JP2016087675A - Tube expansion plug and design method for tube expansion plug - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a tube expansion plug.SOLUTION: A tube expansion plug, which expands a heat transfer tube in such a manner that the plug is inserted in the heat transfer tube on an inner peripheral surface of which plural inner fins are formed, has a shank, and a head part formed on a tip side of the shank. The head part has a substantially circular shape such that a diameter of a cross section thereof is gradually increased from a tip side to a maximum diameter part. The head part is equipped with a main tube expansion part which is formed from the maximum diameter part toward the tip side, and an upper limit and a lower limit of a curvature radius R of a longitudinal section of the main tube expansion part has a relationship of the following expression with a diameter D of the maximum diameter part. The upper limit R=-9.37×D+196.69×D-1375.5×D+3214, the lower limit R=-14.43×D+286.66×D-1897.6×D+4190.SELECTED DRAWING: Figure 5

Description

  The present invention relates to a tube expansion plug and a tube expansion plug design method.

  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 large number of heat-radiating plates made of, for example, an aluminum alloy in which holes for inserting the heat transfer tube are formed in advance are set to the length of the heat transfer tube. Arrange so as to overlap at a predetermined pitch along the direction. Next, the heat transfer tube is inserted into the hole of each heat radiating plate. Furthermore, the heat transfer tube is expanded by pushing a tube expansion plug into the heat transfer tube, and the outer diameter of the heat transfer tube is made larger than the hole diameter of the heat radiating plate. Thus, the outer periphery of the heat transfer tube and the inner peripheral surface of the hole of the heat radiating plate are brought into close contact with each other.

  In the step of expanding the heat transfer tube by pushing in the tube expansion plug (expansion step), the inner fins of the heat transfer tube may fall down. If the inner fin falls down, the heat transfer tube cannot be expanded until the heat transfer tube has a predetermined outer diameter, and the adhesion between the heat transfer tube and the heat radiating plate 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, as the high slim fins are formed, there is a problem that the inner fins easily fall down during tube expansion, and a desired tube expansion rate cannot be obtained.

  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 resistance. Therefore, there has been a problem that the load (tube expansion load) applied in the tube expansion plug insertion direction at the time of tube expansion increases, and the heat transfer tube is easily buckled and the tube expansion plug is easily worn.

  The present invention has been made in view of the conventional situation as described above, and provides a tube expansion plug that can suppress the collapse of the inner fin and obtain a sufficient tube expansion rate while reducing the tube expansion load at the time of tube expansion. Objective.

  As a result of diligent studies by the present inventors, it has been found that the radius of curvature of the head portion of the pipe expansion plug contacting the inner peripheral surface of the heat transfer pipe is an important parameter for the pipe expansion load and the pipe expansion ratio during pipe expansion. If the curvature radius of the head portion is reduced, the tube expansion load can be suppressed while the tube expansion rate is decreased. Further, when the curvature radius of the head portion is increased, the tube expansion rate can be increased while the tube expansion load is increased. The inventors of the present invention have further studied diligently, and found the shape of a tube expansion plug having an optimum radius of curvature for obtaining a predetermined tube expansion rate and suppressing the tube expansion load most.

The tube expansion plug of the present invention is a tube expansion plug that expands the heat transfer tube by being inserted into a heat transfer tube having a plurality of internal fins formed on the inner peripheral surface, and is formed on the shaft portion and the tip side thereof. A head portion, and the head portion has a substantially circular shape whose cross section gradually increases in diameter from the tip end side to the maximum diameter portion, and the head portion extends from the maximum diameter portion to the tip end portion. The upper and lower limits of the radius of curvature R of the longitudinal section of the main expanded portion have a relationship expressed by the following formula with the diameter D of the maximum diameter portion.
Upper limit R = −9.37 × D ³ + 196.69 × D ² −1375.5 × D + 3214
Lower limit R = −14.43 × D ³ + 286.66 × D ² −1897.6 × D + 4190

Further, in the tube expansion plug of the present invention, the head portion includes a pre-expansion tube portion that is smoothly connected to the main tube expansion portion between the tip portion and the main tube expansion portion. A spare pipe having a radius of curvature of 5 mm or more and 7.9 mm or less is connected from the tip portion having a diameter smaller than the minimum tube inner diameter of the heat transfer tube to a preliminary tube expansion end portion having a diameter larger than the minimum tube inner diameter. The tube expansion end diameter may be expressed 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 diameter of the maximum diameter portion may be not less than 5.7 mm and not more than 7.0 mm.

  Further, in the tube expansion plug of the present invention, the heat transfer tube before tube expansion is made of aluminum or an aluminum alloy, the outer diameter is 6 mm or more and 8 mm or less, the bottom wall thickness is 0.45 mm or more and 0.65 mm or less, The ratio of the bottom wall thickness to the diameter is 0.05 or more and 0.11 or less, and the present invention can be applied to the inner fin formed in a spiral shape in the longitudinal direction of the heat transfer tube.

  Further, in the tube expansion plug of the present invention, the head portion has a rear surface expanded portion between the maximum diameter portion and a rear end portion having a smaller diameter than the maximum diameter portion, and the rear surface expanded portion is the maximum diameter portion. To the rear end portion may be connected with a curvature radius of 10 mm or less.

Further, a design method according to the tube expansion plug of the present invention is a tube expansion plug design method for expanding the heat transfer tube by inserting the heat transfer tube into a heat transfer tube having a plurality of inner surface fins formed on an inner peripheral surface thereof. And a head portion formed on a tip side thereof, wherein the head portion is a substantially circular shape whose transverse section gradually increases in diameter from the tip portion side to the maximum diameter portion. The head portion is provided with a main expanded portion formed from the maximum diameter portion toward the distal end portion, and a curvature radius R of a longitudinal section of the main expanded portion is represented by a diameter D of the maximum diameter portion or less. Between the upper and lower limits of the equation.
Upper limit R = −9.37 × D ³ + 196.69 × D ² −1375.5 × D + 3214
Lower limit R = −14.43 × D ³ + 286.66 × D ² −1897.6 × D + 4190
However, D is the diameter of the said largest diameter part, R is the curvature radius of the longitudinal cross-section of the said main expansion part.

