JP6125888B2 - Method for forming sprayed coating by plasma spraying method and method for manufacturing member for heat exchanger - Google Patents

Description

The present invention relates to a method for forming a thermal spray coating by a plasma spraying method capable of obtaining a thermal spray coating with high adhesion in a short construction period, and a method for manufacturing a member for a heat exchanger.

  In the thermal spraying method, powder materials such as metals and ceramics and wire materials are supplied to a combustion frame or plasma jet, and these are softened or melted, and sprayed onto the surface of the substrate at a high speed to form a thermal spray coating on the surface. This is a surface treatment technology to be formed. As such a thermal spraying method, atmospheric plasma spraying method, low-pressure plasma spraying method, high-speed flame spraying method, gas flame spraying method, arc spraying method, etc. are known, and by using these various spraying methods, it has excellent durability, A high quality film can be obtained.

  Among various thermal spraying methods, the plasma spraying method is suitable when it is desired to obtain a finer coating than a coating formed by flame spraying or arc spraying using a wire material. Further, the plasma spraying method is characterized by high safety because it eliminates the need for the combustion gas and oxygen gas required for the high-speed flame spraying method, for example. When the work to be coated is a large structure such as a building, or when it is installed in a place that is difficult to move, it is necessary to carry out construction by bringing thermal spray equipment. Plasma spraying is the best method when on-site construction is required and high quality coatings are required.

  In local construction, the plant or equipment in which the work is built is stopped to form the sprayed coating, so a short film-forming operation is desired, and it is important to improve the film-forming speed. is there. In order to increase the deposition rate, more material may be attached to the deposition surface in a certain time. 5A and 5B are schematic views for explaining a conventional thermal spraying method.

  In FIG. 5A, a thermal spray material 102 is supplied together with a carrier gas to a plasma jet 101 ejected from a nozzle 100 to generate a material frame 103 which is a flow of the thermal spray material melted and accelerated by the plasma jet 101. A state in which the thermal spray coating 105 is formed on the film formation surface 104 of the substrate 120 is shown. FIG. 5B shows a state where the supply amount of the thermal spray material 102 is doubled. These drawings are schematic views showing an example for comparing the states when the thermal spray coatings 105 and 106 having the same thickness and the same thickness as the thermal spray material are formed. The thermal spray coating 105 when the thermal spray material is a standard amount (FIG. 5A) is formed of four layers of thermal spray beads 101, and the thermal spray coating 106 when the thermal spray material is twice the amount (FIG. 5B). )) It is formed of two layers of sprayed beads 111.

  In general, it is known from experience that when the thermal spray material contains a large amount of Cr, the amount of generated fumes increases. The fume is obtained by agglomerating a part of the thermal spray material heated by the plasma jet 101, so that nano-sized particles that have been cooled and re-solidified in a soot shape. When fumes accumulate on the deposition surface 104 that is the layer between the sprayed beads 101 and 111 or the interface between the sprayed coatings 105 and 106 and the substrate 120, the adhesion of the sprayed coatings 105 and 106 is reduced. When the sprayed coating 105 having a constant thickness is obtained with the standard amount of the sprayed material 102 (FIG. 5A), the number of layers of the sprayed bead 101 is increased, and the amount of fumes is dispersed.

  When the sprayed coating 106 having a constant thickness is obtained in a short time with twice the amount of the sprayed material 102 (FIG. 5B), the thickness of each sprayed bead 111 is increased. When the thickness of the thermal spray bead 111 increases, the residual stress in the thermal spray coating 106 increases, and a part of the residual stress works as a shear stress that peels off the coating. In addition, more fumes accumulate between the layers of the laminated spray beads 111. These phenomena have a great influence on the adhesion of the thermal spray coating 106 and act to cause peeling.

  In order to obtain a sprayed film having a constant thickness in a short time by spraying a standard amount of sprayed material, the plasma spray gun can be handled by a robot to increase the scanning speed on the substrate. However, it is difficult to install a large robot in field construction, and an effective scanning speed cannot be obtained with a small traverser.

  The following techniques are known as methods for obtaining high adhesion of the thermal spray coating. For example, in Patent Document 1, the space between the spray gun and the film formation is an inert atmosphere. Patent Document 2 describes a method of sucking fume before reaching the film formation surface.

