METHOD AND APPARATUS FOR MANUFACTURING FIN-INTEGRATED TUBE FOR USE IN HEAT EXCHANGER

Abstract

The method of manufacturing a fin-integrated tube for a heat exchanger includes step of disposing a rolling roller group including rolling rollers so as to surround the periphery of a tube, each of the roller crests of the rolling rollers being rounded at an end thereof into an R-shape, widths of the R-shaped ends being gradually increased from one axial end to the other axial end for each of the rolling rollers, and step of causing the roller crests to press the periphery of the tube from the one axial end to the other axial end by axially moving and rotating the rolling roller group relative to the tube so as to deform a part of the periphery of the tube into a spirally projecting portion while shaping it into a spiral fin by gradually squeezing the part of the periphery of the tube using the R-shaped end portions.

Description

This application claims priority to Japanese Patent Application No. 2013-18326 filed on Feb. 1, 2013, the entire contents of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method and an apparatus for manufacturing a high temperature-resistant fin-integrated tube for use in a heat-exchanger mountable on a vehicle.

2. Description of Related Art

There are known various heat exchangers which can be used in a cooling system, a driving system and an air-conditioning system of a vehicle. FIG. 19 shows a common fin-integrated tube for use in a heat exchanger. This fin-integrated tube includes a tube 200 through which heat-exchanging medium flows and a plurality of hat-shaped rings 201 brazed to the tube 200 such that the tube 200 passes through a stack of the hat-shaped rings 201 as fins 202.

It is known to form a plurality of fins integrally with a tube serving as a radiator to provide a compact and highly-efficient heat exchanger. For example, refer to Japanese Patent Application Laid-open No. 2001-332666. This patent document describes carving the outer or inner wall of a tube to form a plurality of fins which are integrally connected to the tube at their thick proximal end portions. The plurality of the fins are formed using a carving knife such that they become thinner from their proximal end portions to their distal end portions to increase their surface area to thereby increase the heat dissipation effect.

As a heat exchanger mountable on a vehicle, the exhaust heat recovery device is receiving attention. The exhaust heat recovery device recovers exhaust heat emitted from an engine. The exhaust heat recovery device includes a fin-integrated tube which contains pure water and is mounted in the exhaust passage of the engine for recovering the exhaust heat. Since this fin-integrated tube is exposed to exhaust gas, it is made of heat-resistant and corrosion-resistant stainless steel and their fins are joined to the tube using a nickel-based brazing material, for example.

However, it turned out that the fins of such a fin-integrated tube may be deformed due to a linear expansion difference in the dissimilar metal joint by the brazing material in a case of a high-efficiency engine that emits high-temperature exhaust gas (900° C., for example). Further, if the number of the fins is increased to increase the heat exchange efficiency, manufacturing time and cost increase greatly because the fins have to be joined one by one to the tube.

The inventors of the present invention studied a possibility of adoption of a fin-integrated tube which does not include any brazing material, and can be manufactured by the method described in the above patent document. However, the method of carving the tube surface to form fins as described in the above patent document, which is suitable for the case where the tube is made of metal easy to carve such as aluminum, is difficult to use in the case where the tube is made of stainless steel. Further, the wall thickness and the rigidity of the tube have to be sufficiently large, while on the other hand, the shapes of the fins formed by carving the outer or inner surface of the tube along its axis and the wall thickness after the carving of the tube are likely to be non-uniform. Hence, it is difficult to reduce individual difference in the radiation performance. As explained above, it has been difficult so far to achieve both reducing the manufacturing cost and increasing the heat exchange efficiency.

SUMMARY

An exemplary embodiment provides a method of manufacturing a fin-integrated tube for a heat exchanger, the fin-integrated tube including a cylindrical tube and a spiral fin integrally formed in a periphery of the tube, including the steps of:

disposing a rolling roller group including a plurality of rolling rollers each having a plurality of roller crests on a periphery thereof so as to surround the periphery of the tube with a predetermined lead angle, each of the roller crests being rounded at an end thereof into an R-shape to be an R-shaped end, widths of the R-shaped ends of the roller crests being gradually increased from one axial end to the other axial end for each of the rolling rollers, so that each of the rolling rollers serves as a gradual roller; and

causing the roller crests of the rolling rollers to press the periphery of the tube from the one axial end to the other axial end by axially moving and rotating the rolling roller group relative to the tube so as to deform a part of the periphery of the tube into a spirally projecting portion while shaping the spirally projecting portion into the spiral fin by gradually squeezing the part of the periphery of the tube using the R-shaped end portions of the roller crests of the rolling rollers.

