Energy-saving continuous electrolytic cleaning device for metal wires
The electrolytic cleaning device, with its tubular sealing structure and liquid pump circulation system, solves the problems of easy electrolyte evaporation and high energy consumption, achieving low-energy and high-efficiency metal wire cleaning.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-10
- Publication Date
- 2026-03-10
AI Technical Summary
In the current electrolytic cleaning process after drawing metal wire, the electrolyte is prone to volatilization, energy consumption is high, and open electrolytic cells pose safety hazards.
The electrolytic cleaning assembly adopts a tubular sealed structure, which combines a liquid pump and a return pipe to achieve electrolyte circulation, uses a condensate tank for heat exchange, and forms a multi-stage electrolytic field. The evaporation and consumption of electrolyte are reduced through connecting plates and sealing structures.
Reduce electrolyte usage and evaporation, lower energy consumption, improve cleaning uniformity and efficiency, and ensure the stability and safety of the cleaning process.
Smart Images
Figure CN121629490A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of metal wire processing technology, and in particular to an energy-saving continuous electrolytic cleaning device for metal wires. Background Technology
[0002] In the metal wire processing, electrolytic cleaning is a crucial step in removing surface contaminants after drawing. In existing technologies, common metal wires such as tungsten and molybdenum wires are typically cleaned in open electrolytic cleaning tanks after drawing. However, this open electrolytic cleaning structure has several drawbacks: First, the electrolyte is exposed to air during cleaning, leading to significant evaporation. This not only increases the frequency and cost of electrolyte replenishment but also potentially causes environmental pollution and operational safety hazards. Second, the entire electrolytic tank is filled with electrolyte, and the current passing through the electrolyte during cleaning generates a large amount of heat. A significant amount of electrical energy is used for electrolyte heating, resulting in high energy consumption. Furthermore, the increased evaporation after heating further accelerates electrolyte loss. Summary of the Invention
[0003] In order to solve at least some of the problems existing in the prior art, the present invention provides an energy-saving continuous electrolytic cleaning device for metal wires that uses less electrolyte, generates less heat during electrolytic cleaning, has less volatile electrolyte, and consumes less energy.
[0004] To achieve the above objectives, the present invention adopts the following technical solution: An energy-saving continuous electrolytic cleaning device for metal wires includes an electrolytic cell for storing electrolyte and several tubular electrolytic cleaning components arranged parallel to each other within the electrolytic cell. Each electrolytic cleaning component includes several insulating sleeves, several electrode tubes, a positive electrode plate, and a negative electrode plate. The insulating sleeves are coaxially distributed, and each end of the insulating sleeve has a positioning groove. A first central through hole is provided between the bottom surfaces of the positioning grooves. The electrode tubes are located between adjacent insulating sleeves and are coaxially distributed with the insulating sleeves. Both ends of the electrode tubes extend into the positioning grooves. Each electrode tube has a conductive post on its upper side. The conductive post includes... The electrolytic cleaning assembly includes positive and negative terminals, which are alternately distributed. All positive terminals are connected to the positive plate, and all negative terminals are connected to the negative plate. The positive and negative plates are connected to an external DC power supply. Each electrolytic cleaning assembly has a liquid inlet branch pipe at the bottom center. The bottom surface of the electrolytic cell has a liquid outlet hole. The lower end of the liquid inlet branch pipe is connected to a main liquid inlet pipe. A reflux pipe is provided between the main liquid inlet pipe and the liquid outlet hole. A liquid pump is provided on the main liquid inlet pipe. Several first lead wire holes are provided on both ends of the sidewalls of the electrolytic cell. The two ends of the metal wire in each electrolytic cleaning assembly coaxially pass through the corresponding first lead wire holes.
[0005] By adopting the above technical solution: the electrolytic cleaning component adopts a tubular sealed structure, with the metal wire passing through the center. The electrolyte flows into the interior from the middle of the electrolytic cleaning component and flows out into the electrolytic tank from both ends. The amount of electrolyte used is significantly reduced, and the contact area between the electrolyte and air is small. On the one hand, this reduces the amount of electrolyte used and lowers costs; on the other hand, it reduces the evaporation loss of the electrolyte. At the same time, less electrolyte means less heat absorption, which can reduce energy consumption. The electrolyte circulation is achieved through a liquid pump and a return pipe, which reduces the amount of electrolyte used and heat generation, and improves the cleaning uniformity and efficiency. It can not only achieve electrolytic cleaning, but also circulate and rinse the stains cleaned off the surface of the metal wire. For each electrolytic cleaning component, the positive and negative electrode posts are alternately distributed inside to form a multi-level electrolytic field, which improves the uniformity and cleaning effect of electrolytic cleaning.
