U.S. patent application number 10/823563 was filed with the patent office on 2005-01-13 for heat exchanger tube.
This patent application is currently assigned to MITSUBISHI ALUMINUM CO., LTD.. Invention is credited to Hyogo, Yasunori, Katsumata, Masaya, Watanabe, Akira.
Application Number | 20050006065 10/823563 |
Document ID | / |
Family ID | 32985625 |
Filed Date | 2005-01-13 |
United States Patent
Application |
20050006065 |
Kind Code |
A1 |
Katsumata, Masaya ; et
al. |
January 13, 2005 |
Heat exchanger tube
Abstract
A heat exchanger tube having higher corrosion resistance is
provided. The heat exchanger tube includes an Al alloy extruded
tube, and a flux layer containing a Si powder and a Zn-containing
flux formed on the external surface of the Al alloy extruded tube,
wherein an amount of the Si powder applied to the Al alloy extruded
tube is not less than 1 g/m.sup.2 and not more than 5 g/m.sup.2,
and an amount of the Zn-containing flux applied to the Al alloy
extruded tube is not less than 5 g/m.sup.2 and not more than 20
g/m.sup.2.
Inventors: |
Katsumata, Masaya;
(Susono-shi, JP) ; Hyogo, Yasunori; (Izu-shi,
JP) ; Watanabe, Akira; (Susono-shi, JP) |
Correspondence
Address: |
OBLON, SPIVAK, MCCLELLAND, MAIER & NEUSTADT, P.C.
1940 DUKE STREET
ALEXANDRIA
VA
22314
US
|
Assignee: |
MITSUBISHI ALUMINUM CO.,
LTD.
Tokyo
JP
|
Family ID: |
32985625 |
Appl. No.: |
10/823563 |
Filed: |
April 14, 2004 |
Current U.S.
Class: |
165/133 ;
165/179 |
Current CPC
Class: |
B23K 35/286 20130101;
B23K 1/203 20130101; B23K 2101/14 20180801; B23K 35/3605 20130101;
B23K 2101/34 20180801; F28F 2255/16 20130101; B23K 35/3603
20130101; F28F 1/126 20130101; F28F 19/06 20130101; F28F 21/084
20130101; B23K 2103/10 20180801; B23K 2101/06 20180801; B23K 1/0012
20130101 |
Class at
Publication: |
165/133 ;
165/179 |
International
Class: |
F28F 013/18 |
Foreign Application Data
Date |
Code |
Application Number |
May 6, 2003 |
JP |
2003-128170 |
Claims
What is claimed is:
1. A heat exchanger tube comprising an Al alloy extruded tube, and
a flux layer containing a Si powder and a Zn-containing flux formed
on an external surface of the Al alloy extruded tube, wherein an
amount of the Si powder applied to the Al alloy extruded tube is
not less than 1 g/m and not more than 5 g/m.sup.2, and an amount of
the Zn-containing flux applied to the Al alloy extruded tube is not
less than 5 g/m.sup.2 and not more than 20 g/m.sup.2.
2. The heat exchanger tube according to claim 1, wherein the
Zn-containing flux contains at least one Zn compound selected from
ZnF.sub.2, ZnCl.sub.2 and KZnF.sub.3.
3. The heat exchanger tube according to claim 1 or 2, wherein a
maximum particle size of the Si powder is 30 .mu.m or smaller.
4. The heat exchanger tube according to any one of claims 1 to 3,
wherein the Al alloy extruded tube contains 0.5% by weight or more
and 1.0% by weight or less Si, 0.05% by weight or more and 1.2% by
weight or less Mn, with a balance being Al and inevitable
impurities.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a heat exchanger tube and,
more particularly, relates to a heat exchanger tube having high
corrosion resistance.
[0003] Priority is claimed on Japanese Patent Application No.
2003-128170, filed May 6, 2003, the content of which is
incorporated herein by reference.
