WO2009130368A1

WO2009130368A1 - An arrangement for sealing a propeller shaft

Info

Publication number: WO2009130368A1
Application number: PCT/FI2009/000054
Authority: WO
Inventors: Sami Palokangas; Lauri Tianen
Original assignee: Abb Oy
Priority date: 2008-04-24
Filing date: 2009-04-24
Publication date: 2009-10-29
Also published as: FI20080315A0; FI20080315A; FI123875B

Abstract

The object of the invention is an arrangement for sealing the propeller shaft (10) of a ship or a corresponding watercraft. The propeller shaft is supported by a bearing (14) against the ship's propulsion unit (2), the outer surface (4) of which is in contact with the surrounding water, with the bearing (14) fitted between the propeller (6) and the machine (8) rotating the shaft. According to the invention, there is a closed intermediate compartment (16) between the bearing (14) and the propeller (6), with a shaft sealing (26) fitted to the joint between the propeller (6) side wall (18) of the compartment and the shaft (10), the said sealing preventing water from leaking into the closed compartment (16). The shaft sealing (26) is substantially within the intermediate compartment (16).

Description

AN ARRANGEMENT FOR SEALING A PROPELLER SHAFT

The object of the invention is an arrangement for sealing the propeller shaft of a ship or a corresponding watercraft according to the preamble part of Claim 1.

The propeller shafts of ships and corresponding large watercrafts are supported against the ship body or the casing of a propulsion unit such as a steering propeller device. The support structure is generally based on bearings, which constitute an advantageous method of controlling both axial and radial forces for the ship's propulsion drive. Compared to a regular bearing support, the operational environment sets additional requirements for such an arrangement in a ship's propulsion drive, where proper sealing between the shaft and the bearing and between them and the ship body components must be ensured. Firstly, sealing must be ensured during actual operation, and secondly, the required maintenance and replacement of parts that wear must be taken care of.

Propeller shaft sealing is always a critical function in a ship's propulsion drive, and particularly in steering propeller devices, as it prevents water around the propeller device from entering the body or the steering propeller unit, also called the pod. If the sealing fails, water may enter the bearing, which will result in premature wear and damage to the bearing. Steering propeller devices such as azimuth pods or thrusters typically utilize roller bearings, which will wear faster if water is mixed with the bearing oil. If the sealing fails, the oil used to lubricate the bearing may flow into the surrounding water, which will cause environmental damage and may well damage the public image of the shipping company and the shipping line. A seal will wear in regular use, and damages are usually a result of this normal wear and/or aging.

In a prior art solution, shaft sealing is in immediate contact with the bearing oil. hi such an arrangement, seal damages or deterioration caused by normal wear may allow water to flow into the bearing or bearing oil to leak into water. Docking is always necessary to repair damages to the propeller shaft bearing, that is, to replace the bearing and the shaft sealing. The matter is made more difficult for large cruisers by the fact that there are very few docks suitable for them in the world. The repair work is not only expensive but also time-consuming, which will result in major indirect costs when the ship must be taken out of traffic. Biologically degradable oils generally have less advantageous properties, and they cannot be used in critical solutions such as lubricating a ship's propeller shaft bearing. Biologically degradable oils could help prevent environmental impacts, but this prevents their use in conventional propeller drives. In prior art solutions, the bearing and the shaft sealing comprise a uniform whole, meaning that the same oil must be used for lubricating the bearing and the shaft sealing.

When damages occur to the sealing, it may in an extreme case lead to water from around the propeller device entering the casing of the propeller device, resulting in corrosion and possible damage to electric and measuring equipment.

According to conventional technique, replacement of the shaft sealing of large ocean vessels has been carried out without docking so that a steel casing has been built around the propeller and emptied of sea water. Sealing has then been replaced within the steel casing. Such a maintenance measure is extremely demanding and difficult also because the casing is heavy and difficult to move. Therefore, such repairs are very infrequent in practice.

The purpose of the present invention is to develop a new and advantageous propeller shaft sealing and bearing arrangement for a ship or a corresponding large watercraft, in which arrangement the problems and deficiencies of prior art solutions are fixed. The particular purpose of the invention is to decrease the possibility that water surrounding the ship could damage the propeller shaft bearings. In addition, the purpose is to create an easier way to replace the ship's propeller shaft sealing without having to dock the ship. In order to achieve this, the invention is characterized by the features specified in the characteristics section of Claim 1. Certain preferred embodiments of the invention are characterized by the features defined in the dependent claims.