[0006] Preferably, each electrolytic cleaning assembly is equipped with a connecting plate, which is positioned between the insulating sleeve and the positive electrode plate. The conductive post passes through the connecting plate, and both ends of the connecting plate are detachably connected to the electrolytic cell. The edges of the connecting plates between adjacent electrolytic cleaning assemblies abut and seal, thus sealing the upper end of the electrolytic cell. By adopting the above technical solution, the detachable connection of the connecting plates makes the installation and maintenance of each electrolytic cleaning assembly more convenient. Furthermore, the abutment seal between the connecting plates completely seals the entire electrolytic cell, further reducing the evaporation and contamination of the electrolyte.
[0007] Preferably, the bottom of the electrolytic cell is equipped with a condensate tank, and the return pipe is configured as a heat exchange coil, which is installed inside the condensate tank. By adopting the above technical solution, the heat exchange coil in the condensate tank allows the electrolyte to exchange heat with the condensate, thereby maintaining a stable electrolyte temperature, ensuring a stable electrolyte concentration, reducing electrolyte evaporation due to heat, and improving the stability of the cleaning process.
[0008] Preferably, the inner sides of both ends of the electrolytic cell are provided with stepped surfaces, and a plurality of connecting posts are provided on the stepped surfaces. Each connecting post has a connecting hole, and both ends of the connecting plate have corresponding slots for the connecting posts. After the slots engage with the connecting posts, they are locked in place by locking components to form a detachable connection. By adopting the above technical solution—where the slots and connecting posts are engaged and locked by locking components—each electrolytic cleaning assembly can be installed and disassembled independently, facilitating inspection and maintenance.
[0009] Preferably, the electrolytic cell has overflow cavities on both outer sides at both ends, and the first lead holes are connected to the overflow cavities. The outer wall of each overflow cavity has second lead holes coaxially distributed with the first lead holes. The upper end of the electrolytic cell is provided with a cover plate, which completely seals the upper end of the electrolytic cell and the upper end of the overflow cavities. By adopting the above technical solution, when there is too much electrolyte in the electrolytic cell, it can enter the overflow cavity through the first lead holes, thereby preventing electrolyte leakage.
[0010] Preferably, the insulating sleeve has through-holes at both ends, and a connecting rod is installed within each through-hole. The connecting rod passes through all the through-holes of the insulating sleeve, and the two ends of the connecting rod are fastened together by fasteners. By adopting the above technical solution, the connecting rods and fasteners ensure that the insulating sleeve and the electrode tube are coaxially fixed, improving structural stability and making the whole unit easier to disassemble, install, and replace.
[0011] Preferably, annular grooves are provided on the outer sides of both ends of the electrode tube, and a sealing ring is provided between the annular groove and the inner wall of the positioning groove. By adopting the above technical solution, the sealing ring enhances the sealing performance between the electrode tube and the insulating sleeve, preventing electrolyte leakage.
[0012] Preferably, the electrode tube has a second central through-hole, the diameter of which is larger than that of the first central through-hole. The second central through-hole provides a larger space for electrolyte flow, while the first central through-hole is used for the passage of the metal wire. The size difference ensures that the electrolyte fully contacts the metal wire while preventing the electrolyte flow rate from being too fast and affecting the cleaning effect. On the other hand, even if the coaxiality of the metal wire deviates significantly from that of the electrode tube, it will not come into contact with the electrode tube, thereby preventing electric shock accidents caused by contact between the metal wire and the electrode tube, and further improving the safety of use.
[0013] Preferably, the diameter of the first central through-hole is configured as r, and the diameter of the second central through-hole is configured as R, where 4mm ≤ r ≤ 6mm, and 10mm ≤ R ≤ 12mm. By adopting the above technical solution, and by reasonably setting the diameters of the first and second central through-holes, a stable electrolytic cleaning effect can be achieved with minimal electrolyte.
