Heating device for the thermal treatment of a rod-shaped workpiece

Abstract

The invention relates to a heating device (1) for the thermal treatment of a rod-shaped workpiece (51), comprising a heating element (2) which has a first electrically conductive contact section (31), a second electrically conductive contact section (32) and a heating section (11) made of a strip-shaped metal material extending between the first contact section (31) and the second contact section (32), wherein the heating section (11) almost completely encloses a cylindrical, in particular circular cylindrical or prismatic, volume (14) extending along an axis of extension (12), wherein the heating section (11) is provided with at least one recess (15) which increases the length of an electrical path (36) between the first contact section (31) and the second contact section (32).

Description

[0001] The invention relates to a heating device for the thermal treatment of a rod-shaped workpiece.

[0002] The object of the invention is to provide a heating device which enables an improved thermal treatment of rod-shaped workpieces.

[0003] This object is achieved for a heating device of the type mentioned above in that the heating device comprises a heating element with a first electrically conductive contact section, with a second electrically conductive contact section, and with a heating section made of a strip-shaped metal material extending between the first contact section and the second contact section. The heating section almost completely defines a spatial volume extending along an axis of extension, preferably cylindrical, in particular circular-cylindrical or prismatic. The heating section is provided with at least one recess which reduces an electrically effective cross-section of the heating section in certain regions and thus increases the electrical resistance of the heating section.

[0004] The strip-shaped metal material is a metal sheet that has a longitudinal extension and a width extension that is considerably greater, in particular at least a factor of 10, than the thickness of the metal sheet. A longitudinal extension of the heating section, determined along the extension axis of the spatial volume enclosed by the heating section, is preferably in a range from 20 mm to 500 mm. A width extension of the heating section, determined transversely to the extension axis of the spatial volume, is preferably in a range from 20 mm to 1000 mm, which, for a purely exemplary circular-cylindrical spatial volume, results in a profile diameter of approximately 6 mm to approximately 320 mm. The thickness of the heating section is preferably in a range from 0.1 mm to 1 mm.

[0005] The heating section of the heating device represents an electrical resistance heating element through which an electrical current flows when an electrical voltage is applied between the first contact section and the second contact section. The current strength of this current flow depends on the applied electrical voltage and on an electrical resistance determined by the properties of the first contact section, the heating section, and the second heating section. The first contact section, the heating section, and the second contact section form an electrical series circuit. The electrical resistance of the heating section is greater than the electrical resistance of the first and second contact sections, so that the heating section experiences greater heating when an electrical voltage is applied compared to the first and second contact sections.

[0006] In order to achieve these electrical properties for the heating section in conjunction with advantageous mechanical properties of the heating section, the heating section, which is made from a strip-shaped metal material, is provided with at least one recess. The effect of the at least one recess is that an electrically effective cross-section of the heating section is reduced in some areas, thereby increasing the electrical resistance of the heating section. This is due to the fact that the at least one recess, which penetrates the heating section in the manner of a bore, a slot, or a notch, creates a local cross-sectional constriction for the current flow, since the current must flow through the remaining cross-section of the heating section.

[0007] Furthermore, it is provided that the heating section is shaped such that it almost completely defines a preferably cylindrical, in particular circular-cylindrical or prismatic, spatial volume extending along an axis of extension. Alternatively, the spatial volume can have a conical shape. The spatial volume serves to partially or completely accommodate the rod-shaped workpiece that is to be thermally treated with the heating device. It is preferably provided that the heating section covers at least 80 percent, preferably at least 90 percent, in particular at least 95 percent, of an outer surface of the workpiece over the length that the heating section has in the direction of the axis of extension.

[0008] For example, the workpiece can be formed by two pipe sections, each of which is introduced into the space defined by the heating section in sections and butt-welded to form a single pipe during the thermal treatment. The space has a cylindrical shape and can be described, in particular, by a profile extruded along an extension axis. This profile can be circular, oval, polygonal, or irregularly ring-shaped.

