U.S. patent application number 11/464504 was filed with the patent office on 2007-06-07 for feeder assembly for particle blast system.
This patent application is currently assigned to Cold Jet, Inc.. Invention is credited to Kevin P. Alford, Richard J. Broecker, R. Kevin Dressman, Daniel Mallaley, Michael E. Rivir.
Application Number | 20070128988 11/464504 |
Document ID | / |
Family ID | 29214512 |
Filed Date | 2007-06-07 |
United States Patent
Application |
20070128988 |
Kind Code |
A1 |
Rivir; Michael E. ; et
al. |
June 7, 2007 |
Feeder Assembly For Particle Blast System
Abstract
A particle blast system includes a feeder assembly having a
rotor with a plurality of pockets formed in the peripheral surface.
The transport gas flowpath includes the pockets, such that
substantially all transport gas flows through the pockets. The seal
adjacent the peripheral surface is actuated by the transport gas
pressure to urge its sealing surface against the rotor's peripheral
surface. At start up, there is no substantial pressure between the
seal and the rotor, reducing start up torque requirements.
Inventors: |
Rivir; Michael E.;
(Loveland, OH) ; Mallaley; Daniel; (Loveland,
OH) ; Broecker; Richard J.; (Loveland, OH) ;
Dressman; R. Kevin; (Loveland, OH) ; Alford; Kevin
P.; (Loveland, OH) |
Correspondence
Address: |
FROST BROWN TODD, LLC
2200 PNC CENTER
201 E. FIFTH STREET
CINCINNATI
OH
45202
US
|
Assignee: |
Cold Jet, Inc.
Loveland
OH
|
Family ID: |
29214512 |
Appl. No.: |
11/464504 |
Filed: |
August 15, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10123974 |
Apr 17, 2002 |
7112120 |
|
|
11464504 |
Aug 15, 2006 |
|
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Current U.S.
Class: |
451/38 |
Current CPC
Class: |
B24C 1/003 20130101;
B24C 7/0069 20130101; B65G 53/4633 20130101; B65G 53/4641
20130101 |
Class at
Publication: |
451/038 |
International
Class: |
B24B 1/00 20060101
B24B001/00 |
Claims
1-30. (canceled)
31. A feeder configured to transport blast media from a source into
a transport gas flow, said feeder assembly comprising: a) a rotor
having a circumferential surface, said rotor being rotatable about
an axis of rotation; b) a plurality of pockets disposed in said
circumferential surface, each of said plurality of pockets being
cyclically disposed between a first position and a second position
when said rotor is rotated about said axis; and c) a transport gas
flowpath, said transport gas flowpath having an inlet and an
outlet, said inlet being configured to be connected to a source of
transport gas, said inlet being in fluid communication with said
outlet through those of said plurality of pockets disposed between
said first and second positions.
32. The feeder of claim 31, wherein said inlet is in fluid
communication with said outlet only through said those of said
plurality of pockets disposed between said first and second
positions.
33. The feeder of claim 31, wherein said plurality of pockets are
arranged such that said inlet is in continuous fluid communication
with said outlet when said rotor is rotated.
34. A method of delivering blast media to a discharge nozzle,
comprising the steps of: a) providing a rotor configured to
introduce said blast media into a flow of pressurized transport
gas, said rotor having a first rotor surface; b) providing a seal,
said seal having a first seal surface disposed adjacent said first
rotor surface; c) starting rotation of said rotor prior to exerting
any substantial force by said first seal surface on said first
rotor surface; d) after rotation of said rotor has started,
exerting force by said first seal surface on said first rotor
surface, forming a seal therebetween sufficient to prevent any
substantial leakage of said pressurized transport gas across said
formed seal.
35. The method of claim 34, wherein said step of exerting force
comprises the step of applying fluid pressure to said seal.
36. The method of claim 35, wherein said fluid pressure is applied
by said flow of pressurized transport gas.
37. The method of claim 36, wherein said fluid pressure applied by
said flow of pressurized transport gas is applied by fluid disposed
in a passageway, said passageway being in fluid communication with
said flow of transport gas and with said seal.
38. The method of claim 37, wherein said fluid disposed in said
passageway is pressurized transport gas.
39. The method of claim 37, wherein a significant portion of said
pressurized transport gas does not flow through said
passageway.
40. The method of claim 36 wherein said flow of pressurized
transport gas is controlled by a valve, there being no substantial
flow of pressurized transport gas when said valve is substantially
closed, further comprising the step of opening said valve to
initiate said flow of pressurized transport gas at approximately
the same time that rotation of said rotor is started.
41. The method of claim 36 wherein said flow of pressurized
transport gas is controlled by a valve, there being no substantial
flow of pressurized transport gas when said valve is substantially
closed, further comprising the step of opening said valve at a time
relative to said starting rotation of said rotor such that said
rotor has started rotating before any appreciable torque is
produced on said rotor as a result of said flow of pressurized
transport gas.
