U.S. patent application number 10/543386 was filed with the patent office on 2006-07-13 for heat exchanger and process for fabricating same.
This patent application is currently assigned to SHOWA DENKO K.K.. Invention is credited to Yoshinori Nakata.
Application Number | 20060151155 10/543386 |
Document ID | / |
Family ID | 36652099 |
Filed Date | 2006-07-13 |
United States Patent
Application |
20060151155 |
Kind Code |
A1 |
Nakata; Yoshinori |
July 13, 2006 |
Heat exchanger and process for fabricating same
Abstract
A heat exchanger (1) which comprises a plurality of flat hollow
bodies (2) arranged in parallel, and an aluminum fin (3) disposed
between each pair of adjacent flat hollow bodies (2) and brazed
thereto. The flat hollow body (2) is made from two plates (6) of an
aluminum clad material comprising an aluminum core and a cladding
of Al--Si brazing material covering at least one outer surface of
the core, by brazing peripheral edges of the two plates to each
other. The core of the clad material is made of an alloy containing
0.4 to 1.5 mass % of Cu and the balance Al and inevitable
impurities. A line graph representing variations in potential
relative to the depth of a surface layer portion of an outer
surface of the flat hollow body (2) from the outermost surface
thereof to a depth of 100 .mu.m has a potential gradient of at
least 0.25 mV at points on the line of the graph. The heat
exchanger can be fabricated easily at a low cost and has
satisfactory resistance to pitting corrosion.
Inventors: |
Nakata; Yoshinori; (Mt.
Sterling, OH) |
Correspondence
Address: |
OBLON, SPIVAK, MCCLELLAND, MAIER & NEUSTADT, P.C.
1940 DUKE STREET
ALEXANDRIA
VA
22314
US
|
Assignee: |
SHOWA DENKO K.K.
13-9, Shiba Daimon 1-chome Minato-ku
Tokyo
JP
1058518
|
Family ID: |
36652099 |
Appl. No.: |
10/543386 |
Filed: |
January 27, 2004 |
PCT Filed: |
January 27, 2004 |
PCT NO: |
PCT/JP04/00712 |
371 Date: |
July 26, 2005 |
Current U.S.
Class: |
165/133 ;
165/134.1; 165/176 |
Current CPC
Class: |
F28F 21/089 20130101;
F28D 1/0341 20130101; B23K 1/0012 20130101; F28F 21/084 20130101;
B23K 2101/14 20180801 |
Class at
Publication: |
165/133 ;
165/134.1; 165/176 |
International
Class: |
F28F 13/18 20060101
F28F013/18; F28F 19/00 20060101 F28F019/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 27, 2003 |
JP |
2003-016903 |
Claims
1. A heat exchanger which comprises a plurality of flat hollow
bodies arranged in parallel and each having a fluid passage
portion, and an aluminum fin disposed between each pair of adjacent
flat hollow bodies and brazed thereto and wherein a refrigerant
flowing thereinto through a fluid inlet flows through the fluid
passage portions of all the flat hollow bodies and is run off
through a fluid outlet, each of the flat hollow bodies being made
from an aluminum clad material having an aluminum core and a
cladding of Al--Si alloy brazing material covering at least an
outer surface of the core, the core of the clad material being made
of an alloy containing 0.4 to 1.5 mass % of Cu and the balance Al
and inevitable impurities, a line graph representing variations in
potential relative to the depth of a surface layer portion of an
outer surface of the flat hollow body from the outermost surface
thereof to a depth of 100 .mu.m having a potential gradient of at
least 0.25 mV at points on the line of the graph.
2. A heat exchanger according to claim 1 wherein the flat hollow
body is made from two plates of an aluminum clad material having an
aluminum core and a cladding of Al--Si brazing material covering
opposite surfaces of the core, by brazing peripheral edges of the
two plates to each other, the flat hollow body having between the
two plates a bulging fluid passage portion and a tank portion
communicating with the fluid passage portion.
3. A heat exchanger according to claim 1 wherein the core of the
aluminum clad material forming the flat hollow body further
contains 0.4 to 1.5 mass % of Mn.
4. A heat exchanger according to claim 1 wherein the core of the
aluminum clad material forming the flat hollow body further
contains 0.06 to 0.35 mass % of Ti.
