Wire drawing die

Abstract

A wire drawing die is a wire drawing die including a bearing, the bearing having a diameter D smaller than 100 μm. A hole is provided in polycrystalline diamond composed substantially only of diamond having an average particle size equal to or smaller than 500 nm. A reduction angle is not smaller than 4° and not larger than 14°. A length of the bearing is not smaller than 20% D and not larger than 100% D. A concentricity between the bearing and a bell or an approach is equal to or smaller than 1.0 μm. A roundness of a hole in the bearing is equal to or smaller than 0.5 μm.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to a wire drawing die. The present application claims priority to Japanese Patent Application No. 2023-060736 filed on Apr. 4, 2023, the entirety contents of which are hereby incorporated by reference.BACKGROUND ART

[0002] A wire drawing die has conventionally been disclosed, for example, in WO2008 / 088048.CITATION LISTPatent Literature

[0003] PTL 1: WO2008 / 088048SUMMARY OF INVENTION

[0004] A wire drawing die in the present disclosure is a wire drawing die provided with a bearing, the bearing having a diameter D smaller than 100 μm,

[0005] a hole is provided in polycrystalline diamond composed substantially only of diamond having an average particle size equal to or smaller than 500 nm,

[0006] a reduction angle is not smaller than 4° and not larger than 14°,

[0007] a length of the bearing is not smaller than 20% D and not larger than 100% D,

[0008] a concentricity between the bearing and a bell or an approach is equal to or smaller than 1.0 μm, and

[0009] a roundness of a hole in the bearing is equal to or smaller than 0.5 μm.BRIEF DESCRIPTION OF DRAWINGS

[0010] FIG. 1 is a cross-sectional view of a binderless polycrystalline diamond die according to an embodiment.DESCRIPTION OF EMBODIMENTSProblem to be Solved by the Present Disclosure

[0011] A conventional wire drawing die has been disadvantageous in difficulty in decrease in thickness thereof.Description of the Embodiment in the Present Disclosure

[0012] An embodiment of the present disclosure will initially be listed and described.

[0013] A wire drawing die in the present disclosure is a wire drawing die provided with a bearing, the bearing having a diameter D smaller than 100 μm, a hole is provided in polycrystalline diamond composed substantially only of diamond having an average particle size equal to or smaller than 500 nm, a reduction angle is not smaller than 4° and not larger than 14°, a length of the bearing is not smaller than 20% D and not larger than 100% D, a concentricity between the bearing and a bell or an approach is equal to or smaller than 1.0 μm, and a roundness of a hole in the bearing is equal to or smaller than 0.5 μm.(Diamond)

[0014] Polycrystalline diamond composed substantially only of diamond is diamond in which what is called a binder is absent. A representative example is diamond manufactured by direct conversion of non-diamond carbon to diamond under an ultra-high pressure and temperature, and it is known as binderless diamond. The average particle size in the present application is defined as being obtained as below. Initially, a texture of a sintered material of polycrystalline diamond is observed with an SEM or a TEM, individual particles (primary particles) are extracted by image processing, an area of the particle is calculated, and a diameter when the area of the particle is assumed as an area of a circular particle is defined as a particle size. An average value of particle sizes per unit area (for example, 50 μm×50 μm) is defined as an average particle size.

[0015] A die hole is generally in a circular shape in a cross-section perpendicular to a direction of wire drawing.(Structure)

[0016] The wire drawing die is provided with a bell, an approach, a reduction, a bearing, a back relief, and an exit sequentially from an upstream side.

[0017] A reduction angle which is an angle of opening of a die hole in the reduction 1s not smaller than 4° and not larger than 14°. When the reduction angle is larger than 14° or smaller than 4°, lifetime of the wire drawing die is shorter. The reduction angle is preferably not smaller than 5° and not larger than 12°.

[0018] A length of the bearing is not smaller than 20% D and not larger than 100% D. A concentricity between the bearing and the bell or the approach is equal to or smaller than 1.0 μm. A roundness of a hole in the bearing is equal to or smaller than 0.5 μm. Preferably, the length of the bearing is not smaller than 30% D and not larger than 70% D. Preferably, the concentricity between the bearing and the bell or the approach is equal to or smaller than 0.8 μm.

[0019] FIG. 1 is a cross-sectional view of a binderless polycrystalline diamond die according to an embodiment. As shown in FIG. 1, a die 1 for wire drawing according to a first embodiment is provided with a die hole 1h. Die 1 is provided with a bell 1a, an approach 1b, a reduction 1c, a bearing 1d, a back relief 1e, and an exit if sequentially from an upstream side.

[0020] Bell 1a is located on a most upstream side of die hole 1h. An angle α formed between tangents 12a and 13a to a side surface of die hole 1h that defines bell 1a is a bell angle. Bell 1a corresponds to an inlet for a wire rod to be drawn and a lubricating material.

[0021] Approach 1b is provided downstream from bell 1a. At a boundary between bell 1a and approach 1b, an inclination of die hole 1h may continuously or discontinuously change. An angle β formed between tangents 12b and 13b to the side surface of die hole 1h that defines approach 1b is an approach angle.