42-45. (canceled)
46. A feeder configured to transport blast media from a source into
a flow of transport gas, said feeder assembly comprising: a) a
first opening and a second opening, said first and second opening
being spaced apart from each other, each opening having a
respective inner diameter; b) a rotor having a circumferential
surface, said rotor being rotatable about an axis of rotation; c) a
plurality of pockets disposed in said circumferential surface, each
of said plurality of pockets being cyclically disposed at a first
location at which blast media is delivered thereinto, and a second
location at which at least a portion of said blast media is
discharged therefrom; and d) said rotor having a first portion of
said circumferential surface, said first portion having a diameter
configured to be received and supported by said inner diameter of
said first opening, said rotor having a second portion of said
circumferential surface, said second portion having a diameter
configured to be received and support by said inner diameter of
said second opening, said diameter of said first portion being no
larger than said inner diameter of said second opening, said
circumferential surface having a maximum diameter between said
first portion and said second portion no greater than the inner
diameter of said second opening of said second portion whereby said
rotor may be installed in said feeder by inserting said first
portion first through said second opening to a position at which
said first portion is received and supported by said first opening,
said second portion being received and supported by said second
opening at said position.
47. The feeder of claim 46, wherein said first and second openings
are defined by respective bearings.
48-49. (canceled)
50. A feeder configured to transport blast media from a source into
a flow of transport gas, said feeder comprising: a) a rotor having
a circumferential surface, said rotor being rotatable about an axis
of rotation; b) a plurality of pockets disposed in said
circumferential surface, each of said plurality of pockets being
cyclically disposed between a charge position at which blast media
is introduced into said pockets and a discharge position at which
blast media is discharged from said pockets; c) a transport gas
flowpath, said transport gas flowpath having an inlet and an
outlet, said inlet being configured to be connected to a source of
transport gas, a portion of said transport gas flowpath being
disposed adjacent said discharge position such that blast media
discharged from said pockets is carried therefrom by the transport
gas; d) a seal having a first surface contacting at least a portion
of said circumferential surface at said discharge position; and e)
said rotor having a diameter no greater than approximately four
inches.
51-54. (canceled)
55. A method of delivering blast media to a discharge nozzle,
comprising the steps of: a) providing a rotor configured to
introduce said blast media into a flow of pressurized transport gas
at a discharge station, said rotor having a first rotor surface,
said rotor having a diameter no greater than approximately four
inches; b) providing a flow of transport gas; and c) sealing
between said first rotor surface and said discharge station
sufficient to prevent any substantial leakage of said pressurized
transport gas.
56. The method of claim 55, wherein said transport gas has a
pressure of at least approximately 30 PSIG.
57. The feeder of claim 50, wherein said seal is configured to seal
against a pressure of the transport gas of at least approximately
30 PSIG.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates generally to particle blast
systems, and is particularly directed to a device which provides
improved introduction of particles into a transport gas flow for
ultimate delivery as entrained particles to a workpiece or other
target. The invention will be specifically disclosed in connection
with a transport mechanism in a cryogenic particle blast system
which introduces particles from a source of such particles, such as
a hopper, into the transport gas flow.
[0002] Particle blasting systems have been around for several
decades. Typically, particles, also known as blast media, are fed
into a transport gas flow and are transported as entrained
particles to a blast nozzle, from which the particles exit, being
directed toward a workpiece or other target.
[0003] Carbon dioxide blasting systems are well known, and along
with various associated component parts, are shown in U.S. Pat.
Nos. 4,744,181, 4,843,770, 4,947,592, 5,050,805, 5,018,667,
5,109,636, 5,188,151, 5,301,509, 5,571,335, 5,301,509, 5,473,903,
5,660,580 and 5,795,214, and in commonly owned co-pending
applications Ser. No. 09/658,359, filed Sep. 8, 2000, titled
Improved Hopper and Ser. No. 09/369,797, filed Aug. 6, 1999, titled
Non-Metallic Particle Blasting Nozzle With Static Field
Dissipation, all of which are incorporated herein by reference.
Many prior art blasting system, such as disclosed therein, include
rotating rotors with cavities or pockets for transporting pellets
into the transport gas flow. Seals are used in contact with the
rotor surface in which the cavities or pockets are formed. Such
seals are usually urged against the rotor surface independent of
whether the rotor is rotating or the system is operating. The seal
force results in seal drag, creating a resisting torque which has
to be overcome by the motor. When the torque is present at the time
the rotor is started turning, a substantial start up load is placed
on the motor, affecting the size and wear of the motor. The prior
art large diameter rotors also provide a sizable moment arm through
which the seal drag produces substantial torque.
[0004] At least for prior art rotors which utilize pockets formed
in a peripheral rotor surface, not all pellets are discharged from
the pockets at the discharge station. Additionally, the pocket
spacing and lack of thorough, uniform mixing of the transport gas
and pellets in the feeder results in pulses.
[0005] Although the present invention will be described herein in
connection with a particle feeder for use with carbon dioxide
blasting, it will be understood that the present invention is not
limited in use or application to carbon dioxide blasting. The
teachings of the present invention may be used in application in
which there can be compaction or agglomeration of any type of
particle blast media.
