JP6238063B2 - Expansion plug - Google Patents

Description

  The present invention relates to a tube expansion plug.

  In general, heat transfer tubes for flowing refrigerant are used in fin tube heat exchangers of air conditioners and refrigerators. As this heat transfer tube, it is known that by using a heat transfer tube in which fine fins (internal fins) are formed in the tube, the heat transfer characteristics in the tube are dramatically improved as compared with the conventional smooth tube.

  When manufacturing a heat exchanger using such a heat transfer tube, first, a number of heat radiation fins made of, for example, an aluminum alloy in which holes for inserting the heat transfer tube are formed in advance are used. Arrange so as to overlap at a predetermined pitch along the direction. Next, the heat transfer tubes are inserted into the holes of the respective radiation fins. Furthermore, a tube expansion plug is pushed into the heat transfer tube, the heat transfer tube is expanded, and the outer diameter of the heat transfer tube is made larger than the hole diameter of the radiation fin. As a result, the outer periphery of the heat transfer tube and the inner peripheral surface of the hole of the radiating fin are brought into close contact with each other.

  In the step of expanding the heat transfer tube by pushing the tube expansion plug (expansion step), the inner fins of the heat transfer tube may fall down. If the inner fins fall down, the heat transfer tubes cannot be expanded until the heat transfer tubes have a predetermined outer diameter, and the adhesion between the heat transfer tubes and the plate fins decreases. In order to prevent this, various tube expansion rods have been developed in which the inner fins do not easily fall down in accordance with the material of the heat transfer tube and the shape of the inner fins (for example, Patent Documents 1 and 2).

JP 2011-208823 A Japanese Patent No. 4913371

  In recent years, heat transfer tubes have been required to further improve heat transfer performance in order to improve air conditioner performance and save power consumption. Among them, heat transfer tubes with high slim fins with narrow width and high inner fin height are required. It is used. However, there is a problem that the inner fin tends to fall down when expanding the tube as the high slim fin is formed.

  In addition, from the background of depletion of copper resources and the like, there is an increasing demand for forming heat transfer tubes from light and inexpensive aluminum or aluminum alloys. Since aluminum and aluminum alloy are inferior in strength to copper alloy, it is necessary to make the bottom wall thickness of the heat transfer tube thicker than that in the case of using copper alloy in terms of pressure strength. Therefore, there has been a problem that the load (expanded load) applied in the expanded plug insertion direction at the time of expanding the tube increases and the heat transfer tube is likely to buckle.

  The present invention has been made in view of the above-described conventional situation, and an object of the present invention is to provide a tube expansion plug that suppresses buckling of a heat transfer tube during tube expansion and suppresses collapse of an inner fin.

  As a result of intensive studies by the present inventors, it has been found that the collapse of the inner fin that occurs during tube expansion and the tube expansion load during tube expansion correlate with the curvature radius of the head portion of the tube expansion plug that contacts the inner peripheral surface of the heat transfer tube. . Increasing the radius of curvature of the head portion is effective for suppressing the collapse of the inner fins, and decreasing the tube expansion load is effective. That is, the suppression of the falling of the inner fin and the reduction of the tube expansion load are effective due to the mutually opposite curvature radii.

The inventors of the present invention have further intensively studied and found that the tube expansion load is the largest when the tube expansion plug is inserted into the heat transfer tube (initial tube expansion load). Therefore, the heat transfer tube is most likely to buckle when the tube expansion plug is inserted. The inventors of the present invention have completed the present invention by paying attention to the fact that buckling can be suppressed by reducing the initial tube expansion load.
That is, a preliminary tube expansion portion having a relatively small radius of curvature is provided on the distal end side of the head portion of the tube expansion plug to reduce the initial tube expansion load. Further, a main pipe expanding section having a relatively large radius of curvature is provided on the rear end side from the preliminary pipe expanding section to reduce the inner fin collapse. Thereby, this pipe expansion plug can simultaneously realize the suppression of the internal fin collapse and the suppression of the heat transfer tube buckling in the pipe expansion process.

The tube expansion plug of the present invention is configured such that the heat radiation fin is expanded by passing through a heat transfer tube in which a plurality of inner surface fins are formed on an inner peripheral surface through insertion holes formed in a plurality of heat radiation fins arranged in parallel at a predetermined interval. An expansion plug to be inserted into the heat transfer tube, and has a shaft portion and a head portion formed on the tip side thereof, and the cross-section of the head portion is maximum from the tip portion. It has a substantially circular shape that gradually increases in diameter to the diameter portion, and includes a preliminary expanded portion and a main expanded portion that are smoothly connected between the distal end portion and the maximum diameter portion, and the preliminary expanded portion is formed of the heat transfer tube. A tip having a smaller diameter than the minimum pipe inner diameter is connected to a pre-expansion end portion having a diameter larger than the minimum pipe inner diameter with a radius of curvature of not less than 5 mm and not more than 7.9 mm. 20.1mm or more and 30mm or less Connected by a radius, the preliminary tube expansion terminates diameter is the diameter of the pre-expanded pipe termination unit, characterized by being represented by the following formula.
D ₂ = {K × β × (α ₂ −α ₁ ) / α ₁ } + β
However, D ₂ is the pre-expanded tube ends diameter, K is a pre-tube expansion coefficient of 0.45 to 0.65, beta is the minimum tube inner diameter of the heat transfer tube of the prior tube expansion, alpha ₁ is an outer diameter of the heat transfer tube of the prior tube expansion, alpha ₂ is the outer diameter of the heat transfer tube after the tube expansion.

