FR2740646A1 - COLD CAGE FOR INDUCTION DEVICE - Google Patents

Abstract

The invention relates to a cold cage for a device for induction of revolution around an axis (XX) divided into sectors (2), each sector (2) comprising an internal metal partition (10) and at least one part of the external partition ( 20) of electrically insulating material, as well as a fluid circulation means. To achieve this means, the invention consists of hollowing out at least two cooling channels (11, 12):. either in the internal metal partition (10), perpendicular to its external surface (10b),. either in the external insulating partition (20), perpendicular to its internal surface (20a), and to join the two partitions (10, 20) so as to close and seal the channels (11, 12).

Description

The present invention relates to cold cages used either in the

  field of electromagnetic induction fusion, either in the field of inductive plasma production or in the field of electromagnetic confinement. Such cold cages are in particular the main element of cold crucibles in which the electromagnetic induction melting of refractory materials, such as metals melting in

very high temperatures.

  In a plasma torch, an inductive coil heats and confines the plasma. A device called cold cage evacuates the heat released by the inductive plasma

which could damage the coil.

  In general, the term cold cage will be

  used in this description to refer to the

  cooling structure of a plasma torch

  inductive or inductive cold crucible, indifferently.

  Such cold cages are generally formed of several partitions assembled to form a body of

  revolution, in particular a cylinder.

  Cold cage partitions made of a good heat conducting metal and cooled by

  a circulation of a coolant.

  As such a cage is disposed within an inductor, which generates currents in the material to be melted or the plasma, induced currents are also born in the metal partitions. These parasitic currents reduce the penetration of the magnetic field into the material. They also reduce the cooling efficiency because the partition itself is directly

heated by induction.

  FIG. 1 illustrates a conventional cold cage structure, as described in the document

FR-A-2 629 299.

  In such a cylindrical cage 1 of axis O-O, partitions in the form of longitudinal sectors 2 arcuate are

  arranged in a circle like the moat of a barrel.

  Sector partitions 2, made of copper, are glued edge-to-edge with intermediate insulating joints. This segmentation prevents the development of induced currents

  following a complete outline of the crucible.

  Each sector partition 2 consists of metal walls welded edge to edge to form longitudinal channels 4 of cooling fluid circulation. Thus, each metal partition, in contact with the molten material or the plasma, is cooled. However, induced currents occur in each sector because the applied magnetic field has axial and radial components while the cross section of a sector wall has a metal outline. Figure 2 illustrates another known structure of

  sector 2 of cold crucible, cross-sectional view.

  Each sector 2 is composed of an arcuate plate 5 of stainless steel glued to a ceramic channel 6. The channel 6 forms a cooling channel 4 surrounded by ceramic edges 7 and 8, extending radially, and a bottom ceramic 9 forming a longitudinal portion of a cylinder. The channel 4 is covered by the metal plate 5 to form a tube

  in which the cooling fluid circulates.

  This structure has the disadvantage of not allowing the circulation of fluid at high pressure and inductive inductive losses at high frequency, especially just at the limit of the inductors, the magnetic field having in these areas a direction

  perpendicular to the metal plate 5.

  The essential object of the present invention is to improve the cooling and efficiency of a cold cage. Another object of the invention is to reduce the inductive losses by currents induced in a cold cage. These objects are achieved, according to the invention, by a new cold cage structure comprising a plurality of internal metal partitions and at least one insulating external partition, made of electrically insulating material, the cold cage being of revolution and divided into sectors, each sector comprising: a metal internal partition, at least a part of an insulating external partition, and a cooling fluid circulation means, each internal partition being covered by at least a part of the external partition, characterized in that, in at least one sector, the fluid circulation means is produced by digging, at least two cooling channels in at least one of the two partitions, the partitions being contiguous, so that the outer surface of each internal partition is covered by the internal surface; external partition, so as to close and return

  sealed the cooling channels.

  The description that follows and the drawings

  annexed, given mainly as non-limiting examples

  will better understand how the invention is realized.

  In the accompanying drawings: Figure 1, previously described, shows a cold cage according to the prior art; 30. Figure 2, previously described, shows a cross-sectional view of cold cage sectors according to the prior art; FIG. 3 represents a perspective view of a cold cage sector according to a first embodiment of the invention; Figure 4 shows a cross section, along the plane IV-IV of Figure 3, cold cage sectors according to the first embodiment of the invention; 5. Figure 5 shows a cross section, along the plane V-V of Figure 3, of cold cage sectors according to the first embodiment of the invention; FIG. 6 represents a cross section of cold cage sectors according to another embodiment

of the invention.

