A plasma torch point cathode structure and preparation method thereof

Abstract

The invention discloses a plasma torch point cathode structure and a preparation method thereof. The point cathode structure comprises a cathode copper substrate and a cathode silver substrate. A through hole is provided in the cathode copper substrate. A cooling cavity is provided at the bottom of the through hole. The cathode silver substrate passes through the through hole, and its bottom end is located in the cooling cavity. At least one small hole is provided at the top center of the cathode silver substrate, and particles are welded in the small hole. The preparation method comprises the following steps: 1) preparing a cathode copper substrate and a cathode silver substrate; 2) installing the cathode silver substrate in the through hole of the cathode copper substrate; 3) preparing a point cathode rough blank; 4) vertically placing the point cathode rough blank in a vacuum atmosphere furnace, vacuuming and heating with a vacuum pump, and then cooling to room temperature to obtain a plasma torch point cathode structure. The point cathode structure of the invention has good electrical conductivity, and the preparation method thereof has a simple process, low processing cost, is suitable for industrial production, reduces the burning speed of the point cathode, and prolongs the life of the point cathode.

Description

Technical Field

[0001] The invention relates to the field of plasma technology, and in particular to a plasma torch point cathode structure and a preparation method thereof. Background Art

[0002] With the continuous development of science and technology, plasma technology has been widely used. It is mainly used in the fields of plasma ignition, plasma spraying, metal smelting, plasma heating to manufacture nanomaterials, cutting, garbage incineration and waste treatment. Plasma is a state formed under the ionosphere or discharge phenomenon. Along with the discharge phenomenon, active chemicals such as excited atoms, excited molecules, dissociated atoms, free atomic groups, atomic or molecular ion groups, and reactions caused by their collision with other chemicals will be generated. In the plasma generator, the discharge action causes the working gas molecules to lose their outer electrons and form an ion state, which generates high temperatures after mutual collision, and the temperature can reach more than tens of thousands of degrees.

[0003] At present, the point cathode structure is used in plasma torches with a power of less than 150KW, and its point cathode arc stability is good. The point cathode of a plasma torch is a component that emits electrons, and its materials are mostly carbon rods and pure silver. Although carbon rods have the advantages of high melting point and good electrical and thermal conductivity, they are easily oxidized at high temperatures. Similarly, metallic silver has excellent electrical and thermal conductivity, but its melting point is low and it is difficult to withstand the high temperature environment of the cathode. In addition, the electron work function of both is large, which leads to the cathode being easily ablated, reducing its life and increasing the cost of use. Summary of the invention

[0004] The technical problem to be solved by the present invention is to overcome the deficiencies of the prior art and provide a plasma torch point cathode structure with low power consumption, simple structure and easy manufacture, and a preparation method thereof.

[0005] The technical solution adopted by the present invention to solve the technical problem is: a plasma torch point cathode structure, comprising a cathode copper substrate and a cathode silver substrate, wherein a through hole is provided in the cathode copper substrate, a cooling cavity is provided at the lower part of the through hole, the cathode silver substrate passes through the through hole, and its bottom end is located in the cooling cavity, at least one small hole is provided at the top center of the cathode silver substrate, and particles are welded in the small hole.

[0006] By providing a cooling cavity, the heat of the point cathode is introduced into the cooling cavity through the cathode silver matrix, so that the point cathode is not easily burned, the service life of the point cathode is extended, and the cost is saved.

[0007] Preferably, the particles are cylindrical particles. The particles can also be stacked into square particles according to the shape of the small holes, but the stability of electron emission from cylindrical particles is better, and the arc formed is more uniform and stable.

[0008] Furthermore, the cylindrical particles are formed by stacking cathode electron emission materials with a purity of more than 95%.

[0009] Preferably, the cathode electron emission material is any one of hafnium, tungsten, tantalum, niobium, zirconium, yttrium or an alloy material thereof (the alloy material refers to any one of hafnium alloy material, tungsten alloy material, tantalum alloy material, niobium alloy material, zirconium alloy material, yttrium alloy material).

