Method and equipment for detecting and controlling residual length of electrode in preparation process of nano powder

Abstract

The invention relates to the technical field of process regulation and control, and particularly discloses a method and equipment for detecting and controlling the residual length of an electrode in a nano powder preparation process. The method comprises the following steps: recording the average voltage U of an electric arc within a period of time t when an electrode is at different heights H, and obtaining the average electric field intensity EH of the electric arc corresponding to the different heights H; a relational expression between the distance h between the electrode sheath gas outlet and the molten pool and the electrode sheath gas pressure P is simulated; the arc voltage U'and the electrode sheath gas pressure P of the electrode at a certain height H are recorded, so that the arc length Larc is calculated, and h can be calculated by substituting the electrode sheath gas pressure P into a formula; and deducting the arc length Larc from the distance h between the electrode sheath gas outlet and the molten pool to obtain the electrode length Lel. According to the invention, the system is provided with instruments, so that the material depth and the electrode length can be continuously monitored on line in a non-stop state.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of process regulation, and more particularly, it relates to a method and device for detecting and controlling the remaining length of an electrode in a nanometer powder preparation process. BACKGROUND

[0002] Nanometer metal powder exhibits many properties that macroscopic materials do not have due to its special size, and its unique optical and electronic properties have great potential application value in the fields of electrochemistry, biomedicine, electronic information, and optics.

[0003] The preparation method of nanometer metal powder usually adopts evaporation condensation method. In the evaporation condensation method, the metal evaporation method includes electric explosion, radio frequency, and direct current arc plasma. Among them, the direct current arc plasma preparation method uses metal raw materials as the arc anode, tungsten, graphite, and other materials as the cathode, and a direct current power source maintains the discharge channel between the anode and the cathode to establish a direct current arc. In order to improve the yield of nanometer powder, the industry usually adopts the method of increasing the discharge strand number and increasing the arc current to input high energy. Therefore, the cathode bears extremely high energy density, the energy density is about 10 6 kW / m 2 , the current density is about 10 8 A / m 2 , and the temperature can reach 10 4 ℃, and the electrode has great ablation loss. Timely online monitoring of the remaining length of the electrode and compensating the suspension height are of great significance to maintaining the normal discharge of the direct current arc plasma system.

[0004] At present, there is no related literature in the industry for precise detection of the electrode length and the material depth. Based on this situation, the applicant urgently needs to develop an arc electrode remaining length detection and control method in a nanometer powder preparation process to make up for the blank of arc electrode control in the industry. SUMMARY

[0005] In order to make up for the blank of arc electrode control in the industry, the applicant provides an electrode remaining length detection and control method and device in a nanometer powder preparation process.

[0006] In a first aspect, the application provides an electrode remaining length detection and control method in a nanometer powder preparation process, which adopts the following technical solution: The electrode remaining length detection and control method in a nanometer powder preparation process includes the following steps: S1, when the system is just started, record the arc average voltage U in a period of time t at different heights H, and obtain the arc average electric field strength E corresponding to different heights H H , E H, H, U satisfy formula (1) : E H =U / (H0-D0-a-L ele0 ); wherein, a is the height position of the electrode clamped by the electrode lifting device, which should be recorded and taken as a preset value when the electrode is installed, H0 is the initial height of the electrode, D0 is the laying thickness of the material, and L ele0 is the initial length of the electrode; The relationship between the distance h between the electrode sheath gas outlet and the molten pool and the electrode sheath gas pressure P is simulated, and h and P satisfy formula (2) : h=A·P B +W, A, B and W are all empirical parameters; S2, record the arc voltage U' and the electrode sheath gas pressure P of the electrode at a certain height H', so as to calculate the arc length L arc , L arc =U' / E H ; The electrode sheath gas pressure P is substituted into formula (2), and h can be calculated; The distance h between the electrode sheath gas outlet and the molten pool is deducted by the arc length L arc , and the electrode length L ele is obtained, that is, L ele =h-L arc .

[0007] Further, the electrode sheath gas pressure P is not less than 40 kPa.

[0008] Further, the arc voltage U is the average value of x% quantile in a period of time t, and the value of x is 0-20.

