Background Art A prior-art sealing ring of this kind will be de- scribed below with reference to Figs 1-3.

Fig. 1 shows in cross section a strand 1 made by means of co-extrusion of a soft rubber material having good sealing properties. Fig. 2 shows in cross section a prior-art sealing ring 2 made from a length of the strand 1. The sealing ring 2 is obtained by bending the length of the strand 1 into a circular annular shape, the ends thereof being brought together and interconnected. The sealing ring 2 has a first sealing portion 6, which is adapted to abut against the bottom 3 of an internal, circumferential groove 4 of an outer pipe 5 (Fig. 3) and which has a waved sealing surface 7. The sealing ring 2 also has a second sealing portion 8, which is adapted to abut against the inner pipe (not shown). The sealing ring 2 has essentially the same width as the groove 4.

One problem associated with the prior-art sealing ring 2 is that the difference between the outer diameter and the inner diameter of the ring causes stress in the ring such that it is distorted, as shown in Fig. 2, after

the length of strand has been bent and its ends inter- connected. This distortion is shown in Fig. 2 as the angle a between the groove bottom 3 and the sealing sur- face 7. When the sealing ring 2 is thus deformed mounting it correctly in the groove 4 will be more difficult and there will be a risk of the sealing effect being con- siderably reduced due to the fact that the sealing ring is not correctly inserted in the groove 4.

Summary of the Invention The object of the present invention is therefore to provide a sealing ring which is not distorted in the manner described above, but which retains its shape once it has been finished and thus is easy to mount, i e insert in a groove provided for this purpose in a pipe, and provides a good sealing effect.

This object is achieved by a sealing ring of the kind which is described by way of introduction and which is characterised in that it is made from a strand made in one piece by means of co-extrusion of a soft rubber material and a hard rubber material, the soft rubber material forming a sealing body, which comprises said sealing portions, and the hard rubber material forming two supporting portions, which are located on both sides of said first sealing portion and which each in cross section have an axial extension that is greater than or equal to their radial extension.

In a preferred embodiment the supporting portions, like said first sealing portion, are adapted to abut against the bottom of the groove.

The total axial extension of the supporting portions and said first sealing portion is essentially equal to the width of the groove.

Each of the supporting portions has in cross section a radial extension that is at least 1/4 of the radial extension of the sealing ring in cross section.

The soft rubber material and the hard rubber mate- rial advantageously have a hardness of respectively 35-65 IRHD and 75-95 IRHD.

Brief Description of the Drawings The invention will now be described in more detail with reference to the accompanying drawings.

Fig. 1 is a sectional view of a rubber strand intended for the manufacture of the prior-art sealing ring described above.

Fig. 2 is a sectional view of the prior-art sealing ring described above.

Fig. 3 is a sectional view of the prior-art sealing ring described above as inserted in an internal, circum- ferential groove of a pipe.

Fig. 4 is a sectional view of a sealing ring accord- ing to the invention.

Fig. 5 is a sectional view of the sealing ring shown in Fig. 4 as inserted in an internal, circumferential groove of a pipe.

Fig. 6 is a sectional view of the sealing ring shown in Fig. 4 during sealing of an annular gap between two pipes.

Description of a Preferred Embodiment With reference to Fig. 4, a sealing ring 10 accord- ing to the present invention is shown in radial cross section. The sealing ring 10 is made from a length of a strand made by means of extrusion in the same manner as the prior-art sealing ring 2 described above. The strand from which the sealing ring 10 is made has the same cross-sectional profile as the sealing ring shown in Fig. 4, which means that it has not been deformed after having been finished, i e after the length of strand has been bent and its ends interconnected. This allows the sealing ring 10 to be mounted relatively easily in an internal, circumferential groove 11 in an outer pipe 12 (see Fig. 5).

The strand from which the sealing ring 10 is made is, in its turn, made in one piece by means of co-extrusion of a soft rubber material suitable for sealing with a hardness of 35-65 IRHD and a hard rubber material with a hardness of 75-95 IRHD.

The soft rubber material forms a sealing body 13 having a sealing portion 14, which is oriented radially outwards and which has a waved sealing surface 15, said sealing surface 15 being adapted to be pressed in a seal- ing manner against the bottom 16 of the groove 11 formed in the pipe 12.

The hard rubber material forms two supporting por- tions 17, which are located on both sides of the sealing portion 14 and which each in cross section have an axial extension that, in the embodiment shown, is essentially equal to their radial extension. To prevent a deformation of the kind described above the supporting portions 17 generally each have an axial extension that is greater than or equal to the radial extension. As shown in Fig. 5, the axial extension or width of the supporting portions 17 and the sealing portion 14 is essentially equal to the width of the groove 11. Each of the support- ing portions 17 has in cross section a radial extension that is approximately 1/3 of the total radial extension of the sealing ring 10 in cross section. In general, the radial extension of the supporting portions 17 is at least 1/4 of the radial extension of the sealing ring 10.

When the sealing ring 10 is mounted in the groove 11 of the pipe 12 (Fig. 5), the sealing surface 15 of the sealing portion 14 and the corresponding, similarly waved outer surface 18 of the supporting portions 17 abut against the whole width of the bottom 16 of the groove 11. The sealing ring 10 is thus kept firmly in place in the groove 11 abutting sealingly against the bottom 16 of the groove.

When the outer pipe 12 with the sealing ring 10 positioned in the groove 11 is slid onto an inner pipe

19 (Fig. 6), a sealing portion 20 formed on the sealing body 13 and oriented radially inwards will abut sealingly against the outer surface of the inner pipe 19. The seal- ing ring 10 thus seals an annular gap 21 between the two pipes 12 and 19.

Various modifications of the sealing ring 10 described above are possible within the scope of the invention, as defined by the appended claims. For exam- ple, if the sealing ring is intended to be arranged in an outer, annular groove of an inner pipe, it will have a radially inner sealing portion enclosed by two support- ing portions made of a hard rubber material.