EP3521740B1 - Oven - Google Patents

Description

The invention relates to an oven with at least one oven pan, in which a first and a second electrical contact are provided, which are electrically insulated from the oven pan, the oven pan being formed from pan segments arranged one behind the other from the first to the second electrical contact and spaced apart from one another, which pan segments are at least partially made of metal are formed and have an electrically insulating coating on their inner side facing the interior of the furnace pan.

Furnaces of the type mentioned are known from the prior art and are used for the production of synthetic graphite, which is required in large quantities for applications in metallurgy, for example for melting electrodes for scrap melting. Synthetic graphite is produced by heating shaped bodies with a high carbon content to temperatures of approx. 3000 ° C. The high-carbon molded bodies are produced in a known manner ( Ullmann's Encyclopedia of Industrial Chemistry, Vol. A5, VCH Verlagsgesellschaft mbH, Weinheim, 1986, pp. 103 to 113 ) by hot mixing of petroleum cokes or pitch cokes, preferably in the form of needle cokes, with coal tar pitch, petroleum pitch or other coking organic liquids as binders, subsequent shaping and firing of the shaped bodies to coke the binder. Alternatively, the fired shaped bodies can be impregnated with pitch or other coking organic liquids and fired again in order to coke the impregnating agent, as a result of which the porosity of the shaped bodies decreases and their strength increases. The so-called Acheson furnace was previously used to graphitize the high-carbon molded bodies, in which the high-carbon molded bodies were embedded in a resistance bed made of silicon carbide-containing material lying transversely to the longitudinal axis of the furnace. This bulk resistance material was connected to a suitable electrical power supply via connection electrodes and heated to the graphitization temperature by means of an electrical current, which also heated the molded bodies. In the last few decades, so-called longitudinal graphitization (Castner furnace) has established itself. In contrast to the Acheson furnace, which had walls made of refractory concrete elements on the side, which were removed after each fire the furnace for longitudinal graphitization consists of a fixed tub made of metal, ceramic or a combination of both, in which a bulk material for thermal insulation and the shaped bodies to be graphitized are inserted as a strand. At the two ends of the strand, a carbon block, electrically insulated from the tub, is pressed onto the shaped body to be graphitized as a power connection electrode. Direct current is applied to the strand via these carbon blocks and the shaped bodies are heated up to a graphitization temperature of 3000 ° C in direct current flow.

The AT 411 798 B discloses a furnace for longitudinal graphitization in which tub segments made of metal and temperature-resistant and electrically insulating concrete ribs standing on a hall floor are arranged alternately and are sealed gas-tight by means of a furnace hood.

The disadvantage of the process of longitudinal graphitization is that only carbon-containing bulk materials can be used for thermal insulation in the furnace trough which have undesirable electrical conductivity. This electrical conductivity leads to the coupling of the metallic furnace pan to the potential gradient of the electrical connection electrodes with the formation of undesired secondary currents in the furnace pan, which on the one hand heat the furnace pan and on the other hand take away energy from the shaped bodies to be graphitized. In the early days of longitudinal graphitization, the metal furnace pans were therefore lined with refractory bricks in order to achieve electrical insulation. This had the significant disadvantage that the cooling times of the graphite electrodes in the furnace after grazing were very long due to the refractory lining functioning as additional heat insulation, which severely restricted the productivity of the graphitizing furnaces. Since the massive concrete ribs form the metallic furnace pan according to the AT 411 798 B Interrupting electrically several times, the disadvantages of coupling the potential gradient were reduced without the metallic segments having to be bricked up. Nevertheless, there remains an electrical potential gradient in the metal tub segments with the formation of side currents, which consume part of the energy required for graphitization. Furthermore is Due to the cast concrete ribs, which occupy a considerable part of the furnace structure (or the furnace length), the heat dissipation after graphitization is hindered, which has a negative impact on productivity as the cooling time is extended.

The U.S. 5,299,225 discloses an oven that reduces cooling times somewhat. The furnace has a furnace pan with several interconnected metal segments into which a cast refractory insulation is inserted. The furnace pan also has an elaborate, heavily ribbed metal construction, whereby the outer surface of the furnace pan is enlarged compared to the furnace pans known up to that point and a better heat dissipation was achieved after graphitization. Nevertheless, the heat transfer through the several cm thick, cast refractory insulation was still severely limited.

