Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02671055 2009-05-29
WO 2008/076366 PCT/US2007/025626
ABRASIVE CONFIGURATION FOR FLUID DYNAMIC REMOVAL OF
ABRADED MATERIAL AND THE LIKE
Cross-Reference to Related Applications
This application claims the benefit of US Provisional Application No.
60/875,094, filed December 15, 2006.
Technical Field
The present invention relates to an abrasive utilized to remove material from
a
workpiece and, more particularly, to an abrasive including fluid-dynamically-
designed
features to efficiently use the mechanical energy of the equipment to remove
(or direct)
abraded material, heat, coolants and waste from the surface of the workpiece.
Background of the Invention
When performing any type of grinding or polishing operation, a large amount of
abraded material is generally created and needs to be captured and removed
from the
work area. Abrasive grinders of the prior art generally comprise a portable
body that is
adapted to be held by a user, the grinder including a motor that drives a
backing plate
which in turn carries an abrasive component for grinding the surface of a
workpiece.
The abrasive component may take the form of a disk, belt, drum, wheel or any
other
configuration suitable for a given grinding/polishing operation.
In a "vacuum" type grinder, a shroud in the vicinity of the backing plate and
abrasive component defines a chamber through which air and entrained particles
flow to
an outlet leading to an accumulation point. The abrasive and backing plate are
provided
with holes that, when aligned, form an air passage to allow the flow of air
and entrained
particles which are drawn by suction applied to the shroud.
One problem with these vacuum-based prior art systems is the large abrasive
area
in relation to the small, peripheral vacuum area, and indirect path flows,
which result in
an increase in the temperature of the workpiece and the instability of the
process. The
generation of heat is particularly problematic in chemical-mechanical
planarization
(CMP) abrasive disks, where the chemistry at the workpiece surface will be
affected by
local temperature changes. Abrasive tools having a large abrasive area coupled
with a
high concentration of fine abrasives also typically become loaded with
workpiece debris
1
CA 02671055 2009-05-29
WO 2008/076366 PCT/US2007/025626
or swarf, limiting the speed of the abrading process, smearing debris on the
workpiece,
and creating additional `workpiece heating'.
Additionally, the vacuum effectiveness cannot be reliably controlled since the
vacuum must be sufficient over the surface area of the entire abrasive so as
to entrain
swarf created at any point on the abrasive (e.g., if grinding on a bevel, only
the cross-
sectional area being cut is in contact with the abrasive).
Conventional porous abrasive tools, having pores positioned throughout the
entirety of the abrasive structure, are well-known in the art. Conventional
porous metal
composite grinding wheels are commonly formed by sintering a loosely-packed
metal
composite, or by adding hollow glass and ceramic spheres to the composite.
However, it
has been found to be difficult to control the size and shape of the porosity
in such
abrasives and, if hollow spheres are used, it is difficult to prevent crushing
the spheres
during manufacture or use. While these porous abrasive tools are capable of
trapping
removed debris, they do not have any type of channel or pathway for clearing
the debris
from the tool itself. Therefore, additional mechanisms are required to move
the abraded
material away from the interface between the workpiece and the abrasive or the
same
clogging, smearing and overheating can occur.
The removal and containment of debris from various types of grinding/polishing
operations may also raise various health and/or environmental issues. For
example, the
removal of asbestos, paint, silica, fiber composites and the like needs to be
carefully
controlled in a manner that minimizes the creation of any airborne
contaminants that may
be inhaled, released into the environment or become re-incorporated into the
workpiece.
Accordingly, there is a need for an abrasive configuration that efficiently
moves
materials (i.e., coolant, air) to, and removes materials (i.e., heat, swarf)
from, a
workpiece during an abrading process.
Summary of the Invention
The needs remaining in the prior art are addressed by the present invention,
which relates to an abrasive utilized to remove material from a workpiece and,
more
particularly, to an abrasive including fluid-dynamically-designed features
that are
configured to efficiently remove abraded material and waste from the surface
of the
workpiece. The direction of flow through the features may also be reversed in
2
CA 02671055 2009-05-29
WO 2008/076366 PCT/US2007/025626
accordance with the present invention (i.e., toward the workpiece) to provide
the
introduction of cleaning fluids, coolants, process chemicals and the like.
