A microspheroidized powder or nanometer powder preparation control system

Abstract

A control system for preparing micron-sized or nano-sized powders is disclosed. The gas supply device includes a gas source, a buffer tank, and a pressure stabilizing tank connected in sequence. The preparation device includes a hopper, a feeder, a radio frequency plasma torch, a main unit compartment, a cyclone separator, a powder collection hopper, and a booster connected in sequence. The hopper, feeder, and radio frequency plasma torch are respectively connected to the pressure stabilizing tank, and the booster is connected to a gas storage tank. The collection device includes a first powder collection device, a second powder collection device, and a third powder collection device. The first powder collection device is connected to the main unit compartment, the second powder collection device is connected to the cyclone separator, and the third powder collection device is connected to the powder collection hopper. The cooling device includes a water chiller and a fan. Valves and / or switches for adjustment and control are provided between each connecting component. A controller is connected to each component and also to the valves and / or switches between the components. This invention provides stable internal gas pressure for each component, resulting in powders with good sphericity and low adhesion.

Description

Technical Field

[0001] This invention relates to the field of powder making equipment technology, and in particular to a control system for the preparation of micron-sized spheroidized powder or nano-powder. Background Technology

[0002] Micron-sized or nano-sized powders are mainly used in additive manufacturing, metal injection molding, and thermal spraying. Plasma spheroidization is one of the current methods for preparing micron-sized or nano-sized powders using plasma. In plasma spheroidization, the working gas sends the powder into a high-temperature plasma in a high-temperature environment. The powder particles melt rapidly and condense into spheres under the action of surface tension. After cooling, they solidify into spherical powders with good sphericity. This preparation method does not produce pollution from electrode evaporation, and the prepared micron-sized or nano-sized powders have uniform composition and good flowability.

[0003] In existing systems for preparing micron-sized or nano-sized powders using plasma spheroidization, the number of devices in the system is limited. Each device requires gas to operate within the working gas flow field. Typically, the working gas is introduced into the hopper to blow the material, while simultaneously being introduced into the plasma torch for powder preparation. The adjustment and control of the gas flow field in the other connected devices are restricted, resulting in unstable gas supply pressure in each device within the system. This leads to the nano-powder spheres easily sticking together, thus affecting the fine powder recovery rate and spheroidization rate. Summary of the Invention

[0004] To overcome the shortcomings of the prior art, this invention discloses a control system for the preparation of micron-sized spheroidized powders or nano-powders, employing the following technical solution:

[0005] A control system for preparing micron-sized spheroidized powder or nano-powder includes a gas supply device, a preparation device, a collection device, and a cooling device;

[0006] The gas supply device includes a gas source, a buffer tank, a gas storage tank, and a pressure stabilizing tank. The gas source, the buffer tank, and the pressure stabilizing tank are connected in sequence. The pressure stabilizing tank is connected to the preparation device to provide working gas with stable pressure. The buffer tank is also connected to the gas storage tank to store excess working gas. The gas source is also connected to the gas storage tank and the preparation device.

[0007] The preparation apparatus includes a hopper, a feeder, a radio frequency plasma torch, a main unit chamber, a cyclone separator, a powder collection chamber, and a booster connected in sequence. The hopper, feeder, and radio frequency plasma torch are respectively connected to the pressure stabilizing tank. The main unit chamber and the powder collection chamber are respectively connected to the buffer tank. The buffer tank is used to purge or back-purge the main unit chamber and the powder collection chamber. The booster is connected to the buffer tank and is used to recover the working gas for recycling.

[0008] The collecting device includes a first powder collecting device, a second powder collecting device, and a third powder collecting device. The first powder collecting device is connected to the main unit compartment, the second powder collecting device is connected to the cyclone separator, and the third powder collecting device is connected to the powder collection bin.

[0009] The cooling device includes a water chiller and a fan. The water chiller is connected to the feeder, the radio frequency plasma torch, the main unit compartment, the cyclone separator, and the powder collection compartment, respectively. The fan is connected to the radio frequency plasma torch.

[0010] The entire micron-spheroidized powder or nano-powder preparation control system has a stable internal gas flow field. The pressure stabilizing tank can supply working gas to the silo, feeder, and radio frequency plasma torch in the preparation device, and can adjust the gas flow rate of the connected branch to maintain the pressure stability in each connected component. The gas storage tank can collect the gas discharged from the buffer tank due to excessive pressure, avoid direct discharge from the buffer tank, and reduce the gas supply load of the pressure stabilizing tank.

[0011] Furthermore, a dryer is connected between the buffer tank and the pressure stabilizing tank, a filter is connected between the powder collection silo and the booster, and the filter is also connected to the buffer tank. A feeding device is provided between the silo and the feeder.

[0012] Furthermore, the micron-sized spheroidized powder or nano-powder preparation control system also includes a vacuum pump, which is connected to the first powder collection device, the second powder collection device and the third powder collection device through switching valves respectively. The vacuum pump is also connected to the silo, the feeder, the powder collection silo, the pressure stabilizing tank and the buffer tank through switching valves. The water chiller is connected to the vacuum pump through a cooling switching valve.

[0013] Furthermore, a high-temperature gate valve is installed between the radio frequency plasma torch and the main unit chamber; an on / off valve is installed between the feeder and the radio frequency plasma torch; on / off valves are installed between the cyclone separator and the powder collection bin, the powder collection bin and the filter, the filter and the booster, and the booster and the buffer tank; regulating valves are installed between the air source and the buffer tank, the buffer tank and the dryer, and the pressure stabilizing tank and the feeder; an on / off valve is installed between the pressure stabilizing tank and the silo; regulating valves are installed between the pressure stabilizing tank and the feeder, and between the pressure stabilizing tank and the radio frequency plasma torch; and on / off valves are installed between the buffer tank and the main unit chamber, and between the buffer tank and the powder collection bin.

[0014] Furthermore, a switching valve is installed at the outlet of the water chiller. The water chiller is connected to the feeder, the radio frequency plasma torch, the main unit compartment, the cyclone separator, the powder collection compartment, and the filter through the cooling switching valve. The buffer tank is connected to the gas storage tank through the switching valve. The gas storage tank is connected to the first powder collection device, the second powder collection device, and the third powder collection device through the switching valve.

