Inductor for surface hardening

Abstract

Inductor (1) for surface hardening of a surface area of ​​a metallic workpiece comprising a conductor loop (2) made of an electrically conductive material (3) which defines an induction surface (4) of the inductor (1) adapted to the surface area to be hardened, and at least one spacer element (5) which projects from the inductor (1) beyond the induction surface (4), characterized in that a recess (6) is provided in the material (3) of the conductor loop (2) in the area of ​​the induction surface (4), into which the spacer element (5) is inserted and the recess (6) is a threaded bore (7) into which the spacer element (5) is screwed, wherein the at least one spacer element (5) has a rotatably mounted rolling element (9, 10) at its projecting end.

Description

State of the art

[0001] The invention relates to an inductor for surface layer hardening according to the preamble of claim 1.

[0002] In inductive surface hardening of metallic workpieces, an inductor with a conductor loop made of electrically conductive material is brought close to the surface to be hardened. The conductor loop, with its workpiece-facing surface, defines an induction area adapted to the surface area to be hardened. Preferably, the induction area of ​​the inductor is selected to be substantially parallel to the surface area to be hardened.

[0003] During surface hardening, a precisely defined target coupling distance between the induction area defined by the conductor loop and the surface area to be hardened should be maintained to ensure uniform hardening. A small distance in the millimeter or submillimeter range is advantageous for achieving the most efficient heating of the surface area by induction. Conversely, an unacceptably small distance, and especially direct contact between the conductor loop and the surface area to be hardened, must be avoided to prevent local overheating and / or material adhesion due to melting.

[0004] It must be taken into account that, especially when the induction current is switched on at the beginning of the hardening process, considerable attractive forces arise between the inductor and the surface area to be hardened, which can pull the inductor towards the surface area being hardened. Furthermore, distortion of the workpiece caused by heating and quenching, which can occur, for example, in the case of a bearing ring in the form of tilting, ring growth, or shrinkage, alters the coupling distance between the inductor and the surface area to be hardened, such as a rolling element raceway on the bearing ring. Such changes cannot always be compensated for with sufficient reliability by a tracking control of the inductor, since the tracking control can only scan the distance at a single point and not across the entire surface of the inductor, and always has a certain time constant in its control.

[0005] To reliably prevent unacceptably small gaps and contact between the conductor loop and the surface area to be hardened, with the associated disadvantages, a planar inductor with a carrier and an induction coil in the form of a conductor loop, which is exposed on a first side of the carrier, is known from DE 10 2013 101 057 A1. Two spacer elements, arranged at a distance from each other and projecting from the carrier beyond the conductor loop on the first side, are inserted into the carrier. The spacer elements are preferably made of ceramic. To prevent subsequent adjustment of the spacer elements, permanent fixing by bonding is provided. To achieve good cooling, the induction coil is hollow inside to allow the passage of a cooling fluid.The induction coil is made from a square tube, which is held by the support. A disadvantage is that the use of spacers necessitates a two-part inductor design consisting of a conductor loop and a support material, because the spacers can only be securely anchored in the support material. Another disadvantage of this known design is the limited adaptability of the conductor loop to curved surfaces requiring hardening, since bent square tubes cannot guarantee consistent radii of curvature—and thus defined coupling distances—under the thermal stresses occurring during operation.

[0006] From DE 35 21 401 A1, an inductor for surface hardening of crankshafts is known, comprising two parallel, upright plates. In a heating position, the inductor is in contact with the crankshaft via insulating spacers. For a replaceable connection between the spacers and the inductor, the spacers are screwed to the plates.

[0007] DE 39 26 571 C1 describes an inductor head for the inductive hardening of cylinder running surfaces of reciprocating engines, featuring an annular inductor loop. The inductor loop is guided concentrically to the cylinder running surface by means of spacers, ideally made of ceramic, that project radially from it and are arranged on its outer circumference. The inductor loop is designed as a waveguide.

[0008] Further inductors are known from DE 10 2019 202 000 A1 and DE 10 2012 206 603 A1.

