U.S. patent application number 12/956605 was filed with the patent office on 2011-03-24 for method for producing a split louver heat exchanger fin.
This patent application is currently assigned to CENTRUM EQUITIES ACQUISITION, LLC. Invention is credited to John A. Kolb.
Application Number | 20110067848 12/956605 |
Document ID | / |
Family ID | 39616878 |
Filed Date | 2011-03-24 |
United States Patent
Application |
20110067848 |
Kind Code |
A1 |
Kolb; John A. |
March 24, 2011 |
METHOD FOR PRODUCING A SPLIT LOUVER HEAT EXCHANGER FIN
Abstract
A method of manufacturing serpentine fins for assembly between
tubes in a heat exchanger core. The method includes providing a
flat metal strip and forming in the strip, multiple rows of split
louvers. Each row of split louvers has louvers formed in pairs of
adjacent, spaced louver banks extending across the width of the
strip. Each row includes ribs formed in the strip parallel to the
louver openings and extending across the pair of louver banks. The
metal strip has unformed portions extending across the strip width
between rows of split louvers for forming folds across the width of
the strip. After forming the rows of split louvers, pressure is
applied to the strip to cause the flat strip to buckle along the
unformed portions forming folds in the strip resulting in the
serpentine fin. Preferably, the strip has ribs formed both in the
center portion and along the edges.
Inventors: |
Kolb; John A.; (New Haven,
CT) |
Assignee: |
CENTRUM EQUITIES ACQUISITION,
LLC
Nashville
TN
|
Family ID: |
39616878 |
Appl. No.: |
12/956605 |
Filed: |
November 30, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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11622512 |
Jan 12, 2007 |
7866042 |
|
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12956605 |
|
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Current U.S.
Class: |
165/181 |
Current CPC
Class: |
B21D 53/02 20130101;
B21D 53/085 20130101; F28D 1/05383 20130101; F28F 1/128 20130101;
Y10T 29/4935 20150115; Y10T 29/496 20150115 |
Class at
Publication: |
165/181 |
International
Class: |
F28F 1/12 20060101
F28F001/12 |
Claims
1. A serpentine fin for assembly between tubes in a heat exchanger
core comprising a metal strip having a width between opposite strip
edges and a length greater than the width and having multiple rows
of split louvers, each row of split louvers comprising louvers
having openings extending in the direction of the strip length and
formed in a pair of adjacent, spaced louver banks extending across
at least a portion of the width of the strip, and including ribs
formed in the strip substantially parallel to the louver openings
adjacent the strip edges and in a center portion of the strip
between the strip edges and extending across the pair of louver
banks, the metal strip having unformed portions extending across
the strip width between rows of strip louvers and ribs, wherein the
strip has folds along the unformed portions extending across the
strip width such that the strip forms a serpentine shape with at
least one row of split louvers between adjacent folds, the folds
being adapted to contact the tubes in the heat exchanger core.
2. The serpentine fin of claim 1 wherein the ribs are elongated,
plastically deformed sections and include at least one angled leg
connected to an adjacent louver.
3. The serpentine fin of claim 1 wherein the louvers have ends
adjacent the unformed portions of the metal strip and wherein the
distance between the louver ends and the folds at the unformed
portions is substantially equal.
4. The serpentine fin of claim 1 wherein the metal strip has a
thickness and the ribs have a height extending from a plane of the
metal strip, and wherein the ratio of the height to the thickness
of the metal strip is between about 4 and 5.
5. The serpentine fin of claim 3 wherein the metal strip has a
thickness and the ribs have a height extending from a plane of the
metal strip, and wherein the ratio of the height to the thickness
of the metal strip is between about 4 and 5.
6. The serpentine fin of claim 1 wherein the louvers are formed at
an angle to a plane of the metal strip and the louver angle is
between about 26 degrees and about 32 degrees.
7. The serpentine fin of claim 5 wherein the louvers are formed at
an angle to a plane of the metal strip and the louver angle is
between about 26 degrees and about 32 degrees.