BRIEF DESCRIPTION OF THE DRAWING
[0006] The accompanying drawings incorporated in and forming a part
of the specification illustrate several aspects of the present
invention, and together with the description serve to explain the
principles of the invention. In the drawings:
[0007] FIG. 1 is a perspective side view of a particle blast system
constructed in accordance with the teachings of the present
invention.
[0008] FIG. 2 is a perspective view of the feeder assembly and
motor of the particle blast system of FIG. 1.
[0009] FIG. 3 is a perspective view of the feeder assembly of the
particle blast system of FIG. 1, similar to FIG. 2 but without the
motor.
[0010] FIG. 4 is a side view of the particle blast system of FIG.
1.
[0011] FIG. 5 is cross-sectional view of the particle blast system
taken along line 5-5 of FIG. 4.
[0012] FIG. 6 is an exploded, perspective view of the feeder
assembly.
[0013] FIG. 7 is a side view of the feeder assembly and motor of
FIG. 2.
[0014] FIGS. 8A-I are cross-sectional views of the feeder assembly
taken along line 8-8 of FIG. 7, showing the rotor in successive
rotational orientations.
[0015] FIG. 9 is a perspective view of the lower pad of the feeder
assembly.
[0016] FIG. 10 is a top view of lower pad of FIG. 9.
[0017] FIG. 11 is a bottom view of the lower pad of FIG. 9.
[0018] FIG. 12 is a cross-sectional view of the feeder assembly
taken along line 12-12 of FIG. 7.
[0019] FIG. 13 is a cross-sectional view of the feeder assembly
taken along line 13-13 of FIG. 7.
[0020] FIG. 14 is top view of the feeder assembly.
[0021] FIG. 15 is a is a cross-sectional view of the feeder
assembly taken along line 15-15 of FIG. 14.
[0022] FIG. 16 is a side view of the feeder assembly.
[0023] FIG. 17 is a cross-sectional view of the feeder assembly
taken along line 17-17 of FIG. 16.
[0024] FIG. 18 is a perspective view of a rotor.
[0025] FIG. 19 is a side view of the rotor of FIG. 18.
[0026] Reference will now be made in detail to the present
preferred embodiment of the invention, an example of which is
illustrated in the accompanying drawings.
DETAILED DESCRIPTION OF AN EMBODIMENT OF THE INVENTION
[0027] Referring now to the drawings in detail, wherein like
numerals indicate the same elements throughout the views, FIG. 1
shows particle blast system, generally indicated at 2, with the
outside cover omitted for clarity. Particle blast system 2 includes
frame 4 which supports the various components. Particle blast
system 2 includes hopper 6, which holds the blast media (not
shown), functioning as a source of blast media. In the embodiment
depicted, particle blast system 2 is configured to use sublimeable
particles, particularly carbon dioxide pellets, as the blast media.
It is noted that the present invention may be used with a wide
variety of blast media, including non-cryogenic blast media.
[0028] Particle blast system 2 includes feeder assembly 8, also
referred to as the feeder, which is driven by motor 10. Feeder 8
includes inlet 12 and outlet 14. A transport gas flowpath is formed
within feeder 8 between inlet 12 and outlet 14 (not seen in FIG. 1)
as described hereinafter. Inlet 12 is connected to a source of
transport gas, and outlet 14 is connected to the delivery hose (not
shown) which transports the carbon dioxide pellets entrained in the
transport gas to the blast nozzle (not shown). As can be seen in
FIGS. 1 and 4, conduit 16 is connected to inlet 12, and includes
end 16a extending outside of frame 4 for easy connection to a
source of transport gas. FIG. 1 illustrates outlet 14 as being
connected to hose 18, which includes end 18a extending outside of
frame 4 for easy connection to the delivery hose (not shown).
[0029] As is well known, the transport gas may be at any pressure
and flow rate suitable for the particular system. The operating
pressures, flow rates and component (such as compressor) size are
dependant on the cross-section of the system blast nozzle (not
shown). The source of transport gas may be shop air. Typically,
despite treatment, the transport gas will have some humidity left
in it. In the depicted embodiment, the transport gas at the rotor
had a pressure of about 80 PSIG with a nominal flow rate of 150
SCFM, at around room temperature, which matched the particular
system blast nozzle used. The operating pressure for such a system
ranges from about 30 PSIG to about 300 PSIG, the upper maximum
being dictated by the rating of the components. The maximum rotor
speed was about 70 RPM, at which the system delivered approximately
7 pounds of CO.sub.2 pellets per minute.
[0030] FIG. 2 shows feeder assembly 8 connected to motor 10,
through coupling 20. As can be seen in FIG. 3, from which motor 10
and cover 22 have been omitted, coupling 20 is a jaw type coupling
formed by the intermeshing of a plurality of legs 24 which extend
from an end of rotor 26. Complementarily shaped legs are found on
motor 10, providing easy disengagement through axial movement
between motor 10 and rotor 26. Coupling 20 allows radial and axial
misalignment and provides for easy disassembly.
