Method for manufacturing heat exchanger

Abstract

In the method for manufacturing the heat exchanger (10), a tube insertion step and a tube expansion step are performed. In the pipe inserting process, the heat transfer pipes are inserted into the through holes of the fins. In the tube expanding step, the outer diameter of the heat transfer tube after the fins are inserted is increased. In the tube expansion step, in order to increase the outer diameter of the heat transfer tube, a tube expansion plug (60) is pressed into the heat transfer tube. The tube expansion plug (60) includes a plug body (62) made of a superalloy and a diamond film (64) covering a surface of the plug body (62).

Description

Technical Field

[0001] The present disclosure relates to a method for manufacturing a heat exchanger. Background Art

[0002] Patent Document 1 discloses a tube expansion plug. The tube expansion plug is used in the manufacturing process of a heat exchanger. Specifically, in a tube expansion process for increasing the outer diameter of a heat transfer tube and fixing fins to the heat transfer tube, the tube expansion plug is pressed into the heat transfer tube.

[0003] Patent Document 1 discloses forming a DLC (Diamond-Like Carbon) film on the surface of a tube expansion plug in order to reduce the amount of lubricating oil used to reduce friction between a heat transfer tube and the tube expansion plug.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent No. 6604701 Summary of the invention

[0007] -Technical problem to be solved by the invention-

[0008] The DLC film is easy to wear. Therefore, there is a problem that the replacement frequency of the expansion plug increases and the cost increases. In addition, if the replacement frequency of the expansion plug is suppressed to a low level, the expansion plug will continue to be used in a state where the DLC film is almost gone, and thus there is a problem that the amount of lubricating oil applied to the heat transfer tube before the expansion process cannot be reduced.

[0009] An object of the present disclosure is to reduce the amount of lubricating oil used in a tube expansion process for increasing the outer diameter of a heat transfer tube.

[0010] -Technical solutions to solve technical problems-

[0011] A first aspect of the present disclosure is a method for manufacturing a heat exchanger 10, the heat exchanger 10 including a plate-shaped fin 20 and a circular tube-shaped heat transfer tube 30, the method for manufacturing the heat exchanger 10 including a tube inserting process and a tube expanding process, in which the heat transfer tube 30 is inserted into a through hole 21 formed in the fin 20 in the tube inserting process, and in which the outer diameter of the heat transfer tube 30 after the fin 20 is inserted in the tube expanding process is increased in order to fix the fin 20 on the heat transfer tube 30. In the tube expanding process, in order to increase the outer diameter of the heat transfer tube 30, a tube expansion plug 60 is pressed into the heat transfer tube 30, the tube expansion plug 60 including a plug body 62 made of a superhard alloy and a diamond film 64 covering the surface of the plug body 62.

[0012] In the first aspect, a pipe expansion plug 60 including a plug body 62 and a diamond film 64 is used in the pipe expansion process. The diamond film 64 has the characteristics of being harder and less susceptible to wear than a DLC film. Therefore, the replacement frequency of the pipe expansion plug 60 can be suppressed to a low level. Moreover, by using the pipe expansion plug 60 including the diamond film 64, it is possible to eliminate the need for lubricating oil for lubricating the contact portion between the heat transfer tube 30 and the pipe expansion plug 60 in the pipe expansion process. In addition, when lubricating oil is applied to the inner surface of the heat transfer tube 30 before the pipe expansion process, the amount of lubricating oil to be applied can be reduced.

[0013] In a second aspect of the present disclosure, based on the first aspect, the heat transfer tube 30 is made of aluminum or aluminum alloy, and is an inner surface grooved tube having a plurality of grooves formed on the inner side surface.

[0014] In the second aspect, the heat transfer tube 30 constituting the heat exchanger 10 is a tube with inner surface grooves made of aluminum or aluminum alloy. In the tube expansion step, the tube expansion plug 60 is press-fitted into the heat transfer tube 30 .

[0015] Here, when the expansion plug 60 is pressed into the heat transfer tube 30 which is a tube with grooves on the inner surface, only a part of the inner surface of the heat transfer tube 30 contacts the expansion plug 60. Therefore, compared with the case where the expansion plug 60 is pressed into a tube having no grooves formed on the inner surface, the contact pressure acting on the outer surface of the expansion plug 60 becomes higher. On the other hand, the outer surface of the expansion plug 60 used in the manufacturing method of the second aspect is composed of a diamond film 64. Therefore, even when the heat transfer tube 30 is a tube with grooves on the inner surface, the amount of aluminum adhering to the expansion plug 60 can be suppressed to a low level.

[0016] According to a third aspect of the present disclosure, in addition to the first aspect or the second aspect, an arithmetic mean roughness Ra of the surface of the diamond film 64 of the tube expansion plug 60 used in the tube expansion step is 0.023 μm or less.