In the tube expansion plug of the present invention, the heat transfer tube is made of aluminum or an aluminum alloy, and the ratio (α ₁ / t) of the outer diameter α ₁ to the bottom wall thickness t of the heat transfer tube before tube expansion is 7 or more and 16 The ratio (j / i) of the fin width j to the fin pitch i of the inner surface fin before tube expansion may be 0.1 or more and 0.7 or less.

  The tube expansion plug of the present invention has a rear surface tube expansion portion between the maximum diameter portion and a rear end portion having a smaller diameter than the maximum diameter portion, and the rear surface tube expansion portion extends from the maximum diameter portion to the rear end portion. May be connected with a radius of curvature of 10 mm or less.

In the tube expansion plug of the present invention, a preliminary tube expansion portion having a relatively small radius of curvature is formed on the tip side of the head portion. As a result, the initial tube expansion load when the tube expansion plug is inserted into the heat transfer tube can be reduced, and buckling of the heat transfer tube can be suppressed. Further, a main pipe expanding portion having a relatively large radius of curvature is formed behind the preliminary pipe expanding portion. Thereby, it is possible to prevent the inner fin from falling when the main expansion portion is expanded.
Therefore, it is possible to simultaneously achieve the suppression of buckling and the reduction of the inner fin collapse which are opposite to each other. According to the pipe expansion plug of the present invention, it is possible to provide a method for manufacturing a heat exchanger in which buckling is unlikely to occur and the inner fins are less likely to collapse.

It is a perspective view which shows the procedure which expands a heat exchanger tube with the tube expansion plug which concerns on embodiment of this invention, and assembles a heat exchanger. FIG. 2A is a partial cross-sectional view showing a tube expansion operation of expanding the heat transfer tube into the heat transfer tube by the tube expansion plug, and FIG. 2A shows a state at the moment of trying to insert the tube expansion plug into the opening of the heat transfer tube; FIG. 2B shows a state immediately before the tube expansion plug is inserted from the opening of the heat transfer tube and clamped by the holding jig. It is a cross-sectional view showing an example of a heat transfer element tube expanded by the tube expansion plug, FIG. 3 (a) shows the entire cross section, FIG. 3 (b) shows an enlarged inner fin. Sectional drawing which shows an example of the heat exchanger tube in which the spiral groove was formed is shown. It is a side view which shows the tube expansion plug which is one Embodiment of this invention, Fig.5 (a) shows the whole tube expansion plug, FIG.5 (b) expands and shows a head part. It is a side view which shows an example of the head part of the conventional pipe expansion plug. It is a graph which shows the relationship between a stroke and a pipe expansion load in the pipe expansion process by the conventional pipe expansion plug. It is a graph which shows the relationship between the curvature radius of the front curved part of a head part, a pipe expansion load, and a fin height reduction rate in the pipe expansion process by the conventional pipe expansion plug.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
In the drawings used in the following description, for the purpose of emphasizing the feature portion, the feature portion may be shown in an enlarged manner for convenience, and the dimensional ratios of the respective constituent elements are not always the same as in practice. Absent. In addition, for the same purpose, portions that are not characteristic may be omitted from illustration.

<Tube expansion process>
FIG. 1 shows a method for manufacturing a heat exchanger using a tube expansion plug 1 according to an embodiment of the present invention.
In this manufacturing method, the expansion plug 1 is inserted into the heat transfer tube 11 in a state where the heat transfer tube 11 is inserted into the insertion holes 15a formed in the plurality of fin members 15 (radiation fins) arranged in parallel at a predetermined interval. In this method, the heat exchanger is manufactured by expanding the tube and bringing the outer periphery of the heat transfer tube 11 into close contact with the inner diameter portion of the insertion hole 15 a of the fin material 15.

The specific procedure of this pipe expansion process is demonstrated below.
First, the fin assembly 16 is formed by stacking a plurality of aluminum or aluminum alloy fin materials 15. An insertion hole 15 a is formed at a position where the heat transfer tube 11 is inserted in each fin material 15. The fin members 15 are arranged so that the insertion holes 15a are aligned in a straight line.
Further, the heat transfer tube 11 is bent into a U shape to form a hairpin pipe. Thereby, the opening part 11a of the heat exchanger tube 11 is aligned on one side, and the U-shaped part 11b is formed on the other side. The pair pin pipe (heat transfer tube 11) is inserted into the insertion hole 15 a of the required number of fin assemblies 16. The opening 11a of each heat transfer tube 11 is arranged on one side of the fin assembly 16.

In this state, the tube expansion plug 1 is forcibly pushed through the opening 11a of each heat transfer tube 11. 2 (a) and 2 (b) are partial cross-sectional views showing the tube expansion operation in which the head unit 3 expands the heat transfer tube 11. FIG.
As shown in FIG. 2A, the head portion 3 of the tube expansion plug 1 is forcibly pushed through the opening portion 11a. Thereby, the heat transfer tube 11 is expanded along the outer peripheral surface of the head portion in order from the opening 11a.
As shown in FIG. 2B, when the head portion 3 is completely inside the opening portion 11a, the outer periphery of the heat transfer tube 11 in the vicinity of the opening portion 11a is clamped with a gripping jig. The tube expansion process up to this point (until clamping by the holding jig) is called a push-type (contraction-type) tube expansion process in which a compressive force is applied to the longitudinal direction of the heat transfer tube 11.

  Even after the clamping process by the holding jig, the head unit 3 is forcibly pushed in until the head unit 3 reaches the vicinity of the U-shaped part 11b of the heat transfer tube 11. At this time, since the opening 11a of the heat transfer tube 11 is fixed (clamped) by the holding jig, a tensile force is applied to the heat transfer tube 11 in the longitudinal direction. In this way, the tube expansion process after the clamping process is called a suspension type (contraction-less type) tube expansion process in which a tensile force is applied to the heat transfer tube 11.

