U.S. patent application number 12/053353 was filed with the patent office on 2012-11-15 for method of polishing transparent armor.
This patent application is currently assigned to 3M Innovative Properties Company. Invention is credited to John L. Barry, Daniel A. Billig, Ann M. Hawkins, James L. McArdle.
Application Number | 20120289125 12/053353 |
Document ID | / |
Family ID | 47142163 |
Filed Date | 2012-11-15 |
United States Patent
Application |
20120289125 |
Kind Code |
A1 |
Billig; Daniel A. ; et
al. |
November 15, 2012 |
METHOD OF POLISHING TRANSPARENT ARMOR
Abstract
A method of polishing transparent armor, preferably to optical
clarity. The method can be used on flat or contoured armor,
manually or via robotic automation. The method includes using a
step-wise progression of diamond, structured abrasive articles.
Inventors: |
Billig; Daniel A.;
(Maplewood, MN) ; Barry; John L.; (Stacy, MN)
; McArdle; James L.; (Stillwater, MN) ; Hawkins;
Ann M.; (Lake Elmo, MN) |
Assignee: |
3M Innovative Properties
Company
|
Family ID: |
47142163 |
Appl. No.: |
12/053353 |
Filed: |
March 21, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60896016 |
Mar 21, 2007 |
|
|
|
Current U.S.
Class: |
451/36 ;
451/41 |
Current CPC
Class: |
B24D 9/00 20130101; B24B
37/22 20130101; B24B 37/26 20130101; B24D 3/14 20130101; B24B
37/245 20130101; F41H 5/0407 20130101; B24B 19/00 20130101; B24B
1/00 20130101; B24D 11/02 20130101 |
Class at
Publication: |
451/36 ;
451/41 |
International
Class: |
B24B 1/00 20060101
B24B001/00; B24D 3/00 20060101 B24D003/00 |
Claims
1.-15. (canceled)
16. A method of finishing transparent ceramic armor selected form
the group consisting of spinel, sapphire, and aluminum oxynitride,
the method comprising the steps of: providing an abrasive article
comprising a structured abrasive layer having a plurality of
abrasive composites; the plurality of abrasive composites
comprising a matrix binder and a plurality of diamond abrasive
particles, the plurality of diamond abrasive particles comprising
from about 4 weight percent to about 30 weight percent of the
structured abrasive layer; the structured abrasive layer adhered to
a first side of a backing, the backing including a second side
attached to a first side of a reinforcing layer with an adhesive
layer, and; contacting the transparent ceramic armor with the
structured abrasive layer, and imparting relative motion between
the abrasive article and the transparent ceramic armor.
17. The method of claim 16 wherein the structured abrasive layer
comprises a network valley region and a plurality of shaped
abrasive composites having a hexagonal shape.
18. The method of claim 17 wherein the structured abrasive layer
comprises an area bearing ratio between about 50 percent to about
70 percent.
19. The method of claim 18 wherein the plurality of diamond
particles comprises from about 6 weight percent to about 30 weight
percent of the structured abrasive layer.
20. The method of claim 19 wherein the plurality of diamond
particles comprises from about 20 weight percent to about 30 weight
percent of the structured abrasive layer.
21. A method of finishing transparent ceramic armor selected form
the group consisting of spinel, sapphire, and aluminum oxynitride,
the method comprising the steps of: rough grinding a first surface
of the transparent armor; intermediate pre-polish grinding the
first surface after rough grinding with a first structured abrasive
article comprising: a structured abrasive layer adhered to a first
side of a backing, the structured abrasive layer having a plurality
of abrasive composites; the plurality of abrasive composites
comprising agglomerates and a matrix binder; the agglomerates
comprising a glass binder and diamond abrasive particles having an
average size of 15 micrometers or less and the agglomerate size is
about 40 to about 400 micrometers; and the structured abrasive
layer having a bearing area ratio between about 40 percent to about
70 percent; intermediate pre-polish grinding the first surface
after pre-polish grinding the first surface with the first
structured abrasive article with a second structured abrasive
article comprising: a structured abrasive layer adhered to a first
side of a backing, the structured abrasive layer having a plurality
of abrasive composites; the plurality of abrasive composites
comprising agglomerates and a matrix binder; the agglomerates
comprising a glass binder and diamond abrasive particles having an
average size of 15 micrometers or less and the agglomerates size is
about 40 to about 400 micrometers; the structured abrasive layer
having a bearing area ratio between about 40 percent to about 70
percent; and wherein the diamond abrasive particles of the second
structured abrasive article have a particle size no more than 50%
of the size of the diamond abrasive particles in the first
structured abrasive article.
22. The method of claim 21 wherein the rough grinding step
comprises using a Blanchard grinding machine.
23. The method of claim 21 wherein after pre-polish grinding the
first surface with the second structured abrasive article, the
first surface is final polished to optical clarity with an abrasive
slurry.
24. The method of claim 21 wherein after pre-polish grinding the
first surface with the second structured abrasive article, the
first surface has an Ra between 0.0 and about 1 .mu.in.
25. The method of claim 21 wherein a second side of the backing of
both the first and the second structured abrasive articles is
attached to a reinforcing layer with and adhesive layer.
26. The method of claim 21 wherein a removal rate, T, is 76.3
.mu.m/min or greater when using the first structured abrasive
article.
27. The method of claim 21 wherein the diamond abrasive particles
comprise about 4 weight percent to about 30 weight percent of the
structured abrasive layer of the first structured abrasive article.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application claims the benefit of U.S. Provisional
Patent Application No. 60/896,016, filed Mar. 21, 2007, the
disclosure of which is incorporated by reference herein in its
entirety.
TECHNICAL FIELD
[0002] This disclosure relates to a method for polishing a
transparent armor, to an optically clear finish, using abrasive
articles. The transparent armor may be flat or curved.
BACKGROUND
[0003] In recent years there has been a tremendous amount of
interest in transparent armor for both military and civilian
protection. It is desired that the transparent armor is abrasion
resistant, relatively low cost, and relatively low weight, and in
many applications, it is desired that the transparent armor is
optically clear. Likewise since there are countless types of
threats (bullets, improvised explosive devices (IEDs), etc.),
transparent armor preferably should be effective against multiple
types of projectiles and preferably against multiple strikes.
[0004] In many instances, transparent armor constructions consist
of a hard ceramic layer, which may be bonded to a polymeric layer.
The hard ceramic layer is abrasion resistant and resists scratches
during normal use. When a projectile encounters the transparent
armor, the hard ceramic layer deforms the projectile and resists
penetration by the projectile while the polymeric layer supports
the ceramic layer and further absorbs energy from the projectile.
The combination of the hard ceramic and polymeric layers causes
disintegration of the projectile and inhibits the penetration of
the projectile through and possibly cause injury. The selection of
the particular ceramic layer, and polymeric layer, depends upon the
desired end properties of the transparent armor.
[0005] One particular transparent armor material is a
polycrystalline magnesium-aluminate spinel ceramic (e.g.,
MgAl.sub.2O.sub.4). This material is typically hot-pressed to form
the shape, and to produce a dense, pore-free ceramic body. Due to
contact with the hot-press platen surfaces, the resulting outer
surfaces of the ceramic have a textured, orange-peel-type surface.
Even if the hot-pressed ceramic body is dense and pore-free, the
rough outer surfaces cause scattering of incident light and thereby
result in a non-transparent product. In order to obtain a
transparent product, both surfaces must be polished smooth.
[0006] However, it is time consuming and difficult to polish the
hot-pressed material to optical clarity. The polishing cost may
contribute significantly to the overall transparent armor cost and
thus inhibit their use.
[0007] What is desired is a cost effective means to polish a
transparent armor material to achieve optical clarity.
SUMMARY OF THE DISCLOSURE
[0008] Briefly, the present disclosure provides a method of
polishing transparent armor to optical clarity. The method can be
used on flat or contoured armor, manually or via robotic automation
using a powered rotary tool. The method includes using a step-wise
progression of diamond, structured abrasive articles.
[0009] In one aspect of the disclosure, the method comprises
providing a transparent armor material that is not optically clear
and has a first surface finish, providing a first structured
abrasive article comprising a backing and a plurality of shaped
composites comprising diamonds therein, securing the first abrasive
article to a rotary grinder to form an abrasive tool, and moving
the first abrasive article relative to the transparent armor such
that the first abrasive article modifies the armor to provide a
second surface finish. The second surface finish is closer to
optically clear than the first surface finish.
[0010] In some embodiments, the rotary grinder is connected to a
robot, so that the robot moves the first abrasive article relative
to the transparent armor.
[0011] In another aspect of the disclosure, the method further
comprises providing a second structured abrasive article comprising
a backing and a plurality of shaped composites comprising diamonds
therein, the diamonds having a smaller particle size than the
diamonds of the first abrasive article, securing the second
abrasive article to a rotary grinder to form an abrasive tool, and
moving the second abrasive article relative to the transparent
armor such that the second abrasive article modifies the armor to
provide a third surface finish that is closer to optically clear
than the second surface finish.
[0012] In yet another aspect of this disclosure, a third structured
abrasive article, having diamonds with a smaller particle size than
the diamonds of the second abrasive article, is used in the same
manner subsequent to the second abrasive article to provide a
fourth surface finish that is closer to optically clear than the
third surface finish.
[0013] Any or all of the abrasive articles may be used to abrade
the surface of the transparent armor manually or by a robot. As
provided above, the transparent armor may be flat or curved.
