Vibration damping spring

Abstract

This vibration damping spring is formed from a wire comprising a copper or copper alloy core wire and a steel cladding layer covering the outer circumferential surface of the core wire. The wire has a diameter of 4 mm or less. The core wire includes a boundary layer which is disposed so as to form the outer circumferential surface of the core wire and which includes a copper or copper alloy matrix phase and a plurality of island regions, which are iron-containing regions, dispersed in the matrix phase. The wire has an area ratio between 20% and 90%, inclusive, in a cross section perpendicular to the longitudinal direction of the wire.

Description

Vibration damping spring

[0001] The present disclosure relates to vibration damping springs.

[0002] Shock absorbers using springs are known. For example, an automobile shock absorber has been proposed in which a shock absorber that contributes to vibration attenuation (vibration control) is disposed between a coil spring and a spring seat (see, for example, Japanese Patent Application Laid-Open No. 2002-178737 (Patent Document 1)). In this shock absorber, vibration control is primarily provided by the shock absorber. Also known is a spring wire that has a copper core wire and a stainless steel coating layer covering the core wire, with the aim of achieving both electrical conductivity and strength (see, for example, Japanese Patent Application Laid-Open No. 59-205105 (Patent Document 2)). In this spring wire, an interdiffusion layer is formed between the core wire and the coating layer, which is said to improve sag resistance and fatigue resistance.

[0003] JP 2002-178737 A JP 59-205105 A

[0004] The vibration damping spring according to the present disclosure is formed from a wire including a copper or copper alloy core wire and a steel coating layer covering the outer surface of the core wire. The wire diameter is 4 mm or less. The core wire includes a boundary layer arranged to form the outer surface of the core wire, the boundary layer having a copper or copper alloy matrix and a plurality of iron-containing island regions dispersed in the matrix. The area ratio of the core wire in a cross section perpendicular to the longitudinal direction of the wire is 20% or more and 90% or less.

[0005] Fig. 1 is a schematic diagram showing the structure of a vibration-damping spring. Fig. 2 is a schematic diagram showing the structure of a wire. Fig. 3 is a schematic cross-sectional view showing the structure of the wire in the vicinity of the boundary layer. Fig. 4 is a flowchart showing an outline of a method for manufacturing a vibration-damping spring. Fig. 5 is the result of EDX analysis of the vicinity of the boundary layer. Fig. 6 is a diagram showing the result of elemental line analysis in a direction perpendicular to the interface between the core wire and the coating layer of a sample of an example. Fig. 7 is a diagram showing the result of elemental line analysis in a direction perpendicular to the interface between the core wire and the coating layer of a sample of a comparative example. Fig. 8 is a schematic diagram showing the structure of a testing device for vibration-damping tests.

[0006] [Problem to be Solved by the Present Disclosure] One of the objects of the present disclosure is to provide a vibration damping spring with excellent vibration damping properties.

[0007] [Effects of the Present Disclosure] According to the above vibration damping spring, it is possible to provide a vibration damping spring with excellent vibration damping properties.

[0008] [Description of Embodiments of the Present Disclosure] First, embodiments of the present disclosure will be listed and described. The vibration damping spring of the present disclosure is: (1) formed from a wire comprising a copper or copper alloy core wire and a steel coating layer covering the outer circumferential surface of the core wire. The wire diameter is 4 mm or less. The core wire is arranged to form the outer circumferential surface of the core wire and includes a boundary layer having a copper or copper alloy matrix and a plurality of island regions that are iron-containing regions dispersed in the matrix. The area ratio of the core wire in a cross section perpendicular to the longitudinal direction of the wire is 20% or more and 90% or less.

[0009] The automobile shock absorber (vibration damping device) of Patent Document 1, in which vibration damping is provided primarily by a shock absorber, provides excellent vibration damping, but has the problem of being difficult to miniaturize. In contrast, the vibration damping spring of the present disclosure is endowed with excellent vibration damping properties in the spring itself. This makes it possible to miniaturize the vibration damping device.

