Heat exchanger and manufacturing method thereof

Abstract

To provide a heat exchanger for enabling the fixation of a heat transfer pipe to the side wall part of a case and the connection of a connection pipe body to the heat transfer pipe in an easy and appropriate manner, and to provide its manufacturing method.SOLUTION: A heat exchanger HE includes a plurality of heat transfer pipes 2 stored in a case 1 into which heating medium is supplied, connection pipe bodies 6 to which the plurality of heat transfer pipes 2 are connected, expanded pipe parts 20 provided in the respective heat transfer pipes 2 so that predetermined pressure contact parts 23 are formed in the respective heat transfer pipes 2, first peripheral walls 21 provided on the expanded pipe parts 20 so as to be located on the end tip 25 sides of the respective heat transfer pipes 2 further than the pressure contact parts 23, and second peripheral walls 62 located at ends 60 of the connection pipe bodies 6 and adapted to be fitted to the expanded pipe parts 20. The first and second peripheral walls 21, 62 having different cross-section shapes are fitted to each other in such a manner that parts in the peripheral directions of the first and second peripheral walls 21, 62 contact each other and other parts separate from each other.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The present invention relates to a heat exchanger used, for example, for hot water heating applications in a water heater, and a method for manufacturing the same.

Background Art

[0002] The applicant has previously proposed, as an example of a heat exchanger, the one described in Patent Document 1. The heat exchanger described in the same document is incorporated into a water heater or the like and used for hot water heating. A plurality of heat transfer tubes are accommodated in a case to which a heating medium is supplied. The ends of the plurality of heat transfer tubes penetrate through holes provided in the side wall portion of the case and are drawn out to the outside. Both ends of a substantially semi-circular connecting pipe body are fitted to this portion. As a result, the plurality of heat transfer tubes are connected in series via the connecting pipe body, and hot water can be appropriately circulated from one end side to the other end side thereof, and hot water heating is possible during the circulation process.

[0003] Further, as a fixing means for the heat transfer tube to the side wall portion of the case, an expanded portion is provided on the heat transfer tube, and this expanded portion is brazed to the side wall portion. The expanded portion has a configuration including, in addition to a pressure contact portion where the outer peripheral surface of the heat transfer tube is in pressure contact with the inner peripheral surface of the hole portion of the side wall portion, a flare processing portion that is wider at the tip end side of the end portion of the heat transfer tube than this pressure contact portion. Different from such a configuration, if only an expanding process for providing a pressure contact portion is performed on the heat transfer tube, the diameter of the tip end side of the end portion of the heat transfer tube may tend to decrease, and it may be difficult to connect the connecting pipe body. On the other hand, according to the above configuration, it becomes possible to easily fit the end portion of the connecting pipe body to the flare processing portion, and the above-mentioned problem can be solved.

[0004] However, in the above prior art, as described below, there is still room for improvement.

[0005] That is, when a flare processing portion that flares outwards is formed at the tip end side of the end portion of the heat transfer tube, although it becomes easier to insert the end portion of the connection tube body into this portion, at the location where the flare processing portion is formed, it is not possible to perform fitting in a state where the heat transfer tube and the connection tube body are in contact with each other. For this reason, simply inserting the end portion of the connection tube body into the end portion of the heat transfer tube makes it difficult to stably temporarily hold the connection tube body. As a result, when transporting the case of the heat exchanger in a state where the connection tube body is fitted to the heat transfer tube to the brazing work process position in the manufacturing process of the heat exchanger, there is a risk that the connection tube body may fall off from the heat transfer tube. In order to improve the efficiency and properness of the manufacturing work of the heat exchanger, it is desirable to appropriately eliminate the above-mentioned risk.

[0006] As a means for eliminating the above-mentioned risk, it is conceivable to eliminate the above-mentioned flare processing portion, but simply doing so makes it difficult to appropriately control the fitting state between the heat transfer tube and the connection tube body. If the fitting tolerance between the heat transfer tube and the connection tube body is not appropriate and the tightening allowance is large, it becomes difficult to fit and connect the connection tube body to the heat transfer tube. On the contrary, if the gap between the heat transfer tube and the connection tube body is large, it becomes difficult to stably temporarily hold the connection tube body on the heat transfer tube.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0008] The present invention has been conceived under the circumstances as described above, and an object thereof is to provide a heat exchanger capable of easily and appropriately fixing a heat transfer tube to a side wall portion of a case and connecting a connecting pipe body to the heat transfer tube, and a method for manufacturing the same.

Means for Solving the Problems

[0009] In order to solve the above problems, the present invention takes the following technical means.

