US3749148A - Hot topping method - Google Patents

Abstract

A hot top method of the type in which reusable hot top casings are relined after each ingot casting. The relining is effected by advancing a plurality of casings in seriatim to fixed lining stations, at which an annular cavity is formed adjacent the inner surface of each casing, and then a slurry is fed into the cavity and the liquid carrier is withdrawn from the slurry to form a liner of solid materials on the inner surface of the casing. The slurry is formed by pulverizing a fibrous material and then mixing the pulverized fibrous material with a major proportion of a finely divided refractory material at a pre-mixing station located remotely from the fixed lining station. The dry pre-mix is then transported to the lining stations and mixed with a liquid carrier to form the desired slurry.

Description

United States Patent 1 Jago et a1. July 31, 1973 [54] TOWING METHOD FOREIGN PATENTS OR APPLICATIONS 1 1 lnvemorsl Edward John Jag", Berea, Ohio; 967,398 8/1964 Great Britain 164/33 Fred Eastwood, late of Bay Village, Ohio y f Primary Examiner-J. Spencer Overholser Donald Todlsh, Medma Ohm Assistant Examiner.lohn E. Roethel [73] Assignee: Foseco International Limited, Hubbard Leydlg, and 05mm Birmingham, England [22] Filed: Oct. 1, 1969 5 ABSTRACT [21 Appl. No.: 863,760 A hot top method of the type in which reusable hot top casings are relined after each ingot casting. The relining is effected by advancing a plurality of casings in se- [g%] {15.8]. riatim to fixed lining Stations at which an annular nil. r "1.6.4,.- 3' is fomled adjacent the inner surface of each casing, 1 0 can 01 and then a slurry is fed into the cavity and the liquid carrier is withdrawn from the slurry to form a liner of 56 R f solid materials on the inner surface of the casing. The I 1 e erences slurry is formed by pulverizing a fibrous material and UNITED STATES PATENTS then mixing the pulverized fibrous material with a 2,81 1,457 10/ 1957 Speil et a1. 106/69 major proportion of a finely divided refractory material 3,253,936 5/1966 Weindel 106/69 X at a pl'e-mixing station located remotely from the fixed lining station. The dry pre-mix is then transported to or a eta 3,373,047 3/1968 Sheets et al 249 197 x ggg g i ggz z gg mm a earner to 3,384,149 5/1968 Eastwood 164/33 2,811,457 10/1957 Speil et a1. 106/69 13 Claims, 3 Drawing Figures Patented July 31, 1973 3,749,148

2 Sheets-Sheet 1 g3 H\\\\ Q 35 53 INVENTOR S FRED EASTWOOD EDWARD JOHN JAGO WALTER DONALD TODISH Patented July 31, 1973 3,749,148

2 Sheets-Sheet 2 F NVENTORS .2 FRED EASTWOOD EDWARD JOHN JAGO WALTER DONALD TODISH Arrvs.

HOT TOPPHNG METHOD CROSS-REFERENCE TO RELATED APPLICATION U.S. application Ser. No. 740,036, filed June 26, 1968, for Composition For Use in Forming Heat Insulating Liners and Method for Making Same."

The present invention relates generally to the art of heat topping and, more particularly, to an improved hot topping method of the type which involves repetitive in situ lining of reusable hot top casings.

In the casting of metal ingots, it is common practice to use a hot top mounted on or at the top of an ingot mould for the purpose of containing feed or head metal and maintaining it molten while the metal in the ingot mould is solidifying. The metal in the hot top is above and in contact with the metal in the ingot mould so that as the metal in the ingot mould shrinks, the feed metal feeds down into the ingot body and thus prevents the formation of shrinkage cavities in the body of the ingot.

The latest type of hot top in commercial use comprises a single metal casting, preferably in the form of a one-piece casting, and a heat insulating liner on the inner surface of the casing. The casing itself is reusable, but the insulating liner must be replaced after each use, i.e., after the casting of each ingot. The liner is generally made of a relatively low cost composition having good heat insulating properties, the composition being preformed in self-supporting slabs or sleeves shaped to fit the particular casing in which they are to be used. After each use of the hot top, the remnants of the used liner, which usually disintegrates to some extent during the casting operation, are then removed from the metal casing and replace-d by a new preformed liner.

Typically, the relining operation includes setting preformed liners in the shape of individual slabs in the casing and driving four slabs down along the four inside walls of the casing with the slabs being wedged against each other in the corners so as to urge the slabs against the casing walls.

Because this method, while a vast improvement over prior methods, is still a time-consuming operation, considerable effort has been directed towards developing a method which can form an insulating liner in situ with a configuration which renders the liner self-retaining against the hot top casing. One such method which is now in commercial use is described in U.S. Pat. No. 3,384,149, issued May 21, 1968, entitled Method For Forming Hot Top Liners, and assigned to the assignee of this invention.

