DE102017130744B4 - Apparatus and method for thermal spraying - Google Patents

Abstract

Device for the thermal spraying of fluids, with a burner (30, 30a) in which a combustion chamber (32) is provided, at which an expansion tube (34) opens out for 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 injected into the combustion chamber (32) via a nozzle (50, 50a) which is exchangeably held on the injector (40, 40a), characterized in that the injector (40, 40a) is detachably held on the burner (30, 30a), and that the nozzle (50, 50a) is adjustably held at an outer end of an exchangeable pipe (55, 64, 66, 68) by means of a thread (58). is.

Description

The invention relates to a device and a method for thermal spraying, in particular for high-velocity suspension flame spraying (HVSFS). HVSFS is a novel process to create nanostructured coatings using thermal spraying by supersonic spraying. Very thin, dense and well-adhering layers can be produced, which are in particular ceramic, such as layers consisting of aluminum oxide, titanium oxide or zirconium oxide (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, 25 October 2006, Pages 1922-1929).

From the DE 10 2005 038 453 A1 a device according to the preamble of claim 1 and a method for high-velocity suspension flame spraying are known. Thereafter, one or more suspensions can be fed into a combustion chamber via one or more nozzles and accelerated there by means of a fuel mixture via an expansion tube. The nozzle is screwed into a thread of a gas mixing block.

From the DE 10 2016 125 587 A1 a nozzle structure for thermal spraying by means of a suspension containing particles or a precursor solution is known. With a tubular element arranged in the direction of the combustion chamber and an end face arranged opposite to the combustion chamber, the nozzle insert has a flange-shaped widening which, in the installed state, bears against a seat formed in the holder. Here, a tube is provided on the nozzle insert, which opens into an internally hollow casing in the direction of the combustion chamber.

HVSFS requires processing of powders with very small particle sizes in the nanoscale range. The HVSFS does not use active atomization in the prior art. The disintegration of the liquid jet occurs in an uncontrolled manner due to turbulence in the combustion chamber.

From M. Rukosuyev, S.A. Baqar, M.B.G. Jun, "Development and Evaluation of Flame-Assisted Dual Velocity Nonoparticle Coating System, Journal of Micro- and Nano-Manufacturing December 2017, Vol. 5, p. 044501-1 - 044501-5 a method for flame spraying is known in which external atomization takes place by means of ultrasound.

However, external atomization can already lead to demixing before it is fed into the burner. Even with such a method, the problems that exist in the prior art cannot be eliminated, namely in particular uncontrolled droplet breakup, processes and spraying results that are difficult to control, as well as unwanted deposits in the nozzle head with the result of blockages, unwanted deposits in the area of the combustion chamber walls, which can become detached in the course of the coating process and can be built into the coating, which impairs the layer quality.

In particular, there is the problem that the nozzle often becomes clogged, which leads to the interruption of the process. The burner must then be dismantled and cleaned in a complex manner.

Against this background, the invention is based on the object of creating an improved device and an improved method for thermal spraying, which is particularly suitable for HVSFS and with which the problems existing in the prior art are at least partially avoided. In particular, the wearing parts should be easy to disassemble and replace, and the media required for thermal spraying should be efficiently fed into the combustion chamber.

According to the invention, this object is achieved by a device for the thermal spraying of fluids according to claim 1 .

The object of the invention is completely achieved in this way.

Since the nozzle can be easily replaced according to the invention, it can be changed quickly in the event of a blockage, so that a coating process only has to be interrupted for a short time. Furthermore, different nozzles adapted to different materials to be sprayed can be used, so that, for example, the injection opening from which the material to be sprayed exits into the combustion chamber of the burner can be suitably adjusted. Since the nozzle is held at the outer end of a tube and can be replaced together with it, quick and easy assembly and disassembly is guaranteed. The injector can also be detached from the torch, which ensures safe and quick access to the nozzle.

Since the HVSFS, depending on the type of material to be sprayed, the material to be sprayed can be present both in the form of a solution and in the form of a suspension, both embodiments are under the in the context of this application Generic term "fluid to be sprayed" summarized.

