A method and apparatus for on-line calibration of plasma fuse atomized particle temperature

Abstract

The application relates to a method and device for online calibration of the temperature of plasma fuse atomized particles, belonging to the field of powder processing and preparation. The method is characterized in that the temperature of the atomized particles is measured based on the heat content method, a multilayer high-temperature shielding structure is used to isolate the interference caused by the high temperature of the plasma jet, and the capillary force is used to balance the high-speed airflow pressure of the jet. After 1-2 seconds, the trace high-temperature particles generated by atomization are loaded into a small test tube containing a medium, the temperature rise of the medium and the temperature rise of the test tube are measured, the heat carried by the particles is inversely calculated, the mass change of the test tube is combined, and finally the particle temperature of the plasma fuse atomization is calculated.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of powder preparation and processing, in particular to a method and device for online calibration of particle temperature during plasma melting wire atomization powder preparation. BACKGROUND

[0002] In recent years, with the development of additive manufacturing technology and injection molding technology, there is an increasing demand for powder materials with high sphericity, high purity, small particle size and good flowability. Traditional spherical metal powder manufacturing mainly uses rotating electrode atomization and vacuum gas atomization technology. The rotating electrode atomization technology produces powder with good sphericity, but the powder particle size is coarse due to the limitation of electrode speed. Vacuum gas atomization includes inert gas atomization (VIGA) using a crucible and induction heating electrode (EIGA) without a crucible, which can control the particle size, but the gas consumption is large and there are many satellite ball powders.

[0003] Plasma atomization powder preparation is a powder preparation technology that has attracted much attention in recent years. It uses high-temperature and high-speed plasma jet to heat and melt metal wire, and then atomizes it into powder. Canada's AP&C company and Pyrogenesis company have been engaged in the preparation of spherical metal powder by plasma atomization method for a long time. They use three plasma torches combined with center wire feeding process to melt the wire and use high-speed plasma jet to break the melt into spherical metal powder. Chinese patents CN214768940U and CN214488838U also use plasma jet as a medium to break the melt into particles to form spherical metal powder. Looking at the above-mentioned plasma atomization technology, they all use the high kinetic energy of plasma jet to break the melt into particles. Compared with conventional high-pressure gas atomization powder preparation, plasma atomization has two inherent advantages. First, the jet itself is in a high-temperature state, and a small amount of gas can obtain high gas kinetic energy, so the amount of gas required to produce the same quality of powder is significantly reduced. Second, the high-temperature jet allows the particles to stay at high temperature for a longer time, making it easier to obtain spherical powder. Currently, most of the related inventions of plasma melting wire atomization powder preparation at home and abroad are focused on the realization of the process method, and there are few methods and strategies for process control of this technology. Parameters and process windows are mainly obtained through a large number of experiments.

[0004] In order to fully exert the special advantages of plasma atomization in preparing spherical metal powder, it is necessary to reasonably control the plasma atomization process. Since the plasma atomization process parameters are many and the parameters are strongly coupled, it is necessary to rely on a large number of experiments to obtain, which is time-consuming and high in cost. Moreover, the process rules of materials with different thermal physical properties cannot be directly transplanted, and the cost of process test is very high. And other regulation strategies are to analyze the temperature field and velocity field of the plasma jet first, and then to regulate the melting and atomization process of the wire. However, the generation of the plasma jet involves the action of strong physical fields such as electric field and gas, and it has the characteristics of high temperature gradient, so it is difficult to directly measure its temperature and velocity. The plasma melting and atomization process also has the effect of strong coupling of multiple complex physical fields, which brings great challenges to the process regulation of plasma atomization powder preparation.

[0005] The method for on-line calibration of particle temperature of plasma fuse atomization provided by the application is based on the key point in the plasma fuse atomization process, that is, the temperature of the atomized particles needs to be in a moderately overheated state in the process. If the temperature of the atomized particles is too low, the particles will quickly solidify to form irregular shapes, and if the temperature of the atomized particles is too high, some alloy elements may be burned. By constructing the mapping relationship between the process variables (such as power, gas flow, and gas composition) and the atomized particle temperature, the process parameter range for producing high-sphericity, reasonable powder particle size can be conveniently and efficiently found out.

