Stopper rods are well known for use in controlling molten metal (especially molten steel) flow from a handling vessel, e. g. a tundish, into a mould. A stopper rod is raised and lowered by a suitable mechanism positioned adjacent the vessel and can thereby be used to close fully or partial or to open fully the outlet from the vessel, thus controlling flow of the metal from the vessel.

Conventionally, a stopper rod is formed as an elongate one-piece bonded graphite structure by isostatic pressing in a suitable mould. The stopper rod usually has a hollow structure in that it is formed to have a longitudinal, centrally-disposed (i. e. axial) bore by use of a suitable removable core in the mould. The lower end of the stopper rod bore may be closed or it may be vented to allow inert gas, e. g. argon, to be passed through the rod.

The gas helps to prevent the build up of alumina (so-called alumina clogging) around the nose (i. e. the lower region) of the stopper rod; it can also help to prevent alumina clogging in the nozzle or shroud through which the molten steel passes from the tundish to the mould. Commonly, for such stopper rods, the gas which is passed through the stopper rod enters its bore through the upper end of the stopper rod, and it is therefore important to form a gas-tight seal at the upper end of the bore, between the bore and the gas supply conduit.

Thus, in the conventional manufacture of a stopper rod, the desired graphite composition is placed around a removable core in a deformable mould, i. e. the graphite composition fills the mould space between the core and deformable mould. The deformable mould is then placed in a tank of liquid, usually water, and the pressure of the liquid is then increased by known means to the pressure required to convert the graphite composition to the desired self-supporting structure. After removal of the isostatically pressed product from the mould, the core is removed to provide the hollow stopper rod.

The upper end region of the stopper rod must be provided with an attachment device by which it can be attached to the lifting and lowering mechanism. The attachment device most commonly comprises a rod which is inserted into an axial bore extending through at least part of the length of the stopper rod from its upper end. For stopper rods in which gas is passed through the bore in use, the attachment rod may be hollow, and the gas may be supplied through the hollow rod (which therefore fulfills the dual purposes of gas supply conduit and attachment device).

The attachment rod may, for example, be attached to the stopper rod by means of a screw threaded engagement with the axial bore and/or with a screw threaded insert located in the bore. Alternatively, for example, the attachment rod may be attached to the stopper rod by means of a retaining pin (or the like) extending substantially perpendicularly to the axes of the rods, through coaxial apertures extending transversly through the rods.

The present invention seeks to provide, among other things, an improved means of attaching and/or sealing a stopper rod to an attachment device of a lifting and lowering mechanism.

Accordingly, in one aspect the invention provides a method of attaching and/or sealing a stopper rod for a molten metal handling vessel to an attachment device for attaching the stopper rod to a lifting and lowering mechanism, in which an upper end region of the stopper rod in use and the attachment device are shaped and sized to be received one inside the other with a gap between their opposed faces, intumescent material is positioned in the gap and is heated so that it expands thereby to lock and/or to seal the stopper rod to the attachment device.

The intumescent material is heated to preferably at least 500 °C, in order to cause the requisite expansion. This heating may advantageously be the conventional pre-heating of a stopper rod (or other refarctory article) prior to use with molten metal (e. g. molten steel). In any case, the stopper rod (or other refractory article), and more particularly the intumescent material, will generally experience temperatures in excess of 500 °C during use with molten steel.

In another aspect the invention provides a stopper rod attached to an attachment device for attaching the stopper rod to a lifting and lowering mechanism, an upper end region of the stopper rod in use and the attachment device being of shape and size to be received one inside the other and being locked and/or sealed together by an expanded intumescent material.

The attachment device preferably comprises an attachment rod. In some embodiments of the invention, the attachment rod may be hollow, and may function as a gas supply conduit (as described above, for example) in addition to functioning as a means of attaching the stopper rod to a lifting and lowering mechanism. The intumescent material may serve to attach the attachment rod to the stopper rod, or it may serve to form a seal between the attachment rod and the stopper rod, or it may perform both of these functions.