JP-A-2-225653 Japanese Patent Laid-Open No. 5-202463

  In the method using the inert atmosphere of Patent Document 1, a large amount of inert gas is required, and field construction is not realistic. Furthermore, the residual stress increases when a thick sprayed coating is formed, and the peeling phenomenon of the coating cannot be eliminated. In particular, when a thermal spray coating is formed on a member having a large area, it is considered that the influence of the residual stress is increased and the separation becomes easier. With respect to the method described in Patent Document 2 in which countermeasures against fume are taken, metal fine powder and high-temperature gas are sucked, so there is a high risk of ignition and it is difficult to ensure safety on site. A device for suction is required, and the spray gun and the suction device must be scanned at the same time, which makes manual work in a limited space difficult and prolongs the construction time in the field.

Therefore, in view of the problems of the prior art, the present invention enables on-site construction in a limited space in a short time, is highly safe during construction, and can be obtained with a thermal spray coating by plasma spraying that can obtain high adhesion. forming method, and an object thereof is to provide a method of manufacturing及beauty heat exchanger member.

In order to achieve the above objective, the following technical measures were taken. That is, in the method for forming a thermal spray coating according to the present invention, a thermal spray material is supplied into a plasma jet from a material port provided outside the tip of a nozzle for ejecting the plasma jet, and the molten thermal spray material is sprayed onto the deposition surface. In the method of forming a thermal spray coating by a plasma spraying method for forming a thermal spray coating, the material port includes a plurality of supply ports, and the thermal spray coating of the thermal spray coating that supplies the thermal spray material into the plasma jet from different directions by the plurality of supply ports. In the forming method, the median diameter (D50 particle size) of the thermal spray material supplied from each supply port is 35 μm to 100 μm, and the D10 particle size of the thermal spray material is 1/3 or more of the median diameter (D50 particle size). The carrier gas flow rate flowing through each supply port is 1 NLPM to 1 mm 2 of the minimum cross-sectional area in the port. 12NLPM, the total supply amount of the spray material of the plurality of supply ports is set to 80 g / min or more, a plurality of material frames are generated, and the plurality of material frames are sprayed onto the film formation surface. .

  According to the present invention, when supplying the thermal spray material to the plasma jet from different directions by a plurality of supply ports, the carrier gas flowing in each supply port is caused to flow at a predetermined flow rate, and the thermal spray material is supplied from the plurality of supply ports. Since a plurality of material frames are generated, the scanning range sprayed by one scan can be widened. For this reason, manual work can be performed in a short time, and the thermal spray bead can be thinned.

  Construction in a short time by manual work is possible, so a robot is not required and construction in a limited space is possible. It can be installed in the atmosphere, and there is no need to create a gas atmosphere, so safety is high. A thermal spray coating having the same layer structure as that formed when a single supply port is formed can be obtained. Since the thermal spray bead does not become thick, generation of residual stress can be suppressed and generated fumes can be dispersed. Therefore, the peeling phenomenon is suppressed and the adhesion of the thermal spray coating can be improved.

When the plurality of supply ports include two supply ports that generate two material frames, the minimum cross-sectional area in each supply port is 0.8 mm ^{2 to} 16.0 mm ² , and the supply port It is preferable that the spraying material supply angle is 65 ° to 115 ° with respect to the axis of the nozzle. In this case, the two material frames can be accurately controlled, and a high-efficiency and good thermal spray coating can be obtained.

It relates the spray material, the median diameter of the spray material supplied from the supply port (D50 particle diameter) of 3 5 μm~100μm, and D10 particle size median diameter of the spray material of (D50 particle diameter) 1 / 3 Ru der more. Since the powder of the heated with evaporable small particle size in a short time is reduced, it is possible to suppress the occurrence of fume, it is possible to further improve the adhesion.

  The thermal spray material that can be used in the method of the present invention is not limited, and is particularly effective when, for example, a thermal spray coating containing 15% or more of Cr in which generation of fume increases is formed.

