US2445866A - Apparatus for electric resistance heating of moving metallic strip - Google Patents

Description

July 27, 1948. G. P. WILSON ETAL 2,445,866

APPARATUS FOR ELECTRIC RESISTANCE HEATING OF MOVING METALLIC STRIPS Filed Aug. 9, 1943 3 Sheets-Sheet l INVENTORS Golda/R WsomLyleW/fazifzfzfibfidabhbfera BY sa e aw A TTORNEY July 27, 1948.

Filed Aug. 9, 1943 P. WILSON ETAL APFARATUS FOR ELECTRIC RESISTANCE HEATING OF MOVING METALLIC STRIPS 3 Sheefs-Sheet 2 INVENTORS Golder-B M75011,llj lekifiavazifivbdebwaters BY Rum 8.1310 66 ATTORNEY Filed Aug. 9, 1945 July 27, 1948. e. P. WILSON ETAL 2,445,866

APPARATUS FOR ELECTRIC RESISTANCE HEATING OF MOVING METALLIC STRIPS 3 Sheets-Sheet 3 INVENTORS Golda/'1 misc/1,4111; MMcMfrfWdel). 1mm

ATTORNEY Patented July 27, 1948 APPARATUS FOR ELECTRIC RESISTANCE HEATING F MOVING METALLIC STRIP Golder P. Wilson, Alton, Ill, Lyle W. McNair, Overland, Mo., and Wade D. Waters, Alton, Ill., assignors to Olin Industries, Inc., a corporation of Delaware Application August 9, 1943, Serial No. 498,008

3 Claims.

This invention relates to the heat-treating of metal and particularly to the continuous electrical heating of metal strip.

Various methods and apparatus have been described heretofore for heating metal strip, particularly in the form of Wire, by passing an elec tric current through the strip, the heatin being effected by the resistance of the strip to the electric current. In such resistance-type furnaces, the electric current has been supplied to the strip either by induction or by means of contact members, usually in the form of brushes, which are subject to wear and have the disadvantage, among others, that they must be replaced frequently. Likewise, such prior heating furnaces have for the most part the disadvantage that they are not adapted for the heating of wide metal strip, and particularly metal strip of high electrical conductivity such as copper and its alloys.

It is therefore an object of this invention to provide improved means for continuously heat-- ing wide metal strip of high electrical conductivityv Another object of this invention is to provide improved means for heating a moving metal strip.

Another object of the invention is to provide a furnace for continuously heating fiat metal strip having the advantages obtained by electrical induction heating and free of the disadvantages attending prior resistance-type furnaces.

Other objects and advantages will become apparent from the following detail description and accompanying drawing, in which Figure 1 is a plan view of an electric furnace illustrating one embodiment of this invention, and

Figure 2 is a side view, partly in section, of same, and

Figure 3 is a sectional View of a strip contact roll illustrating one embodiment of the invention, and

Figure 4 is a diagrammatic View of an electrical contact assembly illustrating another embodiment of the invention.

In accordance with this invention a novel process and apparatus are provided in which fluid conductors connected to a source of electromotive force supply an electric current through contact rolls to a moving strip of the metal to be heated. The moving strip is advanced length wise in a path designed to maintain the strip in contact with the rolls and the rolls are maintained in electrical contact with the fluid conductor, which, for instance, may be any suitable molten metal or liquid such as any suitable electrolyte or Woods metal or mercury. The electromotive force may be obtained from any suitable source, although in the preferred form of the invention, a transformer with a single turn secondary is employed.

Referring to the drawing, in one embodiment of the invention, the strip l of the metal to be heated is advanced lengthwise horizontally through the furnace over contact rolls 2 and 3. In order to insure good electrical contact between the strip 5 and rolls 2 and. 3, the strip is brought into contact with a substantial proportion of the roll surface by first passing the strip over roll 4 around rolls 2 and 3 and over roll 5.

In the preferred form of the invention, a transformer having a laminated core i l and a primary coil it with leads i3 is employed as the source of electromotive force for passing a current through the strip. The secondary of the transformer is a single loop comprising a stationary metal bar or plate it, liquid metal contacts 6, i, 8 and 9, metal contact rolls 2 and 3 and the moving metal strip I between the contact rolls 2 and 3 all of which are insulated from the supporting framework. The bar or plate partially encircles the primary I2 and is connected at one end to the liquid contacts 6 and 8 and at the other end to liquid contacts I and 9. Liquid contacts 6 and 8 are in contact with each end of contact roll 2 through axle 26 and liquid contacts 7 and 9 are in contact with each end of contact roll 3 through axle 21. A complete electric circuit is thus provided for the current induced from the primary I2, the current flowing through the plate or bar [0, the liquid contacts, the contact rolls and the moving strip l intermediate the contact rolls. By thus making the strip a composite part of the secondary loop of the transformer, one of the chief advantages of electric induction heating is obtained, namely a current of very high amperage and relatively low voltage may be passed through the strip without having to resort to any expensive leads to the liquid conductors or special sources of electric power, the usual 220 volt or 440 volt cycle power lines ordinarily available being entirely satisfactory for the input to the primary.