[0015] Furthermore, three gas supply pipelines are provided between the pressure stabilizing tank and the radio frequency plasma torch. The three gas supply pipelines are a central gas pipeline, a side gas pipeline, and a cooling gas pipeline. Each of the central gas pipeline, side gas pipeline, and cooling gas pipeline is equipped with a regulating valve.

[0016] Furthermore, the micron-sized spheroidized powder or nano-powder preparation control system also includes a gas composition detection sensor, a pressure sensor, and a temperature sensor. The gas composition detection sensor is connected to the radio frequency plasma torch. Multiple pressure sensors are installed on the silo, feeder, radio frequency plasma torch, main unit chamber, cyclone separator, powder collection chamber, pressure stabilizing tank, buffer tank, and gas storage tank, respectively. Multiple temperature sensors are installed on the feeder, radio frequency plasma torch, main unit chamber, cyclone separator, powder collection chamber, and filter, respectively.

[0017] Furthermore, the micron-sized spheroidized powder or nano-powder preparation control system also includes a flow detection device and a humidity detection device. Multiple flow detection devices are provided and are respectively connected to the silo, feeder, radio frequency plasma torch, and main unit chamber. The humidity detection device is connected to the main unit chamber.

[0018] Furthermore, the micron-spherical powder or nano-powder preparation control system also includes a monitoring device, which includes multiple cameras and a display. The multiple cameras are connected to the display and are respectively installed at the hopper, feeder, radio frequency plasma torch, and main unit compartment.

[0019] Furthermore, the micron-sized spheroidized powder or nano-powder preparation control system also includes a controller, which is connected to the gas supply device, preparation device, collection device, cooling device, monitoring device, flow detection device, humidity detection device, gas composition detection sensor, pressure sensor, and temperature sensor, respectively, to control the operation of each component, and is also connected to the valves and / or switches between each component to control the opening and closing of each valve and / or switch.

[0020] A control system for the preparation of micron-sized or nano-sized powders has the following advantages compared to existing technologies:

[0021] (1) The pressure stabilizing tank of the present invention has a pressure stabilizing function and has multiple output pipelines, which respectively provide working gas to the silo, feeder, radio frequency plasma torch, main unit silo and powder collection silo. The pressure stabilizing tank is also connected to the radio frequency plasma torch through three gas supply pipelines, which can effectively balance the internal pressure required by each component, so that the radio frequency plasma torch can fully and evenly heat the material. At the same time, it can individually adjust the internal pressure and flow rate of each component, reducing the impact on the internal pressure of other components.

[0022] (2) The controller of this invention controls the buffer tank to discharge excess gas into the storage tank and controls the storage tank to supply gas to the collection device. This avoids the pressure stabilizing tank from directly regulating the gas pressure of the collection device, reducing the load of using the pressure stabilizing tank for gas supply. It also avoids the gas in the storage tank from being directly discharged into the atmosphere, which would waste the working gas. The working gas is recycled, saving costs and reducing environmental pollution.

[0023] (3) The powder prepared by this invention has good sphericity, no hollow spheres, good flowability, and can be graded and recycled, which can realize the sieving of different grades of powder, which is beneficial to obtaining spherical micron powder and nano powder with good purity.

[0024] (4) The present invention can better monitor the working status of each component in the preparation device, and can better prepare micron or nano-sized powders, thereby improving powder quality and yield. Attached Figure Description

[0025] Figure 1 This is a schematic diagram illustrating the principle of a micron-sized spheroidized powder or nano-powder preparation control system according to the present invention;

[0026] Figure 2 This is a schematic diagram of gas flow during vacuuming before powder preparation in the micron-spherical powder or nano-powder preparation control system of the invention embodiment;

[0027] Figure 3 This is a schematic diagram of material flow with airflow during the powder preparation process in the powder preparation control system for micron-sized or nano-sized powders, as described in an embodiment of the present invention.

[0028] Figure 4 This is a schematic diagram of the airflow direction during the vacuuming process in the powder collection process of the metal micron-spheroidized powder or nano powder preparation control system in an embodiment of the present invention;

[0029] Figure 5 This is a schematic diagram of the airflow direction during powder collection in the micron-spherical powder or nano-powder preparation control system of this invention.

[0030] In the diagram: 1. Hopper; 2. Feeder; 3. Feeding device; 4. RF plasma torch; 5. Main unit hopper; 6. First powder collection device; 7. Cyclone separator; 8. Second powder collection device; 9. Third powder collection device; 10. Powder collection bin; 11. Filter; 12. Booster; 13. Buffer tank; 14. Pressure stabilizing tank; 15. Air storage tank; 16. Air source; 17. Fan; 18. Water chiller; 19. Humidity detection device; 20a. First cooling switch valve; 20b. Second cooling switch valve; 20c. Automatic switch valve; 20d. Third cooling switch valve; 20e. Fourth cooling switch valve; 20f. Fifth cooling switch valve; 20g. Sixth cooling switch valve; 20h. 7. Cooling switch valve; 21a. First flow controller; 21b. Second flow controller; 21c. Third flow controller; 21d. Fourth flow controller; 21e. Fifth flow controller; 21f. Sixth flow controller; 22a. First regulating valve; 22b. Second regulating valve; 22c. Third regulating valve; 22d. Fourth regulating valve; 22e. Fifth regulating valve; 23a. First switch valve; 23b. Second switch valve; 23c. Third switch valve; 23e. Fourth switch valve; 23f. Sixth switch valve; 23g. Seventh switch valve; 23h. Eighth switch valve; 23i. Ninth switch valve; 23j. Tenth switch valve; 23k. Eleventh switch valve;

[0031] 23m, the twelfth switching valve; 23n, the thirteenth switching valve; 23p, the fourteenth switching valve;

[0032] 23q, the fifteenth switching valve; 23r, the sixteenth switching valve; 23s, the seventeenth switching valve;

[0033] 23t, the eighteenth switching valve; 23w, the nineteenth switching valve; 23x, the twentieth switching valve;

[0034] 23y, Twenty-first switch valve; 23z, Twenty-second switch valve; 24, Dryer; 25a, First safety valve; 25b, Second safety valve; 25c, Third safety valve; 25d, Twenty-third switch valve; 26, High-temperature gate valve; 27a, First check valve; 27b, Second check valve; 28, Pressure control valve. Detailed Implementation

[0035] Preferred embodiments of the present invention will now be described with reference to the accompanying drawings. Those skilled in the art should understand that these embodiments are merely illustrative of the technical principles of the present invention and are not intended to limit the scope of protection of the present invention. It should be noted that in the description of the present invention, terms such as "upper," "lower," "inner," and "outer," indicating directional or positional relationships, are based on the directional or positional relationships shown in the accompanying drawings. This is merely for ease of description and does not indicate or imply that the device or element must have a specific orientation, or be constructed and operated in a specific orientation; therefore, it should not be construed as a limitation of the present invention.

