U.S. patent application number 16/149122 was filed with the patent office on 2019-03-14 for welded, laminated apparatus, methods of making, and methods of using the apparatus.
This patent application is currently assigned to Velocys, Inc.. The applicant listed for this patent is Anna Lee Tonkovich, Thomas Yuschak. Invention is credited to Anna Lee Tonkovich, Thomas Yuschak.
Application Number | 20190076948 16/149122 |
Document ID | / |
Family ID | 44202141 |
Filed Date | 2019-03-14 |
United States Patent
Application |
20190076948 |
Kind Code |
A1 |
Yuschak; Thomas ; et
al. |
March 14, 2019 |
Welded, Laminated Apparatus, Methods of Making, and Methods of
Using the Apparatus
Abstract
The invention describes methods of welding onto laminated
devices using a low temperature welding process. Also described are
laminated devices with welds that do not disrupt a brazed core
block of sheets in the laminated devices. Novel laminated devices
with welded features for servicing the devices are also
described.
Inventors: |
Yuschak; Thomas; (Lewis
Center, OH) ; Tonkovich; Anna Lee; (Dublin,
OH) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Yuschak; Thomas
Tonkovich; Anna Lee |
Lewis Center
Dublin |
OH
OH |
US
US |
|
|
Assignee: |
Velocys, Inc.
Plain City
OH
|
Family ID: |
44202141 |
Appl. No.: |
16/149122 |
Filed: |
November 28, 2018 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13039303 |
Mar 2, 2011 |
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16149122 |
|
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61309851 |
Mar 2, 2010 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
Y10T 428/12903 20150115;
B23K 9/04 20130101; Y10T 137/0318 20150401; B23K 1/0012 20130101;
B23K 2101/14 20180801; Y10T 137/85938 20150401; B23K 9/0052
20130101; Y10T 29/49718 20150115 |
International
Class: |
B23K 1/00 20060101
B23K001/00; B23K 9/04 20060101 B23K009/04; B23K 9/00 20060101
B23K009/00 |
Claims
1. Laminated apparatus comprising: a core block comprising sheets
of metal bonded together, at least in part, by a braze composition
disposed between the sheets; a welding composition disposed on the
core block and adhering to the braze composition; wherein the
welding composition has a composition that differs from the
composition of the braze composition; and wherein the welding
composition is diffused 2 mm or less into the core block.
2. The apparatus of claim 1 wherein the welding composition forms a
continuous weld across more than one metal sheet and more than one
of the braze composition disposed between the sheets.
3. The apparatus of claim 1 comprising fluid channels disposed in
the sheets and inlets to the fluid channels disposed on edges of
the sheets.
4. The apparatus of claim 3 having resistance to leakage such that,
when the fluid channels are pressurized with N2 at 100 psig (6.9
bar gauge), the pressure decreases by less than 0.5 psi (0.034 bar)
after 15 minutes.
5. The apparatus of claim 3 comprising: a first set of fluid
channels wherein each channel comprises an inlet and an outlet; a
second set of fluid channels wherein each channel comprises an
inlet and an outlet; a first welded inlet manifold, a first welded
outlet manifold; a second welded inlet manifold, and a second
welded outlet manifold; wherein the first welded inlet manifold is
in fluid communication with the inlets of the first set of fluid
channels; wherein the first welded outlet manifold is in fluid
communication with the outlets of the first set of fluid channels;
wherein the second welded inlet manifold is in fluid communication
with the inlets of the second set of fluid channels; wherein the
second welded outlet manifold is in fluid communication with the
outlets of the second set of fluid channels; and wherein each of
the manifolds are connected to the core block by a welding
composition wherein the welding composition has a composition that
differs from the composition of the braze composition; and wherein
the welding composition is diffused 2 mm or less into the core
block.
6. The apparatus of claim 5 wherein at least 2 of the manifolds are
welded to the core block on a same side of the core block.
7. The apparatus of claim 1 comprising subassemblies that have been
diffusion bonded.
8. A method of conducting a unit operation in the apparatus of
claim 1 comprising: passing a fluid into a channel in the core
block and conducting a unit operation on the fluid in the core
block.
9. The method of claim 8 wherein a first fluid is passed into a
first set of inlets and into a first set of channels in the core
block; a second fluid is passed into a second set of inlets and
into a second set of channels in the core block; and wherein the
first fluid and the second fluid flow in adjacent sheets within the
core block and the first fluid exchanges heat with the second fluid
in the core block.
