U.S. patent application number 12/903502 was filed with the patent office on 2011-04-21 for low turbulence argon purging system.
This patent application is currently assigned to PCC STRUCTURALS INC.. Invention is credited to James Barrett, David Brayshaw, Ting-Kwo Lei, Lee Patrick, Scott Wittkop.
Application Number | 20110089225 12/903502 |
Document ID | / |
Family ID | 43876862 |
Filed Date | 2011-04-21 |
United States Patent
Application |
20110089225 |
Kind Code |
A1 |
Patrick; Lee ; et
al. |
April 21, 2011 |
Low Turbulence Argon Purging System
Abstract
Apparatus and method for purging atmospheric air from a chamber
with a gas including means for generating a substantially
non-turbulent, laminar flow front of the gas into the chamber with
minimal turbulence to displace the atmospheric air in the chamber,
the chamber having exhaust means associated therewith to permit the
displaced atmospheric air to exit the chamber. The chamber is
preferably a welding chamber and the gas is preferably argon.
Inventors: |
Patrick; Lee; (Sherwood,
OR) ; Brayshaw; David; (Happy Valley, OR) ;
Wittkop; Scott; (Beavercreek, OR) ; Barrett;
James; (Milwaukie, OR) ; Lei; Ting-Kwo;
(Clackamas, OR) |
Assignee: |
PCC STRUCTURALS INC.
Portland
OR
|
Family ID: |
43876862 |
Appl. No.: |
12/903502 |
Filed: |
October 13, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61251751 |
Oct 15, 2009 |
|
|
|
Current U.S.
Class: |
228/221 ; 228/57;
417/65 |
Current CPC
Class: |
B23K 9/325 20130101;
B23K 26/123 20130101 |
Class at
Publication: |
228/221 ; 228/57;
417/65 |
International
Class: |
B23K 31/02 20060101
B23K031/02; B23K 37/00 20060101 B23K037/00; E21B 43/12 20060101
E21B043/12 |
Claims
1. Apparatus for purging atmospheric air from a chamber with a gas
comprising means for generating a substantially non-turbulent,
laminar flow front of the gas into the chamber with minimal
turbulence to displace the atmospheric air in the chamber, said
chamber having exhaust means associated therewith to permit the
displaced atmospheric air to exit the chamber.
2. The apparatus of claim 1 wherein the means for generating a
laminar flow front comprises a perforated plate positioned within
the chamber having a plurality of spaced-apart holes formed
therethrough, a purge support plate positioned in a spaced relation
beneath the perforated plate, said purge support plate having a
plurality of spaced-apart diffusers affixed thereto and a manifold
means communicating with the diffusers and adapted to supply the
gas to the diffusers, whereby the gas is emitted to the diffusers
to enter the space between the purge support plate and the
perforated plate to pass through the holes in the perforated plate
creating a low turbulent, laminar flow front of gas to displace the
atmospheric air in the chamber.
3. The apparatus of claim 1 in the form of a welding chamber.
4. A method for purging atmospheric air from a chamber comprising
the steps of: (a) providing an airtight chamber having exhaust
means associated therewith; (b) providing means for generating a
substantially non-turbulent, laminar flow front of a gas into the
chamber to displace the atmospheric air in the chamber; and (c)
exhausting the displaced atmospheric air from the chamber through
the exhaust means.
5. The method of claim 4 wherein the means for generating the
substantially non-turbulent, laminar flow front of the gas provided
in step (b) comprises the apparatus of claim 2.
6. The method of claim 5 wherein the chamber is a welding
chamber.
7. A method of welding comprising the steps of: (a) providing an
airtight weld chamber having exhaust means associated therewith;
(b) providing means for generating a substantially non-turbulent,
laminar flow front of an inert gas into the chamber; (c) conducting
an initial purge with the inert gas according to step (b) at a
desired flow rate to displace atmospheric air from the chamber and
exhausting the displaced atmospheric air from the weld chamber
through the exhaust means until an oxygen content in the weld
chamber is at a desired level; and (d) conducting a maintenance
purge after step (c) by decreasing the flow rate of inert gas so as
to maintain the weld chamber at or below the desired oxygen level
during welding.
8. The method of claim 7, including conducting a standby step after
conclusion of welding in step (d) by halting the continuous flow of
inert gas into the weld chamber, and initiating short bursts of
inert gas periodically to maintain a desired gas pressure in the
weld chamber.
