GB2183920A

GB2183920A - Electromagnetic door seal

Info

Publication number: GB2183920A
Application number: GB08529166A
Authority: GB
Inventors: Bernhard Hugo Friese
Original assignee: MORGAN MARINE Ltd
Current assignee: MORGAN MARINE Ltd
Priority date: 1985-11-27
Filing date: 1985-11-27
Publication date: 1987-06-10
Also published as: GB8529166D0

Abstract

A first L-shaped contact member 16 is connected to the door frame and a second such member 16 is connected to the door. A pair of primary contacts comprises a spring contact 20 having a resiliently displaceable portion 27 supported at both ends, and an end face 25a of the first contact member. As the door is closed the end face 25a approaches the displaceable portion 27 in a substantially perpendicular direction to make sealing contact. The seal includes a pair of secondary contacts comprising a spring contact 24 having a resiliently displaceable portion 27, and an end face 18a of the second contact member, the sealing contacts serving to screen the primary contacts from a screened area. The contact pressure can be varied by adjustment of the second contact member 16. <IMAGE>

Description

SPECIFICATION Electromagnetic door seal This invention pertains to metal enclosures which are intended to screen sensitive elec- tronic equipment from high intensity electromagnetic radiation such as is produced by a lightning strike or a nuclear explosion for example.

In such enclosures leakage around the edges of the door can be a major problem and some form of electromagnetic seal must be provided. Existing seals are all susceptible to leakage, particularly where mitred corner joints are employed since these tend to open up when the door is closed. Leakage can also be caused by poor contact pressure and/or contact area. The aim of the present invention is to provide a form of seal arrangement which is less prone to leakage.

According to the present invention the solution lies in the provision of an electromagnetic seal arrangement for a door, comprising first and second metal contacts, one of which is associated with the door frame and the other of which is carried by the door, the first contact including a resiliently displacable contact region supported on both sides thereof, and the arrangement being such that as the door is closed the second contact approaches the displacable region in a substantially perpendicular direction to make sealing contact therewith.

Such an arrangement allows the closing pressure of the door to be applied directly to the contacts, and a substantial area of contact can be maintained. Mitred corner joints can also be employed without risk of gaps appearing under contact pressure.

The second contact preferably has an outwardly curved contact surface to maintain a good contact area on displacement of the first contact.

A further source of leakage arises from reradiation from the metal contacts. To alleviate this problem, the seal arrangement preferably includes a pair of secondary contacts, one associated with the door frame and the other carried by the door, the secondary contacts being arranged to screen the first and second contacts from the electromagnetically screened area. The secondary contacts also provide a safeguard in the event of failure of the first and second contacts.

The invention will now be exemplified with reference to the accompanying drawing which shows a transverse section through a seal arrangement in accordance with the invention.

The seal arrangement is employed in an electromagnetic radiation proof enclosure, the wall of which comprises an inner steel screen 1 and an outer reinforced plastics cladding 2.

The enclosure has a door opening provided with a rectangular door frame comprising an inner steel box member 3 welded around the periphery of the opening such that its outer face 3a is in the plane of the inner face 1a of screen 1. A similar member 4 is welded to box member 3 such that the outer faces 3a, 4a of the box members are flush. The door frame further includes an outer steel box member 5 which is joined to the cladding 2 and is spaced from screen 1 by a steel distance piece 6 welded to box members 3 and 5. The faces 5a and 6a of box member 5 and spacer 6 that face the door opening are again flush.

The opening contains a door having a Tsection edging 7 arranged with its stem 8 directed inwardly. Within the edging, the door again comprises an inner screen 9 and an outer cladding 10. The cladding 10 abuts the stem 8 and the cross piece 11 of edging 7.

The door is secured to the box member 5 by hinges 12, only one of which is shown.

Around the periphery of the door there are a number of adjustable carrier blocks 13.

These are mounted at the free end of stem 8, directed towards the middle region of the door, by bolts 14 pasing through slots 15 running perpendicular to the plane of the door.

The blocks 13 are welded to an L-section stainless steel contact member 16 arranged with one limb 17 parallel to the plane of the door directed towards the door frame and the other limb 18 directed inwardly. The steel screen 9 of the door is welded to the corner of contact member 16 such that the outer face 9a of the screen is flush with the outer face 17a of limb 17.

The free end of limb 17 is rounded and its outer face 17a is provided with a groove 19 to retain a stainless steel spring contact 20 which extends over its inner face 17b. The end face 18a of limb 18 is also curved outwardly. A similar L-section stainless steel contact member 21 is welded to box member 4 with one limb 22 extending into the door opening parallel to the plane of the door. The free end of this limb is again rounded and has a groove 23 on its inner face 22a to retain a further stainless steel spring contact 24 extending over outer face 22b. The other limb 25 of member 21 extends outwardly beyond the outer face of box member 4 and again has an outwardly curved end face 25a.

The spring contacts 20 and 24 are of identical shape and are provided in 300mm lengths arranged end-to-end with no intervening gaps.