  In the push-in and suspension-type tube expansion process, the head portion 3 of the tube expansion plug 1 can expand the heat transfer tube 11 by pushing the heat transfer tube 11 and plastically deforming it. Since the expanded heat transfer tube 11 is joined to the fin material 15 so as to push the insertion hole 15 a of the fin material 15, the heat transfer tube 11 can be mechanically joined to the fin material 15.

Next, the clamp by the holding jig is released, and the tube expansion plug 1 is pulled out. This process is called a drawing process. When the suspension-type tube expansion process is completed, the heat transfer tube 11 is expanded. Therefore, the drawing process does not plastically deform the heat transfer tube 11. However, the vicinity of the opening 11a of the heat transfer tube 11 is reduced in diameter by being clamped by a holding jig. Therefore, in the drawing process, the opening 11a is expanded again.
Through the above steps, the tube expansion step is completed. FIG. 2 (a), the by inserting a tube expanding plug (b), the outer diameter of the heat transfer tube 11 is expanded tube from the expanded tube before the outer diameter alpha ₁ in the tube expanding Kosoto径alpha _2.

<Heat transfer tube>
FIG. 3A shows a cross-sectional view of the heat transfer tube 11 expanded by the tube expansion plug 1 of the present embodiment before expansion. FIG. 3B is an enlarged view of a part of the inner fin 12 of the heat transfer tube 11 shown in FIG.
A plurality of internal fins 12 projecting toward the center are formed on the inner peripheral surface of the heat transfer tube 11. A plurality of inner fins 12 are formed adjacent to each other at a predetermined interval in the circumferential direction of the inner peripheral surface of the heat transfer tube 11 so as to extend over the entire length of the heat transfer tube 11. For example, 30 to 72 inner fins 12 are formed along the circumferential direction.
The heat transfer tube 11 can obtain such a cross-sectional shape by extruding, for example, a copper alloy, aluminum, or an aluminum alloy.

The inner fin 12 is formed in an isosceles trapezoidal shape in a cross-sectional view having a top portion 12a facing the center of the heat transfer tube 11 and inclined portions 12b and 12b extending so as to sandwich the top portion 12a in the cross section of the heat transfer tube 11. Has been. Since a plurality of these inner surface fins 12 are formed at predetermined intervals in the circumferential direction of the inner peripheral surface of the heat transfer tube 11, a fin groove 14 is formed between the adjacent inner surface fins 12, 12.
The height h of the inner fin 12 is, for example, about 0.05 mm to 0.35 mm. Moreover, the fin width j of the inner surface fin 12 shall be 0.05 mm-0.4 mm, for example. The fin width j means the width of the top portion of the inner fin 12, and when the top portion 12a has a semicircular cross section as shown in FIG. . The fin pitch i of the inner fins 12 (that is, the width of the fin grooves 14) is determined by the inner diameter of the heat transfer tube 11 and the number of inner fins 12 formed, and is, for example, 0.05 mm to 0.7 mm.

  By providing the inner surface fins 12 on the inner surface of the heat transfer tube 11, the surface area of the inner surface of the heat transfer tube 11 can be increased to increase the heat transfer efficiency. In order to further increase the heat transfer efficiency, a high slim fin having a narrow fin width j and a high inner fin (that is, a large height h) is effective. However, as the high slim fin is formed, the inner fin 12 tends to fall when the tube expansion plug 1 is inserted. When the inner fin 12 falls, not only the heat transfer characteristics of the heat transfer tube are deteriorated, but also a predetermined tube expansion rate cannot be obtained, and the heat transfer tube 11 and the insertion hole 15a (see FIG. 1) of the fin material 15 are provided. It does not adhere sufficiently, and the performance as a heat exchanger is greatly reduced. By performing the pipe expansion using the pipe expansion plug 1 provided with the head portion 3 which will be described in detail later, it is possible to suppress the collapse of the inner fin.

The bottom wall thickness t of the heat transfer tube 11 (the wall thickness of the tube corresponding to the fin groove 14) is about 0.3 mm to 0.8 mm. The outer diameter α ₁ of the heat transfer tube 11 (outer diameter before expansion α ₁ ) is, for example, about 5 to 10 mm. The heat transfer tube 11 is expanded at a tube expansion rate of 3% to 8% with the tube expansion plug 1 inserted. That is, the outer diameter α ₂ after pipe expansion (outer diameter after pipe expansion α ₂ ) is set to 5.15 mm to 10.8 mm.

The heat transfer tube 11 may be made of copper alloy, aluminum, or aluminum alloy.
When an aluminum alloy is used for the heat transfer tube 11, the aluminum alloy is not particularly limited, and is typically pure aluminum such as 1050, 1100, 1200, etc. defined by JIS, or 3000 represented by 3003 with Mn added thereto. A series aluminum alloy or the like can be applied. Of course, you may comprise the heat exchanger tube 11 using either the 5000 type | system | group -7000 type | system | group aluminum alloy prescribed | regulated to JIS other than these.

  Aluminum or an aluminum alloy is inferior in strength to a copper alloy. Therefore, it is necessary to make the bottom wall thickness t of the heat transfer tube 11 thicker than the bottom wall thickness of the heat transfer tube formed of a copper alloy in terms of pressure resistance. When the heat transfer tube 11 made of aluminum and aluminum alloy having a thick bottom wall thickness t is to be expanded, the tube expansion load increases. Thereby, the heat transfer tube 11 made of aluminum or an aluminum alloy is likely to be buckled in the tube expansion process.

