Tungsten wire rope and endoscope snare using the same

Abstract

To provide a wire rope or a miniature rope increased in abrasion resistance and tensile strength with high yield and capable of suppressing reduction of strength caused by a twisted wire, wherein the wire rope has advantages of high shock resistance because of the use of the twisted wire, high flexibility and the like, durability must also be high because of repeated bendability, the wire rope is used for an endoscope, single crystal pulling-up, a filament, motion transmission of a precision device, or the like, and particularly, high strength, low elongation, high durability, and high elasticity are required of the miniature rope used for an endoscope without enlarging the outer diameter.SOLUTION: According to an embodiment, a tungsten wire rope or a miniature rope is composed of tungsten strands with a rhenium content of 3 wt%-30 wt%, wherein 3-40 pieces of the tungsten strands are arranged.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] An embodiment of the present invention relates to a tungsten wire rope and an endoscopic snare using the same. [Background technology]

[0002] Wire ropes have the advantages of being highly impact resistant and flexible due to the twisted wires. They are also required to be highly durable because they are repeatedly bent. Wire ropes are used in endoscopes, single crystal pulling, filaments, and for transmitting motion in precision equipment. In particular, wire ropes (miniature ropes) used in endoscopes require high strength, low elongation, high durability, and high elasticity without increasing the outer diameter. Figure 1 shows an example of the tip of a polypectomy (endoscopic polypectomy) snare. There is a control section (handle: not shown) on the opposite side of the tip. By manipulating the handle, snare loop 11 is extended or retracted from sheath 12 via control wire 13. This allows colon polyps and other such objects to be tightly bound and removed. Endoscopic snares must be resistant to bending, as their own elasticity allows them to maintain their loop shape before and after removal. In recent years, they have also been used to crush hard stones such as gallstones, so they require thinner and stronger structures.

[0003] Wire ropes used for endoscopes are twisted wires with 6, 18, 36, or more surrounding wires wound around a single core wire, and the core wire and surrounding wires are made of stainless steel (SUS) or a combination of different materials such as stainless steel and tungsten (W).

[0004] Japanese Patent Laid-Open Publication No. 2001-226888 (Patent Document 1) discloses a wire rope with tungsten core wires and stainless steel peripheral wires. The peripheral wires are stainless steel, which has excellent abrasion resistance, and do not easily wear even when rubbed against hard objects, while the core wires are tungsten, which has high tensile strength, and can increase tensile strength without increasing the wire thickness, thereby compensating for the low abrasion resistance of tungsten and increasing tensile strength. Japanese Patent No. 6631979 (Patent Document 2) discloses a wire rope in which the core wires are made of stainless steel and the peripheral wires are made of tungsten. The wire rope has improved wear resistance and flexibility, and high tensile strength, due to the outer periphery of the core wires being harder than the center. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2001-226888 [Patent Document 2] Patent No. 6631979 Summary of the Invention [Problem to be solved by the invention]

[0006] In Patent Document 1, tungsten is used for the core wire to increase tensile strength, but the peripheral wires remain unchanged from conventional ones, so the improvement effect is not necessarily sufficient. In Patent Document 2, tungsten is used for the peripheral wire, but the strength of the core wire remains unchanged, so the strength of all wires is not improved. In addition, the peripheral wires are in contact with each other, which does not address the drawback of tungsten, as described in Patent Document 1, that it has low wear resistance and easily breaks when rubbed against a hard object. Furthermore, when producing the core wire, a method of generating a difference in the inner and outer cross-sectional hardness of the core wire by wire drawing using a die can cause residual stress inside, which can induce cracks and reduce the yield of the wire drawing process.

[0007] The breaking strength of a stranded wire divided by the "cross-sectional area of the wire x number of twists" is the "wire-equivalent breaking strength." For stainless steel wire ropes, the wire-equivalent breaking strength is lower than the breaking strength of a single wire. Table 1 shows the results of a tensile test on a wire rope with a wire size of Φ0.12 mm and 7 twists, in which both the core wire and the surrounding wires are stainless steel.

