Definition and Function

The intermediate shaft is an important component of the ship's shaft system, connecting the main engine and propeller shaft (stern shaft) of the ship. Its main function is to transmit the torque generated by the main engine, smoothly transfer the power from the main engine to the propeller, and make the propeller rotate to push the ship forward or backward. In this power transmission process, the intermediate shaft plays a role in extending the power transmission path, buffering vibration, and compensating for shaft installation errors.

Structural characteristics

Shaft body: The shaft body of the intermediate shaft is usually made of high-quality alloy steel, such as 40Cr, 35CrMo, etc. These alloy steels have high strength, toughness, and wear resistance, and can withstand the huge torque transmitted from the host. The surface smoothness of the shaft body is required to be high, usually through grinding and other processing procedures to reduce friction loss during rotation and better match with the bearing.

Connection section:

The connecting parts at both ends are the key structure of the intermediate shaft. It usually adopts flange connection, with bolt holes on the flange for connecting with the flange of the main engine output shaft and stern shaft. The size of the flange and the specifications of the bolts need to be determined based on the torque transmitted by the intermediate shaft to ensure the reliability of the connection. When connecting flanges, it is necessary to ensure the accuracy of the fit between the flanges and use high-strength bolts and suitable gaskets to prevent loosening or leakage during operation.

Some intermediate shafts may also be connected by couplings, such as elastic couplings. Elastic couplings can compensate for axial, radial, and angular displacements of the shaft system to a certain extent, while also buffering vibrations transmitted from the main engine, reducing damage to the shaft system and ship equipment.

working principle

When the ship's main engine starts and outputs torque, the torque is transmitted to the shaft of the intermediate shaft through the connecting structure (flange or coupling) at both ends of the intermediate shaft. The shaft transmits torque along its own axis direction to the connected stern shaft, which drives the propeller to rotate. During this process, the rotational motion of the intermediate shaft itself is relatively stable, thanks to its excellent material properties and manufacturing process. For example, its alloy steel shaft body can effectively resist torsional stress, while a suitable connection structure ensures stable transmission of power. At the same time, the intermediate shaft to some extent isolates the vibration transmission between the main engine and the propeller, reducing the impact of vibration on the entire shaft system through its own elastic deformation (if an elastic coupling is used) or reasonable structural design.

advantage

Stable and efficient power transmission: Through reasonable structural design and high-quality materials, the intermediate shaft can stably transmit the huge torque generated by the main engine, ensuring that the propeller obtains sufficient power to propel the ship. Its stable power transmission characteristics help improve the propulsion efficiency of ships and reduce energy losses.

Enhance the integrity and adaptability of the shaft system: It connects the main engine and stern shaft, making the shaft system an organic whole. Moreover, by adopting appropriate connection methods (such as elastic couplings), the intermediate shaft can adapt to some small errors in the installation process of the shaft system, and also provide certain buffering and compensation for the vibration, deformation, and other situations of the ship during navigation, improving the adaptability and reliability of the shaft system.

Disadvantages and countermeasures

Easy to cause fatigue damage: Due to the long-term exposure of the intermediate shaft to alternating torque transmitted by the main engine, fatigue cracks are prone to occur on the surface or connection parts of the shaft body. The response measures include precise strength calculations and fatigue analysis during the design phase, as well as reasonable selection of shaft dimensions and materials; Strictly control the processing quality during the manufacturing process, such as surface roughness, heat treatment quality, etc; During use, regular non-destructive testing (such as ultrasonic testing, magnetic particle testing, etc.) should be conducted on the intermediate shaft to promptly detect and address fatigue cracks.

High requirements for installation and alignment: The installation accuracy of the intermediate shaft directly affects the normal operation of the shaft system. If the alignment between the intermediate shaft, the output shaft of the main engine, and the stern shaft is not good, it will cause significant vibration, eccentric wear, and other problems in the shaft system during operation. During the installation process, it is necessary to use professional alignment tools and measuring equipment, strictly follow the installation standards for operation, and conduct careful debugging and inspection after installation.

Application scenarios

Ship power system: In the power systems of various types of ships (including cargo ships, passenger ships, warships, oil tankers, etc.), the intermediate shaft is an essential component. It serves as a bridge between the main engine and propeller of the ship, ensuring stable propulsion power and normal navigation.