EP2816135A1 - Plasma powder spray method for coating of panels for boiler walls in connection with a laser beam apparatus - Google Patents

Abstract

The invention relates to a thermal spraying method for producing a protective layer in the plasma powder spraying process applied to hot gases, in particular flue gases and consisting of a predetermined metallic base material walls of incinerators, in particular waste incineration plants. In order to produce a protective layer with a thickness of 0.6 to 1.5 mm thickness, so as to increase the service life of, for example, pipe-web-tube segments, at least the steps Cleaning the metallic walls; Placing a plasma gas in rotation about the central longitudinal axis (X1) of a plasma powder injection device (2); Internal feeding of a coating material as powder simultaneously through two inner feed openings (24, 26), which inner feed openings (24, 26) are arranged opposite one another with their mouth openings, at least one powder jet (4, 6) being produced; Melting the coating material; and Connecting the coating material impinging on the metallic wall by means of at least one laser beam (11, 12) of a laser beam system (3) to form a diffusive composite of the coating material relative to the base material of the metallic wall proposed.

Description

The invention relates to a thermal spraying method for producing a protective layer in the plasma powder spraying method on hot gases, in particular flue gases acted upon metallic walls. However, the invention also relates to a thermal spray device for carrying out the method.

The DE 196 38 228 A1 is concerned with a method for producing a hot gas corrosion resistant connection of pipes thermally sprayed by a corrosion-protected pipe in which the one pipe to be welded is coated with a corrosion-resistant material prior to thermal spraying, for example the plasma spraying process, in the region of its abutting edge adjacent to the second pipe ,

The US 4,192,672 relates to metal alloys which have relatively large, hard precipitates as self-fluxing powders, eg nickel-based, in order to improve the wear resistance of such powders. In particular, the deals US 4,192,672 with the production of such powders. Such powders are to be sprayed by means of plasma spraying, wherein the addition is melted simultaneously or subsequently.

The EP 0 223 135 A1 also deals with self-fluxing metal alloys which can be applied by plasma spraying. If not sprayed by plasma spraying, the layer can be melted on site by means of an autogenous flame. The plasma spraying method discloses EP 0 223 135 A1 a melting temperature in a range of 1100 to 1250 ° C.

In power plants, in particular in waste incineration plants or their combustion boilers, there is a very aggressive, corrosive environment due to the very specific composition of the fuel (waste). The walls of the Boilers, but also their panels and / or tube bundles or superheater tube bundles must therefore be protected in particular against variants of high-temperature corrosion. From a variety of protective measures against high temperature corrosion and wear, for example, the thermal spraying, for example as flame spraying or as a plasma spraying known

By means of flame spraying, powders as coating material are applied to the materials to be coated, e.g. Applied steel materials. For this purpose, the workpiece to be coated is first cleaned and then blasted with corundum or the like. A preheating of the base material to a temperature of 150 ° C to 250 ° C before blasting is often necessary, said preheating temperature is recommended in particular in the flame spraying with self-fluxing powders. The coating materials have a melting point below the melting temperature of the material to be coated, and are melted after spraying in the base material. The protective layer has a relatively large layer thickness of up to 2 mm at relatively high porosity of 15 to 20% before melting. These factors cause meltdown. The melting is usually carried out with a hard acetylene-oxygen flame, so that the protective layer is heated to a temperature of up to 1200 ° C. As a result of this melting, the layer thickness decreases by about 20% by volume. Especially for heat resistant steels such as e.g. From the material 15Mo3, 13CrMo45 or 10CrMo910 the high heat input leads to a disadvantageous structure change.