[0022] Reduction 1c is provided downstream from approach 1b. At a boundary between approach 1b and reduction 1c, an inclination of die hole 1h may continuously or discontinuously change. An angle γ formed between tangents 12c and 13c to the side surface of die hole 1h that defines reduction 1c is the reduction angle.

[0023] Bearing 1d is provided downstream from reduction 1c. At a boundary between reduction 1c and bearing 1d, an inclination of die hole 1h may continuously or discontinuously change. A diameter D of die hole 1h that defines bearing 1d is constant. Bearing 1d is cylindrical. Bearing 1d is a portion smallest in diameter in die hole 1h.

[0024] Back relief 1e is provided downstream from bearing 1d. At a boundary between bearing 1d and back relief 1e, an inclination of die hole 1h may continuously or discontinuously change. An angle θ of the side surface of die hole 1h that defines back relief 1e is a back relief angle.

[0025] Exit if is provided downstream from back relief 1e. At a boundary between bearing 1d and back relief 1e, an inclination of die hole 1h may continuously or discontinuously change. An angle φ of the side surface of die hole 1h that defines back relief 1e is an exit angle.

[0026] RD and D satisfy relation of D<RD≤1.050 D where RD represents a diameter of reduction 1c. Therefore, a portion having diameter RD in the relation is reduction 1c. A cross-sectional area of reduction 1c is larger than 100% and not larger than 110% of the cross-sectional area of bearing 1d.

[0027] The length of bearing 1d is denoted as L. L and D satisfy relation of 20% D≤L≤100% D. Preferably, L and D satisfy relation of 30% D≤L≤70% D. A portion where die hole 1h has diameter D is bearing 1d. (Method of Identifying Shape of Die Hole h)

[0028] In order to measure shapes of bell 1a, approach 1b, reduction 1c, bearing 1d, back relief 1e, and exit 1f, die hole 1h is filled with a transfer material (for example, repliset manufactured by Struers) to make a replica to which the shape of die hole 1h has been transferred. With this replica, a tool microscope with transmitted illumination is used to clarify a contour of die hole 1h and to obtain a cross-sectional view of die hole 1h like die hole 1h in FIG. 1.

[0029] In the cross-sectional view, a cylindrical portion smallest in inner diameter is defined as bearing 1d. The diameter of the bearing is denoted as D. In the cross-sectional view, a portion located upstream from bearing 1d adjacently to bearing 1d and having inner diameter RD which satisfies D<RD≤1.050 D is defined as reduction 1c. In the cross-sectional view, a portion located downstream from bearing 1d adjacently to bearing 1d and having an inner diameter BD which satisfies D<BD≤1.025 D is defined as back relief 1e.

[0030] In measurement of a reduction angle γ, in the cross-sectional view of die hole 1h, tangents 12c and 13c are drawn at both of side surfaces at a reference point 11c (a portion where relation of RD=1.050 D is satisfied) in reduction 1c and an angle formed between two tangents 12c and 13c is defined as reduction angle γ.(Method of Measuring Concentricity)

[0031] In measurement of the concentricity between bell 1a or approach 1b and bearing 1d, for example, a digital microscope (VHX8000) manufactured by Keyence is employed as a measurement apparatus. Measurement conditions include a magnification of 2,500× and transmitted illumination. Die hole 1h is observed from a direction in parallel to a centerline 1p to find a contour of a region which looks glowing white. The contour (bell or approach portion) located outermost of the region which looks glowing white within a range of 150 to 250% D with respect to diameter D of die hole 1h is defined as the contour of bell 1a or approach 1b. A circle is approximated from the contour, and the center of the circle is defined as the center of bell 1a or approach 1b. The contour of bearing 1d is similarly found. A circle is approximated from the contour, and the center of the circle is defined as the center of bearing 1d. A distance W between the center of bell 1a or approach 1b and the center of bearing 1d is referred to as the concentricity(Method of Measuring Roundness)

[0032] In the present application, a difference between a maximum diameter and a minimum diameter in measurement of a diameter of a wire rod subjected to wire drawing works by the die in directions around 360 degrees is defined as the roundness. For measurement, a wire diameter measurement device (LDSN) manufactured by Cersa is employed, and the diameter of the drawn wire rod is measured at 250 points around 360 degrees. A difference between a maximum value and a minimum value of measurement values at these 250 points is defined as the roundness. The shape of die hole 1h (the shape of bearing 1d) is transferred to the wire rod and the roundness of bearing 1d is reflected on the wire rod.

