SECURING OBJECTS

Abstract: An arrangement for securing objects to a panel (1) forming part of a container designed to provide shielding against emi comprises a cavity in the panel and a receptacle (5) which fits into the cavity and has a flange (5B) which rests on an electrically conductive surface layer (3) of the panel. The body of the receptacle is swaged outwardly at a position (6) adjacent to the flange (5B) so as to secure the receptacle mechanically and electrically to the conductive surface layer (3). An insert (7) of synthetic plastics material in the cavity receives a screw or bolt (not shown) for securing equipment to the panel.

Description: This invention relates to an arrangement for securing objects to a panel designed to provide shielding against electromagnetic interference. This invention arose in the design of a transportable electrical equipment container made from a frame carrying panels forming the walls, floor and roof. The panels were formed from a central layer of an electrically insulating foam and outer layers of aluminium, which is conductive and provides the required shielding. A problem was encountered in securing equipment to the panels on the inside of the container since any holes drilled through the inner aluminium layer allowed leakage into the container of any electromagnetic interference which might have penetrated through the outer layer of aluminium. This invention provides an arrangement for securing objects to a panel designed to provide shielding against electromagnetic interference, the arrangement comprising: a cavity in the panel opening into an electrically conductive surface thereof, a receptacle which fits into the cavity and has a flange which rests against and makes electrical contact with a part of the electrically conductive surface surrounding the cavity; and a body of material which is secured in the receptacle and which receives or is about to receive a fastening device. By employing the invention the receptacle provides a continuous conductive inner surface to the panel and so avoids the problem of the leakage of the electromagnetic interference. To ensure good electrical contact between the receptacle and the conductive layer a lip is preferably formed by swaging or otherwise deforming the material of the receptacle after it has been inserted into the cavity thereby nipping the conductive surface of the panel between the flange and the lip. The layer of electrically insulating material will normally be foam plastics or some other material which is relatively compressible compared to the material forming the conductive surface of the panel. This enables it to be compressed during the swaging process. To give improved shielding against electromagnetic interference there is preferably a second electrically conductive layer on a side of the layer of insulating material opposite to the first electrically conductive layer. The base of the receptacle, which is preferably flat, may rest against this second conductive layer to give extra support. The body of material inside the receptacle can take any form which serves its purpose i.e. of providing a mechanical connection between the fastening device and the inside surface of the receptacle. In one embodiment it takes the form of a plastic insert secured inside the receptacle with adhesive, this plastic insert having a hole in it to take a fastening device in the form of a self-tapping screw. Alternatively the inside of this plastic insert could be threaded to accept a bolt. A preferred embodiment of the invention will now be described with reference to the accompanying drawing which shows a horizontal cross-section through an arrangement for securing objects to a panel. A container designed to exclude electromagnetic radiation at radio frequency is formed from panels, one of which is shown at 1 and comprises an inner layer 2 of rigid foam plastics, which is electrically and thermally insulating, and outer layers 3 and 4 of aluminium, which provide shielding against electromagnetic interference. The layer 3 is on the inside of the container. A cylindrical cavity is formed by drilling through layers 2 and 3. A receptacle 5, made from aluminium, has a body 5A, flange 5B and end face 5C. The body 5A of the receptacle is inserted into the cavity so that its end face 5C rests against layer 4 and the flange 5B rests against a region of layer 3 bordering the cavity. After insertion a swaging operation is performed to form a lip 6. During this process the aforementioned region of the layer 3 bordering the cavity is nipped between the lip 6 and the flange 5B. This gives good mechanical support to the receptacle and ensures that the receptacle and layer 3 are in good electrical contact all around the edge of the cavity. A nylon insert 7 is then secured in the receptacle by an adhesive layer 8. In the illustrated embodiment the insert 7 has a pre-formed hole 9 to accept a self-tapping screw, though in alternative embodiments the hole could be formed with a thread; or could be replaced by a fastening device embedded in the insert 7. The electrically insulating properties of the nylon of the insert 7 is of significance since it enables equipment to be fixed to the inside surfaces of the container without making electrical contact therewith.

Claims: An arrangement for securing objects to a panel (1) designed to provide shielding against electromagnetic interference, characterised by: a cavity in the panel (1) opening into an electrically conductive surface (3) thereof, a receptacle (5) which fits into the cavity and provides a continuous conductive inner surface to the panel and has a flange (5B) which rests against and makes electrical contact with a part of the electrically conductive surface (3) surrounding the cavity; and a body (7) of material which is secured in the receptacle and which receives or is adapted to receive a fastening device. An arrangement according to claim 1 characterised in that the panel (1) comprises a layer (2) of electrically insulating material and a conductive layer (3) bonded to it and forming the electrically conductive surface, and in that the receptacle (5) is deformed outwardly in the vicinity of the flange to form a lip (6) so that a border region of the conductive layer surrounds the cavity and is held between the lip (6) and the flange. An arrangement according to claim 2 characterised in that the lip (6) is formed by a swaging process. An arrangement according to claims 2 or 3 in which the electrically insulating material (2) is relatively compressible compared with the material forming a conductive layer (3). An arrangement according to claim 2, 3 or 4 characterised by a second electrically conductive layer (4) on a side of the layer of insulating material opposite to the first mentioned electrically conductive layer (3) and in that a face (5C) of the receptacle rests against the second layer. An arrangement according to any preceding claim characterised in that the body (2) of material is secured in the cavity by adhesive. An arrangement according to any preceding claim characterised in that the body (2) of material is electrically insulating.

Inventors: HENDERSON, WILLIAM IAIN MACKIE, LEASK, SAMUEL HALL, MATTHEWS, CHRISTOPHER F., MORRISON, DAVID JOHN, SMITH, MOIRA, THORNLEY, DAVID JOHN
Applicants: THE MARCONI COMPANY LIMITED
Application year: 1987
Main classification: H05K9
IPC codes: H05K9