[0009] Further, in the S1 step, the electrode height H is raised to the arc voltage U close to the no-load voltage of the direct current power supply.

[0010] Further, in the S1 step, the no-load voltage of the direct current power supply is not less than 200 V.

[0011] Further, after the S2 step, the material depth D can be calculated according to formula (3) : D= H'-L arc -L ele -C, C is the distance between the electrode terminal in the initial state and the initial material height. In general powder preparation, high-frequency arc starting is adopted, so C can be taken as 2-5 mm in the initial state.

[0012] In a second aspect, the application provides an electrode residual length detection and control device in a nano-powder preparation process, which adopts the following technical scheme: The electrode residual length detection and control device in a nano-powder preparation process is specially used for the electrode residual length detection and control method in the nano-powder preparation process, and comprises: An arc generator comprises an electrode base, an electrode fixed on the electrode base, and an electrode sheath gas pipeline provided on the electrode base, wherein an electrode sheath gas outlet of the electrode sheath gas pipeline is located at a top end of the electrode; An electrode lifting device is fixed on the electrode base to control the electrode to lift in a vertical direction; A height measurer is installed on the electrode lifting device to record the electrode height H; A sheath gas flow controller is installed on the electrode sheath gas pipeline to record the electrode sheath gas flow and control the sheath gas flow; An electrode sheath gas pressure gauge is installed on the electrode sheath gas pipeline to record the electrode sheath gas pressure P; A voltage gauge is electrically connected to the electrode to record the arc voltage U.

[0013] Further, the electrode sheath gas points to the electrode tip, and the electrode sheath gas flow is not less than 50 SLPM.

[0014] Further, the electrode sheath gas flow is controlled in a range of 150-200 SLPM.

[0015] The present application has at least the following advantages: First, the electrode length L ele By indirect method, the applicant finds that the electrode length L ele The sum of the arc length L arc and the distance h between the electrode sheath gas outlet and the molten pool is the electrode length, thus, the arc length L arc and the distance h between the electrode sheath gas outlet and the molten pool are calculated to obtain the electrode length; The arc can be equivalent to multiple gas discharge channels in parallel to form multiple electric fields, thus, the arc is simplified as a uniform electric field in the present application, and the average arc equivalent electric field strength E H corresponding to the arc average voltage U at different electrode heights H is calculated by the uniform electric field formula; when the electrode is at a certain height H', the average arc equivalent electric field strength E H is substituted, and the arc length L arc is calculated according to the arc voltage U'; Since the electrode length is short, the distance between the electrode sheath gas outlet and the anode material liquid surface is close, and a large back pressure is formed after the electrode sheath gas hits the anode material liquid surface, thus, there is a relationship between the distance h between the electrode sheath gas outlet and the molten pool and the electrode sheath gas pressure P; the present application can obtain the empirical relationship between h and P through multiple experiments; the electrode sheath gas pressure P is substituted into formula (2) to obtain the size of h.

[0016] The error rate between the electrode residual length calculated according to the above formula and the actual electrode residual length is reduced to within 10%, and the accuracy of indirect detection is high; the measurement parameters of the application are realized by the system self-instrument of the voltage meter, height measuring device and electrode sheath gas pressure meter originally installed in the process, so as to realize uninterrupted online monitoring of the material depth and electrode length in the non-stop state. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 A structure diagram of an electrode residual length detection and control device in a nano-powder preparation process.

[0018] Figure 2 A structure diagram of an electrode residual length detection and control device in a nano-powder preparation process. Figure 1 A specific structure diagram of an arc generator.

[0019] BRIEF DESCRIPTION OF DRAWINGS: 1, arc generator; 11, electrode base; 12, electrode; 13, electrode sheath gas pipeline; 14, electrode sheath gas outlet; 2, electrode lifting device; 3, height measuring device; 4, sheath gas flow controller; 5, voltmeter. DETAILED DESCRIPTION

[0020] The nano-metal powder is prepared by using a direct current arc plasma method. In the direct current arc plasma method, tungsten, graphite and other materials are used as cathodes, and the cathode electrode discharges to evaporate the metal into metal vapor. At present, in order to increase the yield of nano-metal powder, the industry chooses to increase the arc current and increase the input energy, but too high temperature is easy to cause the electrode to produce ablation. Therefore, the applicant needs to obtain the length of the remaining electrode in time and accurately, and at the same time adjust the suspension height of the electrode to maintain normal discharge parameters.

