Definition and Function

The stern shaft sealing ring is a key component used in ship shaft systems to seal the gap between the stern shaft and stern tube. Its main function is to prevent leakage of liquids such as seawater and lubricating oil (if it is an oil lubrication system) during the rotation of the stern shaft. It ensures the sealing of the internal compartments of the ship, prevents seawater from invading and damaging the equipment inside the ship, and also prevents lubricating oil from leaking into the sea, protecting the environment.

Structural composition

Sealing element:

The sealing element is the core part of the stern shaft sealing ring, commonly including lip seals and mechanical seals. Lip seals are generally made of rubber material, shaped like lips that tightly adhere to the surface of the stern shaft. When the stern shaft rotates, the elastic lip of the lip seal can adapt to the movement of the stern shaft and prevent liquid from passing through. Mechanical seals consist of a moving ring and a stationary ring. The moving ring rotates with the stern shaft, while the stationary ring is fixed to the stern tube. The high-precision mating surfaces of the two are maintained in close contact through springs or other elastic elements, forming a seal.

Auxiliary sealing components:

Including O-ring seals, sealing gaskets, etc. O-ring seals are usually installed in the grooves of the sealing element to enhance the sealing effect and prevent liquid leakage from the side of the sealing element. The sealing gasket is used to seal the connection between the fixed sealing element's gland and the stern tube, ensuring the sealing performance of the gland.

Cap and spring (for some seals):

The gland is used to fix and compress the sealing element. It is usually connected to the stern tube through bolts and can adjust the clamping force on the sealing element. For lip seals, appropriate clamping force can make the lip better fit the stern shaft; For mechanical seals, the gland may also serve to secure the stationary ring. Springs are mainly used in mechanical seals to provide axial preload force for the moving and stationary rings, ensuring that the sealing surface can still maintain tight contact when the stern shaft rotates and is subjected to axial force.

working principle

Working principle of lip seal: When the stern shaft rotates, the lip of the lip seal slides on the surface of the stern shaft. The tight fit between the lips and stern shaft, as well as the elasticity of the rubber material, prevent the passage of liquid. If it is to prevent seawater from entering, the pressure of seawater will make the lips more tightly adhere to the stern shaft; If it is to prevent lubricant leakage, lip seals achieve sealing under their own elasticity and lubricant pressure.

Working principle of mechanical seal: The stern shaft drives the rotating ring, and the stationary ring is fixed on the stern tube. The mating surfaces of the dynamic and static rings are tightly fitted under the preload force of the spring. When the stern shaft rotates, the relative motion between the moving ring and the stationary ring is sealed through the sealing surface. The liquid pressure will further enhance the sealing effect, ensuring tight contact between the sealing surfaces and preventing liquid leakage.

advantage

Good sealing performance: Both lip seals and mechanical seals can effectively prevent liquid leakage when the stern shaft rotates. Mechanical seals have higher sealing accuracy and are suitable for occasions with strict sealing requirements; Lip seals have a simple structure and can provide reliable sealing even under normal working conditions.

Adapt to stern shaft movement: Due to the good elasticity and adaptability of the sealing element, it can adapt well to the rotation and certain axial displacement of the stern shaft. This ensures that the movement of the stern shaft within the normal operating range does not affect the sealing performance of the sealing device.

Long service life (under normal maintenance): Using high-quality sealing materials and reasonable structural design, the stern shaft seal ring can have a long service life under normal maintenance and use conditions. Regular inspection and replacement of worn parts can ensure the continuous stability of sealing performance.

Disadvantages and countermeasures

Wear of sealing components: Due to frequent rotation of the stern shaft and friction between the sealing components and the stern shaft, the sealing components are prone to wear. Once severely worn, it may lead to seal failure. The countermeasure is to regularly check the wear of the sealing components, and replace them in a timely manner when the wear exceeds the specified limit. Meanwhile, sealing materials with better wear resistance can be used to extend their service life.

The installation and debugging requirements are high: the installation accuracy and debugging process of the stern shaft sealing ring have a significant impact on its sealing performance. If installed improperly, such as inaccurate installation of sealing components, improper tightening force of the pressure cover, etc., it may lead to poor sealing effect. Therefore, it is necessary to strictly follow the installation instructions for installation and debugging, and be operated by professional personnel.

Application scenarios

The stern shaft seal of ship shaft system: The stern shaft seal ring is an essential sealing device between the stern shaft and stern tube of various ships (including cargo ships, passenger ships, oil tankers, warships, etc.). It ensures the waterproofness of the ship and the sealing of the lubricating oil, which is an important guarantee for the safe navigation of the ship and the normal operation of the equipment.