GB2199522A - Introducing additives to molten metal in flow - Google Patents

Abstract

During transfer of molten metal from a first containing vessel (2) to a second containing vessel (4) through a hollow carrier (3), additive(s) are injected (6) into the first containing vessel or the hollow carrier as the metal passes therethrough; and the metal is subjected to turbulent flow conditions as the metal and additives pass through the hollow carrier. The invention may be applied to continuous casting (as shown) in which the melt passes from a tundish (2) to a mould (4). Alternatively, in uphill ingot teeming, the hollow carrier replaces the conventional runner leading to the mould base from the pouring vessel (Fig. 2, not shown). In a further alternative, the hollow carrier may be incorporated as part of a blast furnace runner system. The additive(s) may be for various purposes and in various forms e.g. wine, powder, gas. Turbulent flow conditions are established by any of a variety of techniques, and the carrier may be force-cooled. <IMAGE>

Description

Improvements in or relating to the Processing of Liquid Metals This invention relates to the processing of liquid metals, and more particularly arrangements for achieving intimate mixing of liquid metals with additions (hereinafter called "additives") such as alloying agents, reactive additions, and second phase additions such as metallic or non-metallic fibres or particles. The additives may be in solid, liquid or gaseous form.

Such additions can be for a number of purposes, such as: 1 Composition control 2 Deoxidation 3 Desulphurisation and/or dephosphorisation Inclusion modification 5 Forming a composite structure having special properties, eg wear resistance, increased strength, improved machineability.

6 Degassing Commonly alloy additions can be made to liquid metals in a melting furnace or processing vessel for the metal in a ladle or tundish, in a mould for the metal or in a runner system of a casting assembly for the metal.

Some elements are particularly difficult to incorporate homogenously throughout a cast metal due to limited miscibility with the parent metal and tendency to segregate during and after casting; others are difficult to add because of the toxic nature of fumes emitted during addition and casting and/or the toxic nature of the form of addition alloy.

An example of such an element is lead in free cutting steels. Oxidisable elements such as carbon, silicon, manganese, aluminium, vanadium, titanium and chromium are characterised by yields of less than 100% through reaction during conventional addition and solution with high oxygen potential slags and atmospheric oxygen.

Calcium or magnesium in elemental alloy form are commonly used during steelmaking and casting operations for the purposes of deoxidation, desulphurisation and inclusion control. Both calcium and magnesium develop high vapour pressures in contact with liquid steel and are characterised by low yields which have led to the development of costly processes such as pneumatic injection of powders and injection in wire form. When using a reactive addition to treat a liquid melt by inject ion or as a slag on top of an agitated melt the efficiency of the process is limited by the degree of contact between the bulk metal and the addition.

When adding a second phase material to a liquid metal for the purpose of forming a composite material, it is often difficult to maintain an even distribution of the second phase in a large bulk of liquid prior to casting; it may also be difficult to avoid degradation or segregation of the second phase during the time periods involved.

It is an object of the present invention to provide an arrangement which can overcome or at least substantially reduce the above mentioned difficulties.

According to the present invention there is provided apparatus for the processing of metals comprising a first metal containing vessel; a second metal containing vessel; a hollow carrier for transferring liquid metal from the first vessel to the second vessel; and a means for injecting additives into the first vessel or hollow carrier and the arrangement being such that, in operation, metal additives transferring from the first vessel to the second vessel are in turbulent flow conditions.

According to another aspect of the present invention there is provided a method of processing metals comprising the steps of transferring molten metal from a first containing vessel to a second containing vessel through a hollow carrier; injecting additives into the first containing vessel or the hollow carrier as the metal passes therethrough; and subjecting the metal to turbulent flow conditions as the metal and additives pass through the hollow carrier.

The first containing vessel and the second containing vessel may comprise appropriate vessels to the processing of metal.

Thus the vessels may both comprise ladles or one may comprise a ladle and the other a converter vessel.

Again, in one embodiment the first containing vessel may comprise a blast furnace and the second vessel a ladle, the hollow carrier being incorporated in the blast furnace runner system. In this case the additives may be such as to enable desulphurisation and/or dephosphorisation and/or desiliconisation of the blast furnace iron prior to it entering a steel.

making vessel.

Yet again, in another significant embodiment the second containing vessel may comprise a metal casting mould, and the first containing vessel may comprise a ladle or tundish.

An important feature provided by the invention is that the material is maintained in a highly turbulent condition by its passage through the hollow carrier.

The carrier thus serves as a mixing medium. The method of addition may be that most suited to the particular materials involved and the end purpose of the mixing. For example, the additive may be introduced in particulate form via a vortex close to the carrier entrance in the first containing vessel.

Alternatively, it may be injected into the first containing vessel or the carrier, or continuously fed, or fed in a strand, or stream fed. The additive may, for example, be an inert gas used for degassing and/or enhancing turbulence.

The additive material may be introduced continuously during the operation at a rate set as a fraction of the liquid metal flow rate. By such continuous addition, there is very even distribution of the additive in the metal, and possible toxic emissions are limited and, therefore, more easily controlled. Because the majority of the mixing occurs in an enclosed space, excluding reaction of the addition element with atmospheric oxygen and slag, yields of alloy additions can be much higher than hitherto.

The present invention is particularly, but by no means solely, applicable in connection with the production of a commercial high quality steel in ingot casting, continuous casting or in continuous forming processes.

The hollow carrier may be horizontal, vertical or at some angle to the vertical and constructed from any suitable material. It may have suitable inlets for inject ion of gas/powder mixtures or wire into the liquid metal.