In accordance with the present invention, an abrasive component (and/or
backing
plate) is formed to include fluid-dynamically-designed features which create
an air flow
stream/pressure differential that draws surface materials (including coolants
or other
process consumables) and the created debris (variously referred to as "swarf",
meaning
in general any material removed by an abrading tool) away from the grinding
surface.
Various other features formed within the abrasive may be specifically designed
to
introduce materials onto the workpiece surface. The abrasive component itself
may take
the form of a disk, belt, drum, wheel or any other suitable design. The fluid-
dynamically-designed features include elements such as apertures, air foils,
blower vanes
and the like.
It is an advantage of the fluid-dynamic design of the inventive fluid-dynamic
abrasive that the created flow properties are used to control environmental
properties
such as the velocity, pressure, density (including abrasive particle density),
chemistry,
cleanliness and temperature at the workpiece surface. The included features
function
individually to remove localized debris, while the entirety functions globally
to manage
the environmental conditions across the workpiece and abrasive tool surface.
By
removing the by-products of the abrasive process (mechanical, chemical, heat,
etc.)
before they can interact with the workpiece (or the abrasive), the chance of
workpiece
contamination (or abrasive clogging/blockage) is significantly reduced. Also
as
mentioned above, a conventional grinding process creates heat at the workpiece
area.
The ability to lower the temperature via the inventive fluid-dynamic abrasive
prevents
overheating of the material.
The apertures and associated pressure differential associated with the fluid-
dynamic abrasive also allow for a more uniform flow over the contact area and
localized
control of the workpiece/abrasive interface (balancing waste entrainment and
abrasive
contact area). The use of a large number of apertures allows the abrasive to
function in
the manner of a serrated cutting tool, creating swarf of minimal chip size,
while
maximizing `cutting tool' clearance. In particular, the aperture dimensions
and
configuration are designed to result in a predictable flow pattern at a finite
granularity/resolution in conjunction with macroscopic or collected vortices
to: move
debris from the surface in a preferred direction (e.g., flow from the edge of
a
disk/drum/wheel to the center, from the center to the edge, a radial flow
around a disk, a
3
CA 02671055 2009-05-29
WO 2008/076366 PCT/US2007/025626
lifting flow above an abrasive belt, etc.). A backing plate may be configured
to include a
plurality of containment channels to balance exhaust and/or coolant flow from
the center
of an abrasive element to its outer periphery.
Advantageously, the unique configuration of the subject abrasive components,
which incorporates various principles of fluid dynamics, has provided the
following
features: the overall process is "cleaner" than prior art arrangements since
the constant
movement (rotational or translational) of the abrasive itself creates the
`pull' to remove
the debris from the surface without allowing re-entry or "clogging" of the
work area or
abrasive surface; the overall process is "cooler" since the same increased air
flow also
functions to remove heat as it is created; the overall process is "uniform" in
terms of
providing the same abrading function and balanced cooling across the entire
face of the
workpiece (regardless of the degree of contact between the workpiece and the
abrasive)
in a manner such that the waste or by-products are not permitted to interact
with, damage
or taint the freshly-exposed surfaces; the overall process is more economical
than prior
art systems requiring utilization and maintenance of a separate vacuum source;
and the
overall process provides a higher quality result, since any potential
contaminants are
immediately and continuously removed from the work area, significantly
reducing any
potential environmental, health or workproduct contamination concerns.
Other and further advantages and features of the present invention will become
apparent during the course of the following discussion and by reference to the
accompanying drawings.
