EP2202332A1 - Method for gas-dynamic acceleration of materials in powder form and device for implementing this method - Google Patents

Abstract

The method of accelerating cold compressed gas dynamics of a metallic or non-metallic powder material (4), comprises supplying the powder material in a supersonic nozzle (1) via an injection point, accelerating the material by a supersonic gas flow and depositing the material by impact on the surface of the piece. The compressed gas is heated to 300-9800 K. The acceleration of the material corresponds to the parameters such as particle size, density of the material and gas parameters. The method of accelerating cold compressed gas dynamics of a metallic or non-metallic powder material (4), comprises supplying the powder material in a supersonic nozzle (1) via an injection point, accelerating the material by a supersonic gas flow and depositing the material by impact on the surface of the piece. The compressed gas is heated to 300-9800 K. The acceleration of the material corresponds to the parameters such as particle size, density of the material and gas parameters and satisfying an equation, L=4.35rho pd p+- 50% and b=0.065rho pd p+- 50%, where L is length of the supersonic nozzle, rho p is density of the material, d p is diameter of the particle, b is height of the nozzle and b=d c r is the diameter of the critical section of the axisymmetric nozzle. An independent claim is included for a device for acceleration of cold compressed gas dynamics of a metallic or non-metallic powder material.

Description

The present invention relates to a method and device for gasodynamic acceleration of powdered materials for use in mechanics and other industrial fields to form functional coatings providing different properties on the treated surfaces. In addition, the present invention can be implemented in processes using high velocity impacts between powder particles and a substrate surface such as sanding of surfaces, breaking up / granulating of powder particles, etc.

Gasodynamic projection systems for powder materials are already known.

The document UK No. 2257423 thus describes a system which comprises a projection module composed of an electric compressed gas heater and a supersonic nozzle connected to the outlet orifice of said heater and comprising a powder injection module in said nozzle, a module of control connected to the electric gas heater compressed by a flexible pipe and by an electric cable, a powder supply container whose outlet is connected to the powder injection module in the nozzle. To secure the operation of the system by decreasing the temperature of the external components of the electric compressed gas heater, said heater comprises a leather cover which envelops a metal frame leaving a free space between it and said frame, the free space being filled with a heat-insulating material and said frame having a heat exchanger and having vents for the circulation of a cooling gas inside the cover. The powder injection module in the nozzle provides, according to a preferred embodiment, the injection of the powder into the supercritical zone of the supersonic nozzle at oblique with respect to the longitudinal axis of the nozzle in order to to increase the efficiency of the projection process by a more uniform distribution of the powder material in the cross-section of the nozzle. The device provides for the use of nozzles having the round or rectangular cross section depending on the geometric shapes of the treated surfaces of a workpiece. Depending on the composition of the material used, the ratio between the length of the supersonic portion of the nozzle and the dimension of the minimum cross section of said nozzle may vary from 20 to 100.

The disadvantage of this device is that the dimensions of the supersonic nozzle as an integral part are in no way related to the size of diameter and the density of the material of the projected particles. Therefore, by using this device, it is impossible to communicate to the particles during their movement in the supersonic part of the nozzle the optimum acceleration to reach the impact velocity on the surface of the maximum treated part susceptible of to be achieved by the projected particles in view of their size and density characteristics and, consequently, to ensure the maximum quality of the resulting coatings.

The document UK No. 2288970 discloses a cold gasodynamic projection system of powder materials which comprises an electric compressed gas heater, a supersonic nozzle (called Laval) connected by an outlet orifice to said heater and having a groove located between the convergent and divergent portions of said nozzle, a powder injection module in the nozzle having injection points for injection of powder into the nozzle and located upstream of the nozzle after the groove, said injection module comprising at least one container of powder supply connected by pipes to said injection points of at least one powder material, and the geometric characteristics of the nozzle portion located upstream of the powder injection points and for accelerating the powder particles injected into the nozzle corresponding to the following conditions: 0.015 <B ( Jump / Sinj -1) / L <0.03, where Sout is the cross sectional area of the nozzle to at its outlet end, Sinj is the cross-sectional area of the nozzle at the position of the powder injection points, L is the length of the portion of the nozzle intended to accelerate the injected powder particles in the nozzle, B is the minimum dimension of the cross section of the nozzle at the position of the powder injection points. The device provides for the use of the nozzles having the round or rectangular cross-section depending on the geometric shapes and composition of the treated surfaces of a workpiece as well as the desired objectives and desired resultant coating characteristics.

