Laser method for producing spherical powder and device for carrying out same

Abstract

The invention relates to the field of producing spherical powder materials. A method for producing spherical powder materials consists in bringing about the phase transition of a condensed phase material and atomizing same and is characterized in that it includes melting or evaporating a material or generating a plasma erosion jet by exposing the end of a rotating hollow cylinder to the action of a system of laser sources, atomizing the melt or the plasma erosion jet using centrifugal force and subsequently condensing spherical powder particles. A device for producing spherical powder materials comprises a laser, a focusing lens and a heated target and is characterized in that it further comprises a system for generating N laser beams, the target being in the form of a rotating hollow cylinder, the end of which is situated in the focal region of said laser beams, and the device still further comprises a processing chamber configured to allow vacuum pumping, the creation of a dynamic vacuum and the admission of an inert gas, as well as a powder collector configured to allow vacuum extraction and a controllable gas leak valve system with a slotted nozzle.

Description

[0001] LASER METHOD FOR PRODUCING SPHERICAL POWDER AND A DEVICE FOR ITS IMPLEMENTATION

[0002] FIELD OF INVENTION

[0003] The invention relates to the field of laser technologies, in particular to the field of producing powder materials using laser radiation and can be used in technological processes for the production of powder materials.

[0004] LEVEL OF TECHNOLOGY

[0005] A known method for producing powders is by atomizing rod material with plasma streams [1]. In this method, a metal rod is dispersed using powerful plasma torches with a total capacity of approximately 100 kW and the resulting particles are accelerated in a Laval nozzle to supersonic speeds to produce spherical particles smaller than 40 µm (1-40 µm) in size at a productivity level of 10 kg / hour. This requires enormous energy and gas consumption (argon). The process efficiency is 10 kW h / kg.

[0006] Also known are methods of gas [2] and liquid atomization, in which a jet of molten metal is dispersed by gas or liquid jets to produce spherical particles measuring 30-150 μm: with enormous energy costs for producing the melt and gas for spraying, with the efficiency of the process, these methods do not allow obtaining micro and nano particles in the range of less than 1 μm. A method for producing ultrafine powders and a device for its implementation are known [3], in which the production of nanopowders of complex compounds and mixed compositions is carried out by evaporating a substance with radiation from a pulse-periodic laser, followed by condensation of the evaporated substance in a gas stream, while the surface of the evaporated substance is moved in the focal plane relative to the focal point of the laser radiation: at a constant speed.

[0007] In a device implementing this method, including an evaporation chamber with a substance to be evaporated, a laser and a nozzle for the gas flow, the following are installed: a drive for moving the evaporated substance, configured to rotate and move at a constant linear velocity the surface of the evaporated substance in the focal plane relative to the focal point of the laser radiation, a fan for purging the evaporation chamber with a gas flow, cyclone filters for collecting nanopowder, located at the outlet of the gas flow from the evaporation chamber; the laser is configured to operate in a pulse-periodic mode, and the nozzle for the gas flow is configured to ensure one direction of the gas flow and laser radiation and is located above the surface of the evaporated substance.

[0008] The disadvantage of this method is that, despite the high pulsed radiation power of 6 kW, the average power is quite low. Increasing the power is impossible, as this would lead to plasma formation and the transfer of the laser radiation absorption region into the surrounding gas. The process throughput does not exceed 100 g / hour with an energy consumption of 40 W h / year.

[0009] The closest in technical essence to the proposed method and the device implementing it is the method for producing spherical powders and the device for implementing it, presented in [4,5], the so-called plasma centrifugal atomization. Using a high-power plasma torch (more than 100-200 kW), rotating at a speed of up to 30,000 rpm, a metal rod with a diameter of 50-70 mm is melted and the melt layer, due to the action of centrifugal force, is scattered in an atmosphere of inert gas and atomized into particles measuring 30-500 µm.

[0010] The process is quite productive, but its efficiency is low (2 kWh / kg) due to high energy consumption. The main drawback of the method is its inability to produce micron-sized particles (<10 µm) and nanoparticles. In terms of the quality of the resulting spherical particles, this is the best method.

