U.S. patent application number 10/565913 was filed with the patent office on 2006-08-17 for flat tube for heat exchanger.
This patent application is currently assigned to T. Tad Co., Ltd.. Invention is credited to Takazi Igami.
Application Number | 20060180299 10/565913 |
Document ID | / |
Family ID | 34100867 |
Filed Date | 2006-08-17 |
United States Patent
Application |
20060180299 |
Kind Code |
A1 |
Igami; Takazi |
August 17, 2006 |
Flat tube for heat exchanger
Abstract
A flat tube having a nearly B-like shape or the like in cross
section, which has one or more partitions therein, and is coated
with a brazing metal on the outer surface thereof, is provided. In
the top portion of the turned-up portion constituting the
partition, there are formed many slits, in order to provide the
conditions that satisfy both of the brazing performance and an
increase of working accuracy of the flat tube, which slits allow
the brazing metal to enter up to the top portion of the turned-up
portion, wherein the length "c" of the slit is 2 mm to 15 mm; the
distance "e" between the edges of the neighboring slits is 3 mm to
10 mm; and "e/c" is 0.6 or more.
Inventors: |
Igami; Takazi; (Aichi,
JP) |
Correspondence
Address: |
JORDAN AND HAMBURG LLP
122 EAST 42ND STREET
SUITE 4000
NEW YORK
NY
10168
US
|
Assignee: |
T. Tad Co., Ltd.
25-3, Yoyogii 3-chome
Shibuya-ku
JP
151-0053
|
Family ID: |
34100867 |
Appl. No.: |
10/565913 |
Filed: |
July 2, 2004 |
PCT Filed: |
July 2, 2004 |
PCT NO: |
PCT/JP04/09794 |
371 Date: |
January 25, 2006 |
Current U.S.
Class: |
165/177 ;
29/890.053 |
Current CPC
Class: |
F28D 1/0391 20130101;
F28F 2275/04 20130101; Y10T 29/49391 20150115 |
Class at
Publication: |
165/177 ;
029/890.052 |
International
Class: |
F28F 1/40 20060101
F28F001/40 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 25, 2003 |
JP |
2003-280425 |
Claims
1. A flat tube for heat exchanger, comprising: a pair of flat face
portions parallelly opposed to each other and a pair of curved
portions connected to both ends of the flat face portions formed
with a strip-shaped metal plate bent in the width direction thereof
to form into a flat cylindrical shape, wherein the strip-shaped
metal plate is coated with a brazing metal on one surface thereof,
and is bent so that the brazing metal is positioned at the outer
surface side of the cylindrical shape; in the central position in
the width direction of one of the flat face portions, a turned-up
portion is bent up to the opposed flat surface side, and the top
portion of the turned-up portion abuts on the inner surface of the
opposed surface side to form a partition within the tube; many
slits for allowing the brazing metal to enter therethrough are
formed intermittently being separated away from each other in the
top portion in the longitudinal direction thereof, wherein the
length "c" of the slit is 2 mm to 15 mm; the distance "e" between
the edges of the neighboring slits is 3 mm to 10 mm; and "e/c" is
0.6 or more.
2. The flat tube for heat exchanger according to claim 1, wherein
the thickness of the strip-shaped metal plate is 0.15 mm to 0.6 mm.
Description
TECHNICAL FIELD
[0001] The present invention relates to an aluminum-made flat tube
for heat exchanger having one or more partitions therein, of which
cross section is formed in a nearly B-like shape or the like, in
particular to an aluminum-made flat tube for heat exchanger, which
is formed by bending a strip-shaped metal plate coated with a
brazing metal at the outer surface side thereof in the width
direction and formed with slits in a top portion of the partition
for allowing the brazing metal at the outer surface side to enter
into the inner surface side through the slits for brazing the
partition and the inner wall surface.
BACKGROUND ART
[0002] There is known a flat tube having a nearly B-like shape or
the like in section, in which slits are intermittently formed in a
top portion of a partition positioned in the central area thereof
so as to allow a brazing metal at the outer surface side of the
tube to enter into the inner surface side through the slits while
brazing to integrally fix the top portion of the partition and the
opposed inner surface of the tube by means of brazing; thereby the
performance against the pressure is increased (for example, refer
to FIGS. 8 and 9 in Japanese Patent Application Laid-open No.
2002-228369).
