Electrochemical polishing device and polishing method thereof

Abstract

The invention discloses an electrochemical polishing device and a polishing method thereof. The device comprises a polishing tank, a pulse direct-current power source, a cathode assembly, an ultrasonic transducer and a multi-point limiting clamp, and the cathode assembly is composed of at least two cathodes connected in parallel and symmetrically arranged on the two sides of a support; the ultrasonic transducer forms a cavitation effect in the polishing process; the multi-point limiting clamp ensures concentric positioning of the support through an adjustable plug pin, a limiting pin and a centering pin. In combination with the device, the invention further provides a polishing method, under the conditions that the temperature is 40-60 DEG C, the pH is 0.5-2.0 and the current density is 0.01-0.05 A / dm < 2 >, high-precision uniform polishing with Ra smaller than or equal to 0.02 mu m on the surface of the metal support is achieved through ultrasonic cavitation and pulse current superposition, pickling or mechanical pretreatment is not needed, the process is simple, batch production can be achieved, the corrosion resistance is remarkably improved, and the fatigue life is remarkably prolonged.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of metal surface micro-nano processing, and particularly relates to an equipment and process for electrochemical polishing of medical metal stents, in particular an electrochemical polishing device combining a pulse direct current power supply, ultrasonic cavitation and a multi-point limiting clamp and a polishing method thereof. BACKGROUND

[0002] Vascular stents used in the medical field are generally divided into coronary stents, renal artery stents, cerebral stents, and large artery stents. Metal stents made by laser engraving process account for a large proportion among them. After laser cutting or heat treatment, the metal stent will have defects such as pits, scratches, burrs and oxide layers on the surface. If it is directly implanted into the human body without processing, it will cause platelet adhesion in the blood vessel, easily forming thrombosis and intimal hyperplasia, or easily scratching the blood vessel when removing thrombus by intracranial stent. Especially for heart stents, there is a higher requirement for surface roughness. Therefore, the stent after cutting or heat treatment also needs to be processed by polishing. The traditional polishing method is mechanical polishing, and the surface roughness of the stent after mechanical polishing cannot meet the requirements.

[0003] The existing metal stent polishing technology is an electrochemical polishing process. The metal stent is immersed in an electrolyte, and is connected to an anode through a conductive tool. The cathode of the power supply is fixed in the electrolyte, and the metal stent anode and the electrolytic cell are formed together. The surface burrs and scratches are removed by the electrochemical reaction after power-on. For example, CN212426236U, CN203890489, etc.

[0004] However, due to the adsorption of a large number of bubbles on the tool and the surface of the stent, it is easy to cause uneven polishing inside the stent, and some points are not smooth, which also causes the phenomenon of hydrogen embrittlement, reduces the fatigue number of the stent, and reduces the service life of the stent. SUMMARY

[0005] The present application aims to overcome the defects of the existing electrochemical polishing technology, such as the accumulation of bubbles on the surface of the bracket, the uneven local polishing and the burr remaining, and the fatigue life reduction caused by hydrogen embrittlement; meanwhile, the processing hardening and the cumbersome process of the traditional mechanical polishing and pickling pretreatment are avoided. To this end, the present application provides an electrochemical polishing device, which comprises a polishing tank, a pulse direct current power supply, a cathode assembly, an ultrasonic transducer and a multi-point limiting clamp; the cathode assembly is composed of two or more parallel cathodes, which are symmetrically arranged on both sides of the metal bracket to realize uniform electric field by sharing current density; the ultrasonic transducer transmits ultrasonic energy to the electrolyte to form cavitation effect in the polishing process, so as to promote the continuous "nucleation-collapse" cycle of bubbles and effectively strip the oxide layer and impurities; the multi-point limiting clamp guarantees the concentric positioning and stability of the bracket under high-frequency vibration through the structure of the radial adjustable pin, the limiting pin and the centering pin. Based on the above device, the present application also provides a corresponding electrochemical polishing method, which comprises the steps of mounting and positioning the bracket, synchronously starting the ultrasonic and pulse power supply, implementing the polishing under the set current density and time, and cleaning and drying after polishing.