[0036] Specific Implementation Example 1, combined with Figures 1 to 5 A micron-spherical powder or nanopowder preparation control system is used to prepare irregular metal or non-metal powders into micron-spherical powders or nanopowders that meet the requirements of use. The prepared micron-spherical powders or nanopowders are spherical powders. The system includes a gas supply device, a preparation device, a collection device, a monitoring device, an electrical control system, a cooling device, and a controller.

[0037] The gas supply device is used to provide the working gas required by the system, including a gas source 16, a gas storage tank 15, a buffer tank 13, a pressure stabilizing tank 14, and a dryer 24. The gas source 16, the buffer tank 13, the dryer 24, and the pressure stabilizing tank 14 are connected in sequence. The pressure stabilizing tank 14 is connected to the preparation device to provide working gas with stable pressure. The buffer tank 13 is connected to the preparation device for purging or back-purging. The buffer tank 13 is also connected to the gas storage tank 15 to store excess working gas. The gas source 16 is also connected to the gas storage tank 15 and the preparation device respectively.

[0038] The preparation device prepares irregular powder into spherical micron-sized powder or nano-powder. It includes a hopper 1, a feeder 2, an RF plasma torch 4, a main unit hopper 5, a cyclone separator 7, a powder collection hopper 10, a filter 11, and a booster 12 connected in sequence. The hopper 1, feeder 2, and RF plasma torch 4 are respectively connected to a pressure stabilizing tank 14, and the gas pressure is regulated and maintained by the pressure stabilizing tank 14. The main unit hopper 5, filter 11, and powder collection hopper 10 are respectively connected to a buffer tank 13. The buffer tank 13 can purge the observation window of the main unit hopper 5 for easy observation, and back-purge the filter 11 and powder collection hopper 10 to help the collection device collect powder. The booster 12 is connected to the buffer tank 13 to recover the working gas for recycling and to increase the power of the working gas circulation in the working gas path, and to control the pressure of the main unit hopper to remain stable.

[0039] The collection device is used to collect powder in the preparation device, including a first powder collection device 6, a second powder collection device 8 and a third powder collection device 9. The first powder collection device 6 is connected to the main unit compartment 5 and collects micron powder with a particle size greater than or equal to 3 microns. The second powder collection device 8 is connected to the cyclone separator 7 and collects medium-sized powder with a particle size greater than 800 nanometers and less than or equal to 10 micrometers. The third powder collection device 9 is connected to the powder collection bin 10 and collects nano powder with a particle size less than or equal to 800 nanometers.

[0040] In this embodiment, there is one powder collection bin. In other embodiments, there may be multiple powder collection bins connected in parallel, and multiple third powder collection devices are provided at the same time, with one third powder collection device connected to each powder collection bin.

[0041] The cooling device is used to cool the preparation device, including a water chiller 18 and a fan 17. The water chiller 18 is connected to the feeder 2, the radio frequency plasma torch 4, the main unit chamber 5, the cyclone separator 7, the powder collection chamber 10, and the filter 11 respectively, and cools each component. The fan 17 is connected to the radio frequency plasma torch 4 and cools it with air.

[0042] The monitoring device monitors the working status of the preparation device, including multiple cameras and a display. The multiple cameras are connected to the display and are respectively installed in the material bin 1, feeder 2, radio frequency plasma torch 4, and main unit bin 5.

[0043] The controller provides electrical control over each component through the electrical control system.

[0044] Each connecting component is equipped with a valve and / or switch for adjustment and control. The controller is connected to each component of the gas supply device, preparation device, collection device, cooling device, and monitoring device to control the operation of each component. At the same time, it is connected to the valves and / or switches between each component to control the opening and closing of each valve and / or switch, and to monitor the pressure, flow, temperature, etc. of each pipeline.

[0045] Furthermore, the silo 1, feeder 2, RF plasma torch 4, main unit chamber 5, cyclone separator 7, powder collection chamber 10, filter 11, booster 12, and buffer tank 13 are sequentially connected to form a working air path. A feeding device 3 is installed between the silo 1 and the feeder 2. A first switching valve 23a is installed between the feeder 2 and the RF plasma torch 4. A high-temperature gate valve 26 is installed between the RF plasma torch 4 and the main unit chamber 5. For the specific structure and working principle of the high-temperature gate valve 26, please refer to the bidirectional sealing high-temperature gate valve for nanomaterials disclosed in CN209587180U. The high-temperature gate valve 26 can be safely opened or closed, has good sealing performance, and is resistant to high temperatures. A tenth switching valve is installed between the cyclone separator 7 and the powder collection chamber 10. A sixth switch 23f is installed between the powder collection bin 10 and the filter 11. A twelfth switch valve 23m is installed between the filter 11 and the booster 12. A thirteenth switch valve 23n is installed between the booster 12 and the buffer tank 13. A second one-way valve 27b is also installed between the thirteenth switch valve 23n and the booster 12 to prevent backflow. The working gas blows the powder into the working gas path and flows to the radio frequency plasma torch 4 for high-temperature heating. The powder is condensed in the main unit bin 5. Some particles remain in the main unit bin 5 and are blown by the working gas to the cyclone separator 7 for separation. The first powder collection device 6, the second powder collection device 8 and the third powder collection device 9 collect the powders of different particle sizes prepared respectively. Finally, the working gas is recycled back to the buffer tank 13. Each switch valve in the controller can open and close the current pipeline according to the working process, thereby controlling the amount of powder from the main unit 5 to the cyclone separator 7 and the powder collection silo 10. The working gas in the working air circuit can be recycled to save resources and reduce costs. Each switch or valve body can adjust each connecting component individually.

