JP6679595B2 - METHOD OF CONDUCTIVE HEATING OF METAL SHEET, ELECTRODE AND HEATING DEVICE FOR THE SAME - Google Patents

Description

The present invention relates to a conductive heating method for a metal sheet, wherein the metal sheet or at least one conductively heated region of the metal sheet has a rectangular or non-rectangular outline, and At least one electrode having a contact area is brought into electrical contact with the metal sheet and an electric current for carrying out conduction heating is supplied to and / or removed from the metal sheet via the contact area. The present invention also relates to an electrode for conductively heating a metal sheet and a conductive heating device for carrying out a method for conductively heating a metal sheet.

The present invention generally relates to the field of metal working, and more particularly to the field of manufacturing metal sheet parts such as automobile parts and chassis parts from metal sheets. The process for producing a molded product from a metal sheet is performed by a production line such as a continuous production line. This production line usually includes equipment for carrying out further processes such as process-related deformations, edging, and optionally shape modification, coating, pressure hardening. Many are intended to produce parts with very high, highest or very high hardness.

During pressure hardening, the metal sheet is heated to about 930 ° C. and cooled while being formed. A martensite structure is realized by selectively cooling (curing) when the metal sheet is pressure-cured by a cooled pressure tool, and a desired tensile strength or the like exceeding expansion / contraction at 1500 MPa in a region of 5%> is desired. The processing material characteristics of can be acquired. The disadvantage of this heat treatment is the relatively long heating period in the conventional heat treatment, for example in a roller hearth furnace. As a result of the long heating period, an unfavorable scale (material combustion) is also formed on the material. As a countermeasure by the conventional technique, the surface of the component is covered with a coating that diffuses when the oven is heated. In that case, the manufacturing of the coating requires more labor and money. Uncoated materials are also industrially pressure cured, in which case the scale of the part is removed after pressing. The disadvantage here is the high tool wear due to the hard scale, which has a wear effect on the tool surface.

As an alternative to the conventional relatively long heat treatment, the metal sheet can be heated by conduction heat treatment. At this time, the metal sheet is heated by electric heat generated by transmitting an electric current. With a reasonably strong current, a typical heat treatment takes less than 10 seconds. The advantage is that only a very thin scale layer is formed in a short period of time, which also has the advantage that tool wear is reduced without the need for a scale protection layer. The conductive heat treatment of a metal sheet is described, for example, in DE 1020060376637A1.

The proposals of the prior art are still limited in practicality. The reason is that it is only suitable for heat treatments of substantially rectangular parts or for rectangular parts of parts. However, in practically manufactured parts, such as automobile chassis parts, the heated metal sheet or the heated area of the metal sheet does not have an ideal rectangular shape. Rather, many parts have irregular shapes. Even if the proposal of the prior art is adopted, the heat treatment becomes uneven, and the desired manufacturing result cannot be obtained. However, conduction heating of metal sheets formed more simply than that, i.e. rectangular metal sheets or metal sheets with rectangular portions, is also difficult.

The problem of so-called hot spots which occurs during conduction heating, especially in the processing of point feeds (e.g. required for deployment blanks), remains unsolved. The hot spot refers to a portion formed by being scattered during conduction heating and having a heating degree that is excessively higher than the surrounding area. As a physical condition for uniform heating in the conductive heat treatment, there is a case where the current density is substantially the same over the cross section of the all-metal sheet. It is particularly difficult to realize this at the power feeding portion or the current extraction portion (the position where each electrode contacts the metal sheet).

A further problem with conventional conductive heat treatments is the inability to achieve the desired heat treatment (austenitization) and associated hardening of the metal sheet material in each peripheral region of the metal sheet where the electrode contacts the metal sheet. Is. Therefore, each peripheral region is either unavailable for practical final parts or has to accept its insufficiently cured state. Therefore, a further manufacturing process for eliminating each peripheral region by a laser cutting method or the like is required. Especially for a small metal sheet, the cutting rate is relatively high, which leads to a relatively disadvantageous material utilization rate.

Therefore, an object of the present invention is to provide a conductive heating method for a metal sheet that solves the above problems, and therefore an electrode and a heating device.

The object of the present invention is solved by the conductive heating method for a metal sheet according to claim 1. The metal sheet or at least one conductively heated area of the metal sheet is rectangular or non-rectangular in profile, and at least one electrode having a contact area is electrically contacted with the metal sheet to perform conductive heating; Electric current is supplied to and / or removed from the metal sheet via the contact area to carry out conduction heating. The electrode has a textured and structured contact area that includes a plurality of spaced apart contact surfaces, the plurality of spaced apart contact surfaces forming a plurality of spaced apart contact sites between the electrode and the metal sheet. In the present invention, a square metal sheet is a special example of a rectangular metal sheet.