9. The method of claim 7 wherein the desired level of oxygen in the
weld chamber is detected by providing a test plate in the weld
chamber and depositing a weld bead on the test plate, wherein a
shiny weld bead deposited on the test plate indicates an acceptable
level of oxygen is present.
10. The method of claim 7 wherein the inert gas is argon.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority to U.S. Provisional Patent
Application No. 61/251,751 filed on Oct. 15, 2009, the entire
contents of which are incorporated by reference herein.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates generally to apparatus and
methods for purging atmospheric air from an enclosed chamber, such
as a welding chamber, and replacing the air with an inert gas.
[0004] 2. Description of Related Art
[0005] In the manufacture/repair of complex investment cast shapes
for aerospace, medical and land based systems markets, it is
oftentimes necessary to perform a welding operation.
[0006] For some alloys, particularly titanium alloys, there is a
requirement to perform welding in a sealed chamber of argon. In
this application, a part is loaded into a chamber and the air is
removed by introducing argon to the chamber and expelling the air
through mixing/volume exchanges.
[0007] The current methodology used to obtain an acceptable inert
atmosphere in a chamber or enclosed work area for processes such as
welding, an atmosphere with extremely low oxygen, <60 ppm O2 and
moisture levels, >-40.degree. F. is obtained as follows. The
standard method to purge a non-interlock chamber is to pipe argon
into the chamber at a high rate of flow, the argon mixing with the
air already in the chamber, which causes both high purity argon and
air to be exhausted from the chamber to atmosphere until an
acceptable work environment is obtained.
[0008] This current production method used to purge large
non-interlock welding chambers (e.g. 11'.times.5'.times.4')
typically takes a minimum of 8-9 volume changes of argon and 30
plus minutes to obtain an acceptable welding environment. This
process wastes large quantities of argon and time (decreases
throughput and creates a large amount of idle time).
SUMMARY OF THE INVENTION
[0009] The present invention solves the problems heretofore
encountered in purging-enclosed chambers by providing a system
which greatly reduces the time and gas required to purge
atmospheric air from the chamber and replace it with another gas,
such as argon. The present invention accomplishes this desired
result by introducing the replacement/purge gas into the enclosed
chamber using a low turbulence, high flow purge system that
produces a laminar flow front which displaces the atmospheric air
in the chamber with very little mixing of the air and
replacement/purge gas, such as argon. In a non-turbulent flow
state, the argon remains below the atmospheric air in the chamber
due to the higher density of argon relative to air and pushes the
air from the chamber through exhaust means at the top of the
chamber. The invention also provides a significant savings in the
amount of inert gas, such as argon, required to displace the air in
the chamber compared with current purging systems/methods. Briefly
stated, the system of the present invention includes an enclosed
chamber, a perforated plate having a plurality of through holes
positioned within the chamber, a purge support plate positioned in
a spaced relationship beneath the perforated plate and manifold
means communicating with a plurality of spaced-apart diffusers
mounted on the purge support plate. An inert gas source, such as
argon, communicates with the manifold means. The inert gas passes
through the diffusers and enters the space between the purge
support plate and the perforated plate to subsequently pass through
the spaced-apart holes and enter the chamber in a laminar flow
front to purge the atmospheric air from the chamber. The chamber
includes controlled vent means to permit the egress of the purged
air and inert gas therefrom.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1 is a fragmented, isometric, exploded view of the
invention in a weld chamber;
[0011] FIG. 2 is a perspective view of the purge/support plate of
the invention;
[0012] FIG. 3 is a perspective view of a portion of the perforated
table top/work platform plate of the invention;
[0013] FIG. 4 is an elevation view of a welding chamber in which
the purge system of the invention is used;
[0014] FIG. 5 is a perspective view of the piping manifold on the
underside of the purge plate of FIG. 2;
[0015] FIG. 6 is a perspective view of the purge/support plate of
FIG. 2 viewed from another angle showing a spaced-apart array of
gas diffusers and support members mounted on the upper side of the
purge plate;
[0016] FIG. 7(A) is a plan view of the work table with the purge
plate and perforated work support plate of the invention depicted
therein;
[0017] FIG. 7(B) is a front elevation view of the work table with
the purge plate and perforated work support plate of the invention
depicted therein; and
[0018] FIG. 7(C) is a plan view of the perforated work support
plate.