Brief Description of the Drawings
Referring now to the drawings,
FIG. I illustrates a prior art tool including an abrasive disk and vacuum
system
for removing debris from the work area;
FIG. 2 is a side view of a prior art conditioning head for a chemical
mechanical
planarization (CMP) system, illustrating the apertured abrasive disk included
within the
conditioning head;
FIG. 3 is an exploded view of a portion of the arrangement in FIG. 2,
illustrating
in particular the impeller and apertured abrasive disk components of the
conditioning
head;
4
CA 02671055 2009-05-29
WO 2008/076366 PCT/US2007/025626
FIG. 4 is a top view of one exemplary fluid-dynamically-designed abrasive disk
formed in accordance with the present invention;
FIG. 5 illustrates an alternative embodiment of the present invention where
the
geometry of the apertures within the abrasive disk are themselves configured
to provide
the fluid dynamic improvements in debris removal;
FIG. 6 shows yet another embodiment of the present invention, where the disk
apertures are tilted to create the desired pressure differential and
directional force
component;
FIG. 7 illustrates another fluid-dynamic-based abrasive disk design of the
present
invention;
FIG. 8 contains an illustration of yet another fluid-dynamic-based abrasive
disk
configuration formed in accordance with the present invention;
FIG. 9 contains an isometric perspective view of an exemplary fluid-
dynamically-designed impeller (backing plate) for use with an abrasive disk in
accordance with the present invention;
FIG. 10 illustrates an alternative fluid-dynamically-designed impeller
configuration;
FIG. 11 illustrates an exemplary fluid-dynamically-designed abrasive belt
formed
in accordance with the present invention;
FIG. 12 illustrates an exemplary fluid-dynamically-designed abrasive drum
formed in accordance with the present invention; and
FIG. 13 illustrates an exemplary fluid-dynamically-designed abrasive wheel
formed in accordance with the present invention.
Detailed Description
The fluid-dynamic based abrasive component of the present invention is
intended
to find use in a variety of applications, where any specific application
mentioned in the
following discussion is intended to merely provide a full illustration of the
various
features of the inventive abrasive component. Indeed, abrasives are used in
grinding/polishing many different surfaces (metals, glass, ceramic and the
like) in a
variety of heavy-duty industrial and/or commercial applications. In industrial
applications, abrasives are typically driven at speeds in the range of 1750 -
3200 rpm.
The generated swarf will follow the path of abrasive grit impact. Other
applications may
5
CA 02671055 2009-05-29
WO 2008/076366 PCT/US2007/025626
utilize a higher speed abrasive or a lower speed abrasive. For example, a
lower speed
abrasive is typically used in semiconductor industry applications when
polishing/treating
the surface of semiconductor wafers and in particular conditioning the
polishing pads
used to perform the polishing operations. Regardless of the application, the
configuration of the subject abrasive is not considered to be dependent upon
its field of
use. Rather, the fluid dynamic properties of the abrasive are designed
specifically for the
operating speeds, fluid properties (viscosity, volume, containment, lift, flow
direction,
pressures, etc.) and the like.
Prior to describing the details of the inventive abrasive, an overview of a
conventional prior art abrasive disk will be described in order to provide a
sufficient
knowledge base for gaining the best understanding of the features of the
present
invention.
FIG. I is a cut-away side view of an exemplary prior art sanding head I that
requires the use of a separate, stand-along vacuum system (not shown) for
removing
debris from the surface of the workpiece being sanded. Sanding head I includes
a shaft
2 rotatably mounted in a casing 3 and mechanically connectible to a drive
motor of an
electric drill (not shown). Shaft 2 is also connected at one end to a backing
plate 4.
Backing plate 4 has in its center, as is known, a hollow cylindrical element 5
which is
closed at its lower end by an end wall 6. An abrasive disk 7 is attached to
shaft 2 in a
manner that allows abrasive disk 7 to rotate and perform the sanding
operation. The
application of a vacuum to a vacuum port 8 then allows for the sanding debris
to be
drawn up around the periphery of abrasive disk 7, through an inner chamber 9
of sanding
head 1, then through vacuum port 8 and into a collection unit (not shown). In
particular,
the debris generated by abrasive disk 7 is projected by centrifugal force
towards the
periphery of disk 7. As shown by the arrows in FIG. 1, the vacuumed debris
along the
periphery is then drawn upward into inner chamber 9 and through port 8 to the
separate
vacuum system.
