Pipe joining methods

Abstract

This invention provides an economical and energy-efficient method for joining stainless steel pipes together, or stainless steel pipes with copper pipes, aluminum pipes, or brass pipes. [Solution] The pipe joining method is a method for joining a first pipe 1 to a connected body 2 having an inner wall surface with an inner diameter larger than the outer diameter of the first pipe 1, wherein one of the first pipe 1 and the connected body 2 is made of stainless steel, and the other of the first pipe 1 and the connected body 2 is made of stainless steel, copper, aluminum, or brass, the first pipe 1 is inserted into the connected body 2, and when brazing the first pipe 1 and the connected body 2 in the atmosphere, hydrogen is used as the combustion gas, and the first pipe 1 and the connected body 2 are joined with brazing material A filling the overlapping portion of the first pipe 1 and the connected body 2 that is not exposed to the atmosphere, and with brazing material B filling the portion of the first pipe 1 that is exposed to the atmosphere, the silver content of brazing material A is greater than that of brazing material B (A > B).

Description

Technical Field

[0001] The present invention relates to a method for joining pipes used in air conditioners and the like, and particularly to a method for joining pipes that can be joined at low cost.

Background Art

[0002] Conventionally, copper pipes have been mainly used for the piping pipes constituting the refrigeration cycle of air conditioners and the like, and brazing using inexpensive phosphorus copper solder or brass solder has been performed for their joining (for example, see paragraph number 0027 “Joining of copper pipes” and FIG. 12 of the patent document). However, recently, due to the depletion problem of copper resources and the increase in demand, the material price has soared. For this reason, there has been a move to adopt stainless steel pipes for some piping pipes where the vibration absorption performance of copper is not required. However, a strong passive film is formed on the surface of the stainless steel pipe, mainly composed of chromium oxide (Cr2O3). This film provides corrosion resistance, but in atmospheric brazing, which is the conventional process for joining pipes to form a refrigeration cycle, the oxide layer formed on this metal surface prevents the solder from sufficiently wetting the base material. The gas used at this time is composed of fuel gas (such as acetylene and propane) and oxygen (oxidizing agent: supporting combustion gas). This fuel gas itself has no reducing action, but when the gas is burned, the inner flame (reducing zone) becomes oxygen-deficient, and a limited reducing action occurs. However, it does not have a reducing power sufficient to remove the aforementioned oxide layer. As a result, there has been a problem that it leads to a decrease in joining strength and a refrigerant leakage failure due to insufficient brazing.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

[0004] The present invention aims to provide a method for joining pipes that addresses the above-mentioned problems. [Means for solving the problem]

[0005] The pipe joining method according to claim 1, the joining having an inner wall surface whose inner diameter is larger than the outer diameter of the first pipe body and The first pipe and of Joining do A method for joining pipes, comprising the first pipe and the connected pipe. body Of these, one is stainless steel, and the rest is stainless steel, copper, aluminum, or brass, and the first pipe is connected to the first pipe. body Insert and connect the first pipe and the connected body When brazing in the atmosphere, hydrogen is used as the combustion gas, and the first pipe and the connected parts body Inside, the first pipe which is not exposed to the atmosphere and the connected body The overlapping portion is filled with brazing material A, and the portion of the first pipe exposed to the atmosphere is joined with brazing material B, wherein the silver content of brazing material A is greater than that of brazing material B (A > B).

[0006] Furthermore, the pipe joining method described in claim 2 is the pipe joining method described in claim 1, wherein the fusion joining of the brazing material and the base material, which is stainless steel, is performed in the flame of a hydrogen burner.

[0007] Furthermore, the pipe joining method described in claim 3 is the pipe joining method described in claim 1, wherein brazing material A and brazing material B are each formed into ring shapes and stacked, brazing material A is placed near the overlapping portion of the pipes, and the pipes are joined by applying a flame from a hydrogen burner.

[0008] Furthermore, the pipe joining method described in claim 4 is the pipe joining method described in claim 1, wherein two types of brazing materials are used with silver content A > B, a plurality of wire supply devices are provided for supplying brazing materials A and B, hydrogen is used as the combustion gas, brazing material A is melted and filled into the overlapping portion of the pipe that is not exposed to the atmosphere, and then brazing material B is supplied to the brazing portion to perform external fillet forming.