[0010] Hafnium, tungsten, tantalum, niobium, zirconium and yttrium have the characteristics of high melting point and low work function. Under the same current density, the working temperature of the emission material is reduced, thereby reducing the burning speed of the cathode at the plasma torch point and increasing the service life. Since the thermal conductivity of hafnium, tungsten, tantalum, niobium, zirconium and yttrium is lower than that of silver or copper, hafnium, tungsten, tantalum, niobium, zirconium and yttrium are welded into the small holes of the cathode silver matrix to improve its thermal conductivity and increase the stability of its electron emission.

[0011] Preferably, the number of the small holes is 1-30.

[0012] When the number of small holes exceeds 30, the area of ​​the point cathode ablation zone is too large, which will reduce the service life of the point cathode; and when the number of small holes exceeds 30, the heat of the point cathode is introduced into the cooling cavity through the cathode silver matrix and the cooling time is long, and the heat of the point cathode is not easy to dissipate, which increases the degree of ablation of the point cathode and reduces its service life.

[0013] Furthermore, the diameter of the small hole is 0.5-3 mm and the depth is 0.9-7.9 mm.

[0014] The diameter and depth of the small hole affect the thickness of the cathode electron emission material in the small hole. When the diameter is less than 0.5mm and the depth is less than 0.9mm, the thickness of the cathode electron emission material in the prepared point cathode is thin and its life is short when in use; when the diameter of the small hole is greater than 3mm, when the number of small holes is the same, the area of ​​the circle surrounded by multiple small holes is larger, thereby making the area of ​​the ablation zone of the point cathode larger, increasing the degree of ablation of the point cathode; when the depth is greater than 7.9mm, the time required for the heat of the ablation zone of the point cathode to be introduced into the cooling cavity through the cathode silver matrix is ​​prolonged, resulting in a slow cooling speed and poor cooling effect, which reduces the service life of the point cathode.

[0015] Furthermore, the bottom end of the cathode silver substrate is arc-shaped, which increases the heat dissipation area of ​​the point cathode, improves the contact area between the bottom end of the cathode silver substrate and the cooling water in the cooling cavity, increases the heat dissipation speed of the point cathode, and extends the service life of the point cathode.

[0016] Furthermore, the outer surface of the cathode silver substrate in the through hole is welded to the inner surface of the cathode copper substrate via a silver welding ring.

[0017] The technical solution adopted by the present invention to solve another technical problem is: a method for preparing a plasma torch point cathode structure, comprising the following steps:

[0018] 1) Making a cathode copper matrix and a cathode silver matrix: leaving a gap for welding between the inner surface of the cathode copper matrix and the outer surface of the cathode silver matrix, and opening at least one small hole at the top center of the cathode silver matrix;

[0019] 2) Install the cathode silver substrate in the through hole of the cathode copper substrate so that its bottom end is located in the cooling cavity of the cathode copper substrate;

[0020] 3) Place a welding ring in the gap of step 1), fill the welding powder into the small hole, and then pour the cathode electron emission material into the small hole to stack it into cylindrical particles, and place a heavy object on top of the cylindrical particles to obtain a cathode rough blank;

[0021] 4) Place the cathode blank obtained in step 3) vertically in a vacuum furnace and evacuate the furnace to a vacuum degree of 10 -5 -10Pa, set the heating rate to 2℃ / min-10℃ / min, raise the temperature in the vacuum atmosphere furnace from room temperature to 800℃-950℃, maintain the highest temperature for 5min-60min and then cool to room temperature to obtain the plasma torch point cathode structure.

[0022] Furthermore, in step 1), the gap is 0.05-0.5 mm, the number of small holes is 1-30, the diameter of the small holes is 0.5-3 mm, and the depth is 0.9-7.9 mm.

