WO2000038860A1

WO2000038860A1 - Refractory product

Info

Publication number: WO2000038860A1
Application number: PCT/EP1999/010107
Authority: WO
Inventors: Ian Proudfoot
Original assignee: Didier-Werke Ag
Priority date: 1998-12-23
Filing date: 1999-12-18
Publication date: 2000-07-06
Also published as: AU1780600A; GB2345015A; GB9828323D0

Abstract

A refractory product for use in metal teeming operations using at least one refractory body liable to be subjected to contact with slag in use, said product comprising a shield (2) of a refractory material resistant to the corrosive effects of slag (5), the shield being provided with mounting means for selectively positioning the shield with respect to said refractory body so as to provide in use a protective barrier between the slag and the refractory body.

Description

REFRACTORY PRODUCT

This invention relates to a device for use in prolonging the life of a refractory device that in use is at least partially submerged in molten metal, particularly steel in a vessel such as a tundish and, more particularly, to a sheath for shielding the refractory device from the erosive and corrosive effects of the molten steel and slags.

Metal teeming, and in particular casting of steel usually begins with the metal being melted in a furnace and then transferred via a ladle and tundish to a mould. Refractory devices are required, amongst other things, for the regulation of the flow of the molten metal exiting from a nozzle mounted in the bottom of these vessels. In the continuous casting of steel, this is typically applied through an opening in the base of the vessel via nozzles and shrouds into a water-cooled mould.

Refractory devices such as stopper rods, sub-entry shrouds and pouring nozzles are often submerged for long periods of time in the molten metal during the metal teeming process. The area of the devices that are most at risk from corrosion are the areas that in use come into in contact with the layer of slag lying on top of the molten metal. Due to the aggressively corrosive nature of the slag, the devices are at risk of corrosion after being submerged or partially submerged in the molten metal for only short periods of time.

An approach to handling this problem has involved forming wear resistant zones in the body of refractory devices at the part anticipated as being likely to protect the device when it is submerged in the melt. This approach requires some care in forming of the refractory body, with special steps being taken to ensure that the wear resistant materials are confined to and provided in the target zones. The physical properties of the materials suitable f.or use in the wear resistant zones, e.g. thermal properties are to some extent generally different from those of the refractory material to be used throughout the mass of the refractory body. Furthermore, the wear resistant materials tend to be more expensive materials than the refractory material preferred for making the refractory body. Therefore for these reasons it is not considered viable to make such refractory components entirely of more durable refractory offering more highly resistant properties- against corrosion. However certain companies in this field have become highly skilled in producing refractory bodies having a monolithic character but exhibiting appropriately enhanced wear characteristics in selected parts by means of co-moulding different compositions into one body shape .

Whilst this approach does improve the expected lifetime of the device, its condition must be monitored at all times to ensure that the wear resistant zone remains in contact with the slag. This places constraints on the duration of a casting or melt-pouring operation. Taking the example of a flow control valve in a tundish, the valve comprising a flow control stopper rod selectively engageable with an outlet nozzle seat, the stopper would normally be raised off the seat by a certain amount to achieve a particular rate of flow of molten metal through the valve to ultimately cast a product in a mould.

The teeming apparatus would usually include a pouring nozzle or a shroud located beneath the flow control valve either of which may be immersed in melt as the casting operation proceeds, but for simplicity discussion here is in relation to the submerged pouring nozzle .

During such a casting operation)^' a band around the submerged pouring nozzle will become continually exposed to the corrosive effects of slag used to protect and lubricate the metal being cast. Although there may be a certain proportion of the wear resistant zone slightly above and below the slag band, these will be of no effect in protecting the submerged pouring nozzle under the particular pouring conditions of that casting operation. It will be understood that changing the position of the submerged pouring nozzle to vary its partially submerged part will affect the flow characteristics within the mould. This in turn may affect the mould level control, turbulence within the mould and thermal stability, with detriment to the quality of the cast product.

The present invention aims to provide a refractory product that overcomes or at least mitigates the problems outlined above. The invention in particular aims to provide a new approach to prolonging the effective product life of a refractory body to be used in metal teeming where wear arising from contact with slag is a foreseeable consequence of normal usage of the refractory body.

According to one aspect of the present invention there is provided a refractory product for use in metal teeming operations using at least one refractory body liable to be subjected to contact with slag in use, said product comprising a shield of a refractory material resistant to the corrosive effects of slag, the shield being provided with mounting means for selectively positioning the shield with respect to said refractory body so as to provide in use a protective barrier between the slag and the refractory body. The refractory body may be a stopper rod, a shroud, a pouring nozzle, heater tubes or the like artefacts normally subjected to contact with slag during operational use.