However, plasma spraying processes for producing the protective layer are also known, for example in US Pat DE 42 20 063 C1 disclosed. That in the DE 42 20 063 C1 The disclosed method has proven itself in practice to the effect that the distortion of workpieces and crack-forming stresses in the base material are avoided. However, it has now been shown that the applied protective layer is only relatively thin. This means that the relatively thin coating no longer withstands the multiple increase in service life extension requirements coupled with increased erosive and corrosive stress. The plasma spraying method according to the DE 42 20 063 C1 alone is not suitable for protective layers In accordance with the increased requirements in their amount to increase because the residual stresses due to the solidification of the molten particles in the impact on the metallic walls are too high and exceed the binding forces of the mechanical clamping and the adhesion forces. A flaking of the thicker protective layer would be the result.

However, laser deposition welding methods are also known in which a coating material is applied by means of a laser of an energy-intensive laser welding system, for example on rollers. In laser deposition welding with powder, the laser usually heats the workpiece defocused and melts it locally. At the same time, an inert gas mixed with fine metal powder is supplied. At the heated point, the metal powder melts and combines with the metal of the workpiece. The connection to the base material can z. B. be influenced by the formation of an intermediate layer on the parameters. In most cases, subsequent post-processing steps, such as milling or turning, are necessary.

The invention has for its object to improve a thermal spray method of the type mentioned above and an apparatus for performing the method with simple means so that with low heat input into the base material, a protective layer can be produced, which meets the high demands of long life.

According to the invention the object is achieved by a thermal spraying method with the features of claim 1, wherein a thermal spray device with the features of claim 8 solves the objective part of the task.

It should be noted that the features listed individually in the following description can be combined with one another in any technically meaningful manner and show further embodiments of the invention. The description additionally characterizes and specifies the invention, in particular in connection with the figures.

According to the invention, a thermal spraying method for producing a protective layer in the plasma powder spraying method on metallic walls exposed to hot gases, in particular flue gases, with a plasma powder injection device comprises at least the steps of cleaning the wall to be coated; a plasma gas is caused to rotate within the plasma spray device; in that a respective arc root point is set in rotation at a cathode and at an anode, in that a powder as coating material is introduced through two inner feed openings, the coating material being merely melted, and the coating material impinging on the wall to be coated by means of at least one laser beam of a laser beam system is connected without mixing zone formation of a diffusive composite with the base material.

With the invention of the coating material by means of the plasma powder injection so only preheated applied to the wall to be coated. The bonding of the coating material to the base material then takes place by means of a laser process, wherein the diffusive bond between the base material and the coating material is formed.

In this respect, the supposed disadvantage is actually accepted by the invention that the coating material, ie the powder, is not produced so molten that the coating to be applied could be produced properly. This is achieved in the invention only by the step of forming the diffusive composite by means of the laser of the laser beam system. However, the perceived disadvantages now advantageously result in that the coating material is not molten, but merely preheated, the laser still being able to have only a very low power in comparison to non-preheated powders in order to form the diffusive compound.

With the invention, such a diffusive transition of the base material to the coating material with a thickness of 100 .mu.m, preferably from 20 .mu.m to 70 .mu.m generated. Thus, the protective layer to be applied may have a thickness which is 100% to 200% greater than a layer thickness, which according to the previously known method according to DE 42 20 063 C1 could be applied. The layer thickness according to the invention may have an amount of 0.2 to 0.4 mm, preferably of 0.6 to 1.5 mm. However, a layer thickness which is high in terms of thickness inevitably leads to a longer service life, which in turn benefits longer plant availability.

Another advantage of the alleged purchase-increasing disadvantage of the non-molten, but merely heated coating material, ie powder is also to be seen in the fact that a much coarser powder can be used. A coarser powder is of course much cheaper to produce than a fine powder, which must be processed with a corresponding number of steps in order to obtain the fine grain size, for example 20μm to 53μm. Advantageously, the coating material, that is to say the powder for the process according to the invention, can be coarse-grained and have a grain size of less than 200 .mu.m, preferably less than 125 .mu.m, more preferably between 63 .mu.m and 104 .mu.m. This results in a comparison with fine coating materials Cost savings of approx. 20% regarding the material price.

