U.S. patent application number 12/552719 was filed with the patent office on 2010-03-04 for heat exchanger made of aluminum alloy and method of producing same.
This patent application is currently assigned to Calsonic Kansei Corporation. Invention is credited to Masami Asano, Takumi Funatsu, Yasunori Hyogo, Masaya Katsumata, Masayoshi Shinhama, Masahiro Sogabe.
Application Number | 20100051247 12/552719 |
Document ID | / |
Family ID | 41376403 |
Filed Date | 2010-03-04 |
United States Patent
Application |
20100051247 |
Kind Code |
A1 |
Sogabe; Masahiro ; et
al. |
March 4, 2010 |
HEAT EXCHANGER MADE OF ALUMINUM ALLOY AND METHOD OF PRODUCING
SAME
Abstract
A heat exchanger comprising a tube, a fin, and a header pipe,
wherein the tube contains, in mass %, 0.15 to 0.45% of Mn, 0.20 to
0.50% of Si, and the balance of Al and unavoidable impurities, and
is coated with a coating of brazing composition containing 1.0 to
5.0 g/m.sup.2 of Si powder, 4.0 to 10.0 g/m.sup.2 of KZnF.sub.3,
and 0.5 to 3.0 g/m.sup.2 of binder; the fin contains, in mass %,
1.20 to 1.80% of Zn, 0.70 to 1.20% of Si, 0.30 to 0.80% of Fe, 0.90
to 1.50% of Mn, one or two or more selected from 0.05 to 0.20% of
Zr, 0.01 to 0.10% of V, and 0.01 to 0.10% of Cr, and the balance of
Al and unavoidable impurities; and the header pipe comprises a core
material, outer sacrificial corrosion protection material, and an
inner brazing material.
Inventors: |
Sogabe; Masahiro;
(Saitama-shi, JP) ; Funatsu; Takumi; (Okegawa-shi,
JP) ; Shinhama; Masayoshi; (Yokohama-shi, JP)
; Hyogo; Yasunori; (Izu-shi, JP) ; Katsumata;
Masaya; (Susono-shi, JP) ; Asano; Masami;
(Mishima-shi, JP) |
Correspondence
Address: |
OBLON, SPIVAK, MCCLELLAND MAIER & NEUSTADT, L.L.P.
1940 DUKE STREET
ALEXANDRIA
VA
22314
US
|
Assignee: |
Calsonic Kansei Corporation
Saitama-shi
JP
Mitsubishi Aluminum Co., Ltd.
Tokyo
JP
|
Family ID: |
41376403 |
Appl. No.: |
12/552719 |
Filed: |
September 2, 2009 |
Current U.S.
Class: |
165/151 |
Current CPC
Class: |
B21D 53/08 20130101;
F28D 1/05366 20130101; B23K 1/0012 20130101; F28F 21/084 20130101;
F28F 2275/04 20130101; F28F 9/06 20130101 |
Class at
Publication: |
165/151 |
International
Class: |
F28F 9/04 20060101
F28F009/04; F28F 1/12 20060101 F28F001/12 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 2, 2008 |
JP |
2008-225324 |
Claims
1. A heat exchanger made of an assembly including a tube, a fin,
and a header pipe, wherein the tube is made of aluminum alloy
having a composition containing, in mass 0.15 to 0.45% of Mn, 0.20
to 0.50% of Si, and the balance consisting of Al and unavoidable
impurities; a coating of a brazing composition that is coated on a
surface of the tube to which the fin is joined and contains 1.0 to
5.0 g/m of Si powder, 4.0 to 10.0 g/m.sup.2 of Zn containing flux
composed of KZnF.sub.3, and 0.5 to 3.0 g/m.sup.2 of binder; the fin
is made of aluminum alloy containing, in mass %, 1.20 to 1.80% of
Zn, 0.70 to 1.20% of Si, 0.30 to 0.80% of Fe, 0.90 to 1.50% of Mn,
one or two or more elements selected from the group consisting of
0.05 to 0.20% of Zr, 0.01 to 0.10% of V, and 0.01 to 0.10% of Cr,
and the balance consisting of Al and unavoidable impurities; the
header pipe comprises a core material, outer sacrificial corrosion
protection material, and an inner brazing material; and the fin is
joined to the tube, and the tube is joined to the header pipe by
brazing in the heat exchanger.
2. A heat exchanger according to claim 1, wherein the tube has flat
surfaces, and the coating of the brazing composition is formed on
at least one flat surface of the tube such that side surfaces of
the tube positioned on both sides of the flat surface are left
not-coated with the brazing composition, and a perimeter b of the
uncoated side surface satisfies b.ltoreq.a.times.1.5, where a
denotes a width of the side surface.
3. A heat exchanger according to claim 1, wherein sacrificial layer
of the header pipe contains 0.60 to 1.20% by mass of Zn, and the
balance consisting of Al and unavoidable impurities.
4. A heat exchanger according to claim 2, wherein the sacrificial
corrosion protection material of the header pipe contains 0.60 to
1.20% by mass of Zn, and the balance consisting of Al and
unavoidable impurities.
5. A heat exchanger according to any one of claims 1 to 4, produced
by a process comprising: constructing an assembly including a fin,
a tube, and a header pipe by making the fin to contact the surface
of the tube coated with the brazing composition, and making the
tube to be assembled with the header pipe; and heating the assembly
to a predetermined brazing temperature, wherein the assembly is
held at an intermediate temperature range from 530 to 575.degree.
C. for 4 to 8 minutes during the heating, and is subsequently
heated to the predetermined brazing temperature.
6. A heat exchanger according to claim 5, wherein the predetermined
brazing temperature is in the range from 580 to 615.degree. C.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a heat exchanger made of an
aluminum alloy and a method of producing the same. Specifically,
the present invention relates to a heat exchanger made of an
aluminum alloy and a method of producing the same in which
separation of fins from tubes can be suppressed.
[0003] Priority is claimed on Japanese Patent Application No.
2008-225324, filed Sep. 2, 2008, the content of which is
incorporated herein by reference.
[0004] 2. Description of Related Art
[0005] Heat exchangers made of aluminum alloy comprises tubes,
fins, and header pipes as main constituents. The heat exchangers
are produced by brazing those constituents. Conventionally, brazing
sheets clad with Al--Si alloy brazing material have been widely
used in their production. Production cost of the heat exchanger has
been reduced by using extruded tubes (hereafter referred to as
tubes) having surfaces coated with a brazing composition composed
of a mixture of a flux, a binder, and a Al--Si alloy powder and/or
a Si powder.
[0006] However, since Si diffuses from the surface into the inside
of the tube wall, the tube is made to have a high Si concentration
in its surface and low Si concentration in the inside layer. As a
result, the tube is formed a potential gradient such that the
surface portion has a relatively high electric potential and the
inside layer has a relatively low electric potential. Such a
potential gradient increases corrosion of the tube and causes
pitting to occur, causing leakage of a refrigerant, and reducing
the strength of the tube.
[0007] It is proposed to improve pitting corrosion resistance of
the tube by using tubes having surface coated with a mixture of a
Zn-containing flux and a Si powder or the like, and forming a
Zn-diffused layer on the surface portion of the tube during the
brazing process, thereby making the tube have a potential gradient
where the surface portion has a relatively low electric potential
and the inside layer has relatively high electric potential.
[0008] However, where the Zn-containing flux is used in the
brazing, a large amount of Zn flows with the brazing liquid filler
and concentrates to fillets joining fins and the tubes.
[0009] The Zn-concentrated fillets potential become less noble and
thereby are corroded preferentially compared to the other portions
of the heat exchanger. Where preferential corrosion of the fillets
occurs, fins are separated from the tube surfaces, reducing heat
transfer efficiency. In such a case, the heat exchanger cannot keep
sufficient efficiency.
[0010] In patent reference 1 (Japanese Unexamined Patent
Application, First Publication, No. 2004-330233), the inventors
proposed a heat exchanger tube having an outer surface coated with
a brazing composition that contained Si powder and a Zn-containing
flux, where the amount of Si powder was controlled to be 1 to 5
g/m.sup.2, and the amount of Zn-containing flux was controlled to
be 5 to 20 g/m.sup.2.
[0011] Since the Si powder and the Zn containing flux are mixed in
the coating of the above-described heat exchanger tube, the Si
powder is fused to form brazing liquid filler at the time of
brazing, Zn contained in the flux uniformly diffuses in the brazing
liquid filler and is spread homogeneously on the tube surface.
Since the diffusion rate of Zn in the liquid phase such as brazing
liquid filler is far faster than the diffusion rate of Zn in a
solid state, the tube surface is made to have a substantially
homogeneous Zn concentration. As a result, a sacrificial anode
layer is homogeneously formed on the tube surface, thereby
improving corrosion resistance of the heat exchanger tube.
[0012] However, according to further investigation by the
inventors, it was discovered that preferential corrosion of fillets
could not be avoided where large amount of Zn concentrates to
fillets. In such a case, even though the Zn concentration in the
tube surface can be homogenized, a large difference in
concentration of Zn between the fillet and the tube may causes
preferential corrosion of the fillet. Therefore, in the process of
carrying out the present invention, a requirement for controlling
the difference in Zn concentration was taken into
consideration.