[0033] The roundness of bearing 1d is a difference between a maximum value and a minimum value of distances from the center of bearing 1d calculated by circle approximation at the contour of bearing 1d obtained in a procedure above.Details of the Embodiment in the Present DisclosureExample 1(Evaluation of Wire Drawing by Binderless (BL) Diamond Die)

[0034] In order to check performance depending on difference in source material for the die, three types of dies identical in shape were prepared and evaluated.Die Source Material

[0035] Three types of A. binderless PCD die, B. single crystal diamond die, and C. PCD die containing a binder were prepared. An average particle size of diamond of A. binderless PCD die was 0.05 μm (50 nm). Tables 1 and 2 show shapes of these types.TABLE 1Tool SpecificationsHole ShapeReductionHole Accuracy (μm)BearingAngleRoundnessSampleSourceDiameter(OpeningBearingof Hole inNumberMaterialD (mm)Angle) °LengthBearingConcentricity1BLPCD0.081230% D0.20.52BLPCD0.08830% D0.20.53BLPCD0.08530% D0.20.54BLPCD0.08430% D0.20.5101BLPCD0.08330% D0.20.55BLPCD0.081430% D0.20.5102BLPCD0.081530% D0.20.52BLPCD0.08830% D0.20.512BLPCD0.08850% D0.20.513BLPCD0.08870% D0.20.514BLPCD0.088100% D 0.20.5111BLPCD0.088110% D 0.20.515BLPCD0.08820% D0.20.5112BLPCD0.08810% D0.20.52BLPCD0.08830% D0.20.531BLPCD0.08830% D0.20.332BLPCD0.08830% D0.20.833BLPCD0.08830% D0.21.0131BLPCD0.08830% D0.21.2TABLE 2Tool SpecificationsHole ShapeReductionHole Accuracy (μm)BearingAngleRoundnessSampleSourceDiameter(OpeningBearingof Hole inNumberMaterialD (mm)Angle) °LengthBearingConcentricity2BLPCD0.08830% D0.20.541BLPCD0.08830% D0.10.542BLPCD0.08830% D0.50.5141BLPCD0.08830% D0.70.52BLPCD0.08830% D0.20.5151Single0.08830% D0.20.5Crystal152PCD0.08830% D0.20.5HavingParticleSize of1 μm2BLPCD0.08830% D0.20.561BLPCD0.1830% D0.20.562BLPCD0.04830% D0.20.563BLPCD0.015830% D0.20.564BLPCD0.015830% D0.20.865BLPCD0.015830% D0.21.0166BLPCD0.015830% D0.21.2In Tables 1 and 2, “BLPCD” refers to polycrystalline diamond which is diamond manufactured by direct conversion of non-diamond carbon to diamond under an ultra-high pressure and temperature and composed substantially only of diamond where no binder is present.

[0037] “PCD having particle size of 1 μm” refers to polycrystalline diamond composed of polycrystalline diamond having an average particle size of 1 μm, the polycrystalline diamond containing 5 volume % or more of binder and diamond as the remainder.

[0038] With this die, an SUS wire rod was drawn at a linear speed of 500 m / min. under an oil lubricated condition. In an example of diameter D of φ0.08 mm, a wire diameter before wire drawing was set to φ0.087 mm. In an example of diameter D of φ0.10 mm, a wire diameter before wire drawing was set to φ0.109 mm. In an example of diameter D of φ0.04 mm, a wire diameter before wire drawing was set to φ0.0435 mm. In an example of diameter D of φ0.15 mm, a wire diameter before wire drawing was set to φ0.0164 mm. These SUS wire rods were subjected to wire drawing works by each die, and when the roundness of the drawn wire rod attained to 0.3 μm or when increment of the wire diameter as compared with the wire diameter of the drawn wire rod at a time point of 100 m after start of wire drawing attained to 0.3 μm, determination as the end of lifetime of the die was made. Alternatively, when curl (warpage of which R is less than 30 mm) of the wire rod occurs, determination as the end of lifetime of the die was made. Tables 3 and 4 show results.TABLE 3RoundnessAmount of(AfterIncreaseCurlWirein WireStateCurlSampleLifetimeDrawingDiameter(InitialStateNumber(km)by 30 km)(μm)Stage)(30 km)1A0.20.1AA2A0.20.1AA3A0.20AA4B0.20AA101C0.30CC5B0.3−0.1AB102C0.3−0.2BC2A0.20.1AA12A0.20AA13A0.20AA14B0.20AB111C0.30BC15B0.20.3BB112C0.40.5BC2A0.20.1AA31A0.20AA32A0.30.1AA: WithoutCurl33B0.30.2AB: Occurrenceof Curl atPoint at 50km131C0.60.5CCTABLE 4RoundnessAmount of(AfterIncreaseCurlWirein WireStateCurlSampleLifetimeDrawingDiameter(InitialStateNumber(km)by 30 km)(μm)Stage)(30 km)2A0.20.1AA41A0.20.1AA42A0.20AA141B0.30.2BC2A0.20.1AA151C1.21.3AC152C0.50.2AB2A0.20.1AA61A0.30.2AA62A0.20.1AA63A0.20.1AA64A0.20.2AA65B0.30.2BB166CWireWireCWiredrawingdrawingdrawingcould notcould notcould notbe donebe donebe doneIn “Lifetime” in Tables 3 and 4, “A” represents lifetime not shorter than 60 km. “B” represents lifetime longer than 30 km and shorter than 60 km, and “C” represents lifetime not longer than 30 km.

