U.S. patent application number 10/029461 was filed with the patent office on 2003-06-26 for heat exchanging apparatus and method of manufacture.
Invention is credited to Dispenza, John A., Warncke, Richard A..
Application Number | 20030116309 10/029461 |
Document ID | / |
Family ID | 21849129 |
Filed Date | 2003-06-26 |
United States Patent
Application |
20030116309 |
Kind Code |
A1 |
Dispenza, John A. ; et
al. |
June 26, 2003 |
Heat exchanging apparatus and method of manufacture
Abstract
Heat exchange surfaces are formed on a core object, by placing
at least a part of a thermally conductive core object within a mold
cavity that defines one or more heat exchange surfaces. A heated
metal slurry such as, e.g., a magnesium alloy heated to a
thixotropic state is injected under a predetermined pressure into
the mold cavity. The heated metal slurry is then cooled to form a
substantially continuous void free interface between the core
object and the slurry when hardened.
Inventors: |
Dispenza, John A.; (Long
Valley, NJ) ; Warncke, Richard A.; (Freehold,
NJ) |
Correspondence
Address: |
John E. Curtin, Esq.
Troutman Sanders LLP
1660 International Drive, Suite 600
McLean
VA
22102
US
|
Family ID: |
21849129 |
Appl. No.: |
10/029461 |
Filed: |
December 21, 2001 |
Current U.S.
Class: |
165/151 ;
29/890.03 |
Current CPC
Class: |
Y10T 29/4935 20150115;
B21D 53/085 20130101; F28F 1/24 20130101; F28F 2255/143 20130101;
B22D 17/007 20130101; F28F 21/084 20130101; F28D 15/0275
20130101 |
Class at
Publication: |
165/151 ;
29/890.03 |
International
Class: |
F28D 001/04; B21D
053/02 |
Claims
We claim:
1. A method of forming heat exchange surfaces on a core object,
comprising: placing at least a part of a thermally conductive core
object within a mold cavity that is formed to define one or more
heat exchange surfaces; injecting a heated metal slurry into the
mold cavity under a predetermined pressure; and cooling the heated
metal slurry thus forming a substantially continuous void free
interface between the core object and the metal slurry when
hardened for effective heat transfer across the interface.
2. A method according to claim 1, including heating a metal to a
thixotropic state, and then performing said injecting step using
the heated thixotropic metal as said metal slurry.
3. A method according to claim 2, including raising the temperature
of the metal to about 900 degrees F. prior to said injecting
step.
4. A method according to claim 2, including using type AZ91D
magnesium alloy as said metal, and raising the temperature of said
alloy to about 900 degrees F. prior to said injecting step.
5. A method according to claim 1, including forming the mold cavity
to define one or more fins about the core object.
6. A method according to claim 1, including providing a heat
conductive pipe as said core object.
7. A method according to claim 6, including inserting a rigid rod
axially through the pipe thus avoiding deforming of the pipe during
the injecting step.
8. A method according to claim 7, including forming the mold cavity
to define one or more fins as the heat exchange surfaces about the
outer circumference of the pipe.
9. A method of forming heat exchange surfaces on a core object,
comprising: arranging a first series of die plates in tandem for
linear movement about a first perimeter of a first molding
apparatus; arranging a second series of die plates in tandem for
linear movement about a second perimeter of a second molding
apparatus; forming each of the first series of die plates to define
first parts of one or more heat exchange surfaces; forming each of
the second series of die plates to define corresponding second
parts of one or more of said heat exchange surfaces; positioning
the first and the second molding apparatus so that corresponding
ones of the first and the second die plates face one another while
being displaced by the apparatus along an axial direction with
respect to an elongated thermally conductive core object; placing
the core object between the facing ones of the first and the second
series of die plates; urging the facing die plates to a closed
position thus forming full mold cavities corresponding to the heat
exchange surfaces about the core object; injecting a heated metal
slurry into the full mold cavities under a predetermined pressure;
and cooling the heated metal slurry thus forming a substantially
continuous void free interface between the core object and the
metal slurry when hardened for effective heat transfer across the
interface.
10. A method according to claim 9, including heating a metal to a
thixotropic state, and then performing said injecting step using
the heated thixotropic metal as said metal slurry.
11. A method according to claim 10, including raising the
temperature of the metal to about 900 degrees F. prior to said
injecting step.