  The plasma output for generating the plasma jet may be 30 kW to 180 kW. When the plasma output is 30 kW or less, the thermal spray material that is a powder cannot be sufficiently melted and accelerated, the film formation rate is reduced, and the film density is reduced. When the plasma output is 180 kW or more, the plasma spraying torch, the power source, and the cooling device become too large, which is unsuitable for on-site construction. The plasma output is the power consumed to generate the plasma jet.

The present invention is a method for producing a heat exchanger member in which a thermal spray coating is formed by a plasma spraying method on the surface of a structural member that receives combustion energy in a heat exchanger that heats water by combustion energy, wherein the thermal spray coating is the above-mentioned A method for producing a member for a heat exchanger, which is a coating obtained by the method for forming a thermal spray coating.

  According to the present invention, when the thermal spray coating is formed on the surface of the structural member for the heat exchanger, the scanning range sprayed by one scan is widened, so that the work can be performed in a short time, and the thermal spray bead is thinned. it can. Construction in a short time by manual work is possible, so a robot is not required and construction in a limited space is possible. It can be installed in the atmosphere, and there is no need to create a gas atmosphere, so safety is high. A thermal spray coating having the same layer structure as that formed when a single supply port is formed can be obtained. Since the thermal spray bead does not become thick, generation of residual stress can be suppressed and generated fumes can be dispersed. Therefore, the peeling phenomenon of the thermal spray coating formed on the heat exchanger member is suppressed, and the adhesion can be improved.

  According to the present invention, the construction can be performed in the air, and it is not necessary to create a gas atmosphere, so the safety is high. Since the scanning range sprayed by one scan becomes wide, construction in a short time by manual work becomes possible. It enables local construction in a limited space without the need for a robot. The thermal spray bead can be made thin, the occurrence of residual stress is suppressed, and the generated fumes are also dispersed, so that high adhesion of the thermal spray coating can be obtained.

It is a partial schematic diagram of a thermal spraying apparatus for carrying out a method for forming a thermal spray coating by a plasma spraying method according to an embodiment of the present invention. It is a graph showing an example of the particle size distribution of a thermal spray material. It is a perspective view of a test piece. (A) is the SEM photograph of the surface layer cross section of the test piece of Example 3, (b) is the SEM photograph of the surface layer cross section of the test piece of Comparative Example 6. (A) And (b) is a schematic diagram explaining the conventional thermal spraying method.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a partial schematic view of a thermal spraying apparatus 1 for carrying out a method for forming a thermal spray coating by a plasma spraying method according to an embodiment of the present invention. The plasma spraying apparatus 1 according to the present embodiment heats and melts a metal thermal spray material with plasma to form liquid particles, and the liquid particles are caused to collide with the deposition surface 20 at high speed by the plasma jet 10. It is an apparatus for forming. The plasma spraying method using electric energy as a heat source is a method of forming a film using argon, hydrogen, nitrogen, etc. as a plasma generation source. Since the heat source temperature is high and the frame speed is high, a material having a high melting point is used. It is possible to form a dense film.

  The plasma spraying apparatus 1 includes a material supply unit 2 that supplies a sprayed material, a plasma spraying torch 3 that ejects a plasma jet, a gas supply unit that supplies a primary gas and a secondary gas that are working gases to the plasma spraying torch 3, and plasma spraying A plasma power supply unit that supplies operating power to the torch 3, a voltage monitor unit that detects a voltage value that is actually applied, and a power supply unit that supplies the plasma spraying torch 3 based on the voltage value detected by the voltage monitor unit A power supply control unit that indicates a current value is provided. A part of the configuration of the material supply unit 2 and illustrations other than the plasma spraying torch 3 are omitted. The material supply unit 2 includes a powder storage unit that stores the material, a transport unit that transports the powder transported from the powder storage unit, and a material port that supplies the transported powder into the plasma jet 10 as the thermal spray material 26. 4. A gas cylinder for carrier gas fed into the material port 4 is provided. The form of the plasma spraying torch 3 is not limited. In this embodiment, the plasma spraying gun 3 is used for on-site construction.