[0021] There is no related technology in the art for accurate measurement of electrode height. The applicant considers transferring the electrode detection method in other fields to this field: in a high temperature environment, the electrode length detection method generally uses image recognition technology, for example, CN117824778A, which uses camera recognition technology to cooperate with a displacement sensor to measure the distance of the electrode descending to the electrode arc starting, and measures the arc length of the electric arc furnace liquid level by an empirical formula. But this image recognition technology is not suitable for the preparation of nano-metal powder, the reasons are as follows: first, the high temperature arc makes the metal raw material evaporate, and the reactor is full of high concentration of metal particles, which interferes with the camera visual positioning and affects the electrode length measurement. Second, this method requires that the camera and the electrode calibration height have high collimation. However, the structure of the direct current arc plasma system is compact, and it is difficult to arrange the camera that meets the requirements. Finally, this method can only measure the material height / depth, but cannot measure the electrode length.

[0022] Based on the above situation, the applicant found through a large number of researches that the remaining electrode length L can be indirectly obtained by constructing an algorithm based on the detection table of the nano-powder production system ele And the material depth D.

[0023] The following embodiments are implemented in the following arc electrode remaining length detection and control device, and the following will be described in conjunction with the drawings of the specification Figures 1-2 The device will be further described in detail.

[0024] An arc electrode remaining length detection and control device in a nano-powder preparation process, referring to Figure 1 The nano-powder preparation process is carried out in an evaporation chamber, the top of the evaporation chamber is provided with an arc generator, and the bottom is provided with a crucible, which serves as an anode. The crucible is used to hold the material to be evaporated. The arc generator excites a high-temperature plasma arc stably, so that the material in the crucible evaporates, and the material forms a molten pool. The vapor state material is cooled at a very high speed to obtain nano-powder.

[0025] Referring to Figure 2 The arc generator includes an electrode base, an electrode, and an electrode sheath gas pipeline. The electrode is fixedly connected to one end of the electrode base and serves as a cathode. The electrode sheath gas pipeline is opened around the electrode base. The electrode sheath gas outlet of the electrode sheath gas pipeline is opened at one end of the electrode base close to the electrode. The gas flow of the electrode sheath gas outlet flows along the outer periphery of the electrode, and the electrode sheath gas flows towards the tip of the electrode.

[0026] Referring to Figure 1 And Figure 2 The electrode base is fixedly connected with an electrode lifting device. The electrode lifting device controls the moving distance of the electrode in the vertical direction by driving the electrode base. The electrode lifting device is fixedly connected with a height measurer. The height measurer can automatically record the height H of the electrode according to the moving distance of the electrode lifting device.

[0027] Referring to Figure 1 And Figure 2 A sheath gas flow controller is installed in the electrode sheath gas pipeline. The sheath gas flow controller is used to adjust the size of the electrode sheath gas flow. The electrode sheath gas flow is not less than 50 SLPM. If the electrode sheath gas flow is too low, the restraining force of the electrode sheath gas on the arc is weak, and the arc is easy to drift horizontally, and the arc voltage is unstable. Although the measurement method of the present application does not require an upper limit value of the electrode sheath gas flow, too high electrode sheath gas flow can easily lead to unstable operation of the nano-powder production process. Therefore, the electrode sheath gas flow is controlled to be 150-200 SLPM. At the same time, the electrode sheath gas pressure P is controlled to be not less than 40 kPa, so that the arc is maintained stable by high pressure restraint.

[0028] Referring to Figure 1Because the electrode length is short, the electrode sheath gas outlet is close to the material liquid surface (the molten pool), and after the electrode sheath gas hits the material liquid surface, a large back pressure is formed, so there is a certain relationship between the electrode sheath gas pressure P and the distance h of the electrode sheath gas outlet from the molten pool. Based on this situation, an electrode sheath gas pressure gauge is fixedly connected at the electrode sheath gas outlet to record the electrode sheath gas pressure P.