[0011] The objective of this iso-relationship is to develop an efficient, highly productive, environmentally friendly method for producing spherical powders of a wide nano-micro size range using laser radiation and devices for its implementation.

[0012] BRIEF DESCRIPTION OF THE INVENTION

[0013] To solve the problem, a laser method for producing powders is proposed, which consists of heating the material of the condensed phase of the end of a rotating hollow cylinder with laser radiation until melting, followed by centrifugal atomization due to the melt dispersion, and also with laser radiation with subsequent condensation of particles under conditions of centrifugal expansion of vapors in a vacuum or at reduced pressure of the surrounding gas.

[0014] In the first version of the method, due to the high concentration of laser radiation energy from the laser system into spots with a diameter of 2 mm on the surface of the end of a rotating cylinder with a diameter of 50-100 mm with a wall thickness of 4 mm at a level of 10 4 - 10 5 W / cm 2 Rapid and efficient heating to melting temperature is achieved with limited heat removal from the end face. Multiple laser sources are used, with focusing spots evenly distributed around the cylinder's perimeter. The process is carried out in an inert gas atmosphere. The resulting melt layer is atomized by centrifugal force into spherical particles with sizes typical of centrifugal atomization (30-400 µm), but with a much higher throughput of hundreds of kilograms per hour and efficiency.

[0015] In the second variant of the method, by increasing the power density to the evaporation threshold and above, an evaporation regime is achieved and a vapor plume is formed. This plume is dispersed by centrifugal force into micron-sized particles and nanoparticles due to expansion in a vacuum or low pressure at a high degree of supersaturation. Since the vapor plume is deflected by centrifugal force, shielding of the surface from laser radiation by vapor and erosive plasma during its formation is eliminated, enabling extremely high power output on the target and high productivity of up to several tens of kilograms per hour.

[0016] To implement the method, a device is proposed that contains a source of high-energy energy flow, a rotating meltable target, characterized in that the radiation of the laser system is focused on the end of the rotating hollow cylinder, creating a layer of melt, which is sprayed using centrifugal force in a chamber with inert gas with condensation of spherical microparticles.

[0017] In another device variant, increasing laser power and creating a vacuum in the chamber ensures the evaporation of the cylinder material and the formation of an erosion plume, which is atomized by centrifugal force to form micro- and nanoscale spherical particles. Upon crossing the plasma formation threshold in power density, a plasma vapor plume is formed, which is also atomized to form nanoparticles due to high supersaturation. Process parameters are regulated by the vacuum level or by gas injection in dynamic vacuum mode and operation at reduced pressure. Deflection of the plumes by centrifugal force eliminates the plasma shielding effect on the surface and allows operation at maximum laser power densities.

[0018] BRIEF DESCRIPTION OF DRAWINGS

[0019] In Fig. 2, devices for producing spherical particles by the method of laser centrifugal atomization during evaporation and near-surface plasma formation and condensation of particles from both the vapor and plasma phases by centrifugal spraying in a vacuum or at reduced pressure of the surrounding gas.

[0020] Fig. 3 shows a fragment of a shadow image of a plasma erosion torch during the spraying process.

[0021] DETAILED DESCRIPTION OF THE INVENTION

[0022] The essence of the method is explained by the drawings in Figs. 1 - 3.

[0023] As noted in the introduction, the main drawback of existing industrial methods and devices for producing spherical powders in the micro- and nanoscale ranges is the low degree of energy flux concentration on the sputtered concentrated phase target and the high costs of heating the material. The closest method and device also have the disadvantage of high energy costs and the inability to produce spherical powders in the micro- and nanoscale ranges (<10 μm).

[0024] A high degree of concentration of the energy flow and its efficient use can be achieved using laser radiation and centrifugal spraying of the melt and a torch of vapor or plasma of the target material.

