GB2141187A - Sealing element - Google Patents

Abstract

A sealing element is provided, which sealing element is more particularly intended for the joining of tubes of small diameter of a circuit of fluid at high temperature. It comprises an annular metal core 12 in which is formed at least one circular recess or groove 14 for receiving a lining 16 of expanded graphite which, before compression of the sealing element, projects from each side of the metal. A recess 18 devoid of graphite performs the function of a collector for receiving, as the case may be, the graphite when the sealing element is compressed, in particular in the case of creep of the graphite due to a particularly high pressure. The recess may be provided between two co-axial annular rings, the lining being moulded on the recess from a wound ribbon of graphite. Alternatively the lining may comprise a thermosetting resin containing a filler.

Description

SPECIFICATION Sealing element The present invention relates to a composite sealing element particularly adapted to the junction of tubes of small diameter intended to be subjected to elevated temperatures.

There are at the present time employed in steam or like circuits, ie installations subjected to high temperatures or stresses due to thermal expansions, bearing in mind the assemblies or when stopping and starting, are particularly large, different types of sealing elements and in particular metals or metalplastics sealing elements provided with grooves or spiraled sealing elements. Unfortunately, the latter do not ensure a sufficient seal and, above all, a reliable seal when they are subjected to large thermal shocks such as those which arise in such installations. Further, the sealing elements provided with grooves have a tendency to mark the bearing surfaces and this requires a repairing of these surfaces for each disassembly.

An object of the present invention is to overcome these drawbacks and to provide a sealing element which does not risk marking the bearing surfaces and ensure a reliable seal notwithstanding the thermal shocks.

This invention indeed concerns a sealing element which comprises an annular metal core having on each of its opposed sides at least one cavity or circular recess spaced from its central orifice, and a lining of a material which is refractory at high temperature and has a good elastic return, such as expanded graphite which is placed in the recess and projects above the recess a height which is a function of its elasticity so that it can be compressed down to a position in which it is flush with the metal core when it is compressed.

Such a sealing element having a metal core may have a single circular recess or a succession of coaxial recesses, but in any case the elastic return of the expanded graphite ensures an effective seal notwithstanding thermal shocks while the metal core limits to the maximum extent the risk of creep of the graphite and protects the fluid against any pollution on the part of this material.

Preferably, when the metal core has a plurality of coaxial recesses, the inner recess at least is left free and forms a collector for receiving graphite which is urged back upon the compression of the sealing element and thus provides an additional safety measure.

In another embodiment, the recesses of the two opposed sides of the core communicate with each other and receive a winding of graphite tape which is moulded so as to exactly marry up with their shape.

The following description of embodiments which are given by way of non-limiting examples and shown in the accompanying drawings will bring out the advantages and features of the invention.

In the drawings: Figure 1 is a perspective view partly cut away of a sealing element according to the invention; Figure 2 is a diametrical sectional view taken along line 2-2 of the sealing element of Figure 1; Figure 3 is a view, partly in radial section, of a modification of the joint according to the invention; Figure 4 is a partial top plan view of the sealing element of Figure 3; Figure 5 is a view similar to Figure 3 of the sealing element compressed between two flanges; Figures 6and 7are diametrical sectional views of another embodiment of the sealing element, respectively before and after the moulding of the lining.

The sealing element shown in Figures 1 and 2 comprises an annular metal core 1 constituted by a central ring 2 provided with a radial flange 4. Each of the opposed axial sides of the core 1 thus has a recess 6, 8 on one side of the flange 4.

Placed inside each of the recesses 6, 8 is a lining formed by a material which is refractory at high temperature, and has a good elastic return, for example expanded graphite. Washers of graphite cut from a sheet are, for example, superposed in each of the recesses 6, 8 so as to fill this recess and also project beyond the inner ring 2.

The lining 10 is fixed, for example by adhesion, to the core 1 of the sealing element so as to be rigid therewith but retains all its elasticity. The height of the extent to which the lining 10 projects beyond the ring 2 is a function of the intrinsec qualities of the material of which this lining is composed and of the compression of clamping it is desired to effect.

Indeed, when the sealing element is compressed, for example between the flanges of two tubes of a steam circuit, the lining 10 must be able to be compressed in such manner as to become flush with the ends of the ring 2. It is then protected from the fluid flowing in the tube by this ring 2 and this avoids any risk of contact between these materials and consequently any risk of pollution of the fluid by the graphite or like material. Further, there is no risk of the graphite being laminated by the steam and its crushing is limited by the contact of the flanges and the ring 2.

It will be understood that, in accordance with the applications, the expanded graphite could be replaced by another material refractory at high temperature, for example by a thermosetting resin combined with fibres of "Monel" (R.T.M), silica alumina or polyamide.

According to a modification shown in Figures 3 and 4, the metal core of the sealing element may have a plurality of circular recesses, or coaxial circular grooves. For example, as shown, the core 12 may have on each of its sides three grooves 14 receiving a lining 16 formed, as in the preceding embodiment, by a sheet of expanded graphite which is cut out and moulded in such manner as to fill the three grooves 14 and to cover the ribs or strips 15 which separate these grooves.