[0023] Furthermore, in step 3), the solder ring is a silver solder ring, the solder powder is composed of 62%-82% silver and 38%-18% copper, the filling height is 0.1-7mm, the diameter of the cylindrical particles is 0.5-3mm, and the height is 1-8mm.

[0024] Through the welding ring and welding powder, after high temperature heating is adopted to form a melt of the welding ring, the cathode silver matrix is ​​welded in the cathode copper matrix, so as to improve the efficiency of preparing the point cathode structure; after high temperature heating is adopted to form a melt of the welding powder, the cylindrical particles are welded in the small hole, and there is no thermal resistance in the combination of the cathode silver matrix and the welding powder, so as to improve the thermal conductivity of the point cathode.

[0025] Beneficial effects of a plasma torch point cathode structure and a preparation method thereof of the present invention:

[0026] (1) The present invention provides a plasma torch point cathode structure, in which a small hole is provided on the cathode silver substrate and a cathode electron emission material is welded into the small hole, so that the ablation zone (i.e., arc zone) of the point cathode during actual ignition is located within the circumference surrounded by a plurality of small holes. Compared with a pure silver cathode, the area of ​​the point cathode ablation zone is reduced, the degree of ablation is reduced, and the life of the point cathode is increased;

[0027] (2) The present invention provides a plasma torch point cathode structure, which has a simple structure and good electrical and thermal conductivity. By placing the bottom of the cathode silver substrate in a cooling chamber, the heat during the ablation of the point cathode is introduced into the cooling chamber through the cathode silver substrate. In addition, the center of the point cathode uses an emission material with a high melting point and low work function, which improves the electron emission capability, reduces the temperature required for electron emission, reduces the ablation speed of the point cathode, and prolongs the service life of the point cathode.

[0028] (3) The present invention provides a method for preparing a plasma torch point cathode structure. The method has a simple preparation process, low processing cost, and is suitable for industrial production. The method adopts a welding method after melting a welding ring and welding powder to improve the preparation efficiency of the point cathode structure. The method adopts a combination of a low work function and a high melting point emission material with a cathode silver matrix. Compared with a conventional pure silver cathode, the method has a stronger electron emission capability, a brighter arc, and a more stable arc shape, which reduces the ablation rate of the point cathode and extends its service life. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 — is a schematic diagram of a plasma torch cathode structure of the present invention;

[0030] Figure 2 -for Figure 1 Top view of the cathode structure at the plasma torch point;

[0031] Figure 3 — is a schematic diagram of a point cathode rough blank during the preparation process of a plasma torch point cathode structure of the present invention.

[0032] The above-mentioned figure marks: 1-cathode copper substrate, 2-cathode silver substrate, 3-small hole, 31-cylindrical particles, 32-solder powder, 4-cooling chamber, 5-weight block, 6-ablation zone. DETAILED DESCRIPTION

[0033] The present invention is further described below in conjunction with the accompanying drawings and examples, but these specific implementation schemes do not limit the protection scope of the present invention in any way.

[0034] Example 1

[0035] See also Figure 1-2A plasma torch point cathode structure, comprising a cathode copper substrate 1 and a cathode silver substrate 2, wherein a through hole is provided in the cathode copper substrate 1, and the bottom end thereof is in an arc shape, a cooling chamber 4 is provided at the lower part of the through hole, the cathode silver substrate 2 passes through the through hole, and the bottom end thereof is located in the cooling chamber 4, 7 small holes 3 are provided at the top center of the cathode silver substrate 2, the diameter of the small hole 3 is 2.05 mm, and the depth is 3.9 mm, and cylindrical particles 31 are welded in the small holes 3, and the cylindrical particles 31 are formed by stacking cathode electron emission materials with a purity of 99%, and the cathode electron emission material is hafnium. By welding the cathode electron emission material in the small holes, when actually igniting, the ablation zone 6 of the cathode is located within the circumference of the cathode silver substrate 2 surrounded by a plurality of small holes 3, and compared with a pure copper-silver electrode (the ablation zone of a pure copper-silver electrode is the entire outer surface of the electrode), the area of ​​the point cathode ablation zone 6 is reduced, and its service life is increased. The outer surface of the cathode silver substrate 2 in the through hole is welded to the inner surface of the cathode copper substrate 1 via a silver welding ring.

