JP2015062951A - Tube expansion method for heat-transfer tube made of aluminum or aluminum alloy - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a tube expansion method for a heat-transfer tube.SOLUTION: This invention relates to the tube expansion method for a heat-transfer tube, for forming a heat-transfer tube by forcibly inserting a tube expansion plug into the inside of a raw heat-transfer tube made of aluminum or aluminum alloy thereby expanding the outer diameter of the raw heat-transfer tube, the tube expansion plug including a head part having an outer diameter larger than the inner diameter of the raw heat-transfer tube. A tube expansion plug which is composed of a shank and the head part formed at this shank tip, and in which the shank and the head part are formed from a hard metal with a hardness of HRA85 -95 and diamond-like carbon film with a 0.5 -3.0 μm thickness is formed on the outer peripheral surface of the head part, is used as the tube expansion plug. A lubrication oil is used which has a flash point of 100°C or less and a kinetic viscosity of 1.0 mm/S(at 40°C) or more is used as the lubrication oil that lubricates between the raw heat-transfer tube and the tube expansion plug.

Description

  The present invention relates to a method for expanding a heat transfer tube made of aluminum or aluminum alloy using a plug for expanding tubes.

  2. Description of the Related Art Conventionally, a heat exchanger such as a cooler indoor unit mainly composed of tubes and fins has a structure in which fins are made of aluminum and tubes are made of copper hairpin pipes. However, in recent years, due to the depletion of copper resources, etc., further cost reduction, improvement of heat exchange performance, pursuit of recyclability, etc. have been made, and all-aluminum heat exchange in which the entire heat exchanger including tubes is made of aluminum A vessel is being considered.

As an example of a heat exchanger composed of tubes and fins, as shown in FIGS. 8 and 9, a heat transfer tube 100 made of copper or a copper alloy having excellent thermal conductivity and workability is meandered as a tube through which a refrigerant passes. There is known a structure in which a plurality of aluminum alloy fin materials 101 are arranged in parallel around the heat transfer tube 100. The heat transfer tube 100 is provided so as to pass through a plurality of through holes provided so as to penetrate the fin material 101 arranged in parallel.
In the heat exchanger structure shown in FIG. 8, the heat transfer tube 100 includes a plurality of U-shaped main tubes 100 </ b> A that linearly penetrate the fin material 101, and adjacent end openings of the adjacent main tubes 100 </ b> A. The tube 100B is connected as shown in FIG. Further, the refrigerant inlet portion 106 is formed on one end side of the heat transfer tube 100 penetrating the fin material 101, and the refrigerant outlet portion 107 is formed on the other end portion side of the heat transfer tube 100. A heat exchanger 105 shown in FIG. 8 is configured.

  In order to manufacture the heat exchanger 105 having the structure shown in FIG. 8, a plurality of through holes are formed in advance in the fin material 101 so as to linearly penetrate the plurality of fin materials 101 arranged in parallel. A heat transfer element tube having an outer diameter slightly smaller than these through holes is inserted into the holes. Next, as shown in FIG. 10, a tube expansion plug 112 having a spherical head portion 110 on the distal end side of the rod portion 111 is used, and this tube expansion plug 112 is forcibly inserted into the heat transfer element tube 103, The heat transfer tube 100 is formed by plastically deforming and expanding the tube 103 so as to expand it. Since the heat transfer tube 100 whose diameter has been increased by the tube expansion process is in close contact with the fin material 101 so as to push the through hole of the fin material 101 from the inside, the fin material 101 and the heat transfer tube 100 can be fixed to each other.

  As an example of this type of tube expansion technique, a tube expansion jig having a spherical main body at the tip of a shaft portion, having a surface treatment layer by diamond-like carbon treatment on the outer peripheral surface of the main body, A technique using a lubricating oil having a kinematic viscosity of 0.5 to 11 cSt (at 40 ° C.) is known as a lubricating oil used at the time of pipe expansion (see Patent Document 1).

