EP3737901B1 - Cold crucible and associated cooling manifold for an induction heating device - Google Patents

Description

The present invention relates to a cold crucible for an induction heating device for heating and melting materials such as metals. The crucible comprises a crucible body which has the general shape of a tube or of a test piece, the peripheral partition of which comprises several sections in the form of arcs of a circle separated from each other by an air gap. . Each section contains a cooling pipe circulating a cooling liquid in order to cool the crucible in operation. The present invention also relates to a cooling manifold which, in operation, is connected to the crucible body and which makes it possible to distribute the cooling liquid in the various pipes. The invention also relates to a method of manufacturing the crucible. The field of the invention is in particular that of metallurgy and foundry.

State of the prior art

In the field of materials, it is very often necessary to melt materials, for example to produce alloys containing several metals or other materials. A known method is to use an induction heating device, formed of electrical conductors which surround a so-called “cold” crucible, in which the material or materials to be heated, called “the load”, are placed. The device comprises an induction coil, surrounding the crucible, in order to generate a magnetic field inside the crucible and thus heat the charge by induction. The crucible is cooled to evacuate the heat coming from the load and the Joule effect of the current induced in it. The crucible has the general shape of a tube so that it comprises a peripheral partition forming an envelope. This partition is cut longitudinally so that the crucible is formed of several sections in the form of sectors, along the majority of the length of the crucible; the partition being arranged in a continuity of material at one end of the crucible. This sectorization of the crucible is necessary in order to electrically isolate the sections from each other, to induce eddy currents in the charge and to prevent the field magnetic field supplied by the inductor is shielded by the crucible. The device also comprises a cooling manifold, or water box, distributing cooling water to pipes arranged in the peripheral partition of the crucible. Pipes are also connected by brazing to the crucible and to the cooling manifold.

However, these solders tend to deteriorate over time, which results in a potential source of contamination for the charge contained in the crucible, significant sealing defects and therefore a limited service life.

The document EP0398821 proposes brazing cooling tubes on a perforated ring, said ring comprising openings distributed around its circumference, for the flow of water between a water collector and the crucible. These openings are distributed over two different circles: a circle formed by the inlet openings, and another circle formed by the outlet openings. A cooling passage is arranged in each sector of the crucible to respectively receive a tube, which separates the input circuit from the output circuit. This embodiment therefore makes it possible to reduce the number of solders but does not solve the problem of leaks. In addition, it is difficult to make brazes without altering the brazes of the adjacent tubes or pipes, in particular during maintenance of the crucible.

In addition, it is necessary to decontaminate the crucible after each use, or at least between loads of different natures, which is a complex operation and further reduces its lifespan. Contamination occurs because residues and impurities are deposited on the walls of the crucible. In the event of a water leak, a violent reaction of the water with the material to be heated may occur, even leading to an explosion.

We also know from the document EP 0 398 821 a crucible associated with a collector which makes it possible to solve contamination problems in the crucible. We also know from the document CN 206488623 a crucible associated with a collector which aims to make the magnetic field acting on the materials to be melted more efficient.

An object of the invention is to remedy all or part of the drawbacks of the state of the art. Another object of the invention is to propose a cold crucible heating device limiting the problems of service life and leaks. It also aims to provide a device facilitating maintenance compared to known devices. It also aims to propose operational manufacturing conditions to produce materials of high purity. Finally, it aims to facilitate the use of a heating device in a cold crucible.

Disclosure of Invention

• un anneau de raccordement comprenant une région annulaire de distribution,
• une enveloppe tubulaire s'étendant depuis l'anneau de raccordement pour définir un volume de chauffe, l'enveloppe étant découpée longitudinalement de façon à réaliser plusieurs secteurs séparés afin d'induire des courants de Foucault dans la charge placée dans le volume de chauffe et d'éviter que le champ magnétique fourni par un inducteur ne soit écranté par le creuset,
• des canaux de liquide de refroidissement disposés longitudinalement dans l'épaisseur du corps de creuset de façon que chaque secteur comprend au moins un canal de liquide de refroidissement.

According to a first aspect of the invention, at least one of the aforementioned objects is achieved with a cold crucible for an induction heating device comprising a crucible body comprising:

• a connection ring comprising an annular distribution region,
• a tubular envelope extending from the connection ring to define a heating volume, the envelope being cut longitudinally so as to produce several separate sectors in order to induce eddy currents in the load placed in the heating volume and to prevent the magnetic field supplied by an inductor from being screened by the crucible,
• coolant channels arranged longitudinally in the thickness of the crucible body so that each sector comprises at least one coolant channel.

Each sector comprises at least two coolant paths: a so-called “go” path and a so-called “return” path of the coolant. The coolant paths of each sector are formed by the at least one coolant channel. Said paths open into the annular distribution region so that said region has, for each sector, a so-called "inlet" orifice and a so-called "outlet" orifice, the orifices being spaced apart from each other along in a radial direction of the crucible.

The assembly thus forms along the periphery of the annular distribution region two distinct concentric regions around the longitudinal axis of the crucible, one of which communicates only with the outward path of the channels and the other communicates only with the return path of the canals.

The crucible body is intended to be removably assembled with a coolant manifold via the connection ring, the manifold comprising coolant distribution elements connecting to the coolant channels, from the made of this assembly, to circulate said liquid between the collector and the channels.

The crucible body has a one-piece structure composed of one and the same material having a continuity of material over at least two sectors.

The cold crucible according to the invention allows easier use, compared to the crucible of the prior art, by limiting or even eliminating the brazing operations carried out on the crucible and by allowing a connection with a collector without angular indexing during the coupling or keying system. Consequently, the crucible according to the invention limits or even eliminates leaks and offers an increased service life. Maintenance is also facilitated compared to known devices.

For the following and for the foregoing, the term "longitudinal" is understood to mean a direction substantially parallel to the axis of the crucible body, plus or minus 15 angular degrees. This axis is generally vertical when the crucible is in the position of use and provided for vertical introduction or extraction. It typically corresponds to the center of the tubular casing, and/or of the induction winding which surrounds the crucible.

Preferably, each channel comprises an added channel partition inserted longitudinally into said channel. The partition forms a sealed or substantially sealed longitudinal contact with at least two distinct regions of the peripheral wall of said channel, so as to define the outward path and the return path on either side of said partition and extending longitudinally to the within the same channel. The added partition makes it possible to form two coolant paths simply and in a reduced space. The partition is for example made of epoxy glass fabric or of fiberglass composite.

