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(11) | EP 1 341 936 B1 |
| (12) | EUROPEAN PATENT SPECIFICATION |
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A METHOD AND A DEVICE FOR PARTIAL HEATING OF METAL SHEETS EIN VERFAHREN UND EINE VORRICHTUNG ZUM PARTIELLEN ERWÄRMEN VON METALLBLECHEN PROCEDE ET DISPOSITIF DE CHAUFFAGE PARTIEL DE FEUILLES METALLIQUES |
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| Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give notice to the European Patent Office of opposition to the European patent granted. Notice of opposition shall be filed in a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been paid. (Art. 99(1) European Patent Convention). |
[0001] The present invention relates to a method and a device for partial heating of metal sheets for the purpose of establishing zones, or lines, permanently lowering the yield point of the sheets. At those zones or lines there will later on be carried out a plastic deformation subsequently to the sheets having, by hardening or cold-working, been given an increased yield point, generally causing deteriorated ductility.
[0002] One prior art method for partial heating of metal sheets is by means of a gas flame which, however, means bad precision, and low efficiency due to high heat leakage and it is also difficult simultaneously to heat both sides of the metal sheet. Also, it is difficult accurately to control the temperature of the sheet and the heating-process is very fine-consuming. The same problem burdens IR heating. Light arc heating, as in tig welding, does broadly speaking involve the same problems as those mentioned above. Laser heating requires high investments and has low efficiency and it is only possible to heat one side at a time, meaning considerable waste of time. The big problem in connection with resistance heating, involving use of an equipment of the point welding type with electrodes of copper or another metal material, is that the metal sheet can practically not at all be moved once it is in contact with the electrodes and feeding current supplied. Further, the electrodes cool the surface of the sheet, meaning that the highest temperature will be formed at the center of the sheet. Induction heating is inaccurate and, when heating jaws are used, the temperature rise is very slow to which should be added that such device is very inflexible. In JP-A-6172846 or JP-A-10317065 rolls or elongated electrodes made of non metallic materials are used for strip continuous heating.
[0003] The object of the present invention is to provide a method and a device as defined in claims 1 and 6 respectively, for partial heating in the context mentioned above, and to eliminate the disadvantages enumerated here. The features characterizing the invention are set out in the subsequent claims.
[0004] Thanks to the invention there have now become available a method and a device which in an excellent manner satisfies its purpose. In addition thereto the method can be carried out conveniently and the device can be manufactured at low cost. According to the invention use is made of a resistance heating device provided with at least one electrode of carbon, graphite or a non-metallic material having similar properties and exhibiting low friction values when the electrode, or the electrodes when they are two in number, mounted one on each side of the sheet, and are displaced while pressed against it. The use of this method and of this device results in a heating pattern having great advantages in comparison with the previously known methods. When, in the case where two electrodes are used, the current feed is initiated, the electrode points will get very hot, meaning that the sheet is heated from both sides, right out to the outermost portion, i.e. not mainly in the center, and simultaneously a resistance heating is generated due to the current passage. Thanks to the invention a very quick heating occurs and the friction between the metal sheets and the electrodes is very low. Moreover, the extension of the heated zone is precise because it is possible to complete the process very quickly and because it can be directed. There is also a possibility to influence the heating process by variation of the electrode pressure, the feeding speed and the current characteristic resulting in different balances in response to the resistance heating and to the heating emanating the hot electrodes.
[0006] The field of application of the invention is partial heating of metal sheets in order to establish zones which are to be plastically deformed subsequently to the sheets having, by hardening or cold working, been given a higher yield point, and hence generally a lower ductility. Its structure could be such that it comprises two opposite electrodes, facing each other at a variable distance between them determined by the thickness of the metal sheet which is to be used. The electrodes consist of carbon, graphite or of a non-metallic material with similar properties. They have a low friction value when pressed against the metal sheet from opposite sides thereof. The electrodes and the sheet can be moved relatively each other during the heating process. They are mounted in electrically conductive electrode holders which enclose them so that only a very short portion of them projects. The electrode diameter can vary from a few mms and upwards and the electrode pressure does not have to be higher than within the order of magnitude of 1,5 - 15 N/mm2. Also, the electrode diameter could be different for those above and those below the sheet, to create an unsymmetric heating. The current source could be constituted by a simple welding transformer. When two electrodes are used they may be mounted one on each side of the sheet making it possible for the current through the sheet to flow from the one electrode to the other. When feed current is switched on the electrode tips turn very hot, even glowing, and they heat the sheet from both sides. The current passage yields a symmetric heating of the sheet.
[0007] In the case when only one electrode is utilized the heating takes place from the one side of the sheet, where the current flows from that electrode to the sheet, which is connected to ground or in contact with an underlying, grounded metal plate, this results in a more unilateral heating, i.e. a non-symmetrical heating in the thickness direction, than what is the case in the embodiment utilizing two electrodes.
