A stopper rod is an elongate article formed from refractory material (e. g. carbon bonded ceramic material) which is used to control the flow of molten metal through an outlet of a vessel, for example a tundish, which contains the molten metal. In use, the stopper rod is held in a substantially vertical orientation with one end of the rod (generally known as the nose portion) which can mate and de-mate with the outlet, positioned lowermost. The stopper rod may be raised or lowered by a suitable mechanism positioned adjacent to the vessel and attached to an end of the rod opposite to that of the nose portion (i. e. the attachment end of the rod), so that it may fully or partially close the outlet or fully open the outlet. Stopper rods are conventionally used in the continuous casting of steel, for example.

It is common for stopper rods to be formed as one-piece moulded articles, normally by isostatic pressing in a mould. Stopper rods for use with aluminium killed steel (for example) are usually hollow, having an axial bore through which an inert gas, such as argon, may be passed. This has been found to reduce the build-up of alumina on the stopper rod, which would hinder its normal functioning and shorten the available casting time. Such hollow stopper rods may have an opening in their nose portion, through which the inert gas may flow, or they may, for example, have a porous nose portion, for this purpose.

In the conventional manufacture of a stopper rod, a deformable mould is filled with the refractory material, in particulate form. Normally, the particulate refractory material comprises a mixture of graphite, one or more metal oxides, e. g. alumina, magnesia and/or zirconia, and a binder, e. g. a resin or a pitch which will decompose to form a carbon bond when heated to a sufficiently high temperature. There is also normally an axial core in the mould, for providing an axial bore in the stopper rod.

The filled deformable mould is then placed in a tank of liquid, e. g. water, and the pressure of the liquid is increased by known means in order to press the particles of refractory material into a self-supporting structure having the required shape. The isostaticaily moulded stopper rod is then removed from the mould and heated. It may initially be heated to about 150-300°C in order to cure the binder, and then heated to about 700-1200 °C to pyrolse the binder and to produce a carbon bond, for example.

European patent application no. 0 358 535 A2 discloses a stopper rod adapted for attachment to an inert gas supply line and lifting mechanism adjacent a tundish, comprising an elongated stopper rod body of a refractory material having an upper end and a lower end and an axial bore extending from the upper end to the lower end and including means at the lower end communicating with the axial bore for emitting an inert gas to an exterior surface thereof, a metal bushing insert copressed and fired within the stopper rod body, the bushing insert having a threaded bore positioned coaxially with the bore of the stopper rod body and adapted to threadably receive a threaded metal rod for attachment to the inert gas supply line and lifting mechanism. The metal bushing insert is preferably spaced a distance from the upper end of the stopper rod body.

According to a first aspect, the present invention provides a stopper rod, comprising a stopper rod body formed from refractory material and having a longitudinal (preferably axial) bore extending at least part of its length from an open attachment end thereof, the longitudinal bore containing a hollow connecting part having an internal profile suitable for connection to an externally threaded attachment rod, the connecting part being joined or joinable to a retaining part located on, and fastened to, an external surface of the stopper rod body, thereby retaining the connecting part in place in the longitudinal bore of the stopper rod body.

According to a second aspect, the invention provides a method of assembling a stopper rod according to the first aspect of the invention, the method comprising locating the retaining part on, and fastening it to, the external surface of the stopper rod body.

According to a third aspect, the invention provides a kit of parts for forming a stopper rod, comprising : (a) a stopper rod body formed from refractory material and having a longitudinal (preferably axial) bore extending at least part of its length from an open attachment end thereof ; (b) a hollow connecting part for insertion into the longitudinal bore of the stopper rod body, the connecting part having an internal profile suitable for connection to an externally threaded attachment rod ; and (c) a retaining part joined or joinable to the connecting part and adapted to be located on, and fastened to, an external surface of the stopper rod body, thereby to retain the connecting part in place in the longitudinal bore of the stopper rod body.

The invention has the advantage that because the hollow connecting part is retained within the longitudinal bore of the stopper rod body by means of a retaining part which is located on, and fastened to, the exterior of the stopper rod body, this generally allows a degree of flexibility in how deeply within the bore the connecting part may be located. In particular, it allows the connecting part to be located at the open end of the longitudinal bore, preferably immediately at the open end of the bore, rather than being spaced a distance from the open end of the bore as is the case with the stopper rod disclosed in EP-A-0 358 535 referred to above. This is because, with the retaining part located on the exterior of the stopper rod body it is not necessary to embed the connecting part behind a minimum longitudinal thickness of the refractory material of the stopper rod in order to provide a sufficient strength of retention (as is the case with EP-A-0 358 535, for example). This does not mean, however, that it is not possible for the connecting part to be spaced a distance from the end of the longitudinal bore, merely that in such embodiments there is preferably means for interconnecting the spaced connecting part with the exterior retaining part.