According to one embodiment, each channel partition has a flat shape. Its cross section is substantially linear and rectilinear in a single direction. According to another embodiment, each channel partition has a two-dimensional shape. By two-dimensional is meant a shape whose cross-section is not rectilinear, for example curved, or comprising at least one element of non-zero thickness on one face of the partition.

Each channel partition is arranged in its channel so that an imaginary geometric plane included in the thickness of the partition is substantially tangential to an imaginary cylinder of revolution concentric with the crucible. This characteristic makes it possible to form in the connection zone of the connection ring two distinct concentric regions around the longitudinal axis of the crucible, one of which communicates only with the forward path of the channels and the other communicates only with the return path. channels. The connection between the collector and the crucible can be made without indexing.

According to one embodiment, each channel partition has a length substantially equal to or less than the length of the channels, and is intended to be inserted into a channel leaving a non-zero gap between the bottom of the channel and the said longitudinal end of passage of the channel partition. In this way the coolant can pass from the forward path to the return path. For example, each channel partition has a length at least equal to 75% of the length of a channel.

Preferably, each channel comprises in its wall two separate grooves arranged and configured to receive and position each partition in said channel. This characteristic allows the channel partitions to be reliably held in position, and allows them to be guided in said channel, improving the reliability of the cooling of the crucible.

• un anneau de raccordement comprenant une région annulaire de distribution,
• une enveloppe tubulaire s'étendant depuis l'anneau de raccordement pour définir un volume de chauffe, l'enveloppe étant découpée longitudinalement de façon à réaliser plusieurs secteurs séparés,
• des canaux de liquide de refroidissement disposés longitudinalement dans l'épaisseur du corps de creuset de façon que chaque secteur comprend au moins un canal de liquide de refroidissement.

According to a second aspect of the invention, at least one of the aforementioned objects is achieved with a cold crucible for an induction heating device, characterized in that it comprises a crucible body comprising:

• a connection ring comprising an annular distribution region,
• a tubular casing extending from the connection ring to define a heating volume, the casing being cut longitudinally so as to produce several separate sectors,
• coolant channels arranged longitudinally in the thickness of the crucible body so that each sector comprises at least one coolant channel.

The crucible body is intended to be removably assembled with a cooling manifold via the connection ring, the manifold comprising cooling liquid distribution elements that can be connected to the cooling liquid channels to circulate said liquid.

According to the second aspect of the invention, said crucible body has a one-piece structure composed of one and the same material having a continuity of material over at least two sectors.

The cold crucible, according to the second aspect of the invention, allows easier use, compared to the crucible of the prior art, by limiting, or even eliminating, the brazing operations carried out on the crucible. Consequently, the crucible according to the invention limits or even eliminates leaks and offers an increased service life. Maintenance is also facilitated compared to known devices.

• un anneau de raccordement comprenant une région annulaire de distribution,
• une enveloppe tubulaire s'étendant depuis l'anneau de raccordement pour définir un volume de chauffe, l'enveloppe étant découpée longitudinalement de façon à réaliser plusieurs secteurs séparés, et
• des canaux de liquide de refroidissement disposés longitudinalement dans l'épaisseur du corps de creuset de façon que chaque secteur comprend au moins un canal de liquide de refroidissement.

According to a variant of the first or second aspect of the invention, the crucible body consists essentially of:

• a connection ring comprising an annular distribution region,
• a tubular casing extending from the connection ring to define a heating volume, the casing being cut longitudinally so as to produce several separate sectors, and
• coolant channels arranged longitudinally in the thickness of the crucible body so that each sector comprises at least one coolant channel.

According to another variant, the crucible is formed by several one-piece elements, each comprising several sectors formed in the same part. These one-piece multi-sector elements each form an angular portion of the crucible and are assembled together by removable mechanical means, for example individual screws or a common flange holding them all against the cooling manifold. Even in this variant, the number of mechanical fasteners is greatly limited, and the good qualities of reliability and non-contamination are retained.

Preferably, according to any aspect or variant, the crucible body has a one-piece structure composed of one and the same material having a continuity of material between the connection ring, the sectors of the casing and the channels. This characteristic has the advantage of further improving the mechanical strength of the crucible and of preserving the geometry of the crucible body during its use. This parameter makes it possible to have a more homogeneous electromagnetic field and therefore a more homogeneous heating of the load. When it comes to melting a material, a better stability of the weld metal pool is obtained. This stability is particularly important when it comes to manufacturing an alloy and letting dissolve, by diffusion in the liquid, each of the constituent elements of the alloy. If the instability of the bath of molten metal becomes too great, the liquid metal is thrown against the walls of the crucible and immediately solidifies, which prevents its homogenization.

According to the first or the second aspect of the invention, the body of the crucible is made of an electrically conductive and heat conductive material.

According to a preferred embodiment, the body of the crucible is made of copper made by work hardening. In the prior art, the brazing operation on the crucible causes the annealing of the copper, which makes the crucible malleable. Without brazing performed on the copper crucible body according to the invention, the latter does not undergo annealing and thus remains rigid (without deformation). In addition, copper has very good thermal conductivity, which allows cooling by conduction from the cooling channels to the ends of the sectors. Alternatively, the crucible body could be stainless steel.

According to an embodiment compatible with the first aspect like the second aspect, the connection ring comprises on its periphery a crucible thread arranged to allow assembly by screwing so that a cooling manifold, provided with a collector which is complementary to it, can be screwed onto the crucible or vice versa. This feature makes it possible to assemble and disassemble the collector from cooling of the crucible easily and quickly in order to improve the decontamination of the crucible after each use.

Thus, the crucible body comprises a one-piece element, forming several sectors which are all separated from each other by longitudinal cutouts as far as their distal end and over their entire length except in the region of the connection ring, called the proximal region. Typically, each sector thus delimited comprises only one cooling channel. This cooling channel forms a blind hole, that is to say with only one end emerging longitudinally, which blind hole is separated into two longitudinal paths by an added partition which is inserted via this emerging end. Preferably, a single one-piece element forms all the sectors, and thus constitutes the entire envelope of the crucible body.

For the following and for the foregoing, the term “distal end” means an end located near the bottom of the crucible body, and the term “proximal end” means an end located near the connection ring of the crucible.

