U.S. patent application number 14/118852 was filed with the patent office on 2014-07-03 for alloys for a heat exchanger tube having an inner protective cladding and brazed disrupter.
This patent application is currently assigned to Constellium France. The applicant listed for this patent is CONSTELLIUM FRANCE. Invention is credited to Lionel Gerber, Sylvain Henry, Elodie Perrin.
Application Number | 20140182821 14/118852 |
Document ID | / |
Family ID | 46321062 |
Filed Date | 2014-07-03 |
United States Patent
Application |
20140182821 |
Kind Code |
A1 |
Perrin; Elodie ; et
al. |
July 3, 2014 |
ALLOYS FOR A HEAT EXCHANGER TUBE HAVING AN INNER PROTECTIVE
CLADDING AND BRAZED DISRUPTER
Abstract
The invention relates to an assembly of two brazing sheets the
first one of which consists of a 3xxx alloy clad on one surface
with a 1xxx alloy, the second one of which consists of an AA3xxx
alloy clad on both surfaces thereof with a 4xxx alloy, which are
assembled together by brazing so as to form a disrupted channel for
the flow of exhaust gases, in particular for an engine vehicle.
Inventors: |
Perrin; Elodie;
(Obersaashem, FR) ; Henry; Sylvain; (Saint Jean de
Moirans, FR) ; Gerber; Lionel; (Colmar, FR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
CONSTELLIUM FRANCE |
Paris |
|
FR |
|
|
Assignee: |
Constellium France
Paris
FR
|
Family ID: |
46321062 |
Appl. No.: |
14/118852 |
Filed: |
May 3, 2012 |
PCT Filed: |
May 3, 2012 |
PCT NO: |
PCT/FR2012/000177 |
371 Date: |
February 5, 2014 |
Current U.S.
Class: |
165/109.1 |
Current CPC
Class: |
Y02T 10/12 20130101;
F28F 19/06 20130101; F28D 2020/0008 20130101; F28D 21/0003
20130101; C22C 21/00 20130101; F28F 21/084 20130101; F28D 2021/0082
20130101; B32B 15/016 20130101; F28F 3/025 20130101; F02B 29/045
20130101; Y02T 10/146 20130101; F02M 26/29 20160201 |
Class at
Publication: |
165/109.1 |
International
Class: |
F28F 21/08 20060101
F28F021/08 |
Foreign Application Data
Date |
Code |
Application Number |
May 20, 2011 |
FR |
1101559 |
Claims
1-13. (canceled)
14. An assembly of two brazing sheets, comprising: a first sheet
comprising an AA3xxx alloy clad on one face with an AA1xxx alloy, a
second sheet comprising an AA3xxx aluminum alloy clad on both faces
thereof with an AA4xxx alloy, wherein said two sheets are assembled
to each other by brazing, so as to form a closed channel and/or
tube with an internal turbulator, inside which exhaust gas can
flow, optionally exhaust gas from an automobile vehicle, alone
and/or in association with another fluid, optionally air, and
further wherein a face of the channel exposed to said gas is said
face coated with said AA1xxx alloy in the first sheet forming the
channel, and wherein the second sheet forms the internal
turbulator.
15. The assembly of two brazing sheets according to claim 14,
wherein said second brazing sheet comprises an aluminum alloy with
the following composition (% by weight): Si: 0.3-1.0 Fe<1.0 Cu:
0.3-1.0 Mn: 0.3-2.0 Mg: 0.3-3.0 Zn<6.0 Ti<0.1 Zr<0.3
Cr<0.3 Ni<2.0 Co<2.0 Bi<0.5 Y<0.5, other elements
<0.05 each and 0.15 total, remainder being aluminum, And further
wherein said second brazing sheet is clad on two faces thereof with
an aluminum brazing alloy comprising from 4% to 15% of silicon and
from 0.01% to 0.5% of at least one of Ag, Be, Bi, Ce, La, Pb, Pd,
Sb, Y and/or Mischmetall, said two sheets being assembled to each
other by fluxless brazing under a protective atmosphere.
16. The assembly of two brazing sheets according to claim 15,
wherein said second sheet comprises an aluminum alloy with the
following composition (% by weight): Si: 0.3-1.0 Fe<0.5 Cu:
0.35-1.0 Mn: 1.0-2.0 Mg: 0.35-0.7 Zn<0.2 Ti<0.1 Zr<0.3
Cr<0.3 Ni<1.0 Co<1.0 Bi<0.5 Y<0.5 other elements
<0.05 each and 0.15 total, remainder being aluminum, wherein
said second sheet is clad on two faces thereof with an aluminum
brazing alloy comprising from 4% to 15% of silicon and from 0.01%
to 0.5% of at least one of Ag, Be, Bi, Ce, La, Pb, Pd, Sb, Y and/or
Mischmetall, said two sheets being assembled together by fluxless
brazing under a protective atmosphere.