5. A heat exchanger according to claim 1 wherein the core of the
aluminum clad material forming the flat hollow body contains up to
0.4 mass % of Si as an inevitable impurities.
6. A heat exchanger according to claim 1 wherein the core of the
aluminum clad material forming the flat hollow body contains up to
0.3 mass % of Fe as an inevitable impurities.
7. A heat exchanger according to claim 1 wherein the core of the
aluminum clad material forming the flat hollow body contains up to
0.4 mass % of Mg as an inevitable impurities.
8. A vehicle having an air conditioner comprising a compressor, a
condenser and an evaporator and adapted for use with a
chlorofluorocarbon refrigerant, the evaporator comprising a heat
exchanger according to any one of claims 1 to 7.
9. A process for fabricating a heat exchanger which comprises a
plurality of flat hollow bodies arranged in parallel and each
having a fluid passage portion, and an aluminum fin disposed
between each pair of adjacent flat hollow bodies and brazed thereto
and wherein a refrigerant flowing thereinto through a fluid inlet
flows through the fluid passage portions of all the flat hollow
bodies and is run off through a fluid outlet, the process being
characterized in that the process includes making each of the flat
hollow bodies from an aluminum clad material having an aluminum
core and a cladding of Al--Si brazing material covering at least an
outer surface of the core, the core being made of an alloy
containing 0.4 to 1.5 mass % of Cu and the balance Al and
inevitable impurities, and brazing the fin to the pair of flat
hollow bodies by maintaining a temperature of at least 550.degree.
C. for 5 to 45 minutes.
10. A process for fabricating a heat exchanger according to claim 9
wherein the fin and the pair of flat hollow bodies are quenched to
400.degree. C. at a cooling rate of at least 50.degree. C./min
after heating for the brazing.
11. A process for fabricating a heat exchanger according to claim 9
which includes making the flat hollow body from two plates of an
aluminum clad material having an aluminum core and a cladding of
Al--Si brazing material covering opposite surfaces of the core, by
brazing peripheral edges of the two plates to each other, and the
plates are brazed for making the flat hollow body simultaneously
with the brazing of the fin.
12. A process for fabricating a heat exchanger according to claim 9
wherein the brazing is effected by vacuum brazing.
13. A process for fabricating a heat exchanger according to claim 9
wherein the core of the aluminum clad material forming the flat
hollow body further contains 0.4 to 1.5 mass % of Mn.
14. A process for fabricating a heat exchanger according to claim 9
wherein the core of the aluminum clad material forming the flat
hollow body further contains 0.06 to 0.35 mass % of Ti.
15. A process for fabricating a heat exchanger according to claim 9
wherein the core of the aluminum clad material forming the flat
hollow body contains up to 0.4 mass % of Si as an inevitable
impurities.
16. A process for fabricating a heat exchanger according to claim 9
wherein the core of the aluminum clad material forming the flat
hollow body contains up to 0.3 mass % of Fe as an inevitable
impurities.
17. A process for fabricating a heat exchanger according to claim 9
wherein the core of the aluminum clad material forming the flat
hollow body contains up to 0.4 mass % of Mg as an inevitable
impurities.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is an application filed under 35 U.S.C.
.sctn.111(a) claiming the benefit pursuant to 35 U.S.C.
.sctn.119(e) (1) of the filing date of Provisional Application No.
60/449, 876 filed Feb. 27, 2003 pursuant to 35 U.S.C.
.sctn.111(b).
TECHNICAL FIELD
[0002] The present invention relates to heat exchangers and a
process for fabricating the same, and more particularly to heat
exchanges for use as condensers or evaporators for motor vehicle
air conditioners wherein a chlorofluorocarbon refrigerant is used,
gas coolers or evaporators for motor vehicle air conditioners
wherein CO.sub.2 refrigerant is used, motor vehicle oil coolers and
motor vehicle radiators, and also to a process for producing the
exchanger.
[0003] The term "aluminum" as used herein and in the appended
claims includes aluminum alloys in addition to pure aluminum.
[0004] Furthermore, the term "potential" as used herein and in the
appended claims refers to a potential as measured in a 5 wt. % NaCl
aqueous solution having a pH of 3 using a saturated calomel
electrode.