[0006] Many engineering and research fields involve the measurement of the temperature of flying particles in high-temperature flow fields. Typical examples include the preparation and reaction of particles in traditional thermal spraying technology, the combustion process of coal powder or solid fuel, and flying particles that cause solid fire spread during a fire. Looking at the existing high-temperature solid particle measurement methods, they can be mainly divided into contact and non-contact types. Contact measurement methods such as thermocouples need to be in contact with high-temperature particles for a certain period of time, and are more suitable for static particles or slow particles with larger size. In addition, the direct contact between the measuring device and the particles will affect the temperature distribution of the particles themselves, and also faces the problems of erosion and wear in high-temperature flow fields. Some works coat (spray or spray weld) hard alloy on the surface of the temperature measuring element to improve the wear resistance of the temperature measuring element itself; or directly install a metal wear-resistant round pipe outside the temperature measuring element to isolate the direct impact and wear of the flowing particles on the temperature measuring element, but such treatment will affect the movement trajectory of the particles, making it difficult to accurately obtain the temperature of high-temperature flying particles.

[0007] Non-contact measurement technology and equipment have the advantages of wide measurement range, fast dynamic response, and little influence on the measured object, and are the focus of attention at present and have developed rapidly in recent years. Non-contact high-temperature measurement technology mainly includes radiation pyrometers and colorimetric pyrometers, and high-temperature particle capture methods based on particle images, which have the common characteristic of calculating particle temperature by using the thermal radiation characteristics of the object. For example, the Chinese patent CN107202651a "A micro-scale pyrotechnic combustion temperature field measurement device and a temperature measurement method thereof" proposes a non-contact high-temperature pyrotechnic combustion temperature measurement method, particle velocity and particle size information. The patent with publication number CN105548607a "A probe for measuring particle slip velocity in gas-solid two-phase flow and a measuring method" also proposes a non-contact normal-temperature gas-solid two-phase flow particle velocity measurement method. The patent with publication number CN106556556a "A device and method for measuring the particle size and mass concentration of smoke dust" proposes a non-contact smoke dust particle size and mass concentration measurement method. This method uses a laser light source to measure the particle size and concentration in a high-temperature medium, which is difficult to prepare for measuring the radiation of high-temperature solid particles, so it is also impossible to measure the temperature of the particles.

[0008] It should be noted that the current temperature measurement method based on high-temperature radiation signal has great limitations in measuring the temperature of particles in the high-temperature plasma jet flow field, because the plasma jet itself is a high-temperature radiator, and the flow field temperature is much higher than the temperature of the particles themselves, so the radiation information obtained by the probe is largely derived from the flow field. At the same time, high-temperature plasma contains a high concentration of electrons and positive ions, and the electromagnetic wave signal and laser projected from the outside will strongly couple, resulting in signal distortion. Therefore, the current measurement of particle temperature in the plasma flow field (such as the plasma spraying process) generally places the radiation probe at a distance (such as more than 100 mm) from the nozzle outlet. At this position, the electrons and ions in the high-temperature plasma re-aggregate, and the energy released by them exchanges fully with the environment medium, and the temperature of the plasma jet has dropped below the threshold value that can be easily detected by the conventional probe.

[0009] In summary, the current method for measuring the temperature of high-temperature flying particles has different degrees of limitations in the plasma fuse atomization process. The particles formed in the plasma atomization process continue to be heated by the high-temperature plasma jet after flying out of the nozzle outlet. Even if a non-contact high-temperature colorimetric pyrometer is used to measure at a distance from the outlet, the measured temperature is difficult to represent the actual temperature of the particles formed in the atomization process, making it difficult to effectively guide and optimize the actual process. SUMMARY

[0010] In order to fully exert the special advantages of plasma atomization in preparing spherical metal powder, the particle temperature and particle size of plasma wire atomization powder preparation need to be calibrated on line, aiming to provide a convenient and efficient means for plasma atomization powder preparation process regulation.

