GB2120369A - An improved metallurgical lance - Google Patents

Abstract

The lance (10) has a refractory tubular body (11) reinforced by a metal tube (15), and is fitted with a removable tip (12) closing an end of the body (11) and serving as a gas- dispersing end of the lance (10). The tip (12) is a refractory concrete casting and includes a plenum (19) and an associated passage through which gas enters the plenum (19) from the tubular body (11); delivery of gas to molten metal is via a plurality of capillary tubes (20) in the tip (12). The tip may be housed in a recess in the end of the lance. The tip is manufactured using a covered mould of readily meltable or combustible material. <IMAGE>

Description

SPECIFICATION An improved metallurgical lance The present invention relates to an improved metallurgical lance.

Amongst the objects of this invention is the provision of an inexpensively-made lance capable of introducing gas to a mass of molten metal with a minimum of disturbances thereof, the lance being furnished with a readily renewable tip, for preference.

According to the present invention, there is provided a metallurgical lance having a tubular refractory body and terminating in a closed, gasdelivery end pierced by a plurality of capillary tubes extending through the closed end, the tubes communicating with a plenum provided in the closed end such as in use to be fed with gas supplied to the plenum from the hollow interior of the lance body.

The embedment of refractory tubing in the body is one way to ensure trouble-free manufacture and to minimise rejects caused by blocked bores.

Tubes with internal diameters of the order of half a millimetre will allow adequate gas flow and will not readily become blocked by frozen metal when the lance is removed from a bath of molten metal.

The refractory body could be made from a pressed and fired refractory, but is preferably a refractory castable such as a hydraulically setting high alumina concrete.

The invention also provides a method of making a metallurgical lance or a replaceable tip piece therefor, which includes the steps of forming a cored mould replicating the lance or a tip piece thereof, the core being made of readily meltable or combustible material and serving to define a plenum inside a finished moulding; mounting a plurality of capillary tube formers on the core; filling the mould with a refractory concrete mix and curing the concrete; and thereafter subjecting the moulded body to heat for removing the core by melting it or burning it away.

Three examples of capillary tube formers are refractory capillary tubing, metal e.g. stainless steel capillary tubing and metal wires. The latter are to be drawn out of the refractory body after manufacture thereof. To ease removal of the wires, they are preferably coated with a release agent such as a wax or grease.

The invention will now be described in more detail by way of example only with reference to the accompanying drawings, in which: Fig. 1 is a schematic, partial longitudinal cross section through a lance according to the invention; and Fig. 2 is a partial longitudinal cross section through a lance forming the preferred embodiment of the invention.

The metallurgical lance 10 of Fig. 1 comprises a main tubular body 11 and a removable endclosing tip 12 through which gas in use is passed to the molten metal. The main body 11 is a refractory pipe 1 4 reinforced by an inner metal tube 1 5. The tube 1 5 forms a conduit for gas delivered to the lance. The refractory pipe could be a conventional fired refractory such as alumina, but preferably is a refractory concrete moulding since the latter is a less costly item to produce.

The metal tube 15, in this example, projects beyond the refractory pipe 14 to form a union.with a metal sleeve 1 6 secured within the tip 12. In this case the union relies on a screw threaded coupling between the tube 1 5 and sleeve 1 6. The nature of the coupling is generally immaterial so long as it affords an easy attachment and detachment of the tip 12 to and from the main lance body 11. A screw threaded coupling, and particularly one as shown in the drawing, is but one example of a coupling which can be used in practising this invention.

The tip 1 2 has a cementitious refractory body 1 8 cast from a refractory concrete, the coupling sleeve 16 being embedded in the body 18. The refractory concrete can comprise an hydraulic or chemical bonding system, exemplified for instance by a phosphate bonding agent. The sleeve 1 6 conveys gas entering it from the tube 1 5 into a chamber or plenum 19 within the body 18. A plurality of refractory capillary tubes 20 communicate with the plenum 1 9 and the exterior of the tip 12. The tubes 20 in use serve to convey gas fed into the plenum 1 9 outwardly therefrom to the molten metal. The tubes are embedded in the concrete from which the tip is moulded.

As shown, the tubes 20 are parallel to themselves and to the longitudinal axis of the lance. Such a disposition is not essential and the tubes 20 could, for instance, fan outwards and upwardly as viewed in the figure. Some, or all, of the tubes could project radially outwards from the said longitudinal axis. In this arrangement, the tubes may lie in one plane perpendicular to the longitudinal axis.