[0006] According to a first aspect of the present application, there is provided an electrochemical polishing device, comprising:

[0007] a polishing tank for containing an electrolyte;

[0008] a pulse direct current power supply, the positive electrode of which is arranged outside the polishing tank and electrically connected to the metal bracket to be polished in the polishing tank as an anode;

[0009] a cathode assembly, the cathode assembly comprising at least two parallel cathodes, each of which is electrically connected to the negative electrode of the pulse direct current power supply and uniformly arranged on the outer circumferential side of the metal bracket;

[0010] an ultrasonic transducer arranged to transmit ultrasonic energy to the electrolyte for forming cavitation effect in the polishing process;

[0011] a multi-point limiting clamp comprising a base and a plurality of adjustable limiting components fixedly connected to the base, for fixing and positioning the metal bracket under the conditions of ultrasonic vibration and electrochemical polishing.

[0012] In some technical solutions, the adjustable limiting component comprises:

[0013] a first limiting member for supporting the bottom of the bracket;

[0014] a second limiting member for radially limiting the outer side of the bracket;

[0015] a third limiting member for centering and supporting the inner side of the bracket.

[0016] In some technical solutions, the first limiting member is a plurality of adjustable pins arranged along the radial direction, which are in contact with the bottom of the metal stent to prevent the metal stent from moving in the vertical direction.

[0017] The second limiting member is a limiting pin inserted into the outer end of the corresponding adjustable pin, which is in contact with the outer side of the metal stent to prevent the metal stent from moving in the radial direction.

[0018] The third limiting member is a centering pin inserted into the middle section of the corresponding adjustable pin, which is in contact with the inner side of the metal stent to achieve concentric centering and prevent radial deviation.

[0019] In some technical solutions, the adjustable pin is connected to the base screw hole through an external nut, and can slide and lock in the radial direction to adapt to metal stents of different diameters.

[0020] In some technical solutions, the limiting pin and the centering pin are provided with replaceable soft pads away from the outer end of the adjustable pin to prevent local damage to the surface of the metal stent.

[0021] In some technical solutions, the material of the multi-point limiting clamp is at least one of platinum and its alloys, titanium and its alloys, iridium and its alloys, palladium and its alloys, and copper and its alloys; and / or,

[0022] The plurality of cathodes are tubular electrodes made of the same material, and the material is selected from stainless steel, nickel alloy, titanium alloy, or copper alloy.

[0023] In some technical solutions, a stirring assembly is further included to enhance the flow of electrolyte during polishing and promote bubble escape.

[0024] The stirring assembly is a combination of a magnetic stirrer and a constant temperature stirrer, and the constant temperature stirrer is used to maintain the temperature of the electrolyte.

[0025] In some technical solutions, the metal stent is any one of the following types: coronary stent, renal artery stent, carotid artery stent, cerebral vascular stent, peripheral vascular stent, and aortic vascular stent.

[0026] According to another aspect of the present application, an electrochemical polishing method is further provided, which utilizes the above-mentioned electrochemical polishing device and includes the following steps:

[0027] (1) Mounting the metal stent to be polished on the multi-point limiting clamp and immersing it in the electrolyte preheated to a set temperature;

[0028] (2) Simultaneously starting the ultrasonic transducer and the pulse DC power supply;

[0029] (3) Connecting the positive output of the pulse DC power supply to the metal stent, and connecting the negative output to the two cathodes in parallel;

[0030] (4) In the ultrasonic cavitation and stirring, the current density is maintained at 0.01-0.05 A / dm 2 , the polishing temperature is 40-60 DEG C, and the polishing time is 1-5 min.

[0031] (5) After the polishing, the pulse direct current source and the ultrasonic vibration are stopped, the metal support is taken out and washed with deionized water and vacuum dried.

[0032] In some technical solutions, the pulse direct current source can output voltage 0-60 V, current 0-10 A, and the pulse mode is sine square wave; and / or,

[0033] The working frequency of the ultrasonic transducer is 18-25 kHz, and the power is 10%-80% of the nominal power under working conditions; and / or,

[0034] The electrolyte is a mixed system containing phosphoric acid and sulfuric acid, and the pH value is 0.5-2.0.