[0003] When a corrosive fluid is circulated inside an aluminum-made
flat tube, the inner surface side of the core metal of the flat
tube is clad with a sacrificial anode material, and the outer
surface side is clad with a brazing metal. In a flat tube having a
nearly B-like shape in section, when a partition at the central
area is formed in a manner of turn-up bending, the top portion and
the inner side of the tube abutting thereon have to be brazed. In
such case, the brazing metal at the outer surface side of the tube
is allowed to enter into the inner surface side through slits
formed in the top portion thereof.
[0004] However, from experiments conducted by the inventor, the
following fact was found; i.e., in the flat tubes using slits, the
reliability of the brazing largely varies depending on the length
of the respective slits, gaps between the slits and the like, and
the workability into a tube of B-like shape in section and accuracy
thereof is largely influenced thereby.
[0005] Accordingly, an object of the present invention is to
determine experimentally optimum conditions for the slits formed in
the top portion of the partition in a flat tube having one or more
partitions and formed into a B-like shape in section.
DISCLOSURE OF THE INVENTION
[0006] An aspect of the present invention, disclosed in claim 1, is
a flat tube for heat exchanger, which includes:
[0007] a pair of flat face portions (1) parallelly opposed to each
other and a pair of curved portions (2) connected to both ends of
the flat face portions (1) formed with a strip-shaped metal plate
bent in the width direction thereof to form into a flat cylindrical
shape, wherein the strip-shaped metal plate is coated with a
brazing metal (3) on one surface thereof, and is bent so that the
brazing metal (3) is positioned at the outer surface side of the
cylindrical shape;
[0008] in the central position in the width direction of one of the
flat face portions (1), a turned-up portion (4) is bent up to the
opposed flat surface side, and the top portion (5) of the turned-up
portion (4) abuts on the inner surface of the opposed surface side
to form a partition within the tube;
[0009] many slits (6) for allowing the brazing metal to enter
therethrough are formed intermittently being separated away from
each other in the top portion (5) in the longitudinal direction
thereof, [0010] wherein the length "c" of the slit (6) is 2 mm to
15 mm; the distance "e" between the edges of the neighboring slits
(6) is 3 mm to 10 mm; and "e/c" is 0.6 or more.
[0011] Another aspect of the present invention, disclosed in claim
2, is the flat tube for heat exchanger according to claim 1,
wherein the thickness of the strip-shaped metal plate is 0.15 mm to
0.6 mm.
[0012] The flat tube for heat exchanger according to the present
invention has a structure as described above, and provides the
following effects.
[0013] The flat tube for heat exchanger according to the present
invention is structured so that the top portion 5 of the turned-up
portion 4, which is formed in the central portion in the width
direction of the flat face portion 1, abuts on the inner surface at
opposite side thereto to form a partition in the tube, wherein many
slits 6 are formed intermittently being separated away from each
other in the top portion 5, and the length of the slits 6 is 2 mm
to 15 mm; the distance between the edges of the neighboring slits 6
is 3 mm to 10 mm; and "e/c" is 0.6 or more. Accordingly, a highly
reliable flat tube for heat exchanger having a satisfactory brazing
strength between the top portion 5 and the inner surface at the
opposite side, which provides a high performance against the
pressure and which generates no deformation nor twist while the
flat tube is being formed, is provided.
[0014] That is, since the length of the slits 6 is prescribed to 2
mm or more, the brazing metal reliably enters to the inner surface
side through the slits 6 while brazing, the reliability on the
brazing is ensured.
[0015] Since the length of the slits 6 is prescribed to 15 mm or
less, the working accuracy to form the turned-up portion 4 by
bending the strip-shaped metal plate in the width direction thereof
can be highly maintained; as a result, the reliability on the flat
tube for heat exchanger can be maintained.
[0016] Also, since the distance between the edges of the
neighboring slits 6 is prescribed to 3 mm or more, no crack is
generated between the edges of the slits 6, a highly reliable flat
tube can be provided.
[0017] Further, since the distance between the edges of the
neighboring slits 6 is prescribed to 10 mm or less, the fillet of
brazed point in the top portion 5 is formed satisfactorily while
brazing, a flat tube for heat exchanger with high strength and
performance against the pressure can be provided.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] FIG. 1 shows a cross sectional view of a flat tube for heat
exchanger according to the present invention, illustrating a
relevant portion of a first embodiment.