17. The assembly of two brazing sheets according to claim 14,
wherein said assembly is provided with at least one fin and/or
separator on an outside face of the first sheet forming the
channel, said fin and/or separator comprising an aluminum alloy
core sheet with the following composition (% by weight): Si:
0.3-1.0 Fe<1.0 Cu: 0.3-1.0 Mn: 0.3-2.0 Mg: 0.3-3.0 Zn<6.0
Ti<0.1 Zr<0.3 Cr<0.3 Ni<2.0 Co<2.0 Bi<0.5
Y<0.5 other elements <0.05 each and 0.15 total, remainder
being aluminum, clad on two faces thereof with an aluminum brazing
alloy comprising from 4% to 15% of silicon and from 0.01% to 0.5%
of at least one of Ag, Be, Bi, Ce, La, Pb, Pd, Sb, Y and/or
Mischmetall, and said fin and/or separator being assembled on the
channel by fluxless brazing under a protective atmosphere.
18. The assembly of two brazing sheets according to claim 14,
wherein said assembly is provided with at least one fin and/or
separator on an outside face of the first sheet forming the
channel, said fin and/or separator comprising an aluminum alloy
core sheet with the following composition (% by weight): Si:
0.3-1.0 Fe<0.5 Cu: 0.35-1.0 Mn: 1.0-2.0 Mg: 0.35-0.7 Zn<0.2
Ti<0.1 Zr<0.3 Cr<0.3 Ni<1.0 Co<1.0 Bi<0.5
Y<0.5 other elements <0.05 each and 0.15 total, remainder
being aluminum, clad on two faces thereof with an aluminum brazing
alloy comprising from 4% to 15% of silicon and from 0.01% to 0.5%
of at least one of Ag, Be, Bi, Ce, La, Pb, Pd, Sb, Y and/or
Mischmetall, and assembled on the channel by fluxless brazing under
a protective atmosphere.
19. The assembly of two brazing sheets according to claim 14,
wherein the channel is coated on an outside face thereof with a
cladding layer made from an AA4xxx alloy and fitted with at least
one fin and/ or separator on said cladding layer, and being
assembled by brazing.
20. The assembly of two brazing sheets according to claim 14,
wherein the channel is made from a core sheet comprising an
aluminum alloy with the following composition (% by weight): Si:
0.3-1.0 Fe<1.0 Cu: 0.3-1.0 Mn: 0.3-2.0 Mg: 0.3-3.0 Zn<6.0
Ti<0.1 Zr<0.3 Cr<0.3 Ni<2.0 Co<2.0 Bi<0.5
Y<0.5 other elements <0.05 each and 0.15 total, remainder
being aluminum, clad on an outside face thereof with an aluminum
brazing alloy containing from 4% to 15% of silicon and from 0.01%
to 0.5% of at least one of Ag, Be, Bi, Ce, La, Pb, Pd, Sb, Y and/or
Mischmetall, and said channel being fitted with at least one fin
and/or separator on the clad, and being assembled by fluxless
brazing under a protective atmosphere.
21. The assembly of two brazing sheets according to claim 14,
wherein the channel is made from a core sheet comprising an
aluminum alloy with the following composition (% by weight): Si:
0.3-1.0 Fe<0.5 Cu: 0.35-1.0 Mn: 1.0-2.0 Mg: 0.35-0.7 Zn<0.2
Ti<0.1 Zr<0.3 Cr<0.3 Ni<1.0 Co<1.0 Bi<0.5
Y<0.5 other elements <0.05 each and 0.15 total, remainder
being aluminum, clad on an outside face thereof with an aluminum
brazing alloy comprising from 4% to 15% of silicon and from 0.01%
to 0.5% of at least one of Ag, Be, Bi, Ce, La, Pb, Pd, Sb, Y and/or
Mischmetall, and said channel being fitted with at least one fin
and/or separator on said clad and being assembled by fluxless
brazing under a protective atmosphere.
22. The assembly of two brazing sheets according to claim 14,
wherein said assembly forms part of a heat exchanger.
23. The assembly of two brazing sheets according to claim 22,
wherein said assembly forms at least part of a heat exchanger known
under the term EGRC (Exhaust Gas Recirculation Cooler) in which
only exhaust gas from an automobile vehicle flows.
