DD243086A1

DD243086A1 - METHOD FOR HIGH TEMPERATURE TREATMENT OF CARBON OR GRAPHITE PRODUCTS IN AN INDUCTION OVEN

Info

Publication number: DD243086A1
Application number: DD28354285A
Authority: DD
Inventors: Wolfgang Foest; Horst Guenther
Original assignee: Elektrokohle Lichtenberg Veb
Priority date: 1985-12-02
Filing date: 1985-12-02
Publication date: 1987-02-18

Abstract

Die Erfindung betrifft ein Verfahren zur Hochtemperaturbehandlung von Kohlenstoff- oder Graphiterzeugnissen in einem Induktionsofen. Die Aufgabe besteht darin, den Waermeverlust durch Waermeleitung zu verringern und damit das vertikale Temperaturgefaelle im Ofen zu verringern. Die Aufgabe wird dadurch geloest, dass an Stelle einer Russisolation ein weiterer Graphiteinsatztiegel, der mit induktiv gut ankoppelndem Material gefuellt ist, eingesetzt wird. Fig. 2The invention relates to a method for the high temperature treatment of carbon or graphite products in an induction furnace. The task is to reduce the loss of heat by heat conduction and thus to reduce the vertical Temperaturgefaelle in the oven. The object is achieved in that instead of a Russisolation another graphite crucible, which is filled with inductively good coupling material, is used. Fig. 2

Description

-2- 243 OSS-2- 243 OSS

Fig. 1 zeigt einen Induktionsofen, der in herkömmlicher Weise beschickt ist. Auf einem Fundament ruht ein Schamottetiegel 3, der von einer wassergekühlten Induktionsspule 4 umgeben ist. In eine Rußpackung 6 ist der Graphitinnentiegel 1 eingebettet: In dem Graphitinnentiegel 1 befindet sich auf dem Boden eine Rußschicht 5 als thermische Isolation in die das Gaseinleitungsrohr 7 hineinragt. Auf die Rußschicht 5 werden die Graphiteinsatztiegel 2 gestellt die das zu behandelnde Material (nicht dargestellt) aufnehmen. Wird nun der Induktionsofen angeschlossen, koppeln die Graphiteinsatztiegel 2 mit dem Einsatzmaterial induktiv an, nicht aber die Rußschicht 5. Die Rußschicht 5 wird überwiegend durch Wärmeleitung erhitzt. Durch unterschiedliche Wärmeableitung und Konvektion entsteht ein vertikaler Temperaturabfall nach unten im Ofen. Wird zur Reinigung des Einsatzmaterials noch Gas durch das Gaseinleitungsrohr 7 dem Ofen zu geführt, tritt ein zusätzlicher Kühleffekt von unten ein, so daß das Temperaturgefälle wesentlich mehr als 6OK betragen kann.Fig. 1 shows an induction furnace, which is charged in a conventional manner. On a foundation rests a fireclay pot 3, which is surrounded by a water-cooled induction coil 4. The graphite inner crucible 1 is embedded in a soot packing 6: In the graphite crucible 1, a soot layer 5 is located on the bottom as thermal insulation into which the gas inlet tube 7 protrudes. On the soot layer 5, the graphite insert crucible 2 are provided which receive the material to be treated (not shown). If now the induction furnace is connected, the graphite insert crucible 2 inductively couple with the feedstock, but not the soot layer 5. The soot layer 5 is predominantly heated by heat conduction. By different heat dissipation and convection creates a vertical temperature drop down in the oven. If gas is still supplied to the furnace through the gas inlet pipe 7 for cleaning the feedstock, an additional cooling effect occurs from below, so that the temperature gradient can be considerably more than 6OK.

Fig. 2 zeigt einen Induktionsofen, wie er nach dem erfindungsgemäßen Verfahren beschickt wird. Bei sonst üblichem Aufbau wird direkt auf das Gaseinleitungsrohr 7 ein zusätzlicher Graphiteinsatztiegel 8 gesetzt, der vorzugsweise einen perforierten Boden aufweist. Dieser Tiegel 8 ist mit einem induktiv gut ankoppelndem Material gefüllt und übernimmt, indem ersieh selbst aufheizt, die Funktion, den Wärmeabfluß von den Graphiteinsatztiegeln 2 zu verhindern. Darüber hinaus wird das ihn durchströmende Reinigungsgas beim Kontakt mit der Oberfläche des in ihm enthaltenen Einsatzgutes erhitzt. Der Zusatztiegel 8 ist mit einer Graphitkörnung der Teilchengröße von 1 bis 10 mm, vorzugsweise 3 mm beschickt. Die Reinheit dieser Graphitkörnung richtet sich nach der Forderung an die Endreinheit des Einsatzgutes in den Tiegeln 2. Die Messung der erreichten Endtemperatur an verschiedenen Punkten in vertikaler Richtung in den Graphiteinsatztiegeln ergaben selbst bei Anwendung von Reinigungsgasen vernachlässigbare Temperaturunterschiede.Fig. 2 shows an induction furnace as it is fed by the method according to the invention. In otherwise conventional construction, an additional graphite insert crucible 8 is set directly on the gas inlet tube 7, which preferably has a perforated bottom. This crucible 8 is filled with an inductively good coupling material and takes over, by itself self-heating, the function of preventing the heat flow from the graphite insert crucibles 2. In addition, the cleaning gas flowing through it is heated on contact with the surface of the starting material contained in it. The additional crucible 8 is charged with a graphite grain size of the particle size of 1 to 10 mm, preferably 3 mm. The purity of this graphite grain depends on the requirement for the final purity of the feedstock in the crucibles 2. The measurement of the final temperature reached at various points in the vertical direction in the graphite crucible furnaces gave negligible temperature differences even when using cleaning gases.