[0019] FIG. 2 shows a cross sectional view illustrating the state
of use of the flat tube after brazing.
[0020] FIG. 3 shows a perspective view schematically illustrating a
turned-up portion 4 of the flat tube.
[0021] FIG. 4 shows an illustration of a strip-shaped metal plate
before being shaped into the turned-up portion 4 of the flat
tube.
[0022] FIG. 5 shows a cross sectional view illustrating a relevant
portion of a flat tube for heat exchanger in a second embodiment
according to the present invention.
[0023] FIG. 6 shows a cross sectional view illustrating a relevant
portion of a flat tube for heat exchanger in a third embodiment
according to the present invention.
[0024] FIG. 7 shows a perspective view illustrating a state of use
of a relevant portion of the flat tube in the third embodiment
according to the present invention.
BEST MODE FOR CARRYING OUT THE INVENTION
[0025] Embodiments of a flat tube according to the present
invention will be described referring to the drawings.
[0026] FIG. 1 shows a cross sectional view illustrating a relevant
portion of a flat tube according to the present invention; FIG. 2
is a cross sectional view illustrating a state of use of a relevant
portion after brazing; and FIG. 3 shows a perspective view
schematically showing a turned-up portion 4 shown in FIG. 1.
[0027] The flat tube for heat exchanger is formed by bending an
aluminum strip-shaped metal plate in the width direction into a
nearly B-like shape in section. As for the strip-shaped metal
plate, a brazing sheet is used. In the brazing sheet, the outer
surface side of the core metal is coated with a brazing metal of an
aluminum alloy up to approximately 10% of the total thickness of
the plate; and the inner surface side of the core metal is coated
with a sacrificial anode material of an aluminum alloy up to
approximately 10% of the total thickness of the plate. The total
thickness of the strip-shaped metal plate is approximately 0.15 mm
to 0.6 mm.
[0028] The flat tube 8 is formed in a cylindrical shape by a pair
of flat face portions 1 opposed parallelly to each other and a pair
of curved portions 2 with which both ends of the flat face portions
1 are connected. And in the central portion in the width direction
of one flat face portion 1, a turned-up portion 4, which is bent up
toward the opposed flat face side, is formed.
[0029] Both end edge portions 9 and 10 of the strip-shaped metal
plate are overlapped with each other. One end edge portion 10 is
formed in a stepped shape, and on the outer surface thereof, the
inner surface of the end edge portion 9 abuts. The inner surface of
the one end edge portion 10 abuts on the top portion 5 of the
turned-up portion 4.
[0030] As shown in FIG. 1 and FIG. 3, in the top portion 5 of the
turned-up portion 4, many slits 6 for allowing a brazing metal to
enter therethrough are formed intermittently being separated away
from each other in the longitudinal direction. The above slits 6
are formed in the following manner. That is, in a state of the
strip-shaped metal plate before bending, the slits 6 are formed as
shown in FIG. 4; and then the strip-shaped metal plate is bent back
at the slits 6 as the center. Here, the length "c" of the slits 6
is 2 mm to 15 mm. Also, the distance "e" between the edges of the
neighboring slits 6 is 3 mm to 10 mm; and "e/c" is 0.6 or more.
[0031] FIG. 5 shows a cross sectional view of another flat tube for
heat exchanger according to the present invention. The point
different from the tube shown in FIG. 1, both end edge portions 9
and 10 of the strip-shaped metal plate are formed parallelly with
respect to the turned-up portion 4; and the end edge portion 9, the
end edge portion 10 and the turned-up portion 4 are overlapped with
each other in the longitudinal direction of the tube section.
[0032] The slits 6 formed in the top portion 5 of the turned-up
portion 4 are identical to those shown in FIG. 1 and FIG. 3.
[0033] FIG. 6 shows still another embodiment according to the
present invention. In this embodiment, a turned-up portion 4 and a
turned-up portion 4a are formed respectively by bending in the
central portion in the width direction of a pair of flat face
portions 1 being opposed to each other, and the respective top
portions abut on each other. And in the top portion 5 of the
turned-up portion 4, slits 6 are formed. The length of the slits 6
and the distance therebetween are identical to those shown in FIG.
1. In this embodiment, one end edge portion 9 and the other edge
portion 10 of the strip-shaped metal plate are overlapped with each
other at an end portion of the flat tube 8. In the above-described
embodiments, a single turned-up portion 4 is formed to form a
single partition. However, two or more turned-up portions may be
formed to form a plurality of partitions. Further, the joint
structure of the partition may employ another mode. However, in the
present invention, it is limited to the structure in which many
intermittent slits 6 are formed in the top portion of the turned-up
portion 4.