[0004] 2. Description of the Related Art
[0005] As shown in FIG. 2, a heat exchanger generally comprises a
pair of right and left pipe bodies called header pipes 5, a
multitude of tubes 1 made of an aluminum alloy installed in
parallel at intervals from each other between the header pipes 5,
and fins 6 installed between the tubes 1, 1. The inner space of
each of the tubes 1 and the inner space of the header pipes 5
communicate with each other, so as to circulate a medium through
the inner space of the header pipes 5 and the inner space of each
of the tubes 1, thereby achieving efficient heat exchange via the
fins 6.
[0006] It is known to constitute the tubes 1 of the heat exchanger
from heat exchanger tubes 11 made by coating the surface of an Al
alloy extruded tube 3, that has flattened cross section and a
plurality of holes 4 for passing the medium as shown in perspective
view of FIG. 1, with a flux containing a brazing material powder so
as to form a flux layer 2. It is also known to make the Al alloy
extruded tube 3 from material (JIS1050) that has high workability
for extrusion forming process, and to use a Si powder, an Al--Si
alloy powder or an Al--Si--Zn alloy powder as the brazing material
contained in the flux layer 2.
[0007] A heat exchanger is manufactured using the conventional heat
exchanger tube 11 described above in a process such as: the heat
exchanger tubes 11 are installed at right angles to the header
pipes 5 that are disposed in parallel at a distance from each
other, ends of the heat exchanger tubes 11 are inserted into
openings (not shown) that are provided in the side face of the
header pipe 5, the fins 6 having corrugated shape are assembled
between the heat exchanger tubes 11, and the assembly is heated in
a heating furnace so that the header pipes 5 and the tubes 1 are
fastened to each other by brazing with the brazing material
provided on the heat exchanger tube 11 while the fins 6 of
corrugated shape are fastened between the tubes 1, 1 by
brazing.
[0008] Wall thickness of the tube 1 that constitutes the heat
exchanger is made smaller than that of the header pipe 5 in order
to achieve high efficiency of heat exchange. As a result, in the
case in which the tube and the header pipe are corroded at
comparable rates, it is likely that a penetrating hole will be
formed by corrosion first in the tube thereby allowing the medium
to leak therethrough. Thus, it has been a major concern in the heat
exchanger to prevent corrosion of the tubes.
[0009] In order to improve the corrosion resistance of the heat
exchanger tube 11, a sacrificial anode layer containing Zn as a
major component is formed on the surface of the tubes in the
conventional heat exchangers. As the process to form the
sacrificial anode layer, such processes are known as thermal
spraying of Zn and coating with a Zn-containing flux. Japanese
Patent Application Unexamined Publication No. 7-227695 discloses an
example that employs Zn-containing flux.
[0010] However, when forming the sacrificial anode layer by thermal
spraying, it is difficult to precisely control the amount of metal
applied by thermal spraying, thus leading to such a problem that
the sacrificial anode layer cannot be formed uniformly on the tube
surface, and the corrosion resistance of the tube cannot be
improved.
[0011] When the Zn-containing flux described in Japanese Patent
Application Unexamined Publication No. 7-227695 as mentioned above
is used, it may be believed that corrosion resistance of the tube
can be improved since the flux and Zn are supplied simultaneously
onto the tube surface. In actuality, however, it is difficult to
achieve a stable coating condition with ordinary coating methods
such as immersion coating and roll coating, and therefore it has
been difficult to uniformly apply the Zn-containing flux. As a
result, Zn distribution in the sacrificial anode layer becomes
uneven, thus leading to insufficient corrosion resistance of the
tubes with preferential corrosion occurring in a portion that has
higher concentration of Zn.
SUMMARY OF THE INVENTION
[0012] The present invention, which has been completed in view of
the background described above, has an object of providing a heat
exchanger tube that has higher corrosion resistance.
[0013] In order to achieve the object described above, the present
invention employs the following constitution.
[0014] The heat exchanger tube of the present invention comprises
an Al alloy extruded tube, and a flux layer containing a Si powder
and a Zn-containing flux formed on the external surface of the Al
alloy extruded tube, wherein an amount of the Si powder applied to
the Al alloy extruded tube is not less than 1 g/m.sup.2 and not
more than 5 g/m.sup.2, and an amount of the Zn-containing flux
applied to the Al alloy extruded tube is not less than 5 g/m.sup.2
and not more than 20 g/m.sup.2.
