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Castings are molded substances that form the basic parts of all kinds of metal products, from heavy machinery to automobile engines to household appliances. More than a dozen types of metal molding and casting processes exist. The traditional, and still most common method of producing cast-to-shape pieces, is sand casting. Technological advancements in recent years, however, have made alternative casting methods such as evaporative, investment, and no-bake casting increasingly attractive because of their cost-effectiveness.
Sand molders, as they are also called, work in foundries that produce castings from iron, steel, and nonferrous metals (i.e., alloys that contain no appreciable amounts of iron). Traditional, manual sand casting begins with the preparation of a mold, which the worker creates from specially treated sand. In the green sand molding method, the molder packs and rams a mixture of sand, clay, and chemicals around a pattern (a model of the object to be duplicated) in a molding box called a flask. Flasks are usually made in two parts, which are separated to allow removal of the pattern without damaging the mold cavity.
A mold is created by following a series of specific steps. After positioning the drag (lower) half of the pattern and flask, the molder sprays it with a parting agent and places reinforcing wire in the flask. Sand is sifted over the pattern and pressed into its contours. Then the molder shovels sand into the flask and packs it in place with hand ramming tools or a pneumatic hammer. With this completed, the molder positions the cope (top) half of the pattern and flask on the drag half and repeats the procedure.
The process of making a casting continues with the separation of the drag and cope and the removal of the pattern. The molder then cuts a hole in the mold through which the liquid metal will be poured. Next, the molder positions a core in the cavity left by the pattern (to produce a hollow casting), reassembles the flask, and pours molten metal into the mold. When the metal cools and solidifies, the casting is removed and the mold is cleaned. Many of the final steps that involve cleaning and assembling molds are often performed by workers known as mold closers or finish molders.
Although a few foundries still construct molds using the traditional manual methods, most molds today are made by machines that pack and ram the sand mechanically. Machines make it possible to turn out large quantities of identical sand molds quickly, simply, and more cost efficiently. Workers who operate these machines are called machine molders or machine line molders, and it is their job to set up the machine, to control the pressure applied to the sand by working the pedals and levers, and to cut pouring spouts in the mold. In addition to this, machine molders assemble the flask and pattern on the machine table and fill the flask with the prepared sand mixture. The workers who operate the machines that pack the sand into the flask are called sand-slinger operators.
In the foundries that still use manual methods, hand molders compact the sand around the pattern with hand tools such as trowels and hand rammers and with power tools such as pneumatic rammers and squeeze plates. Molds for small castings, such as jewelry, are usually made on a workbench by bench molders, while those for large, bulky castings are made on the foundry floor by floor molders. Some molders are skilled in making many different kinds of molds; other molders specialize in only a few types.