BACKGROUND ART
[0005] Evaporators for use in motor vehicle air conditioners
wherein a chlorofluorocarbon refrigerant is used include those of
the layered type which are widely known. Such layered evaporators
comprise a plurality of flat hollow bodies arranged in parallel and
brazed to and communicating with one another each at at least one
of upper and lower ends thereof, and a corrugated aluminum fin
disposed between each pair of adjacent flat hollow bodies and
brazed thereto. The refrigerant flowing into the evaporator through
a fluid inlet flows through fluid passage portions of all the flat
hollow bodies and is run off through a fluid outlet. The flat
hollow body is made from two plates of aluminum brazing sheet which
has an aluminum core and a cladding of Al--Si brazing material
covering opposite surfaces of the core, by brazing the peripheral
edges of the two plates to each other. Between the two plates, the
hollow body has a bulging refrigerant channel (fluid passage
portion) and bulging tank portions communicating with the
refrigerant channel. The adjacent flat hollow bodies in each pair
are brazed to and communicate with each other (see, for example,
the publications of JP-A No. 1997-264635 and JP-A No. 2001-324293).
With this evaporator, the two plates of aluminum brazing sheet are
brazed to each other for forming each flat hollow body
simultaneously with the brazing of the corrugated fin to the hollow
body by the vacuum brazing method.
[0006] The aluminum brazing sheets already known for use in making
the flat hollow body include one comprising a core which is made
from an alloy containing at least 0.3 mass % to less than 0.6 mass
% of Mn, over 0.6 mass % to up to 1.0 mass % of Cu, less than 0.1
mass % of Si, up to 0.3 mass % of Fe and 0.06 to 0.35 mass % of Ti,
and the balance aluminum and inevitable impurities, and a cladding
made of an Al--Si alloy brazing material having a limited Ca
content of up to 0.006 mass % (see, for example, the publication of
JP-A No. 2000-135588).
[0007] With the evaporator flat hollow body disclosed in the
publications of JP-A No. 1997-264635 and JP-A No. 2001-324293, the
surface of the hollow body is conventionally subjected to a
chromate treatment so as to give improved corrosion resistance.
However, the treatment requires cumbersome work. Furthermore,
Cr.sup.6+ is harmful and necessitates a troublesome waste liquid
treatment. The evaporator therefore has the problem of being
cumbersome to fabricate. Moreover, use of Cr.sup.6+ is to be
prohibited in the near future in Europe.
[0008] It is also likely that pitting corrosion resistance can not
be expected of the flat hollow body made from the aluminum brazing
sheet disclosed in the publication of JP-A No. 2000-135588, unless
the body is subjected to the chromate treatment.
[0009] An object of the present invention is to overcome the above
problem and to provide a heat exchanger which has satisfactory
resistance to pitting corrosion and which can be fabricated easily
at a lost cost, and a process for fabricating the same.
DISCLOSURE OF THE INVENTION
[0010] The present invention provides a heat exchanger which
comprises a plurality of flat hollow bodies arranged in parallel
and each having a fluid passage portion, and an aluminum fin
disposed between each pair of adjacent flat hollow bodies and
brazed thereto and wherein a refrigerant flowing thereinto through
a fluid inlet flows through the fluid passage portions of all the
flat hollow bodies and is run off through a fluid outlet, each of
the flat hollow bodies being made from an aluminum clad material
having an aluminum core and a cladding of Al--Si alloy brazing
material covering at least an outer surface of the core, the core
of the clad material being made of an alloy containing 0.4 to 1.5
mass % of Cu and the balance Al and inevitable impurities, a line
graph representing variations in the potential of a surface layer
portion of an outer surface of the flat hollow body from the
outermost surface thereof to a depth of 100 .mu.m relative to the
depth having a potential gradient of at least 0.25 mV at points on
the line of the graph.