[0014] In another aspect or the disclosure the method comprises
finishing transparent ceramic armor selected form the group
consisting of spinel, sapphire, and aluminum oxynitride, the method
comprising the steps of: providing an abrasive article comprising a
structured abrasive layer having a plurality of abrasive
composites; the plurality of abrasive composites comprising a
matrix binder and a plurality of diamond abrasive particles, the
plurality of diamond abrasive particles comprising from about 4
weight percent to about 30 weight percent of the structured
abrasive layer; the structured abrasive layer adhered to a first
side of a backing, the backing including a second side attached to
a first side of a reinforcing layer with an adhesive layer, and;
contacting the transparent ceramic armor with the structured
abrasive layer, and imparting relative motion between the abrasive
article and the transparent ceramic armor.
[0015] Other features and advantages of the disclosure will be
apparent from the following detailed description of the invention
and the claims. The above summary is not intended to describe each
illustrated embodiment or every implementation of the present
disclosure. The figures and the detailed description that follow
more particularly exemplify certain preferred embodiments utilizing
the principles disclosed herein.
BRIEF DESCRIPTION OF THE DRAWING
[0016] FIG. 1 is a schematic cross-sectional side view of a first
embodiment of a structured abrasive article suitable for use with
the method of the present invention.
[0017] FIG. 2 is a schematic cross-sectional side view of a second
embodiment of a structured abrasive article for use with the method
of the present invention.
[0018] FIG. 3 is a top-view of the structured abrasive article of
FIG. 2.
Detailed Description of the Presently Preferred Embodiments
[0019] The present invention provides a method of polishing
transparent armor to optical clarity. The method can be used on
flat or contoured armor, the polishing being done manually, via
robotic automation, or using a flat lapping machine such as a
Strasbaugh 6DC. As used herein, "flat" means at least essentially
planar. The method includes using a step-wise progression of
diamond, structured abrasive articles. Alternatively, the method
can include a rough grinding step using, for example, a Blanchard
grinding machine, an intermediate pre-polish grind and finishing
step using one or more structured abrasive articles in a step-wise
progression, and a final polish using a polishing abrasive
slurry.
[0020] As used herein, the term "optically clear", when referring
to an item, means that a human can readily see through the item,
without significant distortion of the visible images. The term
"optical clarity" means that a human can see clearly, without
significant distortion or indistinctness or ambiguity. An item that
is optically clear or that has optical clarity is generally
transparent to the human eye. For many embodiments, an item that is
optically clear has an Ra (surface finish) approaching zero, with
little or no subsurface occlusions or fissures. In some
embodiments, an optically clear item has >85% transmission in
the visible and near-infrared wavelength range.
[0021] The Ra of a surface is the measurement of the arithmetic
average of the scratch depth. It is the average of 5 individual
roughness depths of five successive measuring lengths, where an
individual roughness depth is the vertical distance between the
highest point and a center line. Rz is the average of 5 individual
roughness depths of a measuring length, where an individual
roughness depth is the vertical distance between the highest point
and the lowest point. Rmax is the maximum roughness depth from the
highest point and the lowest point in the measuring length.
[0022] The surface finish is usually measured with a profilometer
which comprises a probe having a diamond tipped stylus. Examples of
such profilometers include Surtronic, Surfcom, and Perthometer. Ra,
Rz, and Rmax are usually recorded in micrometers or microinches.
Extremely fine or smooth surface finishes, too smooth for a
profilometer to measure, can be measured with a passive measurement
device, such as a WYKO interferometer, and are usually recorded in
nanometers or angstroms. In various embodiments of the invention,
the Ra of the polished transparent armor can be between about 0.0
to about 1.0 .mu.in, or between about 0.0 to about 0.2 .mu.in.
Transparent Armor
[0023] The transparent armor is a polycrystalline ceramic, such as
a magnesium-aluminate spinel (MgAl.sub.2O.sub.4). The armor
generally has a hardness of at least 10 GPa. Spinel and other armor
materials, such as aluminum oxynitride (Al.sub.23O.sub.27N.sub.5)
and sapphire (Al.sub.2O.sub.3), are used as transparent armor by
those of skill in the art.
[0024] The transparent armor has a first outer surface and a second
outer surface. In accordance with the typical manufacturing process
to form the pieces (e.g., sheets or plates) of some transparent
armor, the material is hot pressed to form the desired overall
shape and to produce a fully dense, pore-free ceramic body. The
shape can be flat or curved. The transparent armor may range in
size of 1 cm by 1 cm to greater than 50 cm by 50 cm and may range
in thickness from 0.05 to 1000 mm thick, typically 0.1 to 100 mm
thick, although often the thickness is about 10 mm.
[0025] After hot pressing the material, the outer surfaces have a
textured, orange-peel-type surface, which has a cloudy appearance.
Even if the ceramic body is dense and pore-free, the surface
texture causes incident light to scatter and thereby provides a
non-transparent or translucent product. The present disclosure
provides a method to obtain optical clarity of the dense, pore-free
ceramic armor piece.
[0026] This disclosure provides a method to polish at least one
surface of the transparent armor to optical clarity; however
typically, polishing is done on both surfaces of the transparent
armor. During polishing, the intent is not to distort the shape
imparted by molding or some other process prior to the polishing
process. Rather during polishing, the intent is to refine the
surface finish of the dense, pore-free armor panel and achieve
optical clarity with the least amount of transparent armor material
removed.
Armor Constructions
[0027] The armor construction is designed for the end application
and to be protective against the targeted type of bullet and/or
explosive device to which it will most likely be exposed. The armor
construction is designed to provide the following properties: 1)
light weight, 2) transparent in the visible and near-IR
wavelengths, 3) optically free of distortion and 4) maximizing
ballistic protection. At the same time, this protective armor
during use must be 1) abrasion resistant (no scratches to inhibit
optical clarity) 2) shock resistant and 3) able to adjust to
changing weather conditions including both temperature and moisture
content. The temperature can range from -50 F to 150 F, typically
-30 F to 140 F. The moisture content can range from low humidity to
high humidity. The moisture content also includes rain, snow,
sleet, hail, drizzle and the like.
[0028] The transparent armor may be incorporated into various
constructions to produce protective armor. One common construction
comprises the transparent armor layer facing the incident ballistic
threat, an adhesive layer, and a force-dissipating backup layer.
The transparent armor layer provides abrasion resistance, strength,
rigidity, and penetration resistance. The increase in hardness and
stiffness is preferred because it causes disintegration of the
ballistic threat and resists penetration of the projectile through
the armor. The force-dissipating backup layer can flex and absorb
the remaining energy of the projectile or remnant fragments of the
projectile. The force-dissipating layer should have good shock
resistance, good impact resistance and high toughness.
[0029] Examples of common laminating adhesives include polyurethane
adhesives, polyvinyl buteral, thermosetting resins, UV curable
resins, acrylic adhesives and the like.
[0030] The force-dissipating layer may comprise: polycarbonate,
polyacrylic (including cast acrylic, polymethylmethacrylate,
modified acrylics and the like), cellulose acetate butyrate,
ionomers, nylons, polyolefins, polyesters, polyurethane
(thermosetting and thermoplastic), combinations thereof and the
like. Polycarbonate and polyacrylic are the preferred materials for
the dissipating layer. The force-dissipating layer may also contain
a protective hard coating on the surface opposite the laminating
adhesive. This force-dissipating layer may range in thickness from
0.1 to 100 mm thick, typically 0.5 to 50 mm thick. Likewise the
force-dissipating layer may be comprised of several thinner layers
of the same or different materials laminated together to form the
thicker layer.
[0031] One common construction comprises the transparent armor, an
adhesive layer, a polyurethane interlayer and an energy-absorbing
layer. This polyurethane interlayer provides further protection in
absorbing the energy from the ballistic, and reducing the
transmission of energy from one layer to the next. In another
common construction, a silicate glass layer is included between the
transparent armor layer and the energy-absorbing layer.
Armor Applications
[0032] The transparent armor may be incorporated into a wide range
of applications including vehicles (e.g., cars, jeeps, trucks
(light and heavy duty)), airplanes, helicopters, tanks, trains,
ships, amphibious vehicles; windows (e.g., side, windshields,
back); stationary objects (e.g., building windows, doors, bus
stops, bullet proof shelters); bulletproof protective clothing
(e.g., eye glasses, goggles, face shields). The transparent armor
may be incorporated into military, police protection, security
services and private applications. The projectiles may be from
bullets fired from a weapon including (e.g., hand guns, machine
guns, automatic weapons, rifles, assault rifles) or explosive
device (e.g., pipe bomb, hand grenade, explosive materials worn by
a suicide bomber, car bombs, and the like).
Abrasive Article
[0033] In FIG. 1, an abrasive article is illustrated as abrasive
article 10. Abrasive article 10 is commonly referred to as a
"shaped abrasive article", having a plurality of abrasive particles
bonded to a backing. The abrasive article 10 has a backing 12,
having a first side 12a and an opposite second side 12b. An
abrasive coating 14 is present on the first side 12a of backing
12.
[0034] Abrasive coating 14 comprises a plurality of abrasive
composites 18, which are composites of abrasive particles 15
distributed in an adhesive matrix 16. Abrasive composites 18 are
separated by a boundary or boundaries associated with the composite
shape, resulting in one abrasive composite 18 being separated to
some degree from another adjacent abrasive composite 18 with a
section of the backing 12 visible between abrasive composites. One
of the earliest references to structured abrasive articles with
precisely shaped abrasive composites is U.S. Pat. No. 5,152,917 to
Pieper et al. Many others have followed.