[0009] To achieve advantageous thermal coupling between the workpiece and the heating section, it is provided that a cross-section of the workpiece in a cross-sectional plane oriented transversely to the extension axis of the spatial volume is geometrically similar, in particular at least nearly geometrically identical, to the profile of the spatial volume. For advantageous handling of the heating device, it is provided that the cross-section of the workpiece is slightly smaller than the profile of the spatial volume in order to enable the workpiece to be inserted into the spatial volume and pushed out of the spatial volume along the extension axis.Alternatively, it is provided that the cross-section of the workpiece is at least almost identical to the profile of the spatial volume, in which case a change in the shape of the heating section is provided for inserting the workpiece into the spatial volume and for removing the workpiece from the spatial volume, for example through an elastic expansion movement for the heating section. It can also be provided that the cross-section or profile of the spatial volume is adjustable, for example to facilitate easy feeding of the workpiece into the spatial volume and subsequently to reduce the cross-section of the spatial volume before the heating process so that a contact force is exerted on the workpiece, which is accompanied by improved thermal coupling between the heating section and the workpiece.After the heating process has been completed, the cross-section of the space volume can be enlarged again to ensure easy removal of the workpiece from the heating section.

[0010] Advantageous further developments of the invention are the subject of the subclaims.

[0011] It is expedient for the first contact section to be band-shaped and / or for the second contact section to be band-shaped. This enables advantageous coupling of the electrical current from the first contact section into the heating section and advantageous coupling of the electrical current from the heating section into the second contact section. In particular, this makes it possible to avoid cross-sectional jumps for the electrically effective cross sections at the transitions between the heating section and the first and second contact sections.

[0012] It is advantageous if the first contact section is angled, in particular bent, towards an adjacent first edge region of the heating section and / or the second contact section is angled, in particular bent, towards an adjacent second edge region of the heating section. This enables an advantageous electrical connection of the first contact section and the second contact section to power cables designed to connect the heating section to a power source. Furthermore, the first contact section and the second contact section can be mechanically connected to one another in a dual function in order to be able to stably define a geometry of the heating section. By way of example, it is provided that the first contact section is angled almost 90 degrees relative to the adjacent first edge region of the heating section.Additionally or alternatively, it is provided that the second contact section is angled almost 90 degrees relative to the adjacent second edge region of the heating section.

[0013] In a further development of the invention, the first contact section is arranged at a distance from and parallel to the second contact section. This promotes an advantageous mechanical connection between the first and second contact sections, provided that the first contact section and the second contact section are opposite each other.

[0014] In a further embodiment of the invention, the heating section has a plurality of recesses, each of which extends, in particular as notches, from an edge region of the heating section. With each additional recess, the cross-section of the heating section through which electrical current can flow is reduced. Preferably, the recesses are arranged such that an effective electrical cross-section along a current path extending between the first contact section and the second contact section along the heating section is substantially constant, in order to ensure the most uniform heating possible for the heating section.If necessary, it may be provided to place one or more recesses in such a way that the current path has local cross-sectional constrictions at which a local temperature increase can be achieved compared to surrounding areas of the heating section, if this is required by the properties of the workpiece.

[0015] Preferably, the first contact section, the second contact section, and the heating section are made in one piece from a metal sheet. This enables the heating element, which is formed by the first contact section, the heating section, and the second contact section, to be manufactured using a cost-effective manufacturing process such as punching, laser cutting, waterjet cutting, or etching. Furthermore, this avoids undesirable electrical contact resistance between the respective contact section and the heating section, which can occur with a multi-part design of the contact sections and the heating section. Preferably, the heating element is made from a stainless steel sheet, which is initially provided with the desired recesses as a flat, strip-shaped metal sheet and is then formed into the desired geometry by plastic deformation in a forming process.

[0016] It is expedient if the first contact section is provided with a coating, in particular with a galvanic coating, which is designed to increase the electrical conductivity of the first contact section and / or if the second contact section is provided with a coating, in particular with a galvanic coating, which is designed to increase the electrical conductivity of the second contact section. In addition to the geometric design of the first contact section and the second contact section, this can influence the electrical properties of the respective contact section. It is preferably provided that the first contact section and / or the second contact section is / are provided in regions or completely with a coating, in particular a coating applied galvanically.For example, in one embodiment of the heating element formed by the first contact section, the heating section, and the second contact section, a local copper, nickel, or gold plating can be provided as a coating made of stainless steel sheet. Optionally, the coating can extend into the heating section in some areas to prevent excessive current flow at the transition between the contact section and the heating section.

