Definition and Function

The lower rudder support is a key component of the ship's rudder system, located at the lower part of the rudder stock. It is mainly used to support the weight of the rudder stock, withstand the radial and axial forces generated by the rotation of the rudder blades, ensure the stable rotation of the rudder stock, and enable the rudder blades to accurately control the ship's heading. Its role is crucial for the navigation safety and maneuverability of ships.

Structural composition

Bearing section:

Sliding bearing type lower rudder bearing:

It is mainly composed of bearing shells and bearing seats. Bearing shells are usually made of wear-resistant materials such as Babbitt alloy, copper alloy, etc. Babbitt alloy bearings have good anti friction and wear resistance, and can withstand high pressure. Copper alloy bearing shells exhibit excellent corrosion resistance and thermal conductivity. The inner surface of the bearing shell is in close contact with the rudder stock, and its shape and size are well adapted to the rudder stock, providing support for it. The bearing seat is used for installing and fixing the bearing shell, which has sufficient strength and rigidity to withstand various forces transmitted from the rudder stock, and is firmly connected to the structure of the ship through bolts and other means.

Rolling bearing type lower rudder bearing:

It generally includes an inner ring, an outer ring, rolling elements (balls or rollers), and a cage. The inner ring is tightly matched with the rudder stock, and the outer ring is installed inside the bearing seat. The rolling element rolls between the inner and outer rings, converting the sliding friction between the rudder stock and the lower rudder support into rolling friction and reducing friction. The function of the cage is to evenly distribute the rolling elements and ensure smooth rolling. The rolling bearing type rudder bearing with this structure can adapt to higher rotational speeds and larger radial forces.

Lubrication system:

The lubrication system is crucial for the normal operation of the lower rudder support. For sliding bearing type rudder bearings, the lubrication method can be oil lubrication or water lubrication. When lubricating with oil, lubricating oil is provided to the gap between the bearing shell and the rudder stock through an oil cup, oil groove, or centralized lubrication system. The lubricating oil forms an oil film between the two, reducing friction and wear. Water lubrication uses water as a lubricant and is suitable for some special rudder bearing designs. For rolling bearing type rudder bearings, grease lubrication is usually used, filling the gap between the rolling elements and the inner and outer rings with grease to lubricate and seal.

Sealing device:

The sealing device of the lower rudder bearing is mainly used to prevent external liquids (such as seawater) and impurities from entering the interior of the bearing, while also avoiding the leakage of lubricating oil or grease inside. 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 rudder support: When the rudder stock rotates in the sliding bearing type rudder support, the weight of the rudder stock and the radial and axial forces generated during the rotation process are transmitted to the bearing seat through the bearing shell. Lubricating oil (or water) forms a lubricating film between the bearing and the steering wheel, turning the friction between the steering wheel and the bearing 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 lower rudder bearing: When the rudder stock rotates, the inner ring rotates together with the rudder stock, and the rolling elements roll between the inner and outer rings. The outer ring is fixed on the bearing seat. The rolling motion of the rolling element reduces the frictional force between the rudder stock and the lower rudder support. 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 lower rudder bearing:

High bearing capacity: By designing the size and material of the bearing shell reasonably, it can withstand large radial and axial forces, which is suitable for large ships or rudder stocks under heavy loads.

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

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

Advantages of rolling bearing type lower rudder bearing:

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

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

High precision: The rolling motion of the rolling elements is relatively stable, allowing the rudder to have high precision during rotation, which is beneficial for accurate control of the ship's heading.

Disadvantages and countermeasures

Disadvantages and countermeasures of sliding bearing type rudder bearings:

High friction loss: The sliding friction coefficient is relatively high, and there will be significant friction loss during the rotation of the rudder stock. The response measures include strengthening the maintenance of the lubrication system, ensuring the quality and supply of lubricating oil (or water), using bearing materials with good self-lubricating properties, regularly checking the wear of the bearing, and timely replacing severely worn components.

High lubrication requirements: If lubrication is poor, it may cause a sharp increase in friction between the bearing and the rudder, resulting in increased wear, difficulty in rotating the rudder, 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 rudder 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 the rolling bearing type rudder bearing is complex, including multiple precision components, with high manufacturing and installation costs. Costs can be reduced through optimization of design and bulk procurement.

Application scenarios

Application scenarios of sliding bearing type rudder bearings:

Large vessels, such as cargo ships and oil tankers, can meet the high load-bearing capacity of sliding bearing type rudder bearings due to the large force borne by the rudder stock. 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., when the rotation accuracy of the rudder stock is not very high, the sliding bearing type lower rudder support can provide stable support to ensure the normal navigation of the ship.

Application scenarios of rolling bearing type rudder bearings:

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

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