[0015] The Zn-containing flux preferably contains at least one Zn
compound selected from ZnF.sub.2, ZnCl.sub.2 and KZnF.sub.3.
[0016] When such a heat exchanger tube is used, since a mixture of
the Si powder and the Zn-containing flux is applied, the Si powder
melts and turns into a brazing liquid during a brazing process, and
Zn contained in the flux is diffused uniformly in the brazing
liquid and is distributed uniformly over the tube surface. Since
the diffusion velocity of Zn in a liquid phase such as the brazing
liquid is significantly higher than the diffusion velocity in the
solid phase, Zn concentration in the tube surface becomes
substantially uniform, thus making it possible to form a uniform
sacrificial anode layer and improve the corrosion resistance of the
heat exchanger tube.
[0017] It is preferable for maximum particle size of the Si powder
to be 30 .mu.m or less. Maximum particle size larger than 30 .mu.m
results in an increase in the erosion depth of the tube and is
therefore not desirable. When maximum particle size of the Si
powder is less than 0.1 .mu.m, Si particles clump, and the erosion
depth of the tube increases also in this case. Therefore, the
maximum particle size is preferably not less than 0.1 .mu.m.
[0018] The Al alloy extruded tube is preferably made of an Al alloy
containing Si and Mn, with the balance being Al and inevitable
impurities, while a Si content is 0.5% by weight or more and 1.0%
by weight or less, and a Mn content is 0.05% by weight or more and
1.2% by weight or less.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] FIG. 1 is a perspective view of a heat exchanger tube of the
prior art.
[0020] FIG. 2 is a perspective view of a heat exchanger of the
prior art.
DETAILED DESCRIPTION OF THE INVENTION
[0021] Next, preferred embodiments of the present invention will be
described in detail.
[0022] The heat exchanger tube of the present invention is made by
forming the external surface of an Al alloy extruded tube with a
flux layer containing a Si powder and a Zn-containing flux.
[0023] The Al alloy extruded tube which constitutes the heat
exchanger tube is made of an Al alloy containing Si and Mn, with
the balance being Al and inevitable impurities, where a Si content
is 0.5% by weight or more and 1.0% by weight or less, and a Mn
content is 0.05% by weight or more and 1.2% by weight or less.
[0024] The reason for restricting the composition of the Al alloy
extruded tube will be described below. Si has an effect in that a
large amount of Si forms a solid solution in the Al alloy extruded
tube, thus resulting in noble potential of the Al alloy extruded
tube, and causes preferential corrosion to occur in the header
pipes and the fins that are brazed with the tubes when assembling
the heat exchanger, thereby suppressing deep pitting corrosion from
occurring in the Al alloy extruded tube, while improving the
brazing characteristic and forming good joint thereby to improve
the strength after brazing. Si content of less than 0.5% cannot
achieve the desired effect, and is therefore not desirable. Si
content higher than 1.0%, on the other hand, lowers the melting
point of the alloy resulting in excessive melting during brazing
and poor extrusion forming characteristic, and is not desirable.
Therefore, Si concentration in the Al alloy extruded tube is set in
a range from 0.5 to 1.0%. More preferable range of Si concentration
is from 0.6% to 0.8%.
[0025] Mn has the effect of turning the Al alloy extruded tube to
noble potential and, because of less likelihood of diffusing in the
brazing material, allows higher potential difference with the fin
or the header pipe so as to make the corrosion preventing effect of
the fin or the header pipe more effective, thereby improving the
external corrosion resistance and the strength after brazing. Mn
content of less than 0.05% cannot achieve sufficient effect of
turning the Al alloy extruded tube to noble potential, and is
therefore not desirable. Mn content higher than 1.2%, on the other
hand, results in poor extrusion forming characteristic, and is not
desirable.