[0017] In a further embodiment of the invention, it is provided that the first contact section is arranged on a first longitudinal edge of the heating section and that the second contact section is arranged on a second longitudinal edge of the heating section, wherein the first longitudinal edge and the second longitudinal edge are spaced parallel to one another. The heating section is preferably designed as a rectangle, so that the first longitudinal edge and the second longitudinal edge of the heating section are formed by the respective longest side edges of this rectangle. It is particularly preferably provided that the two longitudinal edges are aligned parallel to the extension axis. By arranging the first contact section on the first longitudinal edge and / or the second contact section on the second longitudinal edge, an advantageous current flow through the heating section is ensured.This applies in particular in the case that the first contact section is arranged at a first end region of the first longitudinal edge and that the second contact section is arranged at a second end region of the second longitudinal edge, wherein the second end region has a maximum distance from the first end region.

[0018] It is advantageous if a third contact section is formed on the first longitudinal edge of the heating section adjacent to the first contact section, wherein a recess extends between the first contact section and the third contact section, and if a fourth contact section is formed on the second longitudinal edge of the heating section adjacent to the second contact section, wherein a recess extends between the second contact section and the fourth contact section. For example, an additional or alternative current feed for the heating section can be made at the third and fourth contact section. For example, it can be provided that, in order to carry out a thermal treatment of a workpiece, the heating section is first completely heated by a current flow between the first contact section and the second contact section.Subsequently, only partial heating of the heating section can be achieved by a current flow between the third contact section and the fourth contact section. Additional contact sections similar to the third and fourth contact sections can also be provided.

[0019] It is preferably provided that a power source is assigned to the heating element, wherein the first contact section is connected to a first terminal of the power source and that the second contact section is connected to a second terminal of the power source, wherein the power source is designed to provide, preferably for a pulsed provision, in particular for a regulated pulsed provision, of electrical energy to the heating section. In this case, the power source forms a component of the heating device and is designed for the continuous or pulsed provision of electrical energy to the heating element. It is preferably provided that the power source is designed for a regulated provision of electrical current to the heating element in order to be able to ensure a predetermined heating of the heating element.Particularly preferably, the power source is designed for a pulsed supply of electrical energy to the heating element, enabling rapid heating of the heating element. After the pulsed supply of electrical energy has ended, the heating element cools rapidly. Both the rapid heating and cooling of the heating element are facilitated by the fact that the heating element has a low thermal mass due to the design of the heating section made of sheet metal.

[0020] In an advantageous development of the invention, it is provided that the first contact section and the second contact section or the third contact section and the fourth contact section are connected to a measuring device which is designed to detect an electrical resistance in an electrical path between the first contact section and the second contact section or between the third contact section and the fourth contact section, wherein the current source is connected to the measuring device and is designed to evaluate signals from the measuring device for a controlled provision of electrical energy to the heating section.

[0021] In a further embodiment of the invention, a direction of greatest extension of the recess forms an angle with the extension axis in a range of 45 degrees to 90 degrees. This combines the desired cross-sectional reduction for the current flow through the heating section with a relatively minimal impairment of the mechanical stability of the heating section. For a recess that extends along a straight line, this straight line forms a parallel line to the extension axis. For a curved recess, the extension axis is defined as the distance between a beginning and an end of the recess.

[0022] It is expedient if an electrically insulating coating is arranged on an inner surface of the heating section. The purpose of this electrically insulating coating is to prevent undesired adhesion of the workpiece to the heating section. Additionally or alternatively, the purpose of the electrically insulating coating can be to prevent undesired dissipation of electrical energy to an electrically conductive workpiece. The coating can in particular be made of a thermally stable plastic material, in particular of PTFE (polytetrafluoroethylene) or PEEK (polyetheretherketone). Furthermore, unlike the heating section, which is provided with at least one recess, the coating can have a closed inner surface so that the at least one recess in the heating section is bridged and the workpiece cannot swell out during the heating process.Preferably, the electrically insulating coating has a thermal conductivity that is higher than the thermal conductivity of the workpiece to be machined.