The exemplary embodiment provides also a manufacturing apparatus for manufacturing a fin-integrated tube for a heat exchanger, the fin-integrated tube including a cylindrical tube and a spiral fin integrally formed in a periphery of the tube, including:

a tube holding part for holding a proximal end portion of the tube so as to be rotatable together with the tube; and

a rolling roller head disposed coaxially with the tube so as to be axially movable relative to the tube;

the rolling roller head having a rolling roller group including a plurality of rolling rollers each having a plurality of roller crests on a periphery thereof, said rolling roller group being configured to surround the periphery of the tube with a predetermined lead angle,

each of the roller crests being rounded at an end thereof into an R-shape to be an R-shaped end, widths of the R-shaped ends of the roller crests being gradually increased from one axial end to the other axial end for each of the rolling rollers, so that each of the rolling rollers serves as a gradual roller,

wherein

the rolling roller head is configured to be driven to axially move in a direction from a distal end to a proximal end of the tube and rotate relative to the tube so as to cause the roller crests of the rolling rollers to press the periphery of the tube in the direction from the distal end to the proximal end so as to deform a part of the periphery of the tube into a spirally projecting portion while shaping the spirally projecting portion into the spiral fin by gradually squeezing the part of the periphery of the tube using the R-shaped end portions of the roller crests of the rolling rollers.

According to the exemplary embodiment, there is provided a high-performance and low-cost heat exchanger for vehicle use, which includes fin-integrate tubes manufactured without use of brazing material.

Other advantages and features of the invention will become apparent from the following description including the drawings and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 is a general view of a manufacturing apparatus for manufacturing a fin-integrated tube according to a first embodiment of the invention;

FIG. 2 is a partially enlarged view of the fin-integrated tube manufactured by a method performed using the manufacturing apparatus according to the first embodiment of the invention;

FIG. 3 is a partially enlarged view of a form rolling part of the manufacturing apparatus according to the first embodiment of the invention;

FIG. 4 is plan and side views of a form rolling roller head constituting the rolling part;

FIG. 5 is a partially enlarged view of an exhaust heat recovery device including the fin-integrated tubes manufactured by the method performed using the manufacturing apparatus according to the first embodiment of the invention;

FIG. 6 is a cross-sectional view of the exhaust heat recovery device;

FIG. 7 is a perspective view of the exhaust heat recovery device;

FIG. 8 is a schematic diagram for explaining a rolling process performed using the rolling roller head of the rolling part of the manufacturing apparatus according to the first embodiment of the invention;

FIG. 9 is a diagram showing an example of the shapes of the roller crests of rolling rollers of the rolling roller head;

FIGS. 10 and 11 are schematic diagrams for explaining a fin shaping process performed using the rolling rollers;

FIG. 12 is a schematic diagram for explaining variation of effect of the rolling rollers depending on variation of the angles of the roller crests of the rolling rollers;

FIG. 13 is a schematic diagram for explaining variation of the effect of the rolling rollers depending on variation of the R-shaped end portions of the roller crests of the rolling rollers;

FIG. 14 is a schematic diagram for explaining a tube extension at the time of the rolling process;

FIG. 15 is a cross-sectional view for explaining effects of a extension absorbing mechanism of the rolling roller head;

FIG. 16 is a side view showing an example of the shapes of the roller crests of rolling rollers of a manufacturing apparatus according to a second embodiment of the invention;

FIG. 17 is a schematic diagram for explaining a tube forming process performed using the rolling rollers of the manufacturing apparatus according to the second embodiment of the invention;

FIG. 18 is a schematic diagram for explaining a method of manufacturing a fin-integrated tube performed using a cored bar as a third embodiment of the invention; and

FIG. 19 is a perspective view of a conventional fin-integrated tube.