[0010] Specifically, the vibration damping spring of the present disclosure is formed from a wire having a core wire and a coating layer. In wire having a copper or copper alloy core wire and a steel coating layer, a diffusion layer is generally formed near the interface between the core wire and the coating layer, as disclosed in Patent Document 2. For example, a diffusion layer is formed in which iron constituting the coating layer diffuses so as to form the outer peripheral surface of the core wire. In an equilibrium state, the iron constituting the coating layer hardly dissolves in the copper constituting the core wire. However, strong processing such as wire drawing causes the iron to diffuse from the coating layer to the core wire, forming a diffusion layer. This diffusion layer contributes to improving the adhesion between the core wire and the coating layer. As a result, the spring wire of Patent Document 2 is thought to have improved sag resistance and fatigue resistance.

[0011] On the other hand, in the vibration-damping spring of the present disclosure, the core wire includes a boundary layer arranged to form the outer circumferential surface of the core wire (the interface with the coating layer). This boundary layer has a copper or copper alloy matrix and multiple island regions containing iron dispersed within the matrix. In other words, the copper-based matrix and the iron-containing phase are separated in the boundary layer. This reduces adhesion between the core wire and the coating layer. Furthermore, the yield stress of the steel coating layer is greater than the yield stress of the copper or copper alloy core wire. As a result, when vibrations that apply stresses exceeding the yield stress of the core wire but less than the yield stress of the coating layer are transmitted to the vibration-damping spring of the present disclosure, the core wire undergoes repeated plastic deformation to absorb the vibration energy, while the coating layer maintains the elasticity of the vibration-damping spring. In this case, due to the low adhesion between the core wire and the coating layer, repeated plastic deformation of the core wire and maintenance of elasticity by the coating layer occur independently. In particular, excellent vibration damping properties can be obtained by setting the wire diameter to 4 mm or less and the area ratio of the core wire in a cross section perpendicular to the longitudinal direction of the wire to 20% to 90%. In this way, the vibration damping spring of the present disclosure is a vibration damping spring with excellent vibration damping properties. By imparting excellent vibration damping properties to the spring itself, the vibration damping spring of the present disclosure can contribute to the miniaturization of vibration damping devices.

[0012] (2) In the above (1), the diameter of the island region may be 0.5 μm or less. This configuration more reliably achieves high vibration damping. Here, the diameter of the island region refers to the diameter of a circle (equivalent circle diameter) corresponding to the area of ​​the island region in a cross section along the longitudinal direction of the wire. The area of ​​the island region can be measured, for example, by cutting the wire along the longitudinal cross section and analyzing the resulting cross section using EDX (Energy-Dispersive X-ray spectroscopy) to determine the area of ​​the iron-containing region.

[0013] (3) In the above (1) or (2), the thickness of the boundary layer may be 5 μm or less. This configuration makes it possible to more reliably obtain high vibration damping properties. The thickness of the boundary layer can be measured, for example, by confirming the presence of the island regions using EDX, as in the case of measuring the diameter of the island regions, and then regarding the thickness of the region where the island regions exist as the thickness of the boundary layer.

[0014] (4) In any of the above (1) to (3), the coating layer may be made of stainless steel. Stainless steel is suitable as a material for the coating layer from the viewpoints of yield stress, strength, corrosion resistance, etc.

[0015] (5) In the above (4), the coating layer may be made of austenitic stainless steel. Austenitic stainless steel, which has high corrosion resistance, is particularly suitable as a material for the coating layer.

[0016] [Details of the embodiment of the present disclosure] Next, an embodiment of the vibration damping spring according to the present disclosure will be described below with reference to the drawings. In the following drawings, the same or corresponding parts are designated by the same reference numerals, and description thereof will not be repeated.

[0017] Fig. 1 is a schematic diagram showing the structure of a vibration damping spring. Fig. 2 is a schematic diagram showing the structure of a wire forming the vibration damping spring. Fig. 3 is a schematic cross-sectional view showing the structure near the boundary layer of the wire. Referring to Fig. 1, the vibration damping spring 1 in this embodiment is formed from a wire 10. More specifically, the vibration damping spring 1 is a coil spring (compression coil spring) in which the wire 10 is processed into a spiral shape.