In accordance with that method, a slurry of a refractory material, a fibrous material and a liquid carrier such as water is fed into an annular cavity formed between the inner surface of the hot top casing and the outer surface of a perforated forming tool. The liquid carrier is withdrawn through the interior of the forming tool so as to build up a layer of the fibrous and refractory materials in the cavity. The forming tool is then withdrawn from the casing in such a manner that the layer of fibrous and refractory materials forms a liner on the inner surface of the casing.

The slurry used in forming the liner generally comprises about 80 to 90 percent by weight of the liquid carrier. As disclosed in Davidson Re. U.S. Pat. No. 25,915, the organic fibrous material that is used may be mechanical pulp or pulp manufactured from Waste paper, and refractory material in a finely divided state can be added to the pulp slurry to provide the desired consistency. The pulp facilitates the binding of the refractory material and also provides the liner with a porosity which substantially increases its insulation qualities.

Unfortunately, the users of hot tops almost uniformly do not have facilities for carrying out mechanical pulping. Also, it would generally be impractical to install all the facilities needed to form a slurry that could be employed in the method for forming a liner in situ as described in the hereinbefore identified patent. It is accordingly necessary to transport or ship to the hot top user a sufficient amount of the liner composition for carrying out the several hundred or even thousands of relining operations that may well take place in one day. Shipping a slurry composition containing about percent by weight of a liquid carrier such as water is obviously expensive and does not offer a practical solution to the problem of providing an economical source of the lining composition.

It is, therefore, a primary object of the present invention to provide an improved hot topping method which permits both the preparation of the lining material and the lining operation to be carried out at the optimum locations, thereby improving the efficiency of the overall system.

It is another object of the invention to provide such a method which does not involve transporting any large volumes of liquid, and which minimizes shipping and storage space requirements.

Other objects and advantages of the invention will become apparent from the following description and upon reference to the accompanying drawings, in which:

FIG. 1 is a perspective view of a hot top with one corner broken away to show the internal structure;

FIG. 2 is an end view, partially in section, of a mechanism for forming the insulating liner in the hot top of FIG. 1; and

FIG. 3 is a side elevation, partially in section of the mechanism of FIG. 2.

One current method of lining reusable hot top casings in situ, i.e., forming the linings in the casings in the mill where the ingots are poured, is described in U.S. Pat. No. 3,384,149, owned by the assignee of the pres ent invention. In that method, a plurality of reusable hot top casings are advanced in seriatim to a fixed lining station where a perforated forming tool is inserted in each casing so as to form an annular cavity between the inner surface of the casing and the outer surface of the forming tool. A pre-mixed slurry, typically containing 80-90 percent water, is then fed into the cavity, and the water is withdrawn through the interior of the perforated forming tool so as to build up a layer of the solid ingredients in the cavity. Finally, the forming tool is withdrawn in such a manner that the layer of solid materials forms a liner on the inner surface of the hot top casing, and the casing is advanced from the lining station to a drying station where the liner is dried sufficiently to permit the use of the lined casing in the casting of another ingot.

Turning now to the drawings, in FIG. 1 there is shown a hot top 10 adapted to be mounted on the top of a bigend-up ingot mold, such as used in the formation of steel ingots for example. The hot top serves to delay the solidification of the feed metal or head metal contained within it so that molten metal can feed downwardly into the main body portion of the metal ingot to compensate ingot. In the particular embodiment illustrated, the hot top includes a one-piece outside metal casing 11, with the lower portion of the outside surface of the casing 11 being complementally formed with respect to the inside walls of an ingot mold so that the lower portion of the hot top can extend down into the upper portion of the mold.

For the purpose of initially mounting the hot top on the lip of a big-end-up mold, an outwardly projecting flange 12 is formed at about the midpoint of the casing so that the hot top can be set on a plurality of wooden blocks spaced around the lip of the mold. The metal casing 11 is also provided with a pair of trunnions 13 located about halfway up the casing for use in inverting the casing, and another pair of trunnions 14 for lifting the hot top.

In order to provide the thermal insulation required to delay solidification of the molten metal in the hot top during the casing of an ingot, the metal casing 11 is lined on the inside with a thin layer 15 having low thermal conductivity. To provide the required thermal insulation, the liner material preferably has a mean heat diffusivity value over the temperature range of 25 to 1500 C. of below about 0.015 centimetergram-second units. The term heat diffusivity is defined as V Kc p wherein X is the thermal conductivity of the material, c is the specific heat, and p is the density. Suitable highly thermally insulating compositions are those described in the Davidson patents Re. US. Pat. Nos. 25,905 and Re. 25,915. The thickness of the liner can vary for different applications, but in general it should be between about 0.5 inch and about 1.5 inches.