  Further, a design method according to the tube expansion plug of the present invention is a tube expansion plug design method for expanding the heat transfer tube by inserting the heat transfer tube into a heat transfer tube having a plurality of inner surface fins formed on an inner peripheral surface thereof. And a head portion formed on the tip side thereof, and the head portion has a substantially circular shape whose transverse section gradually increases in diameter from the tip portion side to the maximum diameter portion. A plurality of pipe expansion plugs provided with a main pipe expansion portion formed from the maximum diameter section toward the tip end side, wherein the diameter of the maximum diameter section and the curvature radius of the longitudinal section of the main pipe expansion section are variously changed. And plotting the expansion rate and the expansion load when the heat transfer tube is expanded by a plurality of the expansion plugs on a graph, and among the plurality of expansion plugs, a group of the ones having the same diameter of the maximum diameter portion And taking a common tangent line between each group of the graph, To group the diameter of the serial maximum diameter portion is the same, the optimum radius of curvature of the radius of curvature which is closest to said common tangent.

  The tube expansion plug of the present invention can optimize the radius of curvature of the main tube expansion portion formed in the head portion, and can increase the tube expansion rate while suppressing the tube expansion load in the tube expansion process. By suppressing the tube expansion load during tube expansion, it is possible to prevent buckling of the heat transfer tube, reduce head wear, and extend the life of the tube expansion plug.

It is a perspective view which shows the procedure which expands a heat exchanger tube with the tube expansion plug which concerns on 1st Embodiment, and assembles a heat exchanger. It is a fragmentary sectional view which shows the pipe expansion process which expands a heat exchanger tube with the pipe expansion plug which concerns on 1st Embodiment. It is a cross-sectional view which shows an example of the heat exchanger tube expanded by the tube expansion plug of 1st Embodiment, Fig.3 (a) shows the whole cross section, FIG.3 (b) expands and shows an internal surface fin. The longitudinal cross-sectional view which shows an example of the heat exchanger tube expanded by the tube expansion plug of 1st Embodiment is shown. The tube expansion plug of 1st Embodiment is shown, Fig.5 (a) is a perspective view, FIG.5 (b) is a side view of a head part. It is a side view of the head part of the tube expansion plug of 2nd Embodiment. FIG. 7A is a partial cross-sectional view illustrating a tube expansion process for expanding the heat transfer tube with the tube expansion plug of the second embodiment, and FIG. 7A illustrates a state at the moment when the tube expansion plug is to be inserted into the opening of the heat transfer tube. (B) shows a state in which the tube expansion plug is completely inserted into the heat transfer tube. It is the graph which put together the relationship between the pipe expansion rate and the pipe expansion load which are the results of a 1st simulation. It is a graph which shows the desirable range of the maximum diameter and curvature radius of the head part of a tube expansion plug calculated | required from the result of the 1st simulation. It is the graph which put together the relationship between the pipe expansion rate and the pipe expansion load which are the results of a 2nd simulation. It is a graph which shows the desirable range of the maximum diameter and curvature radius of the head part of a tube expansion plug calculated | required from the result of the 2nd simulation. It is the graph which put together the relationship between the pipe expansion rate and the pipe expansion load which are the results of the 3rd simulation. It is a graph which shows the desirable range of the maximum diameter and curvature radius of the head part of a tube expansion plug calculated | required from the result of the 3rd simulation. It is a graph which shows an example of the correlation of the stroke (pushing amount) in a pipe expansion process and the pipe expansion load (load of the insertion direction added to a pipe expansion plug) at the time of using a general pipe expansion plug.

Hereinafter, embodiments 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 tube 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 (heat radiating plates) 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 necessary number of hairpin pipes (heat transfer tubes 11) are inserted into the insertion holes 15a of the fin assembly 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.
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.
FIG. 2 is a partial cross-sectional view showing a tube expansion operation in which the head unit 3 expands the heat transfer tube 11. The tube expansion plug 1 expands the heat transfer tube 11 along the outer peripheral surface of the head portion 3. 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. By inserting a tube expanding plug 1 as shown in FIG. 2, 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 shows an enlarged view of a part of the inner fin 12 of the heat transfer tube 11 shown in FIG. FIG. 4 shows a longitudinal sectional view of the heat transfer tube 11.

  As shown in FIG. 3A, a plurality of inner surface fins 12 projecting toward the center are formed on the inner peripheral surface of the heat transfer tube 11. As shown in FIG. 4, the inner fin 12 is formed in a spiral shape with respect to the length direction of the heat transfer tube 11 over the entire length in the length direction of the heat transfer tube 11. A plurality of inner surface 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. For example, 30 to 72 inner fins 12 are formed along the circumferential direction.

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. These inner surface fins 12 are arranged at predetermined intervals in the circumferential direction of the inner peripheral surface of the heat transfer tube 11, and fin grooves 14 are 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 pitch i of the inner fins 12 is determined by the inner diameter of the heat transfer tube 11 and the number of inner fins 12 to be formed, and is, for example, 0.05 mm to 0.7 mm.

  The inner fin 12 is formed so as to draw a spiral along the inner circumferential surface of the heat transfer tube 11 in the length direction thereof. The twist angle θ of the inner fin 12 is formed to be about 15 ° to 40 °. Note that the torsion angle θ is the extension line S of the spiral groove or spiral fin displayed on the inner side of the heat transfer tube 11 as shown in FIG. Indicates the angle between the outer surface and the outer surface.

  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. Moreover, when the internal fin 12 is formed in a spiral shape in the length direction of the heat transfer tube 11, when the refrigerant flows through the heat transfer tube 11, the heat exchange efficiency with the refrigerant can be improved. In order to further increase the heat transfer efficiency, a high slim fin having a narrow fin width j and a high inner fin 12 (that is, a high 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 11 deteriorate, but also a predetermined tube expansion rate cannot be obtained, and the insertion hole 15a between the heat transfer tube 11 and the fin material 15 (see FIG. 1). Does not adhere sufficiently, and the performance as a heat exchanger is greatly reduced. By performing tube expansion using the tube expansion plug 1 provided with the head portion 3 that will be described in detail later, it is possible to suppress the collapse of the inner surface fins 12 and obtain a sufficient tube expansion rate.

