DEVICE FOR CURRENT TRANSMISSION IN A HEATING PROCESS

Abstract

 A device (1) for transmission of electric current in a continuous Joule effect heating process to a steel strip, wire, pressed or drawn wire (2), comprising at least a support structure (12) for the continuous Joule effect heating process of a steel strip, wire, pressed or drawn wire (2), and a plurality of electrodes (3) having their entire body made of graphite and being mounted inside said support structure (12) on a contact element (11), said electrodes (3) being in physical and electrical contact with said steel strip, wire, pressed or drawn wire (2), and being arranged in a row of lower electrodes (3) and a row of upper electrodes (3), in respect of said steel strip, wire, pressed or drawn wire (2), and said rows are staggered and capable of achieving a serpentine passage of said steel strip, wire, pressed or drawn wire (2) between said electrodes (3).

Description

FIELD OF THE INVENTION

[0001] The present invention relates to a device for transmission of electric current in a continuous Joule effect heating process to a steel strip, wire, pressed or drawn wire, according to claim 1.

[0002] More particularly, the device comprises innovative electrodes for transmission of electric current to a steel strip, wire, pressed or drawn wire in a continuous heating process. Devices of this kind are disclosed in patent documents FR 608538 A and CN 201713552 U.

BACKGROUND OF THE INVENTION

[0003] In the field of thermal treatments for steel components, in this case strips, wires, pressed or drawn wires, various technologies are known, allowing to carry out processes such as hardening, tempering, annealing and others; all these treatments provide for a heating stage, up to a desired temperature, followed by a cooling stage, so as to modify the mechanical properties, the crystal structure of the grains and also the distribution of the chemical species inside the steel element.

[0004] This field includes also facilities for continuous treatment of steel strip, wire, pressed or drawn wire, with the steps of unwinding, heat treating and rewinding their coils at a predetermined speed.

[0005] In the heating stage, energy is being supplied substantially in the form of heat to steel to be treated; such a heating stage may be implemented with various technologies, such as by convection, conduction and radiation, where the material is introduced in a chamber heated by burners or electric resistors.

[0006] Indirect heating by convection, conduction and radiation provides for taking to the required temperature the entire insulated structure, thus including supports, walls and others, to warrant a uniform heat distribution in the element to be processed, and consequently a uniform thermal treatment.

[0007] The Joule effect heating, also known as "resistance heating", provides for the passage of an electric current inside the element to be processed through the thermal treatment (direct heating).

[0008] The Joule effect heating technologies, involving an induction heating, are not considered in this disclosure, because these are not suitable for treating the materials considered adapted to be treated with the device of the present invention, in view of the difficulty of making a winding suitable to be produce a sufficient heating homogeneity and efficiency for all sizes of the specific elements to be treated.

[0009] Each abovementioned solution has some recognized drawbacks. For instance, in the indirect heating plants, use of burners or electric resistors produces a relatively low efficiency, in view of the poor directivity of the energy/heat flow, that cannot be sent selectively only to the element to be treated, and is then diffused to the entire oven environment. The costs related to this technology therefore are high, since they comprise high costs of insulation and low efficiency of use of the energy resources.

[0010] Another problem of indirect heating consists of the high dead time, due to the need of cooling the whole environment, before allowing to make any change in the device using said technology. The direct heating increases efficiency and reduces the heating and cooling dead times.

[0011] In the field of Joule effect direct heating, in the specific continuous heating treatment of steel strip, wires, pressed or drawn wires, the state of the art comprises electrodes in the form of contact rollers made of the same materials of the elements to be treated, said electrodes having a support structure which must also allow the rotation of the rollers and the passage of electric current to the element, so as to heat the element through the Joule effect. In this case, the amount of current (Ampere) to be transmitted by rollers in contact with a steel strip, flows through a very limited section, causing several troubles. Indeed, the contact between roller and material must have such a pressure to warrant the most possible electric continuity, in order to ensure a good passage of current. If these conditions are not met, concentric sparks and discharges occur, irreparably spoiling the surface of both the roller and the material. Said contact pressure causes also deformations of material, such as the lamination effect, more particularly where the increasing temperature of the material substantially reduces the mechanical properties.