1. A method for partial heating of metal sheets in order to establish areas in form of
zones or lines at least on one side of said metal sheet within which a plastic deformation
shall later take place, said sheets having before that, by hardening or cold-working,
been given an increased yield point, generally causing deteriorated ductility, characterized in that the partial heating is generated by electrical resistance heating with the aid of
at least one electrode, consisting of carbon, graphite or a non-metallic material
having similar properties, said electrode having a low friction coefficient when pressed
against the metal sheet during a simultaneous relative displacement of the electrode
and the metal sheet relatively each other.
2. A method according to claim 1, characterized in that use is made of two electrodes each of which is placed at one side of the metal sheet
to be partially heated, the current then flowing from the one to the other electrode
via the interposed metal sheet.
3. A method according to claim 2, characterised in that, when current is supplied, the metal sheet is heated from both of its sides, and
resistance heating being obtained during the passage of the current.
4. A method according to claim 1, characterized in that, the heating is carried out with one electrode from one side, the current passing
from that electrode to the metal sheet or to an underlying metal plate for ground
connection so as to establish an unilaterial and unsymmetrical heating.
5. A method according to claim 1, characterized in that, the electrode diameter varies from a minimum value of about 1 mm, and in that the electrode pressure comes up to about 1,5 - 15 N/mm2, said electrode diameter at the top and bottom side of the metal sheet is either
the same or different.
6. A device for partial heating of metal sheets in order to establish areas in form of
zones or lines at least on one side of said metal sheet within which a plastic deformation
is subsequently to take place, said sheets having before that, by hardening or cold-working,
assumed a higher yield point, generally causing a deteriorated ductility, characterized in that it comprises at least one electrode which is brought into contact with the metal
sheet to be heated by electrical resistance heating and said electrode consists of
carbon, graphite or a non-metallic material having similar properties, the electrode
having a low friction value and means to contact, at a predeterminal pressure the
metal sheet, the electrode and the metal sheet being at the same time displaced relatively
each other.
7. A device according to claim 6, characterized in that it comprises two opposite electrodes which are positioned at a distance from each
other that can be varied to match the thickness of the metal sheet to be heated and
which have a low friction value when at opposite sides of the metal sheet contacting
the latter, the electrodes and the metal sheet being simultaneously displaced relatively
each other.
8. A device according to claim 6, characterized in that it comprises one electrode, arranged unilaterally and unsymmetrically to heat the
metal sheet, which itself is either at ground potential or connected to an underlying
metal plate.
1. Verfahren zum partiellen Erwärmen von Metallblechen, um Bereiche in der Form von Zonen
oder Linien auf wenigstens einer Seite der Metallbleche einzurichten, innerhalb derer
plastische Verformung später eintritt, wobei die Bleche zuvor durch Härten oder durch
Kaltumformen eine erhöhte Streckgrenze erhalten haben, was normalerweise verschlechterte
Duktilität verursacht, dadurch gekennzeichnet, dass das partielle Erwärmen durch elektrisches Widerstandsheizen mittels wenigstens einer
Elektrode, bestehend aus Kohlenstoff, Graphit oder einem nichtmetallischen Werkstoff
mit ähnlichen Eigenschaften, erzeugt wird, wobei die Elektrode einen niedrigen Reibungskoeffizienten
aufweist, wenn sie bei gleichzeitiger relativer Verschiebung der Elektrode und des
Metallbleches in Bezug zueinander an das Metallblech angedrückt wird.
2. Verfahren nach Anspruch 1, dadurch gekennzeichnet, dass zwei Elektroden verwendet werden, die jeweils auf einer Seite des Metallbleches,
das teilweise zu erwärmen ist, angesetzt werden, wobei der Strom dann von der einen
Elektrode über das dazwischen angeordnete Metallblech zu der anderen Elektrode fließt.
3. Verfahren nach Anspruch 2, dadurch gekennzeichnet, dass wenn Strom angelegt wird, das Metallblech von seinen beiden Seiten aus erwärmt wird
und während des Stromdurchgangs Widerstandserwärmung erzielt wird.
4. Verfahren nach Anspruch 1, dadurch gekennzeichnet, dass das Erwärmen mit einer Elektrode von einer Seite durchgeführt wird, wobei der Strom
von dieser Elektrode zu dem Metallblech oder zu einer untergelegten Metallplatte zum
Anschluss an Erde fließt, um einseitiges und unsymmetrisches Erwärmen einzurichten.
5. Verfahren nach Anspruch 1, dadurch gekennzeichnet, dass der Elektrodendurchmesser von einem Mindestwert von etwa 1 mm abweicht und dass der
Elektrodendruck etwa 1,5 N/mm2 bis 15 N/mm2 beträgt, wobei der Elektrodendurchmesser an der Oberseite und an der Unterseite des
Metallbleches entweder gleich oder unterschiedlich ist.