[0017] In the manufacturing method of the third aspect, in the tube expansion process, the tube expansion plug 60 having a relatively small surface roughness of the diamond film 64 is pressed into the heat transfer tube 30 made of aluminum or an aluminum alloy. The diamond film 64 has a relatively low affinity with aluminum. In particular, in this aspect, the surface roughness of the diamond film 64 formed on the tube expansion plug 60 is relatively small. Therefore, the amount of aluminum adhering to the tube expansion plug 60 in the tube expansion process is reduced.

[0018] According to a fourth aspect of the present disclosure, based on the first aspect or the second aspect, the inner diameter of the heat transfer tube 30 before the tube expansion process is the inner diameter before the tube expansion process, the tube expansion plug 60 has a base end 60b and a top end 60a, and includes a first portion 71, an expanded diameter portion 76, and a second portion 72, the first portion 71 is a portion located between the base end 60b and the top end 60a and having the largest outer diameter, the expanded diameter portion 76 is a portion from the top end 60a to the first portion 71, and the outer diameter of the expanded diameter portion 76 gradually increases from the top end 60a toward the first portion 71, the second portion 72 is a portion of the expanded diameter portion 76 whose outer diameter is equal to the inner diameter before the tube expansion, and the arithmetic mean roughness Ra of the surface of the diamond film 64 located in the second portion 72 is smaller than the arithmetic mean roughness Ra of the surface of the diamond film 64 located in the first portion 71.

[0019] In the fourth aspect, the expansion plug 60 includes a first portion 71 and a second portion 72. When the expansion plug 60 is inserted into the heat transfer tube 30 from the top end 60a side, the second portion 72 initially contacts the inner surface of the heat transfer tube 30. Then, when the expansion plug 60 is further inserted into the heat transfer tube 30, the heat transfer tube 30 is pressed toward the radially outer side by the region between the second portion 72 and the first portion 71 in the expansion plug 60 and expanded.

[0020] During the process of inserting the expansion plug 60 into the heat transfer tube 30, the second portion 72 of the expansion plug 60 first contacts the inner surface of the heat transfer tube 30. In the expansion plug 60 of the fourth aspect, the arithmetic mean roughness Ra of the surface of the diamond film 64 located at the second portion 72 is smaller than the arithmetic mean roughness Ra of the surface of the diamond film 64 located at the first portion 71. Therefore, the surface roughness of the second portion 72 that first contacts the inner surface of the heat transfer tube 30 during the process of inserting the expansion plug 60 into the heat transfer tube 30 is relatively small, thereby being able to suppress the amount of aluminum adhering to the expansion plug 60 to be low.

[0021] According to a fifth aspect of the present disclosure, in addition to the fourth aspect, the arithmetic mean roughness Ra of the surface of the diamond film 64 located at the first portion 71 is 0.023 μm or less.

[0022] In the fifth aspect, the numerical range of the arithmetic mean roughness Ra of the surface of the diamond film 64 located at the first portion 71 is determined.

[0023] According to a sixth aspect of the present disclosure, in addition to the fourth aspect, the arithmetic mean roughness Ra of the surface of the diamond film 64 located at the second portion 72 is 0.013 μm or less.

[0024] In the sixth aspect, the numerical range of the arithmetic mean roughness Ra of the surface of the diamond film 64 located at the second portion 72 is determined.

[0025] According to a seventh aspect of the present disclosure, based on the fourth aspect, the arithmetic mean roughness Ra of the surface of the diamond film 64 located at the first portion 71 is less than 0.023 μm, and the arithmetic mean roughness Ra of the surface of the diamond film 64 located at the second portion 72 is less than 0.013 μm.

[0026] In the seventh aspect, the numerical range of the arithmetic mean roughness Ra is determined for each of the surface of the diamond film 64 located at the first portion 71 and the surface of the diamond film 64 located at the second portion 72 .

[0027] The eighth aspect of the present disclosure is based on any one of the first to seventh aspects above, and the manufacturing method of the heat exchanger includes a coating process, which is a process performed before the tube expansion process, in which lubricating oil is coated on the inner surface of the heat transfer tube 30, and in the coating process, the amount of the lubricating oil coated on the inner surface of a heat transfer tube 30 is less than 0.5g per 1m length of the heat transfer tube 30.

[0028] In the eighth aspect, in the coating step, a predetermined amount of lubricating oil is coated on the inner surface of the heat transfer tube 30. The coating step is performed before the tube expansion step. The timing of performing the coating step is not limited to the timing immediately before the tube expansion step.

[0029] According to a ninth aspect of the present disclosure, in addition to any one of the first to seventh aspects, the tube expansion step is performed in a state where the inner side surface of the heat transfer tube 30 is not coated with lubricating oil.

[0030] In the ninth aspect, in the tube expansion step, the tube expansion plug 60 is press-fitted into the heat transfer tube 30 whose inner surface has not been coated with lubricating oil.