[0023] In a further development of the invention, it is provided that an electrical insulator is arranged between the first contact section and the second contact section, which electrical insulator mechanically connects the first contact section to the second contact section, wherein a cross-section of the spatial volume delimited by the heating section is determined by a distance between the first contact section and the second contact section. For example, it is provided that the heating section is designed as a cylindrical shell with a longitudinal slot and that the extension axis of the spatial volume corresponds to a cylinder axis of the cylindrical shell. The first longitudinal edge and the second longitudinal edge delimit the longitudinal slot and are provided with the first contact section and the second contact section, respectively. The first contact section and the second contact section are arranged at opposite end regions of the first and second longitudinal edges.Preferably, additional contact sections extend over the entire first longitudinal edge and over the entire second longitudinal edge. Particularly preferably, contact sections formed on the first longitudinal edge are mechanically connected to contact sections arranged opposite each other on the second longitudinal edge to ensure sufficient dimensional stability for the heating section. Electrical insulators, for example made of plastic material, are preferably arranged between the opposing contact sections, which determine the spacing between the contact sections.

[0024] An advantageous embodiment of the invention is illustrated in the drawing. Figure 1 is a strictly schematic, perspective view of a heating device with a heating element and a power source, Figure 2 is a strictly schematic front view of a variant of the heating element according to the Figure 1with adjustable inner diameter, and Figure 3 a strictly schematic representation of a blank for the heating element according to the Figure 1 and 2 as a flat laser cut before plastic deformation.

[0025] One in the Figure 1 The heating device 1, shown purely schematically, comprises a heating element 2 and a power source 3, which is electrically connected to the heating element 2 via electrical connecting lines 4, 5, 6, 7.

[0026] The heating element 2 is designed for thermally treating a schematically illustrated workpiece 51, which, purely by way of example, is circularly cylindrical. Accordingly, the heating element 2 has a heating section 11 made from a metal sheet, in particular a stainless steel sheet. The heating section 11 is designed, purely by way of example, as a cylindrical shell that extends along an extension axis 12 and is provided with a longitudinal slot 13. Furthermore, the heating section 11 has a plurality of recesses 15, which are described in more detail below. Preferably, the heating section 11 is provided on an inner surface 16 with a coating 17, which, with the exception of the longitudinal slot 13, has a closed inner surface 18 and also covers the recesses 15.Preferably, the coating 17 is made of a thermally highly resilient plastic material and is applied to the heating section 11 with a uniform layer thickness, so that the inner surface 18 of the coating 17 is also designed as a cylinder jacket.

[0027] Preferably, the coating 17 is applied in a materially bonded manner to the inner surface 16 of the heating section 11. Thus, the inner surface 18 of the coating 18 of the heating section 11 almost completely defines a circular cylindrical volume 14; only in the region of the longitudinal slot 13 is there no limitation of the volume 14.

[0028] The task of the heating element 2 is to heat the workpiece 51, for example, to bring about a change in a structure or a matrix of the workpiece 51. In order to ensure advantageous thermal coupling between the heating element 2 and the workpiece 51, the spatial volume 14 delimited by the heating section 11 with the coating 17 applied thereto is geometrically similar to the workpiece 51. A difference between the geometry of the workpiece 51 and the spatial volume 14 lies in particular in the dimensions, since an inner diameter 19 of the spatial volume 14 is selected to be slightly larger than an outer diameter 52 of the workpiece 51 in order to ensure advantageous reception of the workpiece 51 in the spatial volume 14.

[0029] Strip-shaped contact sections are attached to a first longitudinal edge 21 of the longitudinal slot 13 and to a second longitudinal edge 22 of the longitudinal slot 13, each separated from the other by the recesses 15. Of particular importance here are the first contact section 31 and the second contact section 32, which are used to supply an electrical current to the heating section 11. Furthermore, the function of a third contact section 33 and a fourth contact section 34 will be discussed in more detail below.

