U.S. patent application number 15/947951 was filed with the patent office on 2018-10-25 for method for manufacturing fin-tube heat exchanger and combustion apparatus including fin-tube heat exchanger.
The applicant listed for this patent is Rinnai Corporation. Invention is credited to Naohiro Ito, Seiichi Muto.
Application Number | 20180304339 15/947951 |
Document ID | / |
Family ID | 63852865 |
Filed Date | 2018-10-25 |
United States Patent
Application |
20180304339 |
Kind Code |
A1 |
Ito; Naohiro ; et
al. |
October 25, 2018 |
METHOD FOR MANUFACTURING FIN-TUBE HEAT EXCHANGER AND COMBUSTION
APPARATUS INCLUDING FIN-TUBE HEAT EXCHANGER
Abstract
The method for manufacturing a fin-tube heat exchanger includes
the step of expanding each heat transfer tube extending through a
corresponding tube insertion hole of a heat transfer fin with a
tube expander inserted in heat transfer tubes. The expanding step
includes a first sub-step of expanding the tube expander in a
radial direction of the heat transfer tube to a radially expanded
state while the tube expander is at rest in a first predetermined
region to be expanded inside the heat transfer tube to bring the
first predetermined region to be expanded into close contact with
the tube insertion holes; and a second sub-step of releasing the
tube expander from the radially expanded state to a radially
contracted state and moving the tube expander to a second
predetermined region to be expanded inside the heat transfer tube.
The first and second sub-steps are alternately repeated.
Inventors: |
Ito; Naohiro; (Nagoya-shi,
JP) ; Muto; Seiichi; (Nagoya-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Rinnai Corporation |
Nagoya-shi |
|
JP |
|
|
Family ID: |
63852865 |
Appl. No.: |
15/947951 |
Filed: |
April 9, 2018 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F28D 1/0426 20130101;
F28F 1/02 20130101; F28F 2215/08 20130101; F24H 1/40 20130101; F28D
2021/0024 20130101; F24H 9/0026 20130101; F28F 1/30 20130101; B21D
39/20 20130101; F28D 1/0477 20130101; F28F 2255/00 20130101; B21D
53/06 20130101; F28F 1/325 20130101; F28F 1/32 20130101 |
International
Class: |
B21D 39/20 20060101
B21D039/20; B21D 53/06 20060101 B21D053/06; F28F 1/02 20060101
F28F001/02; F28F 1/32 20060101 F28F001/32 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 21, 2017 |
JP |
2017-084266 |
Claims
1. A method for manufacturing a fin-tube heat exchanger comprising
heat transfer fins having tube insertion holes and heat transfer
tubes made of aluminum or stainless steel and respectively
extending through the tube insertion holes of the heat transfer
fins, the method comprising the step of: expanding each of the heat
transfer tubes extending through the corresponding tube insertion
hole with a tube expander inserted in the heat transfer tube,
wherein the expanding step comprises: a first sub-step of expanding
the tube expander in a radial direction of the heat transfer tube
to a radially expanded state while the tube expander is at rest in
a first predetermined region to be expanded inside the heat
transfer tube to bring the first predetermined region to be
expanded into close contact with the corresponding tube insertion
hole; and a second sub-step of releasing the tube expander from the
radially expanded state to a radially contracted state and moving
the tube expander to a second predetermined region to be expanded
inside the heat transfer tube, wherein the first sub-step and the
second sub-step are alternately repeated.
2. The method for manufacturing the fin-tube heat exchanger
according to claim 1, wherein the tube expander comprises: a
cylinder comprising a plurality of head segments divided in a
circumferential direction; a core rod to be respectively pushed
from end of the heat transfer tube into opening of the cylinder in
the heat transfer tube; and a conversion mechanism to convert axial
pushing force of the core rod into a movement of the head segments
in an expanding radial direction, wherein the core rod is pushed
into the cylinder to move the head segments in the expanding radial
direction to expand the cylinder to the radially expanded state,
and the core rod is pulled from the cylinder to move the head
segments in a contracting radial direction to contract the cylinder
to the radially contracted state.