8. A serpentine fin for assembly between tubes in a heat exchanger
core comprising a metal strip having a width between opposite strip
edges and a length greater than the width and having multiple rows
of split louvers, each row of split louvers comprising louvers
having openings extending in the direction of the strip length and
formed in a pair of adjacent, spaced louver banks extending across
at least a portion of the width of the strip, and including ribs
formed in the strip substantially parallel to the louver openings
adjacent the strip edges and in a center portion of the strip
between the strip edges and extending across the pair of louver
banks, the ribs being elongated, plastically deformed sections and
including at least one angled leg connected to an adjacent louver,
the metal strip having unformed portions extending across the strip
width between rows of strip louvers and ribs, wherein the strip has
folds along the unformed portions extending across the strip width
such that the strip forms a serpentine shape with at least one row
of split louvers between adjacent folds, the folds being adapted to
contact the tubes in the heat exchanger core.
9. The serpentine fin of claim 8 wherein the louvers have ends
adjacent the unformed portions of the metal strip and wherein the
distance between the louver ends and the folds at the unformed
portions is substantially equal.
10. The serpentine fin of claim 9 wherein the metal strip has a
thickness and the ribs have a height extending from a plane of the
metal strip, and wherein the ratio of the height to the thickness
of the metal strip is between about 4 and 5.
11. The serpentine fin of claim 10 wherein the louvers are formed
at an angle to a plane of the metal strip and the louver angle is
between about 26 degrees and about 32 degrees.
12. A serpentine fin for assembly between tubes in a heat exchanger
core comprising a metal strip having a width between opposite strip
edges and a length greater than the width and having multiple rows
of split louvers, each row of split louvers comprising louvers
having openings extending in the direction of the strip length and
formed in a pair of adjacent, spaced louver banks extending
substantially across the width of the strip, and including ribs
formed in the strip substantially parallel to the louver openings
between the strip edges and extending across the pair of louver
banks, the metal strip having unformed portions free of louvers and
ribs extending across the strip width between rows of strip louvers
and ribs, wherein the strip has folds along the unformed portions
extending across the strip width such that the strip forms a
serpentine shape with at least one row of split louvers between
adjacent folds, the folds being adapted to contact the tubes in the
heat exchanger core.
13. The serpentine fin of claim 12 wherein the ribs are formed in
the strip adjacent the strip edges.
14. The serpentine fin of claim 12 wherein the ribs are formed in
the strip in a center portion of the strip.
15. The serpentine fin of claim 12 wherein the ribs are formed in
the strip adjacent the strip edges and in a center portion of the
strip.
16. The serpentine fin of claim 12 wherein the ribs are elongated,
plastically deformed sections and include at least one angled leg
connected to an adjacent louver.
17. The serpentine fin of claim 12 wherein the louvers have ends
adjacent the unformed portions of the metal strip and wherein the
distance between the louver ends and the folds at the unformed
portions is substantially equal.
18. The serpentine fin of claim 12 wherein the metal strip has a
thickness and the ribs have a height extending from a plane of the
metal strip, and wherein the ratio of the height to the thickness
of the metal strip is between about 4 and 5.
19. The serpentine fin of claim 12 wherein the louvers are formed
at an angle to a plane of the metal strip and the louver angle is
between about 26 degrees and about 32 degrees.
Description
[0001] This application is a divisional of U.S. application Ser.
No. 11/622,512 filed Jan. 12, 2007.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to the manufacture of heat
exchangers and, in particular, to the manufacture of a split louver
serpentine fin for heat exchanger cores.
[0004] 2. Description of Related Art
[0005] In the manufacturing of cores for motor vehicle radiators,
charge air coolers and other air-cooled heat exchangers, fins
formed from thin gauge metal strip such as copper or aluminum are
placed between and in contact with the tubes which carry the fluid
to be cooled. The heat exchanger core tubes typically extend
between the manifolds, or the inlet and outlet tanks, of the heat
exchanger. The fins are the chief heat exchange medium between the
coolant and the ambient air. The ability of the fins to transfer
heat from the tubes to the air passing over the fins greatly relies
on the design of the fins, with some including dimples or
protrusions to aid in the heat transfer. To increase the heat
transfer rate even further, louvers have been incorporated into the
fins. The louvers turbulate the air in a manner which has been
found to increase the efficiency of the radiator. The louver
configuration may be so-called full louvers, where each louver in
the row extends over essentially the entire distance between the
tubes, or split louvers, where two side-by-side banks of louvers
are employed in the row, so that each of the two louvers extends
over less than half of the distance between each tube.