[0046] Furthermore, the air source 16, buffer tank 13, dryer 24, and pressure stabilizing tank 14 are sequentially connected to form the main air supply line. The pressure stabilizing tank 14 is connected to the silo 1, feeder 2, and radio frequency plasma torch 4 to form branch air supply lines. The dryer 24 mainly dehumidifies and dries the airflow input to the pressure stabilizing tank 14. Regulating valves are installed between adjacent connected components of the main air supply line. A 23rd switch valve 25d is installed at the outlet of the air source 16 to disconnect the connection between the air source 16 and the main air supply line in a timely manner. A fourth regulating valve 22d is installed between the 23rd switch valve 25d and the buffer tank 13. The buffer tank 13 and the dryer... A first regulating valve 22a is installed between pressure tank 14 and silo 1; a twentieth switching valve 23x is installed between pressure tank 14 and silo 1; a second regulating valve 22b is installed between pressure tank 14 and feeder 2; the controller controls the powder feeding gas flow rate, the feeding amount, and the initial rate of injection into the radio frequency plasma torch 4; three gas supply pipelines are installed between pressure tank 14 and radio frequency plasma torch 4, namely three gas supply branches, specifically the central gas pipeline, the side gas pipeline, and the cooling gas pipeline connecting to radio frequency plasma torch 4; the three gas supply branches are respectively equipped with a third regulating valve 22c, a fifth regulating valve 22e, and a third regulating valve 22b. The sixth regulating valve 22f, controlled by the controller, regulates the opening of the third regulating valve 22c, the fifth regulating valve 22e, and the sixth regulating valve 22f, thereby adjusting the flow rates of the center gas, side gas, and cooling gas of the radio frequency plasma torch 4. This controls the on / off state of each gas supply branch and the stability of the pressure, ensuring stable operating pressures in the hopper 1, feeder 2, radio frequency plasma torch 4, main unit hopper 5, and powder collection hopper 10. The center gas is used for ionization to generate the plasma flame, the side gas serves as auxiliary or protective gas for the center gas, and the cooling gas is used to cool the generating device of the radio frequency plasma torch. This setup ensures that the material is heated evenly and fully within the radio frequency plasma torch 4, and protects the generator of the radio frequency plasma torch 4 from overheating. The pressure of the main chamber 5, the combined flow rate of each gas, and the cooling temperature determine the spheroidization rate of the powder and the particle size of the nanoparticles. The gas source 16 delivers the working gas to the pressure stabilizing tank 14 through the buffer tank 13. The pressure stabilizing tank 14 separately distributes the required working gas to the hopper 1, the feeder 2, and the radio frequency plasma torch 4, making it easier to ensure the pressure stability of each component in the working gas path. Each regulating valve adjusts the gas flow rate according to the pressure required by each connected component.

[0047] When the radio frequency plasma torch 4 is working, the power supply is connected. When it starts working, the voltage is increased, the fifth regulating valve 22e connecting to the side gas is closed, the sixth regulating valve 22f connecting to the cooling gas is opened, and the third regulating valve 22c connecting to the center gas is opened to ignite the radio frequency plasma torch 4. After ignition, the fifth regulating valve 22e connecting to the side gas is opened, and the radio frequency plasma torch 4 enters normal operation.

[0048] Another startup scheme for the radio frequency plasma torch 4 is as follows: When starting work, the voltage is increased, the fifth regulating valve 22e connecting to the side gas is closed, the sixth regulating valve 22f connecting to the cooling gas is opened, the third regulating valve 22c connecting to the center gas is closed, and the pressure control valve 28 between the gas source 16 and the radio frequency plasma torch 4 is opened, so that the pure gas from the gas source is directly supplied to the center gas to ignite the radio frequency plasma torch 4. After ignition, the pressure control valve 28 is closed, the fifth regulating valve 22e connecting to the side gas is opened, and the third regulating valve 22c connecting to the center gas is opened, and the radio frequency plasma torch 4 enters normal operation.

[0049] Furthermore, the buffer tank 13, the gas storage tank 15, and the collecting device are sequentially connected to form an auxiliary gas supply line. A nineteenth switch valve 23w is installed on the auxiliary gas supply line between the buffer tank 13 and the gas storage tank 15. When the working gas pressure in the buffer tank 13 exceeds the range, the nineteenth switch valve 23w opens, discharging the excess working gas into the gas storage tank 15. The gas storage tank 15 can also replenish the buffer tank 13 with gas to ensure the pressure of the buffer tank 13 is stable. A switch valve is installed on the auxiliary gas supply line between the gas storage tank 15 and the collecting device. A seventeenth switch valve 23s is connected to the gas outlet of the gas storage tank 15. The first powder collecting device 6 is connected to the seventeenth switch valve 23s through a second switch valve 23b installed at the outlet. The second powder collecting device 8 is connected to a switch valve 23s installed at the outlet. The third switch valve 23c is connected to the seventeenth switch valve 23s. The third powder collection device 9 is connected to the seventeenth switch valve 23s via the fifth switch valve 23e. The seventeenth switch valve 23s can control the opening and closing of the auxiliary gas supply line between the gas storage tank 15 and the collection device. The second switch solenoid valve 23b, the third switch valve 23c, and the fifth switch valve 23e control the gas entering the first powder collection device 6, the second powder collection device 8, and the third powder collection device 9, respectively. The working gas released from the buffer tank 13 due to excessive pressure into the gas storage tank 15 provides a protective atmosphere for the collection device. This avoids the problem of unstable gas pressure caused by directly using the working gas in the pressure stabilizing tank 14 to the preparation device, and makes reasonable use of the released working gas.

[0050] The buffer tank 13 delivers the working gas exceeding the internal pressure to the gas storage tank 15, saving resources. The gas storage tank 15 supplies gas to the collection device separately, without affecting the working gas supplied by the pressure stabilizing tank 14 in the working gas line. This further ensures the stability of the gas flow field of the entire system and facilitates the separate control of the pressure in the preparation device and the collection device.

[0051] The buffer tank 13 is connected to the filter 11 by the eleventh switch valve 23k and to the powder collection bin 10 by the seventh switch valve 23g. When preparing to collect powder, the airflow back-purges the filter 11 and the powder collection bin 10, which helps to collect powder.

[0052] Furthermore, a twenty-third switch valve 25d is installed at the outlet of the gas source 16 and connected to the gas storage tank 15 through the eighteenth switch valve 23t. The eighteenth switch valve 23t controls the connection and disconnection between the gas storage tank 15 and the gas source 16. The eighteenth switch valve 23t is connected to the buffer tank 13 through the fourth regulating valve 22d. A pressure control valve 27 is connected between the gas source 16 and the radio frequency plasma torch 4. It is opened before the pressure stabilizing tank 14 supplies gas to the radio frequency plasma torch 4, so that the gas source 16 is connected to the radio frequency plasma torch 4, which serves as an ignition mechanism.

