Band spring

Abstract

A strip spring (20) comprising a metal strip (10) made of high-carbon steel, which forms a plurality of windings (12, 14, 16) wound in a helical, spiral, or roll-shaped manner in a common plane (18), wherein the windings (12, 14, 16) are held in a tensioned state, in particular at least during transport of the strip spring (20) to an assembly site, characterized in that, in order to maintain the tensioned state, an outermost winding (12) of the plurality of windings (12, 14, 16) is welded to a second outermost winding (14) of the plurality of windings (12, 14, 16) lying radially further inward, wherein welding points (22, 24) of the welding are point-shaped, linear, circular, or annular, and wherein the welding point (22, 24) or the welding points (22, 24) are arranged at a distance from axial edges (26) of the metal strip (10).

Description

State of the art

[0001] The invention relates to a band spring according to the preamble of claim 1.

[0002] Band springs with a metal band made of high-carbon steel, forming a plurality of turns wound helically, spirally, or coil-like in a common plane, are already known. The turns are held in a tensioned state during transport of the band spring to an installation site. These designs utilize, among other things, holding platforms, housings, or retaining bands surrounding the outer circumference of the band spring. All these designs generate waste and unnecessary material consumption.

[0003] The object of the invention is, in particular, to provide a generic device with advantageous properties with regard to transport securing. This object is achieved according to the invention by the features of claim 1, while advantageous embodiments and further developments of the invention can be found in the dependent claims. Advantages of the invention

[0004] The invention relates to a band spring with a metal band made of high-carbon steel, which forms a plurality of turns that are wound helically, spirally or coil-like in a common plane, wherein the turns are held in a tensioned state, in particular at least during transport of the band spring to an assembly location.

[0005] It is proposed that, to maintain the tensioned state, an outermost turn, in particular the radially outermost turn, of the majority of turns is welded to a radially inner second outermost turn of the majority of turns, wherein the weld points are spot-shaped, linear, circular, or annular, and wherein the weld point(s) are spaced apart from the axial edges of the metal strip. This advantageously creates an independent transport securing mechanism for the strip spring. Advantageously, the need for additional retaining elements such as retaining straps, mounting platforms, or housings is eliminated, thereby reducing material usage and / or avoiding the generation of packaging and / or assembly waste.The spot, line, or circular welds ensure reliable fixation of the strip spring in its tensioned state during transport, without impairing its function or integrity. Since the welds are positioned at a distance from the axial edges of the metal strip, this also prevents the strip from being weakened or deformed at the edges, which could, for example, compromise a flat surface on one axial side during assembly. At the same time, the welds can be easily broken during assembly, either manually or by an assembly robot. This results in a material-saving, process-reliable, and user-friendly solution that simplifies assembly and ensures the functionality of the strip spring.

[0006] A band spring is preferably a spring component consisting of an elongated metal band formed by spirally or coil-like winding of the metal band in a common plane. In particular, the band spring differs from a three-dimensionally helically wound coil spring. The coils are preferably each formed by a complete wrapping of the metal band around a central axis. In particular, all coils are arranged in the common plane.

[0007] In particular, one of the two flat sides of the wound metal strip is directed radially towards the central axis. The strip spring is held under tension in the tensioned state. In particular, the coils of the strip spring are prevented from unwinding independently in the tensioned state. The strip spring comprises more than three, preferably more than five, and preferably more than seven (nested) coils. The weld is, in particular, a metallurgical bond between the outermost coil and the radially inner second outermost coil. Preferably, the welds are applied from a radial outside of the outermost coil in a direction that is at least substantially perpendicular to the central axis. The welds are, in particular, spot welds, line welds, and / or circular welds.Polygonal welds are also conceivable. The weld is, in particular, a spot weld and / or a weld forming a circular joint. "Spot-shaped" is understood to mean, in particular, locally limited to a small area, whereby spatially limited, two-dimensionally extended welds can preferably also be understood as spot-shaped. The welds are preferably positioned such that a distance remains between the area of ​​the metal strip that is at least temporarily plasticized during welding and each axial edge of the metal strip. The welds are arranged entirely on the flat surface area of ​​the metal strip. High-carbon steel is generally difficult to weld, especially using many conventional welding methods such as arc welding or electrode welding.This is mainly due to the high hardenability of high-carbon steel (a high carbon content can lead to the formation of an undesirable martensitic structure in the heat-affected zone during rapid cooling) and a tendency to crack formation in a heat-affected zone during and after welding.