[0018] 1 and 2 , the wire 10 forming the vibration damping spring 1 includes a core wire 20 and a coating layer 30. The core wire 20 is made of copper (pure copper; copper content of 99.9% by mass or more) or a copper alloy. Examples of copper alloys that can be used include C1020 and C5191 as specified in JIS H 3250. In this embodiment, the core wire 20 is made of copper (pure copper with a copper content of 99.9% by mass or more).

[0019] In this embodiment, the cross section of the core wire 20 perpendicular to the longitudinal direction Y of the wires 10 (the direction along the arrow in FIG. 2 ) is circular. Note that the cross section shape is not limited to a circle and may be, for example, an ellipse or a rectangle (including a shape in which the portions corresponding to the vertices are arc-shaped). The core wire 20 has an outer circumferential surface 21. In this embodiment, the outer circumferential surface 21 has a cylindrical surface shape.

[0020] The coating layer 30 covers the outer peripheral surface 21 of the core wire 20. In this embodiment, the coating layer 30 has a hollow cylindrical shape. The coating layer 30 has an inner peripheral surface 31 and an outer peripheral surface 32. The inner peripheral surface 31 and the outer peripheral surface 32 each have a cylindrical shape. The inner peripheral surface 31 is in contact with the outer peripheral surface 21 of the core wire 20 over the entire circumference. The outer peripheral surface 32 is the outer peripheral surface 11 of the strand 10. The coating layer 30 is made of steel. Various steels can be used, such as stainless steel specified in JIS, spring steel, carbon steel, and mild steel. Examples of stainless steel include austenitic stainless steels such as JIS SUS304 and SUS316. The coating layer 30 may also be made of stainless steel (e.g., austenitic stainless steel). In this embodiment, the coating layer 30 is made of austenitic stainless steel SUS304.

[0021] Referring to Figure 2, the wire diameter D of the wire 10 is 4 mm or less. Here, the wire diameter D refers to the diameter of the cross section of the wire 10 perpendicular to the longitudinal direction Y if the cross section is circular. If the cross section is other than circular, the wire diameter D refers to the diameter of a circle having an area corresponding to the cross section (circle-equivalent diameter). The area ratio of the core wire 20 in the cross section of the wire 10 perpendicular to the longitudinal direction Y is 20% or more and 90% or less.

[0022] Referring to FIG. 3 , the core wire 20 includes a boundary layer 22. The boundary layer 22 is arranged to form the outer circumferential surface 21 of the core wire 20. The boundary layer 22 has a matrix 23 and a plurality of island regions 24 dispersed in the matrix 23. The matrix 23 is made of copper or a copper alloy. In this embodiment, the matrix 23 is made of pure copper. The island regions 24 are regions containing iron. In this embodiment, the island regions 24 contain iron and chromium, which are elements contained in SUS304, the material of the coating layer 30. The diameter of the island regions 24 is 0.5 μm or less. The diameter of the island regions 24 decreases with increasing distance from the outer circumferential surface 21 of the core wire 20 (the interface with the coating layer 30). The thickness t of the boundary layer 22, which is the region where the island regions 24 exist, is 5 μm or less.

[0023] In the vibration-damping spring 1 of this embodiment, the boundary layer 22 of the core wire 20 has a pure copper matrix 23 and iron-containing island regions 24 dispersed within the matrix 23. In other words, the copper-based matrix 23 and the iron-containing island regions 24 are separated into separate phases in the boundary layer 22. This reduces adhesion between the core wire 20 and the coating layer 30. As a result, when the vibration-damping spring 1 expands or contracts, repeated plastic deformation of the pure copper core wire 20 and the maintenance of elasticity by the SUS304 coating layer 30 occur independently. In this way, the vibration-damping spring 1 has excellent vibration-damping properties. Furthermore, excellent vibration-damping properties are achieved by having the wire diameter D of the wire 10 be 4 mm or less and the area ratio of the core wire 20 in a cross section perpendicular to the longitudinal direction of the wire 10 being 20% ​​to 90%. Furthermore, having the wire diameter D of the wire 10 be 4 mm or less facilitates miniaturization of the vibration-damping spring 1. As described above, the vibration damping spring 1 of this embodiment is a compact vibration damping spring with excellent vibration damping properties. The vibration damping spring 1 can contribute to the miniaturization of vibration damping devices by imparting excellent vibration damping properties to the spring itself. A miniaturized vibration damping device can be used, for example, as a vibration damping device for reducing vibration of a structure when a door is opened or closed.