10. A method of welding a metal onto laminated apparatus,
comprising: providing laminated apparatus comprising sheets of
metal bonded together, at least in part, by a braze composition
disposed between the sheets; applying a metal onto the laminated
apparatus by a welding technique wherein a wire moves in a
reciprocating motion and wherein a spark is generated when the wire
touches and/or is pulling away from the laminated apparatus; and
wherein molten metal is applied to the surface while the wire moves
away from the surface.
11. The method of claim 10 wherein, within 30 seconds of active
welding, and without liquid cooling, the temperature of the
laminated article is 100.degree. C. or less (preferably 50.degree.
C. or less) throughout the entire apparatus.
12. The method of claim 10 wherein a weld is formed at a rate of 25
cm per minute or greater.
13. A method of repairing a crack comprising applying a metal
according to the process of claim 10 onto a crack in laminated
apparatus.
14-19. (canceled)
20. The apparatus of claim 1 further comprising a solid-walled
enclosure that encloses plural apertures within a single,
contiguous space on a side of the core block; wherein the
solid-walled enclosure comprises a solid, continuous wall that is
welded on one side to the core block by the welding
composition.
21. A process of operating the apparatus of claim 16, comprising:
opening the manifold while leaving the enclosure welded to the core
block; and performing service on the core block.
22. The process of claim 21 wherein the step of performing service
comprises at least one of: regenerating catalyst, replacing
catalyst, regenerating sorbent, replacing sorbent, cleaning, or
diagnostic testing.
23. The method of claim 8 wherein the unit operation comprises a
Fischer-Tropsch reaction.
Description
RELATED APPLICATIONS
[0001] This application claims priority to U.S. provisional patent
application 61/309,851, filed 2 Mar. 2010.
INTRODUCTION
[0002] Laminated devices are often formed by brazing together metal
sheets, using an added material (braze) interlayer between adjacent
sheets in order to achieve adhesion and or joining and or a
substantially hermetic seal between two or more layers. A problem
with welding an additional piece on to such a laminated device in
proximity to braze boundary layers is that conventional welding
often results in cracks that form between the sheets. Laminated
apparatus, especially microchannel apparatus can be deformed or
weakened by welding processes. Thus, there is a need for methods
repairing cracks in laminated apparatus and also for laminated
apparatus that is less susceptible to cracking.
SUMMARY OF THE INVENTION
[0003] In one aspect, the invention comprises a method of welding a
metal onto laminated apparatus, comprising: providing laminated
apparatus comprising sheets of metal bonded together, at least in
part, by a braze composition disposed between the sheets; applying
a metal onto the laminated apparatus by a welding technique wherein
a wire moves in a reciprocating motion (moving alternatively back
and forth) and wherein a spark is generated when the wire touches
and/or is pulling away from the laminated apparatus and wherein
molten metal is applied to the surface while the wire moves away
from the surface. Typically, the process is carried out in an inert
atmosphere such as by a shroud of inert gas blowing around the wire
and apparatus. It may be the case that a braze composition is
present between all the sheets; however, in some devices, there is
a braze composition only between some sheets--this could be the
case, for example, where some sheets are prebonded by diffusion
bonding (to form a subassembly) and the resulting diffusion-bonded
laminated pieces are subsequently joined to single sheets or
another diffusion-bonded laminated piece by brazing.
[0004] In some alternative embodiments, the method can be
characterized as intermittent arc discharge with a reciprocating
welding wire. Likewise, molten metal is applied to the surface
while the wire moves away from the surface.
[0005] Further, the method could be used to weld a solid metal
article to a brazed, laminated structure. The solid article could
be a header, a footer, and inlet or outlet nozzle, an enclosure
(see below), a structural support element useful either during
operation or in a ambient state, a connector used for lifting or
supporting the laminated device, or other useful component.
[0006] This process can be conducted with very low heating of the
laminated apparatus and, in preferred embodiments, within 30
seconds of active welding (according to the inventive process) and
without the application of liquid quenching, the temperature of the
laminated article is 100.degree. C. or less throughout the entire
apparatus. In another embodiment, the temperature of the laminated
article is 50.degree. C. or less within 30 seconds of completing
the welding step. This contrasts with conventional welding
processes in which the laminated article is much hotter, typically
red hot, during the welding and for several minutes after welding
has ceased.
[0007] The inventive process enables the production of unique
structures, and the invention includes apparatus made by the
inventive process. Generally, the process results in a structure in
which there is little diffusion, at the welding site, of welding
composition into the core block. The core block comprises laminated
sheets which have been joined into a stack. Core blocks may have
more than 10 or more than 100 or more than 1000 layers.