[0031] FIG. 5 illustrates a cross sectional view of hopper 6 and
feeder 8. As shown, hopper exit 28 is aligned with inlet 30 of
feeder 8. Seal assembly 32 seals between exit 28 and feeder 8,
sealingly engaging upper surface 34a of upper seal pad 34. Ramrod
assembly 35 is illustrated extending to the side. Inlet 12 has
coupling 12a threaded thereto. Outlet 14 has coupling 14a threaded
thereto.
[0032] FIG. 6 is an exploded perspective view of feeder 8. Feeder 8
includes feeder block 36 in which inlet 12 and outlet 14 are
formed. Feeder block 36 includes cavity 38 defined by wall 38a and
bottom 38b. Feeder block 36 is secured to plate 37 which is secured
to base 40 which is secured to frame 4. A pair of spaced apart
bearing supports 42, 44 respectively carry axially aligned sealed
bearings 46, 48.
[0033] Rotor 26 is made from 6061 hard coat anodized aluminum, and
is depicted as a cylinder, although various other shapes, such as
frustoconical may be used. In the depicted embodiment, rotor 26 has
a diameter of two inches. The present invention includes the use of
a rotor having a diameter of approximately four inches. Threaded
hole 26b is formed in the end of rotor 26 to provide for removal or
rotor 26. Rotor 26 includes peripheral surface 50, in which a
plurality of spaced apart pockets 52 are formed. In the embodiment
shown, there are four circumferential rows of pockets 52, with each
circumferential row having six pockets 52. Pockets 52 are also
aligned in axial rows, with each axial row having two pockets 52.
The axial and circumferential rows are arranged such that the axial
and circumferential widths of pockets 52 overlap, but do not
intersect, each other.
[0034] In this embodiment, rotor 26 is rotatably carried by
bearings 46, 48, for rotation by motor 10 about rotor axis 26c.
Rotor 26 is retained in place by motor 10 at end 26a, with thrust
bearing plate 56 and retaining plate 54 retaining rotor 26 at the
other end. Thrust bearing plate 56 is made of UHMW plastic. The fit
between bearings 46, 48, and rotor 26 allows rotor 26 to be easily
withdrawn from feeder assembly 8 by removing retaining plate 54 and
thrust bearing plate 56, and sliding rotor out through bearing 46.
A threaded shaft, such as a bolt, may be inserted into hole 26b to
aid in removal of rotor 26.
[0035] In the embodiment depicted, the configuration of feeder 8
does not require any axial loading on rotor 26, either from sealing
or the bearings. The end play or float of rotor 26 was about 0.050
inches.
[0036] Lower seal pad 58 is disposed partially in cavity 38, with
seal 60, located in groove 62, sealingly engaging groove 62 and
wall 38a. Lower seal pad 58 includes surface 64 which, when
assembled, contacts peripheral surface 50 of rotor 26, forming a
seal therewith, as described below. As used herein, "pad" is not
used as limiting: "Seal pad" refers to any component which forms a
seal.
[0037] Upper seal pad 34 includes surface 66 which, when assembled,
contacts peripheral surface 50 of rotor 26. Fasteners 68 engage
holes in upper seal pad 34 to hold it in place, without significant
force being exerted by surface 66 on rotor 26. Intermediate seal 70
may be disposed between upper seal pad 34 and lower seal pad
58.
[0038] Upper seal pad 34 and lower seal pad 58 are made of a UHMW
material. The ends of surfaces 64 and 66 adjacent bearing 46 are
chamfered to allow easier insertion of rotor 26.
[0039] Ramrod assembly 35 includes two ramrods 35a and 35b which
are moved between a retracted position to a position at which they
extend into entrance 30 of feeder 8. Ramrods 35a and 35b are
actuated by pneumatic cylinders 33a and 33b respectively, which are
carried by mounting plate 31. Mounting plate 31 is secured at
either end to bearing supports 42 and 44 by fasteners 27, with
spacer 29 disposed adjacent mounting plate 31. Spacer 29 includes
openings 29a and 29b which align with openings 30a and 30b in seal
34. Copending application Ser. No. 09/658,359 provides a
description of the operation of ramrods. Any functional number of
ramrods may be used, for example only one or more than two. They
may be oriented differently than as shown in FIG. 6, such as at
90.degree. to that illustrated, aligned with axis of rotation 26c.
They may operate simultaneously, alternating or independently. They
may be disposed at angles to each other.
[0040] FIGS. 8A-I are cross-sectional views of the feeder assembly
taken along line 8-8 of FIG. 7, and show rotor 26 in successive
rotational orientations. FIG. 8A shows lower pad seal 58 disposed
in cavity 38, with seal 68 engaging wall 38a, and upper pad seal 34
overlying lower pad seal 58. Referring also to FIGS. 9-11, which
show various views of lower seal pad 68, upper pad seal 34 is
disposed adjacent upper surface 58a of lower pad seal 58. On one
side, labyrinth seal 70 is formed between upper pad seal 34 and
lower pad seal 58 by the cooperation of step 58b with downwardly
extending wall or lip 34c. Thus, lower pad seal 58 overlaps with
upper pad seal 34 at this stepped joint keeps ambient air from
entering the hopper. With the stepped design, lower pad seal 58 can
move vertically independent of upper pad seal 34, allowing
substantially all force on lower seal pad 58 functions to urge
surface 64 in sealing contact with surface 50, as described below.
