GB2105828A - Monolithic lining of vessels such as furnaces and parts thereof - Google Patents

Abstract

An induction furnace (10) is monolithically lined or repaired by the steel liner method, the latter being a hollow drum (15') which is vibrated during the lining operation to consolidate the refractory lining formulation. The drum (15') is perforated and its opening (16) are occluded by an air-permeable and normally moisture-impermeable plastics material; during the lining operation the drum is evacuated to draw air via the occluded openings (16) from the interface between the refractory formulation and the drum (15'), thereby obtaining a lining having a void-free inner surface after removal of the drum (15') e.g. by melting down. The process can be used for relining other vessels such as ladles and tundishes, and relining furnace runners is also described. <IMAGE>

Description

SPECIFICATION Monolithic lining of vessels such as furnaces and parts thereof The present invention relates to monolithic lining of vessels such as furnaces and parts thereof with refractory materials.

More particularly, the invention relates to lining the walls of furnaces such as induction furnaces and the troughs or runners of blast furnaces. Vessels such as ladles and tundishes could also be lined by means of the present invention.

The invention is applicable to lining vessels, furnaces and parts thereof de novo and to repairing existing linings, and the word "lining" is used herein to cover both usages of the invention.

Lining materials used in practising the invention can be dry refractory formulations, of which many examples are known. Such materials bind together if modestly heated when they include a resin plastics binder. Lining materials may alternatively employ chemical binders which similarly are activated by heat, or they may be formulated so as to fuse upon firing, for instance in the course of heating up the furnace after lining in accordance with the invention.

Refractory concrete compositions may also be convenient for use, such compositions being curable at room temperature if hydraulically boned or at modest temperatures, for instance in the range 150 - 300 Celsius, if chemically bonded.

With existing methods, it is difficult to obtain linings possessing smooth surfaces which will be exposed to molten metal. Common defects are pits, pockets or voids. These cannot be prevented ordinarily unless painstaking care and time is expended during the lining process. The presence of such defects will be responsible for accelerated degradation of a lining, possibly weakening it and serving as sites at which chemical attack and erosion may commence. From such sites, molten metal break-out may result.

Our aim has been to devise a lining method able to minimise or eliminate superficial voids in a lining.

According to the present invention, there is provided a method of lining a vessel which is to contain molten metal with refractory material, wherein a shell or former the exterior of which conforms to the required inside wall of the lining is placed in the vessel, a refractory lining formulation is placed in the vessel around the shell, and the lining formulation is consolidated by vibrating the shell and by sucking air from the interface between the lining formulation and the shell, and wherein for the purpose of extracting the said air the shell being of perforate form and having an air-permeable material occluding the openings thereof.

The invention also provides a method of lining a metal melting furnace runner with refractory material, wherein a trough-shaped shell orformerthe exterior of which conforms to the required runner profile is lowered into the runner, a refractory lining formulation is admitted to the space within the runner around the former, and the latter is vibrated to consolidate the lining formulation, and wherein consolidation is assisted by sucking air from the interface between the lining formulation and the former, for which purpose the former is of perforate form and has an air-permeable material occluding the openings thereof.

Suction and vibration can be applied to the system simultaneously or separately, e.g. repetitively, depending on whichever routine is found to yield the best consolidation.

Further details of the invention will now be given in the following description by way of example with reference to the accompanying drawings, in which Figure lisa diagrammatic illustration of part of an induction furnace and apparatus used for lining it according to the invention; Figure2 is an illustration similar to Figure 1 showing modified apparatus for use in the present method; Figure 3 is a transverse view illustrating apparatus used in repairing the lining of a runner of a blast furnace; and Figure 4 is a plan view of the arrangement shown in Figure 3.

Application of the present method for repairing a damaged furnace lining, or for forming a new or replacemet lining, is illustrated in Figures 1 and 2.

Reference is first made to Figure 1 which illustrates a furnace 10, which by way of example is shown as an induction furnace. For simplicity, the top reaches of the furnace 10 have been omitted.

The furnace 10 has a base 11 comprising suitably supported firebricks, and an upstanding cylindrical heating element 12 comprising awater-cooled copper pipe formed into a helical coil.

Formation of a new lining 13 commences by pouring the lining material into the furnace, to form a bed on the base 11. The bed is then tamped to consolidate it, usually, but consolidation might be left until later in the procedure, particularly when lining small furnaces.

Next, a thin steel shell 15 is placed inside the furnace, the shell having a closed bottom end which is stood on the bed of lining material.

The shell is ported at intervals, and the ports 16 are closed by plastics material which is air-permeable and desirably water-impermeable or hydrophobic.