When aluminum or an aluminum alloy is used as the heat transfer tube 11, the ratio (α ₁ / t) of the outer diameter α ₁ of the heat transfer tube 11 to the bottom wall thickness t of the heat transfer tube 11 before the expansion is 7 or more and 16 or less. Is preferred.
When α ₁ / t is less than 7, the tube expansion load when the heat transfer tube 11 made of aluminum or an aluminum alloy is expanded becomes large. Thereby, the heat transfer tube 11 is likely to buckle. In addition, since the tube expansion load is increased, the force applied to the inner surface fins 12 during tube expansion is increased, and the inner surface fins 12 are liable to fall. When α ₁ / t exceeds 11, the pressure resistance of the heat transfer tube 11 made of aluminum or an aluminum alloy is lowered, which is not preferable.

  Further, regarding the inner fin 12 of the heat transfer tube 11, if the fin width j is increased with respect to the fin pitch i, the tube expansion load at the time of tube expansion increases and the heat transfer tube 11 is likely to buckle. Further, when the fin width j is reduced with respect to the fin pitch i, the inner fin 12 is erected in an elongated shape, so that the inner fin 12 is likely to fall down. Therefore, when the heat transfer tube 11 made of aluminum or an aluminum alloy is used, the ratio (j / i) of the fin width j to the fin pitch i of the inner surface fin 12 before the expansion of the heat transfer tube 11 is 0.1 or more and 0. .7 or less is preferable.

<Another example of heat transfer tube>
In addition to the heat transfer tube 11 described above, the tube expansion plug 1 of the present embodiment may use a heat transfer tube 20 with a spiral groove (inner heat transfer tube 20) in which inner fins 22 are formed in a spiral shape.
FIG. 4 shows a longitudinal sectional structure of a heat transfer tube 20 with a spiral groove applicable to the present invention. The heat transfer tube 20 may be made of copper alloy, aluminum, or aluminum alloy. Further, in the heat transfer tube 20, similarly to the heat transfer tube 11 described above, a protruding inner fin 22 is formed on the inner periphery, and a fin groove 23 is formed between adjacent inner fins. Moreover, the outer diameter before and after the expansion of the heat transfer tube 11 and the equivalent range, the bottom thickness before the expansion, the fin width, and the fin pitch are satisfied.

The heat transfer tube 20 of this example is different from the heat transfer tube 11 described above in that the inner fin 22 is formed so as to draw a spiral along the inner peripheral surface of the heat transfer tube 20 in its length direction.
The plurality of inner surface fins 22 formed on the inner surface of the heat transfer tube 20 are all formed in a spiral shape at the same pitch, and the fin groove 23 formed between the inner surface fins 22 is also the heat transfer tube. 20 is formed in a spiral groove shape so as to draw a spiral at a predetermined pitch.

By forming the inner fin 22 in a spiral shape with respect to the length direction of the heat transfer tube 20, when the refrigerant flows through the heat transfer tube 20, the heat exchange efficiency with the refrigerant can be improved.
Even if it is the heat exchanger tube 20 provided with the inner surface fin 22 formed helically with respect to the longitudinal direction, the tube expansion plug 1 of the present embodiment can be expanded while suppressing buckling and the collapse of the inner surface fin 22.

<Tube expansion load of conventional method and internal fin collapse>
The tube expansion load and the collapse of the inner fin when the tube expansion process described above is performed using a conventional tube expansion plug will be described.

FIG. 6 shows a head portion 103 of a tube expansion plug 101 conventionally used as an example. The tube expansion plug 101 has a circular cross-sectional shape.
The tube expansion plug 101 has a head portion 103 fixed to the tip of a support rod 102. The head portion 103 is formed to bulge into a barrel shape, and a maximum diameter portion 103c is formed at a central portion viewed from the side. The diameter gradually increases from the front end portion 103a to the maximum diameter portion 103c, and the diameter gradually decreases from the maximum diameter portion 103c to the rear end portion 103d.
The front end portion 103a to the maximum diameter portion 103c are connected by a front curved portion 106 that is one curved surface. The front curved portion 106 is formed with a radius of curvature r.
The maximum diameter portion 103c to the rear end portion 103d are connected by a rear curved portion 107 that is one curved surface.

FIG. 7 shows an example of the correlation between the stroke (pushing amount) and the tube expansion load (load in the insertion direction applied to the tube expansion plug) in the tube expansion process using the conventional tube expansion plug 101. In the graph of FIG. 7, the drawing process is omitted.
As shown in FIG. 7, the tube expansion load in the tube expansion process reaches its peak immediately after the tube expansion plug is inserted. This means that the largest tube expansion load (initial tube expansion load) is generated when the head portion of the tube expansion plug is inserted into the opening of the heat transfer tube. The initial tube expansion load is generated in the state shown in FIG. The initial pipe expansion load is generated during the push-type pipe expansion process (that is, the process before clamping with the gripping jig). In the push-in type tube expansion process, a compressive force is applied to the heat transfer tube. Therefore, when the initial tube expansion load is generated, the heat transfer tube is most likely to buckle. Therefore, in order to prevent the occurrence of buckling of the heat transfer tube, it is important to reduce the initial tube expansion load.

  The initial tube expansion load has a correlation with the curvature radius r of the front curved portion 106. In the conventional pipe expansion plug 101, when the curvature radius r of the front curved portion 106 is reduced, the pipe expansion load can be reduced. Along with this, the initial tube expansion load is also reduced, and buckling of the heat transfer tube 11 during tube expansion can be suppressed. It is considered that when the radius of curvature r of the front curved portion 106 is reduced, the contact portion in the insertion direction between the inner peripheral surface of the heat transfer tube and the head portion 103 is shortened, so that the pipe expansion load is reduced.

