U.S. patent application number 14/489076 was filed with the patent office on 2015-03-19 for friction-stir extruders and friction-stir extrusion processes.
This patent application is currently assigned to Lockheed Martin Corporation. The applicant listed for this patent is Lockheed Martin Corporation. Invention is credited to Randy Jay Brown, Michael Russell Eller, Zhixian Li, Kevin John Schuengel.
Application Number | 20150075242 14/489076 |
Document ID | / |
Family ID | 51656102 |
Filed Date | 2015-03-19 |
United States Patent
Application |
20150075242 |
Kind Code |
A1 |
Eller; Michael Russell ; et
al. |
March 19, 2015 |
FRICTION-STIR EXTRUDERS AND FRICTION-STIR EXTRUSION PROCESSES
Abstract
A friction-stir mandrel includes a textured end portion integral
with a body portion. The textured end portion is configured to
friction-stir process a starting material forced across the
textured end portion and through a die in a plasticized state to
form a pipe. A pipe can be formed by forcing a starting material
across a textured end of the mandrel and through a die in a
plasticized state, so that the textured end of the mandrel breaks
up existing grains of the starting material. The pipe is formed
from material that is forced through the die. The friction-stir
mandrel can be used with porthole die friction-stir extrusion,
seamless tube friction-stir extrusion, and tube friction-stir
drawing processes to provide tubing in which the grains are broken
up by the textured portion of the friction-stir mandrel. The
textured portion can include features, such as threads, ridges,
studs, protrusions, and the like.
Inventors: |
Eller; Michael Russell; (New
Orleans, LA) ; Li; Zhixian; (Slidell, LA) ;
Schuengel; Kevin John; (Bay St. Louis, MS) ; Brown;
Randy Jay; (Slidell, LA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Lockheed Martin Corporation |
Bethesda |
MD |
US |
|
|
Assignee: |
Lockheed Martin Corporation
Bethesda
MD
|
Family ID: |
51656102 |
Appl. No.: |
14/489076 |
Filed: |
September 17, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61879397 |
Sep 18, 2013 |
|
|
|
Current U.S.
Class: |
72/68 ; 72/256;
72/283 |
Current CPC
Class: |
B21C 3/16 20130101; B21C
25/02 20130101; B21C 3/02 20130101; B21C 23/085 20130101; B21C
25/04 20130101; B21C 1/24 20130101; B21C 37/20 20130101 |
Class at
Publication: |
72/68 ; 72/256;
72/283 |
International
Class: |
B21C 37/20 20060101
B21C037/20; B21C 25/02 20060101 B21C025/02; B21C 3/02 20060101
B21C003/02 |
Claims
1. A friction-stir mandrel, comprising: a textured end portion
integral with a body portion, the textured end portion configured
to friction-stir process a starting material forced across the
textured end portion and through a die in a plasticized state to
form a pipe.
2. The friction-stir mandrel of claim 1, wherein the friction-stir
mandrel is configured to rotate while the starting material remains
rotationally stationary.
3. The friction-stir mandrel of claim 1, wherein the friction-stir
mandrel is configured to remain rotationally stationary while the
starting material rotates.
4. The friction-stir mandrel of claim 1, further comprising a
smooth cap formed over an end of the textured end portion, the
smooth cap configured to provide a final smooth interior surface on
the formed pipe.
5. The friction-stir mandrel of claim 1, wherein a diameter of the
textured end portion is slightly larger than an inside diameter of
the formed pipe and smaller than an outside diameter of the formed
pipe.
6. The friction-stir mandrel of claim 1, wherein the friction-stir
mandrel is integral with the die.
7. The friction-stir mandrel of claim 1, wherein the friction-stir
mandrel is configured to pierce through the starting material.
8. The friction-stir mandrel of claim 1, wherein the friction-stir
mandrel is configured to be drawn into the die in conjunction with
drawing the starting material over the friction-stir mandrel by a
tube gripper.
9. The friction-stir mandrel of claim 1, wherein the starting
material comprises a metal.
10. The friction-stir mandrel of claim 9, wherein the metal
comprises aluminum or an aluminum alloy.
11. The friction-stir mandrel of claim 1, wherein the textured end
portion comprises one of threads, ridges, studs, or
protrusions.
12. A method of forming a pipe, comprising: forcing a starting
material across a textured end of a mandrel and through a die in a
plasticized state, so that the textured end of the mandrel breaks
up existing grains of the starting material; and forming the pipe
from material forced through the die, wherein the formed pipe has
fine equiaxed resultant grains in multiple orientations on an
interior surface of the formed pipe than the existing grains of the
starting material.
13. The method of claim 12, further comprising: rotating the
mandrel while the starting material remains rotationally
stationary.
14. The method of claim 12, further comprising: rotating the
starting material while the mandrel remains rotationally
stationary.
15. The method of claim 12, further comprising: forming a smooth
interior surface on the formed pipe via a smooth cap formed over an
end of the textured end.
16. The method of claim 12, wherein the starting material comprises
a metal.
17. The method of claim 16, wherein the metal comprises aluminum or
an aluminum alloy.
18. The method of claim 12, wherein the textured end comprises one
of threads, ridges, studs, or protrusions.
19. The method of claim 12, wherein the pipe comprises a seamless
tube pipe.
20. A porthole die friction-stir extrusion method, comprising:
loading a feedstock billet into a container; abutting one end of
the feedstock billet with a ram and abutting another end of the
feedstock billet against a die mandrel; rotating the feedstock
billet and the container against a die cap while pressure is
applied by the ram; extruding plasticized feedstock through
passages of the die mandrel, wherein grains of the plasticized
feedstock are broken up by a textured mandrel tip of the die
mandrel; and forming a hollow tube from the extruded plasticized
feedstock.
21. The porthole die friction-stir extrusion method of claim 20,
further comprising: rotating the die mandrel while rotating the
feedstock billet and the container.
22. The porthole die friction-stir extrusion method of claim 20,
further comprising: smoothing an interior surface of the extruded
hollow tube via a mandrel bearing attached to an end of the
textured mandrel tip.
23. The porthole die friction-stir extrusion method of claim 20,
further comprising: extruding the plasticized feedstock through a
hollow punch aperture integrally formed with the die mandrel.
24. The porthole die friction-stir extrusion method of claim 20,
further comprising: extruding the plasticized feedstock through a
rotating hollow punch aperture.
25. The porthole die friction-stir extrusion method of claim 20,
wherein the textured mandrel tip comprises one of threads, ridges,
studs, or protrusions.
26. A seamless tube friction-stir extrusion method, comprising:
loading a feedstock billet into a container; abutting one end of
the feedstock billet with a ram and a concentrically-located
mandrel, and abutting another end of the feedstock billet against a
die; piercing through the feedstock billet with the
concentrically-located mandrel up to the die; applying pressure to
the feedstock billet by the ram; extruding plasticized feedstock
through the die and over a textured portion of the
concentrically-located mandrel, wherein grains of the plasticized
feedstock are broken up by the textured portion of the
concentrically-located mandrel; and forming a seamless tube from
the extruded plasticized feedstock.