[0036] Example 2

[0037] See also Figure 1-3 , a method for preparing a plasma torch point cathode structure, comprising the following steps:

[0038] 1) Manufacturing a cathode copper substrate 1 and a cathode silver substrate 2: leaving a gap for welding between the inner surface of the cathode copper substrate 1 and the outer surface of the cathode silver substrate 2, the gap is 0.2 mm, and 7 small holes 3 are opened at the top center of the cathode silver substrate 2, the diameter of the small holes 3 is 2.05 mm, and the depth is 3.9 mm;

[0039] 2) Install the cathode silver substrate 2 in the through hole of the cathode copper substrate 1 so that its bottom end is located in the cooling cavity 4 of the cathode copper substrate 1;

[0040] 3) A silver solder ring is placed in the gap of step 1), and solder powder 32 is filled into the small hole 3. The solder powder 32 is composed of 72% silver and 28% copper, and the filling height is 2 mm. Tantalum with a purity of 99% is then poured into the small hole 3 to form a cylindrical particle 31 with a diameter of 2 mm and a height of 4 mm. A weight block 5 is placed above the cylindrical particle 31 to obtain a cathode rough blank, such as Figure 3 As shown;

[0041] 4) Place the cathode blank obtained in step 3) vertically in a vacuum furnace and evacuate the furnace to a vacuum degree of 10 -3 Pa, set the heating rate to 5 °C / min, raise the temperature in the vacuum atmosphere furnace from room temperature to 850 °C, keep the highest temperature for 20 min and then cool to room temperature to obtain the plasma torch point cathode structure, such as Figure 1 shown.

[0042] Example 3

[0043] A method for preparing a plasma torch point cathode structure comprises the following steps:

[0044] 1) Manufacturing a cathode copper substrate 1 and a cathode silver substrate 2: leaving a gap for welding between the inner surface of the cathode copper substrate 1 and the outer surface of the cathode silver substrate 2, the gap is 0.15 mm, and 9 small holes 3 are opened at the top center of the cathode silver substrate 2, the diameter of the small holes 3 is 2.5 mm, and the depth is 5 mm;

[0045] 2) Install the cathode silver substrate 2 in the through hole of the cathode copper substrate 1 so that its bottom end is located in the cooling cavity 4 of the cathode copper substrate 1;

[0046] 3) A silver solder ring is placed in the gap of step 1), and solder powder 32 is filled into the small hole 3. The solder powder 32 is composed of 78% silver and 22% copper, and the filling height is 2.5 mm. Tantalum with a purity of 98% is poured into the small hole 3 to form cylindrical particles with a diameter of 2.45 mm and a height of 5.1 mm. A weight block 5 is placed above the cylindrical particles 31 to obtain a cathode rough blank;

[0047] 4) Place the cathode blank obtained in step 3) vertically in a vacuum furnace and evacuate the furnace to a vacuum degree of 10 -2 Pa, set the heating rate to 5 °C / min, raise the temperature in the vacuum atmosphere furnace from room temperature to 870 °C, maintain the highest temperature for 30 min and then cool to room temperature to obtain the plasma torch point cathode structure.