[0011] With the heat exchanger of the present invention, each of
the flat hollow bodies is made from an aluminum clad material
having an aluminum core and a cladding of Al--Si alloy brazing
material covering at least the outer surface of the core, and the
core of the clad material is made of an alloy containing 0.4 to 1.5
mass % of Cu and the balance Al and inevitable impurities. A line
graph representing variations in the potential of a surface layer
portion of the outer surface of the flat hollow body from the
outermost surface thereof to a depth of 100 .mu.m relative to the
depth has a potential gradient of at least 0.25 mV at points on the
line of the graph. Accordingly, the flat hollow body can be
prevented from pitting although the body is not subjected to the
chromate treatment. Moreover, the heat exchanger can be fabricated
by a process including making each flat hollow body from the
aluminum clad material described and brazing a fin to each pair of
adjacent flat hollow bodies, with a temperature of at least
550.degree. C. maintained for the brazing for 5 to 45 minutes, and
is therefore easy and inexpensive to fabricate.
[0012] With the heat exchanger of the present invention, the flat
hollow body may be made from two plates of an aluminum clad
material having an aluminum core and a cladding of Al--Si brazing
material covering opposite surfaces of the core, by brazing
peripheral edges of the two plates to each other, the flat hollow
body having between the two plates a bulging fluid passage portion
and a tank portion communicating with the fluid passage
portion.
[0013] The flat hollow body to be used may comprise an aluminum
clad tube which is made from a hollow billet and which has an
aluminum core and a cladding of Al--Si alloy brazing material
covering at least the outer surface of the core. Alternatively, the
flat hollow body may be made by forming a plate of an aluminum clad
material having an aluminum core and a cladding of Al--Si brazing
material covering opposite surfaces of the core. The flat hollow
body is not limited to these examples.
[0014] With the heat exchanger of the present invention, the core
of the aluminum clad material forming the flat hollow body may
further contain 0.4 to 1.5 mass % of Mn. The core of the aluminum
clad material forming the flat hollow body may further contain 0.06
to 0.35 mass % of Ti. The core of the aluminum clad material
forming the flat hollow body may contain up to 0.4 mass % of Si as
an inevitable impurities. The core of the aluminum clad material
forming the flat hollow body may contain up to 0.3 mass % of Fe as
an inevitable impurities. The core of the aluminum clad material
forming the flat hollow body may contain up to 0.4 mass % of Mg as
an inevitable impurities. In these cases, the flat hollow body is
given further improved resistance to pitting corrosion.
[0015] The present invention provides a vehicle having an air
conditioner comprising a compressor, a condenser and an evaporator
and adapted for use with a chlorofluorocarbon refrigerant, the
evaporator comprising the heat exchanger described above.
[0016] The present invention provides a process for fabricating a
heat exchanger which comprises a plurality of flat hollow bodies
arranged in parallel and each having a fluid passage portion, and
an aluminum fin disposed between each pair of adjacent flat hollow
bodies and brazed thereto and wherein a refrigerant flowing
thereinto through a fluid inlet flows through the fluid passage
portions of all the flat hollow bodies and is run off through a
fluid outlet, the process being characterized in that the process
includes making each of the flat hollow bodies from an aluminum
clad material having an aluminum core and a cladding of Al--Si
brazing material covering at least an outer surface of the core,
the core being made of an alloy containing 0.4 to 1.5 mass % of Cu
and the balance Al and inevitable impurities, and brazing the fin
to the pair of flat hollow bodies by maintaining a temperature of
at least 550.degree. C. for 5 to 45 minutes.
[0017] The heat exchanger described above can be fabricated
relatively easily and inexpensively by the process of the
invention.
[0018] In the heat exchanger fabricating process of the invention,
it is desirable that the fin and the pair of flat hollow bodies be
quenched to 400.degree. C. at a cooling rate of at least 50.degree.
C./min after heating for the brazing.
[0019] The heat exchange fabricating process of the invention may
include making the flat hollow body from two plates of an aluminum
clad material having an aluminum core and a cladding of Al--Si
brazing material covering opposite surfaces of the core, by brazing
peripheral edges of the two plates to each other, and the plates
are brazed for making the flat hollow body simultaneously with the
brazing of the fin. The brazing may be effected by vacuum
brazing.