6. Vorrichtung zum partiellen Erwärmen von Metallblechen, um Bereiche in der Form von
Zonen oder Linien auf wenigstens einer Seite der Metallbleche einzurichten, innerhalb
derer plastische Verformung später eintreten soll, wobei die Bleche zuvor durch Härten
oder durch Kaltumformen eine erhöhte Streckgrenze erhalten haben, was normalerweise
verschlechterte Duktilität verursacht, dadurch gekennzeichnet, dass sie wenigstens eine Elektrode umfasst, die in Kontakt mit dem Metallblech, das durch
elektrisches Widerstandsheizen erwärmt werden soll, gebracht wird, und wobei die Elektrode
aus Kohlenstoff, Graphit oder einem nichtmetallischen Werkstoff mit ähnlichen Eigenschaften
besteht, wobei die Elektrode einen niedrigen Reibungswert aufweist, sowie Mittel,
um mit dem Metallblech bei einem vorbestimmten Druck in Kontakt zu kommen, wobei die
Elektrode und das Metallblech gleichzeitig relativ zueinander verschoben werden.
7. Vorrichtung nach Anspruch 6, dadurch gekennzeichnet, dass sie zwei gegenüberliegende Elektroden umfasst, die in einem Abstand voneinander angeordnet
sind, der verändert werden kann, um mit der Dicke des zu erwärmenden Metallbleches
übereinzustimmen, und die einen niedrigen Reibungswert aufweisen, wenn sie sich auf
gegenüberliegenden Seiten des Metallbleches in Kontakt mit dem letztgenannten befinden,
wobei die Elektroden und das Metallblech gleichzeitig relativ zueinander verschoben
werden.
8. Vorrichtung nach Anspruch 6, dadurch gekennzeichnet, dass sie eine Elektrode umfasst, die einseitig und unsymmetrisch zum Erwårmen des Metallbleches,
das selbst entweder geerdet oder mit einer unterliegenden Metallplatte verbunden ist,
angeordnet ist.
1. Procédé de chauffage partiel de feuillards métalliques afin d'établir des endroits
sous forme de zones ou de lignes au moins sur une face du feuillard métallique dans
lesquels une déformation plastique aura lieu ultérieurement, une augmentation de la
limite d'élasticité, entraînant en général une moins bonne ductilité, ayant été donnée
au feuillard avant cela par trempe ou par travail à froid, caractérisé en ce que l'on produit le chauffage partiel par un chauffage par résistance électrique à l'aide
d'au moins une électrode consistant en carbone, en graphite ou en une matière non
métallique ayant des propriétés analogues, l'électrode ayant un petit coefficient
de frottement, lorsqu'elle est pressée sur le feuillard métallique pendant un déplacement
relatif simultané de l'électrode et du feuillard métallique l'un par rapport à l'autre.
2. Procédé suivant la revendication 1, caractérisé en ce que l'on fait usage de deux électrodes, chacune d'entre elles étant placée d'un côté
du feuillard métallique à chauffer partiellement, le courant passant ensuite d'une
électrode à l'autre par l'intermédiaire du feuillard métallique interposé.
3. Procédé suivant la revendication 2, caractérisé en ce que, lorsque l'on alimente en courant, on chauffe le feuillard métallique par ses deux
faces, et le chauffage par résistance est obtenu pendant le passage du courant.
4. Procédé suivant la revendication 1, caractérisé en ce que l'on effectue le chauffage par une électrode d'un côté, le courant passant de cette
électrode au feuillard métallique ou à une plaque métallique sous-jacente pour connexion
à la terre de manière à établir un chauffage unilatéral et dissymétrique.
5. Procédé suivant la revendication 1, caractérisé en ce que le diamètre de l'électrode varie à partir d'une valeur minimum d'environ 1 mm, et
en ce que la pression de l'électrode est comprise entre environ 1,5 et 15 N/mm2, le diamètre de l'électrode du côté supérieur et du côté inférieur du feuillard métallique
étant le même ou différent.
6. Dispositif de chauffage partiel de feuillards métalliques, afin d'établir des endroits
sous forme de zones ou de lignes sur au moins une face du feuillard métallique dans
lesquelles a lieu ensuite une déformation plastique, une augmentation de la limite
d'élasticité, entraînant en général une moins bonne ductilité, ayant été donnée au
feuillard avant cela par trempe ou par travail à froid, caractérisé en ce qu'il comprend au moins une électrode qui est mise en contact avec le feuillard métallique
à chauffer par chauffage par résistance électrique et l'électrode consiste en carbone,
en graphite ou en une matière non métallique ayant des propriétés analogues, l'électrode
ayant un petit coefficient de frottement et des moyens pour venir en contact à une
pression déterminée à l'avance avec le feuillard métallique, l'électrode et le feuillard
métallique étant déplacés en même temps l'un par rapport à l'autre.
7. Dispositif suivant la revendication 6, caractérisé en ce qu'il comprend deux électrodes opposées qui sont mises en position à une distance l'une
de l'autre qui peut être modifiée pour s'adapter à l'épaisseur du feuillard métallique
à chauffer et qui ont un petit coefficient de frottement lorsque sur des faces opposées
du feuillard métallique elles viennent en contact avec ce dernier, les électrodes
et le feuillard métallique étant déplacés simultanément les uns par rapport aux autres.
8. dispositif suivant la revendication 6, caractérisé en ce qu'il comprend une électrode disposée unilatéralement et dissymétriquement pour chauffer
le feuillard métallique qui lui-même est mis au potentiel de terre ou est relié à
une plaque métallique sous-jacente.