US3737489A

US3737489A - Method of applying refractory lining on hot metallurgical ladles,soaking pits and furnaces

Info

Publication number: US3737489A
Application number: US00077059A
Authority: US
Inventors: C Murton
Original assignee: Air Repair Inc
Current assignee: Air Repair Inc
Priority date: 1970-10-01
Filing date: 1970-10-01
Publication date: 1973-06-05
Anticipated expiration: 1990-06-05
Also published as: DE2148325A1; GB1364538A

Abstract

ABOUT 4% OF AN ORGANIC BINDER, FROM ABOUT 40% TO 70% OF CLAY, AND FROM ABOUT 28% TO ABOUT 58% QUARTZITE. TO FACILITATE ITS APPLICATION, THE REFRACTORY MIXTURE IS MIXED WITH ABOUT 4% TO 6% WATER.

A METHOD FOR RELINING METALLURGICAL LADLES, SOAKING PITS, AND FURANCES AT TEMPERATURES FROM ABOUT 400* TO ABOUT 3000*F. BY POPELLING A MIXTURE OF REFRACTORY MATERIALS AGAINST A PRIOR-EXISTING LINING WITHOUT PRIOR COOLING THEREOF, THE RELINING THICKNESS BEING FROM ABOUT 1/4 INCH UP TO 10 INCHES OR MORE. THE REFRACTORY MIXTURE CONSISTS ESSENTIALLY OF, BY WEIGHT, FROM ABOUT 1/14% TO

Description

June 5, 1973 c. B. MURTON 3,737,489 METHOD OF APPLYING REFRACTORY LIN ING ON HOT METALLURGICAL LADLES, SOAKING PITS AND FURNACES Filed Oct. 1, 1970 FIG.

INVE/V TOR. CRAWFORD B. MU]? T'O/V Attorney United States Patent 01 ice 3,737,489 Patented June 5, 1973 METHOD OF APPLYING REFRACTORY LINING ON HOT METALLURGICAL LADLES, SOAKING PITS AND FURNACES Crawford B. Murton, Pittsburgh, Pa., assignor to Air Repair, Inc., Pittsburgh, Pa. Filed Oct. 1, 197 0, Ser. No. 77,059 Int. Cl. C04b 35/14, 35/66; F27d 1/16 US. Cl. 264--30 9 Claims ABSTRACT OF THE DISCLOSURE A method for relining metallurgical ladles, soaking pits, and furnaces at temperatures from about 400 to about 3000 F. by propelling a mixture of refractory materials against a prior-existing lining without prior cooling thereof, the relining thickness being from about inch up to 10 inches or more. The refractory mixture consists essentially of, by weight, from about to about 4% of an organic binder, from about 40% to 70% of clay, and from about 28% to about 58% quartzite. To facilitate its application, the refractory mixture is mixed with about 4% to 6% water.

BACKGROUND OF THE INVENTION Field of the invention This invention relates to a system for relining metallurgical ladles, furnaces, soaking pits, and the like at elevatedtemperatures. The invention also pertains to a refractory composition for use as a liner at temperatures of from 400 to about 3000 F.

Description of the prior art In the past refractory lining for hot metal furnaces and ladles have been constructed of refractory brick laid up with mortar. With repeated use the lining eroded away until a thin remaining lining was replaced with a new lining or refractory brick laid up with mortar. Moreover, during the period of normal service life, certain areas of severe wear required patching by removing the affected areas and relaying new brick.

The successful use of the so-called pneumatic gun in the construction industry for the placement of concrete was soon followed by attempts to use the gun for the application of refractory walls and linings of metallurgical furnaces and ladles. Although those attempts proved successful for the application of refractory linings to cold ladles and furnaces, most attempts to apply refractory linings to hot furnaces, such as at about 200 F. or more, have been unsuccessful. In metallurgical ladles, especially iron and steel ladles, attempts to reline them hot have been totally unsuccessful.

As a result the advantages of quickly applying a reliner by the use of a pneumatic gun in a relatively short time to hot ladles and furnaces have been defeated by the inability to make the lining without waiting for the walls to cool to at least below about 350 F. Accordingly, a furnace or ladle has been out of operation for long periods of time while cooling down to the necessary temperature for the replacement or repair of the lining.