27. The seamless tube friction-stir extrusion method of claim 26,
further comprising: rotating the concentrically-located mandrel
during the extruding.
28. The seamless tube friction-stir extrusion method of claim 26,
further comprising: forming a recrystallized microstructure in an
interior wall of the seamless tube.
29. The seamless tube friction-stir extrusion method of claim 26,
wherein the textured portion comprises one of threads, ridges,
studs, or protrusions.
30. A tube friction-stir drawing method, comprising: loading a
first end of a tube work piece into a die tool and tool carrier of
a container; inserting a mandrel tool at a second end of the tube
work piece; engaging the first end of the tube work piece; drawing
a textured portion of the mandrel tool inside the die tool while
continuously drawing the tube work piece over the textured portion,
wherein grains of the drawn tube work piece are broken up by the
textured portion of the mandrel tool; and forming a drawn tube of
smaller diameter and thinner wall thickness.
31. The tube friction-stir drawing method of claim 30, further
comprising: rotating the mandrel tool during the drawing.
32. The tube friction-stir drawing method of claim 30, further
comprising: rotating the container and the tube work piece during
the drawing.
33. The tube friction-stir drawing method of claim 30, wherein the
textured portion comprises one of threads, ridges, studs, or
protrusions.
34. The tube friction-stir drawing method of claim 30, wherein the
engaging the first end of the tube work piece includes using a
gripper at the first end.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims the benefit of U.S. Provisional
Application No. 61/879,397, filed on Sep. 18, 2013, the disclosure
of which is incorporated in its entirety by reference herein.
BACKGROUND
[0002] Metal extruded products such as tubes are widely used for
various applications in both structural and pressure flow
applications. Aluminum tubes produced by conventional extrusion
processes are a popular material for scaffolding, medical devices,
structural framing, bicycle frames, and heat exchangers. Drawn
aluminum tubes are widely used for various applications in both
structural and pressure flow applications. Similarly, seamless
extruded tubes are also widely used for various applications in
both structural and pressure flow applications.
[0003] The use of aluminum tubes in heat exchangers is typically
limited to low temperature and cryogenic applications, such as
processing liquid natural gas (LNG). However, aluminum tubes have
been used in seawater service applications such as desalination
with moderate to good success. In addition, aluminum tubes have
been tested for decades as a candidate material for ocean thermal
energy conversion (OTEC) heat exchangers. OTEC is a method for
generating electricity based on the temperature difference that
exists between deep water and shallow water of a large body of
water, such as an ocean, sea, gulf, or large deep lake. An OTEC
system utilizes a heat engine, i.e., a thermodynamic device or
system that generates electricity based on a temperature
differential, which is thermally coupled between relatively warmer
shallow water and relatively colder deep water.
[0004] Even though aluminum is a good selection from a cost
perspective, the poor resistance to corrosive seawater can result
in a lower service life than titanium or stainless steel
alternatives. However, aluminum tubes produced with conventional
extrusion processes have only found limited usages in heat
exchanger applications with seawater service. Corrosion testing
reveals that conventionally extruded aluminum alloys can exhibit
severe pitting corrosion after two to three years of exposure to
seawater. The aluminum samples in the surface seawater corrosion
tests exhibited much less pitting occurrences with substantially
less maximum depth of pits, relative to the aluminum samples in
deep seawater. Deep seawater may be pulled from a depth of
approximately 1,000 meters and can cause accelerated pitting
corrosion in aluminum tubes because the deep seawater has less
dissolved oxygen (DO) and a lower pH than surface seawater. The
lower values of DO and pH tend to prevent the natural aluminum
oxide layer from reforming to stop growth of initiated pits, as
well as prevent new pits from forming. Since deep seawater is
generally used in the OTEC thermodynamic cycle, this corrosion
phenomenon can affect conventionally extruded tubes.
SUMMARY
[0005] Aspects of the disclosure can include a friction-stir
mandrel having a textured end portion integral with a body portion.
The textured end portion is configured to friction-stir process a
starting material that is forced across the textured end portion
and through a die in a plasticized state to form a pipe.
[0006] Embodiments include a method of forming a pipe, having the
steps of forcing a starting material across a textured end of a
mandrel and through a die in a plasticized state, so that the
textured end of the mandrel breaks up existing grains of the
starting material. The method also includes the step of forming the
pipe from material forced through the die. The formed pipe has
smaller resultant grains on an interior surface than the existing
grains of the starting material.
[0007] Embodiments include a porthole die friction-stir extrusion
method, having the steps of loading a feedstock billet into a
container, and abutting one end of the feedstock billet with a ram
and abutting another end of the feedstock billet against a die
mandrel. The method also includes rotating the feedstock billet and
the container against a die cap while pressure is applied by the
ram. The method also includes extruding plasticized feedstock
through passages of the die mandrel. Grains of the plasticized
feedstock are broken up by a textured mandrel tip of the die
mandrel. The method also includes forming a hollow tube from the
extruded plasticized feedstock.
[0008] Embodiments include a seamless tube friction-stir extrusion
method, having the steps of loading a feedstock billet into a
container, and abutting one end of the feedstock billet with a ram
and a concentrically-located mandrel, and abutting another end of
the feedstock billet against a die. The method may also include
piercing through the feedstock billet with the
concentrically-located mandrel up to the die, and applying pressure
to the feedstock billet by the ram. The method also includes
extruding plasticized feedstock through the die and over a textured
portion of the concentrically-located mandrel. Grains of the
plasticized feedstock are broken up by the textured portion of the
concentrically-located mandrel. The method also includes forming a
seamless tube from the extruded plasticized feedstock.
[0009] Embodiments include a tube friction-stir drawing method,
having the steps of loading a first end of a tube work piece into a
die tool and tool carrier of a container, and inserting a mandrel
tool at a second end of the tube work piece. The method also
includes engaging a gripper at the first end of the tube work
piece, and drawing a textured portion of the mandrel tool inside
the die tool by the gripper while continuously drawing the tube
work piece over the textured portion. Grains of the drawn tube work
piece are broken up by the textured portion of the mandrel tool.