[0009] Furthermore, the pipe joining method according to claim 5 is the pipe joining method according to any one of claims 1 to 4, wherein the object to be joined is a second pipe. [Effects of the Invention]

[0010] According to the pipe joining method described in claim 1, the first pipe and the connected body (second pipe) are joined by filling the overlapping portion of the first pipe and the connected body (second pipe) that is not exposed to the atmosphere with brazing material A, and joining the portion of the first pipe exposed to the atmosphere with brazing material B. Since the silver content of brazing material A is greater than that of brazing material B (A > B), the joining can be done inexpensively.

[0011] Furthermore, according to the pipe joining method described in claim 2, in addition to the effects of the invention described in claim 1 above, the molten joint between the brazing material and the base material, which is stainless steel, is placed within the flame of a hydrogen burner (the work is performed within the flame of a hydrogen burner), so the work can be carried out without worrying about surface oxidation.

[0012] Furthermore, according to the pipe joining method described in claim 3, in addition to the effects of the invention described in claim 1 above, the brazing material A and brazing material B are each formed into ring shapes and stacked, brazing material A is placed near the overlapping part of the pipes, and the joint is melted and joined by applying a flame from a hydrogen burner. Therefore, the placement of brazing material A and brazing material B is easy, and moreover, because the flame is applied from a hydrogen burner, the welding work can be performed efficiently.

[0013] Moreover, according to the pipe joining method described in claim 4, in addition to the effects of the invention described in claim 1 above, two types of brazing materials with the silver content A > B are used, and a plurality of wire supply devices are provided for supplying brazing material A and brazing material B. Hydrogen is used as the combustion gas. After melting and filling the overlapping portion of the pipe that is not exposed to the atmosphere with the brazing material A, the brazing material B is supplied to the brazing portion to perform external fillet forming, so that the welding operation can be efficiently performed.

Brief Description of Drawings

[0014] [Figure 1] Figure 1 is a schematic diagram of a state in which a first pipe (stainless steel pipe) of a pipe joining method according to an embodiment of the present invention is inserted into a second pipe (stainless steel pipe). [Figure 2] Figure 2 is a schematic diagram of a state in which, after inserting the first pipe (stainless steel pipe) of Figure 1 into the second pipe (stainless steel pipe), a brazing material A (for example, a silver brazing material) is applied to the exposed portion on the atmosphere side (not shown) and a hydrogen burner is injected. [Figure 3] Figure 3 shows the state not shown in Figure 2, and is a schematic diagram of a state in which a brazing material A (for example, a silver brazing material) is applied to the exposed portion on the atmosphere side. [Figure 4] Figure 4 is a schematic diagram of a state in which the brazing material A filled into the overlapping portion of the pipe not exposed to the atmosphere is joined with the brazing material B (for example, a phosphorus copper brazing material) at the portion of the pipe exposed to the atmosphere. [Figure 5] Figure 5 is a schematic diagram of a state in which an auxiliary burner and an auxiliary flame cover the brazing target portion with a reducing flame in a state (not shown) where the brazing material A and the brazing material B are laminated on the exposed portion on the atmosphere side. [Figure 6] Figure 6 shows the state not shown in Figure 5, and is a schematic diagram of a state in which the brazing material A and the brazing material B are laminated on the exposed portion on the atmosphere side. [Figure 7] Figure 7 is a schematic diagram before joining of another pipe joining method different from the pipe joining method of Figures 1 to 6. [Figure 8]FIG. 8 shows another connected body different from the connected body of FIG. 1, for example, a confluence unit. FIG. 8(a) is a schematic left side view of the confluence unit, FIG. 8(b) is a schematic cross-sectional view of FIG. 8(a), FIG. 8(c) is a schematic right side view of FIG. 8(a), and FIG. 8(d) is a schematic perspective view of FIG. 8(a). [Figure 9] FIG. 9 is a schematic perspective view of a state before joining the first pipe and the connected body of FIG. 8.

MODE FOR CARRYING OUT THE INVENTION

[0015] A method for joining pipes according to an embodiment of the present invention will be described with reference to FIGS. 1 to 9.

