EP0771136A1 - Cooled casing for induction device - Google Patents

Abstract

A cold cage is claimed for use in electromagnetic induction melting with an induction device incorporating several internal metallic partitions (10) and at least one external electrical insulating partition (20). The cold cage is circular and divided into sectors (2). Each sector (2) incorporates one internal metallic partition (10), at least one part of the external insulating partition (20) and a system for the circulation of fluid. Each internal partition (10) is covered by at least a part of the external partition (20). In at least one sector (2), the system for circulating the fluid is created by cutting out at least two cooling channels (11,12) in one or more of the two partitions (10, 20). The partitions are coupled in such a manner that the outer surface (10b) of each internal partition (10) may be overlapped by the internal surface (20a) of the external partition (20) in a manner that closes and seals the cooling channels (11,12).

Description

The present invention relates to cold cages used either in the field of electromagnetic induction fusion, or in the field of inductive plasma production or in the field of electromagnetic confinement.

Such cold cages in particular constitute the main element of cold crucibles in which the electromagnetic induction fusion of refractory materials, such as metals melting at very high temperatures, is practiced.

In an plasma torch, an inductive coil heats and confines the plasma. A device called a cold cage dissipates the heat given off by the inductive plasma which could damage the coil.

In general, the term cold cage will be used in the present description to designate the cooling structure of an inductive plasma torch or of an inductive cold crucible, equally.

Such cold cages are generally formed from several partitions assembled to form a body of revolution, in particular a cylinder.

Cold cage partitions are known which are made of a metal which is a good conductor of heat and which are cooled by the circulation of a heat transfer fluid.

As such a cage is disposed within an inductor, which generates currents in the material to be melted or the plasma, induced currents also arise in the metal partitions. These stray currents decrease the penetration of the magnetic field into the material. They also decrease the cooling efficiency, since the partition is itself directly heated by induction.

FIG. 1 illustrates a conventional cold cage structure, as described, in document FR-A-2 629 299.

In such a cylindrical cage 1 with axis O-O, partitions in the form of arcuate longitudinal sectors 2 are arranged in a circle in the manner of a barrel stave. The partitions of sectors 2, in copper, are glued edge to edge with joints 3 insulating intermediates. This segmentation prevents the development of induced currents along a complete contour of the crucible.

Each sector partition 2 consists of metal walls welded edge to edge to form longitudinal channels 4 for cooling fluid circulation. Thus, each metal partition, in contact with the molten material or the plasma, is cooled.

However, induced currents appear in each sector because the magnetic field applied has axial and radial components while the cross section of a sector partition has a metallic outline.

FIG. 2 illustrates another known structure of sector 2 of a cold crucible, seen in cross section.

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

This structure has the drawback of not allowing the circulation of fluid at high pressure and of causing inductive losses at high frequency, in particular just at the limit of the inductors, the magnetic field having in these zones a direction perpendicular to the metal plate. 5.

The essential object of the present invention is 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.

• . une cloison interne métallique,
• . au moins une partie de cloison externe isolante, et
• . un moyen de circulation de fluide de refroidissement,

chaque cloison interne étant couverte par au moins une partie de cloison externe, caractérisée en ce que, dans au moins un secteur, le moyen de circulation de fluide est réalisé par creusement, d'au moins deux canaux de refroidissement dans l'une au moins des deux cloisons, les cloisons étant accolées, de sorte que la surface externe de chaque cloison interne soit recouverte par la surface interne de cloison externe, de façon à fermer et rendre étanches les canaux de refroidissement.These aims are achieved, according to the invention, by a new cold cage structure comprising several metallic internal 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:

• . an internal metal partition,
• . at least part of an insulating external partition, and
• . a means for circulating coolant,

each internal partition being covered by at least one part of 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 joined, so that the external surface of each internal partition is covered by the internal surface of external partition, so as to close and seal the cooling channels.

• . la figure 1, précédemment décrite, représente une cage froide selon l'art antérieur ;
• . la figure 2, précédemment décrite, représente une vue en coupe transversale de secteurs de cage froide selon l'art antérieur ;
• . la figure 3 représente une vue en perspective d'un secteur de cage froide selon un premier mode de réalisation de l'invention ;
• . la figure 4 représente une coupe transversale, selon le plan IV-IV de la figure 3, de secteurs de cage froide selon le premier mode de réalisation de l'invention ;
• . la figure 5 représente une coupe transversale, selon le plan V-V de la figure 3, de secteurs de cage froide selon le premier mode de réalisation de l'invention ;
• . la figure 6 représente une coupe transversale de secteurs de cage froide selon un autre mode de réalisation de l'invention.

