Intermittent electrochemical polishing method for inner surface of capillary metal pipe

Abstract

The invention discloses an intermittent electrochemical polishing method for the inner surface of a capillary metal tube, which comprises the following steps: taking the capillary metal tube as an anode, and introducing a cathode filament into the capillary metal tube to form an anode-cathode system; the polishing solution flows in the capillary metal tube, intermittent electrochemical polishing treatment is conducted on the capillary metal tube, the intermittent electrochemical polishing current is 0.5 A to 10 A, the intermittent time is 5 s to 60 s, the polishing time is 5 s to 60 s, and the overall polishing time is 2 min to 60 min. The inner surface roughness Ra is smaller than or equal to 0.1 micron, the uniformity reaches 95%, the process efficiency is improved by 30%, and the method is particularly suitable for the fields with high-precision requirements such as medical instruments and microreactors.

Description

Technical Field

[0001] The present invention relates to the technology of metal surface treatment, and particularly to an intermittent electrochemical polishing method applicable to the inner surface of capillary metal tubes. Background Art

[0002] Due to their excellent mechanical properties and microscale fluid transmission characteristics, metal capillary tubes are widely used in fields such as precision medical devices (such as cardiovascular stents, minimally invasive surgical catheters), aerospace fuel injection systems, and microreactors. However, the surface finish of the inner surface of such tubes directly determines their performance. For example, a rough inner wall of a cardiovascular stent may lead to thrombus formation, and defects on the inner surface of a microreactor will cause reactant residue or uneven mass transfer. Therefore, achieving high-precision polishing (surface roughness Ra ≤ 0.1 μm) of the inner surface of capillary metal tubes is a key technical bottleneck for improving the reliability of devices. In conventional physical methods, particles cannot uniformly and fully act on the inner surface of capillary tubes, and conventional chemical methods cannot ensure the full action of reactants on the inner surface. As a result, it is very difficult for existing methods and technologies to achieve modification of the inner surface of capillary metal tubes, such as polishing, etching, and preparation of functional coatings on the inner surface of capillary tubes. Summary of the Invention

[0003] In view of the above-mentioned defects or deficiencies in the prior art, it is desirable to provide an intermittent electrochemical polishing method for the inner surface of capillary metal tubes with simple process and low cost to solve the above technical problems.

[0004] An intermittent electrochemical polishing method for the inner surface of capillary metal tubes, wherein the capillary metal tube is used as the anode, and a cathode wire is passed into the interior of the capillary metal tube to form an anode-cathode system; the polishing solution flows inside the capillary metal tube to perform intermittent electrochemical polishing on the capillary metal tube. The intermittent electrochemical polishing current is 0.5 A to 10 A, the intermittent time is 5 s to 60 s, the polishing time is 5 s to 60 s, and the overall polishing time is 2 min to 60 min.

[0005] Furthermore, the polishing time and the intermittent time alternate with each other. When polishing, the polishing solution stops flowing, and when intermittent, the polishing solution starts to flow, taking away all the reactants generated during polishing and filling the inner surface of the capillary metal tube with the polishing solution again.

[0006] Furthermore, the temperature of the polishing solution is 30°C to 100°C, and the flow rate of the polishing solution is 10 mL·min -1 ~1000 mL·min -1 。

[0007] Furthermore, the capillary metal tube is made of stainless steel, titanium or titanium alloy, and the inner diameter is 0.4 mm to 5.0 mm.

[0008] Further, the volume percentage of water in the electrochemical polishing solution is 0% to 50%.

[0009] Further, after the electrochemical polishing, a post-treatment step is further included: cleaning the capillary metal tube with deionized water and absolute ethanol, and drying it with nitrogen and then drying it at 50°C to 120°C for 1 h to 24 h.

[0010] Further, the diameter of the cathode wire is 0.1 mm to 0.8 mm, and it is located at the central position of the capillary metal tube.

[0011] Further, when the length of the capillary metal tube is ≥200 mm, segmented polishing is adopted, and after each segment of polishing is completed, it is reversely installed for another segment of polishing.

[0012] Further, the method uses a polishing device, including a bracket for vertically fixing the capillary metal tube; a peristaltic pump, and the peristaltic pump forms a loop with the polishing solution and the capillary metal tube through a pipeline.

