US 3210455 A
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Oct 1965 K. SEDLATSCHEK 3,210,455
INDUCTION FURNACE SUSCEPTOR ENCLOSURE FOR DEVELOPING HEAT BY INDUCTION CURRENT AND THE METHOD FOR PRODUCING SUCH SUSCEPTOR ENCLOSURES Filed May 17. 1961 INVENTOR. (1419A 51501 A 7176/7654.
United States Patent M 3,210,455 INDUCTION FURNACE SUSCEPTOR ENCLOSURE FOR DEVELOPING HEAT BY INDUCTION CUR- RENT AND THE METHOD FOR PRODUCING SUCH SUSCEPTOR ENCLOSURES Karl Sedlatschek, Singervilla, Reutte, Tirol, Austria, assignor to Schwarzkopf Development Company, Dobbs Ferry, N.Y., a corporation of New York Filed May 17, 1961, Ser. No. 112,743 Claims priority, application Austria, May 17, 1960, 3,7 5 1/ 60 2 Claims. (Cl. 13-27) This invention relates to furnaces in general and more particularly to induction furnaces having a metallic susceptor enclosure of large size.
In recent years there has been developing increasing need for shaped bodies formed of refractory metals such as tungsten, molybdenum, tantalum, niobium and alloys of these metals which all have a high melting temperature, namely above 2,000 C. Such bodies are usually produced by powder metallurgy techniques, for instance, by compacting powder bodies of such refractory metals into the desired shape and thereafter giving the compact the desired strength by a known type of heat treatment wherein the compacted refractory mounted particles are sintered into a strong shaped metal body.
In the past where feasible the refractory metal powder was compacted into rods through which electric heating current was passed in a suitable non-oxidizing surrounding until the compacted particles of the rod have reached the required sintering stage. In case of large sintered metal bodies or, for instance, in case of short sintered bodies with large cross sections, it is not feasible to heat them directly to sintering temperature by passing current through such bodies. In such cases the compact of refractory metal powder particles must be sintered through indirectly applied heat in high temperature sintering furnaces. For such indirect sintering of refractory metal particle compacts, extensive use is made of induction furnaces utilizing susceptor enclosures.
The susceptor enclosure is electrically conductive and carries induced electric current for developing heat with which the surrounded to-be-sintered compact is heated to the desired sintering temperature. Such induction furnace susceptor enclosures may be formed of graphite or high melting metals. The use of a susceptor enclosure of graphite is limited by the fact that the surrounded sintered compact may accept or combine with some of the carbon of the susceptor enclosure. Accordingly, in many applications susceptor enclosures of refractory metal having high melting temperature, such as tungsten or molybdenum, are used. However, great technical difficulties are encountered in producing induction furnace susceptor enclosures out of refractory metal such as tungsten, molybdenum and their alloys in cases where the cylindrical or crucible shaped susceptor enclosure has to be of large volume for surrounding the required corresponding large volume of the to-be-sintered refractory metal compact.
Construction of strong large volume induction furnace susceptor enclosures out of such refractory metals requires large compacting presses and large high temperature furnaces for sintering the large volume refractory metal susceptor enclosures under a protective non-oxidizing or reducing atmosphere. Proposals have been made to form such large cylindrical susceptor enclosure of superimposed rings of refractory metal. However, the production of such large refractory metal rings in itself presents great difficulty.
It should be noted that induction furnace susceptor enclosures of high melting refractory metals have application not only for sintering of shaped bodies of refrac- Patented Oct. 5, 1965 tory metals but also for the production of metals by chemical conversion of metal carbides or metaloxides, for instance, in the production of tantalum or niobium powder. Such induction furnace susceptor enclosures are also of value in the production of cemented refractory metal bodies such as metalcarbides, metalborides. All these applications require for economic reasons the use of large induction furnaces with correspondingly large susceptor enclosures.
