Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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ABRASIVE BELT WITH ANGLED SHAPED ABRASIVE PARTICLES
BACKGROUND
Abrasive belts having precisely shaped abrasive composites formed from small
abrasive particles dispersed in a cured resin binder and molded into shaped
structures can
be aligned at an angle other than zero or ninety degrees with respect to the
edge of the belt
as disclosed in US patent 5,489,235 to Gagliardi. See Figure 1. The abrasive
composites on
the abrasive belt create a scratch pattern that crosses the previous scratch
pattern (non-
scribing pattern). The crossing patterns lead to a more random, less uniform
scratch pattern
which provides finer surface finishes.
SUMMARY
Shaped abrasive particles, as disclosed for example in US patent 8,142,531,
provide
significantly improved cut over the shaped abrasive composites disclosed in
Gagliardi.
When attempting to rotate the shaped abrasive particles with the significantly
improved cut
for positioning on a belt as disclosed in Gagliardi, a new problem was
discovered. Namely,
the shaped abrasive particles, when aligned at an angle other than zero or
ninety degrees to
the longitudinal axis of the belt, created a significant side force or side
load that must be
counteracted in order for the belt to track properly. No such side force or
side loads were
created by the belt disclosed in Gagliardi when using the abrasive composites.
The inventors discovered that when the shaped abrasive particles are rotated a
significant angular amount relative to the longitudinal axis of the belt, due
to the aggressive
cut of the shaped abrasive particles, the belt may have a tendency to track
off to the side of
the grinding machine; especially, as the load on the work piece is
significantly increased.
This can be especially problematic in situations when a high work piece load
is applied for
a short duration, the work piece removed from the belt, and then reapplied for
another short
duration high load cycle. The belt tracking system of the grinding machine
sees repeated
cycles with high belt side load and then no belt side load. Adjusting the belt
to track properly
with no side load present can cause the belt to not track properly when the
side load is
present and vice versa. This problem is most acute for abrasive belts that are
short, narrow,
or under low tension and contain larger sized shaped abrasive particles.
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The inventors determined that one way to solve this problem was to limit the
angular
rotation of the shaped abrasive particles on the belt thereby limiting the
generated side loads
during grinding while still providing a non-scribing, finer finish on the work
piece.
Hence, in one embodiment, the invention resides in an abrasive belt
comprising: a
backing and an abrasive layer adhered to the backing by a make coat resin and
the abrasive
layer comprising a plurality of shaped abrasive particles; a first belt side
and a second belt
side opposing the first belt side with the first and second belt sides
generally aligned with a
longitudinal axis of the grinding belt; at least 30% of the shaped abrasive
particles in the
abrasive layer having a first face and placed onto the backing such that an
angle between
the first face and the longitudinal axis is greater than 0 degrees and less
than or equal to 20
degrees.