[0006] Many heat exchangers employ serpentine fins, in which a fiat
metal strip is folded into convolutions to create the multiple fins
between spaced tubes. When louvers are incorporated into the fins,
the structural integrity of the fin is compromised, particularly
where serpentine fins are used. A process known as hard-tool
forming is typically used in forming the serpentine fin, wherein
the louvers are formed with a pair of dies which have a star
configuration for forming the convolutions at the same time. The
complexity of the dies and machinery for performing the formation
of the fins make the process costly. There has been progress made
in providing low-cost fin rolls for making ordinary louvered fins
by a process known as air-forming. In the air-forming process, the
rolls only need to have the die formation for the louvers, and the
star shape of the roll may be eliminated. As the rolls push out the
strip of metal having the cut and formed full louvers, backpressure
is applied at different locations to the metal strip to force the
metal to buckle, create the convolutions in the strip of metal, and
form the finished serpentine configuration in the desired fin per
inch density. However, the air-forming process often produces
convolutions that are more random in placement with respect to the
rows of louvers compared to the use of hard tooling. The use of the
air-forming process has been found to distort the full louvers,
change the angle of the louvers, and sometimes close the louver
opening altogether. Because of the difficulties in forming full
louver serpentine fins, it is believed that the air forming process
has not been used for split louvers (which offer better heat
transfer performance), and that it has been necessary to make split
louver serpentine fins solely with a hard tooling process.
SUMMARY OF THE INVENTION
[0007] Bearing in mind the problems and deficiencies of the prior
art, it is therefore an object of the present invention to provide
an improved method for manufacturing louvered serpentine fins using
an air-forming process.
[0008] It is another object of the present invention to provide a
method for manufacturing split louvered serpentine fins which is
cost-effective, yet produces a quality fin.
[0009] A further object of the invention is to provide a method for
manufacturing louvered serpentine fins with a louver which does not
decrease the structural integrity of the fin.
[0010] It is yet another object of the present invention to provide
a method for manufacturing split louvered serpentine fins which
results in fins having consistently high efficiency and heat
transfer rates.
[0011] Still other objects and advantages of the invention will in
part be obvious and will in part be apparent from the
specification.
[0012] The above and other objects, which will be apparent to those
skilled in the art, are achieved in the present invention which is
directed to a method of manufacturing serpentine fins for assembly
between tubes in a heat exchanger core. The method includes
providing a flat metal strip for making heat exchanger fins, the
strip having a width between opposite strip edges and a length
greater than the width and forming in the strip, while the strip is
substantially flat, multiple rows of split louvers. Each row of
split louvers has louvers with openings extending in the direction
of the strip length and formed in a pair of adjacent, spaced louver
banks extending at least a portion across of the width of the
strip. Each row includes ribs formed in the strip substantially
parallel to the louver openings and extending across the pair of
louver banks. The metal strip has unformed portions extending
across the strip width, between rows of split louvers and ribs, for
forming folds across the width of the strip. After forming the rows
of split louvers, an initial pressure is applied to the metal strip
to cause the substantially flat strip to buckle in the unformed
portions and begin to form folds in the strip. At least one row of
split louvers is between adjacent folds along the length of the
strip. Thereafter further pressure is applied to the metal strip to
complete formation of the folds of the strip to form the serpentine
fin. The distance between the adjacent folds conforms to the
desired spacing distance between the heat exchanger core tubes.
[0013] The ribs formed in the strip may be along the edges of the
strip or the ribs may be in a center portion between the edges.
Preferably, the strip will have ribs formed both in the center
portion and along the edges.