One problem with this arrangement, however, is that the removal of debris
relies
on the separate vacuum system capturing all of the material that has moved to
the
periphery of the disk. Clearly, some of the debris will always remain in a
central portion
of the abrasive disk. Also, as mentioned above, this approach is also
problematic in
situations where less than full face abrasive contact is maintained (i.e.,
edge grinding)
and the vacuum flow is formed only at the periphery of the disk.
6
CA 02671055 2009-05-29
WO 2008/076366 PCT/US2007/025626
While the prior art arrangement of FIG. 1 shows a conventional sanding head as
used for many diverse applications, there are also specialized applications as
mentioned
above that require the use of an abrasive for operations such as fine
polishing of glass,
planarizing of semiconductor wafers and, even more particularly, re-
conditioning the
polishing pad surface of the material used to planarize semiconductor wafers.
As is well-
known in the art, chemical mechanical planarization (CMP) systems use an
abrasive disk
to remove collected debris and planarizing fluids from the surface of a
polishing pad
(referred to as a "conditioning" process). FIG. 2 is a cut-away side view of
an exemplary
prior art CMP conditioning head 20, and FIG. 3 contains an exploded view of
certain of
the pertinent elements within conditioning head 20. US Patent 6,508,697,
issued on
January 21, 2003 to the assignee of this application contains a complete
description of
such a conditioning arrangement and is herein incorporated by reference.
For the purposes of understanding the benefits of the fluid-dynamic abrasive
of
the present invention, the aspects of conditioning head 20 related to its
abrasive disk will
be briefly described. Referring to both FIGs. 2 and 3, prior art conditioning
head 20
comprises an outer housing 22 including an inlet port 24 for dispensing
conditioning/cleaning agents onto a polishing pad 26 and a vacuum outlet port
28. An
abrasive conditioning disk 30 is disposed at the bottom of conditioning head
20 and
functions to rotate against the surface of polishing pad 26, sufficiently
abrading the
surface to remove any embedded particulates. As fully described in the above-
referenced patent, abrasive conditioning disk 30 includes a plurality of
apertures 32
formed across the entire surface. The exploded view of FIG. 3 best illustrates
the
placement and size of apertures 32. In this particular embodiment, an impeller
34 is
disposed between abrasive disk 30 and outer housing 22, where impeller 34 is
used to
provide the rotational motion to abrasive disk 30.
The application of a vacuum force through port 28, as shown by the arrows in
FIG. 2, allows for the dislodged debris and other effluent materials to be
pulled off of
polishing pad 26, through apertures 32 of abrasive disk 30 and along blades 36
of
impeller 34 into vacuum port 28. Impeller blades 36 function to sectionalize
the
vacuum. This improves the localized pressure and corresponding removal of the
effluent
and, in some embodiments, may also include apertures for either dispensing
conditioning
materials or evacuating debris (or both). While the use of an apertured
abrasive disk has
been successful in improving the removal of effluent from the pad's surface,
7
CA 02671055 2009-05-29
WO 2008/076366 PCT/US2007/025626
improvements in flow efficiency, containment, and partial-contact cleaning
ability (i.e.,
just beyond the edge of the pad 12 where the vacuum force will be broken) are
desirable.
By incorporating fluid dynamic considerations into the configuration of an
apertured abrasive component (e.g., disk, belt, drum, wheel or the like), the
various
embodiments of the present invention, as described below, will create an
extremely
localized pressure differential (i.e., a pressure differential in the region
of the aperture,
also referred to variously as a "venturi") that assists or replaces the vacuum
removal
operation, balance flow across the radial direction and direct flow toward the
periphery,
thereby improving the performance of the abrasive. Indeed, the fluid-dynamic
design is
useful in any abrasive application, from industrial heavy-duty abrasive tasks
to the
highly-specialized pad conditioning of polishing pads in the semiconductor
industry.