[0020] With the heat exchanger fabricating process of the
invention, the core of the aluminum clad material forming the flat
hollow body may further contain 0.4 to 1.5 mass % of Mn. The core
of the aluminum clad material forming the flat hollow body may
further contain 0.06 to 0.35 mass % of Ti. The core of the aluminum
clad material forming the flat hollow body may contain up to 0.4
mass % of Si as an inevitable impurities. The core of the aluminum
clad material forming the flat hollow body may contain up to 0.3
mass % of Fe as an inevitable impurities. The core of the aluminum
clad material forming the flat hollow body contains up to 0.4 mass
% of Mg as an inevitable impurities.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] FIG. 1 is a perspective view partly exploded and showing a
layered evaporator embodying the invention. FIG. 2 is a line graph
representing variations in the potential of a surface layer portion
of the outer surface of each of flat hollow bodies of the
evaporator shown in FIG. 1 from the outermost surface thereof to a
depth of 100 .mu.m relative to the depth.
[0022] FIG. 3 is a graph showing a heating pattern in Examples and
Comparative Example.
BEST MODE OF CARRYING OUT THE INVENTION
[0023] An embodiment of the invention will be described below with
reference to the drawings.
[0024] FIG. 1 shows a layered evaporator embodying the present
invention.
[0025] With reference to FIG. 1, the layered evaporator 1 is for
use in vehicles, such as motor vehicles equipped with a motor air
conditioner (refrigeration cycle) wherein a chlorofluorocarbon
refrigerant is used and which has a compressor, condenser and
evaporator, the evaporator being adapted for use in the
refrigeration cycle. The evaporator 1 comprises a plurality of flat
hollow bodies 2 arranged in parallel and brazed to and
communicating with one another each at the upper end thereof, and a
corrugated aluminum fin 3 disposed between each pair of adjacent
flat hollow bodies 2 and brazed thereto. The refrigerant flowing
into the evaporator through a fluid inlet 4 flows through all the
flat hollow bodies 2 and is run off through a fluid outlet 5.
[0026] The flat hollow body 2 is made from two plates 6 of aluminum
brazing sheet (clad material) which has an aluminum core and a
cladding of Al--Si brazing material covering opposite surfaces of
the core, by brazing the peripheral edges of the two plates 6 to
each other. Between the two plates, the hollow body has a generally
U-shaped bulging refrigerant channel 7 (fluid passage portion) and
bulging tank portions 8 communicating with respective opposite ends
of the refrigerant channel 7.
[0027] The core of the aluminum brazing sheet making the plates 6
is made of an alloy containing 0.4 to 1.5 mass % of Cu and the
balance Al and inevitable impurities. FIG. 2 shows a line graph
representing variations in the potential of a surface layer portion
X of each of the inner and outer surfaces of the flat hollow body 2
from the outermost surface thereof to a depth of 100 .mu.m relative
to the depth. The line graph has a potential gradient of at least
0.25 mV at points on the line of the graph.
[0028] With the core of the aluminum brazing sheet making the plate
6, Cu is an element required to make the potential gradient not
smaller than 0.25 mV to thereby give the flat hollow body 2
improved resistance to pitting corrosion. If the Cu content is less
than 0.4 mass %, the above potential can not be made at least 0.25
mV, whereas if the content is over 1.5 mass %, the core material
itself exhibits impaired corrosion resistance. Accordingly, the Cu
content of the core should be 0.4 to 1.5 mass %. Furthermore, the
line graph representing variations in the potential of the surface
layer portion of the outer surface of the flat hollow body 2 from
the outermost surface thereof to a depth of 100 .mu.m relative to
the depth should have a potential gradient not smaller than 0.25 mV
at points on the line of the graph because if the potential
gradient is less than 0.25 mV, satisfactory resistance to pitting
corrosion is not available. Preferably, the potential gradient is
at least 0.30 mV.
[0029] The core of the aluminum brazing sheet making the plate 6
may further contain 0.4 to 1.5 mass % of Mn. The presence of Mn in
the core affords further improved resistance to pitting corrosion,
whereas if the content is less than 0.4 mass %, satisfactory
pitting corrosion resistance is not available. When the content is
in excess of 1.5 mass %, the core exhibits an excessive strength to
entail the likelihood that the clad material will not be formed
into the hollow body smoothly. When the core contains Mn, it is
therefore desirable that the content thereof be 0.4 to 1.5 mass
%.