[0014] Preferably, the insulating sleeve is made of transparent insulating resin, and the electrode tube is made of aluminum alloy. By adopting the above technical solution: the insulating resin ensures insulation performance, prevents short circuits, and the transparent insulating resin allows direct observation of the internal electrode tube and metal wire; the aluminum alloy electrode tube has good conductivity and corrosion resistance, extending its service life.
[0015] Therefore, the present invention has the following beneficial effects: (1) Through the sealing structure of the tubular electrolytic cleaning component and the connecting plate, the evaporation and consumption of electrolyte are effectively reduced, and energy consumption and heat generation are reduced; (2) The circulation of electrolyte and the cooling of the condensate tank ensure the stability of electrolyte temperature and avoid local overheating to ensure the quality of electrolytic cleaning; (3) The circulation of electrolyte can not only ensure the uniformity of electrolyte, but also physically rinse the stains removed by electrolytic cleaning on the surface of the metal wire, thereby improving the cleaning effect. Attached Figure Description
[0016] Figure 1 This is a schematic diagram of one structure of the present invention.
[0017] Figure 2 for Figure 1 Exploded view.
[0018] Figure 3 This is a schematic diagram showing the connection of the electrolytic cell and the reflux pipe.
[0019] Figure 4 This is a schematic diagram showing the connection between the electrolytic cleaning assembly and the electrolytic cell.
[0020] Figure 5 for Figure 4 Exploded view.
[0021] Figure 6 for Figure 4 A sectional view.
[0022] Figure 7 This is a schematic diagram of the layout of the electrolytic cleaning components.
[0023] Figure 8 This is a schematic diagram showing the connection between the electrolytic cleaning assembly and the connecting plate.
[0024] Figure 9 This is a schematic diagram of a single electrolytic cleaning assembly.
[0025] Figure 10 for Figure 9 The front view.
[0026] Figure 11 for Figure 9 Top view.
[0027] Figure 12 for Figure 10 Sectional view at point AA.
[0028] Figure 13 for Figure 11 Sectional view at point BB.
[0029] Figure 14 for Figure 10 A partial exploded view.
[0030] In the diagram: Electrolytic cell 1, liquid outlet 11, first lead hole 12, condensate tank 13, stepped surface 14, connecting column 141, connecting hole 142, locking piece 143, overflow cavity 15, second lead hole 151, cover plate 16, electrolytic cleaning assembly 2, insulating sleeve 21, positioning groove 211, first central through hole 212, connecting through hole 213, connecting rod 214, fastener 215, electrode tube 22, second central through hole 221, annular groove 222, sealing ring 223, positive electrode plate 23, negative electrode plate 24, conductive column 25, positive electrode column 251, negative electrode column 252, liquid inlet branch pipe 26, liquid inlet main pipe 27, liquid pump 271, connecting plate 28, slot 281, return pipe 3, heat exchange coil 31, metal wire 4. Detailed Implementation
[0031] To make the technical problems to be solved, the technical solutions, and the beneficial technical effects of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and several exemplary embodiments. It should be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the scope of protection of this invention.
[0032] It should be understood that the terms "first," "second," etc., used herein are for descriptive purposes only and should not be construed as indicating or implying relative importance, nor should they be construed as implicitly specifying the number of technical features indicated. Features specified as "first" or "second" may expressly or implicitly indicate that at least one of those features is included.
