DEVICE FOR SEALING BETWEEN TWO METAL PLATES USED AS ELECTROMAGNETIC FIELD SCREENS

Abstract: A device for achieving a seal between the edge portions of two metal plates which are used as screens against electromagnetic fields, the device including a metallic sealing strip which is intended to be compressed along these edge portions. The sealing strip (1) comprises a helically wound metal element with a cornered cross section, and the edge portion of one metal plate (6) is intended, by engaging against a support (4), to be pressed against the sealing strip (1) both in the cross-sectional and in the longitudinal direction of the strip, so that the turns of the helically wound metal element are twisted in the longitudinal direction of the strip in relation to their original positions. Parts of the cornered sides of the metal element will thus be pressed against said edge portions, which gives good metallic contact.

Description: DEVICE FOR SEALING BETWEEN TWO METAL PLATES USED AS ELECTRO- AGNETIC FIELD SCREENS TECHNICAL FIELD The invention relates to a device for sealing between the edge portions of two metal plates used as screens against electromagnetic fields, including a metallic sealing strip intended to be compressed along the edge portions. BACKGROUND ART Electronic equipment associated, for example, with modern telephony and data transmission installations, is often fitted into metallic apparatus cabinets which screen off electromagnetic fields. For this screening to be effective, metallic sealing strips must generally be applied between the edge portions of the cabinet sides and adjacent to possible doors. Sealing strips are also required at the edges of cable compartment hatches in the floor in front of, and between different apparatus cabinets. Sealing strips in the prior art are comprised of such as a metallic net, which is placed round an " elastic, elongate core, or ah elongate metal -strip with a plurality of projecting, resilient " tongues. A disadvantage with these sealing strips is that their sealing action decreases with time, due to the metal plates oxidising, which gives deteriorated metallic contact. The known sealing strips are also relatively expensive, resulting in large costs for the total length of sealing strip required in a modern telephone exchange, for example. DISCLOSURE OF INVENTION The object of the present invention is to provide a device for sealing between the edge portions of metal plates according to the above, the sealing action of the device being maintained for a considerably longer time than for previously available sealing devices, and which is furthermore cheap to manufacture. This is achieved by the device including a sealing strip, which is a helically wound metal element of sharp-cornered cross section. If this sealing strip is compres¬ sed in a suitable way between the edge portions of the metal plates, parts of the sharp-cornered sides of the element will be pressed against these edge portions so that good metallic contact is obtained. The distinguishing features of the invention are disclosed in the claims. BRIEF DESCRIPTION OF DRAWING The invention will now be described in detail with reference to the accom- panying drawing, on which Figures 1 and 2 illustrate in side view and end view, respectively, a device in accordance with the invention before the sealing strip is compressed, and Figure 3 and 4 are views corresponding to Figures 1 and 2, after the the sealing strip has been compressed. BEST MODE FOR CARRYING OUT THE INVENTION In Figures 1 and 2 there is illustrated in side view, and end view from the right in Figure 1, an embodiment of a device implemented in accordance with the * invention. The device includes a sealing strip 1, which is accomodated in a through-like groove 2 in the edge portion of one of two metal plates between which sealing is required. The sealing strip 1 is not shown in a compressed state an " d--comprises a metal element " wound into a helical " shape. " The metal element has a sharp-cornered cross section with a thickness of about 1 mm, and is manufacturing from such as stainless steel. This cross section is preferably quadratic, but may have some other shape with edges, e.g. it may be hexagonal or rectangular. In a practical embodiment, the diameter of the helical strip is about 7 mm. The through-like groove 2 is made in a metal section 3, made from such as aluminium, and constituting an edge portion of one of the two metal plates between which sealing is required. For example, the metal plates may comprise the lower part of one of the sides in an apparatus cabinet and a hatch to a cable compartment in the floor on one of the sides of the cabinet. Substantially the lower half (in the Figure) of the groove 2 is defined by a semicircular surface and its upper right-hand portion by two flat surfaces forming a right angle, while its upper left-hand side portion is open. Of these surfaces, the one flat surface facing downwards towards the groove is denoted by the numeral 4. The metal section 3 also has a flat surface 5 outside the groove and directed upwards in the Figure. A sealing device corresponding to the one in Figures 1 arid 2 is illustrated in Figures 3 and 4, but after the sealing strip 1 has been compressed by the edge portion of a metal plate thrust into the groove 2. This plate is denoted by the numeral 6, and in the illustrated position engages against the flat surfaces 4 and 5 as well against the sealing strip. The plate 6 can thus constitute the above- mentioned hatch to a cable compartment, and the metal section 3 may be the edge portion of the lower part of one side in an apparatus cabinet. The thickness of the plate 6 exceeds the original distance between the sealing strip 1 and surface 4 by about 1 mm in a practical embodiment. The surface 4 will thus function as support for the plate 6 after the latter has been inserted into the groove 2. If the plate 6 is displaced in the longitudinal direction of the sealing strip 1 simultaneously as it is thrust into the groove 2, the turns of the helically wound metal element will be twisted from . their original positions, this movement taking place in the longitudinal direction of the strip, and about the bottom¬ most contact points of the turns with the groove. The metal element then assumes the position illustrated in Figure 3, " for .example. Parts of the sharp- cornered sides of the metal element will thus be pressed against the bottom of the groove 2 and the underside of the plate 6. As a result of this, there is good metallic contact between the edge portions of both metal plates, and thereby effective screening against electromagnetic fields. The metalic contact ought not to be notably affected by an oxide layer occuring in time on the metal plates, since the fairly sharp corners of the metal element will be able to cut through such a layer. The illustrated sealing device is furthermore considerably cheaper to manufac¬ ture than the previously available devices that can be used in a similar connection.

Claims: CLAIMS 1. Device for providing a seal between the edge portions of two metal pla which are used as screens against electro-magnetic fields, including a metal sealing strip (1) comprising -a helically wound metal element and which intended to be compressed along these edge portions, characterized in that t metal element has a cornered cross section, and that by engagement agains support (4) the edge portion of one metal plate (6) is caused to be press against the sealing strip (1), both in the cross-sectional and longitudi direction of the strip, so that the turns of the helically wound metal eleme are twisted in the longitudinal direction of the strip in relation to their origi positions, whereby parts of the cornered sides of the metal element are press against said edge portions. 2. Device as claimed in claim 1, characterized in that the sealing strip (1) placed in a through-like groove (2) in the edge portion of the other metal pla and that said support (4) consists of a- flat surface facing towards the bottom the groove. 37 Device -as claimed~in claim l . or 2, characterized In that the cross section the metal element is quadratic.

Inventors: NILSSON UNO SIGURD, NILSSON, UNO, SIGURD
Applicants: ERICSSON TELEFON AB L M, TELEFONAKTIEBOLAGET LM ERICSSON
Application year: 1986
Main classification: H05K9
IPC codes: F16J15, G12B17, H05K9