[0025] The diagram of laser centrifugal atomization is shown in Fig. L, where a circular system 1 of several continuous or pulse-periodic lasers 12 forms, with the help of fiber cables 15, collimators 7, focusing optics 2, several focal spots with a diameter of, for example, 2 mm on the surface of the end of a cylinder 3 with a diameter of, for example, 50 mm and a wall thickness of 4 mm. The cylinder is located in a cylindrical chamber 4, pumped out by a vacuum system 10 and filled with an inert gas 9, for example, nitrogen or argon at a pressure of 0.1 MPa. The cylinder rotates at a speed of 25 - 40,000 rpm by a motor 5 and is moved by a system 6 in the direction of the laser system 1 while maintaining a constant size of the focal spot on the end of the cylinder as material is removed from the end of the cylinder. The cylinder material melts and the melt 14 is sprayed by centrifugal force. The powder particles 13 are slowed down, cooled in a gas atmosphere and settle on the walls and flow into the collector 1 1.The laser centrifugal atomization process produces spherical particles measuring 30–200 µm. The process performance is calculated at a power density of 10. 5 W / cm 2 with 4 laser sources with a power of 10 kW each, it is 100 kg / hour - with an efficiency of 0.4 kW h / kg.

[0026] To obtain microparticles smaller than 30 µm and nano-sized particles, the atomization process is transferred to vacuum conditions or reduced pressure gas atmosphere in chamber 4. By increasing the power density of laser radiation of the system: lasers 1 to the evaporation threshold of the cylinder material and above, a vapor torch or plasma vapor torch (near-surface optical discharge) 19 (Fig. 3) is obtained, which is deflected from the normal to the surface by centrifugal force and is sprayed (atomized). Limit supersaturation occurs and condensation proceeds intensively under vacuum conditions or at reduced pressure with the formation of micro and nano particles 13, which are sucked through collector 16 by vacuum system 17 and directed to the fraction separation system. A dynamic vacuum is maintained in chamber 4 during operation of gas leak 9 through nozzle 18.Since the vapor torch and plasma torch are deflected toward the horizontal surface, the effect of target shielding by vapor and plasma disappears, which allows the use of laser radiation parameters with the maximum power density and a sharp increase in the efficiency of the process for producing micro- and nano-spherical powders. The process productivity at 10. 6 W / cm 2 The production rate reaches 100 kilograms per hour, and the efficiency is 0.8 kW h / kg. Thus, the claimed invention allows for the implementation of a highly efficient industrial complex for the production of spherical powder.

[0027] Literature

Claims

1. A method for producing powder materials consisting of melting a condensed phase material and its atomization, characterized by the fact that a system of laser sources is used to melt the core of a rotating hollow cylinder, followed by atomization of the melt by centrifugal force and condensation of spherical powder particles in a gas.

2. A method for obtaining powder materials, consisting of evaporation of the material followed by condensation of the vapor, characterized in that the evaporation of the end of a rotating hollow cylinder is carried out by a system of laser sources in a vacuum or under reduced pressure and the vapor is sprayed by centrifugal force followed by condensation of micro- and nano-sized spherical powder particles.

3. A method for producing powder materials, consisting of evaporation of the material followed by condensation of the vapor, characterized in that the evaporation of the end of a rotating hollow cylinder and the formation of an erosive plasma torch, a near-surface optical discharge, are carried out by a system of laser sources in a vacuum or at reduced pressure and the plasma is sprayed by centrifugal force followed by condensation of micro- and nano-sized spherical powder particles.

4. A device for producing powder materials containing a laser, a focusing lens, a heated target, a blowing system, and a target characterized in that it includes a system for generating N laser beams focused on the end of the target. The target is made in the form of a rotating hollow cylinder, the end of which is located in the focal region of the laser beams. beams, in addition, the device contains a process chamber with the possibility of vacuum pumping and filling with inert gas and a powder collector 5. A device for producing powder materials containing a laser, a focusing lens, a heated target, a target blowing system, and characterized in that a focused beam generation system is introduced into it. N laser beams, the target is made in the form of a rotating hollow cylinder , the end of which is located in the focal region of the laser beams, in addition, the device contains a process chamber with a dynamic vacuum, an annular powder collector with a vacuum suction, and an adjustable gas leak system with a slot nozzle.

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