What's New?

The structure of crankshaft generally consists of main journal, connecting rod journal, crank, counterweight, front end and rear end.

Crankshaft cooperates with the connecting rod to convert the gas pressure acting on the piston into rotational power, which is transmitted to the transmission mechanism of the chassis. Meanwhile, the other auxiliary devices such as fan, water pump, alternator, etc are driven. When working, crankshaft bears gas pressure, inertia force and inertia moment. The force is large and complex, and it bears the impact of alternating loads. Crankshaft is also a high-speed rotating part. Therefore, crankshaft is required to have sufficient stiffness and strength, good ability to withstand impact loads, wear resistance and good lubrication.

To avoid journal worn and fatigue fracture and ensure the crankshaft works in good condition and have a longer life, suitable materials and strengthen process technology and machining technology in the manufacturing process are necessary.

Materials are required to have high strength, impact toughness, fatigue strength and wear resistance. Commonly used materials include: steel #35 1035 (060A35), #40 1040 (1.1186), #45 1045 (S45C) or ductile iron QT600-2 for general crankshafts; 40Cr, 42Mn2V and other materials can be used for crankshaft for high-speed engines and heavy-duty vehicles.

There are very high requirements on crankshaft's dimensional accuracy, machined surface shape accuracy and position accuracy. But its stiffness is relatively poor and prone to deformation, which brings many difficulties to the machining of crankshafts. The surfaces that need machining include main journal, connecting rod journal, keyway, and the excircle. According to the structural characteristics of the crankshaft and the requirements for machining, the machining processes can be roughly summarized as milling the two end faces, drilling oilway holes, roughing and finishing the journals, roughing and finishing the excircle. Precision grinding of connecting rod journal, main journal and excircle etc.

Heat treatment is the most commonly used method to improve crankshaft performance . Common heat treatments include the following methods.

Carbon steel crankshaft forgings should be normalized and annealed after rough machining.

Alloy steel crankshaft forgings are annealed first, and then quenched and tempered after rough machining. If it needs higher hardness for journal surface, surface quenching or nitriding treatment can be used.

The ductile iron crankshaft is normalized and annealed after rough machining. The hardness is HB220~229. If it needs higher hardness for journal surface, high-frequency quenching can be used.

Generally speaking, due to poor hardenability, carbon steel crankshafts use final normalizing instead of quenching and tempering, which can also eliminate structural defects and improve cutting performance. Alloy steels mainly use quenching and tempering to obtain tempered sorbite that meets comprehensive mechanical properties.