US3321171A - Heat insulation boards - Google Patents

Description

May 23, 1967 g GORKA ET AL 3,321,171

HEAT INSULATION BOARDS Filed April 26, 1965 Fl 9. n

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INVENTORS Norbert W. Kcleto BY Edward R.Gorko fianf7 ATTORNEY United States Patent 3,321,171 HEAT INSULATION BOARDS Edward R. Gorlra and Norbert W. Kaleta, Tonawanda, N.Y., assignors to National Gypsum Company, Buffalo, N.Y., a corporation of Delaware Filed Apr. 26, 1965, Ser. No. 450,778 8 Claims. (Cl. 249201) This invention relates to a heat insulating material. More particularly, it relates to a high temperature heat insulating board adapted to be placed in or on casting molds used in the casting of steel and other metals to control the solidification of the molten mass therein.

In forming steel or other metal ingots, molten metal is poured into a cast iron ingot mold, allowed to solidify therein, and thereafter removed as a hot, solidified ingot which is then processed by rolling, stamping, forging, or the like. However, as the molten metal cools in the mold, it tends to shrink, causing cavities or pipes to form in the upper portion of the solidifying ingot, making it necessary to cut or crop that portion of the ingot containing the pipe, thereby resulting in low metal yield. In order to minimize the formation of pipes in the ingot, it is customary practice in the industry to line the upper portion of the ingot mold with exothermic side boards. Thus, side boards consisting of or containing an exothermic material are disposed at the top portion of the mold so that when the boards are contacted by the rising molten metal of the ingot, the exothermic material ignites and supplies extra heat to the top portion of the metal to thereby minimize the formation of pipes upon solidification. Such exothermic side boards have a number of disadvantages, however, which adversely affect their use in commercial operations. Thus, the exothermic boards are relatively expensive to use, so that the cost of the exothermic materials may outweight the advantages of increased ingot yield. Also, such boards are often quite difficult and expensive to fabricate, thereby further increasing their cost. For example, the exothermic boards are generally formed by introducing the components into a mold and compressing the components into a unitary body. Alternatively, the components may be formed into a slurry and cast to shape in suitable molds. In both of these methods, however, the boards are produced on an individual basis, that is, each operation produces but a single board. As a result, the cost of such boards is relatively expensive. In addition, since the exothermic boards are placed against the inner Wall of the cast iron ingot mold, much of the heat evolved from the exothermic material is Wasted, for it is dissipated to the mold itself instead of being utilized to delay the solidification of the ingot head material. Therefore, there is a need for a material which is free from the above disadvantages, but which is capable of preventing or minimizing the formation of pipes or other detrimental cavities in the metal ingots.

An object of the present invention is to provide a high temperature heat insulating material.

Another object of the present invention is to provide a rigid, incombustible heat insulating body having low thermal conductivity at high temperatures.

Another object is to provide a preformed heat insulating body adapted to be placed in or on ingot molds to control the solidification of molten metal therein, thereby preventing or minimizing the formation of pipes or other detrimental cavities in the metal ingots.

Another object is to provide an ingot liner board which is relatively simple and inexpensive to produce, but which is highly effective in use.

A further object is to provide a rigid, incombustible, heat-insulating material for use in lining molten metalcontacting portions of ingot molds and/or hot-tops.

3,321,171 Patented May 23, 1967 A still further object of this invention to to provide a preformed heat insulation board for metal ingot molds which is relatively inexpensive, both as to the cost of the components of the board and as to the cost of its mantlfacture, the board providing good heat insulation for the molten metal within the ingot mold.

Various other objects and advantages will appear from the following description of the invention, and the novel features will be particularly pointed out hereinafter in the appended claims.

In the drawings:

FIGURE 1 is a top perspective view of the top portion of an ingot mold having the novel heat-insulating boards of this invention lining the upper portion of the mold cavity.