As in the previous case, the disadvantage of this device is that the dimensions of the supersonic nozzle as an integral part are in no way related to the size of the diameter and the density of the material of the projected particles. Therefore, by using this device, it is impossible to communicate to the particles during their movement in the supersonic part of the nozzle the optimum acceleration to reach the impact velocity on the surface of the maximum treated part susceptible of to be reached by the projected particles taking into account their size and density characteristics and, consequently, to ensure the maximum quality of the resulting coatings. However, since the typical ratio of the Sout and Sinj areas is Sout / Sinj ≈ 2 - 4, the formula 0.015 < B (Jump / Sinj -1) / L <0.03 used by this method and this device, in fact, does not determine the ratio of the length of the nozzle portion for accelerating the powder particles to the minimum dimension of the cross-section at the position of the powder injection points. For example, a nozzle having B = 0.1 mm, L = 5 mm and Sout / Sinj = 2 and thereby satisfying the proposed formula would not allow a coating to be made from particles having sizes in the range. indicated because the acceleration path would be too short for the particles to reach the speed necessary to make a deposit.

The document US 6,743,468 The closest known state of the art describes a method and device for depositing coatings on the surface of a workpiece by kinetic projection and thermal spraying using one and the same nozzle. The device according to this invention comprises a gas heater allowing the user to switch from the kinetic projection mode which is carried out without thermal softening of the particles to thermal projection mode with thermal softening of particles before the projection. Such a nozzle construction broadens the spectrum of applications of the method in kinetic projection. The method according to this invention uses particles having a diameter diameter d _p = 50 - 250 μm and nozzles having dimensions as follows: the length of the supersonic portion is L = 60 - 400 mm, the diameter of the critical section of the axisymmetric nozzle is to _cr = 1.5 - 3.5 mm.

The disadvantage of this method and this device is that the dimensions of the supersonic nozzle as an integral part are optimized only taking into account the use of particles having sizes in the range claimed in the patent ( d _p = 50 - 250 μm) and are in no way related to the density of the material of the particles. Therefore, it is impossible, in carrying out this invention, to communicate to the particles projected during their movement in the supersonic part of the nozzle the optimum acceleration to reach the impact velocity on the surface of the treated part. maximum likely to be achieved if they are of a size distinct from those claimed. For example, this device is unable to provide a high impact speed on the surface of a workpiece treated with particles having a size of less than 1 μm in diameter because particles of such dimensions would be slowed considerably in a compressible boundary layer formed by a supersonic jet impacting a target.

In this technical context, the object of the present invention is to impart to the particles during their movement in the supersonic part of the nozzle the optimum acceleration to reach the impact velocity on the surface of the maximum treated part susceptible to to achieve the given gas parameters (composition, temperature and stagnation pressure) by means of the development and application of the nozzles having the optimal geometrical parameters, in particular the ratio between the length of the supersonic part and the critical section, specifically calculated for the use of particles having a size and density of the material constituting them.

• l'augmentation du rendement de déposition et de la qualité des revêtements déposés par la projection gazodynamique à froid ;
• la possibilité d'utiliser dans la projection gazodynamique à froid et le sablage des surfaces, selon une réalisation préférée, les particules ayant une taille inférieure à 1 µm et d'obtenir une résolution spatiale inférieure à 1 mm;
• l'augmentation du rendement des procédés de sablage des surfaces et de morcèlement/granulation de particules.

The present invention offers the following improvements over the state of the art:

• the increase of the deposition efficiency and the quality of the coatings deposited by the cold gasodynamic projection;
• the possibility of using in the cold gasodynamic projection and sanding of the surfaces, according to a preferred embodiment, the particles having a size of less than 1 μm and of obtaining a spatial resolution of less than 1 mm;
• the increase in the efficiency of sand blasting and particle grinding / granulation processes.