On the opposite side, vent 96 is formed, which allows pressurized
transport gas to escape from pockets 52 as they pass thereby, as
described below. Vent 96 is defined by step 34d formed in upper
seal 34 and surface 58c a portion of which is downwardly inclined.
The slight incline of a portion of surface 58c prevents water from
puddling when water ice that may build up on the feeder thaws.
[0041] Surface 64 includes two openings 72 which are in fluid
communication with inlet 12 through upstream chamber 74, and two
openings 76 which are in fluid communication with outlet 14 through
downstream chamber 78. It is noted that although two openings 72
and two openings 76 are present in the illustrated embodiment, the
number of openings 72 and openings 76 may vary, depending on the
design of feeder 8. For example, a single opening may be used for
each. Additionally, more than two openings may be used for
each.
[0042] Feeder 8 has a transport gas flowpath from inlet 12 to
outlet 14. In the depicted embodiment, passageways 80 and 82 are
formed in feeder block 36. Lower seal pad 58 includes recess 84,
which is aligned with inlet 12 and together with passageway 80,
places upstream chamber 74 in fluid communication with inlet 12.
Lower seal pad also includes recess 86, which is aligned with
outlet 14 and together with passageway 82, places downstream
chamber 78 in fluid communication with outlet 14.
[0043] Upstream chamber 74 is separated from downstream chamber 76
by wall 88 which extends transversely across lower seal pad 58, in
the same direction as axis of rotation 26c. Lower surface 88a of
wall 88 seals against bottom 38b of cavity 38, keeping upstream
chamber 74 separate from downstream chamber 78. Wall 90 is disposed
perpendicular to wall 88, with lower surface 90a engaging bottom
38b.
[0044] As illustrated, in the depicted embodiment, inlet 12 is in
fluid communication with outlet 14 only through individual pockets
52 as they are cyclically disposed by rotation of rotor 26 between
a first position at an individual pocket first spans openings 72
and 76 and a second position at which the individual pocket last
spans openings 72 and 76. This configuration directs all of the
transport gas entering inlet 12 to pass through pockets 52, which
pushes the blast media out of pockets 52, to become entrained in
the transport gas flow. Turbulent flow occurs in downstream chamber
78, promoting mixing of media with the transport gas. Such mixing
of the media minimizes entrains the media in the transport gas,
minimizing impacts between the media and the feeder components
downstream of the pockets. This means that the particles are only
significantly in contact with the rotor, minimizing heat transfer
to the particles from other components of feeder 8. The significant
flow of the transport gas through each pocket 52 acts to
effectively clean all media from each pocket 52.
[0045] For cryogenic particles, this transport gas flowpath, in
which all or substantially all flows through pockets 52, aids in
the transfer of heat from the transport gas to rotor 26, which
helps reduce or prevent water ice (which forms due to humidity in
the transport gas) from freezing on the rotor and other parts of
feeder 8. Heat transfer between rotor 26 and non-moving components
of feeder 8 is minimized by use of the UHMW pad seals surrounding
rotor 26. Substantially all heat gain or loss of the rotor is from
the particles and transport gas. The small mass of rotor 26 makes
it easier for the transport gas to heat rotor 26. Additionally,
rotor 26 could carry a heater element, or passageways could be
provided for the flow of heated air primarily for heating rotor 26.
Such passages could be in rotor 26. Of course, the necessary
rotational coupling for such heater element or passageways would
have to be provided.
[0046] Although the depicted embodiment is configured to direct all
the transport gas through the pockets, is possible to configure a
particle blast system to utilize this aspect of the present
invention, but without directing all transport gas through the
pockets, such as by bypassing a portion of the transport gas flow
around the feeder, or even bypassing a portion of the transport gas
flow around the pocket. The present invention is applicable to such
particle blast systems.
[0047] FIGS. 8A-I illustrate the progress of pocket 52a past
openings 76 and 72 as rotor 26 is rotated. In the depicted
embodiment, rotor 26 rotates clockwise, presenting pockets 52 in an
endless succession first past openings 76 and then openings 72 in a
periodic, cyclical nature. It is noted that alternatively, rotor 26
could rotate in the opposition direction, exposing pockets first to
openings 72 and then openings 76. Pockets 52 are filled with blast
media, in particular in this embodiment carbon dioxide pellets,
from hopper 6 through opening 92 in upper seal pad 34. The action
of the small radius (e.g, in the depicted embodiment, four inches
or less) of rotor 26 past opening edge 92a tends to bite into any
agglomerated chunks of pellets, breaking them apart, reducing
blockage and promoting more complete fill.
[0048] In FIG. 8A, leading edge 52b of pocket 52a is illustrated
located about midway in opening 76. Once leading edge 52b has
traveled past edge 76a of opening 76 a sufficient distance, pellets
will begin to exit pocket 52a.