An object of the invention is to provide large induction furnace metallic susceptor enclosures, for body aggregates that are to be heated within the induction furnace, that overcome the difiiculties heretofore encountered in producing such large susceptor enclosures. In accordance With the invention, large induction-furnace susceptor enclosures are formed of a plurality of complementary arcuate enclosure segments each produced separately out of refractory metals and thereafter assembling the complementary enclosure segments along their complementary abutting segment-boundary surfaces and thereafter sintering the assembly of complementary enclosure segments at elevated temperature to form the desired large metallic susceptor enclosures.
The invention will now be explained by reference to the accompanying drawings wherein FIG. 1 shows a portion of an induction-furnace susceptor structure exemplifying the invention, and
FIG. 2 is a perspective view of an arcuate section of the susceptor structure of FIG. 1.
Induction-furnaces operating with susceptor structures have been long known in the art, having been described, for instance, in French Patent 590,537 of 1925. In connection with all such known induction-furnaces, it was very diflicult to provide large-volume or large-size susceptor structures out of refractory metals having high melting temperatures, such as, tungsten, molybdenum and their alloys. In accordance with the invention, these heretofore encountered difliculties are eliminated by forming the required large-size refractory-metal susceptor structures out of complementary interfitting small refractory-metal wall segments, each of which is readily produced with available conventional induction-furnace equipments. These individual refractory wall segments are then assembled into the desired large size refractory metal susceptor structures of substantial uniform wall thickness with their complementary surfaces engaging each other. Thereupon, heat, as by a surrounding induction coil system, is applied to the assembly of the engaging interfitting wall segments to cause their abutting complementary surfaces to be joined by sintering to each other into an integral large volume susceptor structure.
FIGS. 1 and 2 show one form of a large-volume refractory metal susceptor structure 10 exemplifying the invention. The large-volume susceptor structure 10 is shown as being of the conventional tubular or cylindrical shape and consists of a united assembly of small-size refractory wall segments 11. In the form shown, all of the individual wall segments are alike in size and each has sideend faces 12 and top and bottom faces 13 shaped for complementary fit and engagement with the corresponding faces 12, 13 of the four adjoining Wall segments 11 assembled adjacent to each other into the required large-volume susceptor structure 10. FIG. 1 also indicates the water cooled hollow metallic induction coil 16.
As an example, a large cylindrical susceptor enclosure is formed of sintered particles of molybdenum or tungsten or their alloys having a melting temperature of 2,000 C. First arcuate segments of such cylindrical susceptor enclosures are formed with an arcuate width that permits compacting the particles with a relatively small compacting press. The segmental cylinder segments are sintered to the desired strength in a relatively small sintering furnace to facilitate the formation of sintering junctions between the individual assembled susceptorenclosure segments. Their abutting edge surface may be given an interfitting profile for instance, the adjacent boundary segment with the complementary abutting edge surfaces of individual arcuate segments of a cylindrical susceptor enclosure being formed with a complementary V-shaped edge surface.
In other words, one end surface of each individual sintered segment of such cylindrical susceptor enclosure has the shape of a V-shaped depression while the opposite end surfaces of the segment has a V-shaped projection fitting into the V-shaped depression of the adjacent similar complementary susceptor enclosure-segment. Alternatively, one end edge region of each segment of such refractory metal cylindrical susceptor enclosure may have a smaller wall thickness with an interior concave side surface and the opposite end region of such segment may have a correspondingly reduced wall thickness with the convex outer side surface of the segment which overlaps and fits into the concave interior surface of the narrow end region of the next similar segment so that when the complete array of so shaped segments are assembled into a complete annular body, their respective overlapping complementary concave and convex end regions will form a continuous cylindrical susceptor enclosure of substantially uniform wall thickness, after the segments have been sintered along the abutting complementary side surface regions, as described above.
The individual segments of the metallic sintered enclo-- sure when so joined will establish good mechanical and electrical conductive connections along their sintered overlapping junction regions to increase the mechanical strength and increase the electrical conductivity at the sintered junction edge surface regions of the individual segments of such hollow metallic susceptor enclosure. A foil of metal or a stratum of metal powder particles may be placed in between the overlapping abutting segment boundary edge surfaces of the assembled suceptorenclosure which may be formed of a lower melting alloy than the metal body of the enclosure to assure good electric conductivity between the sintered junction surfaces or junction regions of the so-formed susceptor enclosure.