[0013] Even further, a capillary metal tube polished by the above method is provided.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0015] The intermittent electrochemical polishing method for the inner surface of the capillary metal tube provided by the present invention significantly solves technical problems such as reactant accumulation, uneven polishing of long tubes, and poor material adaptability in traditional processes by dynamically regulating current, time parameters, and the flow state of the polishing solution. The present invention has efficient reaction control and uniform polishing. By adopting intermittent current control and alternating polishing intervals, combined with the synergistic effect of the stationary (polishing stage) and flowing (intermittent stage) of the polishing solution, reaction products (such as bubbles and metal ions) are forcibly removed to avoid the formation of a "shielding layer", enabling the inner surface to continuously contact fresh polishing solution, with the polishing efficiency increased by more than 30% and the roughness uniformity reaching ±5%. For long capillary tubes (≥200 mm), the segmented polishing eliminates the flow rate difference between the inlet and outlet by reverse installation, and the full-length roughness fluctuation is reduced from ±15% in the traditional process to ±5%, breaking through the length limitation. The present invention is suitable for stainless steel, titanium, and their alloys. By synergistically optimizing the temperature and flow rate of the polishing solution, the high temperature accelerates the reaction rate, and the flow rate matches the pipe diameter to prevent microchannel blockage. The device of the present invention is simplified and has low cost. The vertical bracket and the peristaltic pump circulation system achieve precise fixation of the capillary tube and accurate control of the liquid flow, improving the operation error tolerance. The inner surface roughness Ra of the final product (capillary metal tube) is ≤0.1 μm, and the axial uniformity reaches 95%, which can meet the requirements of high-precision scenarios such as minimally invasive catheters and aviation fuel pipes.

[0016] It should be understood that the content described in the Summary of the Invention section is not intended to limit the key or important features of the embodiments of the present invention, nor to limit the scope of the present invention. Other features of the present invention will become readily understood through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments read in conjunction with the accompanying drawings:

[0018] Figure 1 is the inner diameter is a picture of the inner surface of a capillary stainless steel tube with an inner diameter of 0.8 mm and a length of 200 mm. The scale bar is 1 mm.

[0019] Figure 2 is the inner diameter is the inner surface of a capillary titanium tube with an inner diameter of 0.8 mm and a length of 200 mm after intermittent polishing (the inner diameter is a 0.5 mm cathode wire, and the electro-chemical polishing parameters are 1.2 A - 20 s - 10 min). The scale bar is 1 mm.

[0020] Figure 3 is the inner diameter is the inner surface of a capillary stainless steel tube with an inner diameter of 0.8 mm and a length of 200 mm after intermittent polishing (the inner diameter is a 0.5 mm cathode wire, and the electro-chemical polishing parameters are 1.7 A - 10 s - 10 min). The scale bar is 1 mm.

[0021] Figure 4 is the inner diameter is the inner surface of a capillary stainless steel tube with an inner diameter of 0.8 mm and a length of 400 mm after intermittent polishing (the inner diameter is a 0.5 mm cathode wire, and the electro-chemical polishing parameters are 1.7 A - 10 s - 20 min - polished in two stages). The scale bar is 1 mm.

[0022] Figure 5 is the inner diameter is the inner surface of a capillary stainless steel tube with an inner diameter of 0.8 mm and a length of 400 mm after intermittent polishing (the inner diameter is a 0.5 mm cathode wire, and the electro-chemical polishing parameters are 1.2 A - 20 s - 10 min - polished in two stages). The scale bar is 1 mm.

[0023] Figure 6 is a schematic diagram of intermittent polishing of the inner surface of a capillary metal tube.

[0024] Among them, 1 - power supply; 2 - capillary metal tube; 3 - water bath heating pot; 4 - peristaltic pump; 5 - polishing solution. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0025] The present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It can be understood that the specific embodiments described herein are only used to explain the related invention and do not limit the invention. Additionally, it should be noted that for ease of description, only the parts related to the invention are shown in the drawings.

[0026] It should be noted that, without conflict, the embodiments in the present invention and the features in the embodiments can be combined with each other. The present invention will be described in detail below with reference to the drawings and in conjunction with the embodiments.

