A cylindrical piece of metal that guides the piston to reciprocate in a straight line in a cylinder. Air in the engine cylinder expands to convert heat energy into mechanical energy; The gas receives piston compression in the compressor cylinder and increases the pressure. The housing of a turbine, rotary piston engine, etc., is also called a cylinder. Cylinder applications: printing (tension control), semiconductor (spot welder, chip grinding), automatic control, robotics, etc.