[0008] In addition, the invention provides welded, laminated
apparatus. The laminated apparatus comprises: a core block
comprising sheets of metal bonded together, at least in part, by a
braze composition disposed between the sheets; a welding
composition disposed on the core block and adhering to the braze
composition; wherein the welding composition has a composition that
differs from the composition of the braze composition; and wherein
the welding composition is diffused 2 mm or less (preferably 1.0 mm
or less, preferably 0.5 mm or less, more preferably 0.3 mm or less)
into the core block. Typically, diffusion into the core block can
be measured by microscopy on a cross-section of the core block.
[0009] Preferably, the core block comprises sheets of metal bonded
together, at least in part, by a braze composition disposed between
the sheets. The core block comprises stacked sheets, and may
include manifolds that are integral to the sheets, but the core
block does not include external manifolds, handles, or external
tubes.
[0010] In a further aspect, the invention provides microchannel
apparatus, comprising: a core block comprising sheets of metal
bonded together; plural microchannels disposed within the core
block; the plural microchannels comprising plural apertures on one
side of the core block; a solid-walled enclosure that encloses the
plural apertures within a single, contiguous space; wherein the
solid-walled enclosure comprises a solid, continuous wall that is
welded on one side to the core block by a weld material; wherein
the continuous wall has an aspect ratio of at least 10:1 of height
to thickness (where height is the direction that the wall projects
from said one side of the core block, and thickness is
perpendicular to height and is the commonly-used understanding of
wall thickness.
[0011] The invention also includes any of the apparatus or methods
described in the section entitled Detailed Description of the
Invention. For example, the invention includes a method in which a
weld is formed over apertures (channel openings) and weld material
is then removed to reopen the channels (see Example 2). The
invention also includes apparatus in which sheets comprising
channels protrude from a face of a core block (see FIG. 3).
[0012] Advantages of the invention include the reduction or
elimination of leaks and cracks. The welding method is particularly
useful for laminated articles in which an interlayer has a melting
point less than that of the laminated sheets, which have a higher
melting point. Welds can be made along cracks, parallel to layers
within a laminate, perpendicular to layers within a laminate, or at
any angle relative to layers in a laminate. It is difficult to weld
onto a block which has been formed from brazing parallel sheets.
This is because the brazing material has a low melting point
compared to the sheet material, which is suitable for obtaining
good brazing. During brazing, the braze material moves around and
quite effectively fills the voids between the sheets. Subsequent
welding onto a brazed article results in re-melting of braze
material in the warm location of the weld, resulting in diffusion
of weld material into braze material. While not wishing to be bound
by theory, when the article cools after welding, the welding and
brazing compositions may cool at different rates, and the material
joining the sheets becomes non-uniform in that location, which may
cause cracks in the filler material between the sheets. These
cracks interfere with the integrity of the device, which, if used
for fluid processing, may result in leaks. These problems are
magnified for devices with many layers, and is also magnified for
devices with longer dimensions, and longer welds, all of which
contribute to cracks, which either must be detected and repaired,
or the article scrapped. This invention avoids these problems by
applying new welding techniques (e.g. CMT, with a passing reference
to fiber laser welding) to minimize the diffusion of weld
composition into braze material in a brazed laminated article.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 shows weld seams.
[0014] FIG. 2 schematically illustrates a perspective view of a
core block with an attached enclosure and a side view with an
optional connected manifold enclosure and piping.
[0015] FIG. 3 shows coolant channels protruding out from coolant
face in a Fischer-Tropsch reactor core.
[0016] FIG. 4 is a view showing repaired braze seams on test FT
reactor.
[0017] FIG. 5 is a view showing process face of small FT test
reactor. Seams 1-3 are within the waveform zones (central region)
of the reactor. Seams 4-9 are within the perimeter zones of the
reactor.
[0018] FIGS. 6-8 illustrate welding methods of sealing leaks in a
laminated device.
DETAILED DESCRIPTION OF THE INVENTION
[0019] The appearance of the weld seam on a part after welding
along a laminate seam can have a distinct semicylinder or partial
cylinder shape (see FIG. 1). The region is typically fairly
straight if it is made by a robotic or automated welding process,
and in some preferred embodiments, the weld seam is substantially
straight as illustrated in the figure below. The radius of the
semicylinder that sits above the laminated part is typically less
than 10 mm and preferably between 0.01 mm to 5 mm, with a more
preferable range from 0.1 mm to 2 mm.
[0020] In some embodiments, the weld has the semicircular shape
described above. The metal sheets have a composition that is
different than the braze interlayer. In some embodiments, the weld
composition is different from the composition of the metal
sheets.
