GB2170281A - Gasket, and joint formed therewith - Google Patents

Abstract

An elongate resilient gasket (10), typically of neoprene with a Shore hardness of 50 to 90, is used to form a seal for a window panel in a wall of a containment box. The gasket has two tongues (14,16) defining between them a slot (18) for receiving the edge of the window aperture in the wall, and when uncompressed has a ridge portion (20) and a prominence (24) on the side facing the window panel. The tongue (14) between the slot and the window panel contains a void (28). When a clamp is screwed down on to a stud on the box wall, a flange thereof presses the window panel against the gasket to form two linear seals along the ridge (20) and prominence (24), to compress the void (28) and to pivot the body (12) of the gasket around the edge of the wall and thereby urge the tongue (16) into a further sealing contact with the inner side of the box wall. <IMAGE>

Description

SPECIFICATION Gasket and joint formed therewith This invention relates to a gasket and to a joint formed therewith. The gasket and joint are particularly useful in the construction of a containment box, in which a removable panel is required to be sealed over an aperture in the box to prevent the escape of any noxious substance contained within the box or the ingress of oxygen or water vapour.

A containment box may be utilized for the remote handling of, for example, toxic or radioactive substances or air sensitive materials. The box construction may be largely of metal, but a transparent window panel may be provided to enable the interior to be observed. A reliable seal must then be established between the panel and the aperture surround. The panel may need to be removable to permit access to the interior of the box, in which case precautions need to be taken against residual particles or droplets of any noxious substance that may have lodged in the joint between panel and box.

Such a joint may be formed using a gasket between the rim of the aperture and the panel edges. The gasket must provide a reliable seal. It is an object of this invention to provide a gasket by means of which an effectively sealed joint can be assembled without requiring excessive clamping pressures and which can be of such a form as to reduce the entrapment of contaminants in the joint internally of the containment box.

According to the present invention there is provided an elongate resilient gasket for sealing between an edge portion of a rigid sheet, for example the edge of an aperture in a wall of a containment box, and an adjacent rigid planar surface overlapping the sheet edge, for example the inner face of a transparent window panel.The gasket is substantially uniform in cross section along its length and comprises a body portion, and first and second tongues extending from the body portion and defining between them a slot for receiving and embracing the said sheet edge, the innermost end of the slot being closed by the body portion of the gasket; wherein the first tongue includes a raised ridge spaced from the body portion of the gasket and extending away from the general plane of the slot, and the body portion is provided with a prominence extending away from the general plane of the slot on the same side of the plane as the said ridge, whereby a concavity is defined between the said ridge and the said prominence.

The invention further provides a joint between an edge portion of a rigid sheet and an adjacent rigid planar surface overlapping the sheet edge. The joint comprises a gasket as aforesaid disposed the length of the joint, the sheet edge being embraced between the first and second tongues of the gasket, and the ridge on the first tongue and the prominence on the body portion of the gasket lying against the planar surface, and compression means for urging the planar surface towards the sheet whereby to sealingly compress the first tongue between them and to rotate the body portion of the gasket, by the pressure of the planar surface against the prominence thereon, about the sheet edge and thereby to urge the second tongue into particle-sealing contact with the sheet adjacent the edge thereof.

The invention still further provides a containment box having an aperture in a wall thereof and a panel sealingly affixed over the aperture, comprising a joint as aforesaid between the pane and the wall about the aperture.

Thus, in use, the ridge and the prominence contact the planar surface when the joint is first assembled. On clamping the joint by urging the sheet and the planar surface towards one another, the edge portion of the sheet lying in the slot presses the first tongue towards the planar surface. This movement is permitted by the resilience of the gasket and tends to flatten the concavity between the ridge on the tongue and the prominence on the body of the gasket, pressing the ridge against the surface to form a first seal and pressing the prominence against the surface to form a second seal. Although the concavity is normally also flattened against the surface, the greatest sealing pressures are localised along two parallel and more nearly linear zones, so that a double seal is provided between the gasket and the planar surface.The clamping pressure may however be relatively light compared with the clamping pressure that would be required if the gasket had a single broad and flat face to be sealingly pressed against the planar surface. Further, as will be described in more detail below, the gasket can be notched to extend the joint around a sharp corner while retaining the seal between at least the prominence on the body portion and the planar surface.

The rotation of the body portion about the sheet edge by means of the reaction between the prominence on the body portion and the planar surface upon clamping the joint tends to press the second tongue, which should be on the inside of a containment box, against the inner face of the sheet member, e.g. the box wall around the aperture therein. This provides a relatively light second seal between the sheet member and the gasket, in addition to the primary seal which lies between the sheet and the first tongue. This second seal provides a safeguard against dust and other debris within the box entering the joint and prevents contaminants from lodging in the slot.

The invention is illustrated by way of example in the accompanying drawings, in which: Figure 1 is a cross section through a first embodiment of a gasket in accordance with the invention; Figure 2 is a cut-away perspective view of a joint incorporating the gasket of Fig. 1.