[0029] Referring to Figure 1 , the input end of the electrode is connected to a direct current power supply, the voltmeter is built in the direct current power supply, and the arc voltage U is automatically read by the control system. The no-load voltage of the direct current power supply is not less than 200V, and a higher voltage setting can be set to realize a greater arc length, so as to eliminate the influence of the cathode and anode voltage drops on the measurement of the arc voltage.

[0030] Embodiment 1

[0031] A method for detecting and controlling the residual length of an arc electrode in the process of preparing a nano powder is performed according to the following steps: S1, a tungsten electrode with a diameter of 10mm and an initial length of 140mm is prepared, and the tungsten electrode is installed on an electrode base; the arc current of the tungsten electrode is set to 100A, the flow rate of the electrode sheath gas is set to 150SLPM, and the laying thickness D0 of the material is set to 45mm.

[0032] Because the behavior of the arc is affected by electromagnetic force and aerodynamic force, the airflow around the arc is heated to produce strong turbulence; at this time, the arc tends to take the shortest discharge channel between the cathode and the anode due to the electromagnetic force, and the arc discharges in the hot gas group due to the lower breakdown voltage of the hot gas; therefore, under the influence of the airflow, the arc cannot take the shortest discharge channel, but is curved and stretched along with the turbulence, resulting in an increase in the arc voltage. Therefore, a percentile needs to be set to eliminate the influence of the bending and stretching. If the percentile value is set too high, the average value of the statistics will contain higher voltage values corresponding to more arc deformation, resulting in a larger measured arc length; therefore, the percentile is usually set to be below 20%.

[0033] Based on the above situation, this embodiment sets to record 10 arc voltage values per second, the recording period t is 20s, and the 5% lower percentile is taken, and the no-load voltage of the direct current power supply is 250V; When the system is just started, the average arc voltage U in a period of time t at different heights H is recorded to obtain the average arc electric field strength E corresponding to different heights H H , E H , H and U satisfy formula (1): E H =U / (H0-D0-a-L ele0 ); Wherein, a is the height position of the electrode lifting device clamping the electrode, which should be recorded and taken as a preset value when the electrode is installed, a = 0 when the electrode lifting device clamps near the electrode sheath gas outlet, a = 0 in the embodiment; H0 is the initial height of the electrode, D0 is the laying thickness of the material 45mm, L ele0 is the initial length of the electrode 140mm.

[0034] At the same time, the relationship between the distance h of the electrode sheath gas outlet and the molten pool and the electrode sheath gas pressure P is simulated, h and P satisfy formula (2): h = A·P B +W; A, B and W are all empirical parameters, and the unit of h is mm and the unit of P is kPa; at this time, the unit of W is mm, B has no unit, and the unit of A is mm×kPa^(-B); when the measurement accuracy requirement is not high, W is 0mm; therefore, according to experience, formula (2) obtained by regression in the embodiment is h = 1.2×P 1.13 .

[0035] S2, record the arc voltage U' and the electrode sheath gas pressure P when the electrode is at a certain height H', so as to calculate the arc length L arc . arc =U' / E H ; Substitute the electrode sheath gas pressure P into formula (2) to calculate h; The distance h of the electrode sheath gas outlet and the molten pool deducts the arc length L arc , that is, the electrode length L ele , that is, L ele =h-L arc ; When the system is started, the electrode height is lifted to H, H is 287.20mm, the arc average voltage U of 5% quantile in 20s is recorded as 186V, deducting the initial length of the electrode L ele0 140mm and the laying thickness of the material D045mm, the corresponding electric field intensity E H is calculated as 18.2V / cm; Read the arc voltage U' under the working height H' of the electrode 174mm as 20V, the arc length L arc is calculated as 11mm; At the same time, read the electrode sheath gas pressure P as 65kPa, substitute into formula (2) h = 1.2×P 1.13 , calculate h as 134mm; Deduct the arc length L arc from h to obtain the electrode length L ele 123mm; S3, measure the distance C between the electrode terminal and the initial material height before the system is started; After the system is started, the material depth D can be calculated according to formula (3), which is D=H'-L. arc -L ele -C, where C is 2mm; The H and L calculated in step S2 arc and L ele Substituting the calculated value into formula (3), the material depth D is calculated to be 38mm; Measured electrode length L after system shutdown ele The thickness is 133mm, and the material depth D is 45mm.