In plasma powder spraying, an arc is generated in a known manner, which extends from the anode to the cathode, wherein an arc base point is arranged both at the anode and at the cathode. In the conventional laminar flow of the plasma gas, the respective arc root points are static, so that they wear the cathode but also the anode at fixed locations very quickly. It is advantageous that the plasma gas in the method according to the invention is set into a rotation, that is rotated about the central longitudinal axis, for example, the anode. It is thus achieved that both the cathode and the anode wear evenly, since the respective arc root point in the circumferential direction of both the cathode and the anode, as seen in accordance with the rotation of the plasma gas, is virtually taken along. apparent is that an arc root on the peripheral surface causes a uniform wear seen in the circumferential direction.

Thus, a rotating ionization of the plasma gas is generated, since of course with the rotating arc base also the arc rotates.

The fact that now two Innenzuführöffnungen are provided for supplying the coating material, ie the powder, two powder jets are generated, which leave the plasma powder injection device, which can also be referred to as a gun. It is surprising that one of the powder jets leaves the pistol centrically along the central longitudinal axis, whereas the second powder jet is deflected relative to the central axis. This is achieved by the two Innenzuführöffnungen are ideally fed simultaneously with coating material, wherein it is expedient that the Innenzuführbohrungen are arranged with their central axis each angled to a perpendicular to the central longitudinal axis of the anode. In a preferred embodiment, an acute angle is formed, wherein it is highly preferred that the angle between the perpendicular to the central longitudinal axis and the central axis of the respective Innenzuführbohrung an angle of 5 ° to 15 °, more preferably 9 °. In a favorable embodiment, the two Innenzuführöffnungen are arranged at least with its mouth opening into the anode relative to the central longitudinal axis exactly opposite one another.

It is advantageous that the two Innenzuführöffnungen are introduced into the anode, which are ideally fed simultaneously with powder. In an expedient embodiment, the powder feed can be controlled separately by the two inner feed openings. In this respect, the two Innenzuführöffnungen can be fed separately controlled, wherein each Innenzuführöffnung can also be assigned a separate powder generator. Thus, the amount of powder required in each case can advantageously be set with the invention. It is conceivable that both Innenzuführöffnungen be charged simultaneously with the maximum possible amount. For example, if the two inner feed openings have a diameter amount of 4.2 mm each, 12 to 14 kg / h could be used as an example Powder are applied. It is possible that the same powder is passed through both Innenzuführöffnungen. So meet both powder jets according to the deflection of a powder jet from the central longitudinal axis also offset from the material to be coated. Since both powders are identical, it is unnecessary to determine which of the two powder jets is deflected and which one does not. Here, however, a further advantage of the invention is to be seen in that two different coating materials, ie powder, can be passed through both inner feed openings. The powders can not only differ in their (metallurgical) composition, but also in terms of powder morphology (eg agglomerated, melted, atomized in the gas stream ...), the powder form (eg pointed, angular, spherical ...), the specific gravity and also, for example, the melting behavior (eg of the white, black or shiny powder) be different. With regard to the different composition of the two powders, for example, a powder jet can thus produce an intermediate layer corresponding to the alloy of the supplied powder, the other powder jet having, for example, a cover layer with the corresponding properties of the supplied powder alloy. Both powder alloys can be mixed together by the action of the laser or the laser but also according to the desired properties of the protective layer, so be mixed. The composition of the powders can be determined as a function of the existing base material and the subsequent operating conditions, in particular the predetermined temperature ranges.

The invention is based on the finding that the deflection of the powder jet out of the central longitudinal axis or not actually depends on the morphology, the powder form, the specific weight and the melting behavior of the respectively supplied powder. Thus, it can be determined at each sample workpieces, which corresponds to the workpiece to be coated, which powder beam is deflected in which composition, and which powder beam is not deflected.

