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Cores are used in manufacturing metal castings that have hollow centers, such as pipes and tubes. The core establishes the open area in the object. Cores for almost any metal casting are produced using the same basic procedures. Cores may be large or small, and can be made by hand or by machine. Bench coremakers, for example, work at benches making smaller cores, usually by hand. In contrast, floor coremakers make large cores on the floor of a foundry.
In general, coremakers begin their work by cleaning a core box with blasts of compressed air. A core box is often a block of wood or metal hollowed out to the shape of the desired core. After it is cleaned, coremakers dust fine sand over the interior of the core box so that the finished core will not stick to the box, but instead will slip out easily. Then they partially fill the box with sand or a sand mixture. They may do this either by hand or with the help of machines. They tightly pack the sand into the box, using hand or power tamping tools. Periodically, when the core sand reaches certain levels in the box, they may insert wires that have been bent to the proper shape to add strength to the core. Special care is taken to ram the sand solidly and compactly into the core box so there will be no air pockets or other weaknesses in the finished core. The box is then inverted on a flat surface and lifted off of the core. Any cracks or chips on the core are repaired or smoothed out. Cores may be baked to harden them before they are used in making metal castings.
Machine coremakers, who usually work in large factories where many identical parts must be produced, operate various types of machines that make sand cores. Other workers involved in the process include core checkers, who verify core sizes and shapes; core-oven tenders, who regulate and maintain correct oven temperatures to harden cores; core setters, who position finished cores in molds before the molten metal is poured in to make castings; and coreroom foundry laborers, who assist coremakers by hauling sand, applying graphite solutions, and transporting cores to and from ovens.