3. A combustion apparatus comprising: a fin-tube heat exchanger
including: heat transfer fins having tube insertion holes; and heat
transfer tubes made of aluminum or stainless steel and respectively
extending through the tube insertion holes of the heat transfer
tubes, wherein a first predetermined region to be expanded inside
each of the heat transfer tubes extending through the corresponding
tube insertion hole is brought into close contact with the
corresponding tube insertion hole with a tube expander that is
expanded in a radial direction of the heat transfer tube to a
radially expanded state while being at rest in the first
predetermined region to be expanded, the tube expander released
from the radially expanded state to a radially contracted state is
movable to a second predetermined region to be expanded inside the
heat transfer tube, and the tube expander at rest in the second
predetermined region to be expanded is configured to be radially
expanded again to the radially expanded state to bring the second
predetermined region to be expanded into close contact with the
corresponding tube insertion hole.
4. The combustion apparatus comprising the fin-tube heat exchanger
according to claim 3, wherein the tube expander comprises: a
cylinder comprising a plurality of head segments divided in a
circumferential direction; a core rod to be respectively pushed
from end of the heat transfer tube into opening of the cylinder in
the heat transfer tube; and a conversion mechanism to convert axial
pushing force of the core rod into a movement of the head segments
in an expanding radial direction, wherein the core rod is pushed
into the cylinder to move the head segments in the expanding radial
direction to expand the cylinder to the radially expanded state,
while the core rod is pulled from the cylinder to move the head
segments in a contracting radial direction to contract the cylinder
to the radially contracted state.
Description
BACKGROUND OF THE INVENTION
Field of the Invention
[0001] The present invention relates to a method for manufacturing
a fin-tube heat exchanger and to a combustion apparatus including a
fin-tube heat exchanger.
Description of the Related Art
[0002] A fin-tube heat exchanger is known as a heat exchanger to be
incorporated in a water heater. As illustrated in FIG. 7, the
fin-tube heat exchanger includes a large number of thin plate-like
heat transfer fins (3) that are disposed in parallel to each other
at predetermined intervals. The heat transfer fins (3) have tube
insertion holes (30) through which heat transfer tubes (31) extend.
It is desirable that the inner periphery of each tube insertion
hole (30) of the heat transfer fins (3) be in close contact with
the outer circumferential surface of a corresponding heat transfer
tube (31) to improve thermal efficiency. To fill the gap
therebetween, the heat transfer tubes (31) are expanded.
[0003] For example, Japanese Patent Application Laid-open No.
2008-93713 discloses a method for expanding metal tubes. With
reference to FIG. 8, the method for expanding tubes involves
forcibly inserting and pushing a spherical body (40) of a tube
expanding jig (4) into a metal tube (31a) to expand the outer
diameter of the metal tube (31a). The body (40) is provided at a
tip of a shaft (41) of the tube expanding jig (4) and has a larger
diameter than that of the inner diameter of the metal tube (31a).
In this method, the body (40), which is coated with diamond-like
carbon, of the expanding jig (4) is forcibly inserted into the
metal tube (31a) with application of a lubricant. The method is
intended for a metal tube (31a) made of copper or aluminum.
[0004] Unfortunately, in a case where the heat transfer tube (metal
tube) (31) is made of stainless steel, forcibly inserting the body
(40) of the expanding jig (4) into the heat transfer tube (31) with
application of a lubricant removes the diamond-like carbon coating
at an early point in time to generate high frictional heat,
resulting in adhesion of the stainless steel on the surface of the
body (40). Continuous use of the expanding jig (4) in such a
condition may disadvantageously damage the inner surface of the
heat transfer tubes (31), which in turn may require higher stress
to push the body (40), resulting in a breakage of the shaft (41).
This requires frequent replacement of the expanding jig (4) and a
process of drying to remove the lubricant inside the heat transfer
tubes (31). Such a high-cost method for manufacturing a heat
exchanger with significantly low productivity is far from an ideal
method for mass production.
SUMMARY OF THE INVENTION
[0005] An object of the present invention, which has been made in
view of these circumstances, is to provide a method for
manufacturing a fin-tube heat exchanger allowing for longer service
life of a tube expander and exhibiting higher productivity, and a
combustion apparatus including a fin-tube heat exchanger.