24. The assembly of two brazing sheets according to claim 22,
wherein said assembly forms at least part of a heat exchanger known
under the term CAC (Charged Air Cooler) in an EGR (Exhaust Gas
Recirculation) loop, inside which a mix of fresh air and exhaust
gas from an automobile vehicle flows.
25. A heat exchanger tube in which exhaust gas flows, optionally
automobile vehicle exhaust gas, alone or associated with another
fluid, optionally air, comprising an assembly of brazing sheets
according to claim 14.
26. A heat exchanger comprising at least one tube according to
claim 25.
Description
FIELD OF THE INVENTION
[0001] The invention relates to the field of brazing sheets for
heat exchanger tubes made from aluminum alloys, particularly those
used for cooling or optimization of engine efficiency, and heating
or air conditioning of the passenger compartment.
[0002] This is particularly applicable to heat exchanger tubes
subject to a severely corrosive environment such as charged air
cooler tubes through which exhaust gas circulation takes place, and
usually provided with a turbulator designed to improve heat
exchange by increasing the exchange surface area and disturbing
internal fluid circulation.
STATE OF THE ART
[0003] Aluminum alloys are used for the fabrication of most
automobiles heat exchangers due to their low density which enables
a weight saving, particularly compared with copper alloys, while
giving good thermal conduction, ease of use and good resistance to
corrosion.
[0004] All aluminum alloys referred to in the following are
designated using the designations defined by the Aluminum
Association in Registration Record Series that it publishes
regularly, unless mentioned otherwise.
[0005] Exchangers comprise tubes for the circulation of internal
fluid and fins or separators, and possibly a turbulator to increase
heat transfer between the internal fluid and the external fluid,
and they are fabricated either by mechanical assembly or by
brazing.
[0006] In the case of Charged Air Coolers, known to those skilled
in the art under the term CAC, the normal configuration is that the
core sheet making up the tube (usually called the tube strip)
usually made from AA3xxx aluminum alloy, is coated on its external
and internal faces with an alloy called the brazing alloy, usually
in the AA4xxx series. This has the advantage that it melts at a
temperature below the core melting temperature and, through
application of a thermal brazing cycle, can create a bond between
two materials to be assembled, in other words brazed, or possibly
to bond the tube strip onto itself so as to close the tube by
brazing, the alternative being welding.
[0007] This configuration is shown in FIG. 1, the core of the tube
strip being referenced as mark 2 and its internal and external
brazing alloy clads being referenced as mark 1. The separators
placed between the different tube rows are composed of an unclad
AA3xxx alloy. Similarly, the turbulators that are inserted into the
tubes are also made from an AA3xxx alloy and are not clad. Inserts
are brazed on the tubes by the 4xxx clad on the outside face of the
tube. The turbulators are brazed in the tubes by the 4xxx clad on
the inside face of the tube. The AA3xxx alloys used for the
separators and turbulators may or may not be identical. The AA3xxx
alloy used for the tube core is usually a so-called "long-life"
alloy, in other words it has good resistance to external saline
corrosion.
[0008] FIG. 2 shows a diagram of such a turbulator tube, the tube
being referenced as mark 1, the turbulator as mark 3 and the
brazing alloy clads as mark 2.
[0009] An example is given in application EP 0283937 A1 by Nihon
Radiator Co. Ltd.
[0010] At the moment there are engine designs in which exhaust
gases are reinjected into the charged air cooler to be mixed with
clean air and returned to the inlet, with the final purpose of
reducing polluting emissions of vehicles.
[0011] In this configuration, exhaust gases that could condense can
generate a particularly severe corrosive environment in the cooler,
characterized particularly by a low pH (that can significantly be
less than 3).
[0012] In the case of a tube configuration according to the state
of the art as described above, a significant diffusion of silicon
contained in the cladding AA4xxx alloy to the core alloy forming
the core of the tube occurs during the brazing operation, thereby
degrading its resistance to corrosion.
[0013] One solution known to those skilled in the art consists of
inserting intermediate cladding during co-rolling, made from an
AA1xxx or AA7xxx alloy, between the tube core alloy and its
internal coating made from AA4xxx brazing alloy.
[0014] Such a configuration is diagrammatically shown in FIG. 3,
the tube core being referenced as mark 3, the outside coating made
from an AA4xxx alloy being referenced as mark 4, the inside coating
also made from an AA4xxx alloy being referenced as mark 1, and
intermediate coating made from an AA1xxx or AA7xxx alloy being
referenced as mark 2.
[0015] Such a coating acts by limiting diffusion of silicon from
the internal cladding to the tube core during brazing, thus
improving its corrosion resistance.
