JP7105111B2 - Double tube joining method in heat exchanger - Google Patents

Description

The present invention relates to a method for joining double tubes in a heat exchanger.

In a vehicle such as an automobile, a fluid that cools or heats a predetermined portion of the vehicle circulates in a circulation circuit, and a heat exchanger is provided in the circulation circuit to exchange heat between the fluids. Sometimes. The heat exchanger is provided with a double tube consisting of an outer tube and an inner tube made of an aluminum alloy. It is known to exchange heat with

In addition, in the above-described heat exchanger having a double tube, as shown in Patent Document 1, an annular inner fin made of an aluminum alloy having a plurality of irregularities arranged in the circumferential direction is provided between the outer tube and the inner tube. It is also known to insert the inner fins into the outer tube and braze the inner fins to the inner circumference of the outer tube and the outer circumference of the inner tube. In this heat exchanger, brazing filler metals are interposed between the inner fins and the inner circumference of the outer tube and between the inner fins and the outer circumference of the inner tube. are joined to each other through the brazing material and the inner fins.

Since the outer tube, the inner tube, and the inner fins are each made of an aluminum alloy, the above-mentioned brazing addition heat is used to suppress the formation of an oxide film on the brazing material during brazing. It is carried out under an inert gas atmosphere in a gas-filled furnace or under vacuum conditions in an internally evacuated furnace.

JP-A-2-309192

However, as described above, if the brazing heat is to be applied in an inert gas atmosphere or in a vacuum, the entire interior of the furnace containing the inner and outer pipes must be filled with an inert gas for the same brazing heat. The tank must be filled or evacuated, and the equipment and the like for realizing this must be large-scaled, leading to an increase in manufacturing costs.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for joining double pipes in a heat exchanger, which can realize brazing between an outer pipe and an inner pipe without using large-scale equipment.

Means for solving the above problems and their effects will be described below.
A double pipe joining method for solving the above problems is applied to a heat exchanger provided with a double pipe consisting of an outer pipe and an inner pipe made of an aluminum alloy. This heat exchanger exchanges heat between a fluid flowing between the inner tube and the outer tube and a fluid flowing inside the inner tube. In the joining method, the outer tube and the inner tube are joined through the brazing filler metal therebetween by applying brazing heat. Specifically, the space between the outer tube and the inner tube is filled with an inert gas before the brazing heat is applied, and then the outer tube and the inner tube are joined together by the brazing heat.

According to this method, brazing addition heat for joining (brazing) the outer tube and the inner tube through the brazing material is performed while the space between the outer tube and the inner tube is filled with an inert gas. Therefore, even if the brazing addition heat is performed in the air, the formation of an oxide film on the brazing material during brazing can be suppressed. Therefore, it is no longer necessary to put the outer tube and the inner tube in a furnace filled with an inert gas or in a vacuum state to suppress the formation of the oxide film to perform the above brazing addition heat. Equipment for realizing heating does not become large-scale. Therefore, brazing between the outer pipe and the inner pipe can be realized without using large-scale equipment.

In the above method for joining double tubes in a heat exchanger, a temperature-raising gas is flowed into the interior of the inner tube before the brazing heat is applied, and then the brazing heat is applied to separate the outer tube and the inner tube. It is conceivable to join them together.

Since the outer tube is more likely to be heated by the brazing heat than the inner tube, the outer tube is more likely to thermally expand than the inner tube due to the heating. If the outer tube thermally expands more than the inner tube in the direction of radial expansion, the distance between the inner circumference of the outer tube and the outer circumference of the inner tube increases, and accordingly the outer tube and the inner tube are separated by the brazing heat. There is a risk that the joint (brazing) through the brazing material will not be performed properly. However, according to the above method, the inner pipe is heated by the temperature-increasing gas that is flowed into the inner pipe before the brazing addition heat is applied, and as a result, the inner pipe thermally expands in the diameter-expanding direction. . For this reason, after the thermal expansion of the inner tube in the radial expansion direction, when the outer tube thermally expands in the radial expansion direction due to the brazing addition heat, the gap between the inner circumference of the outer tube and the outer circumference of the inner tube is reduced. It is possible to suppress an increase in the distance between the outer tube and the inner tube due to the increase in the distance, and to prevent the outer tube and the inner tube from being properly joined through the brazing material due to the additional brazing heat.