[0035] The above technical solutions of the present application have at least the following beneficial effects:

[0036] 1. By superimposing ultrasonic cavitation and pulse current, small bubbles are continuously formed and uniformly collapsed, avoiding current shielding and local over-corrosion caused by large bubbles covering the same area, so that the polishing is more uniform;

[0037] 2. The parallel distribution of the cathode assembly greatly reduces the single-point current density, and the effective balance of the electric field by symmetrical arrangement realizes the all-around uniform polishing of the inner and outer sides of the metal support and the complex grid structure;

[0038] 3. The multi-point limiting clamp structure takes into account the radial and axial positioning, overcomes the displacement and inclination risk of the workpiece under ultrasonic vibration, and ensures accurate concentricity and repeatability;

[0039] 4. The surface roughness of the polished workpiece can be reduced to Ra≤0.02 μm, and the burrs and oxide skin layer are significantly removed without the need for pickling or mechanical grinding;

[0040] 5. The fatigue life and corrosion resistance of the obtained support are greatly improved, and the process flow is simple and easy to implement, suitable for batch and automated production. BRIEF DESCRIPTION OF DRAWINGS

[0041] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following will briefly introduce the drawings and their marks used in the embodiments, and obviously, the drawings described below are only some embodiments of the present application, and those skilled in the art can obtain other drawings according to these drawings without creating any creative labor.

[0042] Figure 1Structure diagram of the metal support and the multi-point limiting clamp involved in the embodiment 1 and the embodiment 3 of the present application;

[0043] Figure 2 Structure diagram of the metal support and the multi-point limiting clamp involved in the embodiment 2 of the present application. DETAILED DESCRIPTION

[0044] In order to more clearly illustrate the technical solutions of the embodiments of the present application or the prior art, the specific embodiments of the present application will be described below with reference to the drawings. Obviously, the drawings in the following description only represent some embodiments of the present application, and for those skilled in the art, other drawings can be obtained from these drawings without creative labor, and other embodiments can also be obtained.

[0045] In order to make the drawing simple, only the parts related to the invention are shown in each drawing, which does not represent the actual structure of the product. In addition, in order to make the drawing simple and easy to understand, in some drawings, only one of the components with the same structure or function is shown schematically, or only one of them is marked. In this paper, "one" not only means "only one", but also means "more than one".

[0046] It should be further understood that the term "and / or" used in the present application specification and the appended claims means any combination of one or more of the associated listed items and all possible combinations, and includes these combinations.

[0047] In this paper, it should be noted that unless otherwise specified and limited, the terms "mounting", "connecting", "connecting" should be understood broadly, for example, it can be fixed connection, or detachable connection, or integral connection; it can be mechanical connection, or electrical connection; it can be directly connected, or indirectly connected through intermediate medium, or the communication inside two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0048] In addition, in the description of the present application, the terms "first", "second" and the like are only used for differentiation and description, and cannot be understood as indicating or implying relative importance.

[0049] The core structure of the application comprises a polishing tank, a pulse DC power supply, a cathode assembly, an ultrasonic transducer, a multi-point limiting clamp and a stirring assembly. The polishing tank is made of corrosion-resistant material and is internally provided with a temperature sensor and a constant temperature circulating device to maintain the temperature of the phosphorus acid-sulfuric acid mixed electrolyte at 40-60 DEG C. The pulse DC power supply is installed outside the polishing tank, the positive electrode is electrically connected to the metal support to be polished through a wire, and the negative electrode is connected in parallel to at least two tubular cathodes which are evenly arranged along the outer periphery of the support to share the current density and ensure the balance of the electric field. The transducer of the ultrasonic transducer is installed inside the side wall of the polishing tank, the working frequency is 18-25 kHz, and the power is 10%-80% of the nominal power, which can continuously deliver ultrasonic energy to the electrolyte, so that the bubbles continuously "nucleate-expand-collapse" on the surface of the support, thereby efficiently stripping the oxide scale and particulate impurities. The multi-point limiting clamp is composed of a base fixed on the tank bottom, an adjustable bolt and a limiting pin fixed on the base. The adjustable bolt supports the metal support from the bottom, the limiting pin on the outside prevents radial deviation, and the optional centering pin on the inside ensures concentric positioning. The stirring assembly is composed of a magnetic stirrer and a constant temperature stirrer, which promotes the flow of electrolyte and the escape of bubbles through continuous stirring to further improve the polishing uniformity.

