US1839613A

US1839613A - Electric furnace

Info

Publication number: US1839613A
Application number: US392556A
Authority: US
Inventors: Hans O Swoboda; William F Metzger
Original assignee: H O SWOBODA Inc
Current assignee: H O SWOBODA Inc
Priority date: 1929-09-14
Filing date: 1929-09-14
Publication date: 1932-01-05
Anticipated expiration: 1949-01-05

Description

Jan. 5, 1932. H. o SWOBODA ET AL ELECTRIC FURNACE Filled Sept. 14, 1929 2 Sheets-Sheet INVENIORS '0 $4, a 4M Patented Jan. 5, 1932 UNITED STATES. PATENT OFFICE HANS O. SWOBODA, OF EDGEWOOD, AND WILLIAM F. METZGER, OF PITTSBURGH, PENN- SYLVANIA, ASSIGNORS TO B. O. SWOIBODA, IN 0., OF PITTSBURGH, PENNSYLVANIA, A

CORPORATION OF PENNSYLVANIA ELECTRIC FURNACE Our invention relates to an electric furnace and, in particular, to an electric furnace having, among other novel features, a specially advantageous construction of the heated chamber, heating elements and supporting members therefor.

In electric furnace practice, it is highly desirable that the heat distribution throughout the furnace be as uniform as it is possible to secure. It is also desirable in some heat treating processes to prevent the treated material from coming in contact with atmospheric oxygen. Another desirable feature of electric furnaces is the provision of means whereby the temperature may be readily controlled and also means whereby zones of different temperatures may be provided. It is also advantageous to have the furnace structure as compact as possible and of such design as to permit easy removability of the heating elements and the heated chamber for renewal or repair.

The electric furnace of our invention is characterized by the fact that it substantially meets all the requirements outlined above. The results obtalned from our furnace are due 1n large measure to the novel arrangement and construction of the parts thereof which will now be described in detail, with reference to the accompanying drawings, in which Figure 1 is a vertical longitudinal section of a present preferred embodiment of our invention;

Figure 2 is a partial section of the embodiment of our invention partly in elevation;

Figure 3 is a perspective view of one of the refractory supporting blocks;

Figure 4 is an elevation showing one of the heating elements we employ in our furnace, and

Figure 5 is a view similar to Figure 4 showing a modification.

Referring in detail to the drawings, the embodiment of our invention about to be de scribed consists of a box-like supporting frame made up of angle irons 10 and sheet metal top, bottom and

end walls

11,12, 13 and 14. A plurality of legs partially shown at 15 afford a support for the furnace at a convenient workin height.

The inside of the furnace shown in Figure 1 is provided with

several linings

16, 17 and 18 of graded heat-insulating material preferably in the form of the usual refractory brick or its equivalent. The heat-resisting lining does not extend throughout the length of the furnace, but an insi e end plate 19 disposed adjacent the end all 14 provides a space for the reception of electrical connections, as will be described in greater detail later. The end plate 19 is secured to the side walls 20 of the furnace by means of suitable lugs 21. r

In accordance with our invention, we provide a novel form of heated chamber for the heat treatment of wire or metallic strip. The heated chamber isin tube 22 which extends the length of the furnace. The ends of the tube 22 are closed except for an opening suflicient to permit the introduction of the strip or wire to be treated by external flanges 23 which are secured to the end walls-13 and 14. It will be apparent that the tube 22 is positioned with respect to the furnace by means of the flanges 23 and that it can be readily removed by taking oil? the flange from either end of the furnace and sliding the tube longitudinally.

If the furnace is of considerable length, it may be desirable to construct it so that the body thereof is divided into an upper and the form of a metallic great length, since the upper portion may be lifted and the tube 22 tion.

Within the furnace, the tube 22 is supported by means of a series of T-shaped refractory blocks 24, such as that shown in perspective in Figure 3. The block 24 consists of a flat base or cap 25 and a vertical portion 26. A recess 27 of semi-elliptical form is provided in the vertical portion 26 and perforations 28 are connected with the recess by slots 29. The block 24 is also provided with a tongue 30 at one end of the vertical portion placed directly in posi- I tapered for engagement with corresponding.

26 and a corresponding groove 31 at the other end thereof. All the blocks 2 1 shown in Figure 1 are identical and when one block is superposed on another, as shown in this figure, the tongue groove 31 of the contact.

The perforations 28 in the vertical portion 26 of the blocks 24 are for the purpose of receiving heating elements 32 in the shape of a loop or hair pin. The structure of the heating element we employ is shown in detail in Figure 4:. We preferably make use of-a plurality of heating elements 32 disposed in the perforations 28 which are symmetrically positioned with respect to the recess 27 in which the heated chamber 22 lies. The arrangement of the refractory supporting blocks 24, the heated chamber 22 and the heating elements'32 may be readily observed from the showin of Figure 2.