  In addition, the fall of the inner fin has a correlation with the curvature radius r of the front curved portion 106. In the pipe expansion plug 101, when the curvature radius r of the front curved portion 106 is reduced, the fall of the inner fin 12 increases. This is considered to be because the contact pressure between the inner peripheral surface of the heat transfer tube 11 and the head portion 103 of the tube expansion plug 101 decreases, so that the surface pressure applied to the inner surface fins 12 increases.

  FIG. 8 is a graph showing the relationship between the initial tube expansion load, the fin height reduction rate of the inner fins, and the curvature radius r of the front curved portion 106. The fin height reduction rate indicates the reduction rate of the height of the inner fin 12 before and after the pipe expansion. When the inner fin 12 falls, the fin height decreases, and the fin height reduction rate increases.

  As shown in FIG. 8, the tube expansion load decreases as the radius of curvature r of the front curved portion 106 increases. That is, buckling is suppressed. On the contrary, the fin height reduction rate becomes large, and the fall of the inner fin becomes remarkable.

  As shown in FIG. 8, it is effective to increase the radius of curvature r of the front curved portion 106 in order to prevent the inner fin 12 from collapsing. In order to reduce the tube expansion load, it is effective to reduce the radius of curvature r of the front curved portion 106. Both the fall of the inner fin 12 and the reduction of the tube expansion load have a correlation with the curvature radius r of the front curved portion 106, and mutually contradicting conditions are required. The pipe expansion plug 1 of the present invention satisfies the contradicting conditions, and realizes the suppression of the collapse of the inner fin 12 and the reduction of the pipe expansion load at the same time.

<Tube expansion plug>
FIG. 5A shows a tube expansion plug 1 according to an embodiment of the present invention. FIG. 5B is an enlarged view of the head portion 3 of the tube expansion plug 1.
As shown in FIG. 5A, the tube expansion plug 1 includes a shaft portion 2 and a head portion 3 that is integrally formed on the distal end side thereof. A screw shaft 2 a is formed on the rear end side of the shaft portion 2. The pipe expansion plug 1 can adjust the length of the pipe expansion plug 1 by screwing an unillustrated extension rod having a screw hole that can be fitted to the screw shaft 2a. Thereby, it is possible to adjust the length of the tube expansion plug 1 so that the tube can be expanded over the entire length of the heat transfer tube 11.

As shown in an enlarged view in FIG. 5B, the head portion 3 is formed in a barrel shape so as to bulge so as to have a diameter larger than that of the shaft portion 2. The head portion 3 is formed with a maximum diameter portion 3c between a tip portion 3a forming a flat surface and a rear end portion 3d connected to the shaft portion 2. Moreover, the cross section of the head part 3 is formed in a substantially circular shape. The diameter of the cross section gradually increases from the front end portion 3a to the maximum diameter portion 3c, and gradually decreases from the maximum diameter portion 3c to the rear end portion 3d. Distal end portion 3a is formed with a diameter D _1, the maximum diameter portion 3c is formed with a diameter D _3.
The “substantially circular” cross section means a shape along the inner periphery of the heat transfer tube 11 having a circular shape. For example, the groove | channel may be formed in the surface of the head part 3 with a circular cross section, and the unevenness | corrugation may be formed in the cross section.

The head portion 3 has a front surface expanded portion 6 from the tip portion 3a to the maximum diameter portion 3c. Further, the head portion 3 has a rear-surface expanded portion 7 from the maximum diameter portion 3c to the rear end portion 3d. That is, the head portion 3 has a front-side expanded portion 6 on the front end side and a rear-surface expanded portion 7 on the rear end side with the maximum diameter portion 3c as a boundary.
The diameter D ₁ of the distal end portion 3a can be smoothly inserted into the inner diameter of the heat transfer tube 11 is formed to the minimum inner diameter β is smaller than the diameter of the heat transfer tube 11 is expanded tube target.

The front surface expanded portion 6 plays a role of expanding and expanding the heat transfer tube 11 radially outward when the tube expansion plug 1 is inserted into the heat transfer tube. The front pipe expansion part 6 is divided into a preliminary pipe expansion part 6A and a main pipe expansion part 6B having different radii of curvature, with the preliminary pipe expansion end part 3b as a boundary.
Preliminary expanded portion 6A is a uniform curved surface having a radius of curvature R _1. The main expanded portion 6B is a uniform curved surface having a radius of curvature R _2.
The curved surface of the preliminary pipe expansion portion 6A and the curved surface of the main pipe expansion portion 6B are smoothly connected at the preliminary pipe expansion end portion 3b. In other words, the pre-expanded pipe 6A and the main pipe 6B are connected without causing an edge at the point where the inclinations of the tangent lines coincide with each other when the longitudinal section is taken.

The radius of curvature _{R 1} of the pre-expanded portion 6A is preferably 5mm or more 7.9mm or less. The pre-expanded tube portion 6A is a portion that abuts the opening 11a of the heat transfer tube 11 and first expands the heat transfer tube while receiving an initial tube expansion load (see FIG. 2A). Therefore, by reducing the radius of curvature R ₁ of the pre-expanded pipe portion 6A, thereby reducing the pipe expansion load immediately after insertion into the opening 11a of the heat transfer tube 11 (initial tube expansion load). The radius of curvature R ₁ of the pre-expanded portion 6A is set to be lower than or equal 7.9 mm, to reduce the initial tube expansion force can be suppressed buckling of the heat transfer tube 11. Further, the curvature radius R ₁ of the pre-expanded pipe portion 6A With more than 5 mm, can be suppressed falling of the inner surface the fins 12.