  A cold cage of revolution according to the invention comprises, for each sector, a metal internal partition and at least a part of external partition

  insulation, that is to say of electrically insulating material.

  Figure 3 shows an internal metal partition of sector 2 cold cage perspective view. Each internal partition 10 of the cage has the shape of a circular cylinder of revolution about an axis X-X. It can be formed of a curved metal plate or a part of

  metal tube split longitudinally.

  The internal partition is preferably copper, good thermal and electrical conductor. Thus, high heat transfers and low inductive losses are obtained. Indeed, the inductive energy dissipated in the metal partition itself, is a function of the geometry of the partition and proportional to the resistivity of the metal used. According to one characteristic of the invention, each sector further comprises a fluid circulation means, each internal partition being covered by at least one

part of external partition.

  According to a first embodiment, the circulation means is made by digging at least two cooling channels in at least one internal partition. Preferably, the two channels are milled perpendicularly to the outer surface 10b of the metal partition. As shown in FIG. 3, the digging of the two channels 11, 12 leaves two longitudinal longitudinal ribs 17 and 18, and a rib

  longitudinal central 13 which separates the two channels.

  The digging of the channels can be interrupted before reaching the ends of the plate leaving at each end a solid border 15, 16. Thus, the channels are closed when the outer wall and the internal wall are assembled. To connect the two channels, the invention provides a transverse cooling channel in at least one of the two partitions, following a circular arc centered on the axis, so as to connect the two cooling channels. This transverse channel 14 can be dug near the edge 15 for example, to put in communication the two longitudinal channels 11, 12. Preferably, the transverse channel 14 is hollowed in the same way as the longitudinal channels 11, 12. Thus, the transverse channel 14 can be cut by milling perpendicular to the outer surface 10b of the metal partition which already has the longitudinal channels 11, 12. It is preferable to perform the milling by rotating the partition wall

around its X-X axis.

  When the external partition 20 is contiguous with the internal partition 10, the fluid can be circulated by two openings made in the external partition 20, at the level corresponding to the end of each channel 11, 12 dug in the internal partition 10. Thus the fluid injected through an opening, passes through the channels 11, 14 and

  12, before being collected by the other opening.

  According to one variant, the cooling channels 11, 12 can be hollowed out to one end of the partition, thus eliminating the edge 16. The cooling fluid can then be injected and collected at

  the end of each channel 11, 12 formed.

  In addition, the transverse channel 14 can be omitted, each longitudinal channel 11, 12 being dug to the two ends of the partition. The fluid can then be injected and collected at one end of the wall by connecting the channels through a U-tube disposed at the other end.

end of the partition.

  Each cooling channel 11, 12 is separated from the material to be melted or from the plasma by a respective wall

lla, 12a.

  Advantageously, the production of the channels in the internal metal partition, and the digging perpendicularly to the surface thereof, makes it possible to obtain walls 11a, 12a of very small thickness and of large surface area. For example, the channel can be milled several times to obtain a wall 11a, 12a thick.

regular and reduced.

  Obtaining a thin wall has a double interest. On the one hand, this thin wall and large area increases heat exchange. On the other hand, the wall may have a reduced thickness relative to the skin depth in which the induced currents develop. By reducing the thickness of this wall, it is therefore possible to reduce the inductive losses and / or to increase

the working frequency.

  According to another advantageous characteristic, at least one sector comprises a slot, made by drilling in the internal partition, the slot being arranged at the median plane of the channels of the sector, so as to

  maintain the watertightness of the cooling channels.

  Thus, the longitudinal rib 13 is split

  longitudinally over substantially its entire length.

  This longitudinal slot 21 passes through the entire internal metal partition. Thus, the transverse currents can no longer develop on the entire surface

  internal of the internal metal partition.

  This slot formed in each metal internal partition is similar to a doubling of the degree of sectoring of the cold cage. For example, a cold cage having eight sectors with a split metal partition similar to a cold cage with sixteen sectors can be realized. A high degree of sectorization is interesting in that it increases the efficiency of the magnetic field inside the cold cage. This slot does not reach the transverse channel 14 so as to maintain the tightness of the channels. Similarly, it is preferable that the slot 21 does not reach the borders 15, 16 of the partition

  10 so that it remains formed of a single piece.