If desired, a refractory bottom ring may be secured to the lower end of the metal casing 11 for the purpose of preventing the creepage of molten metal up behind the insulating liner 15 and to protect the lower end of the casing 11. In the illustrative embodiment, however, the bottom ring is obviated by use of an insulating liner which wraps around the lower end the casing, whereby the liner itself serves the purpose of the bottom ring. However, where it is desired to use a bottom ring instead of a wrap around-type liner, a conventional sand ring may be used and held to the casing by means of conventional spring clips. Also, a conventional wiper strip may be fitted over the lower outside corner of the hot top, extending entirely around the hot top with the upper end of the wiper strip bent outwardly to bear against the mold wall to prevent the molten metal from rising in the gap between the hot top and the mold.

In a typical steel mill, ingots are cast in large batches, or heats." Thus, every time the ingots in a given heat are stripped from the molds in which they are cast, an equal number of hot top casings must be relined before they can be reused in the casting of another heat of ingots. Of course, one of the necessary steps in the relining operation is removal of the residue from the previous liner; the liners usually disintegrate during the casting operation, but sometimes there is still a residue of the used liner which clings to the hot top casing and must be removed therefrom, before a new liner can be applied.

The magnitude of the problem posed by the necessity of relining the hot top casings after each use will be readily appreciated when it is recognized that hundreds or even thousands of ingots are cast every day in a modern steel mill. In the lining method illustrated in FIGS.

2 and 3, which is described in more detail in the aforementioned U.S. Pat. No. 3,384,149, a plurality of onepiece hot top casings 11, from which the residue of the previously used liner has already been removed, are transported in seriatim by means of a roller conveyor 20 to a fixed lining station including a casing table indicated generally at 21. The casings 11 are inverted before they arrive at the lining station'so that the wider end of the hot top opening is at the top of the casing as it enters the lining station. The casing table 21 includes a central support plate 22 which is covered with a sealing gasket 23, and both the plate 22 and the gasket 23 are large enough in diameter to overlap the edges of the casing opening. As a casing 11 enters the lining station, it rides over a plurality of rollers 24 which are mounted in vertically movable brackets 25 in a channel formed in the table adjacent the main supporting plate 22. After the casing 11 has reached a center position on the table 21, the rollers 24 are lowered by lowering the brackets 25 so that the casing comes to rest on the sealing gasket 23 on top of the central support plate 22.

After the casing 11 has come to rest on the sealing gasket 23 by lowering of the rollers 24, the entire casing table 21 is raised into telescoped relation with a liner forming tool 26 which is mounted directly above the table 21 in axial alignment therewith. Raising of the table 21 is accomplished by means of a hydraulic piston 27 mounted on the top end of a vertical piston rod 28 which extends downwardly into a cylinder 29 connected to a suitable source of pressurized hydraulic fluid. The forming tool 26 is complementally formed with respect to the interior of the hot top casing 11 so that after the casing 11 and the tool 26 have been moved into telescoped relationship with each other, an annular cavity is formed between the perforated outside walls of the tool 26 and the solid inside walls of the metal casing 11. Since the tool 26 and the casing l l are complementally formed with respect to each other, this annular cavity will be of substantially uniform width around the entire circumference of the tool.

After the casing 11 and the forming tool 26 have been moved into telescoped relationship, a slurry containing finely divided refractory material, fibrous material, and a liquid carrier is fed into the annular cavity by means of a manifold assembly 30 extending around the top of the forming tool 26. The slurry is fed into the manifold assembly through a feed pipe 31 which conducts the slurry into an annular manifold tube 32 having a plurality of inside ports 33 opening into corresponding registering passageways 34 communicating with the annular cavity 35 between the casing 11 and the forming tool 26. In order to prevent any leakage of the slurry down along the outside walls of the casing 11, an air filled sealing gasket 36 is mounted directly below the slurry passageways 34 for engaging the outer sur face of the hot top casing 11 as it is moved into telescoped relationship with the forming tool 26. Air is supplied to the sealing gasket 36 through a pipe 37 connected to a suitable source of pressurized air.

As the slurry enters the cavity 35 from the manifold assembly 30, the slurry flows downwardly into the cavity 35, which is closed at the bottom by means of the sealing gasket 34 bearing against the bottom of the forming tool, with the carrier liquid being extracted through the perforated walls of the hollow forming tool 26 so as to build up a composite layer of the solid fibrous and refractory material on the outer surface of the tool. The liquid extraction through the perforated walls of the tool 26 is effected by a pressure differential which may be achieved by several different means. For example, the slurry supplied from the inlet manifold 30 is ordinarily under a certain feed pressure, and this pressure itself is sufficient in certain cases to force the carrier liquid from the cavity through the perforated walls into the interior of the tool 26. In addition, a vacuum may be drawn on the inside of the tool 26 so as to increase the pressure differential across the perforated walls and thereby enhance the extraction of carrier liquid therethrough.

