US1884600A - Induction process of graphitizing carbon - Google Patents

Description

Oct. 25, 1932. I. H. DERBY 1,884,600

INDUCTION PROCESS OF GRAPHITIZING CARBON Filed April 23, 1951 2 Sheets-Sheet 1 Summon Ira E ery,

Gttorneg.

Patented ea. 25, 193.2v

UNITED STATES PATENT OFFICE IRA H. DERBY, OF INDIANAPOLIS, INDIANA, ASSIGNOR TO PETER C. REILLY, OF INDIANAPOLIS, INDIANA INDUCTION'PROCESS F GRAPHITIZING CARBON Application filed April 23; 1931 This invention relates to a process of graphitizing carbon, and articularly fabricated carbon bodies in the orm of rods, tubes, crucibles and the like. The graphitization is carried out by raising the carbon material which has been previously admixed with a suitable binder, and moulded and heated to a temperature suificient to drive ofi' the volatile matter, to the high temperature required for graphitizing by induction heating means which develops medium frequency currents directly in the carbon material.

In processes known heretofore, it has been thought to be impossible to graphitize carbon bodies of substantial size commercially, be

cause of expense and unreliability of apparatus, and even for graphitizing small masses of a diameter of four inches it was necessary to employ frequencies in the neighborhood of twenty thousand cycles per second.

In the patent to Edwin F. Northrup, No. 1,694,791, granted December 11, 1928, there is described an electric furnace in which materials can be heated by induction and I have found that this furnace may be modified to graphitize fabricated carbon bodies quickly and cheaply without the use of extensive and complicated apparatus.

In the above patent it was pointed out that for eflicient operation of the Northrup furnace, the magnetic induction should not extend beyond the center of the charge. I have found this especially true in the graphitizing of carbon material according to my method and I find it to be commercially practicable to graphitize fabricated carbon rods having a diameter of three inches or larger in a comparatively short time, and in a very simple and economical manner which requires considerably less energy than was necessary in processes known heretofore.

The induction heating may be carried out by employing currents of a frequency in the neighborhood of one thousand cycles per second by the use of rotating apparatus, such as a standard motor-generator set. The efliciency of the process resides in the fact that the heating occurs substantially directly in the carbon material where it is very effective in-bringing about the necessary changes temperature 0 Serial No. 532,379.

which characterize graphitization. The process is materially enhanced by surrounding the carbon material with a thick layer of refractory insulation which should also be a poor electrical conductor. Fine carbon powof carbon material which hasbeen fabricated by shaping a doughy mass of amorphous carbon powder admixed with a suitable binder such as tar or pitch and molded, pressed, or extruded to the form desired. After the plastic mass has been formed in the shape desired, the volatile matter is baked out of it before it is subjected to the graphitizing process.

The preliminary heating before the material is placed in the graphitizing zone may be advantageously carried out by placing the formed and baked mass which has reached a condition in which it is a conductor of electricity, in an internally fired retort such as is used in calcining carbon. The heating may be carried out by directly firing with gas or oil, or in any other convenient or inexpensive manner.

The process then consists in subjecting the 89 carbon body to progressively increasing temperatures up to the graphitizing point, and then to progressive cooling. This is preferably brought about by producing relative movement between the carbon mass and the 35 source of heat, and also contemplates moving the formed carbon mass with respect to the source of heat or maintaining the carbon mass stationary and moving the heating means. 90

During this reheating just mentioned, the

f the previously baked material is raised to approximately 1500 C. before it passes into' the graphitizingzone which is heated by induction coils supplied with medium frequency currents. In the graphltizing chamber or zone the temperature s raised to about 2800 C. or 3000 C. which is sufficient to change the carbon into graphite and to thereby materially increase its conv this process.

Fig. 2 is a horizontal sectional view of a modified form of apparatus for carrying out this process; and s Fig. 3 is a side elevation of the apparatus shown in Fig. 2.

