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Ingots are uniform masses of metal cast from molten metal with known physical properties and used for storage and transportation. The molds used for casting ingots determine their physical and metallurgical characteristics, and they are typically cast in the production stage of the foundry. Ingots are commonly used for a variety of metals, including gold, silver, platinum, tin, lead, aluminum, steel, and cast iron.
Ingot is a term applied rather loosely to any mass of metal specifically cast from a molten state of known physical composition, weight, shape and size. This uniformity is intended to help account for the quantities of metal that are cast, stored, or transported. A multitude of metals are commonly smelted in ingot form including gold, silver, platinum and tin. Ingot designs include a wide variety of shapes and sizes defined by the intended function and metallurgical requirements of the final product.
Metals have been smelted into forms with known characteristics for as long as metallurgy has existed. From the ancient Chinese sycee to the gold, silver and lead bars of the Roman Empire, the ingot was an accepted method of presenting precious metals for storage and transportation. The practice of casting metals into standardized forms continues today with the vast majority of metal products starting life as bullion. The main motivators behind the practice are the accounting and logistical benefits of producing products of a uniform character. Each ingot consists of a mass of metal of a known composition, size, shape and weight which facilitates registration, storage and transportation.
The molds used for this purpose are more than just containers for cooling molten metal. The physical characteristics of the finished ingot at the atomic level will depend on how the molds are designed. The crystalline structure and integrity of the finished product depend on the distribution of alloy additives, gases and impurities during cooling, a process that is largely dictated by the design of the mold. The mold designs are then formulated to produce an ingot that is not only physically practical but metallurgically compatible with the intended end use. These considerations will determine the shape, internal surface area and dimensions of the mold, as well as the location of the mold fill port.
Ingots are typically cast in the production stage of the foundry. Molten metal is typically poured directly from the furnace into pre-prepared molds in one step or in a continuous process. Once the molten metal has solidified to the point that it can be manipulated, the finished object is ejected from the mold. From there it is typically moved to a clean-up area where surface contaminants such as slag, mold grit and lubricants are removed. The ingot is then marked, if the process requires it, and moved into memory.
Most metals and alloys intended for sale or manufacturing processes are cast into ingots. These include gold, silver, tin, platinum, lead, aluminum, steel and cast iron. Most bars are formed as basic oblong shapes with tapered sides, although their design may differ to meet transportation, storage, or manufacturing process requirements. Depending on their intended end use, their weight can range from a couple of ounces to a hundred tons or more.
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