  The plasma spray gun 3 includes a discharge electrode portion arranged around the gun axis, and the discharge electrode portion is composed of a cathode and an anode. The cathode is provided with a protruding electrode at the center of the axis, and an anode is disposed on the outer periphery of the cathode via an insulator. The cathode includes an anode terminal, and a part of the cathode forms a nozzle 5 for ejecting the plasma jet 10. The plasma power output for generating the plasma jet is adjusted to 30 kW to 180 kW. In the present embodiment, the plasma output for generating the plasma jet 10 is adjusted to 30 kW to 180 kW. When the plasma output is 30 kW or less, the thermal spray material 26 which is a powder cannot be sufficiently melted / accelerated, the film forming speed is reduced, and the film density is lowered. When the plasma output is 180 kW or more, the plasma spraying torch 3, the power source, and the cooling device become too large, which is unsuitable for on-site construction. The plasma output is the power consumed to generate the plasma jet.

  The nozzle 5 is configured along an axis extending in the direction to be sprayed, and a material port 4 for supplying a spray material is disposed outside the tip of the nozzle 5. The material port 4 is hollow and can spray the spray material 26 together with the carrier gas 25. In addition, the plasma spray gun 3 is connected to a supply hose from the gas supply unit, a power cable for supplying power from the power source, and the like.

  An arc is generated between the pair of discharge electrodes of the plasma spray gun 3, the working gas supplied from the gas supply unit is introduced into the arc to form a plasma state, and the plasma jet 10 is ejected from the nozzle 5. The thermal spray material 26 is supplied through the material port 4 into the jetted plasma jet 10 to generate the material frames 11A and 11B. The thermal spray material 26 becomes a material frame 11 that flies at high speed while being melted, and collides with the deposition surface 20. The melted thermal spray material 27 is sequentially deposited on the deposition surface 20 to form the thermal spray coating 30.

  The material of the base material 21 that can be used in the method of the present invention is not limited, and examples thereof include simple metals such as Fe, Al, Ti, Mg, and Ni, various alloy steels including stainless steel, and carbon steel. In particular, the method of the present invention can be applied to a structural member that receives combustion energy in a heat exchanger that heats water using the combustion energy, and the material of such a structural member is a carbon steel pipe or an alloy steel containing Cr. A steel pipe is used.

  The thermal spray material to which the method of the present invention can be applied is not limited, for example, a group of Cr, Al, Ta, Fe, Y, W, Nb, V, Ni, Co, Ti, Ta, B, Si, Mo, Zr, Fe A material composed of carbide, boride, or a combination of one or more elements selected from In particular, coating with a thermal spray material containing a large amount of Cr component has an advantage that good high-temperature oxidation resistance and sulfidation corrosion resistance can be obtained. On the other hand, when a large amount of Cr is contained like a thermal spray material having a composition containing 15% or more of Cr, generation of fumes generally increases. Therefore, the method of the present invention capable of suppressing fume can be effectively operated. it can.

  As shown in FIG. 1, the material port 4 is composed of two supply ports 6 arranged outside the tip of the nozzle 5. In this embodiment, two supply ports 6 are provided, but three or more supply ports may be provided. The form of each supply port 6 is not limited to that shown in the figure, and any form may be used as long as the sprayed material is blown out.

  Each supply port 6 is disposed at an angle θ of 90 ° with respect to the axis of the nozzle 5 near the tip of the nozzle 5. The front end 6 a of each supply port 6 is located in the vicinity of the side of the plasma jet 10 ejected from the nozzle 5, and the spray material 26 is introduced into the plasma jet 10 immediately after being blown from each supply port 6. The The axes of the two supply ports 6 and 6 are on the same straight line, and the front end ports 6a and 6a are opposed to each other. With such an arrangement of the supply ports 6, the thermal spray material 26 is introduced into the plasma jet 10 from two different directions orthogonal to the jet direction of the plasma jet 10.

  The thermal spray material 26 placed on the carrier gas 25 is supplied into the plasma jet 10 from two different directions to generate the first and second material frames 11A and 11B as shown in the figure. These two material frames 11A , 11B is sprayed onto the deposition surface 20 to form a film. In this embodiment, since there are two supply ports, two material frames are generated. However, when the number of supply ports is four, for example, four, the number of material frames is four. The number of supply ports does not have to be the same as the number of material frames, and the number of supply ports may be larger than the number of material frames. For example, the number of supply ports may be four and the number of material frames may be two. In short, a plurality of material frames independent of each other may be generated by using a plurality of supply ports.