[0008] Furthermore, it is proposed that the weld points be friction stir weld spots, friction stir weld circles, or friction stir weld rings. This allows for a particularly high-quality and / or material-friendly connection of the coils. Friction stir welding advantageously creates the joint below the melting point of the material, so that neither molten metal nor spatter is produced. This results in high weld strength and simultaneously minimal thermal influence on the surrounding material. This allows the spring characteristics and / or elasticity of the high-carbon steel of the metal strip to be preserved. In addition, temperature-controlled friction stir welding can be performed. This allows for precise control of the heat input into the high-carbon steel, further minimizing the risk of edge embrittlement or distortion.The locally confined welding zone allows for precise positioning of the weld points at a distance from the axial edges, thus preserving the integrity of the strip edges. At the same time, this advantageously creates a uniform, reproducible joint that ensures secure transport of the strip spring without compromising its ease of assembly, as the weld points can still be designed to be manually broken open. In temperature-controlled friction stir welding, a rotating, non-consuming friction stir welding tool is used, which is positioned at the weld point and immersed into the two superimposed coils under controlled axial force. During the welding process, the temperature at the joint is continuously monitored, for example, using a pyrometer or thermocouples integrated into a shoulder of the friction stir welding tool.The tool speed of the friction stir welding tool and the axial force are preferably controlled as a function of the measured temperature, so that the joint is kept within a predetermined temperature range below the melting point of the high-carbon steel. Additionally, preheating or post-heating of the weld areas can be provided to reduce temperature gradients and prevent the formation of hardenable microstructures. This temperature-controlled process advantageously achieves plastic mixing of the two coils without melting, resulting in a particularly favorable joint structure. This significantly reduces the susceptibility of the high-carbon steel to cracking, and the elastic properties of the strip spring are advantageously largely preserved.

[0009] Furthermore, it is proposed that a sacrificial material be arranged in the area of ​​the friction stir welding points, circles, or rings, preferably between the outermost and second-outermost turns. This sacrificial material fills and / or compensates for material dilutions that can occur in one or both turns during friction stir welding. This advantageously results in a homogeneous, low-stress connection between the turns. It also advantageously maintains the homogeneity of the metal strip's surface. This improves the integrity of the turns, particularly since the strip material of the outermost and second-outermost turns is protected from material weakening. The sacrificial material can be formed monolithically with the metal strip or applied to the metal strip prior to friction stir welding.

[0010] Alternatively, it is proposed that the weld points be laser weld spots, lines, circles, or rings. This allows for a particularly precise and locally confined connection between the outermost and second-outermost coils. Laser welding advantageously enables highly focused energy input with a minimal heat-affected zone, thereby significantly reducing the thermal stress on the high-carbon steel and the risk of edge embrittlement. Furthermore, laser welding allows for the precise positioning of the weld spots at a distance from the axial edges of the metal strip. Due to the low heat input of laser welding, the original spring characteristic is also largely preserved. Additional advantages include the high process speed and the ease with which laser welding can be automated.

[0011] Alternatively, it is also proposed that the weld points be resistance weld spots, circles, or rings, in particular micro-resistance weld spot, circle, or ring welds. This allows for a particularly material-friendly and / or controlled connection between the outermost and second-outermost turns. In resistance welding, heat is generated directly in the contact area of ​​the turns to be joined by electrical resistance, which advantageously allows the heat-affected zone to remain very small. This minimizes the risk of structural changes or edge embrittlement in the high-carbon steel. Due to the low heat input in resistance welding, the weld spots can be advantageously designed to provide reliable transport securing, yet can be easily and manually broken during assembly without damaging or weakening the metal strip.Alternatively, it is also possible to leave some or all welds, especially spot welds, unbroken. This can lead to improved operational performance.

[0012] If the third outermost turn, located radially further inwards, is unaffected by the welding process, it is advantageous to prevent the heat or mechanical stress introduced during welding from spreading to other turns and altering their material properties or geometry. Furthermore, breaking the transport securing device during assembly can be advantageously simplified. All radially innermost turns are preferably also unaffected by the welding process.