For embodiments in which an attachment rod is attached to the stopper rod body by means of a retaining pin (as described above), there is preferably also intumescent material around the retaining pin, between the pin and the transverse apertures extending through the stopper rod, in order to provide a gas-tight seal around the retaining pin.

The intumescent material preferably comprises an expandable graphite composition, e. g. an exfoliated graphite composition, but additionally or alternatively it may comprise an expandable perlite or mica (or other lamellar mineral) composition, for example. Most preferably, the intumescent material comprises a mixture of expandable graphite and non-expandable graphite.

One or more binders may also be present, for example one or more of the following resins: polyester, epoxy, acrylic, phenol formaldehyde. Phenol formaldehyde resins are generally preferred.

The relative proportions of expandable graphite and non-expandable graphite will depend upon the required degree of expansion relative to the initial dimensions of the intumescent material. The skilled person will be able to select the appropriate relative amounts for each particular requirement.

Preferably, however, the weight percentage of expandable graphite (based upon the total weight amount of expandable and non-expandable graphite only), is at least 1.0%, more preferably at least 2.0%, even more preferably at least 5.0%, especially at least 10.0%; preferably it is no more than 99.0%, more preferably no more than 90.0%, even more preferably no more than 50.0%, especially no more than 30.0%. A particularly preferred weight range for the expandable graphite is 15.0-25.0%, based upon the total weight amount of expandable and non-expandabie graphite only.

The proportion (weight percentage) of binder in the entire intumescent composition is preferably in the range 5.0-30.0%, more preferably 8.0- 25.0%, especially 10.0-20.0%.

The expandable graphite is preferably expandable by virtue of water intercalated between the basal planes (i. e. the planes of hexagonally-bonded carbon atoms separated from each other by Van der Waals forces). If the temperature of the expandable graphite is raised to an activation temperature the intercalated water vaporises and the basal planes are pushed apart causing the whole mass of graphite to expand. If the expandable graphite is caused to expand in a confined volume, it is believed that the exfoliated basal planes self compress and wrap around each other forming a very effective seal.

The intumescent material may conveniently be substantially in the form of a ferrule or strip of the material; it may comprise a gasket. Additionally or alternatively, the intumescent material may be in the form of a paste, putty, gel or liquid. Preferably, the intumescent material is located in an axial bore extending through at least part of the length of the stopper rod, for sealing and/or locking between the bore of the stopper rod and an attachment rod inserted into the bore. Additionally or alternatively, the intumescent material may be used to line a socket or other recess or cavity in the attachment device, for sealing and/or locking between the attachment device and an exterior surface of the stopper rod.

The inventors of the present invention have found that the expansion of the intumescent material may provide a uniform, gas-tight seal between the stopper rod and the attachment device. Additionally or alternatively, the expansion of the intumescent material may lock the stopper rod and attachment device together with sufficient strength to withstand repeated uses of the stopper rod to open and close the outlet of a tundish for molten steel, for example.

In one embodiment, the upper end of the stopper rod, i. e. the end to be uppermost in use, is formed to have an annular shoulder above which extends a relatively short length or neck of reduced diameter. For example, for a stopper rod of overall length 1000 mm and maximum diameter 130 mm, the length of reduced diameter may be from 75 to 200 mm and it may be from 110 to 120 mm in diameter. The intumescent material may then be positioned inside a suitably-dimensioned socket on the lifting and lowering mechanism.

The socket may take the form of a shroud or bell attached at one end to an arm of the lifting and lowering mechanism and open at its other end to receive the neck of the stopper rod.

The attachment of the bell or shroud to the arm of the lifting and lowering mechanism is preferably releasable, e. g. by screw-threaded means so that when it is desired to remove the stopper rod from the mechanism it can readily be unscrewed, still attached to the bell or shroud. The stopper rod and bell or shroud may then be disposed of together at the end of the useful life of the stopper rod. This releasable arrangement also conveniently enables the intumescent material to be expanded between the stopper rod and an appropriate attachment socket at the point of manufacture of the stopper rod rather than in situ where the stopper rod is to be used.

