Brazing material having metal powder molded and brazing method in manufacturing of fin tube type heat exchanger using the same

Abstract

To provide a brazing material which is a new molding, and a method for improving a brazing process of a fin tube type heat exchanger using the same.SOLUTION: Powder is solidified into a prescribed shape still as power and formed into a molding without melting metal power obtained by pulverizing a metal serving as a brazing material such as a nickel alloy. The metal power having a particle diameter range of a median diameter 20-75 μm is contained by 90% or more, and the range of filling factors of the metal powder in the molding is 50-80%. A fin tube type heat exchanger 100 is structured such that a groove 112 obtained by notching a part of a tube through-hole 111 of a fin 110 to the outer peripheral side is provided. A brazing material 200 formed by molding the metal powder molded into a rod shape is inserted through the groove 112, and heat is input to execute brazing.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present invention relates to a brazing material. The present invention also relates to a brazing method for manufacturing a fin-tube heat exchanger using the brazing material of the present invention. A fin-tube heat exchanger is a structure that has a heat sink made of multiple layers of fins made of metal or ceramic, with tubes that pass through it, and the fins and tubes are joined by brazing. [Background technology]

[0002] Below, (1) a conventional brazing material and (2) a conventional method for manufacturing a fin-tube heat exchanger will be described in order. (1) Conventional brazing materials Conventional brazing materials are made from metals suitable for brazing, such as copper or copper alloys, aluminum or aluminum alloys, or nickel or nickel alloys, and may contain trace elements. Their melting points are above 450°C, and when heated, they melt above their melting point and solidify below their melting point. Some brazing materials also contain flux as a solvent. Two types of conventional brazing material compacts are known: a rod-shaped brazing material made of a metal block, and a paste-like brazing material containing powdered metal and having fluidity.

[0003] The first compact, the rod-shaped brazing material, is a metal ingot made by melting and sintering the metal material. It is often provided as a rod with a rectangular or circular cross section. The metal is melted and sintered, and is dense and has a so-called packing ratio (the ratio of apparent density to true density) of 95% to 100%. Basically, metal blocks contain metal oxides. Therefore, in order to remove these metal oxides, flux and solvents may be included in the brazing material of the metal block. These flux and solvents are not molten and widely dispersed within the metal, but are scattered within the metal block as small nodules of flux and solvent. In this case, the filling rate of the entire compact varies depending on the volume of the binder and solvent, but the filling rate of the metal block other than the small nodules of flux and solvent remains high, at 95% to 100%, and is still high density. There are a variety of binders available, including mixtures of polymeric materials such as polymethacrylic acid, polyacrylic acid, polymethacrylic acid esters, and polyacrylic acid esters with ethers, esters, alcohols, and water that dissolve these materials. This first compact, a rod-shaped metal brazing material, has been used for a long time and is relatively inexpensive to procure, but it also has many disadvantages. For example, since the metal block is solidified into a rod shape, it may be difficult to accurately abut the thick, linear rod-shaped brazing material against narrow brazing areas or non-linear, curved brazing areas, which can make the work take a long time. In addition, since the brazing metal is melted during the molding process and then sintered to form a dense structure, the brazing heat is only directly input to the outer surface, and the specific surface area is not large, so heat diffusion to the internal metal occurs through heat conduction, and the heat input efficiency cannot be said to be good.

[0004] The second type of compact, paste-type brazing material, contains the metal that will be used as the brazing base material in the form of metal powder, which is then mixed with a binder to create a highly viscous, fluid paste. Silver brazing paste containing flux is widely used. Because it is a fluid paste, it can be squeezed out in fixed amounts using a dispenser, making it widely used for brazing. It is also convenient for application to flat substrates using screen printing. Additionally, brazing filler metals such as nickel alloys, which have been attracting attention in recent years, are hard and difficult to process, so a technology has become popular in which they are powdered using an atomization method, mixed with a binder, and used as a paste. This second compact, a paste-like brazing material, is relatively easy to handle since it can be simply squeezed out of a dispenser and applied to the area to be brazed, but it also has many disadvantages. Furthermore, it is difficult to apply paste brazing material directly from the dispenser outlet to the inside of the equipment or to hidden areas where the brazing point is not exposed. Therefore, the only option is to first apply it to the area near the brazing point, then apply heat to melt and liquefy the brazing material, and then allow it to travel by capillary action to the inside of the equipment or to the hidden brazing point. As a result, there are disadvantages such as residual brazing material adhering to the traces of the material, which can mar the appearance and result in brazing material loss. Furthermore, when using a paste-type brazing material, after the brazing material has spread to the brazing point, a process of evaporating and drying the binder, etc. is required, which is time-consuming and costly.

[0005] (2) Conventional manufacturing method for finned tube heat exchangers Next, a method for manufacturing a finned tube heat exchanger according to the prior art will be briefly described. The main components of fin-tube heat exchangers used in water heaters and the like are a combination of fins, which act as radiators, and tubes, which act as heat transfer pipes through which a heat medium circulates.

