Note: Descriptions are shown in the official language in which they were submitted.
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BAUXITE-ZIRCONIA ABRASIVE AND PRODUCTS CONTAINING SAME
a) Field_of the Invention
The present invention relates to bauxite-
zirconia abrasive grain and more particularly re-
lates to such grains which contain from about 25
to about 50, and preferably from about 35 to about
50 weight percent zirconia. The invention further
relates to coated and bonded abrasive products in-
corporating such grains.
b) History of the Prior Art
Alumina (aluminum oxide) is and has been used
as the primary abrasive material for a long time.
Alumina has enjoyed such use due to a combination of
ready availability, toughness and hardness. While
other harder substances, such as diamond, are known,
which have been used as highly effective abrasives,
until recently no commercially competitive substance
has been available having overall abrasive properties
superior to those of alumina.
20 ~ Attempts have been made to alloy alumina with -
other oxides such as zirconia (zirconium oxide) to ob-
tain an abrasive having properties superior to alumina.
Such attempts have met with some success when at least
about 10% zirconia is fused with aluminum oxide and when
the fused zirconia-alumina mixture i9 rapidly solidified.
U. S. Patent 3,156,545 to Kistler et al dis-
closes that an abrasive having a grinding removal
rate comparable to the removal rate of alumina can
be prepared by rapidly cooling a composition contain-
ing alumina, zirconia and a substantial amount, i.e.,
about 15% to about 60% by volume, of glass, such as
silicon dioxide, to form a glassy matrix in which
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particles of zirconia and alumina are imbedded. The
resulting abrasive on the average, was not, however,
substantially superior to alumina in steel removal
rate.
Other alumina-zirconia alloys have, however,
been disclosed in subsequent ~. S. Patents wherein
high purity alumina and zirconia are used. The
products disclosed in the subsequent patents do
show substantial improvement in performance by the
disclosed alumina-zirconia abrasives when compared
with alumina.
For example, U. S. Patent 3,181, 939 to Marshall
and Roschuk discloses that high strength abrasives
can be obtained when from about 10 to about 60%
weight percent zirconia is fused with alpha alumina
and the resulting fusion is rapidly cooled. U. S.
Patent 3,181,939 discloses that such abrasives
are suitable for steel snagging operations where
high strength is required. The patent, however,
20 ' requires that the alpha alumina be of high purity,
usually at least 99~8~/o by weight aluminum oxidè,
and furthe~ indicates that the purity of the zir-
conia should be preferably at least about 99%.
As disclosed in U. S. Patent 3~891~408 to
Rowse et al and U. S. Patent 3~893~826 to Quinan
et al, the best grinding and polishing abrasive
- characteristics are obtained when the proportions
of zirconia to alumina are such that a eutectic
structure is formed when the fused alumina-zirconia
mixture is rapidly cooled. The Quinan et al and
Rowse et al Patents similarly teach that high purity
alumina and zirconia should be used.
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1~137~Z7
BRIEF DESCRIPTION OF THE INVENTION
It has now been discovered that, despite
the teachings of U. S. Patents 3,181,939; 3,891,408;
and 3,893,826; highly effective alumina-zirconia
abrasives can be prepared using readily available
impure materials such as bauxite as the source of
alumina and baddeleyite as the source of zirconia.
It has in fact now been unexpectedly found that
alumina-zirconia abrasives can be prepared from
impure starting materials which in at least some
respects are superior to the abrasives prepared from
pure alumina and zirconia starting materials.
Furthermore, in accordance with the present invention,
contrary to the teachings of Rowse et al, it has
been found that at least 0.8 and preferably at
least 1.1% silica should be intentionally incorporated
into or retained in the abrasive composition. The
percentage of silica should not, however, exceed -~
about 3 weight percent of the composition.