[0013] Based on the above-described circumstances, an object of the
present invention is to provide a heat exchanger that exhibits high
joint ratio of fins and tubes, in which corrosion of the tubes can
be controlled to be a shallow level, and separation of the fins can
be prevented. Another object of the present invention is to provide
a method of producing the same heat exchanger.
SUMMARY OF THE INVENTION
[0014] A heat exchanger according the present invention is made of
an assembly including a tube, a fin, and a header pipe, wherein
[0015] the tube is made of aluminum alloy having a composition
containing, in mass %, 0.15 to 0.45% of Mn, 0.20 to 0.50% of Si,
and the balance consisting of Al and unavoidable impurities, and a
coating of a brazing composition that is coated on a surface of the
tube to which the fin is joined and contains 1.0 to 5.0 g/m.sup.2
of Si powder, 4.0 to 10.0 g/m.sup.2 of Zn containing flux composed
of KZnF.sub.3, and 0.5 to 3.0 g/m.sup.2 of a binder; and the fin is
made of an aluminum alloy containing, in mass %, 1.20 to 1.80% of
Zn, 0.70 to 1.20% of Si, 0.30 to 0.80% of Fe, 0.90 to 1.50% of Mn,
one two or more elements selected from the group consisting of 0.05
to 0.20% of Zr, 0.01 to 0.10% of V, and 0.01 to 0.10% of Cr, and
the balance consisting of Al and unavoidable impurities; the header
pipe comprises a core material, an outer sacrificial corrosion
protection material, and an inner brazing material; and the fin is
joined to the tube, and the tube is joined to the header pipe by
brazing in the heat exchanger.
[0016] The assembly of the above-described heat exchanger may
comprises a plurality of tubes, a plurality of fins, and at least
two header pipes, wherein each of the tubes has a constitution of
the above-described tube, each of the fins has a constitution of
the above-described fin, and each of the header pipes has a
constitution of the above-described header pipe.
[0017] In the above-described heat exchanger, the tube may has flat
surfaces, and the coating of the brazing composition may be formed
on at least one flat surface (joint surface) of the tube such that
side surfaces of the tube positioned on both sides of the flat
surface are left not-coated with the brazing composition, and a
perimeter (peripheral length) b of the uncoated side surface
satisfies b.ltoreq.a.times.1.5, where a denotes a width (height) of
the side surface.
[0018] In the above-described heat exchanger, perimeter b of the
uncoated side surface may be measured as a peripheral length of the
side surface on a cross section perpendicular to the lengthwise
direction of the tube. The width a of the side surface coincident
to the thickness of the tube.
[0019] In the above-described heat exchanger, the tube may
comprises: two main flat surfaces that are parallel to each other,
elongate along a lengthwise direction of the tube; and two side
surfaces positioned on both sides of the main surfaces, wherein a
contact plane being in contact with the side surface is inclined
from the flat surface.
[0020] In the above-described heat exchanger, a sacrificial
corrosion protection material of the header pipe may contains 0.60
to 1.20% by mass of Zn, and the balance consisting of Al and
unavoidable impurities.
[0021] A heat exchanger according to any one of the above-described
constitutions may be produced by a process comprising:
[0022] making the fin contact the surface of the flat tube coated
with the brazing composition;
[0023] making the tube be assembled with the header pipe; and
[0024] heating the assembly having the fin, tube, and header pipe
to a predetermined brazing temperature, wherein the assembly is
held at an intermediate temperature range from 530 to 575.degree.
C. for 4 to 8 minutes during the heating, and is subsequently
heated to the predetermined brazing temperature.
[0025] In the above-described heat exchanger, the predetermined
brazing temperature may be in the range from 580 to 615.degree.
C.
[0026] According to the heat exchanger of the present invention,
the tube added with appropriate amounts of Mn and Si has a
corrosion resistance superior to the conventional alloy such as
1050 alloy or Al--Cu based alloy. Therefore, it is possible to
reduce the amount of Zn contained in the flux for forming a
sacrificial corrosion protection layer. As a result, it is possible
to reduce the amount of Zn flowing to the fillet with the brazing
liquid filler, thereby suppressing the preferential corrosion of
the fillet. Thus, it is possible to prevent separation of the
fin.
[0027] According to the heat exchanger of the present invention, Mn
added to the tube suppresses the fluidity of the brazing liquid
filler during the brazing process. Therefore, brazing liquid filler
formed during the brazing process does not flow excessively to the
fillet, and partial portion of the brazing liquid filler remains on
the tube surface. As a result, it is possible to reduce a
difference in the Zn concentration between the fillet and the tube
surface, thereby suppressing preferential corrosion of the fillet,
and preventing separation of the fin.
[0028] In the heat exchanger of the present invention, the fin may
be added with appropriate amounts of Si and Fe. Therefore, it is
possible to generate intermetallic compounds of Si, Fe, and Mn.
Since the intermetallic compounds increase the sacrificial
corrosion protection effect by the fins, it is possible to reduce
the content of Zn contained in the fin to provide the sacrificial
corrosion protection effect. As a result, it is possible to reduce
diffusion of Zn from the fin to the fillet, thereby preventing
preferential corrosion of the fillet, and preventing separation of
the fin.
[0029] Therefore, according to the present invention, it is
possible to provide a heat exchanger, wherein fins are not likely
to fall down compared to the conventional heat exchanger.
[0030] Since the fins are not likely to separate in the heat
exchanger according to the present invention, corrosion proof of
the tube by the sacrificial corrosion protection effect of the fin
can be maintained for a long period of time. As a result, it is
possible to prolong a life of the tube compared to a conventional
heat exchanger.
[0031] In the heat exchanger of the present invention, it is
preferable to form the coating of brazing composition on the
surface of the tube to which the fin is brazed leaving an uncoated
portion on the side surface. It is preferable to control the
perimeter of the uncoated portion on the side surface of the tube
to be within 1.5 times the width of the side surface of the
tube.
[0032] In the heat exchanger of the present invention having the
tube brazed with fin, Zn-containing portion constitutes an anode
portion, and Zn-free portion constituting the cathode portion is
protected from corrosion by preferential corrosion of the anode
portion. As the Zn-free portion (side surface of the tube) acting
as the cathode portion has a large area, Zn-containing portion
(brazing composition coated surface) is corroded severely by the
sacrificial anode effect.
[0033] Therefore, by reducing the area of Zn-free portion as much
as possible, it is possible to suppress the progress of corrosion,
inhibit preferential corrosion of the fillet, and suppress
separation of the fins.
[0034] In a heat exchanger, an outer surface of header pipes having
a large surface area may act as a cathode and increases corrosion
of the fillet. However, by constituting the header pipe of core
layer, outer sacrificial corrosion protection material, and inner
brazing material, and by having the sacrificial corrosion
protection material contains 0.60 to 1.20% by mass of Zn so as to
have the sacrificial corrosion protection material of the header
pipe be corroded preferentially, it is possible to suppress the
preferential corrosion of fillet, thereby suppressing separation of
the fin.
[0035] During the heating process in the process of producing a
heat exchanger according to the present invention, the assembled
fin, tube, and fillet are held at an intermediate temperature range
from 530 to 575.degree. C. for 4 to 8 minutes, and subsequently
heated to a brazing temperature. In this method, since the assembly
is held for a predetermined duration at a temperature range at
which flow of brazing liquid filler does not occur but diffusion of
Zn to the tube does occur, it is possible to ensure sufficient
diffusion of Zn into the tube wall of the tube. Therefore, it is
possible to suppress the excessive concentration of Zn into the
fillet. Therefore, it is possible to suppress the preferential
corrosion of fillet, thereby suppressing separation of the fin from
the heat exchanger.
BRIEF EXPLANATION OF DRAWINGS
[0036] FIG. 1 is a schematic diagram showing a front view of a heat
exchanger according to one embodiment of the present invention.
[0037] FIG. 2 is a schematic diagram showing a cross section of a
partial portion of an assembly comprising header pipes, tubes, and
fins according to the present invention at a state before
brazing.
[0038] FIG. 3 is a schematic diagram showing a cross section of a
partial portion of an assembly comprising header pipes, tubes, and
fins according to the present invention at a state after
brazing.
[0039] FIG. 4 is a transversal cross section of a tube according to
the present invention.
[0040] FIG. 5 is an exemplary drawing showing an anode portion and
a cathode portion in the cross section of the tube according to the
present invention.
[0041] FIGS. 6A to 6C respectively show examples of a
cross-sectional shape of side surface of a tube according to the
present invention. FIG. 6A shows an example in which side surface
of the tube has a flat surface constituting a main area and curved
corner surfaces in the vicinity of the surface of the tube. FIG. 6B
is a diagram showing an example in which the tube has a curved side
surface. FIG. 6C is a diagram showing an example in which the side
surface of the tube is constituted of two flat surfaces inclined to
each other forming an angle .theta..
[0042] FIGS. 7A and 7B respectively show examples of a cross
section of a tube according to the present invention. FIG. 7A shows
an example where the side surface S1 of the tube has a flat
surface. FIG. 7B shows a cross section of an example shown in FIG.
6B, where a whole area of the side surface S2 is a curved
surface.
[0043] FIG. 8 is a diagram showing an exemplary state of brazing a
fin to a tube according to the invention, where the fin is brazed
to the tube by fillets.
[0044] FIG. 9 shows a state of the brazing tube, fins, and header
pipes by fillets, where a surface of the header pipe is composed of
a Zn-containing sacrificial corrosion protection material.