[0014] The ribs are elongated, plastically deformed sections and
may include at least one angled leg connected to an adjacent
louver. The ribs have a height extending from a plane of the metal
strip and the ratio of the height to the thickness of the metal
strip is preferably between about 4 and 5.
[0015] The louvers have ends adjacent the unformed portions of the
metal strip and after applying the further pressure to the metal
strip, the distance between the louver ends and the folds at the
unformed portions may be substantially equal. The louvers are
formed at an angle to a plane of the metal strip and the louver
angle is preferably between about 26 degrees and about 32
degrees.
[0016] During the formation of the split louvers and the folding of
the strip, the strip may be continually moving such that the
initial pressure is a backpressure applied by contacting the strip
at a first location and such that the further pressure is a further
backpressure applied by contacting the strip at a second location
downstream of the first location with respect to strip
movement.
[0017] In another aspect the invention is directed to a serpentine
fin for assembly between tubes in a heat exchanger core. The
serpentine fin comprises a metal strip having a width between
opposite strip edges and a length greater than the width and having
multiple rows of split louvers. Each row of split louvers comprises
louvers having openings extending in the direction of the strip
length and formed in a pair of adjacent, spaced louver banks
extending at least a portion across of the width of the strip. The
strip includes ribs formed in the strip substantially parallel to
the louver openings adjacent the strip edges and in a center
portion of the strip between the strip edges and extending across
the pair of louver banks. The metal strip has unformed portions
extending across the strip width between rows of strip louvers and
ribs, wherein the strip has folds along the unformed portions
extending across the strip width such that the strip forms a
serpentine shape with at least one row of split louvers between
adjacent folds. The folds are adapted to contact the tubes in the
heat exchanger core.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] The features of the invention believed to be novel and the
elements characteristic of the invention are set forth with
particularity in the appended claims. The figures are for
illustration purposes only and are not drawn to scale. The
invention itself, however, both as to organization and method of
operation, may best be understood by reference to the detailed
description which follows taken in conjunction with the
accompanying drawings in which:
[0019] FIG. 1 is a top plan view of a metal strip having split
louvers formed therein in accordance with the present
invention.
[0020] FIG. 2 is a cross sectional view of the split louvers of
FIG. 1 along line 2-2.
[0021] FIG. 3 is a close up view of the portion of FIG. 2 in the
vicinity of the end rib in the split louvers.
[0022] FIG. 4 is a close up view of the portion of FIG. 2 in the
vicinity of the center rib in the split louvers.
[0023] FIGS. 5-8 are side elevational views of an air forming
machine showing the forming of the louvers and ribs by fin rolls,
and the progression of the forming of the convolutions of the
serpentine strip.
[0024] FIG. 9 is a side view of a portion of a heat exchanger core
showing the serpentine split louver fin of the present invention
between heat exchanger core tubes.
[0025] FIG. 10 is an end view of a heat exchanger core showing the
serpentine split louver fin of the present invention between heat
exchanger core tubes.
[0026] FIG. 11 is a perspective view of a portion of a heat
exchanger core showing the serpentine split louver fins of the
present invention sandwiched between heat exchanger core tubes.
DESCRIPTION OF THE PREFERRED EMBODIMENT(S)
[0027] In describing the preferred embodiment of the present
invention, reference will be made herein to FIGS. 1-11 of the
drawings in which like numerals refer to like features of the
invention.
[0028] FIGS. 1-4 depict the preferred split louver fin
configuration formed in a flat metal strip in accordance with the
present invention, prior to forming the serpentine convolutions. A
length of metal strip 12 of aluminum or preferably copper has split
louvers 40 extending in rows 25 across the width of the strip, ribs
18a and 18b formed adjacent the louvers within the rows, and
unformed portions 22 extending across the strip width between rows
of the louvers. The louvers are formed by cutting the strip and
twisting and plastically deforming the cut portions. The opposite
ends of each of the louvers maintain connection with the remaining
metal strip by a twist portion. Each row 25 of split louvers is
made up of a pair of banks 25a, 25b of individual louvers 40, which
are separated from each other by unformed portion 24 extending in
the direction of the strip width. The adjacent, spaced louver banks
25a, 25b extend across at least a portion of the width of the strip
12, and preferably extend across substantially all of the strip
width. The louvers 40, the openings between the louvers, and ribs
18a, 18b extend in the direction of the strip length 21.