The corners are mitred, again with no intervening gaps. Each contact comprises a hooked end portion 26 for retention on the respective limb 17, 22, leading into a flat portion 27 which is spaced parallel to the respective limb, terminating in a supporting foot 28.

Spring contact 20 and limb 25 form a pair of primary contacts, and spring contact 24 and limb 18 form a pair of secondary contacts. As the door is closed limbs 25, 18 approach the mid regions of flat sections 27 of the respective contacts 20, 24 in a substantially perpendicular direction. When contact is made the respective end faces 25a, 18a resiliently displace the mid regions of sections 27 towards the respective limbs 17, 22, the peripheral regions of sections 27 being supported away from the limbs. When the door is fully closed the sections 27 assume a curvature equal to that of the end faces 25a, 18a so that contact is made over substantially the entire surface of these end faces. It should be noted that the contact pressure is only partly due to the resilience of the spring contacts as pressure applied to the door during closure is also applied directly to the spring contacts.The correct relative spacing of L-section members 16 and 21 is achieved by slackening bolts 14 and adjusting the position of member 16 perpendicular to the plane of the door; This adjustment can also be used to take up any possible fatigue in the spring contacts after prolonged use. Because of the nature of the contact displacement there is no opening of the contacts at the mitred corners so that an effective seal is maintained in these regions.

During a high level electromagnetic pulse a substantial current will be induced in the screen 1, which flows through box members 3, 4, through the primary and secondary contacts (but mainly the primary contacts) to the door screen 9. Any re-radiation of energy from the primary contacts is prevented from entering the enclosure by the secondary contacts 18, 24. The current in the secondary contacts will be much smaller so that re-radiation from them will not be significant. The use of two sets of contacts also provides a safety margin so that breakdown of one set will not be fatal.

A further advantage of this arrangement is that the contacts are clearly visible with the door open so that any damage, distortion or deterioration can easily be seen. Cleaning, lubrication and replacement of the contacts is also made easy.

Claims

1. An electromagnetic seal arrangement for a door, comprising first and second metal contacts, one of which is associated with the door frame and the other of which is carrid by the door, the first contact including a resiliently displaceable contact region supported on both sides thereof, and the arrangement being such that as the door is closed the second contact approaches the displaceable region in a substantially perpendicular direction to make sealing contact therewith.

2. A seal arrangement according to Claim 1, in which the second contact has an outwardly curved contact surface.

3. A seal arrangement according to Claim 1 or 2, in which the first contact is a spring metal contact and the resiliently displaceable contact region is supported from a rigid support surface by two spacer portions of the contact on either side of the contact region.

4. A seal arrangement according to Claim 3, in which the spring contact includes a hook portion engaged over an edge of the rigid support surface.

5. A seal arrangement according to any preceding claim, which includes a pair of secondary contacts, one associated with the door frame and the other carried by the door, the secondary contacts being arranged to screen the first and second primary contacts from an electromagnetically screened area.

6. A seal arrangement according to Claim 5, in which the secondary contacts are in accordance with any of Claims 1 to 4.

7. A seal arrangement according to Claim 6, in which one of the primary contacts and one of the seconary contacts are both carried by a first contact member and the other two contacts are carried by a second contact member.

8. A seal arrangement according to Claim 7, in which the first contact member carries the second primary contact and the first secondary contact, and the second contact member carries the first primary contact and the second secondary contact.

9. A seal arrangement according to Claim 8, in which the first and second contact members are substantially L-shaped.

10. A seal arrangement according to Claim 9 as appended to Claim 3, in which the first contact member carries the first secondary contact on one of its inner faces and the second primary contact is provided by the end face of the other limb of the first contact member, and the second contact member carries the first primary contact on one of its inner faces and the second secondary contact is provided by the end face of the other limb of the second contact member.

11. A seal arrangement according to any of Claims 7 to 10, in which the first contact member is associated with the door frame and the second contact member is associated with the door.

12. A seal arrangement according to any preceding claim, in which the spacing between the first and second contacts is adjustable.

13. A seal arrangement according to Claim 12 as appended to any of Claims 7 to 11, in which the spacing is adjusted by adjustment of the spacing between the first and second contact members.

14. A seal arrangement according to Claim 13, in which the contact member associated with the door is adjustable and the other contact member is fixed.

15. A seal arrangement according to Claim 14, in which the adjustable contact member is adjustably mounted on an edge member incorporated in the door.

16. A seal arrangement according to Claim 15, in which the adjustable contact member is secured to carrier means which are in turn adjustably mounted on the edge member.

17. A seal arrangement according to Claim 16, in which the carrier means are adjustably mounted on the edge member by screw fasteners inserted through slots in the edge member.

18. A seal arrangement according to any of Claims 14 to 17, in which the adjustable contact member is connected to an electromagnetic screen which is incorporated in the door.

19. A seal arrangement according to Claim 18 as appended to Claim 10, in which the screen is connected to the corner of the second contact member extending substantially in the opposite direction to the limb that carries the first primary contact.

20. An electromagnetic seal arrangement for a door substantially as described with reference to the drawing.