[0030] Purely by way of example, it is provided that all contact sections arranged on the first longitudinal edge 21, to which the contact sections 31 to 34 also belong, are arranged in a first plane 41. Furthermore, it is provided purely by way of example that all contact sections arranged on the second longitudinal edge 22 are arranged in a second plane 42. It is preferably provided that the first plane 41 and the second plane 42 are aligned parallel to one another. By way of example, it is provided that an electrical insulator 61 is arranged between the contact sections arranged on the first longitudinal edge 21 and the contact sections arranged on the second longitudinal edge 22, with which electrical insulator 61 the contact sections are mechanically connected to one another at a defined distance 65. The contact sections 31 to 34 and the further contact sections not designated are each arranged along a bend line which is connected to the first longitudinal edge 21 orthe second longitudinal edge 22, is bent relative to the heating section 11. It is preferably provided that the heating element 2 is manufactured using a bending process with plastic deformation of the heating section 11 and bending of the contact sections.

[0031] As the representation of the Figure 1can be seen, the power source 3 is electrically connected to the contact sections 31 to 34 via the connecting lines 4 to 7. An electrical power supply to the heating element 2 takes place via the two connecting lines 4 and 5. Via the two connecting lines 6 and 7, the power source 3 can, for example, determine an electrical resistance of a section of the heating element 2 in order to calculate a temperature of this section, which in turn can be used as a basis for current regulation for the current provided to the contact sections 31 and 32. The attachment of the connecting lines 4 to 7 to the contact sections 31 to 34 is provided for reasons of clarity of representation. In a practical application of the heating device 1, a combination of the connections between the power source 3 and the heating element 2 is preferable, as shown in the Figure 3 is indicated.

[0032] In the embodiment of the heating element 2 according to the Figure 1 The insulator 61 is firmly bonded to the opposing inner surfaces of the contact sections, whereby the opposing contact elements have a fixed distance from each other. Accordingly, the inner diameter 19 of the space 14 is also fixed.

[0033] The heating element 2 as shown in the Figure 2 differs from heating element 2 according to the Figure 1 merely in that the insulator 61 is made of an electrically insulating and shape-changing, in particular rubber-elastic, material. Furthermore, it is provided that oppositely arranged contact sections, of which Figure 2Due to the sectional view, the contact sections 33 and 35 are visible, can be adjusted in their distance 65 from each other by a screw connection 62, which comprises a screw 63 and a nut 64 screwed onto it. As a result, the inner diameter 19 of the space 14 can be adapted within certain limits to the requirements of the workpiece 51. In particular, an adjustment of the contact pressure exerted by the heating element 2 on the workpiece 51 can be carried out, which also entails an adjustment of the thermal coupling between the heating element 2 and the workpiece 51. Furthermore, from the Figure 2 It can be seen that the recess 15 extends from the contact section 33 to just before the contact section 35.

[0034] In the Figure 3 the heating element 2 is according to the Figure 1as a raw component before carrying out a plastic deformation. By way of example, the heating element 2 has a rectangular shape and is designed as a plane-parallel plate. Purely by way of example, the heating element 2 made from a steel sheet has been structured by laser cutting. In the course of the laser cutting process for producing the heating element 2, the recesses 15, which each extend from one of the two longitudinal edges 66, 67 in the direction of the respective opposite longitudinal edge 66, 67, are produced. Purely by way of example, a longitudinal extent of the respective recess 15 is aligned transversely, i.e. at a 90-degree angle, to the extension axis 12. The recesses 15 form a symbolically Figure 3drawn current path 36 is predetermined, which runs from the first contact section 31 to the second contact section 32 and which is considerably longer than a distance 68 between the first contact section 31 and the second contact section 32. Purely by way of example, the recesses 15 are arranged and dimensioned such that a cross-section of the heating element 2 available for the current flow along the current path 36 is at least largely constant and thus at least substantially the same electrical resistance is present along the current path 36.

[0035] By way of example, it is provided that the contact sections are each provided with a coating 71, starting from the lower or upper longitudinal edge 66, 67 up to just before a lower or upper bending line 69, 70. This coating 71, which serves to increase the electrical conductivity of the contact sections, is in particular a copper layer, gold layer, or nickel layer galvanically applied to both sides of the contact sections. The bending lines 69, 70 are formed after the forming of the raw component according to the Figure 3 to the longitudinal edges 21, 22, as shown in the Figure 1 are shown.