12. A method according to claim 10, including using type AZ91D
magnesium alloy as said metal, and raising the temperature of said
alloy to about 900 degrees F. prior to the injecting step.
13. A method according to claim 9, including forming the die plates
to define one or more fins about the core object.
14. A method according to claim 9, including providing a heat
conductive pipe as said elongated core object.
15. A method according to claim 14, including inserting a rigid rod
axially through the pipe, thus avoiding deforming of the pipe
during the injecting step.
16. A method according to claim 15, including forming the die
plates to define one or more fins as said heat exchange surfaces
about the outer circumference of the pipe.
17. A heat exchanging device produced according to the method of
claim 1.
18. A heat exchanging device produced according to the method of
claim 9.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention concerns apparatus for effecting heat
transfer, and a method of making such apparatus.
[0003] 2. Discussion of the Known Art
[0004] Current trends toward miniaturization of electrical and
electronic devices, have yielded products that need efficient heat
dissipation in order to operate properly. This is due to the fact
that such products typically consume a relatively large amount of
electrical current with respect to their physical size. Cooling
techniques such as, e.g., metal heat sinks and fans are used to
maintain the operating temperatures of electronic components and
devices at safe values, so that they will continue to operate over
their expected lifetimes without failure caused by excessive
heating. In particular, semiconductor and other solid state devices
designed to operate at high power levels are typically joined to
finned, cast aluminum heat sinking structures. Adequate heat
dissipation is especially important for electrical power supplies,
radio frequency transmitters, modern desk-top and notebook
computers, cellular telephones, and most all modern consumer
electronics products.
[0005] It is generally known that structures used for transferring
heat away from a heat source should have relatively high thermal
conductivities (i.e., low thermal resistance), and have exposed
surfaces of sufficient area to allow heat conducted from the source
to radiate into a lower temperature environment. Further, the
physical interface between a heat sink structure and its associated
heat source should extend over as large an area as possible with
minimal thermal resistance. Use of thermally conductive pastes such
as a zinc-oxide silicone compound at the interface is a common
practice. The compound fills air voids that are created when part
of the heat sink structure is joined against a surface of a
component to be cooled. In the absence of such a compound, the air
voids act as thermal insulators and reduce the overall efficiency
of the heat sink structure.
[0006] Heat sink configurations in the form of aluminum or copper
radiating fins are also arranged on the circumference of heat pipes
through which a working fluid (i.e., a liquid or a gas) is
conducted, to transfer heat from one location to another. The fins
are typically joined to the pipes by friction, solder or epoxy.
Discontinuous interfaces between the fins and the associated pipe
typically present significant thermal resistance, and the
efficiency of heat transfer is compromised accordingly. Also, the
effective contact area between a heat pipe and its surrounding fins
is generally limited due to the process by which the fins, usually
made of sheet metal, are formed. Moreover, the fins are often
attached manually one at a time, making the assembly procedure
labor intensive and costly.
[0007] It is also known that certain electronic components or
devices may be encapsulated with a conductive plastics compound to
form heat radiating surfaces about the devices. The geometry of the
radiating surfaces is, however, limited by the flow characteristics
of the plastics compound, its brittle nature when loaded with a
material to increase its thermal conductivity, and a generally
lower radiating efficiency in comparison to that obtained with most
metals.
[0008] U.S. Pat. No. 5,040,589 (Aug. 20, 1991), discloses a method
and apparatus for injection molding of metal alloys, wherein a
selected alloy is heated to a thixotropic or semi-solid state, and
then injected as a slurry into a mold to form a useful product. See
also U.S. Pat. Nos. 4,694,881 and 4,694,882, both issued Sep. 22,
1987, and disclosing methods for making thixotropic materials. All
relative portions of the mentioned '589, '881 and '882 U.S. patents
are incorporated by reference. Certain metal products typically
formed by die casting and subsequent finishing steps may be
produced instead by injection molding of magnesium alloys,
according to the patented methods. Such molding is claimed to
result in net-shape products with lower porosity, closer
dimensional tolerances, and reduced manufacturing cost with respect
to the same products when die cast.
[0009] As far as is known, however, injection molding of metals has
not been used to produce heat exchanging structures directly on
thermally conductive core objects or heat sources.
SUMMARY OF THE INVENTION
[0010] According to the invention, heat exchange surfaces are
formed on a core object by placing at least a part of a thermally
conductive core object within a mold cavity formed to define one or
more heat exchange surfaces, injecting a heated metal slurry into
the mold under a predetermined pressure, and cooling the heated
metal slurry thus forming a substantially continuous void free
interface between the core object and the metal slurry when
hardened for effective heat transfer across the interface.