[0006] FIG. 9 is a diagram simply showing the configuration of a fin-tube heat exchanger to be brazed using a brazing material according to the prior art. 9(a) is a perspective view of the fin 10 viewed from a slight angle with the surface of the fin 10 through which the tube 20 is inserted facing the front, and FIG. 9(b) is a longitudinal cross-sectional view taken along the longitudinal centerline of the fin 10 with the surface through which the tube 20 is inserted facing the front. In other words, it is a cross-sectional view taken vertically through the center of the tube 20 and the groove 14 (described later). Note that the longitudinal cross-section in FIG. 9(b) is shown hatched. The multi-layered fin 10 has a plurality of heat dissipation fins 11 stacked at predetermined intervals, each of which has a tube through-hole 12 penetrating through it, and a tube 20 inserted through the tube through-hole 12.

[0007] The fins 10, which act as heat sinks, are made by pressing a thin metal plate to form tube insertion holes, then cutting it to the specified dimensions. The tube insertion holes are formed to match the outer shape of the tubes. They can be circular or flat. Fin materials are often made of stainless steel or copper alloys due to their moldability, heat transfer properties, and light weight. A fin-tube heat exchanger is configured by stacking a predetermined number of fin materials (e.g., several hundred sheets) at predetermined intervals (e.g., several millimeters) according to the dimensions of the heat exchanger, and arranging the fins 10 in multiple layers. When these multi-layered fins 10 are stacked, all of the tube through-holes drilled in the fins 10 are aligned in the same position, forming a continuous hole space. Although there may be one tube through-hole 12, there are often multiple tube through-holes 12. This is because, in order to improve the circulation performance of the heat transfer medium, a U-shaped curved portion is provided at the end of the tube to turn the circulation path back and forth across the fins 10 multiple times.

[0008] The tubes 20 are hollow heat transfer tubes through which a heat transfer medium circulates, and are configured so that a liquid or gaseous heat transfer medium circulates inside. Stainless steel, copper, or copper alloy pipes are often used as the material for the tubes 20 in terms of workability, heat transfer, workability, and corrosion resistance. In cases where the multilayered fins 10 are moved back and forth multiple times to improve the heat transfer medium circulation performance, a curved pipe section is often inserted into the end of the tubes later to form a so-called U-shaped bent section. As shown in FIG. 9, tubes that serve as heat transfer tubes are inserted into the tube through holes formed in the overlapping of the multi-layered fins 10. In addition, a tool called a billet, which expands the inner diameter of the tube 20, is inserted into the end of the tube, and the outer diameter of the tube is slightly expanded in proportion to the outer diameter.By expanding the diameter of the tube, the outer edge of the tube can be made to adhere tightly to the inner edge of the tube through hole in the fin material.

[0009] In the manufacturing process of a conventional fin-tube heat exchanger, the outer periphery of the tube is brazed to the inner periphery of the tube through-hole of the fin. Here, since the heat dissipating fins 11 of the multi-layered fins 10 are stacked one on top of the other with very narrow gaps between them, it is not possible to directly insert the bar-shaped brazing material 30a made of a metal block into the interior. The area to be brazed is the contact area 13 between the outer periphery of the tube 20 inside the multi-layered fin 10 and the inner periphery of the tube through-hole 12 of each heat dissipation fin 11. However, because this is the narrow inner part of the multi-layered fin 11, it was difficult with conventional technology to directly access the rod-shaped brazing material 30a made of a metal block. Therefore, as shown in FIG. 9, grooves 14 are provided on the outer periphery of the fins 11 to which rod-shaped brazing material 30a made of a metal block is abutted, and the brazing material 30a is placed and attached in the grooves 14. Heat is applied to melt the brazing material 30a, and the molten brazing material is transported by capillary action through the narrow gaps between the fins 11 to the joints 13, causing the "wet" to spread at the joints.

[0010] The brazing procedure in the prior art will now be described. FIG. 10 is a diagram showing a case where a bar-shaped brazing material 30a made of a metal block is used in the prior art. 10(a) and 10(b) show an example in which a rod-shaped brazing material 30a made of a metal block is placed in the groove 14. Since it is a hard rod-shaped member, it is placed along the linear groove 14.

[0011] 10(c) and 10(d) are diagrams showing the case where a paste-like brazing material 30b used in the prior art is used. A paste-like brazing material 30 is applied in a heap into the groove 14 using a dispenser (not shown). Even with the use of paste-like brazing material 30b, the portion to be brazed is the abutting portion 13 between the tube 20 inside the multilayered fin 11 and the tube through-hole 12, and since it is difficult to insert a dispenser into the narrow width of the fin 11, it remains difficult to directly access the abutting portion 13. Therefore, the paste-like brazing material 30b is applied to the groove 14 by being squeezed out from a dispenser (not shown).

