U.S. patent application number 09/966523 was filed with the patent office on 2003-04-03 for apparatus to provide dry ice in different particle sizes to an airstream for cleaning of surfaces.
Invention is credited to Opel, Alan E..
Application Number | 20030064665 09/966523 |
Document ID | / |
Family ID | 25511541 |
Filed Date | 2003-04-03 |
United States Patent
Application |
20030064665 |
Kind Code |
A1 |
Opel, Alan E. |
April 3, 2003 |
Apparatus to provide dry ice in different particle sizes to an
airstream for cleaning of surfaces
Abstract
Apparatus and method for producing and metering dry ice pellets
and particles selectively from the same apparatus without
modification, by appropriate reversal of a production wheel and
accompanying selection of dry ice in the form of block or of
pellets for a supply to the production wheel.
Inventors: |
Opel, Alan E.; (Monrovia,
CA) |
Correspondence
Address: |
Donald D. Mon
Suite 303
750 East Green Street
Pasadena
CA
91101
US
|
Family ID: |
25511541 |
Appl. No.: |
09/966523 |
Filed: |
September 28, 2001 |
Current U.S.
Class: |
451/40 ;
451/99 |
Current CPC
Class: |
B24C 1/003 20130101 |
Class at
Publication: |
451/40 ;
451/99 |
International
Class: |
B24B 001/00; B24C
001/00 |
Claims
1. Apparatus for dry ice blast cleaning that is capable of both
metering and blasting preformed dry ice pellets, and also capable
of producing and blasting smaller dry ice granules, with said
apparatus comprising: a base; a carrier movably supported relative
to the base; a driver for powering the carrier in either of two
substantially different directions; a means for controlling the
movement direction of the carrier; a means for controlling the
movement rate of the carrier; a first set of passages located on
the carrier with a geometry that meters pellets when the carrier is
moved in a first direction; a second set of passages located on the
carrier that incorporate a working edge that defines a cutting
surface during the movement of the carrier in a second and
substantially different direction; a feeder for receiving and
delivering a supply of dry ice and advancing same in a feed path in
contact with the carrier passages as they move across the feed
path; a duct having an outlet, the dry ice particles being directed
from the carrier passages to flow from the outlet, there being
substantially no storage of particles in the duct; and an
accelerator for accelerating the dry ice particles, the accelerator
being connected to the outlet.
2. Apparatus according to claim 1 wherein the carrier is a wheel
rotatably supported on a carrier axis.
3. In a system for providing a blasting stream of air and dry ice
particles entrained in said air, a particle generator adapted
selectively to produce shaved granules of dry ice from block dry
ice, or pellets from a supply of pelletized dry ice, without
modification of said generator, said generator comprising: a
receptacle to receive dry ice in pellet or block form, said
receptacle having an end wall with an opening, and a chute
receiving product from said opening; a production wheel having an
axis of rotation, an upstream face and a downstream face, said
production wheel being mounted in said receptacle for selective
rotation in either a first or a second direction, said downstream
face facing said opening in said receptacle wall, and said upstream
face facing into said receptacle for bearing contact by dry ice
pellets or by dry ice block, said production wheel including a
pellet metering slot extending between said upstream and downstream
faces, a metering edge facing in said second direction and an entry
edge facing in said first direction, said metering edge lying in
the plane of said upstream face, and said entry edge being recessed
into said upstream face by a ramp; and a shaving slot extending
between said upstream face and said downstream face, a cutting edge
facing in said second direction, raised above the plane of said
upstream face, and an edge spaced from said cutting edge to admit
shavings to said slot, whereby in one direction of rotation with
pellets bearing against said upstream face, said metering edge
drives particles into its respective slot, and in the other
direction of rotation, said cutting edge shaves dry ice particles
from a block of dry ice into its respective slot, no edge adversely
affecting dry ice in said receptacle when the production wheel is
rotated to produce particles generated by the other edge.
4. Apparatus according to claim 3 in which said cutting edge of
said shaving slot is adjustably positionable above the plane of
said upstream face, whereby, when pellets instead of block dry ice
are encountered in said second direction, a mixture of particles of
various ratios of more and less massive particles are generated,
the ratio between them being determined by the position of said
cutting edge.
5. The method of selection by metering pellets of dry ice and
shaving of particles from block dry ice, utilizing a movable
surface that can be reversed in direction, having a set of pellet
metering slots facing in one direction, and a set of shaving slots
facing in the opposite direction, said method comprising: with
pellets pressed against the movable surface in a direction so the
pellet metering slots admit pellets to a user device; and with
block ice pressed against the movable surface in the opposite
direction so the shaving slots remove dry ice particles from the
block and pass them to a user device.