The U.S. 5,631,919 discloses a furnace for longitudinal graphitization with two rows of metal tub segments arranged one behind the other and spaced apart from one another. The mutually facing ends of successive tub segments are slidably mounted in a U-shaped recess of a support body made of electrically insulating material, in particular concrete. The tub segments are thus electrically isolated from one another by the distance between the mutually facing ends of successive tub segments or by concrete bodies that are received between the mutually facing ends. An adhesive, electrically insulating coating is provided on the inside of the tub segments, the layer thickness of which in the dried state is between 0.127 mm and 1.27 mm. The coating serves to electrically isolate the carbon bodies inserted in the tub segments from the tub segments. The disadvantage here is that the support bodies have to be provided in the area of the mutually facing ends of successive tub segments.

The U.S. 4,394,766 discloses a furnace for longitudinal graphitization with metal tub segments arranged one behind the other and spaced apart from one another, which have a heat-resistant inner coating which is cast and stabilized with anchors. The gap between the spaced apart tub segments increases due to temperature Changes in length of the tub segments, isolates successive tub segments electrically from one another and is covered by a cover body which has a heat-resistant inner coating and an outer seal resting on the tub segment. The massive formation of the inner coating is particularly disadvantageous here. In addition, the furnace construction is complicated because of the covering bodies to be arranged over each gap.

The WO 87/06685 A1 discloses a furnace for longitudinal graphitization with metal tub segments arranged one behind the other and spaced apart from one another. The tub segments are clad on the inside with refractory bricks and electrically isolated from each other.

It is now the object of the invention to create a furnace as stated at the beginning which avoids the formation of an undesired current flow in the metallic furnace pan, so that the energy consumption for graphitizing the shaped bodies introduced into the furnace trough is reduced and the quality of the shaped bodies to be graphitized is improved. In addition, it is an object of the invention to improve the productivity in the graphitization of the shaped bodies by minimizing the cooling time after graphitization and to minimize the expenditure for the production of furnace pans for longitudinal graphitization.

For this purpose, the invention provides a furnace as defined in claim 1. Advantageous embodiments and developments are specified in the dependent claims.

According to the invention it is provided that adjacent tub segments are connected to one another via a length compensation element arranged between facing ends of the adjacent tub segments, which length compensation element is at least partially made of metal, has an electrically insulating coating on its inside facing the interior of the furnace tub and perpendicular to the inside the tub segments is designed to be deflected. The furnace thus has at least one furnace pan into which a molded body containing carbon and to be processed by heat is introduced can be. Instead of a single molded body to be processed, a series of molded bodies, preferably arranged one behind the other and connected to one another and containing carbon, to be processed by heat, can be introduced into the furnace. If the furnace has a second or more furnace pans, the furnace pans are advantageously arranged next to one another in order to be able to form the furnace with small length dimensions, in which case at least one shaped body to be processed can then be introduced into each furnace pan. The shaped body to be processed is expediently placed in a bed of carbon-containing material, which has a heat-insulating effect but also has electrical conductivity. In particular, the furnace can be a graphitization furnace for performing longitudinal graphitization of the shaped body to be processed. To process the shaped body, an electrical voltage is applied to it, so that the shaped body is heated by the resulting current flow through the shaped body. For this purpose, a first and a second power contact, electrically insulated from the furnace pan, are provided in the furnace pan or in each furnace pan. The current contacts are connected or can be connected to an electrical energy source provided outside the furnace pan and are set up to establish an electrical connection with the molded body to be processed. Appropriate arrangements and designs of current contacts in a furnace pan are known to those skilled in the field of furnaces for longitudinal graphitization. For example, the current contacts can be arranged in end walls made of ceramic material at two ends of the furnace pan. The furnace pan is formed from pan segments which are arranged one behind the other from the first to the second power contact and are spaced apart from one another. The distance between adjacent tub segments, ie one behind the other in the direction from the first to the second power contact, enables a temperature-dependent, collision-free linear expansion of the tub segments. The tub segments are at least partially made of metal, ie are electrically conductive. In order to electrically isolate the tub segments from the molded body to be processed, through which current flows in the operating state of the furnace, and the material of the bed, the tub segments have an electrically insulating coating on their inside facing the interior of the furnace tub. Neighbors, from each other spaced tub segments are connected to each other via a length compensation element arranged between the adjacent tub segments in order to avoid a gap between the facing ends of the adjacent tub segments, ie the length compensation element is arranged between the facing ends of two adjacent tub segments. The length compensation elements are at least partially made of metal and are therefore electrically conductive. In order to electrically insulate the entire furnace pan and not just the pan segments, the length compensation elements also have an electrically insulating coating on their inside facing the interior of the furnace pan. In this way, an undesired current flow in the furnace pan or in the pan segments and the length compensation elements, which would occur on the inner wall of the furnace pan due to electrically uninsulated surface areas, is prevented. The electrically insulating coating itself should have the lowest possible heat storage capacity and the lowest possible layer thickness in order to facilitate the cooling of the furnace after the heating process has ended. The layer thickness of the electrically insulating coating is preferably less than 1 mm, more preferably less than 0.5 mm and particularly preferably less than 0.2 mm. Since the tub segments expand differently as a result of the fluctuating furnace temperature, the length compensation elements arranged between the tub segments also have a temperature-dependent fluctuating extension. The electrically insulating coating is advantageously designed to be at least slightly elastic in order to reliably adhere to the length compensation elements deformed by the influence of temperature. In addition, it is provided that the length compensation element is designed to be deflected perpendicular to the inside of the tub segments. A length compensation element constructed in this way with, for example, an undulating course in its longitudinal direction is particularly suitable for changes in its longitudinal extent between the mutually facing ends of two adjacent tub segments. Preferably, the length compensation element does not protrude beyond the inside of the tub segments in the direction of the interior of the furnace tub in order not to make handling of the bed in the furnace tub more difficult by protruding parts of the length compensation elements.