Let's take an example. It is desired to deposit a coating from a powder material with particles having a diameter of about 100 nm (nanoparticles). Deposition will not occur if a traditional gas-jet projection nozzle is used, ie, with the length of the supersonic portion of about 100 mm and the diameter of the critical section of about 3 mm. mm. This is because particles of such small dimensions will not reach high impact velocities at the target surface due to considerable slowing down in a compressible boundary layer formed by a supersonic jet. impacting a target.

There is one more aspect to consider. If it is desired to obtain a high spatial resolution of the process implemented, such as, for example, the deposition of cords of less than 1 mm in width or the direct manufacture of three-dimensional objects by powder spraying, the outlet orifice of the nozzle used must have dimensions specially provided for this purpose. The supersonic part of such a nozzle must be shortened. Depending on the chosen dimensions of a nozzle, the particles to be sprayed must be selected having a size that would allow them to reach the maximum impact velocity at the target surface likely to be reached. However, the particles of small dimensions are well accelerated in the nozzle, but strongly slowed in the compressible boundary layer. The coarse particles, on the contrary, undergo almost no slowing in the compressible boundary layer, but at the same time, their acceleration in the nozzle is difficult. Therefore, it is a matter of choosing a particle size that would allow the projected particles to reach the maximum impact velocity on the target surface and, thus, to obtain the deposition efficiency and the quality of the maximum deposited coatings or other performance characteristics specific to the process used (sanding of the surfaces, fragmentation / granulation of particles).

où L est la longueur de la partie supersonique de la buse, ρ_p est la densité d'une particule dudit matériau, d_p est le diamètre d'une particule, b = h est la hauteur de la buse, b = d_cr est le diamètre de la section critique de la buse axisymétrique.The present invention advantageously solves the problems mentioned above by proposing a cold gas-dynamic acceleration method of at least one powder material comprising feeding said powder material into a supersonic nozzle via an injection point, its acceleration by a supersonic gas flow and its deposition by impact on the surface of a workpiece, the method taking into account the size of the particles and the density of the material constituting them as well as the parameters of the gas in order to give the particles of powder entrained by the gas flow the maximum speed that can be reached at their impact on the surface of the treated part by accelerating the flow of gas and powder in the supersonic part of the nozzle whose length and transverse dimension correspond to the following conditions: $$\mathrm{The}=4,35{\rho }_p{d}_p\pm 50\%;b=0,065{\rho }_p{d}_p\pm 50\%,$$

where L is the length of the supersonic portion of the nozzle, ρ _p is the density of a particle of said material, d _p is the diameter of a particle, b = h is the height of the nozzle, b = d _cr is the diameter of the critical section of the axisymmetric nozzle.

The above values are obtained by means of mathematical modeling performed for a wide range of particle and nozzle dimensions, gas pressures and temperatures (air, nitrogen, helium) and compared with experimental measurements of the velocity of particles of different sizes and their density at the outlet orifice of the nozzle.

The method according to the invention can use as compressed carrier gas: compressed air, compressed nitrogen, compressed helium or a mixture of these gases.

According to one possible embodiment, the compressed gas is heated to temperatures between 300 and 9800 K.

The powder materials used are, for example, made up of particles having a size of between 0.1 and 1000 μm.

The method may use: metallic powder materials, nonmetallic powder materials, metal powder mixtures having values of ρ _p d _p near, non-metallic powder mixtures having values of ρ _p d _p near or mixtures of metallic and non-metallic powders having values of ρ _p d _p near.

