METHOD FOR LASER HARDENING OF A CARD WIRE

Abstract

A method for laser beam hardening of sections to be hardened (A) of a card wire (10) is disclosed. Thereby the card wire (10) is moved in a conveying direction through a working space (26). In the working space (26), an inert gas atmosphere is created by continuously or discontinuously introducing inert gas (G). In the working space (26), a laser beam area (27) is generated through which the sections to be hardened (A) of the card wire (10) are moved. Thereby the sections to be hardened (A) are heated. After exiting out of the laser beam area (27) the sections to be hardened (A) cool and are hardened by progressing through this temperature profile. The hardening in the inert gas atmosphere inside working space (26) avoids formation of oxide layers (scaling) and annealing colors.

Claims

1. A method for laser hardening of a card wire (10) comprising a base section (11) and multiple teeth (12) projecting from the base section, wherein the method comprises the following steps: generating at least one continuous laser beam area (27) inside a working space (26); supplying an inert gas (G) into the working space (26); conveying the card wire (10) in a conveying direction (F) into the working space (26) such that a section to be hardened (A) of each tooth (12) is moved through the at least one continuous laser beam area (27), whereby at least one outer surface (18, 19) of each section to be hardened (A) is moved through the at least one continuous laser beam area (27), such that the section to be hardened (A) is heated; and cooling of the section to be hardened (A).

2. The method according to claim 1, wherein conveying the card wire (10) in the conveying direction comprises moving the card wire (10) non-stop continuously in the conveying direction (F).

3. The method according to claim 2, wherein the card wire (10) is moved with a constant speed in the conveying direction (F).

4. The method according to claim 1, wherein the at least one continuous laser beam area (27) has a non-circular contour having a length (x) in the conveying direction (F) and a width (y) orthogonal to the conveying direction (F) and wherein the width (y) is smaller than the length (x).

5. The method according to claim 1, wherein the at least one continuous laser beam area (27) comprises at least one straight outer edge.

6. The method according to claim 5, wherein the at least one straight outer edge of the at least one continuous laser beam area (27) is oriented parallel to the conveying direction (F).

7. The method according to claim 5, wherein an intensity of laser light in the at least one continuous laser beam area (27) changes abruptly at the at least one straight outer edge of the at least one continuous laser beam area (27).

8. The method according to claim 1, wherein the at least one continuous laser beam area (27) is generated by at least one beam forming optic (31) that forms an incident laser beam (30) into an exiting laser beam (32), whereby the exiting laser beam forms the at least one continuous laser beam area (27).

9. The method according to claim 8, further comprising capturing at least a part of the laser light of the exiting laser beam (32) with a beam dump (38).

10. The method according to claim 9, further comprising cooling the beam dump (38) with a cooling medium (K).

11. The method according to claim 9, wherein the beam dump (38) comprises at least one incident surface (39) for the exiting laser beam (32) arranged inclined relative to a travel direction of the laser light passing through the at least one continuous laser beam area (27).

12. The method according to claim 1, wherein generating at least one continuous laser beam area (27) comprises emitting a laser beam (29) from a laser beam source (28) that comprises a wavelength of 900 nm to 1100 nm.

13. The method according to claim 1, further comprising applying the laser light in the at least one continuous laser beam area (27) on the section to be hardened (A) for an application period of 50 ms and to 70 ms.

14. The method according to claim 1, further comprising annealing the card wire (10) prior to moving the card wire (10) into the at least one laser beam area (27).

15. The method according to claim 1, further comprising cleaning the card wire (10) prior to moving the card wire (10) into the at least one continuous laser beam area (27).

16. The method according to claim 1, further comprising generating a first laser beam area (27a) and a second laser beam area (27b) that is spaced apart from the first laser beam area (27a).

17. The method according to claim 16, further comprising moving a first outer surface (18) of the section to be hardened (A) through the first laser beam area (27a) and a second outer surface (19) opposite to the first outer surface (18) of the section to be hardened (A) through the second laser beam area (27b).