The advantage of the present invention is that the electrode according to the invention makes it possible to achieve a relatively steep thermal gradient in the contact area between the electrode and the metal sheet, the advantageous effect of which is also in the area of the electrode. That is, the heat treatment is performed. In this way, the cutting rate can be greatly reduced, especially for small parts. In many cases, an additional manufacturing step of cutting the peripheral area of the metal sheet may be omitted.

Generally, in conductive heat treatment, the metal sheet remains cold in the pressure contact area of the cooled electrode. Furthermore, an affected area of the electrode is formed, which is not sufficiently heated. There, a complete austenitizing treatment and a subsequent hardening treatment are not possible. It applies especially to the edges of metal sheets. Its physical cause is the thermal cooling effect of the electrode and its consequent effect. As a general rule, the resistance amount of the metal sheet increases as the heating amount increases. When the edge region of the metal sheet is cold, the amount of resistance does not increase significantly. The edge area of the metal sheet is connected in series with the rest of the metal sheet. If there is a large resistance, the voltage drops more and more output is converted, so that the heat treatment is performed again. As a result, an electronic avalanche which is disadvantageous in the heating performance (the influence range of the electrode) on the edge of the metal sheet is brought about.

A further advantage of the present invention is that the disadvantageous hot spots that have hitherto been generated uniformly in the region where the heat treatment is usually insufficiently performed (the influence area of the electrode) are not intentionally avoided but rather intentional. Is to use.

Therefore, a large number of small hot spots are generated on the metal sheet in front of the electrodes, and the intervals between the hot spots are approximately equivalent to the thickness of the metal sheet. In this way, it is possible to advantageously act uniformly, not as hot spots due to uneven heating, but in the edge regions of the metal sheet (otherwise under-affected areas of the electrode which are not sufficiently heated). In addition, since the new electrode shape of the present invention does not cover the entire surface of the metal sheet, it is advantageous that less heat is dissipated from each cooled electrode. Furthermore, heat can be generated better and better in exposed areas within the electrode area. As a result, the metal sheet warms to the target temperature in front of the electrode and in its immediate electrode area.

The aforesaid object is further solved by an electrode for conductively heating a metal sheet, which has a contact surface in electrical contact with the metal sheet. The electrode has a textured and structured contact area that includes a plurality of spaced apart contact surfaces, the plurality of spaced apart contact surfaces forming a plurality of spaced apart contact sites between the electrode and the metal sheet.

The aforesaid problem is further solved by a conductive heating device implementing a method of conductively heating a metal sheet. The conduction heating device has at least one electrode as described above as a power supply electrode, a current extraction electrode, and / or a power transmission electrode.

The electrodes according to the present invention having irregularities and structured contact areas may be used as feed electrodes, current extraction electrodes and / or power transmission electrodes. The power supply electrode is for supplying power (supplying current) to the metal sheet to execute the conductive heating process. The current extraction electrode is for extracting current from the metal sheet. The power transmission electrodes are for transmitting current from one metal sheet to another metal sheet when the metal sheet heating is performed on pairs of trapezoidal surface areas, for example. Also, a transition electrode may be applied to the metal sheet to intentionally not heat a particular area.

The present invention further provides a conductive heating method for a metal sheet, wherein even if the metal sheet or at least one conductively heated area of the metal sheet has a non-rectangular contour, the heated area is uniform. To be heated. In technical terms, a metal sheet is called a "blank" and a non-rectangular blank is called a "machined blank". Moreover, it provides the suitable conduction heating apparatus for that.

It is made possible by the conductive heating method of metal sheets. The metal sheet or at least one conductively heated region of the metal sheet has a non-rectangular contour. An array of power supply electrodes and current extraction electrodes adapted to the contour is configured, and each power supply electrode and each current extraction electrode are separated and arranged along the contour, and are connected to a plurality of power sources that are electrically separated from each other. To be made. The capacity of the power supply is such that it gives substantially the same current density to the metal sheets between all the paired power supply electrodes and current extraction electrodes. An advantage of the present invention is an array of a feed electrode and a current extraction electrode manufactured according to the contour of a metal sheet or a heated region thereof, in which each electrode is separated and arranged along the contour. That is, a structure operated by power sources that are electrically separated from each other is realized. In this way, for example, the contour of the heated area may be divided into rectangular surface areas or at least substantially rectangular surface areas, in which each surface area is provided with an electric current exactly at the desired current density. An adapted feeding electrode and current extraction electrode can be constructed. Adjacent, likewise substantially rectangular, surface areas may be provided with further pairs of feed and current extraction electrodes, a regulated voltage or regulated current being acted upon by a second power supply, said adjoining surface areas. And the same current density. In this way, all heated areas are divided into substantially rectangular surface areas, giving the same current density in each surface area. By having the same current density in all surface areas, cross flow between surface areas can be avoided and unexpected heating results can be avoided. The current density necessarily adapts to the resistance situation and cannot in principle be forced to be uniform. However, only uniform current density gives uniform heating, since the same output is always produced per region. The purpose here is to set the resistance situation in the spreading blank by the above-mentioned method so as to obtain a uniform current density. In this way, uniform conduction heating can be achieved for unevenly shaped metal sheets or for unevenly heated areas of the metal sheet. Therefore, according to the present invention, an advantageous conductive heat treatment can be universally applied to a metal sheet having an arbitrary shape. Here, the metal sheet can be regarded as a resistance medium through which a current supplied through the electrodes flows, so that the current density is substantially the same and uniform.