[0045] FIG. 10 shows a state of a brazing tube, fins, and header
pipes by fillets, where a surface of the header pipe is free of
Zn.
[0046] FIG. 11 is an exemplary drawing showing a concentration
profile of Zn in the surface portion of the tube, showing profiles
obtained by a brazing process of the fin to the tube in a case
where the heating temperature is raised monotonously to the brazing
temperature, and in a case where the heating temperature is held at
an intermediate temperature for a predetermined duration and
subsequently raised to the brazing temperature.
[0047] FIG. 12 is a drawing explaining a concentration profile of
Zn on the surface portion of the tube obtained by a brazing process
of the fin to the tube in a case where heating temperature is
raised monotonously to the brazing temperature.
[0048] FIG. 13 is a drawing showing a concentration profile of Zn
in the surface portion of the tube, showing a profile obtained by a
brazing process of the fin to the tube in a case where a heating
temperature is held at an intermediate temperature range for a
predetermined duration and subsequently raised to the brazing
temperature.
DETAILED DESCRIPTION OF THE INVENTION
[0049] In the following, an embodiment according to present
invention is explained in detail with reference to the
drawings.
[0050] FIG. 1 is a schematic diagram that shows an embodiment of a
heat exchanger according to the present invention. The heat
exchanger 100 mainly comprises two header pipes 1, 2 that are
bilaterally arranged in parallel to each other intervening a
predetermined interval (clearance), a plurality of flat tubes 3
that are in parallel to each other and each joined to the header
pipes 1, 2 at right angles, and a plurality of corrugated fins that
are each joined to the upper and/or lower tubes 3. Header pipes 1,
2, tubes 3, and fins 4 are constituted of below-described aluminum
alloys.
[0051] Specifically, the header pipe 1 and header pipe 2 have side
surfaces opposed to each other, and a plurality of slits are formed
in the side surface with a predetermined interval along lengthwise
direction of each header pipe. An end portion of each tube 3 are
inserted into the opposed slits of the header pipes 1, 2 such that
the tube 3 is installed between the header pipes 1, 2. Thus, a
plurality of tubes 3 are installed between the header pipes 1, 2
and are arranged with a predetermined interval. Each fin 4 is
brazed to an upper surface or a lower surface of the tube 3. That
is, as shown in FIG. 3, fillets 8 are formed at joint portions
where end portions of the tube 3 are inserted to the slits 6 of the
header pipes 1, 2, and the tube 3 is brazed to the header pipes 1,
2. In addition, ridge portions (peak portions) of the wavy
corrugated fin 4 are opposed to surface of adjacent tubes 3 and
fillets 9 are formed between the ridge portions and the tube
surface. Thus, corrugated fins are brazed to the surface of the
tube 3.
[0052] At a state before brazing, surfaces of each tube 3, that is
the surfaces to which the fin 4 is joined, are coated with a
coating for brazing (coating 7 of a brazing composition). The
coating 7 includes 1.0 to 5.0 g/m.sup.2 of Si powder, 4.0 to 10.0
g/m.sup.2 of Zn-containing fluoride based flux (e.g., KZnF.sub.3),
0.5 to 3.0 g/m.sup.2 of a binder (for example, acrylic resin).
[0053] A tube 3 of the present embodiment has a constitution of a
flat multi-port tube, as shown in FIG. 4 and FIG. 5 showing a
transversal cross section of the tube 3. The tube 3 has a plurality
of passages 3c in its interior, flat upper surface 3A, flat lower
surface 3B, and side surfaces 3D adjacent to the surfaces.
[0054] At a state before the brazing, for example, the coating 7 of
brazing composition may be formed on the surface 3A and the surface
3B of the tube leaving uncoated portion on both sides of the coated
portion. That is, boundaries between the coated portion and
uncoated portion defines a width of the coating. Here, the width of
the coating is measured along a direction perpendicular to the
lengthwise direction of the tube.
[0055] A surface of the flat tube 3 of the present embodiment
comprises: two main flat surfaces that are parallel to each other,
elongate along a lengthwise direction of the tube 3, and constitute
the surface 3A and surface 3B of the tube 3; and two side surfaces
3D positioned on both sides of the main surfaces, wherein a contact
plane in contact with the side surface 3D is inclined from the main
surface.
[0056] It is preferable that a height (width) a of the side surface
3D, that is, a thickness of the main body of the tube 3 and a
perimeter b of the uncoated portion of the side surface satisfies
b.ltoreq.a.times.1.5. Here, the perimeter b of the uncoated portion
denotes a peripheral length of the uncoated portion on a cross
section perpendicular to the lengthwise direction of the tube.
[0057] For example, side surface 3D of the tube 3 shown in FIG. 4
and FIG. 5 may have a shape composed of a flat face 3G and curved
corner surface 3H as shown in FIG. 6A. For example, where the tube
3 has a thickness (dimension of side surface) of X, the flat
surface 3G of the side surface 3D may have a width of 0.45X, and
each of the corner portions (curved portions of the side surface
3D) may have a height of 0.275X.
[0058] As another example of the side surface of the tube 3, the
side surface may be a curved surface. For example, as shown in 6B,
the side surface 3J may have an arc shaped outline on a transversal
cross section of the tube such that a curvature radius R of the
side surface 3J satisfies R>1.003(X/2), where X is the thickness
(dimension of the side surface) of the tube 3.
[0059] Alternatively, the side surface of the tube 3 may be
constituted of two flat faces (inclined faces) 3K inclined to each
other. As shown in FIG. 6C, in a transversal cross section of the
tube 3, the inclined surfaces 3K may constitute a corner forming an
corner angle .theta. of .theta.>84.degree.. In the
above-described examples, the limitations of the shapes,
R>1.003(X/2) in FIG. 6B and .theta.>84.degree. are both
defined based on a boundary conditions so as to satisfy
b.ltoreq.a.times.1.5 defined in the present invention.
[0060] An assembly (assembled body) comprising a tube 3 and a fin 4
joined to the tube 3 through a fillet 9 may be formed by brazing a
fin 4 made of an aluminum alloy of the below-described composition
to a tube 3 made of the aluminum alloy of the below explained
composition to have a transversal cross section as shown in FIG. 4
to FIGS. 6A-C, using a coating 7 of brazing composition selected
from the below-described composition. In such an assembly, a side
surface 3D not provided with a coating 7 of brazing composition
constitutes a cathode portion 9 protected from corrosion, and the
fin 4 and the fillet 9 constitute anode portions that are
preferentially corroded.
[0061] Corrosion rates of the preferentially corroded anode
portions (fin 4 and fillet 9) are largely affected by the area
ratio of cathode portions (side surfaces 3D of the tube 3) to the
anode portion. As the area ratio of the cathode portion (side
surfaces 3D of the tube 3) is decreased, the corrosion rate of the
anode portion (fin 4 and fillet 4) is decreased.
[0062] For example, when the tube 30 has a flat side surfaces S1 as
shown in FIG. 7A, relative area fraction of the side surface is
decreased compared to a tube 31 having a curved surface S2 as shown
in FIG. 7B. As a result, it is possible to decrease the corrosion
rate of the fillets 9. Thus, the shape of the tube 30 is superior
to the shape of tube 31 in suppressing separation of the fin.
[0063] In a structure of the tube 3, it is possible to suppress
increase of corrosion by decreasing the area of the side surface 3D
(cathode portion) free of Zn, thereby suppressing preferential
corrosion of fillet 9, it is possible to inhibit the separation of
fin 4. To decrease the area of a side surface 3D of a tube 3, it is
effective to make the side surface 3D to be constituted of flat
surfaces.
[0064] In the following, composition used in the coating 7 of the
brazing composition is explained.
Silicon (Si) Powder
[0065] A Si powder is eroded with Al (aluminum) as a constituent of
the tube and forms brazing filler joining the fin 4 and the tube 3.
At the time of brazing, Si powder is fused to form a brazing liquid
filler, and Zn contained in the flux homogeneously diffuses into
the brazing liquid filler and is spread uniformly on the surface of
the tube 3. The Diffusion rate of Zn in the brazing liquid filler
(liquid phase brazing metal) is far faster (greater) than a
diffusion rate of Zn in a solid phase. Therefore, the Zn
concentration on the surface of the tube 3 is substantially
homogenized. That is, the homogenous Zn-diffused layer is formed,
and corrosion resistance of the tube 3 is improved.
Amount of Coating of Si Powder: 1.0 to 5.0 g/m.sup.2
[0066] Where the amount of Si powder in the coating is less than
1.0 g/m.sup.2, brazability is deteriorated. On the other hand, when
an Si is coated with an amount exceeding 5.0 g/m.sup.2, excessive
formation of brazing metal tends to cause concentration of Zn. In
addition, corrosion depth of the tube is increased, and it is
impossible to obtain the intended effect for preventing separation
of fins. Therefore, the amount of Si powder in the coating is
controlled to be in the range of 1.0 to 5.0 g/m.sup.2.
Grain Size of Si Powder: 1 to 6 .mu.m in D(50)
[0067] Where the grain size (grain diameter) of Si powder is less
than 1 .mu.m in D(50), it tends to increase a possibility of
failing in forming a braze joint of fin 4 to tube 3, and the
residual ratio of fin (ratio of fin escaped from separating)
decreases. On the other hand, where the grain size of Si particle
exceeds 6 .mu.m in D(50), the depth of corrosion in the tube 3 is
increased. Therefore, it is preferable to control the grain size of
Si powder to be within 1 to 6 .mu.m in D(50), where D(50) denotes
grain size where the cumulative volume of particles having equal
size or smaller size than that size constitute 50% in volume of all
the particles. D(50) may be measured using a laser beam scattering
method.