[0010] The heat exchanger provided by the first aspect of the present invention includes a case into which a heating medium is supplied, a plurality of heat transfer tubes each of which is drawn out from inside the case so that each end portion thereof is inserted into a plurality of hole portions provided in a side wall portion of the case, at least one connecting pipe body for connecting these plurality of heat transfer tubes to each other, an expanding portion provided on each heat transfer tube so that a pressure contact portion where an outer peripheral surface of each heat transfer tube is in pressure contact with an inner peripheral surface of each hole portion is formed, a first peripheral wall portion provided on the expanding portion so as to be located on the end tip side of each heat transfer tube with respect to the pressure contact portion, and a second peripheral wall portion located at an end portion of the connecting pipe body and fitted to the expanding portion. The heat exchanger is characterized in that the first and second peripheral wall portions have different cross-sectional shapes, and a part in the circumferential direction of the first and second peripheral wall portions is in contact with each other, and another part is fitted in a state of being separated from each other. and the second peripheral wall portion has a hollow circular cross-section and is fitted inside the first peripheral wall portion. The inner peripheral surface of the first peripheral wall portion has a larger radius of curvature than the outer peripheral surface of the second peripheral wall portion, and a plurality of first curved surface portions are provided at intervals in the circumferential direction so as to be in contact with a part of the outer peripheral surface of the second peripheral wall portion. The outer peripheral surface of the second peripheral wall portion has a plurality of second curved surface portions provided so as to connect the plurality of first curved surface portions without contacting each other. It is characterized by this.

[0011] According to such a configuration, the following effects can be obtained. That is, since the first and second peripheral wall portions have different cross-sectional shapes and are fitted in a partially contacting state, even when the tightening allowance, which is their fitting tolerance, is relatively large, it is possible to fit them relatively easily. Therefore, it is possible to improve the assembly workability. Of course, if the first and second peripheral wall portions are in partial contact, an appropriate frictional force can be generated between them, and when the connecting pipe body is fitted to the heat transfer pipe, stable temporary holding of the connecting pipe body becomes possible. For this reason, for example, before performing the brazing work of the connecting pipe body to the heat transfer pipe, it is possible to eliminate the risk of the connecting pipe body falling off from the heat transfer pipe. According to the present invention, when an expanded portion is formed by subjecting the heat transfer pipe to an expansion process, the first peripheral wall portion may be formed so as to cause a certain degree of tightening allowance with respect to the second peripheral wall portion of the connecting pipe body, and it is possible to relax the dimensional accuracy of the first peripheral wall portion during the expansion process. Different from the present invention, for example, when the first and second peripheral wall portions are both hollow circular and have the same shape, it is necessary to finish their sizes quite precisely so that their fitting tolerance becomes an appropriate tolerance. However, according to the present invention, their sizes may be finished relatively roughly so that a certain degree of tightening allowance is generated between the first and second peripheral wall portions. Therefore, it is possible to further facilitate the manufacturing work and improve the productivity. Furthermore, according to such a configuration, if a round pipe with a hollow circular cross-section is used as the connecting pipe body, there is no need to perform special processing on the second peripheral wall portion of this connecting pipe body, and it can be directly fitted with the first peripheral wall portion of the heat transfer pipe. Therefore, the manufacturing becomes easy. On the other hand, since the plurality of first curved surface portions provided on the first peripheral wall portion of the heat transfer pipe are in contact with the outer peripheral surface of the second peripheral wall portion of the connecting pipe body at intervals in the circumferential direction, the mutual fitting state of the first and second peripheral wall portions can be made stable.

[0012] In the present invention, preferably, each of the heat transfer pipes and the connecting pipe body is configured using a round pipe, and each hole portion of the side wall portion is circular, and the pressure contact portion is a shape in which the outer peripheral surface of each heat transfer pipe is pressure contacted with the inner peripheral surface of each hole portion, whereas the first peripheral wall portion has a non-circular cross-sectional hollow shape with a cross-sectional shape different from that of the pressure contact portion.

[0013] According to such a configuration, the heat transfer pipe and the connecting pipe body are configured using round pipes, and the manufacturing cost can be reduced. Also, the configuration of the pressure contact portion and the first peripheral wall portion of the expanded portion can be made reasonable.

[0016] The method for manufacturing a heat exchanger provided by the second aspect of the present invention is such that, in a state where the ends of a plurality of heat transfer tubes are inserted into a plurality of holes provided in a side wall portion of a case into which a heating medium is supplied, an expanding process is performed on each of the heat transfer tubes to form an expanded portion including a pressure contact portion where the outer peripheral surface of each heat transfer tube is in pressure contact with the inner peripheral surface of each hole, and a first peripheral wall portion arranged on the tip side of the end of each heat transfer tube relative to this pressure contact portion; and after this expanding process, a tube body connection process of fitting an end portion of a connection tube body for connecting the plurality of heat transfer tubes to the first peripheral wall portion of each heat transfer tube. The method for manufacturing a heat exchanger is characterized in that, in the expanding process, the first peripheral wall portion is formed to have a cross-sectional shape different from that of a second peripheral wall portion constituting the end portion of the connection tube body, and in the tube body connection process, the first and second peripheral wall portions are fitted in such a manner that a part of these in the circumferential direction is in contact with each other and another part is spaced apart from each other.