According to the present invention, the metal sheet can suppress the scale and be heated to a desired temperature. In this way, the work associated with tool wear due to the scale rubbing the tool surface during scale removal of the part and subsequent pressure hardening of the heated metal sheet can be eliminated. The heat treatment can be performed in 10 seconds or less. The heating period can be set by the power supply amount. Generally, the more current that passes through the metal sheet, the faster the heat treatment can be performed.

As the metal sheet, a metal sheet made of a conductive metal such as steel, titanium, aluminum or magnesium can be considered. In an advantageous variant according to the invention, the material thickness of the metal sheet is constant, at least before further processing after the conductive heat treatment and optionally the step of being deformed.

The power feeding electrode is for supplying an electric current from a power source to the metal sheet. The current extraction electrode is for returning the current from the metal sheet to the power supply. The capacity of each power supply according to an advantageous modification of the present invention is spread over all the paired power supply electrodes and current extraction electrodes, and the same current density is supplied from each power supply electrode to the metal sheet, and metal is supplied via the current extraction electrodes. The capacity is enough to remove from the sheet.

The number of feed electrodes used can be the same as or different from the number of current extraction electrodes used. In the same case, it is advantageous for one feed electrode and one current extraction electrode to form one electrode pair connecting to the same power supply. Further, for example, two power supply electrodes or two current extraction electrodes may be electrically connected. In this way, the electrodes that are not connected to each other can be connected to different power supplies at different voltages, and thus generate the same current density in adjacent surface areas in the metal sheet.

Here, the plurality of electrically isolated power sources needs to be electrically isolated at least at one of the connecting portions. In an advantageous variant of the invention, the power sources are not connected to each other and are not grounded. In this way, as in the case of multiple spot welds operating simultaneously in the chassis, the potentials of adjacent power supplies will float at the contact lines. "Einschwimmen" is a term well known in the resistance welding art.

In order to ensure the same current density of the metal sheet, current is supplied to the metal sheet from a further power source or current is supplied from the metal sheet to a further power source between the pair of current extraction electrodes and the power feeding electrodes which are assigned to each other. It is further advantageous not to arrange another electrode for being taken out. In this way, it is possible to avoid fluctuations in the same current density desired in the metal sheet.

As previously mentioned, the conductively heated area can be divided into substantially rectangular surface areas. Also, the conductively heated region can be divided into a trapezoidal surface region or a substantially trapezoidal surface region. It is also advantageous to combine them, i.e. to divide the conductively heated area into rectangular and / or trapezoidal surface areas. In order to achieve the same current density in the trapezoidal surface region, in an advantageous variant of the invention, a pair of metal sheets are arranged next to each other along the transition region between a plurality of electrically insulated metal sheets. Are electrically connected to each other by the power transmission electrodes arranged in the. By appropriately arranging the metal sheet and the metal sheet facing each other, a rectangular surface area is likewise formed on the two trapezoidal surface areas connected via the transition electrodes, and at least one feeding surface is formed on one surface thereof. At least one current extraction electrode can be connected to the electrode, the other side of which. In this way, the flexibility and adaptability of the method according to the invention is further increased. Here, it is advantageous to connect trapezoidal surface areas with identical or symmetrical contours of each metal sheet to one another via transition electrodes.

In an advantageous variant of the invention, even trapezoidal surface areas of the same metal sheet can be electrically connected in pairs via the power transmission electrodes, so that they behave like a rectangular surface area. For this purpose, each trapezoidal surface area must be arranged appropriately, in particular with the same bevel.

In this way, a uniform resistance situation can be achieved in the trapezoidal surface area as well, as a result. Since the method of the present invention simplifies various complicatedly formed metal sheets into one rectangle or a combination of a plurality of rectangles, the same current density can be realized with almost no operation.

In an advantageous variant of the invention, one, some or all of the feed and current extraction electrodes are each of maximum length and are long electrodes which extend over part of the contour of the conductively heated region. Formed and connected at one end to a power source. In this way, it is advantageous for power to be supplied to or extracted from a particular location of the electrode. As a result, calculations and planning for the required electrodes are simplified.