The bottom wall thickness t of the heat transfer tube 11 (the wall thickness of the tube corresponding to the fin groove 14) is 0.45 mm or more and 0.65 mm or less. The outer diameter α ₁ of the heat transfer tube 11 (outer diameter before expansion α ₁ ) is, for example, 6 mm or more and 8 mm or less.
The heat transfer tube 11 is expanded at a tube expansion rate of 3% to 8%, for example, with the tube expansion plug 1 inserted. In this case, 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.

In the case of using aluminum or an aluminum alloy as the heat transfer tube 11, the ratio (t / α ₁ ) of the bottom wall thickness t of the heat transfer tube 11 to the outer diameter α ₁ of the heat transfer tube 11 before the expansion is 0.05 or more and 0.11. The following is preferable.
The tube expansion plug 1 of the first embodiment (or the tube expansion plug 21 of the second embodiment) can perform the tube expansion step with respect to such a heat transfer tube 11 while increasing the tube expansion rate while suppressing the tube expansion load. Also, if the t / alpha ₁ exceeds 0.11, there is a risk that the tube expansion load tube expansion of the heat transfer tubes 11 made of aluminum or aluminum alloy becomes too large. Furthermore, when t / α ₁ is less than 0.05, the pressure resistance of the heat transfer tube 11 made of aluminum or an aluminum alloy may be insufficient.

<First Embodiment of Tube Expansion Plug>
Fig.5 (a) is a perspective view which shows the pipe expansion plug 1 of one Embodiment which concerns on this invention. FIG. 5B is a side 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 FIG. 5B, the head portion 3 is formed in a barrel shape so as to bulge so as to have a larger diameter than the shaft portion 2. Moreover, the cross section of the head part 3 is formed in a substantially circular shape. The “substantially circular” cross section means a shape along the inner periphery of the heat transfer tube 11 having a circular shape. For example, a groove may be provided on the surface of the head portion 3 having a circular cross section, and a convex portion may be formed on the cross section.

  The head portion 3 has a front end portion 3 a that forms a flat surface, and a rear end portion 3 d that is connected to the shaft portion 2. A maximum diameter portion 3c is formed between the front end portion 3a and the rear end portion 3d. The cross section of the head portion 3 gradually increases from the tip portion 3a having the diameter FD to the maximum diameter portion 3c having the diameter D. Further, it gradually decreases from the maximum diameter portion 3c to the rear end portion 3d.

In the head portion 3, a portion from the distal end portion 3 a to the maximum diameter portion 3 c is a main expanded portion 6. Further, a portion from the maximum diameter portion 3c to the rear end portion 3d is a rear surface expanded portion 7. In other words, the head portion 3 has the main expanded portion 6 on the front end side and the rear expanded portion 7 on the rear end side with respect to the maximum diameter portion 3c.
The diameter FD of the tip 3a is formed to be smaller than the minimum inner diameter β (see FIG. 2) of the heat transfer tube 11 to be expanded, and can be smoothly inserted into the inner diameter of the heat transfer tube 11.

  The diameter (maximum diameter) D of the maximum diameter portion 3c is appropriately set based on the inner diameter β of the heat transfer tube 11 to be expanded and the necessary expansion rate. In the tube expansion plug 1 of this embodiment, the tube expansion process can be performed by increasing the tube expansion rate while suppressing the tube expansion load by setting the maximum diameter D to 5.7 mm or more and 7.0 mm or less.

  When the main pipe expansion portion 6 is inserted into the heat transfer tube 11, the main pipe expansion portion 6 plays a role of expanding and expanding the heat transfer pipe 11 radially outward. The main expanded pipe portion 6 is a curved surface that connects the distal end portion 3a to the maximum diameter portion 3c with a radius of curvature R.

  The radius of curvature R of the main expanded portion 6 is preferably 3 mm or greater and 30 mm or less. By setting the radius of curvature R of the main pipe expanding portion 6 to 3 mm or more, the fall of the inner fin 12 can be suppressed. Moreover, when the curvature radius R of the main pipe expansion part 6 exceeds 30 mm, a pipe expansion load will become large and the concern that the heat exchanger tube 11 will buckle in a pipe expansion process will increase. Therefore, it is preferable that the curvature radius R of the main pipe expansion portion 6 is 30 mm or less.

Moreover, the curvature radius R of the main expansion part 6 does not exceed the upper limit of the following (Formula 1) using the diameter D of the maximum diameter part 3c, and does not fall below the lower limit of the following (Formula 2).
Upper limit R = −9.37 × D ³ + 196.69 × D ² −1375.5 × D + 3214 (Formula 1)
Lower limit R = −14.43 × D ³ + 286.66 × D ² −1897.6 × D + 4190 (Formula 2)

By setting the radius of curvature R of the main pipe expansion portion 6 to the relationship shown in (Expression 1) and (Expression 2), it is possible to supply the expansion plug 1 that optimizes the balance between the expansion load and the expansion ratio in the expansion process.
The above (Formula 1) and (Formula 2) are obtained from a simulation assuming a plurality of pipe expansion plugs 1 in which the diameter D of the maximum diameter section 3c and the radius of curvature R of the longitudinal section of the main pipe expansion section 6 are variously changed. It has been. In this simulation, the expansion rate and the expansion load when the heat transfer tube 11 is expanded by a plurality of tube expansion plugs 1 are plotted on a graph. Among the plurality of tube expansion plugs 1, the diameter D of the maximum diameter portion 3c is the same. As a group, the common tangent line of each group of the graph is taken, and the radius of curvature R closest to the common tangent line is determined as the optimum radius of curvature for the group having the same diameter D of the maximum diameter portion 3c. .
Note that the grounds of the above (formula 1) and (formula 2) will be described in detail in a later embodiment.