PREFERRED EMBODIMENTS OF THE INVENTION

First Embodiment

FIG. 1 is a general view of a manufacturing apparatus according to a first embodiment of the invention, which manufactures a fin-integrated tube 2 shown in FIG. 2. The fin-integrated tube 2 is used for various vehicle-mounted heat exchangers. The fin-integrated tube 2 is made from a cylindrical tube material 2′. The tube material 2′ is plastic-deformed by a rolling roller head 4 of a form rolling part 6 to form the fin-integrated tube 2 including a tube 21 and a fin 22 wound spirally on the outer periphery of the tube 21 at a predetermined pitch. FIG. 3 is a partially enlarged view of the form rolling part 6 which is a main part of the manufacturing apparatus. FIG. 4 is plan and side views of the rolling roller head 4 of the form rolling part 6.

FIG. 5 is a partially enlarged view of an exhaust heat recovery device including the fin-integrated tubes 2. FIG. 6 is a cross-sectional view of the exhaust heat recovery device. FIG. 7 is a perspective view of the exhaust heat recovery device. The heat recovery device is for recovering exhaust heat emitted from an engine, and exchanging heat with engine cooling water. The exhaust heat recovery device is used for warming the engine to increase fuel economy. As shown in FIGS. 6 and 7, the exhaust heat recovery device includes a heating section (heat exchanging section) 1 housing a plurality of the fin-integrated tubes 2, a heat guard 100 above which a tank is disposed, and a condensing section 101 having a LCC pipe P through which the engine cooling water (LLC) flows. The heating section 1 is mounted inside a duct D provided midway of the exhaust passage of the engine. The condensing section 101 is disposed in the upper space of the tank. The heating section 1 and the condensing section 101 are loop-connected to each other through a steam passage 102 and a valve 103 to constitute a loop heat pipe (heat loop) enclosing working medium. The loop heat pipe operates to transfer heat by evaporation and condensation of the working medium. In this embodiment, pure water is used as the working medium.

The heating section 1 includes a plurality of the fin-integrated tubes 2 which are arranged in rows along the flow direction of the exhaust gas and in rows along the direction perpendicular to the flow direction of the exhaust gas within the duct D. Each of the fin-integrated tubes 2 includes the tube 21 extending in the direction perpendicular to the flow direction of the exhaust gas and the spiral fin 22 projecting radially outward from the periphery of the tube 21. The bottom end of the tube 21 is closed, and the top end of the tube 21 penetrates through a core plate 3 forming the bottom plate of the tank and opens to the lower space in the tank. The inside of the tank is partitioned into the upper space and the lower space by a tank inner 4. The tank inner 4 is formed with the steam passage 102 projecting upward. The lower space to which the fin-integrated tubes 2 open and the upper space in which the condensing section 101 is disposed are in communication through the steam passage 102.

The steam introduced from the steam passage 102 into the condensing section 101 exchanges heat with the engine cooling water by contacting with the LLC pipe, and becomes condensed water. The condensed water is refluxed back to the heating section 1 by opening or closing the valve 103 depending on the pressure inside the tank. A partition 105 having an oxygen introducing hole 104 is provided in the lateral direction of the steam passage 102 for removing oxygen generated by contact between high-temperature steam and metal, for example. A copper oxide containing case 106 containing granular copper oxide 107 is provided below the space partitioned by the partition 105. The generated hydrogen is guided from the hydrogen introducing hole 104 to the copper oxide containing case 106, and reduced to be removed.

As shown in FIG. 5, the fin 22 is integrally connected to the tube 21 at its proximal end portion, and exchanges heat with the exhaust gas contacting the fin surface at its thin distal end portion which is spirally joined to the tube 21 in layers at a predetermined fin pitch (Fp) in the axial direction of the tube 21. The fin-integrated tube 2 is exposed to high-temperature exhaust gas in the duct D. Accordingly, the fin-integrated tube 2 is made of a heat-resistant and oxidation-resistant metal such as stainless steel. As described in the foregoing, conventional fin-integrated tubes manufactured by brazing have a concern that their fins may be deformed in a usage environment where the temperature of exhaust gas is high (100 to 900° C., for example) causing the heat exchange efficiency to be lowered.