[0011] The present application proposes a kind of based on heat content method measurement particle temperature, i.e. using an indirect contact temperature measurement mode, using multilayer high temperature shielding structure, isolate the interference brought by plasma jet high temperature, and using capillary force balance jet high-speed airflow pressure.1-2 second micro high temperature particles generated are loaded into test tube with medium, using the temperature rise of medium and test tube, back calculation the heat carried by particle.Combined with the mass change of test tube, finally calculate the particle temperature.

[0012] Technical scheme is as follows:

[0013] 1.An on-line calibration device for the particle temperature of plasma wire atomization, as shown in the structure of the accompanying Figure 1 It is characterized by testing particle temperature based on heat content method, and the device is a stainless steel container with a diameter of 200mm, one or several small test tubes containing fixed volume medium are placed in the central position, the material of each test tube is quartz glass or metal, the diameter is 2-4mm, the outer wall of test tube is wrapped with 50mm thick heat preservation cotton, three layers of coaxial centering test plates are placed above the test tube, the uppermost is a graphite plate resistant to burning, the plate thickness is 5-10mm, there is a small hole with a diameter of 4mm corresponding to each test tube, a water-cooled copper plate is placed in the middle position, the plate thickness is 3-5mm, there is a hole with a diameter of 3mm corresponding to the test tube, the lowermost is a thin-walled stainless steel plate, the plate thickness is 1mm, and there is a hole with a diameter of 1mm corresponding to the center position of the test tube.

[0014] 2.Further, the total thickness of the above three layers of shielding plates does not exceed 15mm;

[0015] 3.Further, a certain amount of buffer medium is placed in each test tube, the medium can be liquid water or oil, and can be natural gel-like substance, the remaining height of the test tube after placing the medium needs to meet formula (1), as shown in the accompanying Figure 2

[0016]

[0017] In the formula, h2 is the height of the top of the medium from the glass tube;

[0018] ɑ is the compression coefficient of plasma atomization nozzle, i.e. the ratio of outlet diameter to throat diameter

[0019] P1 is the input end pressure of plasma gas;

[0020] γ is the surface tension coefficient of the medium;

[0021] ​θ is the angle between the medium in the test tube and the tube wall;

[0022] d is the inner diameter of the test tube;

[0023] ρ is the density of the medium;

[0024] g is the acceleration of gravity;

[0025] 4. Two armored thermocouples are arranged in each test tube and tube wall, the thermocouple end diameter is 1 mm, one thermocouple is inserted into the test tube, the other thermocouple is fixed to the test tube wall by spot welding or heat-resistant glue, and the thermocouples are connected to the data collector;

[0026] 5. Further, a method for on-line calibration of the temperature of the plasma fuse atomized particles, the operation steps are:

[0027] 3.1 Place the test device on the two-dimensional moving platform, after the test starts, do not send the wire under the same process parameters, move the temperature measuring device to the position directly below the plasma fuse atomizing nozzle, stay for 1-2 seconds, then move away; then start sending the wire, form a particle beam, stay for 1-2 seconds, then move the temperature measuring device to the position directly below the plasma fuse atomizing nozzle again, stay for 1-2 seconds, then move away;

[0028] 3.2 Further, when the high-temperature particles at the measured position accurately enter the lower test tube, the data recorder or acquisition card measures the temperature change of the water and the outer wall of the test tube during the short experiment;

[0029] 3.3 Further, based on the obtained temperature data, the particle temperature is calculated based on the enthalpy method, and the enthalpy method is used to first calculate the enthalpy change of the particles, according to formula (2):

[0030] ΔQ1+ΔQ2=ΔQ3+ΔQ4 (2)

[0031] In the formula,

[0032] ΔQ1 is the enthalpy change of the water before and after the particles enter the water cooling;

[0033] ΔQ2 is the enthalpy change of the test tube in the process;

[0034] ΔQ3 is the enthalpy change of the particles in the process;

[0035] ΔQ4 is the enthalpy change caused by the influence of the external environment.