Referring first to Fig. 1, the reference characters A, B, C, represent the preheating, the graphitizing and the cooling zones, respec tively, of one form of furnace which is suitable for carrying out this process. As here shown, the preheating zone A is made up of an inner wall or lining 4 of refractory material, and is circular in cross section, but it is obvious that any other suitable cross sectional form may be adoped. This refractory lining 4 may be made in the form of a single tube, or of bricks of any suitable size and shape.

intimately surrounding the inner wall 4 is a middle wall 5 of heat insulating material adapted to hold the heat inside the furnace and to reduce external 'radiation'to a very high degree. The walls 4 and 5 are held in proper relation by an external'sectional steel casing 6composed of short sections fastened together in any suitable manner known in the art. The details of the structure of this preheating zone are not important, it only being necessar that a chamber be provided capable of having heat delivered to it and re tainlng it through a period sufiicient to raise the incoming carbon material to a suitable temperature, usually in the neighborhood of 1500 C. Heat inlets and outlets 7 are provided .for the preheating chamber.

Directly inline with the preheating zone A and rigidly connected with it is a. graphitizing through the furnace. Outside of the insulating wall 9 is still another wall 10, nere shown as madeup of refractory bricks arranged to support within them electric heating coils 101 supplying the necessary induction currents to the furnace. Outside of the lining 10 is an outer casing 11 of insulation capable of withstanding high temperatures and yetformingan efiicientelectrical and heat insulator, v

Embedded within the wall 10 is a series of electrical conductors 12 to which current may be supplied through leads 13. These conductors are hollow and may have cooling fluid supplied to them through pipes 14 connected to their inletand outlet ends. The details of this furnace structure generally are old and Well known in the art, and are pointed out here merely as a practical embodiment which may be used in practicing processes embodying this invention. The use of powdered or thermatomic carbon as an electrical and heat insulator is, however, a special adaptation of the induction furnace to use with this invention.

Below the graphitizing zone B is a third or cooling zone C made up of an insulating Wall 15 and an exterior metal casing 16. The restricted outlet opening from graphitizing zone B flares and merges with wall 15 which is of cross section substantially the same as that of the inner wall 4 of zone A. The purpose of this cooling zone is to provide a heat insulating chamber into which the graphite is introduced from the graphitizing chamber and gradually brought from its extremely high temperature to ambient temperature by progressive steps so as not to produce any undesirable effects on the finished product.

The operation of the apparatus just described is as follows: The fabricated carbon bodies composed of carbon powder mixed with a suitable binder such as tar or pitch and compacted to a solid mass from which the volatile material has been baked out, are

introduced into the preheating zone A by suitable propelling and supporting means. As here shown the carbon bodies 17 are made up of rod-like sections connectedtogether by mortise and tenon joints 18 whereby the material made up of several sections may be made to pass through the furnace as an integral structure. The treatment to which the hardened bodies have been subjected prior to introduction into zone A renders them partially conducting to currents of electricity,

.and when they enter the zone A their temperature is raised to approximately 1500 C. As pointed out previously, this initial preheating may be carried out by any suitable mexpensive means, such as oil firing. Although the preheating zone Ais here shown in the form of a calcining retort, it is obvious i that this zone may be heated in any other suitable manner, as by the use of electrical resistance coils or by an electrical induction furnace, if desired.

From the zone A, the bodies pass through a restricted opening 8a of lining 8, and into the graphitizing zone where their temperature is raised to about 2800 or 3000 C. The movement of the bodies through the furnace is progressive and extremely slow so that in passing from the beginning to the end of the graphitizing zone,'the material will be raised to a sufiiciently high temperature and maintained at that temperature long enough to completely efi'ect graphitization. The heating coils 12 may be supplied with medium frequency alternating current so as to induce electric currents directly in the carbon material passing through the chamber thereby raising the temperature of the bodies. A frequency of a range between 60 and 2000 cycles is suitable for obtaining the desired temperature in the bodies to be graphitized. This rise in temperature from 1500 to about 3000 is brought about by supplying current by direct induction of electric current in the conducting material as distinguished from pri-- rents and radiates this heat to the carbon material.

When the graphiti zing process is complete, the graphitized product passes through the outlet opening 8?) from the graphitizing zone into the cooling zone C which is constructed in any desired form well known in the art for economizing the heat contained in the material, and conserving it until the temperature is slowly and gradually brought to a loW value where the product .can safely be subjected to room temperature without deleterious efiects.