  A rear pipe expanding portion 7 is formed behind the maximum diameter portion 3 c of the head portion 3. The rear surface expanded portion 7 is a curved surface having a curvature radius BR. 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 (see FIG. 1) 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 11 that is expanded again has undergone expansion and contraction, work hardening has occurred. Therefore, when the curvature radius BR of the rear surface expanded portion 7 is not set appropriately, excessive stress is applied to the heat transfer tube 11 in the drawing process, and the heat transfer tube 11 is broken. 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.
In order to prevent such a phenomenon, it is preferable that the curvature radius BR of the rear surface expanded portion 7 is 10 mm 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.

  The shaft portion 2 of the pipe expansion plug 1 is made of a steel material having high strength, for example, chromium molybdenum steel represented by JIS regulation SCM435. The head portion 3 of the tube expansion plug 1 is integrally formed from a 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 3, 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.

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 as the lubricating oil used together with the pipe expanding plug 1 for expanding the pipe.
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.

  According to the tube expansion plug 1 of the first embodiment, the radius of curvature of the main tube expansion portion 6 formed in the head portion 3 can be optimized, and the tube expansion rate can be increased while suppressing the tube expansion load in the tube expansion step. By suppressing the tube expansion load during tube expansion, buckling of the heat transfer tube 11 can be prevented, wear of the head portion 3 can be reduced, and the life of the tube expansion plug 1 can be extended.

<Second Embodiment of Tube Expansion Plug>
Next, a second embodiment of the tube expansion plug will be described.
FIG. 6 shows a tube expansion plug 21 according to the second embodiment. 7A and 7B are partial cross-sectional views of the heat transfer tube 11 when the tube expansion process of the heat transfer tube 11 (see FIGS. 3 and 4) is performed using the tube expansion plug 21. FIG.
In the tube expansion plug 21 of the second embodiment, as compared with the tube expansion plug 1 of the first embodiment described above, a preliminary tube expansion portion 26A is formed between the main tube expansion portion 26B and the tip portion 23a in the head portion 23. Is different.
In addition, about the component of the same aspect as the above-mentioned 1st Embodiment, the same code | symbol is attached | subjected and the description is abbreviate | omitted.

FIG. 14 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 when a general tube expansion plug is used. As shown in FIG. 14, the tube expansion load in the tube expansion process peaks 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 tube expansion plug 21 of 2nd Embodiment can suppress the initial tube expansion load at the time of inserting in the opening part 11a by having the preliminary | backup expansion part 26A.

  The tube expansion plug 21 includes a shaft portion 22 and a head portion 23 that is integrally formed on the distal end side thereof. The head part 23 is formed in a barrel shape so as to bulge so as to be larger in diameter than the shaft part 22. In the head portion 23, a maximum diameter portion 23 c is formed between a front end portion 23 a forming a flat surface and a rear end portion 23 d connected to the shaft portion 22. Moreover, the cross section of the head part 23 is formed in a substantially circular shape. The diameter of the cross section gradually increases from the front end portion 23a to the maximum diameter portion 23c, and gradually decreases from the maximum diameter portion 23c to the rear end portion 23d. The tip portion 23a is formed to have a diameter FD, and the maximum diameter portion 23c is formed to have a diameter D.

  The head portion 23 has a front tube expansion portion 26 from the tip portion 23a to the maximum diameter portion 23c. Further, the head portion 23 is a rear-surface expanded portion 27 from the maximum diameter portion 23c to the rear end portion 23d.

The front pipe expansion part 26 plays a role of expanding and expanding the heat transfer tube 11 radially outward when the tube expansion plug 21 is inserted into the heat transfer tube 11. The front expanded portion 26 is divided into a preliminary expanded portion 26A and a main expanded portion 26B having different radii of curvature, with the preliminary expanded end portion 23b as a boundary.
The pre-expanded portion 26A is a uniform curved surface having a curvature radius SR. The main expanded portion 26B is a uniform curved surface having a curvature radius R.
The curved surface of the preliminary pipe expansion portion 26A and the curved surface of the main pipe expansion portion 26B are smoothly connected at the preliminary pipe expansion end portion 23b. That is, the pre-expanded portion 26A and the main expanded portion 26B 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.

As shown in FIG. 7A, the preliminary pipe expanding portion 26A is a part that abuts the opening 11a of the heat transfer tube 11 and first expands the heat transfer tube 11 while receiving an initial tube expansion load.
The radius of curvature SR of the pre-expanded portion 26A is preferably 5 mm or more and 7.9 mm or less.
Generally, the tube expansion load is the largest when the tube expansion plug is inserted into the heat transfer tube (initial tube expansion load) (see the graph shown in FIG. 14). By reducing the radius of curvature SR of the preliminary expanded portion 26A, the expanded tube load (initial expanded tube load) immediately after being inserted into the opening 11a of the heat transfer tube 11 can be reduced. By setting the curvature radius SR of the pre-expanded portion 26A to 7.9 mm or less, the initial tube expansion load can be reduced and the buckling of the heat transfer tube 11 can be suppressed. Moreover, the fall of the inner surface fin 12 can be suppressed by setting the curvature radius SR of the preliminary expanded portion 26A to 5 mm or more.

As shown in FIG. 7B, the main pipe expanding portion 26 </ b> B plays a role of further expanding the heat transfer tubes 11 that have been preliminarily expanded along the preliminary expansion portions 26 </ b> A outward in the radial direction in the expansion process of the heat transfer tubes 11.
Further, the radius of curvature R of the main expanded portion 26B does not exceed the upper limit of the following (Formula 1) using the diameter D of the maximum diameter portion 23c, and does not fall below the lower limit of the following (Formula 2).
Upper limit R = −9.37 × D ³ + 196.69 × D ² −1375.5 × D + 3214 (Formula 1)
Lower limit R = −14.43 × D ³ + 286.66 × D ² −1897.6 × D + 4190 (Formula 2)

  By setting the curvature radius R of the main pipe expanding portion 26B to the relationship shown in (Expression 1) and (Expression 2), it is possible to supply the expanded pipe 21 that optimizes the balance between the expanded load and the expanded ratio in the expanded process.

