GB2213165A

GB2213165A - Cathodic corrosion protection of a component at a stern tube of a ship

Info

Publication number: GB2213165A
Application number: GB8827843A
Authority: GB
Inventors: Guenter Mewes; Bergen Ernst-Peter Von; Guenter Pietsch
Original assignee: Blohm and Voss GmbH
Current assignee: Blohm and Voss GmbH
Priority date: 1987-12-01
Filing date: 1988-11-29
Publication date: 1989-08-09
Anticipated expiration: 2008-11-29
Also published as: AU613122B2; AU2646888A; CN1019206B; DE3740679C2; NL193321B; JP2583792B2; GB2213165B; KR960011021B1; GB8827843D0; SE8804356D0; JPH01195198A; SE8804356L; KR890010282A; DE3740679A1; NL8802940A; NL193321C; CN1035141A

Description

r n I- &,,; / 13 1 6j Apparatus for the cathodic corrosion Drotection of a

component at a stern tube of a shiD The invention relates to an apparatus for the cathodic corrosion protection at a stern tube of a ship, the apparatus being equipped with the features set forth in the preamble of claim 1.

In devices for cathodic corrosion protection it is important that all the parts to be protected such as the outer skin of the ship, the ships rudder, and the ships shaft together with the running sleeve are electrically conductively connected together so that these parts act as a cathode and can participate in the electrochemical element action.

In the devices of the above named kind (German laying open print DE-OS 25 20 948) this requirement is not always reliably satisfied because although the housing of the seal arrangement is admittedly mechanically connected with the stern tube via one of the flange rings, it is not however electrically connected because the stern tube is not included in the named cathode system.

Accordingly the protective current emerging from the sacrificial anode does not enter or only enters insufficiently into the outer surface of the seal housing so that that latter is exposed practically unprotected to the corrosion by the seawater. One has attempted to overcome this evil by making the seal housing of bronze or of a similar corrosion resistant material. It is obvious that such materials are costly and the invention is accordingly based on the problem of being able to manufacture the seal housing of less expensive material, namely of steel or of grey cast iron, without having to tolerate an increased incidence of corrosion.

This object is satisfied in accordance with the invention in that the housing of the sealing arrangement is electrically conductingly connected with the running sleeve via a current bridge which bridges the gap space between the housing and the running sleeve.

Through this measure the sealing housing is now likewise included into the cathode system and thus subjected to the anticorrosive action of the sacrificial anodes. In accordance with embodiments of the invention the current bridge is formed as a floating ring, slip contact, electrically conductive sealing cuff or as a current conducting oil/water emulsion in the ring chamber.

Furthermore, it is provided that the sacrificial anodes, as is customary, are mounted on the ring flange or on the running sleeve, or on the seal housing. The latter solution exploits the characteristic of cathodic installations that the protective current emerging from the anodes preferably enters into the cathode parts disposed in the proximity thereof so that increased corrosion protection takes place at the seal housing.

Further embodiments serve the purpose of constructing the sacrificial anodes so that the current flux between the sacrificial anodes and the housing to be protepted only takes place to the degree which is necessary for reliable protection, thus prolonging the lifetime of the sacrificial anodes as far as possible. For this purpose provision is made to reduce the active surface of the sacrificial anodes or to insert a partly electrically conducting insert between the sacrificial anode and the mounting surface.

Finally, provision is made for operating the system of the 1 invention with,galvanic current or with external current (outside current) and accordingly to use zinc and aluminium or their alloys, or carbon or platinum for the sacrificial anodes.

The invention will now be described in the following in more detail with reference to schematic drawings in which:

Fig. 1 shows a longitudinal section through a seal arrangement with a current bridge and a sacrificial anode arranged at the seal housing, Fig. 2 a longitudinal section through a seal arrangement with a current bridge and a sacrificial anode arranged on the running sleeve.