[0040] “Amount of increase in wire diameter” refers to a difference between the wire diameter at a time point of 100 m after start of wire drawing and the wire diameter at a time point of 30 km after wire drawing. The wire diameter is defined as an average value in measurement of the diameter of the wire rod subjected to wire drawing works by the die in directions around 360 degrees. For measurement, a wire diameter measurement device (LDSN) manufactured by Cersa was employed, and the diameter of the drawn wire rod was measured at 250 points around 360 degrees. There is also a sample having a negative amount of increase in wire diameter. This is because use of high-hardness diamond such as BLPCD may cause ring wear and the wire rod may be ground and decrease in thickness during wire drawing.

[0041] The “curl state” was evaluated as “A” when R of warpage of the drawn wire rod was not less than 50 mm, evaluated as “B” when R was not less than 30 mm and less than 50 mm, and evaluated as “C” when R was less than 30 mm.

[0042] In the die having lifetime evaluated as “C”, the curl state was poor from the initial stage and deteriorated with progress of wire drawing works, and the die failed in wire drawing by 30 km. Therefore, roundness of the bearing at the time of the end of the lifetime of the die was shown as the “roundness (after wire drawing by 30 km).”

[0043] In sample number 166, break occurred in a stage of wire drawing by 5 km. Since evaluation could not be continued, wire drawing was stopped.

[0044] It can be seen from Tables 3 and 4 that, when the reduction angle was not equal to or smaller than 14°, the length of the bearing was not smaller than 20% D and not larger than 100% D, the concentricity between the bearing and the bell or the approach was equal to or smaller than 1.0 μm, and the roundness of the hole in the bearing was equal to or smaller than 0.5 μm, evaluation of B or higher was obtained in evaluation of lifetime, the curl state (initial stage), and the curl state (30 km).

[0045] It can be seen that there were more evaluations A when the reduction angle was more preferably not smaller than 5° and not larger than 12°. Furthermore, it can be seen that there were more evaluations A when the length of the bearing was within a range not smaller than 30% D and not larger than 70% D. In addition, it can be seen that there were more evaluations A when the concentricity was equal to or smaller than 0.8 μm.(Additional Aspect 1)

[0046] A wire drawing die is provided with a bearing, the bearing having a diameter D smaller than 100 μm,

[0047] a hole is provided in polycrystalline diamond composed substantially only of diamond having an average particle size equal to or smaller than 500 nm,

[0048] a reduction angle is not smaller than 4° and not larger than 14°,

[0049] a length of the bearing is not smaller than 20% D and not larger than 100% D,

[0050] a concentricity between the bearing and a bell or an approach is equal to or smaller than 1.0 μm, and

[0051] a roundness of a hole in the bearing is equal to or smaller than 0.5 μm.(Additional Aspect 2)

[0052] In the wire drawing die according to Additional Aspect 1.

[0053] the reduction angle is not smaller than 5° and not larger than 12°.(Additional Aspect 3)

[0054] In the wire drawing die according to Additional Aspect 1 or 2,

[0055] the length of the bearing is not smaller than 30% D and not larger than 70% D.(Additional Aspect 4)

[0056] In the wire drawing die according to any one of Additional Aspects 1 to 3,

[0057] the concentricity between the bearing and the bell or the approach is equal to or smaller than 0.8 μm.

[0058] It should be understood that the embodiment and the example disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the terms of the claims rather than the embodiment above and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.REFERENCE SIGNS LIST

[0059] 1 die; 1a bell; 1b approach; 1c reduction; 1d bearing, 1e back relief, 1f exit; 1h die hole, 1p centerline; 11c reference point; 12a, 12b, 12c, 13a, 13b, 13c tangent.

Examples

example 1

(Evaluation of Wire Drawing by Binderless (BL) Diamond Die)

[0034]In order to check performance depending on difference in source material for the die, three types of dies identical in shape were prepared and evaluated.

Die Source Material

[0035]Three types of A. binderless PCD die, B. single crystal diamond die, and C. PCD die containing a binder were prepared. An average particle size of diamond of A. binderless PCD die was 0.05 μm (50 nm). Tables 1 and 2 show shapes of these types.

TABLE 1Tool SpecificationsHole ShapeReductionHole Accuracy (μm)BearingAngleRoundnessSampleSourceDiameter(OpeningBearingof Hole inNumberMaterialD (mm)Angle) °LengthBearingConcentricity1BLPCD0.081230% D0.20.52BLPCD0.08830% D0.20.53BLPCD0.08530% D0.20.54BLPCD0.08430% D0.20.5101BLPCD0.08330% D0.20.55BLPCD0.081430% D0.20.5102BLPCD0.081530% D0.20.52BLPCD0.08830% D0.20.512BLPCD0.08850% D0.20.513BLPCD0.08870% D0.20.514BLPCD0.088100% D 0.20.5111BLPCD0.088110% D 0.20.515BLPCD0.08820% D0.20.5112BLPCD0.08810% D0.20.52...