According to the invention, the axial distance between the injection opening of the nozzle and the combustion chamber wall can be adjusted by means of a thread.

According to a further embodiment of the invention, the injector has a separate supply for a fluid to be injected and for an atomizing gas up to the nozzle.

In this way, an atomization of the fluid to be sprayed that is as controlled as possible can be ensured.

According to a further embodiment of the invention, the nozzle has a nozzle chamber which opens into the combustion chamber via an injection opening.

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

According to a further embodiment of the invention, the injector has at least two mutually coaxial tubes for supplying atomizing gas and fluid to be sprayed to the nozzle.

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

According to a further embodiment of the invention, an inner tube has an outer surface with a structure that supports atomization of the fluid. The fluid to be sprayed preferably reaches the nozzle chamber through the internal pipe. In this case, the atomizer gas flowing around the outside generates controlled turbulence in this way, resulting in uniform atomization. The fluid to be sprayed can flow through the inner tube and the atomizing gas can flow in the surrounding cavity. Likewise, an inverted arrangement with the fluid to be sprayed flowing on the outside and with the atomizing gas flowing on the inside is conceivable.

According to a further embodiment of the invention, the outer surface of the inner tube has stabilizing elements which are preferably arranged in a spiral manner.

In this way, the medium flowing around is provided with a twist, so that a particularly uniform and controlled atomization can take place.

In a further embodiment of the invention, the inner tube is itself provided with a preferably conical nozzle opening at its outer end.

This also ensures improved mixing or improved atomization of a medium guided through it.

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

In this way, 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 that are difficult to mix or that react with one another or otherwise adversely affect one another.

According to a further embodiment of the invention, the injector is detachably held on the burner, in particular by means of a thread or a quick-release fastener.

In this way, the injector, which is used exclusively for feeding, atomizing and injecting the fluid to be injected into the combustion chamber, can be easily detached and pulled out of the burner to the rear. In this way, the injector can easily be exchanged or the nozzle replaced.

The nozzle is preferably made of brass or stainless steel. The tubes and associated parts through which the atomizing gas and the fluid or fluids to be sprayed are conducted are preferably made of stainless steel. The gas mixing block is preferably made of copper.

According to a further embodiment of the invention, at least one channel for supplying fluid consists of plastic, in particular PTFE, or of ceramic or is coated with plastic or ceramic at least on its inner surface.

In this way, fluids sensitive to, reacting with, or otherwise adversely affected by metallic conduits can be safely carried to the nozzle where atomization and injection into the combustor occurs.

According to a further embodiment of the invention, the internal channel for supplying fluid to be sprayed can be driven in rotation.

In this way, an even better and more uniform atomization of the fluid to be sprayed can be guaranteed.

According to a further embodiment 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 a further embodiment of the invention, the burner has a gas mixing block which is cooled by means of a cooling medium, in particular water or compressed air.

In this way, pre-mixed fuel can be fed into the combustor and at the same time the thermal load on the burner can be reduced.

According to a further embodiment of the invention, the heat shield has an annular ceramic shield in the area of the combustion chamber end of the nozzle, which is connected to the cooled gas mixing block of the burner via a thermally conductive annular structure, preferably in the form of a pressed-in copper ring.

This results in a simple assembly of the heat shield with very high effectiveness at the same time.

Although usually only one injector is provided, via which the material to be thermally sprayed is injected into the combustion chamber, several injectors can also be provided for special purposes, e.g. two or more injectors can be interchangeably accommodated in assigned bores of a common outer tube.

The invention is also achieved by a method for thermal spraying, in particular by means of high-velocity suspension flame spraying (HVSFS), in which a fluid to be sprayed and an atomizing gas are fed separately into a nozzle of an injector, mixed there and ejected into a combustion chamber in which the material to be sprayed is accelerated through an expansion tube by means of a burning fuel mixture in order to coat an object.

