GB2218264A - Gasket carrier - Google Patents

Abstract

A gasket carrier (10) comprises a channel-forming member 12 for receiving a RFI shielding gasket 14. The channel- forming member 12 is provided with first and second resilient jaws 22, 24 which hold the gasket 14 in position. <IMAGE>

Description

A GASKET CARRIER This invention relates to apparatus for use with electric al and electronic equipment.

Equipment containing electronic or electrical circuitry in which electric signals are changing in magnitude is a potential radiator of electromagnetic interference.

Such interference is also generated by a wide range of natural phenomenon including atmospheric and electrostatic activity. This interference may be very slight, or very severe, and is classified as radio frequency interference (RFI) if it falls anywhere in the frequency spectrum from a few kilohertz to many gigahertz.

Although shielding of electronic and electronic components to prevent such interference can be substantially effected using, for example, an aluminium can or wire mesh "cage", there are many circumstances where, at a joint between screen and screened component, a gap may occur, for example at the edges of connectors.

indicators, meters, inspection panels, doors or wave guide flanges. Any such gap can function as an efficient slot aerial for reception and transmission of electromagnetic signals, this forming a potentially serious RFI hazard.

It is thus necessary to seal such joints using an electrically conductive gasket A known design of such gasket, manufactured by the present applicants under the trade mark TWINSHIELD, includes a combination of a wire mesh strip for interference shielding, attached, by adhesive, to neoprene or a silicone or other elastomer which may be of solid or closed cell sponge form, for environmental sealing, this having an adhesive layer for connection to a mating surface. It is a disadvantage of such a design, however, that the adhesive bonds between the elastomer sponge and mesh strip and mating surface are vulnerable to failure in circumstances where the equipment to which the gasket is attached is subject to extremes of pressure or temperature (e.g. during a paint stoving process during manufacture).Furthermore, the application of the adhesive requires a separate and messy manufacturing step, this leading to increased expense.

A further known design, manufactured by the present applicants under the trademark TRIMSHIELD includes a composite gasket material formed from a resilient netted wire mesh, which may have an elastomer sponge core to provide increased resilience, strips of the mesh being retained in an elongate aluminium extrusion.

Disadvantages of this design are that, although the design is more robust than the sponge-mesh design, it is significantly more expensive to manufacture, can only be assembled in relatively short lengths and is expensive to fit to equipment due to the need to tap or screw the aluminium extrusion in place.

According to the invention, there is provided a gasket carrier having a channel forming member for receiving a gasket, the member including at least one resilient jaw adapted to retain the gasket in the channel.

An embodiment of the invention will now be described, by way of example, with reference to the accompanying drawings in which: Fig. 1 is a perspective view of an embodiment of the invention; Fig. 2 is a cross sectional view in the plane 2-2 of the embodiment shown in fig. 1; Fig. 3 shows a corner piece for connecting strips of the carrier shown in figs. 1 and 2 together.

With reference to figs. 1 and 2, an embodiment of the gasket carrier of the invention, generally designated 10, is shown. The carrier 10 includes a channel forming member 12 which is formed as an extrusion from a plastics material, preferably PVC or, if high temperature stability is required, reinforced polycarbonate.

The channel forming member 12 defines a channel 14 in which a shielding gasket 16 (shown in phantom lines) is held. The gasket, preferably, comprises a resilient netted wire mesh 18 having an elastomer sponge core 20.

The channel forming member 12 is provided with first and second jaws 22, 24 which form sides of the channel.

The jaws 22, 24 have sufficient resilience to allow them to be displaced from the position shown in fig. 2 outwardly when a gasket is inserted in the channel 14 the jaws then act to retain the gasket in the channel, as shown.

The channel member 12, as shown in fig. 1, is provided with a plurality of slots 26 formed in a base portion 19 of the channel member, the slots being stamped out of the member 12. after extrusion. The slots 26 allow electrical continuity between the gasket 16 and a surface 40 to which the gasket is connected to be maintained.