[0017] According to such a configuration, the heat exchanger provided by the first aspect of the present invention can be manufactured easily and appropriately.

[0018] In the present invention, preferably, the expanding process is performed using a split punch that has an expandable and contractible portion that can be inserted into each heat transfer tube and can expand and contract in the radial direction, and a portion for expanding the pressure contact portion and the first peripheral wall portion is provided on the outer peripheral surface of this expandable and contractible portion.

[0019] According to such a configuration, by expanding the heat transfer tubes using a split punch having a predetermined configuration, the pressure contact portion and the first peripheral wall portion of the heat transfer tubes are formed simultaneously. Therefore, productivity can be further enhanced.

[0020] In the present invention, preferably, the expandable and deformable portion of the split punch is configured by combining a plurality of segments formed as separate members. Among the plurality of segments, the portion corresponding to the pressure contact portion has a plurality of first outer surface portions in the shape of a circular arc in cross section with the same radius of curvature and a uniform distance from the center of the expandable and deformable portion during pipe expansion. On the other hand, the portion corresponding to the first peripheral wall portion has a plurality of second outer surface portions in the shape of a circular arc in cross section with non-uniform radii of curvature and a non-uniform distance from the center of the expandable and deformable portion during pipe expansion.

[0021] According to such a configuration, by performing a pipe expansion operation using the split punch, the pressure contact portion of the heat transfer pipe can be appropriately formed into a predetermined configuration by the first outer surface portions of the plurality of segments of the split punch, and the first peripheral wall portion can be appropriately formed into a cross-sectional shape different from that of the pressure contact portion by the second outer surface portions of the plurality of segments.

[0022] Other features and advantages of the present invention will become more apparent from the following description of the embodiments of the invention with reference to the accompanying drawings.

Brief Description of the Drawings

[0023]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Mode for Carrying Out the Invention

[0024] Hereinafter, preferred embodiments of the present invention will be specifically described with reference to the drawings.

[0025] The heat exchanger HE shown in FIG. 1 is, for example, incorporated in a water heater and used to heat the hot water for supplying hot water. This heat exchanger HE has a basic configuration similar to that described in Patent Document 1, and includes a substantially rectangular frame-shaped case 1 with openings at the top and bottom, a plurality of barrel pipes 39 housed therein, a plurality of fins 9, a plurality of heat transfer tubes 2, and a plurality of connecting pipe bodies 6 that connect the heat transfer tubes 2 to each other.

[0026] The heat exchanger HE is used in a reverse combustion type water heater. A burner (not shown) is arranged at the upper part of the case 1, and combustion gas (an example of a heating medium) generated by this burner is supplied into the case 1. The hot water passing through the body pipe 39 and the plurality of heat transfer pipes 2 is heated using the combustion gas, and hot water is generated.

[0027] In addition to absorbing heat for heating hot water, the plurality of body pipes 39 serve to cool the plurality of side wall portions 10b to 10d of the case 1, and are provided along the inner surfaces of the plurality of side wall portions 10b to 10d. These plurality of body pipes 39 are connected via header portions 35a and 35b provided on the outer surface portion of the side wall portion 10a of the case 1. The hot water supplied to the water inlet 38 of the body pipe 39 passes through the body pipe 39 and the plurality of header portions 35a and 35b as shown by the arrow of the broken line in FIG. 1, then flows into the plurality of heat transfer pipes 2, and after passing through these, reaches the hot water outlet 37.

[0028] Both the plurality of heat transfer pipes 2 and the plurality of connecting pipe bodies 6 are configured using round pipes made of metal (for example, stainless steel). The plurality of heat transfer pipes 2 are of the fin tube type inserted and joined through the plurality of fins 9, are horizontally installed in the case 1, and are arranged side by side in the vertical and horizontal directions. Both ends of each heat transfer pipe 2 are inserted through hole portions 11 provided in the side wall portions 10a and 10c of the case 1 and drawn out to the outside of the case 1. As shown in FIGS. 2 and 3,

[0029] The plurality of connecting pipe bodies 6 are, for example, bend pipes having a substantially semi - arc shape in the overall side view, and both ends 60 thereof are fitted and connected to the ends of the plurality of heat transfer pipes 2. As a result, the plurality of heat transfer pipes 2 are connected in series via the plurality of connecting pipe bodies 6.