Although this process is shown as applied to a rod-like mass,'it is obvious that by proper adaptation of the furnace, the process may be applied to bodies of any other shape and cross section in a similar manner. Among the great advantages may be mentioned the fact that it involves great economy in electri'cal heating, since the initial preheating temperature of the material to 1500 (l, or thereabouts, may be carried out by cheap fuel. Another advantage is that greater economies are possible in obtaining the graphitizing temperature since there are no great resistance losses, as in the resistance methods of graphitizing, the heat being produced directly in the carbon material or transferred from the surrounding furnace in such manner that extremely good heat insulation may be provided. Whereas processes heretofore known have required as much as three kilowatt hours of electrical energy to produce a pound of graphite, this process will produce a pound of'graphite by the expenditure of less than one kilowatt hour of energy, one kilowatthour being the maximum requirement.

In Fig. 1 the process is illustrated as being carried out with a stationary furnace through which the carbon bodies to be graphitized are continuously passed, but this arrangement is not essential. The relative movement between the carbon bodies and the source of heat may likewise be carried out in the manner illustrated in Figs. 2 and 3 21, an insulating covering 22, and a rigid outer support 23of insulating material. The outer wall of the furnace is carried by suitable supports 24 which space it from the supporting base on which the apparatus as a whole is mounted.

On either side of the furnace and in spaced parallel relation thereto are two electrically conducting rails 25 and 26 to which alternating current of suitable frequency is supplied from a generator 27. Mounted in bridging relation to the rails 25 and 26 and in electrically conducting contact therewith, is a car 28 having a plurality of metal wheels 29 contacting with the rails 25 and 26. Mounted on the car 28 is an induction coil 30 which surrounds the furnace wall 23 in inductive relation thereto. This coil 30 is connected to the wheels 29 in such manner that current from the source 27 passes through track rails 25 and 26, wheels 29, and coil 30, thereby producing electrical currents in the carbon mass 20 as in the apparatus heretofore described.

Suitable means may be provided for moving the car 28 along the furnace wall at any desired speed so as to insure that the graphitizing process is completed as the car travels along. This propelling means may be an electric motor geared to one axle of the car so=as to drive the car at the speed desired. The coil 30 may be supplied with cooling fluid from means carried by the car.

The apparatus shown in Figs. 2 and 3 is merely illustrative and is intended to indicate that this process may be carried out equally well by moving the carbon mass to be treated or by moving the source of heat. It will be obvious that when the car 28 has made a traverse from left to right,-or from right to left, as the case may be, to graphitize the material contained in the furnace, it must be returned to its initial position before a second charge can be treated. The details of the process will be sufficiently obvious to those skilled in the art without further explanation.

- Although there is herein shown and described only two forms of apparatus for carrying out processes embodying my invention, it will be obvious that various changes and modifications may be made in the details, within the scope of the appended claims,

without departing from the spirit-and scope of my invention.

What is claimed is k 1. A process of graphiti zing fabricated carbon bodies which consists in surrounding such bodies with elcctro-thermal refractory insulating material, and then heating such bodies by heat radiated from the inner surface of the insulating material and by currents induced directly in the bodies by analternating current source having a frequency not exceeding 2000 cycles per second.

2. A process of graphiti'zing fabricated carbon bodies in a coreless induction furnace, which consists in surrounding such bodies with carbonaceous electrical and heat insulating refractory material, and then raising the temperature of such bodies by heatradiated from the inner surface of the insulating material, and by currents induced directly in the bodies by the action of an alternating current source having a frequency not exceeding 2000 cycles per second.

3.' A process of graphitizing fabricated carbon bodies having a minimum lateral dimension in excess of three inches in a coreless induction furnace, which consists in surrounding such bodies with carbonaceous electro-thermal refractory insulating material, and then heating such bodies by heat radiated from the inner surface of the insulating material, and by currents induced directly in the bodies bythe action of an alternating current source having a frequency of 2000 cycles per second or less.

4. A process of heat treating fabricated carbon bodies in a coreless induction furnace at a temperature in excess of 2500 degrees Centigrade, which consists in surrounding the bodies with electrothermal refractory insulating material, and then heating such bodies by electric induction from an alternating current source having a frequency of 2000 cycles per second or'less.

In testimony whereof-I have signed my name to this specification.

ERA H. DERBY.

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