[0033] like Figures 1-13The energy-saving continuous electrolytic cleaning device for metal wires includes an electrolytic cell 1 for storing electrolyte and several tubular electrolytic cleaning components 2, which are arranged in parallel within the electrolytic cell 1. Each electrolytic cleaning component 2 includes several insulating sleeves 21, several electrode tubes 22, a positive electrode plate 23, and a negative electrode plate 24. The insulating sleeves 21 are coaxially distributed, and each end of the insulating sleeve 21 is provided with a positioning groove 211. A first central through hole 212 is provided between the bottom surfaces of the positioning grooves 211. The electrode tubes 22 are located between adjacent insulating sleeves 21 and are coaxially distributed with the insulating sleeves 21. Both ends of the electrode tubes 22 extend into the positioning grooves 211. Each electrode tube 22 is provided with a conductive post 25 on its upper side, and the conductive post 25 includes a positive electrode post. 251, negative electrode post 252, positive electrode post 251 and negative electrode post 252 are alternately distributed. All positive electrode posts 251 are connected to positive electrode plate 23, and all negative electrode posts 252 are connected to negative electrode plate 24. Positive electrode plate 23 and negative electrode plate 24 are connected to an external DC power supply. Each electrolytic cleaning component 2 has an inlet branch pipe 26 at the bottom center. The bottom surface of the electrolytic cell 1 has an outlet hole 11. The lower end of the inlet branch pipe 26 is connected to the inlet main pipe 27. A return pipe 3 is provided between the inlet main pipe 27 and the outlet hole 11. A liquid pump 271 is provided on the inlet main pipe 27. Several first lead holes 12 are provided on the side walls at both ends of the electrolytic cell 1. The two ends of the metal wire 4 in each electrolytic cleaning component 2 pass through the corresponding first lead hole 12 coaxially. In this structure, the electrolytic cleaning component 2 forms a sealed tubular channel, allowing the metal wire to fully contact the electrolyte as it passes through. The current is distributed alternately through the positive and negative terminals to generate a uniform electric field, achieving efficient electrolytic cleaning. At the same time, the electrolyte is circulated by the liquid pump 271, injected from the inlet branch pipe 26, and returned through the outlet hole 11 and the return pipe 3, reducing electrolyte retention and evaporation, reducing heat accumulation, ensuring a stable cleaning process with low energy consumption, and also physically rinsing the metal surface. Combined with electrolytic cleaning, this improves the cleaning effect.
[0034] like Figures 5-8 As shown, each electrolytic cleaning assembly 2 is equipped with a connecting plate 28, which is positioned between the insulating sleeve 21 and the positive electrode plate 23. Conductive posts 25 pass through the connecting plate 28, and both ends of the connecting plate 28 are detachably connected to the electrolytic cell 1. The edges of the connecting plates 28 between adjacent electrolytic cleaning assemblies 2 abut against each other, sealing the upper end of the electrolytic cell 1. The inner sides of both ends of the electrolytic cell 1 are provided with stepped surfaces 14, and several connecting posts 141 are provided on the stepped surfaces 14. Each connecting post 141 has a connecting hole 142. Both ends of the connecting plate 28 are provided with slots 281 corresponding to the connecting posts 141. After the slots 281 are engaged with the connecting posts 141, they are locked by locking members 143 to form a detachable connection. In this structure, the connecting plate 28 achieves rapid sealing of the upper end of the electrolytic cell 1, preventing electrolyte evaporation and external contamination; at the same time, the detachable connection facilitates regular cleaning and component replacement.
[0035] like Figure 2 and Figure 3 As shown, the bottom of the electrolytic cell 1 is equipped with a condensate tank 13, and the return pipe 3 is configured as a heat exchange coil 31, which is installed inside the condensate tank 13. The heat exchange coil 31 uses cooling water to exchange heat with the electrolyte in the condensate tank 13 to ensure the temperature stability of the electrolyte.
[0036] like Figure 6 As shown, both ends of the electrolytic cell 1 are provided with overflow cavities 15, and the first lead holes 12 are connected to the overflow cavities 15. The outer wall of the overflow cavity 15 is provided with second lead holes 151 coaxially distributed with the first lead holes 12. The upper end of the electrolytic cell 1 is provided with a cover plate 16, which completely seals the upper end of the electrolytic cell 1 and the upper end of the overflow cavity 15. The overflow cavity 15 collects any electrolyte that may overflow and guides the metal wire smoothly in and out through the second lead holes 151. In some embodiments, an overflow pipe is provided at the bottom of the overflow cavity and connected to a return pipe, so that the electrolyte in the overflow cell can be recycled.
[0037] like Figures 12-14 As shown, the insulating sleeve 21 has through-holes 213 at both ends, and a connecting rod 214 is provided inside the through-holes 213. The connecting rod 214 passes through all the through-holes 213 of the insulating sleeve 21, and the two ends of the connecting rod 214 are fastened together by fasteners 215. The connecting rod 214 and the fasteners 215 firmly connect the insulating sleeve 21 and the electrode tube 22, maintaining coaxiality; and the overall installation and disassembly are also very convenient. In some embodiments, annular grooves 222 are provided on the outer sides of both ends of the electrode tube 22, and a sealing ring 223 is provided between the annular groove 222 and the inner wall of the positioning groove 211.