[0030] As shown in FIG. 4, each heat transfer pipe 2 is provided with an enlarged pipe portion 20 having a larger outer diameter and inner diameter than other portions of each heat transfer pipe 2. This enlarged pipe portion 20 includes a pressure contact portion 23, first and second bulging portions 20a and 20b, an auxiliary portion 22, and a first peripheral wall portion 21.

[0031] The end portion 60 of the connecting pipe body 6 is fitted into the expanded pipe portion 20, and this end portion 60 has a hollow circular cross-section. Among the end portion 60 of the connecting pipe body 6, the portion 62 that fits with the expanded pipe portion 20 so as to be located inside the expanded pipe portion 20 corresponds to an example of the "second peripheral wall portion" of the connecting pipe body in the present invention (hereinafter referred to as the second peripheral wall portion 62). Further, in the present embodiment, a bulging portion 63 is formed on the connecting pipe body 6, and this bulging portion 63 is set to abut against the end tip 25 of the heat transfer pipe 2.

[0032] The pressure contact portion 23 of the expanded pipe portion 20 is located within the hole portion 11 of the side wall portion 10a and is a portion that is in pressure contact with the inner peripheral surface of the hole portion 11. Due to the presence of this pressure contact portion 23, the side wall portion 10a and the heat transfer pipe 2 are fixed (temporarily fixed). The hole portion 11 is a circular hole portion (see also Fig. 5(a)), and the pressure contact portion 23 has a hollow circular cross-section.

[0033] The first and second bulging portions 20a, 20b of the expanded pipe portion 20 are respectively located inside and outside the side wall portion 10a so as to sandwich the side wall portion 10a of the case 1 in the axial length direction of the heat transfer pipe 2, and are annular bulging portions whose outer peripheral surfaces partially bulge outward in the radial direction of the heat transfer pipe 2. Preferably, the first and second bulging portions 20a, 20b are arranged in contact with the side wall portion 10a. Due to the presence of such first and second bulging portions 20a, 20b, the heat transfer pipe 2 is more reliably and firmly fixed to the side wall portion 10a. The region between the first and second bulging portions 20a, 20b is the above-described pressure contact portion 23.

[0034] The auxiliary portion 22 is a portion located between the second bulging portion 20b and the first peripheral wall portion 21. The second bulging portion 20b has a hollow circular cross-section similar to the pressure contact portion 23, while the first peripheral wall portion 21 has a non-circular hollow cross-section as will be described later. The auxiliary portion 22 is a portion that causes the change in the cross-sectional shape described above in the range from the second bulging portion 20b to the first peripheral wall portion 21.

[0035] The first peripheral wall portion 21 is a portion on the end tip 25 side of the heat transfer tube 2 rather than the second bulging portion 20b and the auxiliary portion 22, has a non-circular shape with a hollow cross-section, and has a different cross-sectional shape from the end portion 60 (including the second peripheral wall portion 62) of the connecting pipe body 6.

[0036] More specifically, as shown in FIG. 5(b), the first peripheral wall portion 21 has, as its inner peripheral surface, a plurality (for example, three) of first and second curved surface portions 21a, 21b. The first curved surface portion 21a is a curved surface portion having a curvature radius R1 larger than the curvature radius R0 of the outer peripheral surface of the second peripheral wall portion 62 of the connecting pipe body 6, and is a curved surface portion that partially contacts the outer peripheral surface of the second peripheral wall portion 62. The plurality of first curved surface portions 21a are provided at equal angular intervals in the circumferential direction of the first and second peripheral wall portions 21, 62. The second curved surface portion 21b is a curved surface portion provided so as to connect the plurality of first curved surface portions 21a so as not to contact the outer peripheral surface of the second peripheral wall portion 62. A gap C is formed between the second curved surface portion 21b and the second peripheral wall portion 62. The curvature radius R2 of the second curved surface portion 21b is, for example, in the relationship of R2 < R0 < R1.

[0037] The connecting pipe body 6 is fitted into the heat transfer tube 2 such that the tip of its end portion 60 is located inside the case 1 rather than the side wall portion 10a. This will bring about the same effect as if the end portion 60 of the connecting pipe body 6 is added as a reinforcing member to the joint portion between the heat transfer tube 2 and the side wall portion 10a, and the strength of the joint portion between the heat transfer tube 2 and the side wall portion 10a is increased. Furthermore, it is also effective in increasing the strength of the joint portion between the connecting pipe body 6 and the heat transfer tube 2.

