EP3521740A1 - Oven - Google Patents

Abstract

Furnace (1) with at least one furnace pan (2), in which a first (3a) and a second (3b) from the furnace pan (2) electrically insulated current contact are provided, the furnace pan (2) from the first (3a) to second current contact (3b) which is arranged one behind the other and is spaced apart from one another, which pan segments (6) are at least partially made of metal and on their inside (8) facing the interior (7) of the furnace pan (2) an electrically insulating coating (9), whereby adjacent pan segments (6) are connected to one another via a length compensation element (10) arranged between the adjacent pan segments (6), which length compensation element (10) is at least partially made of metal and on the interior (7) of the furnace pan (2) facing inside (11) has an electrically insulating coating (12).

Description

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

Furnaces of this kind 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 high-carbon moldings to temperatures of about 3000 ° C. The high-carbon moldings are in a known manner ( Ullmann's Encyclopedia of Industrial Chemistry, Vol. A5, VCH Verlagsgesellschaft mbH, Weinheim, 1986, pp. 103-113 ) by hot mixing of petroleum cokes or pitch cokes, preferably in the form of needle cokes, with coal tar pitch, petrol pitch or other cokeable organic liquids as a binder, then shaping and firing the moldings for coking the binder produced. Alternatively, the fired moldings may be impregnated with pitch or other cokerable organic liquids and remelted to coke the impregnating agent, thereby decreasing the porosity of the molded articles and increasing their strength. For graphitizing the carbonaceous moldings formerly the so-called Acheson furnace was used, in which the high-carbon moldings were embedded transversely to the furnace longitudinal axis lying in a resist fill from siliziumcarbidhaltigem material. This resist charge was connected via terminal electrodes with a suitable electrical power supply and heated by electric current to the graphitization temperature, whereby the moldings were heated. In recent decades, the so-called longitudinal graphitization (Castner furnace) has prevailed. In contrast to the Acheson stove, which had side walls made of refractory concrete elements, which removed after each fire were made, the furnace for longitudinal graphitization of a solid trough of metal, ceramic or a combination of both, in which a bulk material for thermal insulation and the graphitizing moldings are inserted as a strand. At the two strand ends, a carbon block electrically insulated from the trough is pressed against the moldings to be graphite as a current connection electrode. Direct current is applied to the strand via these carbon blocks and the molded articles are heated in a direct passage of current up to the graphitization temperature of 3000 ° C.

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

A disadvantage of the process of longitudinal graphitization is that only carbonaceous bulk materials can be used for heat insulation in the furnace tub, which have an undesirable electrical conductivity. This electrical conductivity leads to the coupling of the metallic furnace trough to the potential gradient of the electrical connection electrodes with formation of undesirable side currents in the furnace trough, which on the one hand heat the furnace trough and, on the other hand, remove energy from the shaped bodies to be graphitized. In the early days of longitudinal graphitisation, therefore, the metallic furnace pans were lined with refractory bricks to achieve electrical insulation. This had the considerable disadvantage that the cooling times of the graphite electrodes in the furnace after graying through the functioning as additional heat insulation refractory lining were very long, which has greatly limited the productivity of Graphitierungsöfen. Since the massive concrete ribs the metallic furnace tub according to the AT 411 798 B several times interrupt electrical, the disadvantages of coupling the potential gradient were reduced without the metal segments had to be bricked. Nevertheless, an electrical potential gradient remains in the metallic tub segments with the formation of secondary currents, which consume part of the energy required for graphitization. Further is the cast concrete ribs occupying a considerable part of the furnace construction (or kiln length) obstructs the heat output after graphitization, which adversely affects productivity due to prolonging the cooling time.

The US 5,299,225 discloses an oven that reduces the cooling times somewhat. The furnace has a furnace trough with a plurality of interconnected metallic segments, in which a cast refractory insulation is inserted. The furnace tub also has a complex, heavily ribbed metal construction, whereby the outer surface of the furnace tub compared to the previously known furnace tubs increased and better heat dissipation was achieved after graphitization. Nevertheless, the heat transfer through the several cm thick cast refractory insulation was still severely limited.