  As shown in Figures 4 and 5, the outer wall 20, of electrical insulating material, is disposed opposite the inner wall. According to a characteristic of the invention, the two partitions are contiguous so that the outer surface of each internal partition is covered by the internal surface of at least one part of the outer partition so as to close and seal

cooling channels.

  The external partitions 20 may in fact be as numerous as the internal partitions 10 and each sector 2 may be made separately by gluing a respective external partition 20 on each internal partition 10. The external insulating partitions 20 are for example formed of plates of composite material curved, like silirite. The sectors are then assembled to form the cold cage 1 of revolution. 3 radial joints, isolate and solidarize the sectors. In particular, these seals insulate the internal metal partitions 10 from each other. The seals 3 are also placed in the slots 21 to electrically isolate the two parts of the partition. According to one variant, the outer partition may be formed of a single curved or tubular piece inside which all the internal metal partitions are fixed. Thus, the cold cage comprises a single external partition of revolution, each sector comprising an internal partition covered by a partition part

external corresponding to the sector.

  Finally, a cold cage according to the invention comprises several internal metal partitions, at least one insulating external partition, the cold cage being divided into sectors, each sector comprising: a metal internal partition,

  at least a portion of the outer insulating partition.

  Finally, according to another variant, the internal metal partitions 10 are firstly assembled into a body of revolution (for example a cylinder), with joints 3 isolating them electrically from each other. A hooping tape is glued on the entire contour of the body of revolution, that is to say, the entire outer surface of the assembled metal partitions. Thus, the outer wall is formed by a hooping tape surrounding the outer surface of the internal partitions assembled in a sector of a body of revolution. This tape can be coated with resin to harden it and withstand the pressure of coolant. More generally, the external partition

  will be formed of an encapsulating resin.

  According to the second embodiment, the fluid circulation means is produced by digging at least two cooling channels in at least one insulating outer partition part corresponding to a sector. FIG. 6 thus represents the digging of longitudinal channels 111, 112 in an external partition

insulating 110.

  In the example of FIG. 6, each sector 2 of cold cage 1 comprises an insulating external partition 110 in which the channels 111, 112 are hollowed on the internal surface of the external partition 110. This digging is performed in a similar manner to the digging the metal partition previously exposed. This dig also leaves a central longitudinal rib 113 and two longitudinal longitudinal ribs 117, 118 on the inner surface of the outer wall 110. A transverse channel can also be hollowed between the longitudinal channels 111,

112, to connect them.

  Advantageously, a thin metal internal wall 120 is adhered to the entire inner surface of the outer wall 110 to close and seal the channels. This internal partition preferably has a

  reduced cross-section so that coupling with

  screw magnetic field is also reduced. The apparent resistance is in fact proportional to the conductive surface traversed by the magnetic field, the resistance being also proportional to the frequency of the

magnetic field.

  By reducing the thickness of the internal metal partition, the section is reduced and the parasitic current in the cold cage decreases. This decrease in

  stray current is an essential advantage of the invention.

  It makes it possible to reduce the inductive losses in the cold cage and / or to increase the working frequency (for a

same rate of losses).

  For example, in both embodiments of the invention, the internal metal partitions may be formed of copper walls of thickness less than one millimeter, in which the current losses

induced will be weak.

  In addition, the internal metal partition 120 can always in the second embodiment have a longitudinal slot 121 to prevent the development of transverse currents. This slot 121 is open parallel to the axis X-X through the internal metal wall 120 in its middle part. The medial portion of the internal partition 120 corresponds to the portion that will cover the central rib 113 of the outer insulating partition 110 when the partitions 110, 120 will be contiguous. The tightness of the channels is thus preserved. If a transverse channel is dug between the longitudinal channels 111, 112 of the outer wall 110, the slot 121 is also limited in length to not reach the transverse channel once the walls contiguous. In this second embodiment also, it is possible to provide a variant in which a single piece of revolution forms the external partition. Longitudinal channels are then dug in each part of the outer wall corresponding to a sector. In each sector, an internal metal partition is then glued inside the piece of revolution. Radial seals 3 are interposed between the internal metal partitions. The final assembly of the cold cage can be done in two ways in cases where the cage contains as many internal partitions as external partitions: either we stick each external partition on each internal partition forming the sectors one by one. Once glued, the sectors are assembled to form the cold cage of revolution; either we assemble in one step all the internal partitions and all the external partitions, glued. It is therefore preferable to keep the entire ring and insert an inner support disc for the cage

  has its form of revolution once the glue is taken.

