US3467172A

US3467172A - Exothermic metallurgical charges

Info

Publication number: US3467172A
Application number: US569477A
Authority: US
Inventors: Arthur G Clem
Original assignee: Amcol International Corp
Current assignee: Amcol International Corp
Priority date: 1966-08-01
Filing date: 1966-08-01
Publication date: 1969-09-16
Anticipated expiration: 1986-09-16

Description

Sept. 16, 1969 A. G. CLEM 3,467,172

EXQTHERMIC METALLURGICAL CHARGES Filed Aug. 1. 1966 MVP/V701? ARTHUR 6. GLEN 3y ATTORNEYS United States Patent M US. Cl. 164-338 1 Claim ABSTRACT OF THE DISCLOSURE This disclosure relates to shaped exothermic charges for insertion in a metal casting mold for retarding the solidification of cast metal.

This invention relates to exothermic metallurgical charges and to the production thereof. More particularly, this invention relates to exothermic charges of improved shape for use in metallurgical operations, particularly the casting of steel .and similar higher melting metals.

This application is a continuation-in-part of copending application Ser. No. 337,628, filed Jan. 14, 1964, and now abandoned.

In the production of castings by the pouring of molten metal, the most troublesome problem is that of shrinkage of the metal in the mold. A general practice in the foundry art is to provide a riser for the mold in which an excess of molten metal is retained to make up for the loss of volume due to shrinkage. Risers are not the complete solution to the casting problem due to the fact that metal ordinarily freezes from the outside surfaces toward the center in the riser, thereby resulting in piping; that is, the creation of a crater in the center of the riser which may extend into the casting, thus causing a defect therein. One measure commonly employed to remedy this defect is that of providing a large sink head of molten metal to properly feed the casting. Another method involves the provision of insulation to the riser to prevent unduly rapid cooling of the metal therein. A further development has been that of providing an exothermic powder directly in the riser which is ignited by the molten metal and provides additional heat to prevent solidification of metal therein. It is also known to provide exothermic powder in cupshaped depressions on the outside of the riser to provide additional heat. By such exothermic charges there is produced superheated metal in the riser with consequent maintenance of fluidity.

The use of exothermic compositions for maintaining the fluidity of the molten metal has also been accomplished by inserting exothermically reactive materials in selected regions of the mold or sand flask where controlled heating of the metal is desirable to prolong its fluidity. Discs of exothermic material can be placed in the riser in contact with molten metal to retain fluidity.

It has been found that the metal in the risers will begin to solidify from the outside radially inwardly, and it is desirable to maintain the riser uniformly fluid during a selected period of time.

Accordingly, one object of the present invention is to provide a new and improved exothermic charge which overcomes the aforementioned disadvantages.

A further object of the present invention is the provision of a new and improved exothermic charge for providing heat to the riser of a foundry mold.

A further object of the present invention is to provide an exothermic charge which directs and focuses the generated heat closer to the outside of the riser than to the inside thereof.

3,467,172 Patented Sept. 16, 1969 Ice The present invention is based on the discovery that exothermic charges of a selected shape are highly effective in maintaining fluidity in the casting of molten metals. Such a shaped exothermic charge when placed in contact with a pool of molten metal focuses and concentrates the heat of the exothermic reaction over a predetermined period of time into desired selected areas of the molten pool thereby improving the effectiveness of the operation by controlling the intensity and amount of the heat injected into the casting.

According to the present invention, the distribution or focusing of the heat into the riser is controlled by providing a shaped exothermic charge for insertion in the riser and, in the illustrated preferred embodiment, having a concave lower surface and upwardly and outwardly tapered side wall elements.

Such a shaped charge will begin to burn along its lower surfaces when it comes in contact with molten metal. This burning will travel upwardly, but since the center of the charge is thinnest, the exothermic charge will burn up in the center first. Thereafter the exothermic charge will continue radiating heat about an annular ring outwardly from the center. The annular ring of heat provides the necessary heat downwardly into the riser and outwardly of the riser to maintain the desired fluency of the molten metal.

It has been discovered that the thickness of the charge will control the length of time that an area is maintained heated by the charge. Consequently, in the illustrated embodiment of the present invention the exothermic charge has a maximum thickness adjacent its outer edge so as to release heat in a pipe-shape direction of the riser over an extended period of time.

The invention can best be understood by reference to the attached drawings wherein:

FIG. 1 illustrates in cross section a sand mold containing molten metal and an exothermic charge in its riser according to the present invention;

FIG. 2 represents a bottom view of the exothermic charge in the riser of the mold of FIG. 1; and

FIG. 3 illustrates in cross section of the exothermic charge according to the present invention and taken along line 33 of FIG. 2.

Referring now to FIG. 1, there is illustrated a known sand casting mold utilizing an exothermic charge according to the present invention. More specifically, there is provided a flask 15 provided with a sand mold 16. A sprue 18 forming a pouring hole communicates with a mold cavity 19.

Additionally, a riser 20 is located so as to provide a reservoir of molten metal to the mold cavity 19 to com pensate for shrinkage of the metal during cooling thereof. In order to control the cooling of the molten metal in the riser 20, there is provided an exothermic charge 21 within the riser 20.

The cross section of the exothermic charge 21 can best be seen in FIG. 3. The exothermic charge 21 has a generally planar upper surface 21, an upwardly and outwardly tapered side wall surface 21b, and a concave lower surface 210.

