MXPA04009660A - Induction furnace for high temperature operation. - Google Patents

Abstract

An induction furnace capable of operation at temperatures of over 3100¦C has a cooling assembly (60), which is selectively mounted to an upper end of the furnace wall (76). The cooling assembly includes a dome (62), which is actively cooled by cooling water coils (68). During the cool -down portion of a furnace run, cooling initially proceeds naturally, by conduction of heat away from the hot zone through a furnace insulation layer (58). Once the temperature within the furnace hot zone (20) reaches about 1500¦C, a lifting mechanism (80), mounted to the dome, raises a cap (16) of the furnace slightly, allowing hot gases from the hot zone to mix with cooler gas in the dome. This speeds up cooling of the hot zone, reducing cool-down times significantly, without the need for encumbering the furnace itself with valves or other complex cooling mechanisms which have to be replaced periodically. The life of a graphite furnace susceptor (10) at the high operating temperature is increased by surrounding the susceptor with a barrier layer (40) of flexible graphite, which inhibits evaporation of the graphite. Additionally, witness disks (154), placed within the susceptor, provide an accurate temperature profile of the hot zone.

Description

INDUCTION OVEN FOR HIGH TEMPERATURE OPERATION BACKGROUND OF THE INVENTION FIELD OF THE INVENTION The invention relates to an induction furnace suitable for operating at temperatures of about 3,000 ° C and more. It finds particular application in conjunction with the graphiting of natural bitumen fibers and other fibers containing carbon, and will be described with particular reference to them. However, it should be appreciated that the furnace is also suitable for other high temperature processes, such as the halogen purification of granitic materials to remove metallic impurities.

DISCUSSION OF THE TECHNIQUE Intermittent induction furnaces have been used for many years to graph fibers and for other high temperature operations. A typical induction furnace includes an electrically conductive container, known as a susceptor. A variable electromagnetic field is generated over time by flowing alternating current (AC) in an induction heating coil. The magnetic field generated by the coil passes through the susceptor. The magnetic field induces currents in the susceptor, which generate heat. The material to be heated is contained within the susceptor, in what is commonly referred to as the "hot zone" or the hottest part of the furnace. For operations requiring high temperatures, up to 3,000 ° C, graphite is a preferred material for forming the susceptor, since it is both electrically conductive and capable of withstanding very high temperatures. However, there is a tendency for graphite to sublime, becoming vapor. Sublimation increases markedly as the temperature rises above about 3,100 ° C. Due to variations in temperature throughout the susceptor, the oven life, at a nominal operating temperature of about 3,100 ° C, is typically measured in weeks. Life at 3,400 ° C is often only a matter of hours. Thus, furnaces that are operated at temperatures of more than 3,000 ° C, tend to suffer a considerable downtime to replace the components. The graffiti of carbon-containing fibers, in particular, benefits from treatment temperatures of over 3,000 ° C. For example, in the formation of lithium batteries, the absorption of lithium depends on the graphite temperature, which improves as the graphite temperature increases. Some improvements have been achieved in the distribution of heat throughout the entire susceptor, measuring the temperatures at different points inside the furnace during heating, by using pyrometers. Then different induction current densities are supplied to multiple sections of the susceptor, along its entire length, according to the measured temperatures. However, pyrometers are susceptible to failure and need to be recalibrated over time. To increase the life time of the susceptor it is convenient to quickly cool the oven, once the heating operation at high temperature is completed. Typically cooling coils carry water around the furnace. However, because the oven is generally well insulated, it often takes about a week to cool the oven from its operating temperature. In some applications, heat exchangers are used to accelerate cooling. In these designs, the oven is cooled to a temperature of approximately 1,500 ° C, due to heat loss through the insulation of the oven. Then the valves located above and below the hot zone are opened, and forced circulation is initiated through an external heat exchanger. This system works well for ovens that rarely work above 2,800 ° C. In furnaces routinely operated above 3,000 ° C, frequent replacement of hot zone components makes these designs costly to operate. In other designs, the loose insulation material, located above the furnace, is struck so that it is detached from the furnace, in order to accelerate cooling. As a result, it is necessary to replace the insulation after each operation of the oven. The present invention provides a new and improved induction furnace, and a method of use, which solves the problems referred to above, and others.