JP 2008-093713 A

According to the technique described in Patent Document 1, the resistance at the time of pipe expansion is reduced by selecting a structure and a lubricating oil in which a hard and lubricated surface treatment layer is formed on the surface of the pipe expansion jig. Thereby, generation | occurrence | production of the abrasion powder which generate | occur | produces at the time of metal pipe expansion is suppressed, adhesion to the pipe expansion jig of abrasion powder is prevented, and malfunctions, such as a metal pipe inner surface roughening, can be eliminated.
However, if the tube expansion process using the tube expansion plug 112 as described above uses the conventional heat transfer element tube 103 made of copper or copper alloy and expands the tube to the heat transfer tube 100, there is a problem in processing. However, when using a heat transfer tube made of aluminum or an aluminum alloy, it has been found that a problem described below newly occurs.

  Compared to copper or copper alloy heat transfer tubes, aluminum or aluminum alloy heat transfer tubes are more likely to cause adhesion of aluminum to the expanded plug 112 during expansion, resulting in increased tube expansion load. There was a problem that caused damage to the heat transfer tube itself. One of the reasons why the tube expansion load increases is due to the fact that aluminum has a higher affinity for the tube expansion plug than copper.

  Further, in recent years, a heat transfer tube applied to a heat exchanger has a groove provided with a plurality of grooves 121 extending in the length direction of the tube on the inner wall like a heat transfer tube 120 having a cross-sectional structure shown in FIG. Tubes are frequently used. Conventionally, when this type of grooved heat transfer tube 120 is made of copper or a copper alloy, a technique for expanding the tube with the tube expansion plug 112 is established to some extent, but when the grooved heat transfer tube 120 is made of aluminum or an aluminum alloy, There is a possibility that the groove 121 may be crushed and deformed during tube expansion.

If the groove 121 is crushed or deformed in the heat transfer tube 120 with the groove, the heat exchange efficiency is lowered, so that the performance as a heat exchanger may be lowered.
For this reason, even if a heat transfer tube made of aluminum or an aluminum alloy is used and the heat transfer tube is a grooved type, it is desired to provide a technique capable of expanding the tube as smoothly as possible without breaking the shape of the groove.

  The present invention has been made in view of the above circumstances, and is a method of expanding a heat transfer tube using a tube expansion plug suitable for expanding a heat transfer tube made of aluminum or an aluminum alloy to constitute a heat exchanger. An object of the present invention is to provide a method capable of expanding the tube while suppressing the resistance at the time and suppressing the deformation of the groove on the inner surface of the heat transfer tube.

In order to solve the above problems, the present invention employs the following configuration.
In the heat transfer tube expansion method according to the present invention, a tube expansion plug having a head portion having an outer diameter larger than the inner diameter of the heat transfer element tube is forcibly inserted inside the heat transfer element tube made of aluminum or an aluminum alloy. A heat transfer tube expansion method for forming a heat transfer tube by expanding the outer diameter of the heat transfer element tube, the tube expansion plug having a shaft portion and a head portion formed on the distal end side of the shaft portion, Using the tube expansion plug formed by forming the head portion from a cemented carbide having a hardness of HRA 85 to 95 and forming a diamond-like carbon film having a thickness of 0.5 to 3.0 μm on the outer peripheral surface of the head portion, the heat transfer As a lubricating oil for lubricating between the raw pipe and the pipe expansion plug, 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 is used.

In the present invention, a diamond-like carbon film having a hardness of 20 GPa to 70 GPa and a critical peel load of 30 N or more can be used as the diamond-like carbon film.
In the present invention, a diamond-like carbon film having a surface roughness Ra of 0.1 μm or less can be used.
In the present invention, a plurality of heat transfer element tubes are arranged so as to penetrate a fin assembly formed by arranging a plurality of fin materials made of aluminum or aluminum alloy, and these heat transfer element tubes are expanded by the tube expansion plug. A method characterized by joining these heat transfer tubes to the fin assembly by using heat transfer tubes may be used.
In the present invention, as the heat transfer element tube, a grooved heat transfer element tube having a plurality of grooves extending in the length direction of the tube at intervals in the circumferential direction of the inner surface of the tube can be used.
In the present invention, as the heat transfer element tube, a heat transfer element tube with a spiral groove having a plurality of spiral grooves extending in the length direction of the tube at intervals in the circumferential direction of the inner surface of the tube can be used.