The description which follows and the appended drawings, given mainly by way of nonlimiting examples will make it easier to understand how the invention is implemented. In the accompanying drawings:

• . Figure 1, previously described, shows a cold cage according to the prior art;
• . 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;
• . 4 shows a cross section, along the plane IV-IV of Figure 3, of cold cage sectors according to the first embodiment of the invention;
• . 5 shows a cross section, along the plane VV of Figure 3, of cold cage sectors according to the first embodiment of the invention;
• . Figure 6 shows 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 metallic internal partition and at least a portion of insulating external partition, that is to say of electrically insulating material.

FIG. 3 shows a metal internal partition 10 of sector 2 of a cold cage seen in perspective. Each internal partition 10 of the cage has the shape of an arc of a cylinder of revolution around an axis X-X. It can be formed of a curved metal plate or a part of a metal tube split longitudinally.

The internal partition is preferably made of copper, a 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 a characteristic of the invention, each sector also comprises a means for circulating fluid, each internal partition being covered by at least one part of external partition.

According to a first embodiment, the circulation means is produced by digging at least two cooling channels in at least one partition internal.

Preferably, the two channels are formed by milling perpendicular to the external surface 10b of the metal partition. As shown in FIG. 3, the digging of the two channels 11, 12 leaves two lateral longitudinal ribs 17 and 18, and a central longitudinal rib 13 which separates the two channels.

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

When the external partition 20 is attached to 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 hollowed out 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.

Alternatively, the cooling channels 11, 12 can be dug up to one end of the partition, thereby removing the border 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 hollowed out to the two ends of the partition. The fluid can then be injected and collected at one end of the partition by connecting the channels by a U-tube placed at the other 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 11a, 12a.

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

Obtaining a thin wall has a double advantage. On the one hand, this thin and large surface wall increases heat exchange. On the other hand, the wall may have a reduced thickness compared 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 increase the working frequency.

According to another advantageous characteristic, at least one sector has a slit, produced by drilling in the internal partition, the slit being arranged at the median plane of the channels of the sector, so as to maintain the tightness of the cooling channels. Thus, the longitudinal rib 13 is split longitudinally over substantially its entire length. This longitudinal slot 21 crosses the entire partition internal metal. Thus, the transverse currents can no longer develop over the entire internal surface of the internal metal partition.

This slot formed in each internal metal partition is analogous to a doubling of the degree of sectorization of the cold cage. For example, it is possible to produce a cold cage comprising eight sectors with a split metal partition similar to a cold cage with sixteen sectors. A high degree of sectorization is advantageous 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 sealing of the channels. Similarly, it is preferable that the slot 21 does not reach the edges 15, 16 of the partition 10 so that it remains formed in one piece.

As shown in FIGS. 4 and 5, the external partition 20, made of electrically insulating material, is arranged opposite the internal partition. According to a characteristic of the invention, the two partitions are joined so that the external surface of each internal partition is covered by the internal surface of at least one part of external partition so as to close and seal the cooling channels.

The external partitions 20 can indeed be as numerous as the internal partitions 10 and each sector 2 can be produced separately by gluing a respective external partition 20 on each internal partition 10. The insulating external partitions 20 are for example formed from plates of composite material curved, like silirite. The sectors are then assembled to form the cold cage 1 of revolution. 3 radial seals isolate and secure the sectors. In particular, these seals insulate the internal metal partitions 10 from one another. The seals 3 are also placed in the slots 21 to electrically isolate the two parts of the partition.

According to a variant, the external partition can be formed in a single curved or tubular part 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 part of external partition corresponding to the sector.

• . une cloison interne métallique,
• . au moins une partie de cloison externe isolante.

Ultimately, 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:

• . an internal metal partition,
• . at least part of an insulating external partition.

Finally, according to another variant, the internal metal partitions 10 are first assembled in a body of revolution (for example a cylinder), with seals 3 electrically insulating them from one another. A shrinking tape is glued over the entire contour of the body of revolution, that is to say the entire outer surface of the assembled metal partitions. Thus, the external partition is formed by a hooping tape surrounding the external surface of the internal partitions assembled in sector of a body of revolution. This tape can be coated with resin to harden it and resist the pressure of coolant. More generally, the external partition will be formed from a resin reinforced with coating.

According to the second embodiment, the fluid circulation means is produced by digging at least two cooling channels in at least one part of the insulating external partition corresponding to a sector. FIG. 6 thus represents the digging of longitudinal channels 111, 112 in an insulating external partition 110.

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

Advantageously, a thin metallic internal partition 120 is bonded to the entire internal surface of the external partition 110 to close and seal the channels.

This internal partition preferably has a reduced cross section so that the coupling with respect to the magnetic field is also reduced. The apparent resistance is in fact proportional to the conductive surface crossed by the magnetic field, the resistance also being proportional to the frequency of the magnetic field.