BRIEF DESCRIPTION OF THE INVENTION In accordance with one aspect of the present invention, an oven is provided. The oven includes a container defining an interior chamber for receiving the articles to be treated, and a heating means that heats the container. A lid selectively closes the interior chamber of the container. A chiller assembly includes a dome defining a chamber and an elevator mechanism, which selectively raises the lid, which allows hot gas to flow from the interior chamber of the container to the dome. In accordance with another aspect of the present invention, a cooling assembly for an oven is provided. The cooler assembly includes a dome that defines an interior chamber. A cooling medium cools the dome. The assembly includes means for selectively providing fluid communication between a hot zone of the induction furnace and the dome, and means for controlling the communication means, according to at least one of the following: the temperature of the hot zone and the temperature of the inner chamber. According to yet another aspect of the present invention, an induction furnace is provided. The furnace includes a susceptor that defines an interior chamber to receive the articles to be treated; the graphite susceptor is formed. An induction coil induces a current in the susceptor, to heat the susceptor. A flexible graphite layer, external to the susceptor, inhibits the escape of carbon vapor that has been sublimated from the susceptor. According to a further aspect of the present invention, a method for operating a furnace is provided. The method includes heating the articles to be treated in a first chamber containing a gas, and actively cooling a second chamber containing a gas. The second chamber is selectively connectable fluidly with the first chamber. After the step of heating, the first chamber is cooled selectively by fluidly connecting the first chamber with the second chamber, which allows heat to flow from the gas of the first chamber to the gas of the second chamber. It is an advantage of at least one embodiment of the present invention that the life of the furnace is significantly increased. It is another advantage of at least one embodiment of the present invention that stopping times for cooling are reduced. Another advantage of at least one embodiment of the present invention is that the cooling assembly is removable from the furnace, which simplifies the separation and replacement of the susceptor and other components of the hot zone. Other advantages of at least one embodiment of the present invention are derived from the greater precision in monitoring the variations in the temperature of the oven, in the whole oven. Still other additional advantages of the present invention will be readily apparent to those of ordinary skill in the art, when the following description is read and the accompanying drawings are reviewed.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a side sectional view of an intermittent induction furnace, according to the present invention; showing an oven lid in a closed position. Fig. 2 is a side sectional view of the intermittent induction furnace of Fig. 1, showing the lid of the furnace in an open position. Figure 3 is an enlarged sectional view, taken in A-A of Figure 2, of the wall of the furnace; which shows a pyrometer mounted on it. Figure 4 is an enlarged side sectional view of the wall of the oven of Figures 1 and 2, showing a pyrometer mounted thereon. Figure 5 is a side sectional view of the cooler assembly of the figure 1. Figure 6 is a graph illustrating the effects of the chiller assembly on the furnace temperature over time. Figure 7 is an enlarged side sectional view of the actuator of Figure 5. Figure 8 is an enlarged sectional view of the sealing and guiding mechanism of Figure 5. Figure 9 is a side elevational view of the dome of the Figure 5, showing the cooling coils mounted outside. Figure 10 is a top plan view of the dome of Figure 5, showing the cooling coils mounted on the outside; and Figure 11 is a side sectional view of the locking mechanism of Figure 5.