[0021] The invention includes microchannel apparatus schematically
illustrated in FIG. 2., comprising: a core block 17 comprising
sheets of metal bonded together; plural microchannels disposed
within the core block; the plural microchannels comprising plural
apertures 19 on at least one side of the core block; a solid-walled
enclosure 21 that encloses the plural apertures within a single,
contiguous space 22; wherein the solid-walled enclosure comprises a
solid, continuous wall that is welded on one side to the core block
by a weld material 23; wherein the continuous wall has an aspect
ratio of at least 10:1 of height to thickness (where height is the
direction (corresponding to 21) that the wall projects from said
one side of the core block, and thickness is perpendicular to
height and is the commonly-used understanding of wall thickness);
and wherein the side of the solid-walled enclosure that is opposite
to the side that is welded to the core block may comprise a
connection to a conduit 27. The connection to the conduit 25 may
comprise a conventional weld, while the connection of the enclosure
to the core block is preferably an inventive weld of the type
described herein. Thus, typically, the connection to the conduit
has a different composition and/or morphology than the weld
material. The conduit may comprise piping 29. Preferably, the weld
to the core block is formed by Cold Metal Transfer (CMT) welding.
The CMT weld may alternatively be described in any of the ways
provided herein. In less preferred embodiments, where the apparatus
is used under low temperature and/or low corrosion conditions, a
header space can be formed via a gasket connecting the enclosure
with a conduit.
[0022] In addition to the use of CMT to join an enclosure to a
brazed article, other low energy input methods of welding may be
used to attach an enclosure or a header to a laminated device. For
example, a fiber laser, such as with a Yb laser, may be used to
join a solid metal article to a brazed article. The laser welding
approach creates a narrow but deep penetration weld that is
particularly useful for creating a structural joint on a pressure
or load bearing part.
[0023] The invention also includes methods of making laminated
apparatus comprising the use of CMT; preferably including CMT to
weld the enclosure on the core block.
[0024] The apertures comprise inlets or outlets for fluid
processing or ports used for instrumentation for process
measurements and controls, diagnostics, or for use during
manufacturing or refurbishment of the apparatus
[0025] The invention also includes methods of accessing the plural
microchannels through said plural apertures, comprising: breaking
the connection between the enclosure and a conduit without
disrupting the weld that attaches the solid-walled enclosure to the
core block, and accessing the plural microchannels through the
solid-walled enclosure and through the plural apertures.
[0026] The invention also includes reattaching the connection to
re-attached piping.
[0027] After breaking the connection, tasks that could be conducted
include: maintenance or inspection of the core block, including
removing material (comprising for example, but not limited to
catalyst, sorbents, fins, waveforms, and other inserted materials),
adding material (catalyst, sorbents, fins, waveforms, inserts), and
inspecting the quality and uniformity of the flow passages through
diagnostic tests, including flow tests, and performing maintenance,
such as cleaning or repair of the passageways.
[0028] The enclosure is a solid metal ring that mates with the
brazed surface and is then used for subsequent welding of headers
or footers to bring or remove fluids to a microchannel brazed
device. The solid ring may be a unitary (preferably made by
molding) part or made from two or four or more parts that are
welded together to form a solid ring. In one embodiment for a
square or rectangular face, it is preferable to form a ring using 4
straight parts with weld joints to form a contiguous square or
rectangular ring. The advantage of a ring (which may be circular,
square, rectangular, or other shape) is that the header or footer
may be cut or ground off many times to have access to the channels
after operation for catalyst refurbishment or for evaluation of
changes to channels or for a cleaning or defouling step after
process operation. It is envisioned that catalysts loaded in a
microchannel device would be removed periodically (from every week
to once every 10 years) and at that time, the header and or footer
would need to be separated from the ring for such refurbishment.
The initial welding across braze seams or joints or across
laminates might only occur once in the life of a brazed device.
[0029] The inventive methods of servicing a laminated device
provide significant advantages over methods that can be conducted
using conventional apparatus (such as simple tub welds) since the
apertures can be accessed without damaging the surface of the core
block. Additionally, since the weld between the enclosure and the
conduit can be removed by simple grinding (optionally vacuum
grinding) rather than cutting; there is less contamination than
conventional methods.
[0030] In some preferred embodiments of the invention, there is a
weld across plural brazing layers (the layers between metal
sheets). The weld can be parallel to the metal sheets,
perpendicular to the metal sheets or at any desired angle with
respect to metal sheets in a core block.