Associated with the foregoing has been the problem of the application of conventional compositions for replacement linings. They simply have not been applicable by centrifugal means to hot walls of metallurgical furnaces and ladles. One difficulty with conventional com positions has been the necessity of mixing large amounts of water with the convenitonal materials for the primary purpose of cooling the interface between the old lining and the newly applied material to a temperature below which steam forms. As a matter of fact, conventional materials usually rely upon mechanical structures such as cracks or crevices in the old wall to support the reliner material. When applied to a smooth vertical wall,

the adherence with the reliner is uncertain and usually subject to premature failure.

When conventional compositions of refractory linings are applied to cold surfaces, the lining must contain enough initial moisture to provide for coalescence of the composition as it travels from the impeller or gun to the wall and to provide for bonding of the components form ing the lining after their placement. In general, the range of the water content of conventional mixes is from about 10% to 20% by weight. As a result it has been necessary to carefully dry the newly applied liner before the furnace or ladle can be returned to service.

For example, it has been found that when a liner in a steel ladle having a thickness of from 4 to 6 inches is applied cold, a period of from 6 to 15 hours is necessary to reduce the moisture content to an acceptable level to create sufiicient bond strength to meet the loading requirements of the ferrostatic head. Similarly, in soaking pits and preheat furnaces, the heating times required are of the order of from 24 to 72 hours. Without those drying and heating programs the performance of the applied lining was uncertain.

Most of the commercially available refractory ma terials applied by pneumatic guns or impellers for relining purposes have contained high alumina cement or other bonding agents that provide room temperature structural strength. Most refractories placed as linings on furnace ladles and soaking pits as applied by so-called gunning or other techniques have been applied at low temperatures compared to the metallurgical furnace operating temperatures. Attempts to apply conventional refractory materials by pneumatic guns or centrifugal impellers at elevated temperatures have resulted in excessive rebound loss such as from 20% to of the total material applied. As a result large quantities of refractory material are lost until the surface on which the material is applied is sufficiently cool to prevent steam formation and thus to permit a build-up to begin.

The major use of mechanical or pneumatic means for the application of refractory linings has been for structures that have been precooled to room temperature in order to avoid the loss of most of the material applied and to avoid shrinkage defects.

Moreover, it has been found that when molten steel at temperatures of from 2800 to 3000 F. is poured into a ladle after the drying, a section through the wall indicates the development of three distinct zones; namely, an inner fusion zone with highly viscous glass-like characteristics, an intermediate zone of sintered, solid phase reaction compounds that provide the strength of durability for the refractory liner, and an outer cold zone that does not reach a temperature high enough to initiate sintering. The cold zone has a strength gradient extending to the cold face of the furnace or ladle having a minimum value at some distance from the sintered zone. Since most metallurgical furnaces and ladles are subject to cyclical temperature changes of an extreme range, the creation of the three zones through the wall generates problems involving their different properties of thermal expansion, thermal conduction and strength.

In summary, the cold refractory placement methods involve a number of difiiculties including extended periods of time for dying the applied refractory, lack of practical means for determining when all of the moisture has been removed from the refractory mass, shrinkage conducive to cracking of the applied refractory mass, and the formation of three distinct zones upon heating having different properties throughout the refractory mass which upon cyclical temperature changes causes premature failure.

Because of the three zone structure developed with conventionally compounded refractory compositions, it has been necessary to apply excess thicknesses of repair lining to provide a sintered zone sufiiciently strong to meet the structural requirement encountered during useage. For example, an extremely thin layer applied to a surface would represent the minimal strength characteristics of that material during drying and would be too fragile to serve as a reline surface. Thicker layers would be required to allow normal attrition to take place and still have suificient thickness left to permit formation of the fused, sintered, and dried zones.