The driving force for providing turbulent flow through the hollow carrier may, for example, be a pressure head in an attached tundish, a vacuum in the receiving vessel or a syphonic system.

Experimental work has shown the importance of creating sufficient turbulence in the hollow carrier to ensure adequate mixing of added reagents. For example, for a 70mm diameter pipe a homogeneous mixture was only obtained within 1 metre of the injection point with a Reynolds No. exceeding 50,000.

Values, with this parameter, for the other carrier geometries can be derived from accepted hydrodynamic theories. It may be preferable, however, that the carrier be long enough to avoid entrance effects and that fully turbulent flow occurs for a substantial distance through the carrier.

Turbulence in the fluid inside the carrier may be enhanced by protrusions from the carrier wall, profiling of the inside surface of the carrier, electromagnetic stirring, injection of gas or suitably reactive materials or any other means of imparting perturbations into the fow of fluid without creating substantial dead zones.

In one embodiment of the invention, where the second vessel is a casting mould, heat may be deliberately extracted from the liquid metal and additives during transfer through the hollow container. This can be done, for example, by natural convection and radiation or by any other suitable means.

By extracting sensible and/or latent heat from the liquid metal through the walls of the carrier, it is possible to ensure that casting takes place at a temperature close to, at or even below the liquidus of the metal (as is fully described and defined in our co-pending aplication 83.06683) and thereby reduce the amount of segregation of the additive and liquid metal.

In order that the invention may be more readily understood one embodiment therefore will now be described by way of example with reference to the accompanying drawings in which: Figure 1 is a diagrammatic representation of a steel continuous casting apparatus incorporating the invention; and Figure 2 is a diagrammatic representation of an uphill casting assembly incorporating the invention.

Referring to Figure 1 it will be seen that the continuous casting apparatus comprises a ladle 1 from which metal is poured into a tundish 2, the metal from the tundish then transfers through a hollow pipe 3 into the normal continuous casting delivery arrangement 5. Additives are injected via a hopper 6 at the outlet from the tundish. The dimensions of the transfer pipe are so chosen to ensure turbulent flow for the metal passing therethrough.

During operation heat may be extracted from the metal flowing through the transfer pipe 3 so that on entry to the continuous casting mould it may be below liquidus temperature and/or has had a proportion of its latent heat removed (as is described in our copending Application No. 83.06683). Heat extraction may simply be by means of exposure to ambient temperature as shown, but may include forced cooling of the kind mentioned hereinabove.

In Figure 2 steel from a ladle 7 passes to a tundish 8. The outlet of the tundish connects to a carrier pipe 9 leading to an ingot mould 10.

The carrier pipe 9 corresponds to the runner system of a conventional uphill casting assembly except that, unlike conventional uphill casting it is ensured that the pipe 9 is filled with inflowing steel to provide sufficient head of liquid metal for turbulent flow conditions to pertain.

It will be seen that the tundish 8 is provided with a hollow outlet stopper 11 through which additives, supplied via a pipe 12, may be introduced to liquid steel at the entrance to the carrier pipe 9.

Claims (17)

CLAIMS:

1. Apparatus for the processing of metals comprising a first metal containing vessel; a second metal containing vessel; a hollow carrier for transferring liquid metal from the first vessel to the second vessel; and a means for introducing additives into the first vessel or hollow carrier and the arrangement being such that, in operation, metal additives transferring from the first vessel to the second vessel are in turbulent flow conditions.

2. Apparatus as claimed in Claim 1 wherein at least one of the metal containing vessels is a ladle or a tundish.

3. Apparatus as claimed in Claim 1 or 2 wherein one of the metal containing vessels is a convertor vessel.

4. Apparatus as claimed in Claim 1 or 2 wherein the first metal containing vessel is a blast furnace, and the hollow carrier is incorporated in the blast furnace runner system.

5. Apparatus as claimed in any one of Claims 1 or 2 in which the second metal containing vessel is a metal casting mould.

6. Apparatus as claimed in any one of the preceding claims wherein the hollow carrier is at least partially horizontal.

7. Apparatus as claimed in any one of the preceding claims wherein at least the inside surface of the hollow carrier is shaped to enhance turbulent flow conditions for transferring metal.

8. Apparatus for the processing of metals substantially as shown in and as hereinbefore described with reference to Figure 1 or Figure 2 of the accompanying drawings.

9. A method of processing metals comprising the steps of transferring molten metal from a first containing vessel to a second containing vessel through a hollow carrier; introducing additives into the first containing vessel or the hollow carrier as the metal passes therethrough; and subjecting the metal to turbulent flow conditions as the metal and additives pass through the hollow carrier.

10. A method as claimed in Claim 9 wherein the metal is steel.

11. A method as claimed in Claim 10 wherein the first containing vessel is a blast furnace and the additives are such as to enable at least one of desuphurisation, dephosphorisation and desiliconisation to occur.

12. A method as claimed in Claim 9,10 or 11 wherein the additives are continuously fed into the first vessel or the hollow carrier.

13. A method as claimed in Claim 12 wherein the additives are introduced at a rate set as a fraction of the liquid metal flow rate.

14. A method as claimed in any one of Claims 9 to 13 wherein the driving force for turbulent flow through the hollow carrier is gravity or pressure difference.

15. A method as claimed in any one of Claims 9 to 14 wherein turbulence in the fluid within the hollow carrier is enhanced by subjecting the fluid to action from an outside agency.

16. A method as claimed in any one of Claims 9 to 15 in which the second containing vessel is a casting mould including the step of extracting heat from the liquid metal and additives during passage through the hollow carrier.

17. A method of processing metals substantially as hereinbefore described with reference to Figure 1 or Figure 2 of the accompany drawings.