Since two powder jets are produced with the invention, it is expedient, if both powder jets, ie the two on the material to be coated incident powder alloy caterpillars are also treated with one laser to form the diffusive composite. In this respect, it is advantageously provided that a double laser beam system, so also two lasers are provided, wherein the respective laser is associated with the respective impinging powder jet.

For applying a protective layer with the method according to the invention, an 80KW plasma spraying system with internal powder feed can be suitably used. By the internal powder supply, preferably by both Innenpulverzuführöffnungen simultaneously, the respective powder is focused in the respective plasma jet one hand, on the other hand, a more uniform melting of the powder is achieved. A melting in the context of the invention is thus only a warming, wherein the powder just does not become molten. By melting the coating material, so the powder within the gun but now the laser power can be advantageously reduced, so that thus advantageously a lower heating of the component to be coated is expected. The metallic wall is heated by the laser beam or by the laser beams only to a temperature of 60 ° C, maximum 80 ° C. In this respect, a further advantage of the invention resides in the fact that the laser of the laser beam system, that is to say the double laser beam system, can have a power of only 2KW to 10KW, preferably of 3KW to 5 KW. Thus, a slight distortion of the metallic wall to be coated, for example of pipe-web-pipe segments or e.g. be achieved by panels of combustion boiler walls.

It is also advantageous that roughening and / or treating the wall to be coated with corundum or the like blasting agent can be dispensed with; because the hitherto envisaged mechanical clamping of the molten powder particles at the moment of impact as a binding mechanism is replaced in the invention by the high energy density of the respective laser at the point of impact to produce a diffusive composite without damaging stresses are introduced into the base material to be coated. Nevertheless, the workpiece to be coated may have anticorrosion coatings, these anticorrosive coatings by means of simple cleaning agents are removable. Also dirt or the like should be removed. In this respect, the surface should indeed be cleaned, for example, by fat, oil, scale and / or mill scale, but roughening and / or activation can be dispensed with in the invention.

In order to be able to achieve the rotation of the plasma gas within the plasma spraying device, ie within the gun, in particular within the anode, the corresponding plasma gas nozzle, that is to say the injector, has at least one combined bore, which is formed by two partial bores introduced into one another. It is provided in purposeful embodiment that one of the partial bores with its central axis is congruent to a central axis of the plasma gas nozzle. The other, second partial bore is arranged at an angle to the central axis of the plasma gas nozzle. It is preferably provided that the other second partial bore is arranged at an acute angle, preferably at an angle of 10 to 30 °, more preferably 16.5 ° to the central axis of the plasma gas nozzle. The goal is that both partial bores have an identical starting point on an outer periphery of the plasma gas nozzle, and open at an inner periphery. In this case, an overall mouth opening is achieved on the inner circumference, which of course is greater than such a mouth opening which can be reached with one of the individual partial bores. At the same time the inner total orifice is smaller than both partial boreholes considered together. In this respect, an advantage over a single nozzle bore oblique to the central axis of the plasma gas nozzle, which would produce a hard plasma jet, is to be seen in that the combined bore according to the invention has quasi an eccentric profile, wherein the total internal orifice is greater than the inlet of the combined bore on the outer periphery of the plasma gas nozzle. Thus, it is advantageously achieved that the amount of gas introduced is homogeneously ionizable, since the gas introduced within the plasma torch distributed homogeneously, as set by the quasi eccentrically expanding inner total orifice a soft plasma gas flow. In a favorable embodiment can be provided to provide a plurality of combined holes in the plasma gas nozzle. In a particularly preferred embodiment, four combined bores are provided which, viewed in the circumferential direction of the plasma gas nozzle, are equally distributed. It is expedient if in particular the second partial bores are in each case equally oriented. By this embodiment of the invention it is achieved that the plasma gas is introduced tangentially to the central longitudinal axis in the plasma torch, so that the plasma gas reaches the arc, which is applied between the cathode and anode, rotating about the central longitudinal axis. In this rotating plasma jet, the powder is now introduced through both Innenzuführöffnungen, as already described.

