High velocity oxygen-air fuel thermal spraying device

Abstract

An apparatus comprises: a labyrinth mixing device arranged to mix a first oxidant gas and a fuel under pressure and to inject the resulting mixture into a combustion chamber; a body (1) of a gas torch accommodating connectors (7) for the fuel and the oxidant gas and the labyrinth mixing device (2); a front part (3) of the gas torch defining the internal geometry of a combustion chamber (4) by means of the labyrinth mixing device (2); an ignition device (30) for initiating combustion of the mixture; and a material delivery device (6) designed to inject a spray material axially into a high-speed gaseous jet. The labyrinth mixing device (2) comprises one or more flanges (23, 24) defining one or more mixing volumes (21, 22) and holes (25, 26, 27), the holes (25, 26, 27) being concentrically disposed on the flanges (23, 24) and penetrating the mixing device (2) and opening at the downstream end of the mixing device (2). The labyrinth mixing device (2) comprises an axial hole (28).

Description

Technical Field

[0001] The present invention relates to the technical field of thermal spraying for applying coatings, and more particularly to high velocity oxygen / air fuel spraying equipment for depositing coating material on a substrate or for producing three-dimensional objects by additive manufacturing.

[0002] The invention is particularly suitable for processing metal based materials and ceramic type materials. Background Art

[0003] High velocity oxy-fuel (HVOF) processes represent the state of the art for spray deposition of wear and corrosion resistant coatings, as their supersonic gas velocities combined with moderate flame temperatures allow deposition of optimal coatings with very high bond strength and density, fine surface finish and low oxide content. However, the new generation of coating materials (fine powders), stringent quality requirements and high production rates required by the industry are pushing HVOF technology to its limits.

[0004] Due to their high hardness, high wear resistance and good fracture resistance, hard metal coatings are attractive and successful composite materials that have been widely used in many industrial applications. In particular, HVOF spray coatings based on tungsten carbide (WC) have been introduced a few years ago as an alternative to electrolytic hard chrome (EHC). Such HVOF spray coatings have been significantly improved from a technical and environmental point of view. In applications where the coating is to be used in an aggressive corrosive environment, HVOF WC-CoCr coatings are usually recommended and, in fact, are used as an alternative to EHC. i The current industrial standard for alternatives to WC. However, it is well known that high carbon losses (i.e., WC decarburization) and undesirable phase transformations in standard HVOF sprayed hard metal coatings are very sensitive to the spraying process in order to limit these effects and maintain the quality of WC-based coatings. Test results have shown that the decarburization of WC is limited to the thermal decomposition of WC into W2C and carbon. The formation of metallic tungsten in the coating is due to the oxidation of W2C. Therefore, effectively inhibiting the thermal decomposition of WC becomes an effective means of effectively inhibiting the formation of tungsten. However, in order to achieve sufficient deformability of the cermet particles during high-speed impact, it is necessary to control the spraying conditions by ii，iii The feed is heated just enough to melt the binder phase.

[0005] With regard to corrosion protection, the main limitation associated with many thermal spray coatings is the presence of small residual pores and microcracks. Corrosive materials can enter the connected pores and degrade the coating and corrode the base material. For very dense coatings, the pores need to be eliminated through process optimization, or the pores need to be sealed to prevent corrosive liquids from entering the coating. Developing curable chemistries that penetrate deeply into small pores to seal HVOF coatings has proven to be very challenging. On the other hand, it is also very challenging to develop corrosion-resistant metal coatings that are dense enough to prevent solutions from penetrating into the coating.

[0006] All these limitations have led to a growing interest within the industry in finding thermal spray processes that can be run under “colder” conditions and / or at higher gas velocities, in order to find very dense and unmodified coatings. In this sense, the development of cold spray processes, which exploit the expansion of inert, heated, high-pressure gases but without the intervention of a combustion process, has allowed a wide range of metals, such as copper and aluminum, to be sprayed with excellent coating qualities. Deposition efficiencies of more than 90% can be achieved, and the resulting coatings show very low porosity levels of the feed material, minimal phase transformations, decomposition and oxidation. The process gas temperature is usually kept in a range such that the sprayed particles are never exposed to temperatures close to their melting point. However, since the accumulation of deposits depends strongly on the particle velocity before impact, the spraying conditions can significantly affect the microstructure and mechanical properties of the coating. It is well known that in CS, bonding occurs when the impact velocity of the particles exceeds a critical value. This critical velocity depends not only on the type of sprayed material, but also on the quality of the powder, the particle size and the particle impact temperature. iv，v Even though a range of CS equipment is available from various manufacturers, each of which exhibits its own advantages and has its potential niche market, and in some successful commercial applications, a limited number of materials have been processed using cold spray on an industrial scale so far, mainly due to the lack of dedicated equipment for this process. vi Designed commercially available powder.

