EP1089039A1 - Electrode comprising an electrode rod - Google Patents

Abstract

Electrode rod is made of a composite material reinforced with heat resistant fibers and having a silicon carbide matrix. An Independent claim is also included for an electrode arrangement comprising an electrode (44) for conveying or deviating an electrode voltage from a stub (46), and the electrode rod (32) connected to the stub.

Description

The invention relates to an electrode rod and an electrode device with an electrode for transmission or derivation an electrode voltage from an electrode stump, with such an electrode rod.

Modern industrial furnaces have a burner tube in which one Combustion chamber is formed in the appropriate feeds Combustion air and fuel are supplied. To be reliable To enable ignition of the fuel / air mixture a separate ignition chamber is generally also provided, into which an electrode rod extends, which with a suitable ignition electrode and is equipped with a suitable one Ignition voltage is supplied.

Such a burner with an electrode rod attached to its front end reaching into the ignition chamber in an insulating tube is guided, and at its rear end with a Ignition electrode is connected, for example from the DE 41 38 434 C1 known.

Such electrode rods usually consist of Kanthal wire, i.e. made of a special alloy that is suitable for High temperature applications is suitable. Through the insulating tube the electrode rod is at high operating temperatures on the desired position and against bending and other Stress protected, especially when the kanthal wire is thermally overstressed and thus loses strength.

At higher temperatures occur in the combustion chamber Kanthal wire thermally induced wear (erosion and embrittlement of material or bending), so that the ignition and in particular the monitoring function of the Electrode rod can no longer be guaranteed.

Such a stick electrode is therefore to be regarded as a wearing part. Due to the frequent change of the electrode rod there is a high maintenance effort.

Electrode rods have also become known through use, in which attempts have been made to produce the electrode rod from a monolithic ceramic, namely from melt-infiltrated SiSiC ceramic. The ceramic tube required for fastening and insulation, which usually consisted of Al ₂ O ₃ , was pushed onto the electrode rod and fastened with a suitable adhesive. A metal dowel pin was used to connect the SiSiC rod to the associated electrode.

The known electrode rod has proven to be extremely brittle proven so that with mechanical stress a considerable There is a risk of breakage. Already during the assembly of the roll pin, in other words when the electrode rod is connected to the associated one Electrode, there was a significant risk of breakage. So is when using the known SiSiC ceramic Largest electrode rod during transport, assembly and disassembly Care required.

The invention has for its object an improved Specify electrode rod that has a long service life and a has the lowest possible susceptibility to breakage.

A suitable electrode device should also be specified, with which such an electrode rod can be used can.

The invention is achieved by an electrode rod that consists of a composite material reinforced with heat-resistant fibers with silicon carbide matrix.

It has been shown that such a composite material has has good strength properties, a high oxidation and Has temperature resistance and a high resistance to temperature changes disposes. Furthermore, it has been shown that such a composite material the necessary electrical Has conductivity.

For the purpose described above, the invention has Composite proven so ideal that the electrode rod on a burner tube is not replaced prematurely must, but has such a long service life, that an exchange only in combination with the whole Burner tube is required in special cases. The invention The electrode rod is therefore not a wearing part represent more.

Silicon carbide is known to be a material with semiconductor properties, which is for the above Described purpose proved to be sufficiently electrically conductive Has.

In an advantageous development of the invention, the fibers are made made of silicon carbide or carbon.

Such fibers have a high heat resistance and are to improve strength and reduce susceptibility to breakage of such a composite material in particular suitable. In addition, silicon carbide fibers have a good Resistance to oxidation. If carbon fibers are used care should be taken to ensure that these Fibers are completely enclosed by the silicon carbide matrix are, since carbon fibers are naturally easily oxidized are. On the other hand, the carbon fiber electrical conductivity additionally improved.

According to a further embodiment of the invention, the silicon carbide existing matrix carbonaceous additives, preferably Carbon black and / or graphite.

Through such additives, the electrical conductivity of the Composite significantly improved. Further facilitate such additives contribute to the production of the composite material Use of sintering processes, pressure sintering or the like Process, if necessary also when using granulation processes.

According to a further embodiment of the invention, the fibers are surface coated.