The heating e ements 32 are connected in series or in parallel by means of connectors 33' and are energized from any convenient source of current through terminals 34. The elements may be connected in groups to different phases of a polyphase system. A bushing 35 is inserted in the furnace to provide an entrance for the power conductors. The hair pin loops are of s uare cross section andhave their ends rounde and 30 of one block engages the block with which it is in holes in the connectors 33. The cross sectional shape of the heaters maybe varied but the fewer contacts made thereby' with the sup orting blocks, the smaller is the amount eat lost by conduction. The heating elements may be withdrawn by removing the connectors 33 and the flange 23, after which the heating elements may be removed by sliding them longitudinally out of therefractory blocks 24.

In order that the temperatures of various portions of the furnace may readily be measured, we provide thermo-couples 36 at spaced points along' the heated chamber. A fuse 36' is provided to interrupt the supply of energy to the furnace if the temperature of the heating elements becomes excessive.

In operation, the heating elements 32 are connectedto a source of current through the terminals 34: and, when the heated chamber 32 has attained the material to be treated is drawn therethrough. As previously stated, this material is usually in the form of wire or strip and may be fed to the furnace from a reel supported adjacent the entering end of the chamber as indicated by the arrows. After passing through the furnace, the wire or strip may be passed throu h a water-cooled chill block or quenc the surfaces of which are lubricated with oil. In this case, the oil vapors will ass into the heated chamber and so provi e a non-oxidizing atmosphere therefor, as indibottom wall of the desired temperature, the

cated in United States Patent No. 1,603,165. Since the openings in the flanges 23 are comparatively small, there is but slight chance of atmospheric oxygen entering the heated chamber. We also contemplate the provision of means for supplying a non-oxidizing atmosphere from an external source. This means;may take the form of a conduit connected to the heated chamber through which a supply of inert or otherwise neutral gas may .be continuously introduced.

The furnace of our invention will be found particularly useful in connection with heat treating processes in which a number of heating steps are involved. In these processes, it will be advisable to employ a plurality of furnaces andsuch auxiliary treating apparatus as may be necessary, for example, motor-driven .means for drawing the'treated material through the furnace, chill blocks or quenches, and the like.

The tubular heated chamber 22 presents marked advantages over the lead or salt baths now used for heat-treating strip continuously. The use of rollers is avoided as Well as all bindin and distortion of the strip resulting there rom. The strip passes through the heated chamber without deformation and retains its normal straight condition through? out the whole process .which is of the straight-line type.

Our furnace provides means for treating strip material at a uniform temperature. The metallic tube 22 which serves as a heated chamber becomes uniformly heated by radiation from the heating elements 32 and any variation in the temperature of points adjacent the heatin elements is avoided because the tube 22 attains a temperature corresponding to the average temperature within the furnace. This permits the heaters to be ositioned close to the material to be heate but prevents any variation in the temperature within the heated chamber between adjacent heaters. The tube 22 also prevents wearing of the refractory blocks as the heated material asses through the furnace and maintains t e material in its normal, fiat shape. In addition, the tubular chamber 22 prevents atmospheric oxygen from gaining access to the material while it is under treatment and affords an enclosure which is absolutely gastight. Its function in equalizing the temperature within the furnace has already been explained. To accomplish these objects, the tube 22 should be of a heat conducting material having good wearing qualities. We

the heating elements and those more remote therefrom. It should not be too great, however, or the sensitivity of the control will be reduced.

By our arrangement of the heating elements and heated chamber, the material under treatment receives heat from both sides as well as above and below. This makes for a uniform product.

The modification of the hair pin loop heat ing element 32 shown in Figure 5 makes it possible to provide for zones of different temperatures within the furnace. Since the mag nitude of the current traversing any cross section of the heating elements is the same the amount of heat generated may be varied by varying the cross-section of the loop so as to vary the resistance thereof. In Figure 5, a hair pin loop 37 is shown having its ends 38 of smaller cross-sectional area than its mid portion 39. The result of this construction is to provide a high temperature zone at the entrance end of the furnace and a zone,

of lower temperature at the exit end. When a heater of varying cross section is employed, the perforations in the refractory supporting blocks will, of necessity, be so dimensioned as to permit passage of the largest section of the heating element.

The furnace described hereinabove makes possible the rapid and satisfactory treatment of metallic strip or wire and is readily adapt able to a large number of straight-line, heattreating processes. The temperature of the heated chamber may be readily controlled by means of well-known control devices.