[0007] Compared to common HVOF spray systems and CS, both processes are characterized by significantly different combinations of particle velocity and temperature. For hard metals and some high-strength metals, these combinations of particle velocity and temperature do not produce the desired coating properties and / or cost-competitive process parameters (high powder feed rate, high deposition efficiency). Therefore, current developments in thermal spray processes are characterized by the search for the best combination of powder particle velocity and temperature while maintaining high powder feed rate and deposition efficiency. vii .

[0008] Generally speaking, the inventions claimed in the various patents feature a variety of systems for spraying deposited coatings of carbides, metals or cermet-type materials, composites, alloys, stainless steels and other materials. The deposition system is configured to control and optimize the size, temperature, velocity and composition of the particles sprayed during the deposition process.

[0009] WO 2009 / 155702 A1 patent claims a unique HVOF torch design that allows the gas temperature to be varied over a wider range (from 800K to 2500K) than any previous HVOF system. Gaseous fuel and oxygen are continuously fed to the combustion chamber where heat is released. Downstream, large amounts of cold nitrogen are injected radially to regulate the temperature. In a similar manner, by injecting room temperature inert gas into the combustion gas jet of HVOF, the so-called thermal spray process is able to control the temperature of the propellant gas within a range of approximately 2300K to 1000K, allowing many powder materials to be sprayed at high impact velocities. viii Deposited in heat softened state.

[0010] Another alternative technique is high velocity air fuel (HVAF) spraying using air as the oxidant gas instead of oxygen as in HVOF. Although the coating quality has been very high since the development of HVAF using the "Aerospray" torch (US Pat. No. 5,120,582; US 5,271,965), the process and coating properties of the coating itself have improved significantly over the past 20 years. After the first improvements in HVAF gun design were made by introducing a permeable burner block into the internal combustion chamber (US Pat. No. 5,932,293), further progress was made by introducing catalytic components in the internal burner (US Pat. No. 6,245,390), always with the purpose of heating the gas and activating combustion in an air-based mixture. These guns have been operated using gaseous fuels such as propane and propylene. So far, it has been found that active combustion HVAF (ACHVAF) sprayed WCCoCr coatings produced using these technologies have better wear resistance than their HVOF counterparts sprayed using common HVOF systems (such as JP5000 and DJ2600), and even better performance than electroplated hard chrome and spray-coated coatings. ix20 to 30 times better. A few years later, the design of the HVAF gun was further improved, allowing the addition of liquid fuel to the oxidizer flow and its application to the structural components of the permeable burner brick to enhance the cooling effect of the structural components (U.S. Patent No. 2010 / 0215864A1). In addition, by annularly introducing a coaxial gas flow, through a narrow continuous slit of a circumferential annular geometry near the entrance to the diverging outlet hole of the accelerating nozzle, an unobstructed converging-diverging gas dynamic virtual nozzle (GDVN) was introduced in the accelerating nozzle (U.S. Patent No. 2011 / 0229649A1). As a result, the hot combustion product gases discharged from the combustion chamber are compressed in diameter by the gas dynamic lift exerted by the coaxial co-flowing gas. Moreover, today, HVAF coatings have so far challenged the WC-CoCr coatings deposited by HVOF, proving that HVAF is a viable technology that is comparable to common HVOF systems. x It has many practical advantages.

[0011] On the other hand, HVOF systems for liquid fuels can also be modified by adding an inert gas (e.g. N2) for cooling purposes. This is the case with technology. Technology by changing the combustion chamber xi The design further reduces the effective flame power. It indicates that this technology is suitable for processing ultrafine (particle size <12μm) and nanostructured metal-ceramic powders.