[0012] When using the rod-shaped brazing material 30a of the metal block shown in Figures 10(a) and 10(b), heat is input from the outside to melt the brazing material 30a to a predetermined temperature, as shown in Figure 11(a). Note that since the rod-shaped brazing material 30a of the metal block is exposed at the top end, heat can be input from multiple points. Although the gap between the fins 10 is narrow, the molten brazing material is guided downward by capillary action, resulting in the state shown in Figure 11(c). When using the paste-like brazing material 30b shown in Figures 10(c) and 10(d), heat is input from the outside to melt the brazing material 30b to a predetermined temperature, as shown in Figure 11(b). Note that, because the paste-like brazing material 30b is also applied in an exposed state at the top end, heat can be input from multiple points. Although the gap between the fins 10 is narrow, the molten brazing material is guided downward by capillary action, resulting in the state shown in Figure 11(c). 11(c) is a diagram enlarging the gaps in the fins 10 to clearly show the state occurring in the gaps in the fins 10, focusing on the vicinity of the joints 13. In the gaps in the fins 10, the brazing material melts and travels down the surface of the fins 10 by capillary action, leaving traces as it reaches the joints 13, causing the "wet" to spread at the joints 13, thereby carrying out the brazing process.

[0013] [Patent Document 1] Japanese Patent Publication No. 55-092288 DISCLOSURE OF THE INVENTION [Problem to be solved by the invention]

[0014] However, the above-mentioned conventional techniques have the following problems. The problem with the brazing material 30 of the prior art is that it can be applied to locations that are easily accessible from the outside, but is difficult to apply to locations that are difficult to access. The same is true for the fluid paste-like brazing material 30b. When the brazing point is inside an equipment structure or when the accessible space is narrow, it is difficult to access with the highly viscous paste brazing material 30b. In such cases, the brazing process must be performed by applying a large amount of the paste brazing material 30b near the brazing point, applying heat, and conducting and flowing the melted brazing material into the brazing point.

[0015] A typical example is the joining of the fins 11 and the tubes 20 in a fin-tube heat exchanger 10. The brazing points 14 of the fin-tube heat exchanger 10 are located inside the narrow gaps between the many closely stacked fins 11 as described above, making them difficult to access from the outside. Therefore, in order to use the conventional paste-like brazing material 30b, it is necessary to apply a large amount of the paste-like brazing material 30b to the outer edge of the fin and then apply heat to the fin so that the molten brazing material flows along the surface of the fin and into the through-hole inside the fin.

[0016] However, the paste-like brazing material 30b of the prior art and the brazing method using it have the following problems. The first problem is that as the filler metal flows to the brazing point, in some places the heat is radiated rather than conducted by the metal, which reduces the heat input efficiency during the brazing process and can result in poor brazing. The second problem is that the brazing material flows over the flat surfaces of the fins 11 and remains attached to the surfaces of the fins 11, resulting in a large loss of brazing material and impairing the aesthetic appearance. The third problem is that the brazing material that melts and flows on the surface of the fins 11 blocks the heat dissipation space or heat reception space between the fins 11 and the atmosphere, reducing the heat exchange efficiency on the surface of the fins 11.

[0017] The present inventors have investigated ways to improve joining in the fin-tube heat exchanger 10 by using a conventional metal block brazing material 30a instead of the conventional paste-like brazing material 30b, and have devised the configuration shown in Fig. 12. However, they have also found that there are still problems to be solved. The configuration proposed by the present inventors and shown in FIG. 12 will be described below, followed by an explanation of the problems that still remain in this method.

[0018] Fig. 12 is a diagram showing an example of the structure of a new fin-tube heat exchanger devised by the present inventors. The example structure shown in Fig. 12 is a new example of the structure devised by the present inventors, and is not known in the prior art, nor is it in any publicly known literature. In the structural example of the new fin-tube heat exchanger, as shown in Figure 12, the brazing point is not a groove on the outer edge of the fin, but a separate groove is provided immediately above the tube through-hole, which is the brazing point. In other words, the groove is provided as a recess that is connected to the tube through-hole and is integrated.

[0019] FIG. 13 is a diagram showing a brazing process assumed for the new fin-tube heat exchanger devised by the present inventors and having the configuration shown in FIG. As shown in Figure 13, a conventional metal block brazing material is inserted straight through into the groove provided adjacent to the tube through-hole and set in place, and in this state heat is applied to the conventional metal block brazing material, melting the brazing material by applying heat, and the molten brazing material is transported along the fin surface to the joint in the center by capillary action, and the wetting process is carried out so that the "wetness" spreads at the joint 13.

[0020] The brazing method for a fin-tube heat exchanger shown in Figure 13 has the advantage of being able to solve all of the first, second, and third problems that were issues with the brazing methods of the prior art described above. In other words, the first problem, which is a decrease in the heat input efficiency that becomes radiant heat, can be solved because there is no process of heat flowing between the fins, so there is basically no need to rely on radiant heat from the fin surface. Furthermore, the second problem of brazing material being wasted and spoiling the appearance can be solved by the fact that the groove and the brazing point are adjacent to each other, so there is no process of the brazing material flowing over the surface of the fin. In addition, the third problem, where the brazing material blocks the heat dissipation space between the fins and the atmosphere, reducing the heat exchange efficiency on the fin surface, can be solved because the grooves and brazing points are adjacent to each other, so the space between the fins is not filled or blocked by the brazing material.