Hence, in this embodiment, the tube material 2′ undergoes a specific rolling process in order to form the continuous spiral fin 22 integral with the periphery of the tube 21. The tube material 2′ before the rolling process is approximately 10 mm in outer diameter, approximately 7 mm in inner diameter, and approximately 1.5 mm in wall thickness. The fin height (Fh) and the fin thickness (Ft) are determined so as to achieve a target heat exchange performance and a target exhaust flow performance (exhaust flow pressure loss). The wall thickness of a part of the peripheral portion of the tube material 2′, which is used as a fin forming portion, is set smaller than the thickness (t) of the tube 21 (or smaller than a half of the wall thickness of the tube material 2′), for example, approximately 0.7 mm, to provide a thin and high fin shape. For example, when the fin pitch is 1.5 mm, the fin forming portion is plastic-deformed in the radial direction such that the fin height is between 1.8 mm and 2.6 mm to achieve the target performances.

Generally, a common rolling process is for plastic-deforming a row material to the shape analogous to the shape of the outer surface of a rolling roller by pressing the rolling roller to the periphery of the row material. Accordingly, common rolling rollers are not suitable for shaping the thin-wall tube material 2′ to have a thin-wall fin by deforming the tube material 2′ to expand radially outward. Hence, a newly developed rolling roller head 4 specialized for use in fin forming is used in this embodiment. A manufacturing apparatus including the rolling roller head 4, and a method of manufacturing the fin-integrated tube using this manufacturing apparatus are explained in the following.

As shown in FIG. 1, the manufacturing apparatus for manufacturing the fin-integrated tube 2 has a processing bench 7 on which a tube holding part 3 for holding and fixing the tube material 2′ to be processed and the for rolling part 6 including a rolling roller head 4 of three-roller type and a rolling head holder 5 are mounted so as to be opposed to each other. The tube holding part 3 includes a holding chuck 31 for holding the proximal end portion (the left end portion in FIG. 3) of the material tube 2′. The holding chuck 31 is mounted to a rotating shaft 32 coupled to a driving part 72. The tube material 2′ can be rotated by rotating the rotating shaft 32. The form rolling part 6 is axially movable on the processing bench 7 by a conveying shaft 61 mounted on a supporting table 62 supporting the rolling head holder 5 to which the roller head 4 is mounted. The driving part 71 drives the conveying shaft 61 in synchronism with the rotating shaft 32 to move the rolling roller head 4 toward the end portion (the right end portion in FIG. 1) of the tube material 2′ disposed coaxially with the rolling roller head 4 at a predetermined speed.

As shown in FIG. 3, the rolling roller head 4 includes a flange portion 44 to which the roller group (the rollers 41, 42 and 43) is mounted and a cylindrical proximal end portion 45. The cylindrical proximal end portion 45 of the rolling roller head 4 is inserted and fixed to a movable sleeve 52 having a container-like shape. The movable sleeve 52 is axially and slidably supported in a slide hole 51 formed so as to open to one end (the left side end in FIG. 3) of the head holder 5. The rolling head holder 5 includes an axially elongated hole 55 penetrating through the lateral wall of the slide hole 51. The movable sleeve 52 includes locking pins 54 formed in the periphery thereof so as to project from the elongated hole 55 to restrict the movable sleeve 52 from moving in the rotating direction. Between the bottom of the movable sleeve 52 and the other end (the right side end in FIG. 3) of the rolling head holder 5, a coil-shaped compression spring 56 is disposed as a biasing member to bias the movable sleeve 52 toward the rolling roller head 4.

The movable sleeve 52 and the spring 56 constitute an extension absorbing mechanism for absorbing extension of the tube material 2′ being form-rolled. The movable sleeve 52 can move to a distance adaptable to extension of the tube material 2′. The spring 56 is disposed in the rear of the movable sleeve 52 (opposite the rolling roller head 4) and always biased forward (toward the tube forming direction) at an appropriate load. The biasing force applied to the movable sleeve 52 can be determined through pretest to such a value that generates a pressing force enabling the roller crests of the rolling rollers 41, 42 and 43 to bite the periphery of the tube material 2′ at the beginning of a forming process and to retract to absorb extension of the tube material 2′. An adjustment screw 57 is mounted to the opening formed in the other end (the right side end in FIG. 3) of the rolling head holder 5. By screwing in the adjustment screw 57 in the axial direction, the compression amount of the spring 56 to which the adjustment screw 57 abuts can be adjusted.