• un anneau de raccordement comprenant une région annulaire de distribution,
• une enveloppe tubulaire s'étendant depuis l'anneau de raccordement pour définir un volume de chauffe, l'enveloppe étant découpée longitudinalement de façon à réaliser plusieurs secteurs séparés,
• des canaux de liquide de refroidissement disposés longitudinalement dans l'épaisseur du creuset de façon que chaque secteur comprend au moins un canal de liquide de refroidissement comprenant une cloison de canal, formant dans chaque canal au moins deux trajets débouchant respectivement par deux orifices écartés l'un de l'autre le long d'une direction radiale du creuset sur la région annulaire de l'anneau de raccordement.

According to a third aspect of the invention, which may conform in whole or in part to the first aspect or in whole or in part to the second aspect of the invention, at least one of the aforementioned objects is achieved with a cooling manifold intended to cooperate with a cold crucible for an induction heating device, the crucible comprising:

• a connection ring comprising an annular distribution region,
• a tubular casing extending from the connection ring to define a heating volume, the casing being cut longitudinally so as to produce several separate sectors,
• coolant channels arranged longitudinally in the thickness of the crucible so that each sector comprises at least one coolant channel comprising a channel partition, forming in each channel at least two paths opening out respectively by two orifices spaced apart the from each other along a radial direction of the crucible on the annular region of the connecting ring.

The collector is characterized in that it has two collector cavities which are substantially circular and are arranged on the same face coming opposite the connecting ring, the collector cavities being offset in a radial direction by relative to the axis of the collector so that each collector cavity is located above a single orifice of each channel once the collector and the crucible are assembled.

The cooling collector according to the invention allows easier use, compared to the collector of the prior art, by allowing a connection with a collector without indexing. Consequently, the collector according to the invention limits or even eliminates leaks and offers an increased service life. Maintenance is also facilitated compared to known devices.

The two cavities are arranged so as to produce an inlet chamber and an outlet chamber which can be connected to a cooling liquid circulation circuit.

Preferably, the manifold comprises a circular manifold partition separating said two manifold cavities. Advantageously, a single manifold partition separates said two manifold cavities, which makes it possible to limit the bulk and facilitate assembly with respect to the crucible body. For example, said manifold partition bears against so-called sealing ends of the channel partitions. According to one embodiment, the collector partition has a cone shape.

According to one embodiment, the collector comprises, around the collector cavities, a collector thread arranged to allow assembly by screwing so that a crucible body also comprising a complementary crucible thread can be screwed onto the collector or vice versa . This characteristic makes it very easy to connect the cooling manifold to a body of the crucible.

Preferably, the cooling manifold is made of stainless steel.

According to a fourth aspect of the invention, one of the aforementioned objects is achieved by an induction heating device comprising a cold crucible body according to all or part of the first aspect or all or part of the second aspect and a cooling manifold according to all or part of third aspect of the invention. According to this fourth aspect, they are arranged so that, when they are assembled together, the coolant distribution elements of the collector are connected to the coolant channels of the crucible body

• fournir une ou plusieurs pièces de départ monoblocs ou ébauches, en un matériau conducteur thermique et électrique, de préférence en cuivre, par exemple un rond plein ou un tube,
• pour chaque pièce de départ, usiner la pièce aux dimensions extérieures et intérieures souhaitées, suivant la taille de creuset souhaitée, pour réaliser un corps de creuset formant un anneau de raccordement duquel s'étend l'enveloppe tubulaire.

According to a fifth aspect of the invention, there is provided a method of manufacturing a cold crucible for an induction heating device, the crucible comprising a crucible body communicating with a cooling manifold, the crucible body comprising a tubular casing s extending from the cooling manifold and surrounding a heating chamber comprised in a heating volume, the casing being cut longitudinally so as to produce several separate sectors, cooling liquid channels arranged longitudinally in the thickness of the crucible so that each sector comprises at least one coolant channel, the method comprising the following steps:

• provide one or more one-piece starting parts or blanks, made of a thermal and electrical conductive material, preferably copper, for example a solid round or a tube,
• for each starting part, machining the part to the desired external and internal dimensions, according to the desired crucible size, to produce a crucible body forming a connection ring from which the tubular casing extends.

• réaliser un filetage de creuset sur le pourtour de l'anneau de raccordement,
• réaliser des alésages correspondant aux canaux de liquide de refroidissement et débouchant dans la surface de l'anneau de raccordement,
• réaliser deux rainures, diamétralement opposées, dans la paroi de chaque canal.
• réaliser des découpes longitudinales sur l'enveloppe à travers toute l'épaisseur de l'enveloppe, les découpes s'étendant entre l'anneau de

raccordement et jusqu'à l'extrémité du corps de creuset opposée à l'anneau.The manufacturing process includes, in this order or another, the following steps:

• make a crucible thread on the circumference of the connection ring,
• make bores corresponding to the coolant channels and opening into the surface of the connection ring,
• make two grooves, diametrically opposed, in the wall of each channel.
• make longitudinal cuts on the casing through the entire thickness of the casing, the cuts extending between the ring of

connection and to the end of the crucible body opposite the ring.

The manufacturing method according to the invention makes it possible to produce a crucible body offering operational manufacturing conditions allowing the production of materials of high purity.

• Cu-Al : utilisé pour la fabrication de fils, barres et tubes à usage électrique, haute conductibilité électrique, bonne résistance aux agents chimiques,
• Cu-C2 : cuivre de très grande pureté, usage électrique et électronique, bonne aptitude au soudage, cuivre raffiné exempt d'oxygène ; la catégorie CU-C2, avec sa plus grande pureté et surtout son oxygène limité à 5ppm convient mieux aux applications nécessitant un vide poussé.

Preferably, a high purity copper rod is chosen. The preferred copper grades are between the Cu-A1 and Cu-C2 ranges according to the AFNOR standard, i.e.:

• Cu-Al: used for the manufacture of wires, bars and tubes for electrical use, high electrical conductivity, good resistance to chemical agents,
• Cu-C2: very high purity copper, electrical and electronic use, good weldability, refined oxygen-free copper; the CU-C2 category, with its greater purity and above all its oxygen limited to 5ppm, is better suited to applications requiring a high vacuum.

The Cu-C2 grade is the preferred grade because it is the purest and the least outgassing, and is particularly suitable for use under ultra-high vacuum.

Larger dimensions are preferably machined by turning and milling.

The channels are preferably made with a deep drilling machine. The bores must be particularly careful in order to respect a deviation from the axis of 0.1 millimeter maximum for a depth of 100 millimeters. Then, the bores must be machined with an H7 tolerance (according to the ISO system), that is to say allowing a sliding assembly, in order to allow the introduction of a calibrated tool to make the two diametrically opposed grooves.