[0006] An embodiment of the present invention is a method for
manufacturing a fin-tube heat exchanger including heat transfer
fins having tube insertion holes and heat transfer tubes made of
aluminum or stainless steel and respectively extending through the
tube insertion holes of the heat transfer fins. The method includes
the step of expanding each of the heat transfer tubes extending
through the corresponding tube insertion hole with a tube expander
inserted in the heat transfer tube. The expanding step includes a
first sub-step of expanding the tube expander in a radial direction
of the heat transfer tube to a radially expanded state while the
tube expander is at rest in a first predetermined region to be
expanded inside the heat transfer tube to bring the first
predetermined region to be expanded into close contact with the
tube insertion hole, and a second sub-step of releasing the tube
expander from the radially expanded state to a radially contracted
state and moving the tube expander to a second predetermined region
to be expanded inside the heat transfer tube. The first and second
sub-steps are alternately repeated.
[0007] In the manufacturing method, the tube expander is not moved
in the heat transfer tubes before being released from the radially
expanded state. In other words, the outer circumferential surface
of the tube expander does not slide on the inner circumferential
surface of the heat transfer tube. This prevents generation of
frictional heat, eliminating the risk of adhesion of the stainless
steel to the surface of the tube expander due to frictional heat,
even in a case where the heat transfer tube is made of stainless
steel. Accordingly, the manufacturing method does not require
frequent replacement of the tube expander and application of a
lubricant and thus eliminates the need for a process and cost of
drying to remove the lubricant.
[0008] Furthermore, the alternate repeating of the first and second
sub-steps can expand the heat transfer tube across substantially
the entire length such that the outer circumferential surface of
the heat transfer tube is brought into close contact with the tube
insertion hole, improving the efficiency in brazing the heat
transfer tube to the heat transfer fin. This can manufacture a heat
exchanger exhibiting high thermal efficiency.
[0009] In the method for manufacturing the fin-tube heat exchanger
described above, the tube expander may preferably include a
cylinder including a plurality of head segments divided in a
circumferential direction, a core rod to be respectively pushed
from end of the heat transfer tube into opening of the cylinder in
the heat transfer tube, and a conversion mechanism to convert axial
pushing force of the core rod into a movement of the head segments
in an expanding radial direction. The core rod is pushed into the
cylinder to move the head segments in the expanding radial
direction to expand the cylinder to the radially expanded state,
and the core rod is pulled from the cylinder to move the head
segments in a contracting radial direction to contract the cylinder
to the radially contracted state.
[0010] The cylinder, which is composed of the head segments, of the
tube expander has an adjustable outer diameter. The distance of the
movement in the expanding radial direction of the head segments of
the cylinder can be adjusted by the outer diameters of the core
rods to be pushed into the openings of the cylinder or the amount
of the pushing of the core rods into the openings of the cylinder.
This can expand the heat transfer tube to a desired diameter.
Furthermore, heat transfer tubes having various outer shapes can be
expanded by changing the shapes of the head segments of the tube
expander.
[0011] Another embodiment of the present invention is a combustion
apparatus including a fin-tube exchanger including heat transfer
fins having tube insertion holes, and heat transfer tubes made of
aluminum or stainless steel and respectively extending through the
tube insertion holes of the heat transfer tubes. A first
predetermined region to be expanded inside each of the heat
transfer tubes extending through the corresponding tube insertion
hole is brought into close contact with the corresponding tube
insertion hole with a tube expander that is expanded in a radial
direction of the heat transfer tube to a radially expanded state
while being at rest in the first predetermined region to be
expanded. The tube expander released from the radially expanded
state to the radially contracted state is movable to a second
predetermined region to be expanded inside the heat transfer tube.
The tube expander at rest in the second predetermined region to be
expanded is configured to be radially expanded again to the
radially expanded state to bring the second predetermined region to
be expanded into close contact with the tube insertion hole.
