FR3076838A1 - Device and method for thermal spraying - Google Patents

Abstract

The present invention relates to a device and a method for the thermal spraying of fluids, in particular for the high-velocity flame spraying of suspensions (HVSFS), with a burner, in which a combustion chamber (32) is provided, at the level of which opens an expansion tube serving to make a spray jet emerge, with a supply of fuel mixture in the combustion chamber (32), and with an injector (40) serving to bring a fluid to be sprayed into the combustion chamber combustion (32) via a nozzle (50), which is maintained so as to be able to be replaced at the level of the injector (40). Figure 4.

Description

Title of the invention: Device and method of thermal spraying [0001] The present invention relates to a device and method of thermal spraying, in particular spraying with flame of high speed suspensions (HVSFS). HVSFS is an innovative process for generating nanostructured coatings using thermal spraying by supersonic spraying. In this context, very thin, dense layers having satisfactory adhesion can be generated, which are in particular made of ceramic, such as layers which consist of aluminum oxide, titanium oxide or oxide of zirconium (cf. A. Killinger, M. Kuhn, R. Gadow, "High-Velocity Suspension Flame Spraying (HVSFS), a new approach for spraying nanoparticles with hypersonic speed", Surface and Coatings Technology, vol. 201, Issue 5, October 25, 2006, pages 1922-1929).

DE 10 2005 038 453 A1 discloses the HVSFS process and a device used to implement said process. According to this, one or more suspensions can be brought into a combustion chamber via one or more nozzles and be accelerated there via an expansion tube by means of a mixture of fuels.

The HVSFS process requires treatment of powders with a very small particle size on the order of a nanometer. In the state of the art, no active atomization is used during the HVSFS process. The disintegration of the liquid jet takes place in this context in an uncontrolled manner by turbulence in the combustion chamber.

We know from the article by M. Rukosuyev, S.A. Baqar, M.B.G. Jun, "Development and Evaluation of Flame-As sisted Dual Velocity Nonoparticle Coating System", Journal of Micro- and Nano-Manufacturing December 2017, Vol. 5, p. 044501-1 - 044501-5 a flame spraying process, in which an external atomization is carried out by means of ultrasound.

External atomization can, however, already lead to separation before being brought into the burner. Likewise, a process of this type does not make it possible to eliminate the problems existing in the state of the art, namely in particular an uncontrolled droplet disintegration, processes and spraying results which are difficult to control, as well as deposits which are not desired in the nozzle head resulting in obstructions, unwanted deposits in the area of the combustion chamber walls, which can peel off during the coating process and can be incorporated into the coating, which affects the quality of layer.

In particular, there is the problem that the nozzle is often clogged, which leads to the interruption of the process. The burner must then be disassembled and cleaned with significant additional resources.

In this context, the present invention aims to create an improved device and an improved method of thermal spraying, which is suitable in particular for HVSFS and thanks to which the problems existing in the prior art are avoided at less in part.

Said objective is achieved according to the invention thanks to a device for thermal spraying of fluids, in particular spraying with flame of high speed suspensions (HVSFS), with a burner, in which a combustion chamber is provided, at the level of which opens an expansion tube serving to exit a spray jet, with a supply of fuel mixture into the combustion chamber, and with at least one injector serving to bring a fluid to be sprayed into the combustion chamber by means of a nozzle, which is held so that it can be replaced at the level of the injector.

The objective of the present invention is thus completely achieved.

Insofar as according to the invention the nozzle can be replaced easily, it can be changed quickly in the event of an obstruction so that a coating process should only be interrupted for a short time. In addition, different nozzles can be used, which are adapted to different materials to be sprayed so that for example the injection opening, from which the material to be sprayed exits into the combustion chamber of the burner, can be adapted to an appropriate way.

Insofar as during the HVSFS, depending on the type of material to be sprayed, the material to be sprayed can be both in the form of a solution and in the form of a suspension, the two modes of achievement are grouped together in the context of the present application under the generic term of “fluid to be sprayed”.

According to another configuration of the invention, the nozzle is fixed at the level of the injector by means of a thread, preferably can be adjusted axially.

