US1547616A - Magnetic material - Google Patents

Description

July 28, 1925. 1,547,616

C. A. SCHARSCHU MAGNETIC MATERIAL ori Filed Dec. 27, 1920 Fig.1.

E C) I Ira/enter; Char-lea AScharschu,

by Mai-4.00

His Attorney;

i l apparatus,

Patented July 28, 1925.

UNITED STATES PATENT OFFICE.

CHARLES A. SCHARSCHU, F PITTSFIELD, MASSACHUSETTS, ASSIGNOR TO GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK.

MAGNETIC MATERIAL.

Original application filed December 27, 1920, Serial No. 433,147. Divided'and this application filed.

April 7, 1922. Serial No. 550,435.

To' all whom it may concern:

Be it known that I, CHARLES A. SCHARSOHU, a citizen of the United States, residing at Pittsfield, in the county of Berkshire, State of Massachusetts, have invented certain new and useful Improvements in Magnetic Material (being a division of myapplication, Serial No. 433,147, filed December 27, 1920), of which the following is a specification.

The present invention comprises an improved magnetic material and in particular silicon steel capable of utilization at high efliciency in varying magnetic fields.

In the construction of cores for electrical especially of the alternating current type, such as transformers and dynamoelectric machines, it is highly important to use magnetic material in which the Watt losses, due to hysteresis and eddy currents, are as low as possible. Consequently efiorts have been made duringthe development of the electrical industry to improve the magnetic properties of core material, and the substitution of silicon-iron and other alloys for 86 ordinary steel has indeed effected a considerable saving electrical energy.

an. Efforts to further improve the magnetic properties of silicon steel have been and are being made by manufacturers of this so material since it is of core loss results in the saving of a large amount of energy; thus a reduction of core loss of one or two per cent is looked upon as an im- 85 portant achievement. 1

Silicon steel usually contains from 3.75% to 4% silicon and about .07 per cent carbon; it is ordinarily made in the open hearth furnace; it is cast into ingots and these are rolled 40 into thin sheets which are used in core construction. The open hearth process results in a material in which a considerable amount of slag is distributed throughout the mass in whlch the sulphur content is generally as high as from 0.03 to 0.04 per cent. I have found that the impurities carried by the slag andespecially the high sulphur content of the product are detrimental characteristics of the magnetic material, since to their presence a large percentage of the hysteresis action is due.

I have discovered that when magnetic realized that a reduction by even a small percentage material of any kind, and especially silicon I substantially free ofslag inclusion and the sulphur co'ntentis red'uced steel, is made to and below .010 and usually aslow "as 0.005 per cent and even the reduction amountingfion the' average 'to about 12 per cent and sm-individual cases still greater.

istics. In'the application from which'thisf application has been divided'and' which'hasf i No. 1,487,275, of March matured into Patent lower; tli at in' such' material the core loss is remarkably ""r educed,

18,1924, claims have been made on a process of 1 making my improved ma-terial whicli--'consists in treating the material in" a fluid state Whether it be 'scrap'or'when already fused 7-0 4 by the open hearth process,"insuchmanneras to exclude the admission of airyexpelthe occluded particles of slag from the in- I terior of'the fused mass to thesurfaceand then pour the material fromunder'neath the sheet of slag on the surface.

This process is preferably carried outbythe use of an induction furnace of a specific construction which constitutes a part of my invention. While the fused mass is in the induction furnace and preparatory to the practice of my invention, the material may be chemically refined in any ordinary or improved manner.- v I In the accompanying drawing, Fig. 1 ii lustrates partly in elevation and partly in vertical section .an induction furnace embodying structural features of my invention; Fig. 2 is a plan view of thefurnac'e chamber, the furnace top being. removed; and Fig. 3 is a top View, the primarytco-il" and housing being shown in part broken away.

The induction furnace shown in the drawing comprises an annular furnace crucible 1, surrounding a magnetic core 2, which has a fiat primary winding 3, supplied with. alternating current by conductors not shown. The primary winding may consist of annularsections, as shown; it is suitably mounted the manner set forth in to Unger. The. furnace crucible is provided which usually is formed with a refractory'lining 5, which is in diso it furnace,

rect contact with the body of metal 6 to be melted, and consists preferably of'particles of highly sintered or fused magnesia molded with a binder such as magnesium sulphate to form a solid mass. This lining rests upon a wall of refractory brick 7, which in turn is supported by a suitablevcasing 8, made of. b01181" plate or the like. I have discovered that the location of the channel or crucible 1 beneath the primary winding 7 3 subjects the molten mass in the crucible, constituting the secondary in the induction to the action of an alternating electro-magnetic field in such a manner that the slag particles occluded in the fused mass tend to separate from the. metal, as will the 'spout of a teapot, so that the fusedmetal may be poured from the furnace from beneath the "top slag layer without causing this slag or any part of it to be mixed with the metal. The pouring spout is provided with a door 13. The charge receiving opening 14 is similarly provided with a door (not shown). A pouring spout of this character 'has heretofore been suggested for use in another kind of furnace, the practice of my process it cooperates with the magnetic function of the apparatus to assist the removal of. the occluded slag particles.