The method also includes forming a drawn tube of smaller diameter
and thinner wall thickness.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] Various exemplary embodiments will be described in detail
with reference to the following figures, wherein:
[0011] FIG. 1 is a schematic diagram of an OTEC power generation
system according to one embodiment;
[0012] FIG. 2 is a cross-sectional view of a heat exchanger
according to one embodiment;
[0013] FIGS. 3A-3B are illustrations of porthole die extrusion
systems according to one embodiment;
[0014] FIGS. 4A-4D are illustrations of a porthole die extrusion
process according to one embodiment;
[0015] FIGS. 5A-5C are illustrations of a porthole
friction-extrusion system according to one embodiment;
[0016] FIG. 6 is an illustration of an extrusion mandrel and die
according to one embodiment;
[0017] FIGS. 7A-7C are illustrations of an indirect
friction-extrusion system according to one embodiment;
[0018] FIGS. 8A-8D are illustrations of an integral hollow punch
and die cap, and a decoupled die mandrel according to one
embodiment;
[0019] FIG. 9 illustrates a seamless tube extruder and extrusion
process according to one embodiment;
[0020] FIGS. 10A-10D illustrate a seamless tube extrusion process
in detail according to one embodiment;
[0021] FIGS. 11A-11F illustrate a friction-extruded seamless tube
process according to one embodiment;
[0022] FIG. 12 illustrates an active end of a mandrel tool
according to one embodiment;
[0023] FIG. 13 illustrates a produced tubing according to one
embodiment;
[0024] FIG. 14 illustrates a rotating mandrel tool and a
non-rotating bearing according to one embodiment;
[0025] FIG. 15 illustrates a mandrel with a threaded extension and
cylindrical screw cap according to one embodiment;
[0026] FIGS. 16A-16C illustrate a two-piece mandrel according to
one embodiment;
[0027] FIGS. 17A-17C illustrate an indirect friction-extrusion
method for seamless tubes according to one embodiment;
[0028] FIG. 18 illustrates a tube-drawing extrusion process
according to one embodiment;
[0029] FIGS. 19A-19D illustrate a tube-drawing extrusion process in
detail according to one embodiment;
[0030] FIGS. 20A-20C illustrate a friction-extrusion tube drawing
process according to one embodiment;
[0031] FIGS. 21A-21C illustrate a rotating mandrel and a
non-rotational container according to one embodiment;
[0032] FIG. 22 illustrates a rotating container and a
non-rotational mandrel according to one embodiment;
[0033] FIG. 23 is a flowchart showing an exemplary porthole die
extrusion method according to one embodiment;
[0034] FIG. 24 is a flowchart showing an exemplary seamless tube
extrusion method according to one embodiment;
[0035] FIG. 25 is a flowchart showing an exemplary tube drawing
method according to one embodiment; and
[0036] FIG. 26 is a flowchart showing an exemplary pipe forming
method according to one embodiment.
DETAILED DESCRIPTION
[0037] Aluminum tubes can be used in heat exchangers, such as those
used in an ocean thermal energy conversion (OTEC) operation. FIG. 1
is a schematic diagram of an exemplary OTEC power generation system
according to one embodiment. However, other OTEC power generation
systems can be used with embodiments described herein. As shown,
the OTEC system 100 can include an offshore platform 102, a
turbo-generator 104, a closed-loop conduit 106, an evaporator
110-1, a condenser 110-2, a hull 112, multiple pumps 114, 116, and
124, and multiple conduits 120, 122, 128, and 130.
[0038] Offshore platform 102 is a tension leg offshore platform,
which has buoyant hull 112, and also includes a deck, caissons, and
pontoons. The hull 112 is supported above seabed 136 by rigid
tension legs that are anchored to the seabed 136 at deployment
location 134. For clarity, the deck, caisson, pontoons, and tension
legs are not illustrated in FIG. 1.
[0039] In some embodiments, offshore platform 102 is deployed at a
deployment location in a body of water other than an ocean (e.g., a
lake, sea, etc.). In some embodiments, offshore platform 102 is an
offshore platform other than a tension leg offshore platform, such
as a semi-submersible, spar, drill ship, jack-up offshore platform,
grazing plant, or the like. Other offshore platform types are
contemplated by embodiments described herein.
[0040] Turbo-generator 104 is a turbine-driven generator mounted on
hull 112. Turbo-generator 104 generates electrical energy in
response to a flow of fluid and provides the generated electrical
energy on output cable 138. Closed-loop conduit 106 is a conduit
for conveying working fluid 108 through evaporator 110-1, condenser
110-2, and turbo-generator 104.
[0041] Evaporator 110-1 is a shell-and-tube heat exchanger that is
configured to transfer heat from warm seawater in surface region
118 and working fluid 108, thereby inducing the working fluid 108
to vaporize. Condenser 110-2 is a shell-and-tube heat exchanger
that is configured to transfer heat from vaporized working fluid
108 to cold seawater from deep-water region 126, thereby inducing
condensation of vaporized working fluid 108 back into liquid form.
Evaporator 110-1 and condenser 110-2 are mechanically and
fluidically coupled with offshore platform 102.
[0042] Turbo-generator 104, closed-loop conduit 106, evaporator
110-1, and condenser 110-2 collectively form a Rankine-cycle engine
that generates electrical energy based on the difference in the
temperature of water in surface region 118 and the temperature of
water in deep-water region 126. In operation, pump 114 pumps
working fluid 108 in liquid form through closed-loop conduit 106 to
evaporator 110-1. Ammonia is an example of a working fluid 108 that
can be used in OTEC systems. However, other fluids that evaporate
at the temperature of the water in surface region 118 and condense
at the temperature of the water in deep-water region 126 can be
used as working fluid 108, and are contemplated by embodiments
described herein.
[0043] Pump 116 draws warm seawater from surface region 118 into
evaporator 110-1 via conduit 120. In some OTEC deployments, the
water in surface region 118 is at a substantially constant
temperature of approximately 25 degrees centigrade (subject to
weather and sunlight conditions). At evaporator 110-1, heat from
the warm water is absorbed by working fluid 108, which induces the
working fluid 108 to vaporize. After passing through evaporator
110-1, the now slightly cooler water is ejected back into ocean 140
via conduit 122. The output of conduit 122 is usually located
deeper in ocean 140 than surface region 118 to avoid decreasing the
average water temperature in the surface region 118.
[0044] The expanded working fluid 108 vapor is forced through
turbo-generator 104, thereby driving the turbo-generator 104 to
generate electrical energy. The generated electrical energy is
provided on output cable 138. After passing through turbo-generator
104, the vaporized working fluid 108 enters condenser 110-2.
[0045] Pump 124 draws cold seawater from deep-water region 126 into
condenser 110-2 via conduit 128. Deep-water region 126 can be
approximately 1000 meters below the surface of the body of water,
at which depth water is at a substantially constant temperature of
a few degrees centigrade. The cold water travels through condenser
110-2, where it absorbs heat from the vaporized working fluid 108.
As a result, working fluid 108 condenses back into liquid form.
After passing through condenser 110-2, the now slightly warmer
water is ejected into ocean 140 via conduit 130. The output of
conduit 130 is usually located at a shallower depth in ocean 140
than that of deep-water region 126 to avoid increasing the average
water temperature in the deep-water region 126. Pump 114 pumps the
condensed working fluid 108 back into evaporator 110-1 where it is
vaporized again, thereby continuing the Rankine cycle that drives
turbo-generator 104.