[0011] For a better understanding of the invention, reference is
made to the following description taken in conjunction with the
accompanying drawing and the appended claims.
BRIEF DESCRIPTION OF THE DRAWING
[0012] In the drawing:
[0013] FIG. 1 is a schematic representation of a heat exchange
assembly having a core pipe and associated heat exchanging fins,
according to the invention;
[0014] FIG. 2 is a perspective view of a heat exchange assembly
similar to the assembly of FIG. 1;
[0015] FIG. 3 illustrates a molding process for producing a heat
exchange assembly according to the invention;
[0016] FIG. 4 is a scanning electron microscope (SEN) image of an
interface between a core pipe and associated heat exchanging fins,
according to the invention;
[0017] FIG. 5 is a graph identifying relative amounts of metallic
elements at both sides of the interface in FIG. 4;
[0018] FIG. 6 illustrates a cooling system for an electronics
equipment enclosure, according to the invention;
[0019] FIG. 7 shows a part of the cooling system of FIG. 6;
[0020] FIG. 8 is an assembly view of a heat sink arrangement for an
electronic component, according to the invention;
[0021] FIG. 9 is an assembly view of a baseboard heating system,
according to the invention;
[0022] FIG. 10 illustrates an automotive radiator assembly,
according to the invention;
[0023] FIG. 11 illustrates an environmental cooling system,
according to the invention;
[0024] FIG. 12 is a perspective view of a half mold or die plate
used in the present method; and
[0025] FIG. 13 is a detail view of one end of the half mold shown
in FIG. 12.
DETAILED DESCRIPTION OF THE INVENTION
[0026] FIG. 1 represents a model of a heat exchange assembly 10,
according to the invention. The assembly 10 includes a core pipe 12
made of copper or equivalent material having relatively high
thermal conductivity, and one or more heat exchanging fins 14 which
are closely joined as a unit about the circumference of the core
pipe 12. The fins 14 are made of, for example, a magnesium alloy
(e.g., type AZ91D) which is capable of being heated to a
thixotropic state, and then injected as a slurry into a mold cavity
under pressure whereby the fins 14 are formed on the core pipe 12,
as explained further below. The material forming the fins 14 also
has a relatively high thermal conductivity, for example, about 42
BTU/ft.multidot.hr.multidot.deg F. for the mentioned type AZ91D
magnesium alloy. The fins 14 are formed with a common cylindrical
base 16 whose inner circumference establishes a substantially
continuous, void-free interface 18 with the outer circumference of
the core pipe 12 once the molded, heated slurry is allowed to cool
and harden. The interface 18 between the inner circumference of the
fin base 16 and the outer circumference of the core pipe 12 thus
ensures an efficient heat transfer across the interface 18 in
either direction.
[0027] FIG. 2 is a perspective view of a heat exchange assembly 20
which was constructed according to the model in FIG. 1. The
assembly 20 has a copper core pipe 22 and a total of seven circular
heat exchanging fins 24. The pipe 22 has an outer diameter of about
0.375 inches, an inner diameter of 0.300 inches, and an overall
length of 6.0 inches. Each of the fins 24 has a diameter of about
2.0 inches, and extends radially from a common cylindrical base 26
whose outer diameter is about 0.500 inches. The fins 24 are each
about 0.040 inches thick, and are spaced apart from one another in
the axial direction by about 0.375 inches. The material used to
form the heat exchanging fins 24 was a magnesium alloy type AZ91D.
The alloy was initially heated to about 900 degrees F., and then
injected as a thixotropic slurry into a mold cavity in which the
copper core pipe 22 was previously placed and supported along an
axis of the cavity. The injection pressure was approximately two
tons per projected square inch.
[0028] FIG. 3 depicts a process by which the heat exchange assembly
20 of FIG. 2 and other heat exchange devices can be manufactured,
according to the invention. A series of die plates or half molds 32
are arranged in tandem for linear movement about the perimeter of
an injection molding machine 34. Another series of die plates or
half molds 36 are arranged in tandem for linear movement about the
periphery of another injection molding machine 38, which may be
substantially identical to the machine 34. The die plates 32 and 36
may also be substantially identical to one another. See FIGS. 12
and 13. The molding machines 34, 38 are positioned so that
corresponding ones of the die plates 32, 38 will face one another
while being displaced by the machines 34, 38 along a common
direction of travel shown by arrows 40 in FIG. 3.