[0024] Next, an example of a manufacturing method for the vibration damping spring 1 of this embodiment will be described. FIG. 4 is a flowchart showing an outline of the manufacturing method for the vibration damping spring. Referring to FIG. 4, in the manufacturing method for the vibration damping spring 1 of this embodiment, a cladding process is first carried out as step S10. In this step S10, a steel pipe having a hollow cylindrical shape to become the coating layer 30 and a metal rod made of copper or a copper alloy to become the core wire 20 are first prepared. In this embodiment, a pipe made of JIS SUS304, an austenitic stainless steel, and a metal rod made of oxygen-free copper (pure Cu) are prepared. The metal rod is then inserted into the pipe to obtain a clad material in which a copper metal rod is inserted into a steel tube.

[0025] Next, a first wiredrawing step is performed as step S20. In this step S20, the clad material produced in step S10 is subjected to wiredrawing. The wiredrawing is performed by passing the clad material through a through hole formed in a die. The wiredrawing may be performed in a single process using one die, or in multiple processes using multiple dies. The area reduction rate, which is the difference between the diameter of the clad material before wiredrawing and the diameter of the clad material after wiredrawing divided by the diameter of the clad material before wiredrawing, is set to 50% or more. This results in a clad wire including a core wire 20 and a coating layer 30.

[0026] Next, a solution treatment is carried out as step S30. In step S30, the clad wire obtained in step S20 is subjected to solution treatment. Specifically, the clad wire obtained in step S20 is subjected to heat treatment by heating to a temperature range of, for example, 900°C to 1100°C, holding for 5 seconds to 20 minutes, and then quenching. As a result, in the metal structure of the stainless steel forming the coating layer 30, the crystal grains elongated by the wire drawing in step S20 are recrystallized, and the martensite structure formed by the wire drawing disappears. As a result, the coating layer 30 work-hardened in step S20 is softened, and becomes ready for further wire drawing. The heating temperature in the solution treatment is set to a temperature that is in accordance with the A phase of the stainless steel constituting the coating layer. Ｃ３ It is preferable to set the temperature at or above this point.

[0027] Next, a second wiredrawing step is performed as step S40. In step S40, the clad wire that has been solution-treated in step S30 is drawn. As in step S20, the drawing may be performed in a single step using a single die, or in multiple steps using multiple dies. This produces a wire 10 including a core wire 20 and a coating layer 30. The area reduction, which is the difference between the diameter of the clad wire before drawing and the diameter of the clad wire (wire 10) after drawing divided by the diameter of the clad wire before drawing, is set to 50% or more. By performing drawing with an area reduction of 50% or more, as shown in FIGS. 2 and 3 , a diffusion layer is formed in the core wire 20 near the outer circumferential surface 21, where iron (Fe) and chromium (Cr) contained in the stainless steel that forms the coating layer 30 diffuse and penetrate. In the diffusion layer, Fe and Cr are present in concentrations that increase closer to the outer circumferential surface 21.

[0028] Next, in step S50, a spring processing step is carried out in which the wire 10 obtained in step S40 is processed into the spiral shape shown in FIG. 1, thereby forming the wire into the shape of a spring.

[0029] Next, an annealing step is carried out in step S60. In this step, the wire 10 formed into the shape of a spring in step S50 is annealed. Specifically, the wire 10 formed into the shape of a spring is heated to a temperature of 400°C or higher, thereby reducing the strain in the wire 10 that occurred in step S50, and separating the diffusion layer formed in step S40 into a matrix phase 23 mainly composed of copper (Cu) and island regions 24 that are phases containing Fe and Cr, thereby forming a boundary layer 22. Through the above steps, the vibration damping spring 1 of this embodiment is completed.