The US 5,631,919 discloses a kiln for longitudinal graphitization having two juxtaposed rows of metal tray segments arranged one behind the other and spaced from each other. The mutually facing ends of successive tub segments are slidably mounted in a U-shaped recess of a support body of electrically insulating material, esp. Concrete. The tray segments are thus electrically isolated from each other by the distance between the facing ends of successive tray segments or by concrete bodies received between the facing ends. On the inner sides of the tub segments an adhesive, electrically insulating coating is provided, the layer thickness in the dried state is between 0.127 mm and 1.27 mm. The coating is used for the electrical insulation of inserted into the tub segments carbon bodies of the tub segments. The disadvantage here is that in each case in the region of the mutually facing ends of successive tub segments, the support body are provided.

The US 4,394,766 discloses a furnace for longitudinal graphitization having metal tray segments arranged one behind the other and spaced from each other and having a cast and anchor stabilized refractory inner coating. The gap between the spaced tub segments takes up temperature Changes in length of the tub segments, electrically isolated successive tub segments from each other and is covered by a cover body, which has a heat-resistant inner coating and an outer seal resting on the tub segment. Here is the massive formation of the inner coating of disadvantage. In addition, the furnace construction is complicated because of the over each gap to be arranged cover body.

It is an object of the invention to provide a furnace as stated above, which avoids the formation of an undesirable current flow in the metallic furnace tub, thus reducing the energy consumption for graphitizing the introduced into the furnace shell moldings and improves the quality of the graphitized moldings. In addition, it is an object of the invention to improve the productivity in the graphitization of the moldings by minimizing the cooling time after graphitization and to minimize the effort for the production of furnace tubs for longitudinal graphitization.

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

According to the invention, it is provided that adjacent trough segments are connected to one another via a length compensation element arranged between the adjacent trough segments, which length compensation element is at least partially formed from metal and has an electrically insulating coating on its inner side facing the interior of the furnace trough. The furnace thus has at least one furnace trough into which a carbon-containing shaped body to be processed by heat can be introduced. Instead of a single shaped body to be processed, it is also possible to introduce into the furnace a row of shaped bodies which are preferably arranged behind one another and are connected to one another and are to be processed by heat. If the oven has a second or more oven pans, the oven pans are conveniently juxtaposed to form the oven of small length dimensions, in which case each oven pans at least one shaped body to be processed can be introduced. The shaped body to be processed is expediently inserted into a bed of carbon-containing material which has a heat-insulating effect but also electrical conductivity. In particular, the furnace may be a graphitizing furnace for carrying out a longitudinal graphitization of the shaped body to be processed. For machining 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 of the furnace tub electrically insulated current contact are provided in the furnace tub or in each furnace tub. The current contacts are connected or connectable to an electrical energy source provided outside the furnace trough and are set up to produce an electrical connection with the shaped body to be processed. Advantageous arrangements and configurations of current contacts in a furnace trough are known to those skilled in the field of furnaces for longitudinal graphitization. For example, the current contacts may be arranged in ceramic walls made of ceramic material end walls at two ends. The furnace trough is formed by trough segments, which are arranged one behind the other from the first to the second current contact and spaced from each other. The distance between adjacent, ie in the direction of the first to the second current contact successively arranged tray segments allows a temperature-induced, collision-free longitudinal expansion of the tub segments. The tray segments are at least partially formed of metal, ie electrically conductive. In order to electrically insulate the tub segments from the mold body to be processed and from the current flowing through the furnace in the operating state and from the material of the bed, the tub segments have an electrically insulating coating on their inner side facing the interior of the furnace tub. Adjacent, spaced-apart tub segments are interconnected via a length compensation element arranged between the adjacent tub segments in order to avoid a gap between the mutually facing ends of the adjacent tub segments, ie the length compensation element is arranged between the mutually facing ends of two adjacent tub segments. The length compensation elements are at least partially formed of metal and thus electrically conductive. In order to electrically insulate the entire furnace trough and not only the trough segments, the length compensation elements also have an electrically insulating coating on their inner side facing the interior of the furnace trough. In this way, an undesirable current flow in the furnace trough or in the tub segments and the length compensation elements, which would be due to electrically uninsulated surface areas on the inner wall of the furnace tub, prevented. The electrically insulating coating itself should have the lowest possible heat storage capacity and the lowest possible layer thickness in order to favor the cooling of the furnace after the end of the heating process. Preferably, the layer thickness of the electrically insulating coating is less than 1 mm, more preferably less than 0.5 mm and particularly preferably less than 0.2 mm. Since the trough segments expand differently as a result of the fluctuating furnace temperature, the length compensation elements arranged between the trough segments likewise have a temperature-varying, fluctuating extent. Conveniently, the electrically insulating coating is at least slightly elastic in order to reliably adhere to the length compensation elements deformed by the influence of temperature.