In preferred embodiments of the invention, at least a portion of the retaining part of the stopper rod is located on the external end surface of the attachment end of the stopper rod body ; it preferably has the general form of a disc including a hole According to a third aspect, the invention provides a kit of parts for forming a stopper rod, comprising : (a) a stopper rod body formed from refractory material and having a longitudinal (preferably axial) bore extending at least part of its length from an open attachment end thereof ; (b) a hollow connecting part for insertion into the longitudinal bore of the stopper rod body, the connecting part having an internal profile suitable for connection to an externally threaded attachment rod ; and (c) a retaining part joined or joinable to the connecting part and adapted to be located on, and fastened to, an external surface of the stopper rod body, thereby to retain the connecting part in place in the longitudinal bore of the stopper rod body.

The invention has the advantage that because the hollow connecting part is retained within the longitudinal bore of the stopper rod body by means of a retaining part which is located on, and fastened to, the exterior of the stopper rod body, this generally allows a degree of flexibility in how deeply within the bore the connecting part may be located. In particular, it allows the connecting part to be located at the open end of the longitudinal bore, preferably immediately at the open end of the bore, rather than being spaced a distance from the open end of the bore as is the case with the stopper rod disclosed in EP-A-0 358 535 referred to above. This is because, with the retaining part located on the exterior of the stopper rod body it is not necessary to embed the connecting part behind a minimum longitudinal thickness of the refractory material of the stopper rod in order to provide a sufficient strength of retention (as is the case with EP-A-0 358 535, for example). This does not mean, however, that it is not possible for the connecting part to be spaced a distance from the end of the longitudinal bore, merely that in such embodiments there is preferably means for interconnecting the spaced connecting part with the exterior retaining part.

In preferred embodiments of the invention, at least a portion of the retaining part of the stopper rod is located on the external end surface of the attachment end of the stopper rod body ; it preferably has the general form of a disc including a hole (e. g. a circular hole) arranged to allow an attachment rod to be inserted into the longitudinal bore of the stopper rod body. Alternative forms of this portion of the retaining part are possible, for example it may comprise a plurality of spokes, or a frameworkstructure.

At least a portion of the retaining part of the stopper rod preferably is located on an external longitudinal surface of the stopper rod body (i. e. the circumferential external surface which extends along the length of the stopper rod). This portion of the retaining part preferably extends only part of the length along the external longitudinal surface of the stopper rod body from the end surface of the attachment end of the stopper rod.

Advantageously, the retaining part may be interlocked with a recess or projection on the external longitudinal surface of the stopper rod body. For example, a radially-inwardly projecting region of the retaining part may be interlocked with a radially-outwardly projecting ledge region of the external longitudinal surface of the stopper rod body. Preferably, the radially-inwardly projecting region of the retaining part is not perpendicular to the longitudinal axis of the stopper rod body, but is incline with respect to the axis. More preferably, the radially-inwardly projecting region of the retaining part tapers inwardly in a direction away from the attachment end of the stopper rod body. This has the advantage of generally reducing the stresses on the inwardly projecting region and/or the outwardly projecting ledge of the stopper rod body. Longitudinal movement of the retaining part, and consequently also the connecting part, with respect to the stopper rod body, preferably is thereby substantially prevented.

In preferred embodiments, the portion of the retaining part located on an external longitudinal surface of the stopper rod body has the general form of a cylinder.

Preferably, the retaining part comprises at least two portions joined together.

The portions of the retaining part may, for example, be joined together generally in a plane perpendicular to the longitudinal bore of the stopper rod body. Alternatively, (e. g. a circular hole) arranged to allow an attachment rod to be inserted into the longitudinal bore of the stopper rod body. Alternative forms of this portion of the retaining part are possible, for example it may comprise a plurality of spokes, or a frameworkstructure.

At least a portion of the retaining part of the stopper rod preferably is located on an external longitudinal surface of the stopper rod body (i. e. the circumferential external surface which extends along the length of the stopper rod). This portion of the retaining part preferably extends only part of the length along the external longitudinal surface of the stopper rod body from the end surface of the attachment end of the stopper rod.