Zn Containing Fluoride Based Flux
[0068] Zn containing fluoride-based flux forms a Zn diffused layer
on the surface of the tube 3 at the time of brazing, and thereby
improving pitting corrosion resistance of the tube. In addition,
the flux removes oxide film from the surface of the tube 3 at the
time of brazing, and increase spreading and wetting of the brazing
filler, thereby improving the brazability.
Amount of Flux in the Coating: 4.0 to 10.0 g/m.sup.2
[0069] Where the amount of flux in the coating is less than 4.0
g/m.sup.2, it is impossible to form the Zn-diffused layer
sufficiently, and the corrosion resistance of the tube is
deteriorated. In addition, it is impossible to destroy and remove
the surface oxide film from the brazed tube sufficiently, resulting
in poor brazing. On the other hand, where the amount of the flux in
the coating exceeds 10.0 g/m.sup.2, Zn is concentrated in the
fillet, especially in the eutectic portion. As a result, corrosion
resistance of the fillet is deteriorated and separation of the fin
is increased. Therefore, the amount Zn-containing fluoride based
flux in the coating was controlled to be 4.0 to 10.0 g/m.sup.2. For
example, KZnF.sub.3 may be used as the Zn-containing fluoride based
flux.
Grain Size of Flux: 1 to 6 .mu.m in D(50)
[0070] Where the grain size of flux (flux powder) is smaller than 1
.mu.m in D(50), depth of corrosion of the tube 3 increases by
aggregation of flux powder. Where the grain size of the flux
exceeds 6 .mu.m in D(50), joining of the fins 4 is likely to poor,
resulting in reduction of the residual ratio of the fins 4.
Therefore, grain size of the flux is preferably 1 to 6 .mu.m. Here,
D(50) denotes the critical grain size (grain diameter) as an
indicator of grain size distribution of a powder, where the
cumulative volume of particles equal to or smaller than the size
constitute 50% in volume of all the particles. D(50) may be
measured using a laser beam scattering method.
Binder
[0071] In addition to the Si powder and Zn-containing fluoride
based flux, the coating composition contains a binder. For example,
acryl-based resin (e.g., acrylic resin) may be used as the
binder.
[0072] Where the amount of binder in the coating is less than 0.5
g/m.sup.2, workability (delamination-resistance) of the coating is
deteriorated. On the other hand, where the amount of the binder in
the coating exceeds 3.0 g/m.sup.2, the brazability is deteriorated.
Therefore, the amount of binder in the coating is controlled to be
0.5 to 3.0 g/m.sup.2. In usual, the binder is evaporated by heating
at the time of brazing.
[0073] In the present invention, a method of coating the brazing
composition comprising Si powder, flux, and binder is not limited.
For example, coating of the brazing composition may be performed by
an appropriate method selected from a spray method, a shower
method, a flow-coater method, a roll-coater method, a brash-coating
method, a dipping method, an electrostatic coating method, or the
like. A portion of the tube coated by the brazing composition may
be whole of the surface of the tube 3. Alternatively, the coating
may be formed on a partial portion of the surface of the tube 3,
provided that at least a portion of sufficient area in the vicinity
of joint portion to which the fin 4 is joined is coated with the
brazing composition such that the fin 4 may be joined to the tube 3
by brazing. Substantially, the side surface of the tube 3 of the
present invention is not coated with the brazing composition.
Depending on the coating method, a partial portion of the side
surface may be coated with the brazing composition during coating
of the brazing composition on e.g., upper surface. Such a tube 3
may also be applied as a tube 3 of the present invention.
[0074] The tube 3 is made of aluminum alloy containing, in mass %,
0.15 to 0.45% of Mn, 0.20 to 0.50% of Si, and the balance
consisting of Al and unavoidable impurities. The tube 3 may be
produced by extrusion of an aluminum alloy of the above-described
composition.
[0075] In the following, a reason for the limitations on the
elements of the aluminum alloy constituting the tube 3.
Manganese (Mn): 0.15 to 0.45% by Mass
[0076] Mn is an element that improves corrosion resistance of the
tube 3 and increases the mechanical strength of the tube 3. In
addition, Mn has an effect of improving extrudability of the
aluminum alloy during extrusion. Further, Mn has an effect of
suppressing fluidity of the brazing metal (brazing liquid filler),
thereby suppressing the difference in concentration of Zn between
the fillet 4 and the tube 3.
[0077] Where the content of Mn is less than 0.15% by mass, it is
impossible to achieve sufficient effects of improving corrosion
resistance and strength of the tube. In addition, fluidity of the
brazing filler cannot be suppressed effectively. On the other hand,
when the Mn exceeding 0.45% by mass is contained, extrudability of
the tube 3 is deteriorated since high pressure extrusion is
required. Therefore, in the tube of the present invention, Mn
content is controlled to be 0.15 to 0.45% by mass. Preferable Mn
content is 0.20 to 0.40% by mass.
Silicon (Si): 0.20 to 0.50% by Mass
[0078] As like as Mn, Si is an element having an effect of
increasing strength and corrosion resistance of the tube 3.
[0079] Where content of Si is less than 0.20%, it is impossible to
effectively increase the corrosion resistance and strength of the
tube. On the other hand, where Si exceeding 0.50% is contained,
extrudability of the aluminum alloy is deteriorated. Therefore, in
the present invention the Si content in the aluminum alloy for
constituting the tube 3 is controlled to be 0.20 to 0.50% by mass.
The Si content is preferably 0.25 to 0.45% by mass.
Next, the constitution of fin 4 is explained
[0080] The fin 4 to be joined to the tube 3 is constituted of an
aluminum alloy containing, in mass %, 1.20 to 1.80% of Zn, 0.70 to
1.20% of Si, 0.30 to 0.80% of Fe, 0.90 to 1.50% of Mn, and further
containing one or two or more element selected from 0.05 to 0.20%
of Zr, 0.01 to 0.10% of V, and 0.01 to 0.10% of Cr, and the balance
consisting of Al and unavoidable impurities. The fin 4 is produced
by casting a molten alloy having the above-described composition in
accordance with the general method, and working the cast alloy into
a corrugated shape through, hot-rolling, cold-rolling or the like.
In the present invention, the method of producing the fin 4 is not
limited to a specific method. It is possible to apply known methods
of producing a fin. In the following, reasons for limiting the
composition of aluminum alloy constituting the fin 4 of the present
invention is explained.
Zinc (Zn): 1.20 to 1.80% by Mass
[0081] The presence of Zn reduces the electric potential of the fin
4 and provides the fin 4 with sacrificial corrosion protection
effect. Here, the sacrificial corrosion protection effect of the
fin denotes an effect that preferential corrosion of the fin
protects other members (e.g., tube) from corrosion.
[0082] Where the content of Zn is less than 1.20%, the fin cannot
exhibits a sufficient sacrificial protection effect. On the other
hand, where the content of Zn exceeds 1.80%, Zn diffuses into the
fillet in large amount during the brazing. As a result, the Zn
concentration in the fillet 9 is increased, and the fillet is
corroded before the fin 4 is corroded. In addition, the corrosion
rate of the fin 4 is increased, and the life of the fin is
shortened. As a result, the fin has the sacrificial corrosion
protection effect only for a short time. Therefore, in the present
invention, the Zn content of the fin 4 is controlled to be 1.20 to
1.80% by mass. The Zn content is preferably 1.45 to 1.55%.
Silicon (Si): 0.70 to 1.20% by Mass
[0083] The presence of Si improves the high-temperature strength
and the room-temperature strength of the fin 4. Where the content
of Si in the fin is less than 0.70%, it is impossible to improve
the high-temperature strength and room-temperature strength
effectively. On the other hand, when Si content exceeds 1.20%,
processability of the aluminum alloy during the work processing of
the alloy to the fin 4 is deteriorated. Therefore, in the present
invention, the Si content in the aluminum alloy for constituting
the fin is controlled to be 0.70 to 1.20%. The Si content is
preferably 0.95 to 1.10%. Iron (Fe): 0.30 to 0.80% by mass
[0084] As like as Si, Fe improves the high-temperature strength and
the room-temperature strength of the fin 4. Where the content of Fe
is less than 0.30%, it is impossible to improve the
high-temperature strength and the room-temperature strength
effectively. On the other hand, where the Fe content exceeds 0.80%,
processability of the aluminum alloy during the work processing of
the alloy to the fin 4 is deteriorated, and the corrosion
resistance of the fin itself is decreased. Therefore, in the
present invention, the Fe content in the aluminum alloy for
constituting the fin is controlled to be 0.30 to 0.80% by mass.
Preferable Fe content is 0.47 to 0.53% by mass.
Manganese (Mn): 0.90 to 1.50% by Mass
[0085] As like as Si, Mn improves high-temperature strength and
room-temperature strength of the fin 4. Where content of Mn is less
than 0.90%, it is impossible to improve the high-temperature
strength and the room-temperature strength of the fin 4
effectively. On the other hand, where the Mn content exceeds 1.50%,
the processability of the aluminum alloy during the work processing
of the alloy to the fin 4 is deteriorated. Therefore, in the
present invention, the Mn content in the aluminum alloy for
constituting the fin is controlled to be 0.90 to 1.50% by mass. The
Mn content is preferably 1.15 to 1.25% by mass.