[0027] An embodiment of the present invention provides a method for electrochemically polishing the inner surface of an intermittent capillary metal tube. The method for electrochemically polishing the inner surface of the intermittent capillary metal tube can be used for polishing the inner surface of the capillary metal tube, and the method for electrochemically polishing the inner surface of the intermittent capillary metal tube includes:

[0028] According to at least one embodiment of the present disclosure, the method for electrochemically polishing the inner surface of the intermittent capillary metal tube includes a one-stage forming method and a two-stage forming method. According to the capillary metal tubes of different lengths, the method for polishing the inner surface of the capillary metal tube is divided into two types. The capillary metal tube with a length less than 200 mm is formed in one stage, and the capillary metal tube with a length greater than or equal to 200 mm is formed in two stages.

[0029] According to at least one embodiment of the present disclosure, the capillary metal tube is pretreated. The pretreatment includes wire cutting of the capillary metal tube (the capillary metal tube is the anode), cleaning (ultrasonic cleaning in a detergent, tap water, ethanol, and deionized water for 30 minutes each), drying with nitrogen, and drying at a temperature of 50 °C to 120 °C for a time of 1 h to 24 h, so that both the inner and outer surfaces of the capillary metal tube are in a clean state.

[0030] The capillary metal tube is stainless steel and its alloys, titanium and its alloys, and the diameter of the capillary metal tube is 0.4 mm to 5.0 mm.

[0031] According to at least one embodiment of the present disclosure, the capillary metal tube is used as the anode and the cathode is used as the cathode for electrochemical polishing. The capillary metal tube is used as the anode, and the cathode wire is used as the cathode. The cathode wire is located at the central position of the capillary metal tube; the diameter of the cathode wire is 0.1 mm to 0.8 mm, and the specific size of the cathode wire can be selected according to the diameter of the metal tube.

[0032] According to at least one embodiment of the present disclosure, the water content (volume ratio) of the electrochemical polishing solution is different, and the volume percentage of water is 0% to 50%.

[0033] The preparation method of the electrochemically polished solution is as follows: Using glycerol as a solvent, measure 400 mL of glycerol, and sequentially add 400 mL of ethylene glycol, 200 mL of ethanol, 2 mL of perchloric acid, 50 g of sodium chloride, 0.5 g of tartaric acid, 0.5 g of oxalic acid, 0.5 g of citric acid, 0.5 g of sulfamic acid, 0.5 g of urea, and 0.5 g of glucose under stirring conditions, and stir evenly to obtain an electrolytic polishing solution.

[0034] The electrochemically polished solution can also be made of the following components by mass percentage: 65% - 66% ethylene glycol solution, 7% - 8% sulfuric acid solution, 18% - 19% hydroxyethyl sulfate, 0.4% - 0.6% triethanolamine, 0.3% - 0.4% glycolic acid, and the balance is purified water. The sulfuric acid solution is concentrated sulfuric acid with a mass fraction of 98%.

[0035] The electrochemically polished solution can also be a product in the prior art. According to at least one embodiment of the present disclosure, post-treatment is further included after the electrochemical polishing. The post-treatment is to clean the capillary metal tube in deionized water and anhydrous ethanol, blow it dry with nitrogen, dry it, and dry it in a tube furnace. The drying temperature is 50°C - 120°C, and the drying time is 1 h - 24 h.

[0036] Vertically fix the capillary metal tube on a bracket, with the polishing solution flowing in from the top and out from the bottom. Pass the cathode wire into the interior of the capillary metal tube so that the cathode wire is located at the center position of the capillary metal tube, and complete the construction of the polishing system.

[0037] According to at least one embodiment of the present disclosure, during the electrochemically polishing of the capillary metal tube, when the heating temperature of the electrochemically polished solution is 30°C - 100°C (intermittent time), the flow rate of the polishing solution is 10 mL·min -1 ~1000 mL·min -1 ; During the intermittent electrochemical polishing process, the polishing time and the intermittent time alternate with each other. When polishing, the polishing solution stops flowing, and when intermittent, the polishing solution starts to flow, taking away all the reactants generated by polishing and making the interior of the capillary metal tube refilled with the polishing solution. Then the polishing process continues to cycle the above two steps until the final polishing time is reached, and the number of cycles can be calculated based on the polishing time and the final polishing time.