[0021] The brazing method proposed by the inventors above is a significant improvement over conventional brazing methods for fin-tube heat exchangers and is highly acclaimed. However, the inventors realized that there was room for further improvement. The room for improvement is the problem of thermal efficiency caused by the rod-shaped brazing material in the form of a metal block. Because the rod-shaped brazing material made from a metal block is formed hard, it can be said that it has a high filling rate and therefore high thermal conductivity. However, because it is a rod-shaped metal block, in the state shown in Figure 13, heat can only be input from the end of the rod, and the heat input area is small compared to the total surface area of ​​the brazing material, so it must be said that the heat input efficiency is actually low. Also, even though the thermal conductivity is high, it starts to melt from the surface, so it takes time for heat to enter the interior. This is where there is room for improvement. Furthermore, because the length of the rod-shaped brazing material in the metal block is long compared to its cross-sectional area, although the thermal conductivity is high, the heat conduction time differs between the peripheral area near the edge and the central area far from the edge, resulting in large temperature variations and an uneven melting state of the brazing material 30a. If the brazing material 30a melts first in the peripheral area near the edge, the material in the central area far from the edge may remain in a metal block state, which may require melting by relying on radiant heat from the surroundings. This also leaves room for improvement.

[0022] Here, we searched for techniques in the prior art that could be applied to these improvements, but found that there was no technique that could be applied to the improvements we pointed out. For example, consider the application of the technology disclosed in Japanese Patent Laid-Open Publication No. 55-92288. Figure 14 shows the prior art technology disclosed in Japanese Patent Application Laid-Open No. 55-92288. As shown in Figure 14, the technology disclosed in Japanese Patent Application Laid-Open No. 55-92288 uses a special metal tube filled with brazing material in the form of metal powder. This metal tube has a higher melting point than the brazing material and is made of a metal material that does not dissolve during wetting treatment. This metal tube has slits, through which the brazing material inside is dissolved and supplied.

[0023] However, the technique disclosed in JP-A-55-92288 has problems. The first problem is that it is difficult to ensure the amount of brazing material used. In other words, the slit width cannot be made too large in order to fill the interior with metal powder, so the brazing material dissolved by heat input remains in the metal tube due to surface tension and capillary action. The technology disclosed in JP-A-55-92288 is applied to the inside of an automobile cam, and after the brazing process, the metal tube is left to serve as an oil supply path, and it is believed that the metal tube has a high melting point. The second problem is that the brazing process cannot be performed uniformly depending on the direction of the slits. As mentioned above, even when heat is input and the brazing process is performed, the metal tube remains and the brazing material leaks only from the slits, so the brazing material does not leak in all directions, and there is a problem that the brazing process cannot be performed uniformly depending on the direction of the slits.

[0024] In view of the above problems, the present invention aims to provide a brazing material that is a novel third formed body, so to speak, different from the brazing material 30a formed into a rod-shaped metal block, which is the first formed body of conventional brazing materials, and the paste-like brazing material 30b, which is the second formed body. Another object of the present invention is to provide an effective method for improving the brazing of fin-tube heat exchangers, which have traditionally had many problems, by using the brazing material of the present invention, which is the new third formed body. [Means for solving the problem]

[0025] In order to achieve the above object, the brazing material of the present invention is a brazing material formed from metal powder obtained by powdering a metal to be used as a brazing material and compressing the powder into a predetermined shape without melting it. Due to the above-mentioned structure, the brazing material of the present invention has an extremely large heat input area. In other words, while in the case of a brazing material made of a metal block according to the prior art, the heat input area is limited to the outer surface of the metal block, in the brazing material made of molded metal powder according to the present invention, the heat input area is the sum of the outer surfaces of the individual metal powder particles, resulting in an extremely large specific surface area and a significant improvement in heat input efficiency. It is easier to understand if we use another physical phenomenon as an analogy. For example, if we explain it in terms of the process of immersing sucrose crystals in hot water, applying heat, and melting them, the brazing material made of a metal block in the prior art is immersed and heat is applied as a single crystal, just like rock candy, and it gradually melts from its outer surface, whereas the brazing material made of molded metal powder of the present invention is a molded block of powdered sucrose with an appropriate particle size, just like a sugar cube, and can melt instantly when immersed in hot water and heat is applied. This is because the area that can receive heat is the sum of the outer surfaces of each powder.

[0026] The brazing material of the present invention, which is obtained by compacting the metal powder, may contain an organic binder in addition to the metal powder. Although it would be ideal to use no binder, the use of an organic binder improves the molding state and also makes it possible to reduce the metal oxide that is the metal powder.