DETAILED DESCRIPTION OF THE PREFERRED MODALITY With reference to Figures 1 and 2, an induction furnace, suitable for operating at temperatures of more than 3,000 ° C includes a susceptor 10 formed of an electrically conductive material, such as graphite. The susceptor includes a cylindrical side wall 12, closed at a lower end by a base 14. A removable insulating cover 16 closes an open upper end 18 of the susceptor, to define an interior chamber 20, which provides a hot zone for receiving the articles that are going to be treated. The lid 16 includes a lid portion 22, formed of graphite, which sits on a pedestal 24, defined by the susceptor adjacent the upper end 18. The lid portion 22 is fixed to a lower surface of an insulating plug 26, elongated , preferably formed from a rigid insulation material, such as a rigid graphite insulation. The cap 26 has a peripheral flange extending outwardly at its upper end. The lid 16 closes the inner chamber 20 during a heating phase of an induction furnace operating cycle, which allows the furnace to operate under a slight positive pressure of an inert gas, such as argon. The inert gas is one that does not react with the components of the furnace or with the product that is being heat treated, to the scale of temperatures to which the components and the product are exposed. This prevents the oxidation of the carbon and graphite components of the furnace, and of the product that is being heat treated. At operating temperatures below about 1,900 ° C, nitrogen can be used as an inert gas, which is replaced with argon when the temperature reaches this level. Preferably the positive pressure is up to about 20 kg / m2. The susceptor 10 is heated inductively by an induction coil 30, powered by an AC source (not shown). The coil 30 produces an alternating magnetic field, which passes through the susceptor, which induces an electric current in the susceptor and which makes it hot. The articles that are to be treated with heat, such as the bitumen fibers to form graphite, are placed in a receptacle 32, which is preferably formed of graphite. The receptacle 32 is loaded in the chamber 20 of the susceptor, before operating the oven. Heat is transferred from the susceptor to the fibers, by radiation. The induced current flowing through the susceptor 10 is not uniform throughout its cross section. The current density is greater at an outer surface 34, and decays exponentially towards an inner surface 36. The thickness of the susceptor is selected to obtain a relatively uniform current profile throughout the susceptor and induce some current and some heat directly in the graphite receptacles 32, inside the oven. A suitable thickness for the oven is approximately 5 cm. The temperature profile across the cross section of the susceptor is of temperature that rises, from the outer surface 34, to a maximum within the susceptor, and then decreases to colder on the inner surface 36. As best shown in the Figures 3 and 4, the outer surface 34 of the susceptor is wrapped with a barrier layer 40, of a flexible graphite sheet material. Suitable graphite sheet can be obtained under the trademark Grafoil® from Graftech Inc., Lakewood, OH, USA Preferably the flexible graphite sheet material is formed by intercalating graphite flakes with an intercalation solution comprising s, such as a combination of sulfuric and nitric s, and then exfoliating the particles interspersed with heat. By exposing to a sufficient temperature, typically about 700 ° C or more, the particles expand in an accordion-like manner to produce particles that have a vermiform appearance. The "worms" can be compressed together to flexible or integrated sheets of expanded graphite, typically called "flexible graphic", without the need for binder. The density and thickness of the sheet material for the barrier layer 40 can be varied by controlling the degree of compression. The density of the sheet material is generally within the approximate scale of about 0.4 g / cm3 to 2.0 g / cm3, and preferably the thickness is about 0.7 to 1.6 mm. An adhesive (not shown) can be applied between the flexible graphite sheet 40 and the external surface 34 of the susceptor 10, to keep the sheet in contact with the susceptor during assembly of the oven. Preferably the graphite sheet covers the entire outer surface 34 of the susceptor, including the side wall 12 and the base 14, although it is also contemplated that the graphite sheet can be used only adjacent to those areas that are heated to the highest temperatures , commonly called the "hot zone". The graphite sheet material serves as a vapor barrier around the susceptor, which inhibits the escape of carbon vapor that has been sublimated from the surface 34 of the susceptor. This causes the partial pressure of the carbon vapor to increase in the region adjacent to the susceptor. Soon a balance is reached between the vaporization rate and the rate of redeposition of the carbon on the susceptor, which inhibits the additional loss of graphite vapor from the susceptor. By continuing with reference to Figures 1 and 3, the susceptor is housed in a pressure vessel 50, formed, for example, of glass fiber, with a lower flange 52, formed of aluminum. The pressure vessel is lined with cooling tubes 54, preferably formed of a