[0053] Furthermore, the water chiller 18 is connected to the feeder 2, the radio frequency plasma torch 4, the main unit compartment 5, the cyclone separator 7, the powder collection bin 10, and the filter 11 as cooling pipes. An automatic switching valve 20c is installed at the outlet of the water chiller 18 for overall control of the cooling water. Cooling switching valves are installed on the cooling pipes. A first cooling switching valve 20a is installed between the automatic switching valve 20c and the feeder 2; a second cooling switching valve 20b is installed between the automatic switching valve 20c and the radio frequency plasma torch 4; a third cooling switching valve 20d is installed between the automatic switching valve 20c and the main unit compartment 5; a fourth cooling switching valve 20e is installed between the automatic switching valve 20c and the cyclone separator 7; and a sixth cooling switching valve 20g is installed between the automatic switching valve 20c and the powder collection bin 10. A seventh cooling switch valve 20h is installed between 20c and filter 11 to control and regulate the cooling water flow on each cooling pipe, ensuring that the working temperature of each component, including feeder 2, RF plasma torch 4, main unit chamber 5, cyclone separator 7, powder collection chamber 10, and filter 11, is suitable and preventing damage to the components due to excessive temperature. Specifically, each of the feeder 2, RF plasma torch 4, main unit chamber 5, cyclone separator 7, powder collection chamber 10, and filter 11 is also connected to the water chiller 18 via a cooling circuit (not shown in the figure) to recover and reuse cooling water, thus saving water resources. Each cooling switch valve is used to control the liquid flow on each cooling pipe, which can cool and reduce the temperature of the components connected to each cooling pipe, ensuring the normal operating temperature required for each connected component.

[0054] Furthermore, the micron-sized spheroidized powder or nano-powder preparation control system also includes a vacuum pump 21, which is controlled by a controller. The vacuum pump 21 is connected to the first powder collection device 6, the second powder collection device 8, and the third powder collection device 9 through the second switch valve 23b, the third switch valve 23c, and the fifth switch valve 23e, respectively, to perform vacuuming operations on the collection devices. The vacuum pump 21 is also connected to the material hopper 1, the feeder 2, the pressure stabilizing tank 14, the buffer tank 13, and the powder collection hopper 10 through the twenty-first switch valve 23y, the twenty-second switch valve 23z, the fifteenth switch valve 23q, the sixteenth switch valve 23r, and the eighth switch valve 23h, to perform vacuuming operations on the working gas path and the main gas supply path. The inlet of the vacuum pump 21 is connected to the twenty-first switch valve through the fourth switch valve 23d. Vacuum pump 21 is connected to the inlet of vacuum pump 21 via the ninth switch valve 23i, the fifteenth switch valve 23q, the sixteenth switch valve 23r, and the eighth switch valve 23h. This connection plays a central control role when evacuating the collection device. Vacuum pump 21 is emptied via the first one-way valve 27a. Gas storage tank 15, buffer tank 13, and pressure stabilizing tank 14 are emptied via the first safety valve 25a, the second safety valve 25b, and the third safety valve 25c, respectively. This arrangement prevents excess air from existing in the working gas path and the main gas supply path, avoids nitrogen and oxygen in the air from affecting the quality and characteristics of the powder, and ensures the purity of the prepared powder.

[0055] Furthermore, the micron-sized spheroidized powder or nano-powder preparation control system also includes a flow detection device, a humidity detection device 19, and a gas composition detection sensor. Multiple flow detection devices are respectively connected to the hopper 1, the feeder 2, the radio frequency plasma torch 4, and the main unit 5. The humidity detection device 19 is connected to the main unit 5. The humidity detection device 19 and the gas composition detection sensor respectively detect the humidity and gas composition of the cooling gas introduced during operation. The flow detection device, humidity detection device 19, and gas composition detection sensor are connected to the controller to provide feedback on the detection information. Preferably, the flow detection device is a flow controller. A first flow controller 21a is installed between the hopper and the twentieth switch valve 23x, a second flow controller 21b is installed between the feeder 2 and the second regulating valve 22b, a third flow controller 21c, a fourth flow controller 21d and a fifth flow controller 21c are installed on the three gas supply branches connected to the radio frequency plasma torch 4, a fourteenth switch valve 23p is installed between the main unit compartment 5 and the buffer tank 13, and a sixth flow controller 21f is installed between the fourteenth switch valve 23p and the main unit compartment 5, so as to control the gas flow of the corresponding gas supply branches more accurately, so as to maintain the working pressure of each connected component and maintain pressure stability.

[0056] The control system for preparing micron-sized or nano-sized powders also includes pressure sensors and temperature sensors. Multiple pressure sensors are installed on the following components: hopper 1, feeder 2, radio frequency plasma torch 4, main unit chamber 5, cyclone separator 7, powder collection chamber 10, pressure stabilizing tank 14, buffer tank 13, and gas storage tank 15. These sensors are connected to the controller to monitor the working pressure of these components in real time and provide timely feedback to the controller, facilitating adjustments to gas flow and component pressure. Similarly, multiple temperature sensors are installed on the following components: feeder 2, radio frequency plasma torch 4, main unit chamber 5, cyclone separator 7, powder collection chamber 10, and filter 11. These sensors are connected to the controller to monitor the working temperature of these components in real time and provide timely feedback to the controller, facilitating adjustments to the cooling system to ensure stable operating temperatures for these components.

[0057] The micron-spherical powder or nano-powder preparation control system also includes an air humidity detection device, which is connected to the controller to provide detection information and thereby control the air humidity for cooling. Preferably, the air humidity detection device is connected to the fan 17.