[0035] Referring to FIG. 2, an alternative embodiment of the
abrasive article 10 is shown. Abrasive article 10 includes a
plurality of shaped abrasive composites 18 attached to a backing 12
forming a structured abrasive article. The backing 12 has a
substantially continuous layer of abrasive particles 15 dispersed
in a binder matrix 16 forming the plurality of shaped abrasive
composites 18 such that the backing 12 is no longer visible in the
valleys between adjacent shaped abrasive composites 18. The
structured abrasive article is attached to a reinforcing layer 20
on a first side 20a of the reinforcing layer 20 by an adhesive
layer 22. In some embodiments, an attachment adhesive layer 24 is
present on a second side 20b of the reinforcing layer 20. A release
liner 26 may be provided that can be removed to attach the abrasive
article 10 to a platen of a grinding or polishing machine. Instead
of an adhesive interface layer 24 to attach the abrasive article to
a grinding tool, other attachment systems such as hook and loop
fasteners, or mechanical fasteners can be used.
[0036] Referring now to FIG. 3, a top-view of the abrasive article
of FIG. 2 is shown. The abrasive article 10 can be in the form of
an abrasive disk as shown or other common converted form such as an
endless belt. The plurality of shaped abrasive composites 18, each
comprises a hexagon, in top-view, separated from adjacent shaped
abrasive composites by a network valley region 28. The network
valley region 28 allows for grinding lubricant to be readily
transported to each of the shaped abrasive composites and for
grinding residue (swarf) to be transported away from the working
surfaces of the shaped abrasive composites.
[0037] Alternative abrasive composite shapes include, without
limitation, circular, diamond, triangular, rectangular, and square.
In one embodiment, the top of each shaped abrasive composite is
planar such that the shaped abrasive composite does not come to a
peak or a tip; however, pyramidal or conical shaped abrasive
composites can be used in some applications.
[0038] The spacing of the shaped abrasive composites may vary from
about 0.3 shaped abrasive composites per linear cm to about 100
shaped abrasive composites per linear cm, or about 0.4 to about 20
shaped abrasive composites per linear cm, or about 0.5 to 10 shaped
abrasive composites per linear cm, or about 0.6 to 3.0 shaped
abrasive composites per linear cm. In one aspect of the abrasive
article, there are at least about 2 shaped abrasive
composites/cm.sup.2 or at least about 5 shaped abrasive
composites/cm.sup.2. In a further embodiment of the invention, the
area spacing of shaped abrasive composites ranges from about 1 to
about 200 shaped abrasive composites/cm.sup.2, or from about 2 to
about 10 shaped abrasive composites/cm.sup.2.
[0039] The height of the abrasive composites as measured from the
top of the valley between adjacent shaped abrasive composites to
the top of the shaped abrasive composite is constant across the
abrasive article 10, but it is possible to have shaped abrasive
composites of varying heights. The height of the shaped abrasive
composites may be a value from about 10 micrometers to about 25,000
micrometers (2.5 cm), or about 25 to about 15,000 micrometers, or
from about 100 to about 10,000 micrometers, or from about 500 to
about 4,000 micrometers.
[0040] In various embodiments, the bearing area ratio can be
between about 20 percent to about 80 percent, or between about 40
percent to about 70 percent, or between about 50 percent to about
70 percent. The bearing area ratio, expressed as a percentage, is
the ratio of the total area of the shaped abrasive composites 18 to
the total area of the abrasive article including the area of the
network valley region 28. Depending on the application or the
workpiece, a larger or smaller bearing area ratio may desirable
depending on the grade of abrasive, the work piece material, the
unit loading pressure, and the desired cut rate and finish.
Backing
[0041] Backing 12 includes those known useful in abrasive articles,
such as polymeric film, cloth including treated cloth, paper, foam,
nonwoven, treated or primed versions thereof, and combinations
thereof. Examples include polyester films, polyolefin films (e.g.,
polyethylene and propylene film), polyamide films, polyimide films
and the like. A thin backing can be reinforced using another layer
for support, such as a thicker film, or a polycarbonate sheet, for
example. In addition, the abrasive article can be attached to a
base or sheet or directly to a polishing apparatus or machine via
any known route, for example, adhesives including pressure
sensitive adhesives are useful.
[0042] Backing 12 serves the function of providing a support for
the shaped abrasive composites. The backing should be capable of
adhering to the binder matrix after exposure of binder precursor to
curing conditions, and be strong and durable so that the resulting
abrasive article is long lasting. Further, the backing should be
sufficiently flexible so that the articles used in the inventive
method may conform to surface contours, radii, and irregularities
in the workpiece.
[0043] As mentioned, the backing may be a polymeric film, paper,
vulcanized fiber, a molded or cast elastomer, a treated nonwoven
backing, or a treated cloth. Examples of polymeric film include
polyester film, co-polyester film, polyimide film, polyamide film,
and the like. A nonwoven, including paper, may be saturated with
either a thermosetting or thermoplastic material to provide the
necessary properties. Any of the above backing materials may
further include additives such as: fillers, fibers, dyes, pigments,
wetting agents, coupling agents, plasticizers, and the like. In one
embodiment, the backing is about 0.05 mm to about 5 mm thick.
Reinforcement Layer
[0044] The reinforcement layer 20 can be used to impart additional
stiffness, resiliency, shape stability, and/or flatness to the
abrasive article 10. The reinforcement layer can be used to
stabilize the abrasive article during shape converting processes
such as laser or water jet cutting. Desirably, the reinforcement
layer comprises plastic such as polycarbonate or acrylic, metal,
glass, composite films, or ceramic. In one embodiment, the
reinforcement layer 20 is substantially uniform in thickness.
Often, the reinforcement layer is desirable to reduce or eliminate
deformations in the abrasive article 10 due to grinding platens
having scratches or gouges that could deform an abrasive article
having only a backing layer.
Abrasive Particles
[0045] Abrasive particles 15 are diamonds, either natural diamonds
or man-made diamonds and may comprise other abrasive particles by
themselves or in combination with the diamonds. The abrasive
particles may be present as individual abrasive particles,
agglomerates of a single type of abrasive particle or agglomerates
of a combination of abrasive particles, or combinations thereof.
The diamonds may include a surface coating (e.g., nickel or other
metal) to improve the retention of the diamonds in the resin
matrix.
[0046] The abrasive particles can have an average particle size of
about 0.01 micrometer (small particles) to about 1000 micrometers
(large particles), or about 0.25 micrometers to about 500
micrometers, or about 3 micrometers to about 400 micrometers, or
about 5 micrometers to about 100 micrometers. Occasionally,
abrasive particle sizes are reported as "mesh" or "grade", both of
which are commonly known abrasive particle sizing methods.
[0047] In one embodiment, the abrasive particles have a Mohs
hardness of at least 8, or at least 9. Examples of such abrasive
particles include fused aluminum oxide, ceramic aluminum oxide,
heated treated aluminum oxide, silicon carbide, diamond (natural
and synthetic), cubic boron nitride, and combinations thereof.
Softer abrasive particles, such as garnet, iron oxide, alumina
zirconia, mullite, and ceria, can also be used. The abrasive
particles may further comprise a surface treatment or coating, such
as a coupling agent or metal or ceramic coatings.
[0048] Abrasive particle 15 may be agglomerates of individual
abrasive particles. Agglomerates typically comprise a plurality of
abrasive particles, a binder, and optional additives. The binder
may be organic and/or inorganic. The matrix material can be a
resin, a glass, a metal, a glass-ceramic, or a ceramic. For
example, glass, such as silica glass, glass-ceramics, borosilicate
glass, phenolic, epoxy, acrylic, and the other resins described in
the context of the composite binder can be used. Abrasive
agglomerates may be randomly shaped or have a predetermined shape
associated with them. Additional details regarding various abrasive
agglomerate particles and methods of making them may be found, for
example, in U.S. Pat. No. 4,311,489 (Kressner), U.S. Pat. No.
4,652,275 (Bloecher et al.), U.S. Pat. No. 4,799,939 (Bloecher et
al.), U.S. Pat. No. 5,549,962 (Holmes et al.), U.S. Pat. No.
5,975,988 (Christianson), U.S. Pat. No. 6,620,214 (McArdle), U.S.
Pat. No. 6,521,004 (Culler et al.), U.S. Pat. No. 6,551,366
(D'Souza et al.), U.S. Pat. No. 6,645,624 (Adefris et al.). U.S.
Pat. No. 7,169,031 (Fletcher et al.) and in U.S. application
2007/0026770 (Fletcher et al.).
[0049] Generally, the average size of the agglomerate particle,
which comprises individual abrasive particles such as diamond
particles, ranges from about 1 micrometer to about 1000
micrometers. Often, if the individual abrasive particles within the
agglomerates are about 15 micrometers or greater, the overall
agglomerate is typically about 100 to about 1000 micrometers, or
about 100 to about 400 micrometers, or about 210 to about 360
micrometers. However, when the individual abrasive particles have
an average size of about 15 micrometers or less, the overall
agglomerate is often about 20 to about 450 micrometers, or about 40
to about 400 micrometers, or about 70 to about 300 micrometers.
[0050] The abrasive particles used in the agglomerates can be any
known abrasive particle, such as those listed above. Further, a
mixture of two or more types of abrasive particles maybe used in
the agglomerates. The mixtures of abrasive particles may be present
in equal ratios, may have significantly more of a first type of
abrasive particle that another type, or have any combination of the
different abrasive particles. Mixed abrasive particles may or may
not have the same average particle size or the same particle size
distribution.
[0051] For transparent armor grinding, it is preferred that the
abrasive article use diamond abrasive particles or abrasive
agglomerates that include diamonds. These diamond abrasive
particles may be natural or synthetically made diamond and may be
considered "resin bond diamonds", "saw blade grade diamonds", or
"metal bond diamonds". The single diamonds may have a blocky shape
associated with them, or alternatively, a needle like shape. The
single diamond particles may contain a surface coating such as a
metal coating (for example, nickel, aluminum, copper or the like),
an inorganic coating (for example, silica), or an organic coating.