[0046] FIG. 2 is a cross-sectional view of a shell-and-tube heat
exchanger according to an embodiment described herein. An exemplary
heat exchanger includes a shell 202, a primary fluid inlet 204, an
input manifold 206, an output manifold 208, a primary fluid outlet
210, a secondary fluid inlet 212, a secondary fluid outlet 214, and
multiple tubes 216, tube plates 220, and baffles 224. Heat
exchanger 110 enables efficient heat transfer between a primary
fluid that flows through tubes 216 and a secondary fluid that flows
through shell 202, such that the secondary fluid flows across the
outer surface of each of the tubes 216. With reference to FIG. 1,
the primary fluid is working fluid 108 and the secondary fluid is
seawater. Shell 202 is a housing that includes a material suitable
for long-term exposure to seawater. Shell 202 and tube plates 220
collectively define a flow vessel for conveying seawater from
secondary fluid inlet 212 to secondary fluid outlet 214.
[0047] Working fluid 108 is conveyed to each of tubes 216 by
primary fluid inlet 204 and input manifold 206. In similar fashion,
working fluid 108 is collected from each of tubes 216 at output
manifold 208 and provided to primary fluid outlet 210. Primary
fluid inlet 204 and primary fluid outlet 210 are fluidically
coupled with closed-circuit conduit 106, such that heat exchanger
110 forms part of the closed-circuit conduit.
[0048] Seawater is provided to shell 202 at secondary fluid inlet
212. In evaporator 110-1, secondary fluid inlet 212 is fluidically
coupled with conduit 120. In condenser 110-2, secondary fluid inlet
212 is fluidically coupled with conduit 128. Seawater exits shell
202 through secondary fluid outlet 214. In evaporator 110-1,
secondary fluid outlet 214 is fluidically coupled with conduit 122.
In condenser 110-2, secondary fluid inlet 214 is fluidically
coupled with conduit 130. FIGS. 1 and 2 depict secondary fluid
inlet 212 and secondary fluid outlet 214 on the same side of the
heat exchanger. However, secondary fluid inlet 212 and secondary
fluid outlet 214 can be located on opposite sides of the heat
exchanger to facilitate efficient heat transfer between the primary
and secondary fluids.
[0049] In one embodiment, each of the tubes 216 is a conduit of
aluminum alloy having length, inner diameter, and tube wall
thickness that are selected for efficient thermal coupling between
seawater and working fluid 108. A shell-and-tube heat exchanger
suitable for a modern OTEC system can include five to six thousand
tubes having a length of up to thirty feet. Each of the tube plates
220 is a mechanically rigid circular plate of aluminum alloy having
a plurality of holes 218. Each end of the tubes 216 is joined to a
different one of the tube plates 220 at holes 218 to collectively
define a tubesheet 222.
[0050] Baffles 224 can be transverse baffles that induce a
transverse component to the flow of seawater through the heat
exchanger. In some embodiments, baffles 224 also provide support
for the tubes 216 in the region between the tube plates 220.
Baffles 224 include a plurality of through-holes for the tubes 216.
The number and placement of baffles 224 is a matter of heat
exchanger design, and one skilled in the art would recognize that
any practical number of baffles 224 can be included in the heat
exchanger. Tube plates 220 and baffles 224 hold the tubes in an
arrangement that facilitates heat transfer between seawater flowing
along the outer surfaces of the tubes 216 and working fluid 108
that flows through the tubes 216.
[0051] One method of forming metal tubes, including aluminum tubes
is a porthole die extrusion process. FIG. 3A is an illustration of
a direct porthole die extrusion system in which a die mandrel 310
is coupled with a die cap 320, and feedstock material 330 such as
aluminum material is forced through the die mandrel 310 and through
the die cap 320 to form a tubular finished product 340. The top
drawing of FIG. 3B illustrates a direct extrusion process in which
a ram 350 pushes against a billet 360 to force the billet material
through a stationary die 370 to form an extruded hollow tube 380.
The bottom drawing of FIG. 3B illustrates an indirect extrusion
process in which a hollow punch 390 with an integral die 395
presses against the billet inside a container. The extruded billet
material 380 is forced through the orifice within the hollow punch
390.
[0052] FIGS. 4A-4D illustrate a porthole die extrusion process in
more detail. A container 410 provides structural support for the
dynamic process. A die mandrel 420 and a coupled die cap 430 are
inserted into the container 410. A die carrier 440 and an aluminum
billet 450 are inserted into the die carrier 440 in FIG. 413. A
press disc 460 is butted against the back side of the aluminum
billet 450. In FIG. 4C, a ram 470 is butted against the press disc
460. FIG. 4D illustrates the tube extrusion 480 as the ram 470
forces the aluminum billet material 450 through the die cap 430 and
die mandrel 420 to form a hollow tube. During the extrusion
process, the die mandrel 420 and die cap 430 remain stationary
while the feedstock material is forced through the die mandrel
bridge and separated into four distinct material flow paths. The
plasticized material re-welds in the die cap 430 and forms a
tubular shape over the die mandrel 420.
[0053] One short-coming of the porthole die extrusion process
described with reference to FIGS. 3A-4D is the finished product has
poor resistance to pitting corrosion in a saltwater environment,
such as that of an OTEC system. A major cause for the poor
corrosion resistance is the presence of a large grain surface. In
addition, the products of this extrusion process have low
mechanical properties, such as bending, fatigue, and fracture
toughness.
[0054] Incorporating friction extrusion tools and processes break
down the original grains of feedstock metal into fine grains. Most
or all of the precipitates are dissolved back into the base metal,
resulting in extruded products having very fine equiaxed grains and
much cleaner grain boundaries with fewer and smaller precipitates
on the tube inside surface of the extrusions. The grains are also
equiaxed in the direction of extrusion, whereby any cross-section
of a friction-extruded tube will show a homogenous grain size.
Friction-extruded tubes can still be heat treated after extruding,
such as aging to improve mechanical properties like tensile
strength, as well as improve corrosion resistance.
Friction-extruded products also exhibit better mechanical
properties, and therefore have a much longer service life, as
compared to conventionally extruded products.
[0055] FIG. 5A illustrates an exterior view of a direct
friction-extrusion system 500. A container 510 holds the die
mandrel and die cap in place during the extrusion. A motor 520 and
a pulley and drive belt system 530 power the extrusion process,
which exerts a force against the feedstock metal via a ram 540. A
metal tube will be extruded to the right side of the figure.
[0056] FIG. 5B is a cross-sectional view of the friction-extrusion
system 500 during the extrusion process. In embodiments described
herein, the die mandrel 550 is decoupled from the die cap 560. The
die mandrel 550 and cylinder 570 containing the feedstock 580
(illustrated by the right-pointed arrow) spin together at a high
rotational speed, while the die cap 560 remains non-rotational.
Frictional heating and considerable force from the ram 540 results
in severe plastic deformation of the feedstock 580.