[0016] A sacrificial alloy typically in the AA7xxx series, may also
be used as the intermediate cladding alloy.
[0017] These "multi-clad" sheets are known to those skilled in the
art and are disclosed particularly in applications JP 2003027166 A
by Kobe Steel Ltd. Shinko Alcoa, JP 2005224851 A by Shinko Alcoa
Kizai KK, WO 2006/044500 A2 and WO 2009/142651 A2 by Alcoa Inc, WO
2007/042206 A1 by Corus Aluminium Walzprodukte GmbH, US
2010/0159272 A1 by Novelis, etc.
[0018] The use of this type of "multi-clad" sheets in a charged air
cooler through which exhaust gas passes is disclosed in application
WO 2008/063855 by Modine Mfg Co.
[0019] Another solution disclosed in applications EP 1762810 A1 and
US 2007/0051503 A1 by Behr America Inc., consists of favoring the
creation of a "brown band" known to those skilled in the art,
between the AA3xxx alloy core of the turbulator and its cladding
composed of an AA4xxx alloy (typically AA4045), during the
conventional type brazing inside the tube. The tube is also
typically made from an AA3xxx alloy clad with AA4xxx on both sides.
In one highly preferred embodiment, the tube and the turbulator are
actually composed of the same material.
[0020] However, although such configurations can slightly improve
the resistance of the tube to corrosion, they may be insufficient
under particularly severe load conditions, which is the case for
heat exchangers subject to recirculation of exhaust gases,
characterized particularly by a low pH.
[0021] Other solutions consist of application of a surface
treatment after brazing to improve the internal corrosion
resistance of the tube. This is the case of the solution disclosed
in application FR 2916525 A1 by Valeo Systemes Thermiques, that
recommends a coating based on resins. Another example of a surface
treatment, in this case an electro-ceramic deposit, is given in
application WO 2010/019664. Application FR 2930023 by Valeo
Systemes Thermiques mentions the possibility of boehmiting the
entire exchanger. Finally, application EP 1906131 A2 by
International Truck discloses a solution consisting of applying a
metal surface treatment based on Ni or Co on the inside face of the
tube and on the turbulator.
[0022] Finally, other solutions lie in the use of a combination of
different materials, particularly aluminum and stainless steel.
Application WO2008/095578 by Behr GmbH & Co. thus claims the
use of stainless steel for the disrupter, the tube being made from
aluminum while application EPI906127 by International Truck
discloses an aluminum tube with stainless steel clad on the inside
face, still with a stainless steel turbulator.
[0023] However, such options are too expensive to provide an
industrially satisfactory product.
PROBLEM THAT ARISES
[0024] The invention is aimed at optimizing the choice of materials
or brazing sheets made from aluminum alloys designed for production
of exchanger tubes with brazed turbulator to improve their
resistance in a severe corrosive environment like that created by
recirculation of automobile vehicle exhaust gases, without
increasing the quantity of materials used or dimensions or the
weight, and for which manufacturing conditions (ease of use and
cost) starting from brazing sheets are at least equivalent to
solutions according to prior art.
PURPOSE OF THE INVENTION
[0025] The purpose of the invention is an assembly of two brazing
sheets, the first being composed of a AA3xxx clad on one face with
on a AA1xxx alloy, and the second sheet being composed of an AA3xxx
aluminum alloy clad on both faces with an AA4xxx alloy, the two
sheets being assembled to each other by brazing, so as to form a
closed channel or tube with an internal turbulator, inside which
exhaust gases flow, particularly exhaust gases from an automobile
vehicle, alone or in association with another fluid, typically air,
the face of the channel exposed to these gases or to this mix being
the face coated with the 1xxx alloy in the first sheet forming the
channel, the second forming the internal turbulator.
[0026] According to one preferred embodiment, the second brazing
sheet is composed of an aluminum alloy with the following
composition (% by weight):
[0027] Si: 0.3-1.0 Fe<1.0 Cu: 0.3-1.0 Mn: 0.3-2.0 Mg: 0.3-3.0
Zn<6.0 Ti<0.1 Zr<0.3 Cr<0.3 Ni<2.0 Co<2.0
Bi<0.5 Y<0.5, other elements <0.05 each and 0.15 total,
the remainder being aluminum,
[0028] clad on its two faces with an aluminum brazing alloy
containing 4 to 15% of silicon and 0.01 to 0.5% of at least one of
the elements Ag, Be, Bi, Ce, La, Pb, Pd, Sb, Y or Mischmetall, said
two sheets being assembled to each other by flux-free brazing under
a protective atmosphere.