[0031] According to a tenth aspect of the present disclosure, based on any one of the first to ninth aspects, in the tube expansion step, the outer diameter of the heat transfer tube 30 is increased to not less than 104% and not more than 112% of the outer diameter of the heat transfer tube 30 before the tube expansion step.

[0032] In the sixth aspect, the tube expansion rate of the heat transfer tube 30 in the tube expansion step is set to 4% or more and 12% or less. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 It is a three-dimensional schematic diagram of a heat exchanger;

[0034] Figure 2is a cross-sectional view of a heat exchanger showing a cross section of a heat transfer tube including a central axis;

[0035] Figure 3 is a cross-sectional view of the heat transfer tube;

[0036] Figure 4 is a flow chart showing a method of manufacturing a heat exchanger;

[0037] Figure 5 It is a three-dimensional diagram of the fins and heat transfer tubes in the tube insertion process;

[0038] Figure 6 is a top view of the pipe expansion device and an assembly provided on the pipe expansion device;

[0039] Figure 7 is a diagram showing a cross section of a heat transfer tube and a tube expansion plug in a tube expansion process;

[0040] Figure 8 is a top view of the expansion plug;

[0041] Fig. 9 is a cross-sectional view of the expansion plug;

[0042] Fig.10 It is a cross-sectional view of the heat transfer tube before expansion. DETAILED DESCRIPTION

[0043] The present embodiment is a method for manufacturing the heat exchanger 10. In this manufacturing method, a tube expansion device 50 including a tube expansion plug 60 is used.

[0044] - Heat exchanger -

[0045] The heat exchanger 10 manufactured by the manufacturing method of this embodiment is a so-called cross-fin type heat exchanger. The heat exchanger 10 is provided in a refrigerant circuit of an air conditioner or the like, and is used to perform heat exchange between a refrigerant and air.

[0046] like Figure 1 As shown, the heat exchanger 10 includes a plurality of fins 20 and a plurality of heat transfer tubes 30. It should be noted that: Figure 1 The number and shape of the fins 20 and the heat transfer tubes 30 shown are merely examples.

[0047] The fin 20 is formed into a rectangular plate shape. The material of the fin 20 is aluminum or aluminum alloy. A plurality of fins 20 are arranged in a row along the thickness direction of each fin 20. It should be noted that the fin 20 may also be formed with a flap (such as a louver or a slit, etc.) for promoting heat transfer.

[0048] A plurality of through holes 21 are formed on the fin 20. Figure 1 In the fin 20 shown, a plurality of through holes 21 are arranged in a row along the long side of the fin 20 (see Figure 5 ).

[0049] like Figure 2 As shown in FIG. 1 , the fin 20 is provided with the same number of sleeve portions 22 as the number of through holes 21. The sleeve portion 22 is a cylindrical portion extending from the peripheral edge of the through hole 21.

[0050] The heat transfer tube 30 is a round tube formed in a hairpin shape. The heat transfer tube 30 is made of aluminum or aluminum alloy. The heat transfer tube 30 includes a pair of straight tube portions 31 and a curved tube portion 32. Figure 2 As shown, the straight tube portion 31 of the heat transfer tube 30 is inserted into the through hole 21 of the fin 20. It should be noted that the shape of the heat transfer tube 30 is not limited to the hairpin shape. The shape of the heat transfer tube 30 may also be a straight tube shape, for example.

[0051] like Figure 3 As shown, the heat transfer tube 30 is an inner surface grooved tube having a plurality of grooves formed on the inner side surface. Specifically, on the inner side surface of the heat transfer tube 30, a plurality of grooves 33 and a plurality of peaks 34 are alternately formed along the circumferential direction of the heat transfer tube 30. The grooves 33 and the peaks 34 extend in a spiral shape toward the axial direction of the heat transfer tube 30, respectively. It should be noted that the grooves 33 and the peaks 34 may also extend in a straight line toward the axial direction of the heat transfer tube 30, respectively.

[0052] It should be noted that the heat exchanger 10 is provided with components such as U-shaped tubes connecting adjacent heat transfer tubes 30. Figure 1 Illustration omitted.

[0053] - Method for manufacturing heat exchanger -

[0054] like Figure 4 As shown, in the method for manufacturing the heat exchanger 10, a preparation step, a tube inserting step, a tube expanding step, a drying step, a brazing step, and a testing step are performed in sequence.

[0055] <Preparation process>

[0056] In the preparation step, the fins 20 and the heat transfer tubes 30 are each formed into a predetermined shape.

[0057] The fin 20 is formed into a rectangular plate shape having a through hole 21 and a sleeve portion 22 by punching a plate material. In the preparation step, a plurality of fins 20 are arranged in a row along the thickness direction of each fin.

[0058] The heat transfer tube 30 is formed into a hairpin shape by bending a straight tube. During the bending process, machining oil adheres to the inner surface of the heat transfer tube 30 .