[0036] The enthalpy changes ΔQ1 and ΔQ2 of the water and the test tube can be calculated by the specific heat capacity formula:

[0037] ΔQ1=c ρ1 ·m1·ΔT1 (3)

[0038] ΔQ2=c ρ2 ·m2·ΔT2 (4)

[0039] c ρ1 - specific heat capacity of water;

[0040] c ρ2 - specific heat capacity of test tube material;

[0041] ΔT1 - temperature change of medium before and after the atomized particles enter;

[0042] ΔT2 - temperature change of test tube before and after the atomized particles enter;

[0043] m1 - mass of water;

[0044] m2 - mass of test tube.

[0045] The enthalpy change ΔQ4 caused by the external environment can be calculated by the temperature change when the wire is not sent.

[0046] 3.4 Calculation of the enthalpy change ΔQ3 of the particles in the measured area After the enthalpy change ΔQ3 of the particles in the measured area is calculated, the temperature of the particles can be obtained according to formula (4):

[0047]

[0048] wherein

[0049] m3 - mass of particles collected in the test tube during the test;

[0050] L - latent heat of the atomized particle material;

[0051] c pm - specific heat capacity of the atomized particle liquid;

[0052] c ps - specific heat capacity of the atomized particle solid;

[0053] T m - melting point of the atomized particle material;

[0054] T1 - ambient temperature.

[0055] Compared with the prior art, the present application can conveniently and simply determine the temperature of the particles formed by the plasma fuse atomization under different process conditions, and only a small amount of online test is needed to establish the relationship between the process parameters and the particle temperature, and then obtain the adjustment parameter window of the plasma fuse atomization production of high sphericity, less component burning loss. The verification of the particle temperature effectiveness is that the particle temperature deviation range is small through multiple measurements at different positions. In addition, it can be seen from the particle shape that if the melting point is just reached, there are some particles with poor sphericity in the particle, that is, the particles are not completely melted. BRIEF DESCRIPTION OF DRAWINGS

[0056] Figure 1The temperature measuring device schematic diagram and physical diagram are as follows:

[0057] 1-plasma torch; 2-NiCrMo (nickel-based alloy 625) wire with a diameter of 1.2 mm; 3-wire feeding mechanism; 4-graphite plate resistant to burning; 5-copper water-cooled plate; 6-thin-walled stainless steel plate; 7-data collector; 8-stainless steel container; 9-water and test tube; 10-particle beam; 11-thermal insulation cotton; 12-thermocouple.

[0058] Figure 2 The test tube schematic diagram for collecting high-temperature particles is as follows:

[0059] Figure 3 The temperature change curve of the embodiment 1 of the application is as follows:

[0060] Figure 4 The temperature data of the embodiment 1 of the application without wire feeding for a short time are as follows:

[0061] Figure 5 The morphology diagram of the tested particles is as follows. DETAILED DESCRIPTION

[0062] Embodiment 1:

[0063] 1. The temperature measuring device shown in the accompanying drawings is placed on a two-dimensional moving platform, the plasma torch is ignited first without wire feeding after the test starts, the plasma parameters are as follows: the main gas is argon, the flow rate is 200 L / min, the auxiliary gas is hydrogen, the flow rate is 6 L / min, the current is 300 A, and the voltage is 64 V, the temperature measuring device is moved to the position 20 mm below the plasma wire melting atomization nozzle, stays for 1-2 seconds, and then is moved away; Figure 1 2. The temperature measuring device shown in the accompanying drawings is placed on a two-dimensional moving platform, the plasma generator parameters are kept unchanged, the wire feeding is started, the wire material is NiCrMo (nickel-based alloy 625) with a diameter of 1.2 mm, the wire feeding speed is 65 mm / s, the temperature measuring device is moved to the position below the plasma nozzle after waiting for 2-3 seconds after the wire feeding, stays for 1-2 seconds, and then is moved away;

