Casting is the process of production of objects by pouring molten material in to a cavity called a mold which is the negative of the object, and allowing it to cool and solidify. Sand casting is a means of producing rough metal castings using a mold usually made from sand formed around a replica of the object to be cast that is removed once the sand has been compacted. Castings made by this process can be further refined by any or all of hammer peening, shot peening, polishing, forging, plating, rough grinding, machine grinding or machining. Sand castings not further worked by polishing or peening are readily recognized by the sand-like texture imparted by the mold. As the accuracy of the casting is limited by imperfections in the mold making process there will be extra material to be removed by grinding or machining, more than is required by other more accurate casting processes. Furthermore, because the mold is destroyed in order to retrieve the object, a new mold must be made for each casting

From the design, provided by an engineer or designer, a skilled patternmaker builds a pattern of the object to be produced, using wood, metal, or plastic; other materials to be used can be polystyrene or even sand strickled into shape. The metal to be cast will contract during solidification, and this may be non-uniform due to uneven cooling. Therefore, the pattern must be slightly larger than the finished product, a difference known as contraction allowance. Patternmakers are able to produce suitable patterns using 'Contraction rules'. Different scaled rules are used for different metals because different metals / alloys contract at different rates. Patterns also have coreprints; these create registers within the molds, into which are placed Sand cores. Sand cores are used to create under cut profiles and holes which cannot be molded

A multi-part molding box (known as a casting flask, the top and bottom halves of which are known respectively as the cope and drag) is prepared to receive the pattern. Molding boxes are made in segments that may be latched to each other and to end closures. For a simple object-flat on one side-the lower portion of the box, closed at the bottom, will be filled with prepared casting sand or green sand-a slightly moist mixture of sand and clay. The sand is packed in through a vibratory process called ramming and, in this case, periodically screeded level. The surface of the sand may then be stabilized with a sizing compound. The pattern is placed on the sand and another molding box segment is added. Additional sand is rammed over and around the pattern. Finally a cover is placed on the box and it is turned and unlatched, so that the halves of the mold may be parted and the pattern with its sprue and vent patterns removed. Additional sizing may be added and any defects introduced by the removal of the pattern are corrected. The box is closed again. This forms a "green" mold which must be dried to receive the hot metal. If the mold is not sufficiently dried a steam explosion can occur that can throw molten metal about. In some cases, the sand may be oiled instead of moistened, which makes possible casting without waiting for the sand to dry. Sand may also be bonded by chemical binders, such as furane resins or amine-hardened resins.

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If it is desired to have most of the-iron or steel-casting in a tough, ductile, state but with a few surfaces hard, it is possible to place metal plates-chills- in the mold, where the metal is to be hardened. The associated rapid local cooling will form a finer-grained and harder metal at these locations. The effect is similar to quenching metals in forge work. The inner diameter of an engine cylinder is made hard by a chilling core.

To produce cavities within the casting-such as for liquid cooling in engine blocks and cylinder heads-negative forms are used to produce cores. Usually sand-molded, cores are inserted into the casting box after removal of the pattern. Whenever possible, designs are made that avoid the use of cores, due to the additional set-up time and thus greater cost.Two sets of castings (bronze and aluminium) from the above sand moldWith a completed mold at the appropriate moisture content, the box containing the sand mold is then positioned for filling with molten metal-typically iron, steel, bronze, brass, aluminum, magnesium alloys, or various pot metal alloys, which often include lead, tin, and zinc. After filling with liquid metal the box is set aside until the metal is sufficiently cool to be strong. The sand is then removed revealing a rough casting that, in the case of iron or steel, may still be glowing red. When casting with metals like iron or lead, which are significantly heavier than the casting sand, the casting flask is often covered with a heavy plate to prevent a problem known as floating the mold. Floating the mold occurs when the pressure of the metal pushes the sand above the mold cavity out of shape, causing the casting to fail.