[0049] FIG. 8B illustrates leading edge 52b just reaching edge 76b
of opening 76. At this position, the entire circumferential width
of opening 76 is exposed to pocket 52a, it being noted that as a
result of the roughly circular shape of the opening of pocket 52a,
the cross-sectional area of the opening of pocket 52a exposed to
opening 76 (as well as opening 72) varies with the angular position
of pocket 52a.
[0050] At the position illustrated in FIG. 8B, transport gas cannot
flow from inlet 12 to outlet 14 through pocket 52a, being blocked
by sealing engagement between rotor 26 and edge 88b of wall 88 .
Because in the embodiment depicted, openings 72 and 76 are always
spanned by at least two pockets 52, inlet 12 is always in fluid
communication with outlet 14, but only through pockets 52.
[0051] Alternatively, the level of edge 88b could be reduced,
creating a gap such that a complete seal with rotor 26 is not
formed by wall 88, providing a continuous flowpath from inlet 12 to
outlet 14 from the first passageway, defined by lower pad seal 58
which is in fluid communication with opening 72 to the second
passageway, defined by lower pad seal 58 which is in fluid
communication with opening 76, through the passageway defined by
edge 88b of wall 88 and the peripheral surface 50 of rotor 26, not
through pockets 52. Such a continuous flow path would reduce
pulsing as the size of the flow path cyclically varies with the
rotation of rotor 26. Of course, in such an embodiment, as pockets
52 are moved between the first and second positions, there is a
substantial increase in the flowpath area, and a substantial volume
of transport gas flows through the aligned pockets 52.
[0052] FIG. 8C illustrates leading edge 52b of pocket 52a at a
first position just reaching edge 72a of opening 72, whereat pocket
52a first begins spanning opening 76 and 72. FIG. 8D illustrates
rotor 26 rotated slightly further, with leading edge 52b just past
edge 72a. Once leading edge 52b passes edge 76a, there is a
continuous transport gas flowpath from opening 72 to opening 76
through pocket 52a. At the position shown in FIG. 8D, transport gas
will flow from upstream chamber 74, through opening 72, pocket 52a
and opening 76a, to downstream chamber 76, as indicated by arrow
94.
[0053] The transport gas pushes pellets from pocket 52a out opening
76, into downstream chamber 78 where mixing of the pellets and
transport gas occurs, and pellets exit feeder 8 through outlet 14,
entrained in the transport gas.
[0054] FIG. 8E illustrates leading edge 52b when it first reaches
edge 72b. FIG. 8F shows leading edge 52b well past edge 72b, with
trailing edge 52c approaching edge 76b at which the flowpath
through pocket 52a will stop, the position at which pocket 52a is
no longer part of the transport gas flowpath (until the next
cycle).
[0055] FIG. 8G shows trailing edge 52c past edge 76b, at edge 72a.
As can be seen, pocket 52a is no longer exposed to downstream
chamber 78, but is exposed to pressurized transport gas. FIG. 8H
illustrates trailing edge 52c past edge 72b, with pressurized
transport gas trapped therein.
[0056] FIG. 8I illustrates pocket 52a rotated further, aligned with
vent 96, which allows the pressurized transport gas that was
trapped within pocket 52a to escape.
[0057] As previously mentioned, upper seal pad is held in
engagement with rotor 26 by fasteners 68 without significant force
being exerted by surface 66 on rotor 26. Ambient pressure is
present within hopper 6. Upper seal pad 34 functions not only in
the filling of pockets 52, but also to keep ambient moisture from
entering the system through feeder 8. Adequate sealing is achieved
between surface 66 and surface 50 without any significant force
urging upper seal pad 34 toward rotor 26.
[0058] The seal between rotor surface 50 and lower seal pad surface
64 is very important. The pressurized transport gas must be
contained, both for efficiency of the delivery of pellets to the
blast nozzle and because leakage into the low pressure side of
rotor 26 and into hopper 6 will cause agglomeration and other
deleterious effects. The present invention utilizes the pressure of
the transport gas to provide substantially all the sealing force
between rotor surface 50 and seal surface 64.
[0059] When pressurized transport gas is not present (in the
depicted embodiment, when transport gas is not flowing through the
transport gas flowpath), there is no substantial force between
rotor surface 50 and surface 64. When rotation of rotor 26 is
started at the same or approximately the same time as transport gas
is allowed to begin to flow (such as occurs in many particle blast
systems when the blast trigger is depressed), there is no
substantial force on rotor surface 50. This means that motor 10
does not have to be sized to start under load, which reduces the
horsepower requirements, allowing a smaller, less expensive motor
to be used. Rotor 26 will be very close to its steady state speed
by the time the transport gas pressure results in substantial
sealing force on rotor surface 50.
[0060] Referring to FIG. 8I for clarity of explanation, as
described above, lower seal pad 58 is disposed partially in cavity
38, with seal 68 sealing between wall 38a and lower seal pad 58.