The metal to be refined may be receivedin a molten state from any suitable source, for example, a Bessemer converter, an open hearth furnace, or an arc furnace, and may consist of soft steel, hard steel, or any alloy steel. My invention is also applicable to the melting of cold material either as scrap or new material directly in the induction furnace. The metal is allowed to attain a temperature of about to 150 C. in excess of its melting point and is maintained in that condition for a period of from 45 minutes to one and one-half hours in addition to the time required for chemical refinement i such is resorted to while the metal is in a fluid state in the induction furnace.

but in the induction furnace used for This is preferably a basic slag consisting,

for example, not exceeding 20%, and in some cases a small amount of fluorspar is added to thin the slag. Any other suitable slag which is basic in character may be used when chemically refined molten metal from any source, such as a Bessemer converter, an open hearth furnace or an arc furnace is introduced into the induction furnace, the same procedure is observed, that is to say, a basic slag of the general character above indicated is added. The molten metal is subjected to the electro-magnetic purifying treatment which will now describe in greater detail. Owing to the location of the primary winding above the crucible element of the furnace, the alternating flux gives to the molten mass a slow but powerful movement from the inner edge of the annular channel downwardly toward the bottom and upwardly along the outer edge of the channel. In this respect the action of the flux upon the fluid metal is different from that of the magnetic flux when the primary winding is concentric with the channel, for in the latter case the molten metal is violently a tated in an irregular manner, causing t e occluded slag particles to mix continuously of lime and silica, the latter with the metal and effectually reventing a separation of the same. By ocating the primary windingabove the crucible channel, the movement of the metal becomes very much slower. There are two forces acting on the molten charge tending to expel the slag from the metal, namely, the compressive effect of the magnetic field upon the charge and the electro-dynamic effect which exerts a diflerent repellent action upon the slag and metal.

The compressive or pinch force of the magnetic field of a current-carrying conductor is a force acting radially inward upon the current-carrying elements of the conductor. As the slag is a poor conductor it tends to be squeezed out somewhat like water being squeezed out of a sponge. The separating action due to the electro-dynamic effect is somewhat comparable to the separation occurring in a centrifugal separator. The

metal is repelled with current-carryin the slag particles. As

greater force t an the magnetic Due to the combined effect of the slow and regular movement of the charge and the expulsive force exerted on the slag particles,

crucible 1 prevents the remixing of the metal field'is applied from above, the

slag particles tend to come to the surface. 1

poured.

' than 0.01 per cent with the'expelled slag when the metal is poured by tilting the furnace, so that the advantage of the preceding melting treatment under the influence of the electromagnetic field is not lost when the metal is The material thus made, furnace gases, may be distinguished from a vacuum-fused product by the fact that it contains a substantial amount of gas. Silicon steel made in accordance with my invention has been found by analysis to contain about 1000 to 2000 cubic centimeters of gas per kilogram of metal. This gas consists largely of hydrogen together with small amounts of carbon dioxide, carbon monoxide and nitrogen. 1

The carbon content of the material is substantially unaffected by the refining treat ment in the induction furnace.

\VVhat I claim as new and desire 'to secure by Letters Patent of the United States is 1. An electromagnetic structure of ferrous material, having a sulphur content less by weight and containing gas in a quantity characteristic of metal fusedin contact with furnace gas at atmospheric pressure, said material being in contact with capable of operating as a core in an alternating magnetic field with a materially lower energy loss than similar material having a higher sulphur content.

2. A ferrous magnetic material containing silicon as an alloying element, having a carbon content substantially no lower than ordinary open hearth silicon steel, having a sulphur content substantially no greater than 0.010 per cent, and being characterized by a substantial gas content which is materially higher than the gas content of similar material fused in a vacuum, said material beingcapable of operating in an alternating magnetic field with materially lower energy loss than similar material having a higher sulphur content. 1

3. A magnetic material consisting largely of iron, containing about 3.75 to 4 per cent silicon, about 0.07 per cent carbon, not substantially more than 0.005 per cent sulphur, and having a gas content of more than about 1000 to 2000 cubic centimeters per kilogram, said material being capable of operating inan alternating magnetic field with a materially-lower energy loss than similar material having asubstant' content. V

In witness whereof, I have hereunto set my hand this 5th day of April, 1922.

CHARLES A. SCHARSCHU'.

ally higher sulphur

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