[0029] As seen in FIG. 12, each die plate 32, 36 forms a half-mold
cavity 37 defining corresponding upper or lower halves of the heat
exchanging fins 24 and common cylindrical base 26 of the assembly
20 in FIG. 2. A number of pairs of the die plates which face one
another over a portion of the travel path 40, are urged by the
associated machines 34, 38 into a closed position thus forming full
mold cavities within them. Guide pins 41 on either one of the
confronting die plates 32, 38 enter corresponding openings 43
formed in the other die plate, so that the confronting plates 32,
38 are properly aligned as they close against one another. Inlets
39 that open at the back of each die plate 32, 36, communicate
through a passage in the die plate with the half mold cavity 37. As
shown in FIG. 3, the inlets 39 of the die plates are positioned to
align with corresponding chambers 47 in the machines 34, 38. A
heated thixotropic metal slurry is then discharged from the machine
chambers 47 into the die plate inlets 39 at a predetermined
pressure and time interval.
[0030] Further, as shown in FIG. 13, axial ends of each of the die
plates 32, 36 have a semi-circular cutout 44 which is formed with
raised semi-circular ribs 46 each having, e.g., a triangular cross
section. Thus, when pairs of the die plates 32, 36 close with one
another, a core pipe 42 (FIG. 3) can extend axially through the
cutouts 44 in all the closed pairs of the die plates 32, 36, with
insubstantial leakage when heated material is injected into the
mold cavities 37 within the closed plates. That is, the raised ribs
45 create an interference fit between the outer diameter of the
core pipe 42 and the inner periphery of the cutouts 44 in each of
the die plates 32, 36. The ribs 46 deform the softer pipe 42 (or
other core part) radially by, e.g., a few thousandths of an inch,
similar to compression fittings known in the plumbing, automotive
and utility fields. Depending on the wall strength of the pipe 42,
it may be necessary to insert a solid rod or mandrel 48 inside the
pipe, as shown in FIG. 3, in order to prevent deformation or
collapse of the pipe wall in response to the outside pressure of
the injected slurry.
[0031] FIG. 4 is a scanning electron microscope (SEM) image showing
a contact interface 50 between a magnesium alloy base 52 that was
injection molded over a surface of a copper pipe 54. Specifically,
a type AZ91D magnesium alloy was injected at about 900 degrees F.
into a mold cavity containing the copper pipe 54, within about
{fraction (1/10)}th of a second at a pressure of about two tons per
projected square inch. The image of FIG. 4 represents a 2,000
magnification setting for the SEM, and a distance of 10 um is shown
by a scale line 56. As seen in FIG. 4, interface 50 is
substantially continuous and void-free.
[0032] FIG. 5 is a graphic representation showing relative amounts
of metallic elements at both sides of the interface 50 in FIG. 4.
Units of distance (arb) along the x-axis in FIG. 5 are such that
about 2,200 arb units equals 50 .mu.m. A region 60 about the
interface 50 wherein both copper and magnesium elements are
detectable, extends over only about 140 arb units or 3 .mu.m. That
is, the interface 50 is quite sharp. Relatively small counts of Mg
and Cu appear at opposite sides of the interface 50 because
background was not subtracted in the graph of FIG. 5.
[0033] FIG. 6 shows a cooling system 70 for an electronics
equipment enclosure 72, and FIG. 7 shows a part of the cooling
system 70 in FIG. 6. One or more heat conductive pipes 74 have a
number of heat radiating fins 76 molded over end portions of each
of the pipes 74, according to the present invention. Central
portions of the pipes 74 intermediate the end portions form a 180
degree bend and are supported in thermal conducting relation within
or in contact with a source of heat, for example, a chassis, a
power supply cabinet, or other heat-generating electrical equipment
78. A vapor barrier or environmental gasket 80 made of, e.g., a
soft elastomer or rubber material creates a water-tight seal
between the heat pipes 74 and the equipment 78.
[0034] An air blower 82 disposed, e.g., at the bottom of the
equipment enclosure 72 directs an outside air flow 84 past the sets
of radiating fins 76 on each of the pipes 74. Accordingly, heat
conducted by the intermediate portions of the pipes 74 away from
the heat source 78, is dissipated via the radiating fins 76 and the
air flow 84 to the outside environment.