[0012] However, in the race for higher particle velocities and controlled temperatures for high quality coatings, both high pressure liquid fuel HVOF spray guns and HVAF systems use high power and large amounts of gas to operate, in contrast to conventional gas fuel HVOF systems that operate at lower power levels (<200kW) and consume gas moderately. The object of the present invention is to provide the best of both conventional methods, but to increase the flexibility in the behavior of the spraying process so as to adapt the particle velocity and its temperature to the specific requirements of each coating and powder, and also to reduce the practical deficiencies found in HVOF and HVAF technologies. To achieve this goal, a new combustion gas torch is proposed, which is based on injecting gas into its combustion chamber in different ways, forming a local flame holder area to activate difficult to burn mixtures for combustion. In addition, in combination with the implementation of low temperature fuel gas (such as natural gas (methane)) and the use of very wide ratios of O2 / air mixtures (various energy conditions and dilutions), very low flame temperatures (if required) can be achieved, while maintaining stable performance in supersonic conditions. Summary of the invention

[0013] A first aspect of the present invention relates to a high velocity thermal spraying apparatus comprising:

[0014] the main body of the torch, which houses the connectors and the labyrinth mixing device for feeding the fuel and oxidant gases,

[0015] A labyrinth-type mixing device is arranged to mix the first oxidant gas and the fuel under pressure and to inject the resulting mixture into the combustion chamber.

[0016] The front part of the gas torch defines the internal geometry of the combustion chamber by means of a labyrinth mixer and is connected downstream to a gas expansion nozzle designed to receive the products of the combustion of the mixture and form a high-speed gaseous jet.

[0017] An ignition device is used to start the combustion of the mixture.

[0018] The material delivery device is designed to inject the spray material axially into the high-speed gas jet.

[0019] According to the invention, the labyrinth mixer comprises one or more flanges and holes. The one or more flanges define one or more intermediate mixing volumes between the body and the labyrinth mixer itself. The holes are concentrically placed on the flanges and pass through the mixer and open at the downstream end of the mixer for connecting the fuel-first oxidant feed part of the labyrinth mixer with the combustion chamber.

[0020] According to the invention, the labyrinth mixing device comprises a through-going axial bore for injecting the spray material (delivered by the carrier gas) into the combustion chamber (and further to the expansion nozzle).

[0021] The high-speed thermal spraying apparatus of the present invention includes a plurality of second oxidant gas injectors for individually injecting a second oxidant gas upstream in a combustion chamber to promote the combustion process. The second oxidant gas injectors are open into the combustion chamber at an upstream peripheral position of the combustion chamber relative to the gas expansion nozzle to form at least two differential regions: a first diluted lower oxygen saturation region, thereby generating a cooler temperature region around the mixing device of the first oxidant gas and the fuel; and a second higher oxygen saturation region, generating a hotter temperature region near the annular peripheral position of the second oxidant injector upstream of the combustion chamber, thereby axially injecting the spray material into the cooler temperature region of the combustion chamber and forming a particle stream that is accelerated and gradually heated downstream.

[0022] In some embodiments, the second oxidant gas injector comprises one or more sequential and closely spaced arrays of narrow continuous slots and / or a series of orifices to allow independent injection of the second oxidant at one or more sequential and closely spaced injection points in the combustion chamber.

[0023] By means of the apparatus of the invention, different gas mixtures are formed at different locations of the combustion chamber, resulting in non-uniform conditions of gas combustion and in the formation of different flame characteristics inside the combustion chamber. Specifically, the stoichiometric ratio or oxygen enrichment ratio allows the formation of high temperature flames in some desired areas of the combustion chamber, whereas other areas are simultaneously characterized by a diluted, lean or even inflammable mixture of gases. In this way, the permanent local oxygen-rich area is intended to act as a flame holder for a very wide range of practical gas parameters or overall gas mixtures, thereby allowing the overall gas mixture obtained to be heated, activated, ignited and burned in the combustion chamber and downstream of the cartridge nozzle in such a wide range of gas mixtures.

[0024] With regard to the forward motion of a high-speed gaseous jet, the terms downstream and upstream must be considered.

