US3848655A

US3848655A - Method of making a steel ingot

Info

Publication number: US3848655A
Application number: US00316874A
Authority: US
Inventors: M Kobayashi; Y Sato; S Matsuyama
Original assignee: Aikoh Co Ltd
Current assignee: Aikoh Co Ltd
Priority date: 1971-12-27
Filing date: 1972-12-20
Publication date: 1974-11-19
Anticipated expiration: 1991-11-19
Also published as: FR2166029B1; AU5014772A; JPS4870628A; DE2263679A1; FR2166029A1; AU468176B2; SE7217023L; GB1421147A; BR7209132D0

Abstract

A method of making a steel ingot which comprises pouring molten steel into a steel ingot forming mold having a molded material for maintaining the side portion of the molten steel in a hot condition at the upper portion of the mold, the molded material being disposed either at the upper end of mold as a separate assembly or at the inner surface of the top portion of the mold, covering the top surface of the molten steel, and thus keeping it warm, with a plate-like molded material having a bulk specific gravity of 0.2 to 0.7 and a thickness of at least 10 mm which comprises 30 to 88 percent by weight of a refractory material, 5 to 45 percent by weight of a fibrous substance and 2 to 20 percent by weight of a binder, and casting a steel ingot having a weight of at least 3 tons and a carbon content of not more than 0.7 percent with the amount of the molten steel at the hot upper portion of the mold is at least 10 percent by weight of the steel ingot.

Description

Sato et a1.

[ 1 Nov. 19, 1974 METHOD OF MAKING A STEEL'INGOT Primary Examiner-C. W. Lanham Assistant Examiner-Victor A. Di Palma Attorney, Agent, or FirmFay & Sharpe [57} ABSTRACT A method of making a steel ingotv which comprises pouring molten steel into a steel ingot forming mold having a molded material for maintaining the side portion of the molten steel in a hot condition at the upper portion of the mold, the molded material being disposed either at the upper end of mold as a separate assembly or at the inner surface of the top portion of the mold, covering the top surface of the molten steel, and thus keeping it warm, with a plate-like molded material having a bulk specific gravity of 0.2 to 0.7 and a thickness of at least 10 mm which comprises 30 to 88 percent by weight of a refractory material, 5 to 45 percent by weight of a fibrous substance and 2 to 20 percent by weight of a binder, and casting a steel ingot having a weight of at least 3 tons and a carbon content of not more than 0.7 percent with the amount of the molten steel at the hot upper portion of the mold is at least 10 percent by weight of the steel ingot.

10 Claims, 2 Drawing Figures [75] Inventors: Yasumasa Sato, Imaichi; Shigeru Matsuyama, Utsunomiya; Masaaki Kobayashi, Imaichi, all of Japan [73] Assignee: Aikoh Co., Ltd., Tokyo, Japan [22] Filed: Dec. 20, 1972.

[21] Appl. No.: 316,874

[30] Foreign Application Priority Data Dec. 27, 1971 Japan 46-105469 [52] US. Cl. 164/43, 249/197 [51] Int. Cl. B22c 1/22 [58] Field of Search 164/125, 123, 43; 249/197 [56] References Cited UNITED STATES PATENTS 1,961,529 6/1934 Rowe 249/204 X 2,165,945 7/1939 Seaver.... 164/123 X 2,272,018 2/1942 Nicholas. 249/197 2,362,097 11/1944 Rowe 249/197 X 3,262,165 7/1966 lngham 249/197 X 3,297,296 1/1967 Edstrom et al. 249/197 3,300,322 l/1967 De Geer et a1. 249/197 X 3,612,155 l/1971 Matsuyama 164/123 METHOD OF MAKING A STEEL INGQT Previously, in the casting of steel ingots, there has been widely employed a method which involves pour ing molten steel into a steel ingot making mold including a heat-insulating or exothermic molded material at the upper end of the mold or at the inner surface of the top portion of the mold so as to retain the warmth of the side portion of the molten steel at the hot top of the mold, adding a granular exothermic antipiping compound to the top surface of the molten steel immediately after pouring the steel into the mold to cover the top surface of the steel and to maintain the warmth of the top portion of the molten steel, in combination with the molded material, and thus retarding the solidification of this portion of the molten steel as compared with the main part of the steel ingots whereby the occurrence of shrinkage holes (pipes) in the main part of the molten steel is prevented at the time of solidification, and a sound steel ingot is produced, which in turn results in an improvement of the efficiency of blooming.