[0027] Here, in the brazing material of the present invention formed from metal powder, it is preferable that the particle size range of the metal powder is 20 to 75 μm, accounting for 90% or more, and that the filling rate of the metal powder (the ratio of apparent density to true density) is in the range of 50% to 80%. The particle size range of the metal powder can be set as above because a certain particle size allows for fast melting and a good molten state. Also, the filling rate of the metal powder can be set as above because if it is too low, it becomes difficult to maintain the molded state, and if it is too high, the improvement in heat input efficiency, which is the technical effect of the present invention, is reduced.

[0028] Next, in the brazing material obtained by molding the metal powder of the present invention, the metal can be any one of nickel alloy, copper, and aluminum, or a combination thereof. These have excellent physical properties as base materials for brazing materials, and since there is accumulated knowledge about them, they are easy to handle. In the case of nickel alloys, chromium, silicon, phosphorus, and boron may be included in the composition of nickel. In the brazing material obtained by molding metal powder according to the present invention, the molded body may be any one of a molded body by extrusion molding, a molded body by vacuum extrusion, a molded body by compression molding, or a combination thereof. In addition, a molding method in which the metal powder is placed in a mold and dried may also be used. The shape of the molded body is not limited, but it can be molded into, for example, a rod shape, a ring shape, or a sheet shape.

[0029] Next, the brazing method for manufacturing a fin-tube heat exchanger using the brazing material formed from the metal powder of the present invention is as follows. First, the fin-tube heat exchanger is based on the premise that it comprises a fin multi-layer structure in which a number of fins are stacked and arranged at a predetermined interval, and tubes inserted into through holes that are drilled through the fin multi-layer structure and formed to run continuously through it, and that the brazing points are configured to be contact points between the inner peripheries of the through holes in the fin multi-layer structure and the outer peripheries of the tubes. In the above configuration, a part of the through hole is cut out toward the outer periphery to form a groove, and a brazing material formed from a rod-shaped metal powder as described in claim 5 is inserted through the groove, and a predetermined heat is input to the brazing material to perform brazing processing. [Effects of the Invention]

[0030] According to the brazing method for manufacturing a fin-tube heat exchanger of the present invention, the brazing material of the present invention used in the brazing process has a high heat input efficiency, thereby improving the problem of low heat input efficiency that was an issue with conventional processing methods.In addition, since the brazing material and the brazing point are adjacent to each other, the problems of brazing material loss and deterioration of appearance that were issues with conventional processing methods are also improved.Furthermore, the problem of the brazing material blocking the heat dissipation space of the fins, which resulted in a deterioration in heat dissipation efficiency, that was an issue with conventional processing methods, is also improved. Furthermore, the problem of uneven molten state of the brazing material, which was a problem with conventional rod-shaped brazing materials made of metal blocks, is also improved by the brazing process method of the present invention because the brazing process time can be shortened. Even if it is assumed that a time difference occurs between the molten state of the peripheral part and the central part when using the brazing material of the present invention, the brazing material of the present invention can be instantly changed into a granular metal powder, so that the metal powder can be melted well in a short time even by radiant heat from the surroundings, and uniform and good wetting occurs during the brazing process. [Brief explanation of the drawings]

[0031] [Figure 1] FIG. 2 is a diagram simply showing an example of the composition of a brazing material formed from metal powder according to Example 1 of the present invention. [Figure 2] FIG. 10 is a diagram showing a brazing material produced by molding metal powder through vacuum extrusion molding. [Figure 3] FIG. 10 shows a brazing material of a metal block made by another manufacturer with the same composition. [Figure 4] FIG. 10 is a diagram showing density depending on the amount of added element. [Figure 5] 1 is a diagram simply illustrating the configuration of a fin-tube heat exchanger 100 that is brazed using a brazing material formed from a metal powder of the present invention. [Figure 6] 1 is a diagram (part 1) showing the procedure of a brazing method between the fins 110 and the tubes 120 in the fin-tube heat exchanger 100 of the second embodiment. [Figure 7] FIG. 2 is a diagram (part 2) showing the procedure of the brazing method between the fins 110 and the tubes 120 in the fin-tube heat exchanger 100 of the second embodiment. [Figure 8] 10A and 10B are diagrams (part 3) showing the procedure of the brazing method between the fins 110 and the tubes 120 in the fin-tube heat exchanger 100 of the second embodiment. [Figure 9] 1 is a diagram simply showing the configuration of a fin-tube heat exchanger that is the subject of brazing treatment using a brazing material according to the prior art; [Figure 10] FIG. 10 is a diagram showing a case where a bar-shaped brazing material 30a made of a metal block is used in the prior art. [Figure 11] 1A and 1B are diagrams illustrating an example of a brazing process in a fin-tube heat exchanger according to the prior art. [Figure 12] FIG. 1 is a diagram simply showing the invention of the brazing process for a fin-tube heat exchanger envisioned by the inventors. [Figure 13] 13 is a diagram showing a brazing process assumed in the new fin-tube heat exchanger devised by the present inventors and having the configuration shown in FIG. 12. FIG. [Figure 14] FIG. 1 is a diagram showing the prior art disclosed in Japanese Patent Application Laid-Open No. 55-92288. BEST MODE FOR CARRYING OUT THE INVENTION

