using a 3d printer. (Designing 3D models is a whole topic on its own and I am not going to talk about that. I recommend Fusion 360.)
All patterns need to be smooth and have a draft angle on them. If they don't, they will not release from the mold properly. I found that the surface of a 3D printed model tends to stick to the sand and I found two ways to smooth the surface without much work. First I tried thinned out white glue sprayed from a spray gun. This worked great but I live in a humid area and, if not kept dry, the mold would get sticky. I finally settled on carefully brushing on epoxy and smoothing with a heat gun.
Make the Flask
Rather than trying to explain how to make a flask, I am just going to give you a link to a video that shows you the process.
Packing the flask to create the Mold
Once you have your pattern, you can begin making your mold. A lot of this process can be seen in the introduction video. First put down a bottom board and bottom flask. You then place the pattern on the bottom board and sprinkle with parting dust (talc in an old sock). You will then riddle sand over the surface of the pattern and bottom board until it is at least 1-2 inch(es) thick. This removes chunks and allows the sand to evenly fill all of the spaces in your pattern. Then lightly add several inches of sand with your scoop. You will then carefully pack the sand, being careful not to cause the pattern to shift in the flask. Continue to do this until the flask is a little over full. You will then strike off the excess sand from the surface with a piece of angle iron or straight piece of wood. You will then repeat the process with the other side of the flask. You can do 2-sided patterns but that will have to be in another Instructable.
Cutting the sprue, pour basin, sprue basin, runners and gates (labeled in picture above)
You will notice in the video that I measure out the placement of everything. In the top flask, cut the sprue with your 1" piece of pipe. Then cut your pour basin. This helps the molten metal to flow down the sprue and not all over the top of your mold. Next, you will need to flip it on its side and add vent holes. For the bottom flask, you need to flip it over. Be sure to put a board on top and flip the top board, flask and bottom board all at the same time. If you watch my video, I forgot to do this and when I flipped it over, the pattern fell out and ruined the mold so I had to repack it.
In the bottom flask, you will now cut in the runner and sprue basin. One of the things you are trying to do is control the turbulence in the metal as it flows into the mold cavity. The sprue basin helps with this. Cut the runner longer than it needs to be so that fast flowing metal and debris will flow past the runner and, again, control turbulence.
When using green sand (sand that uses water instead of oil binder) you need to have vents to allow steam to escape. I poked 4 evenly spaced holes with a screwdriver or you can use an 1/8" rod.
Step 4: Pouring the Metal
This is probably the easiest part of the process but also the most dangerous. This process will be different depending on your furnace.
Set up your furnace and fill your crucible with as much metal as you can. Fire off your furnace and start the melt. Place extra pieces of metal on top of the furnace to preheat them and drive off any moisture. Keep adding metal, as it melts, until the crucible is full. Your metal needs to reach 2200 F. to cast brass properly. At first I used a Venturi burner (from my forge) to fire my furnace but I was only able to reach 2000 F. I ended up adding a blower (see picture) and now I get 2300 F.
Set up your mold. You will want to screw or clamp your flask together or weight it down because steam can cause your mold to split open and leak metal. In the intro video, I use screws and I think, with proper venting, they are adequate.
Once everything is ready, make sure you know what you are going to do, especially if you are working with someone else. I always talk through a dry run. You will need to have your ingot molds preheated and your skimming tool ready and preheated. Turn off your furnace, skim off the dross and add the phosphor copper shot. The ratio is 1 oz. per 100 lbs. My crucible is 25 lbs. so I add 1/4 oz.(7 grams.)
Remove crucible with lifting tongs and set it down in the pouring shank, which should be on a dry flat surface. Pick it up, lock the crucible, move to the mold and pour the metal. You should pour quickly and at a consistent rate. Only stop when the pour basin is full. Pour any excess into the ingot molds.
Empty the mold
You don't have to wait long to empty the mold but just realize that the metal will be really hot. Now would be a good time to take a break and drink your favorite beverage. When emptying the flask, conserving the sand is important, both when packing and unpacking the mold. Everything can be reprocessed and used again, so try not to spill sand on the ground.
Step 5: Clean Up
When you have removed your casting from the sand, you will need to clean the surface. I start with a hand held wire brush and a bucket of water and try to remove as much sand from the casting as I can. Next you will need to remove the runners, gate and sprue from your mold. You could use a hack saw but any blade you use will dull quickly because of sand particles still embedded in the surface. I have found that a cutoff wheel on a 4 inch grinder works best.
After the initial cleaning, what you do next will depend on the object. For my plaques, I sandblasted them to even out the surface and then lightly sanded and polished the tops of the letters. For my bells you will see in the next step, I had to sand them starting at 60 grit and ending at 800 grit. I then took them to the buffer for a final polish.
Step 6: Files and Pictures
Here pictures of some of the things I have created. As well as the files I used to create some of them. Enjoy casting.
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