Furthermore, in this embodiment, it is preferable that the curvature radius R of the main pipe expansion part 26B is 20.1 mm or more and 30 mm or less. The main pipe expansion part 26B plays a role of further expanding the heat transfer pipe 11 preliminarily expanded along the preliminary pipe expansion part 26A outward in the radial direction in the pipe expansion process of the heat transfer pipe 11 (see FIG. 7B). Therefore, the main pipe expanding portion 26B applies a large load to the inner surface fin 12 with respect to the preliminary pipe expanding portion 26A. That is, the main pipe expanding portion 26 </ b> B acts predominantly against the falling of the inner fin 12. Increasing the radius of curvature R of the main expanded portion 26B can suppress the collapse of the inner fin 12.
When the radius of curvature R of the main expanded portion 26B is less than 20.1 mm, the inner fin 12 is not easily collapsed. 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 23 b that becomes the boundary between the preliminary pipe expansion portion 26 A and the main pipe expansion portion 26 B is formed larger than the minimum inner diameter β of the heat transfer tube 11. Therefore, in the tube expansion process, the minimum inner diameter portion of the heat transfer tube 11 (that is, the top portion 12a of the inner fin 12) contacts the main tube expansion portion 26B after contacting the preliminary tube expansion portion 26A.

Also, pre-expanded tube ends diameter _{D 2} is the pre-expanded tube coefficient K as 0.45 to 0.65, it is preferable to satisfy the following (Equation 3).
D ₂ = {K × β × (α ₂ −α ₁ ) / α ₁ } + β (Formula 3)
Note that β is the minimum tube inner diameter of the heat transfer tube 11 before the tube expansion, α ₁ is the outer diameter of the heat transfer tube 11 before the tube expansion, and α ₂ 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. Accordingly, in the front pipe expansion section 26, the preliminary pipe expansion section 26A is relatively large and the main pipe expansion section 26B is relatively small. Since the pre-expanded portion 26A is formed to have a small radius of curvature SR, there is a risk that the inner fin 12 will fall significantly because the pre-expanded portion 26A is relatively large.
Conversely, pre-expanded tube ends diameter D ₂ is smaller Smaller preliminary pipe expansion coefficients K. Accordingly, in the front pipe expansion section 26, the preliminary pipe expansion section 26A is relatively small, and the main pipe expansion section 26B is relatively large. Since the main expanded portion 26B is formed to have a large radius of curvature R, there is a possibility that the initial expanded load during expansion is increased and the heat transfer tube 11 is buckled because the main expanded portion 26B is relatively large.
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 27 is formed behind the maximum diameter portion 23 c of the head portion 23. It is a uniform curved surface having a rear surface expanded portion 27 and a radius of curvature BR. The radius of curvature BR of the rear surface expanded portion 27 is preferably 10 mm 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.

According to the tube expansion plug 21 of the second embodiment, the same effect as that of the first embodiment can be obtained by having the main tube expansion portion 26B similar to that of the first embodiment.
Further, in the tube expansion plug 21 of the second embodiment, a preliminary tube expansion portion 26 </ b> A having a relatively small curvature radius SR is formed on the distal end side of the head portion 23. Thereby, the initial tube expansion load when inserting the tube expansion plug 21 into the heat transfer tube 11 can be reduced, and buckling of the heat transfer tube 11 can be suppressed.

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

  The relationship between the radius of curvature R of the main expansion portion of the expansion plug and the diameter (maximum diameter) D of the maximum diameter portion (relationship shown in the above (Expression 1) and (Expression 2)) is based on the following simulation results. is there.

(First simulation)
As a first simulation, the maximum diameter D is 5.7 mm, 5.8 mm, 5.85 mm, 5.9 mm, 5.95 mm, 6.0 mm, 6 with respect to the heat transfer tube (before tube expansion) shown in Table 1. Assume a tube expansion process performed using tube expansion plugs of 1 mm, 6.5 mm, and 7.0 mm. Further, the radius of curvature R of the main expanded portion is 2 mm, 4 mm, 5 mm, 6 mm, 7 mm, 9 mm, 11 mm, 12 mm, 13 mm, 15 mm, 17 mm, 20 mm, 25 mm, 30 mm, 40 mm, and 50 mm with respect to each maximum diameter D. A tube expansion plug is assumed.

  A simulation for expanding the heat transfer tube shown in Table 1 using such a tube expansion plug was performed. The simulation is based on the finite element method (FEM), and derives the tube expansion load and the tube expansion rate at the time of tube expansion.

FIG. 8 is a graph showing the result of the first simulation in which the vertical axis represents the tube expansion load and the horizontal axis represents the tube expansion rate. Note that the graph of FIG. 8 is obtained by extracting and plotting the main points of the simulation results for the sake of easy understanding.
As a matter of course, as the maximum diameter D (see FIG. 5) of the head portion is increased, the tube expansion rate and the tube expansion load increase.

  Next, attention is focused on a group (a group of plots of the same mark in FIG. 8) having the same maximum diameter D of the head portion. It can be seen that in a group having the same maximum diameter D, the pipe expansion rate and the pipe expansion load change by changing the curvature radius R (see FIG. 5) of the head portion. In a group having the same maximum diameter D, when the curvature radius R of the head portion is increased, both the tube expansion rate and the tube expansion load are increased. The increase in the tube expansion load is not constant with respect to the increase in the tube expansion rate, and a convex curve is drawn downward. As the tube expansion rate increases, the tube expansion load initially increases with a gentle slope and gradually increases. This suggests that there is a well-balanced radius of curvature R that suppresses the tube expansion load while increasing the tube expansion rate.

  As shown in FIG. 8, a group of graphs having the same maximum diameter D of the head portion can draw a common tangent (hereinafter, a common tangent). Regarding the radius of curvature in each group, it can be said that the point on the common tangent line or the closest point is the radius of curvature in which the balance between the pipe expansion load and the pipe expansion ratio is the best. A point on the common tangent line in each group or the radius of curvature R of the closest point will be referred to as an optimum point.