Although we have described but one preferred embodiment of our invention, it will be obvious that numerous changes therein may be found desirable. As an example, the number and arrangement of the heating elements may be varied, as well as the dimensions of the heated chamber. Any change in the number of heating elements will neccssi tate a corresponding change in the design of the refractory supporting block, and, in the larger sizes, it may be advisable to form this block in two pieces instead of one. In order to lessen the loss of heat by conduction through the refractory blocks, the portions thereof which engage the heated chamber may be made of small area by chamfering the edges of the supporting projections or alter: nate projections may be shortened so as to be out of contact with the heated chamber altogether. Since the heating elem nts 32 are ofsquare cross section, they engage the supporting blocks only at their edges, so that the amount of heat transmitted through the line of contact is very small.

These modifications, however, as well as others which may occur to those skilled in the art, do not alter the spirit of our invention and are to be considered a part thereof if they are within the scope of the appended claims.

. We claim 1. In an electric furnace, a frame, a lining of refractory brick in said frame and heating means comprising two opposed series of T- shaped blocks each having a recess in the vertical portion of the T, a heat-conducting tube disposed in said recesses, alined perforations in said vertical portions adjacent said recesses and electric heating elements passing therethrough.

2. An electric furnace including a frame, a refractory lining therein and heating means comprising a plurality of T-shaped blocks in lateral alinement, a portion of the vertical leg of the T being cut away from said blocks, a heat conducting tube in said cut-away portion, transverse holes in said legs adjacent said portions and heating elements passing therethrough.

3. A furnace heater comprising a plurality of refractory members having spacing shoulders and body portions provided with alined openings, a heating element and a heated chamber extending therethrough.

4. An electric furnace including a plurality of alined refractory blocks each having a lateral spacing shoulder providing a free space between adjacent blocks, each block having transverse recesses, a tubular chamber in said recesses and electric heating elements traversing said blocks.

5. A furnace including a plurality of alined refractory blocks, each having spacing shoulders for separating the body portions of adjacent blocks, said body portions having recesses, a tubular chamber disposed in certain of said recesses and heating elements in other recesses.

6. A furnace including a plurality of refractory members having lateral spacing shoulders and spaced supporting fingers adapted to be alined for receiving a tubular chamber thereon and electric heatingelcments therebetween.

7. The combination with a tubular heating chamber, of axially disposed heating elements external to said chamber and transversely extending refractory supports for said chamber, said supports having spacing shoulders and spaced supporting fingers for engaging said chamber and heating elements at a plurality of spaced points and providing free spaces therebetween.

8. The combination with a heat-conducting tubular chamber of a plurality of spaced refractory blocks surrounding said chamber,

having spaced fingers for supporting the chamber .at certain points leaving the surface of the chamber largely free, and external heating means supported on said blocks.

9. A supporting block for furnace heating elements, having a lateral spacing shoulder thereon, fingers integral with said block for supporting a heating chamber thereon and receiving heating elements therebetween.

10. A refractory block for electric furnaces having a spacing shoulder along one side and provided with spaced fingers for supporting a heating chamber and for receiving a heating element for said chamber therebetween whereby a large portion of the chambers surface is subject to direct radiation from said element.

11. In a furnace, a refractory wall, a plurality of refractory blocks seated therein having abutting spacing shoulders and spaced supporting fingers for a heating'element, and a tubular chamber supported on said fingers parallel to said element so as to expose a large portion of its surface to direct radiation therefrom.

12. In a heater, an elongated metallic continuously extending heating chamber, supporting means for said chamber providing supports spaced axially and circumferentially of the chamber, and heating means intermediate said supports. I

18. In a heater, an elongated heat absorbing and heat distributing continuously extending heating chamber, refractory supporting means for said chamber providing supports spaced axially and circumferentially of the chamber, and resistance heating elements intermediate said supports and in ipaced heating relationship with said cham- 14. In a heater, an elongated metallic continuously extending heating chamber, supporting means for said chamber providing supports spaced axially and circumferentially of the chamber and extending in axial alinement one with the other, said supports providing alined openings therebetween, and axially extending heating means within said openings.

15. In a heater, an'elongated metallic continuously extending heating chamber, sup porting means for said chamber providing supports spaced axially and circumferentially of the chamber and extending in axial alinement one with the other, said supports providing alined openings therebetween, and axially extending heating means within said openings in spaced heating relationship with said chamber.

16. In a heater, an elongated metallic continuously extending heating chamber, refractory means embracing said chamber at points spaced axially thereof, said supporting means each providing a plurality of circumferentially spaced chamber supporting fingers, and resistors intermediate said supports and in spaced heating relationship to said chamber, said chamber being of such thickness and so disposed with respect to the resistors as to effect a uniform temperature distribution within the chamber.

17., In a heater, an elongated metallic continuously extending heating chamber having chamber having open ends for the continuous passage therethrough of the material to be heated, refractory supporting means for said chamber providing supports spaced axially and circumferentially thereof, and heating means intermediate said supports.

In testimony whereof, we have hereunto set our hands.

HANS O. S /VOBODA.

WILLIAM F. METZGER.