As shown in FIG. 4, the rolling roller head 4 includes, as a rolling roller group surrounding the periphery of the tube material 2′ in three directions, the three rolling rollers 41, 42 and 43 disposed in a concentric pattern at even intervals. Each of the rolling rollers 41, 42 and 43 includes a plurality of the roller crests 44 at its periphery to form a desired fin shape. The rolling rollers 41, 42 and 43 are rotatably supported by the rolling roller head 4 such that they are inclined by a predetermined lead angle (three degrees in this embodiment) to the center axis of the tube material 2′.

As shown in FIG. 8, the roller crests 44 are formed of concavo-convex portions arranged in the axial direction at even pitch. The three rolling rollers 41, 42 and 43 are displaced by a predetermined pitch from one another in the axial direction. Accordingly, by sending the rolling roller head 4 in synchronism with rotation of the tube material 2′ (one pitch per one rotation), the tube material 2′ is pushed in between the rolling rollers 41, 42 and 43, and the rolling rollers 41, 42 and 43 move relative to the tube material 2′ in the axial direction while being driven to rotate. As a result, the roller crests 44 of the rolling rollers 41, 42 and 43 move past the periphery of the tube material 2′ in succession while pressing the periphery to form the fin 22 projecting spirally.

It is not easy to form such a fin shape which is thin and has a large heat transfer area. Hence, this embodiment uses the three rolling rollers 41, 42 and 43 as a gradual roller whose roller crests 44 change in shape stepwise along the axial direction. More specifically, as shown in FIG. 9, the end portions of the roller crests 44 of each of the rolling rollers 41, 42 and 43 are rounded so as to be R-shaped portions having a circular arch shape (referred to as the “R-shaped end portions” hereinafter), the sizes (widths) of the R-shaped end portions becoming gradually larger from one axial end to the other axial end. The roller crest 44 at the one axial end has a roughly triangular-cross section as a whole and is formed to a shape of sufficiently small “R” at its end, so that it can bite the tube material 2′ easily. The arc diameters of the R-shaped end portions are gradually increased along the axial direction, and accordingly, the roller crests 44 near the other axial end (near the rolling head holder 5) have an inverted U-shaped cross-section as a whole.

The tube material 2′ is not deformed easily because the rolling roller head 4 applies load in three directions. In addition, since the three rolling rollers 41, 42 and 43 serve as a gradual roller, the processing load can be reduced. The roller crests 44 of the rolling roller group constituted of the three rolling rollers 41, 42 and 43 are shaped such that the R-shaped end portions become gradually larger in the time order of abutment on the tube material 2′. Some of the adjacent R-shaped end portions may be the same in shape, if the arc diameters (R) of the R-shaped end portions of the roller crests 44 increase stepwise in the axial direction as a whole.

Preferably, the R-shaped end portions of the roller crests 44 of the rolling rollers 41, 42 and 43 are different from one another in shape except those at their both ends. FIG. 9 shows an example of this case, where each of the rolling rollers 41, 42 and 43 includes 13 rows of the roller crests 44 arranged along the axial direction, the arc diameter R at the 1st row being a mm (R=a) for all of the rolling rollers 41, 42 and 43, the arc diameters R at the 12nd and 13rd rows being 6a mm (R=6a) for all of the rolling rollers 41, 42 and 43. In this example, the arc diameter R at the 2nd row is a mm for the rolling roller 41, a+0.02 mm for the rolling roller 42, and a+0.04 mm for the rolling roller 43. For the 3rd to 10th rows, the arc diameter R is increased with the increase of the row number for all of the rolling rollers 41, 42 and 43. The arc diameter R at the 11th row is 6a-0.05 mm for the rolling roller 41, 6a-0.03 mm for the rolling roller 42, and 6a-0.01 mm for the rolling roller 43. It is possible to disperse the processing load to thereby form the fin shape with high precision by differentiating the roller crests 44 in shape, and to reduce variation of the formed fin shape by equating the shapes of the roller crests 44 of the rolling rollers 41, 42 and 43 at the beginning and end of the fin forming process.