[0013] Furthermore, it is proposed that a protective element be inserted between the second-outermost and third-outermost turns, designed to shield the third-outermost turn from welding effects during weld production, or that a spacer-creating shape (or a shape that creates an insulating air gap barrier), e.g., a V-shape, be incorporated into the second turn, e.g., stamped into it. This advantageously allows the third-outermost turn to be reliably and easily shielded from thermal and mechanical influences during weld production. In particular, the protective element or the spacer-creating shape creates an insulating gap between the second and third turns, specifically preventing welding heat generated on a radial inner surface of the second-outermost turn from being transferred to the third-outermost turn.The protective element can, for example, be designed as a thin intermediate layer made of a temperature-resistant and electrically non-conductive material, such as ceramic or mica. Alternatively, the protective element can be a thin metallic sheet with low thermal conductivity, a coating of heat-resistant lacquer, or a film made of a high-temperature-resistant polymer, such as polyimide.

[0014] It is further proposed that at least two of the weld points be arranged at locations on the outermost coil that are spaced apart by at least 45°, preferably at least 90°, and preferably at least 180°, relative to a rotational direction around a central axis of the spring band. This advantageously achieves a particularly stable and reliable transport securing mechanism for the spring band. These evenly distributed weld points fix the outermost coil at several widely separated locations, effectively preventing twisting or partial lifting of the outermost coil relative to the second outermost coil. Furthermore, this allows the individual weld points to be less thick, thus advantageously simplifying break-up during assembly. Two or more than two weld points can also be arranged radially adjacent to each other.It is conceivable that the weld points are distributed over the entire circumference of the outermost coil.

[0015] Furthermore, it is proposed that at least one of the weld points be located in the immediate vicinity of a spring end of the metal strip and / or a functional element formed by the spring end of the metal strip, such as an end hook, an end tab, or another mounting element (e.g., a mounting hole). This creates a particularly easy-to-assemble, material-saving, and / or mechanically stable fastening system. Advantageously, the spring end is securely fixed during transport. The immediate vicinity of the spring end is defined in particular by all points in space, preferably on a surface of the metal strip, preferably the outermost coil of the spring strip, which are no more than eight, preferably no more than five, and preferably no more than three times the width of the metal strip from the spring end.

[0016] If the high-carbon steel has a carbon content between 0.60% and 1.00%, preferably around 0.80%, a particularly high elasticity and restoring force of the band spring can be advantageously achieved. The increased carbon content leads to greater strength and improved fatigue strength of the spring material, ensuring that the band spring reliably retains its shape even under repeated stress and that its function is guaranteed in the long term. At the same time, this material enables a particularly compact and / or lightweight design of the band spring.

[0017] Furthermore, if the weld points of the welding form a transport lock for the band spring, and can be broken manually, e.g. during assembly of the band spring, a particularly simple, and especially tool-free, assembly can be advantageously enabled.

[0018] If the weld points of the weld can be broken open manually without creating weak points such as holes, significant thinning or deformation of the metal strip or significant material embrittlement, it is advantageous to avoid impairing the mechanical integrity or service life of the strip spring through the transport securing device.

[0019] Furthermore, it is proposed that the metal strip have a thickness, particularly a constant thickness, of at least 80 µm, preferably at least 120 µm, and preferably at least 150 µm, and / or at most 250 µm, preferably at most 200 µm, and preferably at most 150 µm. This advantageously enables a reliable weld formation, especially since sufficient material is available to create a reliable, metallurgical bond between the outermost and the second outermost coil, e.g., by friction stir welding, without weakening the metal strip or causing perforations. Strip springs with corresponding thicknesses are used in a variety of technical applications.Band springs of this type are used, for example, in precision mechanics and the watchmaking industry, where they serve as energy storage devices in watch movements and precision mechanical instruments. Their high elasticity and minimal material fatigue give them a particularly long service life. Furthermore, such band springs are used in medical technology, for instance, in spring systems for surgical instruments. Band springs of this size are also used in electromechanical assemblies such as relays, switches, and micromechanisms in electronic devices.

[0020] Furthermore, it is proposed that a radial inner surface of the second outermost coil in the area of ​​the weld(s) be at least undeformed, i.e., preferably homogeneously formed with a surrounding surface of the metal strip. This advantageously ensures reliable function of the strip spring. In particular, the corresponding surface can be achieved by the proposed gentle welding processes for high-carbon steels, such as friction stir welding.