FIGURE 2 is a sectional view of an ingot mold having the novel heat-insulating boards of this invention lining the upper portion of the mold cavity.

FIGURE 3 is a sectional view of the upper portion of an ingot mold provided with a hot-top, the metal receiving cavity of the hot-top being lined with the novel heatinsulating boards of the present invention.

FIGURE 4 is a sectional view of another embodiment of the invention in which an ingot mold is provided with a hot-top formed of the heat-insu1ating boards of the present invention.

According to the present invention, there are provided preformed, rigid, incombustible, heat-insulating boards of basic mineral wool composition, especially well adapted to be placed in or on ingot molds to control the solidification of the molten metal therein. The composition of these heat-insulating boards consists essentially of from about 30% to about 45 by weight of mineral wool, from about 40% to about 55% by weight of finely divided silica flour, from about 1% to about 4% by weight of cellulose fibers, from about 3% to about 6% by weight of a starch binder, and from about 3% to about 6% by weight of finely divided clay.

Boards or sheets of this composition are especially well suited for use in lining the upper open end of an ingot mold. When used in this manner, the boards provide a heat-insulating layer around that portion of the mold to control the rate of solidification of the molten mass. Thus, since the boards have low thermal conductivity at high temperatures, the heat of the melt is not dissipated through the walls of the mold but is retained in the molten metal. Accordingly, the boards, due to their high temperature heat-insulating property, reduce the amount of heat radiated from the melt in that portion of the ingot mold. In this manner, there is provided a reservoir of molten metal in the upper portion of the mold which feeds the pipe or shrinkage cavity as it tends to form in the solidifying ingot. In other words, the melt in the upper portion of the lined mold does not solidify as rapidly as the molten metal in the lower portion of the mold, but remains in a fiowable molten condition to supply molten metal to the pipe or shrinkage cavity forming in the solidifying mass. Consequently, the formation of pipes in the metal ingot is prevented or at least: minimized. In addition, heat-insulating boards of the above composition are incombustible, making them especially well suited for use at the temperatures encountered in the production of steel ingots. The boards have good strength so they are not susceptible to breakage in handling and they do not change shape or otherwise deteriorate in storage.

Furthermore, the heat-insulating boards of the present invention are relatively inexpensive to use for they are inexpensive both as to the materials employed and the cost of manufacture. Thus, boards of the composition set forth above, due to the types and amounts of materials used, can be made in large sheets or mats in a continuous commercial operation on a conventional Fourdrinier paper-making machine, and the large sheets or mats cut into boards of any desired shape and size. Therefore, it is not necessary to press or cast the boards individually, as with the boards used heretofore, for the heat-insulating boards of the present invention may be made in large quantities in a continuous commercial operation. Generally, in the production of these boards on a Fourdrinier, the individual components are formed into slurries, the slurries transferred to one or more stock chests and pumped to a machine chest from where the stock is flowed onto a moving wire of the machine to form a wet fibrous mat. Water is subsequently removed from the mat to form a self-supporting sheet which is then pressed, cut into predetermined lengths, and dried to form rigid sheets. The rigid sheets are then trimmed to form heat-insulating boards of a desired shape and size.

The boards thus formed usually have a thickness of from about /2 inch to 1 inch or more. Generally, boards A5 to /4 inch in thickness are preferred for lining the upper portion of the mold cavity of ingot molds. For some applications, a number of the boards may be laminated together to form thick bodies or blocks of heatinsulating material. The boards have a density of from about 25 to 40 pounds per cubic foot, with densities in the range of 30 to 35 pounds per cubic foot being preferred. The boards have a modulus of rupture of at least about 350 p.s.i.