[0029] According to an even more preferred embodiment, the second
sheet forming the turbulator is composed of an aluminum alloy with
the following composition (% by weight): Si: 0.3-1.0 Fe<0.5 Cu:
0.35-1.0 Mn: 1.0-2.0 Mg: 0.35-0.7 Zn<0.2 Ti<0.1 Zr<0.3
Cr<0.3 Ni<1.0 Co<1.0 Bi<0.5 Y<0.5 other elements
<0.05 each and 0.15 total, the remainder being aluminum,
[0030] clad on its two faces with an aluminum brazing alloy
containing 4 to 15% of silicon and 0.01 to 0.5% of at least one of
the elements Ag, Be, Bi, Ce, La, Pb, Pd, Sb, Y or Mischmetall, said
two sheets always being assembled together by fluxless brazing
under a protective atmosphere.
[0031] Furthermore, the first brazing sheet forming a channel or a
tube, may be provided with fins or separators on its outside face,
themselves made from an aluminum alloy core sheet with the
following composition (% by weight):
[0032] Si: 0.3-1.0 Fe<1.0 Cu: 0.3-1.0 Mn: 0.3-2.0 Mg: 0.3-3.0
Zn<6.0 Ti<0.1 Zr<0.3 Cr<0.3 Ni<2.0 Co<2.0
Bi<0.5 Y<0.5 other elements <0.05 each and 0.15 total, the
remainder being aluminum, clad on its two faces with an aluminum
brazing alloy containing 4 to 15% of silicon and 0.01 to 0.5% of at
least one of the elements Ag, Be, Bi, Ce, La, Pb, Pd, Sb, Y or
Mischmetall, and assembled on the channel or tube by fluxless
brazing under a protective atmosphere.
[0033] Preferably, said fins or separators are made from a core
sheet made from aluminum alloy with composition (% by weight):
[0034] Si: 0.3-1.0 Fe<0.5 Cu: 0.35-1.0 Mn: 1.0-2.0 Mg: 0.35-0.7
Zn<0.2 Ti<0.1 Zr<0.3 Cr<0.3 Ni<1.0 Co<1.0
Bi<0.5 Y<0.5 other elements <0.05 each and 0.15 total, the
remainder being aluminum, clad on its two faces with an aluminum
brazing alloy containing 4 to 15% of silicon and 0.01 to 0.5% of at
least one of the elements Ag, Be, Bi, Ce, La, Pb, Pd, Sb, Y or
Mischmetall, and assembled on the channel or tube by fluxless
brazing under a protective atmosphere.
[0035] According to another variant, the brazing sheet forming the
channel or the tube is coated on the outside face of said channel
or tube with a cladding layer made from an AA4xxx alloy and fitted
with fins or separators on this coat, assembled by brazing.
[0036] Furthermore, the channel or tube may be made from a core
sheet made from an aluminum alloy with the following composition (%
by weight):
[0037] Si: 0.3-1.0 Fe<1.0 Cu: 0.3-1.0 Mn: 0.3-2.0 Mg: 0.3-3.0
Zn<6.0 Ti<0.1 Zr<0.3 Cr<0.3 Ni<2.0 Co<2.0
Bi<0.5 Y<0.5 other elements <0.05 each and 0.15 total, the
remainder being aluminum, clad on its outside face with an aluminum
brazing alloy containing 4 to 15% of silicon and 0.01 to 0.5% of at
least one of the elements Ag, Be, Bi, Ce, La, Pb, Pd, Sb, Y or
Mischmetall, and fitted with fins or separators on this layer
assembled by fluxless brazing under a protective atmosphere.
[0038] Also preferably, the channel or tube may be made from a core
sheet made from an aluminum alloy with the following composition (%
by weight):
[0039] Si: 0.3-1.0 Fe<0.5 Cu: 0.35-1.0 Mn: 1.0-2.0 Mg: 0.35-0.7
Zn<0.2 Ti<0.1 Zr<0.3 Cr<0.3 Ni<1.0 Co<1.0
Bi<0.5 Y<0.5 other elements <0.05 each and 0.15 total, the
remainder being aluminum, clad on its outside face with an aluminum
brazing alloy containing 4 to 15% of silicon and 0.01 to 0.5% of at
least one of the elements Ag, Be, Bi, Ce, La, Pb, Pd, Sb, Y or
Mischmetall, and fitted with fins or separators on this layer
assembled by fluxless brazing under a protective atmosphere.