Once machining is complete, a channel partition can be introduced into each channel. For example, the channel partition is made of composite materials based on resin and fiberglass. It is for example machined by milling and is adjusted in order to obtain a sliding fit in the grooves of each channel.

To introduce the channel partitions more easily, it is possible to use a mallet.

According to one embodiment, the grooves can be made so as to have a longitudinal depth slightly less than the depth of each channel so that, when the channel partition is put in place, the bottom of the channel corresponds to a passage zone between the forward path and the return path of the channel.

According to a first embodiment of the channel partitions, the distal ends of the grooves form an axial stop for positioning said partition, which facilitates assembly. The channel partitions have identical dimensions over all their lengths. The lengths of the partitions are identical to the lengths of the depths of the grooves so that the upper or proximal end of each partition is flush with the surface of the connecting ring.

According to a second embodiment of the channel partitions, these have, near their proximal end, one or two shoulders. In this embodiment, the channels can be made with or without grooves. Further, a notch is made in one groove (or both grooves, or near the opening) of each channel and on the annular region so that each shoulder rests on a notch.

According to a variant of the second embodiment, circular machining is carried out on the transverse face on which the coolant channels open out so as to form a circular connection groove, when the bores have not yet been made, and a succession of grooves between the openings of the bores when the bores are made.

Optionally, a hardening resin is introduced into said connection grooves or the notches so as to fill them in order to ensure the seal between two channels. The resin is applied until it reaches the height of the proximal end of the channel walls. The resin makes it possible to improve the tightness on the one hand between the inlet orifice and the outlet orifice of each channel and on the other hand more generally between the crucible body and the cooling manifold. The resin is preferably of the type which is sufficiently rigid to be able to be machined and to be able to withstand the coolant. For example, the resin is Stycast ^® 2850FT.

In order to apply the resin, plugs are used to obstruct the orifices of each channel. Preferably, each plug has a slot whose shape and thickness are complementary to the shape and thickness of the channel partitions. For example, the caps are made of polytetrafluoroethylene called “PTFE”.

Once the resin has been applied, it may be necessary to remove the excess resin by machining so as to produce a continuous plane surface between the proximal ends of the partitions and the resin, when the connecting grooves (between each pair of channels along the periphery of the annular region) are made, or between the proximal ends of the partitions, the resin and the surface of the annular region of the connecting ring, when notches are made.

A planar bearing along the diameter including the channel partitions is necessary so that a manifold partition, separating the outward and return cavities of the cooling manifold, comes to bear on said planar bearing (including the channel partitions) and makes continuous contact so as to form a seal when the cooling manifold is connected to the crucible body. Thus the cooling liquid can circulate between said cooling manifold and said crucible body without the cooling liquid passing through one of the paths outside the passage provided for this purpose.

Furthermore, said crucible body has a second bearing surface made on the annular region of the connection ring between the heating volume and the orifices of the channels. The second staff defines the border between the heating volume and the channels. It is made in such a way that a manifold barrier bears against said second bearing surface and makes continuous contact so as to form a seal with respect to the heating volume. Preferably, the second span is a chamfer. This feature has the advantage of facilitating centering and therefore placing in position of the cooling manifold relative to the crucible body. The chamfer also has the advantage of being compact.

Preferably, each end of the manifold bulkhead and manifold barrier includes an O-ring to provide a seal.

The manufacturing method according to the invention makes it possible to produce any type of crucible; for example bottomless straight crucibles, called "continuous casting" or also crucibles of the "pocket" type called "semi-levitation" for example hemispherical and conical.

• des découpes longitudinales dites « hautes » sur l'enveloppe à travers toute l'épaisseur de l'enveloppe, les découpes s'étendant entre l'anneau de raccordement vers l'extrémité du corps de creuset opposée à l'anneau sans atteindre l'extrémité distale du corps de creuset,
• des découpes longitudinales dites « basses » par électroérosion formant des fentes, chaque fente traversant toute l'épaisseur de l'enveloppe, étant suffisamment étroite pour ne pas laisser s'échapper un matériau à chauffer, et s'étendant dans le prolongement des découpes hautes jusqu'à l'extrémité distale opposée à l'anneau de raccordement.

Preferably, we do:

• so-called "high" longitudinal cutouts on the casing through the entire thickness of the casing, the cutouts extending between the connection ring towards the end of the crucible body opposite the ring without reaching the distal end of the crucible body,
• so-called "low" longitudinal cuts by electroerosion forming slots, each slot passing through the entire thickness of the casing, being narrow enough not to allow material to be heated to escape, and extending in the extension of the high cuts to the distal end opposite the connection ring.

• placer un noyau à l'intérieur du corps de creuset,
• obturer l'extérieur des découpes hautes au moins dans leur partie se raccordant avec les fentes, par exemple en plaçant un ruban d'obturation adhésif autour de l'enveloppe du corps de creuset,
• remplir les découpes hautes par de la résine,
• découper les fentes par électroérosion, notamment à fil,
• retirer ou dissoudre la résine.

The cutting of the slots is carried out according to the following steps:

• place a core inside the crucible body,
• seal the outside of the high cutouts at least in their part connecting with the slots, for example by placing an adhesive sealing tape around the casing of the crucible body,
• fill the high cutouts with resin,
• cut the slots by electro-erosion, in particular with wire,
• remove or dissolve the resin.

For example, each slot has a width of 0.35 millimeters. When cutting slots by electroerosion, it is imperative to maintain the sectors in position between them, otherwise they would deform during cutting (release of internal stresses in the copper).

To hold the sectors in position, a cylindrical core is inserted inside the crucible, the core being adjusted to the internal diameter of the crucible body. For example, the core is made of polytetrafluoroethylene called “PTFE”. Preferably, the core is placed in the body of the crucible at the level with the high cutouts and away from the area where the slots will be made. Then, an adhesive tape is inserted on the outside of the body of the crucible facing the core. Finally, a resin is applied in the high cutouts. This implementation makes it possible to unite the sectors with each other.

When cutting by electroerosion, it is essential that the wire allowing the cutting cannot come into contact with the resin, so that the cutting of the slots is not disturbed.

Once the slits have been made, the resin is dissolved using an appropriate solvent.

The cooling manifold is preferably made in two parts. These two parts are machined separately by turning and milling then assembled by welding. When assembled, the collector defines two circular cavities.