DETAILED DESCRIPTION OF THE INVENTION
[0019] As shown in FIG. 1, the present invention not only
recognizes the density difference between argon and air but also
relies on the inert gas distribution system to provide a
non-turbulent, laminar flow front of inert gas. This system is
designed to provide for multiple inlets which rapidly distribute a
large volume of inert gas such as argon at a low pressure across
the entire chamber floor. This is accomplished by controlling pipe
size and the addition of flow restriction diffuser devices to
equalize the flow of all supply outlets. Also, the exhaust outlet
must be sized to accommodate a high flow with minimal back
pressure. This system can also be accompanied with a perforated
plate system which protects piping outlets/flow restriction device,
increases uniformity of gas flow, and also provides a stable
working platform to support the workpiece to be welded, for
example.
[0020] A presently preferred embodiment of the invention depicted
in the drawings is directed to a welding chamber 2, but it will be
understood that the invention is useful for other types of chambers
where an inert atmosphere is required for work to be performed.
[0021] As depicted in FIG. 1, the welding chamber 2 is a housing
which encloses an airtight interior space 12 within which the
welding operation is to be performed. The welding chamber 2
includes one or more conventional viewing windows 3 and sealed,
gloved ports 5 for the welder to gain access to the airtight
interior space 12. The present invention provides a laminar flow of
an inert gas such as argon into the interior space 12 of the
welding chamber 2 by way of two spaced-apart plates 4 and 6 and a
gas manifold system 8. While the welding chamber 2 is shown in the
figures as having a rectangular cross-section in the plan view,
other cross-sectional shapes, including without limitation a
square-, circle-, or oval-shaped cross-section configuration, could
also be employed.
[0022] The first of these plates is a steel purge/support plate 4
with a raised flange 16 around its perimeter. A plurality of
spaced-apart diffusers 20 are situated on the plate 4 wherein each
diffuser communicates with a pipe of the manifold system 8 for the
supply of inert gas thereto. The diffusers 20 are made up of a
sintered mass of metal spheres having a predetermined porosity to
permit a controlled gas flow therethrough. In the presently
preferred embodiment, the porosity of the diffusers is about 40
microns. A presently preferred diffuser 20 is sold by Granger
Industrial Supply, referred to in the Granger catalog as an exhaust
muffler and identified as Granger item #1A325 at catalog page No.
3290. It will be understood that the type of diffuser and its
porosity will depend upon the specific application and the gas flow
desired.
[0023] In the present embodiment, the purge/support plate 4
measures about 5 feet wide and 10 feet long and is fitted with
forty diffusers 20 at a spacing of about 11 inches in each of four
longitudinally extending rows, with ten diffusers 20 in each
row.
[0024] Between the rows of diffusers 20 are situated a plurality of
spaced-apart steel support spacers 22 which are tac welded to the
purge plate 4. The spacers 22 are about 1 inch diameter cylindrical
pieces and extend upwardly from the plate 4 about 1 inch, which is
slightly higher than the tops of the diffusers 20.
[0025] The top plate is a perforated steel plate 6 which serves the
dual function of supporting the workpiece during welding and also
to distribute the inert gas within the welding chamber 2. The
perforated plate 6 has a plurality of spaced-apart holes 7 formed
therethrough for the passage of inert gas into the chamber 2. The
through holes 7 are, by way of example, 1/4 inch in diameter and
spaced apart at 1 inch increments in each row. The holes 7 in a row
are staggered or offset from the holes 7 in adjacent rows. For
purposes of economy, the steel plate 6 is about 1/4 inch thick to
permit the holes 7 to be punched rather than individually drilled.
Accordingly, two of the 1/4 inch thick plates 6 are used and placed
one on top of the other with the through holes 7 in alignment in
each of the 1/4 inch plates to provide a composite perforated plate
6 that is 1/2 inch in total thickness. A 1/2 inch thick plate 6 is
desired in the welding operation to provide the necessary strength
to support a workpiece and resist warpage due to the thermal
effects of the welding operation.
[0026] The perimeter of the perforated plate 6 is placed on the
raised flange 16 of the purge plate 4 and is secured thereto around
the perimeter by screws, for example, with a gas sealing gasket 18
applied between the flange 16 and the perimeter of the plate 6. The
plurality of support spacers 22 engage the central area of the
underside of the perforated plate 6 and maintain a small
spaced-apart relationship between the underside of the plate 6 and
the tops of the diffusers 20 so as not to damage or crush the
diffusers which might otherwise occur.
[0027] In order to create a raised platform or work table of a
convenient height for the weld chamber 2, a plurality of vertical
legs 14, cross beams 15, and longitudinal beams 17 are provided to
support the purge plate 4 and the attached upper perforated plate
6. As stated above, the upper perforated plate also functions as
the workpiece support table top.