[0040] Finally, these brazing sheets may advantageously be used in
the composition of turbulator tubes in a heat exchanger,
particularly of the type known under the term EGRC (Exhaust Gas
Recirculation Cooler) in which only the exhaust gases from an
automobile vehicle flow, or of the type known under the term CAC
(Charged Air Cooler) in an EGR (Exhaust Gas Recirculation) loop,
inside which a mix of fresh air and exhaust gases from an
automobile vehicle flows.
[0041] The invention also applies to this type of heat exchanger
tube in which exhaust gases flow, particularly automobile vehicle
exhaust gases, alone or associated with another fluid, typically
air, made from said brazing sheets and also applies to a heat
exchanger comprising at least one tube of this type.
DESCRIPTION OF THE FIGURES
[0042] FIG. 1 shows a brazing sheet with three layers, the core
sheet being referenced as mark 2 and the brazing alloy (also called
the cladding layer), present on each of the faces of the core being
referenced as mark 1.
[0043] FIG. 2 diagrammatically shows a tube 1 with turbulator 3, a
fin or separator (not shown), outside the tube, that can be
assembled on the external face of the tube by brazing. Similarly,
the turbulator is assembled on the inside face of the tube by
brazing. To achieve this, the two faces of the tubes are coated
with a material called the brazing or cladding material, usually in
the AA4xxx series (mark 2 in the figure).
[0044] FIG. 3 diagrammatically shows the brazing sheet used for the
tube in FIG. 2, but in which an intermediate cladding made from an
AA1xxx or AA7xxx alloy has been inserted between the tube core
alloy and its internal coating made from an AA4xxx brazing
alloy.
[0045] The tube core is referenced as mark 3, the outside coating
made from an AA4xxx alloy is referenced as mark 4, the inside
coating also made from an AA4xxx alloy is referenced as mark 1, and
the intermediate coating made from an AA1xxx or AA7xxx alloy is
referenced as mark 2.
[0046] FIG. 4 diagrammatically shows a tube 1 with a turbulator 4
according to the invention, said turbulator itself being composed
of a brazing sheet clad, and the tube 1 also being made from a
brazing sheet composed of a core sheet, typically made from an
AA3xxx alloy, coated on the inside face of the tube with a cladding
layer 3 made from an AA1xxx alloy and on the outside face with an
AA4xxx brazing alloy layer 2, on which uncoated fins are
brazed.
DESCRIPTION OF THE INVENTION
[0047] The invention consists of selecting the most appropriate
aluminum alloys forming the brazing sheets used to make channels or
tubes of a heat exchanger with a turbulator, more particularly
adapted to exchanger tubes subjected to a severe corrosive
environment particularly such as tubes through which exhaust gases
from an automobile vehicle recirculate.
[0048] The turbulator placed inside the tube will be designed
precisely to disturb internal fluid circulation and to increase
heat exchange with the outside medium.
[0049] This turbulator typically consists of a sheet corrugated
along its length similar to an exchanger fin or separator, at least
within the scope of the invention, this embodiment being well known
to those skilled in the art, as mentioned in the "State of the art"
section.
[0050] Still for elements considered within the scope of the
invention, both the tube and the disrupter are made by bending and
assembly of brazing sheets, using usual methods known to those
skilled in the art.
[0051] The turbulator is assembled inside the tube by brazing. The
brazing sheet forming the turbulator is made from a core sheet made
from an AA3xxx alloy, coated on its two faces with a cladding layer
made from a AA4xxx brazing alloy, for this purpose.
[0052] The tube itself is composed of another brazing sheet
consisting of a core sheet made from an AA3xxx alloy, and the
invention consists particularly of forming a lining by cladding on
the tube inside face, by selecting an AA1xx alloy for this
purpose.
[0053] According to the invention, this tube may be coated on its
outside face with a cladding layer made from an AA4xxx alloy to
enable brazing of uncoated fins, also called separators, on said
outside face of the tube or possibly brazing of the tube on
itself.
[0054] The different alloy clads making up the brazing sheets may
typically be made by co-rolling, a frequently used method known to
those skilled in the art.
[0055] Patent EP 1687456 B1 issued by the applicant discloses a
brazing sheet composition consisting of a core sheet made from an
AA3xxx alloy coated on one or both faces with an AA4xxx brazing
alloy making fluxless brazing possible under a controlled
atmosphere (also called a protective atmosphere), typically of
nitrogen and/or argon, in a furnace used in a standard manner for
use of the Nocolok.RTM. process.