FIGS. 10 and 11 are schematic diagrams for explaining the fin shaping process using the rolling rollers 41, 42 and 43 as a gradually R-changing roller. At the beginning of the tube forming process, the fin forming portion of thickness of t of the periphery of the tube material 2′ is pushed into the shape analogous to the roller crests 44 at a small load. Thereafter, the R-shaped end portions of the roller crests 44 pushing into the periphery of the tube material 2′ are gradually increased in size, as a result of which the tube material 2′ is squeezed between the lateral sides of the roller crests 44 to be plastic-deformed so as to extend upward. Accordingly, since the pushing force is dispersed to the lateral sides, the fin shaping process can be smoothly performed by squeezing up the fin forming portion so as to change from a roughly trapezoidal shape to a desired fin shape using the roller crests.

As shown in FIG. 10, the root portions between adjacent roller crests are shaped such that they become gradually deeper in the direction from the end at which the R-shaped end portion is minimum to the end at which the R-shaped end portion is maximum. As shown in FIG. 11, the fin height is gradually increased. Accordingly, the depth of the root portion at the end at which the R-shaped end portion is minimum can be made sufficiently small to prevent the rolling rollers 41, 42 and 43 from being broken, because it is only required to hold the fin 22 at this end. The root portions are shaped such that their depths gradually increase with the progress of the fin shaping process so as to provide necessary spaces for holding the fin being formed to project radially outward.

Next, the advantages of using the roller crests of the rolling rollers 41, 42 and 43 are explained with reference to FIGS. 12 and 13. As shown in FIG. 12, the roller angle (the angle theta formed by the lateral sides of adjacent roller crests 44) is V-shaped when their R-shaped end portions are small, and becomes gradually narrower as the R-shaped end portions become larger. Accordingly, the pushing force is dispersed to the lateral sides to facilitate the fin shaping. As shown in FIG. 13, the roller crests 44 are rounded at their ends, and the widths of their ends are gradually increased (as roller crests of a totally gradually R-changing roller). Accordingly, it is possible to prevent a shearing stress from concentrating in their ends and to disperse the shearing stress to the lateral sides. Further, since the arc diameters (R) are gradually increased, most of the portion being shaped by the following roller is limited in the area facing a 45-degree lateral sector of the circumference of the leading roller. This makes it possible to extend the fin forming portion upward by a large amount, because the forming load can be sufficiently dispersed to the lateral sides while squeezing the thick wall portion at the fin proximal end portion.

Next, effects of the extension absorbing mechanism provided in the rolling head holder 5 are explained with reference to FIGS. 14 and 15. In this embodiment, as shown in FIG. 14, extension toward the chuck 31 occurs in the tube material 2′ when the leading roller crest 44 (the first crest in FIG. 14) of each of the rolling rollers 41, 42 and 43 bites the periphery of the tube material 2′. Since this extension is accumulated for each of the roller crests biting the periphery of the tube material 2′, the tube material 2′ is likely to be axially compressed and deformed. On the other hand, the rolling head holder 5 shown in FIG. 15 is configured such that the proximal end portion 45 of the rolling roller head 4 is resiliently supported by the movable sleeve 52 and the spring 56 so as to be movable relative to the rolling head holder 5. Accordingly, the rolling head holder 5 shown in FIG. 15 can release the tube extension stress occurring between the tube material 2′ rotating pivoted at one end thereof and the rolling roller head 4 advancing forward at a constant speed by receiving the tube extension stress in the movable sleeve 52 and retracting the spring 56 while compressing it. Hence, according to the rolling head holder 5 shown in FIG. 15, it is possible to prevent the tube material 2′ from being deformed by absorbing the extension of the tube material 2′.

