US3373966A - Apparatus for forming large carbonaceous bodies - Google Patents

Description

March 19, 1968 G. ROWE ET AL 3,373,966

7 APPARATUS FOR FORMING LARGE CARBONACEOUS BODIES Filed Dec. 1, 1965 INVENTORS /4 GAYLE L. IROWE J9EE RWILSON BY ATTORNEY United States Patent Ofi ice 3 ,3 73,966 Patented Mar. 19, 1968 3,373,966 APPARATUS FOR FORMING LARGE CARBONACEOUS BODIES Gayle L. Rowe, Parma Heights, and Joe R. Wilson, North Olmsted, Ohio, assignors to Union Carbide Corporation, a corporation of New York Filed Dec. 1, 1965, Ser. No. 510,921 5 Claims. (Cl. 249-80) This invention relates to an apparatus suitable for forming large diameter carbonaceous bodies.

A process which is currently employed for making carbon articles is the subject of US. Patent 3,092,437. This process uses as the starting material an electrically conductive mixture of comminuted carbonaceous materials such as carbon and graphite particles, and sulfur. After intimate blending of the raw materials, the mix is enclosed in a mold and a pressure, sufiicient to compress and decrease the volume of mix by approximately 20%, is applied thereto. Generally, a pressure of at least 500 pounds per square inch is required with a relatively coarse particle blend, and for finer materials, pressures as high as 1200 pounds per square inch or higher are required. The compressed blend is then uniformly heated while it is in the mold and while subjected to pressure as in the compacting process to a maximum temperature of 400 C. and usually to about 350 C. or until the binder material, such as pitch, has become thermoset, but not to a temperature at which the binder is carbonized. The initial temperature rise should be high enough to allow the sulfur in the mix to become dissolved in the pitch throughout the mold charge and later must be increased to a level at which the sulfur and pitch react to provide a thermoset bond in the carbonaceous body. Uniform heating of the compacted blend is best accomplished electrically and the preferred method is by the passage of an electric current therethrough.

The above-described process has been successful in the fabrication of carbonaceous articles having a diameter of up to 40 inches. However, the formation of larger articles or billets is impractical since electrical resistance heating cannot be practically employed. This is true be cause the required transformer output current increases as a function of the cross sectional area of the carbonaceous body being formed. Thus, if the diameter of the body were 70 inches, the required transformer rating would exceed that of any standard commercially available transformer. Of course, a special transformer might be constructed to provide the required low voltage and high current output, but other difiiculties such as nonuniform heating due to current channeling, and the cost of attendant tooling such as current distribution pressure rams, large and complex copper shunts, etc., would still prevail. Therefore, in order to form extremely large diameter carbonaceous bodies, a different manner of heating, such as induction heating is preferable. The use of induction heating involves the use of a high strength electromagnetic field and this, coupled with the high pressures and temperatures which must be employed in the process, necessitates the use of special apparatus heretofore unavailable.

It is the primary object of this invention, therefore, to provide an induction heating apparatus which is capable of withstanding high pressure and temperature for the formation of extremely large diameter carbonaceous bodies.

Other objects and advantages of this invention will become apparent from the following description, taken in conjunction with the accompanying drawing, wherein:

FIGURE 1 is a cross sectional view of one embodiment of the apparatus of the invention;

FIGURE 2 is an elevational view in section partially broken away of an embodiment of a cooling means which is an essential component of the apparatus of FIGURE 1; and

FIGURE 3 is a top sectional view taken along lines 33 of FIGURE 2.

Broadly stated, the invention comprises an improvement in an apparatus for forming large diameter carbonaceous bodies by induction heating means which improvement comprises a fiberglass mold shell having an epoxy resin bond therein, a cooling means placed in proximity to the fiberglass shell, and a refractory lining placed adjacent the cooling means. The fiberglass mold shell provides the hoop strength component of the apparatus and enables the apparatus to withstand over 2000 pounds per square inch of pressure on a confined mix or body. The cooling means maintains the temperature at the inner surface of the fiberglass mold shellwell below the temperature at which the epoxy resin bond contained therein softens. This is an important consideration since the curing temperature which is employed in the process of forming a carbonaceous body is almost twice that at which the epoxy resin bond material will soften. Since the cooling means will be positioned within a strong electromagnetic field, a special configuration is required and one embodiment of a suitable cooling system is hereinafter further described. The refractory lining, which surrounds the cooling means, serves the dual purpose of providing a partial heat dam between the charge material and the cooling means, and also provides a smooth surface whereby the carbonaceous body may be easily removed from the apparatus after processing.