non-magnetic material, such as copper. The cooling coils are arranged in vertical tortuous circuits. The cooling tubes are electrically insulated from each other, to prevent current flow in the circumferential direction. A cooling fluid, such as water, is operated through the cooling tubes at all times, to prevent overheating of the tubes and other components of the furnace. The cooling tubes are embedded in a thick layer 56 of a refractory material, comprising primarily silicon carbide; what provides good thermal conductivity, good resistance and good thermal insulation. A layer 58 of an insulation material, such as carbon black, is packed between the refractory material and the susceptor 10, adjacent the sides 12 and the base 14. The flexible graphite layer 40 is held in place, during the operation of the furnace, by layer 58 of insulation material. The carbon black preferably is in the form of a fine powder, which allows it to be extracted by vacuum from the furnace, when it is time to replace or repair the susceptor 10. Then the susceptor is easily removed from the furnace. The thickness of layer 58 of the insulating material is kept to a minimum to allow rapid cooling times. The level of insulation is preferably selected to prevent excessive heat losses, and at the same time to provide the shortest cooling time possible. The increased energy requirements for heating, as compared to a conventional furnace, are counteracted by the gain in furnace productivity, derived from the rapid stopping time for cooling. Referring now to Figure 5, a cooling assembly 60 is selectively mountable at an upper end of the furnace, to close the upper end of the chamber 20 of the susceptor. The cooling assembly includes a dome 62, formed of copper or other non-magnetic material. The dome 62 defines an interior dome chamber 64, gas-tight, which maintains an inert gas at a slight positive pressure. During the heating portion of the oven operating cycle, a lower end 66 of the dome is closed with respect to the chamber 20 of the susceptor, by the lid of the oven 16 (Figure 1). It is not necessary for the lid 16 to seal the inner chamber 20 of the ambient environment, since the dome serves that purpose. The dome is actively cooled during the cooling portion of the furnace cycle. Specifically, as shown in Figures 9 and 10, cooling coils 68 are provided on an outer surface of the dome and are connected with an external heat exchanger 70. Preferably the entire surface of the dome is used for cooling, in order to Maximize the rate of heat removal. A first set of cooling coils 68A surrounds a cylindrical side wall 72 of the dome; while a second set of cooling coils 68B is disposed outside with respect to an upper wall 74 of the dome. The cooling assembly 60 is movable by a hoist (not shown) suitably disposed from a position away from the oven to a position on the upper end of the oven. A peripheral flange 76, at the lower end of the dome, is secured to an upper portion 78 of the furnace wall (comprising the upper ends of the refractory material and the glass fiber pressure vessel, respectively), which extends through on top of the susceptor (figure 2). The dome serves as a heat exchanger for the oven during cooling. As shown in Figure 5, a lifting mechanism 80 is operable to lift the lid 16 of the oven. This creates an opening 82 (Figure 2) between the furnace chamber and the dome chamber 64. Specifically, the lid 16 is raised from the closed position, shown in Figure 1, where the lid portion 22 sits on the pedestal 24, to an open position, shown in Figure 2, where the lid portion is spaced from the pedestal. The rapid mixing of the hot gas from the susceptor chamber 20 and the cold gas inside the dome 62 takes place by natural convection. The degree of opening is adjusted by raising the lid 16 using a feedback control to limit the temperature inside the dome chamber 64, less than the copper melting point, preferably in the approximate range of 200 to 300 ° C, if optionally, higher temperatures are optionally maintained when detection and temperature control are particularly accurate. Cover 16 is movable, in infinitely variable quantities, in the direction of the arrow B, to a position in which it is totally housed in the dome (figure 5). The entire cooling assembly 60 is detachable from the furnace, which allows the susceptor 10 to be easily removed for repair or replacement. An immobilizing mechanism 84, which is best shown in Figure 11, selectively immobilizes the peripheral flange 76 of the cooling mechanism to the wall 78 of the furnace. In that way, the dome 62 seals the upper end of the chamber 20 and the dome chamber 64 with respect to the external environment, during an operation of the oven. The immobilizing mechanism 84 includes a cooling coil 86, which is fed with cooling water, to keep the immobilizing mechanism cool. Optionally, as shown in Figure 1, an external support 88 holds most of the weight of the dome, to avoid potential damage to the upper end of the wall of the oven 78. With reference to Figure 5, one or more temperature detectors 90, such as thermocouples, are located within the dome 62. The temperature detectors provide a signal to control the system 92, which signals the lifting mechanism 80 to lower the lid to decrease the size