Definition and Function

Definition: The intermediate bearing is an important component in the ship's shaft system. It is installed on the intermediate shaft between the ship's main engine and stern shaft, mainly used to support the intermediate shaft, reduce the span of the shaft system, and bear the radial force generated by the intermediate shaft during operation, ensuring that the intermediate shaft can rotate stably and effectively transmit the power of the ship's main engine to the stern shaft and propeller.

Function:

Supporting function: The intermediate bearing bears part of the weight of the intermediate shaft, preventing excessive bending deformation of the intermediate shaft due to its own gravity. By setting reasonable support spacing, the deformation of the intermediate shaft can be controlled within the allowable range, ensuring the geometric stability of the shaft system and facilitating its normal operation.

Radial force bearing function: When the ship's main engine outputs power to rotate the intermediate shaft, the intermediate shaft will be subjected to radial forces generated by various factors, such as the imbalance of the shaft system itself and the hydrodynamic effect of the propeller. The intermediate bearing can effectively withstand these radial forces, avoid collisions and friction between the intermediate shaft and adjacent components, and ensure the stable position of the intermediate shaft in the radial direction.

Reduce vibration transmission function: The intermediate bearing can also isolate and reduce the vibration transmitted from the main engine to the stern shaft to a certain extent, reducing the vibration level of the shaft system. This is because the internal structure and lubrication state of the bearing can absorb and buffer some vibration energy, improving the working stability of the shaft system.

Structural composition

Bearing body:

Shell part: The shell of the intermediate bearing is generally made of cast iron or cast steel, with sufficient strength and stiffness to withstand various forces transmitted from the intermediate shaft, and provide protection and installation foundation for the internal bearing components. The shape of the shell is usually cylindrical, and there may be mounting ears or flanges on the outside to secure the intermediate bearings to the base of the ship.

Internal structure: There are bearing bushings or rolling element tracks inside (if it is a rolling bearing). The bearing liner is usually made of wear-resistant materials such as Babbitt alloy, copper alloy, etc. Babbitt alloy lining has good anti friction and wear resistance, and can adapt to the rotation requirements of the intermediate shaft; Copper alloy bushings perform well in terms of corrosion resistance and thermal conductivity. For intermediate bearings of rolling bearing type, there are inner rings, outer rings, rolling elements (balls or rollers) and retainers inside. The inner ring is tightly matched with the intermediate shaft, and the outer ring is fixed inside the bearing body. The rolling elements roll between the inner and outer rings, and the retainers are used to separate and fix the rolling elements.

Lubrication system:

The lubrication system is crucial for the normal operation of the intermediate bearing. There are two main lubrication methods: oil lubrication and grease lubrication. The oil lubrication system includes oil cups, oil tanks, or centralized lubrication devices, through which lubricating oil is delivered to the gap between the bearing and the intermediate shaft, forming an oil film and reducing the friction coefficient. Lubricating grease is the process of filling the interior of a bearing with lubricating grease and bringing it to the parts that require lubrication through the rotation of rolling elements or intermediate shafts.

Sealing device:

The sealing device of the intermediate bearing is mainly used to prevent the leakage of lubricating oil or grease, as well as to prevent external impurities (such as seawater, dust, etc.) from entering the interior of the bearing. Common sealing forms include rubber seals and labyrinth seals. Rubber seals use their elastic deformation to fill the sealing gap, providing a direct sealing effect; Maze seals use a series of complex channels to prevent the entry of liquids and impurities, and have a good sealing effect.

working principle

Working principle of sliding bearing type intermediate bearing: When the intermediate shaft rotates in the sliding bearing type intermediate bearing, the weight of the intermediate shaft and the radial force generated during the rotation process are transmitted to the bearing body through the bearing liner. Lubricating oil forms a lubricating film between the bearing liner and the intermediate shaft, turning the friction between the intermediate shaft and the bearing liner into liquid friction or mixed friction (a combination of boundary friction and liquid friction), thereby reducing friction. The sealing device prevents external substances from entering and internal lubricant leakage, ensuring the normal working environment of the bearing.