If, in the context of the description, reference is made to a longitudinal direction of the furnace, the furnace pan, the pan segments or the length compensation elements, this is understood to mean the direction from the first to the second electrical contact.

According to a preferred embodiment of the present invention it can be provided that the tub segments are electrically isolated from the length compensation element connected to them. In this way, an undesired flow of current in the furnace pan, i.e. in the pan segments and length compensation elements, is prevented even better. Even if parts of the electrically insulating coating on the inner wall of the furnace pan are damaged, in particular chipped, the electrical insulation between the pan segments and the length compensation elements connected therewith prevents an undesired flow of current between two or more pan segments.

For a particularly advantageous furnace construction it can be provided that the length compensation element is designed in a meandering shape.

In order to be able to set up the furnace easily and to be able to repair or replace individual tub segments if necessary, it is advantageous if at least one tub segment is screwed to a length compensation element so that it can be separated. Advantageously, all tub segments are separately screwed to the length compensation element connected to them.

A particularly stable construction of the furnace can be achieved if the tub segment screwed to the length compensating element has an outwardly bent edge on which a connecting section of the length compensating element rests, and at least one screw extends through the bent edge of the tub segment, the connecting section of the length compensating element and through extends two flanges which abut on the opposite sides of the bent edge of the tub segment and the connecting portion of the length compensation element. The outwardly bent edge of the The tub segment points away from the interior of the furnace tub and can, for example, be angled at right angles from the inside of the tub segment. The connecting section of the length compensation element, which in the screwed state rests against the bent edge of the tub segment, is expediently an end section of the length compensation element. The flanges have a larger extension perpendicular to the inside of the tub segments than the head of the screw or a nut screwed onto it and thus increase the area in which the force of the tightened screw acts on the bent edge of the tub segment and the connecting section of the length compensation element. The flanges are preferably releasably connected to the bent edge of the tub segment and the connecting section of the length compensation element by means of the at least one screw.

In order to be able to avoid an undesired current flow in the furnace pan particularly reliably, it can be provided that the outwardly bent edge of the pan segment and / or the connecting section of the length compensation element also have an electrically insulating coating on the mutually facing sides and the at least one screw in one electrically insulating sleeve is added. The outwardly bent edge of the tub segment and the connecting section of the length compensation element thus rest against one another, electrically insulated from one another. Since the at least one screw including the screw head and a nut screwed on it is electrically isolated from the bent edge of the tub segment and from the connecting section of the length compensation element by means of the electrically insulating sleeve, a current flow from one tub segment via the length compensation element to the adjacent tub segment is prevented. The electrically insulating coating of the bent edge of the tub segment and / or the connecting section of the length compensation element on the mutually facing sides of the bent edge and the connecting section is preferably formed in the same way as the electrically insulating coating on the inside of the tub segments and on the inside of the length compensation elements .