[0058] A method for controlling the preparation of micron-sized spheroidized powder or nanopowder, employing any of the micron-sized spheroidized powder or nanopowder preparation control systems described above, comprises the following steps:

[0059] Step 1: Initially, all components and valves are in the closed state. The controller controls the water chiller 18 to open, the automatic switching valve 20c to open, and the cooling switching valve of the cooling pipeline between the water chiller 18 and the vacuum pump 21 to open. The controller controls the first switching valve 23a, the high-temperature gate valve 26, the tenth switching valve 23j, the twenty-first switching valve 23y, the twenty-second switching valve 23z, the fifteenth switching valve 23q, the sixteenth switching valve 23r, and the eighth switching valve 23h on the working gas line to open, and controls the ninth switching valve 23i at the inlet of the vacuum pump 21. The fourth switch valve 23d and the first one-way valve 27a at the outlet are opened, controlling the vacuum pump 21 to perform vacuuming operation on the working gas path between the material bin 1 and the powder collection bin 10 and the main gas supply path between the pressure stabilizing tank 14 and the buffer tank 13; vacuuming is to prevent too much air from mixing into the entire system, because air contains oxygen, which is easy to oxidize during the preparation of micron-sized spheroidized powder or nano powder, affecting the properties of the prepared powder; the cooling water output from the water chiller 18 is cooled by the vacuum pump 26c through the automatic switch valve 20c and the fifth cooling switch valve 20f;

[0060] Step 2: The controller shuts off the vacuum pump 21, closes the cooling switch valve of the cooling pipe between the water chiller 18 and the vacuum pump 21, turns on the gas source 16, and opens the safety valve 25d and the fourth regulating valve 22d between the gas source 16 and the buffer tank 13. The working gas enters the buffer tank 13 for storage. The working gas in the buffer tank 13 is dried by the dryer 24 and then enters the pressure stabilizing tank 14. The main gas supply line is connected. When the working gas pressure in the buffer tank 13 is greater than the preset pressure value of the buffer tank 13, the nineteenth switch valve 23w is opened, and the working gas enters the storage tank 15 for standby. At this time, the controller closes the valve between the gas source 16 and the buffer tank 13.

[0061] The preset pressure values ​​of buffer tank 13 include static preset pressure values ​​and dynamic preset pressure values. The static preset pressure value is one preset pressure value of buffer tank 13 when the radio frequency plasma torch 4 is not working, and the dynamic preset pressure value is another preset pressure value of buffer tank 13 when the radio frequency plasma torch 4 is working. Generally, the static preset pressure value is lower than the dynamic preset pressure value. This is mainly because after the radio frequency plasma torch 4 is ignited, the gas in the working gas path heats up and expands, and the pressure increases. It is necessary to leave space for gas expansion in buffer tank 13. Therefore, when the radio frequency plasma torch 4 is not working, the working gas pressure in buffer tank 13 is greater than the static preset pressure value, the nineteenth switch valve 23w is opened, and the working gas enters the gas storage tank 15 for standby. After the pressure in buffer tank 13 is less than or equal to the static preset pressure value, the nineteenth switch valve 23w is closed. When the radio frequency plasma torch 4 is working, the working gas pressure in buffer tank 13 is greater than the dynamic preset pressure value, the nineteenth switch valve 23w is opened, and the working gas enters the gas storage tank 15 for standby. After the pressure in buffer tank 13 is less than or equal to the dynamic preset pressure value, the nineteenth switch valve 23w is closed.

[0062] Step 3: The controller pressure tank 14 supplies gas to the radio frequency plasma torch 4, and simultaneously controls the valves of each gas supply branch to open. The twentieth switch valve 23x is opened, and the pressure tank 14 supplies gas to the silo 1 to prevent powder backflow. The second regulating valve 22b, the third regulating valve 22c, the fifth regulating valve 22e, and the sixth regulating valve 22f are opened. The pressure tank 14 fills the feeder 2, the radio frequency plasma torch 4, the main unit silo 5, the cyclone separator 7, the powder collection silo 10, the filter 11, and the booster 12 with working gas to form a protective atmosphere. After the pressure tank 14 stabilizes the gas supply to the radio frequency plasma torch 4 and reaches the preset gas pressure, the flow detection device detects and feeds back to the controller in real time. The controller closes all output gas valves of the pressure tank 14 and enters a static standby state.

[0063] Step 4: The controller controls the operation of the water chiller 18, and the cooling switch valves on each cooling pipe are opened. The first cooling switch valve 20a, the second cooling switch valve 20b, the third cooling switch valve 20d, the fourth cooling switch valve 20e, the sixth cooling switch valve 20g and the seventh cooling switch valve 20h are opened. The feeding device 3 is opened and the high-temperature gate valve 26 is opened. At the same time, the controller controls the operation of each component in the preparation device, and the high-voltage electrical appliances enter the heat preparation state.

[0064] Step 5: The controller controls the pressure stabilizing tank 14 to control the opening of each regulating valve of the radio frequency plasma torch 4 in a PID manner. The high-temperature gate valve 26 between the radio frequency plasma torch 4 and the main unit compartment 5, the tenth switch valve 23j between the cyclone separator 7 and the powder collection compartment 10, the sixth switch valve 23f between the powder collection compartment 10 and the filter 11, the twelfth switch valve 23m between the filter 11 and the booster 12, and the thirteenth switch valve 23n between the booster 12 and the buffer tank 13 are all opened. The regulating valve between the buffer tank 13 and the pressure stabilizing tank 14 is opened. The controller controls the booster 12 to start up and controls the speed of the booster 12 motor in a PID manner according to the pressure of the main unit compartment 5, thereby controlling the pumping capacity of the booster. Since the method of controlling the booster 12 in a PID manner is existing technology, it will not be described in detail. The gas enters a circulation state in the silo 1, feeder 2, radio frequency plasma torch 4, main unit 5, cyclone separator 7, powder collection silo 10, filter 11, booster 12 and buffer tank 13. The controller controls the opening of the regulating valve between the pressure stabilizing tank 14 and the buffer tank 13 in a PID manner according to the preset pressure of the pressure stabilizing tank 14, and the equipment enters a dynamic standby state.

[0065] Step 6: The controller controls the power-on of each component and starts the ignition switch to start the radio frequency plasma torch 4. The controller controls the opening of each regulating valve at the radio frequency plasma torch 4 so that the pressure of each part of the equipment reaches the preset value. When the radio frequency plasma torch 4 is working, the gas expands due to heat. The controller will automatically discharge the excess gas to the gas storage tank 15 for later use according to the pressure value set by the buffer tank 13.