[0034] Many flat tubes as described above are disposed parallel to
each other as shown in FIG. 7, fins 7 are disposed between the
respective flat tubes 8, and both ends of the respective flat tubes
8 are inserted into tube insertion holes in tube headers (not
shown) respectively. In a state that the heat exchanger has been
assembled, the entire of the heat exchanger is placed in a high
temperature furnace to melt the brazing metal on the outer surface
of the flat tube 8, and then cool down the same to solidify;
thereby the flat tubes 8 and the fins 7, the flat tubes 8 and the
tube insertion holes are integrally fixed by means of brazing. At
the same time, one end edge portion 9 and the another end edge
portion 10 of the flat tubes 8 itself, and the top portion 5 of the
turned-up portion 4 and the inner surface abutting thereon are
integrally fixed by means of brazing.
[0035] Referring to FIGS. 2 and 3, when the brazing metal 3 is
melted in the furnace, the brazing metal at the outer surface side
of the tube enters into the top portion 5 of the turned-up portion
4 from the slits 6, and continuously fixes the top portion 5 and
the inner surface of the tube abutting therewith in a brazing
manner. Simultaneously, the outer surfaces of the overlapped
turned-up portion 4 are also brazed integrally.
(Verification of Numerical Limitation in the Present Invention)
[0036] In the flat tube 8 according to the present invention, many
slits 6 for allowing the brazing metal to enter therethrough are
formed intermittently being separated away from each other in the
longitudinal direction of the top portion 5. The length "c" of the
slits 6 is 2 mm to 15 mm; the distance "e" between the edges of the
neighboring slits 6 is 3 mm to 10 mm; and "e/c" is 0.6 or more. The
above values were obtained as the optimum values in the present
invention on the basis of the following experiments.
[0037] As the samples for the experiments, flat tubes 8 shown in
FIG. 1 were formed. The longer diameter of the section was 24 mm;
and the shorter diameter thereof was 2 mm. The thickness of the
plate was 0.2 mm, 0.3 mm and 0.4 mm respectively. TABLE-US-00001
TABLE 1 Slit length C Gap e Brazing Work- Sample (mm) (mm)
performance ability e/c Judgment (1) 2 3 .largecircle.
.largecircle. 1.5 .largecircle. (2) 2 5 .largecircle. .largecircle.
2.5 .largecircle. (3) 2 8 .largecircle. .largecircle. 4.0
.largecircle. (4) 2 10 .largecircle. .largecircle. 5.0
.largecircle. (5) 4 3 .largecircle. .largecircle. 0.75
.largecircle. (6) 4 5 .largecircle. .largecircle. 1.25
.largecircle. (7) 4 8 .largecircle. .largecircle. 2.0 .largecircle.
(8) 4 10 .largecircle. .largecircle. 5.0 .largecircle. (9) 8 5
.largecircle. .largecircle. 0.63 .largecircle. (10) 8 10
.largecircle. .largecircle. 1.25 .largecircle. (11) 12 8
.largecircle. .largecircle. 0.67 .largecircle. (12) 12 10
.largecircle. .largecircle. 0.83 .largecircle. (13) 15 9
.largecircle. .largecircle. 0.6 .largecircle. (14) 15 10
.largecircle. .largecircle. 0.66 .largecircle. .largecircle.:
acceptable X: unacceptable
[0038] TABLE-US-00002 TABLE 2 Slit length C Gap e Brazing Work-
Sample (mm) (mm) performance ability e/c Judgment (15) 1 1 X X 1.0
X (16) 1 3 X .largecircle. 3.0 X (17) 1.5 3 X .largecircle. 2.0 X
(18) 1.5 6 X .largecircle. 4.0 X (19) 2 2 .largecircle. X 1.0 X
(20) 2 12 X .largecircle. 6.0 X (21) 2 20 X .largecircle. 10.0 X
(22) 4 2 .largecircle. X 0.5 X (23) 4 12 X .largecircle. 3.0 X (24)
4 20 X .largecircle. 5.0 X (25) 8 2 .largecircle. X 0.25 X (26) 8 4
.largecircle. X 0.5 X (27) 8 12 X .largecircle. 1.5 X (28) 8 20 X
.largecircle. 10.0 X (29) 12 2 .largecircle. X 0.16 X (30) 12 5
.largecircle. X 0.42 X (31) 12 7 .largecircle. X 0.58 X (32) 12 12
X .largecircle. 1.0 X (33) 12 20 X .largecircle. 1.67 X (34) 15 2
.largecircle. X 0.13 X (35) 15 5 .largecircle. X 0.33 X (36) 15 8
.largecircle. X 0.53 X (37) 15 12 X .largecircle. 0.8 X (38) 15 20