[0008] [Table 1]

[0009] The problem to be solved by the present invention is to provide a wire rope which has improved abrasion resistance and tensile strength with high yield and which is free from deterioration of strength due to stranding. [Means for solving the problem]

[0010] In order to solve the above problems, the tungsten wire rope according to the embodiment is made of tungsten wires having a rhenium content of 3 mass% or more and 30 mass% or less, with the remainder being W and unavoidable impurities, and the wires are arranged in an arrangement of 3 to 40 wires. The tensile strength of the tungsten wire is 3600 MPa or more. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 2 is a plan cross-sectional view showing an example of the tip portion of an endoscope snare. [Figure 2] 1 is a cross-sectional view showing an example of a wire rope according to an embodiment. [Figure 3] FIG. 10 is a cross-sectional view showing another example of a wire rope according to an embodiment. [Figure 4] Rhenium-tungsten binary phase diagram DETAILED DESCRIPTION OF THE INVENTION

[0012] 2(a) shows a cross-sectional view of a wire rope according to an embodiment, in which a central core wire 22 is provided with six peripheral wires 23 (23a, 23b, 23c, 23d, 23e, 23f) wound around the central core wire, and the entire structure is formed as a single stranded wire (wire rope). The winding direction of the peripheral wires 23 around the central core wire 22 may be either a so-called Z twist or the opposite S twist.

[0013] Figure 2(b) shows a stranded wire with 19 peripheral wires wound around a single core wire. Figure 2(c) shows a stranded wire with 37 peripheral wires wound around it. Figure 2(d) shows a stranded wire composed of only 24 peripheral wires. This type of twisting is also called a cross lay or point contact lay due to the contact state of the wires. Wires of approximately the same diameter are twisted together so that the angles of each layer are approximately equal. The lengths of the wires twisted in each layer are equal, and the wires between each layer are in point contact. With two wires, the wires only contact each other at one point, which is unstable. For this reason, three or more wires are recommended. Also, for ropes of the same diameter, the more wires there are, the thinner the wire diameter becomes. This increases the rope's flexibility, but also decreases its strength, abrasion resistance, and deformation resistance. For this reason, 40 or fewer wires are preferable. The number of wires between 3 and 40 refers to the total number of wires in both the axial wire and the peripheral wire.

[0014] Figure 3 shows an example of an embodiment of a wire rope using wires of different diameters. Figure 3(a) is called a Seale type, in which the number of wires in the inner layer 32 and the outer layer 33 is the same, and the outer layer wires are completely contained in the recesses of the inner layer wires. Figure 3(b) is called a Warrington type, in which the outer layer wires are of two sizes, large and small, and the number of wires in the outer layer is twice the number of wires in the inner layer. The combination of the inner and outer layers reduces gaps. Figure 3(c) is called a Filler type, in which the number of wires in the outer layer is twice the number of wires in the inner layer, and the gaps between the inner and outer layers are filled with thin wires (filler wires) 34, the same number as the inner layer wires. Figure 3(d) is called a Warrington Seale type, which is a combination of the Warrington and Seal types.

[0015] A wire rope formed by twisting a plurality of wire ropes of the above embodiment can also be implemented.

[0016] The axial core wire 22 and the peripheral wire 23 have a rhenium (Re) content of 3 mass % or more 30 mass % or less of tungsten wires (ReW wires). Hereinafter, tungsten containing Re may also be referred to as ReW. The Re content of each wire is not particularly limited as long as it is within the range, but in order to improve the homogeneity of the wire rope, it is preferable that all wires have the same Re content. Note that the same Re content means that it is within ±2.0 of the average value. mass This indicates that the value is within %.

[0017] When pulled as a twisted wire, each wire is twisted. This causes the equivalent breaking strength of the twisted wire to be lower than the breaking strength of a single wire. The more elastically stretched the wire is, the more twisted the wire is, so the lower the elastic modulus of the wire, the greater the decrease in the equivalent breaking strength of the twisted wire. The equivalent breaking strength is the breaking strength of the twisted wire divided by the cross-sectional area of the number of wires. For example, as shown in Table 1, the breaking strength of a 0.12mm Φ SUS wire is 2440MPa on its own. The breaking strength of a 0.12mm Φ x 7-strand wire is 172N, which when divided by the cross-sectional area of the seven wires, is 2170MPa.

[0018] The breaking strength equivalent to the wire is preferably greater than 90% of the breaking strength of the wire. This allows the diameter of the wire rope to be made smaller while still maintaining the required strength. By using tungsten, which has a high modulus of elasticity, as the wire, it is possible to prevent a decrease in the breaking strength equivalent to the wire. Furthermore, the low abrasion resistance of tungsten is due to the fact that the Re content is 3. mass This is improved with ReW of % or more.

[0019] Re content is 20 mass If the Re content is less than 20%, the inherent difficulty of tungsten to be worked is not improved, and cracks are likely to occur in the wire during wire drawing. This may result in a decrease in yield due to breakage during the wire drawing and twisting processes. mass % or more is desirable.