[0031] The invention also provides a method of using the any of the
above-described apparatus comprising passing a fluid through
channels in the core block, and a conducting a unit operation on
the fluid as it passes through the channels. The apparatus may be
used for processes such as heat exchange, mixing, heating, cooling
(including a heat sink for electronic devices), chemical reaction,
chemical separation. The apparatus may also comprise an
electrochemical device, which utilizes a solid or liquid
electrolyte and electrodes to obtain electrical work from a
spontaneous chemical reaction (including but not limited to
batteries and fuel cells), or conversely, to apply electrical work
to generate chemical species (including but not limited to
eletrolyzers, oxygen generators and reverse fuel cells), or to
produce an electrical signal in response to a change in the device
environment (including but not limited to sensors and analytical
devices). The apparatus may also be a thermoelectric device. In
some preferred embodiments, the apparatus is a chemical
reactor.
[0032] In preferred embodiments, sheet thicknesses are 1 cm or less
(such as may contain waveforms, engineered catalyst structures,
fins, etc.), 2 mm or less, and in some embodiments 1 mm or
less.
[0033] As used herein, the term "microchannel" refers to any
conduit having at least one dimension (height, length, or width)
(wall-to-wall, not counting catalyst) of 1 cm or less, including 2
mm or less (in some embodiments about 1.0 mm or less) and greater
than 100 nm (preferably greater than 1 .mu.m), and in some
embodiments 50 to 500 .mu.m. Microchannels are also defined by the
presence of at least one inlet that is distinct from at least one
outlet. Microchannels are not merely channels through zeolites or
mesoporous materials. The length of a microchannel corresponds to
the direction of flow through the microchannel. Microchannel height
and width are substantially perpendicular to the direction of flow
of through the channel. In the case of a laminated device where a
microchannel has two major surfaces (for example, surfaces formed
by stacked and bonded sheets), the height is the distance from
major surface to major surface and width is perpendicular to
height.
[0034] In some embodiments, the laminated apparatus may comprise
one or more waveforms. A "waveform" is a 3-dimensional contiguous
piece of thermally conductive material that at least partially
defines one or more microchannels. The waveform may have a gap
between the waves that is in the microchannel dimension or may be
larger. In exemplary form, this gap may be in the microchannel
dimension because then heat is easily transferred to the long
direction in the wave that separates the heat transfer channels
before conducting down the more conductive wave form to the heat
transfer channels. The waveform may be made of copper, aluminum,
FeCrAlY, metals, oxides, or other materials. The waveform
preferably has a thermal conductivity greater than 1 W/m-K.
[0035] As is standard patent terminology, "comprising" means
"including" and neither of these terms exclude the presence of
additional or plural components. For example, where a device
comprises a lamina, a sheet, etc., it should be understood that the
inventive device may include multiple laminae, sheets, etc. In
alternative embodiments, the term "comprising" can be replaced by
the more restrictive phrases "consisting essentially of" or
"consisting of."
[0036] "Unit operation" means chemical reaction, vaporization,
compression, chemical separation, distillation, condensation,
mixing, heating, or cooling. A "unit operation" does not mean
merely fluid transport, although transport frequently occurs along
with unit operations. In some preferred embodiments, a unit
operation is not merely mixing.
[0037] "A process of operating" means repairing, maintaining,
refurbishing, or diagnosing; and may include preparations conducted
prior to conducting unit operations, scheduled or unscheduled
maintenance, or other uses of the apparatus.
[0038] Microchannel apparatus (such as microchannel reactors)
preferably include microchannels (such as a plurality of
microchannel reaction channels) and a plurality of adjacent heat
exchange microchannels. The plurality of microchannels may contain,
for example, 2, 10, 100, 1000 or more channels capable of operating
in parallel. In preferred embodiments, the microchannels are
arranged in parallel arrays of planar microchannels, for example,
at least 3 arrays of planar microchannels. In some preferred
embodiments, multiple microchannel inlets are connected to a common
header and/or multiple microchannel outlets are connected to a
common footer. In some preferred embodiments, there may be multiple
separate flow streams. One fluid stream may flow through a
plurality of microchannels. A second fluid stream may flow through
a second plurality of microchannels, or may flow through one or
more macrochannels. During operation, heat exchange microchannels
(if present) contain flowing heating and/or cooling fluids.
Non-limiting examples of this type of known reactor usable in the
present invention include those of the microcomponent sheet
architecture variety (for example, a laminate with microchannels)
exemplified in U.S. Pat. Nos. 6,200,536 and 6,219,973 (both of
which are incorporated by reference).