[0059] <Intubation process>

[0060] like Figure 5As shown, in the pipe inserting step, the straight pipe portion 31 of the heat transfer pipe 30 is inserted into the through holes 21 of the plurality of fins 20 arranged in a row in the preparation step. In the pipe inserting step, an assembly 15 consisting of the fins 20 and the heat transfer pipe 30 is formed. In the assembly 15 at the end of the pipe inserting step, there is a gap between the sleeve portion 22 of the fin 20 and the heat transfer pipe 30, and the fin 20 has not yet been fixed to the heat transfer pipe 30.

[0061] <Tube expansion process>

[0062] The tube expansion process is a process of increasing the outer diameter of the heat transfer tube 30 in order to fix the fin 20 on the heat transfer tube 30. During the period from the end of the preparation process to the end of the tube expansion process, the process of applying lubricating oil to the inner side surface of the heat transfer tube 30 is not performed. Therefore, the tube expansion process is performed in a state where the inner side surface of the heat transfer tube 30 is not substantially coated with lubricating oil, which is used to reduce the friction between the heat transfer tube 30 and the tube expansion plug 60.

[0063] like Figure 6 As shown, the pipe expansion step is performed using a pipe expansion device 50. The structure of the pipe expansion device 50 will be described later.

[0064] In the tube expansion process, the assembly 15 formed in the tube insertion process is placed on the tube expansion device 50. The tube expansion device 50 presses the tube expansion plug 60 into the straight tube portion 31 of the heat transfer tube 30 constituting the assembly 15. The outer diameter dh of the thickest part of the tube expansion plug 60 is larger than the inner diameter di of the straight tube portion 31 of the heat transfer tube 30 before tube expansion. Figure 7 As shown, when the expansion plug 60 is pressed into the straight tube portion 31 of the heat transfer tube 30, the straight tube portion 31 is pressed and expanded by the expansion plug 60, and plastic deformation occurs, resulting in an increase in the outer diameter of the straight tube portion 31.

[0065] In the pipe expansion process of the present embodiment, the increase rate R of the outer diameter of the heat transfer pipe 30 is 4% or more and 12% or less. The increase rate R is a value expressed as a percentage (Do-do) / do. "do" is the outer diameter of the straight pipe portion 31 of the heat transfer pipe 30 before pipe expansion. "Do" is the outer diameter of the straight pipe portion 31 of the heat transfer pipe 30 after pipe expansion. Therefore, the outer diameter Do of the straight pipe portion 31 after pipe expansion is 104% or more and 112% or less of the outer diameter do of the straight pipe portion 31 before pipe expansion.

[0066] When the outer diameter of the straight tube portion 31 of the heat transfer tube 30 is increased in the tube expansion process, the outer side surface of the straight tube portion 31 is closely attached to the inner side surface of the sleeve portion 22 of the fin 20 (see Figure 2 As a result, the fins 20 are fixed to the heat transfer tubes 30 .

[0067] <Drying process>

[0068] The drying process is a process for removing the processing oil attached to the inner surface of the heat transfer tube 30. In the drying process, the assembly 15 that has undergone the tube expansion process is heated, and a gas such as air is made to flow through the heat transfer tube 30 of the assembly 15. The oil attached to the inner surface of the heat transfer tube 30 is heated and evaporated, and is discharged to the outside of the heat transfer tube 30 by the gas flowing through the heat transfer tube 30.

[0069] <Brazing process>

[0070] In the brazing process, the U-shaped tubes and other components for connecting the adjacent heat transfer tubes 30 are mounted on the assembly 15 by brazing. When the brazing process is completed, the heat exchanger 10 is completed.

[0071] <Testing process>

[0072] In the test process, an airtightness test of the heat exchanger 10 is performed. Specifically, in the test process, high-pressure gas is supplied to the heat transfer tube 30 to check whether there is gas leakage from the heat transfer tube 30.

[0073] - Pipe expansion device -

[0074] like Figure 6 As shown, the tube expansion device 50 includes a plurality of tube expansion plugs 60 and a plurality of rods 51. The number of the tube expansion plugs 60 included in the tube expansion device 50 is twice the number of the heat transfer tubes 30 provided on the assembly 15 (in other words, the same as the number of the straight tube portions 31 provided on the assembly 15). The number of the rods 51 included in the tube expansion device 50 is the same as the number of the tube expansion plugs 60. The tube expansion device 50 also includes a connecting block 52, a driving portion 53, and a retaining block 54.

[0075] The expansion plug 60 is a bullet-shaped member that gradually tapers toward the tip. The expansion plug 60 will be described in detail later.

[0076] The rod 51 is a steel member. Each of the plurality of rods 51 corresponds to one expansion plug 60. At the top end of each rod 51, one expansion plug 60 corresponding to the rod 51 is connected.