[0057] As the plasticized feedstock 580 enters the stationary die
cap 560, the material flowing through the die mandrel 550 is
frictionally-processed in the weld chamber 590 when the material
comes in contact with the features of the stationary die cap 560,
as illustrated in FIG. 5C. As a result, the frictionally processed
material flows over the male piece of the die mandrel 550 to form
an extruded tube 595 with very fine grains. FIG. 5C illustrates the
extruded tube 595, produced by a rotating container 570 and
feedstock 580, as well as a rotating die mandrel 550. However, the
die cap 560 is fixed, i.e., not rotating. The decoupled die mandrel
550 and die cap 560 provide a fine-grained surface on the inner
surface of the extruded tube 595.
[0058] In some embodiments illustrated in FIG. 6, the die cap has a
conical feature 610 to allow for less pressure and enhanced
material flow characteristics in the weld zone. In other
embodiments, the die mandrel tip has a textured surface 620 to
assist with shearing through material grains and to refine the
microstructure for round shape extrusions. The textured surface 620
includes, but is not limited to surfaces containing features, such
as threads, ridges, studs, and protrusions. The tip of the mandrel
can have a plain cylindrical feature for forming a smooth diameter
tube. In still other embodiments, a mandrel bearing 630 can promote
a smooth interior finish on the resultant extruded tube. The
bearing is held in place with a bearing nut 640 that is attached to
the die mandrel, and does not affect the forming of the tube.
During operation, the textured die mandrel 620 and feedstock 650
rotate, but the mandrel bearing 630 does not rotate because it has
a rotational degree of freedom from the die mandrel and is held
stationary by the extrusion forces applied to the bearing
exterior.
[0059] FIGS. 7A-7C illustrate an indirect friction-extrusion
system, according to embodiments described herein. FIG. 7A is a
cross-sectional view of a setup assembly of an indirect
friction-extrusion system in which a container 710 and billet 720
rotate, while die mandrel 730 and die cap 740 remain
non-rotational. FIG. 7B is a close-up view showing material flowing
through the die mandrel 730 to form a tube 750. The hollow punch
740 is integral with the die cap and is coupled with the die
mandrel 730 using threaded fasteners 760. FIG. 7C is an isometric
view showing a container 710 moving towards a stationary hollow
punch 740 to produce a length of tubing 750.
[0060] Two different embodiments are described for an indirect
friction-extrusion system. In the first embodiment, the die cap and
integral hollow punch rotate, while the container remains
non-rotational. The hollow punch pushes the die mandrel and die cap
into the billet towards the stationary container. In the second
embodiment, the rotating container and billet push the billet
against a stationary die mandrel, die cap, and hollow punch. As the
container is pushed with ram force, the plasticized aluminum billet
is forced through the die mandrel and out the die cap, through the
hollow punch aperture as a finished tube. The second embodiment is
illustrated in FIGS. 7A-7C. FIGS. 7A-7C also illustrate a hollow
punch that is integral with the die cap and is coupled with the die
mandrel as a single integral assembly.
[0061] Another embodiment includes a hollow punch that is integral
with the die cap, but is decoupled with the die mandrel and is
separated by a thrust bearing, with reference to FIGS. 8A-8D. FIG.
8A illustrates a container 810 with a hex boss 820, which is
configured to receive a hex-shaped billet 830. Any other
polygonal-shaped boss and billet combination is contemplated by
embodiments described herein. FIG. 8B illustrates that the
container 810 and enclosed billet 830, as well as the die mandrel
840 are rotating, while the die cap and integral hollow punch 850
are stationary. The integrated hollow punch and die cap 850 are
coupled with the die mandrel 840 using threaded fasteners, wherein
the thrust bearing 860 rotates with the container 810 and billet
830. FIG. 8C illustrates the plasticized billet material is forced
through openings in the die cap 850. The roughened surface of the
rotating die mandrel 840 breaks up large grains of billet material
830. As a result, the extruded tube 870 contains fine-grain
material on the interior surface of the tube. FIG. 8D illustrates
the length of tubing 870 produced as the container and billet
material move towards the stationary hollow punch.
[0062] Some embodiments include removing the male mandrel portion
and using a die cap designed with a non-circular geometric shape,
such as a square, hexagon, or other polygonal shape. Some
embodiments include non-circular geometric shapes that also have a
non-circular hollow. The initial circular hollow can be formed into
a non-circular shape, such as a square, hexagon, or other polygonal
shape through the use of a secondary die.
[0063] FIGS. 3A-8D illustrate embodiments for porthole die
extruders and porthole die extrusion processes. Embodiments for
seamless extruders and seamless extrusion processes are described
herein under.
[0064] FIG. 9 illustrates a seamless tube extruder 900 and
extrusion process. A billet 910 is pierced with a mandrel 920,
while pressure is applied to the billet material. The extruded
material forms a hollow seamless tube 930 over the mandrel 920. All
of the components illustrated in FIG. 9 are stationary or only
allowed to move in one axis, i.e. towards the die and away from the
die. Seamless extruded tubes can be produced in this manner by
either a direct process (a moving ram forced against the billet
material) or an indirect process (a die is forced against a
stationary billet).
[0065] FIGS. 10A-10D illustrate the seamless tube extrusion process
in detail. A container 1010 receives a die tool 1020 and tool
holder 1030 in FIG. 10A. A press disc 1040 is pressed against a
back end of a billet 1050, and a ram 1060 is positioned against the
press disc 1040. The press disc 1040, billet 1050, and ram 1060 are
positioned inside the carrier 1010, as illustrated in FIG. 10B. A
mandrel 1070 pierces the billet 1050, as illustrated in FIG. 10C.
The ram 1060 continues to press against the billet 1050 to force
billet material through the die 1020 and over the surface of the
mandrel 1070, as illustrated in FIG. 10D. The ram 1060 continues to
press against the billet 1050 until the billet material 1050 has
been extruded, to form a resultant hollow tube 1080. The press disc
1040, scrap billet, and tube 1080 are removed from the container
1010 at the conclusion of the processing.
[0066] One short-coming of the seamless tube extrusion process
described with reference to FIGS. 10A-10D is the resultant tubes,
particularly aluminum tubes have poor resistance to pitting
corrosion, especially in a saltwater environment such as OTEC heat
exchangers. Incorporating frictional heating and extensive plastic
deformation into a seamless tube extrusion process improves the
strength and corrosion resistance of seamless tubing. During
friction extrusion, the original grains of the feedstock metal are
broken down into fine grains. In addition, most or all of the
precipitates are dissolved back into the base metal. The resultant
extruded products have very fine grains and much cleaner grain
boundaries, as well as fewer and smaller precipitates inside of the
tubing. This resultant microstructure exhibits better mechanical
properties and much better resistance to corrosive environments,
such as seawater. As a result, the service life of the tubing is
greatly extended.
[0067] FIGS. 11A-11F illustrate how friction processing is
incorporated into the seamless extrusion process described above.