By such a surface coating, for example consist of pyrolytic carbon, pitch or the like the fibers become melt infiltration later or pyrolysis protected against reactions, so that the improved strength properties due to the fibers largely preserved. In addition, the coated Composite fibers fracture tolerant because of coated fibers at least partially crack propagation can stop.

According to a further embodiment of the invention, the fibers are directed in the matrix with a preferred direction along and arranged transversely to the electrode rod.

The strength of the Electrode rod especially on the rod-shaped body occurring loads adjusted.

The fibers used for reinforcement can according to the invention be formed as long fibers, which can be woven over the Extend total length of the electrode rod, or as Short fibers can be formed with a length of the order of magnitude of about 2 to 10 mm and average diameters in the On the order of about 2 to 20 µm.

According to a further embodiment of the invention, the fibers are combined into fiber bundles (rovings).

When using long fibers, these can be called so-called Prepregs are processed in the form of a laminate structure the possibly several layers of woven fibers (Cross-ply layers) and / or unidirectional fibers (UD layers) are provided.

By using such cross-ply layers and / or UD layers give the electrode rod a targeted texture give to particularly well adapted to the mechanical stress To achieve strength properties.

The laminate used for this, the one for laminate construction can be used, preferably as an already coherent, Prefabricated prepreg placed in a mold become. The prepreg can be exposed to heat at elevated temperatures Shape the temperature (a few hundred degrees Celsius) well (like a plastic), since the organic binder components plasticize and the entire prepreg into shape "flows into".

There is a connection to this known process route Carbonization of the organic components by pyrolysis a temperature of the order of about 1000 ° C below Exclusion of air to produce a porous molded body, the then in a manner known per se with a silicon melt is melt infiltrated so as to be a fiber reinforced Manufacture moldings with silicon carbide matrix.

In a preferred alternative, a preform is woven out Fibers manufactured as a laminate from a fabric or Laid with the addition of a price cursor and a solvent will be produced. After preheating to approx. 200 ° C to drive out the organic components are controlled Heating to 1000 to 1100 ° C to drive off the organic Components and to generate the SiC matrix from the precursor or prepreg. Because of the bubbles that occur, the process must can be repeated several times.

Another production variant is silicon carbide powder used in which the fibers are statistically divided as short fibers are, these fiber bundles can be summarized, wherein the shaped body by a sintering process, preferably by pressure sintering at a sufficiently high temperature (in the Order of magnitude from approximately 1800 to 1900 ° C) with exclusion of air will be produced.

In a preferred development of the invention, the electrode rod has two end sections and a middle section, wherein the middle section is a rectangular, preferably has a square cross section.

With such a shape, a variety of Manufacture electrode rods in a cost-effective manner by these are separated from plate-shaped material by sawing.

In a preferred development of this embodiment, the two End sections a circular cross section.

In this way the connection to an electrode, e.g. an ignition electrode, at one end and the use of a Ceramic guide sleeve relieved at the other end.

The surface of the electrodes is preferably ground, the circular cross sections at the end portions can also be generated by grinding.

An electrode device according to the invention has an electrode for the transmission or derivation of an electrode voltage of an electrode stump with a Electrode rod is connected.

The electrode rod can, for example, in connection with a Ignition electrode, an ignition and monitoring electrode, one Monitoring electrode or a ground electrode can be used.

In a preferred development of the invention, the electrode rod at one of its two end sections by means of a dowel pin connected to the electrode stump.

This makes it easy to manufacture and durable Connection of the electrode rod with the electrode stump of the Electrode allows.

The dowel pin is preferably made of metal, e.g. made of spring steel, existing sleeve, for example can be slit lengthways.

According to a further embodiment of the invention is on a second of the end portions of the electrode rod is a ceramic Insulating tube provided, the one facing away from the central section Side by means of an adhesive or a sintered Nose is fixed to the end section.

In this way, the guidance of the electrode rod in the area allows an ignition chamber of a burner tube and a precise positioning in the area of the end section guaranteed.

Alternatively, a second one of the end portions of the Electrode rod in an externally attached, ceramic insulating tube be insertable.

This design has the advantage that the electrode rod itself no manipulations are required, so the leadership in the radial direction only through the ceramic insulating tube is guaranteed, into which the end section is pushed is. The axial position of the electrode rod is in this version through the connection with the electrode stump over the Dowel pin guaranteed.