Preferred minimum cross-sectional area of the supply port 6 is 0.8mm ² ~16.0mm ^2, more preferably 1.5mm ² ~7.0mm ^2. If the minimum cross-sectional area is too small, it cannot be fed in a sufficient supply amount, and if it exceeds 16.0 mm ² , the density of the powder becomes non-uniform inside the port, and the powder cannot be accelerated uniformly by the carrier gas 25. The cross-sectional shape of each supply port 6 is preferably circular, but may be, for example, an ellipse or a rectangle, and the cross-sectional area may be reduced by narrowing the middle part of each supply port 6 and then widened from there. It is good also as the shape which extended the front-end | tip exit of the supply port 6. FIG. In the present embodiment, the supply angle θ of the thermal spray material 26 by each supply port 6 is 90 ° with respect to the axis of the nozzle 5 that is the jet direction of the plasma jet 10, but the supply angle θ is 65 ° to 115 °. It is preferable that If the supply angle θ of the thermal spray material 26 is smaller than 65 °, the material frame 11 is not divided into a plurality of parts, and if it is larger than 115 °, the molten powder easily adheres to and accumulates on the nozzle 5 so that stable thermal spraying is performed. It becomes difficult. The angle adjustment mechanism of each supply port 6 may be a stationary type or a variable type using a conventional configuration.

  The flow rate of the carrier gas 25 flowing into each supply port 6 is preferably 1 NLPM to 12 NLPM, more preferably 3 NLPM to 8 NLPM, per square mm of the minimum cross-sectional area in the port. There is a correlation between the flow rate of the carrier gas 25 and the blowing speed of the thermal spray material 26. Therefore, the flow rate of the carrier gas 25 needs to be adjusted according to the plasma output and the powder particle size. For example, when the flow velocity of the plasma jet 10 is increased with a high plasma output, in order to obtain a plurality of material frames, it is necessary to increase the flow rate of the carrier gas 25 regardless of the thermal spray material. When the flow rate of the carrier gas 25 is smaller than 1 NLPM, the action of transferring the thermal spray material introduced into the plasma jet to a position away from the axis becomes weak, and the material frames are not independent from each other. When the flow rate of the carrier gas 25 is larger than 12 NLPM, some of the powder escapes across the plasma jet 10, and appropriate heating and acceleration cannot be applied to the powder, making it difficult to form a sound film. .

  The supply amount of the thermal spray material 26 introduced into the plasma jet 10 is 80 g / min to 500 g / min, more preferably 150 g / min to 300 g / min. The supply amount here is the total amount of the thermal spray material supplied through a plurality of supply ports. If the supply amount of the thermal spray material 26 is less than 80 g / min, the effect of forming a film in a short time cannot be achieved, and if it exceeds 500 g / min, the thermal spray bead 31 tends to be thick, which is influenced by residual stress and fume. Adhesion decreases.

  The plasma jet 10 formed by adjusting the plasma power supply output to 30 kW to 180 kW is ejected from the nozzle 5, and the supply angle θ of the thermal spray material 26 supplied thereto, the blowing speed of the thermal spray material 26, and the supply amount of the thermal spray material 26 are set. By adjusting to a value satisfying the above conditions, a plurality of good material frames 11A and 11B can be obtained.

  In order to obtain a plurality of material frames 11A and 11B, the thermal spray material 26 must be sprayed to the plasma jet 10 sprayed outward. Therefore, it is indispensable that the position for supplying the thermal spray material 26 exists outside the nozzle 5, so that each supply port 6 is in the vicinity of the outside of the tip of the nozzle 5 directed toward the film formation surface 20. The distance n between the tip outlet 6a of each supply port 6 and the plasma jet 10 is preferably 4 mm to 9 mm. When three or more supply ports are arranged, the outlets of the supply ports need only exist on the same circumference with the axis of the nozzle as the center.