The abrasive article of the invention may contain a blend of
diamond with other abrasive particles
[0052] The preferred amount of abrasive particles in the structured
abrasive coating is dependent on the overall abrasive article
construction and the process in which it is used. For example, when
the abrasive construction is used in a transparent armor polishing
application, a particularly useful range of diamond abrasive
particles is about 4 weight percent to about 30 weight percent, or
about 6 weight percent to about 30 weight percent, or about 20
weight percent to about 30 weight percent.
[0053] Abrasive article 10 may include optionally diluent
particles, which are not abrasive particles. The particle size of
these diluent particles may be on the same order of magnitude as
the abrasive particles. Examples of such diluent particles include
gypsum, marble, limestone, flint, silica, glass bubbles, glass
beads, aluminum silicate, and the like.
Binder Matrix
[0054] Abrasive particles 15 are adhered with binder matrix 16 to
form composites 18 of the abrasive article 10. Binder matrix 16 is
an organic or polymeric binder, and is derived from a binder
precursor. During the manufacture of abrasive article 10, the
binder precursor is exposed to an energy source which aids in the
initiation of the polymerization or curing of the binder precursor.
Examples of energy sources include thermal energy and radiation
energy, the latter including electron beam, ultraviolet light, and
visible light. During this polymerization process, the binder
precursor is polymerized or cured and is converted into a
solidified binder. Upon solidification of the binder precursor, the
adhesive matrix is formed.
[0055] Binder matrix 16 can be formed of a curable (via energy such
as UV light or heat) organic material. Examples include amino
resins, alkylated urea-formaldehyde resins, melamine-formaldehyde
resins, and alkylated benzoguanamine-formaldehyde resin, acrylate
resins (including acrylates and methacrylates) such as vinyl
acrylates, acrylated epoxies, acrylated urethanes, acrylated
polyesters, acrylated acrylics, acrylated polyethers, vinyl ethers,
acrylated oils, and acrylated silicones, alkyd resins such as
urethane alkyd resins, polyester resins, reactive urethane resins,
phenolic resins such as resole and novolac resins, phenolic/latex
resins, epoxy resins such as bisphenol epoxy resins, isocyanates,
isocyanurates, polysiloxane resins (including alkylalkoxysilane
resins), reactive vinyl resins, phenolic resins (resole and
novolac), and the like. The resins may be provided as monomers,
oligomers, polymers, or combinations thereof.
[0056] The binder precursor can be a condensation curable resin, an
addition polymerizable resin, a free radical curable resin, and/or
combinations and blends of such resins. One binder precursor is a
resin or resin mixture that polymerizes via a free radical
mechanism. The polymerization process is initiated by exposing the
binder precursor, along with an appropriate catalyst, to an energy
source such as thermal energy or radiation energy. Examples of
radiation energy include electron beam, ultraviolet light, or
visible light.
[0057] Examples of free radical curable resins include acrylated
urethanes, acrylated epoxies, acrylated polyesters, ethylenically
unsaturated monomers, aminoplast monomers having pendant
unsaturated carbonyl groups, isocyanurate monomers having at least
one pendant acrylate group, isocyanate monomers having at least one
pendant acrylate group, and mixtures and combinations thereof. The
term acrylate encompasses acrylates and methacrylates.
[0058] One binder precursor comprises a urethane acrylate oligomer,
or a blend of a urethane acrylate oligomer and an ethylenically
unsaturated monomer. Useful ethylenically unsaturated monomers are
monofunctional acrylate monomers, difunctional acrylate monomers,
trifunctional acrylate monomers, or combinations thereof. The
binder formed from these binder precursors provides the abrasive
article with its desired properties. In particular, these binders
provide a tough, durable, and long lasting medium to securely hold
the abrasive particles throughout the life of the abrasive article.
This binder chemistry is useful when used with diamond abrasive
particles because diamond abrasive particles last substantially
longer than most conventional abrasive particles. In order to take
full advantage of the long life associated with diamond abrasive
particles, a tough and durable binder is desired. Thus, this
combination of urethane acrylate oligomer or blend of urethane
acrylate oligomer with an acrylate monomer and diamond abrasive
particles provides an abrasive coating that is long lasting and
durable.
[0059] Examples of acrylated urethanes include those known by the
trade designations "PHOTOMER" (for example, "PHOTOMER 6010"),
commercially available from Henkel Corp., Hoboken, N.J.; "EBECRYL
220" (hexafunctional aromatic urethane acrylate of molecular weight
1,000), "EBECRYL 284" (aliphatic urethane diacrylate of 1,200
molecular weight diluted with 1,6-hexanediol diacrylate), "EBECRYL
4827" (aromatic urethane diacrylate of 1,600 molecular weight),
"EBECRYL 4830" (aliphatic urethane diacrylate of 1,200 molecular
weigh diluted with tetraethylene glycol diacrylate), "EBECR YL
6602" (trifunctional aromatic urethane acrylate of 1,300 molecular
weight diluted with trimethylolpropane ethoxy triacrylate), and
"EBECRYL 840" (aliphatic urethane diacrylate of 1,000 molecular
weight), commercially available from UCB Radcure Inc., Smyrna, Ga.;
"SARTOMER" (for example, "SARTOMER 9635, 9645, 9655, 963-B80,
966-A80", etc.), commercially available from Sartomer Company, West
Chester, Pa.; and "UVITHANE" (for example, "UVITHANE 782"),
commercially available from Morton International, Chicago, Ill.
[0060] The ethylenically unsaturated monomers or oligomers, or
acrylate monomers or oligomers, may be monofunctional,
difunctional, trifunctional or tetrafunctional, or even higher
functionality. The term acrylate includes both acrylates and
methacrylates. Ethylenically unsaturated binder precursors include
both monomeric and polymeric compounds that contain atoms of
carbon, hydrogen, and oxygen, and optionally, nitrogen and the
halogens. Ethylenically unsaturated monomers or oligomers
preferably have a molecular weight of less than about 4,000, and
are preferably esters made from the reaction of compounds
containing aliphatic monohydroxy groups or aliphatic polyhydroxy
groups and unsaturated carboxylic acids, such as acrylic acid,
methacrylic acid, itaconic acid, crotonic acid, isocrotonic acid,
maleic acid, and the like. Representative examples of ethylenically
unsaturated monomers include methyl methacrylate, ethyl
methacrylate, styrene, divinylbenzene, hydroxy ethyl acrylate,
hydroxy ethyl methacrylate, hydroxy propyl acrylate, hydroxy propyl
methacrylate, hydroxy butyl acrylate, hydroxy butyl methacrylate,
vinyl toluene, ethylene glycol diacrylate, polyethylene glycol
diacrylate, ethylene glycol dimethacrylate, hexanediol diacrylate,
triethylene glycol diacrylate, trimethylolpropane triacrylate,
glycerol triacrylate, pentaerythritol triacrylate, pentaerythritol
trimethacrylate, pentaerythritol tetraacrylate and pentaerythritol
tetramethacrylate. Other ethylenically unsaturated monomers or
oligomers include monoallyl, polyallyl, and polymethallyl esters
and amides of carboxylic acids, such as diallyl phthalate, diallyl
adipate, and N,N-diallyladipamide. Still other nitrogen containing
compounds include tris(2-acryl-oxyethyl)isocyanurate,
1,3,5-tri(2-methacryloxyethyl)-s-triazine, acrylamide,
methylacrylamide, N-methyl-acrylamide, N,N-dimethylacrylamide,
N-vinyl-pyrrolidone, and N-vinyl-piperidone, and "CMD 3700",
commercially available from Radcure Specialties. Examples of
ethylenically unsaturated diluents or monomers may be found in U.S.
Pat. Nos. 5,236,472 and 5,580,647.
[0061] In general, the ratio between these acrylate monomers
depends upon the weight percent of diamond abrasive particles and
any optional additives or fillers desired in the final abrasive
article. Typically, these acrylate monomers range from about 5
parts by weight to about 95 parts by weight urethane acrylate
oligomer to about 5 parts by weight to about 95 parts by weight
ethylenically unsaturated monomer. Additional information
concerning other potential useful binders and binder precursors is
found in PCT WO 97/11484 and U.S. Pat. No. 4,773,920.
[0062] Acrylated epoxies are diacrylate esters of epoxy resins,
such as the diacrylate esters of bisphenol A epoxy resin. Examples
of acrylated epoxies include "CMD 3500", "CMD 3600", and "CMD
3700", all commercially available from Radcure Specialties; and
"CN103", "CN104", "CN111", "CN112", and "CN114", all commercially
available from Sartomer Company.
[0063] Examples of polyester acrylates include "PHOTOMER 5007" and
"PHOTOMER 5018", commercially available from Henkel
Corporation.
[0064] Aminoplast monomers have at least one pendant alpha,
beta-unsaturated carbonyl group. These unsaturated carbonyl groups
may be acrylate, methacrylate or acrylamide type groups. Examples
of such materials include N-(hydroxymethyl)-acrylamide,
N,N'-oxydimethylenebisacrylamide, ortho and para
acrylamidomethylated phenol, acrylamidomethylated phenolic novolac,
and combinations thereof. These materials are further described in
U.S. Pat. Nos. 4,903,440 and 5,236,472.
[0065] Isocyanurates having at least one pendant acrylate group and
isocyanate derivatives having at least one pendant acrylate group
are further described in U.S. Pat. No. 4,652,274. The preferred
isocyanurate material is a triacrylate of tris(hydroxy ethyl)
isocyanurate.