[0020] Figure 4 shows the binary phase diagram of Re-tungsten. When the Re content is higher than about 28 wt%, as shown in 41, it is not possible to form a solid solution with tungsten, and the σ phase shown in region 42 is generated. This phase is very hard, and can become the origin of fracture during wire drawing, reducing the processing yield, or can become the origin of fracture during use as wire, reducing durability. Therefore, the Re content is set to 30 mass The Re content of the ReW wire is preferably 3% or less. mass % or more 30 mass % or less, even 20 mass % or more 30 mass% or less is preferable.

[0021] Since a higher strength of the wire allows the wire to be thinner, it is preferable that the tensile strength of all ReW wires be 3600 MPa or more.

[0022] The diameter of the wire is preferably 0.15 mm or less. When the diameter of the wire is 0.15 mm or less, twisting becomes easy. When the diameter of the wire exceeds 0.15 mm, twisting becomes difficult and wire breakage becomes more likely. The lower limit of the diameter of the wire is not particularly limited, but 0.01 mm or more is preferable. When the diameter is less than 0.01 mm, the wire diameter is too thin and there is a possibility of wire breakage. For this reason, the diameter of the wire is preferably 0.01 mm or more and 0.15 mm or less, and more preferably 0.05 mm or more and 0.13 mm or less.

[0023] The present invention provides a thinner, stronger, and more durable tungsten wire rope that can be used in endoscopic snares and for crushing hard stones, such as gallstones, which are subject to a heavy load.

[0024] Next, a method for manufacturing a ReW wire according to this embodiment will be described. The manufacturing method is not particularly limited, but the following method can be given as an example.

[0025] W powder and Re powder were mixed together. mass % or more, 30 mass% or less. The mixing method is not particularly limited, but a method of using water or an alcohol-based solution to form a slurry of powders and mixing them is particularly preferred because it produces powder with good dispersibility. The Re powder to be mixed preferably has a maximum particle size of less than 100 μm. Also, an average particle size of less than 20 μm is preferred. The W powder is either pure W powder excluding unavoidable impurities, or doped W powder containing a K amount taking into consideration the yield to wire rod. The W powder preferably has an average particle size of less than 30 μm. If the maximum particle size or average particle size of the Re powder is above the above range, coarse σ phases are likely to be formed. Also, if the average particle size of the W powder is above the above range, formability decreases during the subsequent press molding process, and breakage, chipping, cracks, etc. are likely to occur in the molded body.

[0026] For example, if the Re content is 18 mass When producing a W-Re mixed powder with a Re content of more than 18%, mass % or less is produced by powder metallurgy or melting, and then finely pulverized by conventional methods. Another method is to mix in the remaining Re to achieve the desired composition. Hereafter, tungsten wire containing Re may be referred to as ReW wire.

[0027] Next, the mixed powder is placed in a predetermined mold and press-molded. The pressing pressure at this time is preferably 100 MPa or higher. To facilitate handling, the molded body may be pre-sintered at 1200 to 1400°C in a hydrogen furnace. The resulting molded body is sintered in a hydrogen atmosphere, an inert gas atmosphere such as argon, or a vacuum. The sintering temperature is preferably 2125°C or higher. If the temperature is lower than 2125°C, densification by sintering will not progress sufficiently. The upper limit of the sintering temperature is 3400°C (below the melting point of W, 3422°C). The relative density after sintering is preferably 90% or higher. By ensuring that the relative density of the sintered body is 90% or higher, it is possible to reduce the occurrence of cracks, chips, breaks, etc. in the subsequent rolling (SW) process.

[0028] Molding and sintering may be performed simultaneously by hot pressing in a hydrogen atmosphere, an inert gas atmosphere such as argon, or in a vacuum. The pressing pressure is preferably 100 MPa or more, and the heating temperature is preferably 1700°C to 2825°C. This hot pressing method can produce a dense sintered body even at a relatively low temperature.

[0029] The sintered body obtained in this sintering step is subjected to a first rolling (SW) process. The first SW process is preferably carried out at a heating temperature of 1300 to 1600°C. The reduction rate of the cross-sectional area (area reduction rate) in one heat treatment (one heat) is preferably 5 to 15%.

[0030] Instead of the first SW process, rolling may be performed. The rolling is preferably performed at a heating temperature of 1200 to 1600°C. The area reduction rate per heat is preferably 40 to 75%. As the rolling mill, a two-way roller rolling mill, a four-way roller rolling mill, a die roll rolling mill, or the like can be used. Rolling can significantly improve manufacturing efficiency. Furthermore, the first rolling and punching process may be combined.

[0031] The sintered body (ReW bar) that has undergone either the first SW process or rolling process is subjected to the second SW process. The second SW process is preferably carried out at a heating temperature of 1200 to 1500°C. The area reduction rate per heat is preferably about 5 to 20%.

