Sand casting is used extensively for large-scale casting, such as engine blocks, and the grates that one sees around trees in cities on sidewalks, and sand casting used to be the primary method of casting in the jewelry field, and still, in some places, it remains important for larger components and parts, such as one finds on vessels, so sand casting is used in the silversmithing industry still.
One will occasionally find a jeweler who uses sand casting for everyday work, and recently there have been several companies that are selling kits for sand casting using garnets and other materials that supposedly make it easy for the jeweler to use. The primary reason that jewelers in the west don’t use sand casting much anymore, is that sand casting relies upon gravity pour to get the metal into the mold; that is, one has to have a significant weight of metal to force the casting into the recesses and interstices of the mold, and this means that one may have to melt two to three or more times the weight of metal just for the sprue button than is necessary for the cast object itself.
When one melts this much metal, and repeatedly melts it, as one is likely to do once you’ve committed to such a large volume of material, then the likelihood of having oxygen, other gases and impurities build up within the cast material is high, and this will end up in the form of pits and porosity in the castings eventually. So, jewelers switched from this procedure to centrifugal casting, where, in addition a much smaller amount of commitment to metal for the button, there’s also a little more control over surface texture. Sand casting in the old days, could produce surface textures as fine as centrifugal casting does today, but this requires a fair bit of time to set the mold up properly, and centrifugal beats out sand casting for certain kinds of production.
The advantage of sand casting is that the process of preparing the mold, melting the metal, pouring it in, is very quick, so that if you have a sand casting set up, you can go from needing a part, to having the part, in ten to fifteen minutes, whereas with centrifugal, it’s going to be much longer before you have the finished component. In sand casting, what occurs is that a metal model or hard model is made, and this means that you need to have a range of hard models on hand to use for sand casting, and this hard model cannot have any undercuts, or should not have undercuts, because if it does, then you cannot lift it out of the sand, leaving a space to pour the metal into, and this, too, is one of the advantages of centrifugal casting, that wax models can have plenty of undercuts and there’s no trouble with that.
During sand casting, the metal model is placed into a frame, and sand is rammed about it until the frame is full and tightly packed. The sand used is moistened, often with a touch of oil or some type, perhaps glycerin, and this helps hold the sand together. The frame is then flipped the other way up, so that the model is exposed, imbedded in the sand; a second frame is then attached, and sand is rammed into the second frame, usually with a parted powder to separate the second lot of rammed sand from the first, and after everything is solid and tight, the two frames are pulled apart, the metal model is removed, channels are cut into the sand for the molten metal to reach the cavity where the model was, and channels are also cut to allow the air to escape from the model area when the metal is poured in. The frames are then reassembled, carefully; the metal is melted and it is poured into the pouring gate , down the sprues that were cut, into the cavity, thus reproducing the model around which the sand was rammed in the first place.
Procedure layout. gas handling because you’re dealing with torches. If you’re using electric equipment such as an induction melting crucible or a kiln to melt the metal, then issues of electrocution and electrical fire are present. The gas handling, of course, carries with it risks of explosion, fire, an oxygen tank knocked over, shooting about the room, and so on. Burns are a hazard, because one is dealing with hot materials. There are fume hazards from the metals, alloys and fluxes used to melt and pour into the sand.
The binders in the sand may be quite toxic, and when hot metal hits them, can generate toxic fumes, so good local ventilation is necessary when doing sand casting. In the past, some sand casting has been done using styrofoam models, where a styrofoam model is prepared, the sand is rammed about it from all directions, and the metal is poured down a casting gate. When the hot metal reaches the styrofoam model, it burns it and replaces it in the sand, thus producing a copy of whatever was made in styrofoam. The fumes from doing this are extremely toxic; this is no longer recommended as a procedure because of the poisonous fumes generated and the pollution hazard of these fumes, as well as the health problems related to them.
Primarily decomposition products and fumes from the metals, the fluxes used to melt, and possibly from the binder used in the sand. Mexican goldsmiths, for instance, will make their own mixtures of casting sand, using Portland cement and motor oil as the binder. The fumes from motor oil would have the potential to be damaging as well. You will have to find out what the binder is in your particular sand, obtain the MSDS sheet for it in order to really know what has gone into it. Certain kinds of sand contain something called furam, which produces a hard, carvable sand once the sand is bound together, and hot metal hitting furam can produce some really quite toxic fumes. Furam, too, may cause damage by skin contact, and so, depending on what the binder is in your sand, you may consider using skin protection.
Tripping, fire safety, materials flying into the eyes by accident, moving about the room with molten metal in crucibles that can pour on you. Those types of hazards.
In a production situation, you’d have to examine the workplace carefully to avoid ergonomic problems; this has largely to do with working height, easy access, and so on.
Electric equipment carries with it fire hazards. Gas equipment for melting metal also has significant fire hazards, and it is essential to maintain a proper maintenance schedule, to check all joints with soapy water, and to make sure there are no flammable materials anywhere near the melting area, and to follow other fire precautions. Fireproof clothing is a good thing to wear when doing a casting, and to avoid burns from molten metal falling onto the shoes, metal shoe covers can be a good idea, particularly if larger quantities of metal are being melted and dealt with.
Skin contact, both for any potential chemicals used as binders in the sand, and for burns and so on. Eyes – it’s a good idea to wear eye protection, whenever around things that can fly through the air or accidentally be flung about. Inhalation of chemical fumes and metal fumes.
Careful layout of studio and procedure, fireproof clothing, eye protection, skin protection, if concerned about the binder used in the sand, eye protection from the radiation – infrared radiation and ultraviolet radiation from melting – good local ventilation for fumes from melting and from the binding material in the sand.
Other forms of casting, centrifugal and so on. These other forms of casting carry with them their own risks. Avoid furam-containing sand for casting, and choose the least unpleasant binder possible: glycerin, for instance, would not be too evil as a binding agent.