[0012] Moreover, in this configuration, it is necessary to electrify and drive current in several complex moving components, such as bearings, supports and rollers, with the consequence that these components must be made of materials capable to withstand this kind of stress.

SUMMARY OF THE INVENTION

[0013] In this situation, the technical object of the present invention is to devise a device for current transmission in a continuous Joule effect heating process, to a steel strip, wire, pressed or drawn wire, suitable to substantially remove at least part of the abovementioned drawbacks.

[0014] An object of the present invention is to make a device, limiting the unwanted effects of metal components used as electrodes in continuous Joule effect thermal treatments with direct heating, such as sparks, indentations, abrasions, deformations of material and others.

[0015] A further object of the device is to provide for a high directivity and selectivity of energy supplied for obtaining heating, thus a device with high energetic efficiency.

[0016] The specified technical problem and objects are met by a device for current transmission in a Joule effect continuous heating process, to a steel strip, wire, pressed or drawn wire, wherein at least an electrode of non-ferrous material is provided at a contact station.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The characteristics and advantages of the present invention are hereinafter clarified by the detailed description of its preferred embodiments, making reference to the annexed drawings, in which:

Fig. 1 is a section plane of a contact station, showing the electrodes in one of the arrangements, according to an embodiment of the invention;

Fig. 2 is a side view of the internal arrangement of a contact station, showing the electrodes in another embodiment of the invention; and

Fig. 3 is a section plane of a contact station for a continuous thermal treatment by means of Joule effect direct heating, showing prior art electrodes (metal rollers).

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] With reference now to Figures 1 and 2, two embodiments of a device 1 are illustrated, for the transmission of current in a Joule effect continuous heating process for a steel strip, wire, pressed and/or drawn wire, generally indicated by reference numeral 2.

[0019] Said device 1 is a part of a heating line for continuous thermal treatment of steel strip, wire, pressed and/or drawn wire 2, wherein said line comprises at least a heating stage.

[0020] A heating stage of a heating line for thermal treatments may include a number of devices 1, crossed by said strip, wire, pressed and/or drawn wire 2, wherein the temperature increases in the advancement direction.

[0021] The steel strip, wire, pressed and/or drawn wire 2 is moved by motion means arranged outside the heating line. Between inlet and outlet, the steel strip, wire, pressed and/or drawn wire 2 define a longitudinal direction 1a. Moreover, the plane defines a vertical direction 1b perpendicular to the longitudinal direction, but not necessarily parallel to the gravitational gradient, and a transversal direction 1c, perpendicular to both the longitudinal 1a and vertical 1b directions.

[0022] The treatment is considered to be continuous when used in this connection, because the thermal treatment is effected on a portion of steel strip2, which is unwound from a coil, processed in said line of thermal treatment, that goes on processing said steel strip 2 without any stop, i.e. continuously. Preferably, said device 1 comprises at least one contact element 11 for the continuous thermal treatment by Joule effect of strip, wire, pressed and/or drawn wire 2.

[0023] Said device 1, as shown in figures 1 and 2, is arranged in a closed outer support structure 12, provided with an inlet 11a and an outlet 11b, allowing the continuous passage through the device 1 of the material 2 to be treated. The group of features shown in figures 1 and 2 will be indicated as the contact station. This contact station is also provided with at least an electric supply.

[0024] Preferably said contact station, in the embodiment shown in figures 1 and 2, further comprises means 13 allowing the physical and electrical contact of said steel strip, wire, pressed or drawn wire 2, during passage of said steel strip, wire, pressed or drawn wire 2 in the contact station for the thermal treatment.

[0025] Said means 13 may have any form, may comprise different structural components or elements, and consist of any material or combinations of materials, said elements being capable of allowing the physical and electrical contact of said steel strip, wire, pressed or drawn wire 2, during passage of said steel strip, wire, pressed and/or drawn wire 2 in the contact station for the thermal treatment.

[0026] Additionally, preferably in one of the preferred embodiments of the invention, the position of said means 13 may be modified, to warrant the best possible position and pressure for the contact.