[0048] Example 4

[0049] A method for preparing a plasma torch point cathode structure comprises the following steps:

[0050] 1) Manufacturing a cathode copper substrate 1 and a cathode silver substrate 2: leaving a gap for welding between the inner surface of the cathode copper substrate 1 and the outer surface of the cathode silver substrate 2, the gap is 0.25 mm, and 12 small holes 3 are opened at the top center of the cathode silver substrate 2, the diameter of the small holes 3 is 1.85 mm, and the depth is 3.5 mm;

[0051] 2) Install the cathode silver substrate 2 in the through hole of the cathode copper substrate 1 so that its bottom end is located in the cooling cavity 4 of the cathode copper substrate 1;

[0052] 3) A silver solder ring is placed in the gap of step 1), and solder powder 32 is filled into the small hole 3. The solder powder 32 is composed of 80% silver and 20% copper, and the filling height is 1.5 mm. Then, hafnium with a purity of 99.9% is poured into the small hole 3 to stack and form cylindrical particles 31 with a diameter of 1.8 mm and a height of 3.8 mm. A weight block 5 is placed above the cylindrical particles 31 to obtain a cathode rough blank;

[0053] 4) The point cathode rough blank obtained in step 3) is placed vertically in a vacuum atmosphere furnace, and a vacuum pump is used to evacuate the furnace to a vacuum degree of 10 Pa. The heating rate is set to 6°C / min, and the temperature in the vacuum atmosphere furnace is increased from room temperature to 840°C. After maintaining the highest temperature for 10 minutes, it is cooled to room temperature to obtain a plasma torch point cathode structure.

[0054] The working principle and use method of the present invention are as follows: when the present invention is working, the prepared cathode silver substrate 2 is first installed on the cathode copper substrate 1, and the welding ring is placed in the gap between the cathode silver substrate 2 and the cathode copper substrate 1, the welding powder 32 is first placed in the small hole 3, and then the cathode electron emission material is poured into the small hole 3 to stack to form cylindrical particles 31, and then the weight block 5 is placed on the cylindrical particles 31, and after vacuuming, the welding ring and the welding powder 32 are heated in a vacuum atmosphere furnace to melt, and after the welding ring is melted, the cathode silver substrate 2 is welded in the cathode copper substrate 1, and after the welding powder 32 is melted, the cylindrical particles 31 are filled and welded in the small hole 3 of the cathode silver substrate 2 under the gravity of the weight block 5, so that the plasma torch point cathode structure is prepared.

[0055] The principle of the present invention using any one of hafnium, tungsten, tantalum, niobium, zirconium, yttrium or their alloy materials as the electron emission material of the point cathode is as follows:

[0056] According to the electron generation theory, materials with high melting points and low work functions are selected. The relationship between electron emission, the temperature of the emitter and the electron work function can be expressed by the following formula.

[0057] J=AT 2 exp(-Ф / KT)

[0058] Where: J is the current density (A / m 2 ); A is the emission constant; K is the Boltzmann constant; T is the temperature (K); Ф is the work function (eV). It shows that thermal electron emission is closely related to the temperature of the emitter and the electron work function. Assuming that the working temperature of the existing material is 1500K and its work function is 4.65eV, then under the same electron current density, the work function of the material is reduced to 3.03eV and the working temperature of the material is reduced to 1000K. The reduction of the work function can greatly reduce the working temperature of the material.

[0059] Table 1 Melting point and work function of metals

[0060]

[0061] As can be seen from Table 1, the melting points of hafnium, tantalum, zirconium and yttrium are higher than silver, and their work functions are lower than silver. Under the same current density, the operating temperature required for them to emit electrons is lower than that of silver, which reduces the operating temperature of the cathode electron emission material and reduces the ablation rate of the point cathode. The work functions of tungsten and niobium are equivalent to that of silver, but their melting points are significantly higher than silver. The higher the melting point of the electron emission material of the electrode, the lower its ablation rate, which further reduces the degree of cathode ablation.

