US3783933A

US3783933A - Method of making an ingot mold stool

Info

Publication number: US3783933A
Application number: US00173435A
Authority: US
Inventors: V Leedy
Original assignee: United States Steel Corp
Current assignee: United States Steel Corp
Priority date: 1971-08-20
Filing date: 1971-08-20
Publication date: 1974-01-08
Anticipated expiration: 1991-01-08

Abstract

A cast iron ingot mold stool having a coating of granulated iron oxide particles fused into the upper surface thereof to prevent cast ingots from sticking thereto.

Description

UnIted States, Patent 1191 1111 3,783,933 Leedy v Jan. 8, 1974 METHOD OF MAKING AN INGOT MOLD 1,920,244 8/1933 Connelly et al 164/97 STOOL 2,204,453 6/1940 Siegert 164/97 3,454,385 7/1969 Amero..... 51/309 X Inventor: Verne y, Palos g 3,093,464 6/1963 COeS 51/309 x 1 Assigneer United States Steel Corporation, FOREIGN PATENTS 0R APPLICATIONS plttsburlgh 2,011,199 2 1970 France 164/57 [22] Fil d; A 20, 1971 6,914,451 3/1971 Netherlands 249/204 [21] Appl' 173435 Primary Examiner-Robert D. Baldwin Assistant Examiner-JohnE. Roethel [52] US. Cl 164/58, 164/97, 249/204 Att0rney-F0rest C. Sexton [51] Int. Cl B22d 27/18 [58] Field of Search 249/204; 164/97,

164/57, 58; 72/42; 51/309 [57] ABSTRACT A cast iron ingot mold stool having a coating of granu- 5 Referenc'es,v Cited lated iron oxide particles fused into the upper surface UNITED'STATES PATENTS thereof to prevent cast ingots-from sticking thereto. 2,090,836 8/1937 Glezen 164/97 4 Claims, 2 Drawing Figures 1 METHOD OF MAKING AN INGOT MOLD STOOL BACKGROUND OF THE INVENTION Steel ingot molds usually consist of upright cast iron mold shells open at the top and bottom. To close the bottom for casting ingots, the mold shell is placed on a thick cast iron mold stool.

ln stripping a steel ingot from the mold, considerable difficulty is sometimes encountered because the ingot tends to stick to the cast iron mold stool, especially if the mold stool is new or reasonably new. Frequently the two are so firmly fused together that the mold stool must be broken free from the ingot. This of course results in excessive stool comsumption and costly time delays. Older mold stools, which have been used through many heats, appear to have a highly corroded and oxidized surface to which the ingot does not readily stick. New, or near new, ingot mold stools, however, do not have such an extensive surface corrosion, and hence do have a tendency to fuse with the ingot cast therein.

To alleviate this problem, several procedures have been employed. Some mills for example spray the mold stool with various solutions which will dry to form a refractory surface. The success of these procedures is rather limited because the molten steel will frequently wash away the coating. As another example, some foreign mills have virtually eliminated the problem by using graphite mold stools. Graphite mold stools however are quite expensive and fragile and do not therefore alleviate the cost problem.

SUMMARY OF THE INVENTION An object of this invention is to provide a new and improved cast iron mold stool which will not stick or fuse to an ingot cast thereon, and which is not significantly more expensive than the conventional cast iron mold stools of the prior art.

Another object of this invention is to provide a cast iron mold stool having densev iron oxide surface layer to be exposed to the ingot metal.

A further object of this invention is to provide an improved cast iron mold stool which has a greater average life-span than conventional cast iron mold stools of the prior art.

Still another object of this invention is to provide a method for making the improved cast iron mold stools of this invention.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a sectional elevation of the mold stool of this invention; and

FIG. 2 is a sectional elevation ofa mold used to cast the ingot mold stool.

DESCRIPTION OF THE PREFERRED v EMBODIMENT With reference to FIG. 1, the ingot mold stool of this invention is much like prior art mold stools in that the main portion thereof comprises a rectangular cast iron block 10. The one distinction, and the crux of this invention, is the coating of dense iron oxide 12 cast into the upper surface thereof. More specifically, the oxide coating consists of granulated hemitite, magnetite or mixtures thereof, which is fused into the cast iron block 10. Although the iron oxide coating 12 could extend over the entire upper surface of cast iron block 10, it

is preferred that it be limited to the general area which will come into contact with molten steel. This is because the cast iron surface wears better against the solid cold surfaces of the ingot mold, whereas the oxide surface is best only on areas in contact with molten metal. Although the thickness of the iron oxide coating is not critical, it is preferable that it be at least about one-fourth inch thick so that it will not be worn away too soon. Although thinner coatings would work suitably, it is likely the coating would be eroded away too soon to afford suitable protection. On the other hand, it need not be thicker than about one-half inch to work suitably.