[0038] In the present embodiment, as shown in FIG. 4(b), brazing portions Ba, Bb are provided. The brazing portion Ba is a portion for brazing the vicinity of the second bulging portion 20b and the side wall portion 10a. The brazing portion Bb is a portion for brazing the end tip 25 of the heat transfer tube 2 and the outer peripheral surface of the connecting pipe body 6, and also enters the above-described gap C.

[0039] Next, an example of the manufacturing method of the above-described heat exchanger HE will be described.

[0040] When manufacturing the heat exchanger HE, a split punch 5 as shown in FIGS. 6 and 7 is used. For ease of understanding, the split punch 5 will be described first.

[0041] The split punch 5 has a substantially cylindrical shape into which the mandrel 4 is inserted. However, the split punch 5 is formed by combining a plurality of segments 50a so as to bundle them, and by externally fitting a plurality of O-rings 55 having elasticity to these segments 50a, the plurality of segments 50a are constrained so as not to disassemble. The plurality of segments 50a correspond to a substantially cylindrical member cut along its axial length direction, for example, divided into six members. An inclined surface 56 is provided on the inner peripheral surface near the tip of the split punch 5. For this reason, as shown in FIG. 7, when the mandrel 4 is advanced to press the inclined surface 56, substantially the entire split punch 5 expands in the radial direction against the elastic force of the O-ring 55. When the mandrel 4 is retracted, the split punch 5 returns to the original non-expanded state shown in FIG. 6 due to the elastic force of the O-ring 55.

[0042] Since the split punch 5 of the present embodiment is configured by combining a plurality of separate segments 50a, the entire length region thereof is a stretchable and deformable portion 50. Preferably, the tip of the mandrel 4 has a tapered shape such as a pyramid shape or a cone shape. In the present embodiment, the tip of the mandrel 4 has a pyramid shape and is provided with a plurality of flat portions 40 that can be in surface contact with the inclined surfaces 56 of the plurality of segments 50a.

[0043] As clearly shown in the enlarged view of the main part of FIG. 6(a), a substantially annular first and second convex portions 51, 52, a first outer surface portion 53 located between these, an auxiliary portion forming portion 54, and a second outer surface portion 57 are provided on the outer peripheral surface near the tip of the split punch 5. Here, the first and second convex portions 51, 52 are portions for forming the first and second bulging portions 20a, 20b of the heat transfer tube 2.

[0044] The first outer surface portion 53 is a portion for forming the pressure contact portion 23 of the heat transfer tube 2. As shown in FIG. 6(c), the first outer surface portions 53 of the plurality of segments 50a are aligned with the same radius of curvature R3. As shown in FIG. 7(c), when the heat transfer tube 2 is expanded, it has a cross-sectional arc shape in which the distance Lc from the center of the expandable and deformable portion 50 is uniform everywhere.

[0045] The second outer surface portion 57 is a portion for forming the first peripheral wall portion 21 of the heat transfer tube 2. However, as described above, there are a plurality of first and second curved surface portions 21a and 21b on the inner peripheral surface of the first peripheral wall portion 21. Therefore, in order to cope with such a situation, as the plurality of segments 50a, as shown in FIG. 6(d), there are two types of segments 50a' and 50a", and two types of second outer surface portions 57 (57a, 57b) with different radii of curvature are formed on them. The second outer surface portion 57a of the segment 50a' is a curved surface with a cross-sectional arc shape corresponding to the first curved surface portion 21a shown in FIG. 5, and the second outer surface portion 57b of the segment 50a" is a curved surface with a cross-sectional arc shape corresponding to the second curved surface portion 21b. When the heat transfer tube 2 is expanded, as shown in FIG. 7(d), the distances La and Lb from the center of the expandable and deformable portion 50 to the second outer surface portions 57a and 57b are made non-identical.

[0046] The auxiliary portion forming portion 54 is a portion for forming the above-described auxiliary portion 22 of the heat transfer tube 2. The two types of segments 50a' and 50a" differ in the shape and size of the second outer surface portion 57 and the auxiliary portion forming portion 54, but the shape and size of the other portions are the same.

[0047] When manufacturing the heat exchanger HE, the split punch 5 described above is used, and the heat transfer tube 2 is expanded by the procedure shown in FIGS. 8(a) to (c).