According to a further embodiment of the invention Dowel pin shrunk onto a heat shrink tube.

This measure has the advantage that the mechanical and electrical Connection between the electrode stump of the electrode and the electrode rod permanently fixed and against environmental influences is protected, and that electrical insulation in this area is ensured. Because in this area the Such a temperature load can only be relatively low Heat shrink tubing easily when using a such an electrode device used in an industrial burner become.

It is understood that the above and those below Features of the invention not yet to be explained in the specified combination, but also in others Combinations or alone can be used without the To leave the scope of the present invention.

Fig. 1

einen Ausschnitt aus einem Brennerrohr mit Gaslanzette zur Zuführung von Brennstoff im Bereich einer Zündkammer, in die ein erfindungsgemäßer Zündstab hineinragt;

Fig. 2

eine erfindungsgemäße Elektrodeneinrichtung, die eine Elektrode zur Übertragung oder Ableitung einer Elektrodenspannung von einem Elektrodenstumpf aufweist, und die mit einem Elektrodenstab an dessen einem Ende verbunden ist, der an seinem anderen Ende mit einer Isolierhülse versehen ist;

Fig. 3

einen vergrößerten Ausschnitt aus dem Matrixwerkstoff, aus dem der Elektrodenstab besteht, in schematischer, vereinfachter Darstellung;

Fig. 4

eine ähnliche Darstellung wie Fig. 3, jedoch mit einem anders aufgebauten Siliziumcarbid-Verbundwerkstoff und

Fig. 5

eine ähnliche Darstellung wie Fig. 3, jedoch mit einem weiter abgewandelten Aufbau des Siliziumcarbid-Verbundwerkstoffes.

Further features and advantages of the invention result from the following description of preferred exemplary embodiments with reference to the drawing. Show it:

Fig. 1

a section of a burner tube with a gas lancet for supplying fuel in the region of an ignition chamber into which an ignition rod according to the invention projects;

Fig. 2

an electrode device according to the invention which has an electrode for transmitting or discharging an electrode voltage from an electrode stump and which is connected to an electrode rod at one end which is provided with an insulating sleeve at its other end;

Fig. 3

an enlarged section of the matrix material from which the electrode rod consists, in a schematic, simplified representation;

Fig. 4

a representation similar to FIG. 3, but with a differently constructed silicon carbide composite and

Fig. 5

a representation similar to FIG. 3, but with a further modified structure of the silicon carbide composite.

In Fig. 1 is a section of a ceramic burner tube 10 shown in longitudinal section, the part of a Industrial burner for furnace firing.

A plate 26 is held in the burner tube 10 on a gas lance 14, in which central outflow openings 28 are provided, over the fuel supplied via the gas lance 14 in the direction the arrows 22 can exit into a combustion chamber 12, the is formed at the front end of the burner tube 10 and to the rear is separated by the plate 26. On one side of the Plate 26 also has an ignition chamber 24 formed therein the gas lance 14 supplied fuel in the direction of the arrow 20 can emerge. The ignition chamber 24 is of an inventive type Electrode rod 32 interspersed in a ceramic Insulating tube 34 is guided on the plate 26 and with its end extends into the combustion chamber 12.

Combustion air is also through axial openings 27 in the plate 26 fed into the combustion chamber 12 in the direction of the arrow 18.

The electrode rod 32 is part of an overall number 30 designated electrode device, in its entirety is shown in Fig. 2. It should be noted that the in Fig. 2 shows the electrode device not to scale the electrode device 30 according to FIG. 1 must match.

The electrode device 30 has an electrode 44 for transmission or deriving an electrode voltage from a cylindrical trained electrode stump 46, which with the Electrode rod 32 mechanically and electrically connected is. The electrode 44 can be, for example Act ignition electrode.

The electrode rod 32 has a central section 36, which has a square cross section, and a first End portion 38 on the electrode 44 side and a second End section 40 on the ignition chamber 24 side. Both end sections 38, 40 are cylindrical.