[0028] A vent 10 is associated with the welding chamber 2 in
communication with the interior space 12 thereof. The vent 10 opens
and closes in a controlled manner to permit air and/or gas to be
purged from the interior 12 of the chamber 2. The vent 10 is opened
for the initial purge cycle and closes when purging is complete.
The inert gas flow rate and vent size, diffuser porosity, etc. are
determined depending upon the application or size of the chamber
2.
[0029] An experimental mockup chamber 2 was constructed, measuring
2'.times.2'.times.2'6''. Improved purging was demonstrated using
diffusers 20. Argon gas initial purging of atmospheric air from
this mockup chamber was accomplished in six minutes using four
diffusers 20 and a 1/2'' diameter vent 10 with a flow rate of argon
of 2.5 cubic feet per minute (CFM).
[0030] A full size welding chamber 2 described above measuring
about 11'.times.5'.times.4' was also purged in six minutes using
forty diffusers 20 (porosity 40 microns) using a 4 inch diameter
vent 10 and an additional 11/2 inch diameter vent and a flow rate
of argon of over 100 CFM for optimum results in the initial purge.
Initial purging was also successful at lower flow rates, but at an
argon flow rate of 70 CFM, the purge time dropped off. Initial
purging trials on the mockup chamber using two flow rates, 2.5 CFM
(150 CF/hour) and 50 CFH showed the same savings in argon usage,
namely, about a 50% savings in argon over standard production. The
lower purging gas flow rate, however, took about three times longer
than the higher flow rate since the lower flow rate was only 1/3
that of the higher rate.
[0031] The low turbulence initial purge cycle provided by the
laminar flow front of the present invention reduces the initial
atmospheric air containing 21% oxygen in the chamber 2 to an
atmosphere of less than 60 parts per million of oxygen, which is
ideal for the welding operation.
[0032] After an acceptable atmosphere is obtained within the
chamber 2 after the initial purge step, the flow rate of argon is
decreased dramatically in a step referred to as the maintenance
purge. In the present example, the argon flow may be controlled at
three levels. High flow is controlled at >100 CFM of argon in
the initial purge; a lower flow is controlled at about 12 CFM of
argon in the maintenance purge; and a standby level is set in which
there is no continuous flow, just short duration bursts of argon
are used to maintain a set chamber pressure.
[0033] During the initial purge of atmospheric air from the
chamber, the exhaust gas may be analyzed to determine the oxygen
content in order to control the flow of argon (or other inert gas)
into the chamber according to the three levels of flow discussed
above. The gas pressure in the chamber is also monitored and
controlled to adjust the inert gas flow rates and to maintain the
set chamber gas pressure during welding. An argon gas pressure in
the weld chamber of between 3''-4'' of water column (manometer) has
been found to be satisfactory for production purposes. Instead of
analyzing the oxygen content in the exhaust gas, we prefer to
conduct a simple weld test wherein a weld bead is deposited on a
test plate within the chamber 2. If the weld bead is shiny, it
indicates that there is an acceptable low level of oxygen present.
On the other hand, if the weld bead on the test plate is
discolored, the oxygen level is too high and additional purging is
conducted.
[0034] After the initial purge of the welding chamber 2 has taken
place and an acceptable oxygen level has been obtained, a simple
timer device may then be used for subsequent initial purge cycles
of that chamber based on the time required for initial purging in
the previous cycle.
[0035] Thus, it will be understood that the present invention
provides a low turbulence, high flow purge system that produces a
laminar flow front which displaces the air in the chamber with very
little mixing, so as to greatly improve the cost and efficiency of
the purge process. The initial trials of the apparatus and method
of the present invention showed a 50% reduction in argon usage and
up to a 75% reduction in standby/turnaround time for each pre-purge
cycle.
[0036] The above-described weld chamber 2 using an argon atmosphere
is ideally suited for welding workpieces made of titanium based
alloys, titanium aluminides, nickel based materials, or other
alloys requiring an inert atmosphere during welding. The present
invention is also suitable for use in purging and maintaining an
inert atmosphere in interlock or antechambers used in combination
with large weld chambers where it is desired to constantly maintain
an inert atmosphere.
[0037] While specific embodiments of the invention have been
described in detail, it will be appreciated by those skilled in the
art that various modifications and alternatives to those details
could be developed in light of the overall teachings of the
disclosure. The presently preferred embodiments described herein
are meant to be illustrative only and not limiting as to the scope
of the invention which is to be given the full breadth of the
appended claims and any and all equivalents thereof.
* * * * *