With such a method, a controlled supply and atomization of a fluid to be sprayed and thus a controlled process during thermal spraying can be guaranteed.

According to a further embodiment of the method according to the invention, several fluids to be mixed are fed separately into the nozzle and atomized there by means of atomizing gas.

In this way, different fluids that are poorly miscible with one another, or that react with one another or otherwise adversely affect one another, can be processed together and thermally sprayed.

According to a further embodiment of the invention, at least one fluid, in particular a fluid that is sensitive or unstable to metallic surfaces, is fed into the nozzle via a plastic channel or ceramic channel or a channel coated with plastic or ceramic.

In this way, fluids that are sensitive or unstable or reactive to metallic channels can be processed.

According to a further embodiment of the method, two or more fluids that are unstable or reactive with one another are fed into the nozzle in separate channels and atomized by means of atomizing gas.

According to a further embodiment of the method, the atomization of the at least one fluid is supported by swirl-generating structures on the outer surface of a channel through which the fluid to be sprayed is supplied and/or by a rotating drive of the channel.

In this way, a particularly good and homogeneous atomization of the fluid to be sprayed is ensured, even with fluids that are very difficult to atomize.

It goes without saying that the features of the invention mentioned above and those yet to be explained below can be used not only in the combination specified in each case, but also in other combinations or on their own, without departing from the scope of the invention.

• 1 eine erfindungsgemäße Vorrichtung zum thermischen Spritzen in schematischer Darstellung;
• 2 eine Längsansicht des Brenners gemäß 1;
• 3 einen vergrößerten Schnitt durch den Brenner gemäß 2 längs der Linie III-III;
• 4 eine vergrößerte Darstellung des Details IV gemäß 3;
• 5 eine vergrößerte Darstellung des Details V gemäß 3;
• 6 eine Längsansicht des Injektors gemäß 3;
• 7 einen Längsschnitt durch den Injektor gemäß 6;
• 8 eine vergrößerte Darstellung des Details VIII im Bereich der Spitze des Injektors;
• 9 eine alternative Ausführung der Düse mit drei zueinander axialen Kanälen für die Zuführung von Zerstäubergas und zwei zu spritzenden Fluiden;
• 10 einen Teilschnitt des vorderen Bereiches der Düse und der umgebenden Gasmischkammer mit der zusätzlichen Anordnung eines Hitzeschildes;
• 11 eine perspektivische Außenansicht der Düse in vergrößerter Darstellung;
• 12 eine angeschnittene perspektivische Darstellung der Düse mit zusätzlicher Andeutung des innenliegenden Rohrs mit Drall erzeugenden Strukturen am äußeren Ende und mit einer Düsenöffnung am innenliegenden Rohr;
• 13 ein Foto des Rohrs gemäß 12;
• 14 ein Foto eines Rohrs mit einer abgewandelten, äußeren Drall erzeugenden Struktur;
• 15 eine schematische Darstellung der Düse im Bereich ihres brennkammerseitigen Endes mit einer ersten Konfiguration, in welcher das zu zerstäubende Fluid innen geführt wird und das Zerstäubergas im äußeren Kanal;
• 16 eine Darstellung gemäß 15 mit umgekehrter Führung von Fluid und Zerstäubergas;
• 17 eine abgewandelte Ausführung des Brenners gemäß 3 und
• 18 eine vergrößerte Darstellung des Details XVIII gemäß 17.

Further features and advantages of the invention result from the following description of preferred exemplary embodiments with reference to the drawing. Show it:

• 1 a device according to the invention for thermal spraying in a schematic representation;
• 2 a longitudinal view of the burner according to FIG 1 ;
• 3 according to an enlarged section through the burner 2 along line III-III;
• 4 an enlarged view of detail IV according to 3 ;
• 5 an enlarged view of the detail V according to 3 ;
• 6 a longitudinal view of the injector according to FIG 3 ;
• 7 according to a longitudinal section through the injector 6 ;
• 8th an enlarged view of detail VIII in the area of the tip of the injector;
• 9 an alternative embodiment of the nozzle with three mutually axial channels for the supply of atomizing gas and two fluids to be sprayed;
• 10 a partial section of the front portion of the nozzle and the surrounding gas mixing chamber with the addition of a heat shield;
• 11 a perspective external view of the nozzle in an enlarged view;
• 12 a cut perspective view of the nozzle with additional indication of the inner tube with swirl-generating structures at the outer end and with a nozzle opening on the inner tube;
• 13 a photo of the pipe according to 12 ;
• 14 a photo of a tube with a modified, external twist-generating structure;
• 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 inside and the atomizing gas in the outer channel;
• 16 a representation according to 15 with reverse flow of fluid and nebulizer gas;
• 17 according to a modified version of the burner 3 and
• 18 according to an enlarged view of detail XVIII 17 .

In 1 a schematic representation of a device according to the invention is denoted overall by the number 10 . The device 10 has a burner 30 which is supplied with a suspension to be sprayed or a solution to be sprayed (collectively referred to as fluid to be sprayed) via a switching valve 26 . The burner 30 also has a fuel gas line 16 for supplying fuel gas (ethene in the present case) and an oxidizing agent 18 (oxygen in the present case). The burner 30 is also provided with water cooling and has a cooling water inlet 12 and a cooling water outlet 14 for this purpose. The suspension to be sprayed is in a container 20. In a container 22 is a flushing medium. The suspension to be sprayed is fed to the burner 30 via the valve 26 by means of the feed pump 24 . The burner 30 and the supply of suspension (fluid to be sprayed) are controlled via a central controller 28, preferably a PLC controller. In this case, the burner 30 is usually accommodated on a robot arm (not shown), which is controlled by the central controller 28 .

2 shows the burner 30 in a longitudinal view.

From the enlarged longitudinal section according to 3 further details of the burner 30 can be seen.

The burner 30 has a combustion chamber 32 to which an expansion tube 34 is connected. Premixed fuel mixture is fed into the combustion chamber 32 via a gas mixing block 38 . The fluid to be injected is supplied via an injector 40 which is detachably attached to the rear of the housing 36 of the burner 30 . The injector 40 reaches up to the combustion chamber 32 with a nozzle at its front end.

At the rear, the combustion chamber 32 facing away from the end of the housing 36 are in 3 the connections 44 and 46 for the fuel gas and the oxygen can also be seen. At its rear end, the injector 40 also has connections 12, 14 for the cooling water supply and the cooling water outlet. Fluid to be injected is fed into the central channel of the injector 40 via an end 56 as indicated by the arrow 43 . There is also a connection 42 for the supply of atomizing gas in 3 recognizable.

In the HVSFS shown here, the fluid to be injected is supplied via the injector 40, as explained in detail below, mixed with atomizing gas in the nozzle and injected into the combustion chamber 32 in a controlled manner. The fuel mixture premixed into the combustor 32 via the gas mixing block 38 ignites, melting the atomized fluid injected into the combustor and resulting in the exit of a heated jet through the expansion tube 34 at supersonic speeds.

According to the detail 4 the combustion chamber end of the injector 40 with the nozzle 50 can be seen. The atomized fluid to be injected exits the nozzle 50 via the injection opening 52 into the combustion chamber 32 . With 48 are the outlets for the fuel mixture in the gas mixture block 38 is premixed. The outlets for the combustible gas mixture 48 are distributed in a ring around the injection opening 52 .

5 shows an enlarged view in the area of the rear end of the housing 36. At the rear end of the housing 36, a quick-release fastener 54 is provided, with the aid of which the injector 40 can be fixed or released by means of two outwardly protruding spring bolts with one hand. If the injector 40 is released, it can be pulled completely out of the burner 40 to the rear.

6 and 7 show an enlarged representation of the injector 40 in longitudinal view and in longitudinal section.