One form of contact roll, at 2 and 3 of Figures 1 and 2, embodyin this invention is illustrated in detail in Figures 3 and 4. The portion of the roll contacting the metal strip l is shown at 3| with metal axle 33 and cup-like metal flanges 32. The flanges 32 are partially submerged in the liquid contacts 35 which liquid 35 is contained in a metal box 34 joined to plate Iii. Good electrical contact is thus provided between the plate [0 and strip 1 through roll 3|, axle 33, flange 32, liquid rolls can be cooled by passing water'through the hollow portion.

In operation, the strip i may be passed through the furnace as a continuous length, for instance by stitching the ends of successive coils together;

or the strip may be handled in the form of individual coils. As illustrated in the drawing, a

coil of the metal to be heated may be unwound from a reel M on the charge side of the furnace and wound up on a reel 36 on the discharge side of the furnace. Any suitable type of reel may be employed, for instance any of the well known eX- pansible-core types 36, Figure 2, the expansion of the core and consequent gripping of the metal coil being effected for instance b operation of an air cylinder l5 with piston shaft l6.

As the strip l enters the furnace and leaves contact roll 2, it becomes progressively hotter'as it advances toward contact roll 3 on the discharge end of the furnace, the temperature being increased with the increased time of passage of the current through the strip. The strip may be cooled after it leaves contact roll 3 or, in order to prevent the strip while hot, and in some instances soft, from coming in contact with contact roll 3 and being scratched thereby or otherwise deformed, a quench pipe 2 5 may be employed to cool the strip just before it reaches contact roll 3. For instance, water or wet steam or other cooling medium, depending upon the speed of cooling necessary to give the desired physical properties of the metal may be injected through pipe 24 and sprayed on the surface of the strip I.

When it is desired to bright anneal or otherwise heat metal strip in a controlled atmosphere this may :be accomplished by enclosing the strip 5 between rolls 2 and 3 in a housing 29, which is provided at each end with openings permitting passage of the strip through the housing. For instance, when brass is annealed wet steam-may be injected through pipe 2Q on the hot strip l to cool the strip and the resulting superheated steam drives out the air and fills the housing 29. Likewise, depending on its temperature, the superheated steam may tend to preheat the relatively cool strip entering the housing 29 from contact roll 2 and thus effect a saving in heat. The COOIlnglndillIll, inert atmosphere and the like may be discharged from the housing 29 through any suitable outlet 30.

When the strip l is heated to relatively high temperature, any appreciable tension on the strip, for instance brought about in advancing the strip through the furnace, may result in some change in dimension of the strip, for instance a thinning of the strip due to stretching. This may be avoided by employing some suitable means for controlling the tension on the strip. For instance pinch rolls 23 adjacent the contact roll 3 andsimilar pinch rolls 3% adjacent the contact roll 2,

both having an adjustable screw-down for regulating the clearance. of the rolls,,may be operated in conjunction with the stripadvancing means to control or preventtension on thestrip between rolls.2 and 3.

For instance on the discharge side of the furnace, a motor 20 may be employed to drive the reel 36 acting through a suitable gear-train enclosed in box 22 and motor i5! acting through a suitable gear-train enclosed in box 37 may be employed as a drag generator, in the usual manner, operating with a dynamic braking action on pinch rolls 2?. Tension is thus provided on the strip l as it passes around contact roll 3 and a good electrical connection is thus provided betweenthe 'rolland strip. Similarly on the charge side of the furnace, motor is acting through any suitable gear-train enclosed in box teimay be employed to drive pinch rolls 38 which thencause the strip i to unwind from the coil supported byreel i i,- and motor ll acting through any suitable gear-train enclosed in box 2| may be employed as a drag generator, in the usual manner, having a dynamic braking action on reel I l. Tension on the strip l between pinch rolls 38 and reel M is thus provided so that a good electrical connection between the strip and contact roll 2 is obtained.

By employing such means for advancing the strip through the furnace, it is possible to prevent any tension, or to provide any desired tension, on the strip l between contact rolls 2 and 3. For instance, the speed of motor 20 which drives reel 38 may be set to provide the desired velocity of strip through the furnace. The speed of motor l3 which drives the pinch rolls 38 may then be so adjusted, for instanceby any suitable automatic regulator, as to provide the desired tension or slack in the strip l between the pinch rolls 23 and 38. The motors ill and i9, employed as drag generators, may likewise be provided with any of the well known automatic regulators for adjusting their field input to provide a constant tension in the strip as it passes over contact rolls 2 and 3. The usual manner of operating such motors as ill or it to obtain a dynamic braking action is accomplished, for example with motor l9, by supplying less power to motor i9 than is required to cause pinch rolls 23 to advance the strip as rapidly as it is being advanced by reel 36. The strip l passing through pinch rolls 23 instead of being driven by them therefore actu-' ally turns them faster than they are being driven by motor :9. The motor is is consequently driven by rolls 23 as a generator oifering resistance to the turning of pinch rolls 23 and putting tension on the strip between the rolls 23 and reel 36.