[0056] This brazing sheet is composed of a core sheet made from an
aluminum alloy with the following composition (% by weight):
[0057] Si: 0.3-1.0 Fe<1.0 Cu: 0.3-1.0 Mn: 0.3-2.0 Mg: 0.3-3.0
Zn<6.0 Ti<0.1 Zr<0.3 Cr<0.3 Ni<2.0 Co<2.0
Bi<0.5 Y<0.5 other elements <0.05 each and 0.15 total, the
remainder being aluminum,
[0058] coated on at least one face with an aluminum brazing alloy
containing 4 to 15% of silicon and 0.01 to 0.5% of at least one of
the elements Ag, Be, Bi, Ce, La, Pb, Pd, Sb, Y or Mischmetall.
[0059] An even more preferred composition for the core alloy is as
follows (% by weight): Si: 0.3-1.0 Fe<0.5 Cu: 0.35-1.0 Mn:
1.0-2.0 Mg: 0.35-0.7 Zn<0.2 Ti<0.1 Zr<0.3 Cr<0.3
Ni<1.0 Co<1.0 Bi<0.5 Y<0.5 other elements <0.05 each
and 0.15 total, the remainder being aluminum, and the coating(s)
remaining unchanged.
[0060] According to two preferred embodiments of the invention,
this first type of sheet and more advantageously the second type
coated on both faces, is selected for making the turbulator, that
can thus be assembled by fluxless brazing under a protective
atmosphere inside the tube, thus resulting in a considerable cost
saving and preventing any risk related to the possible entrainment
of residual flux into the circuit.
[0061] Similarly these two alloy compositions in the same coating
configuration on two faces, can advantageously be used for making
fins or separators and their assembly by fluxless brazing on the
uncoated, outside face of the tube or channel, in other words
directly on the core AA3xxx alloy of the tube, in contact with the
AA4xxx alloy of the fins according to the above-mentioned preferred
compositions.
[0062] Obviously, still according to the invention, it would also
be possible to coat the outside of the tube or channel with a
cladding layer of AA4xxx brazing alloy, so that clad or unclad
standard fins or separators could be assembled to it by
brazing.
[0063] Furthermore, the two types of sheets with the
above-mentioned compositions may advantageously be used for making
the tube or channel itself, always coated on the inside face with a
cladding layer made from an AA1xxx alloy and on its outside face
with an AA4xxx brazing alloy enabling fluxless brazing of standard
fins under a protective atmosphere.
[0064] Obviously, the invention is very useful particularly for
heat exchangers comprising this type of tube and more particularly
heat exchangers known to those skilled in the art under the name
EGRC (Exhaust Gas Recirculation Cooler), in which only the exhaust
gases from an automobile vehicle flow or of the type known as
Charged Air Cooler (CAC) in an EGR (Exhaust Gas Recirculation) loop
inside which a mix of fresh air and automobile vehicle exhaust gas
mix flows, in both cases particularly corrosive media.
[0065] Details of the invention will be better understood after
reading the following examples that are in no way limitative.
EXAMPLES
[0066] Several sheets of 3916 core alloy and AA4045 brazing alloy
were cast with AA1050 alloy sheets and one sheet of each alloy 3920
and 4945.
[0067] The 3916 alloy had the following composition (% by
weight):
[0068] Si: 0.18 Fe: 0.15 Cu: 0.65 Mn: 1.35 Ti: 0.08 other elements
<0.05 each and 0.15 total, remainder being aluminum,
[0069] The 3920 alloy had the following composition (% by
weight):
[0070] Si: 0.5 Fe: 0.15 Cu: 0.5 Mn: 1.65 Mg: 0.5 Ti: 0.08 other
elements <0.05 each and 0.15 total, remainder being
aluminum.
[0071] The 4945 alloy is an AA4045 alloy that also contains 0.15%
of Bi.
[0072] Assemblies were made from these sheets to obtain the
cladding percentages (% total thickness) indicated in table 1
below, at the end of the transformation.
[0073] These assemblies were hot and then cold rolled to produce
0.40 mm thick clad strips for the tubes and 0.20 mm thick clad
strips for the turbulators. A 2 h restoration treatment at
280.degree. C. was then applied to these strips after a temperature
rise at a rate of 45.degree. C./h.
[0074] Tube mockups were fitted with turbulators brazed using the
Nocolok.RTM. process for references 1 to 3 in table 1 and fluxless
brazed for reference 4, with a temperature increase phase up to
600.degree. C. at a rate of about 40.degree. C./min, constant
temperature for 2 min at 600.degree. C. and then a temperature
reduction at a rate of about 50.degree. C./min, all under nitrogen
with a flow of 8 l/min.
[0075] The tested configurations are shown in table 1 below.