[0032] EXAMPLES Hereinafter, examples of the brazing material of the present invention will be described with reference to the drawings, but the present invention is not limited to these examples. Example 1

[0033] A brazing material 100 according to Example 1 of the present invention will be described. As an example, the brazing material will be described mainly with a nickel alloy as the base material and containing a small amount of binder. FIG. 1 is a diagram simply showing an example of the composition of a brazing material formed from metal powder according to Example 1 of the present invention. In the examples shown in FIG. 1, the base material is a nickel alloy, but the composition of the brazing material formed from the metal powder of the present invention can be varied, and the composition shown in FIG. 1 is merely one example. In the example shown in FIG. 1, the compounding ratio after drying is 97.6% nickel brazing metal powder and 2.4% binder. In addition to nickel alloys, there are a variety of other possible metals, such as copper alloys. While copper alloys are widely used in conventional technology, the present invention can also be applied to Cu-Mn-Ni copper alloys and Cu-Sn-Ti copper alloys, which are considered to be difficult to process. Other metal powders such as gold, silver, tin, aluminum, lead, phosphorus, chromium, tungsten, molybdenum, titanium, platinum, palladium, zinc, indium, molybdenum, and manganese, as well as combinations thereof, can also be used.

[0034] The prototype is shown below. The prototype was made using nickel brazing filler with the number 1 compound listed in Figure 1. The nickel brazing material, nickel, was powdered by atomization or other methods to form a metallic powder of nickel brazing material. The powder was not melted, but was compressed into a rod shape by vacuum extrusion molding to obtain a molded body.

[0035] FIG. 2 shows a brazing material obtained by molding a metal powder experimentally produced by vacuum extrusion molding using the composition of List 1 shown in FIG. Figure 2(a) shows the appearance of the brazing material formed from metal powder. The prototypes shown are all formed into rods with a circular cross section. Figure 2(b) shows a micrograph of the cross section of the brazing material prototype formed from the metal powder shown in Figure 2(a) at 30x magnification. Figure 2(c) is a magnified microscope photograph taken at a higher magnification than Figure 2(b), at 300x magnification. As shown in Figure 2(c), it can be seen that even when formed into a rod shape by vacuum extrusion, the nickel alloy remains in a granular state as a metal powder without being melted.

[0036] For comparison, the cross section of a brazing material made from a metal block with the same composition by another manufacturer was also observed. Figure 3 shows a brazing material made of a metal block from another manufacturer with the same composition. Figure 3(a) shows the appearance of a metal block brazing material made by another company with the same composition. Only one piece is shown. Figure 3(b) shows a micrograph of the cross section of a metal ingot brazing material from another manufacturer with the same composition as Figure 3(a). The cross section is a longitudinal section. The magnification is 30x. Figure 3(c) is a magnified microscope photograph taken at a higher magnification than Figure 3(b), at 300x magnification. As shown in Figures 3(b) and 3(c), the brazing filler metal in the metal block is a molten nickel alloy that has been formed into a mass. When observed under a microscope at magnifications of 30x and 300x, the three-dimensional structure is not visible, and it can be seen that the metal block is a uniform, homogeneous mass. The state of the brazing material formed from the metal powder of the present invention shown in Figures 2(b) and 2(c) is clearly different from the state of the brazing material in the form of a metal block shown in Figures 3(b) and 3(c), and the powdery, granular metal powder can clearly be seen. It can be seen that the brazing material formed from the metal powder of the present invention has never been melted, and is in a physically compressed state while maintaining its granular powder form.

[0037] Regarding the particle size range of the metal powder in the brazing material molded from the prototype metal powder, it was confirmed that 90% or more of the powder had a median diameter of 20 to 75 μm. Specifically, this is within the range shown in Table 1 below, and it can be said that the overall diameter is essentially 63 μm or less. [Table 1]

[0038] Next, the packing ratio of the brazing material formed from the metal powder was measured. In the present invention, the packing ratio represents the ratio of the apparent density to the true density. For comparison, a brazing material made by another company using a metal block with the same composition is also shown. As a result, it was found that the filling rate of the prototype was as shown in Table 2 below. [Table 2] The packing ratio was calculated by the ratio of the actually measured density to the theoretical value using the calculated density values ​​of each metal shown in FIG. In addition, in [Table 2], the fill rate of the competitor's metal block brazing material is in the range of approximately 82% or 90%, but it is thought that such a low value range is calculated because flux and binder are also mixed in. If only the metal block portion of the competitor's metal block brazing material is measured, the fill rate is expected to be 95% or more.

