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a shaft consisting of one or more cranks and several coaxial crank journals resting on bearings.
Each crank of the crankshaft has two flanges and a journal for attaching a connecting rod. The axes of a crankpin are displaced relative to the axis of rotation of the crankshaft. In order to balance the crankshaft in operation, the flanges often have counterweights. The crankshaft is the rotating unit of a crank gear; it is used in piston engines, pumps, compressors, and forging and pressing machinery. In piston engines, the number of cranks on the crankshaft is usually equal to the number of cylinders, the arrangement of the cranks depends on the operating cycle and the conditions for counterbalancing the engine and arranging the cylinders.
Crankshafts are made whole, cast, or forged of carbon steel and alloy steel or high-strength cast iron. However, since antifriction bearings cannot be used with whole crankshafts, built-up crankshafts are sometimes made. Depending on production conditions, large crankshafts (journal diameter, to 1 m) can also be of built-up design. The simplest crankshafts to produce are those in which the axes of all of the crankpins are located in a single plane. The simplest crankshaft is the crank.