US3006046A - Hot top for ingot mold and method of making the same - Google Patents

Description

Oct. 31, 1961 H. D. SHEPHARD, JR, ET AL 3,006,045

HOT TOP FOR INGOT MOLD AND METHOD OF MAKING THE SAME Filed Aug. 26, 1958 ENTORS. i fi Mgk 3,006,046 HOT TOP FOR INGOT MOLD AND METHOD F MAKlNG THE SAME Harry D. Shephard, .lr., Pittsburgh, and Willis C. Mellott, Connelisviile, Pa, assignors to Hot Tops, Incorporated, Mount Braddock, Pen, a corporation of Pennsylvania Filed Aug. 26, 1958, Ser. No. 757,240 3 Claims. (Cl. 22--193) The present invention relates to the casting of ingots and more particularly to refractory lined hot tops for use on ingot molds.

The casting of metal ingots requires the use of a feeder head or reservoir of molten metal to feed the ingot with metal as it cools and shrinks. Without such a feeder heat, referred to in the foundry as a hot top, shrinkage or contration cavities known as pipe form in the ingot and render the ingot partially or wholly unsatisfactory for use. To maintain such a reservoir of metal molten long enough to feed the cooling ingot, the hot top must be uneconomically oversized or possess excellent heat insulation and/ or a source of heat.

Many hot tops presently in use are formed of a cast metal construction and are lined with heat insulating refractory materials to protect the casing and to reduce heat losses. It is a common practice, for example, to line the cast metal casing with refractory bricks or other forms of refractory materials. For holding the refractory lining in place within the metal casing, the latter is, in most instances, formed with an integral projecting ledge on which the lining rests or is supported. in order to protect the exposed bottom of the casing a preformed sand ring is clipped to the casing and extends beneath both it and the refractory lining.

In many instances it is desirable to employ an exothermically reacting (heat producing) material for supplying additional -heat or insulation or both to the hot top. While such material can be added in granular form on top of the molten metal in the hot top, it has been found that a highly effective heat producing action can be obtained by the use of such heat producing material in the form of liners or sleeves mounted within the hot top. One illustrative heat producing material which is adapted for use in sleeve form is disclosed in US. Patent No. 2,591,105. This material is a composition formed of an oxidizable metal such as aluminum with an oxidizer such as iron or manganese oxide in an amount substantially less than that amount required to react stoichiometrically with, that is, completely oxidize, the aluminum. The composition also contains a fluoride compound to facilitate the start of the reaction (upon contact with molten metal) and to facilitate maintaining the reaction to completion. The patent gives the following composite range and preferred composition for steel castings:

For a more detailed description of such exothermically reacting material reference should be made to Patent No. 2,591,105.

The invention herein is, of course, not to be limited Patented Oct. 31, 1961 to any particular exothermically reacting material. For example, materials having below 30% aluminum are useful in many applications and it may be desirable to use as little as /z% or as much as 10% or more fluoride, although it is generally believed that fluorides in excess of 5% are ineffective in promoting the exothermic reaction.

In application Serial No. 563,465, filed February 6, 1956 by Harry D. Shephard, one of the inventors herein, now abandoned, there are described various hot tops including refractory material and lined with an inner liner of exothermically reacting material. Such hot tops are known to produce excellent results, although they are beset with construction problems in achieving a satisfactory mounting of the inner heat producing liner in the refractory. It has been found to be extremely difficult, for example, to line satisfactorily a cast iron hot top casing with slabs of bricks of refractory material and include a heat producing inner liner. What happens is that molten metal poured into the hot top will find its way into cracks between the casing, the refractory, and the inner liner. When this occurs, the hot top may be broken or at the least the cracks will be enlarged. Furthermore, as the metal solidifies in the cracks, fins will be formed on the ingot which will then hang in the mold. As a result, defects known as hanger cracks are produced in the ingot and it or a substantial part of it must be rejected.

Some attempts have been made to use the sand ring as a support for the heat producing inner liner by making the ring large enough to afford a supporting shoulder. Also, specially shaped refractory lining materials have been employed. None of these has been entirely successful however.

It is the principal object of the present invention to produce and support an auxiliary lining in a cast metal hot top casing by an improved method wherein a refractory and/or insulating supporting liner is formed directly in place in the casing.

