Array type arc heater cathode and preparation method

Abstract

The invention belongs to the technical field of aerodynamic thermal protection of hypersonic aircrafts, and discloses an array type arc heater cathode and a preparation method. The array type electric arc heater cathode comprises a needle-shaped array and a base body, wherein the needle-shaped array is embedded into the base body; the needle-shaped array is composed of needle-shaped metal wires, and the metal wires are made of low-work-function materials. The base body is made of high-thermal-conductivity metal. The preparation method comprises the steps of material preparation; preparing a template; threading the template; a fixed array; drying the array; casting the array; and repairing the array. According to the array type electric arc heater cathode and the preparation method, the whole cathode arc spots are dispersed into spot-shaped arc spots, the heat flux density of a single arc spot is reduced, then cathode ablation is reduced, and the array type electric arc heater cathode has the advantages that the number of the arc spots is larger, the arc spots are more dispersed, and the current of the single spot is smaller; the defects of oxide skin, ablation pits, ablation holes and the like caused by overlarge heat flux density of cathode arc spots are overcome, the service life of the cathode is prolonged, and the cathode has engineering practical value.

Description

Technical Field

[0001] The present invention belongs to the technical field of aerodynamic thermal protection of hypersonic aircraft, and in particular relates to an array type electric arc heater cathode and a preparation method thereof. Background Art

[0002] High-power arc heaters are currently the only equipment that can simulate the thermal environment of hypersonic vehicles on the ground for a long time and more realistically. As hypersonic vehicles develop towards higher Mach numbers, arc heaters are needed to simulate high-speed and high-pressure thermal environments, which requires their cathodes to work for a long time under higher pressures and larger currents. At present, arc heater cathodes are mainly made of oxygen-free copper. The cathode is easily ablated when operating under high voltage and high current, forming ablation defects such as oxide scale, ablation pits, and ablation holes, which can no longer meet existing usage requirements.

[0003] The main reason for cathode ablation is that the heat flux density of the arc spot is too concentrated, which quickly forms a molten pool. In order to reduce cathode ablation, various arc control technologies have been studied and developed, such as multi-electrode technology, multi-heater technology, etc. Although they can reduce ablation to a certain extent, these technologies mainly disperse the arc from a macroscopic perspective to reduce electrode ablation. The arcs are easily disturbed by various factors, and the arc division is not stable. Previous studies have shown that adding low work function elements to oxygen-free copper cathodes can attract and disperse arcs, transforming arc spots from discharging on the substrate to discharging on low work function elements, and then transforming single arc spots into dispersed arc spots, thereby improving the cathode's ablation resistance. At present, reducing cathode ablation and designing stable dispersed cathode arc spots are the core work of ground heat protection experimental research on arc heaters.

[0004] Currently, there is an urgent need to develop an array arc heater cathode and a preparation method. Summary of the invention

[0005] One technical problem to be solved by the present invention is to provide an array type electric arc heater cathode, and another technical problem to be solved by the present invention is to provide a method for preparing an array type electric arc heater cathode.

[0006] The array type arc heater cathode of the present invention comprises a needle array and a substrate, wherein the needle array is embedded in the substrate; the needle array is composed of needle-shaped metal wires, the material of the metal wires is a low work function material; and the material of the substrate is a high thermal conductivity metal.

[0007] Furthermore, the low work function material includes hafnium, lanthanum and niobium. Since the arc heater mainly works in the air, the low work function element in the cathode is easily oxidized and poisoned during discharge, so that the cathode no longer has excellent electron emission ability. Therefore, the selected low work function element not only needs to have basic conditions such as high melting point and low work function, but also needs to consider the element's ability to discharge stably in the air. Hafnium, lanthanum, niobium, etc. are more suitable.

[0008] Furthermore, the metal with high thermal conductivity includes copper and silver.

[0009] Furthermore, the spacing, diameter and height of the metal wires are determined according to the heat transfer between the metal wires and the substrate, and it is required to minimize the melting volume of the metal wires in the needle-shaped array.