As the carrier liquid is extracted through the perforated walls of the forming tool 26, the extracted liquid is collected inside the forming tool and discharged by gravity through a discharge port formed by an aperture in the bottom of the forming tool 26 and registering apertures 41 and 42 formed in the sealing gasket 23 and the central support plate 22. The discharged liquid then enters an effluent chamber 43 formed in the bottom of the table 21 and then on out through a waste line 44. While the carrier liquid is being extracted through the perforated walls of the forming tool 26, the solid fibrous and refractory material in the slurry are directed against the outer surface of the forming tool, with the fibrous material quickly building up a random mat which acts as a filter to retain the finely divided refractory material within the liner cavity 35 while permitting the carrier liquid to pass through into the interior of the tool. Consequently, a composite layer of f1- brous and finely divided refractory material builds up around the outer surface of the forming tool 26 until it completely fills the annular cavity 35, thereby forming a green" liner on the inner surface of the hot top casing 11.

After the liner cavity 35 has been filled with the composite layer of fibrous and refractory material, and sufficient carrier liquid has been extracted therefrom to enable the green liner to maintain its integrity on the casing walls, the forming tool and the lined casing are moved relatively away from each other, and the casing is transferred to a drying station to dry the green liner before it is used in the casting of another ingot. In order to break the green liner loose from the outer surface of the forming tool before the tool and the casing are telescoped away from each other, compressed air is admitted into the interior of the forming tool 26 just before the casing table 21 is retracted away from the forming tool 26. This compressed air applies a brief burst of pressure against the inner surface of the green liner, through the perforated walls of the tool, so as to break the green liner away from the forming tool. Alternatively, other suitable means, such as a collapsible forming tool for example, may be used to break the liner away from the forming tool before the tool and the casing are moved relatively away from each other.

In order to transfer the lined casing away from the lining station after the table assembly 21 has been lowered to its fully retracted position, the transport rollers 24 are raised into engagement with the lower end of the hot top casing so as to raise the casing slightly off the sealing gasket 23. The casing is then transferred onto a continuation of the roller conveyor 20 which transports the casing and the green liner therein to a drying station where the green liner is dried sufficiently to permit the casting of molten metal in the lined casing. The drying station may take the form of a conventional drying oven or any other suitable drying means.

To form a self-retaining liner, the illustrative hot top casing 11 is provided with a pair of peripheral recesses or grooves 51 and 52 extending completely around the inner surface thereof. Consequently, when the insulating liner is formed in situ as shown in FIG. 3, the recesses 51 and 52 form a part of the annular cavity 35 and thus the composite layer of refractory and fibrous material which fills the cavity projects into these recesses 51, 52. In other words, the insulating liner is always complementally formed with respect to the inner surface of the hot top casing Ill, and thus any recesses formed in the inner surface of the casing will be occupied by complementally formed projections on the liner which is formed in situ. In the particular configuration illustrated, the two grooves 51, 52 are occupied by complementally formed ribs 53, 54 which serve to prevent axial movement of the liner within the casing. Of course, axial movement of the insulating liner within the casing is not a problem as long as the casing remains in the inverted position shown in FIGS. 2 and 3, but the casing naturally must be inverted at some subsequent point before it is mounted on top of an ingot mold, and it is then that the retaining ribs 53, 54 serve to retain the liner within the inverted casing.

In accordance with the present invention, a relatively dry pre-mix for the slurry used in the in situ formation of hot top liners is formed at a station located remotely from the lining station by pulverizing in a relatively dry environment at least one fibrous material, and then mixing the pulverized fibrous material with a major porportion of a finely divided refractory material in the presence of sufficient liquid to prevent dusting. This dry pre-mix is then transported to the remotely located lining station at the steel mill where it is blended with water or other suitable liquid carrier to form a slurry for use in the in situ hot top lining method. This method provides significant economic advantages in that the solid ingredients of the lining composition may be prepared at a single pre-mixing station for a number of different remotely located steel mills. Thus, the solid ingredients for the lining slurry may be prepared at a single mechanical pulping facility, for example, and then transported to the different steel mills where the water or other carrier liquid is blended with the pre-mixed solid ingredients. Since the water typically comprises about percent by weight of the slurry, it can be seen that significant savings in shipping and storage space and costs, as well as handling costs, are realized. And yet the quality of the hot top liners produced by this technique has surprisingly been found to be equal or even superior to the quality of liners prepared from a slurry in which the fibrous material is pulped in the carrier. In this connection, it should be noted that attempts have been made heretofore to form apulp slurry by reducing the water content below about 50 percent by weight, but it was found that caking and agglomeration of the fibers resulted. Pulp slurries have also been prepared in the usual manner and then dried to remove a substantial portion of the water, but in this case the subsequent addition of water to the dried pulp slurry required that a mechanical dispersing step, similar to the mechanical pulping itself, be carried out.