[0025] The fuel and the first oxidant stream can be injected separately into the body of the gas torch through corresponding connectors, alternatively, they can be premixed and further injected outside the gas torch. After entering the feed part of the labyrinth mixing device, the fuel-first oxidant premix is ​​squeezed through the orifices of the first flange, thereby expanding it into the first intermediate mixing volume in the next step. The same compression and expansion process is repeated through the continuous flanges and other intermediate mixing volumes of the mixing device, after which the fuel-first oxidant mixture is injected into the combustion chamber according to the pattern of the defined holes.

[0026] The labyrinth mixer device can be designed to be continuously cooled by the internal flow of the mixture of the fuel and the first oxidant and to allow the mixture of the fuel and the first oxidant to be injected at different downstream locations, thereby forming a cooler area of ​​the combustion chamber. This adjacent area near the mixer where the mixture of the fuel and the first oxidant is injected is also designed to buffer the contact of the labyrinth mixer device with the higher temperature combustion area downstream of the combustion chamber. In addition, the mixer device designed with slots and holes in the gas path acts as a flame arrester to prevent flashback.

[0027] In some embodiments, the internal combustion chamber is designed to generate different combustion conditions inside the geometry of such a combustion chamber due to different local distribution of the mixture of the first oxidant gas and the fuel and the separate addition of the second oxidant gas at the upstream periphery.

[0028] In some embodiments, the labyrinth mixing device is partially contained within the body of the gas torch, such that the mixing device is enclosed at its upstream end by the material delivery device, while its downstream end, where the exhaust gas mixture injector area is located, faces the combustion chamber, and wherein the body of the gas torch includes one or more connectors that feed the fuel and first oxidant gas streams to the fuel-first oxidant feed portion of the mixing device. The geometry of the combustion chamber is defined between the labyrinth mixing device and the converging shape of the gas torch front portion of the gas torch, wherein the front portion is open to the gas expansion nozzle system.

[0029] For exemplary purposes only, the present invention may be implemented using natural gas (methane) as the cryogenic fuel gas, and the cryogenic fuel gas and air as the first oxidant gas. The oxygen gas may be the second oxidant gas injected separately by the second oxidant injector. According to the present invention, the gaseous fuel and air are continuously fed into the mixing region near the downstream of the mixer, while oxygen is radially injected into the upstream of the combustion chamber at different stages to support the combustion process.

[0030] The gas torch of the present invention can operate over a wide range of gas temperatures while maintaining a supersonic gas flame speed. The gas temperature can be varied over a wider range than conventional high velocity oxy-fuel systems, primarily due to the design of the gas mixing device and the use of different air and oxygen mixtures distributed along the combustion chamber.

[0031] In some embodiments, the coating material to be sprayed is injected axially into the labyrinth mixing device to the combustion chamber with the support of a carrier gas from an appropriate external feeder. In addition, the material delivery device may include at least two inlets and one outlet, the one outlet terminating inside the labyrinth mixing device. The first inlet is for a first gas (coating material carrier gas) flow at a relatively reduced first pressure, the first gas flow is used to carry the selected spraying material, and the second inlet is for a gas flow (injection gas) with a higher pressure, the higher pressure is close to the pressure inside the combustion chamber, so that the first gas flow with the coating material is sucked into the labyrinth mixing device and then into the combustion chamber. In some embodiments, the properties of these gases for injecting the coating material into the combustion chamber can be selected according to additional functions (inert, oxidizing, fueling, chemical reaction...). The coating material can be supplied as a spray powder, which has appropriate characteristics for a correct spraying process to produce the target coating properties, and also allows fine processing according to the process status of the technology through liquid precursors (solutions, suspensions...), these spray powders are usually submicron-sized particles.