However, since the exothermic antipiping agent added to the top surface of molten steel within the mold immediately after the pouring of the molten steel is a granular mixture and contains finely divided powders of a low specific gravity, the fine powders scatter during the addition and during exothermic reaction following addition. As a result of the large quantities of powder dust generated, the ingot making operation is hampered. Furthermore, the dust exerts an adverse effect on plant personnel, and is undesirable from the view point of environmental pollution. The scattering of the fine powder also results in a decrease of the effective ingredients of the antipiping agent. Furthermore, a non-uniform heat retaining layer results from the addition of the antipiping agent, that is, the low specific gravity substance gathers in the upper layer and a high specific gravity substance gathers in the lower layer. Since the granular substance is added according to this method, the top surface ofthe molten steel is not uniformly covered, i.e., the layer of the granular substance added is usually thick at the central part of the top surface of the molten steel and is thinner at the peripheral portions near the wall of the mold. It is therefore necessary to follow granular substance addition with a separate spreading operation to cover the top surface of the molten steel uniformly with the granular substance.

The present invention provides a method of making a steel ingot, which is free from the above-mentioned defects as a result of using a plate-like molded material of specified properties and thickness, as well as of specified composition to maintain the top surface of the molten steel at the hot top of the mold in a hot condition.

Specifically, the present invention provides a method of making a steel ingot which comprises pouring mol' ten steel into a steel ingot making mold including a molded material for maintaining the side portions of the molten steel in a hot condition at a hot top of the mold, said molded material being disposed either at the upper end of said mold or the inner surface of the top portion of said mold, covering the top surface of the molten steel at the hot top, and thus keeping it warm,

with a plate-like molded material having a bulk specific gravity of 0.2 to 0.7 and a thickness of at least 100 mm and consisting of to 88 percent by weight of a refractory material, 5 to percent by weight of a fibrous substance and 2 to 20 percent by weight of a binder, and casting a steel ingot having a weight of at least 3 tons and a carbon content of not more than 0.7 percent with the amount of the molten steel at the hot top being at least 10 percent.

The bulk specific gravity of the plate-like molded material which covers the top surface of the molten steel at the hot top and thus keeps it warm is 0.2 to 0.7 because if it is less than 0.2, pores in the molded material are large and communicate with the outer atmosphere, resulting in a reduced heat-retention effect and a re duced strength of the molded material. On the other hand, if it exceeds 0.7, the molded material has poor heat-retention properties, and cannot be used for ingot making in accordance with this invention. The reason for the thickness of the molded material being at least 10 mm is that with thicknesses below l0 mm, the heatretention effect of the material is poor.

The refractory material, a constituent of the platelike molded material, may be any refractory substance, and examples thereof are chrysolite, quartz, sand, refractory silicates magnesia, alumina, mullite, Alundum, slug, aluminum slug, diatomaceous earth, quartzite, paigeite, obsidian, perlite, magnesite, limestone, dolomite, fly ash, and bauxite. The refractory material is used in a proportion of 30 to 88% by weight of the plate-like molded material because if the proportion is less than 30 percent by weight, the refractory property and strength of the molded material are reduced, and amounts in excess of 88 percent by weight are undesirable because of the necessity of incorporating the fibrous substance and the binder, etc., in order to maintain the strength of the molded material and improve its heat-retention properties.

The fibrous substance contained in the plate-like molded material is a material which reinforces the molded material so as to avoid breakage by due to handling that may occur during the movement of the molded material or its installation in the mold, and which makes the molded material into a porous stance oflow bulk specific gravity and thus improves its heat-retention properties. Examples ofthe fibrous substance that can be used are pulp, sawdust of wood, beaten materials of waste paper, etc., cotton, other cel lulosic fibrous substances, asbestos, slug wool, rock wool, glass wool, steel wool, regenerated cellulose fibers, and other artificial fibers. The proportion of the fibrous substance is 5 to 45 percent by weight of the plate-like molded material. If it is less than 5 percent by weight, the fibrous substance does not reinforce the molded material and reduces its heat-retention properties, while on the other hand, it is not necessary to' use it in an amount exceeding 45 percent by weight to achieve the desired effects. i I

Examples of the binder used in the plate-like molded material are resin binders such as phenolformaldehyde resins, urea-formaldehyde resins, furan resins or epoxy resins, water glass, cement, clay, dextrin, and starch. The reason for the proportion of the binder being limited to 2-20 percent by weight of the plate-like molded material is that if it is less than 2 percent by weight, the binder has a poor effect in bonding the individual components together and the molded material is susceptible to disintegration, making it difficult to handle. On the other hand, it is not necessary to use it in an amount exceeding 20 percent by weight to achieve the desired effects.

