Multi-function gasket

[54] MULTI-FUNCTION GASKET

[75] Inventor: Samuel S. Buonanno, Monroe, N.Y.

[73] Assignee: Schlegel Corporation, Rochester, N.Y.

[21] Appl. No.: 181,834
[22] Filed: Apr. 15,1988

[51] Int. a." H05K 9/00

[52] U.S.C1 174/35 GC

[58] Field of Search 174/35 GC, 35 R;

219/10.55 D

[56] References Cited

U.S. PATENT DOCUMENTS

2,477,267 7/1949 Robinson 174/35 GC

3,312,769 4/1967 La Kaff 174/35 GC

3,446,906 5/1969 Zulauf 174/35 GC

3,555,168 1/1971 Frykberg 174/35 GC

3,700,368 10/1972 Wells 425/115

3,781,390 12/1973 Wells 264/46.2

3,889,043 6/1975 Ducros 174/35 GC

4,098,633 7/1978 Kersten 174/35 R X

4,652,695 3/1987 Busby 174/35 GC

4,659,869 4/1987 Busby 174/35 GC

4,684,762 8/1987 Gladfelter 174/36

4,720,606 1/1988 Senn 174/35 GC

FOREIGN PATENT DOCUMENTS

221904 5/1985 German Democratic Rep. ... 174/35 R

OTHER PUBLICATIONS

Chomerics Corp. catalog, pp. 15-43 (publication date unknown).

Schlegel EMI Shielding Gaskets-Technical Data published May, 1987, less than one year prior to filing.

Primary Examiner—Morris H. Nimmo
Attorney, Agent, or Firm—Steele, Gould & Fried

[57] ABSTRACT

A multi-function gasket for electrical apparatus and the like, operation of which tends to generate or be adversely affected by electromagnetic and radio frequency interference (EMI/RFI), comprising: a continuously molded, resilient foam core having a sealed outer boundary layer when cured; a flexible, electrically conductive and substantially abrasion resistant sheath surrounding the foam core and bonded to the boundary layer as the foam expands within and fills the interior of the sheath during the molding; and, mounting structure for affixing the gasket. The apparatus may be sealed against EMI/RFI leakage, noise emission and enviromental infiltration through perimeter gaps of electrically conductive doors, access panels and the like by the actions and interactions of the sheath, the foam core and the boundary layer. The flexible sheath is continuously pressed into positive engagement with the conductive surfaces between which it is mounted by the resilient foam core, forming a continuous electrical path across the gaps and preventing EMI/RFI leakage through the gaps. The boundary layer prevents noise emission and environmental infiltration across the gaps. The sheath protects the boundary layer against damage from abrasion and the like.

"Q-Lon"weatherstrip advertising brochure, Oct., 1982.

18 Claims, 2 Drawing Sheets

1

MULTI-FUNCTION GASKET

BACKGROUND OF THE INVENTION

1. Field of the Invention 5 This invention relates generally to the field of gaskets

and seals. More particularly, this invention relates to the fields of: gaskets for electrical apparatus and the like which are prone to generate, or be adversely affected by electromagnetic interference (EMI) and/or radio frequency interference (RFI) from gaps in shielded or conductive housings; seals which are intended to reduce or eliminate noise emission; and, seals which are intended to reduce or eliminate environmental contami- J5 nation or infiltration. Most particularly, this invention relates to a field of hybrid or multi-function gaskets and seals which combine the protective features of preventing EMI/RFI leakage, preventing audible noise emission and preventing environmental infiltration. 2o

2. Description of Prior Art

Electromagnetic interference (EMI) has been defined as undesired conducted or radiated electrical disturbances from an electrical or electronic apparatus, including transients, which can interfere with the operation of 25 other electrical or electronic apparatus. Such disturbances can occur anywhere in the electromagnetic spectrum. Radio frequency interference (RFI) is often used interchangeably with electromagnetic interference, although it is more properly restricted to the radio fre- 30 quency portion of the electromagnetic spectrum, usually defined as between 10 kilohertz (KHz) and 10 gigahertz (GHz). Comprehensive technical summaries are available from a number of sources.