Referring now to FIGURE 1, an apparatus 10 which is employed in the formation of large carbonaceous bodies comprises induction heating means 12 which enclose a fiberglass mold shell 14 is cooling means 16 which is surrounded by the refractory liner 18. A carbonaceous charge 20 having been surrounded by a coke packing 22 is situated within the area defined by the refractory liner 18. Pressure is ap plied through suitable rams and extensions such as asbestos board extenions 24, 26, wood extensions 28, 30, 32 and a steel ram 34. Wood, asbestos or other materials which are not thermally affected by the inductive field should be used for the extensions.

In operation, heat is generated within the carbonaceous charge 20 by the electro-magnetic field created by the induction coils 12 Cooling means 16 is so structured and so positioned "within the electro-magnetic field as to be minimally aifected thereby and thus cools the inner face of the fiberglass shell 14. Pressure is applied to the charge 20 through the various extensions 24-34 thereby forming the charge.

The cooling means 16 which form a part of the apparatus 10 is illustrated in FIGURES 2 and 3.

Referring to FIGURE 2, a cooling means 16 comprises a plurality of thermally conductive tubes 36 arranged substantially parallel to the mold axis and perpendicular to the induction coils 12. The tubes are separated at certain places (for example, number 38 in FIGURE 2) in order to minimize the effect of circular eddy current 14. Contiguous with the mold shell paths. An electrically conductive sheet 4 2 is attached to the tubes 36 and is a part of the cooling means 16. The sheet 42 which is split or separated at various places (illustrated by numeral 44 in FIGURES 2 and 3) prevents hot spots from forming in the fiberglass shell 14 during operation. The sheet 42 is also provided with a plurality of grooves or slots 48, to reduce circular eddy current paths.

FIGURE 3 illustrates, by means of a top view, several essential components in the apparatus of the invention. In FIGURE 3, the fiberglass shell 14 encloses cooling means which comprises sheet 42 and tubes 36 attached thereto. The tubes are surrounded by the refractory lining 18. The separations 44, in the sheet 42 are also illustrated.

It has been dis-covered that an efficient cooling system is achieved by using copper tubes having a /2 inch diameter and, in addition, a sixteen ounce copper sheet brazed to the copper tubes. It is important to note that the tubes must be perpendicular to the coils of the induction means and substantially parallel to the magnetic field produced thereby in order to avoid heat generation therein due to the electro-magnetic field. Cooling is provided by passing water or other suitable coolant through the tubes at any convenient, flow rate. Other suitable material such as aluminum may be used for the tubes and the sheet. However, copper is preferred since it is inexpensive and is characterized by an excellent thermal conductivity. It has been discovered that the novel cooling means described herein performs extremely well in the apparatus of the invention. It will be appreciated, however, that modifications of this system may be made without departing from the scope of the invention.

The refractory liner may be composed of any suitable material such as alumina. The materials must be chosen such that the liner when placed in a mold affords a smooth finish and a high thermal resistance. A typical material which is satisfactory is a product manufactured by Refractory Insulation Company, a subsidiary of Combustion Engineering Corporation, the product being named R & I Hot Top Moldit.

The following example indicates a typical process in which the apparatus of the invention is useful.

Example A 58" carbonaceous billet was prepared by placing a carbonaceous charge comprising the following ingredients in a mold similar to that illustrated in FIGURE 1:

The charge material was first for-med into a solid billet before being in position in the apparatus of the invention. Pre-forming was accomplished by heating the charge to a temperature between 110 C. and 130 C. while in a auxiliary mold initially under a pressure of about 500 lbs./in. and finally at about 8001200 lbs./ in; The preformed billet, having been placed in the apparatus of the invention, was then subjected to a temperature of approximately 300 C. and a pressure of 825 lbs./in. The apparatus included as the cooling means a 16 ounce copper sheet having /2" copper tubes brazed thereto. The sheet was divided and separated into six sections as indicated by numeral 44 in FIGURE 2. A fiberglass mold shell surrounded the cooling means and a refractory liner composed of R & I Hot Top Moldit surrounded the cooling tubes.