The radius of curvature _{R 2} of the main expanded portion 6B is preferably 30mm or less than 20.1 mm. In the tube expansion process of the heat transfer tube 11, the main tube expansion portion 6B plays a role of further expanding the heat transfer tube 11 preliminarily expanded along the preliminary tube expansion portion 6A outward in the radial direction (see FIG. 2B). Accordingly, the main pipe expansion portion 6B applies a large load to the inner surface fin 12 with respect to the preliminary pipe expansion portion 6A. That is, the main pipe expanding portion 6B acts predominantly against the falling of the inner fin 12. By increasing the curvature radius R ₂ of the main expanded portion 6B, it can be suppressed falling of the inner surface the fins 12.
The radius of curvature _{R 2} of the main expanded portion 6B is, in the case of less than 20.1 mm, the inclination of the inner surface the fins 12 is undesirably remarkable. Moreover, when it exceeds 30 mm, a pipe expansion load becomes large, and an initial stage pipe expansion load also becomes large in connection with it. Therefore, the concern about the occurrence of buckling of the heat transfer tube 11 is increased.

The diameter D ₂ (preliminary pipe expansion end diameter D ₂ ) of the preliminary pipe expansion end portion 3 b that becomes the boundary between the preliminary pipe expansion portion 6 A and the main pipe expansion portion 6 B is formed larger than the minimum inner diameter β of the heat transfer tube 11. Therefore, the minimum inner diameter portion of the heat transfer tube 11 (that is, the top portion of the inner fin 12) does not contact the preliminary tube expansion portion 6A and does not contact the main tube expansion portion 6B.
Also, pre-expanded tube ends diameter _{D 2} is the pre-expanded tube coefficient K as 0.45 to 0.65, satisfying the following equation.
D ₂ = {K × β × (α ₂ −α ₁ ) / α ₁ } + β
Β is the minimum tube inner diameter of the heat transfer tube 11 before the tube expansion, α1 is the outer diameter of the heat transfer tube 11 before the tube expansion, and α2 is the outer diameter of the heat transfer tube 11 after the tube expansion.

Preliminary expanded tube ends diameter D ₂ is increased by increasing the pre-expanded tube coefficient K. Along with this, in the front expanded portion 6, the preliminary expanded portion 6A becomes relatively large, and the main expanded portion 6B becomes relatively small. A preliminary expanded portion 6A is formed smaller radius of curvature R _1, that the pre-expanded pipe portion 6A becomes relatively large, there is a possibility that the inclination of the inner surface fin 12 becomes remarkable.
On the contrary, when the preliminary expansion coefficient K is decreased, the preliminary expansion end diameter D2 is decreased. Accordingly, in the front expanded portion 6, the preliminary expanded portion 6A becomes relatively small, and the main expanded portion 6B becomes relatively large. The main expanded portion 6B because it is larger radius of curvature R _2, that the main expanded pipe portion 6B is relatively large, the initial tube expansion load increases heat transfer tube 11 of the tube expansion there is a possibility that buckling.
By setting the preliminary tube expansion coefficient K to 0.45 or more and 0.65 or less, the collapse of the inner fin 12 and the buckling of the heat transfer tube 11 can be suppressed at the same time.

A rear pipe expanding portion 7 is formed behind the maximum diameter portion 3 c of the head portion 3. Rear expanded portion 7, a uniform curved surface having a radius of curvature R _3.
When the tube expansion plug 1 is pulled out from the heat transfer tube 11 (in the drawing step), the rear surface tube expansion portion 7 plays a role of smoothing the drawing by expanding the heat transfer tube 11 whose diameter is reduced by the elastic deformation again radially outward. . In addition, it plays a role of expanding the vicinity of the opening 11a of the heat transfer tube 11 having a reduced diameter again by clamping with a gripping jig.

Since the opening 11a of the heat transfer tube to be expanded again has undergone expansion and contraction, work hardening has occurred. Therefore, if you do not set the radius of curvature R ₃ of the rear expanded portion 7 properly, in drawing process, joined by excessive tensile stress in the heat transfer tube 11, the breaking of the heat transfer tube 11 takes place. Moreover, in this drawing process, when an excessive tensile stress is applied, the heat transfer tube 11 itself is stretched, and at that time, shrinkage occurs in the radial direction. That is, the expanded heat transfer tube 11 is reduced in diameter.
To prevent this phenomenon, the radius of curvature R ₃ of the rear expanded portion 7 is preferably set to 10mm or less. By setting it as 10 mm or less, it can suppress that an excessive tensile stress is added to the heat exchanger tube 11.

  In the pipe expansion plug 1 shown in FIG. 5A, the shaft portion 2 is made of a steel material having high strength, for example, chromium molybdenum steel shown by JIS regulation SCM435. Moreover, the head part 3 is integrally formed from the cemented carbide. The head portion 3 is coupled to the shaft portion 2 by caulking, or is coupled by brazing means using silver brazing or the like.

As the cemented carbide constituting the head portion, a cemented carbide obtained by sintering carbides of Group IVa, Va, and VIa group elements with an iron-based metal such as Fe, Co, or Ni can be used. For example, WC-Co alloy, WC-TiC-Co alloy, WC-Ta-Co alloy, WC-TiC-Ta-Co alloy, WC-Ni alloy, WC-Ni-Cr alloy, etc. It can be used as appropriate.
As an example, a range of HRC 85 to 95 can be obtained in a cemented carbide obtained by adding 5 to 17% by mass of Co to WC particles, and thus can be applied to the constituent material of the tube expansion plug 1 of the present embodiment. As the above-mentioned cemented carbide, a cemented carbide of the kind specified by JISV10, V20, V30, V40, V50, V60, etc. can be used.