[0039] In many preferred embodiments, the microchannel apparatus
contains multiple microchannels, preferably groups of at least 5,
more preferably at least 10, parallel channels that are connected
in a common manifold that is integral to the device (not a
subsequently-attached tube) where the common manifold includes a
feature or features that tend to equalize flow through the channels
connected to the manifold. Examples of such manifolds are described
in U.S. patent application Ser. No. 10/695,400, filed Oct. 27, 2003
which is incorporated herein. In this context, "parallel" does not
necessarily mean straight, rather that the channels conform to each
other. In some preferred embodiments, a microchannel device
includes at least three groups of parallel microchannels wherein
the channel within each group is connected to a common manifold
(for example, 4 groups of microchannels and 4 manifolds) and
preferably where each common manifold includes a feature or
features that tend to equalize flow through the channels connected
to the manifold.
[0040] Microchannels can incorporate materials paced inside the
microchannels, such as catalysts, sorbents, or other materials.
Such materials may be incorporated into the channels as
particulates or small pieces Catalysts, sorbents, or other coatings
can be applied onto the interior surface of a microchannel using
techniques that are known in the art such as wash coating.
Techniques such as CVD or electroless plating may also be utilized.
In some embodiments, impregnation with aqueous salts is preferred.
Pt, Rh, and/or Pd are preferred in some embodiments. Typically this
is followed by heat treatment and activation steps as are known in
the art. Other coatings may include sol or slurry based solutions
that contain a catalyst precursor and/or support. Coatings could
also include reactive methods of application to the wall such as
electroless plating or other surface fluid reactions.
[0041] The sheets of metal in a laminated apparatus are preferably
a stainless steel or a superalloy, such as a nickel, cobalt, or
iron based superalloy. Other examples include, but are not limited
to, FeCrAlY, titanium alloys, and Ni--Cr--W superalloy. Sheets
typically range in thickness from 10 .mu.m to 1 cm, more typically
100 .mu.m to 5 mm. Sheets may be solid (such as dividing walls) and
may contains holes or slots as well as partially etched channels
and other features such as is known in the art of laminated
devices.
[0042] Prior to brazing surfaces are preferably cleaned and may be
coated with a surface layer such as a Ni layer.
[0043] Materials for brazing are well known in the art. Brazing is
typically conducted in vacuum or an inert atmosphere. As is well
known, during brazing, a relatively low temperature brazing
material is melted between metal sheets and then some diffusion
occurs between the brazing material and the sheets and, after
cooling, a braze composition (which typically differs somewhat from
the composition of the original brazing material) remains between
the sheets. Techniques such as microscopy and other known
metallurgical techniques can be used to identify and characterize a
braze composition between sheets in a laminated device.
[0044] The present invention is generally applicable to brazed
laminates. For nickel-based metal sheets, a preferred brazing
material is NiP. One standard braze material is BNi-6 or a
combination of 10-12.5% Phosphorous in nickel. Brazing often uses a
transient liquid phase (TLP) interlayer which acts as a melting
point depressant for a metal. At an elevated temperature that
exceeds the operational temperature requirement but does not
approach the melting point of the parent material or a temperature
which contributes significant diffusion bonding or grain growth of
metals across laminate shim boundaries, the TLP transforms from a
solid to a liquid phase to flow and fill all voids between layers.
As the braze process occurs the TLP depressant material, which may
be phosphorous or boron or others diffuses from the braze
interlayer to change the melting point of the metal.
[0045] Some nonlimiting examples of brazing compositions include
the following each of these braze interlayers would be advantaged
by the described invention.
TABLE-US-00001 MBF AWS & AMS Nominal Composition, wt. % Alloy
Classifications Cr Fe Si C* B P W Co Ni 15 13.0 4.2 4.5 0.03 2.8 --
-- 1.0* Bal 20 AWS BNi2/AMS 4777 7.0 3.0 4.5 0.06 3.2 -- -- -- Bal
30 AWS BNi3/AMS 4778 -- -- 4.5 0.06 3.2 -- -- -- Ba 50 AWS BNi-5a
19.0 -- 7.3 0.08 1.5 -- -- -- Bal 51 AWS BNi-5b 15.0 -- 7.25 0.06
1.4 -- -- -- Bal 55 5.3 -- 7.3 0.08 1.4 -- -- -- Bal 60 AWS BNi6 --
-- -- 0.10 -- 11.0 -- Bal 80 15.2 -- -- 0.06 4.0 -- -- -- Bal Foils
are available with more rigid dimensional tolerances as specialty
or "A" grades *Maximum concentration
TABLE-US-00002 Braze Temp. Density MBF AWS & AMS Melting Temp.
.degree. C. (.degree. F.) (Approx.) g/cm.sup.3 Alloy
Classifications Solidus Liquidus .degree. C. (.degree. F.)