In the stern tube seals shown in Figs. 1 and 2 a running sleeve 2, 2.1 is located on the shaft 1. The shaft 1 is journalled in a non illustrated bearing sleeve which is carried by a stern-frame boss 3 to which a seal housing 4 is also secured. The seal housing 4 consists of four axially flush housing rings 4.1, 4.2, 4.3, 4.4 which are arranged alongside one another and three seal rings 5.1, 5.2, 5.3 which are each inserted between two housing rings. The sealing rings are formed as lip seals of which two face the seawater W and one faces a lubricant chamber S. A ring chamber 6.1, 6.2 is in each case carved out between two seal lips. I In the embodiment of Fig. 1 a block-like sacrificial anode 7 is secured to the seal housing 4,' and indeed to its outer surface facing the seawater W. A ring-like groove 9 in which a floating ring 8 is guided is formed in the housing ring 4.4 adjacent the lubricant chamber S. The ring engages around the running sleeve 2 with a small degree of play and - 4 a device 10 providing security against rotation and secured in the ring- like groove engages into the ring from the outside. The device providing security against rotation simultaneously acts as a contact element for the current transfer from the housing ring 4.4 to the floating ring 8.

In the embodiment of Fig. 2 a block-like sacrificial anode 7 is secured to the ring flange 2.1 of the running sleeve 2 and indeed at the flange side facing the seal housing 4. in this embodiment a blind bore 12 is formed in the housing ring 4.4 adjacent to the lubricant chamber S. Here the current bridge is for med as a slip segment 11 which is guided with radial play in the blind bore 12 and is pressed by means of a spring 13 onto the outer surface of the running sleeve 2, with the spring 13 simultaneously serving as a contact element.

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Claims

P a t e n t c 1 a i m s

1. Apparatus for the cathodic corrosion protection of a component at a stern tube of a ship which is equipped with a seal arrangement comprising a metallic housing fixed to the stern tube and one or more sealing rings of rubber elastic material which are connected with the housing and cooperate with the running sleeve of the propeller shaft, wherein blocklike sacrificial anodes exposed to the seawater are secured to the component to be protected and wherein the running sleeve forms a cathode, charaterized in that the housing of the sealing arrangement is electrically conductively connected with the running sleeve via a current bridge which bridges the gap space between the housing and the running sleeve.

2. Apparatus in accordance with claim 1, characterized in_ that the current bridge is formed as a floating ring (8) which engages the running sleeve (2) with a little play and which is guided with play but secured against rotation in the housing (4) in a ring groove (9), with the device (10) securing the ring against rotation simultaneously serving as contact element.

Apparatus in accordance with claim 1, characterized in_ that the current bridge comprises a slip segment (11) which slidingly contacts the running sleevd (2) and which is guided in a recess (12) of the housing (4) with radial play, with the slip surface of the slip segment being pressed onto the running sleeve (2) by means of a spring (13), with the spring (13) simultaneously serving as contact element.

- G - 4. Apparatus in accordance with claim 1, characterized in that the current bridge is formed by at least one of the sealing rings (5.1, 5.2, 5.3) which is made electrically conductive for this purpose.

5. Apparatus in accordance with claim 1, characterized in_ that the current bridge is so constructed that at least one of the ring chambers (6.1, 6.2) located between the sealing rings is filled with a conductive medium, for example an oil in water emulsion of a specific mixing ratio.

6. Apparatus in accordance with one of the claims 1 to 5, characterized in that the sacrificial anodes (7) are located on the housing (4) and indeed at its seawater side outer surface.

7. Apparatus in accordance with one of the claims 1 to 5, characterized in that the sacrificial anodes (7) are located on the ring flange (2.1) of the running sleeve (2).

8. Apparatus in accordance with one of the claims 1 to 7, characterized in that the running sleeve (2, 2.1) is electrically insulated relative to the shaft (1) and the propeller.

9. Apparatus in accordance with one of the clc-ims 1 to 8, characterized in that the sacrificial anodes (7) consist of zinc, aluminium or their alloys with an adequate protective potential, or consist of carbon or platinum, with the installation operating with galvanic current or with external current ( i.e. from an external power source).

published 1989 at The Patent Office, State House, 5671 High HOIborn, LondonWCIR4TP. Further copies me:ybe Obtained from The Patent Omce. Sales Branch, St Max7 Cray, Orpingtor Kent BES 3RD. Printed by Multaplex techniques Itd, St Mary Cray. Kent, Con. 1/87 i