Further, as shown in FIG. 5A, the tube expansion plug 1 may have a diamond-like carbon film 5 formed on the entire outer peripheral surface of the head portion 3. When the diamond-like carbon film 5 is formed, the film thickness is preferably in the range of 0.5 μm to 3.0 μm. When the film thickness of the diamond-like carbon film 5 is less than 0.5 μm, the effect of suppressing the aggregation of aluminum is lowered, and the adhesion of aluminum to the tube expansion plug 1 is likely to occur during tube expansion. Further, when the film thickness of the diamond-like carbon film 5 exceeds 3.0 μm, the diamond-like carbon film 5 is likely to be peeled off.
The hardness of the diamond-like carbon film 5 is preferably 20 GPa or more and 70 GPa or less. When the hardness of the diamond-like carbon film 5 is less than 20 GPa, the wear resistance is reduced and the life of the tube expansion plug 1 is shortened, and when the hardness is more than 70 GPa, the film formation itself is difficult.

  Further, the critical peel load of the diamond-like carbon film 5 is preferably 5N or more. When the critical peel load of the diamond-like carbon film 5 is less than 5N, the film is easily peeled and the life of the tube expansion plug 1 is shortened. Further, when the critical film thickness load of the diamond-like carbon film 5 is 30 N or more, it is difficult for aluminum to adhere even if the tube is expanded for a longer distance.

Although the lubricating oil used at the time of pipe expansion together with the pipe expansion plug 1 is not particularly illustrated, it is preferable to use a lubricating oil having a flash point of 100 ° C. or lower and a kinematic viscosity of 1.0 mm ² / S (at 40 ° C.) or higher.
If it illustrates as a lubricating oil which can be used for this condition, Daphne punch oil AF-2A (Idemitsu Kosan make: kinematic viscosity 1.37mm < ² > / S) can be mentioned.

  EXAMPLES Hereinafter, although an Example is shown and this invention is demonstrated further in detail, this invention is not limited to these Examples.

(Test 1)
Test 1 was conducted on the front pipe expansion portion of the pipe expansion plug, the initial pipe expansion load, and the inner fin collapse.
Several types of tube expansion plugs shown in FIGS. 5A and 5B were prepared. The head portion of the tube expansion plug is made of cemented carbide (HRA90) equivalent to VM40, and the shaft portion is made of JIS standard SCM435. The rear surface expanded portion of these expanded plugs has a curvature radius of 7.5 mm.

As heat transfer tubes expanded by these tube expansion plugs, several types of heat transfer tubes having inner fins formed linearly in the longitudinal direction as shown in FIGS. The heat transfer tube is made of JIS3003 alloy.
Using the prepared tube expansion plug, the tube expansion process of the heat transfer tube was performed. During the expansion, the heat transfer tube was immersed in a lubricating oil (Daphney punch oil AF-2A: manufactured by Idemitsu Kosan Co., Ltd .: kinematic viscosity 1.37 mm ² / S) and immediately expanded. The insertion speed of the expansion plug during expansion was 500 mm / min.
The combination of expansion pipe and heat transfer tube is No. 1-No. 30 is summarized in Table 1. In Table 1, the outer diameter tube expansion rate is expressed as a percentage in the following equation, with α ₁ being the outer diameter of the heat transfer tube before tube expansion and α ₂ being the outer diameter of the heat transfer tube after tube expansion.
100 × (α ₂ −α ₁ ) / α ₁
Table 2 shows the initial tube expansion load, the stable tube expansion load, and the reduction rate of the inner fins, which are generated as a result of the tube expansion process. As shown in FIG. 7, the stable tube expansion load means a load in a region where the tube expansion load is stable.

If the initial tube expansion load is 500 N or more, buckling tends to occur. Further, when the stable tube expansion load is 450 N or more, buckling tends to occur.
When the reduction rate of the inner fins is 15% or more, the inner fins fall and the heat exchange effect decreases, which is preferable. In addition, the outer diameter may not be expanded sufficiently due to the fall of the inner fin.

As shown in Table 1 and Table 2, among the tube expansion steps using various combinations of tube expansion plugs and heat transfer tubes, No. 1 was used. 1-No. It can be seen that in the tube expansion process of 24, the tube expansion load and the height reduction rate of the inner surface fins can be suppressed. In contrast, no. 25-No. In 30 pipe expansion processes, the pipe expansion load is high or the reduction rate of the inner fins is large. In particular, no. In the tube expansion process of Nos. 26, 28, and 29, buckling occurred at the initial stage of tube expansion.
From the results shown in Tables 1 and 2, by appropriately setting the radius of curvature of the pre-expanded portion, the radius of curvature of the main expanded portion, and the diameter of the end portion of the pre-expanded tube, the inner fin collapses while suppressing the expansion load. It was confirmed that suppression was possible.
Further, the ratio (α ₁ / t) of the outer diameter α ₁ to the bottom wall thickness t of the heat transfer tube is 7 or more and 16 or less, and the ratio (j / i) of the fin width j to the fin pitch i of the inner surface fin is It was confirmed that a more preferable tube expansion process can be performed when the ratio is 0.1 or more and 0.7 or less.