If reference is made in the description to a longitudinal direction of the furnace, the furnace trough, the trough segments or the length compensation elements, this is to be understood as the direction from the first to the second current contact.

According to a preferred embodiment of the present invention it can be provided that the tub segments are electrically insulated from the associated length compensation element. In this way, an undesirable flow of current in the furnace tub, ie in the tub segments and length compensation elements, even better prevented. Even if parts of the electrically insulating coating on the inner wall of the furnace tub damaged, in particular knocked off, no unwanted current flow between two or more well segments can be due to the electrical insulation between the tub segments and the associated length compensation elements set.

For a particularly advantageous furnace construction it can be provided that the length compensation element is deflected perpendicular to the inside of the tub segments, preferably meander-shaped. Such a constructed length compensation element with, for example, wavy course in its longitudinal direction is particularly suitable for changes in its longitudinal extent between the facing ends of two adjacent tub segments. Preferably, the length compensation element does not project beyond the inside of the tub segments in the direction of the interior of the furnace tub, in order not to complicate the handling of the bed in the furnace tub by protruding parts of the length compensation elements.

In order to easily build the oven and repair or replace individual tub segments if necessary, it is advantageous if at least one tub segment is detachably bolted to a length compensation element. Advantageously, all tub segments are separably screwed to the respectively associated length compensation element.

A particularly stable construction of the furnace can be achieved if the screwed with the length compensation element tub segment has an outwardly bent edge on which abuts a connecting portion of the length compensation element, and at least one screw through the bent edge of the tub segment, the connecting portion of the length compensation element and two flanges extending, which rest on the opposite sides of the bent edge of the tub segment and the connecting portion of the length compensation element. The bent-out edge of the tub segment has away from the interior of the furnace trough and may, for example, be angled perpendicularly from the inside of the trough segment. The connecting portion of the length compensation element, which rests in the screwed state on the bent edge of the tub segment, is expediently an end portion of the length compensation element. The flanges have perpendicular to the inside of the tub segments a greater extent than the head of the screw or a nut screwed thereon and thus increase the area in which the force the tightened screw acts on the bent edge of the tub segment and the connecting portion of the length compensation element. The flanges are preferably releasably connected by means of the at least one screw with the bent edge of the tub segment and the connecting portion of the length compensation element.

In order to be able to avoid particularly undesirable current flow in the furnace trough, it can be provided that the edge of the trough segment bent to the outside and / or the connecting section of the length compensating element 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 portion of the length compensating element are thus electrically isolated from each other. Since the at least one screw, including the screw head and a nut screwed thereon, is also electrically insulated from the bent edge of the tub segment and from the connecting section of the length compensating element by the electrically insulating sleeve, a flow of current from one tub segment via the length compensating element to the adjacent tub segment is prevented. The electrically insulating coating of the bent edge of the tub segment and / or the connecting portion of the length compensation element on the mutually facing sides of the bent edge and the connecting portion is preferably formed in the same manner 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 on the mutually facing sides of the outwardly bent edge of the tub segment and of the connection section of the length compensation element extends beyond the contact surface between the outwardly bent edge of the tub segment and the connection section of the length compensation element. In this way, the tub segment and the length compensation element are still electrically isolated from each other even if due to assembly or manufacturing inaccuracies of the bent edge of the tub segment and the connecting portion of the length compensation element in the screwed together state are undesirably offset from a desired position deviating from each other. It can also be provided that the electrically insulating coating on only one of the mutually facing sides of the outwardly bent edge of the tub segment and 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 addition.