[0030] In the manufacturing method of the vibration-damping spring 1 of this embodiment, the heating temperature for the annealing treatment in step S60 is set to a higher temperature (for example, 400°C or higher) than when the purpose is solely to reduce strain. As a result, after a diffusion layer (a layer in which Fe and Cr are diffused into the copper that forms the core wire 20) is formed in step S40, the high-temperature annealing treatment in step S60 separates the diffusion layer into a matrix phase 23 mainly composed of Cu and island regions 24 that are phases containing Fe and Cr, forming a boundary layer 22. As a result, the adhesion between the core wire 20 and the coating layer 30 is reduced. In this way, the manufacturing method of the vibration-damping spring 1 of this embodiment makes it possible to manufacture a vibration-damping spring 1 with excellent vibration-damping properties.

[0031] The wire forming the vibration damping spring of the present disclosure was fabricated, and the state of formation of the island regions (boundary layers) was confirmed. Furthermore, the vibration damping spring of the present disclosure was fabricated, and an experiment was conducted to confirm the improvement of vibration damping properties. The experimental procedure was as follows.

[0032] (1) Formation State of Island Regions (Boundary Layers) A wire 10 was prepared by performing steps S10 to S40 of the manufacturing method described in the above embodiment. Then, assuming the annealing step of step S60, the wire 10 was subjected to a heat treatment at 380°C to 420°C to prepare samples. A sample (as-drawn sample) was also prepared without step S60. The state of each element near the boundary between the core wire 20 and the coating layer 30 of the obtained sample was analyzed by EDX. FIG. 5 shows the results of EDX analysis near the boundary layer. FIG. 5 shows the analysis results of samples subjected to heat treatment at temperatures of 380°C, 400°C, and 420°C to simulate the annealing step of step S60, as well as the as-drawn sample. For the samples at each heat treatment temperature, the results of analysis of Cu, Fe, and Cr by K line, as well as dark field images (ADF images; Annular Dark Field images) are shown.

[0033] 5 , when the heat treatment corresponding to step S60 is not performed or when the heat treatment temperature is 380° C., which is lower than 400° C., no island regions 24 are observed. In contrast, when the heat treatment temperature is 400° C. or higher, 400° C. or 420° C., it is found that a large number of island regions 24, where Fe and Cr are present but Cu is not present, are dispersed and formed in a region within the core wire 20 close to the outer circumferential surface 21 of the core wire 20 (the interface between the core wire 20 and the coating layer 30).

[0034] Fig. 6 shows the results of elemental line analysis in a direction perpendicular to the interface between the core wire 20 and the coating layer 30 of a sample of an example where the heat treatment corresponding to step S60 was performed at a temperature of 400°C. Fig. 7 shows the results of elemental line analysis in a direction perpendicular to the interface between the core wire 20 and the coating layer 30 of a sample of a comparative example where the heat treatment corresponding to step S60 was omitted. In Figs. 6 and 7 , the positive region on the horizontal axis corresponds to the coating layer 30, and the negative region corresponds to the core wire 20. Referring to Figs. 6 and 7 , it can be seen that the content of each element near the interface (the outer surface 21 of the core wire 20) changes more sharply in the sample of the example where the island regions 24 are formed, compared to the sample of the comparative example where the island regions 24 are not observed. In other words, by performing heat treatment at 400°C or higher, the mother phase 23, which is mainly composed of Cu, and the island regions 24, which are phases containing Fe, Cr, and Ni, are separated, and the thickness of the diffusion layer, which is thought to contribute to the adhesion between the core wire 20 and the coating layer 30, is reduced.

[0035] (2) Vibration Damping Test: Using the manufacturing method described in the above embodiment, samples of vibration damping springs were produced by varying the area ratio of the core wire in a cross section perpendicular to the longitudinal direction of the wire, and by adjusting the heat treatment temperature in step S60 to vary the presence or absence of island regions. For comparison, pure copper wires and SUS304 wires were prepared and processed into spring shapes to prepare samples. The wire diameter of the wire forming the vibration damping spring was 2 mm, the outer diameter of the vibration damping spring was 20.0 mm, the spring constant was 3 N / mm, and the free height of the spring was 30 mm. The spring constant was adjusted by the number of effective turns of the spring. These samples were then subjected to vibration damping tests, and the loss factor and the range of motion of the vibration damping spring were calculated.