In the above-described method for joining double tubes in a heat exchanger, at least one of the outer tube and the inner tube has a protrusion projecting toward the other in the radial direction of the outer tube and the inner tube. It is conceivable that the brazing addition heat is performed in a state in which the brazing material is interposed between the outer tube and the inner tube at the convex portion.

If the outer tube and the inner tube are joined by brazing through the inner fins inserted between the outer tube and the inner tube, the inner fins are inserted between the outer tube and the inner tube, The inner fins must be brazed to the inner periphery of the outer tube and to the outer periphery of the inner tube, respectively, and it is undeniably time-consuming to realize them. However, according to the above method, the protrusion is formed on at least one of the outer tube and the inner tube. By positioning the inner tube inside the outer tube, the protrusion protrudes from at least one of the outer tube and the inner tube toward the other. Since the joining is performed by attaching, such joining does not require much labor. Therefore, the outer tube and the inner tube can be joined by brazing without taking much time.

In the method for joining double tubes in a heat exchanger, the protrusion is formed on the outer periphery of the inner tube so as to protrude toward the inner periphery of the outer tube, and the brazing material is applied to the protrusion. It is conceivable to use a brazing material powder that is applied to the surface.

In the method for joining double tubes in a heat exchanger, the protrusion is formed on the outer periphery of the inner tube so as to protrude toward the inner periphery of the outer tube, and the brazing material is formed on the outer periphery of the inner tube. It is conceivable that it shall be clad with

In the above-described method for joining double tubes in a heat exchanger, the convex portion is formed on the outer periphery of the inner tube so as to protrude toward the inner periphery of the outer tube, and the brazing material is formed on the inner periphery of the outer tube. It is conceivable that it should be clad around.

In the method for joining double tubes in a heat exchanger, the protrusion is formed on the outer periphery of the inner tube so as to protrude toward the inner periphery of the outer tube, and the brazing material is formed on the outer periphery of the inner tube. It is conceivable that it is applied by thermal spraying.

Sectional drawing which shows the structure of the double tube in a heat exchanger. FIG. 2 is a cross-sectional view showing the double tube of FIG. 1 as seen from the direction of arrow AA. Sectional drawing which expands and shows the circumference|surroundings of the convex part in an inner pipe|tube and an outer pipe|tube. Sectional drawing which shows the other example of the structure around the convex part in an inner pipe|tube and an outer pipe|tube.

An embodiment of a method for joining double pipes in a heat exchanger will be described below with reference to FIGS. 1 and 2. FIG.
2. Description of the Related Art In vehicles such as automobiles, a refrigeration cycle is used to perform air conditioning such as heating and cooling of the interior of the vehicle. In such a refrigeration cycle, the refrigerant (fluid) for heating and cooling (cooling and heating) the vehicle interior circulates in a circulation circuit. A heat exchanger is provided for effecting the exchange.

The heat exchanger, as shown in FIG. 2 to exchange heat with the refrigerant flowing inside. The outer tube 1 and the inner tube 2 of the double tube of the heat exchanger are joined together by brazing.

As shown in FIG. 2, the inner tube 2 is formed with a protrusion 3 protruding radially from the outer periphery toward the outer tube 1 side. By inserting the inner tube 2 into the outer tube 1 in a state in which a brazing composition (brazing material) is applied to the outer periphery of the convex portion 3, a gap between the outer pipe 1 and the inner pipe 2 (convex portion 3) is formed. The brazing material comes to intervene. Then, the outer tube 1 and the inner tube 2 are joined to each other through the brazing material between the outer tube 1 and the inner tube 2 by performing additional brazing heat while the space between the outer tube 1 and the inner tube 2 is filled with an inert gas.