[0077] The rods 51 connected with the expansion plugs 60 are arranged parallel to each other with a predetermined interval therebetween. The interval between the rods 51 is substantially equal to the interval between the straight tubes 31 in the assembly 15. The rods 51 are arranged substantially coaxially with the straight tubes 31 of the heat transfer tubes 30 in the assembly 15 provided on the expansion device 50. The expansion plugs 60 mounted on the rods 51 are opposite to the open ends of the corresponding straight tubes 31.

[0078] The connection block 52 is a long and thin member made of steel. The connection block 52 is arranged so that its longitudinal direction is perpendicular to the axial direction of the rod 51. The base ends of all the rods 51 are connected to the connection block 52.

[0079] The driving unit 53 is a component for driving the connecting block 52. The driving unit 53 is composed of, for example, a feed screw and a motor. The driving unit 53 is configured to reciprocate the connecting block 52 along the axial direction of the rod 51. When the driving unit 53 drives the connecting block 52, the expansion plug 60 moves along the axial direction of the rod 51.

[0080] The holding block 54 is a steel member for holding the assembly 15. The holding block 54 is arranged to face the expansion plug 60 across the assembly 15. The holding block 54 holds the curved tube portion 32 of the heat transfer tube 30 of the assembly 15 and restricts displacement of the assembly 15 during the tube expansion process.

[0081] -Expansion plug-

[0082] like Figure 8 and Fig. 9 As shown, the expansion plug 60 includes a metal member 61 and a diamond film 64 .

[0083] The metal member 61 includes a head 62 and a base 63. The head 62 and the base 63 are each integral. The head 62 and the base 63 are joined to each other by, for example, brazing or screwing.

[0084] The head 62 is a plug body. The material of the head 62 is a superhard alloy. The superhard alloy is an alloy composed of metal carbide and iron group metal. As a superhard alloy, there is a WC-Co alloy, for example.

[0085] The head 62 is a bullet-shaped portion that tapers toward the top. Figure 8 and Fig. 9 The shape of the head 62 shown is only an example. As the shape of the head 62, there are, for example, a spherical shape, an ellipsoidal spherical shape, a conical shape, a polygonal pyramid shape, and the like.

[0086] The base 63 is a short cylindrical part. The material of the base 63 is, for example, chrome-molybdenum steel. The base 63 is joined to the base end of the head 62. The base 63 and the head 62 are arranged coaxially. The outer diameter of the base 63 is smaller than the maximum value dh of the outer diameter of the head 62.

[0087] The diamond film 64 is provided to cover the outer surface of the head 62 of the metal member 61. The diamond film 64 is a film-shaped diamond formed by CVD (Chemical Vapor Deposition) method. The thickness of the diamond film 64 is about 8 μm.

[0088] The top end 60a of the expansion plug 60 is Figure 8 The left end of the expansion plug 60 is shown. The base end 60b of the expansion plug 60 is Figure 8The right end of the expansion plug 60 is shown.

[0089] The expansion plug 60 includes a first portion 71. The first portion 71 is a circular portion orthogonal to the central axis of the expansion plug 60. The first portion 71 is located between the top end 60a and the base end 60b of the expansion plug 60 and is the portion with the largest outer diameter in the expansion plug 60. Therefore, the outer diameter of the first portion 71 coincides with the maximum value dh of the outer diameter of the head 62.

[0090] The portion of the expansion plug 60 consisting of the head 62 and the diamond film 64 is divided into an expanded diameter portion 76 and a reduced diameter portion 77. The expanded diameter portion 76 is a portion located on the side of the tip 60a with respect to the first portion 71. The outer diameter of the expanded diameter portion 76 gradually increases from the tip 60a of the expansion plug 60 toward the first portion 71. The reduced diameter portion 77 is a portion located on the side of the base end 60b with respect to the first portion 71. The outer diameter of the reduced diameter portion 77 gradually decreases from the first portion 71 of the expansion plug 60 toward the base end 60b.

[0091] The expansion plug 60 includes a second portion 72. The second portion 72 is a circular portion orthogonal to the central axis of the expansion plug 60. The second portion 72 is a portion of the expanded diameter portion 76. The second portion 72 is a portion located between the top end 60a of the expansion plug 60 and the first portion 71 and having an outer diameter equal to the inner diameter di of the heat transfer tube 30 before expansion.

[0092] like Fig.10 As shown in FIG. 1 , the inner diameter di of the heat transfer tube 30 before expansion is the minimum value of the inner diameter of the heat transfer tube 30 before expansion in the expansion process. More specifically, the inner diameter di of the heat transfer tube 30 before expansion is the virtual circle ( Fig.10 The diameter of the imaginary circle (indicated by the two-dot chain line) is a circle passing through the tops of all the peaks 34 in the cross section perpendicular to the central axis of the heat transfer tube 30.