The said plastics material could for instance be in the form of inserts closely fitting the ports 16, with the outward-facing surfaces flush with the outside of the shell 15. Alternatively, the plastics material could sheath the ported area of the shell 15 so as to form a smooth exterior. Associated with the shell is a duct system 18 for connecting the ports 16 to a suction pump, not shown.

Plastics materials having the characteristics just noted are commercially available. Examples include "Filtroplast" (RTM) obtainable from Schumacher Filters Limited and "Vyon" (RTM) obtainable from Porvair Limited. These plastics are high-density sintered polyolefins, e.g. polythene, or PVC-vinyl acetate plastics which are readily welded and machined.

Metals and ceramics of air-permeable form are known and may be used instead of the aforementioned plastics to occlude the ports of the shell 15.

The ported shell 15 is centred within the heating element 12 using temporary spacers, and then more lining material is introduced, into the gap between the shell 15 and the heating element 12. The material has to be consolidated and this is accomplished either manually, by ramming ortamping tools, or preferably by vibrating the shell 15. Vibrators, e.g.

employing motor-driven, out of balance weights, are readily available and their coupling to the shell can be secured by any convenient means. Preferably, at the same time as consolidating the material, suction is applied to the ports 16. This draws air away from the filling of lining material adjacent the shell through the aforementioned plastics material and enables the lining material to form a void- or pocket-free contact with the shell 15.

Filling of the space between the shell 15 and heating element 12 can proceed in stages, if desired, until complete filling to adjacent the top of the shell is accomplished. With this procedure, suction may be applied to just those pots 16 covered by lining material. Reduction of the capacity of the suction system may then be possible.

Suction and vibration can be applied simultaneously or separately, e.g. alternately during filling the said space, depending on whichever routine is found to yield the best results.

When the consolidated lining 13 reaches the desired level, the ducting system 18 is removed, as well as the shell. Alternatively the shell might be left in situ in the furnace 10, when it will be subsequently melted down when the furnace is first switched on, and the lining is thereby fired.

A modified shell arrangement is shown in Figure 2, and has the advantage that it avoids the cumbersome ducting arrangement schematically shown in Figure 1. The shell 15' is a cylindrical drum closed at both its ends, its top end having an outlet 19 for connection to the suction pump. Again, the shell 15 is ported and furnished with the aforementioned plastics material, and the lining procedure is as described above.

For furnaces for melting metals other than steel, it may be preferred to make the shell 15, 15' from some other, compatible metal.

For relining small furnaces, e.g. research furnaces, it may be possible to dispense with the metal shell and use a shell fabricated from the aforementioned permeable e.g. plastics material.

Note that the shell 15' could be fabricated with an expanded metal mesh or a perforated metal sheet forming at least its side wall, the said permeable material then forming a sheath thereabout.

The lining material can be any material used conventionally for the purpose such as a resin bonded dry refractory mix which is cured at a suitable temperature. Alternatively, the material could be a hydraulically-bonded or chemically bonded refractory concrete. The latter type of con crete may be bonded with phosphate or lignosul phonate binding agents, inter alia, and cured by heating typically to 150 - 300"C.

Substantially the same equipment and procedure may be employed for lining vessels such as ladles or tundishes. Since leaving the shell in place may be undesirable then, it may be drawn out of the lining when the latter has reached a self-supporting state, e.g. where the lining is concrete. To assist removal of the shell, it can be given a preliminary release coating.

On occasions when a furnace or other vessel lining is repairable, substantially the same procedure and equipment is used. Before introducing the lining material (which will form a new facing on the existing lining) the lining is cleaned and if necessary chiselled to provide a key for the facing. Cleaning will generally involve removal of slag and frozen metallic deposits.

Sometimes it may be advantageous to use an expansible shell. The shell may be in two interfittig halves which are thrust apart, e.g.a by hydraulic rams, to assist in the consolidation. Expansible shells may be particularly preferred when lining vessels having inwardly tapering shapes. One use of such a shell is now described with reference to Figures 3 and 4.

The apparatus shown in these figures is employed here for re-lining or repairing the runner 20 or trough along which pig iron or slag is tapped from a blast furnace F. The preliminary step of the method involves cleaning the damaged lining 21 by removing frozen slag or metal deposits, their outlines being indicated at 23. Then, a trough or U-shaped former 26 whose exterior shape conforms to the required configuration of the refractory lined runner is lowered into and supported centrally in the runner recess.

The former is a metal structure in which opposite sides 26a thereof are hinged to the base 26b thereof.

At least the sides 26a have spaced apart ports 26c occluded by the aforementioned permeable material e.g. as described above.

Having positioned the former 26, the gap 27 between it and the existing sound lining 21 is filled with the desired lining material 28. Filling, and topping up, is performed with the aid of suction and vibration of the former by vibration means 25. The suction helps to obtain a substantially void-free packing of the lining material around the former 26, the suction being applied simultaneously with or separately from the vibration as described herein be fore. Packing the lining material 28 in place may be assisted by forcing apart the sides 26b of the former 26, using rams 32.

