GB2112912A - Installation or repair of refractory linings - Google Patents

Abstract

A method of installing a refractory lining in a container comprises siting within the container a former, depositing in the resulting gap between the former and a backing layer adjacent to the container wall or between the former and the container wall, a substantially dry powder mix comprised of a low density refractory material of low thermal conductivity and a binder, and subjecting the facing layer so formed to low temperature heating to activate the binder.

Description

SPECIFICATION Installation or repair of refractory linings This invention relates to the installation or repair of refractory linings and is particularly, but not necessarily exclusively, concerned with the linings of containers for molten metals, e.g., ladles and the like.

Hitherto, molten metal containers such as ladles have been lined with either conventional refractory bricks with interposed mortar, or with refractory materials in the form of mouldable, castable or gunning mixes, which can be rammed, slung, cast or gunned into place by methods well known to those skilled in the art. Brick linings have the disadvantage of being laborious and requiring skilled operatives, and the ladle can be out of commission for considerable periods.

Linings formed from mouldable, castable and gunnable mixes allow much greater rapidity in producing a lining but the necessary relatively high water content of the mix, to allow its placement and consolidation, usually known as tempering water, must be completely removed before molten metal can be poured into the container. Prolonged and careful heating must therefore necessarily take place in order to dry thoroughly the lining, resulting in the ladle or the like being out of commission for a considerable period of time, and resulting in the consumption of considerable amounts of energy.

Particularly when ladles or the like are used to contain molten steel, it is necessary to guard against the phenomenon known as "skulling", where adverse heat transfer characteristics of the refractory lining cause the molten steel in contact with the lining to chill and solidify, resulting in a loss of yield, and possible damage to the lining on the removal of the "skull". Thus, it is known to subject a ladle or the like to considerable preheating, with attendant high energy costs, and known to apply an insulating layer to the face of the lining, formed by preformed insulating refractory boards. However, because of the large variety of shapes and sizes of ladles and the like, such boards must be precision cut to shape or custon made to suit a particular ladle or the like. Also, such boards must be fitted by hand, a time consuming operation requiring skilled operatives.

The object of the present invention, is to provide a means of lining and or repairing a lining in, e.g., a container for molten metal such as a ladle or the like, which avoids the above mentioned disadvantages.

According to the present invention, a method of installing a refractory lining on the interior of a container, comprises siting within the container a former, depositing in the resulting gap between the former and a backing layer adjacent to the container wall or between the former and the container wall, a substantially dry powder mix comprised of a low density refractory material of low thermal conductivity and a binder, and subjecting the facing layer so formed to low temperature heating to activate the binder. The low temperature heating may be in the range 1500C to 3000C.

The former may be made from a heat destructible material such as cardboard, and burned out either during low temperature heating to set the binder or as molten metal is poured into the container. It is however preferred to provide a removable and re-useable former which can be used alone or in conjunction with a heatdestructible former, and to subject the removable and re-useable former and/or the container and/or the material to vibration during and/or subsequent to depositing the dry powder mix, to consolidate the facing layer prior to activating the binder.

Preferably, the refractory material is sinterable and once molten metal is poured into the container, the facing layer is at least partially sintered to produce a relatively strong insulating facing layer of refractory material in contact with the molten metal.

When the insulating facing layer is installed adjacent a backing layer, the backing layer can be of conventional construction. It is however, possible to install a backing layer by siting a former within the container, depositing in the resulting gap between the former and the container wall a substantially dry powder mix of a high density, high strength refractory material and a binder, subjecting the backing layer so produced to low temperature heating to activate the binder. The insulating hot face layer may then be installed adjacent to the high density lining in the manner defined above.

According to a still further possibility within the invention, an insulating facing layer can be formed directly on to a backing layer utilising the refractory material of the backing layer. Thus, a vibratable former can be wrapped with a heat destructible matecial of open weave or loose fibrous construction, and with the former in place and a substantially dry powder mix of refractory material and binder deposited between the former and the container wall, vibration of the former and/or container causes the finer fraction of the powder to penetrate the material wrapped on the former. On ths destruction of the wrapped material, e.g., during low temperature heating to set the binder, the refractory lining is left with a less dense insulating facing layer integral with the denser backing layer.