[0050] In actual use, first, the metal support to be polished is installed on the multi-point limiting clamp, ensuring that the bottom of the support is in contact with the adjustable bolt and forms multi-point constraint with the limiting pin on the outside and the centering pin on the inside. Then, the electrolyte preheated to 40-60 DEG C is injected into the polishing tank, and the constant temperature circulating device is started to stabilize the temperature. Then, the ultrasonic transducer and the pulse DC power supply are started simultaneously, the positive electrode of the pulse power supply is electrically connected to the metal support, and the negative electrode current is distributed in parallel to each cathode to maintain a current density of 0.01-0.05 A / dm2. During the polishing process, the ultrasonic cavitation and the stirring assembly work together to complete the uniform polishing of the surface of the metal support within 1-5 minutes. After polishing, the power and ultrasonic vibration are turned off in turn, the metal support is taken out and washed with deionized water, and finally dried under vacuum conditions to obtain a high-gloss metal support with a surface roughness Ra≤0.02 μm.

[0051] In another alternative, the cathode assembly can be expanded to three or more parallel cathodes to further reduce the local current density and improve the polishing consistency, and the pulse DC power supply can be changed to output a bipolar square wave to slow down the electrode polarization. For alloy supports of different hardness, the working frequency of the ultrasonic transducer can be adjusted to 10-40 kHz, and a multi-frequency switching technology can be used to balance the cavitation impact and polishing fineness. The clamp components can also be made of PEEK or polypropylene to meet different corrosion resistance and cost requirements.

[0052] Through the above embodiments and preferred schemes, the present invention can reduce the surface roughness Ra of the metal bracket to ≤0.02μm, increase the fatigue life by more than 20% compared with the unpolished metal bracket, shorten the polishing cycle by about 30%, and show high consistency and repeatability in mass production, significantly improving production efficiency and product quality.

[0053] Example 1

[0054] 1. Cutting: Use a laser cutting machine to cut the MP35N cobalt-chromium tube with an outer diameter of 23 mm into the shape of the valve stent according to the drawing. The laser cutting process must strictly follow the drawing dimensions to ensure cutting accuracy and avoid affecting subsequent processing.

[0055] 2. Cleaning: Use 1 mol / L sodium hydroxide aqueous solution to clean the surface of the cut stent for 10 minutes to remove oil stains on the stent surface;

[0056] 3. Drying: The cleaned stent is vacuum dried at a vacuum degree of -0.1Mpa and a temperature of 50 degrees Celsius.

[0057] 4. Pre-ultrasonication and preheating of the polishing solution: Add the polishing solution (perchloric acid) to the polishing tank. Connect an ultrasonic generator and a heating device below the polishing tank. After adding the solution, start ultrasonication and heating at a frequency of 26 kHz and a power of 40%, and then heat to 50 degrees Celsius.

[0058] 5. Polishing: Place the bracket on the polishing tool. The polishing tool is made of platinum-iridium alloy and has a tool diameter of 0.3mm. Figure 1 As shown, connect the polishing fixture to the positive terminal of a DC pulse power supply via a wire. Then, hang the polishing fixture vertically and secure it in the polishing tank. Connect a 304 stainless steel sheet, the cathode material, to the negative terminal of the power supply and secure it in the tank. Power on with a voltage of 18V and a current of 0.01 / dm² for 300 seconds. Remove the fixture after the timer expires.

[0059] 6. Cleaning: Clean the polished stent in the previous step with deionized water, and then vacuum dry it to obtain the polished medical cobalt-chromium stent.

[0060] 7. Appearance inspection: The polished stent was observed under a digital microscope and compared with a roughness measuring block. It was found that the roughness of the stent after polishing could reach 0.02um, and there was no unevenness inside or outside the stent.

[0061] Example 2

[0062] 1. Cutting: Use a laser cutting machine to cut the 25mm outer diameter MP35N cobalt-chromium tubing into the shape of the surgical valve seat according to the drawing. The laser cutting process must strictly adhere to the drawing dimensions to ensure cutting accuracy and avoid affecting subsequent processing.

[0063] 2. Cleaning: Place the cut petal seat in a 1 mol / L sodium hydroxide solution and clean for 15 minutes. This step is to thoroughly remove the oil on the petal seat surface and provide a clean surface foundation for subsequent processes.