As already mentioned, with a preferred angle of inclination of the inner feed opening of 9 ° with respect to the plasma jet axis in the direction of the anode orifice in the rotating plasma jet, splitting of the powder jet into two powder jets is achieved. At a spray distance of 100 to 180 mm, preferably from 130 to 150 mm, the impact surfaces of the two powder jets can be influenced in such a way via the parameter selection of gas pressure, gas quantity and powder quantity as a function of the abovementioned powder data such that they adjoin one another optimally and thus with a lower power per Laser can be melted down and diffusively connected to the base material.

A further advantage is that the impact surfaces of the two powder jets are changeable. These can, for example, one behind the other, offset from each other or next to each other. For this purpose, only the plasma spray device, so the gun must be rotated according to the desired position of the impact surfaces around the burner axis. Of course, the laser or laser will be adjusted with the optics corresponding to the actual impact surfaces. Ideally, the powder jets are adjustable so that the impact surfaces adjoin one another without overlapping.

According to the invention, a device for plasma spraying for producing a protective layer in the plasma spraying process on hot walls, in particular flue gases acted upon metallic walls for carrying out the method according to the invention in its anode two introduced Innenzuführöffnungen, which with respect to a central axis of the plasma powder injection device exactly Of course, manufacturing tolerances with respect to the diametrical arrangement are possible and are within the scope of the invention. The two inner feed openings have with their central axis to a perpendicular to the central axis of the plasma powder injection device an acute angle, most preferably of 9 °. Furthermore, it is advantageously provided that a plasma gas nozzle has at least one combined bore, preferably a plurality of combined bores, more preferably four combined bores, through which the gas to be ionized is introduced into the plasma spraying device. In addition, at least one laser is combined with the plasma spraying device, which processes the plasma powder merely melted, ie heated, impinging application powder in such a way that the diffusive composite of the protective layer is formed with the base material.

The method according to the invention and the device according to the invention are particularly suitable for use, for example, on pipe-web-tube segments and / or, for example, on panels for combustion boiler walls in waste incineration plants, without restricting the application thereof. In particular, in waste incineration plants can be made of a magnitude high protective layer thickness, which inevitably leads to a longer service life of the coated pipe web segments and / or panels, which in turn benefits a longer plant availability. In this respect, the invention proposes a method for producing a protective layer on hot gases, in particular flue gases acted and consisting of a given metallic base material walls of incinerators, heat exchangers or similar plants proposed in which by means of a plasma torch and a laser beam system, preferably a double laser beam system a powder of metallic, carbide, oxide ceramic or silicidischen materials or mixtures of these materials is applied to the previously cleaned metallic walls to form the protective layer and diffused by the respective laser beam with the base material. The base materials to be coated in this case can be used as the base materials approved in the plants concerned, with base materials with the designation 15Mo3, 13CrMo45 and / or 10CrMo910 also being mentioned by way of example here should. It is also leading that in the invention instead of a laser welding system, a laser beam system is used to form the diffusive composite. A laser welding system has a much shorter and very energy-intensive laser beam than the laser beam system, wherein the base material must be melted at a laser welding machine, and wherein the filler metal is supplied in electrode form or cold powder, the laser welding system must be operated at much higher energies than the ideally used laser beam system.

Fig. 1

eine Plasmaspritzvorrichtung kombiniert mit einer Doppel-Laserstrahlanlage, als Laser-Plasmabrennervorrichtung in prinzipieller Ansicht,

Fig. 2

einen Querschnitt durch eine Plasmadüse der Plasmaspritzvorrichtung aus Figur 1,

Fig. 3

einen Längsschnitt durch eine Anode der Plasmaspritzvorrichtung aus Figur 1, und

Fig. 4

Beschichtungsbeispiele von Rohr-Steg-Rohr Elementen.