Advantageously, the retaining part may be interlocked with a recess or projection on the external longitudinal surface of the stopper rod body. For example, a radially-inwardly projecting region of the retaining part may be interlocked with a radially-outwardly projecting ledge region of the external longitudinal surface of the stopper rod body. Preferably, the radially-inwardly projecting region of the retaining part is not perpendicular to the longitudinal axis of the stopper rod body, but is incline with respect to the axis. More preferably, the radially-inwardly projecting region of the retaining part tapers inwardly in a direction away from the attachment end of the stopper rod body. This has the advantage of generally reducing the stresses on the inwardly projecting region and/or the outwardly projecting ledge of the stopper rod body. Longitudinal movement of the retaining part, and consequently also the connecting part, with respect to the stopper rod body, preferably is thereby substantially prevented.

In preferred embodiments, the portion of the retaining part located on an external longitudinal surface of the stopper rod body has the general form of a cylinder.

Preferably, the retaining part comprises at least two portions joined together.

The portions of the retaining part may, for example, be joined together generally in a plane perpendicular to the longitudinal bore of the stopper rod body. Alternatively, the retaining part portions may be joined together generally in a plane longitudinal of the stopper rod body, for example However the portions of the retaining part are joined together, they are preferably joined subsequent to the retaining part being located on the stopper rod body, for example in order to facilitate their attachment to the stopper rod body. The retaining part portions may generally be joined by any suitable means, for example they may be welded together, bonded, joined by means of a screw-threaded attachment, joined by the use of fixing means (e. g. screws or rivets), or the like.

The connecting part of the stopper rod is preferably joined to an underside of the portion of the retaining part located on an external end surface of the stopper rod body. The connecting part is preferably welded or bonded to the retaining part, but it may be joined to the retaining part in some other way. Alternatively, the connecting part may be integrally formed with the retaining part, but this is generally less preferred.

As mentioned above, it is preferred for the connecting part to be located immediately at the open end of the longitudinal bore of the stopper rod body, i. e. rather than being spaced a distance from the open end of the bore.

The internal profile of the connecting part suitable for connection to an externally threaded attachment rod preferably comprises a screw thread. The connecting part may, for example, comprise a screw-threaded nut. Alternatively, however, the internal profile of the connecting part may comprise means to provide a"twist-and-lock"type of connection.

In some preferred embodiments, the connecting part comprises a plurality of components connectable directly or indirectly together. For example, the connecting part may comprise a radially outer component and a radially inner component connected together during use. Preferably, the radially outer component has an internal screw thread and the radially inner component has a corresponding external screw thread, and the components are screw threaded together. The radially inner component is preferably provided with the internal profile, e. g. a screw thread, suitable for connection to an externally threaded attachment rod.

Advantageously, the connecting part may be joined to the retaining part by means of the retaining part being clamped between the radially outer component and the radially inner component.

The longitudinal bore of the stopper rod body preferably inclues an annular surface against which a corresponding surface of a screw-threaded attachment rod inserted into the bore may be seated, and preferably sealed. For example, the longitudinal bore may include an annular ledge against which a radially outer annular region of the attachment rod may be seated. In embodiments in which the connecting part comprises a radially outer component and a radially inner component connected together, the radially inner component and the annular surface of the longitudinal bore preferably define between them a gap suitable for retaining a radially extending projection (e. g. a circumferential flange or collar) on the attachment rod.

In some embodiments, the annular surface is provided by an insert located in the longitudinal bore, for example seated against an annular ledge in the bore. The insert preferably includes an aperture to allow an inert gas to be supplie to the longitudinal bore from the attachment rod, which is preferably hollow. The surface of the ledge in the bore and/or the insert against which the corresponding surface of the attachment rod may be seated is preferably concave (e. g. conical or frusto-conical).

The connecting part and/or the retaining part are preferably formed from metal, e. g. steel. The refractory material of the stopper rod body preferably comprises carbon-bonded ceramic material, for example a mixture of graphite, one or more metal oxides, e. g. alumina, magnesia and/or zirconia, and a binder such as a resin or pitch which has decomposed to form a carbon bond under high temperature treatment. Where present, the insert may be formed from a ceramic material and/or metal and/or a cermet material, for example.