[0013] Thus, a rapid replacement is possible. The axial spacing between the nozzle injection opening and the combustion chamber wall can thus be adjusted simultaneously.

According to another configuration of the invention, the nozzle is provided at an outer end of a tube and can be replaced in conjunction with it.

Similarly, an easy replacement of the nozzle is possible with an embodiment of this type.

According to another configuration of the invention, the injector has a separate supply for a fluid to be sprayed and for an atomizing gas up to the nozzle.

Thus, atomization as far as possible controlled the fluid to be sprayed can be ensured.

According to another configuration of the invention, the nozzle has a nozzle chamber, which opens into the combustion space via an injection opening.

The actual atomization of the fluid to be sprayed takes place in the nozzle chamber. Then the atomized fluid arrives from the nozzle chamber into the combustion space via the injection opening.

According to another configuration of the invention, the injector has at least two coaxial tubes with respect to each other serving to supply atomizing gas and the fluid to be sprayed towards the nozzle.

Thus, this results in a very controlled supply of atomizing gas and of the fluid to be sprayed to the nozzle.

According to another configuration of the invention, a tube located inside has an outer surface with a structure, which promotes atomization of the fluid. Preferably, the fluid to be sprayed arrives in the present case in the nozzle chamber through the tube located inside. Because of the atomizing gas circulating in this case outside, turbulence is thus generated in a controlled manner so that it results in a homogeneous atomization. In this context, the fluid to be sprayed can flow through the tube located inside and the atomizing gas can flow into the hollow space surrounding it. In the same way, one can imagine an inverted arrangement with a spraying fluid flowing outside and with an atomizing gas flowing inside.

According to another configuration of the invention, the outer surface of the tube located inside has stabilizing elements, which are preferably arranged in the form of a spiral.

Thus, the medium circulating outside is provided with vortices so that a particularly homogeneous and controlled atomization can take place.

In another configuration of the invention, the tube located inside is provided, at its outer end itself, with a preferably conical nozzle opening.

This also makes it possible to guarantee an improved mixing or an improved atomization of a medium thus guided.

According to another configuration of the invention, the injector has channels for a separate supply of a first fluid, a second fluid and an atomizing gas.

Thus, a first fluid to be sprayed and a second fluid to be sprayed can only be mixed in the nozzle. This is particularly advantageous for fluids of this type, which only mix with difficulty or which react with each other or which otherwise have a harmful effect on each other.

According to another configuration of the invention, the injector is detachably held at the burner, in particular by means of a thread or a quick-closing system.

Thus, the injector, which is used exclusively for supplying, atomizing and injecting the fluid to be sprayed into the combustion chamber, can be easily detached and removed from the burner towards the rear. Thus, the injector can be changed easily or the nozzles are easily replaced.

The nozzle is preferably made of brass or stainless steel. The tubes and associated parts, through which the atomizing gas and the spraying fluid or the spraying fluids are guided, preferably consist of stainless steel. The gas mixing block is preferably made of copper.

According to another configuration of the invention, at least one channel for supplying fluid is made of plastic, in particular PTFE, or ceramic or is coated with plastic or ceramic at its inner surface .

Thus, fluids, which are sensitive with respect to metal alloys, which react with them or have a harmful effect, can be guided without problem to the nozzle, in which atomization and injection are carried out in the combustion chamber.

According to another configuration of the invention, the channel located inside serving to bring the fluid to be sprayed can be driven in rotation.

Thus, an even better and more homogeneous atomization of the fluid to be sprayed can be guaranteed.

According to another configuration of the invention, a heat shield is provided between the nozzle and the combustion chamber.

This has the advantage that the heating of the nozzle is reduced, which counteracts the formation of deposits in the nozzle.

According to another configuration of the invention, the burner has a block of gas mixture cooled by means of a cooling medium, in particular water or compressed air.

Thus, a premixed fuel can be brought into the combustion chamber and the thermal stress of the burner can be simultaneously reduced.

According to another configuration of the invention, the heat shield has an annular shield made of ceramic in the region of the end on the combustion chamber side of the nozzle, which is connected to the block of mixture of cooled gas of the burner by means of a thermally conductive structure of annular shape, preferably in the form of a pressed copper ring.