In an advantageous modification of the present invention, the pair of the power supply electrode and the current extraction electrode is connected to the power source at both ends which are diagonally opposed to each other. The advantage is that the total resistance for each current line passing through the metal sheet is the same. The reason is that, in any case, since the power supply electrode and the current extraction electrode must pass through a large portion with a large difference, the current components always have the same total value. This also facilitates achieving the same current density desired in the metal sheet. here,
Total resistance = internal resistance of power source + resistance feeder line + electrode + metal sheet.

In an advantageous variant of the invention, one, a plurality or all of the feed electrodes, current extraction electrodes and / or power transmission electrodes are configured as cooling electrodes cooled by a cooling medium. As a cooling medium, for example, cooling water can be passed through a hollow tube provided in each electrode. The advantage of cooling the electrode is that it does not become unfavorably hot and avoids resistance changes of the electrode due to heating. A further advantage is that the adjacent metal sheets are also cooled by the cooled electrodes, and by appropriately placing the electrodes in the desired unheated areas of the metal sheets, heating and the associated hardening can be avoided. The advantage thereby is that the uncured cutting area can be defined on the basis of the position and arrangement of the electrodes, for example during subsequent processing of the part (ie the deformed metal sheet). In this way, the edges can be excised by conventional means, such as shearing, which are very economically applicable. No more labor intensive hard cutting methods are required. The uncured edge region is advantageous in the joining process of the parts in the later welding process. The curing process can be performed by a subsequent pressure curing process.

In an advantageous variant of the invention, conduction heating is carried out by direct current. This avoids electrical losses and other detrimental effects due to the inductance and capacitance inherent in the system as compared to alternating current. Further, in this way, no reactive power is generated. The existing electrical output can be fully utilized as active power. The cross-section of the wire and the power supply (eg transformer) can be designed smaller because it does not introduce inductive losses. In addition, energy is saved. Each power supply may supply three-phase power as a three-phase system. Also, the application of simpler electrical engineering laws that apply to direct current simplifies calculations and planning for the entire system, especially for each electrode and their placement.

The present invention does not require any complicated suppression treatment to achieve a uniform current density in the metal sheet. Therefore, the conduction heating device can be realized relatively easily and cost effectively.

In an advantageous variant of the invention, one or more or all of the feed electrodes, the current extraction electrodes and / or the power transmission electrodes are separated from one another during conduction heating in order to stretch the metal sheet. This makes it possible to compensate for the heating area of the metal sheet expanding due to heat during heating.

In an advantageous variant of the invention, parallel conductors are connected to the electrodes in order to feed the power supply electrodes, transmit power to the power transmission electrodes, transmit power from the power transmission electrodes and / or draw current from the current extraction electrodes. The parallel conductor is arranged across the metal sheet in parallel with the current line through a part of the metal sheet to be heated and electrically insulated from the metal sheet. The parallel conductors may be arranged over the edge area of a rectangular or trapezoidal surface area, which is heated in particular. It is advantageous to arrange the current lines in a desired direction in the heated surface area adjacent to the parallel conductors without performing a heat treatment on a specific area of the metal sheet by appropriately arranging the parallel conductors in this way. Is. In particular, undesired currents passing through the unheated areas of the metal sheet can be avoided by the current-dissipating effect (repulsion of parallel current-passing conductors). The lines of force also repel each other. In this way, for example, so-called Tailored Tempered Blanks (metal sheets that are hardened only in certain desired areas, but not in other areas) can be produced. It is desirable, for example in chassis parts, to bring certain deformation characteristics in case of a car accident. The parallel conductors need to be electrically insulated, but not necessarily thermally insulated. In this way, the parallel conductors can provide the desired cooling effect of the metal sheet.

In an advantageous variant of the invention, one, several or all parallel conductors are configured as conductors cooled by a cooling medium.

The invention further relates to a conductive heating device for carrying out the method for conductively heating a metal sheet, wherein the metal sheet or at least one conductively heated region of the metal sheet has a non-rectangular contour. The conduction heating device comprises an array of feed electrodes and current extraction electrodes adapted to the contour, which are arranged along the contour separate from each other and to a plurality of power sources which are electrically separated via individual feed lines. Connected or connectable. The capacity of the power supply is such that it gives the same current density in the metal sheets between all the paired power supply electrodes and current extraction electrodes. In the embodiments of the conduction heating device and further conduction heating devices described below, the advantages described for the conduction heating method above can also be realized.

In an advantageous variant of the invention, the conduction heating device is arranged to carry out the method described above. Thus, for example, the power supply can be configured as a DC power supply.

