Foundry Equipment, Etc.
Crucibles, Pouring Rings, Pouring Shank & Lift Tongs
In an effort to provide more fodder for heated argument, I will go so far as to say that steel crucibles should be used with great caution. In truth, I believe steel crucibles have no place when casting aluminum. Quite simply, the corrosive nature of molten aluminum creates so many problems that steel crucibles are really only good for melting and pouring large volumes of ingot material. However, when it comes time to cast your molds “for real”, a proper set of foundry crucibles is a must in my opinion.
There are basically two types of foundry crucibles available that are of use to the hobby foundryman. Most common are the clay-graphite crucible and the more specialized yet more durable is a silicon carbide crucible.
Clay-graphite is a relatively inexpensive material that is particularly suited for melting many non-ferrous alloys and they are readily available for fairly little investment from several online sources (see the links section for supplier suggestions). One down-side to clay-graphite crucibles is that they require tempering before use and they are somewhat delicate and don’t tolerate rough treatment very well. One advantage to them is that they can be reliably checked for cracking by “ringing” them before use. Ringing a crucible basically involves a gentle blow to the side of the crucible with a soft-faced instrument (like a wooden hammer handle) and listening to the “ring” the crucible demonstrates. If it rings sharp and true (like a bell), the crucible can be expected to perform properly. If the crucible rings dull and muted, the crucible is damaged and should be immediately discarded.
Silicon carbide material is considerably more expensive than clay-graphite, but it has many advantages. First, silicon carbide is considerably more durable and handles rough treatment much better than clay-graphite. Another advantage is that silicon carbide crucibles can be used with most metal alloys commonly found in the home foundry (ferrous and non-ferrous). Also, while these crucibles need to be fired once before use, they don’t really require tempering like a clay-graphite crucible. Finally, as with clay-graphite, a silicon carbide crucible can be “ring checked” for integrity but the results can be somewhat less reliable. One significant negative to silicon carbide crucibles is their cost. In most markets, silicon carbide crucibles run about two to three times more expensive than a comparable clay-graphite crucible.
No matter which crucible material you choose, two things should be firmly established in your mind before you start: 1) Crucibles are consumables and should be treated as such. They have a finite life and any attempt to ignore this is an invitation to potential disaster/injury as a result of a spilled load of molten metal. Ring your crucibles before each use, visually inspect them before each pour, treat them gently and store them in a safe and secure location between uses and they should provide a good, long service life. 2) Only melt one type of metal in each crucible………forever. In other words, if the first metal you melt in your new crucible is aluminum, then that crucible should only be used to melt aluminum for its entire service life.
Pattern Filler/Fillet Materials
Pattern filler materials are an area of constant experimentation for me. The ability to form nice, smooth fillets and fill pattern seams and other imperfections is a nice addition to your pattern making arsenal. However, of the many techniques that I have tried (particularly with lost foam metal casting or LFMC) the best overall filler material I have found is a wax/lemon oil mixture.
The basic filler wax formula I use is as follows:
100g White Beeswax
100g Plain Toilet Ring Wax
8-12g Lemon Oil Polish
Combine the waxes in a double boiler and gently melt until the wax is completely fluid and clear. Slowly add the lemon oil polish and stir the mixture well. Remove from heat and pour the wax into an appropriate mold (like an old ice tray) and let it harden.
This filler wax can be applied in a number of ways. I prefer to soften small batches in a double-boiler arrangement and pour/spoon it into a large plastic syringe. While the wax is soft, the syringe will act like a caulking gun and apply wax right where you want it. Once the wax is on the pattern, smooth and shape it will blunt tools (I like a “ball-on-a-stick” tool) and let it set firmly. The wax will remain pretty workable right up until the time comes to pour the mold. Be careful to use wax sparingly in LFMC patterns as the wax outgases when melted and will ruin a casting if applied too thick. On wood patterns, be aware that the wax has an affinity for molding sand and will foul the mold when the pattern is pulled unless the wax is sealed. Try coating the wax with shellac to avoid this problem.
Here is a manifold pattern that clearly shows how wax fillets can be used. The dark yellow areas on this foam pattern are made with the wax formula above and formed with simple wooden wax carving tools. I discovered that the wax fillets I used on the large flange were too large after fouling the casting because of outgassing from the wax. The lesson: Use fillet wax sparingly.
Foundry Furnace Pyrometer
Here are a few shots of my furnace pyrometer. I haven't quite completed it in these photos (the wooden handle/VOM carrier is not shown), but it works very well. I used 1/2" black pipe for the structure and modified a pipe bushing in my lathe to create a secure mount for the MIFCO thermocouple. The thermocouple wires pass through the pipe to the handle and are terminated with a standard type K thermocouple terminal that plugs right in to my digital VOM.
Ingot Mold
Here is a shot of one of my cast iron ingot molds. It's simply a cast iron baking pan for muffins and I got in on eBay for under $10. This mold is pretty thin and I don't expect it to last very long, but it makes nice ingots nonetheless. If you're shopping for cast iron cookware for ingot molds, look for products made by Lodge. Lodge is the heaviest cast iron cookware I have ever found and should last a lifetime even in foundry use.