[0066] Depending upon how the free radical curable resin is cured
or polymerized, the binder precursor may further comprise a curing
agent, (which is also known as a catalyst or initiator). When the
curing agent is exposed to the appropriate energy source, it will
generate a free radical source that will start the polymerization
process.
[0067] Another preferred binder precursor comprises an epoxy resin.
Epoxy resins have an oxirane ring and are polymerized by a ring
opening reaction. Such epoxide resins include monomeric epoxy
resins and polymeric epoxy reins. Examples of preferred epoxy
resins include 2,2-bis-4-(2,3-epoxypropoxy)-phenylpropane, a
diglycidyl ether of bisphenol, which include "EPON 828", "EPON
1004", and "EPON 1001F", commercially available from Shell Chemical
Co., Houston, Tex., and "DER-331", "DER-332", and "DER-334",
commercially available from Dow Chemical Co, Midland, Mich. Other
suitable epoxy resins include cycloaliphatic epoxies, glycidyl
ethers of phenol formaldehyde novolac (for example, "DEN-431" and
"DEN-428"), commercially available from Dow Chemical Co. Examples
of usable multi-functional epoxy resins are "MY 500", "MY 510", "MY
720" and "Tactix 742", all commercially available from Ciba
Specialty Chemicals, Brewster, N.Y., and "EPON HPT 1076" and "EPON
1031" from Shell. The blend of free radical curable resins and
epoxy resins are further described in U.S. Pat. Nos. 4,751,138 and
5,256,170.
[0068] In one embodiment, the binder materials, when incorporated
with the abrasive particles in the abrasive article, have high
thermal resistance. Specifically, the cured binder has a glass
transition temperate (i.e., Tg) of at least 150.degree. C., or at
least 160.degree. C., or at least 175.degree. C. is desired, or at
least 200.degree. C. Large amounts of heat are generated during the
grinding process; the abrasive article, in particular the binder,
should be able to withstand the grinding temperatures with minimal
degradation. High temperature resistance in epoxies is generally
understood; see for example, High Performance Polymers and
Composites, pp. 258-318, ed Jacqueline I. Kroschwitz, 1991.
Generally, multi-functional epoxies provide high thermal
resistance.
Additives
[0069] The abrasive agglomerates, abrasive coating and the backings
of this invention can have additives, such as abrasive particle
surface modification additives, coupling agents, fillers, expanding
agents, fibers, pore formers, antistatic agents, curing agents,
suspending agents, photosensitizers, lubricants, wetting agents,
surfactants, pigments, dyes, UV stabilizers, and anti-oxidants. The
amounts of these materials are selected to provide the properties
desired.
[0070] A coupling agent may provide an association bridge between
the binder and the abrasive particles, and any filler particles.
Examples of coupling agents include silanes, titanates, and
zircoaluminates. The coupling agent can be added directly to the
binder precursor, which may have about 0 to 30%, preferably 0.1 to
25% by weight coupling agent. Alternatively, the coupling agent can
be applied to the surface of any particles, typically about 0 to 3%
by weight coupling agent, based upon the weight of the particle and
the coupling agent. Examples of commercially available coupling
agents include "A174" and "A1230", commercially available from OSi
Specialties, Danbury, Conn. Still another example of a commercial
coupling agent is an isopropyl triisosteroyl titanate, commercially
available from Kenrich Petrochemicals, Bayonne, N.J., under the
trade designation "KR-TTS".
[0071] The abrasive agglomerates or abrasive coating may further
optionally comprise filler particles. Fillers generally have an
average particle size range of 0.1 to 50 micrometers, typically 1
to 30 micrometers. Examples of useful fillers for this invention
include: metal carbonates (such as calcium carbonate-chalk,
calcite, marl, travertine, marble, and limestone; calcium magnesium
carbonate, sodium carbonate, and magnesium carbonate), silica (such
as quartz, glass beads, glass bubbles, and glass fibers), silicates
(such as talc, clays--montmorillonite; feldspar, mica, calcium
silicate, calcium metasilicate, sodium aluminosilicate, sodium
silicate, lithium silicate, and hydrous and anhydrous potassium
silicate), metal sulfates (such as calcium sulfate, barium sulfate,
sodium sulfate, aluminum sodium sulfate, aluminum sulfate), gypsum,
vermiculite, wood flour, aluminum trihydrate, carbon black, metal
oxides (such as calcium oxide--lime; aluminum oxide; tin oxide--for
example, stannic oxide; titanium dioxide) and metal sulfites (such
as calcium sulfite), thermoplastic particles (such as
polycarbonate, polyetherimide, polyester, polyethylene,
polysulfone, polystyrene, acrylonitrile-butadiene-styrene block
copolymer, polypropylene, acetal polymers, polyurethanes, nylon
particles) and thermosetting particles (such as phenolic bubbles,
phenolic beads, polyurethane foam particles), and the like. The
filler may also be a salt such as a halide salt. Examples of halide
salts include sodium chloride, potassium cryolite, sodium cryolite,
ammonium chloride, potassium tetrafluoroborate, sodium
tetrafluoroborate, silicon fluorides, potassium chloride, and
magnesium chloride. Examples of metal fillers include, tin, lead,
bismuth, cobalt, antimony, cadmium, iron, and titanium. Other
miscellaneous fillers include sulfur, organic sulfur compounds,
graphite, and metallic sulfides.
[0072] Either of the agglomerates, or abrasive coating, or both may
include fillers or other materials that are pore formers. Pores may
be desired for constructions where quick agglomerate or coating
break-down is desired. Examples of pore formers include organic
materials that are sacrificed; for example, organic materials can
be used to occupy volume in the agglomerate or abrasive coating,
and then are removed, for example, by burning or dissolving.
Examples of sacrificial pore formers are styrene balls and dextrin
powder. Pores may also be formed by permanent pore formers, such as
glass or alumina hollow beads or bubbles, or by foamed inorganic
materials.
[0073] An example of a suspending agent is an amorphous silica
particle having a surface area less than 150 meters square/gram,
commercially available from DeGussa Corp., Ridgefield Park, N.J.,
under the trade designation "OX-50". The addition of the suspending
agent may lower the overall viscosity of the abrasive slurry. The
use of suspending agents is further described in U.S. Pat. No.
5,368,619.
[0074] It may be desirable in some embodiments to form the shaped
abrasive composites from an abrasive slurry which has controllable
settling of the abrasive particles. As an example, it may be
possible to form an abrasive slurry having diamond abrasive
particles homogeneously mixed throughout. After casting or molding
the composites and backing from the slurry, the diamond particles
may settle out at a controlled rate so that by the time the organic
resin has hardened to the point where the diamond particles may no
longer settle, the diamond particles have departed from the backing
and are located only in the composites.
[0075] The binder precursor may further comprise a curing agent. A
curing agent is a material that helps to initiate and complete the
polymerization or crosslinking process such that the binder
precursor is converted into a binder. The term curing agent
encompasses initiators, photoinitiators, catalysts and activators.
The amount and type of the curing agent will depend largely on the
chemistry of the binder precursor.
[0076] Polymerization of ethylenically unsaturated monomer(s) or
oligomer(s) occurs via a free-radical mechanism. If the energy
source is an electron beam, or ionizing radiation source (gamma or
x-ray), free-radicals which initiate polymerization are generated.
However, it is within the scope of this invention to use initiators
even if the binder precursor is exposed to an electron beam. If the
energy source is heat, ultraviolet light, or visible light, an
initiator may have to be present in order to generate
free-radicals. Examples of initiators (that is, photoinitiators)
that generate free-radicals upon exposure to ultraviolet light or
heat include, but are not limited to, organic peroxides, azo
compounds, quinones, nitroso compounds, acyl halides, hydrazones,
mercapto compounds, pyrylium compounds, imidazoles,
chlorotriazines, benzoin, benzoin alkyl ethers, diketones,
phenones, and mixtures thereof. An example of a commercially
available photoinitiator that generates free radicals upon exposure
to ultraviolet light include those having the trade designation
"IRGACURE 651" and "IRGACURE 184", commercially available from Ciba
Geigy Company, Hawthorne, N.J., and "DAROCUR 1173", commercially
available from Merck & Company, Incorporated, Rahway, N.J.
Examples of initiators that generate free-radicals upon exposure to
visible light may be found in U.S. Pat. No. 4,735,632. Another
photoinitiator that generates free-radicals upon exposure to
visible light has the trade designation "IRGACURE 369",
commercially available from Ciba Geigy Company.
[0077] Typically, the initiator is used in amounts ranging from 0.1
to 10%, preferably 2 to 4% by weight, based on the weight of the
binder precursor. Additionally, it is preferred to disperse,
preferably uniformly disperse, the initiator in the binder
precursor prior to the addition of any particulate material, such
as the abrasive particles and/or filler particles.
[0078] In general, it is preferred that the binder precursor be
exposed to radiation energy, preferably ultraviolet light or
visible light. In some instances, certain abrasive particles and/or
certain additives will absorb ultraviolet and visible light, which
makes it difficult to properly cure the binder precursor. This
phenomena is especially true with ceria abrasive particles and
silicon carbide abrasive particles. It has been found, quite
unexpectedly, that the use of phosphate containing photoinitiators,
in particular acylphosphine oxide containing photoinitiators, tend
to overcome this problem. An example of such a photoinitiator is
2,4,6-trimethylbenzoyldiphenylphosphine oxide, commercially
available from RASF Corporation, Charlotte, N.C., under the trade
designation "LUCIRIN TPO". Other examples of commercially available
acylphosphine oxides include those having the trade designation
"DAROCUR 4263" and "DAROCUR 4265", both commercially available from
Ciba Specialty Chemicals.