[0026] Therefore, Mn concentration in the Al alloy extruded tube is
set in a range from 0.05 to 1.2%.
[0027] The flux layer formed on the tube surface contains the
Zn-containing flux and the Si powder, so that a molten brazing
material layer is formed over the entire surface of the tube after
brazing. Since the brazing material layer contains Zn uniformly
distributed therein, the brazing material layer has similar effect
as that of the sacrificial anode layer so that the brazing material
layer is subject to preferential planar corrosion. Therefore deep
pitting corrosion can be suppressed and corrosion resistance can be
improved.
[0028] The amount of a Si powder applied to the heat exchanger tube
is preferably not less than 1 g/m.sup.2 and not more than 5
g/m.sup.2. When the amount is less than 1 g/m.sup.2, sufficient
brazing strength cannot be achieved because of insufficient amount
of the brazing material, and sufficient diffusion of Zn cannot be
achieved. When the amount is more than 5 g/m.sup.2, Si
concentration in the tube surface increases and the rate of
corrosion increases, and is therefore not desirable.
[0029] The flux layer contains at least the Zn-containing flux. In
addition to the Zn-containing flux, a flux which does not contain
Zn may also be contained.
[0030] The Zn-containing flux preferably contains at least one Zn
compound selected from ZnF.sub.2, ZnCl.sub.2 and KZnF.sub.3. The
flux which does not contain Zn preferably contains at least one
fluoride such as LiF, KF, CaF.sub.2, AlF.sub.3 or SiF.sub.4 or a
complex compound of the fluoride such as KAlF.sub.4 or
KAlF.sub.3.
[0031] As the Zn-containing flux is contained in the flux layer of
the heat exchanger tube, a Zn-diffused layer (brazing material
layer) is formed on the tube surface after brazing, so that the
Zn-diffused layer functions as a sacrificial anode layer, thereby
improving the anti-corrosion effect of the tube.
[0032] Also, because a mixture of the Si powder and the
Zn-containing flux is applied, the Si powder melts and turns into a
brazing liquid during a brazing process, Zn contained in the flux
is diffused uniformly in the brazing liquid and is distributed
uniformly over the tube surface. Since diffusion velocity of Zn in
a liquid phase such as the brazing liquid is significantly faster
than the diffusion velocity in a solid phase, Zn concentration in
the tube surface becomes substantially uniform, thus making it
possible to form a uniform Zn-diffused layer and improve the
corrosion resistance of the heat exchanger tube.
[0033] The amount of the Zn-containing flux applied to the heat
exchanger tube is not less than 5 g/m.sup.2 and not more than 20
g/m.sup.2. An amount of less than 5 g/m.sup.2 results in
insufficient formation of a Zn-diffused layer that does not have
sufficient anti-corrosion effect, and is therefore not desirable.
An amount of more than 20 g/m causes excessive Zn to be
concentrated in a fillet that is the joint of the fin with other
components which results in higher rate of corrosion in the joint,
and is therefore not desirable.
[0034] The heat exchanger can be constituted by brazing the heat
exchanger header pipes and the fins to the heat exchanger tube
described above.
[0035] That is, the heat exchanger is constituted from the heat
exchanger tube of the present invention, the heat exchanger header
pipes and the fins that are joined with each other. Similarly to
the heat exchanger, described in conjunction with the prior art,
the heat exchanger comprises a pair of right and left pipe bodies
called "heat exchanger header pipes", a plurality of heat exchanger
tubes installed in parallel at intervals from each other between
the heat exchanger header pipes, and fins installed between the
heat exchanger tubes. The inner space of the heat exchanger tube
and the inner space of the heat exchanger header pipe are
communicated with each other, so as to circulate a medium through
the inner space of the heat exchanger header pipe and the inner
space of the heat exchanger tube, thereby to achieve efficient heat
exchange via the fins.
EXAMPLES
[0036] Al alloy extruded tubes having 10 cooling medium passing
holes and cross section measuring 20 mm in width, 2 mm in height
and wall thickness of 0.20 mm were produced, by extrusion forming
of billets made of an Al alloy containing 0.7% by weight of Si and
0.5% by weight of Mn.