It is particularly favorable if the electrically insulating Coating on the facing sides of the outwardly bent edge of the tub segment and of the connecting portion of the length compensation element extends beyond the contact surface between the outwardly bent edge of the tub segment and the connecting portion of the length compensation element. In this way, the tub segment and the length compensation element are still electrically isolated from each other if, due to assembly or manufacturing inaccuracies, the bent edge of the tub segment and the connecting section of the length compensation element are undesirably offset from a target position when they are screwed together. It can also be provided that the electrically insulating coating extends on only one of the mutually facing sides of the outwardly bent edge of the tub segment and the connecting section of the length compensation element beyond the contact area between the outwardly bent edge of the tub segment and the connecting section of the length compensation element.

According to a further preferred embodiment of the invention it can be provided that the tub segment screwed to the length compensation element is inseparably connected to a first flange on which a second flange inseparably connected to the length compensation element rests, and at least one screw passes through the first flange and through the second flange extends. The first flange is expediently provided on the end of the tub segment facing the length compensation element and the second flange is provided on the end of the length compensation element facing the tub segment. For example, the first and the second flange are welded to the tub segment or the length compensation element. The first and the second flange are connected to one another in the assembled state of the furnace by means of the at least one screw. In addition, the first and the second flange have an electrically insulating coating on their inside facing the interior of the furnace pan.

In the case of the first flange inseparably connected to the tub segment and the second flange inseparably connected to the length compensation element, an undesired flow of current To be able to avoid particularly reliably in the furnace pan, it can be provided that the first flange and / or the second flange have an electrically insulating coating on the mutually facing sides and the at least one screw is received in an electrically insulating sleeve. In the screwed state, the first and the second flange therefore rest against one another in an electrically insulated manner from one another. Since the at least one screw including the screw head and a nut screwed onto it is electrically isolated from the first and second flange by means of the electrically insulating sleeve, a current flow from one tub segment via the length compensation element to the adjacent tub segment is prevented. The electrically insulating coating of the first and / or the second flange is preferably formed in the same way as the electrically insulating coating on the inside of the tub segments and on the inside of the length compensation elements.

It is particularly advantageous if the electrically insulating coating has enamel or at least one of magnesium oxide, chamotte or glasses with heat-resistant binders, preferably potassium water glass, sodium water glass, silica sol, silicone resins, inorganic phosphates, for example aluminum phosphate or magnesium phosphate, water-soluble aluminates or water-soluble aluminosilicates. Such a coating can reliably insulate the tub segments and the length compensation elements against electrical current even at high temperatures, for example up to about 800 ° C., and can be made thin. Such a surface temperature on the inside of the tub must be expected, especially if the radiant heat from electrodes briefly heats the metal wall of the furnace when it is removed from the furnace. The electrically insulating coating can, for example, be applied to the tub segments and the length compensation elements in a flowable state and then harden. The electrically insulating coating can either be applied to the inside of the tub segments and the length compensation elements after the furnace tub has been set up, e.g. in existing furnaces for longitudinal graphitization, or the tub segments and length compensation elements are applied to the furnace before the furnace is assembled provided electrically insulating coating, in which case the electrically insulating coating can also be burned on, for example. A burned-on enamel.

Due to the small thickness of the electrically insulating coating, the heat output from the furnace to the outside is not hindered in the cooling phase after graphitization. In contrast to other furnace designs, in which the furnace pan is bricked up or provided with cast refractory insulation instead of the thin electrically insulating coating, the productivity of the graphitizing furnace is not restricted. By eliminating the ceramic segments required for certain furnace designs as an electrical intermediate layer between the tub segments of a furnace tub, which ceramic segments also have very poor heat conduction, the cooling time of the graphitizing furnace is shortened and productivity is increased compared to a known furnace with the same furnace dimensions of the furnace according to the invention.

For a particularly simple and inexpensive furnace construction, it can be provided that at least one tub segment is inseparably connected, in particular welded, to a length compensation element. Appropriately, the mutually facing ends of the tub segment and the length compensation element are inseparably connected or welded to one another. However, this construction does not provide any electrical insulation of the tub segment from the length compensation element at their common connection point or welding point, so that damage to the electrically insulating coating on the inside of at least two tub segments results in an undesirable current flow in the furnace tub between the damaged points of the electrically insulating coating over the Lead length compensation elements. To avoid or reduce such an undesirable current flow in the furnace trough, the trough segment inseparably connected to the length compensation element is formed from segment parts arranged one behind the other in the direction from the first to the second power contact, with adjacent segment parts of the trough segment connected to one another via an electrically insulating intermediate layer and are electrically isolated from each other.