Therefore, in accordance with the invention,
there is provided an abrasive composition comprising
particles of a co-fused mixture including zirconia,
bauxitç and silica, if necessary, which has been so-
lidified from an essentially~homogenous molten state
within about three minutes and preferably within one
minute from the time that initial cooling to solidify
the composition is commenced. The finished abrasiye
composition contains from about 25 to about 50 and
preferably from about 35 to about 50 weight percent
of zirconia; from about 49.2 to about 74.2 and pre-
ferably about 49.2 to about 64.2 weight percent alumina;
and from about 0.8 to about 2.5 and preferably from
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` 1113727
about 1.1 to abo~lt 2.4 weir,llt pcrcent silica.
The invention further comprises th~ method of
manuacturing the novel abrasive composition and
coated and bonded abrasive articles incorporating
the novel abrasive composition.
DETAILED DESCRIPTION OF THE INVENTION
The abrasive composition in accordance with
the invention is a composition comprising particles
of co-fused bauxite and zirconia. The particle size
of the abrasive composition may be from 6 to 900
grit as defined by the U. S. Department of Commerce
commercial standard CS 271-65, issued April 12,
1965. The grit size is preferrably between about 6
and about 180 and most desirably is between about 14
and about 80.
The bauxite and zirconia are fused, i.e., melted
together, to form a co-fused mixture of bauxite and
zirconia. Sufficient bauxite and zirconia, are pre-
ferably used to obtain from about 49.2 to about 64.2
20 - weight percent alumina; from about 35 to about 50
weight percent zirconia and desirably from about 0.8
to about 2.5 weight percent silica in the co-fused
mixture after solidification. The preferred so-
lidified composition contains from about 40 to about
45 weight percent zirconia; from about 1.1 to
2.4 weight percent silica and from about 50.5 to
about 58.9 weight percent alumina. Desirably, the
composition also contains up to about 2.5 weight
percent titania (titanium dioxide) and preferably
contains from about 0.25 to about 2 weight percent
titania. The most preferred composition contains
from about 0.25 to about 1.6 weight percent titania.
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11~37;~7
The silica content in the most preferred composition
is from about 1.3 to about 2.0 weight percent silica.
The abrasive composition in accordance with
the invention is prepared using unpurified calcined
bauxite or only partially purified bauxite, i.e.,
alumina made by the fusion and reduction of calcined
bauxite with metallic iron and carbon. When un-
purified calcined bauxite is used directly, iron and
. carbon should be incorporated into the bauxite-
zirconia fusion to remove iron oxide and some but not
all silica and titania. "Bauxite", as used herein in-
cludes unpurified calcined bauxite, partially purified
bauxite, or synthetic bauxite. Bauxite is the pre-
ferred alumina source since it requires less re-
fining than pure alumina and usually contains suf-
ficient silica and titania to provide the silica and
titania requirements of the composition in accordance
with the invention. Bauxite used by the abrasive
industry usually contains from about 3 to about 4.5
~ weight percent titania, from about 3 to about 8
weight percent silica and from about 3 to about 10
weight percent iron oxide (Fe2O3).
The bauxite which is used may be synthetically
produced, i.e., the bauxite which is used may be formed
; by combining pure alumina with desirable impurities such
as silica and titania to obtain a composition which can
be substituted for naturally occurring bauxite.
From about 0.1 to about 0.5 weight percent of par-
ticulate carbon is usually incorporated into the blend
prior to fusion when partially purified bauxite is
u~ed~ More carbon, i.e., from about 2 to about 5
weight percent is added, with from about 5 to about 10
"' ' . : - ~ , '
~` 1 11 37Z~7
weight percent m~allic iron, when unpurified cal-
cined bauxite is used. The percentages of carbon
and iron added are dependent upon the quantity of
iron oxide, silica and titania impurities in the
bauxite. The appropriate quantities of iron and
carbon to be added can be readily calculated by
those skilled in the art. Any particulate carbon is
suitable and petroleum coke is frequently used.
During the fusion and carbon reduction process, if
metallic iron is present, excess titanium, silicon
and iron separates from the fusion and is removed.
After fusion, using partially purified or unpurified
bauxite as described above, the mixture usually
contains the desired quantity of silica and titania.