[0066] Step 7: The controller controls the second regulating valve 22b between the pressure stabilizing tank 14 and the feeder 2 to adjust the output gas flow rate according to the process requirements. The material is fed from the hopper 1 through the feeder 2 under the blowing of the working gas and enters the radio frequency plasma torch 4 for plasma spheroidization. The spheroidized powder is condensed in the main unit hopper 5. The micron powder remains in the main unit hopper 5, and the other powders enter the cyclone separator 7 for sieving. The nano powder enters the powder collection hopper 10. When needed, the fourteenth switch valve 23p between the buffer tank 13 and the main unit hopper 5 is quickly opened to purge the observation window of the main unit hopper 5.

[0067] Step 8: The controller controls the vacuum pump 21 to turn on, and the fifth cooling switch valve 20f of the cooling pipeline between the water chiller 18 and the vacuum pump 21 is opened. At the same time, the controller controls the fourth switch valve 23d, the second switch valve 23b, the third switch valve 23c, and the fifth switch valve 23e to open. The vacuum pump 21 evacuates the first powder collection device 6, the second powder collection device 8, and the third powder collection device 9 to prepare for powder collection.

[0068] Step 9: The controller controls the vacuum pump 21 to shut down, the fifth cooling switch valve 20f of the cooling pipeline between the water chiller 18 and the vacuum pump 21 to shut down, controls the eleventh switch valve 23k between the buffer tank 13 and the filter 11 to open, and controls the seventh switch valve 23g between the powder collection bin 10 to open for backflushing, so that the powder can enter the powder collection device. The controller controls the seventeenth switch valve 23s at the outlet of the gas storage tank 15 to open, so that the auxiliary gas supply line is connected. The gas storage tank fills each of the powder collection devices with working gas. The controller controls each of the powder collection devices to work, and collects the powder in the corresponding connected main unit compartment 5, cyclone separator 7 and powder collection bin 10 respectively. Micron powder is collected in the first powder collection device 6, and nano powder is collected in the third powder collection device 9.

[0069] Furthermore, the method for controlling the preparation of micron-sized spherical powders or nanopowders also includes:

[0070] Step 10: The controller controls the filter 11 and the booster 12 to open, and simultaneously controls the opening of the switching valves in the working gas path section between the powder collection bin 10, the filter 11, the booster 12 and the buffer tank 13. The sixth switching valve 23f, the seventh switching valve 23k, the twelfth switching valve 23m and the thirteenth switching valve 23n are opened, and the second one-way valve 27b is opened, so that the working gas in the preparation device is recovered into the buffer tank 13. The controller performs PID control on the speed of the booster 12 to ensure that the pressure of the main chamber 5 is constant. The pressure of the main chamber 5 can be adjusted within the range of 0-130KPa, and can be adjusted according to different powder preparation requirements.

[0071] It should be noted that the booster 12, as the gas circulation power source, must start the circulation before the RF plasma torch 4 is ignited. Under the control of the controller, the gas pressure in each component space is at the required intensity. After ignition, it can be automatically or manually adjusted to the required pressure in the working state and the gas pressure of each part can be adjusted according to process requirements. In each operation step, the opening and closing of each component, valve and / or switch only describes the current state. The order of opening and closing of each component and valve and / or switch depends on the actual operation. Generally, the relevant valve and / or switch is opened first, and then the related component is opened. When closing, the relevant component is closed first, and then the relevant valve and / or switch is closed to ensure the normal operation of each component and prevent damage to the component due to excessive gas pressure.

[0072] The motor speed of the booster compressor 12 determines the pumping capacity of the booster compressor 12, which in turn determines the pressure of the main chamber 5. The controller uses the PID control method to adjust the motor speed of the booster compressor 12 to ensure that the pressure of the main chamber 5 is at the value required by the process. The preset pressure of the booster compressor 12 is 500 kPa, and the preset pressures of the air source 16, the buffer tank 13, and the pressure stabilizing tank 14 are also 500 kPa. The controller can also adjust the booster compressor 12 using a self-regulating valve.

[0073] The aforementioned micron-spheroidized powder or nano-powder preparation control system also includes an alarm. When gas leakage in the system causes a sudden change in gas pressure or the gas pressure of each component exceeds the preset pressure value, or when cooling water leaks in the cooling pipe, the alarm will sound, prompting the staff to handle and repair the system within a preset time. If the problem is not handled within the preset time, the system will shut down in an emergency. When the temperature of each component is too high and exceeds the preset temperature value, the alarm will sound, and the system will shut down in an emergency.

[0074] When the micron-sized or nano-sized powder is prepared and the system needs to be shut down, the system will automatically shut down according to the set program. The automatic shutdown operation steps are as follows: the radio frequency plasma torch 4 is extinguished, the high voltage connected to the radio frequency plasma torch 4 is turned off, after the temperature of each component drops to the shutdown requirement, the gas supply device stops supplying gas, the fan is turned off, the water chiller is turned off, the entire system is shut down, the pressure of each component is adjusted to the set pressure value under static conditions, and all valves and / or switches in the system are closed.

[0075] In Example 2, a cooling device is connected to the booster compressor 12, which can be either air-cooled or water-cooled. Preferably, the booster compressor 12 is connected to a water chiller 18 through a cooling switch valve to cool it down and ensure that the booster compressor 12 works normally. An automatic humidifier is also connected to the fan 17, which can automatically turn on or off according to the air humidity detected by the humidity detection device 19 to humidify the air at the fan 17. The fan 17 blows in the humidified air to ensure that the humidity in the system is suitable. Other settings are the same as in Example 1.

[0076] In Example 3, the main unit compartment 5 and the gas storage tank 15 in the micron-spheroidized powder or nano-powder preparation system are connected by a switch valve. The gas storage tank 15 can replenish the main unit compartment 5 with gas to ensure the normal operation of the main unit compartment 5, while not affecting the gas pressure stability of the entire working gas path. Other settings are the same as in Example 1.

[0077] In Example 4, during cold winters, the entire system needs to maintain a constant temperature when the equipment is shut down to prevent malfunctions. The water chiller 18 requires cooling of relevant equipment during operation (feeder 2, RF plasma torch 4, main unit compartment 5, cyclone separator 7, powder collection compartment 10, and filter 11 operate at temperatures below 50°C). When the equipment is shut down, the connected equipment needs to maintain a constant temperature (1°C to 10°C). Therefore, the water tank of the water chiller 18 is connected to an electric heater to maintain a constant temperature within the water tank. In winter, when the temperature drops below zero, to prevent the cooling system from freezing and causing equipment damage, the system automatically... The temperature of each component of the measuring equipment is measured, and the equipment enters the anti-freeze mode. The first cooling switch valve 20a, the second cooling switch valve 20b, the third cooling switch valve 20d, the fourth cooling switch valve 20e, the sixth cooling switch valve 20g, and the seventh cooling switch valve 20h are opened. The electric heater and the water in the water tank of the water chiller 18 circulate in the cooling pipes and cooling circuit to ensure that the components connected to the water chiller 18 maintain a constant temperature. Since the water temperature provided by the water chiller 18 cannot meet the constant temperature requirement of the feeder 2, a heater is connected to the feeder 2. Electric heating or water bath heating can be used to ensure that the feeder 2 operates at a constant temperature. Other settings are the same as in Embodiment 1.