It has been found that since the metal in the risers will begin to solidify from the outside radially inwardly, it is desirable to concentrate the heat from the exothermic charge closer to the outside of the riser than to the center of the riser, thus maintaining a larger fluidized bed of molten metal. Advantageously the illustrated arrangement provides such a structure. More specifically when the exothermic charge 21 is ignited in a riser upon contact with molten metal, it will begin to burn along its lower surface 21c. This burning will travel upwardly, but since the center of the exothermic charge is thinnest, the exothermic charge will burn up in the center area first. Thereafter the exothermic charge will continue radiating heat about an annular ring outwardly from the center. This annular ring of heat will provide the necessary heat direction downwardly into the riser and outwardly of the center of the riser to maintain the desired fluency of molten metal in the riser until the mold or sand flask is completely full of molten metal. This reduces the amount of flaws in the castings which ordinarily would result from the cooling of the molten metal during pourmg.

The exothermic materials which compose the shaped charges can be any of the compositions which have heretofore been used in the foundry art. For instance, they can be composed of alumino-thermic materials such as mixtures of aluminum (15-30%) and iron oxide (Fe O 45-85%) with other materials such as copper .and nickel, binders such as bentonite, oxidizing agents such as manganese dioxide and sodium nitrate, and catalysts such as metal fluorides which facilitate the start of the exothermic reaction, cause the reaction to occur at lower temperature and control the speed of the reaction so that it proceeds quietly without waste of heat. Among such fluorides are alkali metal fluorides and alkali metal aluminum fluorides, including sodium fluoride, cryolite, potassium aluminum fluoride and mixtures thereof.

Other exothermic materials include mixtures of ferrosilicon with an oxidizing agent such as sodium nitrate or other alkali metal nitrate, an alkali metal chlorate or perchlorate or manganese dioxide as described in the Kinnear Patent No. 2,791,815, May 14, 1957. Other suitable exothermic mixtures include mixtures of aluminum, alumins and calcium fluoride with lesser quantities of sodium nitrate and iron oxide as disclosed in the Sotfel Patent No. 2,490,327, Dec. 6, 1949 and. chromium thermite, titanium thermite, manganese thermite, silicon thermite, boron thermite and beryllium thermite mixtures, as disclosed in the Depler Patent No. 2,337,314, Dec. 21, 1943. Other suitable exothermic compositions are shown in the Pletsch et al. Patent No. 2,798,818, July 9, 1957; the Henderson et al. Patent No. 2,805,145, Sept. 3, 1957; the Cross Patent No. 3,025,153, Mar. 13, 1962; the Udy Patent No. 2,513,602, July 4, 1950; the Pletsch et al Patent No. 2,791,816, May 14, 1957; the Vautin Patent No. 1,318,709, Oct. 14, 1919; the Comstock et al. Patent No. 2,162,938, June 20, 1939; and the Strauss et al Patent No. 2,591,105, Apr. 1, 1952.

The exothermic materials are compounded in appropriate proportions to provide adequate green strength. Suitable binder materials include clays such as montrnorillonite clays (e.g., bentonite) and cork gum. Other binders such as aqueous sodium silicate (e.g., water glass) and aqueous emulsions of urea-formaldehyde, melamineformaldehyde, or phenol-formaldehyde resins can be used.

The shaped exothermic charge of this invention has the desirable advantage of reducing the amount of molten metal which must be contained in risers or headings ac- 4 cording to conventionalpractice. This results in substantial economy since the metal in the riser or feeder is lost as waste. Moreover, by appropriately focusing and concentrating the heat from the exothermic charge to the critical area of the casting, it is possible to prevent flaws such as piping to occur. By the procedure of this invention, the most economical results are obtained with respect to metal yield. This allows reduction of the diameter and height of risers. It has been found that one pound of exothermic material in appropriately shaped charges can save as much as 10-15 pounds of steel, depending upon the design of the casting.

I claim:

1. In combination, a casting mold provided with a mold cavity having a sprue communicating with said cavity for pouring molten metal and a riser communicating between said cavity and the exterior of said mold for providing a reservoir of molten metal to the mold cavity to compensate for shrinkage of the metal during cooling thereof, and a shaped exothermic charge in said riser to prevent premature cooling of the molten metal in said riser and being formed of an exothermic composition and a binding agent therefor, said charge having upwardly and outwardly tapered side wall elements, a generally planar upper surface, oriented approximately normal to the axis of the riser, and a concave lower surface so that the energy released upon ignition of the exothermic composition when in contact with the surface of molten metal in said riser is concentrated axially down said riser.

References Cited UNITED STATES PATENTS 1,294,209 2/1919 Walker 164-125 X 2,335,008 11/1943 Hites 164-360 2,476,296 7/1949 Hardy 164-360 X 3,273,211 9/1966 Miraldi 164-125 X 3,314,116 4/1967 Wittmoser et al. 164-360 X 1,312,401 8/1919 Huber 164-54 X 2,925,637 2/ 1960 Edmonds et al. 164-53 FOREIGN PATENTS 864,420 1/ 1941 France.

67,350 7 1892 Germany. 1,256,395 2/1961 France. 40,596 1956 Poland.

OTHER REFERENCES American Foundryman, October 1947, pp. 51-61. Feeding Casting, by S. L. Finch, p. and FIGS.

9 and 10 especially relied on.

J. SPENCER OVERHOLSER, Primary Examiner V. RISING, Assistant Examiner US. Cl. X.R.