[0032] In some embodiments, the coating materials are first processed (heated and accelerated) by their path in the combustion chamber, but only after being output from the nozzle downstream of the combustion chamber do the coating materials reach their effective spraying conditions (spraying material velocity and temperature). The gas expansion nozzle has an axial nozzle bore comprising an inlet bore and a subsequent outlet diffuser bore (1° to 6°) which opens downstream. Preferably, the radial dimension of the inlet bore of the nozzle is ( to ) is slightly larger than the outlet hole of the converging outlet part of the combustion chamber To prevent the heated powder stream from contacting the walls of the inlet hole. In general, the design of the nozzle follows well-known rules for gas expansion using supersonic flows in thermal spraying. In some embodiments, the nozzle is between 20m and 250mm long, with an initial cylindrical section followed by a diverging section downstream. Typically, very different coating materials with different physical properties or particle characteristics require different nozzle geometries for proper handling during spraying.

[0033] In some embodiments, the high velocity thermal spray apparatus includes a gas collimator arrangement at the output to control supersonic gas expansion in the surrounding environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to complete the description and for a better understanding of the present invention, a set of drawings is provided. Said drawings constitute an integral part of the specification and illustrate embodiments of the present invention, which should not be interpreted as limiting the scope of the present invention, but should be interpreted as examples of how the present invention can be implemented. The drawings include the following figures:

[0035] Figure 1 Shown is a longitudinal cross-sectional view of a preferred embodiment of the present invention, which is a high velocity oxygen / air fuel (HVOAF) torch for ejecting a stream of spray particles at supersonic speeds to accumulate a coating of such heated particles on a surface downstream of the discharge end of the apparatus shown.

[0036] Figure 2a Shows Figure 1 A partial enlarged view of the labyrinth mixing device and combustion chamber.

[0037] Figure 2b It shows that Figure 2a A magnified view of a portion of a labyrinth mixing device and combustion chamber showing the high velocity gaseous gases inside the combustion chamber and the resulting different temperature zones.

[0038] Figure 3 The second oxidant injector is shown in a rear view of the combustion chamber housing along AA', showing the inlet passage and orifices through which the second oxidant gas is injected into the combustion chamber.

[0039] Figure 4 A front view of a labyrinth-type mixing device is shown, showing an annular series of closely spaced orifices through which a fuel and first oxidant mixture is fed to a combustion chamber.

[0040] Figure 5 An enlarged cross-sectional view of the nozzle is shown, with the main parts shown being the first inlet cylindrical hole, the second diffusion hole and the collimator output.

[0041] Figure 6 An enlarged cross-sectional view of an embodiment having an attached material delivery device (eg, a powder injector) is shown, illustrating the nature of the venturi-type design that allows powder to be injected axially into an expanding jet of gas.

[0042] Figure 7 The microstructure of a cermet type coating (WCCoCr sintered powder) obtained using the apparatus of the invention is shown as an example of a very hard coating that can be produced.

[0043] Figure 8a The microstructure of a first aluminum type coating (AlSi16Sc0.4Zr0.2 powder) obtained using the apparatus of the invention is shown as an example of processing an aluminum alloy without particles adhering to the barrel.

[0044] Figure 8b The microstructure after corrosion of the first aluminum type coating (AlSi16Sc0.4Zr0.2 powder) obtained by using the apparatus of the present invention is shown.

[0045] Fig. 9 The microstructure of a second coating of the aluminum (99.9% powder) type obtained using the apparatus of the invention is shown as an example for the treatment of aluminum alloys.

[0046] Fig.10 The microstructure of a bronze type coating obtained using the apparatus of the invention is shown as an example for the treatment of copper-based alloys.

[0047] Fig.11 The microstructure of a coating of a hot working tool steel type obtained with the apparatus according to the invention is shown as an example for the processing of steels and metal alloys. DETAILED DESCRIPTION

[0048] With reference to the accompanying drawings, Figure 1 A better understanding of the present invention may be obtained, Figure 1is a longitudinal cross-sectional view of a high velocity oxygen / air fuel (HVOAF) torch constructed in accordance with a preferred embodiment of the present invention. However, the disclosed embodiments are merely exemplary, and it should be understood that the invention may be embodied in many different and alternative forms.

[0049] from Figure 1 As can be seen in the figure, the HVOAF torch comprises a body 1 housing a labyrinth mixing device 2. The labyrinth mixing device 2 comprises two flanges 23 and 24 in the middle portion. The labyrinth mixing device 2 comprises a through axial bore 28 which is closed at its upstream end by a material delivery device such as an axial powder sprayer 6 which receives the end of a gas injection supply pipe 60 and the end of a coating material carrier gas supply pipe 61. The gas injection supply pipe 60 is at a higher pressure than the coating material carrier gas supply pipe 61.