[0064] 3. Drying: The cleaned petal seat is vacuum dried, with the vacuum degree controlled at -0.1Mpa and the temperature set at 80 degrees Celsius. Drying can effectively prevent moisture residue and avoid adverse effects on subsequent polishing.

[0065] 4. Pre-ultrasonication and preheating of the polishing solution: Add a polishing solution consisting of phosphoric acid, sulfuric acid, and chromic anhydride in a volume ratio of 70:25:5 to the polishing tank. Connect an ultrasonic generator and a heating device below the polishing tank. After adding the solution, activate ultrasonication and heating. Set the ultrasonic frequency to 18 kHz and the power to 80%. Simultaneously, heat the polishing solution to 50°C. This pretreatment optimizes the polishing solution's performance and enhances polishing results.

[0066] 5. Polishing: Place the petal seat on a polishing tool made of titanium alloy with a diameter of 0.8 mm, such as Figure 2 As shown. Connect the polishing tool to the positive terminal of a DC pulse power supply via a wire, then hang it vertically and secure it in the polishing tank. Connect a 304 stainless steel sheet as the cathode to the negative terminal of the power supply and secure it in the polishing tank. Turn on the power supply, set the voltage to 10V, the current density to 0.04A / dm², and the polishing time to 300 seconds. After the timer expires, quickly remove the disc holder.

[0067] 6. Cleaning: Clean the polished valve seat with deionized water to remove the polishing liquid remaining on the surface, and then vacuum dry it to obtain the polished medical cobalt-chromium surgical valve seat.

[0068] 7. Appearance Inspection: The polished valve seat was observed under a digital microscope and compared with a roughness gauge. The test confirmed that the polished valve seat had a roughness of 0.02 μm, and the inner and outer surfaces were uniform with no significant differences, meeting the high-precision requirements of medical surgical valve seats.

[0069] Example 3

[0070] 1. Cutting: Use a laser cutting machine to cut the 3.0mm outer diameter 316LVM stainless steel tube into the shape of the coronary stent according to the drawing. Strictly adhere to the drawing dimensions to ensure cutting accuracy and prevent any adverse effects on subsequent processing.

[0071] 2. Cleaning: Place the cut coronary stent in a 1 mol / L sodium hydroxide solution and clean for 10 minutes. This step is mainly to thoroughly remove oil stains on the stent surface and provide a clean surface condition for subsequent processes.

[0072] 3. Drying: The cleaned coronary stent is vacuum dried, maintaining a vacuum of -0.1 to -0.08 MPa at 100 degrees Celsius. Drying effectively prevents residual moisture and reduces interference with subsequent polishing.

[0073] 4. Pre-ultrasonicate and preheat the polishing solution: Add stainless steel polishing solution (20% oxalic acid, 10% propylene glycol, 1-2% corrosion inhibitor, and the balance water) to the polishing tank. Connect an ultrasonic generator and heating device below the polishing tank. After adding the solution, turn on the ultrasonic wave without heating. Set the ultrasonic frequency to 18 kHz and the power to 40%. This pretreatment can optimize the polishing solution's performance and enhance the polishing effect.

[0074] 5. Polishing: Place the coronary stent on a polishing tool made of titanium alloy with a diameter of 0.8 mm. Figure 1 As shown. Connect the polishing fixture to the positive terminal of a DC pulse power supply via a wire, then hang it vertically and secure it in the polishing tank. Connect a 304 stainless steel sheet as the cathode to the negative terminal of the power supply and secure it in the polishing tank. Turn on the power supply, set the voltage to 25V, the current density to 0.05A / dm², and the polishing time to 120 seconds. After the timer expires, quickly remove the bracket.

[0075] 6. Cleaning: Clean the polished coronary stent with deionized water to remove the polishing liquid remaining on the surface, and then vacuum dry it to obtain a polished medical 316LVM stainless steel coronary stent.

[0076] 7. Appearance Inspection: The polished coronary stent was observed under a digital microscope and compared with a roughness gauge. The inspection confirmed that the stent's roughness after polishing reached 0.02 μm, and the inner and outer surfaces of the stent were uniform with no significant differences, meeting the high-precision requirements of medical coronary stents.

[0077] The above-described embodiments merely represent several implementation methods of the present invention. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art would be able to make various modifications and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be determined by the appended claims.