In an advantageous variant of the invention, the conduction heating device comprises a stretching device which stretches the metal sheet at least in the conductively heated region during heating. A stretching device is included in particular for separating certain power supply electrodes, current extraction electrodes and / or power transmission electrodes from each other during conduction heating.

In an advantageous variant of the invention, the electrode arrangement of the conduction heating device comprises power transmission electrodes for transmitting electricity between two metal sheets which are simultaneously heated in the conduction heating device.

In the above-mentioned conduction heating apparatus, the conduction heating method for a metal sheet includes, for example, disposing a metal sheet to be heated in the conduction heating apparatus, pressing an electrode of the conduction heating apparatus onto the metal sheet, and applying a current passing through the metal sheet. It may be advantageous to carry out the conduction heat treatment by flowing through the electrodes and, after sufficient heat treatment, to remove the electrodes from the metal sheet, before turning off the current. In this way, the metal sheet may be subjected to subsequent processing at elevated temperatures, for example, pressed to form the desired shape.

To supply the direct current, the power supply may include, for example, a welding rectifier. This allows the required direct current to be provided simply and cost-effectively at the desired height, which corresponds to thousands of amps.

The power supply electrode, the current extraction electrode, and / or the power transmission electrode can be made of copper or a copper alloy such as CuCoBe or CuBe2. In particular, the latter alloys can provide very hard and durable electrodes. The parallel conductors described above can be of the same or different materials. For electrical shielding of the parallel conductors, for example, a plasma sprayed ceramic layer may be provided on the surface of the parallel conductors.

In an advantageous variant of the invention, the conduction heat treatment can be carried out using temperature encapsulation means. In this case, the metal sheet is thermally shielded from the environment by the external heat enclosing means such as the heat insulating means of the conduction heating device. In this way, the amount of heat radiated to the environment is reduced, reducing costs and heating time. According to the results of the experiments carried out, even a simple insulating plate provided good results. Even better is something like insulation from furnace engineering. In this way, the environmental influences that affect the heat treatment are also avoided.

Hereinafter, the present invention will be described in more detail by way of examples with reference to the drawings.

In the drawing,
Is an unprocessed metal sheet for manufacturing automobile B pillars, Are two, unprocessed metal sheets shown in FIG. Is a conduction heating device and the two raw metal sheets shown in FIG. Is a further conduction heating device and the two unprocessed metal sheets shown in FIG. Is the placement of parallel conductors on a metal sheet, according to a cross-sectional view, Is a further conduction heating device and the two unprocessed metal sheets shown in FIG. Is a further conduction heating device and the two unprocessed metal sheets shown in FIG. FIG. 7 illustrates an embodiment of an electrode according to a perspective view.

In the drawings, the same symbols are used for corresponding structures.

FIG. 1 shows, in a top view, a metal sheet 1 cut into a specific shape and separated from a steel coil or the like. The metal sheet 1 is a non-workpiece for a B pillar of an automobile before the deformation processing by a press machine. In order to conductively heat the metal sheet 1 over the entire area with a uniform current density, the metal sheet 1 is first divided into a substantially rectangular surface area 2, 4 and a substantially trapezoidal surface area 3. Depending on the division of the surface regions 2, 3, 4 the electrodes arranged in the conduction heating device are also manufactured and then connected to the metal sheet 1 in order to carry out the conduction heating treatment.

In the case of a non-rectangular surface area (here surface area 3) obtained by the aforementioned division, in order to further optimize the manufacturing method, two metal sheets 1 are simultaneously subjected to a conduction heating device according to an advantageous embodiment of the invention. Heat with. For this, the two metal sheets 1 are first arranged as shown in FIG. 2 and the required electrodes are constructed appropriately.

FIG. 3 shows the metal sheets 1 shown in FIG. 2 in the conduction heating device 10, where the metal sheets 1 are arranged a little closer together as in FIG. About the conduction heating apparatus 10, the electrode array containing the feeding electrodes 11, 12, 13, 14, 15 and the current extraction electrodes 16, 17, 18, 19, 20 and the power transmission electrode 31 which were manufactured according to the above is shown. . As shown in FIG. 3, each pair of the feeding electrode and the current extracting electrode is connected to the rectangular surface regions 2 and 4 of the metal sheet 1, and each of them is connected to a power source 21, 22, 23, 24, 25 (for example, a rectifier that provides direct current). Connected transformer) or via an electrical switch not shown in FIG. The current between each electrode is indicated by the arrow showing the current line on each metal sheet 1. In the intermediate region of the metal sheet 1 (that is, both trapezoidal surface regions 3), the feeding electrode 12 is connected to the metal sheet 1 shown on the right side, and the current extraction electrode 19 is connected to the metal sheet 1 shown on the left side. In order to ensure the same current density over the vertical orientation of the trapezoidal surface area 3, each trapezoidal surface area 3 is connected to a plurality of power transmission electrodes 31 in the middle of the metal sheet 1. The power transmission electrodes 31 are electrically insulated from each other by being arranged, for example, as metal blocks at predetermined intervals. In this way, an electrically single rectangular area is formed from the two trapezoidal surface areas 3 between the electrodes 12, 19.