[0050] The body 1 is fixed to the front part 3 of the gas torch, thereby forming a combustion chamber 4. The combustion chamber 4 is closed at its downstream end by a gas expansion nozzle 50, which is provided with an axial nozzle hole, which includes an inlet hole 52 and a subsequent outlet diffuser hole 51, which is open downstream of the outlet diffuser hole 51. The radial dimension of the inlet hole 52 should be slightly larger than the radial dimension of the outlet hole of the converging outlet part 31 of the combustion chamber 4, so as to prevent the spray powder flow from contacting the wall of the inlet hole 52.

[0051] The labyrinth mixing device 2 is provided with holes 25, 26 and 27 which connect the fuel-air feed 20 with the combustion chamber 4. Such holes are concentrically placed on the flanges 23 and 24 and at the downstream end of the mixing device 2, thereby creating two interconnected intermediate mixing volumes 21 and 22.

[0052] The fuel and air streams can be premixed outside the gas torch and injected into the body through the connector 7. After entering the fuel-air feed portion 20 of the mixing device 2, the fuel-air premix is ​​squeezed through the orifices of the first flange 23, thereby expanding in the next step into the first intermediate mixing volume 21. The same compression and expansion process is repeated through the second flange 24 and the second intermediate mixing volume 22 of the mixing device 2, after which the fuel-air mixture is injected into the combustion chamber 4.

[0053] Inside the combustion chamber 4, the oxygen flow is fed at two sequential locations, first through an array of narrow continuous slots 33 and then through a series of orifices 32 in the shape of an annulus, both of which are closely spaced circumferentially at the upstream end of the front part 3, as shown in FIG. Figure 3The combustion mixture is then ignited with the help of a spark plug 30 placed in a radial orifice downstream of the front portion 3. Such radial orifices terminate in a combustion chamber 4. This sequential array of fuel, air and oxygen injection points results in the formation of a plurality of combustion zones characterized by substantially different temperatures due to different dilutions and oxidant to fuel ratios, such as Figure 2b Schematically shown in . Near the wall of the cylindrical part at the most upstream end, the fuel-air mixture generates a region of generally high dilution in the combustion chamber, thereby forming a low-temperature region 40, which evolves into a boundary that surrounds the wall of the mixing device 2 until it embeds the particle jet 44. At the junction area between the labyrinth mixing device 2 and the front part 3, the second oxidant gas injectors 33 of the first array provide a sudden increase in oxygen saturation, resulting in a corresponding increase in the temperature of the gas combustion mixture in this combustion zone 41. A few millimeters downstream in the wall of the combustion chamber, the second oxidant gas injectors 32 of the second array provide an additional oxygen supply, thereby newly increasing the ratio of oxidant to fuel, and as a result, the gas temperature in this combustion zone is Figure 2b The two fluid streams are mixed together when reaching the vicinity of the low temperature zone 40, enveloping the particle jet 44 and forming a fourth combustion zone 43 with an intermediate temperature around it. In this way, the feed material is injected into the coldest area of ​​the combustion chamber and gradually heated in and along the entire spray gun nozzle 50.

[0054] In a preferred embodiment of the present invention, since the high-pressure gas injection flow (gas injection supply pipe 60) draws the low-pressure gas flow into the material conveying device 6 and then into the mixing device 2, so that the low-pressure gas flow passes through the axial hole (28) to reach the combustion chamber 4, the material conveying device 6 allows the implementation of a low-pressure carrier gas flow to carry the feed powder 30 material to the gas torch (coating material carrier gas supply pipe 61).

[0055] References

[0056] i L.-M.Berger.Application of hardmetals as thermal spraycoatings.Int.Journal of Refractory Metals and Hard Materials 49(2015),pp.350–364.

[0057] iiChang-Jiu,L.and G.-J.Yang.Relationships between feedstockstructure,particle parameter,

[0058] coating deposition,microstructure and properties for thermallysprayed conventional and nanostructured WC–Co.Int.Journal of RefractoryMetals and Hard Materials,39(2013),pp.2-17. iii T.Varis et al.FormationMechanisms,Structure,and Properties of HVOF-Sprayed WC-CoCr Coatings:AnApproach toward Process Maps.J.Therm.Spray Technol.Volume 23(6)August 2014,pp.1009-1018.