As used herein, the term "shaped abrasive particle", means a ceramic abrasive
particle with at least a portion of the abrasive particle having a
predetermined shape. Shaped
abrasive particles exclude abrasive composites formed from abrasive particles
dispersed in
a cured resin binder and molded into shaped structures as used for example in
US patent
5,489,235. Ceramic shaped abrasive particles are generally homogenous or
substantially
uniform and maintain their sintered shape without the use of a binder such an
organic or
inorganic binder that bond smaller abrasive particles into an agglomerated
structure and
excludes abrasive particles obtained by a crushing or comminution process that
produces
abrasive particles of random size and shape. In many embodiments, the ceramic
shaped
abrasive particles comprise a homogeneous structure of sintered alpha alumina
or consist
essentially of sintered alpha alumina. In many embodiments, the ceramic shaped
abrasive
particle is made from a boehmite sol gel that is molded, dried, calcined and
sintered to form
a ceramic alpha alumina shaped abrasive particle. Often the shape is
replicated from a mold
cavity used to form the precursor shaped abrasive particle. Except in the case
of abrasive
shards (e.g. as described in U.S. application Ser. No. 12/336,877), the shaped
abrasive
particle will generally have a predetermined geometric shape that
substantially replicates
the mold cavity that was used to form the shaped abrasive particle. The mold
cavity could
reside on the surface of an embossing roll or be contained within a flexible
belt or production
tooling. Alternatively, the shaped abrasive particles can be precisely cut
from a sheet of
dried sol-gel by a laser beam into the desired geometric shape. Suitable
shaped abrasive
particles are disclosed in the following non-limiting patents and
publications:
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US2014290147 (Everts et al.); US2014007518 (Breder et al.); US2013337262
(Barnes et
al.); US8840696 (Czerepinski et al.); US8753742 (Arcona et al.); US8758461
(Czerepinski
et al.); US2013263525 (Erickson); US8728185 (Adefris); US2013040537 (Adefris
et al.);
US2012227333 (Adefris et al.); US8764865 (Adefris et al.); US2010319269
(Erickson);
US8034137 (Adefris et al.); US8142532 (Adefris et al.); US8142531 (Adefris et
al.);
US8142891 (Adefris et al.); US5984988 (Berg et al.); EP2692815 (Frei et al.);
EP2692814
(Fuenfschilling et al.); EP2692816 (Fuenfschilling et al.); EP2692817
(Fuenfschilling et
al.); EP2692820 (Fuenfschilling et al.); EP2692813 (Buehler et al.); EP2692819
(Fuenfschilling et al.); and EP2692821 (Fuenfschilling et al.)
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view of an abrasive belt.
FIG. 2 is a perspective view of a shaped abrasive particle.
FIG. 3 is a graph of Side Force vs Cycle for various abrasive belts.
FIG. 4 is a graph of Cut vs Cycle for various abrasive belts.
DETAILED DESCRIPTION
Coated Abrasive Article
Referring to FIG. 1, a coated abrasive article in the form of an abrasive belt
10
comprises a backing 12 having a first layer of binder, hereinafter referred to
as the make
coat resin 14, applied over a first major surface 15 of the backing 12.
Attached or partially
embedded in the make coat 14 are a plurality of shaped abrasive particles 16
forming an
abrasive layer 18. In some embodiments, the abrasive layer 18 comprises a
patterned
abrasive layer with at least some of the shaped abrasive particles spaced and
positioned onto
the backing in a pre-determined pattern. The shaped abrasive particles can be
spaced from
each other a pre-determined amount in the X and Y directions and have a
specified angular
rotation about the Z-axis that is parallel to a shaped abrasive particle
longitudinal axis 20 of
an individual shaped abrasive particle.
The abrasive belt has a first belt side 22, a second belt side, 24, and a belt
longitudinal
axis 26. The belt can be left as shown in FIG. 1 for use in a cartridge
grinder where the belt
is unwound, directed over the work piece, and then rewound. Alternatively, the
ends 28 of
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the belt can be spliced and joined together to form an endless abrasive belt
in the form of a
loop using readily known methods.
Over the shaped abrasive particles 16 a second layer of binder, hereinafter
referred
to as the size coat resin 30 can be applied. The size coat has been minimized
in FIG. 1 to
better illustrate the orientation of the shaped abrasive particles. The
purpose of make coat
resin 14 is to secure shaped abrasive particles 16 to backing 12 and the
purpose of size coat
30 is to reinforce shaped abrasive particles 16 in the abrasive layer 18 to
better secure them
within the abrasive layer and to the backing.
Referring now to FIG. 2, one embodiment of a shaped abrasive particle 16 is
shown.
The shaped abrasive particle 16 has a first face 32 and an opposing second
face 34 separated
by a thickness t. The first face and the second face are joined to each other
by a sidewall 36.
In some embodiments, the sidewall is a sloping sidewall having a specific
draft angle, a,
between the second face and the sidewall as disclosed in US patent 8,142,531.