Surface 98 is spaced apart from surface 64, and together they
define arcuate wall 100. Although walls 88 and 90 extend from
arcuate wall 100, arcuate wall 100 is a relatively thin wall which
is sufficiently flexible to transmit a substantial portion of
pressure exerted against surface 98 to rotor surface 50 by surface
64. Surface 98a of surface 98 defines a portion of upstream chamber
74. When transport gas is flowing through the transport gas
flowpath, the pressure of the transport gas within upstream chamber
74 bears on surface 98a, urging the overlying portion surface 64a
of surface 64 against rotor surface 50. The flexibility of arcuate
wall 100a allows arcuate wall to conform to the shape of rotor
surface 50, and transmit a substantial portion of the pressure to
surface 64a, urging surface 64a into sealing contact with rotor
surface 50.
[0061] Similarly, surface 98b of surface 98 defines a portion of
downstream chamber 76. When transport gas is flowing through the
transport gas flowpath, the pressure of the transport gas within
downstream chamber 76 bears on surface 98b, urging the overlying
portion surface 64b of surface 64 against rotor surface 50. The
flexibility of arcuate wall 100b allows arcuate wall to conform to
the shape of rotor surface 50, and transmit a substantial portion
of the pressure to surface 64b, urging surface 64b into sealing
contact with rotor surface 50.
[0062] In the illustrated embodiment, seal surface 64 contacts
rotor surface 50 over an angle of about 180.degree.. The depicted
configuration allows the sealing force to be exerted throughout
substantially the entire contact angle, and substantially normal to
rotor surface 50. Of course other seal arrangements, even those
that are not activated by gas pressure, may also be used with the
pockets being part of the transportation gas flowpath.
[0063] It is noted that as the pressure of the transport gas
increases, the required sealing force between rotor surface 50 and
surface 64 increases. In the depicted embodiment, the sealing force
between rotor surface 50 and surface 64 is proportional to the
transport gas pressure. In turn, the load on rotor 26 and motor 10
is proportional to the transport gas pressure. This reduces rotor
and seal wear, and increases motor life.
[0064] Although in the depicted embodiment it is the gas pressure
of the transport gas within the transport gas flowpath which urges
surface 64 against rotor surface 50, the pressure which actuates
the seal against rotor surface 50 may come from any source. For
example, inner surface 98 may be exposed to pressurized transport
gas by a chamber or passageway connected to but not within the
direct transport gas flowpath. The pressure of the gas within such
a chamber or passageway may be controlled separate from the
pressure of the transport gas. The chamber may be not connected to
the transport gas flowpath, with a separate source of fluid
pressure being used to urge surface 64 into sealing engagement with
rotor surface 50.
[0065] Configurations other than as depicted in the illustrated
embodiment may be used to provide the sealing force. For example, a
plurality of internal passageways may be formed adjacent surface 64
which urge surface 64 into sealing engagement with rotor surface 50
when pressure is present in such internal passageways. It is noted
that the dynamic pneumatically actuated seal unloads rotor 26 when
not in operation, make rotor removal easier than designs that
require seals be unloaded before rotor removal.
[0066] It is noted that only one circumferential row of pockets 52
is visible in FIGS. 8A-I. In the depicted embodiment, there is an
additional circumferential row of pockets 52 which is axially
aligned with the depicted row, and two other circumferential rows
of pockets 52 which aligned with each other but staggered with
respect to the other two aligned circumferential rows. Thus, in the
depicted embodiment, there are always at least two pockets 52
exposed to both openings 72 and 76, allowing the transport gas to
flow continuously from upstream chamber 74 to downstream chamber
76. The arrangement of pockets 52 in the depicted embodiment thus
keeps inlet 12 in continuous fluid communication with outlet 14.
The depicted configuration, including the arrangement of pockets
52, the flow through pocket, and downstream mixing chamber 78,
functions to reduce pulsing of blast media.
[0067] The shape and depth of pockets 52 may vary. Obviously,
sufficient wall thickness must remain between pockets 52 to
maintain structural integrity and sufficient sealing at surface 50.
Different pocket opening shapes may be used. It is noted that
openings with leading edges that are parallel to edges 72a, 72b,
76a and 76b, and/or too much axial width can allow deflection in
surfaces 64, as well as 66, resulting in the pocket opening gouging
those surfaces. In the depicted embodiment, the volume of pockets
52 was as large as possible, given the physical constraints, so as
to maximize the volume for receiving and transporting pellets. In
the depicted embodiment, laminar flow does not occur through
pockets 5, promoting better removal of pellets as the transport gas
flows therethrough.
[0068] The size and number of pockets 52, as well as rotational
speed of rotor 26, determine how much blast media can be introduced
into the transport gas flow and ultimately bow much blast media can
be directed toward a target from the blast nozzle. Rotor 26 is
substantially smaller in diameter than other radial transport
rotors, being in the depicted embodiment about two inches in
diameter. The smaller diameter results in less torque developed by
the seal pressure. This, in addition to the lack of significant
seal drag at start up, allows a smaller motor to be used. The small
diameter rotor also has a lower moment of inertia, which also
reduces the power required for rotation. In contrast, prior art
motors were at least one horsepower. In the depicted embodiment,
for the same pellet delivery rate, motor 10 is can be a half or
quarter horsepower motor, perhaps even lower. This lower torque
requirement allows, if desired, the use of a pneumatic motor.