  With a plurality of good material frames, the amount of the molten sprayed material 27 contained in each material frame 11A, 11B is sufficient, and the adjacent material frames 11A, 11B are spaced apart from each other without being overlapped. It is a material frame that has an appropriate extent toward the surface 20. Adjacent material frames 11A and 11B are not separated from each other without overlapping each other, but it does not mean that the thermal spray materials 27 included in the respective material frames 11A and 11B are not mixed at all. This means that the individual sprayed beads 31 are separated to a state where they can be formed.

The distance w between the closest edges of the material frames 11A and 11B on the deposition surface 20 is about 3 mm to 20 mm. If the distance between the material frames 11A and 11B is too close, a portion having a large thickness of the sprayed bead 31 is formed, and if it is too far, the one-time spraying range becomes large and the construction work becomes difficult. Each material frame 11A in the deposition surface 20 on the area where 11B spreads is ^{2cm 2 ~8cm} 2 about. In order to form the thermal spray coating 30 by stacking a number of thin thermal spray beads 31, the operation of manually reciprocating the plasma thermal spray gun 3 is repeatedly performed. For example, the scanning speed is about 3 m / min to 50 m / min, and the thickness of the thermal spray bead 31 formed by one scanning is about 70 μm to 150 μm.

  In order to obtain a constant film thickness, a number of thin sprayed beads may be stacked, but if the thickness of the sprayed bead 31 formed by one scan is less than 50 μm, a long time is required for the construction. When the thickness of the thermal spray bead 31 is larger than 300 μm, peeling easily occurs due to the influence of residual stress and fume.

  In the plasma spraying method, it is possible to cope with spray materials having various particle diameters by changing the plasma output and the amount of plasma gas which are the spraying conditions. For example, when the particle size is large, the thermal spray material is melted under a spraying condition with high heating capability, and when the particle size is small, the heating capability is lowered to suppress generation of fumes due to overheating.

  In the present invention, it is important to use a thermal spray material having a particle size distribution adjusted to a predetermined value after generating a plurality of material frames. In particular, in order to suppress the generation of fume with a thermal spray material having a high Cr content, it is only necessary to reduce the powder having a small particle diameter that is easily evaporated. However, it is not practical to use a thermal spray material that completely eliminates a powder having a small particle size, and there is a particle size distribution in the thermal spray material, and powders of small to large particles are mixed. Thermal spraying conditions are selected in accordance with the powder having the largest particle size and the center particle size, but fume is likely to be generated because the heating conditions are too high for powders having a small particle size.

  In order to suppress fume, it is only necessary to select a thermal spray material that contains a large amount of powder with a large particle size. To obtain a dense and good quality thermal spray coating, select a thermal spray material that also includes a medium particle size powder. is necessary. In the present invention, the spray material is selected using a median diameter index representing the relationship between the cumulative volume of powder and the particle size, thereby reducing the proportion of powder having a small particle size and suppressing the generation of fumes. The volume cumulative amount represents what percentage of the total amount of particles equal to or less than a specific particle size. For example, D10 particle size is a particle that accumulates from a small particle size to a cumulative volume amount of 10%. It represents the diameter.

  A thermal spray material having a median diameter (D50 particle size) of 30 μm to 100 μm and a D10 particle size of 1/3 or more of the median diameter (D50 particle size) may be selected. More preferably, the median diameter (D50 particle diameter) is in the range of 35 μm to 80 μm, and the D10 particle diameter is ½ or more of the median diameter (D50 particle diameter). Among them, the D10 particle size is preferably 15 μm or less, and more preferably a thermal spray material in which fine particles of 15 μm or less are not present. FIG. 2 shows the particle size distribution of a thermal spray material having a median diameter (D50 particle size) of 77 μm and a D10 particle size of ½ or more of the median diameter (D50 particle size).

  If the median diameter (D50 particle size) is smaller than 30 μm, it will be difficult to suppress the generation of fume because of excessively small powder, and if it exceeds 100 μm, it will be difficult to form a dense film and the film quality will deteriorate. If a thermal spray material that satisfies the above conditions is used, the mixing ratio of small-diameter powder that becomes superheated in the plasma jet 10 in a short time is reduced, and the evaporation amount is remarkably reduced. If the amount of evaporation can be reduced, the generation of fumes can be suppressed.