The power transmission electrodes 31 may be separated from each other with a width of 20 mm and a distance of 5 mm, for example. In order to ensure uniform spacing of the power transmission electrodes, they can be fixed, for example, on a separating plate and pressed onto the metal sheet 1 as a single power transmission electrode array. For industrial use, for example, all the electrodes can be incorporated in a hydraulic press and fixed to a large bottom plate.

In many cases, metal sheets, such as the metal sheet 1 shown in Figure 1, are not cured by heat treatment in all areas, for example in certain areas in order to obtain the desired deformation properties in the event of a car accident. The present invention is also suitable for this. FIG. 4 shows a further conduction heating device 10 which is configured so as not to heat each surface region 4 of the metal sheet 1. For this reason, the electrodes 14 or 17 are not directly connected to the respective power supply 22 or 25, but via the parallel conductors 26, 27 guided in the current direction in each metal sheet. Due to the parallel conductors 26, 27, a parallel flow of the current lines towards the power transmission electrode 31 can still be ensured in the adjacent surface region 3, and this parallel flow is possible only with the parallel electrodes 26, 27. The parallel electrodes 26, 27 are also coolable, the advantage being that the metal sheet 1 is also cooled so that undesired heat transfer from the heated surface area of the metal sheet to the unheated surface area 4 is avoided. That's what it means.

In an advantageous embodiment, some or all of the remaining electrodes 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 are cooled. The power transmission electrode 31 can also be configured as a cooling electrode. FIG. 5 shows an example of the cooling electrode formed by the parallel conductors 27. In the vertical direction, holes 28 are formed which pass through the respective electrodes and form cooling water channels. A cooling liquid such as cooling water can be guided through this cooling water passage. If the electrodes are configured as parallel conductors 26, 27, they are configured to be insulated on the outer surface, ie they do not make electrical contact with the metal sheet 1. The remaining electrodes 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 31 obviously need to be in electrical contact with the metal sheet 1. FIG. 5 is an example of an upper and lower pair arrangement of the metal sheet 1 by the two parallel conductors 27. The parallel conductor 27 arranged below the metal sheet 1 is supported by the counter bearing 32 that opposes the pressing force F acting on the parallel conductor 27 arranged above the metal sheet 1.

FIG. 6 shows a further embodiment of the conduction heating device 10 corresponding to the device 10 of FIG. 4 except for the differences described below. As shown in FIG. 6, the non-heated surface region of the metal sheet 1 is slightly enlarged as compared with FIG. 4 and includes the edge region of the surface region 3 adjacent to the surface region 4 in addition to the surface region 4. Therefore, the parallel conductors 26, 27 and the power transmission electrode 31 in the conduction heating device are not configured as linear electrodes, but are inclined according to the desired surface area to be heated, so that their configuration is adapted. . Accordingly, the power supply electrode 12 and the current extraction electrode 19 are slightly shorter than in FIG.

The metal sheet 1 may be arranged differently from FIGS. 2 to 6, for example, as shown in FIG. 7. The rectangular surface regions 2 and 4 are connected to the power supply electrode, the current extraction electrode and the power supply associated therewith as described above. The trapezoidal surface areas 3 in the middle part are adjacent to each other in order to connect the surface areas 3 between the metal sheets 1 while maintaining the same current density and thereby the same heating characteristics, as compared with the above-mentioned embodiment. The difference is that instead of the power transmission electrodes arranged in (1), the power transmission electrodes 31 that intersect as shown in the drawing are arranged to form a spider-like structure. Here, the power transmission electrodes 31 continue to be electrically insulated from each other, for example because the electrodes are configured as cables which rub against each other or are electrically insulated at different heights. In this way, a uniform resistance situation can be achieved similar to a rectangular metal sheet.

The advantage of this embodiment is that it omits two power supplies. This is because the blank rectangular surface areas 2, 4 can be connected to the power supply as a series circuit. In this way, the surface area 2 is connected in series with the power supply 22. The electrodes 14, 16 may be connected to each other or integrated into one electrode. The surface region 4 is connected to the power supply 22 in series. The electrodes 15, 17 may be connected to each other or integrated into one electrode.

As described above, it is advantageous to connect the pair of the power feeding electrode and the current extracting electrode to the power source at both ends which are diagonally opposed to each other. Further, as shown in the drawing, in order to position the power supply part and the current extraction part as far as possible, it is further preferable to arrange the connection part of the connection line of the power source as far as possible on one side (left / right) electrode of the metal sheet. It is advantageous.