A shield is defined as a metallic or otherwise electri- 35 cally conductive configuration inserted between a source of EMI/RFI and a desired area of protection, which has the capability of absorbing and/or reflecting EMI/RFI and reducing the energy levels thereof. As a practical matter, such shields normally take the form of 40 an electrically conductive housing which is electrically grounded. The energy of the EMI/RFI is thereby dissipated harmlessly to ground. Such a shield may be provided to prevent EMI/RFI radiating from a source or to prevent EMI/RFI (generated randomly or by de- 45 sign) from reaching a target, or both. Most such housings are of necessity provided with access panels, hatches, doors and/or removable covers.

The gaps between the panels, etc. and the housing provide an undesired opportunity for EMI/RFI to pass 50 through the shield. The gaps also interfere with electrical currents running along the surfaces of the housings from EMI/RFI energy which is absorbed and is being conducted to ground. The gaps reduce the efficiency of the ground conduction path and may even result in the 55 shield becoming a secondary source of EMI/RFI leakage, from gaps which act as slot antennas.

Various configurations of gaskets have been developed over the years to close the gaps of such shields and to effect the least possible disturbance of the ground 60 conduction currents. Each seeks to establish as continuous an electrically conductive path as possible across the gap(s). However, there are inevitable compromises between: the ability of the gasket to smoothly and thoroughly engage and conform to the surface of the hous- 65 ing adjacent the gaps; the conductive capacity of the gasket; the ease of mounting the gasket; the ability of the gasket to withstand abrasive wear and tear, as well

2

as repeated compression and relaxation; and, the cost of manufacturing the gasket.

Electrical or electronic apparatus are often prone to acoustically noisy operation, which may become quite annoying to those in audible range of the apparatus, even in the absence of any specific technical difficulty caused by the audible noise. Noise emission can of course also result in technical problems under certain circumstances. Audibly noisy apparatus are sometimes provided with seals to reduce noise emission, but such seals are often only marginally effective at best. Moreover, such seals are not effective to prevent EMI/RFI leakage.

Electrical or electronic apparatus are also notoriously prone to damage or malfunction from environmental contamination or infiltration, the most common and perhaps most destructive contaminants being dust and moisture. Many electrical and electronic apparatus are provided with cooling fans, which are intended to draw air along a predefined path within the apparatus to maximize cooling. When the path is well defined, a filter can be used to collect dust and other debris prior to infiltration. Unfortunately, gaps of the kind described above too often provide alternate paths for contaminated air to enter the apparatus and eventually cause problems. Environmental seals, such as used in windows and doors have of course been known for some time, but such seals have never been capable of preventing EMI/RFI leakage.

The following patents are illustrative of the kinds of gaskets which have been proposed to prevent EMI/RFI leakage. Even a cursory analysis of such prior art will reveal the inability of such gaskets to function as EMI/RFI gaskets and as environmental infiltration seals and as audible noise seals; the inability of such gaskets to be manufactured relatively inexpensively; and, the inability of such gaskets to withstand abrasive wear and tear.

An RFI shielding gasket disclosed in U.S. Pat. No. 3,555,168 is formed as a conductive foil lamina bonded to a resilient foam backing by a flexible adhesive and is mounted by a pressure-sensitive adhesive on the back of the foam backing. The gasket is a flat member produced from flat layers of flat stock, rather than by extrusion or molding. In a preferred embodiment, the foam is a closed cell, medium density neoprene foam from 0.015 to 0.500 inches thick. The resulting laminate is die cut to shape, and is said to be RFI tight and dust tight. A seal disclosed in U.S. Pat. No. 3,312,769 has a resilient core, preferably neoprene sponge, surrounded by a metallic mesh, preferably an alloy of nickel and copper such as Monel. There is no indication the the core is bonded to the metallic mesh in any fashion. A sealing gasket disclosed in U.S. Pat. No. 2,477,267 comprises a resilient gasket having a network of electrically conductive wires embedded therein and therethrough, the wires having portions exposed on opposite surfaces, of the gasket. A seal disclosed in U.S. Pat. No. 3,466,906 comprises a body of resilient plastic foam material having a plurality of interconnected open cells and a coating of electrically conductive material provided throughout the body on the surfaces of the plastic elements. A conductive coating is preferably applied by electroplating to form a conductive surface on the seal. A seal available from Chomerics Corporation is denoted by the trademark MESH STRIP. The seal is available as resilient, single and dual, all-metal strips or compressed shapes. The seal is also available with an elastomer core,