[0093] In the tube expansion step, the tube expansion plug 60 is inserted into the heat transfer tube 30 from the top end 60a side (see Figure 7 ). During the process of inserting the expansion plug 60 into the heat transfer tube 30, the second portion 72 initially contacts the inner surface of the heat transfer tube 30. Then, when the expansion plug 60 is further inserted into the heat transfer tube 30, the heat transfer tube 30 is pressed radially outward by the region between the second portion 72 and the first portion 71 in the expansion plug 60 and expanded.

[0094] - Surface roughness of expansion plug -

[0095] The expanded tube plug 60 used in the manufacturing method of the present embodiment has a surface of the diamond film 64 ground. In the expanded tube plug 60, the arithmetic mean roughness Ra of the surface of the diamond film 64 located at the second portion 72 is smaller than the arithmetic mean roughness Ra of the surface of the diamond film 64 located at the first portion 71. In addition, in the expanded tube plug 60, the arithmetic mean roughness Ra of the surface of the diamond film 64 located at the first portion 71 is 0.023 μm or less, and the arithmetic mean roughness Ra of the surface of the diamond film 64 located at the second portion 72 is 0.013 μm or less.

[0096] [Table 1]

[0097]

[0098] The numerical range of the surface roughness of the diamond film 64 will be described with reference to Table 1. Table 1 shows the results of the tube expansion test performed on each of the test pieces 1 to 6. The test pieces 1 to 6 are tube expansion plugs 60 in which only the surface roughness of the diamond film 64 is different from each other.

[0099] The expansion test is to insert the expansion plug 60 into a straight heat transfer tube and expand the heat transfer tube. The heat transfer tube used in the expansion test is an aluminum alloy tube with grooves on the inner surface. The outer diameter of the heat transfer tube is 7mm and the length is 150mm. The expansion rate in the expansion test is 10%. The expansion test is carried out in a state where 0.01g of lubricating oil is applied to the inner surface of the heat transfer tube.

[0100] In the tube expansion test, a tube expansion plug 60 as a test piece was inserted into the heat transfer tube, and it was visually confirmed whether aluminum of the heat transfer tube adhered to the tube expansion plug 60 pulled out from the heat transfer tube after tube expansion. As shown in Table 1, no aluminum was observed to adhere to the surface of the tube expansion plug 60 for each of the test pieces 1, 2, and 3. On the other hand, aluminum was observed to adhere to the surface of the tube expansion plug 60 for each of the test pieces 4, 5, and 6.

[0101] If aluminum adheres to the tube expansion plug 60 during the tube expansion process, it means that the heat transfer tube 30 is damaged during the tube expansion process. Therefore, in the tube expansion process, it is necessary to use the tube expansion plug 60 to which aluminum does not adhere during the tube expansion test.

[0102] Therefore, in the tube expansion step of the manufacturing method of the present embodiment, the tube expansion plug 60 is used, in which the arithmetic mean roughness Ra of the surface of the diamond film 64 located at the first portion 71 is 0.023 μm or less, and the arithmetic mean roughness Ra of the surface of the diamond film 64 located at the second portion 72 is 0.013 μm or less. As a result, in the tube expansion step of the manufacturing method of the present embodiment, aluminum does not substantially adhere to the tube expansion plug 60.

[0103] As described above, in the process of inserting the expansion plug 60 into the heat transfer tube 30, the second portion 72 initially contacts the inner surface of the heat transfer tube 30. Therefore, a relatively large load acts on the surface of the diamond film 64 located at the second portion 72 compared to other portions of the surface of the diamond film 64. Therefore, the material forming the heat transfer tube 30 (aluminum in this embodiment) is easily adhered to the surface of the diamond film 64 located at the second portion 72 compared to other portions of the surface of the diamond film 64.

[0104] Therefore, in the tube expansion step of the manufacturing method of the present embodiment, the tube expansion plug 60 is used in which the "arithmetic mean roughness Ra of the surface of the diamond film 64 located at the second portion 72" is smaller than the "arithmetic mean roughness Ra of the surface of the diamond film 64 located at the first portion 71". As a result, in the tube expansion step of the manufacturing method of the present embodiment, aluminum does not substantially adhere to the tube expansion plug 60.

[0105] In the tube expansion test, the tube expansion thrust was measured for each of the specimens 1 to 6. The tube expansion thrust is the force that needs to be applied to the tube expansion plug 60 in order to insert the tube expansion plug 60 as the specimen into the heat transfer tube. The tube expansion thrust of the specimens 1 and 3 is much smaller than that of the specimen 2. It can be inferred that the surface roughness of the second portion 72 affects the tube expansion thrust. Therefore, for the tube expansion plug 60 used in the tube expansion process of this embodiment, it is more preferable that the arithmetic mean roughness Ra of the surface of the diamond film 64 located at the second portion 72 is 0.010 μm or less.