Further advantageous details and effects of the invention are explained in more detail below with reference to exemplary embodiments illustrated in the figures. Show it:

Fig. 1

a plasma spraying device combined with a double laser beam system, as a laser plasma torch device in a basic view,

Fig. 2

a cross section through a plasma nozzle of the plasma spraying device FIG. 1 .

Fig. 3

a longitudinal section through an anode of the plasma spray device FIG. 1 , and

Fig. 4

Coating examples of pipe-web-pipe elements.

In the different figures, the same parts are always provided with the same reference numerals, so that these are usually described only once.

FIG. 1 shows a laser plasma powder injection device 1, which has a plasma powder injection device 2 and a double laser beam system 3.

The plasma powder injection device 2 generates two split powder jets 4 and 6 which strike a workpiece 7 to be coated. The workpiece 7 to be coated is, for example, a pipe-web-tube segment 8, as shown by way of example in FIG FIG. 4 is shown. The workpiece 7 is acted upon by aggressive, hot flue gases, which arise, for example, in waste incineration algae.

One of the powder jets 4 emerges centrically from the central longitudinal axis X1 of the plasma powder injection device 2. The other plasma powder jet 6 emerges distracted from the central axis X1 of the plasma powder injection device 2 out of this. However, both powder jets 4 and 6 form a total spray cone 9.

The two powder jets 4 and 6 strike the workpiece 7 to be coated, wherein the respective powder of the respective powder jet 4 or 6 is only melted in the plasma powder injection device 2, and is not molten before the exit.

To form a diffusive composite of the applied powder, ie the coating material with the workpiece 7, ie with its base material, the double laser beam system 3 is provided which generates two laser beams 11 and 12 corresponding to the two powder jets 4 and 6.

In FIG. 2 a plasma gas nozzle 13 of the plasma powder injection device 2 is shown in a cross section. The plasma gas nozzle 13 can also be referred to below as injector 13. The plasma powder injection device 2 can also be referred to below as the plasma burner 2.

By way of example, the injector 13 has four combined bores 14, which are distributed identically in the circumferential direction of the injector 13. Each of the combined bores 14 is formed from two partial bores 16 and 17. A first partial bore 16 has a central axis x, which is congruent to a respective central axis of the injector 13. A second partial bore 17 has a central axis y, which is arranged at an angle relative to the central axis x of the first partial bore 16 and thus to the respective central axis of the injector 13. In the most preferred embodiment the angle between the two central axes x and y an amount of 16.5 °. Each of the two partial bores 16 and 17 has a diameter of 1.8 mm by way of example. On an outer circumference of the injector 13, both partial bores 16 and 17 have a common starting point. In this respect, the inlet opening 18 on the outer circumference of the injector 13 is identical to the diameter of the two partial bores 16, 17. Both partial bores 16 and 17 form on an inner circumference 18 of the injector 13 an inner total orifice 20. Due to the fact that the second partial bore 17 is introduced at an angle to the first partial bore 16 in the injector 13, the total internal orifice 20 will be larger than the diameter of a single partial bore 16 or 17. At the same time the inner total orifice 20 will be smaller than the sum of the two diameters of the partial bores 16 and 17. Insofar a combined bore 14 is produced in each case, which has an eccentric course, with the combined bore 14 starting from the on The outer circumference arranged approach point eccentrically, so quasi semi-conical in the direction of the inner circumference 19 extended. All partial holes 16 and 17 of the four combined holes 14 are each oriented the same. By means of this configuration, the plasma gas is introduced tangentially to the plasma torch axis (central longitudinal axis X1) in the plasma torch and thus reaches about the central longitudinal axis X1 of the plasma torch 2 rotating an arc 21 between an anode 22 and a cathode 23 (FIGS. FIG. 3 ) of the plasma burner 2.