[0012] In the combustion apparatus including the fin-tube heat
exchanger described above, the tube expander preferably includes a
cylinder including a plurality of head segments divided in a
circumferential direction, a core rod to be respectively pushed
from end of the heat transfer tubes into opening of the cylinder in
each of the heat transfer tubes, and a conversion mechanism to
convert axial pushing force of the core rod into a movement of the
head segments in an expanding radial direction. The core rod is
pushed into the cylinder to move the head segments in the expanding
radial direction to expand the cylinder to the radially expanded
state, while the core rod is pulled from the cylinder to move the
head segments in a contracting radial direction to contract the
cylinder to the radially contracted state.
[0013] The heat transfer tube in the combustion apparatus is
expanded by the tube expander across substantially the entire
length to enhance the contact between the heat transfer fins and
the heat transfer tubes. The heat transfer tubes are thereby firmly
brazed to the tube insertion holes of the heat transfer fins. This
can improve the brazing efficiency and thus can provide a
combustion apparatus with high thermal efficiency.
[0014] According to the method for manufacturing the fin-tube heat
exchanger of the present invention, the tube expander can move to
the second predetermined region to be expanded inside the heat
transfer tube without sliding on the inner surface of the heat
transfer tube. This prevents generation of frictional heat between
the heat transfer tube and the tube expander, eliminating the risk
of adhesion of the stainless steel to the surface of the tube
expander, even in a case where the heat transfer tube is made of
stainless steel. Accordingly, the manufacturing method does not
require frequent replacement of the tube expander and allows for a
longer service life of the tube expander. Furthermore, the tube
expander can move in the heat transfer tube without application of
a lubricant. This can reduce costs and eliminates the need for a
process of drying to remove the lubricant, resulting in higher
productivity.
[0015] According to the combustion apparatus including the fin-tube
heat exchanger of the present invention, the contact between the
heat transfer fins and the heat transfer tubes can be enhanced to
improve the brazing efficiency. Therefore, the combustion apparatus
including the heat exchanger can exhibit high thermal
efficiency.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1 is a perspective view of a heat exchanger;
[0017] FIG. 2 is a schematic view of a water heater including the
heat exchanger illustrated in FIG. 1;
[0018] FIG. 3 is a schematic view of a tube expander in a radially
contracted state that is used in a step of expanding heat transfer
tubes in a method for manufacturing a heat exchanger according to
an embodiment;
[0019] FIG. 4 is a cross-sectional view of the tube expander in a
radially contracted state that is used in a step of expanding heat
transfer tubes in a method for manufacturing a heat exchanger
according to an embodiment;
[0020] FIG. 5 is a schematic view of a tube expander in a radially
expanded state that is used in a step of expanding heat transfer
tubes in a method for manufacturing a heat exchanger according to
an embodiment;
[0021] FIG. 6 is a cross-sectional view of the tube expander in a
radially expanded state that is used in a step of expanding heat
transfer tubes in a method for manufacturing a heat exchanger
according to an embodiment;
[0022] FIG. 7 is a plan view of a heat transfer fin and heat
transfer tubes of a conventional heat exchanger; and
[0023] FIG. 8 is a partial cross-sectional view of a metal tube for
illustrating a conventional method for expanding the metal
tube.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0024] Embodiments of the present invention will now be described
with reference to the attached drawings. A heat exchanger (51)
illustrated in FIG. 1 includes large number of thin plate-like heat
transfer fins (2) for absorbing heat. The heat transfer fins (2)
are disposed in parallel to opposite side walls (a front side wall
(501) and a rear side wall (502)) of a case (5) between the side
walls (501, 502). Herein, the outer face of the front side wall
(501) is a front face of the heat exchanger (51). When viewed from
the front face of the case (5), a depth direction corresponds to a
front-back direction, a width direction corresponds to a horizontal
direction, and a height direction corresponds to a vertical
direction.
[0025] For example, the heat exchanger (51) is used in a water
heater illustrated in FIG. 2, which is an example of combustion
apparatuses. The water heater includes a casing (55) accommodating
a container (53) and a fan case (34). The container (53) includes a
burner (33) having a downward combustion face (33a) and disposed at
an upper portion of the container (53). The fan case (34) is
communicated with the container (53) and includes a fan (34a)
driven by a motor (M) to transfer an air-fuel mixture gas to the
burner (33) in the container (53).