Because the seal formed between the stopper rod and the lifting and lowering mechanism is gas-tight, the normal provision of an inert gas, e. g. argon, through a bored stopper rod is unaffected.

According to a third aspect, the invention provides an article for use with molten metal, the article being formed at least in part from refractory material, the article including sealing and/or fixing means formed at least in part from intumescent material.

The article according to the third aspect of the invention may, for example, comprise a stopper rod, a nozzle (e. g. a collector nozzle or a submerged entry nozzle), or a shroud (e. g. a submerged entry shroud). The sealing and/or fixing means may, for example, be arranged for sealing between a nozzle or shroud and an outlet from a metallurgical handling vessel.

Embodiments of the invention will now be described by way of example only with reference to the accompanying drawings in which : Figure 1 is a diagrammatic representation in elevation of a stopper rod for use in the invention; Figure 2 and 2A are an elevation and a plan view respectively of a gasket of intumescent material; Figure 3 is a view similar to Figure 1 showing the gasket of Figure 2 in position on the stopper rod; Figure 4 is a diagrammatic representation showing the stopper rod of Figure 3 about to be positioned in a receiving socket in a portion of a lifting and lowering mechanis ; Figure 5 is an illustration of a gasket of intumescent material for sealing between a stopper rod and an attachment rod; Figure 6 is an illustration of a stopper rod according to the invention, including the gasket of Figure 5; and Figure 7 is a schematic illustration of an assemble stopper rod and attachment rod according to the invention.

In Figure 1 a stopper rod 10 has an elongated body portion 11 terminating at its upper end in a shoulder 12 from which extends a narrow (with respect to body portion 10) neck 13.

In Figures 2 and 2A is shown a cylindrical gasket 14 of intumescent material having a bore 15 of diameter to be a push fit over neck 13 of stopper rod 10. Gasket 14 is of length substantially equal to the length of neck 13 of the stopper rod and of outside diameter a little less than the outside diameter of shoulder 12 of the stopper rod.

In Figure 3, the gasket 14 has been positioned over the neck of the stopper rod, the length of which it covers entirely while leaving an outer peripheral rim of shoulder 12 uncovered.

In Figure 4, the gasketed stopper rod of Figure 3 is about to be inserted in the socket 16 of a shroud 17 which is attached releasably to an arm 18 of a lifting and lowering mechanism 19. The internal walls of the socket 16 may contain a screw-thread or other protuberance/depression features to improve the locking effect of the expanded intumescent material.

When in position in socket 16, heating of the gasket 14 causes it to intumesce and this expansion firmly locks the stopper rod to the shroud of the lifting and lowering mechanism. The stopper rod may then be lifted or lowered as desired, as indicated by the arrows.

Figure 5 shows a gasket 21 of intumescent material for use in the axial bore of a stopper rod, for sealing between the wall of the bore and an attachment rod inserted into the bore. The gasket 21 comprises a simple hollow cylindrical (or ferrule-like) shape.

Figure 6 shows (in axial cross-section) a stopper rod 10 according to the invention. The stopper rod, which is formed from carbon bonded ceramic material, has an axial bore 23, and an inert gas outlet 25 containing a porous plug 27. At the upper end 28 of the stopper rod, a screw threaded retaining insert 29 is screwed into the upper region of the axial bore 23; the insert 29 is arranged to retain an attachment rod in the bore (see Figure 7). There is also an upper washer or plug insert 31 arranged in the bore above the retaining insert 29. Below the retaining insert 29, a gasket 21 of intumescent material is also located in the axial bore.

Figure 7 shows, schematically, an attachment rod 33 retained and sealed in the stopper rod 10 of Figure 6. It can be seen that the gasket 21 of intumescent material has been expanded to form a seal between the wall of the axial bore 23 and the outer surface of the attachment rod 33. The attachment rod 33 has an axial bore 35 through which an inert gas may be supplie to the axial bore 23 of the stopper rod 10.