FIG. 8 shows an advantageous embodiment of an electrode 80 which can be used as a power supply electrode, a current extraction electrode, and / or a power transmission electrode. The electrode 80 has holes 28 that form cooling water channels. The upper portion of the electrode 80 including the contact region 83 with the metal sheet in the electrode 80 shown in FIG. 8 is uneven and is formed in a specific structure. The uneven and structured contact area 83 thus formed comprises a plurality of ridges, on top of which the respective contact surface 81 for the actual electrical contact with the metal sheet 1 is formed, i.e. each contact surface. Between the electrode 81 and the metal sheet 1, a plurality of single spaced contact sites are formed with the electrode 80. Formed between each ridge, or its contact surface 81, are a plurality of interstices 82, which may in particular have a groove shape.

In the illustrated embodiment, a comb-like structure is formed in which grooves 82 are formed between the ridges of the contact surface 81. These uneven surfaces in contact with the metal sheet to be heated make it possible to avoid intentionally interspersed hot spots (i.e. areas where the metal sheet is very heated). The generation of a large number of small interspersed contact surfaces over the surface of a heated metal sheet or a part of that surface surprisingly results in no damage to the contact surfaces or the generation of scattered hot spots. Can be heated uniformly. In this way, the detrimental effects of conventional electrodes, which cause some undesirable hot spots, are offset. Therefore, particularly uniform heating of the metal sheet is promoted. This is advantageous for performing a controlled and highly reproducible curing process on the metal sheet.

This also enlarges the usable area of the metal sheet, especially since the area of the metal sheet below the electrodes can likewise be heat treated in the desired manner. According to the results of the experiments carried out, by using the electrode according to the present invention, for example, as the above-mentioned comb electrode, the thermal gradient between the hot spot line and the cooling region generated is very steep, so that This results in complete heat injection. Therefore, exactly one heat treatment is performed on the hot spot line. Accordingly, the cutting rate is reduced because it is no longer necessary to cut the previously unusable transition region from the part.

Due to the disadvantage of uncontrolled heating of the metal sheet in the area of hotspots, hotspots have traditionally been considered disadvantageous and efforts have been made to avoid them. Also, if the temperature coefficient of the metal sheet is positive, the heating will increase the specific electrical resistance at such portions of the metal sheet, thus heating the hot spot area relatively quickly and damaging the metal sheet in the maximum temperature area ( Melting) can occur, so a phenomenon like an electronic avalanche occurred.

Therefore, according to the present specification, unexpected or scattered hot spots are avoided. Instead, a large number of small adjacent contact sites are formed, which is advantageous for a controlled and reproducible heat treatment, i.e. a hardening treatment of metal sheets. The effect can be further enhanced by cooling the electrode. The large number of small contact sites allows for the linear generation of "mini hot spots" that offset the cooling provided by the cooling effect of the electrodes.

The contact area 83 of the electrode is an area that is directly electrically contacted with the metal sheet. The uneven and structured contact areas in the electrodes can be realized, for example, by means of a plurality of horned (eg rectangular) electrode edges, as in FIG. The uneven and structured contact areas can be formed by point ridges on the surface instead of the linear pattern shown. The surface structure of the contact area can be regular or irregular.
Below, the matters described in the claims at the beginning of the application will be added as they are.
[1] A conductive heating method for a metal sheet (1), wherein the metal sheet (1) or at least one conductively heated region of the metal sheet (1) has a rectangular or non-rectangular contour. To carry out the conduction heating, at least one electrode (80) having a contact area (83) is brought into electrical contact with the metal sheet (1), and a current for carrying out the conduction heating is applied to the contact area (83). ) Via and / or withdrawing from said metal sheet (1) via said), said electrode (80) being uneven and structured comprising a plurality of spaced contact surfaces (81). Different contact areas (83), and the plurality of contact surfaces (81) form a plurality of spaced contact sites between the electrode (80) and the metal sheet (1). ,Method.
[2] The method according to [1], characterized in that the electrode (80) is used as a power supply electrode, a current extraction electrode and / or a power transmission electrode together with a textured and structured contact area (83).
[3] The method according to [1] or [2], characterized in that a plurality of small hot spots are generated in the metal sheet (1) by the plurality of contact portions during conductive heating.
[4] The non-rectangular contour of the conductively heated region is divided into a substantially rectangular surface region and / or a trapezoidal surface region (2, 3, 4), and the surface region (2, 3, 4). ), There is provided an adapted electrode arrangement comprising at least a feed electrode, a current extraction electrode (11-20) and a power transmission electrode (31) if there is at least one trapezoidal surface area. The method according to any one of [1] to [3], wherein the method is performed.
[5] A plurality of the metal sheets (1) each include at least one trapezoidal surface region (3) in a region to be conductively heated, and the plurality of metal sheets (1) are conductively heated to form a pair of the metal sheets (1). , Electrically connected to each other by a plurality of power transmission electrodes (31) electrically insulated from each other and arranged adjacent to each other along the transition region between the metal sheets (1), The method according to any one of [1] to [4].
[6] An electrode (80) for conductively heating a metal sheet (1), comprising a contact surface for making electrical contact with the metal sheet (1), and having a plurality of spaced contact surfaces (81) asperities and structuring. A plurality of spaced contact areas (83), wherein the plurality of spaced contact surfaces (81) form a plurality of spaced contact sites between the electrode (80) and the metal sheet (1). And the electrode.
[7] The uneven and structured contact areas (83) of the electrode (80) are arranged in a row or in rows in a comb shape and next to each other, with a plurality of cornered edges to complete or partial The electrode according to [6], characterized in that
[8] The uneven and structured contact area (83) of the electrode (80) comprises ridges with the contact surface (81), with groove-shaped gaps (82) formed between the ridges. The electrode according to [6] or [7], which is characterized in that
[9] A conduction heating device (10) for carrying out the conduction heating method for a metal sheet (1), wherein at least one electrode (80) according to [6] to [8] is a power supply electrode, a current extraction electrode, And / or as a power transmission electrode.
[10] The conduction heating according to [9], wherein the conduction heating device (10) is configured to perform the method according to any one of [1] to [5]. apparatus.