Next, the convex portion 3 will be described in detail.
The convex portion 3 is formed to extend in the longitudinal direction of the outer tube 1 and the inner tube 2 (horizontal direction in FIG. 1). More specifically, the convex portion 3 is formed so as to be spirally twisted around the center line of the outer tube 1 and the inner tube 2 . Furthermore, as shown in FIG. 2, a plurality of (three in this example) projections 3 are formed at equal intervals in the circumferential direction of the outer tube 1 and the inner tube 2 . Therefore, on the outer periphery of the inner tube 2, peaks formed by the protrusions 3 and valleys between the adjacent protrusions 3 are alternately formed in the circumferential direction of the inner tube 2. As shown in FIG.

Formation of the protrusions 3 on the inner tube 2 can be performed, for example, by the following method. A tube material made by extruding an aluminum alloy into a cylindrical shape is used as a material for forming the inner tube 2, and the convex portion is formed by rolling the tube material (material of the inner tube 2) using a roll or the like, or by press working. 3 is formed. Incidentally, as the aluminum alloy, it is preferable to use a 1000-series or 3000-series aluminum alloy which is excellent in workability and brazeability.

For the outer tube 1 as well, a tube material formed by extruding an aluminum alloy similar to that of the inner tube 2 into a cylindrical shape is used as a material for forming the outer tube 1 . The brazing of the outer tube 1 and the inner tube 2 is performed at the projections 3 continuously or intermittently in the extending direction of the projections 3 . In addition, the brazing of the outer tube 1 and the inner tube 2 may be performed at least one of the plurality of protrusions 3, and may be performed at all of the plurality of protrusions 3, or may be performed at one or two. can be considered.

Next, the brazing of the outer tube 1 and the inner tube 2 at the convex portion 3 will be described in detail.
When brazing the outer tube 1 and the inner tube 2, the outer tube 1 is formed so that the inner circumference of the outer tube 1 has a larger diameter than the outer circumference of the convex portion 3 of the inner tube 2. A brazing composition containing brazing material powder and flux powder is applied to the outer periphery of the convex portion 3 of the tube 2 . FIG. 3 is an enlarged view of the protrusions 3 and their surroundings in the inner tube 2 and the outer tube 1, and the brazing material 4 (brazing composition) is arranged around the protrusions 3. . More specifically, projections 3a projecting toward the inner tube 2 are formed on the outer circumference of the convex portion 3, and portions of the projections 3a on both sides in the width direction of FIG. The brazing material 4 is arranged.

When the brazing of the outer tube 1 and the inner tube 2 is continuously performed at the projections 3 in the direction in which the projections 3 extend, the brazing composition is applied to the outer periphery of the projections 3 in the direction in which the projections 3 extend. Apply continuously to Examples of the method of applying the brazing composition at this time include roll transfer and brush application.

Further, when the outer pipe 1 and the inner pipe 2 are brazed intermittently in the direction in which the convex portion 3 extends, the brazing composition is applied to the outer periphery of the convex portion 3. Apply intermittently in the direction of extension. As a method of applying the brazing composition at this time, for example, there is a method of applying the brazing composition on the convex portions of the roll to the outer periphery of the convex portions 3 by using a roll having concavo-convex portions in the roll transfer. can give. In addition, even if a normal roll is used instead of the above-described uneven roll, if the brazing composition on the normal roll is intermittently removed, intermittent It is possible to apply the brazing composition to the

The inner tube 2 with the brazing composition applied to the projections 3 is inserted into the outer tube 1 . After inserting the inner tube 2 into the outer tube 1 to form a double tube, the space between the outer tube 1 and the inner tube 2 is filled with an inert gas such as nitrogen gas, argon gas, or helium gas, A temperature-raising gas such as heated air is flowed into the inner tube 2 . Filling the space between the outer tube 1 and the inner tube 2 with the inert gas means continuously flowing the inert gas between the outer tube 1 and the inner tube 2, or the gap between the outer tube 1 and the inner tube 2. It can be realized by connecting connectors, valves, etc. to both ends of the outer tube 1 in a state in which an inert gas is filled between them to seal the inert gas.