6. A method according to claim 5 in which said pellets are pressed
against the surface, and the surface is rotated in said opposite
direction to generate particles of mixed mass size.
7. A method according to claim 5 in which said movable surface is
on a rotatable production wheel.
Description
FIELD OF THE INVENTION
[0001] Cleansing of surfaces by the blast of an airstream carrying
particles of dry ice. Apparatus providing a selectible capability
of either metering preformed dry ice particles while substantially
maintaining the size and distribution integrity of said particles
or the capability to granulate a block of solid preformed dry ice
without modifying the apparatus itself.
BACKGROUND OF THE INVENTION
[0002] The use of dry ice (solid CO.sub.2) particles in a
pressurized airstream to clean surfaces is known art. In this
process, the dry ice particles are conveyed through a hose to a
nozzle from which the air and the entrained particles are
discharged onto the surface that is to be cleaned. The fact that
dry ice sublimes directly to a gas makes these particles
particularly suited for blasting onto many types of surfaces with
the advantage that they leave no residue and are less likely to
modify critical surface characteristics.
[0003] While in the solid condition, particles of dry ice have
useful structural properties for blast cleaning applications. They
are able to dislodge and sweep away surface contaminants such as
paint on heavy solid surfaces, and preservative coatings on
structures as fragile as small electrical coils. Obviously a
particle large enough and structurally integral enough to remove a
baked-on enamel from a heavy metal structure cannot be used to
cleanse the surface of a delicate wire coil. It would destroy the
coil. Yet the same material--dry ice--can be used successfully for
both purposes.
[0004] The difference resides in the size and structure of the
particles. For heavy blasting, where it is advantageous that each
individual particle impact generates significantly higher kinetic
energy, it is common to use preformed dry ice particles in pellet
form of a predetermined size and distribution. Such pellets are
separately prepared by equipment specifically designed to produce
them from a bulk supply of liquid carbon dioxide. They are placed
as pellets in a storage bin or hopper in the dry ice blasting
apparatus and are metered from it into the airstream and conveyed
to an accelerator either through eduction or through a pressurized
airstream requiring the use of an airlock. An example is found in
U.S. Pat. No. 4,038,789.
[0005] However, this same equipment cannot dispense the smaller
granular particles that are preferred in many applications. These
dry ice granules cannot optimally be stored for subsequent metering
because their highly hygroscopic nature coupled with a high surface
to mass ratio that produces a strong tendency to clump when stored
for even very short time period. In addition, even when very small
quantities of dry ice granules are stored, the weight of the
granules in the upper portion is sufficient to combine and compress
the particles below them into undesirable larger sizes of dry
ice.
[0006] This challenge was resolved by equipment as presented in
U.S. Pat. No. 5,520,572. Such particles are customarily extracted
by scraping or shaving preformed dry ice (usually in block form but
it could also be in nugget or pellet form) and then immediately
feeding the dry ice granules into the airstream at a selectable
rate with substantially no storage. However, the conventional
granulated dry ice blasting apparatus which existed prior to this
invention, when used to create and then inject such particles into
an airstream, could not also instead satisfactorily meter the
larger preformed dry ice pellets. If this was attempted without
significantly modifying the granulator mechanism it would result in
damaging pellet integrity and thus changing the cleaning
characteristics of the dry ice particles.
[0007] To convert a machine from one mode to the other, prior to
this invention, required a complete shutdown of the machine, the
removal of one major part of the apparatus (a production wheel),
and the installation of another. This is time consuming, and
prevents the use of the same tool when different: areas of a work
piece require different types of particles.
[0008] Alternatively, another mechanism such as a grinder has been
added after the metering device to grind preformed dry ice pellets
in a secondary process step added between metering and conveyance.
This method adds to the cost and complexity of the apparatus and
often creates plugging and feed backup due to improper management
of the near constant need to frequently adjust the grinder for
variances in pellet sizes, pellet hardness, desired flow rates and
humidity levels. This method also requires pellets to granulate and
cannot granulate dry ice in block form.
[0009] Until now, most users of dry ice blasting equipment have
opted for the more expensive alternative or purchasing two separate
machines: one type of apparatus for pellet blasting; and another
type of apparatus for granule blasting. It is an object of this
invention to provide one apparatus with means in one mechanism to
both meter (or otherwise produce) and dispense either preformed dry
ice pellets or dry ice granules by the mere reversal of direction
of a movable carrier (sometimes called a "production wheel"). The
savings of time and expense are obvious. Only one set of tooling is
required, and no part of it needs to be exchanged when particles of
different size or nature are desired.