A further problem with conventional methods of pneumatic or mechanical gunning is the determination of how thick a relining has been applied. Those conversant with pneumatically placed refractory materials know that variation in thickness to magnitude is the rule rather than the exception because the application is made normally and controlled visually. An exception to the preceding statement is the technique used in slingering ladles where a centerally located form is used to form an annular space between the ladle shell and the form.

However, a general statement can be made regarding all conventional systems, e.g., brick linings, cold pneumatically gunned linings, or mechanically slingered ladle repair or construction techniques. All rely upon the total consumption of the refractory lining and subsequent tearing out of the lining when it has eroded so thin that it is unsafe. In other words, the initial lining thickness must be so great that the capacity of the ladle is curtailed as compared to the optimum thickness of lining compatible with safety standards, heat balance, and maximization of ladle capacity. The curtailment in overall capacity can result in lost production ranging from 8% to 17%. This loss results from using a ladle until the lining has worn dangerously thin, tearing out the old lining, relining, and then drying for an extended period of time usually fifteen hours. Capacity has been sacrified to give a few extra charges. It is better to determine the optimim wall thickness and then repair the ladle cyclically and perpetually maintaining maximum charge weight and minimum down time for the ladle.

SUMMARY OE THE INVENTION In accordance with this invention it has been found that the foregoing difficulties may be overcome by a method for applying a refractory mixture which method comprises the steps of lowering a centrifugal impeller vertically into a furnace or ladle to be relined, which furnace or ladle has a temperature of from about 400 to 2800 F rotating the impeller as it is moved vertically, either upwardly or downwardly, while feeding the refractory mixture through the rotating ends of the impeller to cause the refractory mixture to be deposited as a lining upon the walls of the furnace or ladle to a thickness that is dependent upon the rate of feed of the composition and upon the vertical movement of the impeller, whereby maximum adherence is obtained through melting of the organic binder present in the refractory mixture and moisture removal is indicated by a change of color of the lining.

The invention also includes a mixture of refractory compositions for lining having a thickness of from about /2 inch to 10 inches or more and which lining may be uniformly and consistently applied as a repair or replacement lining on an existing metallurgical furnace or ladle at temperature of from about 400 to about 2800 F., and which mixture having a particle size of about 8 mesh is composed of, by weight, from about to about 4% organic binders, from about 40% to 70% of clay, and from about 28% to 58% quartzite.

DESCRIPTION OF THE DRAWINGS For a better understanding of the nature of this invention reference is made to the drawings in which:

FIG. 1 is a vertical sectional view through a metallurgical ladle showing one type of centrifugal impeller disposed therein, and

FIG. 2 is an enlarged, fragmentary, sectional view through the ladle and repaired lining in condition ready for use.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The process of the present invention comprises the steps of 1) setting up a ladle to be relined in an upright position;

(2) introducing a centrifugal impeller vertically and substantially axially into a ladle;

(3) rotating the impeller at a sufficient speed to apply a mixture of refractory material upon the inner surface of the ladle at a rate depending upon the desired thickness and rate of vertical movement of the impeller; and

(4) holding the ladle for a period of time sufficient to expel any included moisture and to allow the organic binder in the mixture to melt and carbonize.

After a heat of liquid metal is poured from a ladle, the ladle is normally inverted to pour out any remaining slag. Thereafter, the stopper rod and nozzle are removed and replaced. The ladle is then ready for reuse, after allowing sufficient time for a reset nozzle to dry out. When the ladle has been used a suflicient number of times, such as 15 to 20 heats, the lining is normally worn thin enough to require replacement. After 70% of the normal lining life has been used, the process of the present invention is employed to apply a replacement lining on the inner surface of the ladle.

As shown in FIG. 1 a ladle 10 is placed upright. The ladle 10 includes a bottom wall 12 and a circular side wall 14 which walls are normally composed of metal plates fabricated to the desired shape. The used ladle 10 also includes a remaining refractory lining 16 which is snugly disposed against the inner surface of the wall 14. The bottom wall 12 also includes a lining 18.