At its first end section 38 facing the electrode 44 this is due to a clamped spring steel pin attached to the electrode stump 46 of the electrode 44. The spring pin 46, which can be designed as a sleeve, which if necessary slit is additionally shrunk by a Shrink tube 50 fixed and insulated. Through this Shrink tube 50 becomes the mechanical and electrical Connection between the electrode stump 46 and the first End section 38 permanently protected against environmental influences and secured against loosening and electronically isolated.

At the opposite second end section 40 is the insulating tube 34 attached, which rests on the central section 36 and at its opposite end with an adhesive 42 a suitable adhesive or through a hinge nose fiber-reinforced SiC matrix material is defined.

In an alternative embodiment of the electrode device 30 attaching the insulating tube 34 to the end portion 40 waived, so that the electrode rod 32 with its end portion 40 are simply pushed into the insulating tube 34 can and is held only in the radial direction. In In this case, the insulating tube 34 is attached to the plate 26 or otherwise specified externally.

The electrode device 30 according to the invention is distinguished in particular from the fact that they are made of an electrode rod 32 a composite material reinforced with heat-resistant fibers with silicon carbide matrix, as explained in more detail below becomes.

The composite material from which the electrode rod 32 is made has a matrix of silicon carbide in which, if appropriate Additives, preferably SiC powder, carbon black and / or graphite, contain are, and which may contain fillers.

To the necessary mechanical properties at the increased To ensure temperatures in the combustion chamber and at the same time ensure sufficient elasticity of the material, the matrix is reinforced with high-temperature fibers.

These fibers are preferably made of fibers Silicon carbide (SiC). If necessary, carbon fibers can also be used for this (C fibers) or other fibers containing B, N, C, Si included, used.

The fiber content of the silicon carbide matrix can be in a range of about 5 to 70 vol .-% and is preferably in a range of about 20 to 40% by volume. The fibers can be used as Short fibers 58 can be formed in the silicon carbide matrix 52 according to FIG. 5 with a preferred direction in the direction the longitudinal extent of the electrode rod 32 may be arranged can.

In addition, the fibers can also be statistically distributed in the matrix 52 may be arranged and possibly to short fiber bundles be summarized as this is shown schematically with the number 56 in Fig. 4 is indicated.

In a further embodiment, which is shown schematically in FIG. 3 is, the fibers 54 are formed as long fibers that for example in the longitudinal direction of the electrode rod 32 can extend as indicated in Fig. 3.

In addition, the fibers can also be in the form of a fabric structure from woven fibers (cross-ply layers) or from unidirectional fibers (UD layers) can be formed, wherein several layers of different structures, possibly in shape can be summarized in a laminate structure.

To use a large number of electrodes in a cost-effective manner To be able to produce is preferably plate-shaped material Made from the composite material from which individual electrodes be separated by sawing. The surfaces of the electrodes are then expediently ground, whereby the cylindrical end portions 38, 40 also through Loops are generated.

The composite material made of a silicon carbide matrix with embedded high-temperature fibers, preferably made of silicon carbide or carbon, can basically be two different ways are made. A first option consists of the mixture of silicon carbide powder, the expediently binders and possibly further additives, such as carbon black and / or graphite and optionally filler are added, and in which the fibers to be embedded are statistically distributed embedded.

In order to produce a homogeneous mixture, a known one can also be used Granulation processes can be used. From the so produced Greenery are initially at elevated temperature by some 100 ° C the organic components expelled and then with the exclusion of air in a temperature range of about 1800 to 1900 ° C a sintering process is carried out to the desired To produce shaped bodies. This can preferably be done by a pressure sintering process can be achieved to a high density To achieve shaped bodies.

There is an alternative to the production of the composite material about the known silicon technology by melt infiltration with a silicon melt, starting with a mixture from the fibers and a carbon-containing material (Precursor) with the addition of binders and fillers this mixture then turns into a green compact a pressing tool is pressed, the green body then under Exclusion of air for the production of a porous molding is pyrolyzed about 800 to 1000 ° C and then this is melt infiltrated with a silicon melt.

In this way, a molded body with a silicon carbide matrix are produced in which the fibers are made of silicon carbide or embedded in carbon based on the reaction.

In this manufacturing variant, the fibers are preferred previously coated with a surface to react to avoid with the silicon melt. So much for short fibers processed, they are preferably bundles of fibers summarized, held together by impregnation become.