[0027] Still preferably, said device 1 comprises at least an electrode 3, connected with said means 13, and arranged inside said support structure 12, wherein said at least one electrode 3 in in physical and electric contact with said steel strip, wire, pressed or drawn wire 2.

[0028] Said connection is a physical and electric contact capable of allowing passage of electric current through said steel strip, wire, pressed or drawn wire 2, so as to heat said material 2 to be treated at the desired temperature.

[0029] The electrodes 3 are indeed preferably in direct contact with electrical connections, for instance connected with the electric network or other sources. The total power of the device is preferably comprised in the range between 50 kW and 500 kW, and more preferably between 200 kW and 300 kW.

[0030] The control of the desired temperature for the process is carried out by controlling the quantity of current supplied, that is passed through said steel strip, wire, pressed or drawn wire 2, between two or more contact stations.

[0031] Preferably, the physical and electric contact with said strip, wire, pressed or drawn wire 2, is made of non-ferrous material.

[0032] Still more preferably, at least one side or surface of said at least one electrode 3 in physical and electric contact with said steel strip, wire, pressed or drawn wire 2 is made of graphite.

[0033] Moreover, preferably three electrodes, wherein at least one of said electrodes 3, and preferably all said electrodes, have the abovementioned inventive features.

[0034] The above described embodiments, comprising electrodes 3 provided with at least one side or surface of non-ferrous material, electrodes 3 provided with at least one side or surface of graphite, and electrodes 3 with the entire body made of graphite, may be used alternatively or in various combinations, to obtain the device 1 according to the present invention.

[0035] Preferably, according to the present invention, at the said contact station, the continuous Joule effect heating of said steel strip, wire, pressed or drawn wire 2, is carried out by the passage of current to said material 2 to be treated, wherein the contact between the moving material 2 to be treated and said non-ferrous material is a sliding contact.

[0036] In a preferred embodiment of the invention, said electrode 3 has a prismatic shape, so as to obtain a wide flat contact surface (instead of the limited contact of a roller, as shown in figure 3, illustrating the known prior art).

[0037] It is to be noted that the prismatic shape of electrodes 3 is one of the forms achieving more advantages for the embodiments of the present invention; however, electrodes 3 of any other shape, having a side or surface or element made of graphite or other non-ferrous material, but still capable of achieving said contact, are in any case comprised in the here described inventive concept.

[0038] Preferably, said electrodes 3 have the form of a right parallelepiped with a preferably rectangular and more particularly square base, and a main axis preferably at right angles with said base. Said main axis is preferably parallel to the cross direction 1c. Said base preferably has a side with a length between 1cm and 10 cm, and more preferably between 4 cm and 6 cm. The length of the main axis is preferably between 1 dm and 5 dm, more preferably between 1 dm and 3 dm, still more preferably of 2 dm, and most preferably of 25 cm.

[0039] Preferably, as an alternative to the above described electrode 3, said electrodes 3 may be in any number that should be capable of warranting the physical and electrical contact with said steel strip, wire, pressed or drawn wire 2.

[0040] With reference now to the position of said electrodes 3 inside the contact station, said electrodes 3, in physical and electrical contact with said steel strip, wire, pressed or drawn wire 2, are arranged in any desired position relative to said steel strip, wire, pressed or drawn wire 2.

[0041] For instance, in the embodiment shown in figure1, a plurality of electrodes 3 are arranged paired above and under the steel material to be treated.

[0042] Still more particularly, the lower rows of electrodes 3 or the upper rows of electrodes 3 are mutually staggered in longitudinal direction, so as to produce a serpentine effect between electrode 3 and steel material 2 to be treated (figure 2). The electrodes 3 also have outer sides, facing the wire, preferably not aligned in the vertical direction 1b, preferably the upper electrodes have outer sides arranged under the outer sides of the lower electrodes, for the purpose of forming said serpentine. The mutual offset of said outer sides is preferably comprised between 0.05 and 2 times the height in the vertical direction 1a of the electrodes 3, and more preferably between 1mm and 1 cm.