The space between the outer tube 1 and the inner tube 2 is filled with an inert gas, and a temperature-increasing gas such as heated air is flowed into the inner tube 2. Perform brazing addition heat. Such brazing heat is applied, for example, by keeping the outer tube 1 and the inner tube 2 in a high-temperature furnace. The temperature in the furnace is preferably 600 to 605° C., which is higher than the melting temperature of the brazing composition, and the time for which the temperature is maintained is preferably 3 to 5 minutes. By applying brazing heat to the outer tube 1 and the inner tube 2 in the furnace in this manner, the outer tube 1 and the inner tube 2 are joined at the convex portions 3 through the brazing composition.

As the brazing filler metal powder contained in the above brazing composition, silicon (Si) single powder or synthetic powder of aluminum (Al) and silicon can be used. Al--Si alloy powders for brazing materials such as A4045 and A4047, which are defined in JIS and AA standards, can also be used as the brazing material powders. The flux powder contained in the above brazing composition may be a fluoride-based flux powder that is commonly used for brazing aluminum alloys.

In addition, if the brazing composition falls off after the brazing composition is applied to the projections 3, the brazing composition may contain a binder as necessary. . As this binder, it is preferable to use acrylic resin such as methacrylic acid polymer, urethane resin, or the like, which decomposes and volatilizes during temperature rise due to brazing addition heat.

As for the component ratio of the brazing composition, the weight of the brazing material powder is in the range of, for example, 10% to 45%, and the weight of the flux powder is in the range of, for example, 30% to 80%, based on the weight of the entire brazing composition. Preferably, the weight of the binder is in the range of 10% to 40%, for example. When Si powder is used as the brazing powder, the ratio of the brazing powder to the entire brazing composition is preferably less than the ratio of the flux powder to the entire brazing composition. Also, when Al—Si alloy powder is used as the brazing powder, the ratio of the brazing powder to the entire brazing composition may be greater than the ratio of the flux powder to the entire brazing composition.

Next, the effect of the method for joining the double pipes in the heat exchanger of this embodiment will be described.
(1) Brazing addition heat for joining (brazing) the outer tube 1 and the inner tube 2 through the brazing material (brazing composition) fills the space between the outer tube 1 and the inner tube 2 with an inert gas. It is done in the Therefore, even if the brazing addition heat is performed in an air atmosphere, it is possible to suppress the formation of an oxide film on the brazing material during brazing. As a result, it is no longer necessary to put the outer tube 1 and the inner tube 2 in a furnace filled with an inert gas or in a vacuum state in order to suppress the formation of the oxide film to perform the above brazing addition heat. Equipment for realizing brazing addition heat does not become large-scale. Therefore, brazing between the outer pipe 1 and the inner pipe 2 can be realized without using large-scale equipment.

(2) Since the outer tube 1 is more likely to be heated than the inner tube 2 by the above brazing heat, the outer tube 1 is more likely to thermally expand than the inner tube 2 in the radial expansion direction. If the outer tube 1 thermally expands more in the radial expansion direction than the inner tube 2, the distance between the inner circumference of the outer tube 1 and the outer circumference of the inner tube 2 (outer circumference of the convex portion 3) widens. There is a risk that the joining (brazing) between the outer tube 1 and the inner tube 2 through the brazing material will not be performed properly due to the brazing heat. Compared to the case where the outer tube 1 is formed so that the inner circumference of the outer tube 1 has the same diameter as the outer circumference of the protrusion 3 in the inner tube 2, the inner circumference of the outer tube 1 is larger than the inner tube 2. This tends to occur when the outer tube 1 is formed to have a diameter larger than the outer periphery of the projection 3 .