A layer of aluminium foil 30 is attached to the base portion 19 by means of adhesive layers 32, 34 at the edges of the base portion 19 so that the adhesive does not overlie the slots 26. Further layers of adhesive 36, 38 are applied to the other side of the aluminium foil 30 and extend over the full surface of the aluminium sheet, with the exception of the area thereof which corresponds to the slots 26 of the channel forming member. The adhesive layers 36, 38 are for connecting the aluminium foil 30 and channel forming member 12 to the surface 40 to which the gasket carrier 10 is to be fitted.

The aluminium foil 30, provides an increased surface area of adhesive for connection to surface 40, with the outermost edges of the aluminium foil 30 providing some degree of conformability to surface 40, as these are not directly connected to the channel forming member 12.

Furthermore, the aluminium foil 30 provides good electrical continuity from the gasket 12 to surface 40.

Preferably. a backing sheet (for example paper) is attached to adhesive layers 36, 38 during manufacture.

the backing sheet being removed from a pre-cut length of carrier to expose the adhesive layers 36, 38 before application of the carrier 10 directly to surface 40.

In order to ensure good electrical continuity, the surface 40 should be clean, dry and free from rust or other corrosion. Specifically in the region corresponding to slots 26, the surface must be bare metal or metallic plated.

If the equipment to which the carrier is to be connected is required to undergo a subsequent painting and stoving process, a further extrusion (not shown) can be provided which engages between jaws 22, 24 or clips over carrier 10 and masks the channel 14 during painting.

Alternatively, a layer of masking tape may be provided over the channel 14, jaws 22, 24 and adjacent surfaces.

The gasket carrier and backing foil 30 also act as a mask for the surface 40 during painting thus eliminating the need for a separate masking step, compared to the prior art. The paint finish also seals any gaps between the outer edges of the foil 30 and surface 40.

Using an extrusion process for the manufacture of the channel forming member 12 it would be possible, also, to make customised shapes of carrier 10 to suit particular applications.

With reference to figure 3, a preformed injection moulded connector (in this case a corner piece) for connecting two lengths of gasket carrier 12 together is shown. The connector, generally designated 50, is provided with two limbs 52, 54 connected at spaced intervals by webs 56, the gap between limbs 52, 54 forming a channel 58 for receiving the gasket 14. Lugs 60, 62, 64, 66 are provided at the ends of the limbs 52, 54 and are so shaped to engage within corresponding side portions 68, 70 of the channel member 12.

The connector piece 50 is, like the channel forming member 12, provided with an adhesive aluminium foil sheet 30 for connection to a base portion of the connector.

An advantage of providing injection moulded corners such as that shown in figure 3 is that such corners have a fixed corner radius which eliminates risk of kinking and subsequent hard spots in the gasket 14 when engaged therewith. Furthermore the fixed height of the connector 50 acts as a compression limiter for the gasket.

A particular advantage of the structure of the carrier 10 is that the resilient jaws 22, 24 may be made sufficiently conformable to allow various gasket types and shapes to be retained within the channel 14, so that one gasket carrier can be used with a variety of products as shown in figures 4a-4e in which figure 4a shows the gasket carrier 10 used with an environmental gasket 80 (i.e. one) having solely an environmental and not an interference shielding function (such a gasket being formed from neoprene or a silicone or other elastomer of solid or closed cell sponge form): figures 4b and 4c show the gasket carrier 10 used with cored mesh gaskets, gasket 82 being of tubular form and gasket 84 being of square sponge-filled form; figure 4d shows gasket 10 used with a composite gasket material formed from a silicone elastomer base into which a close matrix of fine metal wires are embedded (manufactured by the present applicants under the trade mark MULTISHIELD); figure Se shows the carrier 10 used with a conventional finger contact type gasket.

The gasket may be removed and replaced subsequently with ease, without requiring the carrier 10 to be removed.

Furthermore, once the carrier is in place, the gasket can be installed as one continuous length with only one joint.

