When designing the crankshaft of a reciprocating machine, the following key factors need to be considered:

Strength and stiffness

Strength: The crankshaft is subjected to complex alternating loads during operation, including gas pressure generated by the reciprocating motion of the piston, reciprocating inertial forces, and rotational inertial forces. Therefore, it is necessary to have sufficient strength to prevent failure forms such as fatigue fracture during long-term operation. The selection of materials is crucial, usually using medium carbon steel or medium carbon alloy steel such as 45 steel, 40Cr, etc., and improving their strength and toughness through appropriate heat treatment processes.

Stiffness: The stiffness of the crankshaft is equally important. If the stiffness is insufficient, it can cause excessive deformation of the crankshaft under stress, affecting the normal movement of components such as pistons and connecting rods, thereby affecting the working accuracy and efficiency of the reciprocating machine, and may also cause uneven wear of various bearing parts. When designing, it is necessary to reasonably determine the journal size of the crankshaft, the thickness and length of the crank arm, and other parameters to ensure that it has sufficient bending and torsional stiffness.

Balance characteristic: When the reciprocating machine is working, the rotation of the crankshaft will generate unbalanced inertia force and inertia moment, which not only causes vibration of the machine, but also increases the load on the bearings, reducing the stability and service life of the machine. Therefore, when designing a crankshaft, balance measures need to be taken, such as setting balance weights on the crank arm. By reasonably calculating and arranging the mass and position of the balance weights, the unbalanced inertia force and inertia moment of the crankshaft can be minimized as much as possible.

Wear resistance and corrosion resistance

Wear resistance: The joint between the crankshaft journal and the bearing has a high relative motion speed and is subjected to significant pressure, making it prone to wear. To improve wear resistance, in addition to selecting suitable materials, it is also necessary to harden the surface of the journal, such as quenching, nitriding, etc., to increase surface hardness, and adopt good lubrication measures to reduce friction and wear.

Corrosion resistance: In some working environments, the crankshaft may come into contact with corrosive media, such as in environments with moisture or chemical gases. Therefore, it is necessary to consider the corrosion resistance of the material or to carry out anti-corrosion treatment on the surface of the crankshaft, such as coating with anti-corrosion coatings, to prevent the crankshaft from being corroded and reducing its performance and lifespan.

Processing processability: The structure of the crankshaft is complex and difficult to process, so its processing processability should be considered in the design to facilitate manufacturing and ensure processing accuracy. Efforts should be made to simplify the structure of the crankshaft, reduce machining processes and difficulties, design machining benchmarks and tolerance requirements reasonably, and ensure efficient and high-quality machining of crankshafts that meet requirements under existing machining equipment and process conditions.