Second Embodiment

FIG. 16 is a side view showing an example of the shape of the roller crests of a modification of the rolling roller head 4 included in a manufacturing apparatus according to a second embodiment of the invention. FIG. 17 is a schematic diagram for explaining a tube forming process performed using the modification of the rolling roller head 4. In the second embodiment, as shown in FIG. 16, each of the rolling rollers 41, 42 and 43 is constituted of a first rolling roller 4a and a second rolling roller 4b to enable performing a two-stage rolling. The first rolling roller 4a, which is a main part of the rolling roller head 4, is a gradually R-changing roller whose R-shaped end portions of the roller crests 44 become larger gradually as is the case of the first embodiment. That is, as shown in FIG. 17, the R-shaped end portions are smaller at the forward end of the tube material 2′ and larger at the rearward end of the tube material 2′ so that the fin forming portion is squeezed radially outward (upward in FIG. 17) gradually (Ft1). In the first rolling roller 4a, the heights (outer diameters D1) of the roller crests 44 are the same, while the depths of the root portions between adjacent roller crests 44 become gradually larger so that the fin forming portion which becomes gradually higher with the progress of the fin shaping process can be held in the root portions securely.

In FIG. 16, the second rolling roller 4b disposed following the first rolling roller 4a is a projecting roller configured such that the heights (outer diameters D2) of the roller crests 44 are higher than those of the first rolling roller 4a, and become gradually larger toward the rear end thereof. As shown in FIG. 17, since the tube material 2′ is gradually pushed radially inward (Fh2: downward in FIG. 17), the fin height can be more increased. Since the tube material 2′ has been made thin by the first rolling roller 4a, the plastic deformation by the second rolling roller 4b can be facilitated.

Third Embodiment

Next, a third embodiment of the invention is described with reference to FIG. 18. FIG. 18 is a schematic diagram for explaining a method of manufacturing a fin-integrated tube performed using a cored bar as a third embodiment of the invention. As shown in FIG. 18, there is slight plastic deformation in the inner wall of the formed tube 21 in the direction in which it was pushed by the rolling rollers 41, 42 and 43. Such plastic deformation can be reduced by performing the forming process using a cored bar 8 mounted to the inner wall of the tube 21. Using the cored bar 8 facilitates the roller crests 44 to bite the tube 21, and minimizes escape of the tube 21 caused by resilient deformation of the tube 21 at the time of pushing the roller crests 44 into the tube 21, to thereby maximize the height of the fin 22. Further, using the cored bar 8 reinforces the thin tube 21 and makes it resistant to bending.

The fin-integrated tube 2 of the invention underwent a heat endurance test in a state of being mounted to the exhaust heat recovery device shown in FIGS. 6 and 7. More specifically, the exhaust heat recovery device was fabricated by disposing a plurality of the fin-integrated tubes 2 inside the duct D to constitute the heating section 1, and the temperature of the gas flowing into the duct D was changed repeatedly (2,000 cycles) within the range from 100 to 900° C. For comparison, the same test was performed for the conventional fin-integrated tube shown in FIG. 19.

It was found that the fin 22 of the fin-integrated tube 2 of the invention did not change in shape before and after the test. Further, the heat exchange performance and the pressure loss were found to be within a predetermined standard. On the other hand, in the case of the conventional fin-integrated tube, the fin deformation gradually increased with the increase of the cycles due to difference in linear expansion coefficient in the dissimilar metal joint thereof. After 2,000 cycles of the change of the gas temperature, the heat exchange performance dropped by 25%, and the pressure loss dropped by 50%. From this test, it was confirmed that the fin-integrated tube 2 of the present invention exhibits high durability under high temperature environment.

The manufacturing method of the present invention enables manufacturing fin-integrated tubes integrally provided with a spiral fin with a high degree of formability by using the three-roller type rolling roller head including gradual rollers. According to the manufacturing method of the present invention, since the tube material 2′ is plastic-deformed, the material is not wasted unlike in conventional machining or cutting work, and it is easy to adjust the heat transfer area (heat exchange performance) of the fin by adjusting the fin pitch depending on the lead angle of the rolling roller.