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

In order to be able to particularly reliably avoid undesirable current flow in the furnace trough in the case of the first flange inseparably connected to the trough segment and the second flange inseparably connected to the length compensating element, it can be provided that the first flange and / or the second flange face one another Have sides an electrically insulating coating and the at least one screw is accommodated in an electrically insulating sleeve. The first and the second flange are thus electrically isolated from each other in the screwed state. Since the at least one screw including the screw head and a nut screwed thereon by means of electrically insulating Sleeve is electrically insulated from the first and second flange, a flow of current is suppressed from a tub segment via the length compensation element to the adjacent tub segment. 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 for the electrically insulating coating to comprise enamel or at least one of magnesium oxide, chamotte or glass with heat-resistant binders, preferably potassium waterglass, sodium waterglass, 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 against electric current even at high temperatures, for example. Up to about 800 ° C, the tub segments and the length compensation elements and be thin. With such a surface temperature on the inside of the tub must be expected, especially when the radiant heat of electrodes during removal from the oven, the metallic wall of the furnace heated briefly. The electrically insulating coating can, for example, be applied in a flowable state to the tub segments and the length compensation elements and then cured. The electrically insulating coating can be applied either after the installation of the furnace trough on the inside of the trough segments and the length compensation elements, for example in already existing furnaces for longitudinal graphitization, or the trough segments and length compensation elements are provided with the electrically insulating coating prior to assembly of the furnace In which case the electrically insulating coating can also be fired, for example, a burnt enamel is.

Due to the small layer thickness of the electrically insulating coating, the heat emission of the furnace to the outside in the cooling phase after graphitization is not hindered. This results in contrast to other furnace designs, in which instead of the thin electrically insulating coating, the furnace trough walled or provided with a cast refractory insulation, no limitation of the productivity of the graphitizing furnace. By eliminating the ceramic segments required for certain furnace designs as an electrical interlayer between the tub segments of a furnace tub, which ceramic segments also have a very poor heat conduction, the cooling time of the graphitizing furnace is shortened and increased productivity at the same furnace dimensions of the furnace according to the invention over a known furnace.

For a particularly simple and cost-effective 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 together. However, this design does not provide for electrical isolation of the tub segment from the length compensation element at their common junction or weld, such that damage to the electrically insulating coating on the inside of at least two tub segments results in undesirable current flow in the furnace tub between the defective locations of the electrically insulating coating over the Length compensation elements lead. In order to avoid or reduce such unwanted current flow in the furnace trough, it is possible for the trough segment, which is inseparably connected to the length compensation element, to be formed from segment parts arranged one behind the other in the direction from the first to the second current contact, adjacent segment parts of the trough segment being 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.

The invention will be further elucidated 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 having a furnace trough with tub segments and length compensation elements;
• Fig. 2 a schematic representation of a portion of the furnace trough of the furnace Fig. 1 in a longitudinal section, wherein the tub segments are bolted with length compensation elements arranged therebetween;
• Fig. 3 a schematic representation of a portion of a differently constructed furnace trough of the furnace Fig. 1 in a longitudinal section, the tub segments compared to Fig. 2 otherwise bolted with length compensation elements disposed therebetween; and
• Fig. 4 a schematic representation of a portion of a furnace trough of the furnace Fig. 1 in a longitudinal section, wherein the tray segments are welded with length compensation elements arranged therebetween.

Fig. 1 shows in a perspective view of a furnace 1 with at least one furnace trough 2, in Fig. 1 In the furnace trough 2, a first current contact 3a and a second current contact 3b are provided, which are arranged electrically isolated from the furnace trough 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 trough 2. The furnace trough 2 has spaced-apart trough 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 current contact 3a to the second current contact 3b. In Fig. 1 By way of example, only three tray segments 6, 6a, 6b, 6c are shown. Of course, the furnace trough 2 can also have only two or more than three trough segments 6. Likewise, the furnace 1 may have more than one furnace trough 2. The tub segments 6 are formed at least partially from metal, ie electrically conductive, and have an electrically insulating coating 9 on their inner side 7 facing the interior 7 of the furnace tub 2. Adjacent trough segments 6a, 6b and 6b, 6c are connected to one another via a length compensation element 10, 10a, 10b arranged between the adjacent trough segments 6a, 6b and 6b, 6c, ie the length compensation element 10, 10a, 10b is in the walls and in the floor the furnace trough 2 provided to a temperature-related relative movement of the tub segments 6 to each other permit. The furnace tub 2 is not limited to a rectangular cross-sectional shape and may, for example, be U-shaped in cross-section. The furnace trough 2 has alternately successive trough segments 6 and length compensation elements 10 in the longitudinal direction L of the furnace 1. The length compensation element 10 is at least partially formed from metal and has on its interior 7 of the furnace trough 2 facing inside 11 an electrically insulating coating 12. In the example illustrated, the electrically insulating coating 9 and the electrically insulating coating 12 are firmly applied to the tray segments 6 or to the length compensation elements 10 and thus to part of the tray segments 6 or of the length compensation elements 10.