In addition to the materials described above, the plate-like molded material for use in the method of making steel ingot according to this invention may also comprise an exothermic substance such as metallic aluminum or aluminum alloys, a carbonized substance such as coke breeze, charcoal powder, carbonized plant stalks or carbonized seed shells, or a carbonaceous substance such as chemically treated expanding graphite.

The amount of molten steel at the hot top is at least 10 percent by weight of the steel ingot. In order to completely prevent the occurrence of shrinkage pipes, it is necessary to maintain the warmth of the molten steel at the top portion of the mold (hot top) which weighs at least 10 percent of the weight of the steel ingot. The present invention is limited to the production of a steel ingot having a weight of at least 3 tons. This is because with a small-sized ingot weighing less than 3 tons, solidification is rapid, and a sound steel ingot cannot be obtained. The carbon content of the steel ingot is limited to not more than 0.7 percent because if it exceeds 0.7 percent, shrinkage pipes tend to occur.

The molded material located on the upper end, or the inside surface of the top portion, of the mold to maintain the side portion of the molten steel at the hot top in a warm condition is a heat-insulating warmth retaining molded article, or a multi-layered molded article comprising an exothermic layer in contact with molten steel and a heat-insulating layer outside this layer, etc.

The method of making a steel ingot in accordance with this invention will be more specifically described below with reference to the accompanying drawings.

FIG. 1 is a vertical sectional view showing a steel ingot being made in accordance with this invention by a top casting method, and

FIG. 2 is a vertical sectional view showing a steel ingot being made in accordance with this invention by the bottom casting method.

FIG. 1 is a vertical sectional view showing steel ingot in accordance with this invention being made by the top casting method. Molten steel is poured by the top casting method into a steel ingot making mold (l) including at its top inside portion a molded material (3) for maintaining the side portion of the molten steel at a hot top (6) in a warm condition. The top surface of the molten steel at the hot top (6) is covered, and thus kept warm, with a molded material (4) having the com position and properties heretofore specified. The state after the completion of pouring is shown in this figure. Dotted line (7) shows the boundary between the hot top (6) and a main part (5) of the steel ingot. Reference numeral (2) designates a moulding board.

FIG. 2 is a vertical sectional view showing a steel ingot in accordance with this invention being made by the bottom casting method. Molten steel is poured from a runner (8) in moulding board (2) by the bottom casting method into the steel ingot making mold (l) including at its top end the molded material (3) for maintaining the side portion of the molten steel at the hot top (6) in a warm condition, and the top surface of the molten steel at the hot top (6) is covered, and thus kept warm, with the molded material (4) of the composition and properties heretofore specified. The state after the completion of pouring is shown in this figure. In the case of ingot making by the bottom casting method, it is preferred that the molded material (4) for covering the top surface of the molten steel be disposed in place before the pouring of the molten steel into the mold (l). Dotted line (7) shows the boundary between the hot top (6) and the main part (5) of the steel ingot.

A example of the method of making steel ingot in accordance with this invention is shown below in compar ison with the conventional method.

A pouring pipe was provided at the center of a moulding board, and six molds for 5 ton steel ingot were arranged redially therearound. A molded material for maintaining the side portion of molten steel at the hot top of the mold in a warm condition was mounted to the top inner side surface of each mold so as to adjust the amount of the molten steel at the hot top to l 1 percent. Molten steel having a carbon content of 0.2 percent was poured into each mold by the bottom cast ing method, and six steel ingots were cast in one casting operation. Of these ingots, three were made in accordance with the method of this invention. Namely, in this casting process, a molded material (thickness 40 mm) having the composition and properties shown below was suspended at the top inner portion of the mold before the pouring of molten steel, and the top surface of molten steel was covered, and thus kept warm, by the plate-like molded material.

The other three ingots were produced by the conventional steel ingot making process. Namely, l5 Kg of a powdery substance for keeping the warmth of the top surface of molten steel previously in general use was added immediately after the completion of the pouring of the molten steel, and the steel ingots were cast while the top surface of the molten steel was covered, and kept warm, with it. According to the conventional method, the warmth-keeping agent (or antipiping compound) could not be uniformly deposited, forming a thick layer at the central portions of the molten metal part and a thinner layer at the peripheral portions of the molten steel near the wall of the mold. It was necessary, therefore, to employ the additional step of render ing the covering layer uniform here. However, this extra operation is not required in the method of this invention, since a molded material is used.