Thus, this results in easy mounting of the heat shield for a very high efficiency at the same time.

Although generally only one injector is provided, through which the material to be thermally sprayed is injected into the combustion chamber, in principle several injectors can also be provided in specific cases, for example two or more injectors may be housed in associated bores of a common outer tube so that they can be replaced.

The objective of the present invention is also achieved by a thermal spraying process, in particular by means of a flame spraying of high speed suspensions (HVSFS), in which a fluid to be sprayed and a gas d atomization are brought separately into a nozzle of an injector, are mixed there and are ejected into a combustion chamber, in which the material to be sprayed is accelerated by an expansion tube by means of a mixture of combustible fuels for put on an object.

A process of this type makes it possible to guarantee a controlled supply and a controlled atomization of a fluid to be sprayed and thus a controlled process during thermal spraying.

According to another configuration of the method according to the invention, several fluids to be mixed are brought separately into the nozzle, are atomized there by means of an atomizing gas.

Thus, different fluids, which hardly mix with each other or which react with each other or have a negative impact otherwise, can be treated and sprayed together thermally.

According to another configuration of the invention, at least one fluid, in particular a sensitive or unstable fluid with respect to metal surfaces, is brought into the nozzle via a plastic channel or a ceramic channel or a channel coated with plastic or ceramic.

Thus, fluids, which are sensitive or unstable or reactive with respect to metal channels, can be treated.

According to another configuration of the process, two or more fluids, which are unstable or reactive with each other, are brought into separate channels in the nozzle and are atomized by means of an atomizing gas.

According to another configuration of the process, the atomization of the at least one fluid is favored by structures generating vortices at the outer surface of a channel, through which the fluid to be sprayed is supplied , and / or by a rotary drive of the channel.

Thus, a particularly satisfactory and homogeneous atomization of the fluid to be sprayed is guaranteed even for fluids which are very difficult to atomize.

It goes without saying that the characteristics of the invention mentioned above and to be explained further below can be used not only in the combination indicated respectively but also in other combinations or alone without leaving the scope of the 'invention.

Other characteristics and advantages of the invention appear from the following description of preferred embodiments with reference to the figures, in which we can see:

[Fig-1] a schematic representation of a device according to the invention of thermal spraying [0055] [fig.2] a longitudinal view of the burner according to Figure 1;

[Fig.3] an enlarged section of the burner according to Figure 2 along the line III-III;

[Fig.4] an enlarged representation of detail IV according to Figure 3;

[Fig.5] an enlarged representation of the detail V according to Figure 3;

[Fig.6] a longitudinal view of the injector according to Figure 3;

[Fig.7] a longitudinal section of the injector according to Figure 6;

[Fig.8] an enlarged representation of detail VIII in the area of the injector tip;

[Fig.9] an alternative embodiment of the nozzle with three axial channels relative to each other for the supply of atomizing gas and two fluids to spray;

[Fig.10] a partial section of the front area of the nozzle and the gas mixing chamber surrounding it with the additional arrangement of a heat shield;

[Fig.l 1] an external perspective view of the nozzle according to an enlarged representation;

[Fig. 12] a perspective section of the nozzle with an additional indication of the tube located inside with structures generating vortices at the outer end and with a nozzle opening at the pipe located inside;

[Fig. 13] a photo of the tube according to FIG. 12;

[Fig. 14] a photo of a tube with a modified structure generating external vortices;

[Fig. 15] a schematic representation of the nozzle in the region of its end on the combustion chamber side with a first configuration, in which the fluid to be atomized is guided inward and the atomizing gas in the outer channel;

[Fig. 16] a representation according to FIG. 15 with an inverted guidance of fluid and atomizing gas;

[Fig. 17] a modified embodiment of the burner according to FIG. 3; and [fig. 71 18] an enlargement of detail XVIII according to FIG. 17.