[0010] The method for preparing the cathode of the array type electric arc heater of the present invention comprises the following steps: S10. Material preparation; Prepare the metal wires needed for the needle array; S20. Template preparation; Use CAD to draw an array drawing with a circular hole array drawn on it, and print two array drawings in a 1:1 ratio; Prepare 2 pieces of EPE foam boards of the same size as the array drawings; According to the order of array drawing, EPE pearl cotton foam board, EPE pearl cotton foam board, array drawing, stack them from bottom to top and bond them with solid glue to obtain the template; S30. Template threading; Use a steel needle to pre-punch the circular holes arrayed on the template, requiring the upper and lower circular holes to be aligned when punched out; Insert the metal wires into each circular hole to obtain a needle-shaped array; Use the steel needle again to pull the two EPE pearl cotton foam boards upward and downward along the gap between the metal wires, until the upper EPE pearl cotton foam board is 5mm away from the top of the metal wire, and the lower EPE pearl cotton foam board is 5mm away from the end of the metal wire; Adjust and fix the EPE foam plates on the upper and lower sides to ensure that the metal wires of the needle array are vertical; S40. Fixed array; The casting method is used for processing. High-temperature materials are needed to fix the bottom of the needle array. The high-temperature materials must not only be resistant to high temperatures and not react with the matrix and the metal wire, but also have to ensure strength and be applicable to various shapes of needle arrays. Alumina powder is the first choice. Alumina powder and glass water are mixed in a ratio of 2:1 to obtain a uniform alumina slurry, and the alumina slurry is poured into the mold. Then the lower section of the needle array is vertically inserted into the alumina slurry and fixed. S50. Drying array; The mold was placed in an oven and baked at 80°C for 5 hours. After the alumina slurry was completely solidified, the EPE pearl cotton foam board and the array drawing were torn off to obtain the array mold. S60. Casting array; The high thermal conductivity metal is melted; at the same time, the array mold is placed in a crucible for preheating; after the high thermal conductivity metal is melted, the crucible is quickly clamped out and placed on a high-frequency vibration platform, and the high thermal conductivity metal liquid is poured into the crucible. The high-frequency ultrasonic vibrator drives the high-frequency vibration platform to vibrate for a predetermined time, and then the crucible is placed in water for rapid cooling; the casting process is completed on the high-frequency vibration platform, which can not only accelerate the fluidity of the high thermal conductivity metal liquid and reduce the bubbles generated during the casting process, but also reduce the reaction time between the high thermal conductivity metal liquid and the metal wire of the needle-shaped array, and control the metal wire to react slightly with the high thermal conductivity metal liquid to achieve a metallurgical bonding state; S70. Repair array; The alumina slurry segment is cut off by a wire cutting machine to obtain the required array arc heater cathode.

[0011] Furthermore, the casting method is replaced by an additive manufacturing method.

[0012] The array-type arc heater cathode of the present invention comprises a needle array composed of metal wires with low work function elements and a substrate, wherein the metal wires are evenly distributed in an array in the substrate, which not only transforms the arc spot from discharging on the substrate to discharging on the metal wires with low work function elements, but also enables the distribution of the needle array to be accurately adjusted artificially to achieve an optimal spotted arc spot state.

[0013] The array-type electric arc heater produced by the preparation method of the array-type electric arc heater cathode of the present invention disperses the entire cathode arc spot into spot-like arc spots, reduces the heat flux density of a single arc spot, and thereby reduces cathode ablation. It has the advantages of more arc spots, more dispersed arc spots, and smaller current of a single spot. It improves the various defects of the cathode arc spot such as oxide scale, ablation pits, ablation holes, etc. formed due to excessive heat flux density of the cathode arc spot, increases the service life of the cathode, and has practical engineering value. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 A schematic structural diagram of an array type arc heater cathode according to an embodiment; Figure 2a is a step-by-step flow chart of a method for preparing an array arc heater cathode of an embodiment (the first step); Figure 2b is a step-by-step flow chart of a method for preparing an array arc heater cathode of an embodiment (second step); Figure 2cis a step-by-step flow chart of a method for preparing an array arc heater cathode of an embodiment (the third step); Figure 2d is a step-by-step flow chart of a method for preparing an array arc heater cathode of an embodiment (step 4); Figure 2e is a step-by-step flow chart of a method for preparing an array arc heater cathode of an embodiment (the fifth step); Figure 2f 1 is a step-by-step flow chart of a method for preparing an array arc heater cathode according to an embodiment (the sixth step).