of the opening 82, if the temperature within the the dome chamber 64 becomes high, and instructs the hoist mechanism to increase the size of the opening by raising the lid 16, if the temperature drops below a preselected level. Optionally, as shown in Figure 5, fluid mixing means, such as fans 94, are provided within the dome chamber 64, to improve the flow of gases between the susceptor chamber 20 and the dome chamber 64. . Above about 1,500 ° C, heat flows more rapidly through the sides of the furnace and, thus, the rate of cooling through the insulating layer 58 is relatively rapid. Thus, the cooling effects of the dome 62 are not beneficial, generally, during an initial period of the cooling portion of the cycle. The lid 16 of the furnace, therefore, is preferably kept closed during this initial cooling period, between about 3,100 ° C and about 1,500 ° C. Once the furnace temperature reaches about 1500 ° C, the insulation material inhibits cooling and the cooling action of the dome 62 becomes effective. Therefore, it is preferable, at this stage, for the lifting of the lid 16. Figure 6 demonstrates the effect of the upper cooling assembly 60 on the cooling rate of the oven. Two curves are shown: one showing the predicted cooling of a domeless furnace, and the other showing the predicted cooling using dome 62. It can be seen that the cooling time is approximately 48 hours when the dome is used, reducing thus the stoppage time for cooling, in total, approximately in half. These results were predicted for a susceptor of 63 cm of internal diameter, 241 cm of height and 4.65 m2 of heat transfer area in the dome (ie, the total area of the side wall 72 of the dome and of the upper wall 74 of the dome). With reference again to FIG. 5, and also with reference to FIG. 7, the lifting mechanism 80 advantageously includes a linear actuator 100. The actuator 100 is coupled at its lower end to a mounting plate 102, by means of a gasket. coupling 104. The mounting plate 102 is mounted to the upper wall 74 of the dome by bolts 106, or other suitable fastening members. The linear actuator 100, which may comprise a piston 107 operated pneumatically or hydraulically, is extended or retracted to push on, or to release one end of a roller chain 108, which passes over a pulley system 110. The other end of the chain 108 is connected to an upper end of a cylindrical hoist bar 112, vertically oriented. The linear actuator 100, the mounting plate 102, the chain 108 and the pulley system 110, are supported within a housing 114, formed of stainless steel or the like, and are not subject to the hot gases, inside the chamber 64. of dome. A lower end of the hoisting bar 112 extends within the dome chamber 64, and is coupled with the oven cover 16, by means of a stainless steel coupling 120. The coupling 120 is mounted to a graphite support bar 121, which extends directly through the cover 16. With reference also to FIG. 8, the bar 112 passes through a first opening 122, in the mounting plate 102. of the actuator, and a second opening 124 in the upper wall 74 of the dome. By continuing with reference to Figure 8, a seal and guide assembly 130 serves to guide the lower end of the bar 112 through the openings 122, 124, and to provide a seal between the dome chamber 64 and the interior of housing 114. Specifically, the seal and guide assembly includes a cylindrical sleeve 132, formed of stainless steel. The sleeve is welded, or otherwise mounted, at a short distance above its lower end 133, to an annular mounting flange 134, which in turn is bolted to the mounting plate 102, around the opening 122. An upper end of the sleeve is mounted to a second annular flange 136 by bolts 138. The lower end 133 of the sleeve 132 extends below the mounting flange 102. An annular seal 140, such as a toroidal ring, is pressed at the end lower 133 of the sleeve 132 against a top surface of the upper wall 74 of the dome. The seal is sealingly engaged with the lifting bar 112, when moving up and down through it. A spacer tube 142 is supported within the sleeve 132, between upper and lower bearings 144, 146, which are seated against the flange 136 and seal 140, respectively. The separator tube 142 receives the lifting rod 1 12 therethrough. Returning once again to the operation of the furnace, several pyrometers 150 (three, in the preferred embodiment) are mounted in thermal communication with corresponding tubes 152, which pass through the wall 12 of the susceptor, into the susceptor chamber 20 ( Figures 2-4). The pyrometers 150 are placed in different regions of the susceptor chamber 20 and allow to monitor the surrounding temperature during heating and cooling of the susceptor chamber. Preferably, the pyrometers 150 point to the control system 92, which uses the detected temperatures to determine when to signal the lifting mechanism 80 to start lifting the lid 16. Several test discs 154 are also placed in the susceptor chamber 20, in various points throughout the hot zone, before starting a kiln cycle. The control discs 154 provide an accurate determination of the maximum temperature at which each disc has been exposed. In a preferred embodiment, the control discs are formed of carbon, which is graphitized during the operation of the oven. The maximum temperature is determined