TECHNICAL FIELD

[0001] The present disclosure relates to a wire drawing die. The present application claims priority to Japanese Patent Application No. 2023-060736 filed on Apr. 4, 2023, the entirety contents of which are hereby incorporated by reference.BACKGROUND ART

[0002] A wire drawing die has conventionally been disclosed, for example, in WO2008 / 088048.CITATION LISTPatent Literature

[0003] PTL 1: WO2008 / 088048SUMMARY OF INVENTION

[0004] A wire drawing die in the present disclosure is a wire drawing die provided with a bearing, the bearing having a diameter D smaller than 100 μm,

[0005] a hole is provided in polycrystalline diamond composed substantially only of diamond having an average particle size equal to or smaller than 500 nm,

[0006] a reduction angle is not smaller than 4° and not larger than 14°,

[0007] a length of the bearing is not smaller than 20% D and not larger than 100% D,

[0008] a concentricity between the bearing and a bell or an approach is equal to or smaller than 1.0 μm, and

[0009] a roundness of a hole in the bearing is equal to or smaller than 0.5 μm.BRIEF DESCRIPTION OF DRAWINGS

[0010] FIG. 1 is a cross-sectional view of a binderless polycrystalline diamond die according to an embodiment.DESCRIPTION OF EMBODIMENTSProblem to be Solved by the Present Disclosure

[0011] A conventional wire drawing die has been disadvantageous in difficulty in decrease in thickness thereof.Description of the Embodiment in the Present Disclosure

[0012] An embodiment of the present disclosure will initially be listed and described.

[0013] A wire drawing die in the present disclosure is a wire drawing die provided with a bearing, the bearing having a diameter D smaller than 100 μm, a hole is provided in polycrystalline diamond composed substantially only of diamond having an average particle size equal to or smaller than 500 nm, a reduction angle is not smaller than 4° and not larger than 14°, a length of the bearing is not smaller than 20% D and not larger than 100% D, a concentricity between the bearing and a bell or an approach is equal to or smaller than 1.0 μm, and a roundness of a hole in the bearing is equal to or smaller than 0.5 μm.(Diamond)

[0014] Polycrystalline diamond composed substantially only of diamond is diamond in which what is called a binder is absent. A representative example is diamond manufactured by direct conversion of non-diamond carbon to diamond under an ultra-high pressure and temperature, and it is known as binderless diamond. The average particle size in the present application is defined as being obtained as below. Initially, a texture of a sintered material of polycrystalline diamond is observed with an SEM or a TEM, individual particles (primary particles) are extracted by image processing, an area of the particle is calculated, and a diameter when the area of the particle is assumed as an area of a circular particle is defined as a particle size. An average value of particle sizes per unit area (for example, 50 μm×50 μm) is defined as an average particle size.

[0015] A die hole is generally in a circular shape in a cross-section perpendicular to a direction of wire drawing.(Structure)

[0016] The wire drawing die is provided with a bell, an approach, a reduction, a bearing, a back relief, and an exit sequentially from an upstream side.

[0017] A reduction angle which is an angle of opening of a die hole in the reduction 1s not smaller than 4° and not larger than 14°. When the reduction angle is larger than 14° or smaller than 4°, lifetime of the wire drawing die is shorter. The reduction angle is preferably not smaller than 5° and not larger than 12°.

[0018] A length of the bearing is not smaller than 20% D and not larger than 100% D. A concentricity between the bearing and the bell or the approach is equal to or smaller than 1.0 μm. A roundness of a hole in the bearing is equal to or smaller than 0.5 μm. Preferably, the length of the bearing is not smaller than 30% D and not larger than 70% D. Preferably, the concentricity between the bearing and the bell or the approach is equal to or smaller than 0.8 μm.

[0019] FIG. 1 is a cross-sectional view of a binderless polycrystalline diamond die according to an embodiment. As shown in FIG. 1, a die 1 for wire drawing according to a first embodiment is provided with a die hole 1h. Die 1 is provided with a bell 1a, an approach 1b, a reduction 1c, a bearing 1d, a back relief 1e, and an exit if sequentially from an upstream side.

[0020] Bell 1a is located on a most upstream side of die hole 1h. An angle α formed between tangents 12a and 13a to a side surface of die hole 1h that defines bell 1a is a bell angle. Bell 1a corresponds to an inlet for a wire rod to be drawn and a lubricating material.

[0021] Approach 1b is provided downstream from bell 1a. At a boundary between bell 1a and approach 1b, an inclination of die hole 1h may continuously or discontinuously change. An angle β formed between tangents 12b and 13b to the side surface of die hole 1h that defines approach 1b is an approach angle.

[0022] Reduction 1c is provided downstream from approach 1b. At a boundary between approach 1b and reduction 1c, an inclination of die hole 1h may continuously or discontinuously change. An angle γ formed between tangents 12c and 13c to the side surface of die hole 1h that defines reduction 1c is the reduction angle.

[0023] Bearing 1d is provided downstream from reduction 1c. At a boundary between reduction 1c and bearing 1d, an inclination of die hole 1h may continuously or discontinuously change. A diameter D of die hole 1h that defines bearing 1d is constant. Bearing 1d is cylindrical. Bearing 1d is a portion smallest in diameter in die hole 1h.