[0062] The present invention measured the burning degree (cathode weight loss) of the cathode after field ignition of Examples 1-4 and the electrode made of pure silver, with a test current of 200A. The measurement results are shown in the following table:

[0063] Table 2 Cathode weight loss measurement results

[0064]

[0065] As can be seen from the above table, compared with the traditional pure silver electrode, the point cathode structure prepared by the method of the present invention reduces the work function of the point cathode, makes the point cathode have better electron emission performance, and improves the melting point of the material at the arc root of the point cathode material, thereby greatly reducing the cathode ablation rate. Under the same test conditions, the weight loss of the point cathode is significantly lower than that of the pure silver electrode, indicating that it improves the arc ablation resistance of the point cathode and reduces the ablation rate.

[0066] The above description is only a preferred embodiment of the present invention and does not constitute any form of limitation to the present invention. Although the present invention has been disclosed as a preferred embodiment as above, it is not intended to limit the present invention. Any technician familiar with the profession can make some changes or modifications to equivalent embodiments of equivalent changes using the technical contents disclosed above without departing from the scope of the technical solution of the present invention. However, any simple modification, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A plasma torch cathode structure, characterized in that: It comprises a cathode copper substrate and a cathode silver substrate, wherein a through hole is provided in the cathode copper substrate, a cooling cavity is provided at the lower part of the through hole, the cathode silver substrate passes through the through hole, and its bottom end is located in the cooling cavity, at least one small hole is provided at the top center of the cathode silver substrate, and particles are welded in the small hole; the particles are cylindrical particles, and the cylindrical particles are formed by stacking cathode electron emission materials with a purity of more than 95%, and the cathode electron emission material is any one of hafnium, tungsten, tantalum, niobium, zirconium, yttrium or their alloy materials.

2. A plasma torch point cathode structure as claimed in claim 1, characterized in that: The number of the small holes is 1-30.

3. A plasma torch point cathode structure as claimed in claim 2, characterized in that: The diameter of the small hole is 0.5-3 mm, and the depth is 0.9-7.9 mm.

4. A plasma torch point cathode structure as claimed in claim 1, characterized in that: The bottom end of the cathode silver matrix is ​​in an arc shape.

5. A plasma torch point cathode structure as claimed in claim 1, characterized in that: The outer surface of the cathode silver substrate in the through hole is welded to the inner surface of the cathode copper substrate via a silver welding ring.

6. A method for preparing a plasma torch point cathode structure according to any one of claims 1 to 5, characterized in that: The following steps are involved: 1) Making a cathode copper matrix and a cathode silver matrix: leaving a gap for welding between the inner surface of the cathode copper matrix and the outer surface of the cathode silver matrix, and opening at least one small hole at the top center of the cathode silver matrix; 2) Install the cathode silver substrate in the through hole of the cathode copper substrate so that its bottom end is located in the cooling cavity of the cathode copper substrate; 3) Place a welding ring in the gap of step 1), fill the welding powder into the small hole, and then pour the cathode electron emission material into the small hole to stack it into cylindrical particles, and place a heavy object on top of the cylindrical particles to obtain a cathode rough blank; 4) Place the point cathode rough blank obtained in step 3) vertically in a vacuum atmosphere furnace, use a vacuum pump to evacuate to a vacuum degree of 10-5-10Pa, set the heating rate to 2℃ / min-10℃ / min, increase the temperature in the vacuum atmosphere furnace from room temperature to 800℃-950℃, maintain the highest temperature for 5min-60min, and then cool to room temperature to obtain a plasma torch point cathode structure.

7. A method for preparing a plasma torch point cathode structure as claimed in claim 6, characterized in that: In the step 1), the gap is 0.05-0.5 mm, the number of small holes is 1-30, the diameter of the small holes is 0.5-3 mm, and the depth is 0.9-7.9 mm.

8. The method for preparing a plasma torch point cathode structure according to claim 6, characterized in that: The solder ring in step 3) is a silver solder ring, the solder powder is composed of 62%-82% silver and 38%-18% copper, the filling height is 0.1-7mm, the diameter of the cylindrical particles is 0.5-3mm, and the height is 1-8mm.

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