FIG. 4 is a top view of one exemplary fluid-dynamically-designed abrasive disk
100 formed in accordance with the present invention. Similar to prior art
abrasive disk 20
described above, fluid-dynamic abrasive disk 100 includes a plurality of
apertures 110
formed therethrough to allow for the abrading debris to be drawn away from the
workpiece surface (not shown). In accordance with the fluid dynamic principles
of the
present invention, a plurality of blower vanes 120 are disposed around the
outer
periphery of disk 100, as shown in FIG. 4. Between each pair of adjacent
blower vanes,
a vacuum outlet channel 130 is formed. Accordingly, when abrasive disk 100 is
rotated
(illustrated by the arrows labeled "R" in FIG. 4) the presence of blower vanes
120 creates
a pressure differential across the surface of abrasive disk 100. That is, the
pressure in the
central area of disk 100 is greater than the pressure around the periphery of
disk 100,
forcing the evacuated debris into vacuum outlet channels 130. In this
particular
embodiment, the configuration of apertures 110 remains similar to those of
prior art
designs. More generally, it is conceivable that such a fluid dynamic abrasive
disk of this
embodiment of the present invention may utilize fewer apertures (or apertures
of varying
size - smaller toward the center to balance flow and abrasive particle
engagement as a
function of revolution), relying on the pressure differential created by
blower vanes 120
to move the debris from the workpiece surface into channels 130.
It is to be understood that a variety of different factors are involved in
determining the pressure differential created by the fluid-dynamic abrasive of
the present
invention. Some of the factors include, but are not limited to, the
rotational/translational
speed of the abrasive, the size, shape, and number of blower vanes/airfoils,
the
distribution of blower vanes/airfoils on the abrasive, the size and number of
outlet
8
CA 02671055 2009-05-29
WO 2008/076366 PCT/US2007/025626
channels, and the like. Any or all of these factors (and others) may be
considered when
implementing the inventive fluid-dynamic abrasive for a particular purpose.
Further, the
abrasive of the present invention may be formed to include only a surface
layer of
abrasive material or a distributed volume of abrasive throughout a cast or
sintered
abrasive material. In these arrangements using only a surface abrasive layer,
the fluid-
dynamic-based attributes are formed as part of the `substrate' or backing
plate upon
which the abrasive layer is affixed.
As shown in FIG. 4 and more particularly described in association with the
remaining figures, the fluid-dynamic-based abrasive of the present invention
functions to
increase the amount of waste material removed from the workpiece surface, and
provides
the additional benefit of also removing heat from the work area. By
specifically
incorporating fluid dynamic principles into the configuration of the apertured
abrasive,
various types of directed flow may be created. That is, the abrasive apertures
may be
configured to direct the flow upward away from the work area (lift), between
the
abrasive and workpiece (flush), or from the center to edge of the
disk/drum/wheel, or
vice versa (radial). The apertures may also be configured to improve the
evacuation of
abraded material from the center portion of the abrasive, relative to prior
art
arrangements, thus improving the cleanliness of the abraded workpiece surface,
as well
as the abrasive itself and aiding in the collection/containment from otherwise
uncontrolled waste dispersion.
FIG. 5 illustrates an alternative disk embodiment of the present invention
where
the geometry of the apertures within the abrasive disk is specifically
configured to
provide the improvements in debris removal. In the cut-away side view of FIG.
5, an
exemplary fluid-dynamic abrasive disk 200 is shown as including a plurality of
apertures
210. In accordance with this embodiment of the present invention each aperture
210
tapers outwardly from a first diameter D1 along bottom surface 230 of abrasive
disk 200
to a second, larger diameter D2 along top surface 240 of abrasive disk 200. In
accordance with the present invention, the tapered apertures (increasing from
DI to D2)
create an inverse pressure gradient as disk 200 is rotated (again, the
magnitude of the
gradient being a function of factors such as taper design, disk rotation
speed, etc.). This
pressure gradient, illustrated by the references +P and -P in FIG. 5, is
created locally at
each aperture 210, thus providing instantaneous and offsetting forces for
particle
entrainment.