In Figure 1, a schematic representation of a device according to the invention is generally designated by the reference number 10. The device 10 has a burner 30, which is supplied with a spray suspension or with a solution to spray (generally designated by spray fluid) via a switching valve 26. The burner 30 also has a combustion gas pipe 16 serving to supply combustion gas (in this case ethylene ) and an oxidizing agent 18 (in this case oxygen). The burner 30 is furthermore provided with a water cooling system and for this purpose has a cooling water inlet 12 and a cooling water outlet 14. The suspension to be sprayed is located in a container 20. A rinsing medium is located in a container 22. The suspension to be sprayed is brought to the burner 30 by means of the discharge pump 24 via the valve 26. The burner 30 and the inlet of suspension (fluid to be sprayed ) are controlled via a central control 28, preferably an API command. In the present case, the burner 30 is usually housed at the level of a robot arm (not shown), which is controlled by means of the central control 28.

FIG. 2 illustrates a longitudinal view of the burner 30.

Other details of the burner 30 can be identified from the enlarged longitudinal section according to FIG. 3.

The burner 30 has a combustion chamber 32, to which an expansion tube 34 is connected. In the combustion chamber 32, a mixture of fuels previously mixed is supplied via a mixing block of gas 38. The supply of the fluid to be sprayed is carried out by means of an injector 40, which is removably fixed at the rear side of the housing 36 of the burner 30. The injector 40 approaches the combustion chamber 32 by a nozzle at its front end.

We can identify in Figure 3 at the rear end, opposite to the combustion chamber 32, the housing 36 also the fittings 44 and 46 for the combustion gas and oxygen. The injector 40 also has, at its rear end, connections 12, 14 for the supply of cooling water and the discharge of cooling water. Fluid to be sprayed is supplied via one end 56 into the central channel of the injector 40, as suggested by the arrow 43. In addition, a connector 42 for supplying atomizing gas can also be identified in Figure 3.

In the case of the HVSFS shown here, the fluid to be sprayed is supplied, as explained below in detail, via the injector 40, is mixed in the nozzle with gas d atomization and is injected in a controlled manner into the combustion chamber 32. The fuel mixture previously mixed in the combustion chamber 32 via the gas mixing block 38 ignites, melts the atomized fluid injected into the combustion chamber and leads to the outlet of a jet heated by the expansion tube 34 at an ultrasonic speed.

We can identify from the detail according to Figure 4 the end, on the combustion chamber side, of the injector 40 with the nozzle 50. The atomized spray comes out of the nozzle 50 through the opening injection 52 into the combustion chamber 32. The reference number 48 designates the outlets for the fuel mixture, which is mixed beforehand in the gas mixing block 38. The outlets for the fuel gas mixture 48 are arranged in the form of a ring distributed all around the injection opening 52.

Figure 5 illustrates an enlargement in the area of the rear end of the housing 36. A quick closing system 54 is provided at the rear end of the housing 36, with the aid of which the injector 40 can be fixed or detached with a handle by means of two spring bolts projecting outwards. If the injector 40 is detached, it can be completely removed from the burner 40 towards the rear.

Figures 6 and 7 illustrate an enlargement of the injector 40 in a longitudinal view and a longitudinal section.

FIG. 8 illustrates the structure close to the injector 40 in the area of the nozzle. The injector 40 has, at its outer end, the nozzle 50. The nozzle 50 is screwed to an outer tube 55 of the injector 40 by means of a thread 58. The fluid to be sprayed is supplied by the 'through a central tube 64 into a nozzle chamber 62 of the nozzle 50. Atomization gas is supplied via a tube 66 coaxial with the central tube 64. In the area of mouth of the central tube 64, a controlled atomization of the fluid to be sprayed is carried out. The nozzle 50 is sealed with respect to the coaxial tube 66 by means of an O-ring 60, which is housed in an associated annular groove. The rotation of the nozzle 50 makes it possible to adjust the latter in an axial direction in the direction of the combustion chamber 32.

The nozzle 50 preferably made of brass is protected by a heat shield 70 relative to the combustion chamber 32, as shown schematically in Figure 10. A heat shield in the form of a ring made of ceramic 72, made for example of aluminum oxide, is disposed in front of the front face, on the combustion chamber side, of the nozzle 50. A copper ring 74 pressed into the outer end of the gas mixing block 38 serves at fixation. While the ceramic ring 72 is used for thermal protection, the copper ring 74 gives rise to heat dissipation in the water mixture block 38 cooled by water. Alternatively, the copper ring 74 could also be made in one piece with a gas mixing block 38 made of copper.