Claims (8)

A method of conductively heating a metal sheet (1) in order to prepare the metal sheet (1) for a subsequent molding, pressure and hardening treatment, comprising :
Said metal sheet (1) to be conductively heated or at least one region of said metal sheet (1) has a rectangular or non-rectangular contour,
Conductive heating is performed by at least one electrode (80) having a contact area (83), said contact area (83) being in electrical contact with said metal sheet (1), said contact area (83) being said supplying a current for executing the conduction heating to the metal sheet (1), and / or in the methods used to draw current from the metal sheet (1),
The at least one electrode (80) has the uneven structured contact area (83) having a plurality of spaced apart contact surfaces (81), the plurality of contact surfaces (81) allowing the at least one A method, characterized in that a plurality of spaced apart individual contact sites are formed between an electrode (80) and the metal sheet (1). The at least one electrode (80) having the textured structured contact area (83) is used as a feed electrode, a current extraction electrode and / or a power transmission electrode. The method described. During conduction heating, a plurality of small hot spot in the metal sheet (1) is equal to or generated by the plurality of contact sites, the method according to claim 1 or 2. Non-rectangular outline of the area to be conductively heated, substantially rectangular, and / or trapezoidal divided into a plurality of surface regions (2,3,4), a plurality of surface regions (2, 3, 4 ) in accordance to be divided, possess at least the feeding electrode (11 to 15) and a current extraction electrode (16-20), the transmission electrode (31) when there is at least one trapezoidal surface area, the 4. Method according to any one of claims 1 to 3, characterized in that an electrode array is provided which is compatible with a plurality of surface areas . A plurality of said metal sheets (1) each comprising at least one trapezoidal surface area (3) in a conductively heated area, said metal sheets (1) being conductively heated in pairs; The pair of 1) are power transmission electrodes (31) electrically insulated from each other, and the plurality of power transmission electrodes (31) are arranged next to each other along the transition region between the metal sheets (1). 5. The method according to any one of claims 1 to 4, characterized in that they are electrically connected to each other by means of. A conduction heating device (10) for carrying out a method of conduction heating a metal sheet (1), comprising:
  The conduction heating device (10) has at least one electrode (80) as a power supply electrode, a current extraction electrode, and / or a power transmission electrode, and the at least one electrode (80) is structured in an uneven shape. A contact area (83), the contact area (83) having a plurality of spaced contact surfaces (81), the contact surface (81) including the at least one electrode (80) and the metal sheet. Characterized in that it is capable of forming a plurality of individual contact portions separated from each other between (1),
  A conduction heating device (10), wherein the conduction heating device (10) is configured to perform the method according to any one of claims 1-5. A plurality of angled edges in which the structured contact areas (83) of the at least one electrode (80) are arranged in a row or in adjacent rows in a comb-like manner one behind the other. by completely or characterized in that it is partially formed, conductive heating apparatus according to claim 6 (10). The uneven and structured contact area (83) of the at least one electrode (80) comprises a plurality of ridges with the contact surface (81), and a groove-shaped gap (82) between the plurality of ridges. Conductive heating device (10) according to claim 6 or 7, characterized in that

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