18. The method according to claim 1, further comprising measuring the heating of the section to be hardened (A).

Description

[0035] Advantageous embodiments of the invention are derived from the dependent claims, the description and the drawings. In the following preferred embodiments of the invention are explained in detail with reference to the attached drawings. The drawings show:

[0036] FIG. 1 a schematic perspective illustration in part of an embodiment of a card wire,

[0037] FIG. 2 a part of the card wire of FIG. 1 in a schematic side view,

[0038] FIG. 3 a cross-section orthogonal to the extension direction of the card wire according to the cutting line III-III in FIG. 2,

[0039] FIG. 4 a schematic basic illustration of a progress of a hardness in an already hardened tooth of the card wire according to FIGS. 1-3,

[0040] FIG. 5 a schematic basic illustration of a device and a method for hardening the card wire with view in a conveying direction,

[0041] FIG. 6 a schematic illustration of the device and the method of FIG. 5 in a side view orthogonal to the conveying direction,

[0042] FIG. 7 a basic illustration of an inventive laser beam area having a length in conveying direction and a width orthogonal to the conveying direction,

[0043] FIG. 8 a highly schematic illustration of a modified embodiment of a device and a method for laser hardening of the card wire.

[0044] The invention refers to laser hardening of a card wire 10, as it is schematically illustrated in FIGS. 1-3. The card wire 10 comprises a base section 11 extending in a longitudinal direction L. The base section 11 can have a polygonal, e.g. a rectangular cross-section. In a width direction B multiple teeth 12 project from the base section 11 that are arranged one after the other in longitudinal direction L. Between two directly adjacent teeth 12 in longitudinal direction L one gap 13 is present respectively. Each tooth 12 has a substantially triangular contour with a corner 14 arranged distant to the base section 11 in width direction B. The corner 14 is formed by two edges 15, 16 limiting the contour of the tooth 12. In the embodiment the one, first edge 15 extends substantially in width direction B and the other second edge 16 extends obliquely inclined with regard to width direction B.

[0045] In a depth direction T orientated orthogonal to the width direction B and the longitudinal direction L, the base section 11 has a thickness or strength that is at least in a section larger than the thickness of the teeth 12. Thereby a projection is formed on the base section 11 having a longitudinal surface 17 that is orientated orthogonal to the width direction B in the embodiment. Each tooth 12 has a first outer surface 18 and a second outer surface 19 opposite to the first outer surface 18. The two outer surfaces 18, 19 are arranged with distance to one another in depth direction T according to the thickness of the tooth 12. The two outer surfaces 18, 19 can be arranged parallel to each other. In the embodiment here the second outer surface 19 extends substantially orthogonal to the depth direction T, whereas the first outer surface 18 is orientated inclined obliquely relative to the depth direction T and the second outer surface 19. The first outer surface 18 extends in a first plane E1 and the second outer surface 19 extends in a second plane E2 (FIG. 3).

[0046] A section to be hardened A adjoins the corner 14 in each tooth. In this section each tooth 12 shall be hardened. The section to be hardened A is arranged with distance to the projection of the base section 11 adjoining the longitudinal surface 17. After hardening of the section to be hardened A by means of the inventive laser hardening, a transition zone Z adjoins the section to be hardened A in which the hardness decreases continuously in direction toward the base section 11. In width direction B the transition zone Z has a dimension after laser hardening by means of the inventive method in the range of less than 0.3 mm and preferably less than 0.2 mm.

[0047] For hardening the section to be hardened A energy is introduced into the section to be hardened A and it is heated. The heating of the section to be hardened A is carried out by radiation with laser light of a laser beam. An embodiment of a device and a method for laser hardening is shown in FIGS. 5 and 6 in a respectively blocked diagram-like schematic illustration.

[0048] For the laser hardening a working space 26 is limited in a housing 25. In the working space 26 the card wire 10 is processed and particularly laser-hardened in sections to be hardened A. In the embodiment the card wire 10 is moved in a conveying direction F through the working space 26 by mean of a not illustrated conveying device. The conveying direction F can be orientated horizontally, for example. During conveying of card wire 10 in conveying direction F it is preferably orientated such that the longitudinal direction L of a card wire 10 is orientated in conveying direction. The width direction B of card wire 10 is preferably orientated parallel to a transverse direction Q of the working space 26 that in turn is orientated orthogonal to the conveying direction F. The conveying direction F and the transverse direction Q can span a plane that extends horizontally. The card wire 10 can be moved through the working space in a lying position so-to-speak.

[0049] In the preferred embodiment described here the card wire 10 is moved through the working space 26 non-stop and processed thereby, particularly hardened. Preferably the speed with which the card wire 10 is moved in conveying direction F is constant and is in the embodiment at least 10 m/min or at least 20 m/min, for example 40 m/min to 50 m/min, wherein the speed depends on the dimension of the teeth 12 and is the lower the larger the teeth 12 are.