[0035] FIG. 8 is an exploded view of a heat sink device 90 for an
electronic component 92, e.g., a processor chip. A relatively thin
metal subframe 94 is fastened over one or more surfaces of the
component 92, and placed with the component inside an injection
mold cavity which defines a number of vertical heat dissipating
elements in the form of, e.g., cylindrical rods 95. A thixotropic
metal slurry is injected into the cavity and adheres to the thin
metal subframe 94 while filing voids in the cavity corresponding to
the rods 95. Perforations 96 in the subframe 94 are also filled
with the injected slurry to form mechanical "locks" between the
slurry when cooled and hardened, and the subframe. The thin metal
subframe 94 aids in protecting the component 92 from the elevated
temperature of the slurry while in the mold cavity.
[0036] When the component with the subframe 94 and integral rods 95
are removed from the mold cavity, the completed assembly may be
mounted on, e.g., a printed wiring board via fasteners (not shown)
that pass through mounting holes 99 in side flanges 98 of the
subframe 94, and the wiring board. Contact pins or leads of the
component 92 may then be soldered or otherwise connected to
corresponding conductors associated with the wiring board.
[0037] FIG. 9 is an assembly view of a baseboard heating system
100. The system 100 comprises a core heat conducting pipe 102
through which a heated working fluid (e.g., hot water) is
circulated by an outside pump (not shown). A number of heat
radiating fins 104 are formed with a common cylindrical base 106 on
the outer circumference of the fluid pipe 102, by way of an
injection molding process such as that described in connection with
FIG. 3. Various length sections of the fluid pipe 102 with the
molded radiating fins 104 may be produced initially, and then
connected to one another through straight or angled pipe couplings
to fit a particular application. Once in place, a slotted
protective cover 108 is fastened over the pipe 102 and the
associated fins 104.
[0038] FIG. 10 shows an automotive radiator assembly 120. A number
of heat conductive (e.g., copper) metal core pipes are arranged
parallel and co-planar with one another, after a series of heat
radiating fins 124 are molded with a common cylindrical base 126
over each of the pipes 122 per the present method. Opposite open
ends of the pipes 122 are joined in fluid communication with
corresponding header or end pipes 128, 130. When heated engine
coolant is pumped through one of the end pipes 128, 130, the
coolant is directed through each of the core pipes 122 and cooled
by outside air which has been directed to flow over the radiating
fins 124 on the pipes 122. The coolant is then returned through the
opposite end pipe to be pumped and circulated through an associated
engine.
[0039] FIG. 11 illustrates an environmental cooling system 150. One
or more sections of a heat conducting, metal core pipe 152 have a
series of heat exchanging fins 154 with a common cylindrical base
156 molded over the outer circumference of the pipe 152, according
to the present method. A cooled working fluid such as, for example,
an evaporated refrigerant, water or air is directed under pressure
through an inlet 158 of the pipe 152. Warm air to be cooled is
directed by outside means (e.g., a blower or fan) between the fins
154 so that the fins absorb heat and conduct it through the fin
base 156 and the pipe 152 into the working fluid. The heated
working fluid exits from an outlet 160 of the core pipe 152, and
cooled air 162 is available to be channeled where desired by
suitable means.
[0040] The various heat exchanging apparatus disclosed herein are
highly efficient because of the formation of a substantially
continuous, void-free thermal interface between a thermally
conductive core pipe or tube, and a number of heat exchanging fins
which are injection molded under pressure over the pipe rather than
being formed and attached individually. The present injection
molding process may also yield fins having thinner cross-sections
and less weight than conventional fins. Magnesium and aluminum
alloys are highly thermally conductive materials having high
strength-to-weight ratios, and are both well suited for injection
molding into the form of heat radiating or cooling fins according
to the present process.
[0041] Importantly, the present process yields an increased contact
area between a number of heat exchanging fins and their
associated-core pipe or component when compared to prior
configurations using individual fins. The process can be used to
form heat sink configurations for various electronic devices and
products that must operate with adequate cooling, including large
scale installations such as wireless telephone base stations where
heat generated by a number of active radio transceivers within a
confined space must be dissipated in an effective and efficient
manner.
[0042] While the forgoing description represents preferred
embodiments of the invention, it will be obvious to those skilled
in the art that various changes and modifications may be made
without departing from the spirit and scope of the invention
pointed out by the following claims.
* * * * *