FIG. 11A illustrates that a rotating mandrel 1110 is used against a
non-rotating ram 1120, press disc 1130, container 1140, die 1150,
and die carrier 1160. A lateral force presses the ram 1120 against
the billet 1170 as the mandrel 1110 rotates into the billet 1170,
as illustrated in FIG. 11B. The rotation of the mandrel 1110 stirs
the billet 1170 near the die 1150 opening, as illustrated in FIG.
11C. This refines the grains of the feedstock material before it is
formed into a tube. The mandrel 1110 spins at a high rotational
speed while all other components remain in a non-rotational state.
Frictional heating, as well as a high force from the ram results in
severe plastic deformation of the feedstock. As the plasticized
feedstock is pressed against the back face of the die 1150, the
material grain structure is broken up as a result of shearing
forces from the mandrel 1110. The ram 1120 continues to press
against the press disc 1130 and billet 1170 to extrude a resultant
seamless tube 1180, as illustrated in FIG. 11D.
[0068] The frictionally processed material flows through a mandrel
tip 1190 to form an extruded tube with a smooth interior finish and
very fine grains, as illustrated in FIG. 11E. In addition, the
mandrel can have textured features 1195, including but not limited
to threads, ridges, studs, and protrusions that assist with
breaking up grains and causing the material to flow towards the die
opening, as illustrated in FIG. 11F.
[0069] FIG. 12 illustrates an exemplary active end of a mandrel
1200. A textured or featured surface 1210 assists with breaking up
the large grains in the billet material. Any textured or featured
surface that breaks down the grains of the material can be used,
including but not limited to a threaded surface, a ridged surface,
a studded surface, or other protrusions on an end portion of the
mandrel 1200. The smooth tip 1220 provides a smooth finish on the
interior surface of the tubing. The smooth tip also minimizes the
amount of excess billet material extruded at end of the resultant
tubing. This prevents the excess extruded billet material from
forming along the interior walls of the resultant tubing. In
addition, the smooth tip 1220 can prevent or reduce a shearing zone
on the interior surface near the end of the resultant tubing,
caused by the rotating threaded region 1210 of the mandrel 1200.
The mandrel 1200 described herein and illustrated in FIG. 12
produces continuously extruded tubing, such as twenty to fifty foot
length tubing with a fine grain structure. The threaded features
1210 of the mandrel 1200 effectively break up the grain structure
in the tube wall and reconsolidate the material to produce a
refined grain structure. The seamless friction extrusion process
continuously pushes the billet out of the die, as illustrated in
FIG. 13 to produce a fine grained interior surface 1310 along the
entire length of the tubing 1320.
[0070] In some embodiments as illustrated in FIG. 14, the rotating
mandrel 1400 is designed with a bearing 1410 on the tip, such that
the bearing remains non-rotating as the feedstock flows over the
bearing. The inside diameter profile of the tubing is last formed
by the mandrel tip 1420.
[0071] There may be instances in which an extrusion force is very
large, which will lower or completely prevent the bearing from
rotating. This can cause an overly preferential interior finish. In
order to account for this or counter this effect, the mandrel 1510
has a textured extension 1520 to allow a cylindrical screw cap 1530
to tighten against the bearing 1540 to keep it in place, as
illustrated in FIG. 15. The bearing 1540 and cylindrical screw cap
1530 are designed with a high strength material to allow piercing
of the billet.
[0072] In some embodiments, the mandrel is a two-piece assembly
with one piece rotating and the other piece non-rotating, as
illustrated in FIGS. 16A-16C. The two-piece mandrel 1600 works
similar to a retractable pin tool. A pin portion 1610 of the
mandrel forms the inside diameter of a tube, while a pin tool
shoulder portion 1620 of the mandrel stirs the billet 1630, as
illustrated in FIG. 16A. The mandrel shoulder portion 1620 can be
coupled with a gear or pulley to rotate independent of the mandrel
pin portion 1610. The mandrel pin portion 1610 is kept stationary
so that it does not rotate with the mandrel shoulder portion 1620,
as illustrated in FIG. 16B. This allows the extruded material to
form over a stationary mandrel to produce a better surface finish.
FIG. 16C illustrates the billet extruding over the mandrel pin
portion 1610 to form an extruded tube 1640.
[0073] An indirect extrusion method can also be used to produce
seamless friction extruded tubes with reference to FIGS. 17A-17C.
FIG. 17A is a cross-sectional view illustrating a container 1710
holding a billet 1720. A press disc 1730 and a ram 1740 with a
mandrel are butted against one end of the billet 1720, and a die
1750 and hollow punch 1760 are coupled with the billet 1720 at the
other end. FIG. 17B illustrates a mandrel 1770 piercing the billet
1720. In FIG. 17C, the hollow punch 1760 presses against the billet
1720 to form a continuous extruded tube 1780. As illustrated in
FIGS. 17A-17C, the hollow punch 1760 pushes against the die 1750
and billet 1720 while the ram 1740 remains stationary in an
indirect extrusion method. In addition, the mandrel 1770 retracts
as the container punch presses forward to maintain the positioning
near the die 1750 in an indirect extrusion process. As the hollow
punch 1760 applies force against the die 1750 and billet 1720, the
tube 1780 is extruded over the mandrel 1770 and out through the
hollow punch 1760.
[0074] In some embodiments of the indirect extrusion method, the
die and feedstock billet are heated before the extrusion process
begins. In other embodiments, the die and feedstock billet require
minimal heating or no heating prior to the extrusion process
because frictional heat is generated in the weld chamber.
Temperatures of approximately 700-800 degrees F. are needed for
aluminum or an aluminum alloy metal to reach a moldable
viscosity.
[0075] Both the direct and the indirect seamless extrusion
processes can be implemented with the mandrel tool described above
to produce seamless friction-extruded tubing. For example, the
mandrel illustrated in FIGS. 17B-17C can be rotating while the
hollow punch presses against the billet, which would break up the
large grains normally present in a seamless extruded tube. In
addition, the tip of the mandrel can be threaded to further break
up the large grains and produce a fine grained interior finish on
the tubing.
[0076] In some embodiments, the feedstock material can be a billet
containing recycled metal, such as machining chips, powder, or
scrap. The feedstock is capped with a solid metal cylinder with a
hole through the center, which matches the outer diameter of the
mandrel tool. Since the ram action pushes the semi-loose metal
chips, scrap, and/or powder through the die mandrel without
sufficient heating, the metal washers are set on the top and bottom
of the feedstock billet to allow sufficient heating of the
feedstock before the plasticized material is allowed to enter the
weld chamber. The washer on the top of the billet presses against
the ram and prevents metal from extruding past the ram in the
opposite direction of the die.
[0077] Another process related to extrusion of tubing is tube
drawing. A tube drawing process is usually performed as a secondary
operation after a tube has been seamless extruded, porthole die
extruded, or electric resistance welded (ERW). The starting work
piece can be oversized and drawn down to a smaller diameter and a
smaller wall thickness, as illustrated generally in FIG. 18.