According to the present invention, aluminum or an aluminum alloy is used by using a tube expansion plug having a diamond-like carbon film having a hardness of HRA85 to 95 and having a good adhesion to a head portion made of a cemented carbide having an appropriate hardness range. Since the manufactured heat transfer tube is expanded, the heat transfer element tube can be expanded with low resistance while preventing the adhesion of aluminum to the surface of the head portion. For this reason, it is possible to obtain a heat transfer tube having a good inner surface property after tube expansion.
Moreover, since the heat transfer tube can be expanded more smoothly than before with a low tube expansion resistance, the outer diameter of the heat transfer tube after the expansion can be made uniform. Therefore, when a heat exchanger is configured by combining a heat transfer tube and a fin material, the heat transfer tube and the fin material can be combined with high accuracy, and the heat transfer between the heat transfer tube and the fin material is excellent, and the heat exchange characteristics are good. A simple heat exchanger.

Also, when expanding a grooved heat transfer element tube having a plurality of grooves on the inner surface side of an aluminum or aluminum alloy heat transfer element tube, the head portion of the tube expansion plug presses the groove on the inner surface side when expanding the tube, and the groove However, if the pipe is expanded using the pipe expansion plug having the above-described configuration, the deformation of the groove can be suppressed and a heat transfer tube having a uniform groove shape can be obtained.
In particular, when expanding a heat transfer element tube with a spiral groove having a plurality of spiral grooves on the inner surface side, the head portion of the tube expansion plug presses the spiral groove on the inner surface side when expanding the tube, deforms the spiral groove, Although there is a possibility of crushing, if the tube is expanded using the tube expansion plug having the above-described configuration, a heat transfer tube having a spiral groove shape in which the spiral groove is not deformed can be obtained.

The perspective view which shows 1st Embodiment of the pipe expansion plug used for implementation of this invention. The cross-sectional view which shows an example of the heat exchanger element pipe expanded by the same expansion plug. The perspective view for demonstrating the state which expands a heat exchanger element tube with the tube expansion plug, and assembles a heat exchanger. The fragmentary sectional view which shows the pipe expansion operation | movement which expands a heat-transfer elementary tube with the tube expansion plug, and processes it into a heat-transfer tube. Sectional drawing which shows an example of the heat exchanger tube in which the spiral groove was formed. The fragmentary sectional view of the heat exchanger tube expanded by the tube expansion plug shown in FIG. The fragmentary sectional view of the heat exchanger tube expanded by the conventional tube expansion plug. The block diagram which shows an example of a general heat exchanger. The fragmentary perspective view of the heat exchanger shown in FIG. Sectional drawing which shows the state which has expanded the heat exchanger tube with the pipe expansion plug. The cross-sectional view which shows an example of the conventional heat exchanger tube.

One embodiment of the tube expansion plug according to the present invention will be described below.
FIG. 1 shows a tube expansion plug according to an embodiment of the present invention. The tube expansion plug 1 according to this embodiment includes a shaft portion 2 and a head portion 3 integrally formed on the tip end side thereof. A screw shaft 2 a is formed on the rear end side of the shaft portion 2. The head portion 3 is formed in a barrel shape so as to be slightly larger in diameter than the shaft portion 2, has a flat surface 3 a on the tip side, and has a maximum diameter portion 3 b on the center side in the longitudinal direction of the head portion 3. Is shaped. The maximum diameter portion 3b of the head portion 3 defines the diameter of the heat transfer tube when a heat transfer element tube which will be described later is expanded into a heat transfer tube.

In the pipe expansion plug 1 of the present embodiment, the shaft portion 2 is made of a steel material having high strength, for example, chromium molybdenum steel indicated by JIS regulation SCM435.
In the pipe expansion plug 1 of this embodiment, the head part 3 is integrally formed from a cemented carbide of HRA85 or more and HRA95 or less. HRA is a kind of Rockwell hardness, and is a value measured at a test load of 600 N and a basic load of 100 N using a diamond conical indenter with a tip radius of 0.2 mm and a tip angle of 120 ° as a scale. First, add a basic load to the test surface, then add a composite load with the test load added, plastically deform, then return the load to the reference load, read the depth of the permanent depression on the reference surface at this time, this value It is an index of hardness obtained by a method of calculating hardness from
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.