[0048] That is, first, as shown in FIG. 8(a), with the end of the heat transfer tube 2 inserted through the hole 11 in the side wall portion 10a of Case 1, as shown in FIG. 8(b), the split punch 5 is inserted into the end of the heat transfer tube 2. Next, as shown in FIG. 8(c), the split punch 5 is expanded to expand the end of the heat transfer tube 2. By this, the expanded portion 20 described with reference to FIGS. 4 and 5 can be provided on the heat transfer tube 2, and the heat transfer tube 2 can also be fixed (temporarily fixed) to the side wall portion 10a. After that, the split punch 5 is returned to its original size and then pulled out from the heat transfer tube 2, and the end portion 60 of the connection pipe body 6 is fitted into the end of the heat transfer tube 2. Such operations are performed for each of the plurality of heat transfer tubes 2. However, by using a plurality of split punches 5, it is also possible to perform the above-described operations on the plurality of heat transfer tubes 2 simultaneously. After finishing the above-described steps, a brazing operation for providing the brazed portions Ba and Bb described above is performed.

[0049] According to the heat exchanger HE of the present embodiment, as shown in FIG. 5(b), the first peripheral wall portion 21 of the heat transfer tube 2 and the second peripheral wall portion 62 of the connection pipe body 6 have different cross-sectional shapes, and a plurality of first curved surface portions 21a of the first peripheral wall portion 21 are fitted in a state of partial contact with the outer peripheral surface of the second peripheral wall portion 62. Therefore, even when the tightening allowance, which is the fitting tolerance between the first and second peripheral wall portions 21 and 62, is relatively large, it is possible to fit them relatively easily (smoothly). Therefore, the assembly workability can be improved.

[0050] Further, since the first and second peripheral wall portions 21 and 62 are in partial contact, in addition to an appropriate frictional force being generated between them, they are in a three-point contact state with three contact portions P shown in FIG. 5(b) at equal intervals. Therefore, when the connection pipe body 6 is fitted to the heat transfer tube 2, it is possible to stably temporarily hold the connection pipe body 6, and for example, before performing the brazing operation of the connection pipe body 6 to the heat transfer tube 2, it is also possible to eliminate the risk of the connection pipe body 6 accidentally falling off from the heat transfer tube 2.

[0051] In the present embodiment, when the heat transfer tube 2 is subjected to an expanding process to form the expanded portion 20, the first peripheral wall portion 21 may be formed so as to produce a certain amount of interference with respect to the second peripheral wall portion 62 of the connecting pipe body 6. Different from the present embodiment, when the first and second peripheral wall portions 21 and 62 are both hollow circular in cross section and have the same cross-sectional shape, if the interference is large, it becomes difficult to fit them, and in order to avoid this, it is necessary to precisely finish their fitting tolerances within a predetermined dimensional range with a narrow range. On the other hand, according to the present embodiment, such a necessity can be eliminated or alleviated, and as the fitting tolerances of the first and second peripheral wall portions 21 and 62, their sizes may be finished relatively roughly so that a certain amount of interference is produced. Therefore, it is possible to further facilitate the manufacturing operation and improve productivity. When the heat transfer tube 2 and the connecting pipe body 6 are made of stainless steel and it is difficult to improve the dimensional accuracy of each part compared with, for example, those made of copper, the above-described effect of the present embodiment becomes more preferable.

[0052] The pressure contact portion 23 of the expanded portion 20 is in pressure contact with the inner peripheral surface of the hole portion 11 provided in the side wall portion 10a of the case 1, and in addition, the first and second bulging portions 20a and 20b sandwich both sides of the side wall portion 10a. For this reason, the heat transfer tube 2 can be appropriately fixed (temporarily fixed) to the side wall portion 10a, the fitting accuracy between the hole portion 11 and the heat transfer tube 2 can be made good, and the brazed portion Ba can be made appropriate.

[0053] Further, since the end tip 25 of the heat transfer tube 2 and the vicinity thereof are the portions processed by the expanding process as the above-described first peripheral wall portion 21, it is also possible to improve the dimensional accuracy of this portion by this. That is, when the first and second bulging portions 20a and 20b are formed in the vicinity of the end tip 25 of the heat transfer tube 2, as a reaction, there is a possibility that the diameters of the end tip 25 and the vicinity thereof may be reduced, but according to the present embodiment, it is also possible to appropriately eliminate such a possibility.

[0054] On the one hand, according to the method for manufacturing the heat exchanger HE described above, each part of the expanded tube portion 20 can be appropriately provided by a single tube expansion operation using the split punch 5. Therefore, it is preferable for enhancing the productivity of the heat exchanger HE.

[0055] FIGS. 9 to Figure 11 show other embodiments of the present invention (Figure 12 is not included in the examples of the present invention) . In these figures, elements that are the same as or similar to those in the above embodiment are denoted by the same reference numerals as in the above embodiment, and redundant descriptions are omitted.