by measuring the size of the graphite crystallites in the exposed discs 154, and comparing the measurements with those obtained from sample discs, accurately calibrated. X-ray diffraction techniques are available for the automatic determination of the crystallite size, from the diffraction patterns produced. The control discs 154 are examined after the furnace is operated to reveal a more detailed pattern of temperature distribution than can be provided by the pyrometers 150 alone. Additionally, discs 154 provide a check for pyrometers 150, which tend to lose their calibration over time, or to fail completely. Due to the low cost of the discs, and the ease of use, many more control discs can be used than is possible with pyrometers. The discs 154 are discarded after each operation of the oven and replaced with new discs. Preferably a database is maintained for each furnace, for storing pyrometer readings and disk measurements, and analyzed for trends. Pyrometer errors, final effects on the induction coil and poorly insulated areas can be detected and corrected in the course of several oven cycles. A typical operation of the oven is as follows. The articles to be treated are loaded, such as natural bitumen fibers that are to be converted to graphite, in one or more of the receptacles 32. The receptacles are closed and placed inside the susceptor chamber 20 together with several new 154 witness discs. The cooling assembly is maneuvered by a hoist (not shown) properly located until the flange 76 is seated on the wall portion 78 of the oven. The atmosphere is replaced within the susceptor chamber 20 and the dome chamber 64, with an inert gas, at a slight positive pressure. The inert gas is continuously passed through the chamber 20 during operation, by means of input and output power lines (not shown). The lid 16 is lowered by the linear actuator 100, to the closed position, in which the lid closes the chamber 20 of the susceptor. The flow of cooling water is started through the cooling tubes 54 (cooling of the dome may be delayed until a later time, before lifting the lid 16). The induction coils 30 are energized to heat the susceptor 10, thereby bringing the susceptor chamber 20 to the operating temperature. This can take from one to two days or more. Once the operating temperature, e.g., 3,150 ° C, is reached, the temperature in the susceptor chamber 20 is maintained at the operating temperature, for a sufficient period of time to achieve the desired level of graphite or to complete the another way a treatment process. The control system 92 employs feedback controls, based on pyrometer measurements, to drive the induction coils 30, according to the detected temperatures. Once the heating phase is completed, the energy for the induction coils 30 is turned off, and the furnace is started to cool by conduction through the insulation layer 58. Once the temperature of the susceptor chamber 20 drops at approximately 1,500 ° C, instructions are given to the linear actuator 100 to slightly raise the lid 16, to an open position, which allows the hot gas inside the susceptor chamber 20, to mix with the coldest gas within the chamber. the 64th dome camera. When the temperature inside the susceptor chamber falls further, the actuator 100 lifts the lid 16 further away from the chamber, which increases the size of the opening 82, so that the maximum cooling rate can be maintained, without overheating the 64 dome camera. Below about 1000 ° C, the pyrometers 150 are preferably replaced by thermocouples. Once the chamber 20 of the susceptor reaches a suitable low temperature, the cooling assembly 60 is removed or otherwise opened to the atmosphere, for example, by opening valves (not shown) in the dome 62. The improved cooling provided by the cooling assembly 60, the flexible graphite barrier layer 40, and the precise temperature monitoring, provided by the witness discs 154 described, all contribute to improving the operation of the furnace. The life of the susceptor is significantly improved by the use of flexible graphite. Tests in which one wall of the susceptor was protected by flexible graphite, while another part was left unprotected, showed visible differences in the thickness of each of those parts of the susceptor, after only a short period of time. It has been found that ovens operating at more than 3,000 ° C take at least four to five times longer between the susceptor replacements than conventional ovens, which operate without the flexible graphite barrier layer 40. The induction furnace It is suitable for prolonged operation at operating temperatures of up to 3,150 ° C, which had not been possible with the previous induction heaters. It will be appreciated that, although the cooling assembly has been described with reference to an induction furnace, the cooling system can also be used to cool other types of furnaces, which operate at high temperatures. The invention has been described with reference to the preferred embodiment. Obviously they will occur to other modifications and alterations when they read and understand the preceding detailed description. It is intended that the invention be considered including all those modifications and alterations that fall within the scope of the claims that follow, or their equivalents.