When the hardness of the cemented carbide constituting the head portion 3 is less than HRA85, the adhesion of the diamond-like carbon film 5 described later is lowered.
When the hardness of the cemented carbide constituting the head portion 3 exceeds HRA95, the toughness of the cemented carbide is lowered, and processing using a pipe expansion plug becomes impossible.

As the cemented carbide satisfying the above-described conditions, 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 a more specific example, since the range of HRC 85 to 95 can be obtained in a cemented carbide obtained by adding 5 to 17 mass% of Co to WC particles, it can be applied to the constituent material of the tube expansion plug 1 of this embodiment. .
More specifically, for example, a cemented carbide of the type defined by JISV10, V20, V30, V40, V50, V60, etc. can be used as the above-mentioned cemented carbide.

In the tube expansion plug 1 of this embodiment, a diamond-like carbon film 5 is formed on the entire outer peripheral surface of the head portion 2. The film thickness of the diamond-like carbon film 5 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 (made by Idemitsu Kosan: kinematic viscosity 1.37mm < ² > / S) can be mentioned.

FIG. 2 shows a cross-sectional structure of a tubular heat transfer element tube 10 made of aluminum or an aluminum alloy, and this heat transfer element tube 10 can be applied when the tube is expanded using the tube expansion plug 1 having the above-described configuration. The heat transfer element tube 10 having such a cross-sectional shape can be obtained, for example, by extruding aluminum or an aluminum alloy.
When the heat transfer element tube 10 of this example is applied to a heat transfer tube of a heat exchanger for a room air conditioner, for example, a plurality of protrusion-shaped heat radiation fins 12 are provided inside a tube body 11 having an outer diameter of about 5 to 10 mm. Is formed.
The radiating fins 12 are formed so as to protrude from the inner peripheral surface of the pipe main body 11 toward the center of the pipe main body 11 and extend over the entire length in the length direction of the inner surface of the pipe main body 11. A plurality of adjacent portions are formed at predetermined intervals in the circumferential direction of the surface.

  In the cross section of the tube main body 11, the radiation fin 12 has a flat top flat portion 12a facing the center of the tube main body 11 and inclined portions 12b and 12b extending so as to sandwich the top flat portion 12a. It is formed in the shape of an isosceles trapezoid. Since a plurality of these radiating fins 12 are formed at predetermined intervals in the circumferential direction of the inner peripheral surface of the tube main body 11, the fins are disposed between the radiating fins 12, 12 adjacent along the inner peripheral surface of the tube main body 11. A groove 14 is formed. The height of the radiation fin 12 is, for example, about 0.05 to 0.35 mm, and the bottom wall thickness of the tube body 11 (the wall thickness corresponding to the fin groove 14) is about 0.3 to 0.8 mm.

  The tube body 11 is made of aluminum or an aluminum alloy. There are no particular restrictions on the aluminum alloy that constitutes the tube body 11, and pure aluminum such as 1050, 1100, and 1200 defined by JIS, or a 3000 series aluminum alloy represented by 3003 in which Mn is added to these, etc. Can be applied. Of course, in addition to these, the tube main body 11 may be configured by using any of 5000 series to 7000 series aluminum alloys defined in JIS.

In order to configure a heat exchanger using the tube body 11 having the structure shown in FIG. 2, a fin assembly 16 is formed by stacking a plurality of aluminum or aluminum alloy fin materials 15 as shown in FIG. The tube body 11 is joined to the assembly 16 in the state of a hairpin pipe 17 bent in a U shape.
When a plurality of through holes are formed at the positions where the hairpin pipes 17 are inserted in the fin materials 15 and the plurality of fin materials 15 are arranged in parallel, the through holes are arranged in a straight line. As shown in FIG. 3, the hairpin pipe 17 is inserted through the through holes of the required number of fin assemblies 16. In the case of this insertion work, the opening 17a of each hairpin pipe 17 is arranged on one side of the fin assembly 16.
The length of the tube expansion plug 1 is adjusted by screwing an unillustrated extension rod having a screw hole that can be fitted to the threaded shaft 2a of the tube expansion plug 1. In this way, the length of the tube expansion plug 1 is adjusted so that the tube can be expanded over the entire length of the hairpin pipe 17.