[0039] The results shown in Table 2 show that the packing ratio of the brazing material molded from the metal powder of the present invention is significantly lower than that of the brazing material made from metal blocks by other companies, at around 60%. This packing ratio can be adjusted by the pressure applied during extrusion molding. In the present invention, the metal powder filling rate in the compact is preferably in the range of 50% to 80%. If the filling rate is less than 50%, the binder content is low, resulting in low hardness and making the rod-shaped brazing material made from the metal powder more likely to break when handled during the brazing process. If the filling rate is greater than 80%, depending on the binder content, the brazing material may become similar to conventional metal ingots, resulting in a risk of reduced heat input efficiency. Therefore, here, the metal powder filling rate in the compact is assumed to be in the range of 50% to 80%.

[0040] Next, the heat input efficiency of the brazing material formed from the metal powder of the present invention was investigated. For the brazing material made from the metal powder of the present invention and the brazing material made from a metal block manufactured by Company A, rods of the same shape, 20 cm long and 2 mm in cross-sectional diameter, were prepared, and their ends were brought into contact with a heat source at 200 degrees to apply heat. The results are summarized below. The brazing material formed from the metal powder of the present invention began to melt at the ends in xx seconds, and the center began to melt xx seconds later. On the other hand, the brazing material made from Company A's metal block began to melt at the edges in xx seconds, and the center began to melt xx seconds later. The reason for this clear difference in the time it takes for the center to melt can be analyzed as follows: the brazing material formed from the metal powder of the present invention has a large total area of ​​the outer surface of the granular metal powder, resulting in a large heat input area, while the brazing material made from the metal block product of Company A only has a heat input area from the edge of the rod-shaped outer surface, and only metal thermal conduction is available toward the center. Thus, it was demonstrated that the brazing material formed from the metal powder of the present invention has an extremely high heat input efficiency. Example 2

[0041] Next, as Example 2 of the present invention, a brazing method for manufacturing a fin-tube heat exchanger using a brazing material formed from the metal powder of the present invention will be described. FIG. 5 is a diagram simply showing the structure of a fin-tube heat exchanger 100 to be brazed using the brazing material formed from the metal powder of the present invention. Fig. 5(a) is a perspective view of the fin 110 viewed from a slight angle with the surface of the fin 110 through which the tube 120 is inserted facing the front, and Fig. 5(b) is a longitudinal cross-sectional view taken along the longitudinal centerline of the fin 110 with the surface of the fin 110 through which the tube 120 is inserted facing the front. In other words, this is a cross-sectional view taken vertically through the center of the tube 120 and the groove 112 (described later). Note that the longitudinal cross-section in Fig. 5(b) is shown hatched.

[0042] The fins 110, which are heat sinks, are made by pressing a thin plate made of copper, SUS, aluminum, or the like to form tube through-holes 111, and then cutting the plate to a predetermined size. The tube through-holes 111 are provided to match the outer shape of the tubes 120. They may be circular or flat. In this example, they are circular. The fin material can be any of those conventionally used. For example, copper, stainless steel, and aluminum alloys are often selected from the viewpoints of formability, heat transfer, and light weight. The brazing method for manufacturing the fin-tube heat exchanger of the present invention can be applied to any of these materials. As shown in Figures 5(a) and 5(b), the finned tube heat exchanger 100 has a multi-layered structure of fins 110. There is no limit to the number of fins 110, and it can be, for example, several hundred. In this example, 36 fins are stacked. There is also no limit to the spacing between the fins 110, and they can be stacked with a gap of, for example, several millimeters. When these multi-layered fins 110 are stacked, all of the tube through-holes 111 drilled in the fins 110 are aligned in the same position, forming a continuous hole space. Note that there may be one or more tube through-holes 111. It is also possible to insert multiple tubes 120, provide U-shaped curved portions at the ends of the tubes to turn the circulation path, and have the tubes travel back and forth across the fins multiple times. For simplicity of explanation, in the example of Figure 5, there is one tube through-hole 111 and one tube 120 is inserted.

[0043] Furthermore, the fin 110 according to the second embodiment has a groove 112 formed on the upper outer side of the tube insertion hole 111. As will be described later, this groove 112 is intended to provide a space for inserting and accommodating the brazing material 200 formed from the metal powder of the present invention in a straight line at a position adjacent to the tube 120. In this way, the groove 112 is provided on the upper outer side of the tube insertion hole 111, and is integrally connected to and adjacent to the tube insertion hole 111. Therefore, when the brazing material 200 formed from the metal powder of the present invention inserted into this groove 112 melts, it immediately reaches the tube 120 directly below, which has the advantage of expanding the "wetting" area.

[0044] The tube 120 is a hollow tube and can be any metal tube with high thermal conductivity, and there are no particular restrictions on the material, but copper or copper alloy tubes are often used in terms of workability, heat transfer, ease of installation, and corrosion resistance.

[0045] The brazing process between the fins 110 and the tubes 120 in the fin-tube heat exchanger 100 according to the second embodiment is carried out in the following procedure. 6 to 8, as with Fig. 5, (a) is a perspective view seen from a slight angle with the surface of the fin 110 through which the tube 120 is inserted facing the front, and (b) is a longitudinal cross-sectional view cut vertically along the center line with the surface of the fin 110 through which the tube 120 is inserted facing the front. In (b), the longitudinal cross-section is shown hatched.