[0036] Conclusion: The error rate between the measured value and the calculated theoretical value of the electrode length is 7.5%, and the error rate between the measured value and the calculated theoretical value of the material depth is 15.6%. The applicant discovered that the measured value was lower than the actual value, mainly because the electric field strength E of the arc used in the measurement did not take into account the sudden voltage drop near the electrode, resulting in a lower calculated arc length L. arc Higher than the actual value, thus increasing the electrode length L ele The material depth D was underestimated. However, the measurement error was less than 10 mm, which is already practical for DC arc plasma systems.

[0037] Example 2

[0038] A method for detecting and controlling the remaining length of an arc electrode during the preparation of nanopowders, comprising the following steps: S1. Continue using the remaining electrode from Example 1. Set the arc current of the tungsten electrode in this example to 120A and the flow rate of the electrode sheath gas to 150SLPM. Based on Example 1, continue to start the system. Since the system will continuously replenish materials during operation, the material laying thickness is maintained at 45mm. In this embodiment, 10 arc voltage values ​​are recorded per second, the recording period t is 20s, and the lower 5% quantile is taken. The open-circuit voltage of the DC power supply is 250V. S2. Raise the electrode height to H, which is 283.67 mm. Record the average arc voltage U at the 5th percentile within 20 seconds as 205 V. Subtract the initial electrode length L. ele0 The electric field strength E is calculated after considering a material thickness of 133mm and a material laying thickness of D045mm. H It is 19.4V / cm; The arc voltage U' at the electrode working height H'=160mm is read as 37V, and the arc length L is calculated. arc It is 19mm; At the same time, the electrode sheath gas pressure P was read as 59 kPa, and substituted into formula (2) h=1.2×P 1.13h is 121 mm; Subtracting the arc length L arc The electrode length L ele is 102 mm; S3, substituting the calculated H, L arc and L ele in step S2 into formula (3), the material depth is calculated to be 37 mm; The measured electrode length L ele is 110 mm, and the material depth D is 45 mm.

[0039] Conclusion: the error rate between the measured value and the calculated theoretical value of the electrode length is 7.2%, and the error rate between the measured value and the calculated theoretical value of the material depth is 17.8%.

[0040] Example 3

[0041] A method for detecting and controlling the residual length of an arc electrode in the preparation process of a nano-powder, according to the following steps: S1, continue to use the residual electrode of Example 2, set the arc current of the tungsten electrode in this example to 150 A, and the flow rate of the electrode sheath gas to 200 SLPM; continue to start the system based on Example 2; since the system will continue to replenish the material during operation, the laying thickness of the material is maintained at 45 mm; This example sets to record 10 arc voltage values per second, the recording period t is 20 s, and takes 5% lower quantile, and the no-load voltage of the direct current power supply is 250 V; S2, raise the electrode height to H, H is 260.67 mm, record the arc average voltage U of 5% quantile in 20 s as 205 V, subtract the initial length L ele0 of the electrode 110 mm and the laying thickness D of the material 45 mm, and calculate the corresponding electric field strength E H is 19.4 V / cm; Read the arc voltage U' of the electrode working height H' = 182 mm as 80 V, and calculate the arc length L arc is 41 mm; At the same time, read the electrode sheath gas pressure P as 68 kPa, and substitute into formula (2) h = 1.2 x P 1.13 , calculate h to be 141 mm; Subtract the arc length L arc from h to get the electrode length L ele is 100 mm; S3, substituting the calculated H', L arc and L eleThe calculated value is substituted into formula (3) and C is 2 mm, and the material depth is 39 mm. The measured electrode length L after the system is shut down ele The material depth D is 44 mm.

[0042] Conclusion: The error rate between the measured value and the calculated theoretical value of the electrode length is 2.9%, and the error rate between the measured value and the calculated theoretical value of the material depth is 11.1%. The measurement error of Example 3 is significantly lower than that of Example 1 and Example 2. The main reason is that the electrode sheath gas is increased, and the electrode sheath gas has a restraining effect on the arc, so that the calculated arc length L arc The deviation between the distance from the electrode terminal to the material is smaller.