The furnace of this invention may be employed to heat metal strip of either high or low conductivity for instance in an annealing operation or in any other operation in which it is desired to continuously heat metal in strip form and any suitable source of electromotive force may (be applied to the fluid conductors. In the preferred embodiment described above an alternating current, which may be of either high or low frequency, or, for instance, any of the available standard commercial frequencies, is applied to the primary leads l3 and the strip is heated by the current induced in the secondary loop. The primary may be composed of a coil l2 with a laminated iron core it, or may consist of a coreless primary coil, or may consist of a primary coil wound about a leg of the core outside the secondary loop.

The temperature to which the strip is heated maybe controlled either :by the power input to the fluid conductors or by the speed of travel of the strip; that is, the higher the power input,

or the slower the speed of travel of the strip, the higher the temperature of the strip. For instance, employing a furnace designed in accordance with the preferred embodiment described above, yellow brass strip about 15 inches wide and 0.006 inch thick may be passed through the furnace at the rate of about 27 feet per minute with a power input into primary I2 of about 31 kilowatts per hour to yield about 540 pounds of brass strip per hour heated to about 700 C.

If it is desired to pickle the strip after it is heated, this may be accomplished by passing the strip through a suitable pickling bath as it leaves the furnace.

If it is desired to heat more than one strand of metal at a time, this may be readily accomplished in accordance with this invention, for instance by providing contact rolls for each of such strands and so connecting the liquid conductors accompanying the contact rolls that the moving strands are electrically connected in series, or parallel as desired, with respect to the source of electromotive force. Similarly, more than one strand of the metal may be heated by simultaneously passing a plurality of strands over contact rolls, either with one on top the other, for example in forming laminated sheet and the like or, for instance with narrow strands, side by side in parallel paths. The word strip, therefore, is used in describing the invention herein and in the claims in a sense inclusive of one or more strands of the metal to be heated.

This invention accordingly provides means for the economical continuous heat treating of magnetic or non-magnetic metal strip of either high or low electrical conductivity in the form of flat strip having any desired width, Wire, or the like and has a wide field of utility without being subject to all the limitations and disadvantages obtained with prior processes and apparatus.

It is to be understood that the embodiments of the present invention as shown and described are only illustrative, and that many changes may be made therein without departing from the spirit and scope of the invention as set forth in the following claims.

Having thus described the inventon, what is claimed and desired to secure by Letters Patent is:

1. In an electric furnace for heating moving metal strip, the combination which comprises a plurality of spaced metal rolls for contacting said moving metal strip, one of said rolls being on the charge end and one on the discharge end of said furnace, liquid electric conductors for supplying an electric current to said strip through said rolls, means for applying an elec-tromotive force to said liquid conductors, means for providing tension on said strip as it passes over each of said rolls and means for providing a substantially lesser tension on said strip between said rolls.

2. In an electric furnace for heatin moving metal strip, the combination which comprises a pluraltiy of spaced metal rolls for contacting said moving metal strip, liquid electric conductors for supplying an electric current to said strip through said rolls, means for applying an electromotive force to said liquid conductors to heat said strip, motor drive means in front of each of said rolls for advancing the strip over said rolls and drag-generator means in back of each of said rolls for providing tension on said strip as it passes over each of said rolls, means between said rolls for rapidly cooling said hot strip and a housing enclosing said strip between said rolls.

3. In an electric furnace for heating moving metal strip, the combination which comprises spaced metal rolls for contacting said moving metal strip one of said rolls being on the charge end and one on the discharge end of said furnace, liquid electric conductors for supplying an electric current to said strip through said rolls, means for applying an electromotive force to said liquid conductors, motor drive means in front of each of said rolls for advancing the strip over said rolls and drag-generator means in back of each of said rolls for providing tension on said strip as it passes over each of said rolls.

GOLDER P. WILSON.

LYLE W. MCNAIR.

WADE D. WATERS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 211,938 Shaw Feb. 4, 1879 1,398,866 Lauth Nov. 29, 1921 1,433,331 Angstrom Oct. 24, 1922 1,937,420 Wood et al. Nov. 28, 1933 1,992,553 Sykes Feb. 26, 1935 2,019,555 Wood et al Nov. 5, 1935 2,044,180 Newton June 16, 1936 2,278,136 Otis et a]. Mar. 31, 1942 2,323,903 Fentress July 13, 1943

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