The invention will now be described, by way of example, with reference to the accompanying drawings, of which : Figure 1 shows, in cross-section, the attachment region of a stopper rod according to the invention, and the bottom region of a threaded attachment rod ; Figure 2 shows, in cross-section and schematically, an entire stopper rod similar to that of Figure 1 ; and Figure 3 shows, in cross-section, an alternative attachment region of a stopper rod according to the invention, and the bottom region of an alternative attachment rod.

Figure 1 shows a stopper rod 1, comprising a stopper rod body 3 formed from carbon-bonded ceramic refractory material and having a longitudinal bore 5 extending from an open attachment end 7 of the stopper rod body. The longitudinal bore 5 contains a hollow connecting part 9 in the form of a screw-threaded metal nut, the connecting part being welded by means of weld 11 to a retaining part 13 located on, and fastened to, an external surface 15 of the stopper rod body, thereby retaining the connecting part in place in the longitudinal bore of the stopper rod body.

The retaining part 13 comprises two portions welded together as indicated at 17. A first portion 19 of the retaining part is generally in the form of a disc having a central hole to allow access to the longitudinal bore, this portion being located on the external end surface 21 of the attachment end of the stopper rod body. An outer circumferential region 22 of the first portion 19 extends around to the external longitudinal surface 23 of the stopper rod body. A second portion 25 of the retaining part 13 is generally in the form of a cylinder. A lower end region of this second portion, i. e. the end region located furthest from the first portion 19, comprises a radially-inwardly projecting region 27 and is interlocked with a radially-outwardly projecting ledge 29 of the external longitudinal surface of the stopper rod body. The retaining part 13, and thereby also the connecting part 9 welded to it, are thereby secured to the attachment end region of the stopper rod body. (Instead of being perpendicular to the longitudinal axis of the stopper rod body, the radially-inwardly projecting region 27 may be incline to the axis, i. e. it may taper inwardly in a direction away from the attachment end surface 21, in order to reduce stresses, as shown in Figure 3, for example.) The first and second portions of the retaining part 13 have been joined together subsequent to being located on the stopper rod body.

The longitudinal bore 5 of the stopper rod body 3 contains an insert 31 seated against an annular ledge 33 in the bore. The insert 31 has a concave upper surface 35 against which the front end surface 35 of the screw-threaded attachment rod 37 is seated and sealed during use once the rod has been screwed into the connecting part 9. The insert 31 has a central aperture 39 to allow an inert gas, e. g. argon, to be supplied to the longitudinal bore of the stopper rod body from the hollow attachment rod 37. The attachment rod as shown inclues a washer 41 and nuts 43, to secure its attachment to the stopper rod.

Figure 2 shows, in cross-section and schematically, an entire stopper rod 1 similar to that of Figure 1. The stopper rod comprises a monolithic body of carbon-bonded ceramic material, containing a longitudinal bore extending part of its length from the open attachment end towards the porous nose portion 45. The nose portion may be formed from a different, more erosion-resistant carbon-bonded ceramic material than that of the remainder of the stopper rod body.

Figure 3 shows, in cross-section, the attachment region of another stopper rod 1 according to the invention. The retaining part 13 is similar to that shown in Figure 1, except that the radially-inwardly projecting region 27 is incline to the axis of the stopper rod, i. e. it tapers inwardly in a direction away from the attachment end surface 21, rather than being perpendicular to it, in order to reduce stresses. The connecting part 9 comprises two components, i. e. a radially outer component 45 and a radially inner component 47. The outer component 45 has an internal screw thread and the inner component 47 has a corresponding external screw thread by which the two components are threadedly interconnected. The outer component 45 has a radially projecting flange 49 which clamps down upon the external surface of the first portion 19 of the retaining part 13, thereby clamping the retaining part between the outer component and the inner component and thus joining the connecting part to the retaining part The inner component 47 has an internal screw thread suitable for threaded attachment to the screw thread 51 of the attachment rod 53 In order to attach the stopper rod 1 to the attachment rod 53, the inner component 47 of the connecting part is threaded onto the screw thread 51 of the attachment rod behind a radially projecting collar 55 on the attachment rod. The attachment rod is then inserted into the longitudinal bore 5 of the stopper rod, and the inner component 47 is screwed into the outer component 45 until the radially projecting collar 55 on the attachment rod seats against an annular surface 57 in the longitudinal bore of the stopper rod, trapping the collar between the inner component 47 and the annular surface 57, and the inner component 47 clamps down onto the external surface of the first portion 19 of the retaining part 13.