Claims

1. An electrochemical polishing device, characterized in that: include: a polishing tank for containing electrolyte; A pulsed DC power supply, the positive electrode of which is located outside the polishing tank and electrically connected to the metal support to be polished in the polishing tank as an anode; A cathode assembly, comprising at least two cathodes arranged in parallel, each cathode being electrically connected to the negative electrode of a pulsed DC power supply and uniformly arranged on the outer periphery of the metal support; an ultrasonic transducer configured to transmit ultrasonic energy into the electrolyte for creating a cavitation effect during polishing; A multi-point limit fixture comprises a base and several adjustable limit components fixedly connected to the base, and is used to fix and position a metal bracket under ultrasonic vibration and electrochemical polishing conditions.

2. The electrochemical polishing device according to claim 1, characterized in that The adjustable limit assembly includes: A first limiting member, used for supporting the bottom of the bracket; A second limiting member is used to limit the outer side of the bracket in radial direction; The third limiting member is used to center and support the inner side of the bracket.

3. The electrochemical polishing device according to claim 2, characterized in that The first limiting member is a plurality of adjustable pins arranged in a radial direction and in contact with the bottom of the metal bracket to prevent the metal bracket from moving in a vertical direction; The second limiting member is a limiting pin respectively inserted into the outer end of the corresponding adjustable pin, which contacts the outer side of the metal bracket and is used to prevent the metal bracket from shifting in the radial direction; The third limiting member is a centering pin respectively inserted into the middle section of the corresponding adjustable pin, which contacts the inner side of the metal bracket to achieve concentric centering and prevent radial deviation.

4. The electrochemical polishing device according to claim 3, characterized in that The adjustable pin is connected to the threaded hole of the base through an external nut and can be slid and locked in the radial direction to adapt to metal brackets of different diameters.

5. The electrochemical polishing device according to claim 3, characterized in that The outer ends of the limit pin and the centering pin away from the adjustable pin are provided with replaceable soft pads to prevent local damage to the surface of the metal bracket.

6. The electrochemical polishing device according to claim 1, characterized in that The multi-point limiting fixture is made of at least one of platinum and its alloys, titanium and its alloys, iridium and its alloys, palladium and its alloys, and copper and its alloys; and / or, The plurality of cathodes are tubular electrodes made of the same material, and the material used is selected from stainless steel, nickel alloy, titanium alloy or copper alloy.

7. The electrochemical polishing device according to claim 1, characterized in that Also included is a stirring assembly for enhancing electrolyte flow and facilitating bubble escape during polishing; The stirring assembly is a combination of a magnetic stirring bar and a constant temperature stirrer, and the constant temperature stirrer is used to maintain the temperature of the electrolyte.

8. The electrochemical polishing device according to claim 1, characterized in that The metal stent is any of the following types: coronary artery stent, renal artery stent, carotid artery stent, cerebral vascular stent, peripheral vascular stent, and aortic stent.

9. An electrochemical polishing method, characterized in that: The electrochemical polishing device according to any one of claims 1 to 8 comprises the following steps: (1) The metal bracket to be polished is mounted on a multi-point limit fixture and immersed in an electrolyte preheated to a set temperature; (2) Synchronously start the ultrasonic transducer and the pulsed DC power supply; (3) The positive electrode of the pulsed DC power supply is electrically connected to the metal bracket, and the negative electrode of the pulsed DC power supply is connected in parallel to the two cathodes; (4) Under the coordination of ultrasonic cavitation and stirring, the current density is maintained at 0.01~0.05A / dm 2 , polishing temperature is 40-60℃, polishing time is 1-5min; (5) After polishing, stop the pulsed DC power supply and ultrasonic vibration, remove the metal bracket, rinse with deionized water, and vacuum dry.

10. The electrochemical polishing method according to claim 9, characterized in that: The pulsed DC power supply can output a voltage of 0-60V, a current of 0-10A, and a pulse mode of a sine square wave; and / or, The operating frequency of the ultrasonic transducer is 18 to 25 kHz, and the power is 10% to 80% of the nominal power under working conditions; and / or, The electrolyte is a mixed system containing phosphoric acid and sulfuric acid, and the pH value is 0.5-2.0.

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