US1849502A - Gray cast iron and method of producing the same from iron-silicon alloys - Google Patents

Description

March l5, 1932. w. J. MERTEN' I GRAY GAST IRON AND METHOD OF PRODUCING `'I'HE SAME-FROM IRON SILICON ALLOYS Filed April 16, 1928 Sera/b TOREY Patented Mar. l5, 1932 UNITED STATES PATENT l OFFICE WILLIAM J. HEBTEN, OF PITTBBUBGH, PENNSYLVANIA, ASSIGNORTO Wm'IINGH-OUSE ELECTRIC MANUFACTURING COMPANY, A CORPORATION F PENNSYLVANIA GRAY CAST IRON -AN D METHOD OF PBODUCING THE SAIE FRM BGN-SILICON ALLOYS appumion mea april 1s, 192s. serial m. 270,204.

My invention relates to the preparation of synthetic iron from sheet-scrap punchings or stampings of iron-silicon alloys4 by the cupola process 'that has characteristics 5 which render it suitable for gray-iron castin s having specialrequirements.

he principal object of my invention is to provide a process of producing an iron from sheet scrap resulting from various cuttings and punchings of iron-silicon alloys that is suitable for preparing gray-iron castings of special characteristics, including high magnetic permeability and physical strength, combined with ood machining qualities and a fair degree o? ductility. Another object of my invention is to provide a process of economically producingl a high-grade iron from the sheet scrap resulting from the punchings or stampings of iron-silicon alloys which consists essentiall in baling the scrap, mixing it with a sma l uantity of ferro-manganese, and melting t e mixture in a cupola furnace, the quantity of sheet scrap and the amount of coke or other fuel utilized for melting it being so poportioned that the iron-silicon alloy will melted and converted into an'iron having characteristics which render it especially` suitable for making castings and particularly those utilized in electrical apparatus, such as motors.

' A further object of my invention is to provide gray-iron castin that have greater physical strength and tter magnetic properties than castings formerly produced from iron prepared 'by the cupola process andin which the amount of chemical components and impurities, such as carbon, phosphorusg manganese and sulphur are of a selective value, or are considerably lower, and the amount of silicon is as high, or higher, than in castings usually produced from iron prepared by the cupola process.`

A still further object of my invention is to provide greg-iron castings from sheet scrap resulting om the stamping or punching of an iron-silicon alloy which contains more than 2 per cent of sillcon and in which the relation between the combined carbon and the graphitic carbon is such that the castings will have unusual Ahardness and strength, combined with good machining qualities.

Heretofore, the sheet scrap, resulting from the stampings or'punchings of high-grade lron-silicon alloys utilized in transformers and other electrical apparatus, has been disposed of by adding it to molten pig iron or other furnace charge in a steel-making furnace. This method of utilizing the scrap was economically undesirable, because impurit1'es, such asoxides or extraneous adhering materials, were often introduced into the melted furnace charge, and, when basic-lined furnaces were employed, the lining deteriorated rapidly. It was accordingly necessary to treat or refine the scrap,.the same as an other inferior and'impure material, whic A made the process expensive and this was esv-peciall'y so where the scrap consisted of stamplngs andcuttings made from speciallyprepared and purified material that involved a` dlicult and expensive process of preparation.

I have made the discovery that high-grade sheet scrap resulting'rom the punchings or stampings of iron-silicon'alloys may be successfully remelted in a cupola furnace without introducing largetamounts of impurities and that gray-iron castings may be prepared from the molten iron that will have high physical strength and good magnetic qualities.

My invention will be better understood when described with reference to the accompanying drawing, the single figure of which 1s a sectional vlew of a cupola or melting furnace.

The cupola or melting furnace, which is of the usual'construction, comprises a refractolgl-lined shell 1, supported onlegs 2, and a mace bottom 3, also refractory lined,

which is held closed b a support 5. A.-

number of tuyres 6, lea g from a common air chamber '7, are positioned in the furnace In practicing my invention, a charge of bedding coke is placed in the furnace through the door 9. Because of the higher melting pointl of iron-silicon alloys, the amount of coke or other fuel required for melting the sheet scrap lobtained therefrom is considerably more than the amount employed in the customary practice ofmelting pig iron.

For a cupola having a diameter of 60 inches, I have found that the charge of coke should be such that the bed extends from the bottom of the furnace to approximately 36 inches above the tuyres. For a cupola of the size specified, approximately '3000' pounds is required for this charge. The bed is then ready to receive the charge of tightly bunf dled sheet scrap.

In accordance with my improved process, the charge I,of bundled scrap is obtained from the numerous cuttings or punchings of high grade silicon-iron alloy which is utilized in the manufacture of transformers and other electrical apparatus. This scrap material is composed of a silicon-iron alloy containing from 2.5 to 4.5 per cent of silicon and in which the total amount of impurities, such as carbon, sulphur, manganese and phosphorus, are not over .2 pei` cent. The scrap, however,

may be slightly contaminated by a varnish about 3000 p'ounds of the baled iron-silicon scrap mixed with approximately 30 pounds of ferro-manganese.

The ferro-manganese is added to the charge of baled silicon-sheet scrap so that sufficient manganese will be introduced into the iron to counteract the effects of sulphur. When coke is utilized for the melting of the iron, it always contains a certain amount of sulphur, as an impurity, some of which combines with the iron toform iron sulphide. The sulphur, in the form of iron sulphide, causes red shortness and is also a powerful agent in increasing the chilling e'ect which makes the iron hard and difiicult to machine. When manganese, however, is present, it combines with the sulphur, to form manganese sulphide in which form the sulphur is not such a potent agent in increasing the chilling effect. It will, therefore, be 'seen that the introduction of manganese may actually increase the ductility of the castings when sulphur is present.