The shaped
abrasive particle has a length, 1, measured along the shaped abrasive particle
longitudinal
axis 20. A perimeter of both the first face and the second face is triangular,
and in some
embodiments the perimeter is an equilateral triangle. Other shaped abrasive
particles can be
used as listed in the definition above.
In some embodiments, at least 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85,
90, or
95 percent of the shaped abrasive particles 16 in the abrasive layer 18 are
placed onto the
backing such than an offset angle, 13, between the first face 32 and the belt
longitudinal axis
26 is greater than 0 degrees and less than or equal to 20 degrees. In other
embodiments, at
least 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, or 95 percent of the
shaped abrasive
particles 16 in the abrasive layer 18 are placed onto the backing such than an
offset angle,
13, between the first face 32 and the belt longitudinal axis 26 is greater
than 0 degrees and
less than or equal to 10 degrees. In other embodiments, at least 30, 35, 40,
45, 50, 55, 60,
65, 70, 75, 80, 85, 90, or 95 percent of the shaped abrasive particles 16 in
the abrasive layer
18 are placed onto the backing such than an offset angle, 13, between the
first face 32 and
the belt longitudinal axis 26 is greater than 0 degrees and less than or equal
to 5 degrees. As
will be shown later in the Examples, a specified range for the angle, 13, has
been shown to
limit the side load or side force generated by the abrasive layer with the
rotated shaped
abrasive particles.
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As used herein in referring to shaped abrasive particles, the term "length"
refers to
the maximum dimension of a shaped abrasive particle and is typically along the
shaped
abrasive particle longitudinal axis 20. "Width" refers to the maximum
dimension of the
shaped abrasive particle that is perpendicular to the length and is typically
perpendicular to
the shaped abrasive particle longitudinal axis 20. The terms "thickness" or
"height" refer to
the dimension of the shaped abrasive particle that is perpendicular to the
length and width.
See Fig. 2 where length and thickness are shown for the triangular shaped
abrasive particle.
Shaped ceramic abrasive particles are typically selected to have a length in a
range
of from 1 micron to 15000 microns, more typically 10 microns to about 10000
microns, and
still more typically from 150 to 2600 microns, although other lengths may also
be used.
Shaped ceramic abrasive particles are typically selected to have a width in a
range
of from 0.1 micron to 3500 microns, more typically 100 microns to 3000
microns, and more
typically 100 microns to 2600 microns, although other lengths may also be
used.
Shaped ceramic abrasive particles are typically selected to have a thickness
in a
range of from 0.1 micron to 1600 microns, more typically from 1 micron to 1200
microns,
although other thicknesses may be used.
In some embodiments, shaped ceramic abrasive particles may have an aspect
ratio
(length to thickness) of at least 2, 3, 4, 5, 6, or more.
The make coat resin 14 and size coat resin 30 comprise a resinous adhesive.
The
resinous adhesive of the make coat resin can be the same as or different from
that of the size
coat resin. Examples of resinous adhesives that are suitable for these coats
include phenolic
resins, epoxy resins, urea-formaldehyde resins, acrylate resins, aminoplast
resins, melamine
resins, acrylated epoxy resins, urethane resins and combinations thereof. In
addition to the
resinous adhesive, the make coat resin or size coat resin, or both coats, may
further comprise
additives that are known in the art, such as, for example, fillers, grinding
aids, wetting
agents, surfactants, dyes, pigments, coupling agents, adhesion promoters, and
combinations
thereof Examples of fillers include calcium carbonate, silica, talc, clay,
calcium
metasilicate, dolomite, aluminum sulfate and combinations thereof A supersize
coating
may be applied over the size coat as well as disclosed in the Examples.
A grinding aid can be applied to the coated abrasive article. A grinding aid
is defined
as particulate material, the addition of which has a significant effect on the
chemical and
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physical processes of abrading, thereby resulting in improved performance.
Grinding aids
encompass a wide variety of different materials and can be inorganic or
organic.
The backing 12 can be any suitable material used for abrasive articles such
as, paper,
film, cloth, nonwovens, vulcanized fiber, plastics, and the like.
