US1598236A - Method of building and starting electric induction furnaces - Google Patents

Description

Aug. 31 1926.

c. A. BRAYToN; JR

NG ELECTRIC INDUCTION FURNACES .us'rnon OF sunmm AND STARTI Fiied Sept. 24, 1920 2 Sheets-Shad 1 yum [224 Aug. 31 1926.

C. A. BRAYTON, JR

METHOD OF BUILDING AND STARTING ELECTRIC INDUCTION FURNACES Filed Sept. 24, 1920 2 Sheets-Sheet 2 jazz far 64%! a E Q J ZM W jzzwvz Eys Patented Aug. 31, 1926.

UNITED STATES PATENT OFFICE.

CHARLES A. BRAYTON. JR., CLEVELAND, OHIO, ASSIGNOR TO THE INDUCTION FURNACE COMPANY, OF CLEVELAND. OHIO, A CORPORATION OF OHIO.

METHOD OF BUILDING AND STARTING ELECTRIC INDUCTION FURNACES.

Application filed September This invention relates to the construction and starting of furnaces of the induction type wherein there is a bath and U-shaped passageways or channels connected to the 6 bath; these channels being looped about a primary core and winding. and with the bath constituting a closed secondary circuit. In such a furnace experience has shown that considerable difficulty presents itself in maintaining the linings of the aforementioned channels and incidentally the proper cross section of metal in thechannels for efficient conductive functioning of the same.

The object of the present invention is to build and start a furnace in which the liir ing is so constructed that it can he maintained at a relatively cool temperature.

Another object is to construct the lining in such a manner that a part of the molding means can later be utilized as a starting means and other parts of the molding means as a permanent part of the furnace.

A further object is to use part of the molding means as a secondary for starting the furnace in which provision has been made to permit longitudinal and transverse expansion and thereby pre ent fracturing of the lining.

A further object is to construct and start an induction furnace in which part of the constructing means may be utilized to place the furnace in operation without resorting to the use of a preliminary molten charge.

The invention is hereinafter more fully described in connection with a convenient embodiment of the same as shown in the drawings and the essential features of the; invention are set out in the claims.

Referring to the drawings, in Fig. 1, I have shown a vertical cross section of a double loop induction furnace, which shows the relative thickness of the lining for the basin and channels, and the location of the primary, while Fig. 2 represents a supporting frame for such a furnace and the rel: tive position of the primary. In Fig.3, I have shown a mold and core for forming the loops, while Fig. 4 shows the manner in which the channel mold and core may be positioned with relation to the. basin support and primary. A vertical section of one loop mold and a part of the basin is shown in Fig. 5 after the refractory material has been 24, 1920. Serial No. 412,551.

filled in, while Fig. 6 is an end elevation of the completed loop mold and a section of the basin showing a starting charge in the basin; Fig. 7, is a view similar to Fig. 5, but showing the condition existing within the loop after the furnace has been placed in operation and Fig. 8 is an enlarged side elevation of a loop showing how the molding means may be utilized later as a reinforcing means for the channel walls.

In induction furnaces of the closed channel type, it is necessary to have the channels beneath the bath to obtain a hydrostatic pressure within the channels. As the channel walls are formed from refractory material considerable difficulty has been experienced in expeditiously molding and drying the same when using the channel coring means as a secondary for starting the furnace. The practice heretofore has been to use a solid metal core about which relatively' thick refractory walls were molded so that cracks, caused by the expansion of the solid core when used as a starting secondary, would not extend thru the full thickness -of the wall.

Another practice has been to use a wooden core that could be burnt out with a blow torch or be withdrawn after the lining material had dried and set. I have found. however, that by constructing a furnace with relatively'thin channel linings it is possible to maintain the linings at a comparatively low temperature by providing proper air circulation about them. I have also found that by thus maintaining the channel linings at a relatively low temperature the growth of any incipient cracks that may be present on the inside of the lining is prevented by reason of the solidification of a part of the molten metal within the. cracks.

I have likewise found that in order to construct a furnace with such channels it was essential to devise a coring means for forming the channels that would not crack the re fractory material when used as a secondary or starting means. I have shown an embodiment of such a core in the drawings of my application for a patent covering the same filed September 24, 1920, Serial .No. 412,550.