It will be understood that the dry powder mix of low density low thermal conductivity refractory for the facing layer can be chosen to suit a particular application. Thus, for example, it can be produced from power station fly ash, olivine sand and appropriate binders, or from low density "bunker grade" fine calcined alumina, graded lightweight alumino-silicate refractory chamotte and appropriate binders. Equally it can be produced from fine calcined magnesia, graded dead-burned magnesia and appropriate binders. In certain circumstances it is advantageous to include in the dry powder mix a glass or ceramic fibrous material or hair-like or needle-like strands of metal.The presence of such materials can be of considerable assistance in preserving a skeletal structure remote from the hot face where bonding can be somewhat weaker, and can be of help in resisting peeling or spalling of the hot face. It will also be understood that the dry powder mix of high density, high strength refractory for the backing layer, when used, can be chosen to suit a particular application. For example, it can be produced from graded calcined bauxite, fine calcined or fused alumina and appropriate binders, or from graded natural andalusite, kyanite, fine calcined alumina and appropriate binders.

Thus, the invention provides a means of installing a lining with an insulating facing layer, which reduces installation time and allows the use of relatively unskilled labour, thereby improving ladle availability and attracting lower labour costs. The invention also reduces considerably the energy costs of producing refractory linings, by eliminating the need for prolonged heating hitherto required to dry and pre-heat thoroughly the lining.

Whilst the invention has been detailed above in conjunction with containers for molten metal, it will be understood that there are other "containers" such as furnaces for the reheating of solid metal where a two part refractory lining with a high strength backing layer and an insulating facing layer is required, and to which the invention can with advantage be applied.

One example of the invention will now be described with reference to the accompanying drawing which is a sectional side elevation through a ladle for transporting the molten metal from a furnace to the location of appropriate moulds.

In the drawing, a ladle 1 is formed by a metal shell 2 having on its internal surface a first backing layer 3 and a facing layer 4.

The backing layer 3 is formed from a high alumina phosphate bonded mouldable, applied to the ladle shell to a depth of 50 mm over the side walls and base by any conventional technique such as hand trowelling, gunning or vibration casting. The ladle is then heated to approximately 3000C for a period of four hours to harden the backing material. After the backing layer so formed had cooled, a steel former was suspended within the ladle, the former having a diameter and a profile such as to create a constant 50 mm gap between the former and the backing layer over the whole of the side wall and base areas. A dry powder mix of a low density, low thermal conductivity material and a binder was then introduced into the gap with the ladle and/or the former subjected to vibration to ensure that the dry powder mix completely filled the gap between the backing layer and the former.The former was then heated to 2000C for 30 minutes to set the binder, the former allowed to cool and then removed from the ladle.

A capping 5 of phosphate-bonded high alumina plastic refractory material was moulded on top of the concentric rings of backings and facing materials.

To test the effectiveness of the lining, the ladle was heated for 30 minutes at 3000 C, after which a 1 tonne charge of molten steel at 1 4500C was poured into the ladle from an electric arc furnace.

During casting of the steel it became evident that the external shell of the ladle was at a much lower temperature than when using conventional dense refractories as a lining. It was also evident during casting that as molten steel level in the ladle fell, the amount of heat retained in the lining was much less than in ladles with conventional dense refractory linings. On examination of the insulating lining after completion of the first cast, it was found that minimal erosion or wear had taken place and that the lining surface was well sintered. A second charge of molten steel and temperature as previously, was introduced into the ladle. Again after casting, minimal wear had taken place and the insulating properties of the lining had been retained.In neither case was there any evidence of skull formation, and no problems occurred with metal freeze build-up around the teeming nozzle during the duration of the casts, indicating that heat losses from the melt had been minimal.

A preferred material for the low density low thermal conductivity refractory material for the facing layer is as follows:- Parts by weight Graded Andalusite 0--8 mm 55-90 Raw Virginia Kyanite -35 mesh 0-10 Fused Alumina200 mesh 0-1 5 Aluminium phosphate powder 0-5 Boric oxide powder 0-5 Expanded Perlite 5-15 Paraffin 0--0.5 A still further preferred material for the facing is as follows: : Parts by weight Graded Andalusite 0--8 mm 72 Raw Virginia Kyanite -35 mesh 9 Fused Alumina200 mesh 7.5 Aluminium phosphate powder 2.5 Boric oxide powder 2.0 Expanded Perlite 7.0 Paraffin 0.2 For the above material, the binder is preferably phenol formaldehyde powder resin in the amount 1-5 parts by weight, it being further preferred that the phenol formaldehyde powder resin is in the amount 3.0 parts by weight.

Thus, in this example of material for the facing layer, graded andalusite is the principal refractory aggregate in the mix, and raw virginia kyanite can be incorporated to ensure positive expansion within the mix at steel making temperatures.

