AU613122B2

AU613122B2 - An apparatus for the cathodic corrosion protection of a component at the screw shaft pipe of a ship

Info

Publication number: AU613122B2
Application number: AU26468/88A
Authority: AU
Inventors: Guenter Mewes; Guenter Pietsch; Ernst-Peter Von Bergen
Original assignee: Blohm and Voss GmbH
Current assignee: Blohm and Voss GmbH
Priority date: 1987-12-01
Filing date: 1988-12-01
Publication date: 1991-07-25
Anticipated expiration: 2008-12-01
Also published as: AU2646888A; CN1019206B; DE3740679C2; NL193321B; JP2583792B2; GB2213165B; KR960011021B1; GB8827843D0; SE8804356D0; JPH01195198A; SE8804356L; KR890010282A; GB2213165A; DE3740679A1; NL8802940A; NL193321C; CN1035141A

Description

613122 S F Ref: 79225 FORM COMMONWEALTH OF AUSTRALIA PATENTS ACT 1952 COMPLETE SPECIFICATION

(ORIGINAL)

FOR OFFICE USE: Class Int Class Complete Specification Lodged: Accepted: Published: Priority: S Related Art: Name and Address of Applicant: Address for Service: Blohm Voss AG Hermann-Blohm-Str. 2 2000 Hamburg 11 FEDERAL REPUBLIC OF GERMANY Spruson Ferguson, Patent Attorneys Level 33 St Martins Tower, 31 Market Street Sydney, New South Wales, 2000, Australia Lo 0 Complete Specification for the invention entitled: An Apparatus for the Cathodic Corrosion Protection of a Component at the Screw Shaft Pipe of a Ship The following statement is a full description of this invention, including the best method of performing it known to me/us 584513 r- TECHNICAL FIELD The invention relates to apparatus for the cathodic corrosion protection at the screw shaft pipe of a ship, the apparatus having the features recited in the precharacterising part of Claim 1.

BACKGROUND OF THE INVENTION In apparatus for cathodic corrosion protection, the important point is that all components to be protected, the shell, the rudder, and the propeller shaft with its sleeve, are electrically interconnected so that these components behave like a cathode and that the electrochemical element effect may develop.

In apparatus of the above-specified type (German Patent Application 2520948 Laid Open for Public Inspection), this requirement is not always safely satisfied because the housing of the sealing means is mechanically 0o0Q joined with the screw shaft pipe through a flange ring but is not electrically 0 C electrically, as the screw shaft pipe is not incorporated in the cathodic oo ooo system.

0 0 oo Therefore, the protective current leaving the sacrificial anodes does not penetrate, or penetrates only insufficiently, the outer surface of the o0 0 sealing housing so that the same is practically unprotected and exposed to corrosion by the sea water, One has attempted to overcome this shortcoming by ood making the sealing housing of bronze or a similar corrosion-resistant material.

Obviously, such materials are expensive, and the goal of the invention is therefore to produce the sealing housing from a less expensive material, namely cast steel or grey cast iron, without need for accepting greater corrosion.

SUMMARY OF THE INVENTION According to the invention, the problem is solved by electrically connecting the housing of the sealing means with the sleeve by means of a shunt bridging the gap between the housing and the sleeve.

By this measure, the sealing housing is incorporated into the cathodic system and, hence, subjected to the anti-corrosive effect of the sacrificial anodes. According to embodiments of the invention, the shunt is configured as a floating ring, a slider contact, an electrically conducting sealing bushing or an electrically conductive oil-water emulsion in the annular chamber.

-2- Li .i _r 1 -3- Further, it is provided to mount the sacrificial anodes in the usual fashion at the annular flange or the bushing or on the sealing housing. The latter configuration makes use of the property of cathodic units that the protective current leaving the anodes enters preferably into adjacent cathode sections so that an increased protection against corrosion is obtained at the sealing housing.

The purpose of other embodiments is to configure the sacrificial anode so that the current flowing between the sacrificial anode and the housing to be protected has only an amplitude required for safe protection so that the service life of the sacrificial anodes is prolonged to the greatest possible extent. To this end, reduction of the active surface of the sacrificial anode is envisaged or a partially electrically conductive insert is placed between 0 the sacrificial anode and the mounting surface.

0 0 0 Finally, in accordance with the invention, provisions are made to operate the apparatus with a galvanic current or an external current and, 0000 0 0n accordingly, to employ zinc or aluminium or alloys thereof or carbon or platinum as materials of the sacrificial anodes.