[0024] Back relief 1e is provided downstream from bearing 1d. At a boundary between bearing 1d and back relief 1e, an inclination of die hole 1h may continuously or discontinuously change. An angle θ of the side surface of die hole 1h that defines back relief 1e is a back relief angle.

[0025] Exit if is provided downstream from back relief 1e. At a boundary between bearing 1d and back relief 1e, an inclination of die hole 1h may continuously or discontinuously change. An angle φ of the side surface of die hole 1h that defines back relief 1e is an exit angle.

[0026] RD and D satisfy relation of D<RD≤1.050 D where RD represents a diameter of reduction 1c. Therefore, a portion having diameter RD in the relation is reduction 1c. A cross-sectional area of reduction 1c is larger than 100% and not larger than 110% of the cross-sectional area of bearing 1d.

[0027] The length of bearing 1d is denoted as L. L and D satisfy relation of 20% D≤L≤100% D. Preferably, L and D satisfy relation of 30% D≤L≤70% D. A portion where die hole 1h has diameter D is bearing 1d. (Method of Identifying Shape of Die Hole h)

[0028] In order to measure shapes of bell 1a, approach 1b, reduction 1c, bearing 1d, back relief 1e, and exit 1f, die hole 1h is filled with a transfer material (for example, repliset manufactured by Struers) to make a replica to which the shape of die hole 1h has been transferred. With this replica, a tool microscope with transmitted illumination is used to clarify a contour of die hole 1h and to obtain a cross-sectional view of die hole 1h like die hole 1h in FIG. 1.

[0029] In the cross-sectional view, a cylindrical portion smallest in inner diameter is defined as bearing 1d. The diameter of the bearing is denoted as D. In the cross-sectional view, a portion located upstream from bearing 1d adjacently to bearing 1d and having inner diameter RD which satisfies D<RD≤1.050 D is defined as reduction 1c. In the cross-sectional view, a portion located downstream from bearing 1d adjacently to bearing 1d and having an inner diameter BD which satisfies D<BD≤1.025 D is defined as back relief 1e.

[0030] In measurement of a reduction angle γ, in the cross-sectional view of die hole 1h, tangents 12c and 13c are drawn at both of side surfaces at a reference point 11c (a portion where relation of RD=1.050 D is satisfied) in reduction 1c and an angle formed between two tangents 12c and 13c is defined as reduction angle γ.(Method of Measuring Concentricity)

[0031] In measurement of the concentricity between bell 1a or approach 1b and bearing 1d, for example, a digital microscope (VHX8000) manufactured by Keyence is employed as a measurement apparatus. Measurement conditions include a magnification of 2,500× and transmitted illumination. Die hole 1h is observed from a direction in parallel to a centerline 1p to find a contour of a region which looks glowing white. The contour (bell or approach portion) located outermost of the region which looks glowing white within a range of 150 to 250% D with respect to diameter D of die hole 1h is defined as the contour of bell 1a or approach 1b. A circle is approximated from the contour, and the center of the circle is defined as the center of bell 1a or approach 1b. The contour of bearing 1d is similarly found. A circle is approximated from the contour, and the center of the circle is defined as the center of bearing 1d. A distance W between the center of bell 1a or approach 1b and the center of bearing 1d is referred to as the concentricity(Method of Measuring Roundness)

[0032] In the present application, a difference between a maximum diameter and a minimum diameter in measurement of a diameter of a wire rod subjected to wire drawing works by the die in directions around 360 degrees is defined as the roundness. For measurement, a wire diameter measurement device (LDSN) manufactured by Cersa is employed, and the diameter of the drawn wire rod is measured at 250 points around 360 degrees. A difference between a maximum value and a minimum value of measurement values at these 250 points is defined as the roundness. The shape of die hole 1h (the shape of bearing 1d) is transferred to the wire rod and the roundness of bearing 1d is reflected on the wire rod.

[0033] The roundness of bearing 1d is a difference between a maximum value and a minimum value of distances from the center of bearing 1d calculated by circle approximation at the contour of bearing 1d obtained in a procedure above.Details of the Embodiment in the Present DisclosureExample 1(Evaluation of Wire Drawing by Binderless (BL) Diamond Die)

[0034] In order to check performance depending on difference in source material for the die, three types of dies identical in shape were prepared and evaluated.Die Source Material