[0032] The ReW bar that has undergone the second SW process is then subjected to a recrystallization treatment, which can be carried out using, for example, a high-frequency heating device in a hydrogen atmosphere, an inert gas atmosphere such as argon, or a vacuum at a treatment temperature in the range of 1800 to 2600°C.

[0033] The ReW bar that has completed the recrystallization treatment is subjected to a third SW process. The third SW process is preferably carried out at a heating temperature of 1200 to 1500°C. The area reduction rate per heat is preferably about 10 to 30%. The third SW process is carried out until the ReW bar has a diameter that can be drawn (preferably 2 to 4 mm).

[0034] After the third SW process, the ReW rod is drawn to a diameter of 0.011 to 0.180 mm. The processing temperature is preferably 600 to 1100°C. The maximum processing temperature varies depending on the wire diameter, with higher diameters being higher. The processing temperature also varies depending on the Re content, with higher temperatures being higher. If the temperature is lower than the maximum processing temperature, cracks and breakage occur frequently. If the temperature is higher than the maximum processing temperature, seizure occurs between the ReW wire and the die, the deformation resistance of the ReW wire decreases, and the drawing force causes diameter fluctuations (thinning) after drawing. The area reduction ratio is preferably 15 to 35%. If it is less than 15%, differences in the internal and external structure and residual stress occur during processing, causing cracks. If it is greater than 35%, the drawing force becomes too large, causing large diameter fluctuations after drawing and resulting in breakage. The drawing speed is determined by the balance between the capacity of the heating device, the distance from the device to the die, and the area reduction ratio. Polishing can be performed during the wire drawing process. The polishing process can be performed by electrochemical polishing (electrolytic polishing) in a sodium hydroxide solution with a concentration of 7 to 15 wt %, for example. Heat treatment to relieve strain may also be performed.

[0035] The wire after wire drawing is electrolytically polished to obtain a ReW wire with a diameter of 0.01 to 0.15 mm. The electrolysis rate is preferably 10% or more and 30% or less. This wire is twisted by a known method to obtain a wire rope. This wire rope is also used to make an endoscopic snare.

[0036] (Example) Re content 3 mass % to 33 mass % and sintered bodies were produced by the above process. These sintered bodies were then processed to form wires. The Re content and wire size are shown in Table 2. The Re content was analyzed by inductively coupled plasma optical emission spectroscopy (ICP-OES). The wire diameter was measured using a laser diameter measuring device (Mitutoyo laser scan micrometer) with a measurement interval of 0.01 seconds, a minimum display of 0.01 μm, and a wire speed of 100 m / min. The breaking strength of the wire was measured using a universal tension and compression testing machine (Minebea TGE-5kN). The test piece was chucked with a flat plate via sandpaper to prevent slipping, and both ends were fixed to the device. The gauge length was 50 mm, and the tensile test was performed at a speed of 10 mm / min. If the fracture was not between the gauge points, the test was repeated. The measurement was carried out three times and the average value was calculated.

[0037] [Table 2]

[0038] Rhenium content 3 3mass % of wire 7 broke in the second rolling step and could not be processed to 0.12 mm.

[0039] Table 3 shows the properties of each wire rope made using the above wires. In Comparative Example 3, wire 9 was used for one core wire and wire 8 for six peripheral wires. The "breaking strength of a single wire" in Comparative Example 3 was calculated by averaging the breaking strength of the individual wires used, "(2440 x 6 + 2690) / 7". When the wire material was changed from stainless steel to tungsten, the decrease in the strength ratio between the strength of a single wire and the strength of the individual wire was improved. The change in material to tungsten also had an effect on the elastic modulus of the wire rope. The breaking strength of the wire rope improved with an increase in the Re content. When the Re content was 20 mass %, the yield decreased due to cracks during the wire drawing process. In addition, the wire using wire 2 with a wire diameter of 0.2 mm also had a low yield during the twisting process.

[0040] The yield was calculated as the cumulative total of the yield from the wire drawing process and the yield from the twisted wire process. For the yield from the wire drawing process, a penetrating eddy current flaw detector was used to wind the wire at a constant speed, and the number of signals detected under measurement conditions set according to the diameter was counted as the number of cracks. A count of 5 or more at 0.5 kg was calculated as NG. For the twisted wire process, 100 m of twisted wire was cut into 100 pieces with a product length of 1 m, and then the yield was calculated as the number of good products found in a visual inspection. A decrease of 20% or more from the set yield was marked "X", a decrease of 20-10% was marked "△", a decrease of 10-0% was marked "〇", and a decrease of more than the set yield was marked "◎".