[0078] The tube-drawing process is illustrated in detail in FIGS.
19A-19D. A work piece 1910 is installed against a die 1920 and tool
carrier 1930, as illustrated in FIG. 19A. A mandrel 1940 is
inserted into the back end of the work piece 1910, as illustrated
in FIG. 19B. The mandrel 1940 is pushed forward until it is located
concentrically within the opening of the die 1920. A gripper 1950
is inserted into the tube from the front end until it is positioned
behind the die 1920 and tool carrier 1930, also illustrated in FIG.
19B. The gripper 1950 has an expanding mandrel on the end of its
rod that will tighten onto the inside of the tube wall, illustrated
in FIG. 19C. The gripper 1950 grips with enough force to pull the
tube through the die 1920 and out of the tool carrier 1930. The
gripper 1950 continues to pull the work piece 1910 through the die
1920 and over the mandrel 1940 to reform the tube diameter and wall
thickness to its final dimensions, illustrated in FIG. 19D. All of
the components are either stationary or are allowed to move in just
one axis, i.e. towards or away from the die 1920. A tube drawing
process can use either a direct process or an indirect process.
[0079] A modification of the above-described drawing process
incorporates friction extrusion into the tube work piece during the
drawing process to produce a fine grain interior surface of the
drawn tubes. FIG. 20A illustrates an exterior view of the container
2010 with a mandrel 2020 inserted into the left-side view of the
work piece 2030 and a gripper 2040 inserted into the right-side of
the work piece 2030. FIG. 20A illustrates the mandrel 2020 is
rotating, while the container 2010 remains stationary.
[0080] FIG. 20B is an interior view of the mandrel 2020 end section
in near vicinity to the gripper 2040 end section within the work
piece tubing. The mandrel 2020 end has a tapered cap design, with a
threaded configuration adjacent to the tapered cap. As the mandrel
2020 is rotated, the threads break up the large grains of the
interior surface of the work piece. As a result, small fine grains
are formed on the interior surface of the reworked work piece.
[0081] FIG. 20C illustrates the gripper 2040 pulling on the work
piece 2030. The mandrel 2020 is lodged between the upper and lower
sections of the die 2050, which forces the work piece 2030 to be
thinned at the exit point of the tool carrier. As a result, the
tube is extended in length and the tube thickness is reduced. In an
example, a ten-foot length original work piece can be used to form
a thirty-foot length finished tube. The tapered cap of the mandrel
tool produces a smooth interior finish.
[0082] In other embodiments, a textured mandrel 2110 is rotated
while pulled from one end of a tube work piece located inside of a
stationary container 2120 completely out through the opposite end
of the tube work piece, as illustrated in FIG. 21A. The mandrel
2110 is rotated while it is pulled through the tube work piece.
FIG. 21B illustrates a textured region 2115 of the mandrel 2110,
which breaks up large grains of the original tube work piece as it
is pulled from one end of the work piece to the other end. Fine
grains result on the interior surface of the drawn tubing. The
mandrel 2110 has a smaller textured portion on one end that is used
to rotate the mandrel 2110 and pull the mandrel 2110 through the
tube work piece. The non-textured portion of the mandrel 2110 will
be the same or almost the same dimension as the inside diameter of
the tube. The textured portion of the mandrel 2110 has features,
such as threads, ridges, studs, or protrusions that are slightly
larger in diameter than the non-textured portion, such that the
threads, ridges, studs, or protrusions engage and stir the tube
wall without penetrating through the tube wall into the container,
as illustrated in FIG. 21C.
[0083] The container can be split into two halves and bolted or
clamped together, such that the resultant drawn friction-extruded
tube can be easily removed. In addition, the smaller diameter
sections of the mandrel shaft can be supported with bearings and/or
linear bearings that stabilize the mandrel along the length that
extends beyond the container. The bearings help control run-out of
the mandrel at significant distances away from the rotary motion
source, such as a motor or spindle.
[0084] FIG. 22 illustrates an alternative embodiment in which the
container 2210 rotates, while the mandrel 2220 remains
non-rotational. The container can have integral features, such as
pulley drives that allow a belt drive to rotate the container. The
drive mechanism includes, but is not limited to a geared motor or a
hydraulic motor. Since the tube needs to rotate with the container,
the tube ends are expanded into each end of the container using a
mechanical or hydraulic expander tool. Alternatively, the tube work
piece can be held in place by a gripper mechanism on each end of
the tube, or the tube work piece can be gripped or secured in such
a way that the container is no longer required. The tube can be
easily removed from the container after it has been expanded and
friction-drawn within the container, since the two halves are
bolted together.
[0085] For a substantially long mandrel tool, the shaft can have a
hex feature or other torque-driving feature that allows the use of
shaft guides along the tube length to assist with transmitting
torque, which is applied to the mandrel tool from the spinning
container and the tube. The shaft guides can be fixed to a grounded
structure and have a matched hex or other torque-driving feature
that allows the shaft to move in only one linear direction.
[0086] The end of the mandrel tool has a textured end and a smooth
end cap, as previously described. Therefore, the textured surface
of the mandrel tool breaks up the large grains on the interior
surface of the original tube work piece. The textured surface of
the mandrel includes, but is not limited to features, such as a
threaded surface or a surface containing ridges, studs, or other
protrusions. The interior of the resultant drawn tube has small
grains and a smooth surface.
[0087] Conventionally-drawn tubing has nominal grain sizes similar
to rolled plates and frequently has very large grains on the
interior surface. As a result, the tubing has a low resistance to
corrosive environments, especially on a large grain surface. The
tubing also has low mechanical properties, pertaining to
bendability, fatigue, and fracture toughness.
[0088] By implementing friction extruding and stir welding
processes described herein, the inside surface of the tube is
treated to produce a fine grain microstructure, which has
significant corrosion advantages over conventionally-drawn tubing.
It has a high resistance to corrosive environments on the ends and
the interior surface. Mechanical properties, such as bendability,
fatigue resistance, and fracture toughness are increased when
embodiments described herein are practiced.
[0089] Feedstock material includes, but is not limited to aluminum
and aluminum alloys, titanium and titanium alloys, steels and steel
alloys including stainless steels, copper and copper alloys, and
super alloys containing nickel, molybdenum, chromium, and cobalt.
Some embodiments include heating the dies and feedstock billet
before the extrusion process begins. However, other embodiments
require minimal or no heating prior to the extrusion process
because adequate frictional heat is generated within the weld
chamber. Still other embodiments include using a billet of recycled
metal scrap, machining chips, or powder.
[0090] One embodiment includes using titanium feedstock chips or
powder to form tubing according to embodiments previously described
herein. Conventional titanium processing and stainless steel
processing are quite costly. However, titanium and stainless steels
formed from a billet of scrap metal or powder metal according to
the porthole die friction-extruded tube and the seamless
friction-extruded tube methods described herein can provide a much
more economical mode of tube manufacturing for titanium and
stainless steel tubing.