[0030] The core of the aluminum brazing sheet making the plate 6
may further contain 0.06 to 0.35 mass % of Ti. The presence of Ti
in the core produces a stratifying effect to give further improved
pitting corrosion resistance, whereas if the content is less than
0.06 mass %, it is impossible to produce improved resistance to
pitting corrosion. If the Mn content is in excess of 0.35 mass %,
the material is difficult to produce. Accordingly, when present in
the core, Ti is contained preferably in an amount of 0.06 to 0.35
mass %.
[0031] The amount of Si to be present as an inevitable impurity in
the core of the aluminum brazing sheet making the plate 6 is
preferably up to 0.4 mass % because if the Si content is in excess
of 0.4 mass %, impaired resistance to pitting corrosion is likely
to result.
[0032] The amount of Fe to be present as an inevitable impurity in
the core of the aluminum brazing sheet making the plate 6 is
preferably up to 0.3 mass % because if the Fe content is in excess
of 0.3 mass %, impaired resistance to pitting corrosion is likely
to result.
[0033] The amount of Mg to be present as an inevitable impurity in
the core of the aluminum brazing sheet making the plate 6 is
preferably up to 0.4 mass % because if the Mg content is in excess
of 0.4 mass %, impaired resistance to pitting corrosion is likely
to result.
[0034] The layered evaporator 1 is fabricated in the following
manner.
[0035] A plurality of plates 6 of the aluminum brazing sheet
described above are prepared, and combinations of plates 6 each
comprising two plates 6 are arranged in parallel, with a corrugated
fin 3 disposed between each pair of adjacent combinations. The
resulting arrangement is heated to braze the two plates 6 of each
combination to each other, form a flat hollow body, braze the upper
end portions of each pair of adjacent flat hollow bodies to each
other and braze the corrugated fin 3 to the adjacent flat follow
bodies 2. For the brazing, the arrangement is held heated at a
temperature of at least 550.degree. C. for 5 to 45 minutes. The
heating temperature for brazing is limited to a temperature of at
least 550.degree. C. because we have found that the period of time
during which the arrangement is held heated at the temperature of
at least 550.degree. C. exerts a great influence on the potential
gradient of the points on the line graph representing variations in
the potential of the surface layer portion of the outer surface of
the brazed flat hollow body 2 from the outermost surface thereof to
a depth of 100 .mu.m relative to the depth. The upper limit of the
heating temperature is about 600.degree. C. Further the period of
time for holding the temperature of at least 550.degree. C. for
brazing is limited to 5 to 45 minutes because if the period is less
than 5 minutes, the arrangement is difficult to braze, whereas if
the period is in excess of 45 minutes, it is impossible to make the
potential gradient not smaller than 0.25 mV after brazing and to
obtain satisfactory resistance to pitting corrosion. Preferably,
the heating time is 15 to 30 minutes.
[0036] It is desirable that the assembly resulting from brazing by
heating be quenched to 400.degree. C. at a cooling rate of at least
50.degree. C./min because if the cooling rate is lower than
50.degree. C./min, the brazing operation is likely to result in
impaired resistance to pitting corrosion. Preferably, the cooling
rate is at least 100.degree. C./min.
[0037] In this way, the layered evaporator 1 is fabricated.
[0038] The layered evaporator 1 thus embodied provides a
refrigeration cycle wherein a chlorofluorocarbon refrigerant is
used, along with a compressor and a condenser, for use as a vehicle
air conditioner in a vehicle, e.g., in a motor vehicle.
Alternatively, the heat exchanger obtained is used as the condenser
of the refrigeration cycle. Further alternatively, the heat
exchanger is installed in a motor vehicle as an oil cooler or a
radiator.
[0039] The heat exchanger of the invention may be installed in
vehicles, such as motor vehicles, equipped with an air conditioner
which has a compressor, gas cooler, intermediate heat exchanger,
expansion valve and evaporator and wherein a CO.sub.2 refrigerant
is used, for use as the gas cooler or evaporator of the air
conditioner.