X .largecircle. 1.33 X (39) 17 5 .largecircle. X 0.29 X (40) 17 10
.largecircle. X 0.58 X (41) 17 15 X .largecircle. 0.88 X (42) 17 20
X .largecircle. 1.18 X (43) 20 5 .largecircle. X 0.25 X (44) 20 10
.largecircle. X 0.5 X (45) 20 15 X .largecircle. 0.75 X (46) 20 20
X .largecircle. 1.0 X .largecircle.: acceptable X: unacceptable
[0039] The thickness of the brazing metal 3 coated on the
respective outer surfaces was 10% of the total thickness of the
plate. As shown in table 1, as for the flat tubes according to the
present invention, various flat tubes of which slit length "c" was
2 mm to 15 mm were formed, and prepared so that the length (gap)
"e" between the edges of the slits was 3 mm to 10 mm; and "e/c" was
0.6 or more.
[0040] Also, as the samples for comparison, as shown in table 2,
various samples other than the flat tubes according to the present
invention, of which slit length "c" was 1 mm to 20 mm, were formed
and prepared so that the edges length (gap) "e" between the slits
was 1 mm to 20 mm.
[0041] The length of the tubes for experiments was 60 mm. The tubes
were placed in a high temperature furnace to melt the brazing metal
and then cooled down. The state of the brazing was examined.
[0042] As demonstrated in table 1 and table 2, in the aspect of the
brazing performance, satisfactory results were obtained in the
following range; i.e., slit length "c" was 2 mm to 20 mm; and the
distance "e" between the edges of slits was 2 mm to 10 mm. That is,
fillet of brazed point having a satisfactory strength was formed
entirely in the top portion 5 of the turned-up portion 4 and the
performance against the pressure was ensured.
[0043] Contrarily, in the cases that the slit length "c" was 1 mm
or 1.5 mm, the brazing metal failed to enter satisfactorily through
the slits and defective brazing was found. In the case where the
distance "e" between the edges of slits was larger than 10 mm, it
was found that a portion without fillet of brazed point (not brazed
portion) exceeded 1/3 of the distance "e" between the edges, and
the total strength of the flat tube was not satisfactory. The
reason of the above is as described below. That is, in the portion
with no slit between the edges, the fillet of brazed point was
formed with the brazing metal, which entered through the slits
while brazing, and the length of the entered metal was constant.
Accordingly, when the distance between edges is too large, a large
portion having no fillet of brazed point was made resulting in a
reduced strength.
[0044] The same results as the above were obtained in any of the
following cases; i.e., the thickness of the plate of the tube was
0.2 mm, 0.3 mm or 0.4 mm.
[0045] In the aspect of the workability of the tube, as shown in
tables 1 and 2, the length of the slits has to be 15 mm or less;
and the distance "e" between the edges of slits has to be 3 mm or
more; and "e/c" has to be 0.6 or more. When the above ranges are
exceeded, cracks or twists are generated between the edges of slits
while the flat tube is being formed and is not suitable to be used
as the flat tube. That is, when the length of the slits exceeds 15
mm, cracks or twists are generated while the flat tube is being
formed. Also, when the distance between the edges of slits is 2 mm
or smaller, cracks are generated while the flat tube is being
formed. Further, when the "e/c" is smaller than 0.6, cracks are
generated while the flat tube is being formed.
[0046] The same results as the above were obtained in any of the
following cases; i.e., the thickness of the plate of the tube is
0.2 mm, 0.3 mm or 0.4 mm.
[0047] Accordingly, it was experimentally verified that the optimum
conditions that satisfy both of the brazing performance and the
workability are as below; i.e., the slit length "c" is 2 mm to 15
mm; the distance "e" between the edges of slits 6 is 3 mm to 10 mm;
and "e/c" is 0.6 or more.
* * * * *