[0016] FIGS. 1 and 2 show an example in which the first pipe (stainless pipe) 1 is inserted into the connected body (for example, the second pipe, stainless pipe) 2 by the flame 6 of the hydrogen burner 5 and brazing is performed. The portion covered by the flame 6 becomes a reducing atmosphere. The gap (clearance) between the first pipe (stainless pipe) 1 and the connected body (for example, the second pipe, stainless pipe) 2 varies depending on the base material and the brazing material used, but is generally set to about 0.05 to 0.25 mm (JIS Z 3621).

[0017] The overlapping portion 3 (gap portion) of the first pipe 1 and the connected body (second pipe) 2 that is not exposed to the atmosphere is blocked from the external reducing atmosphere when the silver brazing material 4 is inserted into the a portion (see FIG. 1) as shown in FIG. 3, so the effect of hydrogen gas cannot be obtained. Therefore, joining by breaking the stainless passive film by silver as in the conventional case becomes necessary, and the conventional silver brazing is used for filling. For example, when the gap is the above-mentioned central value (diameter: 0.175 mm), the OD (outer diameter) of the outer pipe [second pipe (stainless pipe)] 2 of the overlapping pipes is 10 mm, the ID (inner diameter) is 8 mm, and the overlap (overlapping portion 3) is 15 mm, the amount of silver brazing (silver content: 40%) used is required to be about 0.22 g in weight (calculated based on the specific gravity of silver brazing being 9.2).

[0018] As shown in Figure 4, for example, phosphor bronze solder (silver content 2%) 7 is used on the portion exposed to the atmosphere and melted with the aforementioned flame to form a fret 8 with a fillet size 5 (leg length in welding) of 3 mm. In this case, the amount of brazing material required for fillet formation is approximately 0.36g (calculated using a specific gravity of 8.1 for phosphor bronze brazing). Using a similar calculation method for a conventional example, the amount of silver solder (40% silver content) used for part 4 exposed to the atmosphere would be approximately 0.41g. As a result, the amount of silver used in this embodiment was reduced by 62%, as shown in Table 1 below, enabling us to provide inexpensive brazing. [Table 1]

[0019] In the above-described embodiment, stainless steel was joined to stainless steel, but the present invention is not limited to this. In other words, a pipe joining method in which a connected body (e.g., a second pipe) 2 has an inner diameter larger than the outer diameter of the first pipe 1 and the first pipe 1, wherein one of the first pipe 1 and the connected body (e.g., a second pipe) 2 is made of stainless steel, and the remaining one of the first pipe 1 and the connected body (e.g., a second pipe) 2 is made of stainless steel, copper, aluminum, or brass, and the first pipe 1 is inserted into the connected body (e.g., a second pipe) 2. In this method, when brazing the first pipe 1 and the object to be connected (for example, the second pipe) 2 in the atmosphere, hydrogen is used as the combustion gas, and brazing material A (for example, silver brazing material) 4 is used to fill the overlapping portion 3 of the pipes that are not exposed to the atmosphere, and brazing material B (for example, phosphor bronze brazing material) 7 is used to join the pipes that are exposed to the atmosphere, with the silver content of brazing material A being greater than that of brazing material B (A > B).

[0020] Specifically, as shown in Figure 3, the brazing material A (for example, silver brazing material) 4 is positioned on the overlapping portion 3, and the hydrogen burner 3 is injected. Then, as shown in Figure 4, the brazing material B (for example, phosphor bronze brazing material) 7 is positioned, and the hydrogen burner 3 is injected.

[0021] Furthermore, the oxide layer that had previously formed was very stable, resulting in poor wettability with conventional, inexpensive phosphorus copper solder or brass solder, necessitating the use of expensive silver solder. Silver can improve the strength of the joint by breaking down the passivation film during the process of mutual diffusion with the components of stainless steel to form an alloy. On the other hand, instead of the simpler atmospheric brazing method, there is a method of joining dissimilar metals, such as stainless steel to stainless steel or stainless steel to copper, in an electric furnace under a hydrogen atmosphere. By heating the inside of this electric furnace in a hydrogen atmosphere, the hydrogen gas acts as a reducing agent, reducing and removing the oxide layer on the stainless steel surface, which allows the use of inexpensive brazing material during the aforementioned joining process. However, operating a furnace brazing system using an electric furnace requires a large amount of electricity, and the maintenance costs of the furnace structure and the need for multiple jigs and fixtures to secure piping components inside the furnace make it not economically viable, especially considering environmental protection. Therefore, in the present invention, we focus on the reducing power of hydrogen and use hydrogen gas as a fuel gas instead of conventional acetylene or the like in atmospheric brazing. As a combustion-supporting gas, air or oxygen in limited quantities is used to suppress oxidation. By controlling the amount of oxygen, almost all of the flame from the hydrogen burner will have reducing power.