[0026] The heat exchanger (51) is of a sensible heat recovery type
and disposed at a middle portion of the container (53). A heat
exchanger (52) disposed below the heat exchanger (51) is of a
latent heat recovery type. In this water heater, the water from a
water supply pipe (38) disposed upstream of and in communication
with the heat exchanger (52) is heated with latent heat of exhaust
gas from the burner (33) at the lower heat exchanger (52), and is
then heated with sensible heat of the exhaust gas at the upper heat
exchanger (51), to discharge hot water heated to a predetermined
temperature from a hot-water supply pipe (39) disposed downstream
of and in communication with the heat exchanger (51). It is noted
that the case (5) illustrated in FIG. 1 is a part of the container
(53) and is heated by the combustion face (33a) of the downward
burner (33) disposed above the case (5), so that the exhaust gas
flows from an upper portion to a lower portion of the case (5).
[0027] Heat transfer tubes (21) are made of stainless steel and
each have a vertically oval cross-section. The heat transfer tubes
(21) are staggered in two rows in a substantially lower half space
of the case (5) such that the heat transfer tubes (21) in the upper
row are eccentric from the heat transfer tubes (21) in the lower
row by a half of a pitch in the horizontal direction. The heat
transfer tubes (21) extend through the front and rear side walls
(501, 502). Each two adjacent ends of the heat transfer tubes (21)
extending outward from the case (5) are covered by a cover (5a).
The covers (5a) are fixed to the front and rear side walls (501,
502) of the case (5). Such a structure allows a fluid to meander
through the heat transfer tubes (21) via the covers (5a).
[0028] The heat transfer fins (2) are thin metal plates made of
stainless steel. The heat transfer fins (2) have tube insertion
holes (20) or burring holes formed by burring. The heat transfer
tubes (21) extend through the tube insertion holes (20). Like the
heat transfer tubes (21), the tube insertion holes (20) are
staggered in two rows such that the tube insertion holes (20) in
the upper row are eccentric from the tube insertion holes (20) in
the lower row by a half of a pitch in a horizontal direction.
[0029] To assemble the heat transfer tubes (21) in the tube
insertion holes (20), each of the tube insertion holes (20) has a
vertically oval shape which is large enough to receive the heat
transfer tube (21) therethrough while being in substantially
contact with the heat transfer tube (21). It is desirable, however,
that the inner periphery of each tube insertion hole (20) be in
close contact with the outer circumferential surface of the heat
transfer tube (21) to improve brazing efficiency and thermal
efficiency. Accordingly, the heat transfer tube (21) is expanded in
diameter with a tube expander (100) inserted into the heat transfer
tube (21).
[0030] With reference to FIG. 3, the tube expander (100) includes a
cylinder (1) that can be accommodated in the heat transfer tube
(21) and a pair of core rods (first and second core rods (12, 13)).
The cylinder (1) includes an oval cylindrical portion (11) and
small-diameter cylindrical portions (10) extending from the
opposite ends of the oval cylindrical portion (11). The
small-diameter cylindrical portions (10) respectively have first
and second openings (10a, 10b). The first and second core rods (12,
13) are respectively inserted through the first and second openings
(10a, 10b) into the cylinder (1). The oval cylindrical portion (11)
has an outer shape substantially the same as the oval cylindrical
shape of the heat transfer tube (21). It is noted that the heat
transfer fins (2) illustrated in FIG. 3 and any other drawing are
rectangular plates each having a single insertion hole (20) for the
purpose of illustration.
[0031] The cylinder (1) is composed of four head segments (1a, 1b,
1c, and 1d) divided in a circumferential direction. These head
segments (1a to 1d) are banded all together substantially without a
gap therebetween. To keep the banding, O-rings (14) as banding
members are respectively attached to the opposite base ends of the
small-diameter cylindrical portions (10). The banding member may be
any elastic member other than an O-ring, and may be a spring, for
example. The cylinder (1) in such a state is referred to as being
in a radially contracted state. As illustrate in FIG. 3, the
cylinder (1) in the radially contracted state has an outer diameter
slightly smaller than the inner diameter of the transfer tube (21)
so as to be movable in the heat transfer tube (21) without sliding
on the inner surface of the heat transfer tube (21).