• Fig. 1 einen Ofen gemäß der Erfindung in einer schematischen Darstellung, der eine Ofenwanne mit Wannensegmenten und Längenausgleichselementen aufweist;
• Fig. 2 eine schematische Darstellung eines Abschnitts der Ofenwanne des Ofens aus Fig. 1, in einem Längsschnitt, wobei die Wannensegmente mit dazwischen angeordneten Längenausgleichselementen verschraubt sind;
• Fig. 3 eine schematische Darstellung eines Abschnitts einer anders konstruierten Ofenwanne des Ofens aus Fig. 1, in einem Längsschnitt, wobei die Wannensegmente im Vergleich zu Fig. 2 auf andere Weise mit dazwischen angeordneten Längenausgleichselementen verschraubt sind; und
• Fig. 4 eine schematische Darstellung eines Abschnitts einer Ofenwanne des Ofens aus Fig. 1, in einem Längsschnitt, wobei die Wannensegmente mit dazwischen angeordneten Längenausgleichselementen verschweißt sind.
• Fig. 1 zeigt in einer perspektivischen Ansicht einen Ofen 1 mit zumindest einer Ofenwanne 2, im in Fig. 1 dargestellten Beispiel genau einer Ofenwanne 2. In der Ofenwanne 2 sind ein erster Stromkontakt 3a und ein zweiter Stromkontakt 3b vorgesehen, die von der Ofenwanne 2 elektrisch isoliert angeordnet sind. Die Stromkontakte 3a, 3b können bspw. in aus keramischem Material bestehenden Stirnwänden 4a, 4b an zwei Enden 5a, 5b der Ofenwanne 2 angeordnet sein. Die Ofenwanne 2 weist voneinander beabstandete Wannensegmente 6 auf, die in Längsrichtung L des Ofens 1, d.h. in Richtung vom ersten Stromkontakt 3a zum zweiten Stromkontakt 3b, hintereinander angeordnet sind. In Fig. 1 sind beispielhaft nur drei Wannensegmente 6, 6a, 6b, 6c dargestellt. Selbstverständlich kann die Ofenwanne 2 auch nur zwei oder mehr als drei Wannensegmente 6 aufweisen. Ebenso kann der Ofen 1 mehr als eine Ofenwanne 2 aufweisen. Die Wannensegmente 6 sind zumindest teilweise aus Metall gebildet, d.h. elektrisch leitfähig, und weisen an ihrer dem Innenraum 7 der Ofenwanne 2 zugewandten Innenseite 8 eine elektrisch isolierende Beschichtung 9 auf. Benachbarte Wannensegmente 6a, 6b bzw. 6b, 6c sind über ein zwischen den benachbarten Wannensegmenten 6a, 6b bzw. 6b, 6c angeordnetes Längenausgleichselement 10, 10a, 10b miteinander verbunden, d.h. das Längenausgleichselement 10, 10a, 10b ist in den Wänden und im Boden der Ofenwanne 2 vorgesehen, um eine temperaturbedingte Relativbewegung der Wannensegmente 6 zueinander zuzulassen. Die Ofenwanne 2 ist nicht auf eine rechteckige Querschnittsform beschränkt und kann bspw. im Querschnitt auch U-förmig sein. Die Ofenwanne 2 weist in Längsrichtung L des Ofens 1 abwechselnd aufeinanderfolgende Wannensegmente 6 und Längenausgleichselemente 10 auf. Das Längenausgleichselement 10 ist zumindest teilweise aus Metall gebildet und weist auf seiner dem Innenraum 7 der Ofenwanne 2 zugewandten Innenseite 11 eine elektrisch isolierende Beschichtung 12 auf. Die elektrisch isolierende Beschichtung 9 und die elektrisch isolierende Beschichtung 12 sind im dargestellten Beispiel auf die Wannensegmente 6 bzw. auf die Längenausgleichselemente 10 fest aufgebracht und somit Teil der Wannensegmente 6 bzw. der Längenausgleichselemente 10.

The invention is explained in more detail below on the basis of preferred, non-limiting embodiments with reference to the drawing. Show it:

• Fig. 1 a furnace according to the invention in a schematic representation, which has a furnace pan with pan segments and length compensation elements;
• Fig. 2 a schematic representation of a portion of the furnace pan of the furnace Fig. 1 , in a longitudinal section, wherein the tub segments are screwed to length compensation elements arranged between them;
• Fig. 3 a schematic representation of a portion of a differently constructed furnace pan of the furnace Fig. 1 , in a longitudinal section, with the tub segments compared to Fig. 2 are screwed in a different way with length compensation elements arranged between them; and
• Fig. 4 a schematic representation of a portion of a furnace pan of the furnace Fig. 1 , in a longitudinal section, the tub segments being welded to length compensation elements arranged between them.
• Fig. 1 shows a perspective view of an oven 1 with at least one oven pan 2, in FIG Fig. 1 The example shown is exactly one furnace pan 2. A first power contact 3 a and a second power contact 3 b are provided in the furnace pan 2 and are arranged to be electrically insulated from the furnace pan 2. The current contacts 3a, 3b can be arranged, for example, in end walls 4a, 4b made of ceramic material at two ends 5a, 5b of the furnace pan 2. The furnace pan 2 has spaced apart pan segments 6 which are arranged one behind the other in the longitudinal direction L of the furnace 1, ie in the direction from the first power contact 3a to the second power contact 3b. In Fig. 1 only three tub segments 6, 6a, 6b, 6c are shown by way of example. Of course, the furnace pan 2 can also have only two or more than three pan segments 6. The furnace 1 can also have more than one furnace pan 2. The tub segments 6 are at least partially formed from metal, ie electrically conductive, and have an electrically insulating coating 9 on their inner side 8 facing the interior 7 of the furnace pan 2. Adjacent tub segments 6a, 6b or 6b, 6c are connected to one another via a length compensation element 10, 10a, 10b arranged between the adjacent tub segments 6a, 6b or 6b, 6c, ie the length compensation element 10, 10a, 10b is in the walls and in the floor the furnace pan 2 is provided in order to allow a temperature-dependent movement of the pan segments 6 relative to one another. The furnace pan 2 is not restricted to a rectangular cross-sectional shape and can, for example, also be U-shaped in cross-section. In the longitudinal direction L of the furnace 1, the furnace pan 2 has alternately successive pan segments 6 and length compensation elements 10. The length compensation element 10 is formed at least partially from metal and has an electrically insulating coating 12 on its inner side 11 facing the interior 7 of the furnace pan 2. In the example shown, the electrically insulating coating 9 and the electrically insulating coating 12 are firmly applied to the tub segments 6 and / or to the length compensation elements 10 and are thus part of the tub segments 6 and / or the length compensation elements 10.

To use the furnace 1 for longitudinal graphitization of a workpiece, ie a molded body containing carbon to be machined by the action of heat, the molded body or the workpiece is inserted into the furnace pan 2 between the electrical contacts 3a, 3b and thus electrically connected. The current contacts 3a, 3b can be designed to press against the molded body. In addition, the shaped body is preferably embedded in a bed of heat-resistant material such as coke. The molded body and the heat-resistant material (coke) are not shown for the sake of clarity. The electrically insulating coating 9 on the inside 8 of the tub segments 6 and the electrically insulating coating 12 on the inside 11 of the length compensation elements 10 isolate the furnace tub 2 from the electrical current that is passed through it for processing the molded body, not shown. Without the electrically insulating coating 9, 12, the electrical current would undesirably pass through the bed of heat-resistant material (for example coke) and through the inner sides 8, 11 of the tub segments 6 and the length compensation elements 10 flow into the furnace trough 2 and are passed on via the trough segments 6 and the length compensation elements 10.

The length compensation element 10 is in Fig. 1 illustrated example perpendicular to the inside 8 of the tub segments 6, ie in the direction of the arrow B, which points in the width direction of the furnace 1, deflected or meandering in the shape of a wave. The length compensation element 10 is thus designed particularly favorably for changes in its longitudinal extension in the direction of the arrow L. The length compensation element 10 is arranged between adjacent tub segments 6a, 6b or 6b, 6c and connected to them, in order to avoid a gap between the mutually facing ends of adjacent tub segments 6 or to close it with the length compensation element 10. The adjacent tub segments 6, 6a, 6b, 6c are thus connected to one another without any gaps. In contrast to known furnace constructions, there is also no need for a cover body which rests on the insides of adjacent tub segments and covers a remaining gap between adjacent tub segments. In the examples shown, the tub segments 6 are firmly connected to the length compensation elements 10.