The pulverizing operation in the present method can be carried out in a conventional hammer mill, ball mill or the like. The fibrous ingredients are thereby reduced to short lengths or flakes that are later amenable by subsequent mixing with a liquid carrier to form a dispersion without the necessity of employing excessive energy such as is required to break up an agglomerated fibrous mixture. By way of illustration, it has been found suitable to equip a hammer mill or ball mill with a screen having openings from about Ma inch to ii: inch. The pulverized material obtained from such mills are not individual elements but are usually present as a conglomeration of several fibers. A size of about 1 to 3 millimeters generally characterizes the pulverized material. While it is desirable to pulverize all fibrous components in accordance with this invention, any fbrous material (such as asbestos) that can be purchased in a pulverized state need not be further processed.

The improved heat insulating composition of this invention comprises by weight, pulverized organic fiber present in an amount from zero percent to about percent, pulverized inorganic fiber present in an amount from zero percent to about 40 percent, refractory aggregate present in the range of from about 50 percent to about 90 percent, and sufficient liquid carrier to prevent dusting. A range of from about one percent to about 20 percent by weight has been found to be suitable for the carrier. Optionally, a binder for the other components may be added in an amount of up to about 20 percent. The particular proportion of inorganic fibrous material and organic fibrous material that are employed may be varied to provide the degree of insulation and formability desired. Indeed, depending on the properties desired, it may be necessary to employ only a single fibrous material, i.e., either organic or inorganic. However, the total of the fibrous ingredients should not be lower than a minimum of five percent by weight and a maximum of about 50 percent by weight to insure good permeability and insulation but retain minimal penetration by the molten metal.

With regard to the specific materials that are used for the components of the present composition, any refractory material previously used for hot top liners may be employed. Suitable examples include alumina, silica, aluminum silicates, magnesium silicate, chromite, zirconia, ball mill dust, zirconium silicate, and magnesium oxide,. Among the inorganic fibrous materials that may be used are asbestos, slag wool, aluminum silicates and silica. For the organic fibrous material, any animal or vegetable fibrous material may be used as can synthetic organic compositions such as rayon and nylon. Suitable examples inclue paper, waste paper or other cellulosic fibrous materials.

The type of binder that is used and the weight percentage that is employed will be in large part dictated by the particular type of forming operation used for the liner. Indeed, in some instances, a sufficient bond is obtained from the entwining of the fibrous material and additional binder need not be included. When drying temperatures between 250 and 450 F. are maintained, suitable binders include urea formaldehyde and phenol formaldehyde resins. When drying temperatures lower or higher than the previous range are used, binders such as colloidal silica, aluminum orthophosphate, sodium silicate and epoxy resins can be employed.

Colloidal silica may be used where a low residual gas content is desired. Aluminum phosphate and colloidal silica can also be employed where molds hotter than 450 F are encountered. Epoxy and other resins capable of setting without heat after addition of a catalyst or accelerator can be employed where molds have temperatures below that necessary to harden other types of binders.

Typically, the liquid carrier that is utilized for the other components of the composition will be water. However, any organic compounds not insoluble with water and having a high evaporation rate at the drying temperature can be employed if production conditions allow. Whenorganic compounds are used, forced air or vacuum drying combined with a condensing system for solvent recovery are economically desirable. Suitable organic compounds include various alcohols, naphthas, chlorinated hydrocarbons and ketones.

After pulverizing the fibrous material and mixing the same with the desired amounts of refractory material, binder and liquid carrier, the resulting mixture may be shipped or otherwise transported to a remote lining location where the liner is to be formed in the hot top casings. At the location of the lining station, liquid carrier (not necessarily the same as the one already present) is added to the shipped composition with slight mixing, to form a slurry that may have, for example, 80 to 95 percent by weight liquid carrier. The slurry can then be used in the method described above and illustrated in FIGS. 2 and 3.

The invention may be further illustrated by means of the following examples which are intended to be illustrative and not in limitation of the scope of the present invention. Unless otherwise indicated, all parts or percentages are by weight.

The properties referred to in the ensuing Examples were determined as follows:

Dispersion time: The time required to obtain a homogeneous slurry.

Forming time: The time required to filter 600 cc. of slurry through a 60 mesh screen at 45 p.s.i., which forms a pad built up on the screen.

Green water: The weight percentage of liquid carrier in the pad described in connection with forming time. Green permeability: A 2 inch diameter specimen is cut from the pad using a rotating blade mounted in a conventional drill press. The specimen is measured and then mounted in a permeability specimen tube described in Section 7, page 13 of the American Foundrymen's Society Foundry Sand Handbook and is tested for permeability by following the procedure set forth on pages 2 through 4 of the same publication. Dry permeability: This is carried out in a manner identical to Green permeability but is determined from a sample that has been dried at 395 F. for 2 hours. Dry density: The weight per unit volume of the sample dried as described in connection with the dry permeability.