The process of the present invention begins with the lowering of a centrifugal impeller, generally indicated at 20, into the open upper end of the ladle 10. The upper end of the impeller 20 usually includes a ring 22 for attachment onto the book of an overhead crane. In addition, the impeller 20 includes rotating means such as a motor 24, with a rotatable shaft 26 having at least two similar branch portions 28 extending preferably in opposite directions of each other. The shaft 26 is a conduit through which the mixture of refractory material descends from an inlet conduit 30.

As the impeller shaft 26 is rotated the mixture of refractory material enters the arms 28 and is expelled at the outer ends onto the inner surface of the remaining lining 16. A new lining 32 is thereby formed and has a thickness that is dependent upon the speed of rotation of the impeller shaft 26 and the speed of vertical movement of the impeller 20. Although the lining 32 may be applied by moving the impeller 20 vertically in either direction (up or down), the lining is preferably applied by lowering the impeller until the arms 28 are disposed near the bottom wall 12. With the shaft 26 substantially coaxially disposed with regard to the vertical wall 13, the shaft is then rotated, as indicated by the arrow 34, and the impeller is lifted as indicated by the arrow 36, at a speed calculated to apply the lining 32 to the desired thickness. The thickness of the lining 32 may vary from about 4 inch up to 6 inches. Greater thicknesses such as up to 10 inches may also be applied where necessary.

The temperature of the ladle 10 including the remaining lining 16, the lining 18 as well as the

outer walls

12 and 14 may vary from as low as 400 F. up to about 3000 F. during application of the lining 32.

The refractory mixture as initially applied for forming the lining 32 contains three basic constituents including organic binders, clay and quartzite. The organic binders may include such materials, as pitch, tar, resins, polyvinylchlorides and polyethyltetrachloride. Such binders-havem'elting points of from about 250 to 400 F. The particle size of the binders is preferably less than A inch. The organic binders are present in an amount varying from about 1.5% to 4%, by weight, of the total mixture. The purpose of the organic binders is to replace most of the Water present in prior existing mixtures which were applied to cold surfaces after a ladle had been cooled to, say 100 F. By elirninating all or substantially all, of the water content of the mixture, the explosions, resulting from steam created when molten steel contacts the newly applied refractory, -'are avoided. The organic binders, however, are provided jin an amount less than 4%. of the total mixture which m'elts upon impingement on the hot surface of the ladle and therefore forms a tacky surface for holding subsequently applied materials impinging in the same area. The heat causes binders to carbonize and leaves a mozaic structure]v of crystalline carbon intermixed with the other constituents of the lining which when applied in particle form provide a mechanical structure which is bonded between the old lining 16 and the new lining 32.

Clay is present in an amount varying from 40% to 70%, by weight, of the total mixture. The preferred clay materials'are' alumina and silica compounds. The clay compounds have wet strength as initially applied and the clay compacts itself in place to hold the entire mixture until all of the organic binders melt and carbonize to form the mozaic of crystalline carbon which provides the basic strength of the new lining 32.

Quartzite is present in an amount varying from 28% to 58%, by; weight, of the entire composition. Typical quartzite compounds include 98% of silica (SiO with about 0.5% of alumina (A1 0 The quartzite acts as a filler.

Water may be added to the mixture of the organic binder, clay, and quartzite either by pre-mixing or during passage of the mixture through the impeller. The amount of water may vary from about 4% to 6%, by weight, of the total mixture. It is noted that clay compounds ordinarily contain about 4% water in various forms, such as water of hydration, and crystallization, which when supplemer ted by the addition of from 4% to 6% of water, totals approximately 10% water for the entire mixture. Higher amounts of water often cause steam explosions.

As the mixture leaves the impeller and travels across the ladle, the latent heat of the ladle causes much of the water to evaporate before it impinges upon the ladle wall. Sufficient water is retained, however, to cause the clay to function as bonding agent until the lining composition is completely formed.

When the mixture of refractory composition first strikes the hot surface of the ladle lining 16, the heat in the lining immediately causes the organic binders to melt and form a sticky or tacky basis for subsequent particles which adhere in place on the tacky binders. However, after a buildup of the lining 32, the initial lining serves as a heat insulator. At that time the wet clay, having the property of plasticity, serves as the primary bonding agent for a buildup of particles of the mixture which thereafter accumulate to the desired thickness as the impeller proceeds vertically.

