GB2098808A - Sealing gasket for radio interference suppression - Google Patents

Abstract

The invention relates to a gasket for use in a radio frequency interference shielding housing to provide a hermetic seal between the two housing parts while electrically connecting the two parts to one another. The gasket (Fig. 6) comprises a wire mesh embedded within a moulded seal with the mesh lying sufficiently close to the surface of the seal so that electrical contact is made with the mesh when the gasket is held under pressure between the housing parts. <IMAGE>

Description

SPECIFICATION Improvements in radio interference suppression The present invention relates to the suppression of radio frequency interference.

It is. known in order to suppress radio frequency interference to house the equipment to be protected in a metallic container.

The purpose of the metallic container is to prevent radiation from escaping from the equipment or to prevent interfering radiation from reaching the equipment. It is sometimes required for the same housing to be hermetically sealed to act not only for the suppression of radio interference but also to provide mechanical protection for the equipment, for example against rain or when the equipment is in a dusty or hostile environment. An instance where such protection may be required is in the case of computer equipment where immmunity to radio interference is important to prevent corruption of data, and where certain elements of the system are known to be sensitive to the ambient atmospheric condi- tions.

When a housing formed in two or more parts is intended to be hermetically sealed and to act as a shield against radio frequency interference, it is important that the mating surfaces of the housing should seal at all points and also be in electrical contact with one another at all points. Though this can be achieved by very precise machining this is often not economical and it is instead preferred to use a gasket which is capable of sealing the joint whilst at the same time electrically connecting the two parts to one another at all points.

In order to provide such a gasket in the past, it has been known to attach a preformed seal, made for example of an elastomeric material, to a preformed wire mesh so that the mesh and the elastomeric material are compressed by the joint to provide the desired sealing properties.

It was found with the known gaskets that they were difficult to manufacture and particular problems were experienced in attempting to secure the elastomer to the mesh by means of an adhesive.

In accordance with a first aspect of the invention there is provided a gasket for use in a radio frequency interference shielding housing which comprises an electrically conductive wire mesh wholly embedded within a moulded seal, the wire mesh being sufficiently close to opposite surfaces of the gasket to make electrical contact with the housing parts when the gasket is compressed between the said parts.

In the present invention, the seal is moulded into the wire mesh and there is no need for two separate elements to be adhered to one another. It has been found, surprisingly, that such integral moulding is possible because the wire mesh is capable, upon being compressed, of braking through any thin film moulded around it to establish electrical contact with the housing parts.

According to a second aspect of the present invention, there is provided a method of manufacturing a gasket for use in a radio frequency interference suppression housing which comprises placing a wire mesh within a mould cavity, placing within the same mould cavity a length of thermoplastic material, applying pressure to the thermoplastic material to urge the wire mesh into close contact with opposite sides of the mould, heating the thermoplastic material to cause it to flow to fill the mould and the spaces within the wire mesh, and allowing the thermoplastic material to cool.

It will be seen that the mesh is in contact with the surfaces of the mould before the thermoplastic material flows so that in the finished gasket the wires of the mesh lie very close to the surfaces which make contact with the housing parts and are capable of breaking through any thin film moulded around them to establish an electrical contact.

The invention will now be described further, by way of example, with reference to the accompanying drawings, in which, Figures 1 and 2 show prior art constructions of a gasket, Figure 3 shows a section through a gasket of the present invention, Figure 4 shows a method of manufacturing the gasket shown in Fig. 3, Figures 5, 6 and 7 are sections through further gaskets of the invention, and Figure 8 is a plan view of a still further embodiment of a gasket.

In Fig. 1 there is shown a section through prior art gasket of the type referred to as a twin seal, sealing both hermetically and against radio frequency interference. The gasket consists of a strip of an elastomerical material 10 bonded by means of an adhesive 12 to a wire mesh 14 which may for example be a knitted cable. The difference between the gaskets shown in Fig. 1 and 2 resides in the fact that the mesh 14 in Fig. 1 has a rectangular section while the mesh 14 in Fig. 2 is of circular section.