[0050] In the working space at least one laser beam area 27 and in the embodiment according to FIGS. 5 and 6 exactly one laser beam area 27 is generated. For this the device comprises a laser beam source 28 that emits a laser beam 29. The emitted laser beam 29 can be directly supplied to a beam forming optic 31 as incident laser beam 30 or alternatively indirectly via one or more optical elements. The optical elements can redirect and/or refract and/or diffract and/or reflect the laser beam and supply it then as incident laser beam 30 to the beam forming optic 31.

[0051] The laser light of the laser beam 29 generated by the laser beam source 28 comprises preferably wavelengths of at least 650 nm or at least 800 nm, e.g. in the range of 800 nm to 1400 nm and in the embodiment a wavelength of approximately 1000 nm.

[0052] The beam forming optic 31 is configured to form the incident laser beam 30 and to form an exiting laser beam 32 therefrom having a defined cross-section in a working plane. For this purpose the beam forming optic 31 can comprise one or more optical components, such as a lens, particularly a free-form lens 33.

[0053] In the working plane inside the working space 26 the exiting laser beam 32 forms the laser beam area 27. In the embodiment according to FIGS. 5 and 6 the working plane extends inside the working space 26 in conveying direction F and either in transverse direction Q or inclined to the transverse direction Q such that the first plane E1 of the first outer surface 18 present in the working space is substantially arranged in the working plane. The exiting laser beam 32 has a defined dimension and energy density in its laser beam area 27 arranged in the working plane. As highly schematically illustrated in FIG. 7, the laser beam area 27 has a length x in conveying direction F and a width y orthogonal to the conveying direction F along the working plane or in transverse direction Q. The length x is preferably different from the width y and particularly longer. In the embodiment the length x can be minimum 10 mm to maximum 100 mm, preferably 15 mm to 70 mm and further preferably 25 mm or 30 mm to 40 mm and particularly 32 mm to 35 mm. The width y of the laser beam area 27 can be adapted to the dimension of the sections to be hardened A of teeth 12 and be, for example, in a range of minimum 0.5 mm or 1.0 mm to 2.0 mm or 3.0 mm.

[0054] The at least one laser beam area 27 has a rectangular or otherwise polygonal contour according to the example. At least it comprises a straight outer edge that is orientated parallel to the conveying direction F and that limits the at least one laser beam area 27 toward the base section 11. At each straight outer edge the intensity of the laser light or the energy density of the at least one laser beam area 27 changes abruptly. A slope m describes a gradient of the intensity of the laser light at the outer edge of the laser beam area and can be determined as follows, for example:

[00002]$m=w\frac{0.9.Math.\stackrel{?}{I}-0.1.Math.\stackrel{?}{I}}{x2-x1}$

with m: slope of the intensity change; [0055] ?: average value of the intensity I of the laser beam area; [0056] w: width of the laser beam area orthogonal to the straight outer edge at 50% of the average intensity ?; [0057] x1: half width of the laser beam area orthogonal to the straight outer edge at 10% of the average intensity ?; [0058] x2: half width of the laser beam area orthogonal to the straight outer edge at 90% of the average intensity ?.

[0059] Preferably the slope is larger than 5, particularly larger than 7 and further preferably larger than 8.

[0060] A low reactive or inert gas atmosphere is created in the working space 26 in order to avoid the formation of metal oxide layers (scale) and the creation of annealing colors due to the laser hardening. For this housing 25 can comprise at least one gas connection 37 in order to supply the inert gas G. The inert gas G can flow continuously or discontinuously into working space 26.

[0061] Preferably the inert gas G is introduced into the working space 26 adjacent to the beam forming optic 31 such that it flows obliquely or orthogonal to the traveling direction of the exiting laser beam 32, for example in transverse direction Q and/or in conveying direction F. In the embodiment the inert Gas G is introduced vertically between the working plane or the laser beam area 27 and the beam forming optic 31. The flow of inert gas G can protect the beam forming optic 31 and serve as seal gas for fume and/or vapor so-to-speak that is created during laser hardening and/or other processings in the working space 26. The inert gas G can remove fume and/or vapor from the laser beam area 27. The inert gas G thus serves not only for creation of a low reactive or inert atmosphere in the working space 26 according to the example, but concurrently also for protection of the beam forming optic 31 and/or for maintaining of a uniform energy density in the laser beam area 27 at the surface of the card wire 10 as far as possible.

[0062] Nitrogen, argon or another noble gas or an arbitrary combination thereof can be used as inert gas G.