[0069] The rotational speed of rotor 26 in the depicted embodiment
is 70 RPM, compared to 20 RPM of similar prior art large diameter
rotors. For the depicted arrangement of pockets 52, this speed
results in the same rate of pocket exposure at the discharge
station as the slower moving, larger diameter rotors of the prior
art. If the large diameter prior art rotors rotated too fast, the
pockets would not fill, similar to cavitation resulting from the
characteristics of the pellets, meaning that rotating the rotor
above a certain speed would not increase the pellet delivery rate.
However, the small diameter rotor, one aspect of the present
invention, is able to fill properly even when rotated at the higher
rotational speed.
[0070] By keeping the rate of pocket exposure, based on diameter,
rotational speed and pocket opening, at approximately the same as
larger prior art rotors, the smaller diameter rotor is used as
described herein. The volume of pocket exposure is also important.
The smaller rotor dictates deeper pockets and more pockets to
obtain the same volume. Filling the deeper pockets requires more
time than shallow pockets of the same volume, thereby affecting
rotational speed. For example, in one embodiment, a 14% deeper
pocket depth was combined with a 14% drop in rotational speed of
the small rotor of the equivalent small rotor rate of pocket
exposure.
[0071] Additional benefit is obtained by the increased speed,
reducing the time that pellets spend in a given pocket, thereby
reducing the time that the pellets can cool the rotor. In the
configuration shown, with oppositely aligned charge and discharge
stations, pellets are in a rotor pocket for approximately half of
each rotation. The "dwell" time for pellets in a pocket are the
same for the same rate of pocket exposure, regardless of rotor
diameter. However, the small diameter rotor reduces the total
variation in temperature by reducing cycle time.
[0072] Different ranges of delivery rates may be achieved by
providing a variety of rotors having different pocket arrangements,
such as pockets of different sizes or a different number of
pockets. The rotor rotational speed can then be varied to control
the exact delivery rate within the range. However, the control
system may provide only a single rotor speed. Rotors may be easily
changed by removal of retaining plate 54, as discussed above.
[0073] Referring to FIG. 12, there is shown a cross-sectional view
taken along line 12-12 of FIG. 7, showing a section through lower
seal pad 58. FIG. 13 is a cross-sectional view taken along line
13-13 of FIG. 7, showing a section through lower seal pad 58 at a
location closer to bottom 38b of feeder block 36. Passageways 80
and 82 can be seen, formed in bottom 38b.
[0074] FIG. 14 is a top view of feeder 8, with plurality of pockets
52 of rotor 26 clearly visible through opening 92. Inclined
surfaces 92b and 92c allow opening to be larger than the opening 92
adjacent rotor 26. It is noted that the width (as taken parallel to
section line 15-15) of opening 92 is larger than similar prior art
feeders, with the ratio of length to diameter of rotor 26 being
substantially larger than that of prior art feeders.
[0075] FIG. 15 is a cross-sectional view taken along line 15-15 of
FIG. 14. Section line 15-15 cuts through downstream chamber 78 so
that wall 88 is seen in full view and wall 90 is seen in section
view.
[0076] FIG. 16 is a side view of feeder 8, and FIG. 17 is a
cross-sectional view taken along line 17-17 of FIG. 16. FIGS. 15
and 17 are similar in that the section is taken through the center
of rotor 26. However, in FIG. 17, the lower portion of the section
is taken closer to outlet 14, showing surface 78a of downstream
chamber 78 and wall 90 in full view.
[0077] Any suitable shape for pockets 52 may be used. FIGS. 18 and
19 provide further illustration of pockets 52 of the rotor depicted
herein. The mouth of the pockets, at surface 50 of rotor 26, have
been enlarged relative to the rest of the pocket. Due to the
cylindrical shape of rotor 26, the wall thickness between adjacent
pockets 52 is smaller closer to the rotor's center. In contrast, at
surface 50, the pocket centers are further apart, allowing the
pocket openings to be larger. It is noted that in the depicted
embodiment the outside edges 52d of either outer circumferential
row of pockets 52 are not the same shape as the pocket openings of
the inner two circumferential rows. This matches existing hopper
throat size, but it will be recognized that such an opening
configuration is a limitation.
[0078] The present invention allows the utilization of a rotor
having a diameter to width (sealing width) of below 1:1, such as in
the depicted embodiment 1:2. Prior art rotors operating at
pressures in the range of 30-300 PSIG, such as is typically found
with cryogenic particle blasting, are known to fall around
8:1.25.
[0079] The foregoing description of an embodiment of the invention
has been presented for purposes of illustration and description. It
is not intended to be exhaustive or to limit the invention to the
precise form disclosed. Obvious modifications or variations are
possible in light of the above teachings. The embodiment was chosen
and described in order to illustrate the principles of the
invention and its practical application to thereby enable one of
ordinary skill in the art to best utilize the invention in various
embodiments and with various modifications as are suited to the
particular use contemplated. It is intended that the scope of the
invention be defined by the claims appended hereto.
* * * * *