[0106] - Features of the embodiment (1) -

[0107] In the manufacturing method of the heat exchanger 10 of the present embodiment, a pipe expansion plug 60 including a metal component 61 and a diamond film 64 is used in the pipe expansion process. The diamond film 64 has the characteristics of being harder and less prone to wear than a DLC film. Therefore, by using the pipe expansion plug 60 including the diamond film 64, the replacement frequency of the pipe expansion plug 60 can be suppressed to a low level.

[0108] In the manufacturing method of the heat exchanger 10 of the present embodiment, the expansion plug 60 including the diamond film 64 is used, so that during the expansion process, lubricating oil is not required to lubricate the contact portion between the heat transfer tube 30 and the expansion plug 60. Therefore, the step of removing the lubricating oil from the heat transfer tube 30 after the expansion process can be omitted, the equipment for manufacturing the heat exchanger 10 can be simplified, and the time required for manufacturing the heat exchanger 10 can be shortened.

[0109] - Features of the embodiment (2) -

[0110] In the heat exchanger 10 manufactured by the manufacturing method of the present embodiment, the heat transfer tube 30 is a tube with inner surface grooves made of aluminum or aluminum alloy. On the other hand, in the tube expansion process of the manufacturing method of the present embodiment, a tube expansion plug 60 including a diamond film 64 is used. The diamond film 64 has a property of having a relatively low affinity with aluminum. Therefore, according to the present embodiment, the amount of aluminum adhering to the tube expansion plug 60 in the tube expansion process can be reduced, thereby extending the service life of the tube expansion plug 60.

[0111] Here, when the expansion plug 60 is pressed into the heat transfer tube 30 which is a tube with grooves on the inner surface, only a part of the inner surface of the heat transfer tube 30 contacts the expansion plug 60. Therefore, compared with the case where the expansion plug 60 is pressed into a tube whose inner surface is not grooved, the contact pressure acting on the outer surface of the expansion plug 60 becomes higher. On the other hand, the outer surface of the expansion plug 60 used in the manufacturing method of this embodiment is composed of a diamond film 64. Therefore, even when the heat transfer tube 30 is a tube with grooves on the inner surface, the amount of aluminum adhering to the expansion plug 60 can be suppressed to a low level.

[0112] - Features of the embodiment (3) -

[0113] In the manufacturing method of the heat exchanger 10 of the present embodiment, the surface roughness Ra of the diamond film 64 of the tube expansion plug 60 used in the tube expansion process is 0.023 μm or less. That is, in the tube expansion plug 60 used in the tube expansion process of the present embodiment, the surface roughness Ra of the diamond film 64 in contact with the heat transfer tube 30 is small. Therefore, according to the present embodiment, the amount of aluminum adhering to the tube expansion plug 60 can be suppressed to a lower level.

[0114] - Features of the embodiment (4) -

[0115] In the manufacturing method of the heat exchanger 10 of the present embodiment, the expansion plug 60 used in the expansion step has a surface of the diamond film 64 located at the second portion 72 with a smaller arithmetic mean roughness Ra than the surface of the diamond film 64 located at the first portion 71. Therefore, in the process of inserting the expansion plug 60 into the heat transfer tube 30, the surface roughness of the second portion 72 that first contacts the inner surface of the heat transfer tube 30 is relatively small. As a result, the amount of aluminum adhering to the expansion plug 60 can be suppressed to a low level.

[0116] Furthermore, in the expansion plug 60 used in the expansion process of the present embodiment, the arithmetic mean roughness Ra of the surface of the diamond film 64 located at the first portion 71 is 0.023 μm or less, and the arithmetic mean roughness Ra of the surface of the diamond film 64 located at the second portion 72 is 0.013 μm or less. That is, in the expansion plug 60 used in the expansion process of the present embodiment, the surface roughness Ra of the diamond film 64 in contact with the heat transfer tube 30 is small. Therefore, according to the present embodiment, the amount of aluminum adhering to the expansion plug 60 can be suppressed to a lower level.

[0117] - Modification of the embodiment -

[0118] In the manufacturing method of the heat exchanger 10 of the present embodiment, a coating step may be performed before the tube expansion step. The coating step is a step of coating the inner side surface of the heat transfer tube 30 with lubricating oil, and the lubricating oil is used to lubricate the contact portion between the heat transfer tube 30 and the tube expansion plug 60 in the tube expansion step. In the coating step, the lubricating oil is coated on the inner side surface of all the heat transfer tubes 30.

[0119] The amount of lubricating oil applied to the heat transfer tube 30 in the coating process is less than the amount of lubricating oil applied to the heat transfer tube in the conventional manufacturing method that does not use the expansion plug 60 including the diamond film 64. Specifically, in the coating process of this modified example, the amount of lubricating oil applied to one heat transfer tube 30 is less than 0.5 g per 1 m length of the heat transfer tube 30. The amount of lubricating oil applied to one heat transfer tube 30 is preferably less than 0.07 g per 1 m length of the heat transfer tube 30. In this coating process, the amount of lubricating oil applied to one heat transfer tube 30 can be reduced to less than 0.01 g per 1 m length of the heat transfer tube 30.

