GB2120588A

GB2120588A - Introduction of refractory filler material into nozzle assemblies of molten metal-holding vessel

Info

Publication number: GB2120588A
Application number: GB08314843A
Authority: GB
Inventors: Eric George Tucker
Original assignee: British Steel Corp
Current assignee: British Steel Corp
Priority date: 1982-05-27
Filing date: 1983-05-27
Publication date: 1983-12-07
Also published as: GB8314843D0

Abstract

A refractory filler material is introduced into the well block (3) of a nozzle assembly (10) in a vessel through which molten metal is discharged through a slide gate valve (5-9). The filler material comprises a pre-formed cylindrical body (12) of granular refractory material which is introduced into position through aligned apertures in the gate valve which is then closed prior to the vessel being charged with the molten material. The body (12) may subsequently collapse so filling the well block outlet. <IMAGE>

Description

SPECIFICATION Improvements in and relating to the introduction of refractory filler material into nozzle assemblies This invention relates to nozzle assemblies in vessels through which molten metal is discharged via a slide gate valve, and more particularly relates to a method of filling such nozzles with a refractory filler prior to the introduction and discharge of the metal.

In the sequence of filling a vessel with molten metal and discharging it to a mould or other vessel through a slide gate valve, it is important to ensure that there is no impediment to the free flow of the molten metal when the slide gate is opened.

Frequently such an impediment occurs because the molten metal tends to solidify in the lower, cooler parts of the nozzle assembly, which includes the well block; whereas, in some cases, metal freezing in this manner may physically hinder the initial opening of the sliding plate of the valve, more commonly, solidification of the metal actually closes the nozzle aperture so preventing the discharge of the main mass of the molten metal. In such circumstances the obstruction may be cleared by oxygen lancing. Such a procedure can however be dangerous for the operatives and may lead to damage to and erosion of the slide gate refractories.

A conventional practice to overcome solidification of metal in the nozzle assembly is to fill the well block/nozzle bore with a granular refractory material prior to the introduction of the molten metal. The material is such that the superficial surface which is contacted by the molten metal sinters giving sufficient strength to avoid the dispersal of the loose granular material into the body of the molten metal whilst the main mass of this material remains free-flowing. Upon the slide gate valve being opened, the main mass of the powder flows freely through the nozzle bore, leaving the 'unsupported sintered layer which then breaks under the head of the molten metal above permitting unimpeded flow through the valve.

It is an object of this invention to provide an improved method by which the nozzle assembly may be filled with a refractory filler.

From one aspect the present invention provides a method of introducing a refractory filler material into a nozzle assembly in a vessel through which molten material is to be discharged through a slide gate valve, in which a pre-formed cylindrical body of granular refractory material is introduced into position through aligned apertures in the gate valve which is then closed prior to the vessel being charged with molten material.

The size of the pre-formed body is such that the refractory material substantially fills the nozzle assembly following closure of the valve. In this regard the pre-formed body of granular material may comprise an outer envelope which decomposes during the vessel pre-heat, or at the ambient temperature between sequential vessel operations, thereby releasing the freely flowable refractory material to fill the nozzle assembly bore.

Such an outer envelope may be made from any material which volatilises at the relevant temperatures; examples of such material include cellulosic paper or cardboard etc. or expanded polystyrene. Alternatively, the outer envelope may comprise a thin metal sheet or strip which is wound in a spiral manner to define an enclosure, the adjoining edges of which are temporarily retained by means of a volatilisable material such as cellulosic paper. The sheet or strip may be of mild steel of thickness approximately to 0.03 mm.

The envelope is preferably closed at each end by means of an end cap of a material similar to that used for the envelope.

The granular refractory material may be, for example, silica sand, zircon sand, chrome sand or carbon powder, and an expansile agent may advantageously be added to this material such that at the temperature prevailing in the nozzle assembly, the total volume of the insert expands, thus aiding the complete filling of the relevant space. Such an expansile agent may be a pretreated carbon or vermiculite producing, for example, up to 50% of more in volume expansion of the total initial mixture volume.

