Ships – Bulkheads and doors – Doors
Reexamination Certificate
1999-11-30
2001-03-27
Avila, Stephen (Department: 3617)
Ships
Bulkheads and doors
Doors
C114S20100A
Reexamination Certificate
active
06205943
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a boat or ship's hull comprising a composite material with an electrically conductive reinforcement. The hull, preferably of reinforced plastic, is arranged with predetermined properties in respect of shielding against electromagnetic radiation and possibly radar reflection. The hull is formed with hatches which can be closed by means of e.g. covers and doors, provided with electrically conductive seats in respect of the radiation leakage round the hatches. The invention also concerns a method of fastening the seals.
PRIOR-ART TECHNIQUE
Modern warships have to an increasing extent hulls that are built in consideration of radar reflection and shielding against electromagnetic radiation. The former can be intended to direct the radar reflection. The latter can be intended to reduce the emission of revealing signals and to protect the equipment from electronic radiation from outside. On ships with a hull made of a composite material, e.g. a plastic hull, this has been carried out according to prior art by providing the outside of the hull with an electrically conductive layer of e.g. glass fibres, whose surfaces have been coated with a conductive material, e.g. aluminium, in these hulls, aluminium covers contained in aluminium frames are fastened. The seals between the frames and the covers are designed according to prior-art technique for seals between metal parts. A putty containing metal particles has been used between the hull and the frames to obtain a satisfactory electric seal and a connection between the frames and the layer, said connection being unbroken along the fastening of the frames. For, inter alia, the putty to obtain sufficient conductive properties, metal particles of silver have been used. The thus achieved composition of metals, which from the viewpoint of the chain of stress is poor, has been devastating. The aluminium surfaces which have been in contact with the putty, i.e. surfaces of the frames and the fibres of the layer, have corroded significantly, which has caused the connections between the surfaces to be cut off, resulting in leaks in the shielding and great costs of repair and maintenance. This technique also suffers from the drawback that the shielding has not been satisfactory also because of disconnection caused by temperature stress, and therefore it has been necessary to shield much equipment in the ships individually. As a result, the manufacture and maintenance of the ships have become expensive.
DESCRIPTION OF THE INVENTION
Technical Problem
An object of the invention is to provide a boat or ship's hull of a composite material as mentioned by way of introduction, having in any case shielding properties and possibly special radar reflecting properties. The hull is provided with at least one hatch which is closable by means of a device, e.g. a cover, and is sealed against electromagnetic radiation by means of sealing devices and which should have the following properties.
The hull, the cover of the hatch and the electrical seals between this and the hull should be made of materials agreeing with each other.
The seals should be inexpensive to manufacture and maintain and should retain a good function during the life of the ship.
A further object is to provide a method for fastening the sealing devices.
Solution
This object is achieved by the hull and the methods for fastening the sealing device being given the features stated herein. More particularly, the present invention is directed to a shielded boat or ship's hull with a cover, door, or the like for closing a hatch in the hull, and a sealing device for electric sealing of the closure of the cover adjacent to that part of the hull which surrounds the hatch. The hull and the cover comprise a composite having fibers of an electrically conductive material. This composite, at fixing surfaces in the area of the closure between the hull and the cover, reaches the surface of the hull and the cover, respectively. The sealing device includes two sealing members, of which a first sealing member is fixed to the fixing surfaces of the hull side of the closure, and a second sealing member is fixed to the fixing surfaces of the cover side of the closure. Each sealing member comprises a flexible, layered element, by means of which the sealing member is fixed by lamination to said surfaces. Parts of the first sealing member are arranged to be kept pressed against parts of the second sealing member when the cover is closed, and the sealing members include fibers of the same kind of material as the fibers in the composite.
The sealing device may further include a resilient member, the sealing device being adapted such that said resilient member, by compression, holds the parts of the first sealing member pressed against the parts of the second sealing member. The layered element may include a strip of a textile material, e.g., a woven strip or strip-shaped mat of carbon fibers; the strip may be fixed by lamination to the fixing surfaces of the hull or cover side along at least one strip edge. The sealing member of the cover as well as of the hull may further comprise two strips, each strip fixed by lamination to the respective fixing surface along two strip edges, at least one of the strips including a non-laminated raised central band adapted to accommodate the resilient member. In addition, the closure may be an overlap closure with stepped outer limitation of the cover and inner limitation of the hull adjacent to the hatch for forming flat, annular, preferably parallel upper surfaces of steps of the cover and the hull, respectively, with these upper surfaces of the steps comprising fixing surfaces.
The present invention further includes a method for fastening the sealing member to a hull or cover or the like. When the hull or cover is hardened in the fastening areas, surfaces of the conductive fibers of the composite are preferably uncovered at the fixing surfaces by, for instance, grinding. The sealing member is then fixed by lamination to the fixing surfaces by means of a fixing agent, for instance, the same matrix as that of the composite, and excess fixing agent in the laminated material is then pressed away. When the fastening area is wet, the method includes lamination of the fixing surfaces, with excess fixing agent in the laminated material being pressed away.
Warships are to an increasing extent made of a plastic composite with high-strength fibres, e.g. carbon fibres, as reinforcement material. The most important reasons are: The hulls become rigid and strong with a low weight, they obtain a small magnetic signature, small maintenance cost and possibilities of a desired shape of the hull, for instance, flat hull surfaces for the desired radar reflection properties. It is known that if an electrically conducive reinforcement is used, the hull can obtain the desired shielding properties. The reinforcement makes the hull function as a Faraday cage. Certain high strength fibres, especially those made of metal and carbon fibres and certain kinds of ceramic fibres and boron fibres have a good electrical conductivity, which makes them suitable for the purpose. However, since they are used enclosed in an insulating matrix, for instance the plastic, the reinforcement has not been directly accessible to be electrically connected via a seal between the hull and, for instance, a cover. One has tried to solve the problem in different ways, for instance as described above, but the results have proved discouraging.
Experiments have shown that if a member that satisfies certain requirements, such as a strip or the like of a fabric, a tricot or a multiaxial mat, is fixed by lamination to a composite surface comprising electrically conductive fibres, e.g. of the type described above, an electric contact, which is satisfactory for sealing purposes, can be obtained between the member and the conductive fibres of the composite. These fibres may constitute the reinforcement, be included therein as a mixture of carbon fibres and glass fibres, or be parti
Hellbratt Sven-Erik
Lonno Anders
Avila Stephen
Jacobson Price Holman & Stern PLLC
Kockums AB
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