[0022] According to the pipe joining method of this embodiment, stainless steel pipes can be joined to each other, either to the same material or to different materials, using hydrogen as the combustion gas. Furthermore, since the joining is done using brazing material A (e.g., silver brazing material) 4, which is filled into the overlapping portion 3 of the pipes that are not exposed to the atmosphere, and brazing material B (e.g., phosphor bronze brazing material) 7, which is used to join the pipes that are exposed to the atmosphere, the connection can be made inexpensively. The silver content is defined as follows: the silver content of brazing material A (e.g., silver brazing material) 4 is greater than that of brazing material B (e.g., phosphorus copper brazing material) 7 (A > B).

[0023] Brazing in the open air can be done manually by an operator or using an automated brazing machine. In all cases, it is desirable to place the workpiece within a hydrogen gas flame (performed within a hydrogen burner flame) once the temperature exceeds the oxidation start temperature of stainless steel (approximately 300°C), and more preferably, maintain this condition until the brazing is complete. This is because the surface oxidation progresses the moment it moves away from the flame. To achieve this, for automated machines, the burner position is stable, so the flame can be set to a wide area (if for some reason it cannot be widened, the alternative to manual brazing described later should be adopted). In manual brazing, the position of the burner held by the worker may cause the flame to detach from the stainless steel brazing area during the process. Therefore, as shown in Figure 5, an auxiliary burner 8 is permanently installed solely for the purpose of creating a reducing atmosphere. The auxiliary flame 9 generated by this process covers the area to be brazed with a reducing flame. Since the purpose is to create a reducing atmosphere, overheating to the brazing temperature is unnecessary, and the effect can be achieved with a relatively low heat input (amount of gas used). The worker can melt the brazing material (not shown) with the flame 11 of the handheld burner 10, allowing them to work without worrying about surface oxidation. In other words, according to the pipe joining method of this embodiment, the molten joint between the brazing material 4 and the base material, the stainless steel pipe 2, is placed within the flame of the hydrogen burner 5 (the work is performed within the flame of the hydrogen burner 5), so the work can be carried out without worrying about surface oxidation.

[0024] Figure 6 shows one embodiment in which a ring-shaped brazing material A (for example, silver brazing material) 4 is placed near the overlap 3, and a ring-shaped phosphorus copper brazing material 7 is placed on top of the ring-shaped silver brazing material 4 in order to be used for the portion exposed to the atmosphere. In this configuration, when the reducing flame strikes the solder and reaches the solder's melting point, the silver solder 4 is guided to the overlapping layer 3 by capillary action. Furthermore, because of the presence of brazing material 4, the brazing material 7 cannot flow into the overlap 3 and instead wets the base material in place, forming the fillet. In other words, according to the pipe joining method of this embodiment, brazing material A and brazing material B are each formed into ring shapes and stacked (see Figure 6), brazing material A is placed near the overlapping portion 3 of the pipe, and the flame from the hydrogen burner 5 is applied to melt and join them. As a result, the placement of brazing material A and brazing material B is easy, and the welding work can be performed efficiently because the flame from the hydrogen burner 5 is applied.

[0025] The wire supply device is equipped with two types of brazing material with silver content A > B, uses hydrogen as the combustion gas, and supplies silver brazing material 4 from the wire supply device to one end (part a) of the overlapping section of the pipe that is not exposed to the atmosphere (see Figure 7). The automatic brazing machine, which forms the fillet, can join the pipes by controlling the supply of phosphorus copper brazing material 7 from a wire supply device to the vicinity of section a immediately after melting and filling the overlapping section 3 of the pipes with a brazing material A (for example, silver brazing material) 4, as controlled by the controller 12. That is, according to the pipe joining method of this embodiment, two types of brazing materials A (for example, silver brazing material) 4 and brazing material B (for example, phosphorus copper brazing material) 7 with the silver content A > B are used, and a plurality of wire supply devices are provided for supplying the brazing materials A (for example, silver brazing material) 4 and brazing material B (for example, phosphorus copper brazing material) 7. After melting and filling the brazing material A (for example, silver brazing material) 4 into the overlapping portion 3 of the pipes that are not exposed to the atmosphere using hydrogen as the combustion gas, the brazing material B (for example, phosphorus copper brazing material) 7 is supplied to the brazing portion to perform external fillet forming, so that the welding operation can be efficiently performed.