[0038] According to at least one embodiment of the present disclosure, the capillary metal is used as the anode for intermittent electrochemical polishing; the intermittent electrochemical polishing current is 0.5 A to 10 A, the intermittent time is 5 s to 60 s, the polishing time is 5 s to 60 s, and the overall polishing time is 2 min to 60 min. The polishing current determines whether the inner surface can achieve the polishing effect, and there are certain differences in the polishing currents required for capillary metal tubes with different inner diameters and different materials; the polishing time and the intermittent time should be matched with the polishing current. When the polishing current is relatively large, the polishing time can be correspondingly reduced, and the intermittent time is determined according to the situation (the time required to completely remove the gas generated by the polishing reaction and fill the capillary metal tube with the polishing liquid can be determined as the intermittent time). When the polishing current is relatively small, the polishing time and the intermittent time are also adjusted accordingly; the polishing time, the intermittent time and the overall polishing time are adjusted according to the reaction situation, and the final number of cycles can be determined according to the polishing time and the overall polishing time.

[0039] The embodiment of the present invention also provides a method for polishing the inner surface of an intermittent capillary metal tube. Through electrochemical polishing treatment, the capillary metal tube is used as the anode and the cathode wire is used as the cathode, and an intermittent electrochemical polishing method is adopted, that is, one polishing time (when the polishing liquid stops flowing) and one intermittent time (when the polishing liquid flows) form a cycle. After several cycles, the inner surface of the capillary metal tube reaches the purpose of polishing.

[0040] Example 1

[0041] The method for electrochemically polishing the inner surface of an intermittent capillary metal tube provided in this embodiment specifically includes:

[0042] (1) The capillary stainless steel tube with an inner diameter of 0.8 mm and a length of 200 mm is ultrasonically cleaned 3 times in a detergent, deionized water, and absolute ethanol in sequence, with each cleaning time being 30 min. Finally, it is ultrasonically cleaned 2 times with deionized water, each time for 30 min;

[0043] (2) The inner and outer surfaces of the capillary stainless steel tube sample are purged with a nitrogen gun and placed in an electrothermal constant temperature blast drying oven at 80 °C for drying for 24 h;

[0044] (3) The above-mentioned capillary stainless steel tube is vertically fixed, and a cathode wire with a diameter of 0.2 mm and a length of 300 mm is passed into the capillary stainless steel tube so that the cathode wire is at the central position of the capillary stainless steel tube;

[0045] (4) Use a constant temperature water bath to heat the electrochemical polishing liquid to 60 °C, connect the polishing liquid and the capillary stainless steel tube through a pipeline to form a polishing system (a peristaltic pump drives the polishing liquid to circulate), the polishing liquid enters from the top and exits from the bottom, and the flow rate of the polishing liquid is 200 mL·min -1 ;

[0046] (5) Use the capillary stainless steel tube as the anode and the cathode wire as the cathode to perform intermittent polishing on the inner surface of the above-mentioned capillary stainless steel tube. The polishing current is 1.7 A, the polishing time is 20 s, the intermittent time is 15 s, and the overall polishing time is 20 min;

[0047] (6) Rinse the polished capillary stainless steel tube with deionized water, blow the inner and outer surfaces with a nitrogen gun, and then place it in a constant temperature air blast drying oven at 80 °C and dry it for 24 h;

[0048] (7) Detect the inner surface of the polished capillary stainless steel tube to determine whether the inner surface of the capillary stainless steel tube reaches the expected polishing effect under this parameter. If not, adjust the three parameters in step (5) until the final expected effect is achieved.

[0049] Example 2

[0050] The difference between the intermittent electrochemical polishing of the inner surface of the capillary metal tube provided in this example and that in Example 1 is as follows:

[0051] In step (1) and all subsequent steps, replace the capillary stainless steel tube with a capillary titanium tube;

[0052] In step (3), use a cathode wire with a diameter of 0.4 mm to replace the cathode wire with a diameter of 0.2 mm;

[0053] In step (4), adjust the temperature of the electrochemical polishing solution to 50 °C, and the flow rate of the polishing solution is 100 mL·min -1 .

[0054] Example 3

[0055] The difference between the intermittent electrochemical polishing of the inner surface of the capillary metal tube provided in this example and that in Example 1 is as follows:

[0056] In step (3), use a cathode wire with a diameter of 0.4 mm to replace the cathode wire with a diameter of 0.2 mm;

[0057] In step (4), adjust the temperature of the electrochemical polishing solution to 70 °C;

[0058] In step (5), adjust the polishing current to 4.0 A, the polishing time to 10 s, the intermittent time to 15 s, and the overall polishing time to 15 min.