Description of Figures and Embodiments

• les figures 1a, 1b, 1c et 1d sont des vues d'un dispositif de chauffage par induction comprenant un creuset dit « poche » raccordé à un collecteur de refroidissement selon un mode de réalisation de l'invention, ledit creuset comprenant des découpes longitudinales dans l'enveloppe du creuset formant des secteurs séparés, chaque secteur comprenant un canal de liquide de refroidissement, la figure la étant une vue de face dudit dispositif, la figure 1b étant une vue en coupe du dispositif de la figure la selon un plan de coupe longitudinal passant par l'axe dudit dispositif et par des découpes diamétralement opposées, la figure 1c étant une vue en perspective et légèrement en contre-plongée du dispositif conforme à la figure 1a, la figure 1d étant une vue en perspective et en coupe du dispositif de la figure la selon un plan de coupe longitudinal passant par l'axe dudit dispositif et par des canaux diamétralement opposés ;
• les figures 2a et 2b sont des vues d'un creuset montrant un corps de creuset comprenant un anneau de raccordement et une enveloppe selon un mode de réalisation de l'invention conformes aux figures la à 1d, la figure 2a étant une vue de face du corps de creuset, la figure 2b étant une vue en coupe d'un corps de creuset conforme à la figure 2a selon un plan de coupe longitudinal passant par l'axe dudit corps de creuset et par des découpes diamétralement opposées ;
• la figure 3 est une vue en coupe d'un corps de creuset conforme à la figure 2a selon une coupe à plans perpendiculaires dont le premier plan passe par l'axe et par des découpes diamétralement opposées du corps de creuset et dont le second plan passe par l'enveloppe, la figure 3 montrant en particulier des secteurs séparés de l'enveloppe, chaque secteur comprenant un canal selon un mode de réalisation de l'invention,
• la figure 4 est un agrandissement d'une partie de l'anneau de raccordement du corps de creuset de la figure 2b, montrant une partie d'une région annulaire dudit anneau, ladite région comprenant une gorge de raccordement ;
• la figure 5 est un agrandissement d'un secteur vu en coupe de la figure 3, montrant des découpes au fond du corps de creuset ;
• la figure 6a est une vue en coupe d'un corps de creuset conforme à la figure 2a selon un plan de coupe longitudinal passant par l'axe dudit corps de creuset et par des canaux diamétralement opposées, une cloison de canal rapportée étant visible dans chaque canal ;
• la figure 6b montre un exemple de cloison de canal rapportée vue de face ;
• les figures 7a, 7b montre une première pièce tubulaire du collecteur de refroidissement selon un mode de réalisation, destiné à être reliée à une seconde pièce dudit collecteur, la figure 7a étant une vue de face de ladite première pièce, la figure 7b étant une vue en coupe de la pièce de la figure 7a montrant un alésage prévu pour le passage des matériaux à chauffer ;
• la figure 8 est une vue en coupe d'une seconde pièce du collecteur de refroidissement comprenant une cloison de séparation de collecteur, un orifice d'entrée d'un liquide de refroidissement et un orifice de sortie du liquide de refroidissement ;
• la figure 9 est une vue en perspective d'un corps de creuset comprenant des canaux de liquide de refroidissement dans lesquels sont insérées des cloisons de canal rapportées dont les extrémités proximales sont visibles ;
• la figure 10 est une vue en perspective d'un bouchon de canal selon un mode de réalisation, le bouchon comprenant une fente destinée à recevoir une extrémité proximale d'une cloison de canal rapportée ;
• les figures 11a et 11b montrent un corps de creuset dit « sans fond », selon un mode de réalisation, comprenant un anneau de raccordement et une enveloppe, la figure 11a étant une vue de face, la figure 11b étant une vue en coupe du corps de creuset de la figure 11a selon un plan de coupe passant par l'axe et des découpes diamétralement opposées du corps de creuset ;
• la figure 12 un agrandissement d'un dispositif de chauffage par induction vu en coupe de la figure 1d, montrant la communication du liquide de refroidissement entre le collecteur de refroidissement et le corps du creuset.

Other characteristics and advantages of the invention will appear on reading the detailed description of in no way limiting implementations and embodiments, with regard to the appended figures in which:

• the figures 1a, 1b, 1c and 1d are views of an induction heating device comprising a so-called "pocket" crucible connected to a cooling manifold according to one embodiment of the invention, said crucible comprising longitudinal cutouts in the casing of the crucible forming separate sectors , each sector comprising a coolant channel, FIG. la being a front view of said device, FIG. figure 1b being a sectional view of the device of FIG. la according to a longitudinal section plane passing through the axis of said device and through diametrically opposite cutouts, the figure 1c being a view in perspective and slightly from below of the device in accordance with the picture 1a , the figure 1d being a view in perspective and in section of the device of FIG. la according to a longitudinal section plane passing through the axis of said device and through diametrically opposite channels;
• the figures 2a and 2b are views of a crucible showing a crucible body comprising a connection ring and a casing according to one embodiment of the invention in accordance with FIGS. figure 2a being a front view of the crucible body, the figure 2b being a cross-sectional view of a crucible body in accordance with figure 2a along a longitudinal section plane passing through the axis of said crucible body and through diametrically opposite cutouts;
• the picture 3 is a cross-sectional view of a crucible body conforming to figure 2a according to a section with perpendicular planes, the first plane of which passes through the axis and through diametrically opposite cutouts of the crucible body and the second plane of which passes through the envelope, the picture 3 showing in particular separate sectors of the envelope, each sector comprising a channel according to one embodiment of the invention,
• the figure 4 is an enlargement of part of the connecting ring of the crucible body of the figure 2b , showing part of an annular region of said ring, said region comprising a connecting groove;
• the figure 5 is an enlargement of a section seen in section of the picture 3 , showing cutouts in the bottom of the crucible body;
• the figure 6a is a cross-sectional view of a crucible body conforming to figure 2a along a longitudinal section plane passing through the axis of said crucible body and through diametrically opposite channels, an added channel partition being visible in each channel;
• the figure 6b shows an example of an added channel partition seen from the front;
• the Figures 7a, 7b shows a first tubular part of the cooling manifold according to one embodiment, intended to be connected to a second part of said manifold, the figure 7a being a front view of said first piece, the figure 7b being a sectional view of the part of the figure 7a showing a bore provided for the passage of the materials to be heated;
• the figure 8 is a sectional view of a second piece of the cooling manifold including a manifold divider, a coolant inlet, and a coolant outlet;
• the figure 9 is a perspective view of a crucible body comprising coolant channels in which are inserted channel partitions whose proximal ends are visible;
• the figure 10 is a perspective view of a canal plug according to one embodiment, the plug comprising a slot intended to receive a proximal end of an added canal partition;
• the figures 11a and 11b show a so-called "bottomless" crucible body, according to one embodiment, comprising a connection ring and an envelope, the picture 11a being a front view, the figure 11b being a sectional view of the crucible body of the picture 11a along a cutting plane passing through the axis and diametrically opposite cutouts of the crucible body;
• the figure 12 an enlargement of an induction heating device seen in section of the figure 1d , showing the communication of coolant between the cooling manifold and the crucible body.