However, according to the double pipe joining method of the present embodiment, the inner pipe 2 is heated by the temperature-increasing gas that is flowed into the inner pipe 2 before the brazing addition heat is applied. thermally expands in the diameter-expanding direction, and the outer circumference of the convex portion 3 is pressed against the inner circumference of the outer tube 1 . For this reason, after the thermal expansion of the inner tube 2 in the radial expansion direction, when the outer tube 1 thermally expands in the radial expansion direction due to the brazing heat, the inner circumference of the outer tube 1 and the inner tube 2 ( It is possible to suppress the distance from the outer periphery of the convex portion 3) from increasing. Therefore, it is possible to prevent the outer tube 1 and the inner tube 2 from being properly joined through the brazing material due to the additional brazing heat as the distance increases.

(3) By inserting the inner tube 2 into the outer tube 1 in a state in which the brazing composition is applied to the outer periphery of the protrusions 3 formed on the inner tube 2, the outer tube 1 and the inner tube 2 (protrusions The brazing material is interposed between the portion 3) and the portion 3). Then, the outer tube 1 and the inner tube 2 are joined to each other through the brazing material between the outer tube 1 and the inner tube 2 by performing additional brazing heat while the space between the outer tube 1 and the inner tube 2 is filled with an inert gas.

If the outer tube and the inner tube are joined by brazing through the inner fins inserted between the outer tube and the inner tube as in the conventional method, the inner fins are inserted between the outer tube and the inner tube. In addition, the inner fins must be brazed to the inner circumference of the outer tube and the outer circumference of the inner tube, respectively.

However, according to the double pipe joining method of the present embodiment, by positioning the inner pipe 2 inside the outer pipe 1, the projections 3 protrude toward the inner circumference of the outer pipe 1, and Since the outer tube 1 and the inner tube 2 are joined by brazing at the projections 3, such joining does not take much time. Therefore, the outer tube 1 and the inner tube 2 can be joined by brazing without taking much time.

Note that the above embodiment can be modified, for example, as follows.
- The convex portion 3 may extend linearly in the longitudinal direction of the outer tube 1 and the inner tube 2 .
- The number of protrusions 3 may be changed as appropriate.

- When the number of protrusions 3 is four or more, the brazing of the outer tube 1 and the inner tube 2 at the protrusions 3 may be performed alternately in the circumferential direction of the inner tube 2 .
- At least one of the outer circumference of the inner tube 2 and the inner circumference of the outer tube 1 may be clad with a brazing material instead of applying the brazing composition to the outer circumference of the inner tube 2 (projections 3). As the brazing material at this time, an Al--Si alloy such as A4045 can be used. After at least one of the outer circumference of the inner tube 2 and the inner circumference of the outer tube 1 is clad with the brazing material, flux is applied to the brazing material. The flux at this time may be a fluoride-based flux or the like that is commonly used for brazing aluminum alloys.

- Instead of applying the brazing composition to the outer circumference of the inner pipe 2 (the projections 3), the outer circumference of the inner pipe 2 may be sprayed with a brazing material.
・After inserting the inner tube 2 to which the brazing composition is applied to the protrusions 3 into the outer tube 1, the inner diameter of the outer tube 1 is reduced by performing a drawing process for reducing the diameter of the outer tube 1. The outer diameter of the protrusions 3 of the inner tube 2 before processing may be smaller than the outer diameter of the protrusions 3, and the outer periphery of the protrusions 3 of the inner tube 2 and the inner periphery of the outer tube 1 may be brought into contact with each other.