[0035] Three types of A. binderless PCD die, B. single crystal diamond die, and C. PCD die containing a binder were prepared. An average particle size of diamond of A. binderless PCD die was 0.05 μm (50 nm). Tables 1 and 2 show shapes of these types.TABLE 1Tool SpecificationsHole ShapeReductionHole Accuracy (μm)BearingAngleRoundnessSampleSourceDiameter(OpeningBearingof Hole inNumberMaterialD (mm)Angle) °LengthBearingConcentricity1BLPCD0.081230% D0.20.52BLPCD0.08830% D0.20.53BLPCD0.08530% D0.20.54BLPCD0.08430% D0.20.5101BLPCD0.08330% D0.20.55BLPCD0.081430% D0.20.5102BLPCD0.081530% D0.20.52BLPCD0.08830% D0.20.512BLPCD0.08850% D0.20.513BLPCD0.08870% D0.20.514BLPCD0.088100% D 0.20.5111BLPCD0.088110% D 0.20.515BLPCD0.08820% D0.20.5112BLPCD0.08810% D0.20.52BLPCD0.08830% D0.20.531BLPCD0.08830% D0.20.332BLPCD0.08830% D0.20.833BLPCD0.08830% D0.21.0131BLPCD0.08830% D0.21.2TABLE 2Tool SpecificationsHole ShapeReductionHole Accuracy (μm)BearingAngleRoundnessSampleSourceDiameter(OpeningBearingof Hole inNumberMaterialD (mm)Angle) °LengthBearingConcentricity2BLPCD0.08830% D0.20.541BLPCD0.08830% D0.10.542BLPCD0.08830% D0.50.5141BLPCD0.08830% D0.70.52BLPCD0.08830% D0.20.5151Single0.08830% D0.20.5Crystal152PCD0.08830% D0.20.5HavingParticleSize of1 μm2BLPCD0.08830% D0.20.561BLPCD0.1830% D0.20.562BLPCD0.04830% D0.20.563BLPCD0.015830% D0.20.564BLPCD0.015830% D0.20.865BLPCD0.015830% D0.21.0166BLPCD0.015830% D0.21.2In Tables 1 and 2, “BLPCD” refers to polycrystalline diamond which is diamond manufactured by direct conversion of non-diamond carbon to diamond under an ultra-high pressure and temperature and composed substantially only of diamond where no binder is present.

[0037] “PCD having particle size of 1 μm” refers to polycrystalline diamond composed of polycrystalline diamond having an average particle size of 1 μm, the polycrystalline diamond containing 5 volume % or more of binder and diamond as the remainder.

[0038] With this die, an SUS wire rod was drawn at a linear speed of 500 m / min. under an oil lubricated condition. In an example of diameter D of φ0.08 mm, a wire diameter before wire drawing was set to φ0.087 mm. In an example of diameter D of φ0.10 mm, a wire diameter before wire drawing was set to φ0.109 mm. In an example of diameter D of φ0.04 mm, a wire diameter before wire drawing was set to φ0.0435 mm. In an example of diameter D of φ0.15 mm, a wire diameter before wire drawing was set to φ0.0164 mm. These SUS wire rods were subjected to wire drawing works by each die, and when the roundness of the drawn wire rod attained to 0.3 μm or when increment of the wire diameter as compared with the wire diameter of the drawn wire rod at a time point of 100 m after start of wire drawing attained to 0.3 μm, determination as the end of lifetime of the die was made. Alternatively, when curl (warpage of which R is less than 30 mm) of the wire rod occurs, determination as the end of lifetime of the die was made. Tables 3 and 4 show results.TABLE 3RoundnessAmount of(AfterIncreaseCurlWirein WireStateCurlSampleLifetimeDrawingDiameter(InitialStateNumber(km)by 30 km)(μm)Stage)(30 km)1A0.20.1AA2A0.20.1AA3A0.20AA4B0.20AA101C0.30CC5B0.3−0.1AB102C0.3−0.2BC2A0.20.1AA12A0.20AA13A0.20AA14B0.20AB111C0.30BC15B0.20.3BB112C0.40.5BC2A0.20.1AA31A0.20AA32A0.30.1AA: WithoutCurl33B0.30.2AB: Occurrenceof Curl atPoint at 50km131C0.60.5CCTABLE 4RoundnessAmount of(AfterIncreaseCurlWirein WireStateCurlSampleLifetimeDrawingDiameter(InitialStateNumber(km)by 30 km)(μm)Stage)(30 km)2A0.20.1AA41A0.20.1AA42A0.20AA141B0.30.2BC2A0.20.1AA151C1.21.3AC152C0.50.2AB2A0.20.1AA61A0.30.2AA62A0.20.1AA63A0.20.1AA64A0.20.2AA65B0.30.2BB166CWireWireCWiredrawingdrawingdrawingcould notcould notcould notbe donebe donebe doneIn “Lifetime” in Tables 3 and 4, “A” represents lifetime not shorter than 60 km. “B” represents lifetime longer than 30 km and shorter than 60 km, and “C” represents lifetime not longer than 30 km.

[0040] “Amount of increase in wire diameter” refers to a difference between the wire diameter at a time point of 100 m after start of wire drawing and the wire diameter at a time point of 30 km after wire drawing. The wire diameter is defined as an average value in measurement of the diameter of the wire rod subjected to wire drawing works by the die in directions around 360 degrees. For measurement, a wire diameter measurement device (LDSN) manufactured by Cersa was employed, and the diameter of the drawn wire rod was measured at 250 points around 360 degrees. There is also a sample having a negative amount of increase in wire diameter. This is because use of high-hardness diamond such as BLPCD may cause ring wear and the wire rod may be ground and decrease in thickness during wire drawing.

[0041] The “curl state” was evaluated as “A” when R of warpage of the drawn wire rod was not less than 50 mm, evaluated as “B” when R was not less than 30 mm and less than 50 mm, and evaluated as “C” when R was less than 30 mm.

