Keresztfej

Keresztfej, or crosshead, is a mechanical component used in certain reciprocating engines and steam locomotives to connect the piston rod to the connecting rod while maintaining alignment and guiding motion. Its primary purpose is to translate the linear motion of the piston into the angular motion of the connecting rod and to transfer thrust while controlling side forces.

In construction, a keresztfej typically consists of a block or shoe that slides along fixed guides within the engine frame. The piston rod is attached to the crosshead by a gudgeon pin or similar joint, while the crosshead itself connects to the connecting rod. The assembly is usually lubricated to reduce wear, as the crosshead experiences high loading during operation. Guide surfaces and lubrication are essential to minimize friction and wear on the sliding interfaces.

There are variations in design, including sliding crossheads and box or shoe-type crossheads, with different guide arrangements depending on engine size and type. The crosshead arrangement is particularly common in large stationary engines, marine engines, and early steam locomotives, where straight-line guidance of the piston rod was advantageous for reducing bending moments on the rod and aligning with the connecting rod.

Historically, the keresztfej played a key role in the development of high-power steam engines and locomotives in the 19th and early 20th centuries. Modern engine design has shifted toward crankshaft and connecting rod configurations that reduce the need for a separate crosshead, though crossheads remain in some older or specialized machinery and in heritage engines.