FIG. 9 illustrates a modification of the nozzle, which is generally designated by the reference number 50a. In the present case, another channel serving to supply a second fluid to be sprayed is additionally arranged coaxially. Thus a tube located inside 64, in which an internal channel 65 is provided, a central tube 66 coaxial with the latter with a central channel 67 of annular shape, as well as an external tube 68, which makes it possible to define an outer annular channel 69, open into the nozzle 50a. The channel located inside 65 can be used to supply the first fluid, the central channel 67 to supply the second fluid, and the external channel 69 to supply atomizing gas. In principle, however, another arrangement can also be envisaged, as described in more detail below with the aid of FIGS. 15 and 16.

It goes without saying that other tubes, preferably coaxial, for supplying other fluids to be sprayed can also be provided.

FIG. 11 illustrates an enlarged perspective external view of the nozzle 50. Two flattened zones 76 parallel to one another are located at the outer end, on the combustion chamber side, of the nozzle 50. so that the nozzle 50 can be easily adjusted or disassembled by means of a key. In addition, the injection opening 52 can also be identified in FIG. 11 at the end of the combustion chamber side and the thread 58.

We can identify from the representation according to Figure 12 the supply of the fluid to be sprayed through the central channel 64 into the nozzle chamber 62. The fluid to be sprayed is guided through the tube central 64 via a clean nozzle opening 79 converging conically into the nozzle chamber 62. A structure 78 is applied to the nozzle end of the central tube 64 by means of an SLM (Laser Selective) Melting) or a 3D metallic printing process. Through structure 78, the circulating medium is provided with a vortex pulse so that improved atomization and a process with better control result.

FIG. 13 illustrates a photo of a structure 78 of this type at the front end of the central tube 64.

A slightly modified embodiment of a structure of this type is shown in Figure 14 and is generally designated by the reference number 78a. Here, the nozzle side end of the tube 64 with its outlet opening can be identified.

Figures 15 and 16 schematically show that the atomizing gas can be guided in the nozzle 50 either by the channel located outside 67, as is suggested by the dotted arrow 80, and the fluid to spraying is guided by the channel located on the inner side 65, as suggested by the arrow 81.

Alternatively, the arrangement can also be reversed in that the atomizing gas is guided by the inner channel 65 as suggested by the dotted arrow 83, and the fluid to be sprayed is guided by the channel 67 outside, as suggested by the continuous arrow 82. In the present case, atomization of the fluid, which then exits into the combustion chamber 32 via the injection opening 52 is carried out in the zone from the outlet end of the inner channel 65 in the nozzle chamber 62.

Insofar as the materials must be thermally sprayed, which are sensitive to metals, react with them or have a harmful effect otherwise, the conduits concerned can also be made of plastic (in particular PTFE ) or ceramic or are coated at least on their inner surface with plastic or ceramic.

Thus, it is therefore possible to also treat materials, which, because of their sensitivity with respect to metals, could not hitherto be thermally sprayed.

In addition, fluids which are unstable can be atomized in a controlled manner, insofar as a separate supply of the fluid and of the atomizing gas is carried out up to the nozzle.

Another improvement during atomization can be obtained in that the pipe located inside 64 is rotated. In this case, the fluid to be sprayed is routed through the pipe located inside 64.

Figures 17 and 18 illustrate by way of example an embodiment of this type. In this case, the burner 30a is provided with a correspondingly modified injector 40a. According to the detail shown in Figure 18, a rotary drive 80 is provided in the area of the outer end of the tube located inside 64, which rotates the tube located inside 64 via 'an engine 82 and a transmission 84.