[0037] Then a flux mixture was prepared by mixing the Zn-containing
flux to Si powder. The flux mixture was applied by spraying onto
the outer surface of the Al alloy extruded tube that was produced
in advance, thereby forming a flux layer. The amounts of the Si
powder and the flux mixture applied to the Al alloy extruded tube
are shown in Table 1. Thus the heat exchanger tubes of Examples 1
to 6 and Comparative Examples 1 to 4 were produced.
[0038] Then fins made of cladding material (JIS3003 or
JIS3003/JIS4045) were assembled on the heat exchanger tubes of
Examples 1 to 6 and Comparative Examples 1 to 4, and the assemblies
were kept at 600.degree. C. in a nitrogen atmosphere for three
minutes so as to carry out brazing. The tubes with the fins brazed
thereon were subjected to corrosion tests (SWAAT, 20 days) to
measure the maximum corrosion depth of the tubes. The test results
are shown in Table 1.
1 TABLE 1 Si powder Maximum Flux Maximum Amount of particle size
Amount of corrosion depth coating (g/m.sup.2) (.mu.m) Composition
coating (g/m.sup.2) Fin (.mu.m) Remark Example 1 1 10 KZnF.sub.3 5
JIS3003 75 -- Example 2 3 10 KZnF.sub.3 10 JIS3003 70 -- Example 3
5 10 KZnF.sub.3 15 JIS3003 80 -- Example 4 5 10 KZnF.sub.3 20
JIS3003 75 -- Example 5 3 10 ZnCl.sub.2 + KAlF.sub.4 10 + 10
JIS3003 95 -- Example 6 3 35 KZnF.sub.3 10 JIS3003 80 somewhat deep
erosion Comparative 3 10 KAlF.sub.4 10 JIS3003 350 -- Example 1
Comparative 3 10 KZnF.sub.3 + 2 + 10 JIS3003 300 -- Example 2
KAlF.sub.4 Comparative -- -- ZnF.sub.2 10 JIS3003/ 175 -- Example 3
JIS4045 Comparative -- -- KZnF.sub.3 20 JIS3003/ 200 -- Example 4
JIS4045
[0039] As shown in Table 1, maximum corrosion depth was less than
100 .mu.m in any of the finned tubes of Examples 1 to 6, indicating
that corrosion of the tubes was suppressed. Example 6 showed a
little deeper erosion because of larger maximum particle size of
the Si powder.
[0040] Extent of corrosion was larger in the comparative examples,
presumably because Zn was not added to the flux in Comparative
Example 1, smaller amount (2 g/m.sup.2) of the Zn-containing flux
(KZnF.sub.3) was added in Comparative Example 2, and Zn was
distributed unevenly since Si powder was not added in the
comparative examples 3 and 4.
[0041] As described in detail above, in the heat exchanger tube of
the present invention, since the mixture of the Si powder and the
Zn-containing flux is applied, the Si powder melts and turns into a
brazing liquid during a brazing process, while Zn contained in the
flux is diffused uniformly in the brazing liquid and is distributed
uniformly over the tube surface. Since diffusion velocity of Zn in
a liquid phase such as the brazing liquid is significantly higher
than diffusion velocity in a solid phase, Zn concentration in the
tube surface becomes substantially uniform, thus making it possible
to form a uniform sacrificial anode layer and improve the corrosion
resistance of the heat exchanger tube.
[0042] Since the amount of the Zn-containing flux is in a range not
less than 5 g/m.sup.2 and not more than 20 g/m.sup.2, Zn can be
distributed uniformly over the tube surface.
[0043] While preferred embodiments of the invention have been
described and illustrated above, it should be understood that these
are exemplary of the invention and are not to be considered as
limiting. Additions, omissions, substitutions, and other
modifications can be made without departing from the spirit or
scope of the present invention. Accordingly, the invention is not
to be considered as being limited by the foregoing description, and
is only limited by the scope of the appended claims.
* * * * *