[0015] In the figure, 1. needle array; 2. substrate; 3. array drawing; 4. EPE pearl cotton foam board; 5. steel needle; 6. metal wire; 7. alumina slurry; 8. high-frequency ultrasonic vibrator; 9. high-frequency vibration platform; 10. crucible. DETAILED DESCRIPTION

[0016] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in combination with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0017] Embodiment: The cathode of the array arc heater of this embodiment is shown in FIG. Figure 1 The material used for the substrate 2 is oxygen-free copper, the low work function material used for the needle array 1 is a hafnium wire segment with a diameter of 1 mm, the needle array 1 is rectangular, the hafnium wire segment spacing is 1 mm, and the height is 30 mm.

[0018] The method for preparing the cathode of the array arc heater of this embodiment comprises the following steps: S10. Material preparation; Cut the hafnium wire with a diameter of 1mm into several hafnium wire segments with a length of 30mm for later use; S20. Template preparation: Use CAD to draw array drawing 3, on which a 12×12 square circular hole array with a diameter of 1mm and a spacing of 1mm is drawn (the diameter and spacing of the circular holes in array drawing 3 can be adjusted as required), print out 2 sheets of array drawing 3 in a 1:1 ratio, and cut them for later use; cut the 2mm thick EPE pearl cotton foam board into 2 pieces of EPE pearl cotton foam boards 4 of the same size as array drawing 3, and stack the 2 pieces of EPE pearl cotton foam boards 4 up and down to obtain a combination. Figure 2a As shown, the array drawing 3 is aligned up and down and placed on the upper and lower sides of the assembly respectively, and each layer is bonded with solid glue to obtain the following Figure 2bTemplate shown; S30. Template threading; like Figure 2b As shown, first, use a steel needle 5 with a diameter of about 1 mm to pre-punch the 1 mm diameter circular holes of the array on the template, and pay attention to aligning the upper and lower circular holes; Figure 2c As shown, secondly, the hafnium wire segments are inserted into each circular hole to obtain a needle array 1; as shown Figure 2d As shown, the steel needle 5 is used again to pull the two EPE pearl cotton foam plates 4 upward and downward along the gap between the hafnium wire segments, until the upper EPE pearl cotton foam plate 4 is 5 mm away from the top of the hafnium wire segment, and the lower EPE pearl cotton foam plate 4 is 5 mm away from the end of the hafnium wire segment; finally, the EPE pearl cotton foam plates 4 on the upper and lower sides are adjusted and fixed to ensure that each hafnium wire segment of the needle array 1 is vertical; S40. Fixed array; The casting method is adopted to mix the aluminum oxide powder and the glass water in a ratio of 2:1 to obtain a uniform aluminum oxide slurry 7, and the aluminum oxide slurry 7 is poured into a mold; Figure 2e As shown, the lower section of the needle array 1 is then vertically inserted into the alumina slurry 7 and fixed; S50. Drying array; The mold was placed in an oven and baked at 80° C. for 5 h. After the alumina slurry 7 was completely solidified, the EPE pearl cotton foam board 4 and the array drawing 3 were torn off to obtain the array mold; S60. Casting array; Put oxygen-free copper into a box furnace and melt it at 1250°C. At the same time, put the array mold into the crucible 10 and preheat it at 500°C for 10 minutes. After the oxygen-free copper is melted, quickly take out the crucible 10. Figure 2f As shown, the crucible 10 is placed on a high-frequency vibration platform 9, oxygen-free copper liquid is poured into the crucible 10, and the high-frequency ultrasonic vibrator 8 drives the high-frequency vibration platform 9 to vibrate for 10 seconds, and then the crucible 10 is immediately placed in water for rapid cooling; S70. Repair array; A wire cutting machine is used to cut off 7 sections of alumina slurry to obtain the required array arc heater cathode.