Preferably, the grooves of the two opposed sides are offset from each other as shown in the drawings.

Further, the core 12 has an additional groove 18 similar to the grooves 14 and disposed between the latter and the central orifice 20 of the sealing element. This groove 18 remains free and devoid of graphite before the sealing element is compressed.

It thus constitutes a collector capable of receiving the graphite which is urged back when the compression is effected and flows or creeps in the direction of the central part of the sealing element. Such a collector protects the element against the fluid flowing in the tubes and passing through the sealing element by preventing the graphite from reaching this fluid.

It will be understood that the tops of the ribs are preferably flat so as to facilitate the covering thereof by the graphite sheet and avoid marking the bearing surfaces.

As in the preceding embodiment the thickness of the graphite layer covering the top of these grooves is a function of the elastic return of this material and of the desired compression of the element. Further, this compression is limited by the contact of the ribs 15 with the flanges 22,24 of the tubes to be united (Figure 5) which permits effecting an effective clamping with exact knowledge of the limits of the forces to be applied.

It is found that this sealing element, in the same way as the preceding element, is capable of resisting frequent and considerable thermal shocks owing in particular to the elastic return of the graphic. It is consequently most particularly adapted to steam circuits constituted by tubes of small diameter.

In the same way as in the preceding embodiment, the lining may be made from a material otherthan expanded graphite, so long as it has suitable properties of elasticity and resistance to elevated temperatures.

In some cases, it may also be found preferable to employ a metal core in which the recesses of the two sides are coincident. Such an embodiment is shown in Figures 6 and 7. In this case, the metal core is formed by two rings, respectively 26 and 28, separated by a recess 30 which extends throughout the axial thickness of the sealing element. Preferably, the confronting surfaces of the rings 26 and 28 are recessed in such manner as to have a V-section groove 27,29 and are outwardly divergent in the direction of each other.

Placed between the two ends of the recess 30 is a lining 32 formed from a ribbon of expanded graphite which is wound coaxially to the rings 26, 28 for a certain number of turns, the end turns or coils of the lining 32 being maintained between the points of the V-section grooves 27, 29 respectively of the rings 26, 28. It will be understood that the width of the ribbon which constitutes the lining 32 exceeds the axial thickness of the rings 26, 28.

In order to form a compact lining, the winding 32 is moulded inside the recess 30 in such manner asto marry up with the shape of this recess by entering the bottom of the grooves 27,29, as shown in Figure 7. Consequently, the section of the lining 32 in the finished state has an ovoidal shape which completely fills the space between the two rings but projects in the form of an annular bead from each of the opposed sides of the metal core constituted by these two rings.

The sealing element thus formed acts in the same manner as the preceding elements, ie it offers to the flanges to be united projections formed by the lining, but the compression or clamping compresses this lining so as to permit contact between the flanges and the metal of the rings 26 and 28. When this contact has been achieved, the compression or clamping has terminated. The seal is however ensured by the elastic return of the graphite which constitutes the lining 32, this elastic return elabling the lining to adapt itself to variations in temperature and in particular to the thermal shocks to which the sealing element is subjected.

In the same way as in the preceding sealing elements, the expansion or the creep of the lining 32 is limited by the inner ring 26 and cannot reach the central orifice 20 of the core of the element, ie come into contact with the fluid flowing in the tubes. Any flattening of the graphite by the steam is also avoided.

It will be understood that the shape and the depth of the grooves may vary. For example, as shown in Figure 5, the grooves 14 and 18 may have a dovetail shape so as to afford an improved retention of the graphite.

Claims (9)

1. A sealing element comprising an annular metal core including at least one circular recess on each of its sides which is spaced from the central orifice of the sealing element, and a lining of a material which is refractory at high temperature and has a good elastic return, placed in the recess and projecting above the recess a height which is a function of its elasticity and enables it to be compressed so as to be flush with the metal core when the sealing element is clamped or compressed.

2. A sealing element according to claim 1, where- in the lining is formed by a sheet of expanded graphite which is cut out and adhered in the recess.

3. A sealing element according to claim 1 or 2, wherein the core has a plurality of coaxial recesses and the lining covers the ribs which separate the recesses in which the lining is placed.

4. A sealing element according to claim 3, wherein the innermost recess is empty before the sealing element is compressed and performs the function of a collector for receiving the graphite which is urged back or creeps upon compression of the sealing element.

5. A sealing element according to any one of the claims 1 to 4, wherein the recesses of the two opposed sides of the metal core are radially offset from each other.

6. A sealing element according to claim 1 or 2, wherein the recesses of the two opposed sides of the core correspond to and communicate with each other so as to form a single recess in which a ribbon of expanded graphite is wound.

7. A sealing element according to claim 6, wherein the lateral surfaces of the recess comprise Vsection grooves which are open in the direction of each other and the ribbon of graphite is pre-moulded so as to fill said grooves and projects from each side of the metal core.

8. A sealing element according to any one of the preceding claims, wherein the lining of a material which is refractory at high temperature is a thermosetting resin combined with fibres of"Monel" (R.T.M), silica alumina, polyamide or the like.

9. A sealing element substantially as hereinbefore described with reference to and as shown in the accompanying drawings.