Another object of the present invention is to provide an improved method of lining a cast metal hot top casing with an auxiliary heat producing material supported by one or more layers of refractory materials wherein the refractory is applied as a granular material, such as green sand, mixed with a binder which may be hardened in place within the casing so that the auxiliary lining is securely supported in place.

Still another object of the present invention is to provide an improved method for lining hot top casings wherein a refractory lining is formed directly in place as a retaining agent to support an auxiliary lining, such as one made of a heat producing material, as well as to afford the desired insulation and protection to the hot top.

A more specific object of the present invention is to provide an improved method for mounting auxiliary lining materials within a cast metal hot top casing whereby the use of independently formed sand rings is eliminated.

A further object of the present invention is to mount auxiliary lining materials in a hot top casing by the use of granular refractory materials such as green sand mixed with a binder capable of being hardened in place by contact with a gas.

It is still another object of the present invention to support an auxiliary heat producing lining in a hot top by the use of a refractory adhesive material which, when set and hardened in place, not only aifords a temperature resistant and insulating refractory liner in the hot top, but also reduces the chances of breakage of the fragile auxiliary liners. A related object is to fill in any gaps, cracks, or other imperfections in a lined hot top by the use of such a refractory adhesive material and thereby prevent the formation of imperfections and fins on the metal ingot or casting which would cause a hanging ingot.

Other objects and advantages of the invention will become apparent as the following description proceeds, taken in connection with the accompanying drawings wherein: FIGURE 1 is an illustration of the apparatus used in the present invention for providing a refractory liner supporting an auxiliary heat producing lining in a cast metal hot top casing;

FIG. 2 illustrates a lined hot top of the type shown in FIG. 1 but with the patterns removed; and

FIG. 3 shows a hot top having a partially preformed refractory lining and an inner auxiliary lining.

Referring to FIGS. 1 and 2 of the drawings, there is shown a hot top produced by the present invention for use on an ingot mold (not shown). This hot top can be filled with molten metal which will fill the voids in the ingot as the metal shrinks in the ingot mold. To keep the hot top metal molten during the solidification of the ingot, the hot top is designed to insulate against heat loss and to heat the metal in the hot top by an exothermic reaction which takes place when one of its liner materials is ignited by contact with the molten metal. To this end a cast metal hot top casing 16 is lined with an insulating refractory liner 11 and an auxiliary heat producing liner 12 supported by the refractory liner 11.

The hot top casing 10, which is cylindrical and formed of cast iron, is comprised of one or more sections and adapted to be set on top of or inserted within an ingot mold. The interior chamber in the casing is usually in the shape of a truncated cone with the larger diameter corresponding approximately to the mouth of the ingot mold. Molten metal is teemed through the small opening of the hot top into the ingot mold and molten metal is allowed to rise into the hot top where it forms a reservoir to feed the ingot. The casing itself, being of cast iron, is reusable.

In order to reduce heat losses from the hot top and add heat to it so that the reservoir metal remains molten, and also to protect the reusable hot top casing against damage such as would be caused by adherent metal particles, the casing is desirably lined with one or more layers 11 of insulating refractory materials supporting an auxiliary lining 12 of exothermically reacting material.

One auxiliary lining of exothermically reacting material which has been found to be particularly suitable for adding heat to a hot top is of the form and composition described in US. Patent No. 2,591,105. This material, when contacted by the molten metal teemed into the mold, reacts to produce a substantial quantity of heat, and finally to leave a highly refractory and insulating reaction product.

A number of materials have been found useful for forming a hot top liner and for supporting an auxiliary lining of the above character. A few such materials are sand, refractory grog, insulating grog, expanded vermiculite and haydite. Other materials having certain desired insulating and/or refractory properties and which are available in or may be crushed to the correct size may be used. The refractory or insulating material is sized by grinding, if necessary, to produce an aggregate having particle sizes ranging from about 4 mesh to about 100 mesh.

In order to form a lining for a hot top, the sized aggregate is then mixed with a binder capable of being hardened when contacted with an acidic gas. In this manner the lining first can be shaped as desired and then hardened rapidly and without the necessity of heating the hot top to set the binder. One gas hardenable binder contemplated for use in the process of the present invention is an aqueous solution of sodium silicate. This solution, when mixed with the refractory aggregate and contacted with carbon dioxide gas sets to harden the mixture and provide a durable and insulating liner in the hot top.