[0029] Ribs 18a, 18b are plastically deformed in the strip
substantially parallel to the louver openings in the direction of
the strip length and extend substantially completely across the
pair of louver banks 25a, 25b, including across the unformed strip
portion 24 between the louver banks. End ribs 18a are located near
the strip edges 27 and center ribs 18b are located in center
portions of the strip between the strip edges. Ribs 18a, 18b extend
across the pair of louver banks, but not beyond the ends of the
louvers into the unformed sections 22 separating the rows of
louvers. End ribs 18a shown in the detailed view of FIG. 3 have
plastically deformed portions and include one angled leg 18'a
extending at an angle downward from the plane 30 of the undeformed
metal strip and a bent portion 18''a that connects to the adjacent
louver 40. The end ribs are ultimately positioned, after assembly
of the fin in the core, near the upstream and downstream ends of
the fin relative to the direction of cooling airflow. Center ribs
18b shown in the detailed view of FIG. 4 also have plastically
deformed portions with angled legs 18'b extending at an angle
downward from an undeformed metal strip portion in plane 30 and
bent portions 18''b that connect to the adjacent split louvers 40.
The number and spacing of center ribs 18b among the louvers in each
row may be determined according to the strength requirements of the
strip during air forming, as will be described in more detail
below. As shown in FIGS. 3 and 4, each split louver 40 has a total
height L and is angled at an angle a from the neutral plane 30 of
the undeformed metal strip 12. In one preferred embodiment, the
strip and louvers have a thickness of about 0.0022 in. (0.056 mm),
and the louvers have angle a of about 30.degree. and height L of
about 0.023 in. (0.58 mm). The ribs have a height a distance h in
one direction from the neutral plane of about 0.0104 in. (0.26 mm).
The ratio of h/s is about 4.7, and signifies that the height of the
rib is about 4.7 times the thickness of the fin material.
[0030] The process of forming the serpentine split louver fins of
the present invention is shown in FIGS. 5-8, and begins by
providing a coil of unformed metal strip for continuous feeding
through a modified prior art air forming machine 10. As shown in
FIG. 5, the air forming machine 10 comprises a front roller 50
which guides the metal strip through a pair of opposing wiping pads
52, one on each side of the metal strip, for cleaning any
contamination thereon. A pair of counter rotating fin rolls 60, 62
having a cylindrical shape are positioned downstream from the
wiping pads with respect to the metal strip. Fin rolls 60, 62 are
sufficiently close to one another to exert a compression force on
the surface of the moving metal strip in a direction normal to the
strip plane, as well as move the strip continuously in direction
21. Unlike prior air forming machines, the surfaces of each of the
fin rolls 60, 62 have a plurality of meshing cutter blades and tool
patterns 44 which cut and form the split louvers 40 and ribs 18a,
18b in the metal strip, to the configuration shown in FIGS.
1-4.
[0031] As the fin rolls 60, 62 push the metal strip downstream 21,
the formed metal strip passes between a backing plate 68 and a
first base portion 48a, which contact the strip to maintain it in a
substantially flat position. The metal strip 12 continues to move
downstream from the backing plate and into contact with a pair of
counter rotating folding shafts 70, 72 respectively positioned
above and below the strip plane. Each folding shaft 70, 72 has a
plurality of arms extending outward from the axis of rotation, and
the ends of the arms are parallel to the strip width. As shown in
FIG. 6, the metal strip contacts arms of the rotating lower folding
shaft 72 and upper folding shaft, which arms provide an initial
backpressure in a direction opposite to the motion of the strip in
direction 21. In particular, the metal strip contacts one of the
lower folding shaft 72 arms forcing an unformed portion 22 into a
radius formed between shaft arms, creating the initial backpressure
on the metal strip between the backing plate 68 and the lower
folding shaft 72. As the backpressure is applied, strip 12 begins
to buckle along a first unformed portion 22 between backing plate
68 and lower folding shaft 72. The unformed portions 22 of the
metal strip have the least amount of structural integrity against
forces which tend to make the metal strip bend across its width,
while the split louvers and the ribs inhibit buckling and folding
in the louver rows. The term air forming refers to the fact that
the folds are made in a controlled fashion in air without the
necessity to use male and female tool sections conforming to the
desired degree of folding.