Fig. 3 shows a gasket in accordance with the invention which consists of an elastomeric block 30 with a wire mesh embedded within the block and designated 32. The wire mesh lies very near the surface of the gasket on three sides and is covered by only a very thin skin which is capable of being penetrated when the gasket is compressed between the parts of a housing by the application of a force represented by the arrows p.

In manufacturing the gasket shown in Fig.

3, a wire mesh knitted cable 32 is placed within a rectangular mould cavity 34 (Fig.

4a). A length of a cold elastomeric thermoplastic material 36 from which the seal is to be formed is placed over the mesh 32 (Fig.

4b) and compressed by means of a press (Fig.

4c) so as to closely compact the wire mesh 32 and urge it into intimate contact with the sides of the mould 34. The mould is then heated to cause the elastomeric material to flow and fill the mould including the spaces within the mesh 32 (Fig. 4d).

Figs. 5, 6 and 7 show alternative cross sections of the gaskets. All these embodiments can be manufactured in a similar manner to that described with reference to Fig. 4 by suitable shaping of the mould.

The wire mesh 32 in Fig. 4 is shown as having an eliptical cross section prior to its being compressed within the mould. It is preferred that the mesh should be passed through a die so as to have a cross section conforming to that of the mould prior to its insertion so that it should lie close to the surface of the moulded seal even before compression by the elastomeric material.

The process as described by reference in Fig. 4 requires the elastomer to be layed on top of the mesh prior to pressure being applied. It is however also acceptable to place the wire mesh and the elastomer side by side one another within the mould cavity since the elastomer will exert pressure in all directions on being compressed. This manner of manufacture is preferred especially when the seal to be formed is not in the form long run but in the form of a shaped gasket having for example a plan view as partially shown in Fig. 8.

Claims (6)

1. A gasket for use in a radio frequency interference shielding housing which comprises an electrically conductive wire mesh wholly embedded within a moulded seal, the wire mesh being sufficiently close to opposite surfaces of the gasket to make electrical contact with the housing parts when the gasket is compressed between the said parts.

2. A method of manufacturing a gasket for use in a radio frequency interference suppression housing which comprises placing a wire mesh within a mould cavity, placing within the same mould cavity a length of thermoplastic material applying pressure to a thermoplastic material to urge the wire mesh into close contact with opposite sides of the mould heating the thermoplastic material to cause it to flow to fill the mould and the spaces within the wire mesh, and allowing the thermoplastic material to cool.

3. A method of manufacturing a gasket as claimed in Claim 2, wherein the thermoplastic material is laid over the wire mesh in the direction in which pressure is applied.

4. A method of manufacturing a gasket as claimed in claim 2, wherein the wire mesh and the thermoplastic material are placed side by side one another in the mould cavity transversely to the direction in which pressure is applied.

4. A method of manufacturing a gasket as claimed in Claim 2, wherein the wire mesh and the thermoplastic material are placed side by side one another in the mould cavity to which direction in which pressure is applied.

5. A gasket constructed substantially as herein before described with reference to and as illustrated in Fig. 3, Fig.

5, Fig.

6, Fig. 7 or Fig. 8 of the accompanying drawings.

6. A method of manufacturing a gasket for use in a radio frequency interference suppression housing, substantially as herein be fore described with reference to and as illustrated in Fig. 4 of the accompanying drawings.

CLAIMS (5 Aug 1982)

1. A gasket for use in a radio frequency interference shielding housing which comprises an electrically conductive wire mesh wholly embedded within a moulded seal having opposite mutually parallel surfaces for sealing against the housing parts, the spaces within the wire mesh being filled by the moulded seal, the wires of the mesh being substantially tangential to the said surfaces so as to make electrical contact with the housing parts when the gasket is compressed between the said parts.

2. A method of manufacturing a gasket for use in a radio frequency interference suppression housing which comprises placing a wire mesh within a mould cavity, placing within the same mould cavity a length of thermoplastic material, applying pressure to the thermoplastic material to urge the wire mesh into a position in which its wires are substantially tangential to opposite sides of the mould, heating the thermoplastic material to cause it to flow to fill the mould and the spaces within the wire mesh, and allowing the thermoplastic material to cool.

3. A method of manufacturing a gasket as claimed in claim 2, wherein the thermoplastic material is laid over the wire mesh in the direction in which pressure is applied.