[0021] If the number of spot, line, circular, or ring-shaped welds is at least three, preferably at least five, and preferably at least ten, a particularly stable and reliable transport securing mechanism for the band spring can be advantageously achieved. Furthermore, this allows the individual welds to be less thick, thus simplifying break-up during assembly.

[0022] The band spring can, in particular, form a coil spring, a drive spring, a leaf spring or any other known type of leaf spring.

[0023] The band spring according to the invention is not intended to be limited to the application and embodiment described above. In particular, the band spring according to the invention may, to achieve a functionality described herein, have a different number of individual elements, components and units than the number mentioned herein. Drawings

[0024] Further advantages will become apparent from the following description of the drawings. The drawings illustrate an embodiment of the invention. The drawings, the description, and the claims contain numerous features in combination. A person skilled in the art will expediently consider the features individually and combine them into meaningful further combinations.

[0025] They show: Fig. 1a a schematic perspective representation of a band spring designed as a driving spring, Fig. 1b a schematic perspective representation of a band spring designed as a coil spring, Fig. 1c a schematic axial view of a section of one of the band springs, Fig. 2a a schematic radial view of a section of a metal strip of one of the strip springs with a spot weld, Fig. 2b a schematic radial view of a section of the metal strip of one of the band springs with a circular weld point, Fig. 2c a schematic radial view of a section of the metal strip of one of the band springs with an annular weld point, Fig. 2d a schematic radial view of a section of the metal strip of one of the band springs with a linear weld point, Fig. 2e a schematic view from a radial direction of a section of the metal strip of one of the strip springs with two spot welds, Fig. 3 a schematic sectional view through a part of all the coils of one of the band springs, Fig. 4a another schematic sectional view through a part of all the coils of one of the band springs and Fig. 4b an alternative further schematic sectional view through a part of all the coils of the band spring. Description of the exemplary implementations

[0026] The Fig. 1a and Fig. Figure 1b shows schematically exemplary band springs 20 in perspective views. The band spring 20 of the Fig. Figure 1a forms an example of a drive spring. The band spring 20 of the Fig. Figure 1b shows an exemplary coil spring. The two band springs 20 are each shown in a tensioned state. The two band springs 20 are each held in the tensioned state by a provision according to the invention. The band springs 20 each comprise a metal strip 10. The band springs 20 are each wound / bent from the metal strip 10. The metal strip 10 is made of a high-carbon steel. The high-carbon steel has a carbon content between 0.60% and 1.00%. In the exemplary case shown, the carbon content of the high-carbon steel of the metal strip 10 is approximately 0.80%. The metal strip 10 has a constant thickness 38 (strip thickness) between 80 µm and 250 µm. In the illustrated case, the thickness 38 is approximately 100 µm. The metal band 10 comprises a plurality of turns 12, 14, 16.The metal band 10 comprises at least one outermost turn 12, a second outermost turn 14, a third outermost turn 16, and further radially inward-lying turns. The . Fig. Figure 1c schematically shows a part of one of the band springs 20 in a side view and is intended to illustrate the coils 12, 14, 16. The coils 12, 14, 16 are in a common plane 18 (see also Fig. 2a) wound helically or spirally (drive spring) or coil-like (coil spring). The turns 12, 14, 16 are held in the tensioned state. The tensioned state is a transport state in which the band spring 20 is held during transport to an assembly location. The band springs 20 each have an outer spring end 36. At the outer spring end 36, the metal band 10 forms a functional element. In the illustrated case, the functional element is an end hook ( Fig. 1a) and an end flap ( Fig. 1b).

[0027] The outermost coil 12 and the radially innermost coil 14, located below the outermost coil 12, are welded together. The weld serves to maintain the tensioned state of the strip spring 20, particularly during transport. The two outermost coils 12, 14 are welded at weld points 22, 24. The weld points 22, 24 form a transport securing device for the strip spring 20. The weld points are spot welds. The weld points 22, 24 of the metal strip 10 are all spaced apart from axial edges 26 of the metal strip 10. The weld points 22, 24 of the metal strip 10 are approximately centered in the middle of the metal strip 10. There are more than three weld points 22, 24. In the example shown, there are more than ten weld points 22, 24. More or less than ten welding points 22, 24 are also conceivable.At least two of the weld points 22, 24 are arranged at locations on the outermost coil 12 that are spaced apart from each other by at least 45°, relative to a direction of rotation around a central axis 34 of the band spring 20. One of the weld points 22, 24 is located in the vicinity of the spring end 36 of the metal band 10. This weld point 22 is located in the vicinity of the functional element formed by the spring end 36 of the metal band 10.