Iron in the form of oxide or alloy may remain in the
fused mixture in very low percentages, i,e., about
1.5 weight percent or less.
Should the bauxite fail to provide sufficient
silica or titania to meet the required silica and
titania content in the preferred composition, addi-
tional silica or titania can be added to the fusion.
The zirconia is preferrably provided in the
form of baddeleyite ore which usually contains from
about 95 to about 99 weight percent zirconia, from
about 0.3 to about 3 weight percent silica, from
about 0.5 to about 2 weight percent titania and from
about 0.5 to about 2 weight percent iron oxide.
When compared with bauxite, the baddeleyite ore is
found to contain lower percentages of silica, titania
and iron oxide impurities than unpurified bauxite.
"Zirconia" as used herein includes baddeleyite ore,
zirconia bubbles made by smelting of zircon ore, and
- purified zirconia.
The only impurities which may occur in the
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1~13727
finished abrasive composition which are believed to
- be somewhat detrimental in excessive quantities,
are alkali and alkaline earth oxides such as calcium
oxide, magnesium oxide and sodium oxide (soda).
Even these impurities do not, however, seem to
detrimentally affect the abrasive composition when
their combined percentage is less than 1 weight
percent. The combined weight percent of these
impurities, in the preferred embodiment, is however,
less than about 0.5 weight percent. In practice,
the resulting abrasive composition manufactured by
co-fusing bauxite and baddeleyite ores usually in
fact contains less than about 0.5 weight percent of
combined calcium oxide (CaO), magnesium oxide (MgO),
and soda (Na2O).
The melted (fused) mixture is solidified within
about three minutes and preferably within one minute
from the time that initial cooling to solidify the
composition is commenced. "Initial cooling" as used
herein means the time at which any portion of the
melted mixture becomes permanently solidified due to
its exposure to a temperature below the solidification
f temperature of the mixture. The solidification
temperature of an alumina-zirconia eutectic mixture,
i.e., a mixture containing about 42 weight percent
zirconia and about 58 weight percent alumina, is
about 1700C and is somewhat higher when greater
percentages of alumina or zirconia are present.
To obtain the best results, solidification time,
i.e.,- time for complete solidification, should be
within about 1 minute and most preferably within
about 20 seconds of the time that initial cooling
to solidify the composition is commenced.
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372~7
Any suitablc method ~or rapidiy cooling the
melted mixture may be used to quickly solidify the
mixture. For example, the mixture may be poured
upon a bed comprising 4.5 cm diameter or smaller
- steel balls. The ball size is preferably about 2
cms in diameter. The mixture may also be rapidly
cooled by pouring upon very small lumps of solidified
composition, i.e., about 0.7 cm in diameter or
smaller or may be rapidly cooled by casting in thin
sheets, i.e., about 2 cm thick or smaller, upon the
surface of a steel plate. It is believed that any
cooling method may be used wherein the melted com-
positon is cast or poured upon a heat sink having a
high heat conductivity, i.e., in excess of about
0.05 calorie-s per second per square centimeter per
cm per degree C at about 1200C, and wherein the
maximum distance through the cast or poured material
to the nearest heat sink surface is less than about
2 and preferably less than about 0.5 cm. Heat sink
materials, such as lumps of previously solidified
composition, which have lower conductivities may be
used provided that the thickness of the cast or
poured melted composition is substantially smaller,
e.g., in the case of lumps of previously solidified
material, less than about 0.7 and preferably about
0.3 cm.
Desirable heat sink materials not only have high -
heat conductivity, but have reasonably high melting
temperatures. Steel is a preferred heat sink material
for these reasons and because of its low cost and avail-
ability. An example of another commercially feasible
heat sink material is cast iron. Examples of other
possible good heat sink materials, which are not
used primarily due to their cost, are: chromium,
~ 1 37 ~
nickel, zirconium and their alloys. I~igh heat
capacity of the heat sink material is also desirable.
After solidification, the resulting com-
position is comminuted to the desired grain size.