The temperature at the interface between the fiberglass shell and the refractory liner was found to be approximately 70 C. maximum at the curing tempera ture of 350 C. in the above-described test. An average temperature at approximately eight points along the interface during the curing cycle indicated that the temperature at the interface was approximately 35 C. throughout the cycle. Under a maximum pressure of 785 lbs/in? the ram-s had a maximum travel of 6.75" during the test. Although the preforming has been indicated as being carried out in an auxiliary mold, the charge material may be preformed within the apparatus of the invention by centrally positioning the loose charge in the mold cavity and within a thin walled sleeve which is withdrawn from the cavity after a coke particle envelope is deposited in the annular space between the sleeve and the inner surface of the mold. By this arrangement the preforming and curing phases of the process occur sequentially within the same apparatus without interruption of the heating cycle. It will be appreciated that any type of dry carbonaceous mix regardless of the binder and filler systems may be processed in the apparatus of the invention as long as pressure is employed during curing of the mix. As another example of a mix which may be satisfactorily employed, the following composition is listed.

A performed carbon or graphite body could be heated to as much as 3000 C. within the apparatus of the invention by induction heating by simply replacing the coke particle envelope 22 in FIGURE 1 with a thermatomic black mixture which would serve as a thermal barrier between the hot charge and the refractory liner. A 3" thick layer of thermatomic black is sufficient. This system could operate fast (650 C. per hour) or slow (25 C. per hour) heating rates.

Induction heating of the carbonaceous bodies and compacted carbonaceous mixes in the apparatus of the invention can be carried out with a wide range of power input by frequency selection. In a 58 diameter graphite billet test a frequency of 180 cycles per second was used as the power soure. As the resistivity and size of the charge varies, it is possible to select a power source with a frequency output that optimizes the particular heating requirements of a specific application. A frequency range of 60 cycles to 4000 cycles per second is preferred.

It will be appraciated that the apparatus of the invention provides a heretofore unavailable means of producing extremely large diameter carbonaceous products when employing induction heating and high pressures. Carbonaceous bodies having diameters of 40 to inches or. more may be readily produced. Fairly uniform heating of the product during the forming phases is easily accomplished in the apparatus of the invention and the product produced has a high quality and structural in tegrity.

What is claimed is:

1. In an apparatus wherein a large carbonaceous body is produced by the application of high pressure and temperature, said high temperature being produced by the electro-magnetic field of an induction heating means, the improvement which comprises a fiberglass mold shell, a refractory liner adjacent to said fiber glass shell, and cooling means positioned between said shell and said liner, cooling means being so structured and so positioned as to be minimally affected by said electromagnetic field whereby said shell is cooled during the application of heat to: said body.

2. The apparatus of claim 1 wherein said cooling means comprises at least one thermally conductive tube substantially parallel to the field produced by said induction:

means, a thermally conductive sheet attached to said tube, said sheet being circumferentially positioned contiguous with said fiberglass sheel and being separated so as to divide said sheet into segments, and a cooling liquid in said tubes.

3. The apparatus of claim 2 wherein said sheet segments have at least one groove therein.

4. The apparatus of claim 3 wherein said tube and said sheet are composed of copper.

5. The apparatus of claim 4 wherein said cooling liquid is water.

References Cited UNITED STATES PATENTS Ford et a1 1847 Frost et al 184 7 Williams 1816 Wagner 18-47 Thiess 18-47 Wagner 18-16 J. HOWARD FLINT, J R., Primary Examiner.

Claims (1)

1. IN AN APPARATUS WHEREIN A LARGE CARBONACEOUS BODY IS PRODUCED BY THE APPLICATION OF HIGH PRESSURE AND TEMPERATURE, SAID HIGH TEMPERATURE BEING PRODUCED BY THE ELECTRO-MAGNETIC FIELD OF AN INDUCTION HEATING MEANS, THE IMPROVEMENT WHICH COMPRISES A FIBERGLASS MOLD SHELL, A REFRACTORY LINER ADJACENT TO SAID FIBER GLASS SHELL, AND

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