  In this state, when the head portion 5 of the tube expansion plug 1 is forcibly pushed through the opening 17a of each hairpin pipe 17, the heat transfer element tube 10 in which the head portion 5 of the tube expansion plug 1 has an inner diameter D as shown in FIG. Can be expanded to the heat transfer tube 18 having an inner diameter d. Since the heat transfer tube 18 having the inner diameter d is coupled to the fin material 15 so as to expand the through hole of the fin material 15, the hairpin pipe 17 can be mechanically strongly joined to the fin material 15.

  When the tube expansion process described above is performed, since the diamond-like carbon film 5 having good lubricity and hardness is formed on the surface of the head portion 5 that contacts and pushes the inner surface of the heat transfer element tube 10, the heat transfer It is possible to suppress as much as possible an increase in deformation resistance when the pipe 10 is expanded in contact with the inner peripheral surface of the raw pipe 10. Further, since the tube expansion plug 1 expands the heat transfer element tube 10 including the heat radiation fins 12 in contact with a plurality of heat radiation fins 12 formed on the inner surface of the heat transfer element tube 10, the heat radiation fins 12 are crushed during expansion. Although the diamond-like carbon film 5 is formed on the surface of the head portion 5, the heat transfer tube 18 having a desired diameter can be formed while minimizing crushing and deformation of the radiating fins 12. Can be expanded.

Since the shaft portion 2 and the head portion 3 of the tube expansion plug 1 are made of a cemented carbide of HRA85 to 95 and the diamond-like carbon film 5 is provided on the head portion 3 with good adhesion, the heat transfer element tube 10 is made of aluminum. Even if it is made of aluminum or an aluminum alloy that easily causes adhesion, tube expansion can be performed with suppressed tube expansion resistance. Therefore, it is possible to manufacture the heat transfer tube 18 including the heat radiation fins 12 which are well-formed while suppressing the deformation of the heat radiation fins 12.
Moreover, since it can be expanded so that the outer diameter of the obtained heat transfer tube 18 can be made uniform by being able to expand the tube while suppressing the deformation of the radiating fin 12, the adhesion strength at the time of joining the fin material 15 and the heat transfer tube 18 can be increased. it can. For this reason, it is possible to maintain excellent heat exchange performance with good thermal conductivity between the heat transfer tube 18 and the fin material 15.

Since the pipe-like plug 1 is coated with a diamond-like carbon film having a thickness of 0.5 to 3.0 μm, it is possible to suppress film peeling at the time of pipe expansion and eliminate the risk of aluminum adhesion. It is possible to manufacture the heat transfer tube 18 provided with the heat radiation fins 12 with the shape being suppressed by suppressing deformation of the fins 12.
If the hardness of the diamond-like carbon film 5 is in the range of 20 to 70 GPa in the tube expansion plug 1, even if a large number of heat transfer elementary tubes 10 are expanded, the wear resistance is less deteriorated. The lifetime can be extended.
If the surface roughness Ra of the diamond-like carbon film 5 is set to a small value, the tube expansion load can be reduced, which is desirable for tube expansion, and the inner fin height reduction rate can be reduced. For example, the surface roughness Ra of the diamond-like carbon film 5 is preferably 0.1 μm or less, and more preferably 0.05 μm or less. The surface roughness Ra can be adjusted by optimizing the conditions for forming the diamond-like carbon film.

Since 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 is used as the lubricating oil used in the tube expansion treatment, the diamond-like carbon film 5 is formed on the surface of the head portion 3. In combination with the points used, the resistance during tube expansion can be further reduced. For this reason, it can be expanded to the heat transfer tube 18 of the target diameter while minimizing the collapse and deformation of the radiating fins 12.