By using the radius of curvature in the vicinity of the optimum point in each group, it is possible to increase the tube expansion rate while reducing the tube expansion load.
When the curvature radius is increased with respect to the optimum curvature radius, the tube expansion load increases and the tube expansion plug is easily worn. Thereby, there exists a possibility of damaging a pipe expansion plug. If the tube expansion load when the tube expansion plug having the optimal radius of curvature is used is 1, the tube expansion load is 1.05 or less, that is, the radius of curvature is 105% or less with respect to the tube expansion load at the optimal point. The wear of the tube expansion plug can be suppressed.

Further, when the curvature radius is smaller than the optimum curvature radius, the tube expansion ratio is reduced, and the heat transfer tube cannot be sufficiently adhered to the heat radiating plate, which may cause a poor connection between the heat transfer tube and the heat radiating plate. If the expansion ratio when the expansion plug with the optimal radius of curvature is used is 1, the expansion ratio is 0.95 or higher, that is, the radius of curvature is 95% or higher with respect to the optimal point expansion load. The tube expansion rate can be secured sufficiently.
From such a viewpoint, the optimum point of the radius of curvature R with respect to the individual maximum diameter D and the range of the effective radius of curvature were confirmed.

Simulation results when the maximum diameter D of the head portion is 5.7 mm, 5.8 mm, 5.85 mm, 5.9 mm, 5.95 mm, 6.0 mm, 6.1 mm, 6.5 mm, 7.0 mm, These are summarized in Tables 2 to 10, respectively.
Tables 2 to 10 describe the optimum point of the curvature radius and the determination result of whether or not it is included in the range of the effective curvature radius for increasing the tube expansion rate while suppressing the tube expansion load.
Note that the optimum points in Tables 2 to 10 are set as the optimum points with the curvature radii closest to the ideal optimum point among the radii of curvature performed in this simulation.

Among the curvature radii shown in Tables 2 to 10 and the curvature radii included in the range of effective curvature radii for increasing the expansion ratio while suppressing the expansion load, the maximum and minimum curvature radii are: The plug diameter is plotted on the horizontal axis and summarized in FIG.
In FIG. 9, an approximate curve of the maximum value of the radius of curvature is drawn by the method of least squares. Similarly, an approximate curve of the minimum value of the radius of curvature was drawn by the least square method.

The radius of curvature can be regarded as an effective range for increasing the tube expansion ratio while suppressing the tube expansion load in the region between the maximum value approximate curve and the minimum value approximate curve. From the approximate curve of the maximum value of the radius of curvature and the approximate curve of the minimum value, the upper limit and the lower limit of the radius of curvature R of the main expanded portion are the diameter (maximum diameter) of the maximum diameter portion using D (Equation 1), ( It is represented by Formula 2).
Upper limit R = −9.37 × D ³ + 196.69 × D ² −1375.5 × D + 3214 (Formula 1)
Lower limit R = −14.43 × D ³ + 286.66 × D ² −1897.6 × D + 4190 (Formula 2)
By setting the curvature radius between the upper limit curvature radius and the lower limit curvature radius, a well-balanced tube expansion plug that increases tube expansion rate while suppressing tube expansion load can be provided.

(Second simulation)
Next, in order to confirm that (Equation 1) and (Equation 2) obtained on the basis of the first simulation result described above can obtain the same result for other heat transfer tubes, the second simulation is performed. Went. In the 2nd simulation, the pipe expansion process with respect to the heat exchanger tube shown in Table 11 from which an outer diameter, bottom wall thickness, fin height, and a twist angle differ was assumed. The second simulation assumes a tube expansion plug having a maximum diameter D of 5.7 mm, 5.9 mm, 6.1 mm, and 7.0 mm with respect to the heat transfer tube (before tube expansion) shown in Table 11. With respect to the above-mentioned expanded plug with the maximum diameter D, a simulation was performed in which the radius of curvature R of the main expanded portion was variously changed.

FIG. 10 is a graph of the result of the second simulation, where the vertical axis represents the tube expansion load and the horizontal axis represents the tube expansion rate. Note that the graph of FIG. 10 is obtained by extracting and plotting the main points of the simulation results for the sake of easy understanding.
Also in FIG. 10, a common tangent line can be drawn between a group of graphs having the same maximum diameter D of the head portion as in FIG. 8 showing the first simulation result.

Similar to the first simulation, in the group having the same maximum diameter D, the expansion rate can be increased while reducing the expansion load by using the radius of curvature near the optimum point.
The simulation results when the maximum diameter D of the head portion is 5.7 mm, 5.9 mm, 6.1 mm, and 7.0 mm are summarized in Tables 12 to 15, respectively.
Tables 12 to 15 describe the optimum point of the curvature radius and the determination result as to whether or not it is included in the effective radius of curvature for increasing the tube expansion rate while suppressing the tube expansion load.
The optimum points in Tables 12 to 15 are set as the optimum points with the curvature radii closest to the ideal optimum point among the radii of curvature performed in this simulation.

  Among the curvature radii shown in Tables 12 to 15 and the curvature radii included in the range of effective curvature radii for increasing the expansion ratio while suppressing the expansion load, the maximum and minimum curvature radii are: The plug diameter is plotted on the horizontal axis and summarized in FIG. FIG. 11 shows the ranges of (Expression 1) and (Expression 2) obtained from the result of the first simulation in an overlapping manner. As shown in FIG. 11, the result of the second simulation is included in the range of (Expression 1) and (Expression 2). From this, even if it is a heat exchanger tube from which the outer diameter shown in Table 11, a bottom wall thickness, fin height, and a twist angle differ, the range shown in (Formula 1) and (Formula 2) can be applied as a preferable range. Recognize.