The composition and properties of the molded material for covering the top surface of molten steel to keep it warm, which was used in this example, were as follows:

Siliceous sand 35% by weight Diatomaceous earth 407: by weight Beaten waste paper 20% by weight Phenol-formaldehyde resin 57: by weight Bulk specific gravity 0.4

In the ingot making process by the conventional method, dust of the fine powdery low specific gravity substance in the agent for keeping the warmth of the top surface of molten steel were vigorously scattered about, especially when it the substance was thrown onto the molten metal, and dust also flew away off the surface of the molten steel also during the exothermic reaction after the addition. However, there was no occurrence of dust in the ingot making process according to the method of this invention, and the working environment and environmental sanitation were greatly improved. The yield of the steel ingot in accordance with the method of this invention was somewhat increased over that in accordance with the conventional method.

As described above, the method of steel ingot making in accordance with this invention contributes to improving undesirable working conditions and environmental sanitation conditions encountered with conventional ingot making methods.

What we claim is:

1. A method of making a steel ingot which comprises pouring at least 3 tons of molten steel into a steel ingot forming mold, said mold being provided with an insulating material for maintaining the side portion of the molten steel in a hot condition at the upper portion of the mold, with said molten steel having a carbon content of not more than 0.7 percent, with the amount of molten steel at the hot upper portion of the mold being at least percent by weight of the steel ingot; covering the top surface of the molten steel, and thus keeping it warm, with a plate-like molded material having a bulk specific gravity of 0.2 to 0.7 and a thickness of at least 10 mm which comprises 30 to 88 percent by weight of a refractory material, 5 to 45 percent by weight of a fibrous substance and 2 to 20 percent by weight of ya binder; and casting a steel. ingot in said mold.

2. The method of claim 1 wherein said insulating material is disposed at the upper end of said mold as a separate assembly.

3. The method of claim 1 wherein said insulating material is disposed on the inner surface of the top portion of said mold.

4. The method of claim 1 wherein said refractory material is selected from the group consisting of chrysolite, quartz, sand, silicates, magnesium, alumina, mullite, Alundum, slug, aluminum slug, diatomaceous earth, quartzite, paigeite, obsidian, perlite, magnesite, limestone, dolomite, fly ash, bauxite and mixtures thereof.

5. The method of claim 1 wherein said fibrous substance is selected from the group materials consisting of pulp, wood sawdust, waste paper, cotton, cellulosic fibers, asbestos, slug wood, rock wool, glass wool, steel wool, regenerated cellulose fibers, artificial fibers and mixtures thereof.

6. The method of claim 1 wherein said binder is a ma terial selected from the group consisting of phenolformaldehyde resins, urea-formaldehyde resins, furan resins, epoxy resins, water glass, cement, clay, dextrin, starch and mixtures thereof.

7. The method of claim 1 wherein said plate-like molded material also contains an exothermic substance.

8. The method of claim 7 wherein said exothermic substance is selected from the group consisting of aluminum, alloys of aluminum and mixtures thereof.

9. The method of claim 7 wherein said exothermic substance is a carbonaceous substance.

10. The method of claim 9 wherein said carbonaceous susbstance is selected from the group Consisting of coke breeze, charcoal powder, carbonized plant stalks, carbonized seed shells, expanded graphite and mixtures thereof.

Claims

1. A METHOD OF MAKING A STEEL INGOT WHICH COMPRISES POURING AT LEAST 3 TONS OF MOLTEN STEEL INTO A STEEL INGOT FORMING MOLD, SAID MOLD BEING PROVIDED WITH AN INSULATING MATERIAL FOR MAINTAINING THE SIDE PORTION OF THE MOLTEN STEEL IN A HOT CONDITION AT THE UPPER PORTION OF THE MOLD, WITH SAID MOLTEN STEEL HAVING A CARBON CONTENT OF NOT MORE THAN 0.7 PERCENT, WITH THE AMOUNT OF MOLTEN STEEL AT THE HOT UPPER PORTION OF THE MOLD BEING AT LEAST 10 PERCENT BY WEIGHT OF THE STEEL INGOT; COVERING THE TIP SURFACE OF THE MOLTEN STEEL, AND THUS KEEPING IT WARM, WITH A PLATE-LIKE MOLDED MATERIAL HAVING A BULK SPECIFIC GRAVITY OF 0.2 TO 0.7 AND A THICKNESS OF AT LEAST 10 MM WHICH COMPRISES 30 TO 88 PERCENT BY WEIGHT OF A REFRACTORY MATERIAL, 5 TO 45 PERCENT BY WEIGHT OF A FIBROUS SUBSTANCE AND 2 TO 20 PERCENT BY WEIGHT OF A BINDER; AND CASTING A STEEL INGOT IN SAID MOLD.

6. The method of claim 1 wherein said binder is a material selected from the group consisting of phenolformaldehyde resins, urea-formaldehyde resins, furan resins, epoxy resins, water glass, cement, clay, dextrin, starch and mixtures thereof.