Shaft forgings are a type of free forging in the forging process. They are mechanical parts used to support rotating parts and rotate with them to transmit motion, torque, or bending moment.

Classification

By structural shape:

Plain shaft: Has a single diameter outer cylindrical surface, simple structure.

Stepped shaft: The shaft has multiple outer cylindrical surfaces with different diameters, which can be used to install parts with different diameters.

Hollow shaft: Has an internal hole, which can save material, reduce weight, and allow the medium to pass through.

Special-shaped shaft: Includes crankshafts, camshafts, and eccentric shafts, etc., with special shapes and functions.

By load-bearing conditions:

Journal: Works under both bending moment and torque, such as shafts in various reducers.
Spindle: Used to support rotating parts, only bears bending moment without transmitting torque. It can be divided into rotating spindles (such as the axles of railway vehicles) and fixed spindles (such as the axles supporting pulleys).

Transmission shaft: Mainly used to transmit torque without bearing bending moment, such as the long plain shaft in the lifting mechanism of a crane and the drive shaft of a car.

By the ratio of length and diameter:

Rigid shaft: The ratio of shaft length to diameter is less than 12, with high rigidity.

Flexible shaft: The ratio of shaft length to diameter is greater than 12, with certain flexibility.

Material

Carbon steel: Such as 35, 45, 50 high-quality carbon steel, 45 steel is widely used. Ordinary carbon steel such as Q235 and Q255 can be used for shafts with smaller loads or less importance.

Alloy steel: Can be used for shafts with large loads, limited axial dimensions and weight, or special requirements. For example, 40Cr alloy steel is used in medium-precision, high-speed applications; Cr15, 65Mn, etc., are used in high-precision, harsh working conditions; 20Cr, 20CrMnTi, 20Mn2B low-carbon steel or 38CrMoA1A carburizing steel are used for shaft parts working under high-speed and heavy-load conditions.

Ductile iron, high-strength cast iron: Good casting performance and vibration damping performance, often used to manufacture shafts with complex outer shapes.

Technical requirements

Dimensional accuracy: The journal diameter accuracy is usually IT6~IT9 grade according to the usage requirements, and the precision journal can reach IT5 grade. The shaft length is usually specified as the nominal size, and the length of each step of the stepped shaft is given with tolerances according to the usage requirements.

Geometric shape accuracy: The geometric shape accuracy (roundness, cylindricity) of the journal should generally be limited within the diameter tolerance. When higher accuracy is required, the allowable tolerance can be specified separately on the part drawing.

Relative position accuracy: The coaxiality between the mating journal and the supporting journal is a common requirement. The radial runout of the mating journal relative to the supporting journal of ordinary precision shafts is generally 0.01~0.03mm, and that of high-precision shafts is usually 0.001~0.005mm.

Application fields

Wind power industry	Shipbuilding	Mechanical manufacturing
Nuclear power industry	Oilfield industry	Chemical industry