GB2122532A

GB2122532A - Manufacture of gas-permeable plugs

Info

Publication number: GB2122532A
Application number: GB08313410A
Authority: GB
Inventors: Alan Hey
Original assignee: K S R INTERNATIONAL Ltd
Current assignee: K S R INTERNATIONAL Ltd
Priority date: 1982-05-20
Filing date: 1983-05-16
Publication date: 1984-01-18
Also published as: GB8313410D0

Abstract

A gas permeable plug (14) for installation in a ladle or tundish wall (11, 12) is produced by moulding a refractory concrete about a plurality of refractory capillary tubes (26) supported by a removable core, the purpose of which is to define a void space (29), inside the moulding (18) with which the tubes (26) communicate. The plug is fast with a gas supply pipe (22) which opens to the void space. When the moulding is cured, the void space is created by melting or burning away the core. <IMAGE>

Description

SPECIFICATION Manufacture of gas-permeable plugs The present invention relates to manufacture of gas-permeable plugs.

It is common practice in the metallurgical industry to blow gas into molten metal for several purposes. These include modification of the chemical constitution of the melt, homogenising the melt and sweeping inclusions to the surface of the melt for incorporation in the slag layer.

One proposed gas injection method has required a gas-porous plug or brick in the wall or bottom of a teeming vessel such as a ladle or tundish. Manufacture of reliable porous plugs or bricks is not easy, and in service there is a considerable risk that they will become inoperative owing to the freezing of a metal skin thereon when the vessel is emptied. Replacement of defective plugs requires the vessels to be taken out of service for substantial periods while they cool down.

An object of this invention is to provide a method of making a gas-admitting plug or brick which is free from the drawbacks of the porous plugs just outlined.

According to the present invention, there is provided a method of making a gas-permeable gas-distributing plug for installation in the wall of a ladle or tundish, comprising the steps of supporting a plurality of capillary tube formers in a chosen disposition, moulding a refractory concrete around them and a core so that the inner, embedded ends of the tubes open to a void space formed within the finished moulding by means of the core, thereafter destroying and removing the core, and securing a gas supply conduit to the plug for feeding gas into the plenum formed at least in part by the void space.

The invention also provides a method of providing a ladle or tundish with a gas-distributing plug, comprising the steps of procuring a ladle or tundish with a through opening in a wall thereof, mounting an orificed brick in the opening, making a plug by the method defined in the last preceding paragraph, and thereafter fitting and securing the plug in the orificed brick.

The invention further provides a gas-permeable, gas distributing plug for installation in the wall of a vessel for molten metal, comprising a moulded concrete member pierced by a plurality of capillary tubes for ejecting gas into a melt, the tubes opening to a void space formed in the concrete member, and the said plug further including an inlet for admitting gas to the void space and thence to the capillary tubes.

The invention will now be described by way of example only with reference to the accompanying drawing, in which the sole figure is a partial cross sectional view of the bottom of a ladle or tundish provided according to the invention with gas-admission means.

The vessel 10 has a metal shell 11 and an inner refractory lining 1 2 as conventional.

Somewhere in the shell and lining are aligned openings in which gas admission means 1 4 is mounted. The said means 14 will normally be located in the bottom of the vessel 10.

An 'orificed brick 1 5 is fitted in the lining opening. The orifice 1 6 is at least partly frustoconical and tapers inwardly in the direction of the interior of the vessel. The frustoconical orifice 1 6 forms a seating for a gaspermeable, gas-distributing member 1 8 (of the admission means 14) which is similarly of frusto-conical shape. The gas distributor 18 is backed by a refractory plug 20 having an orifice 21 in which the end of a metal gas conduit 22 is mounted. A mounting plate 24 through which the conduit 22 passes is bolted to the shell to retain the gas distributor 1 8 and backing plug 20.Tightening the bolts 25 thrusts the gas distributor 1 8 into firm contact with the frusto-conical wall of the orifice in brick 1 5. Such contact guards against leakage of molten metal.

The gas distributor 1 8 has a plurality of capillary refractory tubes 26 embedded therein. The tubes extend from the inner face 27 of the distributor 1 8 to a recess 28 in the opposite face thereof. The recess 28 forms a plenum 29 in the gas distributing means 14 in conjunction with the plug 20. In use, gas is pumped into the plenum 29 via the conduit 22 and is dispersed into the melt by the tubes 26.

The capillary tubes 26 have bores of such diameters that gas has free passage therethrough but molten metal is prevented from entering them. Their diameters can be of the order of 0.5 to 0.6 mm but this size is not distinctive of the invention. The bore sizes as well as the number of tubes 26 can be varied to suit the desired gas flow rate and gas pressure.

At least the gas distributor member 18, and possibly the brick 1 5 and backing plate 20, is made from cementitious material. The member 18, or each of the members 15, 18 and 20 is cast from a refractory concrete, which can comprise an hydraulic or chemical binding system e.g. a phosphate binding system.

The casting of member 1 8 involves casting about the tubes 26. The tubes can be held in place by a wax former or core which defines the recess 28. The wax is melted away when the casting has cured. The former could be made of a combustible material instead, which is burned away upon curing of the casting.