  FIG. 5 shows a longitudinal cross-sectional structure of a heat transfer tube made of aluminum or an aluminum alloy applied to the present invention, and the heat transfer tube 20 of this example projects on the inner periphery of the tube main body 21 like the heat transfer tube 18 of the previous embodiment. The point that the strip-shaped heat radiation fin 22 is formed, the point that the fin groove 23 is formed between the adjacent heat radiation fins, the outer diameter, the wall thickness, and the heat radiation fin in which the tube main body 21 is in the same range as the structure of the previous form. The points that satisfy the height are equivalent.

In the heat transfer tube 20 of this embodiment, the point different from the first embodiment is that the radiating fins 22 are formed so as to draw a spiral in the length direction along the inner peripheral surface of the heat transfer tube 20. is there.
The plurality of radiating fins 22 formed inside the tube main body 21 are all formed in a spiral shape with the same pitch, and the fin groove 23 formed between the radiating fins 22 is also the tube main body. 21 is formed in a spiral groove shape so as to draw a spiral at a predetermined pitch.
Even the heat transfer tube 20 provided with the radiation fins 22 of the present embodiment can be expanded by the tube expansion plug 1 in the same manner as the heat transfer tube 18 of the first embodiment.

  By forming the radiating fins 22 in a spiral shape in the length direction of the tube body 21 as in this embodiment, the spiral groove-type fin grooves 23 are also formed in a spiral shape in the length direction of the tube body 21. Therefore, when the refrigerant flows through the tube body 21, the heat exchange efficiency with the refrigerant can be improved.

Next, about the shape of the radiation fin 22, it is preferable to comprise so that it may endure the process at the time of pipe expansion. For example, the heat radiation fins 22 that are three-dimensionally shaped are formed inside the tube main body 21, and the tube main body 21 including the heat radiation fins 22 having such a three-dimensional shape is formed by the tube expansion plug 1. In the case of expanding the pipe, if the radiating fins 22 are arranged in a spiral shape, the pipe expanding plug 1 may expand the pipes while tilting the radiating fins 22 along their twisting direction.
In this respect, if the tube expansion plug 1 is provided with the diamond-like carbon film 5 described above, the tube expansion process can be performed while suppressing the radiating fins 22 from being collapsed or the spiral groove-like fin grooves 23 from being crushed. .
In addition, for the purpose of further preventing the deformation of the radiating fins 23, it is preferable to devise a method such as inclining the radiating fins 22 in advance in the direction opposite to the direction in which the tube expansion plug 1 is assumed to tilt the radiating fins 22. By inclining the radiating fins 22 in advance in this way, it is possible to provide a target structure in which the radiating fins 22 are not crushed even after the pipe expansion by the pipe expansion plug.

The shape shown in FIG. 1 is that the head portion length is 7.3 mm, the head portion maximum diameter is 5.9 mm, the shaft portion length is 36.3 mm, the shaft portion outer diameter is 5.5 mm, the screw shaft length is 10 mm, and the head portion is equivalent to VM40. Tube expansion was performed using a tube expansion plug made of a cemented carbide (HRA90) and having a shaft portion made of JIS SCM435. In this tube expansion plug, a diamond-like carbon film having a thickness of 1.0 μm and a hardness of 30 GPa was formed on the outer surface of the head portion.
As a heat transfer element tube for expansion, a heat transfer element tube having an outer diameter of 7.0 mm, a bottom wall thickness of 0.5 mm, and 45 heat dissipating fins (width 0.15 mm, inner fin height 0.3 mm) on the inner periphery is provided. The tube was expanded with the tube expansion plug (maximum outer diameter φ5.9 mm, plug front surface R = 10 mm). This heat transfer element tube is made of JIS3003 alloy.
The heat transfer element tube was expanded to a heat transfer pipe having an outer diameter of 10 mm by expanding the heat transfer element tube having the structure described above with the tube expansion plug having the structure described above.