[0059] iv T.Schmidt,F. H.Assadi,H.Kreye:Development of a generalizedparameter window for cold spray deposition,Acta Materialia 54(2006),pp.729 / 742.

[0060] v Raletz,F.,Vardelle,M.and Ezo,G.:Critical particle velocity undercold spray conditions,Surface&Coatings Technology 201(2006),pp.1942 / 1947.

[0061] vi A.Vardelle et al.The 2016Thermal Spray Roadmap.Journal of ThermalSpray Technology,

[0062] Volume 25(8)December 2016,p.1376–1440.

[0063] vii L.-M.Berger,R.Puschmann,J.Spatzier and S.Matthews.Potential ofHVAF Spray Processes.Thermal Spray Bulletin 1 / 13,p.16–20.

[0064] viii Seiji Kuroda,Makoto Watanabe,KeeHyun Kim,and HiroshiKatanoda.Current Status and Future Prospects of Warm SprayTechnology.J.Therm.Spray Technol.Volume 20(4)June 2011,pp.653-676.

[0065] ix A.Verstak and V.Baranovski:AC-HVAF Sprayed Tungsten Carbide:Properties and Applications.Building on 100 Years of Success:Proceedings ofthe 2006 International Thermal Spray Conference,B.R.Marple,M.M.Hyland,Y.C.Lau,R.S.Lima and J.Voyer,Eds.,May 15-18,2006(Seattle,WA,USA),ASMInternational,Materials Park,OH,2006.

[0066] x G.Bolelli et al.Tribology of HVOF-and HVAF-sprayed WC–10Co4Crhardmetal coatings:A comparative assessment.Surface&Coatings Technology 265(2015)125–144.

[0067] xiV.Wesling,R.Reiter,L.Lau and G. nanoHVOF–Process technologyfor and properties of a new high density protective coating.Mat.-wiss.u.Werkstofftech.2014,45,No.6.

Claims

1. A high velocity thermal spraying apparatus for depositing material on a substrate as a surface coating, or for accumulating bulk material for additive manufacturing, comprising: a labyrinth-type mixing device (2) designed to mix a first oxidant gas and a fuel under pressure and to inject the resulting mixture into a combustion chamber (4), thereby forming a low-temperature diluted combustion mixture in the combustion chamber near the labyrinth-type mixing device, the first oxidant gas being air, a body (1) of the gas torch, which houses the connectors (7) for feeding fuel and oxidant gas and the labyrinth mixing device (2), air as the first oxidant gas and oxygen as the second oxidant gas, a front part (3) of the gas torch, which defines the internal geometry of the combustion chamber (4) by means of the labyrinth-type mixing device (2) and is connected downstream to a gas expansion nozzle (50) designed to receive the products of the combustion of the mixture and to form a high-speed gaseous jet, an ignition device (30) placed at the front portion (3) for starting the combustion of the combustion mixture in the combustion chamber, a material delivery device (6) designed to inject the spray material axially into the high-speed gas jet; a plurality of second oxidant gas injectors (32, 33), said plurality of second oxidant gas injectors (32, 33) being arranged at a junction area between said labyrinth mixing device (2) and said front portion (3) for separately injecting oxygen as said second oxidant gas upstream in said combustion chamber to promote said combustion and increase the oxidant to fuel ratio in a mixture of said fuel and said first oxidant gas from said labyrinth mixing device, said second oxidant gas injectors (32, 33) opening into said combustion chamber (4) at an upstream peripheral position of said combustion chamber relative to said gas expansion nozzle (50) to form at least two differential regions: a first diluted lower oxygen saturation region, thereby producing a cooler temperature region of said labyrinth mixing device surrounding said first oxidant gas and fuel; and a second higher oxygen saturation region, producing a hotter temperature region near an annular peripheral position of said second oxidant gas injectors upstream of said combustion chamber, thereby axially injecting spray material into said cooler temperature region of said combustion chamber and forming a particle stream which is accelerated and gradually heated downstream, And wherein the labyrinth mixing device (2) comprises one or more flanges (23, 24) and holes (25, 26, 27), wherein the one or more flanges (23, 24) define one or more mixing volumes (21, 22) between the body (1) and the labyrinth mixing device (2), and the holes (25, 26, 27) are all concentrically placed on the flanges (23, 24) and pass through the labyrinth mixing device (2), and are open at the downstream end of the labyrinth mixing device (2) for connecting the fuel-first oxidant feed part (20) of the labyrinth mixing device (2) with the combustion chamber (4), And wherein the labyrinth mixing device (2) further comprises a through axial hole (28), wherein the through axial hole (28) is used to inject the spray material into the combustion chamber (4). And wherein the material delivery device (6) includes at least two inlets and one outlet, wherein the one outlet terminates inside the axial hole of the labyrinth mixing device (2), the first inlet is used for a first carrier gas flow at a first pressure, the first carrier gas flow is used to carry the selected spraying material, and the second inlet is used for an injection gas flow with a second pressure, the second pressure is higher than the first pressure and higher than the pressure inside the combustion chamber (4), so that the first carrier gas flow with the spraying material is sucked into the labyrinth mixing device (2) and then sucked into the combustion chamber (4) and the gas expansion nozzle (50).