[0079] Optionally, the curable compositions may contain
photosensitizers or photoinitiator systems which affect
polymerization either in air or in an inert atmosphere, such as
nitrogen. These photosensitizers or photoinitiator systems include
compounds having carbonyl groups or tertiary amino groups and
mixtures thereof. Among the preferred compounds having carbonyl
groups are benzophenone, acetophenone, benzil, benzaldehyde,
o-chlorobenzaldehyde, xanthone, thioxanthone, 9,10-anthraquinone,
and other aromatic ketones which may act as photosensitizers. Among
the preferred tertiary amines are methyldiethanolamine,
ethyldiethanolamine, triethanolamine, phenylmethyl-ethanolamine,
and dimethylaminoethylbenzoate. In general, the amount of
photosensitizer or photoinitiator system may vary from about 0.01
to 10% by weight, more preferably from 0.25 to 4.0% by weight,
based on the weight of the binder precursor. Examples of
photosensitizers include those having the trade designation
"QUANTICURE ITX", "QUANTICURE QTX", "QUANTICURE PTX", "QUANTICURE
EPD", all commercially available from Biddle Sawyer Corp., New
York, N.Y.
[0080] In one embodiment, the binder precursor is cured with the
aid of both a photoinitiator and a thermal initiator acting on the
same functional type. Examples of initiators include organic
peroxides (e.g., benzoil peroxide), azo compounds, quinones,
nitroso compounds, acyl halides, hydrazones, mercapto compounds,
pyrylium compounds, imidazoles, chlorotriazines, benzoin, benzoin
alkyl ethers, diketones, phenones, and mixtures thereof. Examples
of suitable commercially available, ultraviolet-activated
photoinitiators are sold under the trade designations IRGACURE 651,
IRGACURE 184, IRGACURE 369 and IRGACURE 819, all commercially
available from the Ciba Geigy Company, Lucirin TPO-L, commercially
available from BASF Corp. and DAROCUR 1173 commercially available
from Merck & Co. Examples of suitable thermal initiators are
sold under the trade designations VAZO 52, VAZO 64 and VAZO 67 azo
compound thermal initiators, all commercially available from E.I.
duPont deNemours and Co.
Method of Making Abrasive Articles
[0081] Abrasive articles 10 can be made via any known method for
making an abrasive article having three-dimensional abrasive
composites. Useful methods are described in U.S. Pat. No. 5,152,917
(Pieper et al.) and U.S. Pat. No. 5,435,816 (Spurgeon et al.), and
other suitable methods can be found in U.S. Pat. No. 5,437,754
(Calhoun), U.S. Pat. No. 5,454,844 (Hibbard et al.), and U.S. Pat.
No. 5,304,223 (Pieper et al.).
[0082] Another useful method of making useful abrasive articles
having three-dimensional, abrasive composites where the composites
comprise abrasive agglomerates fixed in a make coat, with optional
size coatings, is described in U.S. Pat. No. 6,217,413
(Christianson).
Method of Polishing
[0083] The method of this disclosure provides an optically clear
finish on at least one side of transparent armor. Usually, both
sides of the armor are processed in order to provide armor through
which one can readily see. The method of this disclosure utilizes a
series of abrasive articles and a series of abrasive polishing
steps. Each abrasive step further refines the surface finish with
the goal to achieve optical clarity in a dense, pore-free ceramic
body. In some embodiments, optical clarity (from the hot pressed
piece) may be obtained in 5 hours of polishing or less. For both
sides of the armor piece, optical clarity may be obtained in 10
hours of polishing or less. For some embodiments, optical clarity
may be obtained in 3 hours or less of polishing, 6 hours or less
for both sides.
[0084] The method includes using a step-wise progression of
diamond, structured abrasive articles, such as abrasive article 10.
The particle size of the diamonds present in abrasive article 10
used decreases as the surface finish of the armor approaches
optical clarity.
[0085] The method includes affixing the abrasive article to a
rotary tool, such as a random orbital sander, and polishing the
surface of the armor with the abrasive article. When that grade of
abrasive article provides no additional improvement in the surface
finish, a next abrasive article, having a smaller diamond particle
size, is used to polish the armor. Similarly, when that grade of
abrasive article provides no additional improvement in the surface
finish, a next abrasive article, having a smaller diamond particle
size, is used to polish the armor. Eventually, optically clear
transparent armor is obtained. Typically, the decrease in diamond
particle size from one abrasive article to the next is about
50%.
[0086] As mentioned, the method of this disclosure utilizes a
rotary tool onto which the abrasive articles are affixed. Examples
of rotary tools include random orbital sanders and rotary sanders.
The tool can be pneumatic or electric, however pneumatic is
preferred for a random orbital sander and electric is preferred for
rotary tools. The rotating hand tools may operate at speed suitable
for the operation; 12,000 rpm is one suitable speed. The speed is
dependent upon many factors including tool design, back up pad and
abrasive article.
[0087] Generally a back up pad, to which the abrasive article is
secured, is attached to the tool. The back up pad may be
constructed from a foam or rubber type material with an appropriate
facing. The back up pad outer face will have some form of receiving
surface such that the fixed abrasive article can be secured to the
back up pad. For example, if a pressure sensitive adhesive is
employed to secure the fixed abrasive article to the back up pad,
then the receiving surface may be a vinyl facing, cloth facing or
rubber facing. Alternatively, if a hook and loop type attachment is
employed to secured the fixed abrasive article to the back up pad,
then the receiving surface may be either a loop facing or hook
facing. The opposite type would then be used on the abrasive
article.
[0088] The transparent armor may be polished, with the rotary tool
having structured diamond abrasive article thereon, either manually
or by a robot. When a robot is used, the tool is often connected to
a portion of the robot, typically referred to as an "arm", which
moves the rotary tool in a manner similar to how a human operator
would move the tool. The piece being polished is held stationary. A
robot arm has minimum of 3 degrees of freedom although a robot with
a minimum of 6 degrees of freedom is preferred, allowing movement
and rotation of the tool in numerous axes. In other embodiments,
the tool is fixed, while the robot moves the piece (i.e., the
transparent armor) with minimum of 3 degrees of freedom although a
minimum of 6 degrees of freedom is preferred, in relation to the
tool.
[0089] The robot uses commercially available `end of arm tooling`
to apply a generally constant contact force between the abrading
tool and the surface being polished (i.e., the transparent armor).
The robot is programmed to have the tool with abrasive article
thereon follow the contour of the transparent armor piece without
significantly changing the contour of the piece. In general, the
robot does not provide sufficient rigidity and accuracy to change
the overall shape of the piece being polished, unlike a CNC
machine. In some embodiments, a CNC machine or other deterministic
grinding process may be used to decrease the surface finish of the
hot pressed piece prior to polishing with the first structured
abrasive article.
[0090] In another embodiment, the method includes an initial rough
grinding step with, for example, a Blanchard grinding machine, an
intermediate pre-polish grind and finish step with one or more of
the structured abrasive articles of FIGS. 2 and 3 in a step-wise
progression attached to a platen of a flat lapping machine such as
a Strasbaugh 6DC, and a final polishing step using polishing
abrasive slurry. Relative motion between the transparent armor and
the structured abrasive article is provided by the lapping machine.
After conclusion of the three steps, the polished surface of the
ceramic transparent armor will be optically clear and the Ra of the
polished transparent armor can be between about 0.0 to about 1.0
.mu.in, or between about 0.0 to about 0.2 .mu.in.
[0091] A working fluid is typically present between the interface
of the abrasive article and the transparent armor during the
polishing steps or during the grinding step or during the
pre-polish grind and finish step. Any known working fluid may be
used. For example, water, aqueous solutions, and the like may be
used, with particular selection known by those with skill of the
art. Various additives may be present in the working fluid.
[0092] Objects and advantages of this invention are further
illustrated by the following examples, but the particular materials
and amounts thereof recited in these examples, as well as other
conditions and details, should not be construed to unduly limit
this invention.
EXAMPLES
[0093] The following sequence of steps was used to polish,
manually, a 13.25 inch.times.11.5 inch curved transparent armor
spinel panel (i.e., a magnesium-aluminate spinel).
[0094] The rotary tool used was a Dynabrade Model 59200 12,000 RPM,
3/8'' orbit, Random Orbital sander. A 3M Stikit Low Profile Backup
Pad, Part #05555, was attached to the rotary tool. A
North/South/East/West tool pattern with subtle variations on each
pass was used in an effort to generate even wear across the armor
plate.
[0095] The following six abrasive articles were progressively used.
All of the abrasive articles were five-inch diameter discs with a
pressure-sensitive-adhesive (PSA) attachment system. Each abrasive
article was used for the time indicated (e.g., 5 minutes, 3
minutes, 6 minutes), after which 3 to 5 surface measurements were
taken. When that abrasive article provided no additional
improvement in the surface finish, the next abrasive article,
having a smaller diamond particle size, was used to polish the
armor.