The tubes 20 provide capillary bores, or "microbores" for the passage of gas to the melt. Their internal diameters can be of the order of 0.5 to 0.6 mm, but this dimension is not distinctive of the invention. The bore size should be large enough that free passage of gas therethrough is possible, but sufficiently small to minimise the likelihood of metal entering and blocking the tubes to gas flow.

The number of tubes 20 will depend, inter alia, on the size of the lance and the amount of gas to be delivered to the melt in unit time. There may, for instance, be ten tubes 20 of the diameter noted in the preceding paragraph.

Capillary tubes similar to or of the type used for thermocouple sheathing are convenient to use.

Those made from recrystallised alumina are suitable for lancing molten steel. Twin-hole and multihole thermocouple sheathing (e.g. having six bores) is available readily and can be embedded in the tip moulding.

The lancing gas flow rate will depend on such factors as the lancing depth beneath the metal surface, the gas supply pressure and the number and bore size of the capillary tubes 20. Variation of the number and bore sizes of the tubes provides a way of tailoring the lance 10 to the lancing conditions.

Production of the tip 1 2 involves casting concrete about a core to form the plenum 1 9 and the recess in which the sleeve 16 is received. A wax core is preferred since the capillary tubes 20 and sleeve 1 6 can be stuck into it and thus held in place during casting and curing. The wax is thereafter melted away by heating the tip, the technique employed being well familiar as the lost wax process. Cores not of wax, but removable by combustion upon heating the cast tip to elevated temperatures, could be substituted, but wax cores are presently preferred.

Gas-tight sealing means is desirably employed when fitting a tip 12 to the main lance body 11.

The sealing means could be a layer of readily frangible cement (not shown) between the confronting faces 23, 24 of the tip and body 14.

The cured cement should be weak enough intrinsically or in its bond to the bodies 14, 1 8 to permit removal of the tip for replacement. A refractory mastic could be used instead of a cement if preferred.

The use of a separable tip is preferred since service conditions are severe, and degradation of the lance is most prominent at its gas-issuing end.

It makes good sense, therefore, to re-tip a lance periodically to extend its service life. Nevertheless, in some cases a removable tip may be considered unnecessary. Then, the formation of the plenum 19 and the incorporation of the tubes 20 will be accomplished when moulding the refractory pipe 14. The tubes will be moulded in situ in an otherwise closed end of the lance pipe 14. In a lance of such a construction, the reinforcing inner tube 15 will normally extend to the plenum 19.

It is not essential to embed capillary tubes in the lance tip 12, for gas-conveying capillary passages could be formed in the course of the tipforming operation. Thus, in performing the method, the refractory material can be moulded or cast about tube or passage forming means constituted by metal wires of appropriate gauge.

When the tip 12 has cured and hardened adequately, the wires are pulled from the tip 12.

To ease their extraction, the wires are precoated with a release agent such as a wax.

A preferred construction is shown in Fig. 2. The lance 10 again comprises a main tubular body 11 formed by a refractory pipe 14 reinforced, for most of its length, by an inner metal tube 1 5. The tube 1 5 stops short of the gas delivery end of the lance 10 and a deep well 30 is thereby formed in this end. The well is closed by a removable gasejecting plug member 31 to which gas is fed by the metal tube 15 in use.

The plug member 31 comprises a moulded refractory body 32, preferably a refractory concrete, united with a generally cup-shaped steel mount 33. The body 32 is of cylindrical shape and is pierced by axial capillary passages 20 for conveying gas into the melt. The mount 33 has its rim 34 embedded in the inner end of the body 32 and the attachment of the mount is rendered secure thanks to a plurality of anchors 35. The anchors 35 are metal lugs welded to the inside of the cup 36 of the mount, and the body 32 is moulded around said anchor legs 35. In this construction, the body 32 and mount 33 cannot be separated since the legs 35 are non-axially directed and here are bent inwardly. There are three anchors 35 spaced uniformly about the plug member 31. It will be recognised that the anchors 35 could take other forms provided they prevent axial separation of the body 32 and the mount 33.

The cup 36 of the mount 33 has its bottom 37 spaced from the bottom end of body 32. The resulting space forms the plenum 1 9. The plenum can be formed as described earlier when moulding the body 32 to the mount 33.