In the above embodiments, stainless steel is used as the material of the fin-integrated tube 2. However, a metal material having good heat conductivity such as aluminum or copper, or an alloy of them may be used depending on the usage environment. The material of the rolling rollers 41, 42 and 43 can be determined depending on the material of the tube material 2′. For example, when the tube material 2′ is made of a hard material, the rolling rollers 41, 42 and 43 may be made of a stronger material such as an ultrahard alloy.

The fin-integrated tube manufactured by the manufacturing method or apparatus of the present invention can be used for various heat exchangers other than exhaust heat recover devices, such as those used in a cooling system, a driving system or an air-conditioning system of a vehicle.

The above explained preferred embodiments are exemplary of the invention of the present application which is described solely by the claims appended below. It should be understood that modifications of the preferred embodiments may be made as would occur to one of skill in the art.

Claims

1. A method of manufacturing a fin-integrated tube for a heat exchanger, the fin-integrated tube including a cylindrical tube and a spiral fin integrally formed in a periphery of the tube, comprising the steps of:

disposing a rolling roller group including a plurality of rolling rollers each having a plurality of roller crests on a periphery thereof so as to surround the periphery of the tube with a predetermined lead angle, each of the roller crests being rounded at an end thereof into an R-shape to be an R-shaped end, widths of the R-shaped ends of the roller crests being gradually increased from one axial end to the other axial end for each of the rolling rollers, so that each of the rolling rollers serves as a gradual roller; and

causing the roller crests of the rolling rollers to press the periphery of the tube from the one axial end to the other axial end by axially moving and rotating the rolling roller group relative to the tube so as to deform a part of the periphery of the tube into a spirally projecting portion while shaping the spirally projecting portion into the spiral fin by gradually squeezing the part of the periphery of the tube using the R-shaped end portions of the roller crests of the rolling rollers.

2. The method of manufacturing a fin-integrated tube for a heat exchanger according to claim 1, wherein the fin-integrated tube is made of stainless steel.

3. A manufacturing apparatus for manufacturing a fin-integrated tube for a heat exchanger, the fin-integrated tube including a cylindrical tube and a spiral fin integrally formed in a periphery of the tube, comprising:

a tube holding part for holding a proximal end portion of the tube so as to be rotatable together with the tube; and

a rolling roller head disposed coaxially with the tube so as to be axially movable relative to the tube;

the rolling roller head having a rolling roller group including a plurality of rolling rollers each having a plurality of roller crests on a periphery thereof, said rolling roller group being configured to surround the periphery of the tube with a predetermined lead angle,

each of the roller crests being rounded at an end thereof into an R-shape to be an R-shaped end, widths of the R-shaped ends of the roller crests being gradually increased from one axial end to the other axial end for each of the rolling rollers, so that each of the rolling rollers serves as a gradual roller,

wherein

the rolling roller head is configured to be driven to axially move in a direction from a distal end to a proximal end of the tube and rotate relative to the tube so as to cause the roller crests of the rolling rollers to press the periphery of the tube in the direction from the distal end to the proximal end so as to deform a part of the periphery of the tube into a spirally projecting portion while shaping the spirally projecting portion into the spiral fin by gradually squeezing the part of the periphery of the tube using the R-shaped end portions of the roller crests of the rolling rollers.

4. The manufacturing apparatus for manufacturing a fin-integrated tube for a heat exchanger according to claim 3, wherein heights of the roller crests of each of the rolling rollers increase stepwise in a direction from one axial end to the other axial end thereof.

5. The manufacturing apparatus for manufacturing a fin-integrated tube for a heat exchanger according to claim 3, further comprising:

a rolling head holder holding the rolling roller head such that the rolling roller head is opposed to the tube holding part on a processing bench, the rolling head holder being formed with a slide hole which opens to an end thereof facing the tube holding part;

a movable sleeve slidably held inside the slide hole and supporting a periphery of a proximal end portion of the rolling roller head; and

a biasing means for biasing the movable sleeve in a direction in which the rolling roller head advances;

the slide hole, the movable sleeve and the biasing means serving as an extension absorbing mechanism for absorbing extension of the tube being form-processed by the manufacturing apparatus.

6. The manufacturing apparatus for manufacturing a fin-integrated tube for a heat exchanger according to claim 3, wherein the fin-integrated tube is made of stainless steel.