[0120] The above embodiments and variations are described, but it should be understood that various changes can be made to the form and specific matters without departing from the spirit and scope of the claims. In addition, the above embodiments, variations and other elements related to the embodiments can be appropriately combined or replaced.

[0121] - Industrial Applicability -

[0122] In summary, the present disclosure is useful for a method of manufacturing a heat exchanger.

[0123] - Explanation of symbols -

[0124] 10Heat exchanger

[0125] 20 fins

[0126] 21 through holes

[0127] 30 heat transfer tubes

[0128] 50 Tube expansion device

[0129] 53 drive unit

[0130] 60 expansion plug

[0131] 62 Head (plug body)

[0132] 64 Diamond film.

Claims

1. A method for manufacturing a heat exchanger (10), the heat exchanger (10) comprising plate-shaped fins (20) and circular tube-shaped heat transfer tubes (30), characterized in that: The manufacturing method of the heat exchanger (10) comprises a tube inserting step and a tube expanding step. In the pipe inserting step, the heat transfer pipe (30) is inserted into the through hole (21) formed in the fin (20). In the tube expansion step, in order to fix the fin (20) on the heat transfer tube (30), the outer diameter of the heat transfer tube (30) after the fin (20) is inserted in the tube insertion step is increased. In the tube expansion process, in order to increase the outer diameter of the heat transfer tube (30), a tube expansion plug (60) is pressed into the heat transfer tube (30), and the tube expansion plug (60) includes a plug body (62) made of superhard alloy and a diamond film (64) covering the surface of the plug body (62).

2. The method for manufacturing a heat exchanger according to claim 1, characterized in that: The heat transfer tube (30) is made of aluminum or aluminum alloy. The heat transfer tube (30) is an inner surface grooved tube having a plurality of grooves formed on the inner side surface.

3. The method for manufacturing a heat exchanger according to claim 1 or 2, characterized in that: The arithmetic mean roughness Ra of the surface of the diamond film (64) of the tube expansion plug (60) used in the tube expansion step is 0.023 μm or less.

4. The method for manufacturing a heat exchanger according to claim 1 or 2, characterized in that: The inner diameter of the heat transfer tube (30) before the tube expansion step is the inner diameter before tube expansion. The expansion plug (60) has a base end (60b) and a top end (60a), and includes a first portion (71), an expanded diameter portion (76) and a second portion (72). The first portion (71) is a portion located between the base end (60b) and the top end (60a) and having the largest outer diameter. The expanded diameter portion (76) is a portion extending from the top end (60a) to the first portion (71), and an outer diameter of the expanded diameter portion (76) gradually increases from the top end (60a) toward the first portion (71). The second portion (72) is a portion of the expanded diameter portion (76) having an outer diameter equal to the inner diameter before the expansion. The arithmetic mean roughness Ra of the surface of the diamond film (64) located at the second portion (72) is smaller than the arithmetic mean roughness Ra of the surface of the diamond film (64) located at the first portion (71).

5. The method for manufacturing a heat exchanger according to claim 4, characterized in that: The arithmetic mean roughness Ra of the surface of the diamond film (64) located at the first portion (71) is 0.023 μm or less.

6. The method for manufacturing a heat exchanger according to claim 4, characterized in that: The arithmetic mean roughness Ra of the surface of the diamond film (64) located at the second portion (72) is 0.013 μm or less.

7. The method for manufacturing a heat exchanger according to claim 4, characterized in that: The arithmetic mean roughness Ra of the surface of the diamond film (64) located at the first portion (71) is less than 0.023 μm, The arithmetic mean roughness Ra of the surface of the diamond film (64) located at the second portion (72) is 0.013 μm or less.

8. The method for manufacturing a heat exchanger according to any one of claims 1 to 7, characterized in that: The method for manufacturing a heat exchanger comprises a coating step, which is performed before the tube expansion step. In the coating step, lubricating oil is coated on the inner surface of the heat transfer tube (30). In the coating step, the amount of the lubricating oil coated on the inner surface of one of the heat transfer tubes (30) is less than 0.5 g per 1 m length of the heat transfer tube (30).

9. The method for manufacturing a heat exchanger according to any one of claims 1 to 7, characterized in that: The tube expansion step is performed in a state where the inner surface of the heat transfer tube (30) has not yet been coated with lubricating oil.

10. The method for manufacturing a heat exchanger according to any one of claims 1 to 9, characterized in that: In the tube expansion step, the outer diameter of the heat transfer tube (30) is increased to not less than 104% and not more than 112% of the outer diameter of the heat transfer tube (30) before the tube expansion step.

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