Incidentally, the true specific gravity of the powder constituting the spray material is ^6g / cm ^{3 ~12g} / cm 3 Tosureba ^well, and more preferably ^{7g / cm 3 ~9g / cm 3} . By using powder having the true specific gravity in the same range, a plurality of clearly divided material frames can be obtained. If the true specific gravity of the powder is less than 6 g / cm ³ , for example, the material frames overlap each other, and if it is greater than 12 g / cm ^3, some powder penetrates the plasma jet 10 from the material frame. As a result, proper melting and acceleration by the plasma jet 10 become difficult.

  As described above, by using the thermal spray coating forming method of the present embodiment, the generated two material frames 11A and 11B can be sprayed onto the film forming surface 20 to form a film. Therefore, it is possible to form the sprayed beads 31 in a wider range by one scan without increasing the relative speed of the plasma spray gun 3 with respect to the film formation surface 20. Therefore, the application of the thermal spray coating 30 is completed only by repeating the scanning of the plasma spray gun 3 on the film formation surface 20 by half the number of times of the conventional method. The obtained thermal spray coating 30 is obtained by laminating only the thin thermal spray beads 31, and the thermal spray coating 30 having a thin film structure can be obtained in a short time. For example, the same coating structure as that of the thermal spray coating shown in FIG. 5 can be obtained with a supply amount twice that of the thermal spraying method shown in FIG. 5A using a single supply port. Since the thermal spray bead 31 does not become thick, the generation of residual stress can be suppressed and the generated fumes can be dispersed. In addition, since the particle size distribution is appropriately adjusted, the amount of evaporation at the time of thermal spraying can be remarkably reduced, and fume can be reduced.

  Therefore, the peeling phenomenon can be effectively suppressed, and the adhesion of the thermal spray coating 30 can be improved. In addition, since it can be constructed manually in a short time, it does not require a robot and can be constructed in a limited space. It can be installed in the air and there is no need to create a gas atmosphere. As a result, it is possible to perform on-site construction in a short time in a limited space, the safety during construction is high, and high adhesion of the thermal spray coating 30 can be obtained.

  As a typical example to which the method for forming a thermal spray coating of the present invention is applied, there is a heat exchanger member in which a thermal spray coating is formed on the surface of a structural member that receives combustion energy in a heat exchanger that heats water by combustion energy. . More specifically, it is a coal fired boiler, and is particularly effective for the construction of a surface coating with a sprayed coating on the boiler tube or the like. In the case of coating to repair the boiler tube surface, construction on site is essential, and it is a work at a high place with a narrow scaffold. For this reason, a large robot cannot be used and spraying is performed manually. However, since the scaffolding is small and the installation place is limited, the number of spraying apparatuses that can be used is limited. By using the thermal spray coating forming method of the present invention, it is possible to perform a wide range of construction in a short time with a small number of thermal spraying apparatuses, and the construction period can be significantly shortened compared to the conventional method. Moreover, since the applied sprayed coating is difficult to peel off and has high adhesion, the durability of the boiler exposed to a high-temperature flame can be significantly improved.

  Hereinafter, the present invention will be described in more detail with reference to examples. The present invention is not limited to the examples. Using the method of the present invention for forming a film with a plurality of material frames and the conventional method for forming a film with a single material frame, a test piece on which a thermal spray coating was formed was prepared and a thermal shock test was performed. The base material of the test piece is SS400 steel for general structure manufactured by simulating a boiler product in which the side surfaces of two short pipes are connected to each other. Since the fumes are likely to be deposited in preference to the concave portion of the base material, the test piece has a shape having irregularities shown in FIG. A test piece was produced by forming a sprayed coating on one side of the substrate. The dimensions of each part of the test piece shown in FIG. 3 are as follows. Pipe inner diameter φa: 40 mm, pipe outer diameter φb: 50 mm, connecting portion width c: 15 mm, plate-side portion width d: 50 mm, and plate-like portion thickness e: 5 mm.

  After the substrate is degreased with an organic solvent as a pre-spraying treatment, it is roughened by blasting with alumina grit having a particle size of F60, resulting in a film thickness of 1 mm under the conditions shown in Examples 1 to 6 and Comparative Examples 1 to 8. Thermal spraying was applied. The thermal spray materials of Examples 1-6 and Comparative Examples 1-8 were Ni-50 wt% Cr and Ni-20 wt% Cr.