Fig. 2 shows a section of the furnace pan 2 of the furnace 1 from Fig. 1 , in a section in the longitudinal direction L of the furnace 1, on an enlarged scale. It can be seen that adjacent tub segments 6, in FIG Fig. 2 The example shown, the tub segments 6b, 6c, are screwed to a length compensation element 10 so as to be separable. The tub segments 6, 6b, 6c screwed to the length compensation element 10 have an outwardly bent, for example flanged, edge 13 on which a connecting section 14 of the length compensation element 10 rests. At least one screw 15, but preferably several screws 15, extend through the bent edge 13 of the tub segment 6, the connecting section 14 of the length compensation element 10 and through two flanges 16a, 16b. The flanges 16a, 16b releasably rest on the sides 13a, 14a of the bent edge 13 of the tub segment 6 and the connecting section 14 of the length compensation element 10, which face away from one another. The screws 15 tension together with a nut mounted thereon 17 the tub segment 6, the length compensation element 10 and the flanges 16a, 16b together. In this embodiment, the tub segments 6 are therefore connected directly to the length compensation elements 10. In the in Fig. 2 In the example shown, both the outwardly bent edge 13 of the tub segment 6 and the connecting section 14 of the length compensation element 10 have an electrically insulating coating 18 on the mutually facing sides 13z, 14z. In a simpler embodiment, only the outwardly bent edge 13 of the tub segment 6 or the connecting section 14 of the length compensation element 10 can have an electrically insulating coating 18 on the mutually facing sides 13z, 14z. The screws 15 are accommodated in a heat-resistant, for example ceramic, electrically insulating sleeve 19 in order to establish an electrically conductive connection from the bent edge 13 of the tub segment 6, 6c via the generally metallic flange 16a and via the screw 15 to the generally metallic flange 16b or to avoid the connecting section 14 of the length compensation element 10. The screw head 15a and the nut 17 are also electrically insulated from the flanges 16a, 16b. For example, the screw head 15 a and the nut 17 rest on bent edges of the electrically insulating sleeve 19.

In Fig. 2 it can also be seen that the electrically insulating coating 18 on the mutually facing sides 13z, 14z of the outwardly bent edge 13 of the tub segment 6 and the connecting section 14 of the length compensation element 10 in areas 20 over the contact surface 21 between the outwardly bent edge 13 of the Tub segment 6 and the connecting portion 14 of the length compensation element 10 also extends.

Fig. 3 shows a section of a differently constructed furnace pan 2 of a furnace 1, in a section in the longitudinal direction L of the furnace 1, on an enlarged scale. It can be seen that the tub segment 6 screwed to the length compensation element 10 is inseparably connected to a first flange 22a, for example welded, and the length compensation element 10 is inseparably connected to a second flange 22b, for example welded. The first flange 22a and the second flange 22b lie against one another in the assembled state of the furnace 1 and are screwed to one another by means of screws 15 which extend through the first flange 22a and through the second flange 22b. In the in Fig. 3 In the illustrated example, the first flange 22a and the second flange 22b have an electrically insulating coating 18 on the mutually facing sides 22az, 22bz. The screws 15 are received in an electrically insulating sleeve 19.

Fig. 4 shows a section of a differently constructed furnace pan 2 of a furnace 1, in a section in the longitudinal direction L of the furnace 1, on an enlarged scale. According to this construction, the tub segments 6 are inseparably connected to the length compensation elements 10, preferably welded. In particular, one end E6 of the tub segment 6 and one end E10 of the length compensation element 10, which ends E6 and E10 face one another, are inseparably connected to one another, preferably welded to one another by means of a weld seam 23. The electrically insulating coating 9 of the tub segment 6 and the electrically insulating coating 12 of the length compensation element 10 are applied in the example shown to the tub segment 6, to the length compensation element 10 connected to it and to the weld seam 23 in the direction of the interior 7 of the furnace tub 2. In order to limit any current flow through the tub segments 6 and the length compensation elements 10 in the event of a damaged electrically insulating coating 9, 12, the tub segment 6 inseparably connected to the length compensation element 10 can be formed from segment parts 6x arranged one behind the other in the direction from the first to the second current contact 3a, 3b Adjacent segment parts 6x1, 6x2 of the tub segment 6 are connected to one another via an electrically insulating intermediate layer 24 and are electrically insulated from one another.