The particle grain size of the oxide coating is not particularly critical. It should of course not be so coarse as to provide a rough texture which can be quickly and easily eroded away, and not so fine that it is dissolved by the molten cast iron. For all practical purposes,

grain sizes less than one-fourth inch and larger than about mesh are preferred.

With reference to FIG. 2, the mold stool described above is cast upside-down according to conventional practices directly over the granular iron oxide layer 12. Specifically, a rectangular sand mold 20 is formed within a molding flask 22. The granular iron oxide 12 is then gently compacted against the bottom surface 24 of sand mold 20. Although the iron oxide 12 can cover the entire bottom surface 24, as noted above, it is preferred that the iron oxide 12 cover only a rectangular portion in the center of bottom surface 24, generally limited to that area which will come into contact with molten steel during ingot teeming. In order to facilitate compaction of the iron oxide l2against surface 24, it is further preferred that some lateral retaining means or form be employed to contain the iron oxide 12 during compaction. As shown, therefore, iron oxide 12, is gently compacted within a low rectangular form 26 which resembles a thin picture frame. Since form 26 serves only to provide temporary support during compaction of iron oxide 12, it is removed thereafter so that the compacted iron oxide 12 is more exposed to the iron cast thereagainst. Instead of a rectangular form 26, I have also successfully used expanded metal grids or screeens (not shown) into which the iron oxide 12 is compacted. In fact, the expanded metal grid or screen probably works better than the rectangular frame 26 since it provides channels through the iron oxide 12 into which the molten cast iron will flow to provide a better fusion bond therewith. Still another procedure is to provide a rectangular depression (not shown) into the bottom surface 24 of mold 20 and compacting the iron oxide 12 into the depression. When the oxide is so placed with or without the use of a retaining means, molten cast iron is poured into gate 28 until the mold is filled. The molten iron in the mold will fuse with the granular iron oxide 12.

As noted above, the oxide particles must be a dense form such as hemitite or magnetite so that it will not be dissolved or washed away by the molten cast iron. I therefore prefer to use a granulated hemitite ore concentrate which is readily available in many mills. The ore concentrate I use has a density of about 200 lb./cu. ft., contains about 5 percent silica, and has a typical screen analysis as follows:

Screen Cumulative 7: On l0 Mesh 2.6 2.6 On 20 Mesh 18.1 20.7

On 35 Mesh 33.7 54.4 On 60 Mesh 23.7 78.1 g On 80 Mesh .7 On lOO Mesh 0.8 88.6

On 200 Mesh 9.3 97.9 Through 200 Mesh 2.1 l00.0

In use, the mold stool is placed on a car (not shown) with the oxide coating 12 facing upward. An ingot mold (not shown) is placed on the mold stool with the open bottom end thereof directly over the oxide coating 12. As noted above, it is preferred that the ingot mold itself rest directly on the cast iron block 10 and not on the coating 12. Molten steel is then teemed into the open top of the ingot mold and there allowed to solidify. As with all mold stools, the molten steel will erode away a small portion of the surface. However, since the primary constituent of the oxide coating 12 is iron, the ingot is not contaminated thereby. After the ingot has solidified, the ingot and ingot mold can readily be lifted free of the mold stool for stripping without any appreciable sticking.

My ingot mold stools have now been used in the production of over 50,000 ingots and never has there been any appreciable sticking. The iron oxide coating 12, depending upon the thickness, will eventually be completely eroded away by the molten steel. By that time, however, the mold stool will have been used a sufficient number of times to have the dense corrosion surface caused by repeated use, and hence there is still no sticking problem. Even though the oxide coating 12 is somewhat short-lived, it does serve a very useful purpose in preventing sticking when the mold stool is new or relatively new, i.e., when sticking is most likely to occur. In assisting the mold stools through this most critical period, the oxide coating 12 does substantially lengthen the average life span of the mold stools.

I claim:

1. A method of making ingot mold stools the steps comprising forming a rectangular sand mold, gently compacting a layer of iron oxide particles on the bottom of said sand mold, casting molten cast iron into said sand mold causing the iron oxide particles to be fused into the surface of the cast iron adjacent thereto.

2. The method of claim 1 in which the bottom of said sand mold is provided with a rectangular form and said iron oxide particles are gently compacted into said form, and the form thereafter removed.

3. The method of claim 1 in which the bottom of said sand mold is provided with a rectangular expanded metal grid and said iron oxide particles are gently com pacted into said grid, and the grid thereafter removed.

4. The method of claim 1 in which the bottom of said sand mold is provided with a rectangular depression and said iron oxide particles are gently compacted into said depression.

Claims

2. The method of claim 1 in which the bottom of said sand mold is provided with a rectangular form and said iron oxide particles are gently compacted into said form, and the form thereafter removed.
3. The method of claim 1 in which the bottom of said sand mold is provided with a rectangular expanded metal grid and said iron oxide particles are gently compacted into said grid, and the grid thereafter removed.
4. The method of claim 1 in which the bottom of said sand mold is provided with a rectangular depression and said iron oxide particles are gently compacted into said depression.