[0064] Figure 1 3. The test tube is taken out, the mass change thereof is determined, the mass m2 of the test tube and the mass m1 of the water are weighed before the experiment, and the mass m3 of the particles is weighed after drying after the experiment;

[0065] 4. The temperature curve is derived from the data collector, as shown in the accompanying drawings;

[0066] 5. When the temperature of the test tube reaches the maximum value, the water temperature and the temperature rising amount ΔT1 and ΔT2 of the test tube at this time are calculated; Figure 2 Figure 3

[0067] 5. When the temperature of the test tube reaches the maximum value, the water temperature and the temperature rising amount ΔT1 and ΔT2 of the test tube at this time are calculated;

[0068] ​​​6. Repeat the above steps several times (usually more than 3 times) and collect the results in a table as shown in Table 1.

[0069] 7. According to the thermal physical parameters of NiCrMo material, the particle temperature is calculated to be 1726K, i.e. the atomized particles just reach the melting point;

[0070] 8. The Figure 5 is a morphology diagram of the particles. It can be seen that the particles do not present a round and spherical shape, and part of the particles still retain irregular edges, which reflects that this part of the particles is in the liquid-solid two-phase zone, which corresponds well to the temperature obtained by testing.

[0071] Table 1 is the heat enthalpy calculation result of Example 1. REF is the measurement result without particle input, which is used to deduct the error of environment or operation.

[0072]

Claims

1. A device for online measurement of the temperature of atomized powder particles, characterized by: A 200mm diameter stainless steel container has one or more small test tubes containing a fixed volume of medium placed in the center. Each test tube is made of quartz glass or metal, with a diameter of 2-4mm. The outer wall of the test tube is wrapped with 50mm thick insulation cotton. Three layers of coaxially aligned test plates are placed directly above the test tubes. The top layer is a 5-10mm thick refractory graphite plate with a small hole of 4mm diameter at the position corresponding to each test tube. The middle layer is a water-cooled copper plate with a thickness of 3-5mm and a hole of 3mm diameter at the position corresponding to the test tube. The bottom layer is a thin-walled stainless steel plate with a thickness of 1mm and a hole of 1mm diameter at the center corresponding to the test tube. The total thickness of the above three test plates does not exceed 15mm. Two armored thermocouples are arranged inside and on the wall of each test tube. The thermocouple ends have a diameter of 1mm. One thermocouple is inserted into the test tube, and the other is fixed to the test tube wall by capacitor spot welding or heat-resistant adhesive. The thermocouple is connected to a data acquisition device.

2. A method for applying the device according to claim 1, characterized in that: The atomized high-temperature particles are sprayed into the device within 3 seconds, and the temperature of the atomized particles is calculated using the enthalpy method; A test tube inside the device is used to capture atomized particles within 3 seconds. During the test, the temperature rise of the medium and the test tube are measured, and their enthalpy changes are calculated. The enthalpy change when no wire is fed is deducted to obtain the enthalpy carried by the particles. The mass change of the test tube before and after capturing the particles is weighed, and the particle temperature is calculated using the enthalpy change method.

3. A method for applying the device according to claim 2, characterized in that: Before the test, the test tube is filled with a medium, which is water, oil or hydrogel. After the medium is placed in the test tube, the remaining height from the top meets the Where h2 is the residual height; ɑ is the ratio of the plasma nozzle outlet to the throat diameter; compression ratio, P1 is the plasma inlet pressure, γ is the surface tension coefficient of the medium, θ is the angle between the medium and the tube wall in the test tube, d is the inner diameter of the test tube, ρ is the medium density, and g is the acceleration of gravity; Place the device on a two-dimensional moving platform. After the test starts, without feeding the wire, move the device to the position directly below the plasma fuse atomizing nozzle under the same process parameters, stay there for 1-2 seconds, and then move away. Then start feeding the wire, wait for 1-2 seconds, move the device again to the bottom of the atomizing nozzle, stay for 1-2 seconds and then move away, use the data acquisition card to measure the temperature changes of the water and the outer wall of a single test tube or multiple test tubes during the short-term experiment.

Images