où L est la longueur de la partie supersonique de la buse, ρ _p est la densité d'une particule dudit matériau, d_p est le diamètre d'une particule, b = h est la hauteur de la buse, b = dc_r est le diamètre de la section critique de la buse axisymétrique.The present method is implemented by a cold gas-dynamic acceleration device of at least one powder material comprising a supersonic nozzle connected to a powder injector, a powder feeder connected by an outlet orifice to said powder injector. This device provides for the use of dismountable and exchangeable flat or axisymmetric nozzles, the length of the supersonic portion and the typical dimension of the critical section of said nozzles corresponding to the following conditions: $$\mathrm{The}=4,35{\rho }_p{d}_p\pm 50\%,b=0,065{\rho }_p{d}_p\pm 50\%,$$

where L is the length of the supersonic portion of the nozzle, ρ _p is the density of a particle of said material, d _p is the diameter of a particle, b = h is the height of the nozzle, b = dc _r is the diameter of the critical section of the axisymmetric nozzle.

One of the advantages of the method and apparatus for the gas-powder spraying of proposed powder materials is that depending on the particle size and the density of the material constituting them selected for a separate technological operation as well as the pressure and gas temperature (for example, air, nitrogen, helium or the mixture of at least two of these gases), the dimensions of the supersonic part of the nozzle used may be calculated so as to ensure the maximum speed of the impact of the particles on the target surface that can be reached, and thereby to advantageously improve the quality of the deposit, the efficiency and the quality of the surface cleaning process, the efficiency of the fragmentation / granulation of particles. At the same time, to ensure the desired spatial resolution of the process of blasting or sanding the surfaces, it is possible to vary the particle size of the powder by choosing the particle size of the desired powder material so as to ensure a high yield of deposition and high quality of the resulting coating, the successful completion of the sanding process of a surface having a fine grain structure corresponding to the size of the projected particles.

For a good understanding, the invention is described with reference to the single figure of the attached drawing showing by way of non-limiting example an embodiment of a device according to the invention.

où L est la longueur de la partie supersonique de la buse, ρ _p est la densité d'une particule dudit matériau, d_p est le diamètre d'une particule, b = h est la hauteur de la buse, b = d_cr est le diamètre de la section critique de la buse axisymétrique.The device for accelerating gasodynamic cold powder materials comprises a removable and exchangeable supersonic nozzle 1 connected to the outlet of an electric heater 2 and a powder injector in said nozzle 3, a powder dispenser 4 whose the outlet port is connected to said powder injector. The supersonic portion of said nozzle may be, according to a preferred embodiment, of flat or axisymmetrical shape, the nozzle having the length of the supersonic portion and the typical dimension of the critical section corresponding to the following conditions: $$\mathrm{The}=4,35{\rho }_p{d}_p\pm 50\%,b=0,065{\rho }_p{d}_p\pm 50\%,$$

where L is the length of the supersonic portion of the nozzle, ρ _p is the density of a particle of said material, d _p is the diameter of a particle, b = h is the height of the nozzle, b = d _cr is the diameter of the critical section of the axisymmetric nozzle.

The process is carried out as follows.

Depending on the method of projection / sanding / granulation of particles and the choice, for this purpose, of powder (density of the material of the particles and their mean teilla) and pressure and gas temperatures (for example, air, nitrogen, helium or the mixture of at least two of these gases), the simulated ratios presented above are used to calculate the main dimensions of the nozzle: the length of the supersonic part and the critical section (the height for a flat nozzle and the diameter of the critical section for an axisymmetric nozzle). Particles entrained by a flow of gas in such a specially calculated nozzle are given the maximum speed that can be achieved at their impact on the surface of the treated part by accelerating the flow of gas and powder in the part. supersonic of said nozzle, flat or axisymmetric.

The use of the specially designed nozzles for a concrete particle size of particles of a desired powder material makes it possible to obtain the maximum impact speed of the particles projected on the surface of the treated part.