Figure 3 is a cross section through the joint shown in Fig. 2; Figure 4 is a cut-away perspective view of an uncompressed joint incorporating the gasket of Fig. 1 at a corner, the clamp being omitted for clarity; and Figure 5 is a cross section through a second embodiment of a gasket in accordance with the invention.

The gasket 10 shown in Fig. 1 is of elongate form with a uniform cross section. It is of a suitably durable resilient material such as neoprene, polyurethane or natural rubber, and is typically manufactured by extrusion. Its mechanical properties will vary somewhat according to the specific application, but suitable stiffness and resilience are commonly achieved in materials having a Shore hardness in the range of 50 to 90, more suitably 50 to 80 and most preferably 70 to 80.

The gasket 10 has a solid body portion 12 and a first tongue 14 and a second tonge 16 which extend from the body portion and define between them a slot 18. The innermost end of the slot is closed by the body portion of the gasket. The first tongue 14 includes a raised ridge portion 20 spaced from the body portion of the gasket and located adjacent the end of the tongue remote from the body portion. The ridge extends away from the general plane of the slot, which is defined by the inner face 22 of the first tongue 14, the second tongue 16 being inclined towards the outer end of the first tongue in the relaxed gasket but being flexed in use, as will be described later herein.

The body portion 12 of the gasket 10 is provided with a prominence 24 extending away from the general plane of the slot 18 on the same side of the plane as the ridge 20, so that a concave surface 26 is defined between the ridge and the prominence.

The first tongue 14 includes an internal void 28 between the ridge 20 and the body portion 12 of the gasket. The purpose of this void is to modify locally the compressibility of the gasket in an assembled joint, as shown in Figs. 2 and 3, in which the gasket 10 is compressed between an edge portion of a rigid sheet member 30, forming part of a stainless steel wall of a containment box around an aperture therein, and an adjacent rigid planar surface of a transparent acrylic or pvc window panel 32.

In the joint, the gasket 10 is disposed the length of the joint. The edge of the sheet 30 is received in the slot 18 and is embraced between the first tongue 14 and the second tongue 16. The ridge 20 on the first tongue and the prominence 24 on the body portion 12 of the gasket lie against the planar surface of the panel 32.

Compression means for urging the planar surface of the panel 32 towards the sheet 30 comprise a clamp member 34 having a first flange 36 bearing against the panel and a second flange 38 bearing against the sheet member 30, and a screw member 40 to draw the clamp member towards the sheet member upon tightening thereof, thereby compressing the gasket 10 in the joint. The screw member 40 comprises an internally screw-threaded shank portion 42 and a head portion 44, provided with a drive slot 46, countersunk into the clamp member. The shank engages a screw-threaded stud 48 welded to the sheet member 30.

Upon tightening the screw 40, the flange 38 of the clamp member 34 contacts the sheet member 30 along a line which defines a fulcrum; the clamp member pivots about the contact line and the flange 36 bearing against the panel 32 causes the first tongue 14 of the gasket 10 to be compressed between the panel and the edge portion of the sheet member. The planar surface of the panel makes contact initially with both the ridge 20 and the prominence 24 on the gasket to create, under light clamping pressure, two parallel narrow sealing zones along the length of the joint between gasket and panel. Upon further tightening of the joint by means of screw 40, the ridge and prominence become flattened and the formerly concave surface 26 between them lies flat against the planar surface of the panel.The pressure of the panel against the prominence on the body portion 12 of the gasket causes the body portion to rotate somewhat about the edge of the sheet 30.

The body portion is sufficiently stiff to transmit this motion to the second tongue 16.

In the unstressed gasket before assembly of the joint the tongue 16 is inclined towards the tongue 14 to form a slot 18 that is wider at its innermost end than at its mouth. The second tongue 16 is relatively flexible so that the gasket can be fitted to the sheet 30 with light pressure from the tongue 16 against the sheet edge received in the slot. The rotation of the body portion 12 about the sheet edge as described above tends to increase the pressure of the second tongue on the sheet and enhances the sealing effect against particles or droplets within the containment box entering the slot.

This feature has the further advantage that a single gasket size is suitable for use with a range of panel thicknesses without loss of sealing. Thus it has been found that a slot of width 3.2 mm at its inner ends can be effectively used with panel thicknesses ranging from 1.5 to 5 mm. It can thus be seen that the panel may even be thicker than the greatest width of the slot.

The void 28 in the first tongue 14 is largely closed when the gasket is fully compressed in the joint. Thus the portion of the first tongue between the ridge 20 and the body portion 12 of the gasket relatively easily compressed, while the body portion itself and the outer end of the tongue including the ridge are relatively stiff. The tongue material lying between the void 28 and the concave surface 26 serves to tie the ridge to the body portion and inhibit movement of the ridge away from the body portion when the joint is tightened, thus maintaining the pressure between the ridge and the planar surface of the panel 32.

The length of the shank 42 of the screw is selected so that the gasket is optimally compressed when the screw is fully tightened against the sheet 30. The length is specific to given lengths of the flanges 36 and 38 of the clamp member 34 and to a given thickness of the panel 32.