Referring to the various parts by numerals, 9 in Fig. 2 represents a metallic base or supporting frame for the refractory material that forms the hearth or basin of the furnace and from which the channel mold and core 11 (Fig. 3) are suspended through properly spaced h0les 12, 13 represents a primary that may be secured to the base by any convenient means. The mold, which may be composed of expanded metal or heavy screening, is first bent about the core to the desired shape and then suspended from the frame through the holes 12 in such a manner as to encircle one leg and winding of the primary. The open ends 14 of the mold 10 are then bent outwardly from the holes to form a seat as shown at 15, Fig. 4, after which a clamping and conducting bar 16 is bolted to the ends of the core. The core is then adjusted and suspended to be co-axial with the mold by any appropriate means such as blocks 17 so that'the end of the core may protrude above the basin after it has been molded. The refractory material best adapted to give the most efficient results has been determined, after considerable experimenting, and consists substantially of a homogeneous mixture of crushed magnesite and sodium silicate. The magnesite may be first mixed from several sizes of screenings of such size as to insure the filling of most of the voids, and this mixture may be then worked into a stiff plastic condition by the gradual addition of the sodium silicate, which may be in concentrated liquid form. The refractory material may then be forced into the channel molds and tamped to a consistent density about the cores as shown at 19, Fig. 5, after which the bottom 20 and sides 21 of the basin may be molded of the same material; the blocks 17 having been removed.

By removin the connecting bar 16 and withdrawing t e bars 20 from between the.

core rod 21 and core jacket 22, an unfilled space within the jacket may be provided t roughoutthe longituidnal length of the core, a part of which is later filled as the core jacket and core rod expand into it during the starting period. After the connect ing bar 16 has been replaced, a starting charge comprised of metallic chips may be heaped about the conducting bar 16, as shown at 18, Fig. 6, and a low voltage charge passed through the primary. As the channel core is short circuited by the conducting bar 16 the current induced in the core will gradually raise the temperature of the same and consequently expel the moisture from the channel linings. The voltage of the primary may be increased from time to time until the resistance of the core increases -the temperature to such an extent that the melting point of the metal composing the core is reached and the core, conducting bar and surrounding charge of chips is reduced to a molten mass. As more solid charge is added, the level of the metal is increased and the walls, as well as the basin, are completely dried out. A large enough charge is placed about the bar so that after having it reduced to the molten state a sufiicient level is obtained in the basinto insure conduction across the openings of the channels without an arcing effect taking place in the basin.

As the voltage in the primary is increased a breaking down or melting action likewise takes place on the outside of the furnace, for the channel mold also has a current induced in it from the fiux set up by the prima and has a tendency to circu ate through the mold and hearth support 9, but encounters a higher resistance at the seat 15 than at any other section of the mold. As the induced current flowing in the mold increases the greater resistance at the seat causes the heat to melt the mold away at this place, and consequently the exterior short circuit is eliminated.

By constructin and starting an induction furnace as have herein set forth it will be evident that I can build a furnace that may have a continuous and homogeneous liningand thereby eliminate the difiiculties encountered in sealing parting lines. which is necessary when the lining is builtin sections and then assembled.

It will also be evident that by my process it is possible to build a furnace with a relatively thin channel lining and thereby increase the life of the lining.

It is likewise to be seen that by my method an induction furnace may be built and started by means of a solid charge without a consequent fracturing of the refractory material which constitutes the lining; and. furthermore, it is evident that by the use of such a process as I have set forth the cost of building and starting an induction furnace may be greatly reduced.

Having thus described my invention, what I claim is:

1. The method of forming the refractory linin of an electric induction furnace and starting the same, which consists in providing a casing for a short circuited metallic core for forming the channel, in which casing there is suflicient cross-sectional air space to permit lateral dis lacement of the core when expanding, pac ing a refractory lining about the core, inducing a low current in the core to heat it and dry out the lining about the core and increasing the current to reduce the core to a molten mass.