[0086] Where the content of Si and Fe are controlled to be in the
above-described ranges, Si and Fe respectively form Mn-containing
precipitates, thereby reducing the amount of solid-solubilized Mn,
and decreasing the electric potential of the fin 4. By this
phenomena, fin 9 is preferentially corroded compared to the primary
portion of the fillet 9, thereby preventing separation of fillet
9.
Zircon (Zr): 0.05 to 0.20% by Mass
[0087] Like Si, Zr improves the high-temperature strength and
room-temperature strength of the fin 4. Where the content of Zr is
less than 0.05%, it is impossible to improve the high-temperature
strength and the room-temperature strength effectively. On the
other hand, where the Zr content exceeds 0.20%, the processability
of the aluminum alloy during the work processing of the alloy to
the fin 4 is deteriorated. Therefore, in the present invention, the
Zr content of the aluminum alloy for constituting the fin is
controlled to be 0.05 to 0.20% by mass. The Zr content is
preferably 0.10 to 0.15% by mass.
Vanadium (V): 0.01 to 0.10%
[0088] As like as Si, V improves the high-temperature strength and
the room-temperature strength of the fin 4. Where the content of V
is less than 0.01%, it is impossible to improve the
high-temperature strength and the room-temperature strength of the
fin 4 effectively. On the other hand, where the V content exceeds
0.10%, the processability of the aluminum alloy during the work
processing of the alloy to the fin 4 is deteriorated. Therefore, in
the present invention, the V content in the aluminum alloy for
constituting the fin is controlled to be 0.01 to 0.10% by mass.
Preferable V content is 0.02 to 0.08% by mass.
Chromium (Cr): 0.01 to 0.10% by Mass
[0089] Like Si, Cr improves the high-temperature strength and
room-temperature strength of the fin 4. Where the content of Cr is
less than 0.01%, it is impossible to improve the high-temperature
strength and the room-temperature strength effectively. On the
other hand, where the Cr content exceeds 0.10%, the processability
of the aluminum alloy during the work processing of the alloy to
the fin 4 is deteriorated. Therefore, in the present invention, the
Cr content in the aluminum alloy for constituting the fin is
controlled to be 0.01 to 0.10% by mass. The Cr content is
preferably 0.02 to 0.08% by mass.
[0090] The aluminum alloy constituting the fin of the present
invention contains one, two or more selected from Zr, V, and C with
a content of the above-described range.
[0091] Next, a constitution of the header pipe 1 is explained.
[0092] As shown in FIG. 2 and FIG. 3, the header pipe 1 is
constituted of a pipe wall having three layered structure including
a core material 11, a sacrificial corrosion protection material 12
provided to the outer periphery of the core material 11, and a
brazing material layer 13 provided to the inner periphery of the
core material 11.
[0093] By providing the sacrificial corrosion protection material
12 to the outer periphery of the core material 11, it is possible
to obtain corrosion protection by the header pipe 1 in addition to
the corrosion protection by the fin 4. Therefore, it is possible to
increase the corrosion resistance of the tube 3, especially in the
vicinity of the header pipe 1.
[0094] Preferably, the material 11 is constituted of a Al--Mn-based
alloy. For example, it is preferable that the core material 11
contains 0.05 to 1.50% by mass of Mn. As the other elements, the
core material may further contain 0.05 to 0.8% by mass of Cu and/or
0.05 to 0.15% by mass of Zr. For example, the balance of the
above-described composition may be Al and unavoidable
impurities.
[0095] Sacrificial corrosion protection material 12 provided to the
outer periphery of the core material 11 is constituted of an
aluminum alloy containing 0.60 to 1.20% by mass of Zn, and the
balance consisting of Al and unavoidable impurities. The
sacrificial corrosion protection material 12 is integrated to the
core material 11 as a clad layer by rolling (clad-rolling). The
contents of the components of the sacrificial corrosion protection
material 12 are limited based on the below described reason.
Zinc (Zn): 0.60 to 1.20% by Mass
[0096] Zn is an element that provides the sacrificial corrosion
protection material 12 with sacrificial corrosion protection
effect.
[0097] Where the content of Zn is less than 0.60%, sufficient
sacrificial corrosion protection effect cannot be obtained. On the
other hand, if the content of Zn exceeds 1.20% by mass,
corrosion-resistance of the sacrificial corrosion protection
material 12 itself is deteriorated. That is, by excessive corrosion
of the sacrificial corrosion protection material, effect of
sacrificial corrosion protection cannot be maintained for a long
time. Therefore, content of Zn in the sacrificial corrosion
protection material 12 is preferably controlled within the range of
0.60 to 1.20%. Preferable content of Zn is 0.70 to 1.10% by
mass.
[0098] Clad ratio of the sacrificial corrosion protection material
12 to the core material is preferably 5 to 10%. That is, thickness
of the sacrificial corrosion protection material 12 is preferably 5
to 10% of total thickness of the sacrificial corrosion protection
material 12 and the core material 11. Where the clad ratio of the
sacrificial corrosion protection material 12 is less than 5%,
sufficient sacrificial corrosion protection effect cannot be
obtained. Where the clad ratio of the sacrificial corrosion
protection material 12 exceeds 10%, increase of the sacrificial
corrosion protection effect does not correspond to the increasing
thickness of the sacrificial corrosion protection material 12.
[0099] The brazing material 13 provided to the inner periphery of
the core material 11 is preferably constituted of Al--Si based
alloy. Preferably, the Al--Si based alloy contains 5.0 to 11.5% by
mass of Si.
[0100] The brazing material 13 is clad to the core material by
rolling. Clad ratio of the brazing material 13 to the core material
11 is preferably 3 to 10% by mass. Where clad ratio of the brazing
material 13 is less than 3%, sufficient brazing metal cannot be
provided for constituting a fillet 8. Where the clad ratio of the
brazing material 13 exceeds 10%, the brazing metal is provided
excessively.
[0101] Next, a method of producing a heat exchanger 100 mainly
constituted of the above-described header pipes 1, tubes 3, and
fins 4 are explained.
[0102] FIG. 2 is an magnified view showing a partial portion of a
pre-brazing assembly 101 constructed of the header pipes 1 (2),
tubes 3 and fins 4, where tubes 3 are coated with the brazing
composition on the surfaces joined with the fins 4. In FIG. 2, tube
3 is assembled to the header pipe 1 such that an end portion of the
tube 3 is inserted to a slit 6 formed in the header pipe 1.
[0103] In the time of brazing, the assembly 101 is heated to a
temperature not lower than the melting point of the brazing
material. By this heating, the brazing material 13 is molten as
shown in FIG. 3, and tube 3 is joined to the header pipe 1, and the
fin 4 is joined to the tube 3. At that time, the brazing material
13 in the inner periphery of the header pipe 1 is fused (molten)
and flows to the vicinity of the slit 6, forming fillets 8 by which
the header pipe 1 and the tube are joined. The coating 7 of the
brazing composition is fused to form a brazing liquid filler that
flows towards the vicinity of fin 4 by capillary effect and forms
fillets 9 by which the tube 3 and the fin 4 are joined.
[0104] At the time of brazing, the assembly is heated to an
appropriate temperature in an appropriate atmosphere such as an
inert atmosphere so as to fuse the brazing composition coating 7
and the brazing material 13. Then an activity of the flux is
increased, and Zn contained in the flux precipitates on the surface
of the brazed material (tube 3) and diffuses into the thickness
direction of the tube 3. In addition, the activated flux decomposes
oxide film on the surface of the tube 3 and oxide films on the
surface of powder particles in the brazing composition, and
increases wetting between the brazing metal and the brazed
material.
[0105] As explained above, heating temperature is not lower than
the melting point of the brazing material. Where the coating 7 of
the brazing composition on the tube 3 and the brazing material 13
of the header pipe 1 have the above-described compositions, the
assembly is heated up to a temperature in a range of 580 to
615.degree. C. and held at that temperature for about 1 to 10
minutes. In the present embodiment, on the way of heating of the
assembly from a room temperature to the above-described heating
temperature, the assembly is retained (held) at an intermediate
temperature within a range of 530 to 575.degree. C. for 4 to 8
minutes. While holding the intermediate temperature, Zn contained
in the flux is diffused into the surface portion of the tube 3 and
fixed in the tube. As a result, the amount of Zn flows to the
fillet is reduced, and separation of the fin 4 is prevented.
[0106] Where the intermediate retention temperature is less than
530.degree. C. or retention time is shorter than 4 minutes, Zn
cannot diffuse into the surface portion of the tube 3 sufficiently.
As a result, a large amount of Zn is contained in the brazing
liquid filler flowing to the fillet 9. On the other hand, where the
retention temperature exceeds 575.degree. C. or the retention time
exceeds 8 minutes, Zn diffuse into the tube wall excessively,
resulting in low Zn concentration on the surface portion of the
tube 3. As a result, a satisfactory sacrificial corrosion
protection layer is not formed on the surface of the tube 3, and a
corrosion resistance of the tube is deteriorated. Therefore,
intermediate retention conditions during the heating process are
held at a temperature range of 530 to 575.degree. C. for a duration
in a range of 4 to 8 minutes.