The binder used in Examples 3 through 5 was a phenol formaldehyde resin (composition number 2320 from Varcum Chemical Co.). About 13 to 15 percent by weight of hexamethylenetetramine is included. The resin has an inclined flow of 15 to 20 mm. at C. A typical screen analysis is as follows: ml, +200- about one percent, and 200-about 99 percent minimum. The resin is commonly employed as a solid shell core binder in the metal casting industry.

Example 1 A heat insulating composition containing less than at least about 20 percent water was attempted to be formed by pulping and then drying the pulp slurry.

A V4 inch layer, 12 X 3 inches, of a waste newsprint mechanical paper slurry (five percent solids) was placed on a 60 mesh screen and allowed to air dry at a temperature of about 100 C. for 24 hours. After this time, the paper was substantially dry, a hard shell having been formed on the exterior of the dried slurry.

The dried pulped paper was broken'up into pieces and stirred into 3 95 gallons of water. A conventional Lightnin mixer, using a single blade and operating at about 75 R.P.M. was employed. After 8 hours very little paper went back into its fibrous state. 1 inch pieces of paper and layer were still present. After 24 hours, small pieces of paper approximately Vs to 56 inch were still present Example 2 A composition as in Example 1 was attempted to be prepared by partially drying a pulp slurry.

Three pounds of a five percent waste newsprint pulp slurry was weighed out and placed upon a cylindrical shaped screen (6 diam. X 4 inches high) to allow drainage.

Drainage was slow; and, after 24 hours, only 16 ounces from a total of about 45 ounces had been drained. The dimensions of the slurry before drainage was approximately 6 inches diam. X 2 16 inches thick (volume 71 cubic inches). After drainage the thickness was 2 inches (volume 57 cubic inches).

Example 3 A heat insulating composition containing less than about 20 percent water was formed by ball milling in accordance with the present invention. Water was then added to form a slurry that can be used to form a hot top liner. The resulting composition was compared to an identical formulation made by adding the other components to a mechanical pulp slurry.

A sample of waste newsprint was passed through a conventional hammer mill having a 3/16 inch screen opening. The collected shredded or pulverized product was added to the composition set forth in Table 1 by mixing with a Day Ribbon Blender:

TABLE 1 Component Per Cent Silica sand (20+300 mesh) 87.5 Pulverized asbestos fiber 1.5 Waste newsprint 6.5 Binder 4.5

Total 100.0

During the mixing, about 17 percent water to reduce dusting was added to the formulation hereinbefore described.

After being allowed to stand for 24 hours, the mixture was dispersed in sufficient water to provide a solids content of 17 percent. The properties of the composition formed in accordance with this invention was compared to a standard having an identical formulation which was prepared by adding the silica sand, asbestos fiber, binder and additional water to a five percent paper slurry to form a 17 percent solids slurry.

Test pads were made by filtration at 45 psi. through a 60 mesh screen. The results are shown in Table 2:

TABLE 2 Properties Standard Present lnvention Dispersion time required 30 minutes 2 minutes Forming time 23 seconds 23 seconds Green water 34.4 23.l Green permeability 1.2 units 3.0 units Drying time required 2 hours l-l V: hours Dry permeability 4.8 units 3.7 units Dry density 0.88 gms/cc. 0.87 gms/cc.

"20 minutes to pulp paper and I0 minutes thereafter to form the dispersion.

EXAMPLE 4 Example 3 was repeated except that the paper employed consisted of waste cardboard boxes.

The results are shown in Table 3:

TABLE 3 Properties Standard Present invention Dispersion time required 30 minutes 2 invention Forming time 23 seconds 23 seconds Green water 34.4 20.5 Green permeability 1.2 units 2.0 units Drying time required 2 hours l 3'; hours Dry density 0.88 gms/cc. 0.89 gms/cc.

"20 minutes to pulp paper and 10 minutes thereafter to form the dispersion.

Example 5 A heat insulating composition as in Example 3 was formed by using only inorganic fibrous elements. These elements were hammer-milled using a V4 inch mesh screen and the collected product was dispersed into a composition formulated as in Table 4 below by mixing with a Day Ribbon Blender:

TABLE 4 Component Percentage Silica sand (20+300 mesh) 83 Asbestos fiber 6 Slag wool 5 Binder 6 Total TABLE 5 Properties Standard Present Invention Dispersion time required l0 minutes 2 minutes Forming time 23 seconds 23 seconds Green water l9.l l8 Green permeability 2.4 units 3.5 units Drying time required 1 A hours 1 A hours Dry density 0.96 gms/cc. 0.98 gms/cc.

From Examples 1 and 2, it can be seen that the use of a pulp slurry that is dried to reduce the water content' does not provide a practical solution to forming a composition for use in making a heat insulating liner which contains a minimum amount of water for shipping yet which can be readily dispersed to form a slurry. Not only is the time required to reduce the water content prohibitively long but the dried, agglomerated product can only be re-dispersed into its fibrous state after an excessive amount of time, even with extreme mechanical stirring being used.