[0059] Example 4

[0060] The differences between the intermittent capillary metal tube inner surface electrochemical polishing provided in this embodiment and that in Embodiment 1 are as follows:

[0061] In step (1) and all subsequent steps, a stainless steel tube with a diameter of 2.0 mm is used to replace the stainless steel tube with a diameter of 0.8 mm;

[0062] In step (3), a cathode wire with a diameter of 0.6 mm is used to replace the cathode wire with a diameter of 0.2 mm;

[0063] In step (5), the polishing current is adjusted to 3.0 A, the polishing time is 15 s, the intermittent time is 15 s, and the overall polishing time is 40 min.

[0064] Embodiment 5

[0065] The differences between the intermittent capillary metal tube inner surface electrochemical polishing provided in this embodiment and that in Embodiment 1 are as follows:

[0066] In step (1) and all subsequent steps, a stainless steel tube with the same diameter but a length of 400 mm is used to replace the stainless steel tube with a length of 200 mm;

[0067] In step (3), a cathode wire with a diameter of 0.4 mm is used to replace the cathode wire with a diameter of 0.2 mm;

[0068] In step (5), the polishing current is adjusted to 1.2 A, the polishing time is 20 s, the intermittent time is 15 s, and the overall polishing time is 30 min;

[0069] After step (5) is completed, the polished stainless steel tube is installed reversely (the stainless steel length is 400 mm, the cathode wire is 300 mm, and the inner surface cannot be fully polished in one pass), and step (5) is repeated once.

[0070] Embodiment 6

[0071] The differences between the intermittent capillary metal tube inner surface electrochemical polishing provided in this embodiment and that in Embodiment 1 are as follows:

[0072] In step (1) and all subsequent steps, a capillary titanium tube with the same diameter but a length of 400 mm is used to replace the stainless steel tube;

[0073] In step (3), a cathode wire with a diameter of 0.3 mm is used to replace the cathode wire with a diameter of 0.2 mm;

[0074] In step (5), adjust the polishing current to 2.0 A, the polishing time to 15 s, the intermittent time to 15 s, and the overall polishing time to 20 min;

[0075] After step (5), install the polished stainless steel tube in reverse and repeat step (5) once.

[0076] Example 7

[0077] The difference between the intermittent electrochemical polishing of the inner surface of the capillary metal tube provided in this example and that in Example 1 is as follows:

[0078] In step (1) and all subsequent steps, replace the stainless steel tube with a length of 200 mm with a stainless steel tube of the same diameter but a length of 400 mm;

[0079] In step (3), use a cathode wire with a diameter of 0.5 mm to replace the cathode wire with a diameter of 0.2 mm;

[0080] In step (5), adjust the polishing current to 1.2 A, the polishing time to 20 s, the intermittent time to 15 s, and the overall polishing time to 20 min;

[0081] After step (5), install the polished stainless steel tube in reverse (the stainless steel length is 400 mm and the cathode wire is 300 mm, and the inner surface cannot be fully polished in one time), and repeat step (5) once. The result is as Figure 5 shown.

[0082] Comparative Example 1

[0083] The difference between the traditional chemical polishing provided in this example and that in Example 1 is as follows:

[0084] After step (2), directly put the above capillary metal tube into the chemical polishing solution and polish it for 20 min;

[0085] Detect the inner surface of the capillary metal tube after the above chemical polishing.

[0086] Comparative Example 2

[0087] The difference between the non-intermittent electrochemical polishing of the inner surface of the capillary metal tube provided in this example and that in Example 1 is as follows:

[0088] In step (5), use the capillary stainless steel tube as the anode and the cathode wire as the cathode to perform non-intermittent electrochemical polishing on the inner surface of the above capillary stainless steel tube. The polishing current is 1.7 A, the polishing time is 20 s, the intermittent time is 15 s, and the overall polishing time is 20 min;

[0089] Please refer to Figure 1As shown, the inner surface of the stainless steel tube with a diameter of 0.8 mm and a length of 200 mm is relatively rough and has no mirror effect. In the figure, 1 cm, 5 cm, 10 cm, 15 cm, and 20 cm respectively represent the length distances from one end of the stainless steel tube. That is, after the above-mentioned stainless steel tube is equally divided into four sections and semi-sectioned, its inner surface is relatively rough, which can be compared with the polished and reflective inner surface.