[0096] Abrasive article #1: 3M Trizact Industrial Diamond
structured abrasive article; having flat-top hexagonal composites
about 30 mil high, 200/230 grade (about 70 micrometer) individual
diamond particles having a Ni coating, on a cloth backing
[0097] Abrasive article #2: 3M Trizact Industrial Diamond
structured abrasive article; having flat-top hexagonal composites
about 30 mil high, 325/400 grade (about 40 micrometer) individual
diamond particles having a Ni coating, on a cloth backing
[0098] Abrasive article #3: 3M Trizact Diamond Tile 677 XA
commercially available structured abrasive article, having flat-top
square composites, 9 micrometer diamond particles agglomerated with
glass binder, on a film backing
[0099] Abrasive article #4: 3M Trizact Diamond Tile 677 XA
commercially available structured abrasive article, having flat-top
square composites, 6 micrometer diamond particles agglomerated with
glass binder, on a film backing
[0100] Abrasive article #5: 3M Trizact Diamond Tile 677 XA
commercially available structured abrasive article, having flat-top
square composites, 3 micrometer diamond particles agglomerated with
glass binder, on a film backing
[0101] Abrasive article #6: 3M Trizact structured abrasive article,
having pyramidal rectangular composites, 1 micrometer diamond
particles, on a film backing.
TABLE-US-00001 TABLE 1 Abrasive Time Ra Rz Rmax Article (min)
(.mu.inch) (.mu.inch) (.mu.inch) Comments #1 5 26.8 212 The spinel
had been 24.6 175 processed with other 20.3 169 products prior to
this step. Starting with molded spinel would require longer time.
#2 5 19.9 145 17.9 125 16.6 144 #2 3 13.1 102 15.4 131 17.7 142 #3
3 10.6 100 (previ- 14.2 123 ously used 11.7 103 disc) 12.3 114 #3 3
10.9 104 (new disc) 13.5 115 12.28.2006 98 13.5 126 #4 3 5.67 74
(previ- 3.74 73 ously used 4.16 51 disc) #4 3 3.18 46 (previ- 2.29
41 ously used 2.14 37 disc) #5 6 3.21 55 (previ- 1.76 33 ously used
1.64 31 disc) 1.26 27 #5 6 1.81 33 (previ- 1.86 37 ously used 1.68
37 disc) 2.82 39 #6 6 1.58 41 2.77 58 1.23 23 #6 6 0.74 25 1.43 36
0.46* 12* 0.98 18 #6 6 0.99 28 1.38 31 2.01 34 100 0.53 11 17 0.51
16 22 #6 6 1.13 22 31 1.05 26 39 0.91 19 27 0.77 16 31 #6 6 0.67 19
24 1.00 21 27 0.32 8.4 18 0.59 15 20 #6 6 1.09 28 42 1.24 24 35
0.83 18 40 0.83 25 63 #6 6 0.60 17 37 1.55 25 36 1.49 26 36 1.26 28
42 #6 6 0.73 24 5542 1.04 23 54 1.01 34 58 1.34 29 #6 6 0.48 8 22
0.93 19 22 0.55 16 29 0.88 20 28 #6 6 0.39 11 18 0.40 9.8 24 0.65
18 28 1.08 21 32 *Taken at ~2'' from edge, which was a clearer
area.
[0102] The following non-limiting examples will further illustrate
the invention. All parts, percentages, ratios, etc., in the
examples are by weight unless otherwise indicated. The following
abbreviations listed in Table 2 are used throughout the additional
examples.
TABLE-US-00002 TABLE 2 TMPTA Trimethylol propane triacrylate;
commercially available from Sartomer Co. under the trade
designation "SR351" PH2 Photo initiator
2-benzyl-2-N,N-dimethylamino-1-(4- morpholinophenyl)-1-butanone,
commercially available from Ciba Geigy Corp. under the trade
designation "Irgacure 369" THI Thermal initiator
2,2'-azobis(2,4-dimethylpentanenitrile), commercially available
from Dupont Chemical Solution Enterprise, Bell WV under the trade
designation "Vazo 52" CaSi Surface-modified calcium metasilicate
filler, commercially available from NYCO, Willsboro NY under the
trade designation "Wollastocoat M400" SCA Silane coupling agent,
3-methacryloxypropyltrimethoxysilane, commercially available from
Crompton Corp. under the trade designation "A-174NT" ASF Amorphous
silica filler, commercially available from DeGussa under the trade
designation "OX-50" 120/140 Mesh-grade diamond abrasive,
commercially available from Pinnacle Abrasives, Walnut Creek, CA,
under the trade designation "120/140 CMDP/CRDH" 200/230 Mesh-grade
diamond abrasive, commercially available from Pinnacle Abrasives,
Walnut Creek, CA, under the trade designation "200/230 CMDP/CRDH"
325/400 Mesh-grade diamond abrasive, commercially available from
Pinnacle Abrasives, Walnut Creek, CA, under the trade designation
"325/400 CMDP/CRDH" 9 .mu.m Micron-grade diamond abrasive,
commercially available from Pinnacle Abrasives, Walnut Creek, CA,
under the trade designation "8-12 MPP" and formed into vitrified
agglomerate abrasive particles using Method 1.
Method 1: Preparation of Vitreous Bonded Diamond Agglomerate
Abrasive Particles
[0103] Vitrified agglomerate abrasive particles were produced as
taught in U.S. Pat. No. 6,551,366 (D'Souza et al). An agglomerate
precursor slurry was prepared as follows. About 31 grams of dextrin
(a temporary starch binder obtained under the trade designation
"STADEX 230" from A. E. Staley Manufacturing Company, Decatur,
Ill.) was dissolved in about 687 grams of deionized water by
stirring using an air mixer with a Cowles blade. Next, about 500
grams of milled glass frit (obtained under the trade designation
"SP1086" from Specialty Glass, Inc. Wilmington, Del.) was added to
the solution. The glass frit had been milled prior to use to a
median particle size of about 2.5 micrometers. Next, about 500
grams of 8-12 micrometer diamond powder (available from Pinnacle
Abrasives, Walnut Creek Calif., under the trade designation "8-12
MPP") was added to the slurry. The slurry was stirred using the air
mixer for an additional 30 minutes after all the above constituents
had been added together.
[0104] The agglomerate precursor slurry was spray dried using a
rotary wheel spray-dryer (obtained under the trade designation
"MOBILE MINOR UNIT" from Niro Inc.). The spray dryer inlet
temperature was set at about 150.degree. C., and the rotary wheel
set at about 15,000 rpm. The slurry was pumped into the rotary
wheel inlet at a pump speed flow rate setting of 4. The outlet
temperature of the spray dryer varied from 90-95.degree. C. during
the spray drying of the slurry. The plurality of precursor
agglomerate abrasive grains was collected at the spray dryer
outlet.
[0105] The spray dried precursor agglomerate grains were mixed with
about 30% by weight of 3 micrometer white aluminum oxide (obtained
under the trade designation "PWA3" from Fujimi Corporation,
Elmhurst, Ill.), based on the weight of the plurality of precursor
agglomerate grains, and heated in a furnace in air. The heating
schedule was as follows: 2.degree. C./min. increase to 400.degree.
C., 1 hour hold at 400.degree. C., 2.degree. C./min. increase to
750.degree. C., 1 hour hold at 750.degree. C., and 2.degree.
C./min. decrease to 35.degree. C. After heating, the agglomerate
abrasive grains were sieved through a 106 .mu.m mesh screen.
Method 2: Procedure for Making Abrasive Articles
[0106] Abrasive slurry was prepared by mixing the abrasive mineral
particles, binder precursor and other materials listed in Table 3
below. The abrasive slurry was mixed for about 30 minutes at about
1200 rpm using a high shear mixer until the slurry temperature
reached approximately 80.degree. F. (26.degree. C.).
TABLE-US-00003 TABLE 3 Description Binder precursor formulation (g)
Abrasive mineral (g) Ex Grade Backing TMPTA PH2 THI CaSi SCA ASF
120/140 200/230 325/400 9 um 1 A10 film 1437 14.1 0 2210 49.8 11.6
280 2 A45 cloth 1386 12.9 12.9 1455 0 27.8 1106 3 A80 cloth 1384
12.8 12.7 1453 0 33.1 1030 4 A160 cloth 1386 12.8 12.8 1455 0 27.7
1000
[0107] The backing for the abrasive articles in Examples 2-4 was a
Y-weight polyester cloth backing having a backing treatment
preparable by at least partially polymerizing an isotropic backing
treatment precursor compromising polyepoxide, polyfunctional
urethane (meth)acrylate, non-urethane polyfunctional
(meth)acrylate, acidic free-radically polymerizable monomer,
dicyandiamide, photoinitiator, as taught in U.S. Pat. No. 7,344,574
(Thurber, et al.). The backing for Example 1 was a polyester film
0.005 inches (127 um) thick and having an ethylene acrylic acid
co-polymer primer on the surface to be coated. The film backing is
commercially available from 3M Company, St. Paul Minn. under the
trade designation "5 mil Scotchpak.TM.."
[0108] The production tool was transparent polypropylene tooling
that had been embossed using a cut knurl nickel-plated master tool.
The polypropylene tool had a plurality of cavities defined by a
hexagonal-based post type pattern. The length of each hexagon
cavity side was about 0.078 inch (1981 um) as measured at the base
of the cavity. The hexagonal cavities were placed such that their
bases were spaced about 0.055 inch (1397 um) apart, and the sides
of the hexagonal cavities were sloped 8 degrees so that the space
between the tops of neighboring cavities was about 0.047 inch (1194
um). The depth of the hexagonal cavities was about 0.030 inch (762
um), which corresponds to the resulting height of the shaped
abrasive composites.
[0109] The abrasive articles of Examples 1-4 were made on an
apparatus similar to that illustrated in FIG. 3 in U.S. Pat. No.