Such comminuting is usually accomplished by jaw
crushing followed by impact crushing or roll crush-
ing.
In accordance with the method for manufacturing
the particulate-abrasive composition, a thoroughly
blended mixture of particles comprising from
about 35 to about 50 weight percent zirconia, and
from about 50 to about 65 weight percent bauxite is
fused. The particle size of the zirconia and bauxite
and other ingredients which are blended are not
particularly critical and may range from as large as
five centimeters to as small as a micron provided
that all components are of approximately the same
particle size. The most desirable particle size
is between about 200 mesh and one-centimeter. The
mixture preferably contains sufficient silica to
obtain from about 0.8 to about 2.5 weight percent,
silica in the composition after solidification. The
silica in the mixture is usually provided by the
bauxite or by baddeleyite which also provides the
zirconia. The mixture of particles is obtained by
blending particles of bauxite and zirconia usually
in the form of baddeleyite. The alumina and zirconia ~ -
containing particles may also be simultaneously
blended with particles containing silica and titania
if additional silica or titania is desired. Usually
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.:
" 1 ~1 3 72~
no additional silica or titania is required but
between about 1.1 and about 2.5 percent silica and
up to 2.5 weight percent titania by combined weight
of bauxite and zirconia may be blended into the
composition provided that the silica and titania in
the finished abrasive composition do not exceed
three weight percent each and preferably do not ex-
ceed two weight percent each. Blends of bauxite
with up to 50 weight percent purified alumina particles
can also be used as the source of alumina.
After blending, the particle blend is fused,
usually at a temperature above about 1800C. After
fusion, the mixture is cooled to solidify the fused
mixture within about three minutes and preferably
within one minute of the time that initial cooling
to solidify the mixture is commenced. The time to
solidify the fused mixture is most desirably less
than about 20 seconds. After the mixture is cooled
and solidified, it is comminuted to form the par- -
ticulate abrasive composition. The comminuting of
the solidified mixture is usually accomplished b.y
jaw crushing followed by impact crushing or roll
crushing as previously mentioned.
The zirconia in the resulting abrasive has been
found to be between about 10 and 25% in the tetragonal
crystal phase and the average size of the primary
alumina and zirconia crystals, if any, is over 60
microns ln length. The diameter of the primary
crystals is between about 30 and about 60 microns.
The spacing of the zirconia eutectic phase particles
is usually between 2500R and 5000~.
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The particulate abrasive composition of the
invention can be utilized to form novel coated and
bonded abrasive products. While such products are
not superior in performance to prior art alumina-
zirconia abrasives in all applications, they do
have superior characteristics in at least some
applications. The bonded abrasive products in
accordance with the present invention include such
products as grinding wheels. To form such bonded
abrasives, the novel particulate abrasive is bound
together by a suitable resin, particularly phenolic
type resins such as phenolformaldehyde, resorcinol-
aldehyde, cresol-aldehyde and amine-aldehyde resins
such as urea-aldehyde and melamine-formaldehyde resins.
The resulting bonded abrasive articles have grinding
characteristics superior to alumina and comparable
to, though not necessarily superior to, prior art
alumina and zirconia grain manufactured from es-
sentially pure alumina and zirconia.
20 ' Coated abrasive articles comprising the novel
abrasive of the invention adhesively bonded to a
flexible backing, have grinding characteristics which,
in at least belt grinding applications, are superior
to any known prior art alumina or alumina-zirconia
coated abrasive article. The superior performance is
particularly unexpected since the present grain
intentionally contains at least 0.8% weight percent
and preferably at least 1.1% weight percent silica
whereas prior art grain such as that disclosed in
U. S. Patent 3,891,408 to Rowse and Watson preferably
contains less than about 0.3%, and essentially below
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137Z7
1% silica, and w~s preferably manufactured from
: purified materials such as purified alumina.