In an experiment, an existing 25 m long graphitization furnace was used, which was designed with two furnace tanks electrically connected in series. The furnace pans consisted of metallic and ceramic segments. The series connection of the two furnace pans was designed in such a way that the connection electrodes, made of graphite, of the two furnace pans one side of the tubs were electrically connected to each other. The power connection (plus and minus connection) was attached to the graphite connection electrodes on the opposite side of the two furnace pans. The oven was now treated in such a way that an oven pan (the one that was coupled to the plus side of the electrical connection) was completely coated with a ceramic coating using an airless paint spraying system with a wet film thickness of 0.15 mm. The coating was produced as follows: 30 parts by mass of liquid colloidal silica sol with 40% solids content (grain size 10 nm) as binder and 10 parts by mass of water were placed in a dissolver in a stirred tank. A solid mixture of 40 parts by mass of magnesium oxide with an average grain size d50 = 4 µm (d90 = 13 µm) and 20 parts by mass of glass powder with an average particle size of 4 µm (d98 = 17 µm) and 0.3 parts by mass of methyl cellulose was introduced into this liquid as a thickener and suspended, the speed of the dissolver disk being increased steadily up to 12 m / sec during the powder introduction and dispersing was carried out at this speed for 10 minutes. The other furnace pan (the one that was connected to the minus side of the electrical connection) remained uncoated. The same starting material was built into both furnace tanks for graphitization, 77 electrodes in each tank. After switching on the power supply, the built-in moldings were heated up to 3000 ° C. After graphitization, the electrodes were finished and the electrical resistance measured. It was found that those graphite electrodes that were graphitized in the coated tub had an average electrical resistance of 0.05 [μOhmm] lower than those electrodes that were graphitized in the uncoated tub.

Claims (10)

1. Furnace (1) comprising at least one furnace tub (2) in which a first current contact (3a) and a second current contact (3b) that are electrically insulated from the furnace tub (2) are provided, the furnace tub (2) being formed from tub segments (6) which are arranged one behind the other from the first current contact (3a) to the second current contact (3b) and are spaced apart from one another, which tub segments (6) are at least partially made of metal and comprise an electrically insulating coating (9) on the inside (8) thereof facing the interior (7) of the furnace tub (2), characterised in that adjacent tub segments (6) are interconnected via a length compensation element (10) arranged between mutually facing ends of the adjacent tub segments (6), which length compensation element (10) is at least partially made of metal, comprises an electrically insulating coating (12) on the inside (11) thereof facing the interior (7) of the furnace tub (2), and is deflected perpendicularly to the inside (8) of the tub segments (6).
2. Furnace (1) according to claim 1, characterised in that the tub segments (6) are electrically insulated from the length compensation element (10) connected thereto.
3. Furnace (1) according to either claim 1 or claim 2, characterised in that the length compensation element (10) has a meandering shape.
4. Furnace (1) according to any of claims 1 to 3, characterised in that at least one tub segment (6) is detachably screwed to a length compensation element (10).
5. Furnace (1) according to claim 4, characterised in that the tub segment (6) screwed to the length compensation element (10) has an outwardly bent edge (13) against which a connecting portion (14) of the length compensation element (10) rests, and at least one screw (15) extends through the bent edge (13) of the tub segment (6), the connecting portion (14) of the length compensation element (10) and through two flanges (16a, 16b) which rest against the sides (13a, 14a) of the bent edge (13) of the tub segment (6) and the connecting portion (14) of the length compensation element (10) that face away from one another.
6. Furnace (1) according to claim 5, characterised in that the outwardly bent edge (13) of the tub segment (6) and the connecting portion (14) of the length compensation element (10) also comprise an electrically insulating coating (18) on the mutually facing sides (13z, 14z) and the at least one screw (15) is received in an electrically insulating sleeve (19).
7. Furnace (1) according to claim 6, characterised in that the electrically insulating coating (18) on the mutually facing sides (13z, 14z) of the outwardly bent edge (13) of the tub segment (6) and the connecting portion (14) of the length compensation element (10) extends over the contact surface (21) between the outwardly bent edge (13) of the tub segment (6) and the connecting portion (14) of the length compensation element (10).
8. Furnace (1) according to claim 4, characterised in that the tub segment (6) screwed to the length compensation element (10) is non-detachably connected to a first flange (22a) against which a second flange (22b) non-detachably connected to the length compensation element (10) rests, and at least one screw (15) extends through the first flange (22a) and through the second flange (22b).
9. Furnace (1) according to claim 8, characterised in that the first flange (22a) and the second flange (22b) comprise an electrically insulating coating (18) on the mutually facing sides (22az, 22bz) and the at least one screw (15) is received in an electrically insulating sleeve (19).
10. Furnace (1) according to any of claims 1 to 9, characterised in that the electrically insulating coating (9, 12, 18) comprises enamel or at least one of magnesium oxide, chamotte or glasses, comprising heat-resistant binders, preferably potassium water glass, sodium water glass, silica sol, silicone resins, inorganic phosphates, for example aluminium phosphate or magnesium phosphate, water-soluble aluminates or water-soluble aluminosilicates.

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