[0107] In the above-described heating process according to the
present invention, it is not necessary to perform the retention at
the intermediate temperature at a constant temperature. For
example, the assembly may be heated from 530 to 575.degree. C. with
a time of 4 to 8 minutes. Alternatively, the assembly may be held
at 570.degree. C. for 4 to a time shorter than 8 minutes. Any other
thermal history may be applied provided that the assembly is
exposed to heating conditions in the temperature range of 530 to
575.degree. C. for a duration of not shorter than 4 minutes and not
longer than 8 minutes.
[0108] In the time of brazing, partial fraction of a matrix of the
aluminum alloy constituting the tube 3 reacts with the brazing
composition of the coating 7 and forms a brazing metal by which the
tube 3 and the fin 4 are brazed. During the brazing, Zn contained
in the flux diffuses into the surface portion of the tube 3, making
the electric potential of the tube surface lower than that of the
inner portion of the tube 3.
[0109] According to the present embodiment, satisfactory brazing
metal is formed in the time of brazing without occurring residual
silicon particles, and a fillet 9 of sufficient size is formed
between the tube 3 and the fin 4. In addition, concentration of Zn
to the fillet 9 is suppressed by the increased size of the fillet
9.
[0110] In the thus obtained heat exchanger 100, an appropriate Zn
diffused layer is formed on the surface of the tube 3, and pitting
of the tube 3 is inhibited. In addition, corrosion of the fillet 9
is suppressed, and joining of the tube 3 and the fillet 4 are
ensured for a long period of time, and satisfactory heat transfer
efficiency is maintained.
[0111] According to the method of producing a heat exchanger 100 of
the present embodiment, the assembly is held at an intermediate
temperature range of 530 to 575.degree. C. for 4 to 8 minutes and
subsequently heated to the brazing temperature. By thus method, it
is possible to retain the assembly at a temperature range at which
flow of brazing liquid filler does not occur but diffusion of Zn
into the tube does occur. Therefore, a large amount of Zn can
diffuse into the tube 3, thereby suppressing excessive
concentration of Zn into the fillet 9. Therefore, it is possible to
suppress preferential corrosion of the fillet 9, thereby preventing
separation of the fin 4 from the heat exchanger.
[0112] In the heat exchanger 100 as described above, by having the
tube 3 to contain appropriate amounts of Mn and Si, that is, 0.15
to 0.45% by mass of Mn and 0.20 to 0.50% by mass of Si, it is
possible to provide a tube having superior corrosion resistance
compared to the conventional tube made of 1050 alloy or Al--Cu
based alloy. In addition, it is possible to reduce the amount of Zn
in the flux for forming the sacrificial protection layer,
specifically to be in the range of 4.0 to 10.0 g/m.sup.2.
Therefore, it is possible to reduce the amount of Zn flowing with
the brazing liquid filler to form the fillet 9. Thus, it is
possible to suppress preferential corrosion of the fillet 9,
thereby inhibiting separation of the fin 4.
[0113] According to the heat-exchanger 100 of the present
embodiment, Mn contained in the tube 3 suppress fluidity of the
brazing liquid filler in the time of brazing. Therefore, excessive
flow of brazing liquid filler to the fillet 9 is avoided, and
partial fraction of the brazing liquid filler remains on the
surface of the tube 3. Therefore, it is possible to suppress the
difference in Zn concentration between the fillet 9 and the surface
of the tube 3, thereby suppressing separation of fin 4.
[0114] According to the heat exchanger 100 of the present
embodiment, appropriate amount of Si and Fe, that is, 0.7 to 1.20%
by mass of Si and 0.30 to 0.80% by mass of Fe are added to the
aluminum alloy constituting the fin. Therefore, it is possible to
form intermetallic compounds of Si, Fe, and Mn, thereby improving
sacrificial corrosion protection effect by the fin. Therefore, it
is possible to suppress the amount of Zn in the fin to provide
sacrificial corrosion protection effect. As a result, as shown in
FIG. 8, it is possible to reduce diffusion of Zn from the fin 4 to
the fillet 9, thereby reducing concentration of Zn in the fillet 9.
Therefore, it is possible to prevent preferential corrosion of the
fillet 9, thereby suppressing separation of the fin 4.
[0115] Therefore, according to the present embodiment, it is
possible to provide a heat exchanger 100 in which possibility of
separation of fins 4 is reduced compared to the conventional heat
exchangers.
[0116] In addition, since separation of fins 4 is not likely to
occur in the heat exchanger 100 of the present embodiment, it is
possible to maintain corrosion protection of the tubes 3 by the
sacrificial effect of the fins 4 for a long period of time. As a
result, it is possible to prolong life of the tube 3.
[0117] In the heat exchanger 100 of the present embodiment, it is
preferable to form the coating of a brazing composition on the
surface leaving the side surfaces uncoated, where the perimeter of
a uncoated side surface is controlled to be within 1.5 times the
thickness of the tube.
[0118] In the heat exchanger 100 of the present invention having
tubes 3 brazed with the fins 4, Zn-containing portions constitute
anode portions, and protect Zn-free portion as a cathode portion
from corrosion by preferential corrosion of the anode portion. That
is, as the Zn-free cathode portion (side surface of the tube) has a
large area fraction, corrosion of the Zn-containing anode portion
(brazing metal coated portion) is increased by the sacrificial
corrosion protection effect.
[0119] Therefore, by suppressing the area of the Zn-free portion in
the tube 3, it is possible to suppress increase of corrosion by the
sacrificial effect, thereby suppressing preferential corrosion of
the fillet 9, and inhibiting separation of the fin 4.
[0120] According to the heat exchanger 100 of the present
embodiment, as like as electric potential of side surfaces of the
tube, electric potential of outer surfaces of header pipes 1, 2
also affect the corrosion of fillet 9 in the vicinity of the header
pipes 1, 2. Since each of the header pipes 1, 2 has a large surface
area, the electric potential of the tube has a large influence.
[0121] As shown in FIG. 9, where the header pipes 1, 2 each
comprises a core material 11, the outer sacrificial corrosion
protection material 12, and inner brazing material 13, and the
sacrificial corrosion protection material 12 contains Zn in an
amount of 0.60 to 1.20% by mass, by the preferential corrosion of
sacrificial corrosion protection material 12 of the header pipes 1,
2, it is possible to suppress preferential corrosion of the fillets
9 in the vicinity of the header pipes 1,2, for example, in the
position shown by the oval dotted line shown in FIG. 9, thereby
suppressing separation of the fin 4.
[0122] On the other hand, if the surfaces of the core material 11
of the header pipes 1, 2 are covered with a Zn-free layer such as
Zn-free brazing material layer or the like that act as cathode
portions, corrosion of the fillet 9 is increased remarkably. If the
fillet 9 is lost from the joint in accordance with the progress of
corrosion, as shown in the portion surrounded by an oval dotted
line on FIG. 10, joining of the fin 4 to the tube 3 is weakened,
resulting in separation of fin 4. By providing the Zn-containing
sacrificial corrosion protection material 12 on the outer surface
of the header pipes 1, 2 as shown in FIG. 9, it is possible to
suppress preferential corrosion of the fillets 9 remarkably,
thereby inhibiting separation of the fins 4.
[0123] In the method of producing a heat exchanger 100 according to
the present invention, the assembly is held at an intermediate
temperature range of 530 to 575.degree. C. for 4 to 8 minutes
before heated up to the brazing temperature. An effect of this
thermal history is explained further with reference to FIGS. 11 to
13.
[0124] In accordance with the above described production method, by
holding the assembly at a temperature range of 530 to 575.degree.
C. for 4 to 8 minutes, a larger amount of Zn diffuses into the tube
3. On the other hand, where the above-described retention at the
intermediate temperature range is avoided, Zn diffuses into the
tube in smaller amount compared to the above-described case. FIG.
11 shows a comparison of the two cases. Where the retention was
performed at a temperature range of 530 to 575.degree. C. for 4 to
8 minutes, as shown in the curve a1, Zn diffuses into a deep
portion in the tube 3. On the other hand, when the above-described
retention is avoided, Zn does not diffuse into the deep portion of
the tube 3.
[0125] FIG. 12 is a diagram showing a Zn concentration profile
along a depth direction in the tube 3 and position of the fin 4,
where the retention has not been performed. FIG. 13 is a graph
showing a Zn concentration profile along a depth direction in the
tube 3 and position of the fin 4, where the retention has been
performed. During the brazing, Si in the brazing material may form
eutectic composition with Al resulting in increase of erosion. The
depth of erosion is shown by the dotted line in each of FIG. 12 and
FIG. 13. When the brazing metal is in a state of molten brazing
liquid filler at the above-described temperature range, the
diffusion of Zn proceeds in the molten brazing liquid filler having
the eutectic composition. On the other hand, when the retention is
not performed, the diffusion depth of Zn in the tube is reduced,
and the amount of Zn concentrating in the fillet 9 generated in the
surface portion of the tube joined with the fin is increased. When
the retention is performed, Zn diffuses deeply into the tube 3, and
the amount of Zn existing in the tube surface and concentrating in
the fillet 9 is decreased. Therefore, the amount of Zn concentrated
in the fillet 9 generated in the surface portion of the tube joined
with the fin is decreased. Therefore, it is possible to inhibit
preferential corrosion of the fillet 9, thereby preventing the
separation of the fins 4.