In einem weiteren Versuch wurde der Zusatztiegel 8 mit gebrannten Kohlenstofformkörpem kleinerer Abmessungen gefüllt. Diese Füllung koppelte mit steigender Temperatur immer besser induktiv an und wurde graphitiert. Diese Formkörper konnten für weniger anspruchsvolle Einsatzzwecke hinsichtlich Graphitierungsgrad und Reinheit verwendet werden. Das Material in den Einsatztiegeln 2 wies jedoch ebenfalls eine hohe Homogenität in den Eigenschaften auf.In a further experiment, the additional crucible 8 was filled with burned Kohlenstofformkörpem smaller dimensions. This filling coupled increasingly better with increasing temperature and was graphitized. These moldings could be used for less demanding purposes in terms of graphitization grade and purity. However, the material in the insert crucibles 2 also had a high homogeneity in properties.

Claims

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Invention claim:

A process for the high temperature treatment of carbon or graphite products in an induction furnace, characterized in that in the induction furnace in addition to the insert crucibles, another graphite crucible with perforated bottom and a filling of inductively good coupling material is placed below the insert pan in the oven.

2. The method according to item 1, characterized in that the inductively good coupling material is lumpy or granular graphite.

3. The method according to item 1, characterized in that the inductively good coupling material is lumpy or granular, easily graphitizable carbon.

For this 1 page drawings

Field of application of the invention

The invention relates to a method for the high temperature treatment of carbon or graphite products in an induction furnace. The treatment is carried out with the aim of graphitizing, cleaning or further cleaning graphitized carbon materials. Products which are used are, for example, electrodes or graphite powder for spectral analysis, graphite moldings for atomic absorption spectrometry and graphites for microelectronics.

Characteristic of the known technical solutions

Carbon materials to which particularly high demands are placed on the quality and uniformity of their properties, such as electrical conductivity and purity, are graphitized in induction furnaces or subjected to high purification. The temperatures used are usually 2,800 to 3,300 K, in vacuum also below. To achieve high-purity or ultrahigh-purity graphite materials, reactive gases, such as chlorine and freons, are passed through the feedstock at these temperatures. The moldings to be cleaned or graphitized are placed in graphite crucible and these crucibles one above the other in a graphite crucible, which is located in the induction furnace used. Zournemischen insulation of the graphite insert crucible down mainly carbon black or carbon fibers or fibers are used, which are located in the lower part of the graphite tin crucible. Despite the thermal insulation, a temperature gradient occurs downwards, mainly due to heat conduction and convection, in the feedstock in the vertical direction. This temperature gradient is further enhanced by the flow of cleaning gas which is relatively cold to the environment and, despite the most favorable design of the induction coil, can reach substantially more than 60 K. This results in that the shaped bodies, depending on their position in the oven, reach different final temperatures and thus obtain different properties. This inhomogeneity of the properties, even in one batch, causes an increased testing and aftertreatment effort and drastically reduces the effective furnace useful volume or the achievable yield.

Object of the invention

The aim of the invention is to change the high-temperature treatment of carbon moldings in the induction furnace so that a substantial homogeneity of the properties of the moldings is achieved.

Explanation of the essence of the invention

The object of the invention is to change the process for the high temperature treatment of graphite moldings in the induction furnace by the feed of the furnace so that the temperature gradient is largely degraded in the vertical direction. According to the invention, this object is achieved in that the thermal insulation layer of soot in the graphite inner crucible by a further graphite crucible, which is filled with inductively coupling material and a perforated bottom is replaced.

The inductively coupling material used is lumped or granular cleaned graphite. The inductively coupling material can also be graphitizable carbon material of any geometry, but with the largest possible surface. Advantageous effect of the inventive solution that the passive heat insulation in the form of poorly conductive carbon black is replaced by an active, self-heating layer.

Thus, the dissipation of heat from the graphite insert crucibles down significantly reduced. With the additional use of cleaning gases, these inevitably flow through the additional crucible feedstock and are heated on contact with its surface. This allows the vertical temperature gradient in the induction furnace to be reduced to negligible levels. This has the consequence that the feed experiences a uniform temperature control and thus is obtained much more homogeneous in its temperature-dependent properties.

embodiment

The invention will be explained in more detail below using an exemplary embodiment. In the accompanying drawings: FIG. 1: an induction furnace in section, according to the previous embodiment