The former 26 can be as long or longer than the runner 20, but normally it will be shorter, e.g. of the order of 2 to 3 metres in length. Relining will then proceed in stages, the former being moved along after each section of lining material has been deposited. In proceeding in this manner, it will usually be appropriate to seal the ends of the former 26 to the lining by timer shuttering 33 or other means to hand.

Relining runners is the subject of B.P.A. No.

7905349, publication No. 2,025,012A to which reference is directed for details.

After forming the lining 28 it is heated for instance by a gas burner, generally after removal of the former. (If the former 26 is left in place, the aforementioned plastics material will need replacing before the former is reused; use of a metallic or ceramic material, instead, should eliminate the need for replacement). For lining materials based on mixtures of refractory materials selected from alumina, mullite, agalmatolite chamotte, graphite, metallic silicon, ferrosilicon and silicon nitride, and containing 1 - 5% by weight of a powdered thermosetting binder resin, heating to about 300do is appropriate.

Higher temperatures may be necessary, depending on the thickness of the lining 28. Time at temperature may vary from 20 to 60 minutes.

According to B.P.A. 7905349, the consolidating vibration is performed for 3 to 10 minutes and should be such that the former vibrates with an amplitude of 0.1 to 2 mm, and at a frequency of 30 cps or higher.

Also, according to the aforesaid application, the water content of the lining mix, should preferably be below 1% by weight. In principle other materials could be used, such as the concretes noted hereinbefore. Thanks to the nature of the preferred plastics materials, water will not be extracted by suction from the areas adjacent the ports 26c, so the application of suction during consolidation is not expected to perturb the concrete in any deleterious way.

Expansion of the former 26 is not essential to consolidation and a more simply constructed rigid former may be utilised.

Former construction could be along the lines suggested above in the description of Figures 1 and 2.

It will be appreciated that the method just described can be followed when it is necessary to replace a runner lining entirely, and is not restricted therefore to just repairing or resurfacing of runners.

Claims (14)

1. A method of lining a vessel which is to contain molten metal with refractory material, wherein a shell or former the exterior of which conforms to the required inside wall of the lining is placed in the vessel, a refractory lining formulation is placed in the vessel around the shell, and the lining formulation is consolidated by vibrating the shell and by sucking air from the interface between the lining formulation and the shell, and wherein for the purpose of extracting the said air the shell being of perforate form and having an air-permeable material occluding the openings thereof.

2. A method of lining a metal melting furnace runner with refractory material, wherein a troughshaped shell or former the exterior of which conforms to the required runner profile is lowered into the runner, a refractory lining formulation is admitted to the space within the runner around the former, and the latter is vibrated to consolidate the lining formulation, and wherein consolidation is assisted by sucking air from the interface between the lining formulation and the former, for which purpose the former is of perforate form and has an air-permeable material occluding the openings thereof.

3. A method according to claim 1 or claim 2, wherein the lining formulation comprises a blend of refractory particles and powdered thermosetting resin, and contains less than 1% by weight water.

4. A method according to claim 1 or claim 2, wherein the lining formulation comprises a refractory concrete mix which includes a chemical binder activatable by heat for curing.

5. A method according to claim 3 or claim 4, wherein the formulation after consolidation is heated for curing the former being optionally removed before the heating step.

6. A method according to claim 1 or claim 2, wherein the lining formulation is a hydraulically bonded concrete which, after consolidation is allowed to cure at room temperature, the former being optionally removed after consolidation.

7. A method according to any of claims 1 to 6, wherein the shell openings are occluded by airpermeable plastics material.

8. A method according to claim 7, wherein the plastics material occluding the openings in the shell is water-impermeable or hydrophobic.

9. A method according to any of claims 1 to 8, wherein the former is an expansible construction, and the method includes the step of expanding it to compress the lining formulation in the course of the consolidation step.

10. A method according to any of claims 1 to 9, wherein the former is a hollow, closed body having a perforated or ported wall occluded by a sheath of the said plastics material, the former being evacuated during the consolidation step.

11. A method according to any of claims 1 to 10 for resurfacing an existing lining, and including the preliminary steps of cleaning frozen deposits from the existing lining, removing any loose sections, and keying the surface.

12. A method according to claim 1 or claim 2 and substantially as herein described by way of example with reference to the accompanying drawings.

13. Avessel lined by the method claimed in claim 1 or any claim dependent thereon, which is any of a furnace, ladle ortundish.

14. A furnace runner for slag or molten metal lined by the method claimed in claim 2 or any claim dependent thereon.