The backing utilized in forming the coated
abrasive in accordance with the invention, can be
any suitable backing such as paper, woven cotton or
polyester cloth or fiber mat. In accordance with
the present invention, the backing and adhesive,
especially when the coated abrasive is an abrasive
belt, should be durable since it has been unexpected-
ly found that the novel abrasive may actually have a
longer useful cutting life than the useful life of
backing material or adhesive. The adhesive which
binds the abrasive to the flexible backlng should be
a heat curable resin such as a phenol-formaldehyde
resin. ~
It has also been unexpectedly found that even -
further improvements in abrasive characteristics in
bonded products can be obtained when the abrasive
grain of the invention is blended with up to 60 weight
percent and preferably from about 5 to about 60
weight percent of another abrasive grain such as -
alumina or partially purified bauxite.
~; The following examples serve to illustrate but
not limit the present invention. Unless otherwLse
indicated, all parts and percentages are by weight.
EXAMPLE I
49.8 weight percent of partially purified par-
ticulate bauxite comprising about 1.2 weight percent
silicon dioxide and 2.9 weight percent titanium dioxide;
49.8 weight percent of particulate zirconia bubbles
comprising about 10.5 weight percent alumina, about
3.5 weight percent silicon dioxide and about 0.9
weight percent titania; and about 0.4 weight percent
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1 ~1 37Z~7
of calcined petroleum coke are mixed in a Patterson-
Kelly Twin Shell Dry V-blender for 10 minutes.
About 39 Kg of the resulting mixure is fused
in a 17 inch diameter, 14 inch deep 150 kw single
phase double electrode furnace. The resulting fused
mixture is poured into a mold filled with about 3l4
inch diameter steel balls. The mold is about 50 cms-
in diameter and about 15 cms~deep.
The crude abrasive, i.e., solidified melt, is
hand separated from the steel balls on an inclined
table which permits the balls to roll away from the
crude.
The crude is crushed in a 18 inch by 10 inch
Economy Allis Chalmers roll crusher. The crude is
passed through the crusher four times and each time
the gap is reduced by a ratio of between 2:1 to 3:1
per pass. After four passes, the abrasive grits are
screened. Oversize grits are returned to the crusher.
The grit is then further treated by three
passes through a Pennsylvania Hammer Mill at 900
rpm and the resulting grits are grade~d.
The abrasive grits are found to contain about
1 4 weight percent silicon dioxide, about 1.6 weight
percent titanium dioxide, about 43 weight percent
zirconium dioxide, and about 0.5 weight percent other
impurities, The balance of the abrasive composition
i8 aluminum oxide.
EXAMPLE II
The procedure of Example I is followed except
essentially pure tabular alumina is substituted for
the bauxite and only about 0.l weight percent of
13727
petroleum coke is added since very little silica
or iron is present. The resulting abrasive grain
contains 0.24 weight percent silica.
EXAMPLE III
The procedure of Example I is followed with the
following exceptions: A much larger furnace and a
ld about seven feet in diameter by seven feet high
is used. Unpurified calcined bauxite is used with
metallic iron and carbon. No zirconia is used and
no steel balls are used in the mold. No impact crush-
ing is used. The result is a brown alumina abrasive
grain.
EXAMPLE IV
The procedure of Example III is followed except
the abrasive is subjected to impact crushing to in-
crease its bulk density.
EX~M~LE V
Each of the grains prepared in Examples I, II,
and III are used in making abrasive belts and are
tested as follows:
A double coated abrasive material is made by
electrostatic coating a 36 grit test grain over a `
coating of 36 grit conventional brown aluminum oxide
grain prepared in accordance with Example III which
is deposited by gravity on the finished cloth.
The fabric selected for the backing material is a
heat set, 4/1 sateen weave polyester, approximately
103 x 40 threads per square inch, cloth finished in
a conventional manner, with a finished weight of
approximately 30 lbs per ream. (Sandpaper ream:
480 9 x 11 sheets).
A maker adhesive mix consisting of a commercial
onestage, liquid phenolic resin with a formaldehyde
- phenol ratio of approximately 1:1 and ground
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1$137Z~7
limestone witll an avera~e par~icle size of between 17
and 25 microns is made using a 1:1 wet weight mix pro-
portion.