[0032] FIG. 6 shows the result of the initial backpressure causing
the metal strip to buckle along the unformed portions 22'a creating
a fold in one direction, and to buckle along the unformed portion
22'b creating a fold in the opposite direction. As the metal strip
moves from backing plate 68 to folding shafts 70, 72, it continues
to buckle, and additional folds 22'a, 22'b are created along the
adjacent unformed portions 22 to create the folds or convolutions
in the strip between each row 25 of split louvers. The fold angles
continue to increase as the strip approaches and passes between the
folding shafts, as shown in FIGS. 7 and 8, which show the
progression of the strip folding.
[0033] A further backpressure is applied to the convoluted strip by
a gathering station downstream of the folding shafts, again in a
direction opposite to the strip movement direction 21. As shown in
FIGS. 6, 7, and 8, this gathering station, has fingers 96,
preferably in the form of a metal brush, mounted on an adjustable
lever 98 which sequentially contact the upper folds 22' of the
convoluted strip as it passes in direction 21. The force of fingers
96 urges the convoluted strip against a second base portion 48b,
and may be adjusted to apply sufficient backpressure to create the
desired density of strip convolutions, i.e., the number of straight
portions containing split louver fins 25 (between folds) in a
distance D of formed serpentine fin strip 12'. This fin strip
density is typically described as number of fins per inch.
Increased backpressure at the gathering station produces a higher
fin density, while lower backpressure at the gathering station
results in a lower fin density. The air forming process continues
until the final fold angle is obtained at folded unformed portions
22' to form the desired number of folds into a length of fin strip
12'. The fin strip 12' is subsequently cut to create the desired
number of fins corresponding to the length of the tubes in the heat
exchanger core.
[0034] FIGS. 9, 10 and 11 show the completed serpentine fin strips
12' integrated with tubes 30 to form heat exchanger core 50. As
shown in FIG. 11, incoming air flowing in direction 35 enters core
50 at leading fin edge 31 and exits at trailing fin edge 33. The
serpentine fin strips 12' are stacked in an alternating pattern
with the tubes, and then compressed and brazed to form the
completed core.
[0035] One particular advantage of the use of ribs with the split
louver serpentine fin made by air forming is shown in FIG. 9 with
respect to the location of the ends of the individual louvers 40
from adjacent tubes 30. It is desirable to ensure that there is
sufficient distance x.sub.1 and x.sub.2 between the louver ends and
the tubes, so that the fold is confined to the unformed area
between louver rows, and the ends of the louvers are not distorted,
closed or crushed, or the louver angle changed, by the folding
process. The present invention of air forming a split louver
serpentine fin has been shown to provide such distance to avoid
damage to the louvers, and more importantly, provide a consistent
distance x.sub.1, x.sub.2 between the louver ends and the tubes,
preferably where x.sub.1 is substantially equal to x.sub.2, to
permit the as-built heat exchanger to come closer to the
theoretical performance of the design. The ribs formed within the
split louver give the louver banks more integrity in the structure
during the air forming of the convolutions as well as in the
production of the radiator core when the tubes and fin strips are
stacked and brazed.
[0036] Thus, the present invention provides an improved method for
manufacturing split louvered serpentine fins using an air-forming
process, which is cost-effective, yet produces a quality fin having
consistently high efficiency and heat transfer rates.
[0037] While the present invention has been particularly described,
in conjunction with a specific preferred embodiment, it is evident
that many alternatives, modifications and variations will be
apparent to those skilled in the art in light of the foregoing
description. It is therefore contemplated that the appended claims
will embrace any such alternatives, modifications and variations as
falling within the true scope and spirit of the present
invention.
* * * * *