  If radial openings have been provided for injecting the cooling fluid at an end portion of the cold cage, it will be possible, during the final assembly, to have a specific connecting piece. It is thus possible to weld or braze a short copper tube around the end portion of the cold cage. This tube then has openings corresponding to each channel end 11,12. These overtures allow the attachment of the injection connections

of fluid.

  The cold cage is attached at its lower part to a short circuit ring. This metal ring is

  generally consists of a disc plane hollowed copper.

  It has on one side a circular groove. The cold cage composed of glued sectors, can then be welded or brazed on the short-circuit ring by introducing the end of the sectors in the circular groove. One of the essential advantages of the invention is the digging of the channels perpendicular to the surface of the partition. Thus, the excavated surface has

  ribs 13, 15, 16, 17, 18 having a large area.

  When bonding the inner wall and the outer wall, it can therefore glue a large area and the attachment has good strength. Thus, the cooling fluid can be subjected to a flow and pressure

high without leaking channels.

  Another major advantage is the reduction of inductive losses in the cold cage. As the metal internal partition is better fixed at the ribs, the wall may be thinner than the walls of the prior art which had to be rigid. By decreasing the thickness of metal, the volume of metal, where the parasitic currents develop, is decreased and the transparency with respect to the induction increases. In addition, the realization of metal partitions requires less metal, so is more economical. Advantageously, the different sectors of the cold cage are obtained from a unitary metal tube which is split into different parts over most of its height, the area not split now.

the assembly of sectors.

Claims (11)

  1. cold cage (1) for an induction device comprising a plurality of internal metal partitions (10) and at least one insulating external partition (20), the cold cage (1) being of revolution and divided into sectors (2), each sector comprising an internal metal partition (10), at least one outer insulating partition (20), and 10. a fluid circulation means, each inner partition (10) being covered by at least one outer wall portion, characterized in that in at least one sector (2), the fluid circulation means is formed by digging at least two cooling channels (11, 12) in at least one of the two partitions (10, 20). ), the partitions being contiguous, so that the outer surface (10b) of each inner partition (10) is covered by the inner surface (20a) of the outer partition (20), so as to close and seal   the cooling channels (11, 12).   2. Cold cage (1) according to claim 1, characterized in that, in at least one sector (2), the fluid circulation means comprises a transverse cooling channel (14) in at least one of the two partitions (10, 20), so as to connect the two cooling channels (11, 12).   Cold cage (1) according to one of the claims   characterized in that cooling channels (11, 12, 14) are hollowed out in at least one of the internal partitions (10).   Cold cage (1) according to one of the claims   1 and 2, characterized in that cooling channels (111, 112) are hollowed out in at least a portion of an outer partition (20) corresponding to a sector (2).   Cold cage (1) according to one of the claims   previous, characterized in that each sector (2) comprises an internal partition (10) and an external partition (20) respectively.   Cold cage (1) according to one of the claims   previous, characterized in that the cold cage (1) comprises a single outer wall (30) of revolution, each sector (2) comprising an inner wall (10) covered by a corresponding outer wall portion to the sector.   Cold cage (1) according to one of the claims   prior art, characterized in that the outer wall (30) is formed by an encapsulated resin encircling the outer surface (10b) of the internal partitions (10).   assembled in sectors (2) of a body of revolution.   Cold cage (1) according to one of the claims   previous, characterized in that at least one sector (2) has a slot (21), made by drilling in the internal partition (10), the slot (21) being disposed at the center plane of the channels (11, 12 ) of sector (2), so as to maintain the watertightness of cooling (11, 12, 14).   Cold cage (1) according to one of the claims   preceding, characterized in that an internal partition (10) is made of copper.   10. cold induction crucible, characterized in that it comprises a cold cage according to one of preceding claims.   11. induction plasma torch, characterized in that it comprises a cold cage according to one of preceding claims.