In a further production variant, a prepreg is used first Made from heat-resistant fibers with carbon-containing Binder with the addition of fillers to one Layered bond that can be formed under the influence of heat are. The prepreg is then placed in a press tool and under the influence of heat at temperatures of some 100 ° C pressed. The molded body thus produced is then pyrolyzed to a C / C material in the absence of air and then with a silicon melt in the absence of air at temperatures melt infiltrated from approx. 1500 to 1600 ° C.

In a further variant, the fibers are used as fiber bundles (Rovings) with a layer e.g. from C, SiC or other carbon-containing materials. The Fibers have a diameter of <10 µm and are in rovings summarized from 1000 or more filaments. These bundles will be coated as a whole by a CVD process. The coated Fibers are laid out as scrims (this can change the direction superimposed fibers can be any), woven or wound Form used. The fabrics used to make it with long fibers 54 according to FIG. 3 are cut into pieces and with a slip consisting of carbosilane (precursor for the SiC matrix), solvents (xylene) and SiC powder soaked. The soaked fabrics become laminate-like placed on top of each other and under pressure at approx. 200 ° C in a prepreg (or preform) converted. In this process the solvent expelled and the carbosilane in polycarbosilane converted. The stable body is then heated to 1100 ° C heated and held sufficiently long until the polycarbosilane has decomposed to SiC (pyrolysis). The resulting gaseous decomposition products create pores in the material. For this reason, the process of soaking and subsequent Repeat heating several times until one is sufficient tight body is achieved. The plate obtained from Fiber ceramics are then further processed by sawing and grinding, to get the desired electrode rods.

Unless carbon fibers or other easily oxidizable fibers it is useful to use the electrode rods after the Cutting and, if necessary, grinding again with one oxidation resistant material, e.g. with SiC, to coat e.g. through a CVD process.

Claims (16)

Electrode rod, characterized in that the electrode rod from a reinforced with high-temperature fibers (54, 58) Composite with silicon carbide matrix (52) consists. Electrode rod according to claim 1, characterized in that the fibers (54, 58) made of silicon carbide or carbon consist. Electrode rod according to claim 1 or 2, characterized in that the matrix (52) made of silicon carbide aggregates, preferably carbon black and / or graphite and / or SiC powder having. Electrode rod according to one of the preceding claims, characterized in that the fibers (54, 58) are surface coated are. Electrode rod according to one of the preceding claims, characterized in that the fibers (54, 58) in the matrix (52) directed with a preferred direction along and are arranged transversely to the electrode rod (32). Electrode rod according to claim 5, characterized in that the fibers (54) are designed as long fibers. Electrode rod according to one of the preceding claims, characterized in that the fibers (58) are short fibers are trained. Electrode rod according to one of the preceding claims, characterized in that the fibers form fiber bundles (56) are summarized. Electrode rod according to one of the preceding claims, characterized in that the electrode rod (32) two End portions (38, 40) and a central portion (36) and that the central section (36) has a rectangular, preferably a square cross section having. Electrode rod according to claim 9, characterized in that the two end portions (38, 40) are circular Have cross-section. Electrode rod according to one of the preceding claims, characterized in that the electrode rod on its Surface has an oxidation-resistant coating. Electrode device with an electrode (44) for transmission or deriving an electrode voltage from one Electrode stump (46), and with an electrode rod (32), which is connected to the electrode stump (46), thereby characterized in that the electrode rod (32) according to a of claims 1 to 11 is formed. Electrode device according to claim 12, characterized in that the electrode rod (32) on a first (38) its two end sections (38, 40) by means of a dowel pin (46) is connected to the electrode stump (46). Electrode device according to claim 13, characterized in that the roll pin (48) shrunk from a Hose (50) is enclosed. Electrode device according to claim 12, 13 or 14, characterized characterized in that on a second (40) of the end portions (38, 40) a ceramic insulating tube (34) is provided is that on a side facing away from the central section (36) Side by means of an adhesive (42) or a sintered Nose is fixed to the end section (40). Electrode device according to one of claims 12 to 14, characterized in that a second (40) of the end portions (38, 40) in an externally attached, ceramic Insulating tube (34) can be inserted.

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