In contrast, Examples 3 through 5 demonstrate that the pulverized, low liquid carrier composition has properties that are equal to or superior to those achieved by the standard method of forming a slurry composition, i.e., prepared directly by pulping in water. Indeed, the relatively low dispersion time and the low green water content characterize a composition that can be economically used to form a hot top liner.

The term pulverized, as used in connection with the present invention, is meant to define the degree of fibrillization and comminution produced by mechanically working the organic and inorganic fibrous materials by, for example, ball milling or hammer milling. The pulverized product produced by mechanically tearing the fibrous materials will be light and fluffy resembling down feathers or snow flakes yet will still be particulate and capable of screening into definite size fractions by any of the standard screening procedures such as, for example, ASTM. Individual feahers or flakes are capable of passing a 56 inch screen but probably would not pass a ,4; inch screen. In contrast to mechanical pulping using water or another similar carrier, the pulverizing operation should take place in a relatively dry state (i.e., sufficiently dry to avoid caking or balling of the pulverized product, so that the fibers may be later dispersed in a liquid carrier without requiring excessiveenergy. In most applications it has been found that the water or other liquid carrier content should be maintained less than about three percent by weight during the pulverizing".

I claim as my invention:

1. A method of forming heat insulating liners in a plurality of hot top casings used with ingot molds, said method comprising the steps of pulverizing in a relatively dry environment at least one fibrous material, mixing the pulverized fibrous material with a major proportion of a finely divided refractory material in the presence of sufficient liquid to prevent dusting and to form a dry pre-mix for forming a heat insulating composition, transporting the resulting composition to a fixed lining station at a location remote from the site of the pulverizing and mixing steps, adding a liquid carrier to said dry pre-mix at said lining station to form a slurry, advancing a plurality of hot top casings in seriatim to said lining station, forming an annular cavity adjacent the inner surface of the casing, feeding the slurry into the cavity and withdrawing the liquid carrier from the slurry so as to form a liner of the fibrous and refractory materials on the inner surface of the casing, and advancing each casing away from the lining station and drying the liner therein sufficiently to permit the casting of molten metal in the lined casing.

2. A method of forming heat insulating liners as set forth in claim 1 wherein said dry pre-mix comprises, by weight, zero percent to about 20 percent of a pulverized organic fibrous material, zero percent to about 40 percent of a pulverized inorganic fibrous material, about 50 percent to about 90 percent of a particulate refractory material, and a liquid carrier present in an amount sufficient to prevent dusting, with the provisio that the total per cent of the pulverized organic and inorganic fibrous materials is from about five percent to about 50 percent.

3. A method as set forth inclaim 2 wherein said dry pre-mix includes up to about 20 percent by weight of a binder.

4. A method as set forth in claim 2 wherein said refractory material is a member selected from the group consisting of silica, alumina, aluminum silicates, magnesium silicate, chromite, zirconia, ball mill dust, zirconium silicate, magnesium oxide and mixtures thereof.

5. A method as set forth in claim 2 wherein said inorganic fibrous material is a member selected from the group consisting of asbestos, slag wool, aluminum silicates, silica and mixtures thereof.

6. A method as set forth in claim 2 wherein said organic fibrous material is a member selected from the group consisting of animal fibrous materials, vegetable fibrous materials, cellulosic fibrous materials, rayon, nylon and mixtures thereof.

7. A method of forming heat insulating liners in a plurality of hot top casings at each of a plurality of steel mills, said method comprising the steps of pulverizing in a relatively dry environment at least one fibrous material, mixing the pulverized fibrous material with a major proportion of a finely divided refractory material to form a dry pre-mix for forming a heat insulating composition, said pulverizing and mixing steps being carried out at a single mixing station, transporting the resulting pre-mix from said mixing station to a plurality of fixed lining stations at a plurality of steel mills located remotely from said mixing station, adding a liquid carrier to said dry pre-mix at each of said lining stations to form a slurry, advancing a plurality of hot top casings in seriatim to each of said lining stations, forming an annular cavity adjacent the inner surface of each cas ing, feeding the slurrying into the cavity and withdrawing the liquid carrier from the slurry so as to form a liner of the fibrous and refractory materials on the inner surface of the casing, and advancing each casing away from the respective lining station and drying the liner therein sufficiently to permit the casting of molten metal in the lined casing.

8. A method as set forth in claim 1 wherein said pulverized fibrous material is pulverized to a size within the range of from about I millimeter to about 3 millimeters.

9. A method as set forth in claim 1 wherein said pulverized fibrous material is capable of passing a V2 inch screen but not a Vs inch screen.

10. A method as set forth in claim 1 wherein said dry pre-mix contains from about one percent to about 20 percent by weight liquid.

1 l. A method as set forth in claim 1 wherein said dry pre-mix contains from about five percent to about 50 percent by weight pulverized fibrous material.

12. A method as set forth in claim 1 wherein said slurry contains from about percent to about percent by weight liquid carrier.