It is not necessary that the clamp member 34 be a continuous length. A number of separate clamp members may be used, preferably abutting but optionally spaced apart. Each clamp member is desirably clamped by at least two screws 40. Since relatively low sealing pressures are required, relatively wide screw spacings are acceptable.

It should be noted that no fixing holes are required in the panel 32.

The gasket 10 can be used as it is to form a straight or curved joint. It can also be used to form an angled joint as depicted in Fig. 4.

In this case the aperture in the containment box wall is rectangular and each right-angled corner includes a joint having the layout shown. The gasket is given a 90 V-notch from the rear, extending through the body portion 12 and having it apex in the slot 18 and in the void 28, The two sides of the notch are then butted together at the corner along a line 50. The seals between the sheet 30 and the first and second tongues 14 and 16, and between the panel 32 and the ridge 20 on the first tongue, are accordingly still continuous. A continuous run of gasket can therefore be used in the joint around the entire aperture, with but a single butt joint between the two ends of the gasket, thereby reducing the number of weak points at which leakage might tend to occur.

The gasket 10 illustrated in Fig. 1 to 4 has finely tapered edges where it is to make sealing contact with the sheet edge and the planar surface, to eliminate all dust traps. Thus the tips of the first and second tongues 14 and 16 to contact the sheet edge, and the tips of the ridge 20 and prominence 24 to contact the planar surface, are feathered to fine points. Also, the concave surface 26 between the ridge and prominence is smoothly curved. However, in practice, manufacturing considerations may dictate that the form of the gasket should be modified, and the gasket 52 shown in Fig. 5 is of such a modified form. The sheet edge-contacting tip 54 of the first tongue, the sheet edge-contacting tip 56 of the second tongue, the planar surface-contacting tip 58 of the ridge and the planar surface-contacting tip 60 of the prominence are all radiused, and the concave surface 62 between the ridge and the prominence has a non-arcuate configuration. The gasket nevertheless retains excellent sealing characteristics and may be used to form a joint around a containment box window panel with a typical leak rate of only 0.05% of the box volume per hour.

Claims (15)

1. An elongate resilient gasket for sealing between an edge portion of a rigid sheet and an adjacent rigid planar surface overlapping the sheet edge, the gasket being substantially uniform in cross section along its length and comprising a body portion and first and second tongues extending from the body portion and defining between them a slot for receiving and embracing the said sheet edge, the innermost end of the slot being closed by the body portion of the gasket; wherein the first tongue includes a raised ridge spaced from the body portion of the gasket and extending away from the general plane of the slot, and the body portion is provided with a prominence extending away from the general plane of the slot on the same side of the plane as the said ridge, whereby a concavity is defined between the said ridge and the said prominence.

2. A gasket according to claim 1, wherein the second tongue is inclined towards the outer end of the first tongue when the gasket is relaxed.

3. A gasket according to claim 1 or claim 2, wherein the first tongue includes an internal void between the ridge and the body portion of the gasket.

4. A gasket according to any one of the preceding claims, of polyurethane, neoprene or natural rubber.

5. A gasket according to any one of the preceding claims, having a Shore hardness in the range of 50 to 90.

6. A gasket according to claim 5, having a Shore hardness in the range of 70 to 80.

7. A joint between an edge portion of a rigid sheet and an adjacent rigid planar surface overlapping the sheet edge, comprising a gasket according to any one of the preceding claims disposed the length of the joint, the sheet edge being embraced between the first and second tongues of the gasket, and the ridge on the first tongue and the prominence on the body portion of the gasket lying against the planar surface, and compression means for urging the planar surface towards the sheet whereby to sealingly compress the first tongue between them and to rotate the body portion of the gasket, by the pressure of the planar surface against the prominence thereon, about the sheet edge and thereby to urge the second tongue into particle-sealing contact with the sheet adjacent the edge thereof.

8. A joint according to claim 7, wherein the compression means comprise a clamp member having a first flange bearing against the panel and a second flange bearing against the sheet member, and means urging the clamp member towards the sheet member.

9. A joint according to claim 8, wherein the urging means comprises a screw member having a head portion abutting the clamp member and an internally threaded shank portion passing through the clamp member in threaded engagement with a complementary screw threaded stud fastened to the sheet member.

10. A joint according to claim 9, wherein the length of the shank portion is selected so that the gasket is optimally compressed when the shank portion is screwed over the stud down to the sheet member.

11. A joint according to any one of claims 7 to 10, wherein the gasket contains at least one V notch extending through the body portion and having its apex in the slot, and the gasket is flexed to bring the opposite sides of the V notch together and form and angle in the joint.

12. A containment box having an aperture in a wall thereof and a panel sealingly affixed over the aperture, comprising a joint according to any one of claims 7 to 11 between the panel and the wall about the aperture.

13. A gasket substantially as herein described with reference to and as illustrated in Figs. 1 to 4 or Fig. 5 of the accompanying drawings.

14. A joint substantially as herein described with reference to and as illustrated in Figs. 2 to 4 of the accompanying drawings.

15. A containment box substantially as herein described with reference to the accompanying drawings.