It will be appreciated that the member 20 could be omitted, when member 18 will be extended downwardly as necessary towards the mounting plate 24. An internal void providing plenum 29 is possible by the adoption of the lost core or lost wax technique.

The conduit 22 can be cemented into the backing plug 20, but if the latter is cast, then in situ casting can be used to bond the conduit into the plug 20. If plug 20 is omitted, the conduit could be similarly fitted to the member 18.

Preferably, however, the conduit 22 is gastightly secured to a thin, gas-impermeable metal jacket (not shown) which encases the gas-distributor member 18 save for its gasejecting end face. The jacket has a conicallyshaped sleeve portion matching the taper of member 18, and a base portion to which the conduit is connected. The sleeve portion may extend the full height of member 1 8. Alternatively, the sleeve portion is shorter than the said height: it may be one third or one half the height. In this way, the metal will be set back from the hot face of the gas admission means 14 which the molten metal contacts.

The base portion of the jacket can serve the purpose of the illustrated plug 20, which may then be omitted. Then, when the recess 28 is not an internal void, the base portion serves in defining the plenum 29 with the recess 28.

Refractory tubing useful for the capillary tubes 26 is readily available as thermocouple sheathing. For introducing gas into molten steel, sheathing made of recrystallised alumina is suitable. Thermocouple sheathing possessing a plurality of bores is available on the market and the as distributor 18 can include a plurality of such multibore elements.

The refractory tubes 26 have been illustrated as parallel to one another, but such a disposition is not indispensible to the invention. The tubes could well fan out from the plenum 29.

Where the gas-distributing member is formed from an assembly of the moulding 18 and a separate backing member 20, sealing means such as a cement or mastic (not shown) can be included at the joint between these members to preclude gas leakage from the plenum 29 via the joint.

If desired, the capillary tubes could be made of a suitably temperature-resisting metal instead of from a refractory material. In either event, said tubes are left in situ in the concrete moulding.

Alernative capillary tube formers can be used. Thus, wires for instance can be employed. The wires are assembled and, held in a chosen disposition by such means as the removable core, and the concrete is cast around them. Once the concrete has set, the tube formers are pulled from the moulding. To ease removal of the tube formers, they can be coated with a suitable release agent such as a wax.

Claims

1. A method of making a gas-permeable gas-distributing plug for installation in the wall of a ladle or tundish, comprising the steps of supporting a plurality of capillary tube formers in a chosen disposition, moulding a refractory concrete around them and a core so that the inner, embedded ends of the tubes open to a void space formed within the finished moulding by means of the core, thereafter destroying and removing the core, and securing a gas supply conduit to the plug for feeding gas into the plenum formed at least in part by the void space.

2. A method according to claim 1, wherein the capillary tube formers are supported by a readily meltable, or combustible, core which is used to establish the void space during moulding, and the core is removed following curing of the moulded concrete by applying heat to melt or burn away the core.

3. A method according to claim 1 or claim 2, wherein the core is used to establish a recess in a face of the plug moulding opposite to a gas-delivering face thereof, and the plug is completed by assembling the plug moulding with an orificed backing member to which the conduit is secured, the plenum being defined by the recess and the backing member.

4. A method according to claim 3, wherein sealing means is incorporated in a joint between the moulding and backing member to guard against leakage of gas from the plenum via the joint.

5. A method according to any of claims 1 to 5, wherein the capillary tubes formed in the moulding have bore sizes allowing free passage of gas but preventing blockage thereof by entry of molten metal into the bores.

6. A method according to any of claims 1 to 5, wherein the capillary tube formers are either capillary tubes left in situ in the concrete moulding and made of refractory or metallic materials, or wires around which the concrete is moulded, said wires being withdrawn from the concrete after it has set.

7. A method of making a gas-permeable, gas-distributing plug for installation in a wall of a ladle or tundish, substantially as herein described with reference to the accompanying drawing.

8. A method of providing a ladle or tundish with a gas-distributing plug, comprising the steps of procuring a ladle or tundish with a through opening in a wall thereof, mounting an orificed brick in the opening, making a plug by the method claimed in any of claims 1 to 7, and thereafter fitting and securing the plug in the orificed brick.

9. A method of providing a ladle or tundish with a gas-distributing plug, substantially as herein described with reference to the accompanying drawing.

10. A ladle or tundish having a gas-permeable, gas-distributing plug, made according to claim 1, installed in its lining and substan tially as herein described with reference to the accompanying drawing.

11. A gas-permeable, gas distributing plug for installation in the wall of a vessel for molten metal, comprising a moulded concrete member pierced by a plurality of capillary tubes for ejecting gas into a melt, the tubes opening to a void space formed in the concrete member, and the said plug further including an inlet for admitting gas to the void space and thence to the capillary tubes.

1 2. A plug according to claim 11, wherein the capillary tubes are formed by refractory or metallic capillary tubing embedded in situ in the concrete member.

1 3. A plug according to claim 11 or claim 12, wherein the concrete member is encased save for a gas-ejecting face thereof in a metal jacket having the inlet gas-tightly secured thereto.

1 4. A gas permeable, gas distributing plug for installation in the wall of a vessel for molten metal, substantially as herein.described with reference to and as shown in the accompanying drawing.