[0036] FIG. 8 is a schematic diagram showing the structure of a test device for vibration damping tests. Referring to FIG. 8, the vibration damping test device 90 includes a vibration excitation table 91, a lower plate 93, an upper plate 94, and a weight 95. An impedance head 91A is installed on the vibration excitation table 91. A contact tip 91B is installed at the tip of the impedance head 91A. The contact tip 91B is in contact with the lower plate 93. The vibration damping spring 1 is disposed between the lower plate 93 and the upper plate 94 so as to contact both the lower plate 93 and the upper plate 94. A weight 95 is placed on the upper plate 94. The load and acceleration were measured using the impedance head 91A, and the loss factor and the range of motion of the vibration damping spring were calculated from the relationship between the excitation frequency and the vibration transmissibility. The weight of the weight was determined so that the sprung load was approximately 100 g. The excitation frequency was approximately 50 Hz. The test results are shown in Table 1.

[0037] In Table 1, Samples A, B, and C are example samples in which island regions are present by setting the heat treatment temperature in step S60 to 400°C, and the area ratio of the core wire also satisfies the conditions for a vibration-damping spring of the present disclosure. Samples D and E are comparative examples in which the area ratio of the core wire does not satisfy the conditions for a vibration-damping spring of the present disclosure. Samples F and G are comparative examples formed from a pure copper wire and a SUS304 wire, respectively. Samples H, I, and J are comparative examples in which the heat treatment temperature in step S60 is set to 350°C, resulting in no island regions.

[0038] Referring to Table 1, samples A to C, which correspond to vibration-damping springs according to examples of the present disclosure, exhibit both a high loss factor and a wide range of motion. In contrast, sample D, in which the area ratio of the core wire is smaller than the range that satisfies the conditions for a vibration-damping spring according to the present disclosure, has a significantly smaller range of motion for the spring with vibration-damping properties than samples A to C. Furthermore, sample E, in which the area ratio of the wire is larger than the range that satisfies the conditions for a vibration-damping spring according to the present disclosure, has an extremely small loss factor, and it can be said that it does not exhibit vibration-damping properties. Furthermore, even if the area ratio of the core wire is within the range that satisfies the conditions for a vibration-damping spring according to the present disclosure, samples H, I, and J, which do not have island regions, have a smaller loss factor than samples A to C.

[0039] The above experimental results confirm that the vibration damping spring of the present disclosure can provide a vibration damping spring with excellent vibration damping properties.

[0040] In the above embodiment and examples, a coil spring has been described as an example of a vibration damping spring of the present disclosure, but the vibration damping spring of the present disclosure is not limited to this. The vibration damping spring of the present disclosure may be a spring of another structure, such as a torsion bar or a spiral spring.

[0041] It should be understood that the embodiments and examples disclosed herein are illustrative in all respects and are not limiting in any respect. The scope of the present invention is defined not by the above description but by the scope of the claims, and it is intended to include all modifications within the meaning and scope of the claims.

[0042] 1 vibration damping spring, 10 wire, 11 outer peripheral surface, 20 core wire, 21 outer peripheral surface, 22 boundary layer, 23 parent phase, 24 island region, 30 coating layer, 31 inner peripheral surface, 32 outer peripheral surface, 90 vibration damping test device, 91 vibration table, 91A impedance head, 91B contact tip, 93 lower plate, 94 upper plate, 95 weight, D wire diameter, Y longitudinal direction, t thickness.

Claims

1. A vibration damping spring formed from a wire comprising a copper or copper alloy core wire and a steel coating layer covering the outer surface of the core wire, wherein the wire diameter is 4 mm or less, the core wire is arranged to form the outer surface of the core wire and includes a boundary layer having a copper or copper alloy parent phase and a plurality of island regions that are iron-containing regions dispersed in the parent phase, and the area ratio of the core wire in a cross section perpendicular to the longitudinal direction of the wire is 20% or more and 90% or less.

2. The vibration damping spring according to claim 1, wherein the diameter of said island region is 0.5 μm or less.

3. A vibration damping spring according to claim 1 or claim 2, wherein the thickness of the boundary layer is 5 μm or less.

4. A vibration damping spring according to any one of claims 1 to 3, wherein the coating layer is made of stainless steel.

5. The vibration damping spring according to claim 4, wherein the coating layer is made of austenitic stainless steel.

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