The sintering of the complementary refractory metal segments into a strong integral electrically highly conductive induction-furnace susceptor enclosure may be effected either in an available sintering furnace of suitable size or may be sintered in the induction furnace in which the susceptor enclosure is to be placed. In the latter case this may readily be done because the assembled segments may be held together by a spiral winding around the assembled susceptor segments a wire or strip of refractory metal such as tungsten, molybdenum or their alloys out of which the individual segments have been made. The soassembled individual segments will have induced therein electric currents which will heat them to the desired sintering temperature at which the abutting interfitting side edge surfaces of the individual segments will be joined to each other to achieve a mechanically strong junction region of the required electrical conductivity. Such joining the individual refractory metal segments into the strong large susceptor structurefor instance by sintering in the inductor furnace wherein it is to be used, as described above-is done under a protective atmosphere which is usually used in forming sintered bodies out of similar refractory powder particles. The Treatise on Powder Metallurgy by C. G. Goetzel, copyright 1949 by Interscience Publishers, Inc., volume 1, chapter XVII, pages 621-649 describes the protective atmospheres required for such sintering operations.
Thus, furnace susceptor enclosures of the invention,
formed of an assembly of complementary refractorymetal enclosure segments joined to each other by electrically conductive mechanically strong sintered junction regions along their overlapping complementary side edge surfaces have various advantages:
(1) Because of the small size of the susceptor-enclosure segments they may be readily produced without requiring large cross-section sintering furnaces.
(2) The susceptor enclosure formed of such complementary refractory metal segments may be provided with any desired number of larger or smaller openings. Such openings may be required in cases where the compacted body which is heated by induction within the susceptor enclosure develops gases which are permitted to pass through the susceptor enclosure openings and be evacuated from the interior of the induction furnace.
(3) In case the heating develops a crack along a wall segment of a susceptor enclosure of the invention, the crack cannot propagate further beyond the boundary of the segment. In addition, the damaged segment can be cut away and replaced by another segment which is again affixed by sintering with the facing end surfaces of the remaining integral susceptor enclosure from which the damaged segment has been removed.
(4) The individual arcuate segments may be provided along their facing end surface with the proper large overlapping junction surfaces along which they are readily sintered to provide between them a strong mechanical junction and a good electrically conductive connection.
The features and principles underlying the invention described above in connection with specific exemplifications thereof, will suggest to those skilled in the art many other modifications thereof. It is accordingly desired that the appended claims shall not be limited to any specific features or details described in connection with the exemplifications thereof.
It is claimed:
1. In combination with an induction current furnace for heating a body to a desired high temperature by heat developed through induced current in the interior of furnace space, of a metallic susceptor enclosure at least partially surrounding said body and effective in carrying in the walls of said enclosure induced electric current and thereby applying heat to said body, said susceptor enclosure consisting of a plurality of arcuate complementary metallic enclosure segments adjoining each other along complementary abutting surfaces, said enclosure segments being affixed tov each other along their complementary abutting surfaces by sintered junction regions.
2. In combination as claimed in claim 1, the complementary abutting surfaces of complementary enclosure segments having complementary overlapping profiles along which they are joined by said sintered junction regions.
References Cited by the Examiner UNITED STATES PATENTS 2,227,176 12/40 Berghaus et al. -221 2,462,289 2/49 Rochow 26430 2,621,123 12/52 Hoyer 75-221 2,747,006 5/56 Barnard 13-27 2,764,887 lO/ 5 6 DAmbly. 2,814,657 11/57 Labino 13-6 2,826,624 3/58 Reese et al. l3-27 3,056,847 10/62 Junker 1327 FOREIGN PATENTS 262,439 3/28 Great Britain.
590,537 3/25 France.
RICHARD M. WOOD, Primary Examiner. MILTON Q- H RSH lELD, Examiner.