[0043] More preferably, the closer electrodes have mutual distances along the longitudinal axis 1a, between the closest points of the same electrodes 3, comprised between 0.5 and 3 times the dimensions of said electrodes along the same longitudinal axis, and more particularly between 1 and 2 times the same dimension. More preferably, said distance between the electrodes is comprised between 1 cm and 1 dm, more preferably between 2 cm and 6 cm, and still most preferably between 3 cm and 5 cm.

[0044] The device 1, for the current transmission in a continuous Joule effect heating process of a steel strip, wire, pressed or drawn wire 2 according to the invention, achieves important advantages.

[0045] Indeed, said graphite / steel contact, when compared with the prior art, since graphite has the property of a non-metallic electric conductor, as well as the properties of inorganic solid lubricant, allows an electric contact with a sliding action of good quality, capable of transmitting current while preventing damages to the surface of the material to be treated.

[0046] Still advantageously, in comparison with prior art electrodes / rollers, producing a metal / metal contact in the heating stage, through a Joule effect direct heating, the electrodes made of non-ferrous material produce a contact metal / non-metal, that does not deform the material to be treated, but merely wears partially the electrode 3 or the face / surface of the electrode 3, in view of the physical properties of said non-ferrous material.

[0047] It has to be pointed out that only some preferred embodiments of the invention were herein described and illustrated, but many variations, additions, modifications and/or many combinations of the individual elements may be resorted to, however without departing from the general innovative concept, nor from its scope of protection, as resulting also from the annexed claims.

Claims

1. Device (1) for transmission of electric current in a continuous Joule effect heating process to a steel strip, wire, pressed or drawn wire (2), comprising

- at least a support structure (12) for the continuous Joule effect heating process to a steel strip, wire, pressed or drawn wire (2), and

- a plurality of electrodes (3) having their entire body made of graphite and being mounted inside said support structure (12) on a contact element (11),

- said electrodes (3) being in physical and electrical contact with said steel strip, wire, pressed or drawn wire (2),

- characterized in that said electrodes are arranged in a row of lower electrodes (3) and a row of upper electrodes (3) in respect of said steel strip, wire, pressed or drawn wire (2),

- and that said rows are staggered and capable to achieve a serpentine passage of said steel strip, wire, pressed or drawn wire (2) between said electrodes (3).

2. Device (1) according to claim 1, wherein said electrodes (3) have the form of a right parallelepiped.

3. Device (1) according to claim 2, wherein said electrodes (3) have the form of a right parallelepiped with rectangular base.

4. Device (1) according to claim 3, wherein said electrodes (3) have the form of a right parallelepiped with square base.

5. Device (1) according to any claim 2 to 4, wherein said electrodes (3) have a base with dimensions between 1 cm and 10 cm.

6. Device (1) according to claim 5, wherein said electrodes (3) have a base with dimensions between 4 cm and 6 cm.

7. Device (1) according to any preceding claim, wherein the steel strip, wire, pressed or drawn wire (2), between device inlet and outlet, define a longitudinal direction (1a) and said electrodes (3) have mutual distances, along said longitudinal direction (1a), between the closest points of of said electrodes, comprised between 0.5 and 3 times the dimensions of said electrodes (3) along said longitudinal axis (1a).

8. Device (1) according to claim 7, wherein said electrodes (3) have said mutual distances comprised between1 and 2 times the dimension of said electrodes (3) along said longitudinal axis (1a).

9. Device (1) according to any preceding claim, wherein, between device inlet and outlet, the steel strip, wire, pressed or drawn wire (2), define a longitudinal direction (1a), and said electrodes (3) have mutual distances, along said longitudinal direction (1a), between the closest points of said electrodes, comprised between 1cm and 1 dm.

10. Device (1) according to claim 7, wherein said electrodes (3) have mutual distances comprised between2 cm and 6 cm.

11. Device (1) according to any preceding claim, wherein said electrodes have outer sides, facing said wire, preferably not aligned in the vertical direction (1 b), said upper electrodes preferably having outer sides arranged under said outer sides of said upper electrodes.

Drawing