(lbm/in.sup.3) 15 965 (1769) 1103 (2017) 1135 (2075) 7.82 (0.283)
20 AWS BNi2/AMS 4777 969 (1776) 1024 (1875) 1055 (1931) 7.88
(0.285) 30 AWS BNi3/AMS 4778 984 (1803) 1054 (1929) 1085 (1985)
8.07 (0.291) 50 AWS BNi-5a 1052 (1924) 1144 (2091) 1170 (2138) 7.70
(0.278) 51 AWS BNi-5b 1030 (1886) 1126 (2058) 1195 (2183) 7.73
(0.278) 55 950 (1742) 1040 (1904) 1070 (1958) 7.72 (0.279) 60 AWS
BNi6 883 (1621) 921 (1688) 950 (1742) 8.14 (0.294) 80 1048 (1918)
1091 (1996) 1120 (2045) 7.94 (0.278)
[0046] In preferred embodiments, a wire in the inventive welding
process preferably has a similar, or the same, composition as the
metal in the metal sheets of the laminate. In preferred
embodiments, the wire has any of the compositions as described
above for the metal sheets.
[0047] The phase diagram of Ni--P shows a eutectic point near 11%
phosphorus by weight in nickel. As the phosphorous diffuses away
from the interlayer into the adjacent metal surface, the local
weight percent of nickel is reduced and the composition changes
which solidifies the braze interlayer. One advantage of the braze
process is that the resulting brazed device can withstand a higher
braze temperature because the resultant phosphorous depleted
interlayer region will only remelt at a higher temperature per the
phase diagram. Unfortunately, the conventional welding temperature
reaches the melt temperature of the parent material (.about.1400 to
1500.degree. C. for Stainless 300 series), often a nickel
containing substance and the result is a remelt of the braze
interlayer and the formation of cracks. The cracks both create leak
problems for an operational device (heat exchanger, reactor,
separations unit, mixer, or other single or combined unit
operation) and mechanical integrity problems if the device is
intended for high pressure and or temperature operation.
Difficulties with welding over short sections of brazed devices and
then inspecting, detecting, and repairing cracks has been
encountered. This problem becomes even more challenging when
attempting to weld along long sections of a brazed device with
hundreds, or even thousands of thin sheets.
[0048] One conventional solution to avoid this problem is to braze,
rather than weld, connections to brazed devices.
[0049] The invention provides a new use and a new advantage for a
welding technique known as cold metal transfer ("CMT"). This
technique is described at
http://www.welding-robots.com/applications.php!app=cold+metal+transfer
as follows:
"Cold" is a relative term in perspective to welding, Cold Metal
Transfer welding is commonly referred to as CMT. The workpieces to
be joined as well as the weld zones remain considerably "colder" in
the cold metal transfer process (CMT) than they would with
conventional gas metal arc welding. The cold metal transfer process
is based on short circuiting transfer, or more accurately, on a
deliberate, systematic discontinuing of the arc, Results are a sort
of alternating "hot-cold-hot-cold" sequence. The "hot-cold" method
significantly reduces the arc pressure. During a normal short
circuiting transfer arc, the electrode is distorted while being
dipped into the weld pool, and melts rapidly at high transfer arc
current. A wide process window and the resulting high stability
define the cold metal transfer process, Automation and
robot-assisted applications is what the process is designed
for.
[0050] The major advancement is that the motions of the wire have
been integrated into the welding process and into the overall
management of the procedure. Every time short circuiting occurs,
the digital process control interrupts the power supply and
controls the retraction of the wire. The forward and back motion
takes place at a rate of up to 70 times per second. The wire
retraction motion aides droplet detachment during the short
circuit. The fact that electrical energy is converted into heat is
both a defining feature and sometimes critical side effect of arc
welding. Ensuring minimal current metal transfer will greatly
reduce the amount of heat generated in the cold metal transfer
process. The restricted discontinuations of the short circuit leads
to a low short-circuit current. The arc only inputs heat into the
materials to be joined for a very short time during the arcing
period because of the interruption in the power supply.
[0051] The reduced thermal input offers advantages such as low
distortion and higher precision. Benefits include higher-quality
welded joints, freedom from spatter, ability to weld light-gauge
sheet as thin as 0.3 mm, as well as the ability to join both steel
to aluminum and galvanized sheets.
[0052] Additional description of the CMT welding process is
presented by Feng et al. in "The CMT short-circuiting metal
transfer process and its use in thin aluminum sheets welding,"
Materials and Design 30 (2009) 1850-1852.
[0053] A process known as controlled short circuit ("CSC") operates
similarly to CMT, and, for purposes of the present invention, comes
within the term "CMT." Frequency of the wire motion is preferably
in the range of 10 to 30 Hz, but other frequencies are also useful.