0) 0 0 BRIEF DESCRIPTION OF THE DRAWINGS In what follows the invention is explained with reference to the 0( schematic drawings. They show: 0 Figure 1, a longitudinal section of the sealing means with a shunt and a 0 00 0'0 t' .0 sacrificial anode placed at the sealing housing; CI Figure 2, a longitudinal section of the sealing means with a shunt and a 0 00000 DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 0 In the sealing means of the screw shaft pipe illustrated in Figures 1 0 0 and 2, a sleeve 2, 2.1 is situated on shaft 1. Shaft I Is supported in a bushing (not shown) which, in turn, is supported by a stem socket 3 to which a sealing housing 4 is attached; housing 4 is composed of four axially flush housing rings 4.1, 4.2, 4.3, and 4.4 and three sealing rings 5.1, 5.2. and 5.3, each inserted between two housing rings. The latter [the sealing rings] are configued as sealing lips two of which face the sea water W and one of which faces the lubricant space S. An annular chamber 6.1, 6.2 Is located between each two of the sealing lips.

-4- In the embodiment of Figure 1, a block-shaped sacrificial anode 7 is mounted on sealing housing 4, namely on the outer surface thereof, facing sea water N. In housing ring 4.4 adjacent lubricant space S, there is an annular groove 9 in which a floating ring 8 is guided, overlaps sleeve 2 with a small clearance, and is engaged from the outside by locking means 10 attached to the annular groove. The locking means also serve as contact element for the flow of current from housing ring 4.4 to floating ring 8.

In the embodiment of Figure 2, a block-shaped sacrificial anode 7 is attached to annular flange 2.1 of sleeve 2, namely on the flange's side facing sealing housing 4. In this embodiment, a bore 12 is provided in housing ring 4.4 adjacent to lubricant space S. In this case, the shunt is configured as a slider segment 11 which is guided in bore 12 with a radial tolerance and urged o by spring 13 onto the outer surface of sleeve 2, with spring 13 acting as the 0 o contact member.

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Claims

1. Apparatus for the cathodic corrosion protection of a component at a stern tube of a ship, said ship being 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, said sealing rings co-operating with the running sleeve of the propeller shaft, wherein block-like sacrificial anodes exposed to the seawater are secured to the component to be protected, said running sleeve forming a cathode, wherein the housing of the sealing arrangement is electrically conductively connected with the running sleeve via a current bridge which bridges a gap space between the housing and the running sleeve.

2. Apparatus as claimed in claim 1, wherein the current bridge is configured as a floating ring which surrounds the running sleeve with a OU small tolerance, said current bridge being housed within a ring groove SVo° provided in the housing, said bridge and housing being adapted to allow S some non-rotational movement of the bridge, said bridge being secured G- against rotation by a stop, said stop also serving as a contact element. o O

3. Apparatus as claimed in claim 1, wherein the current bridge comprises a slip segment which slidingly contacts the running sleeve and S° which is guided in a recess of the housing with radial play, with the slip surface of the slip segment being pressed onto the running sleeve by means of a spring, said spring also serving as contact element. SoOO0

4. Apparatus as claimed in claim I, wherein the current bridge is anal formed by at least one of the sealing rings which is made electrically conductive for this purpose.

Apparatus as claimed in claim 1, wherein the current bridge Is so constructed that at least one ring chamber is provided, and at least one of said ring chambers is located between the sealing rings and is filled with a conductive medium, for example an oil In water emulsion of a specific mixing ratio.

6. Apparatus as claimed in any one of claims I to 5, wherein the sacrificial anodes are located on the housing, namely at Its seawater side outer surface.

7. Apparatus as claimed in any one of claims I to 5, wherein the sacrificial anodes are located on a ring flange provided as part of the running sleeve. I- TA j437w g kPtci; 6

8. Apparatus as claimed in any one of claims 1 to 7, wherein the running sleeve is electrically insulated from the shaft and a propeller, said propeller being provided as part of the ship.

9. Apparatus as laimed in anyone of clais 1 to 8, whe n sacrificial anodes consist of zinc, aluminium or their_-s with a higher chemical potential than the metal of whic s ip is constructed or consist of carbon or plati the installation operating with galvanic curr with external current from an external power c\.1 Apparatus substantially as hereinbefore described with reference to the accompanying drawings. 0 0 0 00 000 S000 0 000 0 00 00 DATED this SECOND day of NOVEMBER 1990 Blohm Voss AG Patent Attorneys for the Applicant SPRUSON FERGUSON if' -riltAA437W EI_.