8th shows the detailed structure of the injector 40 in the area of the nozzle. The injector 40 has the nozzle 50 at its outer end. The nozzle 50 is screwed to an outer tube 55 of the injector 40 via a thread 58 . The fluid to be sprayed is fed via a central tube 64 into a nozzle chamber 62 of the nozzle 50 . Atomizing gas is supplied via a tube 66 coaxial with the central tube 64 . In the region of the mouth of the central tube 64, the fluid to be sprayed is atomized in a controlled manner. The nozzle 50 is sealed off from the coaxial tube 66 by an O-ring 60 received in an associated annular groove. By rotating the nozzle 50, it can be adjusted in the axial direction towards the combustion chamber 32.

The nozzle 50, which is preferably made of brass, is shielded from the combustion chamber 32 by a heat shield 70, as shown in FIG 10 shown schematically. A heat shield in the form of a ceramic ring 72, for example made of aluminum oxide, is arranged in front of the end face of the nozzle 50 on the combustion chamber side. A copper ring 74 pressed into the outer end of the gas mixing block 38 is used for fixing. While the ceramic ring 72 is used for heat shielding, the copper ring 74 leads to heat dissipation into the water-cooled gas mixing block 38. Alternatively, the copper ring 74 could also be made in one piece with a gas mixing block 38 made of copper be trained.

9 Figure 12 shows a modification of the nozzle, generally indicated at 50a. In this case, a further channel for supplying a second fluid to be sprayed is additionally arranged coaxially. An inner tube 64, in which an inner channel 65 is provided, a central tube 66 coaxial thereto with an annular central channel 67, and an outer tube 68, whereby an outer annular channel 69 is defined, thus open into the nozzle 50a. The inner channel 65 can be used to supply the first fluid, the middle channel 67 to supply the second fluid and the outer channel 69 to supply atomizing gas. In principle, however, another arrangement is also conceivable, as described below with reference to FIG 15 and 16 is described in more detail.

It goes without saying that further, preferably coaxial, pipes can also be provided for the supply of further fluids to be sprayed.

11 shows an enlarged perspective external view of the nozzle 50. At the outer end of the nozzle 50, on the combustion chamber side, there are two parallel flattened areas 76, so that the nozzle 50 can be easily adjusted or removed using a wrench. In 11 the injection opening 52 at the end on the combustion chamber side and the thread 58 can also be seen.

According to the illustration 12 the supply of the fluid to be sprayed via the central channel 64 into the nozzle chamber 62 can be seen. The fluid to be sprayed is guided via the central tube 64 via a separate, conically tapering nozzle opening 79 into the nozzle chamber 62 . A structure 78 is applied to the nozzle-side end of the central tube 64 by means of SLM (Selective Laser Melting) or 3D metal printing processes. The structure 78 provides the medium flowing around with a twisting impulse, resulting in improved atomization and a better controlled process.

13 shows a photo of such a structure 78 at the front end of the central tube 64.

A slightly modified version of such a structure is in 14 shown and generally designated by the numeral 78a. The end of the tube 64 on the nozzle side with its outlet opening can also be seen here.

In the 15 and 16 shows schematically that in the nozzle 50 the atomizing gas can either be routed through the outer channel 67, as indicated by the dashed arrow 80, and the fluid to be sprayed is routed through the inner channel 65, as indicated by the arrow 81.

Alternatively, the arrangement can also be reversed, in that the atomizing gas is guided through the inner channel 65, as indicated by the dashed arrow 83, and the fluid to be sprayed is guided through the outer channel 67, as indicated by the solid arrow 82 tet is In any case, in the region of the exit end of the inner channel 65 in the nozzle chamber 62 , the fluid is atomized and then exits via the injection opening 52 into the combustion chamber 32 .

If materials are to be thermally sprayed that are sensitive to metals, react with them or are adversely affected in any other way, the lines in question can also be made of plastic (especially PTFE) or ceramic or at least be coated with plastic or ceramic on their inner surface.

In this way, it is now also possible to process materials that previously could not be thermally sprayed due to their sensitivity to metals.

Furthermore, fluids that are unstable can be atomized in a controlled manner since the fluid and atomizing gas are supplied separately to the nozzle.