In some embodiments, travel speed of the wire along the surface is
preferably less than about 30 inch per minute; in some embodiments
travel speed is in the range of 1 to 25 inches per minute or 15 to
25 inches per minute.
[0054] The inventive process can be used to seal protruding
features in laminated devices. An example is shown in FIG. 3. As
with all aspects of the invention, the invention includes
structures formed by the methods of the invention.
[0055] Shim Side Repairs [0056] One option to seal leaks along the
shim side of a device, is to seal along the protruding edges of the
shims. As shown in FIG. 3, the CMT may weld in the resultant corner
which is 0.125'' away from the end of the laminate as shown in FIG.
3. Identify start and stop point of repair based on previously
collected leak test results Program robot for start and stop points
with wire placed about 1.5 wire diameters away from the seam to be
repaired [0057] Surface preparation: [0058] Wire brush seam prior
to repair [0059] Wipe seam with acetone [0060] Set weld parameters:
[0061] Feed angle=10.degree. [0062] Wire feed speed=150 inches per
minute [0063] Arc Length Value=+3.0 [0064] Travel Speed=20 inches
per minute [0065] Run repair and visually inspect to ensure seam
was covered If seam was not fully covered in the known leak zone:
grind down repair and perform second pass Repeat until all coolant
side zone leaks have been welded (see FIG. 4) Post repair machining
[0066] Mill/Grind down repair beads on faces in zones where rings
will be attached to .about.20 mil (500 microns) pad height Post
repair leak check [0067] Repeat leak test procedure to ensure that
all leaks have been sufficiently sealed. If additional leaks exist,
re-repair as necessary The invention includes apparatus in which
sheets comprising channels protrude from a face of a core block.
Advantageously, this design can be combined with welds along the
protruded sheets that have superior leak resistance. In some
preferred embodiments, the protruded sheets are enclosed within an
enclosure of the type described herein.
Example 1
[0068] The brazed device was leak checked to confirm the presence
of leaks. The device consisted of SS 304L laminates that are brazed
with a nickel phosphorous (BNi6) interlayer (0.001'' thick, 25
microns), brazed at 960 C for 1 hour with a pressure of 60 lbf per
in2 (4 bar). If leaks were found then they were repaired using Cold
Metal Transfer (CMT) welding. SS304L, 40 mil (100 microns) diameter
filler wire was used for the repair.
[0069] For devices with fins or waveforms or channels that need to
be kept clean of weld material, a shroud is placed over such areas
prior to welding. It is preferred but not required that shrouds are
placed over openings or sides of a device not undergoing welding
while repairing an affected or leaky face of a device.
Crack repair was accomplished on a device schematically illustrated
in FIG. 5. [0070] Perimeter zone repairs [0071] Cover waveform
sections preferably with high temperature ceramic tape to protect
them (note: repairs are not occurring in zones directly adjacent to
the copper waveforms). [0072] Identify start and stop point of
repair based on leak test results [0073] Program robot for start
and stop points with wire centered over seam to be repaired [0074]
Surface prep prior to welding: [0075] Wire brush seam prior to
repair [0076] Wipe seam with acetone [0077] Set weld parameters:
[0078] Wire Feed Speed=120 inches per minute [0079] Arc Length
Value=+3.0 [0080] Travel Speed=20 inches per minute [0081] Run
repair and visually inspect to ensure seam was covered [0082] If
seam was not fully covered in the known leak zone: grind down
repair and perform second pass [0083] Repeat until all perimeter
zone leaks have been welded The waveforms can be covered with a
metal film to protect them during welding.
Example 2
[0084] Alternate inventive methods for sealing leaks across brazed
joints along shim or laminae. The seam or opening of the channel is
welded over directly (preferably by CMT). The fully closed channels
are then reopened using machining, plunge electro-discharge
machining, Molecular Decomposition Process Grinding MDP, grinding
or other process to reopen just the flow passage ways while leaving
the brazed joint fully covered with the CMT weld. FIGS. 6-8
illustrate this process. Preferably, the welds are ground flat
prior to machining to reopen the channels. The illustrated in the
figures had a leak rate greater than 0.5 psig loss in 15 minutes at
100 psig fixed pressure before repair of the braze leaks with CMT
and a leak rate less than 0.5 psig loss in 15 minutes at 100 psig
fixed pressure after braze repair. This test can be used as a
method to characterize preferred embodiments of the inventive
apparatus. In each case, leak testing is conducted with nitrogen
gas at room temperature.
[0085] The invention thus includes a method in which a weld is
formed over apertures (channel openings) and weld material is then
removed to reopen the channels--this method has been demonstrated
to reduce leaking in a laminated device.
* * * * *
References