The process wherein rammed sand articles formed from silicate treated sand, are hardened by contact with an acid reacting gas, such as CO is, of course, well known. The reaction between the sodium silicate binder and CO is believed to form a silica gel and sodium carbonate according to the following chemical equation:

Percent Sodium silicate (1:2::Na O:SiO 74 Granulated sugar 12 Water 14 In accordance with the present invention, the refractory and auxiliary liner supporting liner 11 is formed from the granular refractory material directly in place in the hot top casing. This is accomplished by inverting the hot top casing 10, supporting it on a suitable table 13 and inserting within the casing walls the auxiliary liners, such as a sleeve of exothermically reacting material. The outer dimensions of such a sleeve are, of course, smaller than the inner dimensions of the casing. Accordingly, the outer surface 14 of the auxiliary liner 12 serves to define the inner surface of the liner 11. Inner and outer patterns, 16 and 17, are supported adjacent the then most uppermost end (the actual bottom) of the casing. These patterns 16 and 17 define the inner and outer surfaces of that portion of the lining which covers the bottom of the casing, and thus forms the bottom of the hot top, and which support the auxiliary lining within the hot top. In this manner, a liner supporting ledge or shoulder 18 is formed which supports the auxiliary lining 12 when the hot top is set right side up.

The granular refractory material is mixed with the sodium silicate binder and the mixture is thoroughly stirred so that the refractory particles are coated with the binder. The mixture is then rammed into place in the annular void defined by the auxiliary liner d2, the patterns 16 and 17 and the casing 10. To apply a suitable hardening gas, for example carbon dioxide when a sodium silicate binder is used, to the liner material, a housing 19 having spaced annular walls 20, 21, defining an annular chamber 22., is positioned on the inverted casing it) and patterns 16 and 17. The annular walls 20 and 21 of the housing are provided with suitable seals 23 and 24, respectively, which contact the patterns and prevent the escape of the CO hardening gas. The CO is supplied from a suitable source, generally through a conduit 27 and is forced to flow through the granular refractory and binder (in the direction of the arrows, FIG. 1) and out through suitable vent holes 28 in the base 13. By the term holes as herein used is meant any suitable vent means, and no restriction as to size is intended. For example the holes could be those voids present in a porous sintered metal block which would also serve in part as the table.

When the liner material is sufficiently hard (generally) in a matter of a few minutes) the gas housing 19 and patterns 16 and 17 are removed, leaving a hard protective refractory liner ll securely mounted within the casing 10 and supporting an auxiliary liner 12. The casing and liners can then be inverted and placed on top of an ingot mold in the usual manner. The liner is prevented from dropping out of the casing during handling by a suitable projec tion defining an annular shoulder 30 at the bottom of the casing and, if desired, by the use of one or more pins 31 projecting from the inner surface of the casing and adapted to engage with and support the refractory liner.

If it is desired to produce an exceptionally strong, hard refractory lining, 'air can be first evacuated from the gas housing and refractory particles before the application of the CO gas. This is accomplished by drawing a vacuum to evacuate the air from the interstices of the granular particles. When such a process is used, suitable seals will, of course, be required to prevent the leakage of air around the patterns.

By varying the pressure under which the carbon dioxide is introduced, from atmospheric to about 15 pounds per square inch gauge, it has been possible to reduce measurably the amount of time required for the carbon dioxide treatment. The CO consumed appears not to vary to any substantial extent, irrespective of the introduction pressure. The instant process is applicable to the manufacture of linings in various sizes and it will be apparent that the time element and the amount of CO consumed necessarily must vary relative to the size of the lining. When employing any reasonable amount of pressure, it has been found that for all practical purposes carbon dioxide introduction is complete Within minutes for the largest lining so far manufactured, and a matter of a very few seconds for those very small in size.

Just as the time required for introducing the carbon dioxide will vary with the size of the lining, so, too, must the amounts of carbon dioxide and sodium silicate employed vary in a like manner. In general, the amount of sodium silicate binder employed is equal to about 2.5% to about 6.5% by weight of the refractory material, while the carbon dioxide required to react with such an amount is determinable from stoichiometric relationships depending upon the amount of silicate employed, the particle size of the refractory material and other factors which will be apparent to one skilled in the art. Ordinarily, complete reaction of all the silicate and carbon dioxide is not required in order to produce satisfactory linings by the herein described technique.