[0036] Furthermore, the contact sections are each provided with a bore 72 to facilitate the screw connection by means of the Figure 2 shown screw connection 62.

Claims

1. Heating device (1) for the thermal treatment of a rod-shaped workpiece (51), comprising a heating element (2) which has a first electrically conductive contact section (31), a second electrically conductive contact section (32) and a heating section (11) made of a strip-shaped metal material extending between the first contact section (31) and the second contact section (32), wherein the heating section (11) almost completely delimits a preferably cylindrical, in particular circular-cylindrical or prismatic, spatial volume (14) extending along an extension axis (12), wherein the heating section (11) is provided with at least one recess (15) which increases a length of an electrical path (36) between the first contact section (31) and the second contact section (32).

2. Heating device (1) according to claim 1, characterized in thatthe first contact section (31) is band-shaped and / or that the second contact section (32) is band-shaped.

3. Heating device (1) according to claim 2, characterized in that the first contact section (31) is angled, in particular bent, towards an adjacent first edge region of the heating section (11) and / or the second contact section (32) is angled, in particular bent, towards an adjacent second edge region of the heating section (11).

4. Heating device (1) according to claim 3, characterized in that the first contact section (31) is spaced apart and arranged parallel to the second contact section (32).

5. Heating device (1) according to claim 1, 2, 3 or 4, characterized in that the heating section (11) has a plurality of recesses (15) which each extend, in particular as notches, from an edge region (66, 67) of the heating section (11).

6. Heating device (1) according to one of the preceding claims, characterized in that the first contact section (31), the second contact section (32) and the heating section (11) are made in one piece from a metal sheet.

7. Heating device (1) according to one of the preceding claims, characterized in that the first contact section (31) is provided with a coating (71), in particular with a galvanic coating, which is designed to increase an electrical conductivity of the first contact section (31) and / or that the second contact section (32) is provided with a coating (71), in particular with a galvanic coating, which is designed to increase an electrical conductivity of the second contact section (32).

8. Heating device (1) according to one of the preceding claims, characterized in thatthe first contact section (31) is arranged on a first longitudinal edge (21) of the heating section (11) and that the second contact section (32) is arranged on a second longitudinal edge (22) of the heating section (11), wherein the first longitudinal edge (21) and the second longitudinal edge (22) are spaced parallel to one another.

9. Heating device (1) according to claim 8, characterized in that a third contact section (33) is formed on the first longitudinal edge (21) of the heating section (11) adjacent to the first contact section (31), a recess (15) extending between the first contact section (31) and the third contact section (33), and a fourth contact section (34) is formed on the second longitudinal edge (22) of the heating section (11) adjacent to the second contact section (32), a recess (15) extending between the second contact section (32) and the fourth contact section (34).

10. Heating device (1) according to one of the preceding claims, characterized in that a power source (3) is assigned to the heating element (11), wherein the first contact section (31) is connected to a first terminal of the power source (3) and that the second contact section (32) is connected to a second terminal of the power source (3), wherein the power source (3) is designed to provide, preferably for a pulse-like provision, in particular for a controlled pulse-like provision, of electrical energy to the heating section (11).

11. Heating device (1) according to claim 10 in conjunction with claim 9, characterized in thatthe third contact section (33) and the fourth contact section (34) are connected to a measuring device which is designed to detect an electrical resistance in an electrical path between the third contact section and the fourth contact section, wherein the current source (3) is connected to the measuring device and is designed to evaluate signals from the measuring device for a controlled provision of electrical energy to the heating section (11).

12. Heating device (1) according to one of the preceding claims, characterized in that a direction of greatest extent of the recess (15) forms an angle with the extension axis (12) in an interval of 45 degrees to 90 degrees.

13. Heating device (1) according to one of the preceding claims, characterized in that an electrically insulating coating (17) is arranged on an inner surface (16) of the heating section (11).

14. Heating device (1) according to one of the preceding claims, characterized in that an electrical insulator (61) is arranged between the first contact section (31) and the second contact section (32), which electrical insulator mechanically connects the first contact section (31) to the second contact section (32), wherein a cross-section of the spatial volume (14) delimited by the heating section is determined by a distance (65) between the first contact section (31) and the second contact section (32).

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