Field of the Invention The present invention relates to a device for mount¬ ing an elastic sealing ring on a bottom ring, which forms part of a casting mould for casting a concrete pipe pro- vided with a socket and which is adapted to form the socket of the concrete pipe, causing the sealing ring to be partially embedded therein.

Background Art Sealing rings for sealing an annular gap between a concrete pipe socket and a concrete pipe spigot end which are intended to be embedded in the concrete pipe socket during casting are elastic and mounted on a bottom ring, which forms part of a casting mould for casting a con- crete pipe provided with a socket. In known methods, the sealing ring is mounted manually on the bottom ring, which is a laborious task the performance of which requires considerable experience and precision. If the sealing ring is incorrectly positioned on the bottom ring, it may end up in an incorrect embedding position in the socket and concrete may penetrate between the sealing ring and the bottom ring during casting, which of course reduces the sealing effect of the sealing ring. It is therefore essential that the sealing ring be correctly positioned on the bottom ring.

Summary of the Invention The object of the present invention therefore is to provide a device by means of which an elastic sealing ring can be mounted on a bottom ring in an automatic and accurate manner. This object is achieved by a device which is of the type stated by way of introduction and characterised by a cylinder, which is arranged to support a plurality of slipped on sealing rings, a supporting element, which is arranged to support the bottom ring, and a ring application unit, which has a plurality of suction heads uniformly distributed along the circumfe¬ rence of the cylinder, which are connected to a suction source and adapted to be brought into suction engagement with one of the sealing rings on the cylinder, to be moved radially outwards for the purpose of expanding the sealing ring, to be moved, with the sealing ring attached thereto by suction, to the bottom ring for the purpose of positioning the sealing ring around the bottom ring, and to release the sealing ring by cancelling the suction effect exerted thereon. Preferably, the cylinder is a vertical column, which is arranged to support the sealing rings stacked on one another, the suction heads conveniently being adapted to be brought into suction engagement with the lowermost sealing ring of the stack and to expand the same. The supporting element is advantageously arranged to support the bottom ring horizontally and in axial alignment with the column underneath the same. Preferably, the supporting element has a positioning means for positioning the bottom ring in a predetermined position on the supporting element.

Brief Description of the Drawings The invention will now be described in more detail with reference to the accompanying drawings. Fig. 1 is a schematic side view and shows a device according to the invention with a ring application unit located in a starting position. Fig. 2 is a schematic sectional view taken along the line A-A in Fig. 1. Fig. 3 is an enlarged schematic sectional view and illustrates the manner in which a suction head is con¬ nected to a suction source. Figs 4-7 correspond to Fig. 1 but show the ring application unit in different operating positions.

Description of a Preferred Embodiment The inventive device illustrated in the drawings has a cylinder 1, which forms a vertical column and which supports a plurality of elastic sealing rings 2 stacked on one another and slipped on the column. At its lower end, the column 1 comprises a retaining ring 3 on which the stack of sealing rings 2 rests. A horizontal table 4 is arranged directly below the column 1. The table 4 supports a bottom ring 5, which forms part of a casting mould for casting a concrete pipe provided with a socket and which is adapted to form the concrete pipe socket, causing a sealing ring 2 to be par¬ tially embedded therein. The table 4 has a positioning means 6 in the way of a ring attached thereto with a slightly conical outer surface, which means is adapted to guide the bottom ring 5, as the bottom ring 5 is placed on the table 4, to the right position in axial alignment with the column 1 and to retain the bottom ring 5 in this position. Moreover, the device has a ring application unit 7, which is reciprocally displaceable in the axial direction of the column 1, i.e. vertically, and which has a plura¬ lity (four in the embodiment shown) of radially displace- able suction heads 8 uniformly distributed along the cir¬ cumference of the column 1 and arranged at the same hori¬ zontal level, which in an initial position (Fig. 1) is the level at which the lowermost sealing ring 2 of the stack is located. Each suction head 8 is circular-arc-shaped, and the radius of the circular-arc-shaped inner surface 9 thereof facing the column 1 is equal to the outer radius of the sealing rings 2. Furthermore, each suction head 8 has an inner duct system 10 with ducts that debouch at the circular-arc-shaped inner surface 9. The inner duct sys¬ tem 10 of each suction head 8 is connected via a fitting 10a to a vacuum source or suction source 11, for example a pump provided separately for each suction head 8 or, preferably, a pump common to all the suction heads 8. To use the device a plurality of sealing rings 2 are slipped on the column 1, either manually or, preferably, by means of a transport device (not shown) positioned above the column 1, and a bottom ring 5 is arranged on the table 4 on top of the ring 6, i.e. in a position axially aligned with the column 1. During these opera¬ tions, the suction heads 8 are in their initial position as shown in Fig. 1, i.e. level with and at a radial dis¬ tance from the lowermost sealing ring 2 of the stack. The suction heads 8 are then displaced synchronously radially inwards to such an extent that their inner surface 9 abuts against the outer surface of the lowermost sealing ring 2 (Fig. 4), the shape of the inner surface 9 being adapted to that of said outer surface. A suction effect is exerted by the suction source 11 on the sealing ring 2 via the duct system 10 in each suction head 8. The suc¬ tion heads 8 are then displaced synchronously radially outwards to stretch or expand the sealing ring 2 (Fig. 5) to such a degree that its inner diameter is larger than the outer diameter of the bottom ring 5 in the portion 5a where the sealing ring 2 is to be applied. The ring application unit 7 is displaced, with the sealing ring 2 attached by suction to the suction heads 8, axially down¬ wards to the level of said portion 5a of the bottom ring 5 (Fig. 6), whereupon the suction effect exerted on the sealing ring 2 is cancelled, causing the latter to be released from the suction heads 8 and to resume, due to its elasticity, its original diameter and, thus, to be mounted on the portion 5a of the bottom ring 5 (Fig. 7) . The ring application unit 7 is then returned to the ini- tial position (Fig. 1) . The bottom ring 5 with the seal¬ ing ring 2 mounted thereon, is removed from the table 4 and replaced by a new bottom ring to be provided with a sealing ring 2, following which the process described above is repeated. The ring application unit 7 and its suction heads 8 are displaced in per se known manner, for example pneuma¬ tically or hydraulically, the displacements as well as the connection and disconnection of the suction source 11 being controlled by means of control equipment known in the art.