In some embodiments, a combination of shaped abrasive particles and other
abrasive
grains such as crushed abrasive particles or diluent particles can be used as
disclosed for
example in US. Patent publication US 2012/0231711 and in US patent number
5,496,386.
In some embodiments, two or more shaped abrasive particles may be placed into
close
proximity by forming multiplexed shaped abrasive structures of duplexed,
triplexed or even
more shaped abrasive particles as disclosed in PCT Application No.
PCT/US2015/045505
filed on August 17, 2015 entitled Coated Abrasive Articles with Multiplexed
Structures of
Abrasive Particles and Method of Making.
Method of Making a Coated Abrasive Article
Pending PCT Application No. PCT/U52014/069726, filed on July 2, 2015;
published PCT No. PCT/U52015/10020, published on July 2, 2015, published PCT
No.
PCT/U52015/100018, published on July 2, 2015, and PCT Patent Application No.
PCT/U52015/045505, filed on August 17, 2015 disclose a method of making
abrasive
articles, an apparatus for making abrasive articles, and production tooling
for an abrasive
particle positioning system and are herein incorporated by reference. In
general, a
production tool having a plurality of cavities dimensioned to hold a single
shaped abrasive
particle or multiple shaped abrasive particles are provided for precise
positioning, rotational
orientation, and transfer of the shaped abrasive particles to a coated backing
thereby forming
a patterned abrasive layer where the X-Y spacing and rotational orientation
about the Z axis
of at least 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, or 95 percent
of each shaped
abrasive particle in the abrasive layer can be predetermined and controlled
for a specific
grinding application. After the shaped abrasive particles are placed into the
production tool,
the production tooling and the coated backing having a make coat resin applied
are brought
into close proximity and the shaped abrasive particles are transferred from
the cavities in
the tooling and onto the backing to form a pre-determined pattern or patterned
abrasive layer
with the shaped abrasive particles. The make coat resin is then cured,
typically a size coat
resin is applied and cured, and the coated abrasive article is converted into
a belt.
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EXAMPLE S
Objects and advantages of this disclosure are further illustrated by the
following
non-limiting examples. 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 disclosure. Unless otherwise noted, all parts, percentages, ratios, etc.
in the Examples
and the rest of the specification are by weight.
PREPARATION OF SHAPED ABRASIVE PARTICLES
Shaped abrasive particles were prepared according to the disclosure of U.S.
Patent
No. 8,142,531 (Adefris et al.). The shaped abrasive particles were prepared by
molding
alumina sol gel in equilateral triangle-shaped polypropylene mold cavities of
side length
0.068 inch (1.73 mm) and a mold depth of 0.012 inch (0.3 mm). After drying and
firing, the
resulting equilateral, triangular shaped abrasive particles resembled FIG. lA
except the draft
angle a of a sloping sidewall was approximately 98 degrees. The fired shaped
abrasive
particles were about 1.3 mm (side length) x 0.27 mm thick and would pass
through a 20-
mesh sieve.
COMPARATIVE EXAMPLE A
The abrasive belt of Comparative Example A was obtained as 3MTm CUBITRONTm
II ABRASIVE CLOTH BELT 984F, 36+ YF-WEIGHT from 3M, Saint Paul, Minnesota.
In the 984F belt, the triangular shaped abrasive particles are applied to the
backing by an
electrostatic deposition process and therefore the first face of each shaped
abrasive particle
is randomly orientated with respect to the belt's longitudinal axis.