[0041] The breaking strength of the stranded wire was also measured using a universal tension and compression testing machine (Minebea TGE-5kN), just like the wire itself. The test piece was chucked with a flat plate via sandpaper to prevent slipping, and both ends were fixed to the device. The tensile test was performed with a gauge length of 50 mm at a speed of 10 mm / min. If the fracture was not between the gauge points, it was measured again. The measurement was performed three times, and the average value was taken.

[0042] There are several mechanical testing methods for measuring the modulus of elasticity, including tensile tests, compression tests, torsion tests, and bending tests, but this time we used a tensile test. In a tensile test, a tensile load is applied to the test piece, and the modulus of elasticity E is calculated by measuring the displacement. In this test, a universal tension and compression testing machine (Minebea TGE-5kN) was used, and a strain gauge was attached at 50 mm from the 100 mm long specimen. The specimen was stretched at a tension rate of 1 mm / min, and the load-displacement relationship was determined. In the tensile test, the modulus of elasticity was calculated using the following formula: E = (σ n+1 -σ n ) / (ε n+1 -ε n ) where E is the elastic modulus, σ is the tensile stress, ε is the tensile strain obtained from the displacement of the strain gauge, and (σ n+1 -σ n ) is the change in tensile stress when the tensile load is changed, (ε n+1 -ε n ) is the amount of change in tensile strain when the tensile load is changed. The measurement was carried out three times, and the average value was used.

[0043] [Table 3]

[0044] As can be seen from the table, the wire rope according to the embodiment has improved abrasion resistance (yield) and tensile strength, and can suppress a decrease in strength due to stranding.

[0045] Although several embodiments of the present invention have been described above, these embodiments are presented by way of example only and are not intended to limit the scope of the invention. These novel embodiments can be embodied in various other forms, and various omissions, substitutions, modifications, etc. can be made without departing from the spirit of the invention. Modifications of these embodiments are included within the scope and spirit of the invention, as well as within the scope of the invention and its equivalents as set forth in the claims. Furthermore, the above-described embodiments can be implemented in combination with each other. The inventions described in the original claims of this application are set forth below. [1] A tungsten wire rope consisting of tungsten wires with a rhenium content of 3 wt% or more and 30 wt% or less, and the wires are arranged in an arrangement of 3 to 40 wires. [2] The tungsten wire rope according to [1], wherein the tensile strength of the tungsten wire is 3600 MPa or more. [3] A tungsten wire rope according to any one of [1] and [2], wherein the diameter of the tungsten wire is 0.15 mm or less. [4] A tungsten wire rope according to any one of [1] to [3], wherein the rhenium content in the wires is 20 wt% or more and 30 wt% or less. [5] A tungsten wire rope according to any one of [1] to [4], in which the breaking strength of the stranded wires divided by the cross-sectional area of the number of wires is greater than 90% of the breaking strength of the wires. [6] A wire rope characterized by being formed by twisting a plurality of tungsten wire ropes according to any one of [1] to [5]. [7] An endoscope snare formed by twisting a plurality of tungsten wire ropes according to any one of [1] to [5]. [Explanation of symbols]

[0046] 11...Snare Loop 12...Sheath part 13...Operating wire 2(a), 2(b), 2(c), 2(d)...Wire rope 22...Shaft core wire 23a, 23b, 23c, 23d, 23e, 23f...Peripheral wires 32...Inner layer wire 33…Outer layer strand 34...Filler wire 41...Tungsten wt% at the rhenium solid solubility limit 42...Tungsten-rhenium σ phase region

Claims

1. A tungsten wire rope comprising tungsten wires having a rhenium content of 3 mass% or more and 30 mass% or less, with the remainder being W and unavoidable impurities, wherein the tungsten wires have a tensile strength of 3600 MPa or more, and the wires are arranged in an arrangement of 3 to 40 wires.

2. 2. The tungsten wire rope according to claim 1, wherein the diameter of the tungsten wire is 0.15 mm or less.

3. 3. The tungsten wire rope according to claim 1, wherein the rhenium content of the wires is 20 mass% or more and 30 mass% or less.

4. 4. The tungsten wire rope according to claim 1, wherein the breaking strength equivalent to the stranded wires divided by the cross-sectional area of the number of stranded wires is greater than 90% of the breaking strength of the stranded wires.

5. A wire rope formed by twisting a plurality of tungsten wire ropes according to any one of claims 1 to 4.

6. 5. An endoscope snare formed by twisting a plurality of tungsten wire ropes according to claim 1.

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