[0028] The weld points 22, 24 of the weld can be manually broken open during assembly of the strip spring 20. The weld points 22, 24 can be manually broken open in such a way that no weak points, such as holes, significant thinning or deformation of the metal strip 20, or significant material embrittlement occur. The third outermost coil 16 is unaffected by the weld. The third outermost coil 16 is not welded to any of the other coils 12, 14 of the strip spring 20 at any point. A radial inner surface 40 of the second outermost coil 14 is at least undeformed in the area of ​​the weld points 22, 24, i.e., homogeneously formed with a surrounding surface of the metal strip 10. The radial inner surface 40 of the second outermost coil 14 may be discolored in the area of ​​the weld points 22, 24, e.g., by a tempering color being visible on its surface.However, it is also conceivable that the radial inner surface 40 of the second outermost winding 14 in the area of ​​the weld points 22, 24 remains uncolored, i.e., is homogeneously colored with a surrounding surface of the metal strip 10.

[0029] The Fig. 2a, Fig. 2b, Fig. 2c, Fig. 2d and Fig. Figures 2e each show exemplary radial views of sections of the metal strip 10, each with one or more of the weld points 22, 24. Weld point 22 of the Fig. 2a is an example of a spot weld. The weld point 22 is produced by friction stir spot welding. The spot weld point 22 is a friction stir weld point. Alternatively, the spot weld point 22 could also be a laser weld point (i.e., produced by laser welding). Alternatively, the spot weld point 22 could also be a resistance weld point (i.e., produced by resistance welding). The weld point 22 of the Fig. 2b is an example of a circular weld. The circular weld 22 is a friction stir weld. Alternatively, the circular weld 22 could also be a laser weld or a resistance weld. The weld 22 of the Fig. 2c is an example of a ring-shaped weld. The ring-shaped weld 22 is a friction stir weld. Alternatively, the ring-shaped weld 22 could also be a laser weld or a resistance weld. The weld 22 of the Fig. The 2D example is linear. Alternative orientations, lengths, and / or thicknesses of the line shape are of course conceivable. In the Fig. 2e two weld points 22, 24 are arranged next to each other at the same radial point of the metal strip 10.

[0030] The Fig. Figure 3 shows a sectional view through a portion of the coils 12, 14, 16 of the strip spring 20. The view shows the strip spring before the outermost coil 12 is welded to the second outermost coil 14. A sacrificial material 28 is arranged between the outermost coil 12 and the second outermost coil 14. In this example, the sacrificial material 28 is an integral part of the second outermost coil 14. Alternatively, the sacrificial material 28 could also be formed by the outermost coil 12 or be formed separately from the metal strip 10 (e.g., glued to the metal strip 10). The sacrificial material 28 is located in a region of the metal strip 10 where the friction stir weld points, circles, or rings are generated during welding.The sacrificial material 28 is intended to fill and / or compensate for material dilutions that may occur during friction stir welding of the two coils 12, 14 together in one of the coils 12, 14 or in both coils 12, 14.

[0031] The Fig. 4a and Fig. Figure 4b shows sectional views through a portion of the coils 12, 14, 16 of the band spring 20 with provisions designed to prevent the third outermost coil 16 from being affected by the welding processes. Fig. 4a A protective element 30 is located between the second outermost turn 14 and the third outermost turn 16. The protective element 30 is made of a material with poor thermal conductivity. The protective element 30 is designed to shield the third outermost turn 16 from the welding effect, in particular from the heat generated during welding, when the weld points 22, 24 are formed. Fig.4b A space-creating shape 32 (here, for example, a V-shape) is introduced into the second turn 14, e.g., stamped in. The resulting distance between a surface of the second outermost turn 14 and an opposing surface of the third outermost turn 16 in the area of ​​the weld points 22, 24 prevents or hinders the conduction of the heat generated during welding to the third outermost turn 16. Reference sign 10 metal band 12 turns 14 turns 16 turns Level 18 20 band springs 22 welding point 24 welding points 26 Axial margin 28 Victim material 30 protective elements 32 Space-creating shape 34 Central axis 36 Spring end 38 Thickness 40 Radial inside