[0010] Another advantage of this invention is its adjustability to
provide mixtures of different mass sizes of particles.
BRIEF DESCRIPTION OF THE INVENTION
[0011] Apparatus according to this invention is incorporated in a
system which includes a supply of pressurized air, a nozzle, a
means to convey and inject dry ice particles into a pressurized
airstream which passes through a means of acceleration such as a
venturi nozzle, and a storage bin to hold dry ice in the form of
pellets or block to be metered into the airstream.
[0012] A carrier is movably supported and contains two different
sets of always-open passages. The carrier is adapted selectively to
be driven in a first direction to implement the action of the first
set of passages or in a second, different substantially direction
to implement the action of the second set of passages. The first
set of passages permits passage and metering of dry ice pellets
only when the carrier is moved in the first direction. The second
set of passages incorporates working edges defining a cutting or
scraping surface during movement of the carrier in the second
direction and thus simultaneously extracts and meters dry ice
granules into the conveyance airstream.
[0013] Therefore in one direction of movement or the other, a
supply of preformed dry ice pellets of a selected size will be
provided to the airlock. To switch from one type of operation to
the other, it is necessary only to reverse the direction of
direction of the carrier and to provide in the storage bin the
appropriate type of dry ice for the type of dry ice particle
desired (pellets or granules).
[0014] In addition, when pellets are used as a supply, it is
possible to adjust the proportion of larger particles and smaller
ones to select ratios of particles of various mass (and therefore
momentum) and provide a mix of particles.
[0015] The above and other features of this invention will be fully
understood from the following detailed description and the
accompanying drawings, in which:
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1 is a partly-schematic axial section of a system which
incorporates the invention;
[0017] FIG. 2 is a cross-section taken at line 2-2 in FIG. 1,
showing the upstream face of a production wheel according to this
invention;
[0018] FIG. 3 is a fragmentary cross-section taken at line 3-3 in
FIG. 2;
[0019] FIG. 4 is a fragmentary cross-section taken at line 4-4 in
FIG. 2;
[0020] FIG. 5 shows a dry ice pellet used in this invention;
[0021] FIG. 6 schematically shows a fragment of dry ice produced by
the production wheel in one of its modes;
[0022] FIG. 7 is a schematic graph showing a mass distribution of
particles generated in one mode;
[0023] FIG. 8 is a similar graph showing a particle size
distribution; and
[0024] FIG. 9 is a similar graph showing a mixture of mass
sizes.
DETAILED DESCRIPTION OF THE INVENTION
[0025] FIG. 1 shows the pertinent parts of an example of a dry-ice
blasting system 10. This example is for a pressurized air
conveyance means using an airlock, but the same principles are
applicable to eductor conveyance systems and are readily understood
by persons skilled in the art. Its objective is to direct a
blasting stream 11 consisting of air and dry ice particles of
desired size against a layer 12 of material to be removed from the
surface of a work piece 13. The stream exits from a nozzle 14 at
the delivery end 15 of a hose 16.
[0026] The inlet end 17 of the hose is connected to the outlet port
18 of an outlet plate 19. Plate 19 is stationary. It does not
rotate. It acts to cover and seal with the bottom surface 20 of
airlock rotor 21, except at its single outlet port 18.
[0027] An air hose 25 receives compressed air from a pump 26 or
other pressure source. Its outlet end 27 seals with the upper
surface 28 of the airlock rotor 21.
[0028] Airlock rotor 21 is rotatably mounted for rotation around a
central axis 30. It is driven by a motor 31. It includes a ring of
transfer chambers 32, arranged in a circle around the central axis.
As the airlock rotor rotates, the transfer chambers sequentially
arrive at the outlet end 27 of air hose 25, and simultaneously
align with the outlet port 18 of the outlet plate 19. During this
alignment, air passes from the air hose 25 to the hose 16, together
with a supply of dry ice particles, as will be discussed. Air hose
25 is appropriately dimensioned adjacent to the airlock so there is
no leakage past it while the hose is even partially aligned with an
airlock port.
[0029] A storage bin 40 includes a frame 42 which forms a
receptacle 43 to receive dry ice 44 and a chute 42a. As
illustrated, there is a block of dry ice in the receptacle.
Alternatively, it can be a collection of dry ice in the receptacle
pellets or nuggets. In both cases, a pressure plate 45 is pressed
against the dry ice.