[0078] In this invention, each switching valve, regulating valve, and cooling switching valve can be an electric valve or a solenoid valve, and can be automatically or manually controlled, as long as it enables the smooth flow or cut-off of the fluid medium.

[0079] The parts of this invention not described in detail are prior art. Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A control system for preparing micron-sized spheroidized powders or nanopowders, characterized in that: It includes a gas supply device, a preparation device, a collection device, and a cooling device; The gas supply device includes a gas source, a buffer tank, a gas storage tank, and a pressure stabilizing tank. The gas source, the buffer tank, and the pressure stabilizing tank are connected in sequence. The pressure stabilizing tank is connected to the preparation device to provide working gas with stable pressure. The buffer tank is also connected to the gas storage tank to store excess working gas. The gas source is also connected to the gas storage tank and the preparation device. The preparation apparatus includes a hopper, a feeder, a radio frequency plasma torch, a main unit chamber, a cyclone separator, a powder collection chamber, and a booster connected in sequence. The hopper, feeder, and radio frequency plasma torch are respectively connected to the pressure stabilizing tank. The main unit chamber and the powder collection chamber are respectively connected to the buffer tank. The buffer tank is used to purge or back-purge the main unit chamber and the powder collection chamber. The booster is connected to the buffer tank and is used to recover the working gas for recycling. The collecting device includes a first powder collecting device, a second powder collecting device, and a third powder collecting device. The first powder collecting device is connected to the main unit compartment, the second powder collecting device is connected to the cyclone separator, and the third powder collecting device is connected to the powder collection bin. The cooling device includes a water chiller and a fan. The water chiller is connected to the feeder, the radio frequency plasma torch, the main unit compartment, the cyclone separator, and the powder collection compartment, respectively. The fan is connected to the radio frequency plasma torch. A filter is connected between the powder collection bin and the booster, and the filter is also connected to the buffer tank. Regulating valves are respectively installed between the air source and the buffer tank, and between the pressure stabilizing tank and the feeder. An on / off valve is installed between the buffer tank and the powder collection bin. The buffer tank is connected to the air storage tank through the on / off valve. The air storage tank is connected to the first powder collection device, the second powder collection device, and the third powder collection device through on / off valves respectively. Three gas supply lines are provided between the pressure stabilizing tank and the radio frequency plasma torch. The three gas supply lines are a central gas line, a side gas line, and a cooling gas line. Each of the central gas line, side gas line, and cooling gas line is equipped with a regulating valve. A pressure control valve is connected between the gas source and the radio frequency plasma torch.

2. The micron-spherical powder or nanopowder preparation control system as described in claim 1, characterized in that: A dryer is connected between the buffer tank and the pressure stabilizing tank, and a feeding device is provided between the silo and the feeder.

3. The micron-spherical powder or nanopowder preparation control system as described in claim 2, characterized in that: It also includes a vacuum pump, which is connected to the first powder collection device, the second powder collection device and the third powder collection device through switching valves respectively. The vacuum pump is also connected to the silo, the feeder, the powder collection silo and the pressure stabilizing tank and the buffer tank through switching valves. The water chiller is connected to the vacuum pump through a cooling switching valve.

4. The micron-spherical powder or nanopowder preparation control system as described in claim 3, characterized in that: A high-temperature gate valve is installed between the radio frequency plasma torch and the main unit chamber; an on / off valve is installed between the feeder and the radio frequency plasma torch; on / off valves are installed between the cyclone separator and the powder collection bin, the powder collection bin and the filter, the filter and the booster, and the booster and the buffer tank; a regulating valve is installed between the buffer tank and the dryer; an on / off valve is installed between the pressure stabilizing tank and the silo; regulating valves are installed between the pressure stabilizing tank and the radio frequency plasma torch; and an on / off valve is installed between the buffer tank and the main unit chamber.

5. The micron-spherical powder or nanopowder preparation control system as described in claim 4, characterized in that: A switch valve is installed at the outlet of the water chiller. The water chiller is connected to the feeder, the radio frequency plasma torch, the main unit compartment, the cyclone separator, the powder collection compartment, and the filter through the cooling switch valve.

6. The micron-spherical powder or nanopowder preparation control system as described in claim 5, characterized in that: It also includes a gas composition detection sensor, a pressure sensor, and a temperature sensor. The gas composition detection sensor is connected to the radio frequency plasma torch. Multiple pressure sensors are installed on the silo, feeder, radio frequency plasma torch, main unit silo, cyclone separator, powder collection silo, pressure stabilizing tank, buffer tank, and gas storage tank, respectively. Multiple temperature sensors are installed on the feeder, radio frequency plasma torch, main unit silo, cyclone separator, powder collection silo, and filter, respectively.

7. The micron-spherical powder or nanopowder preparation control system as described in claim 6, characterized in that: It also includes a flow detection device and a humidity detection device. Multiple flow detection devices are provided and are respectively connected to the silo, feeder, radio frequency plasma torch, and main unit compartment. The humidity detection device is connected to the main unit compartment.

8. The micron-spherical powder or nanopowder preparation control system as described in claim 7, characterized in that: It also includes a monitoring device, which includes multiple cameras and a display. The multiple cameras are connected to the display and are respectively installed in the hopper, feeder, radio frequency plasma torch, and main unit hopper.

9. The micron-spherical powder or nanopowder preparation control system as described in claim 8, characterized in that: It also includes a controller, which is connected to the gas supply device, the preparation device, the collection device, the cooling device, the monitoring device, the flow detection device, the humidity detection device, the gas composition detection sensor, the pressure sensor, and the temperature sensor, respectively, to control the operation of each component, and is also connected to the valves and / or switches between each component to control the opening and closing of each valve and / or switch.

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