EXAMPLES
Example 1
[0126] An aluminum alloy having a composition shown in Table 1 was
cast from molten alloy for constituting tubes, and aluminum alloy
having a composition shown in Table 2 was cast from a molten alloy
for constituting fins. For constituting header pipes, an aluminum
alloy for core material, an aluminum alloy for sacrificial
corrosion protection material, and an aluminum alloy for brazing
material, each having a composition as shown in Table 3 were cast
from molten alloys.
[0127] The aluminum alloy for a tube was subjected to heat
treatment for homogenization, and was subsequently subjected to hot
extrusion so as to have a shapes as shown in transversal cross
section in FIG. 4 and FIG. 6A. In the tube shown in FIG. 4, the
wall thickness was 0.30 mm, the width was 18.0 mm, the total
thickness was 1.5 mm, the height of flat face of the side surface
was 0.6 mm, and the curvature radius of the corner portion was 0.45
mm. In the tube shown in FIG. 6A, the wall thickness was 0.30 mm,
the width was 18.0 mm, the total thickness was 1.5 mm, the height
of flat face of the side surface was 0.9 mm, and the curvature
radius of the corner portion was 0.3 mm.
[0128] In addition tubes 31 having an arc shaped section of the
side surface 3 as shown in FIG. 6B and FIG. 7B were produced such
that a radius of the arc was 0.75 mm or 1.5 mm. A tube having a
side surface constituted of inclined flat faces as shown in FIG. 6C
was formed such that the angle between flat faces was
90.degree..
[0129] The aluminum alloy for the fins was subjected to
homogenization heat treatment, hot rolling, and cold rolling,
thereby obtaining a plate of 0.08 mm in thickness. The plate was
subjected to corrugated processing. Thus, fins 4 were produced.
[0130] An aluminum alloy for sacrificial corrosion protection
material, an aluminum alloy for core material, and an aluminum
alloy for brazing material were each subjected to hot rolling and
cold rolling to obtain plates each having a thickness of 0.12 mm,
1.30 mm, and 0.08 mm. Three layered clad plate was obtained using
the aluminum alloy plate for core material as a center layer, and
arranging the aluminum alloy plate for sacrificial corrosion
protection material on one side, and aluminum alloy plate for
brazing material on another side of the core material. The three
layered clad plate was processed to an seam-welded pipe having a
circular section. Header pipe 1 was produced by working the
seam-welded pipe. Outer layer of the header pipe 1 was sacrificial
corrosion protection material, and inner layer of the header pipe 1
was a brazing material.
TABLE-US-00001 TABLE 1 Mn Si (mass %) (mass %) Al Al alloy for tube
0.25 0.25 balance
TABLE-US-00002 TABLE 2 Zn Si Fe Mn Zr V Cr (mass %) (mass %) (mass
%) (mass %) (mass %) (mass %) (mass %) Al Al alloy 1.45 0.95 0.50
1.15 0.10 0.05 0.05 balance For fins
TABLE-US-00003 TABLE 3 Cu Mn Zr Zn Si (mass %) (mass %) (mass %)
(mass %) (mass %) Al Al alloy for Core 0.50 1.10 0.10 -- -- balance
Header pipe material Sacrificial -- -- -- 0.95 -- balance corrosion
protection material Brazing -- -- -- -- 9.75 Balance material
[0131] Next, brazing composition was roll-coated on the surface of
the tube 3, and was dried.
[0132] The brazing composition was constituted of a mixture of
silicon powder (grain size: 2.8 .mu.m in D(50)), flux powder
composed of KZnF.sub.3 (grain size: 2.0 .mu.m in D(50)), and
acrylic resin (containing alcohol such as isopropyl alcohol as a
solvent). The amount of each component mixed in the composition was
controlled such that the amount of the component in the coating had
a value as shown in Table 4.
TABLE-US-00004 TABLE 4 Coated amount (g/m.sup.2) Side surface
Residual KZnF.sub.3 of tube Fin-tube Corrosion ratio of Si flux
Ratio of brazing joint ratio depth of tube fin No. powder powder
Binder shape perimeter condition (%) (.mu.m) (%) 1 -- 5.5 1.2 Flat
+ R: 0.45 1.34 1 0 70 0 Comparative 2 0.5 5.5 1.2 Flat + R: 0.45
1.34 1 65 68 10 Comparative 3 1.6 5.5 1.2 Flat + R: 0.45 1.34 1 95
72 72 4 2.5 5.5 1.2 Flat + R: 0.45 1.34 1 96 73 75 5 4.4 5.5 1.2
Flat + R: 0.45 1.34 1 96 75 78 6 6.0 5.5 1.2 Flat + R: 0.45 1.34 1
100 265 30 Comparative 7 2.5 -- 1.2 Flat + R: 0.45 1.34 1 10
>400 6 Comparative 8 2.5 3.5 1.2 Flat + R: 0.45 1.34 1 96 320 25
Comparative 9 2.5 4.5 1.2 Flat + R: 0.45 1.34 1 98 75 80 10 2.5 6.5
1.2 Flat + R: 0.45 1.34 1 99 70 72 11 2.5 8 1.2 Flat + R: 0.45 1.34
1 99 70 70 12 2.5 9 1.2 Flat + R: 0.45 1.34 1 99 69 70 13 2.5 5.5
0.6 Flat + R: 0.45 1.34 1 96 72 73 14 2.5 5.5 2.4 Flat + R: 0.45
1.34 1 95 72 74 15 2.5 11 1.2 Flat + R: 0.45 1.34 1 99 68 5
Comparative 16 2.5 5.5 -- Flat + R: 0.45 1.34 1 55 280 28
Comparative 17 2.5 5.5 3.5 Flat + R: 0.45 1.34 1 69 295 35
Comparative 18 2.5 5.5 1.2 Semicircular 1.57 1 98 98 65 Comparative
Arc 19 2.5 5.5 1.2 Flat + R: 0.45 1.34 2 98 72 80 20 2.5 5.5 1.2
Flat + R: 0.45 1.34 3 98 95 65 Comparative 21 2.5 5.5 1.2 Curved
shape 1.05 1 99 72 76 R: 1.5 22 2.5 5.5 1.2 Flat + R: 0.3 1.22 1 99
71 80 23 2.5 5.5 1.2 flat faces 1.41 1 93 75 70 angle: 90.degree.
Condition 1: Heat to 570.degree. C., hold 570.degree. C. for 4
minutes, heat to 600.degree. C., and hold 600.degree. C. for 2
minutes Condition 2: Continuously heating to 600.degree. C. and
hold 600.degree. C. for 2 minutes, where heating from 530 to
575.degree. C. with 6 minutes Condition 3: Continuously heating to
600.degree. C. and hold 600.degree. C. for 2 minutes, where heating
from 530 to 575.degree. C. with 1 minutes
[0133] Next, header pipes 1, tubes 3, and fins 4 were constructed
to form constructed bodies having a shape of heat exchangers 100 as
shown in FIG. 1, and the heat exchangers were subjected to brazing
using a condition selected from the below-described three
conditions. In each case, the brazing was performed in a nitrogen
atmosphere in a furnace.
[0134] In the condition 1, the assembly was heated from a room
temperature to 570.degree. C., kept at 570.degree. C. for 4
minutes, subsequently hearted to 600.degree. C., and held at
600.degree. C. for 2 minutes.
[0135] In condition 2, the assembly was continuously heated to
600.degree. C., and held at 600.degree. C. for 2 minutes, where the
assembly passed the temperature range from 530 to 575.degree. C.
for 6 minutes.
[0136] In condition 3, the assembly was continuously heated to
600.degree. C., and held at 600.degree. C. for 2 minutes, where the
assembly passed the temperature range from 530 to 575.degree. C.
for 1 minutes.
[0137] After the brazing, each heat exchanger was subjected to
evaluation of brazability. In each case, a tube 3 of 100 mm in
length containing 33 joint portions joined to the fin 4 was cut out
from the heat exchanger. In each of the joint portion, a proportion
of a length of the braze-joint to a width of fin (18 mm) was
examined, and a ratio was calculated from the result of examination
at 33 joint portions, and was shown in Table 4 as a joint ratio.
Based on the value of a joint ratio, the brazability was
evaluated.
[0138] In addition, after the brazing, each of heat exchangers 100
was subjected to sea water acetic acid test (SWAAT) for 20 days to
evaluate the corrosion resistance. After the test, the depth of
corrosion of the tube 3, and the residual ratio of fin 4 (total
length of fins remaining after the test/total length of brazed
fins.times.100) were measured. The results were shown in Table
4.
[0139] From the results shown in Table 4, the followings was
understood.
[0140] If the coated amount of Si is small, the separation of fin 4
occurs remarkably. Whereas, if the coated amount of Si is too
large, the corrosion resistance of the tube 3 is deteriorated and
the separation of the fins is increased (See Nos. 1 to 6).
[0141] If the coated amount of the flux is too small, the tube 3
has inferior corrosion resistance, and the failure of joint
formation with the fin 4 increases. If the coated amount of flux is
too large, the separation of the fin 4 occurs remarkably (See Nos.
1 to 7).
[0142] If the coated amount of binder is too small or too large,
the tube 3 has inferior corrosion resistance (See Nos. 16 and
17).