Referring now more particularly to the drawings, indicates an ingot mold, which may be of cast iron or other suitable material, the mold having side walls 11 and end walls 12 forming a mold cavity 13. Incombustible heat-insulating boards 14 of the composition set forth hereinabove line the side and end walls of the upper portion of the mold, the boards being disposed against the walls and held in place by any suitable means (not shown) such as clips, hangers, and the like. Generally, it is preferred to line both the side and end walls of the upper open end of the ingot mold, the boards extending into the mold cavity a distance of from about 6 inches to about 24 inches from the top of the mold. If desired, only the side surfaces or the end surfaces may be lined with the heat-insulating boards of this invention.

As shown in FIGURE 2, when the ingot mold 10 is filled with molten metal, such as steel, the ingot liner boards 14, due to their heat-insulating property, reduce the amount of heat radiated from the molten steel in the upper portion of the mold so that a reservoir of molten steel 15 is provided in the upper portion of the mold, this reservoir supplying molten steel to the pipe or shrinkage cavity as it tends to form in the solidifying ingot 16 in the mold.

While the invention has been described heretofore as providing heat-insulating boards for use in lining the upper portion of ingot molds, it is to be understood that the heat-insulating boards are capable of being used for other heat-insulating applications. Another embodiment of the invention is shown in FIGURE 3. In this embodiment, the heat-insulating boards are used to line the cavity of a conventional refractory hot-top 17 which has been fitted over the upper open end of an ingot mold 10, the boards 14 being secured to the hot-top by any suitable means (not shown). In this manner, when molten steel is poured into the mold and the hot-top through central opening 18, the heat-insulating liner boards enable the hot-top to perform its function efiiciently and economically. Thus, hot-tops lined with the boards of the present invention are thermally efficient, for the molten metal therein does not solidify as quickly as the molten metal in the ingot mold and remains in a fiowable molten condition to feed the pipe forming in the solidifying ingot.

In the embodiment shown in FIGURE 4, a hot-top 20 is positioned on ingot mold 10. Hot-top 20 is formed of an outer supporting wall 21 positioned on the periphery of the top of ingot mold 10, and a plurality of laminated heat-insulating boards 14a, 14b, 14c and 14a secured to wall 21 and enclosing the mold cavity. Wall 21 is preferably formed of -a suitable metal and may be secured to the laminated boards by bolts (not shown) or other suitable means. Hot-tops formed in this manner are inexpensive both as to cost of ingredients and cost of production and provide good heat insulation for the molten metal.

The heat-insulating boards of the present invention may be prepared on a conventional Fourdrinier machine in the manner described hereinbelow. It is to be understood, however, that the following description'is illustrative of a preferred embodiment of the invention but is not intended to limit the invention to the materials, proportions, or conditions set forth therein.

A slurry of mineral wool fibers is prepared and transferred to a first stock chest at a solids concentration of about 5%. Preferably, the mineral wool is of a size such that essentially all of the fibers pass through a screen having 1 /2 inch openings. The feed rate from this stock chest is controlled so that the dry fibrous mat contains from about 38% to 42% by weight of mineral wool fibers. A slurry of finely divided clay, at a solids concentration of about 58%, is then introduced into this stock chest, the feed rate being controlled so that the dry mat contains from about 3.5% to 4.5% by Weight of clay. The clay serves mainly to control the shrinkage and to increase the strength of the board at high temperatures. Generally, it is preferred to use kaolin clay when the heat-insulating boards are formed on a Fourdrinier, for kaolin facilitates formation of the fibrous mat. Other types of clay, such as ball clay, bentonite and the like, may, of course, be used, particularly when the boards are formed by methods other than on a Fourdrinier. A slurry of finely divided silica flour, at a solids concentration of about 8%, is also introduced into this stock chest, the feed rate being controlled so that the dry mat contains from about 48% to 52% by weight of silica. The inclusion of the finely divided silica in the composition provides a number of advantages in the formation and performance of the heat-insulating boards. For example, the use of the finely divided silica provides faster drainage of the fibrous sheet on the Fourdrinier than clay of the same concentration, making it possible to produce the sheets at higher machine speeds and consequently at lower costs. Also, the finely divided silica contains no chemically combined water that would cause bubbling or boiling when the boards come in contact with the molten steel. Furthermore, the silica flour serves to keep the boards from shrinking and/or deteriorating at high temperatures. The silica should have a particle size such that about 99% will pass through a ZOO-mesh screen.