[0040] According to the foregoing embodiment, the flat hollow body
2 is made from two plates 6 of the brazing sheet described above by
brazing the plates to each other, whereas the material for making
the hollow body is not limited only to the sheet. The flat hollow
body may comprise an aluminum clad tube having a core in the form
of a flat tube made from an alloy containing 0.4 to 1.5 mass % of
Cu, and the balance Al and inevitable impurities, and a cladding of
Al--Si alloy brazing material covering at least the outer
peripheral surface of the core having inner and outer peripheral
surfaces. This clad tube may be made by forming the brazing sheet
into a flat tube and brazing opposite edge portions of the tube to
each other. Alternatively, the clad tube may be formed by extruding
a hollow billet which comprises a hollow body provided by the above
core and having a cast Al--Si alloy brazing material at least
around the outer of the inner and outer peripheral surfaces of the
hollow body. The clad tube may be formed from an extruded tube
containing 0.4 to 1.5 mass % of Cu, and the balance Al and
inevitable impurities, by immersing the tube in a molten Al--Si
alloy brazing material to thereby cover at least the outer of the
inner and outer peripheral surfaces of the tube with the brazing
material. Furthermore, the flat hollow body is not limited to these
examples.
[0041] The present invention will be described below in detail with
reference to Examples and Comparative Example.
EXAMPLES 1-11 AND COMPARATIVE EXAMPLE 1
[0042] Rectangular aluminum brazing sheets were prepared which
comprise a core made from one of the four kinds of alloys shown in
Table 1 and having a thickness of 0.4 mm, and cladding of JIS A4004
covering each of opposite surfaces of the core. Each sheet had a
cladding ratio of 15%. A recessed portion is formed by press work
in the entire portion of each aluminum brazing sheet except at a
peripheral edge portion thereof. TABLE-US-00001 TABLE 1 Composition
(mass %) Alloy Al Cu Mn Ti Si Fe Mg A Bal. 0.4 0.8 0.2 0.1 0.2 0.2
B Bal. 0.6 0.6 0.2 0.1 0.2 0.1 C Bal. 0.8 0.6 0.2 0.1 0.2 0.1 D
Bal. 1.0 0.5 0.2 0.1 0.2 0.1
[0043] Subsequently two aluminum brazing sheets of the same kind
were fitted together in combination, with the recessed portions
facing toward each other and the peripheral edge portions thereof
in contact with each other. The combination was heated to
550.degree. C. in a vacuum heating furnace, thereafter further
heated to 600.degree. C., and quenched to 400.degree. C. at a
cooling rate of at least 100.degree. C./min, whereby the two sheets
were brazed to each other to obtain a flat hollow body. The same
procedure as above was repeated by holding combinations of sheets
heated at a temperature of at least 550.degree. C. for brazing for
varying periods of time T.
[0044] A line graph was determined which represented variations in
the potential of surface layer portions of the inner and outer
surfaces of each flat hollow body, each from the outermost surface
to a depth of 100 .mu.m, relative to the depth. The line graphs had
a potential gradient of at least 0.25 mV at points on the line of
each graph in Examples 1 to 11, whereas the graph of Comparative
Example 1 had a potential gradient of less than 0.25 mV at points
on the line of the graph. Table 2 shows the average of the
potential gradients at the points on each of the lines for Examples
1 to 11 and Comparative Example 1.
[0045] The flat hollow bodies were further subjected to a SWAAT
960-hr test and checked for the resulting corrosion. Table 2 shows
the maximum corrosion depth in each of the flat hollow bodies
tested. TABLE-US-00002 TABLE 2 Average Maximum Temp. holding
potential Corrosion time gradient Depth Alloy (T, min) (mV/.mu.m)
(mm) Example 1 A 5 0.265 0.18 Example 2 A 15 0.263 0.19 Example 3 A
30 0.255 0.21 Example 4 B 5 0.323 0.11 Example 5 B 15 0.317 0.12
Example 6 B 30 0.305 0.12 Example 7 B 45 0.278 0.11 Example 8 C 5
0.335 0.11 Example 9 C 30 0.318 0.09 Example 10 D 5 0.343 0.08
Example 11 D 30 0.320 0.09 Comp. Ex. 1 B 60 0.236 Penetrating
INDUSTRIAL APPLICABILITY
[0046] The heat exchanger of the present invention is suitable for
use as the evaporator or condenser of motor vehicle air
conditioners adapted, for example, for use with a
chlorofluorocarbon refrigerant.
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