1. 1. Des particules de poudre de cuivre de 1 µm de diamètre moyen sont projetées par la méthode gazodynamique à froid. La pression de stagnation de l'azote ou de l'aire, selon une réalisation préférée, est de 2,0 MPa, la température de stagnation est de 700 K. Les rapport simulés pour une buse plate sont L = 4,35ρ _pd_p ± 50%, h = 0,065ρ _pd_p 50%. On introduit ρ _p = 8940 kg/m³ et d_p = 1.10^-6 m et obtient les dimensions optimales de la buse L = 20 - 60 mm et h = 0,29 - 0,87 mm qui assureront la vitesse maximale d'impact des particules projetées à la surface de cible.
2. 2. Pour les particules d'aluminium (ρ _p = 2700 kg/m³) de la même taille projetées par une buse axisymétrique, on obtient L = 6 - 18 mm et d_cr = 0,09 - 0,26 mm. La pression de stagnation de l'azote ou de l'aire est de 2,0 MPa, la température de stagnation est de 500 K.
3. 3. On souhaite obtenir une résolution spatiale de 0,5 mm lors de projection de particules de cuivre. On choisi une buse avec 0,5 mm de diamètre d'orifice de sortie et, en conséquence, d'environ 0,3 mm de diamètre de section critique. La pression de stagnation de l'hélium est de 2,0 MPa, la température de stagnation est de 300 K. Selon la formule d_cr = 0,065ρ _pd_p ± 50%, on obtient la taille nécessaire des particules de cuivre et, selon la formule L = 4,35ρ_pd_p ± 50%, on calcule la longueur de la partie supersonique de la buse nécessaire pour communiquer aux particules l'accélération optimale. Dans ce cas, on obtient d_p = (0,34 - 1,03)·10^-6 m = 0,34 - 1,03 µm et L = 13,2 - 40 mm.
4. 4. Pour le sablage d'une surface, prenons la poudre d'Al₂O₃ avec 10 µm de diamètre moyen de particules. La pression de stagnation de l'aire est de 0,6 MPa, la température de stagnation est de 300 K. Les rapports simulés pour une buse plate sont L = 4,35ρ_pd_p ± 50%, h = 0,065ρ_pd_p ± 50%. On introduit ρ _p ≈ 4000 kg/m³ et d_p = 10·10^-6 m et obtient les dimensions optimales de la buse L ≈ 90 - 270 mm et h ≈ 1,2 - 3,7 mm qui assureront la vitesse maximale d'impact des particules projetées à la surface de cible.

Non-limiting examples of embodiments of the present invention with the particles of different sizes are now described.

1. 1. Copper powder particles of 1 μm average diameter are projected by the cold gasodynamic method. The stagnation pressure of the nitrogen or the area, according to a preferred embodiment, is 2.0 MPa, the stagnation temperature is 700 K. The simulated ratios for a flat nozzle are L = 4.35 ρ _{p. p} ± 50%, h = 0.065 ρ _p d _p 50%. We introduce ρ _p = 8940 kg / m ³ and d _p = 1.10 ^-6 m and obtain the optimal dimensions of the nozzle L = 20 - 60 mm and h = 0.29 - 0.87 mm which will ensure the maximum speed of impact of particles projected on the target surface.
2. 2. For aluminum particles (ρ _p = 2700 kg / m ³ ) of the same size projected by an axisymmetric nozzle, L = 6 - 18 mm and d _cr = 0.09 - 0.26 mm are obtained. The stagnation pressure of the nitrogen or the area is 2.0 MPa, the stagnation temperature is 500 K.
3. 3. It is desired to obtain a spatial resolution of 0.5 mm when spraying copper particles. A nozzle with a 0.5 mm diameter outlet orifice and, consequently, a diameter of about 0.3 mm in critical section is chosen. The helium stagnation pressure is 2.0 MPa, the stagnation temperature is 300 K. According to the formula _a = 0.065 ρ _p d _p ± 50%, we obtain the necessary size of the copper particles, and according to the formula L = 4,35ρ _p d _p ± 50%, is calculated the length of the supersonic portion of the nozzle necessary to communicate to the particles the optimum acceleration. In this case, one obtains d _p = (0.34 to 1.03) · 10 ^-6 m = 0.34 to 1.03 microns and L = 13.2 to 40 mm.
4. 4. For sandblasting a surface, take Al ₂ O ₃ powder with 10 μm average particle diameter. The area of the stagnation pressure is 0.6 MPa, the stagnation temperature is 300 K. The reports simulated for a slot nozzle are 4,35ρ L = _p d _p ± 50%, h = _p d 0,065ρ _p ± 50%. We introduce ρ _p ≈ 4000 kg / m ³ and d _p = 10 · 10 ^-6 m and obtain the optimal dimensions of the nozzle L ≈ 90 - 270 mm and h ≈ 1.2 - 3.7 mm which will ensure the maximum speed impact of the particles projected on the target surface.