[0091] Some embodiments include incorporating metal matrix
composite particles, such as aluminum oxides, silicon carbides, and
boron carbides, as well as carbon nano-particles into a composite
billet in conjunction with embodiments described herein for
porthole die friction-extruded tubes, seamless friction-extruded
tubes, and drawn friction-extruded tubes. The carbon nano-particles
can be mixed with a metal feedstock, such as aluminum to form a
matrix nano-composite billet. The friction-extrusion mandrels and
processes described herein provide smaller finer grains on the
interior surface of the tubing. The nano-particles improve the
mechanical and metallurgical properties of the tubing for a higher
strength-to-weight ratio and high temperature resistance to allow
for higher operating temperatures. As a result, the carbon
nano-particle matrix friction-extrusion tubing can be extended to
conditions comparable to titanium tubing, but at a cost of that for
aluminum tubing. In addition, friction extruding enables mass
production of the nanocomposite tubing.
[0092] Embodiments described herein provide corrosion-resistant
tubing that can be used in a saltwater environment, such as in OTEC
heat exchangers. Another embodiment includes a thermal desalination
system and method in which seawater is flash evaporated off the
exterior of the heat exchanger tubes. Fresh water is condensed on
the inside of the tubes.
[0093] Embodiments described herein for porthole die friction-stir
extruded tubes, seamless friction-stir extruded tubes, and
friction-stir drawn tubes provide advantages of a very fine grain
size on the interior surfaces of the tubes, high resistance to
corrosive environments, both on the surface and the interior of the
tubes, and high mechanical properties such as bending, fatigue, and
fracture toughness. These advantages are realized by a
friction-stir mandrel tool, which includes a textured end portion
that is integral with a body portion. The textured end portion is
configured to friction-stir process a starting material forced
across the textured end portion and through a die in a plasticized
state to form a pipe. The textured end portion includes, but is not
limited to features, such as threads, ridges, studs, or
protrusions. The starting material can include a metal, such as
aluminum or an aluminum alloy.
[0094] The friction-stir mandrel tool can be configured to rotate
while the starting material remains rotationally stationary.
Likewise, the mandrel tool can be configured to remain rotationally
stationary while the starting material rotates. The mandrel tool
can also have a smooth cap formed over an end of the textured end
portion, wherein the smooth cap is configured to provide a final
smooth interior surface on the formed pipe. A diameter of the
textured end portion is slightly larger than an inside diameter of
the formed pipe, and smaller than an outside diameter of the formed
pipe. In some embodiments, the mandrel tool is integral with the
die. In other embodiments, the mandrel tool is configured to pierce
through the starting material. In a tube-drawn process, the mandrel
tool is configured to be drawn into the die in conjunction with
drawing the starting material over the mandrel tool.
[0095] FIG. 23 is a flowchart showing an exemplary porthole die
friction-stir extrusion method 2300. A feedstock billet is loaded
into a container in step S2310. One end of the feedstock billet is
abutted with a ram, and another end of the feedstock billet is
abutted against a die mandrel in step S2320. The feedstock billet
and the container are rotated against a die cap while pressure is
applied by the ram in step S2330. Plasticized feedstock is extruded
through passages of the die mandrel in step S2340. Grains of the
plasticized feedstock are broken up by a textured mandrel tip of
the die mandrel. A hollow tube is formed from the extruded
plasticized feedstock in step S2350. In some embodiments, the die
mandrel rotates while the feedstock billet and the container
rotate. In other embodiments, an interior surface of the extruded
hollow tube is smoothed by a mandrel bearing attached to an end of
the textured mandrel tip. In still other embodiments, the
plasticized feedstock is extruded through a hollow punch aperture
integrally formed with the die mandrel. The plasticized feedstock
can be extruded through a rotating hollow punch aperture.
[0096] FIG. 24 is a flowchart showing an exemplary seamless tube
friction-stir extrusion method 2400. A feedstock billet is loaded
into a container in step S2410. One end of the feedstock billet is
abutted with a ram and a concentrically-located mandrel. Another
end of the feedstock billet is abutted against a die in step S2420.
The feedstock billet is pierced with the concentrically-located
mandrel up to the die in step S2430. Pressure is applied to the
feedstock billet by the ram in step 2440. Plasticized feedstock is
extruded through the die and over a textured portion of the
concentrically-located mandrel in step S2450. Grains of the
plasticized feedstock are broken up by the textured portion of the
concentrically-located mandrel. A seamless tube is formed from the
extruded plasticized feedstock in step S2460. In some embodiments,
the concentrically-located mandrel is rotated during the extruding.
In other embodiments, a recrystallized microstructure is formed in
an interior wall of the seamless tube.
[0097] FIG. 25 is a flowchart showing an exemplary tube
friction-stir drawing method 2500. A first end of a tube work piece
is loaded into a die tool and tool carrier of a container in step
S2510. A mandrel tool is inserted at a second end of the tube work
piece in step S2520. The first end of the tube work piece is
engaged in step S2530. A textured portion of the mandrel tool is
drawn inside the die tool while the tube work piece is continuously
drawn over the textured portion in step S2550. Grains of the drawn
tube work piece are broken up by the textured portion of the
mandrel tool. A drawn tube of smaller diameter and thinner wall
thickness is formed in step S2560. In some embodiments, the mandrel
tool is rotated during the drawing. In other embodiments, the
container and the tube work piece are rotated during the
drawing.
[0098] FIG. 26 is a flowchart showing an exemplary pipe forming
method 2600. A starting material is forced across a textured end of
a mandrel and through a die in a plasticized state in step S2610.
The textured end of the mandrel breaks up existing grains of the
starting material. The pipe is formed from material forced through
the die in step S2620. The formed pipe has smaller resultant grains
on an interior surface than the existing grains of the starting
material. The textured end includes, but is not limited to
features, such as threads, ridges, studs, or protrusions.
[0099] In addition to a saltwater environment, embodiments
described herein can be implemented in several other
corrosion-inducing environments, including but not limited to
aircraft hydraulic tubing, liquid natural gas cryogenic heat
exchangers, and heat exchangers used in an acidic environment. The
pharmaceutical and food processing industries require a high degree
of cleanliness. Some instances of pharmaceutical and food
processing use marine-grade aluminum, such as 50/52 or 58,
titanium, or a high nickel-content stainless steel because of the
extremely corrosive environment. Embodiments described herein
provide an efficient and economical alternative for these
environments.
[0100] While the invention has been described in conjunction with
the specific exemplary embodiments thereof, it is evident that many
alternatives, modifications, and variations will be apparent to
those skilled in the art. Accordingly, exemplary embodiments as set
forth herein are intended to be illustrative, not limiting. There
are changes that can be made without departing from the spirit and
scope of the invention.
* * * * *