When expanding the pipe, the heat transfer element pipe was immediately expanded after being immersed in a lubricating oil (Daphney punch oil AF-2A: manufactured by Idemitsu Kosan Co., Ltd .: kinematic viscosity 1.37 mm ² / S).
As a result of the tube expansion, a heat transfer tube having a tube expansion load of 299 N and a heat dissipating fin excellent in inner surface properties with less deformation and crushing as shown in FIG. 6 was obtained. The expansion ratio of this heat transfer tube is 6.0%, and the reduction rate of the radiating fin height is 10%. The rate of reduction of the radiating fin height is a comparison between the radiating fin height in the state of the heat transfer element tube before the expansion and the height H of the radiating fin 31 of the heat transfer tube 30 shown in FIG. Indicates the rate of decrease.
The inner fin height reduction rate indicates a value calculated by the formula {(fin height before tube expansion−fin height after tube expansion) / fin height before tube expansion}} × 100. These individual heights can be calculated using the results of cross-sectional imaging of each tube using a CCD camera.

In the tube expansion plug, a tube expansion plug in which the dimensions of the constituent materials and the respective parts are made equal, in which a diamond-like carbon film is not formed on the surface of the head portion, is prepared and transmitted under the same conditions as in the above embodiment. A heat transfer tube was manufactured by expanding the heat element tube.
In this case, the tube expansion load was 600 N, and the heat transfer tube 33 having the cross-sectional shape shown in FIG. 7 was manufactured. This heat transfer tube had a radiation fin height reduction rate of 25% and a tube expansion rate of 5.36%.
As shown in FIG. 7, the cross section of the obtained heat transfer tube 33 has a shape in which the heat radiating fins 35 are deformed. It can be estimated that this is because the tube expansion load is as extremely high as 600 N, and the tube expansion load is high, so that a large force is applied to the radiation fin 35 from the tube expansion plug, and the radiation fin 35 is deformed.

The following is the hardness of the cemented carbide (HRA) and the diamond-like carbon film (μm), hardness (GPa), lubricant flash point (° C), and kinematic viscosity ( Tables 1 and 2 show the results of a tube expansion test equivalent to the above by changing (mm ² / S). As the cemented carbide, each cemented carbide shown in Table 1 and Table 2 corresponding to the cemented carbide tool association standard (CIS019D) was used, and each cemented carbide head portion was constructed to constitute a tube expansion plug. The sizes of the shaft portion and head portion of each tube expansion plug, the outer diameter, and the like are the same as those in the above example. The results of measuring the surface roughness of the DLC film of each tube expansion plug are also shown in Tables 1 and 2.

Tables 1 and 2 show tube expansion load (N), inner fin height reduction rate (%), tube expansion rate (%), aluminum aggregation state, tube expansion plug life (distance 2000 m, 5000 m), and oil drying properties.
In the evaluation items in Tables 1 and 2, the inner fin height reduction rate indicates the height reduction rate before and after the pipe expansion test according to the above-described calculation formula (the denominator is the fin height before pipe expansion). The pipe expansion ratio indicates the outer diameter pipe expansion ratio before and after the pipe expansion test (the denominator is before pipe expansion). For the aluminum aggregate strip, the appearance of the pipe expansion plug is observed after pipe expansion, and there is no adhesion in the circumferential direction of the pipe expansion plug. A case where the adhesion range was about ½ was indicated by Δ, and a case where the adhesion range was more than ½ was indicated by a cross. Expanded plug life is determined by observing the appearance of the expanded plug after each expansion distance and evaluating that no change is observed in the aluminum adhesion due to wear of the diamond-like carbon film. / 4 or less is indicated by ◯, circumferential direction 1/3 or less is indicated by Δ, circumferential direction ½ or less is indicated by ▲, and the case where it exceeds 1/2 in the circumferential direction is indicated by ×. Oil-drying means that 1 g of lubricating oil is sampled in a petri dish and the weight after heating at 140 ° C. for 2 minutes is 5% or less before heating. The case of is indicated by a cross.

From the test results of the samples Nos. 1 to 13 and 17 to 28 shown in Table 1, the cemented carbide hardness HRA 85 to 95, the DLC film thickness 0.5 to 3.0 μm, and the kinematic viscosity of the expanded lubricating oil 1.0 mm ² With the above, the tube expansion load is low (200 to 300 N), the inner fin height reduction rate is small (7 to 13%), the tube expansion rate is excellent, aluminum agglomeration hardly occurs, and the tube expansion plug life is long. It can be seen that can be obtained.
In addition, in the test result of the sample of No. 1-13, 17-28, it turns out that the sample of No. 9-13, 17-28 of 30 N or more of critical peeling loads is especially excellent in a pipe expansion plug lifetime.