  Thermal shock test: A test piece on which a sprayed coating is formed is heated in an electric furnace at 700 ° C. for 30 minutes, then taken out of the furnace, and cooled to a temperature of 80 ° C. or less by water cooling as one cycle. Was repeated 10 cycles. The surface of the sprayed coating was observed with a magnifying glass every cycle, and the presence or absence of cracks or peeling was visually observed.

  Plasma output of Examples 1 to 6 and Comparative Examples 1 to 8, number of supply ports (number of material frames), minimum cross-sectional area in each supply port, Cr concentration of sprayed material, median diameter of sprayed material (D50 particle size) Table 1 shows the D10 particle size, the amount of sprayed material supplied from all supply ports, the carrier gas flow rate at each supply port, and the test results. The relationship between the cumulative volume of the powder and the particle size was measured with a laser scattering / diffraction particle size distribution analyzer. The ○ mark in the test results indicates no peeling in the thermal shock test, and the X mark indicates that there is peeling during thermal spraying or in the thermal shock test. FIG. 4A is a SEM photograph of the cross section of the surface of the test piece of Example 3. Since fume is dispersed, defects that deteriorate the characteristics of the film between the interface between the substrate and the film and between the film layers are recognized. Absent. FIG. 4B is a SEM photograph of the surface layer cross section of the test piece of Comparative Example 6. It can be seen that the thermal spray coating of Comparative Example 6 has few layers, and a large amount of fumes are deposited on the substrate and coating interface and between layers to form coating defects.

  The disclosed embodiments and examples are illustrative and not restrictive. For example, another configuration may be provided in the film forming apparatus for carrying out the method for forming a thermal spray coating of the present invention as necessary.

DESCRIPTION OF SYMBOLS 1 Plasma spray apparatus 2 Material supply part 3 Plasma spray gun 4 Supply port (material port)
5 Nozzle 10 Plasma jet 11A, 11B Material frame 20 Deposition surface 21 Base material 25 Carrier gas 26 Thermal spray material 27 Molten thermal spray material 30 Thermal spray coating 31 Thermal spray bead

Claims (5)

Thermal spray coating by plasma spraying method in which a thermal spray material is supplied into the plasma jet from a material port provided outside the tip of the nozzle that ejects the plasma jet, and the molten thermal spray material is sprayed onto the deposition surface to form a thermal spray coating In the formation method of
The material port is composed of a plurality of supply ports, and a method for forming a sprayed coating in which the sprayed material is supplied into the plasma jet from different directions by the plurality of supply ports, and the median of the sprayed material supplied from each supply port The diameter (D50 particle size) is 35 μm to 100 μm, and the D10 particle size of the thermal spray material is 1/3 or more of the median diameter (D50 particle size). A plurality of material frames are generated by setting the number of sprayed materials of the plurality of supply ports to 1 NLPM to 12 NLPM per square mm of the minimum cross-sectional area, and a total supply amount of the sprayed material of the plurality of supply ports being 80 g / min or more. A method for forming a sprayed coating by a plasma spraying method, characterized by spraying on a film forming surface. Wherein a minimum cross-sectional area of 0.8mm ² ~16.0mm ² in the supply port, be 65 ° to 115 ° with respect to the feed angle of the spray material according to the respective supply ports axis of the nozzle A method for forming a thermal spray coating by plasma spraying according to claim 1. The method of forming a thermal spray coating by plasma spraying according to claim 1 or 2, wherein the thermal spray material contains 15% or more of Cr . The plasma output for generating the said plasma jet is 30 kW-180 kW, The formation method of the sprayed coating by the plasma spraying method in any one of Claims 1-3 characterized by the above-mentioned. In a heat exchanger for heating water by combustion energy, a method for producing a heat exchanger member in which a thermal spray coating is formed by a plasma spraying method on the surface of a structural member that receives combustion energy ,
The method for producing a member for a heat exchanger, wherein the thermal spray coating is a coating obtained by the method for forming a thermal spray coating according to any one of claims 1 to 4 .