[0030] A bias 46 such as an adjustable compression spring or
pneumatic cylinder presses against plate 45 so as to push the ice
against a movable carrier (often called a "production wheel"
herein) 50. Movable carrier 50 is mounted to the frame for rotation
around horizontal axis 51. It is driven by an adjustable speed,
bi-directional motor 52. Movable carrier 50 has an upstream face 53
and a downstream face 54. These faces are parallel to one another.
The upstream face is borne against by the dry ice. The downstream
face faces into chute 42a.
[0031] Chute 42a will direct freshly-passed dry ice to fall against
upper surface 28 of airlock rotor 21. When a transfer chamber 32 in
the airlock is beneath the chute, it receives a supply of particles
or pellets from the chute.
[0032] As the airlock rotates it presents a sequence of transfer
chambers 32 to the outlet chute 33. Each chamber receives an amount
of particles proportional only to the speed of the rate determining
element (moveable carrier 50). The displaced volumetric rate of the
chambers 32 is greater than the production capacity of the moveable
carrier assembly 50 and its associated parts at maximum speed. The
chute 42a is partially closed while the next chamber arrives. The
partially full chamber ultimately reaches outlet port 18, at which
time air pressure from air hose 25 will blow the particles out,
thereby combining the air and the particles to constitute a
blasting airstream.
[0033] The object of this invention is to meter and/or produce dry
ice particles of specific sizes and characteristics by the use of a
single movable carrier 50. It is intuitively evident that metering
preformed pellets, extracting granules, or extracting a mixture of
particle sizes on demand from any form of preformed solid dry ice
involves different considerations.
[0034] Pellets 60 are sold by suppliers or are generated in-plant
from liquid carbon dioxide in a generally cylindrical shape such as
shown in FIG. 5. Generally they are formed as a stack of flat
lozenges, because of the way they are made from liquified carbon
dioxide gas. A common size used in dry ice blasting is called
"rice-size" and they have an approximate nominal length of about
0.08 to 0.60 inches and a nominal diameter of about 0.125
inches.
[0035] The form of the granules 65 (FIG. 6) made from a block of
dry ice (rather than from pellets) is schematically shown in FIG.
6. and is similar in shape and size to granulated white table
sugar, shown here as a cubic structure. In any event, they are not
similar to the pellets of FIG. 5. Their mean dimensions are
preferably about 0.030 inches. It is evident that a different
device is needed to generate the particles of FIG. 6 than to
dispense the pellets of FIG. 5.
[0036] Dispensing of Pellets
[0037] A first set of passages 70 to dispense pellets 60 is
provided on the upstream face of movable carrier 50. There may be
any suitable number of these passage, spaced angularly and/or
radially apart from one another. They will all face in the same
rotational direction and in alignment with the first rotational
direction of the movable carrier 50. In FIG. 3, they face in the
counter-clockwise direction (the "first" direction). Actually the
choice of direction is optional. It is merely necessary that
pellets be dispensed when the movable carrier 50 turns in one
direction, and granules (or, as will be seen, a mixture) are
produced when the movable carrier turns in the other direction.
Also, that the device which is functional in one direction should
not impede or excessively adversely affect the desired function of
the other direction.
[0038] FIG. 3 shows a selected passage of the first set of passages
70, this for metering pre-formed pellets from a supply of pellets.
Because these passages all are similar, only one will be described
in detail. The upstream face 53 and downstream face 54 are shown
with slot 71 between them.
[0039] Slot 71 exits freely to the chute 55. Because its object is
to pass as large a proportion of pellets as possible, with minimal
change in pellet integrity, the slot requires relief from the
surface of the group of pellets, and a cut-off which will both
divert and organize (to at least a limited extent) the particles so
they can pass through the slot. In turn, the slot must be large
enough to pass properly aligned pellets without fragmenting them,
but small enough to reject them when the movable carrier 50 is not
moving. The fate of the rejected pellets is left to a sequential
slot of the same kind.
[0040] A relief ramp 75 is formed in upstream face 53, sloping
gradually from face 73 to an edge 76, the leading edge of slot 71.
It is a gradual ramp, which forms a recess dimension 78. This
enables pellets which abut the upstream face to move axially and
gradually toward the slot.
[0041] A diverter blade 80 faces toward the slot, and overhangs
part of it as shown in FIG. 3. This diverter blade 80 may be
configured to be adjustable and thus may be used to change the
width of the passage if different pellet sizes are utilized. Its
diverter edge 81 is substantially in the plane of upstream face 53,
and in no case does 81 protrude from the face more than the cutting
edge 92 in FIG. 4, described later. Viewed in the plane of FIG. 3,
there is a width 82 between diverter edge 81 and leading edge 76,
which will accommodate the expected diameter of pellet.