[0038] like Figures 13-14 As shown, the electrode tube 22 has a second central through hole 221 at its center, and the diameter of the second central through hole 221 is larger than the diameter of the first central through hole 212. In some embodiments, the diameter of the first central through hole 212 is configured as r, and the diameter of the second central through hole 221 is configured as R, where 4mm ≤ r ≤ 6mm, and 10mm ≤ R ≤ 12mm. The second central through hole 221 provides a spacious electrolyte flow channel, promoting full contact between the electrolyte and the metal wire; this design also prevents the metal wire from contacting the electrode tube and causing a short circuit, thereby improving safety in use.
[0039] In some embodiments, the insulating sleeve 21 is made of transparent insulating resin, and the electrode tube 22 is made of aluminum alloy. In this structure, the transparent insulating resin facilitates observation of the internal cleaning status and electrolyte condition, enabling timely maintenance; meanwhile, the aluminum alloy electrode tube has good conductivity, corrosion resistance, and compatibility with the electrolyte environment, extending the service life of the equipment.
[0040] Referring to the accompanying drawings, the working principle of the present invention is as follows: The metal wire 4 enters from the first lead hole 12 at one end of the electrolytic cell 1, and passes sequentially through the first central through hole 212 and the second central through hole 221 of the corresponding electrolytic cleaning assembly 2. During the passage of the metal wire 4, the DC power supply provides power through the positive electrode plate 23 and the negative electrode plate 24. The positive electrode post 251 and the negative electrode post 252 alternately generate an electric field, causing the electrolyte to undergo an electrolytic reaction and remove the stains on the surface of the metal wire 4. At the same time, the liquid pump 271 drives the electrolyte to be injected into the electrolytic cleaning assembly 2 from the liquid inlet main pipe 27 through the liquid inlet branch pipe 26. The electrolyte circulates in the tubular channel, carrying away heat and dirt, and then enters the return pipe 3 through the liquid outlet hole 11. The return pipe 3, as a heat exchange coil 31, is cooled in the condensate tank 13 and then returned to the system, realizing the continuous utilization of the electrolyte and temperature control. The overflow chamber 15 and the cover plate 16 ensure a seal to prevent the electrolyte from evaporating and overflowing. Throughout the process, the amount of electrolyte used is small, the volatility is low, the heat generation is small, the cleaning is uniform and efficient, and the energy consumption is significantly reduced.
[0041] In the description of this invention, it should be understood that the directions or positional relationships indicated by up, down, left, right, inner end, outer end, one end, and the other end are based on the orientation or positional relationships shown in the accompanying drawings. They are only for the purpose of more clearly describing the technical solutions of this invention, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and should not be construed as a limitation of this invention.
[0042] Although specific embodiments of the invention have been described in detail herein, they are given for illustrative purposes only and should not be construed as limiting the scope of the invention. Various substitutions, alterations, and modifications can be conceived without departing from the spirit and scope of the invention.