2. The high-speed thermal spraying equipment according to claim 1, characterized in that: The second oxidant gas injector (32, 33) comprises one or more sequential and spaced arrays of continuous slots and / or a series of orifices to allow independent injection of the second oxidant gas in one or more sequential and closely spaced injection points of the combustion chamber (4).

3. The high-speed thermal spraying equipment according to claim 1, characterized in that: The combustion chamber is designed to generate different combustion conditions within the geometry of the combustion chamber due to different local distributions of the mixture of the first oxidant gas and fuel and the separate upstream addition of the second oxidant gas.

4. The high-speed thermal spraying equipment according to claim 1, characterized in that: The low-temperature diluted combustion mixture is formed at the outlet of the holes of the labyrinth mixing device (2) in the combustion chamber.

5. The high-speed thermal spraying equipment according to claim 1, characterized in that: An oxygen-rich, high-temperature flame region (42) is formed in the combustion chamber downstream of the plurality of second oxidant gas injectors.

6. The high-speed thermal spraying equipment according to claim 1, characterized in that: The labyrinth mixing device (2) is partially accommodated inside the main body (1) of the gas torch, so that the labyrinth mixing device (2) is closed at its upstream end by the material delivery device (6), and its downstream end is located inside the combustion chamber (4), and wherein the main body (1) of the gas torch includes at least one connector (7), and the at least one connector (7) feeds the fuel and the first oxidant gas flow to the feed part (20) of the labyrinth mixing device (2).

7. The high-speed thermal spraying equipment according to claim 1, characterized in that: The geometry of the combustion chamber is defined between the labyrinth mixing device (2) and the converging shape of the front part (3) of the gas torch, wherein the front part opens toward the gas expansion nozzle (50).

8. The high-speed thermal spraying equipment according to claim 1, characterized in that: The properties of the gas of the injected gas stream flowing through the second inlet are selected for additional functions such as oxidation, fueling, dilution, chemical reaction enhancement or other.

9. High velocity thermal spraying equipment according to any one of the preceding claims, characterized in that The gas expansion nozzle (50) is provided with an axial nozzle bore comprising a first inlet cylindrical hole (52) followed by a second outlet diffuser hole (51) which opens downstream.

10. The high-speed thermal spraying equipment according to claim 9, characterized in that: The radial dimension of the first inlet cylindrical hole (52) of the gas expansion nozzle (50) is slightly larger than the outlet hole of the converging outlet portion (31) of the combustion chamber (4) to prevent the spray powder flow from contacting the wall of the first inlet cylindrical hole (52).

11. The high-speed thermal spraying equipment according to claim 9, characterized in that: The length of the gas expansion nozzle (50) is selected between 20 mm and 250 mm.

12. The high-speed thermal spraying equipment according to claim 9, characterized in that: The gas expansion nozzle (50) has a gas collimator device (53) at the output to control the supersonic gas expansion in the surrounding environment.

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