[0063] For laser hardening the card wire 10 is moved through the working space 26 such that the sections to be hardened A of the individual teeth 12 move subsequently through the laser beam area 27. During this movement the sections to be hardened A are heated in the laser beam area 27 and cool quickly after exiting the laser beam area 27, whereby the hardness increases. The cooling is effected by thermal conduction within the card wire 10 out of the heated sections to be hardened in direction toward the base section 11. An additional cooling can be achieved by heat dissipation in the atmosphere inside working space 26. A gas flow effected by the introduction of the inert gas G inside the working space 26 can contribute to an additional cooling of the heated sections.

[0064] As schematically illustrated in FIG. 7, the laser beam area 27 is positioned such that only the sections to be hardened A of teeth 12 are moved through the laser beam area 27. The other sections of the card wire 10 that shall not be hardened, particularly the base section 11, is moved outside the laser beam area 27 through the working space 26.

[0065] In the embodiment the application period during which the laser light of the exiting laser beam 32 in the laser beam area 27 acts on each point of the section to be hardened A passing therethrough is maximum 150 ms or maximum 100 ms. Preferably the application period can be in a range of 30 ms to 90 ms and further preferably in a range of 50 ms to 70 ms. In an embodiment the application period is approximately 60 ms.

[0066] After hardening of a section to be hardened A of a tooth 12 the tooth 12 comprises a hardness progress, as basically schematically illustrated in FIG. 4. The abscissa of the diagram defines a distance d from the corner 14 of a tooth 12 in width direction B. The ordinate indicates the hardness H depending on the distance d. After hardening the hardness H is highest and substantially constant in each section to be hardened A. In the transition zone Z the hardness decreases. Outside of the hardened section A the hardness H corresponds to the value comprised by the non-hardened material of the card wire 10. The dimension of the transition zone Z in width direction B is small and preferably smaller than 0.2 mm. The non-hardened base section 11 provides sufficient elasticity and deformability and the card wire 10 can also be wound on a roller after hardening without problems without forming cracks or other damages.

[0067] As moreover illustrated in FIGS. 5 and 6, behind the working plane or the plane in which the card wire 10 is moved through the working space 26 a beam dump 38 can be present in travel direction of the exiting laser beam 32. The beam dump 38 is configured to capture the laser light of the exiting laser beam 32 at least partly that does not impinge on the card wire 10, but that passes through the laser beam area 27, in particular through a gap 13 between two teeth 12 (compare also FIG. 7). The beam dump 38 has at least one and according to the example two incident surfaces 39 arranged obliquely relative to the travel direction of the laser light of the exiting laser beam 32. The incident surfaces 39 can be arranged V-shaped, for example. Due to the inclination of the incident surfaces 39 relative to the travel direction of the laser light, the area is enlarged on which the laser light impinges on the at least one incident surface 39 compared with the area of the laser beam area 27. The energy density of the laser light impinging on the at least one incident surface 39 is thus reduced. Therefore, also the absorption per area unit is sufficiently low in the beam dump 38.

[0068] In the embodiment the at least one incident surface 39 is realized by an outer surface of a heat sink 40. The heat sink 40 and thus the at least one incident surface 39 can be cooled by means of a cooling medium K, e.g. air, water or another fluid. For this purpose inside the heat sink 40 at least one cooling channel 41 can be present in the embodiment through which cooling medium K flows. The cooling circuit of cooling medium K is only highly schematically indicated in FIG. 5.

[0069] Based on FIG. 6, additional optional configuration possibilities for carrying out the method or for configuration of the device are illustrated. Additional stations for processing the card wire 10 can be present inside housing 25 that are preferably arranged before the laser beam area 27 in movement direction of the card wire 10. For example, it can be a cleaning station and an annealing station 42. The cleaning station 41 is configured to clean at least the sections to be hardened A of the card wire 10. The annealing station 42 is configured to at least anneal the base section 11 of card wire 10.

[0070] The cleaning station 41 can be configured to output a cleaning substance and to spray it onto the sections to be hardened A of the card wire 10 in order to remove contamination. As an option, card wire 10 can be dried subsequently in the cleaning station 41, e.g. by means of blow drying using a gas.