Description of an exemplary embodiment

The embodiments which will be described below are in no way limiting; it will be possible in particular to implement variants of the invention comprising only a selection of characteristics described below isolated from the other characteristics described, if this selection of characteristics is sufficient to confer a technical advantage or to differentiate the invention from to the state of the prior art. This selection includes at least one preferably functional feature without structural details, or with only part of the structural details if only this part is sufficient to confer a technical advantage or to differentiate the invention from the state of the prior art.

In particular, all the variants and all the embodiments described can be combined with each other if nothing prevents this combination from a technical point of view.

The figures 1a, 1b, 1c and 1d illustrate an induction heating device 1 intended to melt materials to produce alloys or melting pure metals to make castings in moulds, or refining in a particular atmosphere during melting. The heating device comprises a so-called “cold” crucible 10 intended to contain said materials to be heated, also called “the charge” (not visible in the figures). The charge is heated using an inductor wound (not shown) around crucible 10 and a generator (not shown). In known manner, the heating device also comprises a cooling manifold 30 distributing a cooling liquid in the crucible 10 connected to the latter.

We will first describe a crucible 10 of the “pocket” or “semi-levitation” type. With reference to figures 1a, 1b, 1c, 1d , 2a, 2b , 6a and 9 , the crucible 10 comprises a crucible body 11 containing the material to be heated.

The crucible body 11 comprises a connection ring 12 intended to allow the connection, on the one hand, mechanically, and, on the other hand, of the flows of cooling liquid between the crucible body and the cooling manifold. The connecting ring is a circular portion of the crucible body and is continuous in material along its circumference. The connecting ring will be described in more detail later.

The crucible body 11 comprises a tubular casing 14 extending axially from the connection ring 12 to define a heating volume. The crucible body comprises sectors 16 made in the tubular casing 14. The crucible body 11 has a one-piece structure composed of a single and same material having a continuity of material between the connection ring 12 and the sectors 16 of the tubular casing 14, including them. In the case of a crucible of the “pocket” or “semi-levitation” type, the crucible body 11 comprises a crucible bottom 110 that is substantially conical. The envelope 14 is cut longitudinally so as to produce several separate sectors 16. With reference to the figure 1b , 2b , 3 and 5 , so-called "high" longitudinal cutouts or interstices 18 are made in radial directions relative to the longitudinal axis of the crucible body and in the thickness of the tubular casing 14 so that the remaining casing portions form angular envelope sectors along the circumference of envelope 14 (see in particular the figure 3 and 5 ). With reference to figure 1b , 2b and 3 , the longitudinal cutouts 18 are made with a transverse depth equal to the distal end of the body of the crucible so that the bottom 110 of the body of the crucible is not cut over its entire thickness but according to a cutout having a width which may be substantially identical to the width of a cutout 18; since the bottom of the crucible 110 is conical. According to another embodiment, the width of the cutout at the level of the bottom 110 of the body of the crucible can be slightly different, either to increase the efficiency of the crucible, or to improve the cooling.

The high cutouts 18 have a width substantially equal to 3 to 4 millimeters. This makes it possible to limit the pressure drops, in particular in the case of production under vacuum.

The bottom of the crucible 110 also has longitudinal cutouts. With reference to figure 1b , 2b and 5 , longitudinal cutouts or slots 19 are made in radial directions with respect to the longitudinal axis of the crucible body and in the thickness of the bottom of the crucible body 110 so that the remaining bottom portions of the body form angular sectors envelope along the circumference of the bottom 110 of the crucible body. The slots 19 are made substantially in the extension of the upper cutouts 18 so that the sectors 16 are separated from the connecting ring to the distal end of the crucible body. Slots 19 have a width substantially equal to 0.35 millimeters.

According to the example shown, the crucible body has an internal diameter of 50 millimeters and comprises 16 sectors. The crucible body shown in figures 1b, 1d , 2b and 6a has at its distal end a pouring opening 111 allowing the charge to be poured by gravity into a mold located below. During use, a retractable finger (not shown) obstructs the end of the crucible body, for example a finger which is itself cooled.

The crucible body includes a coolant channel 15 in each sector 16. With reference to 1d figures , 3 and 6a , each cooling channel 15 is arranged longitudinally in the thickness of each sector. The channels 15 have a tubular shape.

With reference to 1d figures and 6a , the channels 15 extend to the bottom of the crucible body 110 so as to form a blind hole whose bottom, called the bottom of the channel, is designated by the reference 151. With reference to the figure 3 and 6a , the channels 15 open onto the upper surface of the connection ring 12 comprising an annular region 120. The annular region 120 forms a continuous part formed in the material of the one-piece crucible body.

The crucible body comprises several added channel partitions 20 so that each partition is provided to be inserted into a channel 15. In addition, each channel 15 is arranged and configured to receive a channel partition 20. It is inserted longitudinally into each channel and forms a tight longitudinal contact with at least two distinct regions of the peripheral internal wall of said channel. From the perspective of the bottom of the channel 151, the distal end of the channel wall 20 is spaced from the bottom of the channel 151 so as to leave a passage. For example, the width of the passage is substantially equal to the radius of the channel. Once inserted into a channel and with reference to figures 6a and 12 , each channel 15 has, inside the latter and on either side of the channel partition 20, a so-called "go" path 22 and a so-called "return" path 21 for the circulation of the coolant in each sector of the crucible body. The coolant can circulate from the outward path to the return path through the passage, provided for this purpose, near the bottom of the channel 151. On the side of the connecting ring (see picture 3 left side, 2b, 11b), the paths open into the annular region 120. For each channel 15, the annular region has a so-called "inlet" orifice 24, corresponding to the entry of a forward path 22, and a so-called "outlet" orifice 23, corresponding to the outlet of a return path 21. The inlet 24 and outlet 23 orifices must be arranged one beside the other and aligned along a radial direction of the crucible.