The melting of the silicon-steel scrap in the cupola is similar to the usual practice. The charge of the baled sheet scrap mixed with the ferro-manganese, and a layer of limestone 10, which serves as a iiuxing agent, rests upon the bed of coke 11. Air is blown through the blast pipe 12, wind box 7 and tuyres 6.

The oxygen unites with'the carbon to form l i carbon monoxide and carbon dioxide, and the hot gases, as the pass upward, carburize and melt the iron. s the iron is melted, the fuel is also consumed and a new layer of coke and baled sheet scrap, to which ferro-manganese has been added, will take the place of the previous layers in the melting zone of the furv nace. The melted iron and slag collect in the Crucible zone of the ,furnace and may be alto .80% man anese, from .02 to .06% phosp phorus and rom 2 to 3% carbon, of which from .20 to 1.5% was combined carbon and the remainder graphitic carbon. By .proper annealing, however, the amount of combine carbon may be substantially reduced or changed entirely into When it is desired to pro uce castings having a high permeability, it is essential that the amount of combined carbon be low. Castings prepared from the iron have a gray fracture, machine well, and have 50 to 7 0l per cent better magnetic properties than iron castings ordinarily produced from liron prepared by the cupola process. The tensile strength of4 such iron castings is between 35,000 to 40 000 pounds per square inch. Undera loa of from 3700 to 5000 pounds at the middle of a bar 18 inches long and 11A; inches in diameter, which was supported at theends, there was a deflection of .15 to .2 of an inch.

raphitic carbon..

As a specific illustration, a gray-iron cast-l l ing prepared in the manner described contained 2.5% carbon, of which .7% was combined carbon and 1.8% carbon in the graphitic form. The amount of silicon was 2.75% and sulphur, manganese and phosphorus were present in the amounts of .1%, .75% and .03%, respectively.

Bars of my improved cast gray iron, when` annealed at 900 C. and permitted to cool in the annealing furnace, had a magnetic'in duction of from 6000 to 8500 at'10 gilberts ica per centimeter and 9500 to 11000 gausses at 50 gilberts per centimeter, the corresponding ranges in permeability being 600 to 800 an to 220, respectively.

The high magnetic induction of the castings results. from the comparatively high k amount of silicon and the small amount of other chemical components and impurities contained in the iron, the amounts of carbon, sulphur, manganese and phosphorus being substantially less than in ordinary cast iron produced by the cupola process.

Gray cast'iron produced by ordinary proc'- esses has a magnetic induction of from 2500 to ordinarily produced by the cupola process,- but my method .provides an outlet' for the high-grade sheet scrap of iron-silicon alloys for which no market has been available except at a` reat sacrifice of its potential value.

ile I have described a specific form of my invention, it will be understood that the char es of the respective materials in v`the cupo a will vary considerably and that the 53 proportions given are to be considered illustrative and not as a limitation of my invention. When coke is utilized as ay fuel, it should be of a high quality and should not Ycontain more than 1 per cent of sulphur. The amount of' ferro-manganese added will be in vproportion to the amount of sulphur present in the cokeand the speed of meting as the manganese combines with sulphur, forming manganese sulphide which counteracts the detrimental eifects of sul hur.

Good castings have been pr uced without the use of ferro-manganese, providin the amount of sulphur inthe fuel is small. do not desire, therefore, to be limited to the use of ferro-manganese in my process, although it is a desirable in dient and is essential when the amount o sulphur in the coke is high. It will also be understood that, for different sized cupolas, the respective charges will be correspondingly varied. `As in ordinary cupola ractice, however, there must be suicient co e or other fuel present to melt the baled sheet scrap and carburize the iron, but for economical o ration of the furnace, too much should not added. ther modifications of my invention will become apparent to those skilled in the art and I desire, therefore, that only such limitations shall be placed upon my invention as are required by the prior art and the appended claims.

I claim as my invention:

.2% which comprises melting the baled scrap in a cupola furnace and casting the molten iron in molds -of the desired shape. Y

2. The process of producing iron castings from the sheet scrap of iron-silicon alloys containing not more than .2% carbon, which comprises mixing tightly baled silicon-sheet scrap with a small quantity of ferro-inanganese, melting the same in a cupola furnace, and casting the iron in molds of the desired shape.

B. In the process of producing iron cast-v ings from the sheet-steel scrap of iron-silicon alloys containingnot more than .2% carbon' the steps which comprise charging a quantity of coke in a cupola furnace, adding a charge of baled silicon-steel scrap mixed with a small amount of errdmanganese and a 'quantity of lime as a fluxing agent and melt-v ing the charge, the amount of coke being s ulicient to melt the silicon-steel scrap and the amount of ferro-manganese adding being in prlgportion to the amount of sulphur in the co e. Y

4. In the process of producing ironl castings from the sheet scrap of iron-silicon alloys containing not more than .2% carbon, the step which comprises melting la mixture of tightly bound silicon-steel scrap and a ysmall quantity of ferro-manganese i-n a. 95

cupola furnace.

-5.` The process of producing iron castings `from iron-silicon alloys containing not more 1928. v WILLIAM J. MERTEN.

1. The process of producing iron castings from baled scrap of iron-silicon alloys in 35 which the carbon content is not' more than

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