By reducing the thickness of the internal metal partition, the section is therefore reduced and the stray current in the cold cage decreases. This reduction of the stray current is an essential advantage of the invention. It reduces the inductive losses in the cold cage and / or increases the working frequency (for the same loss rate).

For example, in the two embodiments of the invention, the internal metal partitions can be formed from copper walls of thickness less than one millimeter, in which the losses by induced currents will be low.

In addition, the internal metal partition 120 may still in the second embodiment include a longitudinal slot 121 to avoid the development of transverse currents. This slot 121 is open parallel to the axis XX through the internal metal partition 120, in its middle part. The middle part of the internal partition 120 in fact corresponds to the part which will cover the central rib 113 of the insulating external partition 110 when the partitions 110, 120 are joined.

The tightness of the channels is thus preserved. If a transverse channel is dug between the longitudinal channels 111, 112 of the external partition 110, the slot 121 is also limited in length so as not to reach this transverse channel once the partitions are joined.

In this second embodiment also, a variant can be provided in which a single piece of revolution forms the external partition. Longitudinal channels are then dug in each part of the external partition corresponding to a sector. In each sector, an internal metal partition is then glued to the interior of the part of revolution. 3 radial seals are interposed between the internal metal partitions.

• . soit on colle chaque cloison externe sur chaque cloison interne en formant les secteurs un à un. Une fois collés, les secteurs sont assemblés pour former la cage froide de révolution;
• . soit on assemble en une étape toutes les cloisons internes et toutes les cloisons externes, encollées. Il est alors préférable de maintenir l'ensemble cerclé et d'insérer un disque support intérieur pour que la cage ait sa forme de révolution une fois la colle prise.

The final assembly of the cold cage can be done according to two possibilities in cases where the cage contains as many internal partitions as external partitions:

• . either glue each external partition on each internal partition by 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 then preferable to keep the whole circled and to insert an interior support disc so that the cage has its shape of revolution once the glue has set.

If radial openings have been provided to inject the coolant to an end part of the cold cage, it will be possible, during the final assembly, to have a specific connecting piece. It is thus possible to solder or braze a short copper tube around the end part of the cold cage. This tube then has openings corresponding to each end of the channel 11,12. These openings allow the attachment of the fluid injection fittings.

The cold cage is fixed at its lower part to a short-circuit ring. This metal ring generally consists of a hollow copper flat disc. It has on one side a circular groove. The cold cage composed of the glued sectors, can then be welded or brazed on the short-circuit ring by introducing the end of the sectors into 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 hollowed out surface has ribs 13, 15, 16, 17, 18 having a large surface. When gluing the internal partition and the external partition, it is therefore possible to glue a large surface and the fixing has good solidity. Thus, the coolant can be subjected to a high flow and pressure without leakage from the channels.

Another major advantage is the reduction of inductive losses in the cold cage. As the internal metal 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 parasitic currents develop, is reduced and the transparency vis-à-vis the induction increases. Furthermore, the production of metal partitions requires less metal, therefore 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 unsplit area maintaining the assembly of the sectors.

Claims (11)

Cold cage (1) for induction device comprising several 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 part of an outer insulating partition (20), and . a means for circulating fluid, each internal partition (10) being covered by at least one part of external partition, characterized in that, in at least one sector (2), the fluid circulation means is produced by digging, at least two channels (11 , 12) for cooling, in at least one of the two partitions (10, 20), the partitions being joined together, so that the external surface (10b) of each internal partition (10) is covered by the internal surface (20a ) external partition (20), so as to close and seal the cooling channels (11, 12). 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 preceding 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 claims 1 and 2, characterized in that cooling channels (111, 112) are hollowed out in at least one part of external partition (20) corresponding to a sector (2). Cold cage (1) according to one of the preceding claims, characterized in that each sector (2) comprises an internal partition (10) and a respective external partition (20). Cold cage (1) according to one of the preceding claims, characterized in that the cold cage (1) comprises a single external partition (30) of revolution, each sector (2) comprising an internal partition (10) covered by a part of external partition corresponding to the sector. Cold cage (1) according to one of the preceding claims, characterized in that the external partition (30) is formed by a resin reinforced with coating surrounding the external surface (10b) of the internal partitions (10) assembled in sectors (2 ) of a body of revolution. Cold cage (1) according to one of the preceding claims, characterized in that at least one sector (2) has a slot (21), produced by drilling in the internal partition (10), the slot (21) being arranged at the median plane of the channels (11, 12) of the sector (2), so as to maintain the tightness of the cooling channels (11, 12, 14). Cold cage (1) according to one of the preceding claims, characterized in that an internal partition (10) is made of copper. Cold induction crucible, characterized in that it comprises a cold cage according to one of the preceding claims. Induction plasma torch, characterized in that it comprises a cold cage according to one of the preceding claims.

Images