[0076] Configuration 1 applies to a simple tube made from a 3916
core alloy coated on its two faces with an AA4045 brazing alloy and
a turbulator made from a AA3003 alloy.
[0077] Configuration 2 is identical except for an additional and
intermediate layer of AA1050 alloy between the core and the AA4045
internal brazing alloy.
[0078] Configuration 3 according to the invention uses a tube made
from a 3916 core alloy coated on the outside with an AA4045 brazing
alloy and on the inside with an AA1050 brazing alloy and a
turbulator made from a 3916 core alloy coated on both sides with an
AA4045 brazing alloy.
[0079] Brazing for these three cases was done using the
Nocolok.RTM. process with flux.
[0080] Configuration 4 according to the invention uses a tube made
from a 3916 core alloy coated on the outside with an AA4045 brazing
alloy and on the inside with an AA1050 alloy and a turbulator made
from an AA3920 core alloy coated on both faces with a 4945 brazing
alloy (containing 0.15% of Bi) in accordance with the
above-mentioned preferred compositions.
[0081] In this case, brazing was done fluxless under a protective
atmosphere in accordance with the patent deposited by the
above-mentioned applicant.
TABLE-US-00001 TABLE 1 Configuration of mockups tested in corrosion
Tube Turbulator Ref. Material Material 1 4045 7.5%/3916/4045 7.5%
3003 2 4045 7.5%/3916/1050 15%/ 3003 4045 7.5% 3 4045 10%/3916/1050
10% 4045 10%/3916/4045 10% 4 4045 10%/3916/1050 10% 4945
10%/3920/4945 10%
[0082] The resistance of tubes to corrosion was tested by means of
a corrosion test alternating immersion and emersion in order to
reproduce the conditions applied to CAC (Charged Air Cooler) type
exchangers in an EGR (Exhaust Gas Recirculation) low pressure loop.
The detailed test conditions used are described in tables 2 and 3
below.
[0083] In practice, the test cycle consists of two repetitions of
steps 1, 2 and 3 and then three repetitions of steps 4, 5 and 6 and
the complete cycle is repeated four thousand times.
TABLE-US-00002 TABLE 2 Corrosion test parameters Repetition Step
Liquid Duration Temperature Position X 4000 X2 1 L1 15 s ambient
immersion 2 Air 45 s ambient emersion 3 Air 15 min 170.degree. C.
emersion X3 4 L1 15 s ambient immersion 5 Air 45 s ambient emersion
6 Air 15 min ambient emersion
TABLE-US-00003 TABLE 3 Composition of L1 used for the corrosion
test (in ppm) Sulfate Nitrate Acetic Formic Propanoic Chloride ions
ions acid acid acid ions pH 320 52 590 3167 474 20 2.5
[0084] Sulfate ions were introduced in the form of sulfuric acid,
nitrate ions in the form of acetic acid and chloride ions in the
form of hydrochloric acid.
[0085] For each tested configuration, the resistance to corrosion
was evaluated by metallographic observation on a cross-section of
the tube and of the turbulator.
[0086] The results obtained from characterizations made on samples
after 300 h are summarized in table 4 below.
TABLE-US-00004 TABLE 4 Characterization of the corrosion test after
300 h Tube-turbulator Ref. Tube Turbulator joints 1 Very severe,
Corrosion by Little corrosion. intergranular local pitting. No Some
separated corrosion. intergranular joints Some leaks corrosion 2
Severe, Corrosion by Little corrosion. intergranular local pitting.
No Some separated corrosion. intergranular joints Some leaks
corrosion 3 Very little and Intergranular Little corrosion. very
shallow corrosion No separated corrosion. No joints intergranular
corrosion 4 Very little and Intergranular Little corrosion. very
shallow corrosion No separated corrosion. No joints intergranular
corrosion
[0087] The tubes in configurations 1 and 2 have severe corrosion
that can result in perforations and a significant deterioration of
some brazing joints between the tube and the turbulator. The unclad
turbulators associated with this type of tube are only slightly
corroded.
[0088] On the other hand, configurations 3 and 4 according to the
invention show very little tube corrosion, often limited to
cladding. Corrosion of brazing joints is also limited. Turbulators
associated with this type of tube are significantly corroded.
However this situation is considered to be significantly
better.
[0089] A single perforation on a tube causes a leak in the complete
heat exchanger circuit. A leak on a turbulator causes a reduction
in the heat exchange quality of the exchanger.
[0090] Therefore it is easy to understand that it is more important
to maintain the integrity of the tube than the integrity of the
turbulator.
* * * * *