For the use of the furnace 1 for the longitudinal graphitization of a workpiece, i. a carbon-containing shaped body to be processed by the action of heat, the molded body or the workpiece between the current contacts 3a, 3b and thus electrically connected to the furnace trough 2 is inserted. In this case, the current contacts 3a, 3b may be formed 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 clarity. The electrically insulating coating 9 on the inner side 8 of the tub segments 6 and the electrically insulating coating 12 on the inner side 11 of the length compensation elements 10 isolate the furnace tub 2 from the electrical current, which is passed through this for processing of the molding, not shown. Without the electrically insulating coating 9, 12, the electric current would undesirably flow into the furnace trough 2 via the fill of heat-resistant material (for example coke) and over the inner sides 8, 11 of the trough segments 6 and the length compensation elements 10 and via the trough segments 6 and 12 the length compensation elements 10 are forwarded.

The length compensation element 10 is in 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, wavy deflected or formed meandering. Thus, the length compensation element 10 is particularly favorable designed for changes in its longitudinal extent in the direction of the arrow L. The length compensation element 10 is arranged between adjacent tub segments 6a, 6b and 6b, 6c and connected to these, in order to avoid a gap between the mutually facing ends of adjacent tub segments 6 or to close them by the length compensation element 10. The adjacent tub segments 6, 6a, 6b, 6c are thus connected to each other without a gap. In contrast to known furnace constructions, no covering body is required which rests against the inner sides of adjacent trough segments and covers a remaining gap between adjacent trough segments. In the illustrated examples, the tub segments 6 are fixedly connected to the length compensation elements 10.

Fig. 2 shows a portion of the furnace trough 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, im in Fig. 2 illustrated example, the tub segments 6b, 6c, are detachably bolted to a length compensation element 10. In this case, the screwed with the length compensation element 10 tub segments 6, 6b, 6c an outwardly bent, for example. Flanged edge 13 on which a connecting portion 14 of the length compensation element 10 is applied. At least one screw 15, but preferably a plurality of screws 15 extend through the bent edge 13 of the tub segment 6, the connecting portion 14 of the length compensation element 10 and two flanges 16a, 16b. The flanges 16a, 16b are on the opposite sides 13a, 14a of the bent edge 13 of the tubing segment 6 and the connecting portion 14 of the length compensation element 10 releasably on. The screws 15, together with a nut 17 mounted thereon, span the tub segment 6, the length compensation element 10 and the flanges 16a, 16b. In this embodiment, therefore, the tub segments 6 are connected directly to the length compensation elements 10. Im in Fig. 2 illustrated example, both the outwardly bent edge 13 of the tub segment 6 and the connecting portion 14 of the length compensating element 10 on the mutually facing sides 13z, 14z an electrically insulating coating 18. In a simpler embodiment, only the outwardly bent edge 13th of the tub segment 6 or the connecting section 14 of the length compensation element 10 on the mutually facing sides 13z, 14z have an electrically insulating coating 18. The screws 15 are housed in a heat-resistant, for example. Ceramic, electrically insulating sleeve 19 to an electrically conductive connection from the bent edge 13 of the tub segment 6, 6c on the generally metallic flange 16a and the screw 15 to the generally metallic flange 16b or to avoid the connecting portion 14 of the length compensation element 10. Also, the screw head 15a and the nut 17 are electrically isolated from the flanges 16a, 16b. For example, the screw head 15a and the nut 17 abut against bent edges of the electrically insulating sleeve 19.

In Fig. 2 In addition, it can 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 connection section 14 of the length compensation element 10 in regions 20 via the contact surface 21 between the outwardly bent edge 13 of Tub segment 6 and the connecting portion 14 of the length compensation element 10 extends beyond.

Fig. 3 shows a portion of a differently constructed furnace tub 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 trough 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 abut each other in the assembled state of the furnace 1, and are screwed together by means of screws 15 extending through the first flange 22a and the second flange 22b. Im in Fig. 3 As shown, 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 portion of a differently constructed furnace tub 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 tray 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 each other, are inseparably connected to each other, preferably welded together by means of a weld 23. In the example shown, the electrically insulating coating 9 of the tub segment 6 and the electrically insulating coating 12 of the length compensation element 10 are applied to the tub segment 6, to the length compensation element 10 connected thereto, 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 case 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 in succession from the first to the second current contact 3a, 3b be, wherein adjacent segment portions 6x1, 6x2 of the tubing segment 6 via an electrically insulating intermediate layer 24 connected to each other and are electrically insulated from each other.