[0026] In the above-described embodiment, the connected body 2 was the second pipe. However, in the present invention, it is not limited thereto. As shown in FIG. 9, the connected body 2 may be a connected body 2 having an inner wall surface with an inner diameter R2 larger than the outer diameter R1 of the first pipe 1, for example, a flow divider shown in FIGS. 8 and 9. In this case, similar to the above-described embodiment, when the first pipe 1 is inserted into the connected body (flow divider) 2 and the first pipe 1 and the connected body (flow divider) 2 are brazed in the atmosphere, hydrogen is used as the combustion gas, and the brazing material A filled into the overlapping portion of the first pipe 1 and the connected body (flow divider) 2 that are not exposed to the atmosphere inside the first pipe 1 and the connected body (flow divider) 2 and the portion of the first pipe 1 exposed to the atmosphere are joined with the brazing material B. The silver content is such that the brazing material A is greater than the brazing material B (A > B).

[0027] Further, a connected body not shown having an inner wall surface with an inner diameter R2 larger than the outer diameter R1 of the first pipe 1, for example, a flow splitter, may also be used. In the case of the flow divider 2 shown in FIGS. 8 and 9, 21 is the first inflow portion, 22 is the second inflow portion, and 23 is the outflow portion. The outer diameter R1 of the first pipe 1 is smaller (R1 < R2) than the inner wall R2 of the connected body (flow divider) 2 so that the first pipe 1 can be inserted into the connected body (flow divider) 2. In the case of a flow splitter not shown, the flow of the flow divider is reversed, the first inflow portion 21 of the flow divider is the first outflow portion of the flow splitter, the second inflow portion 22 of the flow divider is the second outflow portion of the flow splitter, and the outflow portion 23 of the flow divider becomes the inflow portion of the flow splitter.

Explanation of Reference Numerals

[0028] 1: The first pipe (for example, a stainless steel pipe) 2: The object to be connected (e.g., a second pipe, a stainless steel pipe) 3: Overlapping area 4: Silver solder 5: Hydrogen burner 6: Flame 7: Phosphor copper wax 8: Auxiliary burner 9: Auxiliary Flames 10: Handheld burner 11: Flame 12: Controller

Claims

1. A method for joining a pipe to a connecting object having an inner wall surface with an inner diameter larger than the outer diameter of the first pipe, wherein the first pipe is joined to the connecting object, Of the first pipe and the connected body, one is made of stainless steel, and the other is made of stainless steel, copper, aluminum, or brass. Insert the first pipe into the object to be connected, When brazing the first pipe and the connected body in the atmosphere, hydrogen is used as the combustion gas, and the first pipe and the connected body are joined with brazing material A filling the overlapping portion of the first pipe and the connected body that is not exposed to the atmosphere, and with brazing material B filling the portion of the first pipe that is exposed to the atmosphere, and the silver content of brazing material A is greater than that of brazing material B (A > B). A method for joining pipes, characterized by the features described above.

2. The molten joint between the brazing material and the stainless steel base material is placed within the flame of a hydrogen burner (the process is performed within the hydrogen burner flame). The pipe joining method according to claim 1.

3. Brazing material A and brazing material B were each formed into ring shapes and stacked, brazing material A was placed near the overlapping part of the pipe, and the two were melted and joined by applying a flame from a hydrogen burner. The pipe joining method according to claim 1.

4. Two types of brazing materials, A and B, with silver content greater than B, are used. Multiple wire supply devices are provided for supplying brazing materials A and B. Hydrogen is used as the combustion gas. After melting and filling brazing material A into the overlapping section of the pipe that is not exposed to the atmosphere, brazing material B is supplied to the brazing section to perform external fillet forming. The pipe joining method according to claim 1.

5. A method for joining pipes according to any one of claims 1 to 4, characterized in that the connected body is a second pipe.

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