2. The method of forming the channel linin of an induction furnace and preventing tie fracturing of the same, which consists in the use of a shell for a short circuited metallic channel core in which the expansion of the core is directed substantially toward the center of the shell and heating the core by an electric current to dry out the lining of the channel.

3. The process of forming a channel lining in an electric furnace and starting the furnace, which consists in'providing a short circuited U-shaped metallic core, one of the elements of which may expand and change position within the other without increasing the cross-section 'of the entire core, placin a refractor lining about the core, radua ly drying t e refractory lining by eating the core by means of an electric current, placing a metallic charge across the terminals of the core and reducing allof the metallic elements of the core and charge to a molten mass by means of an electric current.

4. The process of forming and dryin the channel lining of an electric furnace, w ich consists of shaping a jacket about a conductin rod to conform to the desired contour 0 the channel but with an unoccupied space between a portion' of the rod and jacket, acking refractory material about said jac et and rod, and passing a low voltage current through the jacket and rod to dry out the refracto material.

5. The process of rying and starting an electric induction furnace, which consists of providing an electrically conductive rod and a jacket therefor, of sufliciently larger crosssection than the cross-section of the rod, throu bout the length of the channel to permit t e rod to move laterally within the jacket, causing a relatively low voltage current to circulate through the core and jacket to heat both and therebydry out the refractory material which forms the channel lining, char in the furnace with non-molten metal an me ting the charge, core and 'acket, and finally increasingthe current w ereby the metallic elements may be reduced to a molten mass.

6. The method of forming the refractory linin of an electric induction furnace, and startin the same, which consists in providing a s ort circuited metallic core for forming the channel in which there is means for providing an unfilled space throughout the entire length of the channel to permit expansion of the core, providing the core with a removable element for maintaining the desired space, packing refractory material about the core, removing said element of the core after the refractory material is set, inducing a current in the core to heat it and dry out the lining and increasing the current to reduce the core to, a molten mass.

lining of an induction furnace and 7. The method of forming the channel reventing the fracturing of the same, which consists in the use of a metallic core wherein there is means for vacating a part of the crosssection of the same throughout the entire length of the core, whereby suflicient cross-sectional space may be provided to form a channel lining, heating vterial composed substantially of a the removal of'the bar may provide an unfilled space within the core, placing the mold and core co-axially and to encompass one leg of a primary, packing refractory material between the mold and core, withdrawing the aforesaid bar and inducing a cur-' rent in the core to heat it and dry out the lining.

The method of forming the refractory 9. lining of an electric induction. furnace, Whlc consistsv in homogeneously mixing screened magnesite of various sizes and a concentrated solution of sodium silicate to a plastic condition, providing a channel lining mold and a short circuited electrically conductive corefor forming the channel proper, tamping the refractory material into the moldand about the core, inducing relative- 1" low current in the core to heat it and ry out the channel lining, and finally reducing the core to a molten mass by the induction of a higher current in the same.

10. The method of forming an induction furnace lining, which consists in providing a metallic core in which provision is made for expansion of the core vmembers, mixing an assortment of fine magnesite screenings with a sufiicient amount of concentrated sodium silicate to work said magnesite into a homogeneous plastic mixture, placing said refractory mixture about the core to the core by an electric current to dry t e refractory material, placing a solid metallic charge acrossthe ends of the core to form ,a closed circuit and finally melting the core and charge by means of an electric current.

11. The method of forming and dryin the channel of an electric furnace, whic consists of molding plastic refracto maomogeneous mixture of ground magnesite and concentrated sodium silicate about a metallic conducting core, connecting the ends of the metallic core by means of a solid metallic charging rod, causing a low voltage current to traverse and dry out the channel refractory lining.

12. The process of forming a channel lining in an electric furnace and starting creasing the cross section of the core, plac ing: a refractory lining about the core which consists of a homogeneous mixture of ground magnesite and sodium silicate in plastic form, gradually (luring the retractory lining by heating the core by means of an electric current, placing the metallic charge across the terminals of the core, and

reducing the metallic elements of the core and charge to a molten mass by means of an electric current. 10

In testimony whereof, I hereunto allix my signature.

CHARLES A. BRAYTON, JR.

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