In FIG. 3 the anode 22 of the plasma powder injection device 2 is shown. In the anode 22, the cathode 23 is accommodated. Both the cathode 23 and the anode 22 are with their central axis X2 and X3 congruent to the central axis X1 of the plasma spraying device 2. The arc 21 is also recognizable, with a representation of the respective arc base points at the anode 22 and the cathode 23 has been omitted. The aim is now that the plasma gas reaches the arc 21 rotating about the central longitudinal axis X1 of the plasma torch 2. Thus, the arc 21 is taken around the central longitudinal axis of the plasma torch 2 rotating, which in FIG. 3 is shown by the two arc 21 and 21a. By the rotating arc 21, the life of both the anode 22 and the cathode 23 can be extended because the respective Arc base points are no longer statically fixed, but rotate both at the anode 22 and at the cathode 23. It is in FIG. 3 it can be seen that the arc root point attaches to the anode 22 in an upper tip region and not directly to the tip itself.

Due to the rotating plasma gas and the rotating arc, there is also a rotating ionization of the plasma gas.

The plasma burner 2 has an internal powder feed.

For internal powder supply 22 two Innenzuführöffnungen 24 and 26 are introduced in the anode. Connections to powder encoders are not shown. The Innenzuführöffnungen 24 and 26 are simultaneously charged with powder with a respective amount of powder through the respective Innenzuführöffnung 24 and 26 is separately controllable. The respective inner feed opening 24 and 26 each have a central axis X4, which is arranged to a vertical Z on the central axis X1, angularly, most preferably at an angle α of 9 °. The two Innenzuführöffnungen 24 and 26 are equally oriented towards a plasma exit side introduced into the anode 22 and open into the interior of the anode 22, and are arranged with their mouth openings 27 relative to the central axis X1 opposite.

With the laser plasma powder injection device 1 is a protective layer on hot flue gases acted upon metallic walls, for example, on raw web-tube segments 8, as in FIG. 4 can be applied by way of example. At a right edge of the picture FIG. 4 an exemplary pipe-web-tube segment 8 is shown in a longitudinal section. In addition, a supervision is shown.

FIG. 4 intended to represent a respective possible location of the incident surfaces 28 and 29 of the powder jets 4 and 6. The position of the impact surfaces 28 and 29 is dependent on the rotation of the plasma powder injection device 2, ie from the position of the gun. Of course, the laser beams 11 and 12 are aligned accordingly.

First, the landing surfaces 28 and 29 may be arranged side by side, as in the lower part of the figure FIG. 4 recognizable. This position is referred to as a neutral position for the following positions for the sake of simplicity, without this having a limiting effect. It can be seen that the powder jets 4 and 6 do not look like this FIG. 1 could be assumed sharply separated, but each have an overlap region 31.

By rotating the plasma torch 2 out of its neutral position, the incident surfaces 28 and 29 could be offset from each other, so that one of the others is virtually leading the way. This position is in the middle of the FIG. 4 shown. By further twisting out of the neutral position, the incident surfaces 28 and 29 can also be arranged directly behind one another, as at the top of the FIG. 4 is recognizable.

The respectively recognizable overlapping areas 31 can also be variable in their amount, as in FIG FIG. 4 indicated. The two powder jets 4 and 6, so the impact surfaces 28 and 29 may ideally be adjacent without overlap.

Of course, the bends of the pipe web segment 8 can be coated with the method according to the invention. Likewise, panels for boiler walls can be coated with the proposed method of the invention.

With the laser plasma spraying device 1, a protective layer having a thickness of, for example, 0.6 to 1.5 mm can be produced. This is possible because two powder jets 4 and 6 are produced, wherein the powder of the respective powder jets is not molten, but merely melted, that is warmed. As a result, the lasers with a lower power can cause a diffusion-free, diffusive composite of the applied powder, that is to say coating material, to the base material. In addition, it can be seen that the plasma gas is introduced tangentially to the central longitudinal axis and is rotated about the central longitudinal axis X1, so that by the rotating arc quasi also a rotating ionization of the plasma gas is generated. In addition, it is advantageous that two Innenzuführöffnungen the anode are charged simultaneously with powder, so that the two powder jets 4 and 6 are formed, one of which is still deflected to the central longitudinal axis X1.