[0032] With reference to FIG. 4, the cylinder (1) has flaring
cavities (15a, 15b) respectively flaring toward the first and
second openings (10a, 10b) at the opposite ends of the cylinder
(1). The flaring cavities (15a, 15b) each have a circular
cross-section. The flaring cavities (15a, 15b) are formed in a
central portion of the cylinder (1) and in communication with each
other via a space (16) having a larger diameter than
minimum-diameter portions of the flaring cavities (15a, 15b).
[0033] The first and second core rods (12, 13) respectively have
tapering shafts (12a, 13a) each having a circular cross-section at
their tips. As illustrated in FIG. 4, a latching member (13b) is
provided at the tip of the tapering shaft (13a) of the second core
rods (13). The latching member (13b) has a head (130) having a
diameter larger than that of the minimum-diameter portion of the
flaring cavity (15b) and smaller than that of the space (16). The
second core rod (13) and the head segments (la to 1d) are assembled
and banded with the O-ring (14) such that the head (130) resides in
the space (16) in the cylinder (1) and the tapering shaft (13a)
resides in the flaring cavity (15b) with a gap therebetween. The
tapering shaft (12a) of the first core rod (12) has no latching
member (13b) described above.
[0034] The flaring cavities (15a, 15b) and the tapering shafts
(12a, 13a) constitute a conversion mechanism to expand the head
segments (la to 1d).
[0035] Next, a step of expanding the heat transfer tubes (21) is
described. The step of expanding tubes involves first and second
sub-steps.
[0036] In the first sub-step, the cylinder (1) in the radially
contracted state with the second core rod (13) extending through
the second opening (10b) is inserted into the heat transfer tube
(21) that is assembled in the tube insertion hole (20) of the heat
transfer fin (2). The cylinder (1) is then rested in a first
predetermined region to be expanded (22) of the heat transfer tube
(21). The tapering shaft (12a) at the tip of the first core rod
(12) is pushed into the flaring cavity (15a) of the cylinder (1)
through the first opening (10a). As the tapering shaft (12a) is
pushed into the flaring cavity (15a) of the cylinder (1), the
cylinder (1) is pushed, so that the tapering shaft (13a) is also
forcibly pushed into the flaring cavity (15b). The flaring cavities
(15a, 15b) of the cylinder (1) are thereby respectively pressed by
the tapering shafts (12a, 13a) of the first and second core rods
(12, 13) in a radial direction. The pressing force acts against
elastic restoring force of the O-ring (14) and is converted into a
force to move the head segments (la to 1d) apart from each other in
the radial direction. This operation forms gaps (S) between the
head segments (la to 1d), so that the outer diameter of the
cylinder (1) is evenly expanded, as illustrated in FIG. 5. The
cylinder (1) in such a state is referred to as being in a radially
expanded state. The cylinder (1) in the radially expanded state can
expand the first predetermined region to be expanded (22) of the
heat transfer tube (21).
[0037] In the first sub-step, the first and second core rods (12,
13) are respectively pushed into the first and second openings
(10a, 10b) at the opposite ends of the cylinder (1). This prevents
the cylinder (1) from being displaced from the first predetermined
region to be expanded (22) during the expanding step.
[0038] In a second sub-step following the first sub-step, the first
and second core rods (12, 13) are removed from the cylinder (1) in
a pulling direction. The radial pressing force of the tapering
shafts (12a, 13a) of the first and second core rods (12, 13) acting
on the cylinder (1) is thereby released, and the elastic restoring
force of the O-ring (14) returns the cylinder (1) to the radially
contracted state, as illustrated in FIGS. 3 and 4. The first core
rod (12) is then pulled out through the first opening (10a),
whereas the second core rod (13) is not pulled out through the
second opening (10b) because the head (130) of the latching member
(13b) at the tip of the tapering shaft (13a) is caught at a
boundary between the flaring cavity (15b) and the space (16). The
second core rod (13) in such a state is pulled further in the
pulling direction (indicated by the arrow in FIG. 4), so that the
cylinder (1) kept in the radially contracted state is pulled by the
head (130) to a second predetermined region to be expanded (22)
inside the heat transfer tube (21). The cylinder (1) is then rested
in the second predetermined region to be expanded (22), and the
first sub-step is performed again. The second predetermined region
to be expanded (22) inside the heat transfer tube (21) is generally
a non-expanded region adjacent to the first predetermined region
expanded in the first sub-step.