As an alternative to an enveloped refractory filler, the base powder composition, with or without the expansile agent, may be in the form of a pre-formed cylinder bonded by a fugitive material such as lignosulphate or napthalen. In this embodiment the powder is released on breakdown of the fugitive binder at, for example, temperatures of between 3000C and 7000C.

In order that the invention may be more fully understood, one embodiment thereof will now be described with reference to the accompanying drawing which schematically illustrates a ladle slide gate valve with the pre-formed body of granular material inserted.

Referring to the drawing, the ladle, only the lower casing 1 of which is shown, is lined with refractory bricks 2 and a well block 3 is mounted adjacent a slide gate assembly.

The latter is shown in its simplest form comprising a metal casing 5 housing a sliding carriage 6, an apertured stationary refractory plate 7 being mounted on the casing and an apertured sliding refractory plate 8 together with a refractory collector nozzle 9 being mounted on the carriage.

A refractory nozzle 10 is mounted within the well block.

Inserted within the aligned apertures in the slide gate assembly is a cylindrical body 12 of granular material in accordance with this invention. This may either be a pre-formed cylinder bonded by a fugitive material such as lignosulphate or napthalene or granular material encapsulated in an envelope which decomposes during ladle preheat or at the temperature existing within the ladle between casts. The envelope may be produced from any suitable material which volatilises at the relevant temperatures, e.g.

cellulosic paper, cardboard or expanded polystyrene, or, alternatively, may comprise thin mild steel strip or sheet spirally wound in edge to edge contact to produce a tube. In this latter case, the adjoining edges of the wound strip or sheet are temporarily held together by, for example, an adhesive paper. The body 12 is shown being inserted into position from below by a rod 13, When the body 12 has been placed into the position shown the sliding carriage 6 is actuated to close the valve, the aperture of the sliding plate 8 then being misaligned with that in the stationary plate 7. During preheating of the ladle, the cylindrical body 12 collapses, thereby filling the well block and nozzle with the refractory material.

Typical dimensions of the cylindrical 'slug' are between 1" and 3" in diameter, depending on the size of the bore, and up to 2 to 3 feet in length.

More than one 'slug' may be introduced at each filling and the method may be adopted at any stage during the life of the ladle, that is, not only prior to the initial charging of the molten metal, but during subsequent charging when the ladle is at a high temperature. Further, although the insertion has been shown to be from below with the ladle vertical, it may be inserted horizontally with the ladle on its side, this often being more suitable when the slide gate assembly requires attention.

Claims

1. A method of introducing a refractory filler material into a nozzle assembly in a vessel through which molten material is to be discharged through a slide gate valve, in which a pre-formed cylindrical body of granular refractory material is introduced into position through aligned apertures in the gate valve which is then closed prior to the vessel being charged with the molten material.

2. A method as claimed in Claim 1 in which the preformed cylindrical body of refractory material substantially fills the nozzle assembly foliowing closure of the valve.

3. A method as claimed in Claim 2 in which the granular material comprises an outer envelope which decomposes during the vessel preheat or at the ambient temperature between sequential vessel operations, thereby releasing the freely flowable refractory material to fill the bore of the nozzle assembly.

4. A method as claimed in Claim 3 in which the outer envelope is made from cellulosic paper or cardboard or expanded polystyrene or thin metal strip or sheet.

5. A method as claimed in any one of the preceding claims wherein the granular refractory material comprises silica sand, zircon sand, chrome sand or carbon powder.

6. A method as claimed in any one of the preceding claims wherein an expansile agent is added to the refractory material such that at the temperature prevailing in the nozzle assembly the total volume of the insert expands.

7. A method as claimed in Claim 6 wherein the expansile agent is pre-treated carbon or vermiculite.

8. A method as claimed in Claim 1 or Claim 2 wherein the granular refractory material is in the form of a pre-formed cylinder bonded by a fugitive material such as lignosulphate or napthalen.

9. A method of introducing a refractory filler material into a nozzle assembly of a vessel substantially as herein described with reference to the accompanying diagrammatic drawing.