・Brazing can be performed in an atmospheric atmosphere by setting the inside of the furnace to the air when performing brazing heat, but the inside of the furnace at that time can be filled with an inert gas instead of the atmosphere or in a vacuum state. It is also possible to

・When performing brazing addition heat in an air atmosphere, it is not always necessary to perform brazing addition heat in a furnace.
- The inner pipe 2 is formed with a convex portion 3 projecting radially from the outer circumference toward the outer pipe 1 side, and the outer pipe 1 and the inner pipe 2 are brazed by the convex portion 3. Instead of or in addition to the projections 3, as shown in FIG. The brazing of the outer tube 1 and the inner tube 2 may be performed at the convex portion 5 . In this case, the brazing material 4 (brazing composition) is arranged on the inner periphery of the convex portion 5 . More specifically, projections 5a projecting toward the outer tube 1 are formed on the inner periphery of the convex portion 5, and portions of the projections 5a on both sides in the width direction of FIG. Brazing material 4 is placed.

Incidentally, when the projections 3 are formed on the inner tube 2 and the projections 5 are also formed on the outer tube 1, the positions of the projections 3 of the inner tube 2 and the projections 5 of the outer tube 1 coincide in the circumferential direction. It may be the same, or it may be off. When the positions of the projections 3 of the inner tube 2 and the projections 5 of the outer tube 1 are shifted in the circumferential direction, under such a state in which the positions of the projections 3 and 5 are shifted in the circumferential direction, The outer periphery of the protrusion 3 is brazed to the outer tube 1 and the inner periphery of the protrusion 5 is brazed to the inner tube 2 . In addition, when the positions of the projections 3 of the inner tube 2 and the projections 5 of the outer tube 1 are aligned in the circumferential direction, the projections 3 of the inner tube 2 and the projections 5 of the outer tube 1 are aligned. Then, the brazing of the outer tube 1 and the inner tube 2 is performed at the protrusions 3 of the inner tube 2 and the protrusions 5 of the outer tube 1 .

DESCRIPTION OF SYMBOLS 1... Outer pipe|tube, 2... Inner pipe|tube, 3... Convex part, 3a... Protrusion, 4... Brazing material, 5... Convex part, 5a... Protrusion.

Claims (6)

It has a double tube consisting of an aluminum alloy outer tube and an inner tube, and performs heat exchange between the fluid flowing between the inner tube and the outer tube and the fluid flowing inside the inner tube. A heat applied to a heat exchanger to join the outer tube and the inner tube through the brazing material therebetween by brazing addition heat that holds the outer tube and the inner tube in a high-temperature furnace. A method for joining double pipes in an exchanger, comprising:
Before performing the brazing addition heat, the space between the outer tube and the inner tube is filled with an inert gas, and a temperature-raising gas is flowed inside the inner tube, and then the outer tube and the inner tube and are joined to each other by said brazing heat. At least one of the outer tube and the inner tube is formed with a protrusion projecting toward the other in the radial direction of the outer tube and the inner tube. 2. The method for joining double pipes in a heat exchanger according to claim 1 , wherein the brazing addition heat is performed with the brazing material interposed between the pipes. 3. The protrusion is formed on the outer periphery of the inner tube so as to protrude toward the inner periphery of the outer tube, and the brazing material is brazing powder applied to the protrusion. 3. A method for joining double tubes in the heat exchanger according to 2 . 2. The protrusion is formed on the outer circumference of the inner tube so as to protrude toward the inner circumference of the outer tube, and the brazing material is clad on the outer circumference of the inner tube. A method for joining double tubes in the heat exchanger according to 1. 3. The protrusion is formed on the outer periphery of the inner tube so as to protrude toward the inner periphery of the outer tube, and the brazing material is clad on the inner periphery of the outer tube. 3. A method for joining double tubes in the heat exchanger according to 2 . The convex portion is formed on the outer circumference of the inner tube so as to protrude toward the inner circumference of the outer tube, and the brazing material is applied by thermal spraying to the outer circumference of the inner tube. 3. The method for joining double tubes in a heat exchanger according to claim 2 .

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