[0056] In the embodiment shown in FIG. 9(a), two second curved surface portions 21b are provided on the inner peripheral surface of the first peripheral wall portion 21 of the heat transfer tube 2, and two gaps C are formed, and the other part of the inner peripheral surface is the first curved surface portion 21a. Such a configuration can be formed by dividing the six segments 50a of the split punch 5A into two segments 50a'' having outer surface portions corresponding to the second curved surface portion 21b and the other four segments 50a' having outer surface portions corresponding to the first curved surface portion 21a, as shown in FIG. 9(b). Note that a mandrel 4 having a circular cross-section is used (the same applies to the embodiments in FIGS. 10 to 12). In the present embodiment, although the first and second peripheral wall portions 21 and 62 are only in contact with each other at two contact portions P, the contact portions P are arranged so as to face each other with the centers of the first and second peripheral wall portions 21 and 62 interposed therebetween, so that it is preferable for stabilizing the fitting state between the first and second peripheral wall portions 21 and 62.

[0057] Also in the embodiment shown in FIG. 10(a), as in FIG. 9(a), two second curved surface portions 21b are provided on the inner peripheral surface of the first peripheral wall portion 21 of the heat transfer tube 2, two gaps C are formed, and the other part of the inner peripheral surface is the first curved surface portion 21a. However, as the split punch 5B for obtaining such a configuration, as shown in Fig. (b) thereof, one having a plurality of segments 50c in a four-divided state is used. Among those plurality of segments 50c, two segments 50c' have outer surface portions corresponding to the first curved surface portion 21a, and the other two segments 50c" have outer surface portions corresponding to the second curved surface portion 21b. Also in the present embodiment, similar to the embodiment of Fig. 9(a), since the first and second peripheral wall portions 21, 62 are arranged such that the two contact portions P face each other with their central portions interposed therebetween, it is possible to ensure a stable fitting state.

[0058] In the embodiment shown in Fig. 11(a), only one second curved surface portion 21b is provided on the inner peripheral surface of the first peripheral wall portion 21 of the heat transfer tube 2, and the other portions of the inner peripheral surface are the first curved surface portion 21a. Such a configuration, as shown in Fig. (b) thereof, can be obtained by using four segments 50c as the split punch 5C, and among these, one segment 50c" has an outer surface portion corresponding to the second curved surface portion 21b, and the other segments 50c' have outer surface portions corresponding to the first curved surface portion 21a. According to the present embodiment, although the first and second peripheral wall portions 21, 62 are not configured to be in point contact at a plurality of locations, the first curved surface portion 21a is in surface contact with the outer peripheral surface of the second peripheral wall portion 62 over a range of at least half of the entire circumference. Therefore, it is preferable for stabilizing the fitting state between the first and second peripheral wall portions 21, 62.

[0059] In the embodiment shown in Fig. 12, the end portion 60 of the connecting pipe body 6 is externally fitted to the expanded portion 20 of the heat transfer tube 2. According to the configuration of the present embodiment, although there is a disadvantage that the end portion 60 of the connecting pipe body 6 cannot enter the inner side of the case 1 more than the side wall portion 10a of the case 1, it is also possible to adopt such a configuration. In the case of the present embodiment, as shown in Fig. (b) thereof, a part of the outer peripheral surface of the first peripheral wall portion 21 of the heat transfer tube 2 is in partial contact with the inner peripheral surface of the second peripheral wall portion 62 of the connecting pipe body 6.

[0060] The present invention is not limited to the content of the above-described embodiments. The specific configuration of each part of the heat exchanger according to the present invention can be freely designed and changed in various ways within the scope intended by the present invention. The specific configuration of each step of the manufacturing method of the heat exchanger according to the present invention can be changed within the scope intended by the present invention.

[0061] In the above-described embodiment, the tube expanding operation is performed using a split punch having six or four segments, but the number of segments is not limited to those. Also, the plurality of segments can be configured such that their sizes are uniformly aligned at equal angular intervals, but alternatively, a configuration can be adopted in which the sizes of the plurality of segments are non-uniform. In the present invention, it is also possible to adopt a configuration in which a pre-expanded flare processing portion is further formed at the most distal position of the expanded portion of the heat transfer tube (a position further on the end tip side than the first peripheral wall portion).

[0062] The heat transfer tube is not limited to being entirely straight tubular, and can also be meandering or spiral, etc. The body pipe 39 of the above-described embodiment can also be included in the heat transfer tube referred to in the present invention. It is not necessary for all of the plurality of heat transfer tubes provided in the heat exchanger to be configured as intended by the present invention. If the mounting structure of some of the heat transfer tubes is configured as intended by the present invention, it will fall within the technical scope of the present invention.

[0063] The heat exchanger according to the present invention is not limited to the reverse combustion type, and can be, for example, a forward combustion type, or can also be configured without a body pipe. Also, the heat exchanger is not limited to being for a water heater. The heating medium is not limited to combustion gas, and can be, for example, the high-temperature exhaust gas of a cogeneration system.