Fused alumina is preferably added as a highly refractory filler in the very fine fraction of the mix, and aluminium phosphate powder and boric oxide powder can be incorporated as glass formers.

Phenol formaldehyde powder resin is incorporated as a low temperature binder to promote initial strength in the mix prior to the glass forming elements taking as the principal binders. Expanded perlite is added to provide a low bulk density mix and has the additional advantage of forming glass at steel making temperatures, which helps to seal surface porosity within the refractory body. Paraffin is added to minimise dust emission during installation.

Claims (21)

Claims

1. A method of installing a refractory lining on the interior of a container, comprises siting within the container a former, depositing in the resulting gap between the former and a backing layer adjacent to the container wall or between the former and the container wall, a substantially dry powder mix comprised of a low density refractory material of low thermal conductivity and a binder, and subjecting the facing layer so formed to low temperature heating to activate the binder.

2. A method as in Claim 1, wherein the low temperature heating is in the range 1 5O0C to 3O00C.

3. A method as in Claim 1 or Claim 2, wherein the former is formed from a heat destructible material such as cardboard, and burned out either during low temperature heating to set the binder or as molten metal is poured into the container.

4. A method as in Claim 1 or Claim 2, wherein the former is removable and re-useable.

5. A method as in any of Claims 1 to 4, wherein the former and/or the container and/or the material is subjected to vibration during and/or subsequent to depositing the dry powder mix, to consolidate the facing layer prior to activating the binder.

6. A method as in any of Claims 1 to 5, wherein the refractory material of the facing layer is sinterable and once molten metal is poured into the container, the facing layer is at least partially sintered to produce a relatively strong insulating facing layer of refractory material in contact with the molten metal.

7. A method as in any of Claims 1 to 6, wherein when the insulating facing layer is installed adjacent a backing layer, the backing layer is of a conventional lining material, conventionally applied.

8. A method as in any of Claims 1 to 6, wherein when the insulating facing layer is installed adjacent a backing layer, the backing layer is itself formed from a substantially dry powder mix of a high density high strength refractory material and a binder, which backing layer is subjected to low temperature heating to activate the blinder.

9. A method as in Claim 8, wherein a former is sited within the container, and a substantially dry powder mix of a high density high strength refractory material and a binder deposited in the resultant gap between the former and the container wall, the backing layer so produced being subjected to a low temperature heating to activate the binder.

10. A method as in Claim 8 or Claim 9, wherein an insulating facing layer is formed directly on a backing layer utilising the refractory material of the backing layers.

11. A method as in Claim 10, wherein a vibratable former is wrapped with a heat destructible material of open weave or loose fibrous construction, and with the former in place within a container of substantially dry powder mix of a high density high strength refractory material and a binder is deposited between the former and the container wall, there being vibration of the former and/or the container to cause the finer fraction of the powder to penetrate the material wrapped on the former and whereby on the destruction of the wrapped material, the dense backing layer has an integral facing layer less in density.

12. A method as in any of Claims 1 to 11, wherein dry powder mix of low density low thermal conductivity material includes a glass or ceramic fibrous material or hair-like or needle-like strands of metal.

13. A method as in any of Claims 1 to 12, wherein a material for the low density low thermal conductivity refractory material is, in parts by weight, graded andalusite 0--8 mm 55-90; raw virginia kyanite -35 mesh 0--10; fused alumina-200 mesh 0--15; aluminium phosphate powder 0--5; boric oxide powder 05; expanded perlite 5-15; paraffin 0--0.5.

14. A method as in Claim 13, wherein the material is, in parts by weight, graded andalusite 0--8 mm 72; raw virginia kyanite -35 mesh 9; fused alumina200 mesh 7.5; aluminium phosphate powder 2.5; boric oxide powder 2.0; expanded perlite 7.0; paraffin 0.2.

1 5. A method as in Claim 13 or Claim 14, wherein the binder is a phenol formaldehyde powder resin in the amount 1-5 parts by weight.

1 6. A method as in Claim 15, wherein the phenol formaldehyde powder resin is in the amount 3.0 parts by weight.

1 7. A methof of installing a refractory lining on the interior of a container substantially as hereinbefore described.

18. A method of installing a refractory lining on the interior of a ladle substantially as hereinbefore described with reference to the accompanying drawing.

19. A refractory lining on the interior of a container when installed by the method of Claim 1.

20. A refractory lining on the interior of a ladle when installed by the method of Claim 1 and substantially as hereinbefore described with reference to the accompanying drawing.

21. A low density refractory material when used in the method of Claim 1 for installing a refractory lining on the interior of a container substantially as hereinbefore described.