Extending from the bottom 37 of the mount is a tubular extension 38. This is externally screwthreaded to the metal pipe 1 5 of the lance 10.

The passages 20 can be formed, as described earlier, by refractory capillary tubes or by using release-coated metal wires.

The well 30 in the end of the lance is deeper than the installed length of the gas-delivering plug member 31. Accordingly, the gas-ejecting end of the body 32 is recessed below the terminal end of the lance 10. This is advantageous: when the lance 10 is lifted from the melt after lancing, the melt will run off readily from the projecting end of the pipe 14 and will not tend to stick and freeze to the body 32 clogging its passages 20.

The gas-ejecting end of the body 32 is shouldered to provide a projecting end portion, pierced by the capillary tubes or passages 20. The end portion is formed with flats, e.g. is square or hexagonal when viewed end-on, to facilitate installation and removal of the tip piece 12.

Claims (20)

1. A metallurgical lance having a tubular refractory body and terminating in a closed, gasdelivery end pierced by a plurality of capillary tubes extending through the closed end, the tubes communicating with a plenum provided in the closed end such as in use to be fed with gas supplied to the plenum from the hollow interior of the lance body.

2. A lance according to claim 1, wherein each capillary tube has a size permitting free passage of gas therethrough but substantialiy preventing entrance of molten metal therein.

3. A lance according to claim 1 , wherein the capillary tube bore is of the order of half a millimetre.

4. A lance according to any of claims 1 to 3, wherein the lance body is a hollow refractory concrete casting reinforced by an inner metal tube.

5. A lance according to claim 4, wherein the closed lance end is integral with the hollow lance casting and the capillary tubes are defined by refractory tubing embedded in the said casting.

6. A lance according to any of claims 1 to 4 wherein the capillary tubes and plenum are contained in a removable tip piece secured to the lance body.

7. A lance according to claim 6, wherein the tip piece is a refractory concrete casting in which the capillary tubes are defined by refractory tubing embedded in the concrete.

8. A lance according to claim 6 or claim 7, wherein coupling means provided to secure the tip piece to the lance body comprise a screwthreaded union between a sleeve embedded in the tip piece and a metal inner tube reinforcing the lance body.

9. A lance according to claim 6 or claim 7, wherein the tip piece comprises a refractory body pierced by the said capillary tubes and a metal mount non-separably secured together, the tip piece being seated in and closing a well formed in the end of the tubular refractory lance body.

10. A lance according to claim 9, wherein the well is deeper than the installed length of the tip piece which thereby has its gas-ejecting end recessed within the end of the refractory lance body.

11. A lance according to claim 9 or claim 10, wherein the metal mount has a cup-shaped portion to which the refractory body of the tip is fastened, the cup-shaped portion and the refractory body together defining the plenum.

12. A lance according to claim 9, 10 or 11, wherein the mount has an externally screwthreaded tubular extensibn fo;screw-threaded connection to a metal inner tube which reinforces the lance body.

13. A lance according to claim 9, 10, 11 or 12, wherein the capillary tubes are defined by refractory tubing embedded in the refractory body of the tip piece.

14. A lance according to any of claims 6 to 13, further including means sealing the tip piece to the lance body against gas leakage therebetween.

1 5. A lance according to any of the preceding claims, wherein the capillary tubes extend in a direction parallel to the longitudinal axis of the lance.

16. A lance according to any of claims 1 to 15, wherein the capillary tubes extend in radial directions from the longitudinal axis of the lance, some or all thereof lying in a common plane.

1 7. Metallurgical lances substantially as herein described with reference to and as shown in the accompanying drawings.

1 8. A method of making a metallurgical lance or a replaceable tip piece therefor, which includes the steps of forming a cored mould replicating the lance or a tip piece thereof, the core being made of readily meltable or combustible material and serving to define a plenum inside a finished moulding; mounting a plurality of capillary tube formers on the core; filling the mould with a refractory concrete mix and curing the concrete; and thereafter subjecting the moulded body to heat for removing the core by melting it or burning it away.

19. A method according to claim 18, for making a tip piece, wherein the mould in part is defined by the core and a metal mount to form an integral component of the tip piece enabling the latter to be coupled to a lance body, and the concrete mix is cast to the metal mount partially embedding the mount so as to produce a nonseparable assembled tip piece.

20. A method of making a metallurgical lance or tip piece therefor, substantially as herein described with reference to the accompanying drawings.