An arrangement according to the invention efficiently prevents water from accessing the bearing housing, trapping any water possibly leaking through the shaft sealing into an intermediate compartment. Liquid possibly entering the intermediate compartment can be removed in a controlled manner. The bearing seal preventing oil from leaking from the bearing housing and the shaft sealing preventing water from entering the bearing and the ship body are structurally separated. Water is prevented from entering the bearing housing even when the shaft bearing is badly worn or damaged. Bearing oil is thus kept clean and its lubricating properties remain good, which extends the life of the bearings and enables longer maintenance intervals.

In an arrangement according to the invention, shaft sealing is inside the ship body or the casing of the ship's propulsion unit, providing better protection for the seal and allowing maintenance of the sealing from the inside. Shaft sealing is installed from the inside, and also fixed to place inside the intermediate compartment.

The invention enables the use of different oils for the lubrication of the bearing and for the shaft sealing. Special requirements for both can be observed, and an optimal result achieved. Particularly, it is possible to use biologically degradable oil for the shaft sealing, which will have contact with the surrounding water. The environmental impacts of ship operation can thus be decreased.

According to an embodiment of the invention, the intermediate compartment is closed by a wall at the bearing, preventing water from entering the propulsion device's motor compartment, for example. The wall comprises a maintenance hatch that can be used for the maintenance and replacement of the shaft sealing.

According to an embodiment of the invention, a temporary seal can be applied between the propeller and the propulsion device casing or body component, or a fixed seal exists that can be activated with, for example, pressurization. Temporary sealing enables the replacement and fixing of the shaft sealing in the intermediate compartment using the maintenance hatch, without docking the ship or other watercraft.

The invention will be described in detail with the help of a certain embodiment by referring to the enclosed drawings, where

- Figure 1 illustrates an arrangement according to the invention,

- Figure 2 is a perspective illustration of an arrangement according to the invention.

Figure 1 is a partial schematic illustration of a ship's propulsion unit 2, comprising an arrangement according to the invention. The propulsion unit is a steering propeller device, which is attached to the ship body with a turning bearing arrangement. Such a steering propeller device is known for example by the product name AZIPOD®, which is a trade mark owned by ABB Oy. An electric motor 8 operating the propeller 6 is mounted inside the casing 4 of the propulsion unit 2. In this embodiment, the electric motor 8 is a synchronous motor with exciter 12 mounted to the propeller shaft 10 in a well-known way. The propeller shaft 10 is supported against the casing 4 of the propulsion unit 2 at both ends. Figure 1 only illustrates the bearing 14 at the propeller end 6, comprising a roller bearing. At the other end of the electric motor 8 another bearing is used in a known manner.

The propulsion unit casing 4 comprises an intermediate compartment 16 on the propeller 6 side between the propeller 6 and bearing 14. The walls of the intermediate compartment 16 comprise the wall 18 on the propeller side, the outer circumference 20 of the propulsion unit end and the wall 22 on the bearing 14 side, which at the same time functions as a support structure of the bearing 14. The propeller shaft 10 passes through the intermediate compartment 16 at the centre of it. At the bearing end of the intermediate compartment 16 there is the outer oil seal 24 of the bearing, preventing bearing lubricating oil from leaking out of the bearing housing. Correspondingly, at the motor end of the bearing 14 there is the inner oil seal 25 of the bearing. Shaft sealing 26 is fitted at the propeller end of the intermediate compartment 16, preventing surrounding water from entering the intermediate compartment 16. The intermediate compartment 16 is thus completely sealed, and in normal operating conditions, it is also free of any liquid. The shaft sealing is fitted inside the closed intermediate compartment, enabling replacement of the sealing within the compartment. The size of the intermediate compartment is such that maintenance and installation measures are possible.

When the bearing housing and its seals are fully isolated from the shaft sealing, oil that is particularly suitable for the bearing and the shaft sealing can be used for each of them. Particularly for the shaft sealing, which is closest to sea water, environmentally friendly oil such as biologically degradable oil can be used.