Although the aluminium foil 30 is desirable to ensure good electrical continuity, this can be omitted and the adhesive applied directly to the base 19 of the channel forming member 12. In this circumstance, it is desirable that the gaps between the slots 26 in the base of the member be of a width less than the shortest RF wavelength within the frequency range of interest.

Furthermore, although a plastics material is preferred for construction of the carrier 10 and corners 50, hard rubber or a metal, or any other material which allows extrusion may be used. If a metal or conductive plastics material is used, the slots 26 may be omitted, provided that a portion of the base 19 is in good electrical contact with the surface 40.

The gasket material 14 should also have some resilience, to enable it to conform to the shape of the slots 26 and form a good electrical connection with surface 40.

Whilst any adhesive (e.g. thermoset, high temperature or pressure sensitive) may be used for connecting the foil 30 to member 12 and surface 40, if the equipment to which the carrier is to be attached is to be painted and subsequently stoved, a thermoset adhesive is preferred. Alternatively a conductive adhesive may be used in which case it is not necessary to ensure that the slot areas are kept clean of adhesive.

Although in the described embodiment, the gasket carrier has been provided with two jaws 22, 24, a single jaw may be employed as shown in figures 5a and Sb.

Claims (24)

1. A gasket carrier comprising a channel forming member adapted to receive a gasket, the channel forming member having at least one resilient jaw for retaining the gasket in the channel.

2. A gasket carrier as claimed in claim 1 wherein the carrier is formed from non-conductive material and includes at least one opening formed in the base of the channel.

3. The gasket carrier as claimed in claim 1 or claim 2 further comprising a conductive strip connected to the base of the channel.

4. The carrier as claimed in claim 3 wherein a layer of adhesive is formed on a first surface of the conductive strip, a part of said surface being free from said adhesive.

5. Apparatus as claimed in claim 4 wherein said adhesive is a thermoset, high temperature or pressure sensitive adhesive.

6. A carrier as claimed in any one of claims 3 to 6 wherein the channel forming member is connected to the conductive strip by means of a second layer of adhesive formed between a second surface of the conductive strip and the base of the channel member, at least part of said second surface being free from said second layer of adhesive.

7. A carrier as claimed in any one of the preceding claims further comprising a mask member for closing the channel.

8. A carrier as claimed in claim 7 wherein the mask member is formed from adhesive tape.

9. A carrier as claimed in cliam 7 wherein the mask member is engagable with said at least one jaw.

10. A carrier as claimed in any one of the preceding claims wherein the channel member is formed as an extrusion.

11. A carrier as claimed in claim 1 wherein t-he channel forming member is formed from conductive material.

12. A carrier as claimed in claim 2 or any claim dependent thereon wherein the base of the channel includes a plurality of said openings, the gap between adjacent openings being less than the shortest wavelength within the working range of the carrier

13. A carrier as claimed in any one of claims 1 to 12 wherein the carrier is formed from plastics material.

14. A connector adapted to connect two carriers as claimed in any one of the preceding claims together.

15. A connector member as claimed in claim 14 having first and second lug means arranged to be engaged by the channel of a respective carrier.

16. A connector as claimed in claim 14 or claim 15 wherein the connector is injection moulded.

17. A connecting member as claimed in any one of claims 14 to 16 or comprising a channel and at least one opening formed in the base of the channel.

18. A connector as claimed in claim 17 further comprising a conductive strip connected to the base of the channel.

19. A connector as claimed in any one of claims 14 to 18 wherein the connecting member is formed from plastics material.

20. A connector as claimed in any one of claims 14 to 19 having a fixed corner radius.

21. A gasket carrier substantially as hereinbefore described with reference to figs 1 and 2 of the accompanying drawings.

22. A connector substantially as hereinbefore described with reference to fig. 3 of the accompanying drawings.

23. In combination a gasket carrier and a gasket as claimed in any one of claims 1 to 13 and 19.

24. In combination a gasket and a connector as claimed in any one of claims 14 to 19 and 21.