As we can see, especially in figure 3 and 6a , each channel 15 has an inlet 24 and an outlet 23 which are formed by the same opening of the channel 15 opening into the annular part. It is this common opening which is itself divided into an inlet opening 24 and an outlet opening 23 by the proximal end 200 of the channel partition 20. All of these openings each opening of a channel 15 is distributed in a single circle corresponding to the annular region 120.

According to a preferred embodiment, each channel further has two diametrically opposed grooves so as to receive and position each channel partition 20. The grooves form two distinct regions extending longitudinally in each channel and form a sealed longitudinal contact with the partition. channel 20 inserted into said channel.

The added channel partitions have a rectangular shape whose thickness is very much less than its length or its width so that they respectively form a plane. With reference to the figure 6b , the channel partition 20 has at its proximal end, designed to be close to the connecting ring, an enlargement of width 210 forming a shoulder. The widening 210 is provided to bear against a notch made on the surface of the annular region 120. Preferably, two diametrically opposite notches are made on the annular region 120 in order to receive the shoulders of the channel partitions.

With reference to figure 3 and 9 , each channel partition 20 is arranged in its channel 15 so that an imaginary geometric plane included in the thickness of the partition is substantially tangential to an imaginary cylinder of revolution concentric with the crucible. This feature makes it possible to radially delimit two coolant distribution regions, a first coolant inlet region comprising all the inlet orifices 24 and a second coolant return region comprising all the outlet orifices 23 It is then possible to connect a cooling manifold having no indexing, for example angular, in order to connect the cooling liquid inlet and outlet flows between the cooling manifold and the crucible body.

With reference to figures 2b, 3 and 4 , the annular region 120 comprises several connecting grooves 121 connecting the openings of the channels, or the notches provided for the channel partitions, so as to form a circular groove. The connecting grooves 121 are designed to be filled with resin forming a seal, radially delimiting, with the proximal ends 200 of the channel partitions, the two regions coolant distribution. With reference to figures 9 and 10 , the openings of the cooling channels are plugged by plugs 40 (see figure 9 showing a plug blocking a channel). Each plug 40 has a substantially cylindrical outer shape, the outer diameter of which is substantially equal to the inner diameter of each channel. Each plug 40 includes a septum slot 41 for receiving a proximal end of a channel septum (see figure 10 ), thus allowing the introduction of the plug into the channel comprising a partition so as to block the orifices of the channel. Once the channels are plugged, the connection grooves 121 are filled with resin. Once the resin has hardened, the plugs 40 are removed and the excess resin is removed, for example by machining, in order to obtain a flat surface and thus serve as a junction surface with a circular cooling manifold partition. Preferably, making the planar bearing may include machining the proximal end of the channel partitions.

With reference to figures 2a, 2b , 6a , the connection ring 12 has on its periphery a connection surface 13 comprising a crucible thread arranged to allow assembly by screwing with a cooling manifold comprising a complementary manifold thread so that the crucible can be screwed onto a manifold Or vice versa.

The figures 11a and 11b shows another type of crucible called "bottomless" or "continuous casting". In this embodiment, the crucible body does not include a conical crucible bottom 110, but has a heating volume having a constant internal diameter up to the end of the crucible body. For the rest, the crucible body of the figures 11a and 11b includes the same characteristics as a so-called “pocket” or “semi-levitation” crucible as described in the other figures.

A description will now be given of a cooling manifold 30 arranged and configured to be connected both mechanically and with respect to the circulation of the flows of cooling liquid between said manifold and a crucible body described above. From a mechanical point of view and reference to the figure 8 , the cooling collector comprises a first peripheral part 30a which has on an internal face a collector thread 31 complementary to the crucible thread so that they can be assembled by screwing.

With reference to figure 1b and 12 , the cooling manifold 30 comprises two manifold cavities forming the distribution elements: a so-called "go" cavity 34 and a so-called "return" cavity 33 which are substantially circular and which are arranged facing the annular region 120 of the connecting ring. The cavities 33, 34 are offset in a radial direction with respect to the axis of the manifold so that the outward cavity 34 faces the inlet orifices 24, and the return cavity 33 faces the outlet orifices 23. The cavities 33, 34 are separated by a circular manifold partition 32. The manifold partition 32 is provided to bear against the so-called “sealing” proximal ends 200 of the channel partitions (see figure 1b and 12 ). With reference to figures 1b, 1d and 12 the collector partition 32 has a conical shape.

The manifold also includes a coolant inlet 38 communicating with the outward cavity 34, and a coolant outlet 37 communicating with the return cavity 33 (see figure 1b and 8 ). The return cavity 33 is delimited radially by the collector partition 32 and by an internal edge 123 of the connection ring 12 (see figure 1b and 12 ).

With reference to Figures 7a, 7b , the collector comprises a second collector part 30b which comprises a tube 35 whose upper end comprises a flange 350. The volume delimited by the tube 35 corresponds to an insertion passage 36 via which the charge is inserted before being introduced into the heating volume delimited by the tubular envelope ( figures 1b and 1d ). The second collector part 30b is intended to be welded to the first collector part 30a (see figure 8 ). Preferably, the first manifold part 30a includes a counterbore 301 on its upper end. The cooling manifold is made by welding the flange 350 of the second manifold part 30b in the counterbore 301 of the first manifold part 30a, so as to obtain the cooling manifold 30 represented on the figures 1b and 1d .

The outgoing cavity 34 is thus delimited radially by the collector partition 32 and by the wall of the tube 35, see figure 12 .

With reference to the figure 12 , once the cooling manifold 30 is connected to the crucible body 11, the manifold partition 32 presses on the proximal ends of the channel partitions and the resin forming a seal, and the tube 35 presses on a chamfer 124 made on the annular region 120.

With reference to figures 1b and 1d , the collector 30 is arranged concentrically with respect to the crucible body 11. The cooling collector 30 comprises an insertion passage 36 via which the load is inserted before being introduced into the heating volume delimited by the envelope tubular.