Claims (28)

1. - A homo, characterized in that it comprises: a container that defines an interior chamber for receiving articles to be treated; means for heating the container; a lid that selectively closes the interior chamber of the container; and a cooling assembly, which includes: a dome, which defines a chamber; and a lifting mechanism that selectively lifts the lid, allowing hot gas to flow from the inner chamber of the vessel, to the dome.

2. - The oven according to claim 1, further characterized in that the dome is selectively mountable on the container.

3. The furnace according to claim 1, further characterized in that the lifting mechanism includes a linear actuator.

4. The furnace according to claim 3, further characterized in that the linear actuator is operatively connected to the lid by means of a hoist bar.

5. - The furnace according to claim 4, further characterized in that the lower end of the hoist bar is mounted to move vertically within the dome, and the linear actuator is carried by the dome.

6. - The oven according to claim 1, further characterized in that the lifting mechanism moves the lid between a first position, in which the lid closes the interior chamber of the container, and a second position, in which the lid is in position inside the dome's camera.

7. - The furnace according to claim 1, further characterized in that the dome chamber is capable of maintaining a positive pressure of an inert gas.

8. - The furnace according to claim 1, further characterized by including: cooling means to actively cool the dome.

9. The furnace according to claim 8, further characterized in that the cooling means includes cooling coils mounted on a surface of the dome, through which a cooling fluid is passed.

10. - The oven according to claim 1, further characterized in that it further includes: a temperature detector, which monitors the temperature of the dome.

11. - The furnace according to claim 1, further characterized in that the heating means includes an induction coil, and the container includes a susceptor; inducing the induction coil a current in the susceptor, to heat the susceptor.

12. - The furnace according to claim 11, further characterized in that the dome is formed of a non-magnetic material.

13. The furnace according to claim 11, further characterized in that the susceptor is formed of graphite; including further the induction furnace: a layer of flexible graphite, external to the susceptor, which inhibits the escape of carbon vapor that has been sublimated from the receiver.

14. - A cooling assembly for an induction furnace, characterized in that it comprises: a dome defining an interior chamber; cooling means for cooling the dome; means for selectively providing fluid communication between a hot zone of the induction furnace and the dome; and means for controlling the communication means according to at least one of: the temperature of the hot zone; and the temperature of the inner chamber.

15. - The assembly according to claim 14, further characterized in that the cooling means include: cooling coils, through which a cooling fluid is passed to cool the dome.

16. - The assembly according to claim 14, further characterized in that the means for selectively providing fluid communication include: a lifting mechanism, which selectively moves a lid of the oven from a first position, in which the lid closes the hot zone with respect to the inner chamber of the dome; and a second position in which hot gas flows from the hot zone towards the dome.

17. An induction furnace, characterized in that it comprises: a susceptor that defines an interior chamber to receive articles that are going to be treated; the susceptor being formed of graphite; an induction coil, which induces a current in the susceptor to heat the susceptor; and a layer of flexible graphite, outside the susceptor, which inhibits the escape of coal vapor that has been sublimated, from the susceptor

18. - The furnace according to claim 17, further characterized in that it additionally includes: a layer of insulation material powder, packed around the flexible graphite layer, which keeps the flexible graphite layer in contact with the susceptor.

19. - A method for operating a furnace, characterized in that it comprises: heating the articles to be treated, in a first chamber containing a gas; actively cooling a second chamber containing a gas; the second chamber being selectively connectable fluidly with the first chamber; after the step of heating, cool the first chamber by fluidly selectively connecting the first chamber with the second chamber, so as to allow heat to flow from the gas of the first chamber, to the gas of the second chamber.

20. - The method according to claim 19, further characterized in that it additionally includes: detecting a temperature of the second chamber; and controlling the size of an opening between the first and second chambers, to ensure that the temperature of the second chamber remains below a preselected level.

21. The method according to claim 19, further characterized in that it further includes: before the step of heating, placing control discs in the first chamber; and after the step of cooling the first chamber, removing the control discs and examining the discs to determine a maximum temperature at which each disc was exposed during the heating step.

22. - The method according to claim 19, further characterized in that the step of heating includes heating the first chamber to a temperature of at least 3,000 ° C.

23. - The method according to claim 22, further characterized in that the step of heating includes: heating the first chamber to a temperature of at least 3,100 ° C.

24. - The method according to claim 22, further characterized by including, before the step of heating: encircling a wall of the first chamber, which is formed of graphite, with a flexible graphite material, which inhibits the evaporation of graphite from the wall, during the heating step.

25. - The method according to claim 19, further characterized in that the gas in the first and second chambers is an inert gas, at a positive pressure.

26. - The method according to claim 19, further characterized in that the step of cooling the first chamber includes selectively connecting the first chamber fluidly with the second chamber, when the temperature inside the first chamber drops to approximately 1,500 ° C. .

27. - The method according to claim 19, further characterized in that the step of fluidly selectively connecting the first chamber with the second chamber, includes: lifting a lid that selectively closes the first chamber, to provide an opening between the chambers first and second; the size of the opening being adjustable by raising or lowering the lid.

28. - The method according to claim 19, further comprising additionally: mounting a dome on the first chamber, to seal the first chamber with respect to the environment; the dome defining the second chamber, and being separated from the first chamber by a lid; the dome carries a lifting mechanism that selectively lifts the lid, which allows fluid communication between the first chamber and the second chamber, during the cooling step.