[0046] First, from the state shown in FIG. 5 (where the tubes 120 serving as heat transfer tubes are inserted into the tube through holes 111 of the multilayered fins 110), as shown in FIG. 6, a rod-shaped brazing material 200 formed from the metal powder of the present invention is inserted into the space formed by the groove 112 on the upper outer side of the tube insertion hole 111. It is preferable that the length of the brazing material 200 formed from the metal powder of the present invention be approximately the same as the penetration length of the multi-layered fin 110 .

[0047] Next, as shown in Fig. 7, a heat source of a predetermined temperature is brought into contact with the end of the brazing material 200 formed from the metal powder of the present invention, and heat is input. For example, a heat source of 1100 degrees is used. The brazing material 200 formed from the metal powder of the present invention has a high heat input efficiency as shown in Example 1, and the brazing material melts efficiently in a short time, and the brazing material melts not only at the ends but also at the center in a short time. As a result, as shown in FIG. 8, the brazing material 200 formed from the metal powder of the present invention quickly melts in its entirety, and the brazing material 200 that melts and becomes liquid in the space of the groove 112 reaches the tube insertion hole 111 directly below in an extremely short time and spreads to the outer periphery of the tube 120 that is in contact with the inner periphery of the tube insertion hole 111, so that the so-called "wetting" spreads in a short time to the contact point between the fin 110 and the tube 120, i.e., the brazing point, and good "wetting" is achieved throughout the brazing point.

[0048] FIG. 8 is a diagram showing the fin-tube heat exchanger 100 in a state where the brazing process between the fins 110 and the tubes 120 has been completed. The brazing material 200 formed from the metal powder of the present invention contains a small amount of binder and requires a short drying process, so it takes a short time to go from the state shown in Figure 6 to the state shown in Figure 8. Nickel alloy brazing material easily solidifies into a metallic state when the temperature drops below 140°C, so it can quickly cool from the heat input temperature of 200°C and reach the state shown in Figure 6. When the state shown in Figure 8 is reached, a strong metal bond is formed between the fins 110 made of SUS metal material and the tubes 120 also made of SUS metal material using a brazing material made of nickel alloy metal material, resulting in an extremely strong fin-tube heat exchanger 100.

[0049] The above has illustrated and explained preferred embodiments of the brazing material formed from the metal powder of the present invention and the brazing processing method for manufacturing a fin-tube heat exchanger using the same. However, it will be understood that various modifications are possible without departing from the technical scope of the present invention. [Industrial Applicability]

[0050] The brazing material of the present invention, which is formed from metal powder molded into a rod shape, can be used as a wide variety of brazing materials. The brazing method for manufacturing a finned tube heat exchanger using a brazing material formed from a rod-shaped metal powder according to the present invention can be applied to the brazing process in the manufacture of a wide variety of finned tube heat exchangers, and can also be applied to brazing two metal or ceramic members in a variety of mechanical devices, not limited to finned tube heat exchangers. [Explanation of symbols]

[0051] 100 Finned tube heat exchanger 110 Fin 111 Tube through hole 112 Groove 120 tubes 200 Brazing material

Claims

1. Brazing material made by pulverizing the metal used as the brazing material and molding it into metal powder.

2. 2. The brazing material formed from a molded metal powder according to claim 1, wherein the molded body has a composition that contains an organic binder in addition to the metal powder.

3. 3. The brazing material formed from metal powder according to claim 1, wherein 90% or more of the metal powder has a particle size range of 20 to 75 μm in median diameter, and a packing rate indicating a ratio of apparent density to true density of the metal powder in the formed body is in the range of 50% to 80%.

4. 2. The brazing material formed from metal powder according to claim 1, wherein the metal is a nickel alloy containing nickel, chromium, silicon, and phosphorus in its composition.

5. 2. The brazing material formed from metal powder according to claim 1, wherein the molded body is any one of a molded body formed by extrusion molding, a molded body formed by vacuum extrusion, and a molded body formed by compression molding.

6. 2. The brazing material formed from metal powder according to claim 1, wherein the predetermined shape is a rod shape.

7. A brazing method for manufacturing a fin-tube heat exchanger using a brazing material formed from the rod-shaped metal powder according to claim 6, comprising: The fin-tube heat exchanger includes a fin multilayer structure in which a number of fins are stacked and arranged at predetermined intervals, and a tube inserted into a through-hole formed in the fin multilayer structure so as to extend through the structure, In a configuration in which the brazing portion is a contact portion between an inner peripheral edge of the through hole of the fin multilayer structure and an outer peripheral edge of the tube, A groove is provided by cutting out a part of the through hole toward the outer periphery, A brazing processing method for manufacturing a fin-tube heat exchanger, in which a brazing material formed from the rod-shaped metal powder described in claim 5 is inserted through the groove, and a predetermined heat is input to the brazing material to braze it.

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