(Third simulation)
Next, in order to confirm that (Equation 1) and (Equation 2) obtained on the basis of the first simulation result described above can obtain similar results for other heat transfer tubes of different materials, A third simulation was performed.
The third simulation assumes tube expansion plugs having a maximum diameter D of 5.7 mm, 5.9 mm, 6.1 mm, and 7.0 mm with respect to the heat transfer tubes (before tube expansion) shown in Table 16. With respect to the above-mentioned expanded plug with the maximum diameter D, a simulation was performed in which the radius of curvature R of the main expanded portion was variously changed.

FIG. 12 is a graph showing the result of the third simulation, where the vertical axis represents the tube expansion load and the horizontal axis represents the tube expansion rate. Note that the graph of FIG. 12 is obtained by extracting and plotting the main points from the simulation results for the sake of easy understanding.
Also in FIG. 12, as in FIG. 8 showing the first simulation result, a common tangent line can be drawn between a group of graphs having the same maximum diameter D of the head portion.

Similar to the first simulation, in the group having the same maximum diameter D, the expansion rate can be increased while reducing the expansion load by using the radius of curvature near the optimum point.
The simulation results when the maximum diameter D of the head part is 5.7 mm, 5.9 mm, 6.1 mm, and 7.0 mm are summarized in Tables 17 to 20, respectively.
Tables 17 to 20 describe the optimum point of the radius of curvature and the determination result as to whether it is included in the effective radius of curvature for increasing the tube expansion rate while suppressing the tube expansion load.
Note that the optimum points in Tables 17 to 20 are set as the optimum points with the curvature radius closest to the ideal optimum point among the curvature radii in this simulation.

Among the curvature radii shown in Table 17 to Table 20 and the curvature radii included in the range of effective curvature radii for increasing the expansion ratio while suppressing the expansion load, the maximum and minimum curvature radii are: The plug diameter is plotted on the horizontal axis and summarized in FIG.
FIG. 13 also shows the ranges of (Expression 1) and (Expression 2) obtained from the result of the first simulation. As shown in FIG. 13, the result of the third simulation is included in the range of (Expression 1) and (Expression 2). From this, it can be seen that the ranges shown in (Equation 1) and (Equation 2) can be applied as preferable ranges even with heat transfer tubes of different materials shown in Table 16.

(Test 1)
Next, the front expanded portion of the expanded plug, the initial expanded load and the collapse of the inner fin were investigated as Test 1.
Several types of pipe expansion plugs having a main pipe expansion section and a preliminary pipe expansion section shown in FIG. 6 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.

Several types of heat transfer tubes that were expanded by these expansion plugs were prepared. 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. 28 is summarized in Table 21.
In Table 21, the outer diameter tube expansion rate is expressed as a percentage in the following equation.
100 × (α ₂ −α ₁ ) / α ₁
Here, α ₁ is the outer diameter of the heat transfer tube before the expansion, and α ₂ is the outer diameter of the heat transfer tube after the expansion.
Table 22 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. The stable tube expansion load means a load in a region where the tube expansion load is stable as shown in FIG.

In Table 21, sample no. 1-No. 4, sample no. 7, no. 8, sample no. 13, no. 14, sample no. 21, no. 22, sample no. 25-No. 28 satisfies the following (Expression 1) and (Expression 2).
Upper limit R = −9.37 × D ³ + 196.69 × D ² −1375.5 × D + 3214 (Formula 1)
Lower limit R = −14.43 × D ³ + 286.66 × D ² −1897.6 × D + 4190 (Formula 2)
Here, R is the radius of curvature R of the main expanded portion, and D is the maximum diameter of the head portion.

As an example, sample No. 1 satisfying (Expression 1) and (Expression 2) is used. 2 and a sample No. that does not satisfy (Expression 1) and (Expression 2). 5, no. 6 is compared. Sample No. 2, No. 5, no. 6 differs only in the radius of curvature of the main expanded portion.
From Table 22, sample no. 2, No. 5, no. The expansion ratios of 6 were 5.71%, indicating that there was no difference in the expansion ratio. Sample No. The stable tube expansion load of No. 2 is 250 N, whereas sample No. 5 is 320 N, sample No. The stable tube expansion load of 6 is 400N. As described above, by satisfying (Equation 1) and (Equation 2) for the radius of curvature of the main expanded portion of the expanded tube plug, the expanded tube load can be reduced without changing the expanded tube rate.

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.
If the reduction rate of the inner fins is 15% or more, the inner fins fall and the heat exchange efficiency decreases, which is not preferable. In addition, the outer diameter may not be expanded sufficiently due to the fall of the inner fin.

As shown in Table 21 and Table 22, among the tube expansion processes using various combinations of the tube expansion plug and the heat transfer tube, No. 1-No. In 24 pipe expansion processes, the pipe expansion load and the height reduction rate of the inner surface fins can be suppressed. In contrast, no. 25-No. In the tube expansion process 28, the tube expansion load is high or the reduction rate of the internal fins is large. In particular, no. 26, no. In the tube expansion process No. 27, buckling occurred at the beginning of tube expansion.
From the results shown in Tables 21 and 22, by setting the radius of curvature of the pre-expanded pipe part, the radius of curvature of the main pipe-expanded part, and the diameter of the end part of the pre-expanded pipe, the inner fin collapses while suppressing the initial pipe expansion load. It was confirmed that it can be suppressed.
Moreover, it was confirmed that a preferable tube expansion process can be performed when the ratio (t / α ₁ ) of the bottom wall thickness t to the outer diameter α ₁ of the heat transfer tube is 0.05 or more and 0.11 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 FIG. 6 with different curvature radii 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 a heat transfer tube expanded by these tube expansion plugs, a heat transfer tube made of JIS3003 alloy was 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. 29-No. 32 is summarized in Table 23. 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 23, in the pipe expansion process using a plurality of pipe expansion plugs, In No. 29, 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. 30, the heat transfer tube was elongated 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. 31, no. In 32 pipe expansion processes, the drawing process was normally performed.
From the results of Test 2, it was confirmed that an excessive tensile stress was not applied to the heat transfer tube at the time of drawing by setting the radius of curvature of the rear surface expanded portion to 10 mm or less.