[0071] The annealing station 42 is configured to anneal the base section 11 of card wire 10 or alternatively the entire card wire 10. For this the annealing station 42 can comprise a heating device 43, a cooling device 44 and as an option a drying device 45. The heating device 43 serves to introduce heat at least in the base section 11 of card wire 10 and to heat it up to a holding temperature. Subsequently, the parts of the card wire 10 heated in this manner are cooled by means of cooling device 44, e.g. by means of spraying a cooling substance thereon, e.g. water. Subsequently, the card wire 10 can be dried by means of the drying device 45, e.g. by blow drying using a gas.

[0072] After cleaning in the cleaning station 41 and/or annealing in the annealing station 42 the sections to be hardened A are hardened in the working space by means of laser hardening. All of these processing steps are carried out inside the working space 26 according to the example.

[0073] FIG. 8 shows a further embodiment for laser hardening of sections to be hardened A of a card wire 10 in a highly simplified schematic basic illustration. In this embodiment two exiting laser beams 32 are generated by means of two separate beam forming optics 31 that generate a laser beam area in each case, according to the example a first laser beam area 27a in a first working plane and a second laser beam area 27b in a second working plane arranged with distance thereto. The two working planes can extend parallel or inclined to one another and are orientated according to the example, such that the first planes E1 of the sections to be hardened A move along the first working plane and the second planes E2 of the sections to be hardened A move along the second working plane. In this arrangement the energy of the laser light can be introduced from two opposite sides into the sections to be hardened A of the card wire 10, namely on the first outer surface 18 by means of the first laser beam area 27a and on the second outer surface 19 by means of the second laser beam area 27b.

[0074] In conveying direction F the laser beam areas 27a, 27b may be arranged offset from one another or can at least partly overlap alternatively.

[0075] As in addition illustrated in FIG. 8, for the two exiting laser beams 32 two separate beam dumps 38 can be provided. The exiting laser beams 32 are not orientated parallel to a common axis, but the traveling directions are orientated under an angle of less than 180? to one another.

[0076] For generation of the two exiting laser beams 32 by means of the two beam forming optics 31 the emitted laser beam 29 of a common laser beam source 28 can be used. As an option, two separate laser beam sources 28 can be used.

[0077] It is possible to monitor the heating of the at least one section to be hardened A that is moved through the assigned laser beam area 27. For example, a pyrometer 46 can be used for this purpose as is schematically shown in FIG. 5. By means of the pyrometer 46 the thermal radiation W that originates from the heated section of the card wire 10 in the at least one section to be hardened A can be determined. Thus, it can be tested by means of the pyrometer 46 whether sufficient energy has been inserted into the at least one section to be hardened A. If applicable, the adjustments of the laser beam source 28 can be modified in order to adapt the energy insertion.

[0078] The invention refers to a method for laser beam hardening of sections to be hardened A of a card wire 10. Thereby the card wire 10 is moved in conveying direction through a working space 26. In the working space 26 an inert gas atmosphere is created by continuously or discontinuously introducing inert gas G. In the working space 26 a laser beam area 27 is generated through which the sections to be hardened A of the card wire 10 are moved. Thereby the sections to be hardened A are heated. After exiting out of the laser beam area 27 the sections to be hardened A cool and are hardened by progressing through this temperature profile. The hardening in the inert gas atmosphere inside working space 26 avoids formation of oxide layers (scaling) and annealing colors.

LIST OF REFERENCE SIGNS

[0079] 10 card wire [0080] 11 base section [0081] 12 tooth [0082] 13 gap [0083] 14 corner [0084] 15 first edge [0085] 16 second edge [0086] 17 longitudinal surface [0087] 18 first outer surface [0088] 19 second outer surface [0089] 25 housing [0090] 26 working space [0091] 27 laser beam area [0092] 27a first laser beam area [0093] 27b second laser beam area [0094] 28 laser beam source [0095] 29 laser beam [0096] 30 incident laser beam [0097] 31 beam forming optic [0098] 32 exiting laser beam [0099] 33 free-form lens [0100] 37 gas connection [0101] 38 beam dump [0102] 39 incident surface [0103] 40 heat sink [0104] 41 cleaning station [0105] 42 annealing station [0106] 43 heating device [0107] 44 cooling device [0108] 45 drying device [0109] 46 pyrometer [0110] A section to be hardened [0111] B width direction [0112] d distance [0113] E1 first plane [0114] E2 second plane [0115] F conveying direction [0116] G inert gas [0117] H hardness [0118] K cooling medium [0119] L length direction [0120] Q transverse direction [0121] T depth direction [0122] W thermal radiation [0123] x length of laser beam area [0124] y width of laser beam area [0125] Z transition zone