As a result of normal wear and aging of seals, it is possible that water enters the intermediate compartment 16 through the shaft sealing 26. The leaked water flows to the bottom of the intermediate compartment 16, and is not able to damage the bearing 14. To remove the water gathering at the bottom of the intermediate compartment 16, the arrangement comprises an outlet tube that is used to pump the water into a designated tank inside the ship. Thus the water is under no circumstances allowed to leak into the propulsion unit or the motor compartment. In a preferable arrangement, a cleaning system is used in connection with the pump and/or tank to remove any impurities from the water. For example the failure of the bearing oil seal may lead to bearing lubricating oil leaking into the intermediate compartment. The arrangement can then prevent the lubricating oil from leaking into sea water. The cleaned water can be lead back into the sea.

Figure 2 is a perspective illustration of the intermediate compartment, applying the same component reference numbers as Figure 1. Figure 2 does not show the casing limiting the intermediate compartment 16 from the outer surface to allow better illustration of the details of the structure according to the invention. Figure 2 illustrates the maintenance hatch 30 for the intermediate compartment 16, allowing access from the propulsion unit into the intermediate compartment 16 for maintenance measures such as replacement of shaft sealing. The maintenance hatch is attached by bolts 32 to the bearing support wall 22. Wall 22 and wall 18 are joined by a support bar 34. Support plates 36 are attached to the frame and wall 22 of the bearing 14, further joined to the support ring 38. When the ship and the propeller are at standstill at a port, the gap 5 between the propeller 6 and the propulsion unit casing 4 is sealed using a temporary seal. A diver installs the temporary seal from the outside, or a fixed seal 7 is activated by pressurization. This way the shaft sealing 26 can be replaced via the closed intermediate compartment 16 without having to interfere with the shaft support, attachment or coupling. When the temporary seal is in place, the maintenance hatch 30 is opened by detaching the fixing bolts, after which the shaft sealing can be replaced via the intermediate compartment. The intermediate compartment and the maintenance hatch are large enough to allow maintenance measures.

According to an embodiment of the invention, a pump is used in connection with the intermediate compartment to remove liquid from the intermediate compartment. The pump designed for the removal of liquids may be fitted inside the intermediate compartment or outside it, or within the ship body. According to an embodiment of the invention, cleaning equipment for the liquid is used in connection with the pump and the outlet tube.

A solution according to the invention is suitable for various turning propeller devices equipped with electrical motors, as well as for mechanical solutions and for the sealing of various fixed shafts, that is, shafts that are not able to turn relative to the ship body, in which case the propeller may be driven by a diesel motor. In the above the invention has been described with the help of a certain embodiment. However, the description should not be considered as limiting the scope of patent protection; the embodiments of the invention may vary within the scope of the following claims.

Claims

1. An arrangement for sealing a propeller shaft (10) for a ship or corresponding watercraft, the said propeller shaft (10) being supported against the ship body or propulsion unit (2) with a bearing (14), the outer surface (4) of the propulsion unit being in contact with the surrounding water and the bearing (14) being fitted between the propeller (6) and the machine (8) rotating the shaft, characterized in that there is a closed intermediate compartment (16) between the bearing (14) and the propeller (6), with a shaft sealing (26) fitted to the joint between the propeller side wall (18) of the intermediate compartment and the shaft (10), which shaft sealing prevents surrounding water from leaking into the closed intermediate compartment (16), and which shaft sealing (26) is substantially within the intermediate compartment (16).

2. An arrangement according to Claim 1, characterized in that the closed compartment comprises a first wall (18) at the propeller end of the intermediate compartment and a second wall (22) at the bearing end of the intermediate compartment, whereby a maintenance hatch has been arranged in the second wall (22).

3. An arrangement according to any of the Claims from 1 to 2, characterized in that there is a gap between the propeller and the ship body component adjacent to the propeller, which gap can be closed with a temporary seal, and that the shaft sealing (26) can be replaced via the closed intermediate compartment (16).

4. An arrangement according to Claim 3, characterized in that the temporary sealing is fitted in place from outside the ship.

5. Arrangement according to Claim 3 or 4, characterized in that the temporary sealing comprises of a seal activated by pressurization.

6. An arrangement according to any of the Claims from 1 to 5, characterized in that the shaft sealing lubricating oil is biologically degradable.

7. An arrangement according to any of the Claims from 1 to 5, characterized in that the arrangement comprises the equipment for pumping liquid away from the intermediate compartment.

8. An arrangement according to Claim 7, characterized in that the pump for removing liquid is located in the intermediate compartment, inside the propulsion unit or inside the ship body.

9. An arrangement according to Claim 7 or 8, characterized in that cleaning equipment for the liquid is arranged in connection with the liquid removal system.