Into a second stock chest is introduced a slurry of finely divided, uncooked starch and a slurry of cellulose fibers. The feed rate of the starch, introduced at a concentration of about one pound of starch per gallon of water, is regulated so that the dry fibrous mat contains from about 4.5 to about 5.5% by weight of the starch. The starch, in the form of a dry milled flour, is preferably obtained from either corn or tapioca, although other suitable starches may be used. The cellulose fibers are introduced into the second stock chest at a concentration of about 3% solids and the feed rate regulated so that the dry mat contains from about 1.5% to 2.5% by weight of cellulose fibers. The cellulose fibers may be obtained from wood pulp, news pulp, kraft pulp, or the like. The cellulose fibers give wet strength to the fibrous mat.

In addition, a small amount, that is, less than about 0.5% each, of a preservative and a fiocculating agent may also be added to the stock chests. Copper pentachlorophenate has been found to be a suitable preservative.

Any conventional flocculating agent may be used. Sufficient fiocculating agent should be added to maintain an almost clear white water below the Fourdrinier wire. Usually, an amount of from 0.05% to 0.1% by weight, based on the total furnish solids, is sufficient.

The slurries from the two stock chests are then delivered from the fan pump to the machine chest from where the stock is flowed onto a moving wire to form a wet fibrous mat. The wet mat is passed over a series of suction boxes to remove some of the water and the mat then pressed to compact the mat and remove additional water and render the mat self-supporting. At this point, the mat has a solids content of about 40%.

The partially dried mat is then cut into desired lengths and transferred to a multi-zone dryer. The temperature and humidity of the first zone of the dryer must be controlled so that the temperature of the fibrous sheets is rapidly increased above about 160 F. without driving oif any appreciable amount of water. It has been found that this control of temperature and humidity is necessary in order to adequately cook the starch binder, for the starch will not swell sufficiently if too much water is removed from the fibrous mat at this point. After retaining the mat in this first zone of the dryer for about an hour, the mat is then passed through several additional drying zones in which the temperature is so regulated that the core temperature of the sheet is maintained below about 280 F. Drying temperatures which result in a higher core temperature are to be avoided, for such higher temperatures will cause dextrinization of the starch binder, which tends to degrade the product. The sheets are maintained in the dryer for a period of time sufiicient to eliminate any visual wet line in the core of the sheets, the water content of the sheets being below about 3%.

At the end of the drying cycle, the sheets, which are now rigid, are removed from the dryer and cut into boards of any desired shape and size. The resulting product is a rigid, incombustible, heat-insulating board.

As noted above, the silica should have a particle size such that essentially all of the silica will pass through a ZOO-mesh screen. This control of the silica fineness is essential, for it has been found that the finely divided silica contributes to the high temperature integrity of the product. Thus, boards formed of a coarser silica, such as 120-mesh silica, have been found to be less resistant to high temperatures than the boards of the present invention and tend to degrade relatively rapidly when exposed to temperatures encountered in the pouring of molten steel.

According to another embodiment of the invention, a facing layer of an exothermic material may, if desired, be applied to and integrated with the exposed surface of the heat-insulating board. Any conventional exothermic material may be used, such as, for example, coal, charcoal, coke, sources of silicon such as ferrosilicon, sources of aluminum, or any other materials which, in the presence of air or oxygen, will oxidize or burn with the liberation of heat. In order to form such composite boards, the exothermic material is mixed with a suitable heat-destructible binder and applied to the surface of the rigid heat-insulating board which is to be in contact with the molten metal. The coated boards are then dried, such as by heating at a temperature below the ignition temperature of the exothermic material, in order to provide an exothermic facing layer integrally bonded to the heat-insulating board.