Claims (10)

Thermal spraying method for producing a protective layer in the plasma powder spraying method on hot_gases, in particular flue gases, exposed to metallic walls, comprising at least the steps of cleaning the metallic walls;
Placing a plasma gas in rotation about the central longitudinal axis (X1) of a plasma powder injection device (2);
Internal feeding of a coating material as powder simultaneously through two inner feed openings (24, 26), which inner feed openings (24, 26) are arranged opposite one another with their mouth openings, at least one powder jet (4, 6) being produced;
Melting the coating material; and
Connecting the coating material impinging on the metallic wall by means of at least one laser beam (11, 12) of a laser beam system (3) to form a diffusive composite of the coating material relative to the base material of the metallic wall. Thermal spraying method according to claim 1, characterized in that the diffusive composite of the coating material to the base material has a thickness of 100 .mu.m, preferably from 20 to 70 .mu.m. Thermal spraying method according to claim 1 or 2, characterized in that the protective layer after spraying and after creating the diffusive composite with the laser has a layer thickness of 0.2 to 0.4 mm, preferably from 0.6 to 1.5 mm. Thermal spraying method according to one of the preceding claims, characterized in that two powder jets (4, 6) are produced, wherein each powder jet (4, 6) is processed with an associated laser beam (11, 12) to form the diffusive composite, one of the Powder blasting (4,6) the plasma powder injection device (2) centric to its central axis (X1) leaves, wherein the other powder jet (4,6) the Plasma spray device (2) deflected to the central axis (X1) leaves the plasma spray device (2). Thermal spraying method according to one of the preceding claims, characterized in that a powder having a coarse grain size of less than 200 μm, preferably less than 125 μm, more preferably between 63 and 104 μm is applied. Thermal spraying method according to one of the preceding claims, characterized in that an arc (21) with its arc base points on one to an anode (22) and the other to a cathode (23) is rotated in accordance with the rotation of the plasma gas. Thermal spraying method according to one of the preceding claims, characterized in that the powder introduced through one of the inner feed openings (24, 26) can be identical to the powder which is introduced through the other, opposite inner feed opening (24, 26), and in that each introduced through one of the Innenzuführöffnungen (24,26) powder may be different from the powder, which is introduced through the other, opposite Innenzuführöffnung (24,26). Thermal spraying device set up in particular for carrying out the thermal spraying method according to one of the preceding claims, for producing a protective layer in the plasma powder spraying process on metallic walls exposed to hot gases, in particular flue gases, characterized by a plasma powder injection device (2) and a laser beam system (3), wherein as coating material Powder is merely melted and a laser beam (11,12) of the laser beam system (3) produces a diffusive composite of the impinging coating material to the base material. Thermal spraying apparatus according to claim 8, characterized in that a plasma gas nozzle (13) of the plasma powder injection device (2) has at least one combined bore (14) which is formed from partial bores (16, 17), of which a partial bore (17) with its central axis (y) is arranged at an angle to the central axis (x) of the other partial bore (16), so that plasma gas is introduced tangentially to the central longitudinal axis (X1) of the plasma powder injection device (2) in an anode (22) of the plasma powder injection device (2), wherein the plasma gas Arc (21) rotatably around the central longitudinal axis (X1) of the plasma powder injection device (2) achieved. Thermal spraying device according to claim 8 or 9, characterized in that in an anode (22) of the plasma powder injection device (2) two Innenzuführöffnungen (24,26) are introduced, the respective central axis (X4) to a perpendicular to a central longitudinal axis (X1) angled, most preferably at an angle of 9 °.

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