A still further improvement in atomization can be achieved by rotating the inner tube 64 . In this case, the fluid to be sprayed is passed through the inner tube 64 .

the 17 and 18 show an example of such a design. Here, the burner 30a is provided with a correspondingly modified injector 40a. According to the 18 In the detail shown, a rotary drive 80 is provided in the region of the outer end of the inner tube 64 , which drives the inner tube 64 to rotate via a motor 82 and a gear 84 .

Claims (18)

Device for the thermal spraying of fluids, with a burner (30, 30a) in which a combustion chamber (32) is provided, at which an expansion tube (34) opens out for 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 injected into the combustion chamber (32) via a nozzle (50, 50a) which is exchangeably held on the injector (40, 40a), characterized in that the injector (40, 40a) is detachably held on the burner (30, 30a), and that the nozzle (50, 50a) is adjustably held at an outer end of an exchangeable pipe (55, 64, 66, 68) by means of a thread (58). is. device after claim 1 , characterized in that the injector (40, 40a) has a separate supply for a fluid to be injected and for an atomizing gas up to the nozzle (50, 50a). Device according to one of the preceding claims, characterized in that the nozzle (50, 50a) has a nozzle chamber (62) which opens into the combustion chamber (32) via an injection opening (52). Device according to one of the preceding claims, characterized in that the injector (40, 40a) has at least two mutually coaxial tubes (64, 66, 68) for supplying atomizing gas and fluid to be sprayed to the nozzle (50, 50a). device after claim 3 or 4 , characterized in that an inner tube (64) has an outer surface with a structure (78, 78a) that supports atomization of the fluid to be sprayed. device after claim 5 , characterized in that the outer surface of the inner tube (64) has a structure (78, 78a) with stabilizing elements, which are preferably arranged in a spiral manner. Device according to one of Claims 1 until 6 , characterized in that the injector (40, 40a) has channels (65, 67, 69) for a separate supply of a first fluid, at least one second fluid and an atomizing gas. Device according to one of the preceding claims, characterized in that the injector (40, 40a) is detachably held on the burner (30, 30a) by means of a thread or a quick-release fastener (44). Device according to one of the preceding claims, characterized in that at least one channel (65, 67, 69) for supplying fluid consists of plastic, in particular PTFE, or ceramic or is coated with plastic or ceramic at least on its inner surface. Device according to one of the preceding claims, characterized in that the inner pipe (64) for supplying fluid to be sprayed can be driven in rotation. Device according to one of the preceding claims, characterized in that a heat shield (70) is provided between the nozzle (50, 50a) and the combustion chamber (32). Device according to one of the preceding claims, characterized in that the Burner (30, 30a) has a gas mixing block (38) cooled by a cooling medium. device after claim 12 , characterized in that the heat shield (70) has an annular shield (72) made of ceramic in the region of the end of the nozzle (50, 50a) on the combustion chamber side, which has a thermally conductive, annular structure (74), preferably in the form of a pressed-in copper ring, connected to the cooled gas mixing block (38) of the burner (30, 30a). Method for thermal spraying with an apparatus (10) according to one of the preceding claims, in which a fluid to be sprayed and an atomizing gas are fed separately into a nozzle (50, 50a) of an injector (40, 40a), mixed there and into a combustion chamber (32) in which they are accelerated by a burning fuel mixture through an expansion tube (34) to coat an object. procedure after Claim 14 , in which several fluids to be mixed are fed separately into the nozzle (50, 50a) and atomized there by means of atomizing gas. procedure after Claim 14 or 15 , in which at least one fluid is fed 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. Procedure according to one of Claims 14 until 16 , in which several fluids that are unstable or reactive with one another are fed into the nozzle (50, 50a) in separate channels (65, 67, 69) and atomized by means of atomizing gas. Procedure according to one of Claims 14 until 17 , in which the atomization of the at least one fluid is supported by swirl-generating structures (78, 79) on the outer surface of a tube (64, 66) through which the fluid is supplied, and/or by a rotating drive of the channel (64). .

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