[0042] In the die having lifetime evaluated as “C”, the curl state was poor from the initial stage and deteriorated with progress of wire drawing works, and the die failed in wire drawing by 30 km. Therefore, roundness of the bearing at the time of the end of the lifetime of the die was shown as the “roundness (after wire drawing by 30 km).”

[0043] In sample number 166, break occurred in a stage of wire drawing by 5 km. Since evaluation could not be continued, wire drawing was stopped.

[0044] It can be seen from Tables 3 and 4 that, when the reduction angle was not equal to or smaller than 14°, the length of the bearing was not smaller than 20% D and not larger than 100% D, the concentricity between the bearing and the bell or the approach was equal to or smaller than 1.0 μm, and the roundness of the hole in the bearing was equal to or smaller than 0.5 μm, evaluation of B or higher was obtained in evaluation of lifetime, the curl state (initial stage), and the curl state (30 km).

[0045] It can be seen that there were more evaluations A when the reduction angle was more preferably not smaller than 5° and not larger than 12°. Furthermore, it can be seen that there were more evaluations A when the length of the bearing was within a range not smaller than 30% D and not larger than 70% D. In addition, it can be seen that there were more evaluations A when the concentricity was equal to or smaller than 0.8 μm.(Additional Aspect 1)

[0046] A wire drawing die is provided with a bearing, the bearing having a diameter D smaller than 100 μm,

[0047] a hole is provided in polycrystalline diamond composed substantially only of diamond having an average particle size equal to or smaller than 500 nm,

[0048] a reduction angle is not smaller than 4° and not larger than 14°,

[0049] a length of the bearing is not smaller than 20% D and not larger than 100% D,

[0050] a concentricity between the bearing and a bell or an approach is equal to or smaller than 1.0 μm, and

[0051] a roundness of a hole in the bearing is equal to or smaller than 0.5 μm.(Additional Aspect 2)

[0052] In the wire drawing die according to Additional Aspect 1.

[0053] the reduction angle is not smaller than 5° and not larger than 12°.(Additional Aspect 3)

[0054] In the wire drawing die according to Additional Aspect 1 or 2,

[0055] the length of the bearing is not smaller than 30% D and not larger than 70% D.(Additional Aspect 4)

[0056] In the wire drawing die according to any one of Additional Aspects 1 to 3,

[0057] the concentricity between the bearing and the bell or the approach is equal to or smaller than 0.8 μm.

[0058] It should be understood that the embodiment and the example disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the terms of the claims rather than the embodiment above and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.REFERENCE SIGNS LIST

[0059] 1 die; 1a bell; 1b approach; 1c reduction; 1d bearing, 1e back relief, 1f exit; 1h die hole, 1p centerline; 11c reference point; 12a, 12b, 12c, 13a, 13b, 13c tangent.

Examples

example 1

(Evaluation of Wire Drawing by Binderless (BL) Diamond Die)

[0034]In order to check performance depending on difference in source material for the die, three types of dies identical in shape were prepared and evaluated.

Die Source Material

[0035]Three types of A. binderless PCD die, B. single crystal diamond die, and C. PCD die containing a binder were prepared. An average particle size of diamond of A. binderless PCD die was 0.05 μm (50 nm). Tables 1 and 2 show shapes of these types.

TABLE 1Tool SpecificationsHole ShapeReductionHole Accuracy (μm)BearingAngleRoundnessSampleSourceDiameter(OpeningBearingof Hole inNumberMaterialD (mm)Angle) °LengthBearingConcentricity1BLPCD0.081230% D0.20.52BLPCD0.08830% D0.20.53BLPCD0.08530% D0.20.54BLPCD0.08430% D0.20.5101BLPCD0.08330% D0.20.55BLPCD0.081430% D0.20.5102BLPCD0.081530% D0.20.52BLPCD0.08830% D0.20.512BLPCD0.08850% D0.20.513BLPCD0.08870% D0.20.514BLPCD0.088100% D 0.20.5111BLPCD0.088110% D 0.20.515BLPCD0.08820% D0.20.5112BLPCD0.08810% D0.20.52...

Claims

1. A wire drawing die provided with a bearing, the bearing having a diameter D smaller than 100 μm, whereina hole is provided in polycrystalline diamond composed substantially only of diamond having an average particle size equal to or smaller than 500 nm,a reduction angle is not smaller than 4° and not larger than 14°,a length of the bearing is not smaller than 20% D and not larger than 100% D,a concentricity between the bearing and a bell or an approach is equal to or smaller than 1.0 μm, anda roundness of a hole in the bearing is equal to or smaller than 0.5 μm.

2. The wire drawing die according to claim 1, whereinthe reduction angle is not smaller than 5° and not larger than 12°.

3. The wire drawing die according to claim 1, whereinthe length of the bearing is not smaller than 30% D and not larger than 70% D.

4. The wire drawing die according to claim 1, whereinthe concentricity between the bearing and the bell or the approach is equal to or smaller than 0.8 μm.

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