7,300,479 (McArdle). The polypropylene production tool was unwound
from a winder. The abrasive slurry was knife coated about 10 inches
(25.4 cm) wide onto the front side of the backing. The knife gap
was set to be approximately 0.026-0.034 inches (660-864
micrometers). The slurry-coated backing was brought into contact
with the cavities of the production tool under pressure of a nip
roll, and the slurry was then irradiated with visible light from
two visible lamps ("D" bulbs, commercially available from Fusion
Corp.) operating at 600 Watts/inch. The nip pressure between the
production tool and the backing was about 80 pounds (27 kg). Upon
exposure to UV radiation, the binder precursor was converted into a
binder and the abrasive slurry was converted into an abrasive
composite. Then, the abrasive composites/backing, which formed the
abrasive article, was wound onto a core. The process was a
continuous process and operated at approximately 30 ft/min (9.1
meters/minute). The shaped abrasive composites/backing was wound up
onto the core and as subsequently used for Examples 2-4 was then
heated for 24 hours at 240.degree. F. (115.degree. C.) to fully
cure, as needed, the shaped abrasive composites and the cloth
backing treatments. The shaped abrasive composites/backing used for
Example 1 was heated for approximately 12 hours in an oven set at
190.degree. F. (88.degree. C.) to complete the cure of the binder
systems and to activate the primer on the polyester backing
[0110] To prepare the abrasive articles for testing, the shaped
abrasive composites/backing sheets were laminated to a 0.762 mm
(0.030 inch) thick polycarbonate sheet reinforcing layer (Lexan.TM.
8010MC, available from GE Polymer Shapes, Mount Vernon, Ind.) for
lamination. In Example 1, pressure sensitive adhesive tape was used
("442 KW", available from 3M, St. Paul, Minn.). In Examples 2-4,
high-strength pressure-sensitive adhesive tape ("9473PC" available
from 3M, St. Paul, Minn.) was used for lamination. Twelve inch
(30.48 cm) diameter circular test discs were then die cut to form
the abrasive articles (abrasive composite pad) for testing.
Method 3: Procedure for Single-Sided Grinding Test
[0111] Grinding tests were performed on a 6DC single-side lapping
machine available from Strasbaugh (San Luis Obispo, Calif.). The
abrasive composite pad was mounted to the machine platen using a
pressure-sensitive adhesive.
[0112] The abrasive composite pads were initially prepared for
testing by conditioning using alumina fixed abrasive (268XA A35,
available from 3M Company, St Paul Minn.). The 5 inch (127 mm)
diameter 268XA A35 discs were mounted to a 6 inch (152 mm)
diameter.times.0.6 inch (15 mm) thick aluminum metal plate to form
a conditioning plate. The conditioning plate was attached to the
upper head of the lapping machine and was run at an applied
pressure of 2 psi (13.8 kPa) for 4 minutes using a 100 rpm platen
speed and counter-rotating 100 rpm conditioning plate speed. During
conditioning, deionized water was supplied at a flow rate of 30
mL/min.
[0113] Transparent spinel (MgAl.sub.2O.sub.4) ceramic test pieces
were obtained from Nutek Precision Optical Corporation, Aberdeen
Md. Three 1.5 inch (38.1 mm) diameter.times.0.44 inch (11.1 mm)
thick pieces were mounted to a 6 inch (152 mm) diameter.times.0.6
inch (15 mm) aluminum metal test sample plate using mounting resin
(Crystalbond 509 Clear, Aremco Products, Inc, Valley Cottage
N.Y.).
[0114] A series of grinding tests was performed using the 6DC
single-side lapping machine with the abrasive composite pads
mounted on the 12 inch (304 mm) diameter machine platen and rotated
at 100 rpm. The sample plate with three mounted spinel test pieces
was rotated at 100 rpm in a direction opposite to that of the
abrasive composite pad, with applied pressure of 5 psi (34.5 kPa).
A 10 vol % solution of Sabrelube 9016 (Chemetall Oakite, Lake Bluff
Ill.) in deionized water was supplied to the abrasive composite pad
surface at a flow rate of 30 mL/min. Multiple 5-minute test cycles
were run for each abrasive composite pad, and the total weight loss
for the three spinel samples recorded after each test cycle. The
material removal rate for the spinel ceramic test samples was
calculated by converting the total weight loss for three spinel
samples (M in grams) to surface thickness removed (T in
.mu.m/minute) using the following equation:
T=9400.times.M/(A.times.D)
Where A=area of each test piece (cm.sup.2) and D=density of each
test piece (g/cm.sup.3). The density of the spinel ceramic test
pieces was assumed to be 3.58 g/cm.sup.3.
Method 4: Measurement of Surface Finish
[0115] The surface finish (Ra) of spinel ceramic test pieces was
measured after the first grinding test cycle, and at the end of
every second grinding test cycle thereafter. Ra is the arithmetic
average of the scratch depth expressed in microinches (.mu.in). Ra
was measured using a Mahr Perthometer profilometer (Model M4P,
available from Mahr Corporation, Cincinnati, Ohio). Each of the
three mounted spinel ceramic test pieces was measured twice, and
the resulting surface finish for the grinding test cycle expressed
as the average of the six measurements.
Example 1
[0116] Abrasive article Example 1 listed in Table 3 was prepared
according to Method 2, and included 9 .mu.m vitrified agglomerate
abrasive particles prepared according to Method 1. Example 1 was
used to grind spinel ceramic test samples according to Method 3 and
resulting surface finishes were measured according to Method 4.
Test results are summarized in Table 4. Example 1 comprised
hexagonal shaped abrasive composites having an abrasive diamond
content of 7.00 weight percent, 2.22 shaped abrasive composites per
linear cm, 5.37 shaped abrasive composites per cm.sup.2 and a
bearing area ratio of 58.0 percent.
Examples 2-4
[0117] Abrasive article Examples 2-4 listed in Table 3 were
prepared according to Method 2. Examples 2-4 were used to grind
spinel ceramic test samples according to Method 3 and resulting
surface finishes were measured according to Method 4. Test results
are summarized in Table 4.
[0118] Example 2 comprised hexagonal shaped abrasive composites
having an abrasive diamond content of 27.60 weight percent, 2.33
shaped abrasive composites per linear cm, 6.12 shaped abrasive
composites per cm.sup.2, and a bearing area ratio of 64.0
percent.
[0119] Example 3 comprised hexagonal shaped abrasive composites
having an abrasive diamond content of 26.20 weight percent, 2.33
shaped abrasive composites per linear cm, 6.12 shaped abrasive
composites per cm.sup.2, and a bearing area ratio of 64.0
percent.
[0120] Example 4 comprised hexagonal shaped abrasive composites
having an abrasive diamond content of 25.70 weight percent, 2.33
shaped abrasive composites per linear cm, 6.12 shaped abrasive
composites per cm.sup.2, and a bearing area ratio of 64.0
percent.
Comparative Example A
[0121] Comparative Example A was a structured, film-backed fixed
abrasive composite pad, grade 9 micron, commercially available from
3M Company, St Paul Minn. under the trade designation "677XA".
Comparative Example A was used to grind spinel ceramic test samples
according to Method 3 and resulting surface finishes were measured
according to Method 4. Test results are summarized in Table 4.
Comparative Example A comprised square shaped abrasive composites
having an abrasive diamond content of 2.28 weight percent by
weight, 2.63 shaped abrasive composites per linear cm, 6.35 shaped
abrasive composites per cm.sup.2, and a bearing area ratio of 44.4
percent.
TABLE-US-00004 TABLE 4 Total Removal Surface Test Cumulative wt
loss rate T finish Ra Example No. Cycle Time (min) M (g)
(.mu.m/min) (.mu.in) Example 1 1 5 4.67 76.3 10.59 2 10 4.74 77.5 3
15 4.74 77.5 9.86 4 20 4.68 76.5 5 25 4.82 78.8 10.22 6 30 4.94
80.7 7 35 4.97 81.2 10.36 Comparative 1 5 1.79 29.2 10.22 Example A
2 10 1.62 26.5 3 15 1.49 24.3 10.16 4 20 1.72 28.1 5 25 1.72 28.1
10.06 6 30 1.86 30.4 7 35 1.98 32.4 10.12 Example 2 1 5 11.04 170.6
33.85 2 10 10.28 158.9 3 15 9.35 144.5 30.48 4 20 8.67 134.0 5 25
7.98 123.3 27.73 6 30 7.51 116.1 7 35 6.84 105.7 26.98 Example 3 1
5 15.11 246.5 52.23 2 10 15.76 257.1 3 15 14.67 239.3 44.30 4 20
13.43 219.1 5 25 12.78 208.5 42.45 6 30 12.00 195.8 7 35 11.28
184.0 39.42 Example 4 1 5 16.55 255.8 63.13 2 10 20.42 315.6 3 15
19.30 298.3 71.13 4 20 18.54 286.5 5 25 17.36 268.3 6 30 15.79
244.0 58.00
[0122] Examples 1-4 produced significantly higher stock removal
rates than Comparative Example A while still producing acceptable
surface finish values. Furthermore, Examples 1-4 have higher stock
removal rates and are significantly faster than using an abrasive
slurry during the pre-polish grind and finish step on a flat
lapping machine while processing ceramic transparent armor to
produce an optically clear surface.
[0123] Other modifications and variations to the present invention
may be practiced by those of ordinary skill in the art, without
departing from the spirit and scope of the present invention, which
is more particularly set forth in the appended claims. It is
understood that aspects of the various embodiments may be
interchanged in whole or part or combined with other aspects of the
various embodiments. All cited references, patents, or patent
applications in the above application for letters patent are herein
incorporated by reference in their entirety. In the event of
inconsistencies or contradictions between the incorporated
references and this application, the information in the preceding
description shall control. The preceding description, in order to
enable one of ordinary skill in the art to practice the claimed
invention, is not to be construed as limiting the scope of the
invention, which is defined by the claims and all equivalents
thereto.
* * * * *