[0009] EP 0 524 341 B1 describes a multi-coordinate probe head that has a probe ball attached to a stylus. Disclosure of the invention

[0010] The object of the invention is therefore to provide an inductor for surface hardening which reliably maintains a predefinable minimum distance to the surface area to be hardened during surface hardening, even with complex surface geometries.

[0011] This problem is solved by an inductor for surface layer hardening with the features of claim 1.

[0012] This creates an inductor for surface hardening of a surface area of ​​a metallic workpiece, comprising a conductor loop made of an electrically conductive material. The conductor loop defines an induction area of ​​the inductor adapted to the surface area to be hardened. The inductor further comprises at least one spacer element that projects from the inductor beyond the induction area. According to the invention, a recess is provided in the material of the conductor loop into which the spacer element is inserted.

[0013] According to the invention, the spacer element is thus inserted directly into and fixed within the material of the conductor loop. The material of the conductor loop has, at least locally, a thickness sufficient to form a recess for receiving the at least one spacer element. In this way, a separate support material for receiving and anchoring the spacer element to the inductor can be dispensed with. The required material thickness also gives the conductor loop increased inherent stiffness, particularly with respect to thermal deformation. The inductor according to the invention is therefore dimensionally stable and adaptable to the profile of the surface area to be hardened.

[0014] In preferred embodiments, at least two spacer elements are inserted into the material of the conductor loop at intervals from each other. Particularly with larger induction areas, the use of multiple spacer elements ensures a more uniform minimum distance to the workpiece across the entire induction area.

[0015] According to the invention, the recess is a threaded bore into which the spacer element is screwed. The screw connection between the conductor loop and the spacer element facilitates the replacement of defective spacers. In particular, non-destructive removal and reuse of the spacers is also possible. In contrast, adhesive bonding has proven disadvantageous because it requires heating with a flame for replacement or repair in order to then release the spacers from the connection using mechanical pressure. This places thermal and mechanical stress on the inductor, which in turn can lead to a shorter service life. Mechanically removing the spacers can also cause distortion of the conductor loop, which requires time-consuming straightening. Furthermore, gluing in new spacers is time-consuming, as the adhesive typically needs to be cured in an oven.With a screw connection, no thermal or mechanical loosening of an adhesive joint is required, and distortion of the conductor loop no longer occurs when the spacers are unscrewed. Straightening the conductor loop and curing of the adhesive are also unnecessary.

[0016] Furthermore, the screw connection facilitates the adjustment of the spacer's projection relative to the support. With adhesive bonding, the projection can only be adjusted using tools (such as counter plates and clamps). If the desired projection is not achieved during gluing, the spacer must be detached and re-glued. Another disadvantage of adhesive bonding is that the projection can change over extended periods of operation compared to its original setting. In contrast, with a screw connection, the distance can be easily adjusted by simply rotating the spacer within the threaded hole.

[0017] Preferably, the threaded bore is a through bore, and the spacer element is secured in the threaded bore by a screw inserted from the back. The screw prevents the spacer element from rotating unintentionally, thus ensuring that the set distance remains constant. The screw is preferably a setscrew. Alternatively, the spacer element can protrude from the threaded bore at the back, and the locking action is achieved by a lock nut placed on the back of the spacer element.

[0018] Preferably, the conductor loop is manufactured from a solid material by machining a block of material or by additive manufacturing. When the conductor loop is manufactured from a solid material, the inductor exhibits particularly high torsional stiffness and can be optimally adapted to the profile of the surface area to be hardened through machining or additive manufacturing. In this way, inductors with exceptionally high dimensional accuracy and service life are obtained.