Claims

[1] Band spring (20), comprising a metal band (10) made of high-carbon steel, which forms a plurality of turns (12, 14, 16) which are wound helically, spirally or coil-like in a common plane (18), wherein the turns (12, 14, 16) are held in a tensioned state, in particular at least during transport of the band spring (20) to an assembly location, characterized by , that to maintain the tensioned state, an outermost turn (12) of the plurality of turns (12, 14, 16) is welded to a radially more inward second outermost turn (14) of the plurality of turns (12, 14, 16), wherein the weld points (22, 24) of the weld are spot-shaped, linear, circular or ring-shaped, and wherein the weld point (22, 24) or the weld points (22, 24) are spaced apart from axial edges (26) of the metal strip (10). [2] Band spring (20) according to claim 1, characterized by, that the weld points (22, 24) are laser weld points, lines, circles or rings. [3] Band spring (20) according to claim 1, characterized by , that the weld points (22, 24) are friction stir weld points, circles or rings. [4] Band spring (20) according to claim 3, characterized by , that in an area of ​​the friction stir welding points, circles or rings a sacrificial material (28) is arranged, preferably between the outermost turn (12) and the second outermost turn (14), which fills and / or compensates for material dilutions that may occur in one of the turns (12, 14) or in both turns (12, 14) during friction stir welding of the two turns (12, 14) together. [5] Band spring (20) according to claim 1, characterized by , that the weld points (22, 24) are resistance weld points, circles or rings, in particular micro resistance weld points, circles or rings. [6] Band spring (20) according to one of the preceding claims, characterized by , that a radially more inward third outermost turn (16) of the majority of turns (12, 14, 16) is unaffected by the welding. [7] Band spring (20) according to claim 6, characterized by , that a protective element (30) is inserted between the second outermost turn (14) and the third outermost turn (16), which is intended to shield the third outermost turn (16) from welding effects when the weld points (22, 24) are produced, or that a space-creating shape (32), e.g. a V-shape, is introduced into the second turn (14), e.g. stamped. [8] Band spring (20) according to one of the preceding claims, characterized by, that at least two of the weld points (22, 24) are arranged at points on the outermost coil (12) that are spaced apart by at least 45°, preferably at least 90° and preferably at least 180°, with respect to a direction of rotation around a central axis (34) of the band spring (20). [9] Band spring (20) according to one of the preceding claims, characterized by , that at least one of the weld points (22, 24) is located in the vicinity of a spring end (36) of the metal strip (10) and / or a functional element formed by the spring end (36) of the metal strip (10), such as an end hook, an end tab or another mounting element. [10] Band spring (20) according to any one of the preceding claims, characterized by that the high-carbon steel has a carbon content between 0.60% and 1.00%, preferably 0.80%. [11] Band spring (20) according to one of the preceding claims, characterized by, that the weld points (22, 24) of the weld form a transport lock for the band spring (20), and can be broken manually, e.g. during assembly of the band spring (20). [12] Band spring (20) according to claim 11, characterized by , that the weld points (22, 24) of the weld can be broken open manually without creating weak points, such as holes, significant thinning or deformation of the metal strip (10) or significant material embrittlement. [13] Band spring (20) according to one of the preceding claims, characterized by , that the metal strip (10) has a thickness (38) of at least 80 µm, preferably of at least 120 µm and preferably of at least 150 µm, which is in particular constant. [14] Band spring (20) according to one of the preceding claims, characterized by, that the metal strip (10) has a thickness (38) of at most 250 µm, preferably of at most 200 µm and preferably of at most 150 µm, which is in particular constant. [15] Band spring (20) according to any of the preceding claims, characterized by , that a radial inner surface (40) of the second outermost winding (14) in the area of ​​the weld point (22, 24) or weld points (22, 24) is undeformed, i.e. preferably homogeneously formed with a surrounding surface of the metal strip (10). [16] Band spring (20) according to one of the preceding claims, characterized by , that the number of point-shaped, circular or ring-shaped weld points (22, 24) is at least three, preferably at least five and preferably at least ten.

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