Sodium silicate is reactive with carbon dioxide over a wide range of conditions and solutions and it is not intended as a part of the present invention to claim the proportions or conditions applicable to this process. It has been found, however, that the application of the sodium silicate in a water solution containing in the range from about 60% to about 80% by weight of sodium silicate is very effective, and it has also been found that somewhat of an excess of Slo to Na O in such a solu tion is also desirable. For example, a satisfactory ratio of SiO has been found to be about 2 to 1.

The presence of a material such as sugar (sucrose) or dextrin or a combination of the two, appears to result in an over-all better product, as apparently this sugar has the dual effect of increasing the strength of the hardened article as well as increasing the friability to assure the later breakdown of the lining after the molten metal has been poured and cooled. An amount of sugar equal to about the amount of water on a weight basis in the silicate solution appears to be most effective.

Referring now to FIG. 3, there is a modified form of liner which can be produced by the process of the present invention. In describing this modified construction, similar reference characters to those used above will be employed where applicable with the distinguishing suflix a. Instead of forming the complete inner liner from the refractory granular and silicate binder mixture, a hot top casing a is lined with refractory brick or slab material 33 and an inner liner 12a of exothermically reacting material. The refractory brick and exothermic liners are held in place by a partial lining or ring 11a of refractory material formed in place by the method of the present invention substantially as described above. This modification has been found to be particularly useful where a special refractory liner must be used in addition to the heat producing liner.

In order to close the annular space left between the hot top and the mold when the hot top is inserted with the mold, steel wiper strips 35 are provided adjacent the lower end of the hot top. The wiper strips 35 are held in place by the hardened refractory. This is accomplished, as shown in FIG. 1, by placing the wiper strips 35 on the casing 10 before the patterns are located and the refractory and binder mixture is rammed in place. When the refractory is hardened and the patterns removed, the Wiper strips 35 project outwardly from the hot top for engaging the ingot mold wall.

We claim as our invention:

1. The method of lining a cast metal hot top casing with a preformed inner liner, comprising the steps of inverting the casing onto a support having a series of passages therein including entrance and exit portions so that the casing surrounds the entrance portion of said passages supporting the inner liner in position Within the casing, mounting a Wiper ring on the inverted exposed bottom end of the casing, positioning an outer pattern on the ring and an inner pattern on the exposed end of the liner, filling the void between the liner and the casing in the patterns with a granular refractory material containing a gas hardenable sodium silicate binder, impregnating said refractory material and binder with carbon dioxide gas to harden said binder by flowing said gas from the exposed end of said casing through said material and out through said passages thereby to set said refractory for supporting said liner, and removing said patterns.

2. The method of lining a cast metal hot top casing with a preformed inner liner, comprising the steps of inverting the casing onto a support having a series of passages therein including entrance and exit portions. so that the casing surrounds the entrance portion of said passages, supporting the inner liner in position within the casing, mounting a wiper ring on the inverted exposed bottom end of the casing, positioning an outer pattern on the ring and an inner pattern on the exposed end of the liner, filling the void between the liner and the casing in the patterns With a refractory material at least a part of which includes a granular refractory material containing a gas hardenable sodium silicate binder, impregnating said refractory material and binder with carbon dioxide gas to harden said binder by flowing said gas from the exposed end of said casing through said material and out through said passages thereby to set said refractory for supporting said liner, and removing said patterns.

3. The method of lining a cast metal hot topcasing with a preformed inner liner comprising the steps of inverting the casing onto a support having a series of passages therein including entrance and exit portions so that the casing surrounds the entrance portion of said passages, supporting the inner liner in position within the casing, positioning an outer pattern on the inverted exposed bottom end of the casing and an inner pattern on the exposed end of the liner, filling the void between the liner and the casing in the patterns with a granular refractory material containing a gas hardenable sodium silicate binder, impregnating said refractory material and binder with carbon dioxide gas to harden said binder by flowing said gas from the exposed end of said casing through said material and out through said passages thereby to set said refractory for supporting said liner, and removing said patterns.

References Cited in the file of this patent UNITED STATES PATENTS 1,982,490 Williams et al. Nov. 27, 1934 2,591,105 Strauss et al. Apr. 1, 1952 2,757,219 Clough et al July 31, 1956 2,821,000 Noveau Jan. 28, 1958 2,896,266 Anthony July 28, 1959 FOREIGN PATENTS 778,039 Great Britain July 3, 1957 785,984 Great Britain Nov. 6, 1957 OTHER REFERENCES Foundry Trade Journal, Oct. 25, 1956, pages 475-477.

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