(Test 2)
Next, the rear surface expanded portion of the expanded tube plug, the initial expanded tube load, and the collapse of the inner fin were investigated as Test 2.
Several types of tube expansion plugs shown in FIGS. 5A and 5B, each having a different radius of curvature of the rear surface tube expansion portion, were prepared. These expanded pipes have a radius of curvature of the preliminary expanded portion of 7 mm, a radius of curvature of the main expanded portion of 22 mm, an end diameter of the expanded preliminary tube of 5.57 mm, and a diameter of the maximum diameter portion of 5.86 mm. The material of the head part and the shaft part is the same as in Test 1 described above.
As heat transfer tubes expanded by these tube expansion plugs, heat transfer tubes made of JIS3003 alloy having inner fins formed linearly in the longitudinal direction as shown in FIGS. 3A and 3B were prepared. These tubes have a minimum inner diameter of 5.4 mm, an outer diameter of 7.0 mm, a bottom wall thickness of 0.5 mm, an outer diameter / bottom wall thickness of 14.0, and a fin width of 0 mm. .15 mm, fin pitch is 0.38 mm, fin pitch / fin width is 0.4, and the number of internal fins is 50.
The result of the expansion process of the heat transfer tube using the prepared expansion plug is No. 31-No. 34 is summarized in Table 1. In addition, the outer diameter of the heat transfer tube after the tube expansion was 7.4 mm.
In the tube expansion process, the opening portion of the heat transfer tube was clamped by a holding jig after the push-in tube expansion step, and then the hanging tube expansion step and the drawing step were sequentially performed. The opening of the heat transfer tube is reduced to an outer diameter of 7.0 mm by the clamp, and is expanded again by the rear surface expanded portion in the drawing process.

As shown in Table 3, among tube expansion processes using a plurality of tube expansion plugs, In No. 31, during the drawing process, a very large drawing force was generated near the opening of the heat transfer tube, and the heat transfer tube was broken.
No. In No. 32, the heat transfer tube was extended in the longitudinal direction due to the resistance at the time of drawing, and the shrinkage occurred accordingly (the outer diameter of the heat transfer tube was reduced). As a result, the heat transfer tube had an outer diameter of 7.35 mm over the entire length. In contrast, no. 33, no. In the tube expansion process 34, the drawing process was normally performed.
From the result of Test 2, it was confirmed that an excessive tensile stress was not applied to the heat transfer tube during drawing by setting the curvature radius of the rear surface expanded portion to 10 mm or more.

  Although various embodiments of the present invention have been described above, each configuration in each embodiment and combinations thereof are examples, and addition, omission, replacement, and configuration of configurations are within the scope not departing from the spirit of the present invention. And other changes are possible. Further, the present invention is not limited by the embodiment.

DESCRIPTION OF SYMBOLS 1 ... Tube expansion plug, 2 ... Shaft part, 3 ... Head part, 3a ... Tip part, 3b ... Pre-expansion end part, 3c ... Maximum diameter part, 3d ... Rear end part, 5 ... Diamond-like carbon film, 6 ... Front pipe expansion 6A ... Preliminary tube expansion portion, 6B ... Main tube expansion portion, 7 ... Rear surface tube expansion portion, 11, 20 ... Heat transfer tube, 11a ... Opening portion, 12, 22 ... Inner surface fins, 14, 23 ... Fin groove, 15 ... Fin material (Radiating fin), 15a: insertion hole, D ₁ ... diameter of the tip, D ₂ ... diameter of the preliminary expansion end, D ₃ ... diameter of the maximum diameter, K ... preliminary expansion coefficient, R ₁ ... radius of curvature of the preliminary expansion , R ₂ ... curvature radius of the main pipe expansion part, R ₃ ... curvature radius of the rear pipe expansion part, h ... fin height, i ... fin pitch, j ... fin width, t ... bottom wall thickness, α ₁ ... outside before pipe expansion Diameter, α ₂ ... Outer diameter after tube expansion, β ... Minimum inner diameter

Claims (3)

In order to closely adhere to the heat radiating fins by expanding the heat transfer tube having a plurality of inner surface fins formed on the inner peripheral surface through the insertion holes formed in the plurality of heat radiating fins arranged in parallel in a predetermined interval, A tube expansion plug to be inserted into the heat transfer tube,
A shaft portion, and a head portion formed on the tip side thereof,
The head portion has a substantially circular shape whose cross section gradually increases in diameter from the tip portion to the maximum diameter portion, and a preliminary tube expansion portion and a main tube expansion portion that are smoothly connected between the tip portion and the maximum diameter portion. And
The pre-expanded portion connects a tip portion having a diameter smaller than the minimum tube inner diameter of the heat transfer tube to a pre-expansion end portion having a diameter larger than the minimum tube inner diameter with a radius of curvature of 5 mm or more and 7.9 mm or less,
The main expanded portion connects the preliminary expanded end portion to the maximum diameter portion with a radius of curvature of 20.1 mm to 30 mm,
A tube expansion plug, wherein the tube expansion end diameter, which is the diameter of the tube expansion end portion, is expressed by the following equation.
D ₂ = {K × β × (α ₂ −α ₁ ) / α ₁ } + β
However, _{D 2} is a pre-expanded tube end diameter,
K is a preliminary expansion coefficient of 0.45 or more and 0.65 or less,
β is the minimum tube inner diameter of the heat transfer tube before expansion,
α ₁ is the outer diameter of the heat transfer tube before expansion,
α ₂ is the outer diameter of the heat transfer tube after tube expansion. The heat transfer tube is made of aluminum or an aluminum alloy,
The ratio (α ₁ / t) of the outer diameter α ₁ to the bottom wall thickness t of the heat transfer tube before expansion is 7 or more and 16 or less,
2. The tube expansion plug according to claim 1, wherein a ratio (j / i) of a fin width j to a fin pitch i of the inner surface fin before tube expansion is 0.1 or more and 0.7 or less. Between the maximum diameter portion and the rear end portion having a smaller diameter than the maximum diameter portion, there is a rear surface expanded portion,
The tube expansion plug according to claim 1 or 2, wherein the rear surface tube expansion portion connects the maximum diameter portion to the rear end portion with a curvature radius of 10 mm or less.

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