[0043] The technical features of the above-described embodiments can be combined in any manner. In order to make the description simple, all possible combinations of the technical features in the above-described embodiments are not described, but as long as the combinations of the technical features do not contradict, they should be considered as the scope of the description.

[0044] In addition, the above-described embodiments only express several embodiments of the present application, and the description is more specific and detailed, but it should not be understood as a limitation on the scope of the patent. It should be noted that for ordinary skilled in the art, without departing from the concept of the present application, a number of modifications and improvements can be made, which are within the scope of the present application. Therefore, the scope of protection of the present application should be subject to the appended claims.

Claims

1. A method for detecting and controlling the remaining electrode length during the preparation of nanopowders, characterized in that: Includes the following steps: S1. When the system is first started, record the average arc voltage U over a time period t at different heights H, and obtain the average arc electric field strength E corresponding to different heights H. H E H The relationship between E, H, and U satisfies formula (1): E H =U / (H0-D0-aL ele0 ); Where 'a' represents the height position of the electrode lifting device clamping the electrode, which should be recorded and used as a preset value during electrode installation; 'H0' represents the initial height of the electrode; 'D0' represents the material laying thickness; and 'L' represents the initial height of the electrode. ele0 This is the initial length of the electrode; The relationship between the distance h between the electrode sheath gas outlet and the molten pool and the electrode sheath gas pressure P is given by equation (2): h = A·P B +W, where A, B, and W are all empirical parameters; S2. Record the arc voltage U' and the electrode sheath gas pressure P at a certain height H' of the electrode, and then calculate the arc length L. arc L arc =U' / E H ; Substituting the electrode sheath gas pressure P into formula (2), h can be calculated; The distance h between the electrode sheath gas outlet and the molten pool minus the arc length L arc That is, the electrode length L ele L ele =hL arc .

2. The method for detecting and controlling the remaining electrode length during the preparation of nanopowder as described in claim 1, characterized in that: The electrode sheath gas pressure P is not less than 40 kPa.

3. The method for detecting and controlling the remaining electrode length during the preparation of nanopowder as described in claim 1, characterized in that: The arc voltage U is the average value of x% quantiles over a period of time t, where x ranges from 0 to 20.

4. The method for detecting and controlling the remaining electrode length during the preparation of nanopowder as described in claim 1, characterized in that: In step S1, the electrode height H is raised to a level where the arc voltage U is close to the DC power supply open-circuit voltage.

5. The method for detecting and controlling the remaining electrode length during the preparation of nanopowder as described in claim 1, characterized in that: After step S2, the material depth D can be calculated according to formula (3), which is D=H'-L. arc -L ele -C, where C is the distance between the electrode terminal and the initial material height in the initial state.

6. A device for detecting and controlling the remaining electrode length during the preparation of nanopowders, characterized in that, The method for detecting and controlling the remaining electrode length during the preparation of nanopowder according to any one of claims 1-5 includes: An electric arc generator includes an electrode base, an electrode fixed on the electrode base, and an electrode sheath gas pipe opened on the electrode base, wherein the electrode sheath gas outlet of the electrode sheath gas pipe is located at the top of the electrode; An electrode lifting device is fixed on the electrode base to control the vertical lifting of the electrode; A height measuring device is installed on the electrode lifting device to record the electrode height H; A sheath gas flow controller is installed on the electrode sheath gas pipeline to record the magnitude of the electrode sheath gas flow and control the sheath gas flow. An electrode sheath gas pressure gauge is installed on the electrode sheath gas pipeline to record the electrode sheath gas pressure P; A voltmeter, electrically connected to the electrode, records the arc voltage U.

7. The electrode remaining length detection and control device in the preparation process of nanopowder as described in claim 6, characterized in that: The electrode sheath gas is directed towards the electrode tip, and the electrode sheath gas flow rate is not less than 50 SLPM.

8. The electrode remaining length detection and control device in the preparation process of nanopowder as described in claim 7, characterized in that: The flow rate of the electrode sheath gas is controlled at 150-200 SLPM.

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