Claims (1)

[Claim 9] claims Device for thermal spraying of fluids, in particular for flame spraying of high-speed suspensions (HVSFS), with a burner (30, 30a), in which is provided a combustion chamber (32), at the level of which a expansion tube (34) for delivering a spray jet, with a supply of fuel mixture into the combustion chamber (32), and with at least one injector (40, 40a) for supplying a fluid to be sprayed in the combustion chamber (32) via a nozzle (50, 50a), which is held at the level of the injector (40, 40a) so that it can be replaced. Device according to claim 1, in which the nozzle (50, 50a) is fixed by means of a thread (58) at the level of the injector (40, 40a), preferably can be adjusted axially. Device according to claim 1 or 2, wherein the nozzle (50, 50a) is provided at an outer end of a pipe (55, 64, 66, 68) and can be replaced in conjunction with it. Device according to any one of claims 1 to 3, in which the injector (40, 40a) has a separate supply for a fluid to be sprayed and for an atomizing gas to the nozzle (50, 50a). Device according to any one of the preceding claims, in which the nozzle (50, 50a) has a nozzle chamber (62), which opens into the combustion space (32) via an injection opening (52). Device according to any one of the preceding claims, in which the injector (40, 40a) has at least two tubes (64, 66, 68) coaxial with each other serving to supply atomizing gas and fluid to be sprayed towards the nozzle (50, 50a). Device according to claim 5 or 6, in which a tube (64) situated inside has an external surface with a structure (78, 78a), which promotes atomization of the fluid to be sprayed. Device according to claim 7, in which the external surface of the tube (64) situated inside has a structure (78, 78a) with stabilizing elements, which are preferably arranged in the form of a spiral. Device according to any one of Claims 3 to 8, in which the injector (40, 40a) has channels (65, 67, 69) for a supply [Claim 10] [Claim 11] [Claim 12] [Claim 13 ] [Claim 14] [Claim 15] [Claim 16] [Claim 17] separated from a first fluid, at least a second fluid and an atomizing gas. Device according to any one of the preceding claims, in which the injector (40, 40a) is detachably held at the level of the burner (30, 30a), in particular by means of a thread or a closure system fast (44). Device according to any one of the preceding claims, in which at least one channel (65, 67, 69) for supplying fluid is made of plastic, in particular PTFE or ceramic or is coated with plastic or ceramic at least at the level of its interior surface. Device according to any one of the preceding claims, in which the tube (64) located inside serving to supply the fluid to be sprayed can be rotated. Device according to any one of the preceding claims, in which a heat shield (70) is provided between the nozzle (50, 50a) and the combustion chamber (32). Device according to any one of the preceding claims, in which the burner (30, 30a) has a gas mixture block (38) cooled by means of a cooling medium. Device according to claim 14, in which the heat shield (70) has an annular shield (72) composed of ceramic in the region of the end, on the combustion chamber side, of the nozzle (50, 50a), which is connected to the cooled gas mixture block (38) of the burner (30, 30a) via an annular thermally conductive structure (74), preferably in the form of a pressed copper ring. Method of thermal spraying, in particular by means of flame spraying of high-speed suspensions (HVSFS), in particular with a device (10) according to any one of the preceding claims, in which a fluid to be sprayed and a gas d atomization are brought separately into a nozzle (50, 50a) of an injector (40, 40a), are mixed there and are ejected into a combustion chamber (32), in which they are accelerated through an expansion tube (34) using a mixture of burning fuels to coat an object. The method of claim 16, wherein a plurality of fluids to be mixed are fed separately into the nozzle (50, 50a) and are there [Claim 18] [Claim 19] [Claim 20] atomized using atomizing gas. Method according to claim 16 or 17, in which at least one fluid, in particular a fluid which is sensitive or unstable with respect to metallic surfaces, is brought into the nozzle (50, 50a) via a channel (65, 67, 69) made of plastic or ceramic or a channel (65, 67, 69) coated with plastic or ceramic. A method according to any of claims 16 to 18, wherein a plurality of fluids, which are unstable or reactive together, are supplied into the nozzle (50, 50a) in separate channels (65, 67, 69) and are atomized by means atomizing gas. Method according to any one of Claims 16 to 19, in which the atomization of the at least one fluid is promoted by structures (78, 79) generating vortices at the external surface of the tube (64, 66) , via which the fluid is supplied, and / or by a rotational drive of the channel (64).