9
CA 02671055 2009-05-29
WO 2008/076366 PCT/US2007/025626
The various, localized venturi will force the removed debris from the central
portion of the workpiece being abraded (not shown) upward, through and outward
toward the periphery of the abrasive disk and thereafter into the waste
stream. By
utilizing the inventive fluid-dynamically-configured apertures, the process of
removing
debris is significantly accelerated when compared to standard prior art
structures; indeed,
the aggregate airflow can be sufficient to eliminate the need for an external
vacuum
source. Since the pressure differential is localized, the removal forces and
effectiveness
are not affected by the workpiece size or abrasive contact area. For example,
in the field
of CMP pad conditioning, the use of the localized venturi complement
separately applied
flows and will allow for a sufficient vacuum to be maintained as the abrasive
moves
outward over the edge of the polishing pad (a situation which, in the past,
would cause
the applied vacuum force to "break" and allow the debris to remain in the
peripheral
region of the pad). By localizing the pressure differential at the point where
abrasion is
occurring and containing it within a backing plate, the swarf can therefore be
directed in
a more predictable manner. The localized aspect of the created flow is also
useful from a
mechanical point of view, in terms of allowing for localized introduction of
coolants,
removal of heat, and the ability to control the stream direction for both
introduced and
removed elements.
Instead of creating apertures of tapered geometry, the plurality of apertures
themselves may be tilted to create a similar pressure differential, as shown
in the
embodiment of FIG. 6. In this case, a fluid-dynamically-configured abrasive
disk 300
includes a plurality of apertures 310. Each aperture 310 has essentially the
same
diameter D, as illustrated along bottom surface 320 and top surface 330 of
abrasive disk
300. However, the apertures are shown as tilted to a predetermined angle 0,
where the
angled arrangement will create the desired pressure differential or impart a
predetermined directional force vector at a predetermined radial position.
The scope of the present invention is intended to cover any fluid-dynamically
configured arrangement of features within an abrasive component. FIGs. 7 and 8
illustrate two more exemplary arrangements, also shown in the form of an
abrasive disk.
FIG. 7 illustrates a fluid-dynamic abrasive disk 400 where each aperture 410
is formed to
comprise a first diameter dl through a certain predetermined thickness of disk
400, and
thereafter taper outward, as shown by opening 420, to a final diameter d2. The
resultant
structure exhibits a funnel-like configuration. Again, the difference in
diameter from d]
CA 02671055 2009-05-29
WO 2008/076366 PCT/US2007/025626
to d2 will provide the pressure differential sufficient to force the debris
upward and away
from the workpiece surface (venturi action). The apertures need not comprise
linear
sidewalls, as shown by the embodiment of FIG. 8, where a fluid-dynamic
abrasive disk
500 includes apertures 510 having a curved or `airfoil'-shaped sidewall(s)
520. As
described above, the rotation of abrasive disk 500 will draw the material from
the
workpiece surface and into a collection system (not shown).
In arrangements that utilize an impeller (or backing plate) in conjunction
with an
abrasive disk, the impeller blades themselves may be configured to improve the
flow of
debris from the workpiece surface to the waste system. It is possible to
design both the
abrasive disk and impeller to exhibit fluid dynamic attributes or,
alternatively, so design
one or the other component. Indeed, by incorporating fluid-dynamic features
into the
impeller design, additional advantages may be obtained. For example, the
movement of
air will function to cool the surface of the workpiece being abraded (thus
preventing
overheating). Moreover, the application of cleaning materials (in conjunction
with the
abrading process) will be considerably more uniform across the workpiece
surface by
virtue of the specific impeller configuration. Additionally, the impeller can
be designed
to contain the removed waste material or alternatively pump `coolant' back
into the
workpiece for additional process benefits.