Ultimately, however, the latent heat in the ladle lining 16 overcomes the insulating effect of the initial organic binder layer and causes more and more of the subsequently applied organic binder particle to melt. At the same time the water is evaporated and driven out of the new lining 32. As the effect of the heat continues to work on the lining 32, the water is evaporated and the organic binders continue to melt outwardly. Meanwhile, the first applied portions of organic binders carbonize and form a moziac structure of crystalline carbon intermixed with the alumina and silica particles in the quartzite and clay. The resulting structure includes a continuous phase of mozaic carbon and the clay containing the spaced particles of silica of the quartzite which is the discontinuous phase.

During the formation of the ultimate structure of the lining 32, the lining undergoes a color change which indicates to an observer when the final structure of the lining 32 is completely formed. When the refractory composition is initially applied, it has a light gray appearance. When all of the water is evaporated, the appearance changes to a dark gray color which signals water has been evaporated. Subsequently, when the organic binders carbonize, the color of the lining again changes to a light beige appearance which is indicative of the complete formation of the lining 32. Those color changes occur very rapidly, on the order of about 10 to 15 minutes, depending upon the thickness and temperature of the ladle when the lining is applied.

The final structure of a typical lining 32 is shown in FIG. 2. The lining 32, being disposed on the prior-existing lining 16, is typically applied to a thickness varying from about inch to about 1 /2 inches. Greater thickness of up to 10 inches, however, may be applied where desirable.

By the proper selection of the components to be com bined the refractory composition is prepared and adhered to hot surfaces immediately without relying upon the mass cooling effect of water and material as was the case with conventional refractory materials. The range of recommended compositions is extensive and embraces basic, acid, and neutral refractory materials which combine the bonding effect of clay together with that of the organic binders; namely, hydrocarbon-sodium silicate, hydrocarbon-phosphate, hydrocarbon-chromic acid, hydrocarbon-clay, hydrocarbon-silica, hydrocarbon-alumina, and lime. A synthesis of all of those bonds is fundamental to the adherence of the refractory composition as it is applied.

Although the thickness of the lining applied may vary from A inch to 10 inches or more, it has been found that the usual thickness to be applied is from about inch to 1 /2 inches per application. A lining having a thickness varying from about A inch to 1 /2 inches is useful for at least 2 heats before relining is required. An iron ladle operating normally between 2300 and 2600 F. may receive smaller quantities and lesser thicknesses of lining than steel ladles operating at from 2750 to 2900 F. Moreover, steel operations producing predominantly low carbon rimmed grades show normal ladle lining erosion of about inch per heat. Therefore, a lining thickness of /2 inch per application using the process of this invention give a minimum of 2 heats service before another application of the lining is required. Initial results indicate that 3 or 4 heats from a /2 inch thick lining are possible.

For a comparison of the time required to replace a lining by the process of this invention with the processes well known in the art including (1) conventional brick and mortar linings, (2) cold ladle gunning, and (3) cold slingered ladle "lining, reference is made. to Table I as follows:

TABLE I.--TIME FOR REPLACING LADLE LININGS 12.5 minutes 1 hour, 27 minutes-.. 1 hour, 15 minutes. 4.6-5.75 hours.

It is deemed readily apparent that the process of this invention provides a replacement lining for a ladle in a period of time (12.5 minutes per heat) which greatly reduces the time that a ladle is out of service as compared with the times required for relining under prior conventional methods. The conventional brick and mortar type of lining requires the use of preburned ladle brick and mortar laid by hand to form a lining inside the ladle. Cold gunning involves shooting a ladle interior with pneumatic equipment to a thickness of approximately 1% inch. The latter must be repeated every 4 or 5 heats for efficient operation. The cold slingering process of lining ladles involves installation of a refractory handling plant and shop space for installation of slingering machinery. The capital investment is high and the process is costly especially if all brick layers have been removed and the system breaks down. i

Heretofore, this invention has been described as a process for applying replacement lining to steel ladles. It is understood, however, that the process may also be used for applying similar linings to the walls of various types of metallurgical vessels, such as soaking pits and furnaces. Because of the differences in temperature of operation of ladles, soaking pits, and furnaces variations in the mixture of the refractory material are involved.