In one experiment, an existing 25 meter long graphitizing furnace was used, which was designed with two electrically series oven pans. 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 connecting graphite electrodes of the two furnace pans were electrically connected to one another on one side of the pans. The power connection (plus and minus connection) was mounted on the opposite side of the two furnace pans on the connecting graphite electrodes. The furnace was then treated such that a furnace pan (the one coupled to the plus side of the electrical connector) was completely coated with a ceramic coating by means of an 0.15 mm wet film thickness airless paint sprayer. The coating was made as follows: in one Dissolvers 30 parts by weight of liquid colloidal silica sol with 40% solids content (particle size 10 nm) as a binder and 10 parts by weight of water were placed in the stirred tank. In this liquid, a solid mixture of 40 parts by mass of magnesium oxide having an average particle size d50 = 4 microns (d90 = 13 microns) and 20 parts by mass of glass powder having an average particle size of 4 microns (d98 = 17 microns) and 0.3 parts by mass of methyl cellulose introduced as a thickener and suspended, wherein the speed of the dissolver disc during the powder input was steadily increased to 12 m / sec and was dispersed 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. In both furnace pans, the same starting material was used for graphitization, 77 electrodes in each well. 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 was measured. It was found that those graphite electrodes which have been graphitized in the coated well had an average of 0.05 [μOhmm] lower electrical resistance than those electrodes which had been graphitized in the uncoated well.

Claims (10)

Oven (1) with at least one furnace trough (2) in which a first (3a) and a second (3b) from the furnace trough (2) electrically insulated current contact are provided, wherein the furnace trough (2) from the first (3a) to second current contact (3b) arranged one behind the other and spaced apart tub segments (6) is formed, which tub segments (6) are at least partially formed of metal and on its interior (7) of the furnace tub (2) facing inside (8) an electrically insulating coating (9), characterized in that adjacent trough segments (6) are connected to one another via a length compensation element (10) arranged between the adjacent trough segments (6), which length compensation element (10) is formed at least partially from metal and has its interior (7 ) of the furnace trough (2) facing the inside (11) has an electrically insulating coating (12). Oven (1) according to claim 1, characterized in that the tub segments (6) are electrically insulated from the length compensation element (10) connected thereto. Oven (1) according to claim 1 or 2, characterized in that the length compensation element (10) perpendicular to the inside (8) of the tub segments (6) deflected, preferably meander-shaped. Oven (1) according to one of claims 1 to 3, characterized in that at least one tub segment (6) is detachably screwed to a length compensation element (10). Oven (1) according to claim 4, characterized in that with the length compensation element (10) screwed tub segment (6) has an outwardly bent edge (13) on which a connecting portion (14) of the length compensation element (10) is applied, and at least one screw (15) through the bent edge (13) of the tub segment (6), the connecting portion (14) of the length compensation element (10) and by two flanges (16a, 16b) extending on the sides facing away from each other (13a, 14a) of the bent edge (13) of the tub segment (6) and the connecting portion (14) of the length compensation element (10) abut. Oven (1) according to claim 5, characterized in that also the outwardly bent edge (13) of the tub segment (6) and the connecting portion (14) of the length compensation element (10) on the mutually facing sides (13z, 14z) an electrically insulating Have coating (18) and the at least one screw (15) is received in an electrically insulating sleeve (19). Oven (1) according to claim 6, characterized in that the electrically insulating coating (18) on the mutually facing sides (13z, 14z) of the outwardly bent edge (13) of the tubing segment (6) and the connecting portion (14) of Length compensation element (10) extends beyond 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) addition. Furnace (1) according to claim 4, characterized in that the tubing segment (6) screwed to the length compensating element (10) is inseparably connected to a first flange (22a) on which a second flange (22b.) Inseparably connected to the length compensating element (10) ), and at least one screw (15) extends through the first flange (22a) and through the second flange (22b). Oven (1) according to claim 8, characterized in that the first flange (22a) and the second flange (22b) on the mutually facing sides (22az, 22bz) have an electrically insulating coating (18) and the at least one screw (15 ) is received in an electrically insulating sleeve (19). Oven (1) according to one of claims 1 to 9, characterized in that the electrically insulating coating (9, 12, 18) enamel or at least one of magnesium oxide, chamotte or glass, 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.

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