EXAMPLES 1-6 AND COMPARATIVE EXAMPLE B
Comparative Example B
Untreated polyester cloth having a weight of 300-400 grams per square meter
(g/m2), obtained under the trade designation POWERSTRAIT from Milliken &
Company,
Spartanburg, SC, was presized with a composition consisting of 75 parts EPON
828 epoxy
resin (bisphenol A diglycidyl ether, from Resolution Performance Products,
Houston, TX),
10 parts of trimethylolpropane triacrylate (obtained as 5R351 from Cytec
Industrial Inc.,
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Woodland Park, NJ), 8 parts of dicyandiamide curing agent (obtained as
DICYANEX
1400B from Air Products and Chemicals, Allentown, PA), 5 parts of novolac
resin (obtained
as RUTAPHEN 8656 from Momentive Specialty Chemicals Inc., Columbus, OH), 1
part of
2,2-dimethoxy-2-phenylacetophenone (obtained as IRGACURE 651 photoinitiator
from
BASF Corp., Florham Park, NJ), and 0.75 part of 2-propylimidazole (obtained as
ACTIRON NXJ-60 LIQUID from Synthron, Morganton, NC).
A 10.16 cm x 114.3 cm strip of this backing was taped to a 15.2 cm x 121.9 cm
x
1.9 cm thick laminated particle board. The cloth backing was coated with 229
g/m2 of a
phenolic make resin consisting of 52 parts of resole phenolic resin (obtained
as GP 8339 R-
23155B from Georgia Pacific Chemicals, Atlanta, GA), 45 parts of calcium
metasilicate
(obtained as WOLLASTOCOAT from NYCO Company, Willsboro, NY), and 2.5 parts of
water using a putty knife to fill the backing weave and remove excess resin.
The shaped abrasive particles prepared according to the disclosure of U.S.
Pat. No.
8,142,531 (Adefris et al.) had nominal equal side lengths of 1.30 mm and a
thickness of 0.27
mm, and a sidewall angle of 98 degrees.
A production tool with an array of vertically-oriented triangular openings
(wherein
length = 1.698 mm, width = 0.621 mm, depth = 1.471 mm, bottom width = 0.363
mm)
arranged in a rectangular array (length-wise pitch = 2.68 mm, width-wise pitch
= 1.075 mm)
was cut into 5 inch (12.7 cm) wide strips at a zero degree offset angle f3.
Sufficient bias cut
tool sections to achieve a total length of 44 inches (111cm) were lined up end
to end and
mounted to a second 15.2 cm x 121.9 cm x 1.9 cm thick particle board. A 1.0 cm
diameter
hole was drilled through the thickness at the midpoint of the 15.2 cm
dimension and
approximately 2.54 cm from each end of both of the laminated particle boards.
A base was
constructed that had a 0.95-cm diameter vertical dowels at each end to engage
the holes in
the particle boards and thereby align the placement of first the abrasive
particle filled tooling
(open side up), followed by the make resin-coated backing (coated side down).
Several
spring clamps were attached to the particle boards to hold the construction
together. The
clamped assembly was removed from the dowels, flipped over (backing now coated
side up
and tooling open side down) and placed back onto the base using the dowels to
maintain
alignment. The back of the laminated particle board was repeatedly tapped
lightly with a
hammer to transfer the abrasive particles to the make-coated backing. Abrasive
grains
having a basis weight of 727 g/m2 were thus applied. The spring clamps were
removed and
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the top board carefully removed from the dowels so the transferred mineral was
not knocked
over on its side. Nominally, close to 100 percent of the shaped abrasive
particles were
positioned a predetermined distance from each other in the X and Y directions
and had an
offset angle 0 of zero degrees.
The tape was removed and the abrasive coated backing and it was placed in an
oven
at 90 C for 1.5 hours to partially cure the make resin. A size resin
consisting of 43.15 parts
of resole phenolic resin (obtained as GP 8339 R-23155B from Georgia Pacific
Chemicals,
Atlanta, GA), 9.7 parts of water, 22.75 parts of cryolite (Solvay Chemicals,
Inc, Houston,
Texas), 22.75 parts calcium metasilicate (obtained as WOLLASTOCOAT from NYCO
Company, Willsboro, NY) and 1.65 parts red iron oxide was applied to each
strip at a basis
weight of 503 g/m2, and the coated strip was placed in an oven at 90 C for 1
hour, followed
by and 8 hours at 102 C.