[0019] According to the invention, the at least one spacer element has a rotatably mounted rolling element at its projecting end. By providing a rotatably mounted rolling element at the projecting end of the at least one spacer element, the rolling elements come into rolling contact when approaching the surface to be hardened. In this rolling contact, relative movement of the contact surfaces to each other is largely avoided, thus protecting the surface to be hardened and preventing scoring. While contact between the spacer element and the surface area to be hardened is not intended during normal operation, the use of a rolling element ensures that, in the event of an impermissible approach of the inductor to the surface to be hardened, not only is the inductor protected, but the surface to be hardened is also protected, thus reducing scrap.

[0020] In a preferred embodiment, the rolling element is formed by a rotatably mounted solid sphere. The advantage is that a solid sphere can be rotated about any axis of rotation, thus enabling rolling in any direction. For example, the solid sphere can be crimped onto the spacer element at its projecting end for mounting.

[0021] In an alternative embodiment, the rolling element can be disc-shaped. For example, the disc-shaped rolling element can be designed as a roller. Disc-shaped rolling elements are particularly suitable when the geometry of the inductor's conductor loop dictates a predetermined feed direction of the inductor during hardening, which corresponds to the direction of movement of the rolling elements across the surface to be hardened. In this case, it may be sufficient to use a disc-shaped rolling element that is mounted to roll in the feed direction.

[0022] The rolling element can be spring-loaded on the spacer element. This spring preload prevents the rolling element from making hard contact with the surface to be hardened, thus further reducing surface damage. Preferably, the spring preload has an end stop that defines a predefinable minimum distance between the conductor loop and the surface to be hardened.

[0023] Preferably, the rolling element is made of a silicon nitride ceramic. Silicon nitride ceramics are distinguished from conventional oxide ceramics by their particularly high temperature and thermal shock resistance. Especially at the moment of contact with the surface to be hardened, the rolling element is subjected to a significant temperature change, which conventional ceramics can only withstand to a limited extent, resulting in chipping of the ceramic after repeated use. The use of silicon nitride ceramics can extend the maintenance-free operating life of the inductor.

[0024] According to a preferred embodiment, the at least one spacer element has a pin-shaped main part that supports the rolling element. The pin-shaped main part of the spacer element is preferably made of a metallic material. Preferably, the pin-shaped main part has an external thread that engages in an internal thread formed in the recess of the conductor loop. Preferably, the spacer element projects a height of 0.5 mm to 5 mm beyond the induction surface. This defines a minimum distance between the conductor loop and the surface to be hardened, which is advantageous during feed hardening.

[0025] The conductor loop material can be partially surrounded, particularly on the side of the loop facing away from the workpiece, by a flux concentration material, such as a soft iron-plastic compound. Such a flux concentration material serves to direct the magnetic flux generated by the conductor loop onto the surface area to be hardened and to heat it particularly efficiently.

[0026] Further advantageous embodiments can be found in the following description and the dependent claims.

[0027] The invention is explained in more detail below with reference to the exemplary embodiments shown in the accompanying figures. Brief description of the drawings Fig. Figure 1 schematically shows an inductor according to the invention in a first, workpiece-oriented perspective view, Fig. Figure 2 schematically shows the inductor made of Fig. 1 in a second, rear perspective view, Fig. Figure 3 schematically shows a cross-section of the inductor according to Fig. 1 at the height of the spacer elements used, Fig. Figure 4 schematically shows a second embodiment of the inductor according to the invention in a rear view. Fig. Figure 5 schematically shows a spacer element with a spring-loaded, disc-shaped rolling element. Embodiments of the invention

[0028] In the various figures, identical parts are always marked with the same reference symbols and are therefore usually only named or mentioned once.

[0029] In the Fig. 1, Fig. 2 to Fig. Figure 3 shows a first embodiment of the invention. Fig. 1, Fig. 2 to Fig. Figure 3 shows an inductor 1 for surface hardening of a surface area of ​​a metallic workpiece. The inductor 1 comprises a conductor loop 2 made of an electrically conductive material 3, which defines an induction area 4 of the inductor 1 adapted to the surface area to be hardened. The inductor 1 further comprises two spacer elements 5, which project from the inductor 1 beyond the induction area 4. A recess 6 is provided in the material 3 of the conductor loop 2, into which the spacer elements 5 are inserted.