Preferably also the refractory product comprises guide means for supporting the shield and permitting passage of the refractory body therethrough. By this arrangement the shield may be selectively held static in a partially submerged condition in molten metal contained in a vessel whilst the refractory body may be independently raised and lowered within the vessel, without requiring relocation of the shield. In this way, during normal operational usage the shield protects the sides of the refractory device in whatever region would be surrounded by slag.

Preferably, the mounting means for selectively positioning the shield comprises means for adjustably raising and lowering the height thereof.

Preferably the shield is provided as a sheath co- extensive with a proportion of the length of the refractory body to be protected.

Advantageously, the sheath is an annular sleeve of dimensions corresponding internally to the exterior surface of the refractory body to be protected in use, and externally of sufficient thickness to resist the corrosive effect of slag for a desired operational period.

Preferably, the sheath is formed of zirconia, zirconia carbon, magnesia carbon or boron nitride.

One embodiment of the present invention will now be described with reference to the accompanying drawings in which : FIGURE 1 is a schematic view of a sheath according to one aspect of the present invention in a "raised" condition, located in operational relation to a partially submerged nozzle; and

Figure 2 is a schematic view of the sheath of Figure 1 in a "lowered" condition.

A sheath 1 according to one aspect of the present invention comprises an annular body 2 of a wear resistant material such as zirconia. Figure 1 of the drawings shows the sheath submerged in a mould 3 of molten metal 4. The outer surface of the sheath is contacted by the layer of slag 5 lying on the surface of the molten metal.

The upper surface of the sheath is provided with connection means to connect the sheath to an actuating mechanism 6, which otherwise may be one known per se for use in teeming operations, but here is adapted for raising and lowering the sheath within the vessel

Figure 1 shows a refractory pouring nozzle mounted in the sheath, the end of the pouring nozzle being submerged in the molten metal in the mould. Whilst a pouring nozzle is shown in the accompanying drawings, it is envisaged that the sheath may be used to shield other refractory devices from the corrosive effects of the slag.

The internal diameter of the sheath is sufficiently greater than that of the external diameter of the nozzle to permit adequate clearance for relative axial movement longitudinally therethrough to allow either the nozzle to be raised and lowered within the sheath, or the sheath to be raised or lowered with respect to the nozzle when held in a desired pouring position. The outer surface of the nozzle is thereby shielded from the highly corrosive layer of slag lying on the surface of the molten metal. In use of the sheath, the sheath is connected to the actuating mechanism and positioned over a mould of molten metal. The sheath is lowered into the molten metal and a refractory body, such as the pouring nozzle shown in the drawings, passes through the sheath such that the tip of the nozzle is submerged but the body thereof is protected by the sheath. Metal teeming can then be proceed as normal .

hen it is considered necessary to adjust the position of the sheath within the melt (in order to present a fresh wear resistant surface to the layer of slag on the melt) , the actuating mechanism is activated and the sheath can be raised or lowered in the melt as necessary. Figure 2 shows the sheath in a lowered position within the melt.

During repositioning of the sheath within the molten metal, the nozzle remains static, held by the usual support means to retain the desired pouring position within the mould. This is clearly sesn in Figure 2 of the drawings where the sheath is in the lowered condition. It is important that the pouring nozzle remain the same position in order to sustain the quality and integrity of the steel.

Advantages of the present invention include a considerably extended lifetime of the submerged refractory devices, simple and effective repositioning of the sheath within the melt thereby allowing the sheath to be used over a prolonged period of time and maintained quality and integrity of the steel. The sheath enables use of cheaper materials in the refractory devices it protects, thereby providing cost savings over several aspects of the teeming operations.

Claims

CLAIMS:

1. A refractory product for use in metal teeming operations using at least one refractory body liable to be subjected to contact with slag in use, said product comprising a shield of a refractory material resistant to the corrosive effects of slag, the shield being provided with mounting means for selectively positioning the shield with respect to said refractory body so as to provide in use a protective barrier between the slag and the refractory body.

2. A refractory product according to claim 1, wherein the refractory product comprises guide means for supporting the shield and permitting passage of the refractory body therethrough.

3. A refractory product according to claim 1 or 2, wherein the mounting means for selectively positioning the shield comprises means for adjustably raising and lowering the height thereof.

4. A refractory product according to any one of the preceding claims the shield is provided as a sheath co^¬ extensive with a proportion of the length of the refractory body to be protected.

5. A refractory product according to claim 4, wherein the sheath is an annular sleeve of dimensions corresponding internally to the exterior surface of the refractory body to be protected in use, and externally of sufficient thickness to resist the corrosive effect of slag for a desired operational period. β. A refractory product according to claim 4 or 5, wherein the sheath is formed of zirconia, zirconia carbon, magnesia carbon or boron nitride.

7. The refractory product according to any one of the preceding claims, wherein the refractory body is a stopper rod, a shroud, a pouring nozzle, heater tubes or the like artefact normally subjected to contact with slag during operational use.

8. A refractory product substantially as hereinbefore described with reference to and as shown in the accompanying figures.