Claims
1. An energy-saving continuous electrolytic cleaning device for metal wires, characterized in that, The utility model relates to an electrolytic tank (1) for storing electrolyte, a plurality of tubular electrolytic cleaning assemblies (2) arranged in parallel in the electrolytic tank (1), each electrolytic cleaning assembly (2) comprising a plurality of insulating sleeves (21), a plurality of electrode tubes (22), a positive electrode plate (23), and a negative electrode plate (24), the insulating sleeves (21) being coaxially arranged, each of the insulating sleeves (21) being provided with a positioning groove (211) at both ends, a first central through hole (212) being provided between the bottom surfaces of the positioning grooves (211), the electrode tubes (22) being arranged between adjacent insulating sleeves (21) and coaxially arranged with the insulating sleeves (21), both ends of each electrode tube (22) extending into the positioning grooves (211), each electrode tube (22) being provided with a conductive column (25) on the upper side, the conductive column (25) comprising positive electrode columns (251) and negative electrode columns (252), the positive electrode columns (251) and the negative electrode columns (252) being alternately arranged, all the positive electrode columns (251) being connected to the positive electrode plate (23), and all the negative electrode columns (252) being connected to the negative electrode plate (24), the positive electrode plate (23) and the negative electrode plate (24) being connected to a direct current power supply, the bottom of each electrolytic cleaning assembly (2) being provided with a liquid inlet branch pipe (26), the bottom surface of the electrolytic tank (1) being provided with a liquid outlet hole (11), the lower end of the liquid inlet branch pipe (26) being connected to a liquid inlet main pipe (27), a reflux pipe (3) being provided between the liquid inlet main pipe (27) and the liquid outlet hole (11), the liquid inlet main pipe (27) being provided with a liquid pump (271), the two ends of each metal wire (4) in each electrolytic cleaning assembly (2) being coaxially arranged through corresponding first lead holes (12) in the side walls of the electrolytic tank (1), each electrolytic cleaning assembly (2) being provided with a connecting plate (28), the connecting plate (28) being arranged between the insulating sleeve (21) and the positive electrode plate (23), the conductive column (25) passing through the connecting plate (28), the two ends of the connecting plate (28) being detachably connected to the electrolytic tank (1), the edges of the connecting plates (28) between adjacent electrolytic cleaning assemblies (2) being abutted and sealed, so that the upper end of the electrolytic tank (1) is closed by the connecting plates (28), the bottom of the electrolytic tank (1) being provided with a condensate tank (13), the reflux pipe (3) being configured as a heat exchange coil (31), the heat exchange coil (31) being arranged in the condensate tank (13), the inner sides of the two ends of the electrolytic tank (1) being provided with stepped surfaces (14), the stepped surfaces (14) being provided with a plurality of connecting columns (141), the connecting columns (141) being provided with connecting holes (142), the two ends of the connecting plate (28) being provided with clamping grooves (281) corresponding to the connecting columns (141), the clamping grooves (281) being clamped into the connecting columns (141) and locked by locking members (143) to form detachable connections. 2. The energy-saving continuous wire electrolytic cleaning device according to claim 1, characterized in that, 3. The energy-saving continuous wire electrolytic cleaning device according to claim 1, characterized in that, 4. The energy-saving continuous wire electrolytic cleaning device according to claim 2, characterized in that, 5. The energy-saving continuous wire electrolytic cleaning device according to claim 1 or 2 or 3, characterized in that, The electrolytic cell (1) is provided with overflow cavities (15) outside both ends, the first lead holes (12) are communicated with the overflow cavities (15), the outer side wall of the overflow cavities (15) is provided with second lead holes (151) coaxially distributed with the first lead holes (12); the upper end of the electrolytic cell (1) is provided with a cover plate (16), which completely closes the upper end of the electrolytic cell (1) and the upper end of the overflow cavity (15).
6. The energy-saving continuous electrolytic cleaning device for metal wires according to claim 1, characterized in that, Both ends of the insulating sleeve (21) are provided with through connection through holes (213), the connection through holes (213) are provided with connecting rods (214), the connecting rods (214) pass through the connection through holes (213) of all insulating sleeves (21), and both ends of the connecting rod (214) are fastened and connected through fasteners (215).
7. The energy-saving continuous electrolytic cleaning device for metal wires according to claim 1 or 6, characterized in that, Both outer sides of the electrode tube (22) are provided with annular grooves (222), and the annular grooves (222) are provided with sealing rings (223) between the inner walls of the positioning grooves (211).
8. The energy-saving continuous electrolytic cleaning device for metal wires according to claim 1, characterized in that, The center of the electrode tube (22) is provided with a second center through hole (221), and the diameter of the second center through hole (221) is greater than the diameter of the first center through hole (212).
9. The energy-saving wire continuous electrolytic cleaning device according to claim 8, characterized in that, The diameter of the first center through hole (212) is configured as r, and the diameter of the second center through hole (221) is configured as R, wherein 4mm≤r≤6mm, 10mm≤R≤12mm.
10. The energy-saving continuous electrolytic cleaning device for metal wires according to claim 1, characterized in that, The insulating sleeve (21) is made of transparent insulating resin, and the electrode tube (22) is made of aluminum alloy.