Compared to these samples, the No. 29 sample (comparative example) with a cemented carbide hardness of HRA83 had a shorter life as a tube expansion plug. In the sample No. 30 (comparative example) in which the hardness of the cemented carbide is HRA96, the cemented carbide portion became brittle and could not be processed by the tube expansion plug. No. 32 sample (comparative example) with a diamond-like carbon film thickness of 3.5 μm could not be formed on the head portion of the tube expansion plug because the film itself was too thick. The sample of No. 33 (comparative example) was a sample having a low lubricating oil kinematic viscosity, and the lubricity was insufficient, and the aluminum aggregation state deteriorated. The sample No. 34 (comparative example) was a sample having a high lubricating oil flash point and a high viscosity, and the oil drying property was insufficient. Since it is advantageous to apply a drying process after the pipe expansion process to reduce the residual amount of the pipe expansion oil, it is desirable that the residual oil content is 5% or less by heating at 140 ° C. for 2 minutes.
Further, from the comparison of the measurement results of the surface roughness Ra in the diamond-like carbon films of Samples 1 to 16, Ra is preferably 0.1 μm or less from the viewpoint of reducing the tube expansion load, and is preferably 0.05 μm or less. It can be seen that it is more desirable to reduce the pipe expansion load and reduce the inner fin height reduction rate.

  DESCRIPTION OF SYMBOLS 1 ... Tube expansion plug, 2 ... Shaft part, 2a ... Screw shaft part, 3 ... Head part, 5 ... Diamond-like carbon film, 10 ... Heat-transfer elementary tube, 11 ... Pipe body, 12 ... Radiation fin, 14 ... Fin groove, 15 ... Fin material, 16 ... Fin assembly, 17 ... Hairpin pipe, 17a ... Opening, 18 ... Heat transfer tube.

Claims (6)

An expansion plug having a head portion having an outer diameter larger than the inner diameter of the heat transfer element tube is forcibly inserted inside the heat transfer element tube made of aluminum or an aluminum alloy to expand the outer diameter of the heat transfer element tube. A heat transfer tube expansion method for forming a heat transfer tube,
The tube expansion plug has a shaft portion and a head portion formed on the distal end side of the shaft portion. The head portion is formed of a cemented carbide having a hardness of HRA85 to 95, and has a thickness of 0. Using a tube expansion plug coated with a diamond-like carbon film of 5 to 3.0 μm,
A heat transfer tube characterized by using 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 a lubricating oil for lubricating between the heat transfer element tube and the tube expansion plug. Tube expansion method.   The method of expanding a heat transfer tube according to claim 1, wherein the diamond-like carbon film is a diamond-like carbon film having a hardness in a range of 20 GPa to 70 GPa and a critical peeling load of 30 N or more.   The method of expanding a heat transfer tube according to claim 1 or 2, wherein a diamond-like carbon film having a surface roughness Ra of 0.1 µm or less is used.   A plurality of heat transfer element tubes are arranged so as to pass through a fin assembly formed by arranging a plurality of fin materials made of aluminum or aluminum alloy, and these heat transfer element tubes are expanded by the expansion plug to form heat transfer tubes. The heat transfer tube expansion method according to any one of claims 1 to 3, wherein the heat transfer tubes are joined to the fin assembly.   5. A grooved heat transfer element tube having a plurality of grooves extending in the length direction of the tube at intervals in the circumferential direction of the inner surface of the tube is used as the heat transfer element tube. The expansion method of the heat exchanger tube as described in any one of these.   2. The heat transfer element tube having a spiral groove having a plurality of spiral grooves extending in the length direction of the tube at intervals in the circumferential direction of the inner surface of the tube is used as the heat transfer element tube. The tube expansion method of the heat exchanger tube as described in any one of -5.

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