13. A method of forming heat insulating liners in a plurality of hot top casings used with ingot molds, said method comprising the steps of pulverizing in a relatively dry environment at least one fibrous material to a size within the range of from about 1 millimeter to about 3 millimeters, mixing the pulverized fibrous material with a major proportion of a finely divided refractory material in the presence of from about one percent to about 20 percent by weight liquid to prevent dusting and to form a dry pre-mix containing from about five percent to about 50 percent by weight of said pulvercasing, feeding the slurry into vthe cavity and withdrawing the liquid carrier from the slurry so as to form a liner of the fibrous and refractory materials on the inner surface of the casing, and advancing each casing away from the lining station and drying the liner therein sufficiently to permit the casting of molten metal in the lined casing.

Claims (12)

1. 2. A method of forming heat insulating liners as set forth in claim 1 wherein said dry pre-mix comprises, by weight, zero percent to about 20 percent of a pulverized organic fibrous material, zero percent to about 40 percent of a pulverized inorganic fibrous material, about 50 percent to about 90 percent of a paRticulate refractory material, and a liquid carrier present in an amount sufficient to prevent dusting, with the provisio that the total per cent of the pulverized organic and inorganic fibrous materials is from about five percent to about 50 percent.
2. 3. A method as set forth in claim 2 wherein said dry pre-mix includes up to about 20 percent by weight of a binder.
3. 4. A method as set forth in claim 2 wherein said refractory material is a member selected from the group consisting of silica, alumina, aluminum silicates, magnesium silicate, chromite, zirconia, ball mill dust, zirconium silicate, magnesium oxide and mixtures thereof.
4. 5. A method as set forth in claim 2 wherein said inorganic fibrous material is a member selected from the group consisting of asbestos, slag wool, aluminum silicates, silica and mixtures thereof.
5. 6. A method as set forth in claim 2 wherein said organic fibrous material is a member selected from the group consisting of animal fibrous materials, vegetable fibrous materials, cellulosic fibrous materials, rayon, nylon and mixtures thereof.
6. 7. A method of forming heat insulating liners in a plurality of hot top casings at each of a plurality of steel mills, said method comprising the steps of pulverizing in a relatively dry environment at least one fibrous material, mixing the pulverized fibrous material with a major proportion of a finely divided refractory material to form a dry pre-mix for forming a heat insulating composition, said pulverizing and mixing steps being carried out at a single mixing station, transporting the resulting pre-mix from said mixing station to a plurality of fixed lining stations at a plurality of steel mills located remotely from said mixing station, adding a liquid carrier to said dry pre-mix at each of said lining stations to form a slurry, advancing a plurality of hot top casings in seriatim to each of said lining stations, forming an annular cavity adjacent the inner surface of each casing, feeding the slurrying into the cavity and withdrawing the liquid carrier from the slurry so as to form a liner of the fibrous and refractory materials on the inner surface of the casing, and advancing each casing away from the respective lining station and drying the liner therein sufficiently to permit the casting of molten metal in the lined casing.
7. 8. A method as set forth in claim 1 wherein said pulverized fibrous material is pulverized to a size within the range of from about 1 millimeter to about 3 millimeters.
8. 9. A method as set forth in claim 1 wherein said pulverized fibrous material is capable of passing a 1/2 inch screen but not a 1/8 inch screen.
9. 10. A method as set forth in claim 1 wherein said dry pre-mix contains from about one percent to about 20 percent by weight liquid.
10. 11. A method as set forth in claim 1 wherein said dry pre-mix contains from about five percent to about 50 percent by weight pulverized fibrous material.
11. 12. A method as set forth in claim 1 wherein said slurry contains from about 80 percent to about 95 percent by weight liquid carrier.
12. 13. A method of forming heat insulating liners in a plurality of hot top casings used with ingot molds, said method comprising the steps of pulverizing in a relatively dry environment at least one fibrous material to a size within the range of from about 1 millimeter to about 3 millimeters, mixing the pulverized fibrous material with a major proportion of a finely divided refractory material in the presence of from about one percent to about 20 percent by weight liquid to prevent dusting and to form a dry pre-mix containing from about five percent to about 50 percent by weight of said pulverized fibrous material for forming a heat insulating composition, transporting the resulting composition to a fixed lining station at a location remote from the site of the pulverizing and mixing steps, adding a liquid carrier to said dry pre-mix at said lining station to form a slurry Containing from about 80 percent to about 92 percent by weight of said liquid carrier, advancing a plurality of hot top casings in seriatim to said lining station, forming an annular cavity adjacent the inner surface of the casing, feeding the slurry into the cavity and withdrawing the liquid carrier from the slurry so as to form a liner of the fibrous and refractory materials on the inner surface of the casing, and advancing each casing away from the lining station and drying the liner therein sufficiently to permit the casting of molten metal in the lined casing.

Images