[0019] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. An array type arc heater cathode, characterized in that: The array-type arc heater cathode comprises a needle array (1) and a substrate (2), wherein the needle array (1) is embedded in the substrate (2); the needle array (1) is composed of needle-shaped metal wires (6), wherein the material of the metal wires (6) is a low work function material; and the material of the substrate (2) is a high thermal conductivity metal.

2. The array type arc heater cathode according to claim 1, characterized in that: The low work function material includes hafnium, lanthanum h and niobium.

3. The array type arc heater cathode according to claim 1, characterized in that: The metals with high thermal conductivity include copper and silver.

4. The array type arc heater cathode according to claim 1, characterized in that: The spacing, diameter and height of the metal wires (6) are determined according to the heat transfer between the metal wires (6) and the substrate (2), and are required to minimize the melting volume of the metal wires (6) of the needle-shaped array (1).

5. A method for preparing an array type electric arc heater cathode, which is used to prepare the array type electric arc heater cathode according to any one of claims 1 to 4, characterized in that: The following steps are involved: S10. Material preparation; Preparing metal wires (6) required for the needle array (1); S20. Template preparation; Draw an array drawing (3) using CAD, on which a circular hole array is drawn, and print two array drawings (3) in a 1:1 ratio; Prepare two EPE foam boards (4) of the same size as the array drawing (3); According to the order of the array drawing (3), the EPE pearl cotton foam board (4), the EPE pearl cotton foam board (4), and the array drawing (3), they are stacked from bottom to top and bonded with solid glue to obtain a template; S30. Template threading; Use a steel needle (5) to pre-punch the circular holes of the array on the template, requiring the upper and lower circular holes to be aligned when punched out; Inserting metal wires (6) into the circular holes respectively to obtain a needle-shaped array (1); Use the steel needle (5) again to pull the two EPE pearl cotton foam boards (4) upward and downward respectively along the gap between the metal wires (6) until the upper EPE pearl cotton foam board (4) is 5 mm away from the top of the metal wire (6) and the lower EPE pearl cotton foam board (4) is 5 mm away from the end of the metal wire (6); Adjust and fix the EPE pearl cotton foam plates (4) on the upper and lower sides to ensure that the metal wires (6) of the needle array (1) are vertical; S40. Fixed array; The process is processed by casting; alumina powder and glass water are mixed in a ratio of 2:1 to obtain a uniform alumina slurry (7), and the alumina slurry (7) is poured into a mold; and the lower section of the needle array (1) is vertically inserted into the alumina slurry (7) and fixed; S50. Drying array; The mold is placed in an oven and baked at 80° C. for 5 h. After the alumina slurry (7) is completely solidified, the EPE pearl cotton foam board (4) and the array drawing (3) are torn off to obtain the array mold; S60. Casting array; The high thermal conductivity metal is melted; at the same time, the array mold is placed in a crucible (10) for preheating; after the high thermal conductivity metal is melted, the crucible (10) is quickly clamped out and placed on a high-frequency vibration platform (9), the high thermal conductivity metal liquid is poured into the crucible (10), the high-frequency ultrasonic vibrator (8) drives the high-frequency vibration platform (9) to vibrate for a predetermined time, and then the crucible (10) is placed in water for rapid cooling; S70. Repair array; The alumina slurry (7) segment is cut by a wire cutting machine to obtain the required array arc heater cathode.

6. The method for preparing the cathode of the array arc heater according to claim 5, characterized in that: The casting method is replaced by an additive manufacturing method.

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