While the boards have been described hereinabove as being formed on a Fourdrinier, it is to be understood that they may also be formed in other ways. For example, the heat insulating boards may also be formed by casting a slurry of mineral wool fibers, cellulose fibers, silica flour, starch and clay in a mold of a suitable shape and size. Such alternative methods of production are generally not preferred, for the costs of production are higher than when the boards are formed on a Fourdrinier.

The heat-insulating boards of the present invention may, if desired, be provided with one or more corrugated surfaces. Thus, the fibrous mat may be provided with corrugations before it has been dried, or the dried rigid boards may be corrugated in any conventional manner.

It will also be understood that the term mineral wool is used herein in a generic sense and includes materials manufactured from rock, slag, glass, and the like.

The percentages set forth in the specification and claims, unless otherwise indicated, are expressed in percentages by weight, based on the total dry weight of the heat-insulating board. Where screen or mesh sizes are given herein, they are based on U.S. Standard Sieve Series.

While the invention has been described in connection with specific embodiments thereof, it will be understood that it is capable of further modifications, and this application is intended to cover any variations, uses, or adaptations of this invention. It will therefore be recognized that the invention is not to be considered as limited to the precise embodiments shown and described, but is to be interpreted as broadly as permitted by the appended claims.

We claim:

1. A heat-insulating composition comprising from about 30% to about 45% by weight of mineral wool, from about 40% to about 55% by weight of finely divided silica, from about 1% to about 4% by weight of cellulose fibers, from about 3% to about 6% by weight of starch, and from about 3% to about 6% by weight of finely divided clay.

2. The composition as defined in claim 1 in which the silica has a particle size such that about 99% will pass through a ZOO-mesh screen.

3. The composition as defined in claim 1 in which the clay is kaolin clay.

4. A rigid, incombustible, heat-insulating board comprising from 30% to 45% by weight of mineral Wool, from 40% to 55 by weight of finely divided silica, from 1% to 4% by weight of cellulose fibers, from 3% to 6% by weight of starch, and from 3% to 6% by weight of finely divided kaolin clay.

5. The heat-insulating board as defined in claim 4 in which the silica has a particle size such that about 99% will pass through a ZOO-mesh screen.

6. The heat-insulating board as defined in claim 4 in which a layer of exothermic material is integrally bonded to one surface of the board.

7. A heat-insulating ingot liner board for lining the upper open end of an ingot mold, said board consisting essentially of from 38% to 42% by weight of mineral wool, from 48% to 52% by weight of finely divided silica flour, from 1.5% to 2.5% byweight of wood fibers, from 4.5% to 5.5% by weight of a starch binder and from 3.5% to 4.5% by weight of finely divided kaolin clay.

8. A hot-top for an ingot casting mold comprising an outer metal supporting wall and a plurality of laminated heat-insulating boards secured to the inner surface of said supporting wall, said heat-insulating boards consisting essentially of from 30% to 45% by weight of mineral wool, from 40% to 55% by weight of finely divided silica flour, from 1% to 4% by weight of cellulose fibers, from 3% to 6% by weight of a starch binder, and from 3% to 6% by weight of finely divided clay.

No references cited.

J. SPENCER OVERHOLSER, Primary Examiner. V. K. RISING, Assistant Examiner.

Claims (1)

1. A HEAT-INSULATING COMPOSITION COMPRISING FROM ABOUT 30% TO ABOUT 45% BY WEIGHT OF MINERAL WOOL, FROM ABOUT 40% TO ABOUT 55% BY WEIGHT OF FINELY DIVIDED SILICA, FROM ABOUT 1% TO ABOUT 4% BY WEIGHT OF CELLULOSE FIBERS, FROM ABOUT 3% TO ABOUT 6% BY WEIGHT OF STARCH, AND FROM ABOUT 3% TO ABOUT 6% BY WEIGHT OF FINELY DIVIDED CLAY.

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