Claims (15)

1. Cold crucible (10) for an induction heating device (1), characterized in that it comprises a crucible body (11) comprising:

   - a connection ring (12) comprising an annular distribution region (120),

   - a tubular casing (14) extending from the connection ring (12) to define a heating volume, the casing being cut longitudinally so as to produce several separated sectors (16),

   - coolant channels (15) arranged longitudinally in the thickness of the crucible body so that each sector (16) comprises at least one coolant channel (15),

   each sector comprising at least two coolant paths, an outward path (22) and a return path (21) for the coolant, formed by the at least one coolant channel (15), said paths leading into the annular distribution region (120) so that said region (120) has, for each sector, an inlet opening (24) and an outlet opening (23), the openings being spaced apart from one another along a radial direction of the crucible,

   thus forming, along the circumference of the annular distribution region, two distinct concentric regions around the longitudinal axis of the crucible, of which one communicates only with the outward path of the channels and the other communicates only with the return path of the channels,

   the crucible body being intended to be removably assembled with a cooling manifold (30) via the connection ring (12), the manifold (30) comprising coolant distribution elements connecting to the coolant channels (15), owing to this assembly, in order to circulate said liquid between the manifold and the channels,

   and in that said crucible body (11) has a one-piece structure composed of one and the same material having a continuity of material over at least two sectors.
2. Crucible (10) according to claim 1, characterized in that each channel comprises a fitted channel partition (20) inserted longitudinally in said channel (15) and forming an impermeable longitudinal contact with at least two distinct regions of the peripheral wall of said channel, so as to define the outward path (22) and the return path (21) on either side of said partition (20) and extending longitudinally inside one and the same channel (15).
3. Crucible (10) according to claim 2, characterized in that each channel partition (20) has a flat or two-dimensional shape and is arranged in its channel (15) so that an imaginary geometric plane comprised within the thickness of the partition is substantially tangential to an imaginary cylinder of revolution concentric to the crucible.
4. Crucible (10) according to claim 2 or 3, characterized in that each channel partition (20) has a length substantially equal to or smaller than the length of the channels, and is provided to be inserted in a channel, leaving a non-zero gap between the bottom (151) of the channel and the longitudinal end, called passage end, of the channel partition.
5. Crucible (10) according to one of claims 2 to 4, characterized in that each channel (15) comprises, in its wall, two distinct grooves arranged and configured to receive and position each partition (20) in said channel.
6. Crucible (10) according to any one of the preceding claims, characterized in that the connection ring (12) comprises, on its circumference, a crucible thread (13) arranged to allow an assembly by screwing so that a cooling manifold (30) equipped with a manifold thread (31) which is complementary to it can be screwed onto the crucible or vice versa.
7. Cooling manifold (30) intended to cooperate with a cold crucible (10) for an induction heating device (1), the crucible comprising:

   - a connection ring (12) comprising an annular distribution region (120),

   - a tubular casing (14) extending from the connection ring (12) to define a heating volume, the casing being cut longitudinally so as to produce several separated sectors (16),

   - coolant channels (15) arranged longitudinally in the thickness of the crucible so that each sector (16) comprises at least one coolant channel comprising a channel partition (20), forming, in each channel, at least two paths (21, 22) leading respectively through two openings (23, 24) spaced apart from one another along a radial direction of the crucible,

   the manifold being characterized in that it has two manifold cavities (33, 34) which are substantially circular and are arranged on one and the same face being face-to-face with the connection ring, the manifold cavities being offset in a radial direction with respect to the axis of the manifold so that each manifold cavity (33, 34) is located above a single opening (23, 24) of each channel once the manifold and the crucible have been assembled.
8. Manifold (30) according to the preceding claim, characterized in that it comprises a circular manifold partition (32) separating said two manifold cavities (33, 34), said manifold partition (32) resting against ends, called sealing ends, (200) of the channel partitions.
9. Manifold (30) according to claim 7 or 8, characterized in that it comprises, around the manifold cavities, a manifold thread (31) arranged to allow an assembly by screwing so that a crucible body (10) also comprising a complementary crucible thread (13) can be screwed onto the manifold (30) or vice versa.
10. Induction heating device (1) comprising a cold crucible body (10) according to one of claims 1 to 6 and a cooling manifold (30) according to one of claims 7 to 9 arranged in order that, when they are assembled together, the coolant distribution elements (33, 34) of the manifold (30) connect to the coolant channels (15) of the crucible body (10).
11. Method for manufacturing a cold crucible (10) for an induction heating device, the crucible comprising a crucible body (11) communicating with a cooling manifold (30), the crucible body comprising a tubular casing (14) extending from the cooling manifold and surrounding a heating chamber comprised within a heating volume, the casing being cut longitudinally so as to produce several separated sectors (16), coolant channels (15) arranged longitudinally in the thickness of the crucible so that each sector (16) comprises at least one coolant channel (15), the method comprising the following steps:

    - providing one or more one-piece starting parts or blanks, made of a thermally and electrically conductive material, preferably of copper, for example a solid circle or a tube,

    - for each starting part, machining the part to the desired external and internal dimensions, according to the desired crucible size, in order to produce a crucible body forming a connection ring from which the tubular casing extends,

    as well as, in this order or in another order, the following steps:

    - producing a crucible thread (13) on the circumference of the connection ring (12),

    - producing bores corresponding to the coolant channels (15) and leading into the surface of the connection ring (12),

    - producing two grooves, diametrically opposite, in the wall of each channel (15),

    - producing longitudinal cuts (18, 19) on the casing (14) through the whole thickness of the casing, the cuts extending between the connection ring (12) and up to the end of the crucible body opposite the ring.
12. Method according to claim 11, characterized in that a circular machining is carried out on the transverse face onto which the channels lead so as to form a circular connection groove (121), when the bores have not yet been produced, and a succession of grooves (121) between the openings of the bores when the bores have been produced, and in that a hardenable resin is introduced into the grooves (121) so as to fill them in order to ensure the sealing between two channels.
13. Method according to claim 11 or 12, characterized in that a channel partition is introduced into each channel after having produced the grooves.
14. Method according to one of claims 11 to 13, characterized in that the following are produced:

    - longitudinal cuts called "top" (18) on the casing (14) through the whole thickness of the casing, the cuts extending between the connection ring (12) towards the end of the crucible body opposite the ring without reaching the distal end of the crucible body,

    - longitudinal cuts called "bottom" by means of spark erosion, forming slits (19), each slit passing through the whole thickness of the casing, being narrow enough to prevent a material to be heated from escaping, and extending in the extension of the top cuts (18) up to the distal end opposite the connection ring.
15. Method according to the preceding claim, characterized in that the cutting of the slits (19) is carried out according to the following steps:

    - placing a core inside the crucible body (11),

    - sealing the outside of the top cuts, at least in their part connecting to the slits, for example by placing an adhesive sealing tape around the casing of the crucible body,

    - filling the top cuts with resin,

    - cutting the slits by means of spark erosion, in particular wire erosion,

    - removing or dissolving the resin.

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