FIG. 9 contains an isometric perspective view of an exemplary fluid-dynamic
impeller 600 formed to include a plurality of impeller blades 610. In
accordance with
the present invention, each blade 610 is specifically designed to exhibit an
airfoil-like
structure (i.e., curvedly tapering inward from the outer periphery 620 of
impeller plate
630 toward the central region 640 of impeller plate 630). The curvature of
blades 610 in
the manner shown will improve the pressure balance and flow of debris from a
workpiece surface toward an associated outlet port. An alternative impeller
configuration is shown in FIG. 10, where a two-dimensional modification of the
blade
profile (compared to the prior art blade shown in FIG. 3) will provide fluid-
dynamically-
based improvement in the movement of debris material from the workpiece
surface. In
this arrangement, an impeller 700 comprises a set of impeller blades 710
disposed in a
type of "pinwheel" configuration such that as the impeller is rotated, the
created pressure
differential will force the debris to the periphery of the system.
While the embodiments of the present invention discussed thus far have
illustrated the formation of a fluid-dynamic abrasive disk, it is to be
understood that the
abrasive may also take the form of a belt, drum, wheel, or any other abrasive
11
CA 02671055 2009-05-29
WO 2008/076366 PCT/US2007/025626
configuration suitable for a specific purpose. FIG. 11 illustrates an
exemplary fluid-
dynamically-designed abrasive belt grinder 800, including a belt 810 that
moves in a
linear direction with respect to the workpiece being abraded, this
translational movement
indicated by arrow L in FIG. 11. A plurality of apertures 820 are formed in
belt 810 that
create a pressure differential between bottom surface 830 and top surface 840
of belt
810, directing the swarf upward and away from a workpiece (a lifting force).
Thereafter,
the swarf is drawn through apertures 845 in a vacuum plenum 850 and ultimately
directed into a containment vessel (not shown). Importantly, the fluid-
dynamically-
designed arrangement of FIG. 11 will draw substantially all of the
swarf/debris from the
workpiece. As mentioned above, there are many situations where the workpiece
being
abraded includes a hazardous material that will be introduced into the exhaust
flow. The
ability to provide an efficient and complete containment of this material in
accordance
with the fluid dynamic aspects of the inventive abrasive greatly diminishes
the potential
for contamination of the environment, inhalation by a worker, and/or re-
incorporation of
the material into the workpiece.
FIG. 12 illustrates an exemplary abrasive drum embodiment of the present
invention. As shown, a drum 900 is formed to include at least an outer surface
910 of
abrasive material (alternatively, the abrasive grit may be disposed through
the thickness t
of the drum), with a plurality of apertures 920 formed therethrough. The
number and
configuration of the apertures is considered to be a matter of design choice.
In
accordance with the present invention, a plurality of airfoils 930 are
disposed on an inner
surface 940 in the manner shown in FIG. 12. As drum 900 rotates (shown by
arrow r in
FIG. 12), the presence of the airfoils will pull any swarf created by the
abrading process
through apertures 920 and toward the center 950 of drum 900. A central vacuum
attachment (not shown) may then be used to remove the entrained swarf.
Yet another embodiment of the present invention is shown in FIG. 13, in this
case
in the form of an abrasive wheel 1000, having an abrasive outer surface 1100.
Abrasive
wheel 1000 is shown as having a thickness T, with a plurality of apertures
1200 formed
through the thickness thereof. A plurality of airfoils 1300 are disposed
around the inner
periphery 1400 of wheel 1000. As wheel 1000 rotates, the combination of
apertures
1200 and airfoils 1300 will draw the swarf towards the center of wheel 1000.
In this
particular embodiment, a containment shroud 1500 is included and disposed
around the
central portion of wheel 1000 to collect the swarf.
12
CA 02671055 2009-05-29
WO 2008/076366 PCT/US2007/025626
Having thus described various embodiments of the present invention, it is to
be
appreciated that there are many other variations, alterations, modifications
and
improvements of the specifically-described embodiments that may be made by
those
skilled in the art. Such variations, alterations, modifications and
improvements are
intended to be part of this disclosure and thus also intended to be part of
this invention.
Accordingly, the foregoing description and drawings are by way of the example
only,
and the scope of this invention is rather defined by the claims appended
hereto.
13