[0042] The axial offset between the recessed edge of the ramp and
the edge of the diverter is a bit larger, and facilitates passage
of the pellets along the angular path defined by the ramp.
[0043] What this arrangement accomplishes is the separation of
pellets which bear against the upstream face from the body of
pellets, with least disruption to the pellets. It should especially
be a noticed that the diverter edge 81 is practically coplanar with
upstream face 53, and that the ramp is "beneath" it.
[0044] Accordingly, this passage is effective only when the
diverter edge is facing into the pellets, i.e., moving in the
"first" direction. When reversed in the second direction of
rotation, it has no effect because the solid block of dry ice (or
other form of dry ice) will not contact it.
[0045] Production and Metering of Granules
[0046] A second set of passages 90 is provided to generate granules
65 when the movable carrier is moved in the substantially different
"second" direction. In this example its effective direction is
opposite from that of the first set of passages 70. When it
extracts granules from preformed solid dry ice instead of from
pellets, it attacks the ice with a working edge that rises above
upstream face 53.
[0047] The passages 90 of the second set have blades 91 which
extend radially to form a cutting edge 92 for a slot 93. Slot 93
extends through the movable carrier. Extracted granules passing
through it are deposited in the chute.
[0048] As seen in FIG. 4, cutting edge 92 rises above the plane of
upstream face 73 of the movable carrier. The other edge 94 of the
slot (which leads during the granulating operation), is preferably
in the plane of the upstream face, and guides the granules into the
slot.
[0049] When the movable carrier is moved in the second direction,
cutting edge 92 bites into the solid dry ice. It will be recalled
that the diverter edge 81 of the pellet slot in the first set of
passages is in the plane of the upstream face. Thus it does not
interfere with the solid dry ice, either by cutting it or by
pushing against it.
[0050] It follows that when pellets are dispensed, the granulating
system does not interfere, and when granules are extracted, the
pellet system does not interfere. To switch from one operation to
the other, it is only necessary to switch the direction of movement
of the movable carrier, and possibly to change the raw material
from pellets to block, or vice versa.
[0051] It is a convenience to form the cutting edges on a separate
blade attached to the movable carrier by fasteners, as shown. This
enables easy maintenance and replacement by the edges.
[0052] Production and Dispensing of Mixed Sizes
[0053] The ability to operate in the granulation mode of operation
with a supply of preformed pellets presents another available
benefit of this invention. While it is possible to completely and
uniformly granulate pellets, the applicant has found that by
varying the opening of slots 93 the, apparatus can produce a
particle stream of different characteristics than either primarily
pellets or primarily granules. It is well known in abrasive grit
blasting that the use of a mixture of particle sizes can deliver
improved performance in some applications. By adjusting the opening
of the slot 93 with an adjustable plate 91 it is possible to
generate from pellets a range of particle sizes from complete and
thorough granulation up to a partial dicing of the pellets and
varying combinations thereof. As used in this specification, the
term "modification" does not include adjustment of plate 91 to work
on pellets. The same production wheel is used for all three modes
of production without modification. Adjustment, when needed, is of
plate 91, and is not a modification requiring reconstruction or
substitution of the production wheel.
[0054] An example of size distribution granules (the granules 65 of
FIG. 6) extracted from a block of dry ice (rather than from
pellets) is schematically shown by graph 100 in FIG. 7 and this
graph 101 can be compared to the distribution of pellets only (the
pellets 60 of FIG. 5), FIG. 8 and a partial granulation of pellets
in the graph of FIG. 9, resulting in mixed mass sizes 105, 106.
Importantly, it will be observed that in all cases there will be
some variation of masses among the generated product. The curves
show their distribution.
[0055] This alternative of providing a mixture of larger and
smaller particles presents major advantages. The effects of the
blasting stream depend on the momentum of the particles. The
smallest particles will abrade a surface, but often not
effectively. Still they can dislodge and flush away smaller
residues while the larger particles strongly impact a surface. The
capacity to vary the proportion of more and less massive particles
is a considerable advantage. For this, pre-formed pellets are
provided instead of a solid block, and can thereby provide
particles of various mass distribution.
[0056] This invention is not to be limited by the embodiment shown
in the drawings and described in the description, which is given by
way of example and not of limitation, but only in accordance with
the scope of the appended claims.
* * * * *