[0090] Please refer to Figure 2 As shown, the inner diameter of the capillary titanium tube with an inner diameter of 0.8 mm and a length of 200 mm after intermittent polishing (the inner diameter is a 0.5 mm cathode wire, and the electro-chemical polishing parameters are 1.2 A - 20 s - 10 min). There is a certain polishing effect on its inner surface. For example, mirror effects appear at 5 cm and 10 cm (a better mirror effect is manifested as two flat light bands), but some positions (such as 1 cm and 15 cm) are still uneven and the parameters need to be further improved.

[0091] Please refer to Figure 3 As shown, the inner diameter of the capillary stainless steel tube with an inner diameter of 0.8 mm and a length of 200 mm after intermittent polishing (the inner diameter is a 0.5 mm cathode wire, and the electro-chemical polishing parameters are 1.7 A - 10 s - 10 min). The polishing effect on its inner surface is further enhanced. Poor mirror effects appear on the surface at 5 cm, 10 cm, and 15 cm (two light bands appear, but they are not flat), but the positions at 1 cm and 20 cm are still relatively rough and have not reached the best effect.

[0092] Please refer to Figure 4 As shown, the inner diameter of the capillary stainless steel tube with an inner diameter of 0.8 mm and a length of 400 mm after intermittent polishing (the inner diameter is a 0.5 mm cathode wire, and the electro-chemical polishing parameters are 1.7 A - 10 s - 20 min - polished in two sections). After further optimizing the parameters, an ideal polishing effect is achieved on the inner surface of the 400 mm capillary tube.

[0093] Please refer to Figure 5 As shown, the inner diameter of the capillary stainless steel tube with an inner diameter of 0.8 mm and a length of 400 mm after intermittent polishing (the inner diameter is a 0.5 mm cathode wire, and the electro-chemical polishing parameters are 1.2 A - 20 s - 10 min - polished in two sections). After applying the optimal polishing parameters, an inner surface with a near-mirror effect is obtained.

[0094] Please refer to Figure 6 As shown, Figure 6 is a schematic diagram of the inner surface polishing of an intermittent capillary metal tube.

[0095] The above are only the preferred embodiments of the present application and are not intended to limit the present application. For those skilled in the art, various changes and modifications can be made to the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included within the protection scope of the present application.

Claims

1. An intermittent electrochemical polishing method for the inner surface of a capillary metal tube, characterized in that, Take the capillary metal tube as the anode, insert the cathode wire into the interior of the capillary metal tube to form an anode-cathode system; the polishing liquid flows inside the capillary metal tube, and the capillary metal tube is subjected to intermittent electrochemical polishing treatment. The intermittent electrochemical polishing current is 0.5 A to 10 A, the intermittent time is 5 s to 60 s, the polishing time is 5 s to 60 s, and the overall polishing time is 2 min to 60 min.

2. The method according to claim 1, characterized in that, The polishing time and the intermittent time alternate with each other. When polishing, the polishing liquid stops flowing, and when intermittent, the polishing liquid starts to flow, taking away all the reactants generated by polishing and making the inner surface of the capillary metal tube refilled with the polishing liquid again.

3. The method according to claim 1 or 2, characterized in that, The temperature of the polishing liquid is 30°C to 100°C, and the flow rate of the polishing liquid is 10 mL·min -1 ~1000 mL·min -1 .

4. The method according to claim 3, characterized in that, The capillary metal tube is made of stainless steel, titanium or titanium alloy, and its inner diameter is 0.4 mm to 5.0 mm.

5. The method according to claim 4, wherein The volume percentage of water in the electrochemical polishing liquid is 0% to 50%.

6. The method according to claim 5, characterized in that After the electrochemical polishing, there is also a post-treatment step: clean the capillary metal tube with deionized water and absolute ethanol, dry it with nitrogen, and then dry it at 50 °C to 120 °C for 1 h to 24 h.

7. The method according to claim 6, wherein The diameter of the cathode wire is 0.1 mm to 0.8 mm, and it is located at the central position of the capillary metal tube.

8. The method according to claim 7, wherein When the length of the capillary metal tube is ≥ 200 mm, segmented polishing is adopted. After each segment of polishing is completed, it is installed in the reverse direction for another segment of polishing.

9. The method according to claim 8, characterized in that, The method uses a polishing device, including a bracket for vertically fixing the capillary metal tube; a peristaltic pump, and the peristaltic pump forms a loop with the polishing liquid and the capillary metal tube through pipelines.

10. A capillary metal tube polished by the method according to any one of claims 1-9.

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