[0039] The alternate repeating of the first and second sub-steps
can sequentially expand each heat transfer tube (21) to bring the
outer circumferential surface of the heat transfer tube (21) into
close contact with the corresponding tube insertion hole (20) of
the heat transfer fin (2).
[0040] According to the manufacturing method described above, the
tube expander (100) with the cylinder (1) being in the radially
contracted state can move in the heat transfer tube (21) without
sliding on the inner surface of the heat transfer tube (21),
causing no frictional heat. This prevents adhesion of the stainless
steel of the heat transfer tube (21) from the inner circumferential
surface of the heat transfer tube (21) to the outer surface of the
cylinder (1) due to frictional heat. This does not require frequent
replacement of the cylinder (1) of the tube expander (100) and
allows for a long service life of the tube expander (100).
Additionally, since the tube expander (100) can move in the heat
transfer tube (21) without application of a lubricant,
manufacturing costs can be reduced. Since application of a
lubricant is not required, the need for a process of drying to
remove lubricant adhering to the inner surface of the heat transfer
tube (21) is also eliminated. As a result, higher productivity of
the heat exchanger (51) can be achieved.
[0041] The tube expander (100) described above can expand each heat
transfer tube (21) in shape and size to bring the heat transfer
tube (21) into close contact with the corresponding tube insertion
hole (20) of the transfer fin (2) without a gap therebetween. This
can improve efficiency in brazing the heat transfer tubes (21) to
the tube insertion holes (20). Furthermore, the heat exchanger (51)
including the heat transfer tubes (21) in highly close contact with
the heat transfer fins (2) excels in thermal efficiency.
Accordingly, incorporating the heat exchanger (51) in a water
heater can provide a combustion apparatus exhibiting high thermal
efficiency.
[0042] An advantage of the cylinder (1), which is composed of the
head segments (la to 1d), of the tube expander (100) lies in its
capability to evenly expand non-circular or oval heat transfer
tubes (21).
[0043] Since the first and second core rods (12, 13) respectively
have the tapering shafts (12a, 13a) at the tips thereof and the
cylinder (1) has the flaring cavities (15a, 15b) at the respective
openings (10a, 10b), the degree of expansion of the transfer tube
(21) can be variously changed depending on the pushing amount of
the first and second core rods (12, 13) into the respective flaring
cavities (15a, 15b). This can enhance the contact between the heat
transfer tubes (21) and the heat transfer fins (2).
[0044] Since the cylinder (1) in the radially contracted state can
move in the heat transfer tube (21), regions to be expanded (22)
inside the heat transfer tube (21) may be any desired regions.
Furthermore, a positional displacement of the cylinder (1) in the
heat transfer tube (21) can be readily corrected by axially moving
the second core rod (13).
[0045] In the embodiment described above, the outer shape of the
cylinder (1) of the tube expander (100) is vertically oval to
conform to the cross-sectional shape of the heat transfer tube
(21). In other words, the head segments (la to 1d) can define
various shapes conforming to not only a circular cross-sectional
shape but also any other cross-sectional shape of the heat transfer
tube.
[0046] Furthermore, although the first and second core rods (12,
13) are respectively inserted through the opposite ends of the
cylinder (1) of the tube expander (100) in the embodiment described
above, a core rod may be inserted only through one end to expand
the cylinder (1) while the other end of the cylinder (1) is
temporarily fixed with a stopper or any other member.
[0047] Moreover, although the tapering shafts (12a, 13a) and the
flaring cavities (15a, 15b) each have a circular cross-section in
the embodiment described above, these components may have any
appropriate cross-sectional shape other than the circular one.
[0048] It is noted that the present invention may be also adapted
to heat transfer tubes (21) made of aluminum.
[0049] Besides the water heater described above, the heat exchanger
(51) may be incorporated in any other combustion apparatus, such as
a condensing water heater, a heat source in a hot water supply
system of a storage type, a water heater with a bath reheating
function, a water heater dedicated for hot-water supply, a heat
source for hot-water supply and heating, and a hot-water
heater.
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