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.
For example, the tube expansion plug according to the embodiment has been described as an example of application to an inner surface spiral grooved tube in which a spiral groove is provided on the inner surface as a heat transfer tube to be expanded, but also to a heat transfer tube in which a linear groove is formed, It can be applied effectively. The tube expansion plug may be applied to a heat transfer tube made of copper or a copper alloy as a heat transfer tube to be expanded.

In addition, as shown in the embodiment, according to the present invention, the head portion is provided with a main expanded portion formed from the maximum diameter portion toward the distal end portion, and the radius of curvature of the longitudinal section of the main expanded portion and the maximum It is possible to provide a tube expansion plug design method in which the relationship with the diameter of the diameter portion is expressed by the following (formula 1) and (formula 2).
Upper limit R = −9.37 × D ³ + 196.69 × D ² −1375.5 × D + 3214 (Formula 1)
Lower limit R = −14.43 × D ³ + 286.66 × D ² −1897.6 × D + 4190 (Formula 2)
However, D is a diameter of the maximum diameter part, and R is a curvature radius of the longitudinal section of the main expansion part.

1, 21 ... tube expansion plug, 2, 22 ... shaft part, 2 a ... screw shaft, 3, 23 ... head part, 3 a, 23 a ... tip part, 3 c, 23 c ... maximum diameter part, 3 d, 23 d ... rear end part, 6 , 26B ... main expanded portion, 7, 27 ... rear expanded portion, 11 ... heat transfer tube, 11a ... opening, 11b ... U-shaped portion, 12 ... inner fin, 12a ... top portion, 12b ... inclined portion, 14 ... fin groove, DESCRIPTION OF SYMBOLS 15 ... Fin material, 15a ... Insertion hole, 16 ... Fin assembly, 23b ... Preliminary pipe expansion end part, 26 ... Front pipe expansion part, 26A ... Preliminary pipe expansion part, R, BR, SR ... Curvature radius, D ... Maximum diameter (diameter ), D 2 _... reserve tube expansion finished diameter, FD ... diameter, h ... height, i ... fin pitch, j ... fin width, t ... bottom wall thickness, alpha _{1 ...} expanded tube before the outer diameter, alpha _{2 ...} pipe expansion Kosoto径, Β ... minimum inner diameter, θ ... twist angle

Claims (7)

A tube expansion plug that expands the heat transfer tube by inserting it into a heat transfer tube in which a plurality of internal fins are formed on the inner peripheral surface,
A shaft portion, and a head portion formed on the tip side thereof,
The head part has a substantially circular shape whose transverse section gradually increases in diameter from the tip side to the maximum diameter part,
The head portion includes a main expansion portion that is formed from the maximum diameter portion toward the tip portion side,
The tube expansion plug in which the upper limit and the lower limit of the curvature radius R of the longitudinal section of the main tube expansion portion have a relationship of the following formula with the diameter D of the maximum diameter portion.
Upper limit R = −9.37 × D ³ + 196.69 × D ² −1375.5 × D + 3214
Lower limit R = −14.43 × D ³ + 286.66 × D ² −1897.6 × D + 4190 The head portion includes a preliminary expanded portion that is smoothly connected to the main expanded portion between the tip portion and the main expanded portion,
The preliminary expanded portion connects the tip portion having a diameter smaller than the minimum tube inner diameter of the heat transfer tube to the preliminary expanded 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 expansion pipe plug according to claim 1, wherein a preliminary expansion end diameter, which is a diameter of the preliminary expansion end portion, is represented by the following expression.
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 tube expansion plug according to claim 1 or 2, wherein a diameter of the maximum diameter portion is 5.7 mm or more and 7.0 mm or less. The heat transfer tube before expansion is
Made of aluminum or aluminum alloy,
The outer diameter is 6 mm or more and 8 mm or less,
The bottom wall thickness is 0.45 mm or more and 0.65 mm or less,
The ratio of the bottom wall thickness to the outer diameter is 0.05 to 0.11,
The said internal fin is formed in the spiral with respect to the longitudinal direction of the said heat exchanger tube, The pipe expansion plug as described in any one of Claims 1-3 characterized by the above-mentioned. The head portion has a rear surface expanded portion between the maximum diameter portion and a rear end portion having a smaller diameter than the maximum diameter 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 radius of curvature of 10 mm or less. A tube expansion plug design method for expanding the heat transfer tube by inserting it into a heat transfer tube in which a plurality of internal fins are formed on the inner peripheral surface,
In the tube expansion plug having a shaft portion and a head portion formed on a tip end side thereof, the head portion having a substantially circular shape whose transverse section gradually increases in diameter from the tip end portion side to the maximum diameter portion. ,
The head portion is provided with a main expansion portion formed from the maximum diameter portion toward the distal end portion,
A method for designing a tube expansion plug, wherein a radius of curvature R of a longitudinal section of the main tube expansion portion is between an upper limit and a lower limit of the following expression represented by the diameter D of the maximum diameter portion.
Upper limit R = −9.37 × D ³ + 196.69 × D ² −1375.5 × D + 3214
Lower limit R = −14.43 × D ³ + 286.66 × D ² −1897.6 × D + 4190 A tube expansion plug design method for expanding the heat transfer tube by inserting it into a heat transfer tube in which a plurality of internal fins are formed on the inner peripheral surface,
A shaft portion and a head portion formed on a tip side thereof, and the head portion has a substantially circular shape whose transverse section gradually increases in diameter from the tip portion side to the maximum diameter portion, The portion is provided with a main expanded portion formed from the maximum diameter portion toward the distal end side, and a plurality of diameters of the maximum diameter portion and a curvature radius of a longitudinal section of the main expanded portion are variously changed. Assuming an expansion plug,
Plotting the expansion rate and the expansion load when the heat transfer tube is expanded by a plurality of the expansion plugs,
Among the plurality of tube expansion plugs, a group having the same diameter of the maximum diameter portion as a group, taking a common tangent line between each group of the graph,
A tube expansion plug design method in which the radius of curvature closest to the common tangent is set to an optimum radius of curvature for a group having the same maximum diameter portion.

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