[0030] The inductor 1 has two connection areas 12 and 13 for connection to a high-frequency alternating voltage. Current flows through the inductor 1 via the two vertically depicted legs of the conductor loop 2 and their cross-connection in the upper region. The two legs and the cross-connection of the conductor loop 2 are traversed by a channel 14. The channel 14 extends from one connection area 12 to the other connection area 13. The channel 14 forms a conduit system for a coolant to cool the inductor 1 during operation.

[0031] The conductor loop 2 of inductor 1 is made from a solid material. Manufacturing the conductor loop from a solid material allows it to adapt more effectively to complex surface geometries of the surface sections to be hardened. In particular, internal material stresses during manufacturing can be reduced by eliminating forming process steps.

[0032] As in Fig. As shown in Figure 1, the induction surface 4 can be convexly curved, for example for hardening a ball raceway of a large rolling bearing. For better clarity, in Fig. Figure 1 shows an induction area 4 extrapolated over the edges of the inductor 1. It is understood that the effective induction area 4 of the inductor 1 is defined by the workpiece-facing surface of the conductor loop 2.

[0033] Preferably, the conductor loop 2 can be manufactured from a solid material by machining a block of material or by additive manufacturing. When manufacturing the inductor by machining, the channel 14 can, for example, be introduced into the block of material by drilling and / or milling. The shaping and surface finishing are preferably carried out by turning, milling, and / or grinding. In additive manufacturing, the channel 14 and the recesses 6 are preferably created in a single 3D printing process.

[0034] The recess 6 is designed as a threaded bore 7 into which the spacer element 5 is screwed. As shown in particular in Fig. As can be seen in Figure 3, the threaded bore 7 can be a through bore in which the spacer element 5 is secured by means of a screw 8 inserted from the rear. In the illustrated embodiment, the screw 8 is a setscrew.

[0035] The locking mechanism secures the set distance against unintentional adjustments. Preferably, the spacer element 5 is inserted into a through-hole in the conductor loop 2 and locked in place from a side of the conductor loop 2 facing away from the surface area to be hardened. This significantly reduces the exposure of the locking mechanism to temperature fluctuations, thus preventing unintentional loosening. However, it is also possible to insert the spacer element 5 into a blind hole and / or to secure it to the workpiece.

[0036] The at least one spacer element 5 has a rotatably mounted rolling element 9 at its projecting end (see Fig. 3) The spacer element 5 comprises a pin-shaped main part 11 that supports the rolling element 9. An external thread may be provided on the main part 11, which engages in the threaded bore 7 of the recess 6. As in Fig. 1 and Fig. As can be seen in Figure 3, the rolling element 9 can be formed by a rotatably mounted solid sphere.

[0037] Preferably, the rolling element 9, 10 is made of a silicon nitride ceramic. However, rolling elements 9, 10 made of another ceramic material or of non-magnetic stainless steel are also conceivable.

[0038] The spacer element 5 preferably projects a height H in the range of 0.5 mm to 5 mm above the induction surface 4. During hardening, a target coupling distance is established between the inductor 1 and the surface area to be hardened, which is greater than the height H. However, if process deviations cause the target coupling distance between the inductor 1 and the surface area to be hardened to fall below the target distance, the spacer elements 5 make contact with the surface to be hardened at a minimum coupling distance of height H. In this way, damage to the inductor and / or the surface area to be hardened can be prevented. In particular, the use of a rolling element on the spacer element protects the surface to be hardened from scoring in the event of contact.

[0039] In Fig. Figure 4 shows a second embodiment of an inductor according to the invention. In contrast to the first embodiment, the conductor loop in this case forms a flat induction surface. Fig. Figure 4 shows a rectangular conductor loop 2 with two parallel waveguide sections 16, 17 lying in one plane and two hollow, bridge-like connecting sections 18. The induction surface of the depicted inductor 1 lies in the plane of the drawing. Fig. 4 and is formed by the waveguide sections 16, 17. The induction surface can be continued at an angle at the end face via the connecting sections 18, for example for hardening a flange of a rolling bearing raceway.