The mixture contains different amounts of components for diiferent applications. The organic binder content has an operative range from about 4% to about 4%, with good results being from 1 to 2.5%, and with the optimum content being about 2%, by weight. The control of refractory properties depends on the desired A1 0 content of the mixture, as follows:

Mixture: A1 0 percent Steel ladle 8-10 Soaking pit and reheat furnace 1012 Iron ladle and cope 12-14 Thus, when the desired A1 0 content is provided by a clay containing 20% A1 0 the mixtures are made proportionately.

Typical examples of the ranges and preferred compositions of the organic binder, clay and quartzite involved are set forth in Table II as follows:

TABLE II.-COMPOSITION RANGE [Weight percent] Total A1203 of Organic mixture binder Clay Quartzite Steel ladle ....1 8-10 2 40-50 (47) 48-58 (51) Soaking pit 10-12 2 60-60 (55) 38-48 (43) Iron ladle and coping 12-14 2 60-70 (65) 28-38 (33) NoTE.--Parenthetical figures are preferred percentages.

The use of mixtures of refractory compositions where organic binders replace the dominant portion of water as used in prior conventional refractory compositions satisfies the prior-existing problems of replacing the lining of a furnace, ladle, or soaking pit in a minimum of time so that the equipment is back in service as soon as possible.

The composition and process of the present invention provides positive adherence of the refractory material applied to hot surfaces and provides a color change indication of when the water content is substantially completely dissipated. Thus, the hot metallurgical equipment is not cooled unduly and it, therefore, does not require subsequent lengthly heating periods to return it to operating temperatures. Moreover, the problems associated with the conventional three zone lining structure are eliminated by the proper application procedures of this invention.

What is claimed is:

1. A method for applying. a lining to a metallurgical vessel comprising the steps of holding a vessel-at a temperature of from about 400 to about 2800 F., propelling a mixture of a refractory composition consisting essentially of, by weight, from about A to about 4% of particles of an organic binder having a melting point of from about 250 F. to about 400 F., from about 40% to about of clay particles, from about 28% to about 58% of quartzite particles, and from about 4% to 6% water to form a lining having a thickness of from about /1 inch to about 10 inches on the inner surface of the vessel, allowing the lining to form a solid mass having a mosaic structure of crystalline carbon intermixed with clay and quartzite, and said lining displaying color changes from initial light gray to intermediate dark gray as the water evaporates and to a final beige appearance as the organic binder carburizes.

2. The method of claim 1 wherein the step of applying the mixture is performed by a centrifugal impeller moved vertically and substantially axially of the vessel.

3. The method of claim 1 wherein the organic binder is a compound selected from a group consisting of pitch, tar, rosin, polyvinylchloride, polyethyltetrachloride, and mixtures thereof.

4. The method of claim 1 wherein the mixture consists essentially of from about 1% to about 2.5% organic binder, from about 40% to about 50% clay, and from about 48% to about 58% quartzite.

5. The method of claim 1 wherein the mixture consists essentially of about 2% organic binder, about 47% clay, and about 51% quartzite.

6. The method of claim 1 wherein the mixture consists essentially of from about 1% to about 2.5% Organic binder, from about 50% to about 60% clay, and from about 38% to about 48% quartzite.

7. The method of claim 1 wherein the mixture consists essentially of about 2% organic binder, about 55% clay, and about 43% quartzite. I

8. The method of claim 1 wherein the mixture consists essentially of from about 1% to about 2.5 organic binder, from about 60% to about 70% clay, and from about 28% to about 38% quartzite.

9. The method of claim 1 wherein the mixture consists essentially of about 2% organic binder, about 65% clay, and about 33% quartzite.

References Cited UNITED STATES PATENTS Rice 106-68 DONALD J. ARNOLD, Primary Examiner I. H. MILLER, Assistant Examiner US. Cl. X.R. 106-68, 69; 264-63; 266-43