Working principle of rolling bearing type intermediate bearing: When the intermediate shaft rotates, the inner ring rotates together with the intermediate shaft, and the rolling elements roll between the inner and outer rings. The outer ring is fixed inside the bearing body. The rolling motion of the rolling elements reduces the friction between the intermediate shaft and the intermediate bearing. Lubricating grease plays a lubricating and sealing role between the rolling elements and the inner and outer rings, while the sealing device prevents grease leakage and external impurities from entering.

advantage

Advantages of sliding bearing type intermediate bearings:

High bearing capacity: By designing the size and material of the bearing liner reasonably, it can withstand large radial forces and is suitable for large ships or intermediate shafts under heavy loads.

Good stability: With appropriate lubrication, it can work stably and has good adaptability to some small amplitude vibrations and impacts during ship navigation.

Simple structure and lower cost: Compared to rolling bearing type intermediate bearings, its structure is relatively simple, without complex rolling components, manufacturing process is relatively simple, and cost is lower. It is more suitable for some cost sensitive ship applications.

Advantages of rolling bearing type intermediate bearings:

Low friction loss: The rolling friction coefficient is small, and the power required for the rotation of the intermediate shaft is small, which can effectively reduce the wear of the intermediate shaft and bearing components, extend the service life, and reduce the load on the main engine, improving the working efficiency of the main engine.

Adapting to high-speed rotation: able to adapt to higher speeds, it can meet the performance requirements of some ships that require fast rotation of the intermediate shaft (such as high-speed passenger ships).

High precision: The rolling motion of the rolling elements is relatively stable, allowing the intermediate shaft to have high precision during rotation, which is beneficial for the effective transmission of ship power.

Disadvantages and countermeasures

Disadvantages and countermeasures of sliding bearing type intermediate bearings:

High friction loss: The sliding friction coefficient is relatively high, resulting in significant friction loss during the rotation of the intermediate shaft. The response measures include strengthening the maintenance of the lubrication system, ensuring the quality and supply of lubricating oil, using bearing liner materials with good self-lubricating properties, regularly checking the wear of bearing liners, and timely replacing severely worn components.

High lubrication requirements: Poor lubrication may lead to a sharp increase in friction between the bearing liner and the intermediate shaft, resulting in increased wear, difficulty in rotating the intermediate shaft, and even jamming. It is necessary to install a reliable lubrication system, such as an automatic lubrication device or an oil cup with oil level monitoring function, and regularly inspect and maintain the lubrication system.

Disadvantages and countermeasures of rolling bearing type intermediate bearings:

High requirements for cleanliness and installation accuracy: The gap between the rolling elements and the inner and outer rings is small, and high requirements are placed on the cleanliness and installation accuracy of the lubricating grease. If there are impurities or improper installation in the lubricating grease, it may lead to increased wear and jamming of the rolling elements. The response measures include strengthening the design and maintenance of sealing devices to prevent impurities from entering, using high-precision measuring tools and installation equipment during installation to ensure installation accuracy.

High cost: The structure of rolling bearing type intermediate bearings is complex, including multiple precision components, and the manufacturing and installation costs are both high. Costs can be reduced through optimization of design and bulk procurement.

Application scenarios

Application scenarios of sliding bearing type intermediate bearings:

Large vessels, such as large cargo ships and oil tankers, have high load-bearing capacity of sliding bearing type intermediate bearings due to the large force borne by the intermediate shaft. At the same time, their low cost also meets the economic requirements of large vessels.

For ships that do not require extremely high precision: For some ordinary cargo ships, inland vessels, etc., in the case where the precision requirements for the rotation of the intermediate shaft are not very high, sliding bearing type intermediate bearings can provide stable support to ensure the power transmission and normal navigation of the ship.

Application scenarios of rolling bearing type intermediate bearings:

High speed vessels, such as high-speed passenger ships and speedboats, require the intermediate shaft to rotate quickly and accurately. The low friction, high precision, and adaptability to high-speed rotation of rolling bearing type intermediate bearings can well meet their performance requirements.

Precise control of ships: For example, warships, ocean research vessels, and other ships that require precise control of power transmission, the stability and accuracy advantages of rolling bearing type intermediate bearings make them an ideal choice.