[0040] For example, the waveguide sections 16, 17 have a material thickness over the majority of their surface that is insufficient to accommodate a recess for receiving a spacer element. To accommodate the spacers 5, the material thickness of the conductor loop 2 can be increased at the positions of the spacers 5 such that recesses 6 for the spacers 5 can be formed in the material 3 of the conductor loop 2. The number and position of the spacers 5 can be selected depending on the surface geometry of the area to be hardened and / or the size and inherent stiffness of the conductor loop 2.

[0041] Furthermore, the above statements regarding the first embodiment apply accordingly.

[0042] In Fig. 5 is a spacer element 5 with a disc-shaped rolling element 10 shown. The spacer element 5 from Fig. 5 can be used as an alternative to the one in Fig.The spacer element 5 shown in Figure 3, with a solid sphere as a rolling element 9, is inserted into the inductor 1 according to the first or second embodiment. When installed in the inductor, the disc-shaped rolling element 10 is preferably oriented such that the axis of rotation of the disc-shaped element 10 is arranged transversely to a relative feed direction between the workpiece and the inductor 1.

[0043] The spacer element 5 has a pin-shaped main part 11, on which an external thread may be arranged. The pin-shaped main part 11 holds a plunger 19, on which the disc-shaped rolling element 10 is rotatably mounted. The plunger 19 can be slidably mounted in the main part 11, with the plunger 19 being pre-tensioned in a protruding position by a spring element 20. The spring-loaded, slidable mounting of the rolling element 10 further reduces damage to the surface area to be hardened when the rolling element 10 is placed on the surface.

[0044] However, alternative designs of the spacer elements are also conceivable, in which, for example, a solid ball is spring-loaded on a plunger and arranged to be displaceable relative to the main part, or a disc-shaped rolling element is fixed directly to the main part. Reference symbol list 1 inductor 2 conductor loops 3 conductive material 4 induction surfaces 5 spacer elements 6 Exclusion 7 threaded holes 8 screws 9, 10 Rolling element 11 pin-shaped main part 12, 13 Connection area 14-channel 16, 17 Waveguide section 18 Connecting section 19 pestles 20 spring element H height

Claims

Inductor (1) for surface hardening of a surface area of ​​a metallic workpiece comprising a conductor loop (2) made of an electrically conductive material (3) which defines an induction surface (4) of the inductor (1) adapted to the surface area to be hardened, and at least one spacer element (5) which projects from the inductor (1) beyond the induction surface (4), characterized in that a recess (6) is provided in the material (3) of the conductor loop (2) in the area of ​​the induction surface (4), into which the spacer element (5) is inserted and the recess (6) is a threaded bore (7) into which the spacer element (5) is screwed, wherein the at least one spacer element (5) has a rotatably mounted rolling element (9, 10) at its projecting end. Inductor (1) according to claim 1, characterized in that the threaded bore (7) is a through bore and the spacer element (5) is secured in the threaded bore (7) by means of a screw (8) inserted from the rear. Inductor (1) according to claim 1 or 2, characterized in that the conductor loop (2) is made from a solid material by machining a block of material or by additive manufacturing. Inductor (1) according to one of claims 1 to 3, characterized in that the spacer element (5) has a pin-shaped main part (11) supporting the rolling element (9, 10). Inductor (1) according to one of claims 1 to 4, characterized in that the rolling element (9) is formed by a rotatably mounted solid sphere. Inductor (1) according to one of claims 1 to 5, characterized in that the rolling element (10) is designed in a disc shape. Inductor (1) according to one of claims 4 to 6, characterized in that the rolling element (9, 10) is made of a silicon nitride ceramic. Inductor (1) according to one of claims 1 to 7, characterized in that the spacer element (5) projects above the induction surface (4) by a height (H) in the range of 0.5 mm to 5 mm.

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