It is desired to obtain a spatial resolution of 1.0 mm when sanding a surface by spraying the SiC powder. We chose a nozzle with 0.1 mm diameter outlet orifice and, therefore, about 0.5 mm critical section diameter. Air stagnation pressure is 1.0 MPa, the stagnation temperature is 300 K. According to the formula _a = d _p 0,065ρ _p ± 50%, we obtain the necessary size of the silicon carbide particles and, according to the formula L = 4,35ρ _p d _p ± 50%, is calculated the length of the supersonic portion of the nozzle necessary to communicate to the particles the optimum acceleration. In this case, we obtain: $$d_p=\left(1,2-3,6\right)\cdot {10}^{-6}\mathrm{m}=1,2-3,6\mathrm{\mu m\; and}\mathrm{The}=16,7-50,1\mathrm{mm}\mathrm{.}$$

Claims (13)

Method for cold gasodynamic acceleration of at least one powder material comprising feeding said powder material into a supersonic nozzle via an injection point, its acceleration by a supersonic gas flow and its deposition by impact on the surface characterized in that it takes into account the size of the particles and the density of said material constituting them, as well as the parameters of the gas, in order to give the powder particles entrained by the gas flow the maximum speed likely to to achieve their impact on the surface of the treated part by accelerating the flow of gas and powder in the supersonic part of the nozzle whose length and transverse dimension correspond to the following conditions: $$\mathrm{The}=4,35{\rho }_p{d}_p\pm 50\%;b=0,065{\rho }_p{d}_p\pm 50\%,$$

where L is the length of the supersonic portion of the nozzle, ρ _p is the density of a particle of said material, d _p is the diameter of a particle, b = h is the height of the nozzle, b = d _cr is the diameter of the critical section of the axisymmetric nozzle. Method according to claim 1, characterized in that it uses compressed air as carrier compressed gas. Method according to claim 1, characterized in that it uses compressed nitrogen as a carrier compressed gas. Method according to claim 1, characterized in that it uses compressed helium as a carrier compressed gas. Method according to claim 1, characterized in that a compressed air, compressed nitrogen and / or compressed helium mixture is used as carrier gas. Method according to one of claims 1 to 5, characterized in that the compressed gas is heated to temperatures between 300 and 9800 K. Method according to one of claims 1 to 6, characterized in that it uses powdered materials consisting of particles having a size between 0.1 and 1000 μm. Method according to one of claims 1 to 7, characterized in that it uses metal powder materials. Method according to one of claims 1 to 8, characterized in that it uses non-metallic powdered materials. Method according to one of claims 1 to 9, characterized in that it uses mixtures of metal powders with values of ρ _p d _p near. Method according to one of claims 1 to 10, characterized in that it uses mixtures of non-metallic powders with values of ρ _p d _p close. Method according to one of claims 1 to 11, characterized in that it uses mixtures of metallic and non-metallic powders with values of ρ _p d _p near. Cold gas-dynamic acceleration device of at least one powder material comprising a supersonic nozzle connected to a powder injector, a powder dispenser connected by an outlet orifice to said powder injector, characterized in that it provides for use of dismountable and exchangeable flat or axisymmetric nozzles, the length of the supersonic part and the typical dimension of the critical section of said nozzles corresponding to the following conditions: $$\mathrm{The}=4,35{\rho }_p{d}_p\pm 50\%,b=0,065{\rho }_p{d}_p\pm 50\%,$$

where L is the length of the supersonic portion of the nozzle, ρ _p is the density of a particle of said material, d _p is the diameter of a particle, b = h is the height of the nozzle, b = d _cr is the diameter of the critical section of the axisymmetric nozzle.

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