A supersize coating consisting of 29.2 parts aqueous dispersion obtained as
CMD35201 (EPI-REZ 522-C) (Rhone-Poulenc, Inc. Louisville Kentucky), 0.35 parts
2-
ethyl, 4-methyl imidazole, obtained as EMI-24 (Air Products and Chemicals,
Allentown,
Pennsylvania), 53.3 parts 98% pure micropulverized KBF4 (95% by weight passes
through
a 325-mesh screen and 100% by weight passes through a 200-mesh screen) was
then applied
to each strip at a basis weight of 300 g/m2 and then the coated strips were
cured at 125 C
for 3 hours. After cure, the strip of coated abrasive was converted into a
belt using
conventional adhesive splicing practices.
EXAMPLES 1-6 AND COMPARATIVE EXAMPLES C
Examples 1-6 and Comparative Example C were made identically to Comparative
Example B with the exceptions of offset angle 0 and coating weights, as shown
in Table 1.
Each basis weight in table 1 is the average weight obtained from two replicate
belts.
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Table 1
Offset Make Particle Size Supersize
Example angle 13
Coating weight, g/m2
degrees
Comp. B 0 229 727 503 300
1 2 260 868 470 235
2 5 200 754 469 261
3 8 237 801 482 240
4 10 235 795 516 257
15 217 770 417 235
6 20 240 878 485 236
Comp. C 30 247 750 475 245
BELT TRACKING TEST
5 An automated tracking and grinding test was conducted on 3 inch (7.62
cm) wide x
36 inch (91.44 cm) belts to evaluate inventive and comparative coated abrasive
belt
constructions. The work piece was 304 stainless steel bars on which the
surface to be
abraded measured 0.75 inch by 0.75 inch (1.9 cm x 1.9 cm). An 8 inch (20.32
cm) diameter,
70 durometer rubber serrated contact wheel was used. The belt was run at 2750
rpm (5760
ft/minute (1756 m/minute)). The work piece was urged against the center part
of the belt at
a normal force of 15 pounds (6.80 kgf). The test consisted of measuring the
weight loss of
the work piece every 15 seconds. During the grinding process, the horizontal
(tracking)
forces were measured. Following each 15-second cycle, the work piece was
cooled in water
and tested again. The test was concluded when cut rate (grams/15 seconds) was
25% of
initial cut rate, or after 40 cycles, whichever came first. The average cut
for the two replicate
belts in grams was then recorded for each offset angle (see FIG. 4), along
with the average
side force for each cycle (see FIG. 3).
As seen in FIG. 3, the side force in pounds increased as the offset angle, 13,
between
the belt longitudinal axis and the first face increased. In general for angles
less than or equal
to 5 degrees, the side force was approximately the same as the
electrostatically coated belt
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Comparative A and nominally zero. Thus, an offset angle, 13, of less than or
equal to 5
degrees had the same side force load as an electrostatically coated belt but
because the
shaped abrasive particles are slightly rotated a non-scribing finish is
obtained.
A significant shift in the side force curve occurred for the 30 degree offset
angle, 13,
upon which no higher offset angles were attempted. Higher offset angles up to
45 degrees
would result in additional increased side forces. As seen in the graph, as the
shaped abrasive
particles wear down from the abrading action, the side force decreases to zero
and actually
become negative for unknown reasons. This confirms that the significantly
increased cut of
the shaped abrasive particles, especially when new, caused the increase in the
belt's side
force when grinding.
All cited references, patents, or patent applications in the above application
for
letters patent are herein incorporated by reference in their entirety, or
specified portion
thereof, in a consistent manner. In the event of inconsistencies or
contradictions between
portions of the incorporated references and this application, the information
in the preceding
description shall control. The preceding description, given in order to enable
one of ordinary
skill in the art to practice the claimed disclosure, is not to be construed as
limiting the scope
of the disclosure, which is defined by the claims and all equivalents thereto.
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