[0143] Where a side surface of the tube has an arc shape in a cross
section, a perimeter of the arc, that is, a perimeter b of the
portion not-coated with the brazing composition preferably
satisfies b.ltoreq.a.times.1.5, where a denotes a thickness of the
tube 3. In sample No. 18, where the ratio of b/a exceeds 1.50,
occurrence of separation of fins 4 slightly increases, resulting in
inferior residual ratio of fin.
[0144] Even though the side surface of the tube 3 has an arc shape,
sample No. 21 in which b.ltoreq.a.times.1.5 is satisfied is
superior both in corrosion resistance and residual ratio of
fins.
[0145] If the assembly passes through the temperature range of 530
to 575.degree. C. during the heating process with a relatively long
time of 6 minutes, it is possible to improve the corrosion
resistance of the tube 3 (see No. 19), and it is possible to
suppress the separation of the fin 4. However, if the assembly
passes through the temperature range of 530 to 575.degree. C.
during the heating process with a relatively short time of 1
minutes, separation of the fins 4 increases (see No. 20).
[0146] Sample No. 23 in which each side surface was made of two
flat faces forming an angle .theta. of 90.degree. and satisfying
b=a.times.1.41 showed superior corrosion resistance of the tube and
a better residual ratio of the fins.
[0147] A target value of corrosion depth of the tube was 75 .mu.m
or less, and a target value of a residual ratio of the fin was 70%
or more.
Example 2
[0148] Heat exchangers 100 were produced in the same manner as in
Example 1, while the tubes were made of aluminum alloy having a
composition shown in Table 5. The depth of corrosion in the tube 3
and the residual ratio of fins 4 were examined in the same manner
as in Example 1. The results are shown in Table 5. In this case,
brazing composition of No. 4 shown in Table 4 was applied as a
coating composition.
TABLE-US-00005 TABLE 5 Fin-tube Corrosion Residual Mn Si joint
ratio depth of tube ratio of fins Tube (mass %) (mass %) Al (%)
(.mu.m) (%) Remark 24 0.13 0.35 balance 95 115 80 25 0.21 0.35
balance 96 75 78 26 0.30 0.35 balance 94 72 76 27 0.39 0.35 balance
95 70 72 28 0.47 0.35 balance 95 72 73 Excessive Mn, Reduced
Extrudability 29 0.30 0.15 balance 96 102 78 30 0.30 0.26 balance
96 72 75 31 0.30 0.44 balance 95 75 70 32 0.30 0.52 balance 95 75
72 Excessive silicon, Reduced Extrudability
[0149] As shown in Table 5, the corrosion resistance of the tube 3
and the residual ratio of fins 4 vary depending on the Mn content
and the Si content of the tube 3. Therefore, preferable contents in
the present invention were specified to be 0.15 to 0.45% by mass of
Mn and 0.20 to 0.50% by mass of Si.
Example 3
[0150] Heat exchangers 100 were produced in a same manner as in
Example 1, while the fins were made of aluminum alloy having a
composition shown in Table 6. The depth of corrosion in the tube 3
and the residual ratio of fins 4 were examined in the same manner
as in Example 1. The results are shown in Table 6. In this case, a
brazing composition of No. 4 shown in Table 4 was applied as the
coating composition.
TABLE-US-00006 TABLE 6 Fin-tube Corrosion Residual joint depth of
ration of Zn Si Fe Mn Zr V Cr ratio tube fins Fin (mass %) (mass %)
(mass %) (mass %) (mass %) (mass %) (mass %) (%) (.mu.m) (%) Remark
33 1.1 0.95 0.5 1.2 0.13 0.05 0.05 95 105 92 34 1.3 0.95 0.5 1.2
0.13 -- 0.05 96 75 74 35 1.5 0.95 0.5 1.2 0.13 0.05 -- 94 70 78 36
1.7 0.95 0.5 1.2 -- 0.05 0.05 95 71 76 37 2.0 0.95 0.5 1.2 0.13 --
-- 95 92 60 38 1.5 0.6 0.5 1.2 0.13 -- -- 96 113 61 39 1.5 0.8 0.5
1.2 0.13 0.05 0.05 96 75 75 40 1.5 1.1 0.5 1.2 0.13 0.05 0.05 95 73
78 41 1.5 1.25 0.5 1.2 0.13 -- -- 95 90 60 42 1.5 0.95 0.25 1.2
0.13 -- -- 94 107 60 43 1.5 0.95 0.41 1.2 0.13 0.05 0.05 95 72 80
44 1.5 0.95 0.69 1.2 0.13 0.05 0.05 96 75 81 45 1.5 0.95 0.85 1.2
0.13 -- -- 94 85 60 46 1.5 0.95 0.5 0.85 0.13 0.05 0.05 95 105 72
47 1.5 0.95 0.5 1.1 0.13 0.05 0.05 95 73 75 48 1.5 0.95 0.5 1.39
0.13 0.05 0.05 96 75 70 49 1.5 0.95 0.5 1.2 0.1 0.05 0.05 96 74 74
50 1.5 0.95 0.5 1.2 0.15 0.05 0.05 96 75 73 51 1.5 0.95 0.5 1.52
0.13 -- -- 96 105 62 52 1.5 0.95 0.5 1.2 0.04 -- -- 95 82 72 Low
strength fin 53 1.5 0.95 0.5 1.2 0.22 -- -- 95 80 76 Processability
of fin was reduced 54 1.5 0.95 0.5 1.2 -- 0.004 -- 96 85 75 Low
strength fin 55 1.5 0.95 0.5 1.2 -- 0.02 -- 95 75 73 56 1.5 0.95
0.5 1.2 -- 0.08 -- 94 75 72 57 1.5 0.95 0.5 1.2 -- 0.12 -- 94 82 71
Processability of fin was reduced 58 1.5 0.95 0.5 1.2 -- -- 0.004
95 89 75 Low strength fin 59 1.5 0.95 0.5 1.2 -- -- 0.02 96 75 71
60 1.5 0.95 0.5 1.2 -- -- 0.08 95 75 72 61 1.5 0.95 0.5 1.2 -- --
0.12 95 80 74 Processability of fins was reduced
[0151] As shown in Table 6, the corrosion resistance of the tube 3
and the residual ration of fin 4 vary depending on the amounts of
constituent elements of the aluminum alloy constituting the fin.
Therefore it was discovered that the Zn, Si, Fe, and Mn contents in
the aluminum alloy of the fins were required to be 1.20 to 1.80% by
mass of Zn, 0.70 to 1.20% by mass of Si, 0.30 to 0.80% by mass of
Fe, and 0.90 to 1.50% by mass of Mn so as to achieve a high joint
ratio of fin-tube joint, to provide high resistivity, and to
increase a high residual ratio of fins. With respect to Zr, V, and
Cr, it was discovered that preferable ranges of those elements in
the fin of the present invention were 0.05 to 0.20% by mass of Zr,
0.01 to 0.10% by mass of V, and 0.01 to 0.10% by mass of Cr.
Example 4
[0152] Heat exchangers 100 were produced in the same manner as in
Example 1, while the header pipes were made of aluminum alloy
having a composition shown in Table 7. The depth of corrosion in
the tube 3 and the residual ratio of fins 4 were examined in the
same manner as in Example 1 (Table 7, Nos. 62 to 66).
[0153] Heat exchangers 100 were produced in a same manner as in
Example 1, while the header pipes were constituted of a three
layered structure comprising a brazing material layer on the outer
surface, and a sacrificial layer on the inner surface of the
aluminum alloy constituting the core layer. The depth of corrosion
in the tube 3 and residual ratio of fins 4 were examined in the
same manner as in Example 1 (Table 7, No. 67).
[0154] The results are shown in Table 6. The brazing composition of
No. 4 shown in Table 4 was applied as a coating composition.
TABLE-US-00007 TABLE 7 Sacrificial corrosion Corrosion Residual
Core material protection material Brazing material Fin-tube depth
of ratio of Header Mn Zn Si joint ratio tube fin pipe (mass %) Al
(mass %) Al (mass %) Al (%) (.mu.m) (%) 62 1.25 balance 0.55
balance 9.75 balance 95 75 70 63 1.25 balance 0.7 balance 9.75
balance 96 73 72 64 1.25 balance 1.1 balance 9.75 balance 96 70 76
65 1.25 balance 3.0 balance 9.75 balance 95 68 79 66 1.25 balance
No sacrificial 9.75 96 265 25 layer 67 1.25 balance 0.7 balance
9.75 balance 96 245 28
[0155] In sample 65, corrosion resistance of the header was
relatively low.
[0156] As shown in FIG. 7, a corrosion resistance of the tube 3 and
the residual ratio of the fins 4 tend to be inferior when the
content of Zn in the alloy forming the sacrificial layer is lower
or higher than a certain range of composition (No. 62, No. 65).
Therefore, in the present invention, the preferable content of Zn
in the sacrificial corrosion protection material of the header pipe
was specified to be 0.60 to 1.20% by mass.
[0157] When the header pipe was constituted of a three-layered
structure having a sacrificial corrosion protection material in the
internal side and brazing material in the outer side, the residual
ratio of the fin 4 was deteriorated (No. 67 of Table 7).
[0158] When the header pipe was constituted of two layered
structure having an outer brazing material but lacking outer
sacrificial corrosion protection material, as shown in sample No.
66 of Table 7, a corrosion resistance of the tube and the residual
ratio of the fins were deteriorated.
[0159] 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.
* * * * *