Explanation of Reference Numerals

[0064] HE Heat exchanger 1 Case 10a Side wall portion 11 Hole portion 2 Heat transfer tube 20 Expanded tube portion 21 First peripheral wall portion 21a First curved surface portion 21b Second curved surface portion 23 Crimping portion (of the expanded tube portion) 25 End tip (of the heat transfer tube) 5, 5A to 5C Split punch 50 Expandable and contractible portion 50a (50a’, 50a”), 50c (50c’, 50c”) Segments 53 First outer surface portion 57 (57a, 57b) Second outer surface portion 6 Connecting pipe body 60 End (of the connecting pipe body) 62 Second peripheral wall portion

Claims

1. A case into which a heating medium is supplied; a plurality of heat transfer tubes extending from inside the case to the outside with their ends inserted into a plurality of holes formed in a side wall of the case; At least one connecting pipe body for connecting the plurality of heat transfer tubes to each other; an expansion portion provided on each of the heat transfer tubes such that a pressure-welded portion is formed in which an outer circumferential surface of each of the heat transfer tubes is pressure-welded to an inner circumferential surface of each of the holes; a first peripheral wall portion provided in the expansion portion so as to be located closer to the tip end of each of the heat transfer tubes than the pressure welding portion; a second peripheral wall portion located at an end of the connecting pipe body and fitted into the expanded pipe portion; A heat exchanger comprising: the first and second peripheral wall portions have different cross-sectional shapes, and circumferential portions of the first and second peripheral wall portions are in contact with each other and are fitted together in a manner such that the first and second peripheral wall portions are spaced apart from each other; the second peripheral wall portion has a hollow circular cross section and is fitted into the first peripheral wall portion, a first curved surface portion having a radius of curvature larger than that of an outer circumferential surface of the second peripheral wall portion, the first curved surface portion having a radius of curvature larger than that of an outer circumferential surface of the second peripheral wall portion, the first curved surface portion having a radius of curvature larger than that of an outer circumferential surface of the second peripheral wall portion, and a second curved surface portion having a radius of curvature larger than that of an outer circumferential surface of the second peripheral wall portion.

2. 2. The heat exchanger of claim 1, each of the heat transfer tubes and the connecting tube body is formed using a round pipe, and each of the holes in the side wall portion is circular; a pressure-welding portion having a shape in which the outer peripheral surface of each of the heat transfer tubes is pressure-welded to the inner peripheral surface of each of the holes, while the first peripheral wall portion has a hollow non-circular cross-sectional shape different from that of the pressure-welding portion.

3. An expansion process in which, with the ends of a plurality of heat transfer tubes inserted into a plurality of holes provided in a side wall of a case into which a heating medium is supplied, each of the heat transfer tubes is expanded to form an expanded portion including a pressure-welded portion in which the outer circumferential surface of each of the heat transfer tubes is pressed against the inner circumferential surface of each of the holes, and a first peripheral wall portion positioned closer to the tip of the end of each of the heat transfer tubes than the pressure-welded portion; a tube connecting step of fitting an end of a connecting tube for connecting the plurality of heat transfer tubes to each other into the first peripheral wall portion of each of the heat transfer tubes after the tube expanding step; A method for manufacturing a heat exchanger, comprising: In the tube expanding step, the first peripheral wall portion is formed to have a cross-sectional shape different from that of a second peripheral wall portion constituting the end portion of the connecting pipe body, a heat exchanger manufacturing method, characterized in that in the tube connecting process, the first and second peripheral wall portions are fitted together such that portions of the first and second peripheral wall portions are in contact with each other and other portions are spaced apart from each other.

4. A method for manufacturing a heat exchanger according to claim 3, comprising the steps of: A method for manufacturing a heat exchanger, in which the tube expansion process is performed using a split punch having an expandable / contractable portion that can be inserted into each heat transfer tube and can expand and contract in the radial direction, and the outer surface of this expandable / contractable portion is provided with a portion for expanding the pressure welding portion and the first peripheral wall portion.

5. A method for manufacturing a heat exchanger according to claim 4, comprising the steps of: The expandable / contractable deformable portion of the split punch is configured by combining a plurality of segments formed as separate members, A method for manufacturing a heat exchanger, wherein among the multiple segments, the portions corresponding to the pressure-welded portions have multiple first outer surface portions which have the same radius of curvature and are uniformly spaced from the center of the expandable / contractable portion when expanded, while the portions corresponding to the first peripheral wall portion have multiple second outer surface portions which do not have the same radius of curvature and are non-uniformly spaced from the center of the expandable / contractable portion when expanded.

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