In the following, the invention is described in more detail with reference to the schematic drawing. There are shown:
FIG. 1 a plasma spraying device in accordance with the invention;
FIG. 2 a plasma torch with a penetration groove;
FIG. 3 a plasma torch with a nebulizer.
In FIG. 1, a plasma spraying device in accordance with the invention is schematically displayed, which plasma spraying device is designated overall in the following by the reference numeral 1. Note that the same reference numerals in different figures designate the same technical features.
The plasma spraying device according to FIG. 1 includes a plasma torch 4 for heating up a plasma gas 5 in a heating zone 6. The plasma torch 4 has a nozzle body 7 for forming a plasma gas stream 8. An aperture 9 is running along a central longitudinal axis 10 through the nozzle body 7, which aperture 9 has an convergent section 11 with an inlet 12 for the plasma gas 5, a throat section 13 including a minimum cross-sectional area of the aperture, and a divergent section 14 with an outlet 15 for the plasma gas stream 8. An introducing duct 16 is provided for introducing a liquid precursor 17, provided by a supply unit 19, into the plasma gas stream 8. In accordance with the present invention, a penetration means 18, is also provided to penetrate the liquid precursor 17 inside the plasma gas stream 8, which is directed to a surface of a substrate 3 for spraying a coating 2 onto the substrate 3.
In the special example of FIG. 1, the introducing duct 16 is provided between the convergent section 11 and the divergent section 14 of the aperture 9 at the minimum cross-sectional area of the aperture 9. It is understood that in another special embodiment the introducing duct 16 can be provided between the inlet 12 of the convergent section 11 and the minimum cross-sectional area of the aperture 9 and/or the introducing duct 16 is provided between the minimum cross-sectional area of the aperture 9 and the outlet 15 of the divergent section 14.
FIG. 2 shows a second embodiment of the present invention wherein the plasma torch 4 includes a penetration groove 181. The penetration groove 18, 181, being provided at an inner wall 19 of the nozzle body 7 and is in particular a circumferential penetration groove 181. The introducing duct 16 is provided between the convergent section 11 and the divergent section 14 of the aperture 9 at the minimum cross-sectional area of the aperture 9 close to the penetration groove 181.
The penetration grove 181 has a triangular shape and has a width 1811 of for example 0.5 mm to 3 mm, in particular between 1 mm and 2 mm, especially is 1.5 mm and has a depth 1812 of 0.05 mm to 2 mm, in particular between 0.75 mm and 1.5 mm, preferably 1 mm.
The introducing duct 16 in the example of FIG. 2 includes at the same time a penetration means 18, which is a penetration groove 181 and a capillary 182.
That is, in addition to the penetration groove 181, the penetration means 18 is provided by the introducing duct 16 being designed as the capillary 182 having an injection hole 183 with reduced diameter, wherein the capillary 182 is provided between the convergent section 11 and the divergent section 14 of the aperture 9, in particular at the minimum cross-sectional area of the aperture 9 close to the penetration groove 181, which is placed downstream with respect to the capillary 182. In the present example, the introducing angle α of the introducing duct 16 is about 90°.
Regarding FIG. 3, a plasma torch 4 with a nebulizer 161 is displayed as a further very important embodiment of the present invention.
In this example the penetration means 18 is provided by the introducing duct 16 being designed as a nebulizer 161, wherein no penetration groove is provided. It is understood, that in an other embodiment a nebulizer 161 can be advantageously combined with a penetration groove 181 and/or with a capillary 182.
According to FIG. 3 the nebulizer 161 is provided between the convergent section 11 and the divergent section 14 of the aperture 9, in particular at the minimum cross-sectional area of the aperture 9 and is arranged under an introducing angle α of about 90° with respect to the central longitudinal axis 10.
The present invention demonstrates for the first time the possibility of injecting liquids inside the nozzle of a plasma torch, either directly or using a nebulizer. Both methods require a special design of the torch nozzle to obtain a pressure sufficiently high at the injection point to avoid solidification of the liquid. For direct injection, a high velocity of the fluid is necessary to penetrate through the plasma flow boundary layer. This is achieved using a very small diameter injection hole (capillary), but is in most cases not advantageously applicable for highly viscous liquids or slurries. If a larger diameter of the injection hole is used which leads to a low injection velocity, mixing of the liquid with the plasma jet can strongly be improved by the penetration grooves, which induce turbulence in the boundary layer and distribute the liquid azimuthally.
Patent Application
20080057212