The maker mix is then heated to 90F and coated
on the backing using a standard roll coating method.
Approximately 20 lbs per ream of adhesive is applied.
Using conventional sandpaper making equipment,
the fused alumina abrasive of Example III is then
gravity coated with approximately 30 lbs per ream of
grain applied. Immediately following the gravity
coating, the test grain is electrostatically projected
on the wet web with approximately 34 lbs per ream
being retained.
The abrasive adhesive coated backing is then
heated to 175F for one hour and 200F for two hours
in a maker rack. After drying, a size coat is
applied by standard roll coating methods with
between 25 and 29 lbs per ream being applied. The
size mix consists of the same 1:1 phenolic resi~- -
filler ratio previously used. However, a non-buffered
synthetic cryolite with an average particle size of
25 microns is used as the filler instead of limestone.
Drying and curing is then accomplished by heating the
coated material for one hour at 150F, five hours at
175F and 16 hours at 225F.
After curing, the material is edge trimmed and
flexed perpendicular to the edge to offer ease of
handling for belt-making. Abrasive belts (2 inches
x 132 inches) are manufactured from the coated abrasive
material according to usual techniques. These are
then evaluated on a conventional heavy duty floor
backstand belt tester using ASI 1018 cold rolled steel
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~1137~7
as a workpiece. In this test, the belt is placed on
the backstand in the standard manner and a 1 x 1 x 36
inch workpiece is positioned so that it engages the
belt on the one inch square side just below the
horizontal di.ameter of the contact wheel.
The abrasive belt in the test is driven at 4200
surface feet per minute (SFPM) over a contact wheel
14 inches in diameter. 63 lbs of dead weight in-feed
force is exerted on the workpiece. Testing is for 30
seconds after which stock removed from the bar is
measured (weight before grind - weight after grind)
and recorded. This sequence is continued until the
measured stock removed is 20 grams or less per grind-
ing interval. Total stock removed in this manner for
the test belt is compared to total stock removed for
the other test belts as shown in Table I.
; TABLE I
Grain Tested Stock Removed
Example I (bauxite-zirconia) 3834 grams
Example II (alumina-zirconia) 1934 grams
Example III (bauxite) 850 grams
This test clearly shows the superior stock re-
moval of the grain of the invention in belt grinding.
EXAMPLE VI
A mold cavity for forming a 6 inch by 2 inch by
. 5/8 inch cup wheel is filled with a blended composition .
comprising 83 weight percent of grain manufactured in
accordance with Example IV; having a grain size dis-
tribution of 50 weight percent of 14 grit, 25 weight
percent of 16 grit, and 25 weight percent of 14
grit; 2.9 weight percent of RCI Varcu ~8121 liquid
phenolic resin having 72 to 76% resin solids, a
viscosity of from about 325 to 405 cps.,
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:
37Z~7
an~ a gel timc of from about 32 to 38 minutes at
121C; 4.55 weight percent of RCI Varcum~ 608 powdered
phenolic resin having a softening point of from 80 to
90C, a hot plate cure at 150C of 45 to 55 seconds,
an inclined plate flow at 125C of 26 to 34 mm and a
hexamethylene tetramine (hexa) content of 8.6 to 9.2
weight percent; 4.55 weight percent of Borden AD6096
polyvinyl butyral modified powdered phenolic resin
having a melting point of 105 to 108C, an inclined
plate flow of 125C of 12 to 17 mm and a hexa content
of 6.1 to 7.2 weight percent; and 5.0 weight percent
powdered fluorspar.
The composition is molded at a sufficient pressure :
to obtain a density of 2.74 grams/cc and is then cured :
at a temperature of about 180C for 9 hours.
EXAMPLE VII
The procedure of Example VI is followed except
that the abrasive of Example IV is substituted by
a mixture consisting of 50 weight percent of 14 grit
abrasive prepared in accordance with Example I, 25
, weight percent of 16 grit abrasive prepared in accor-
dance with Example I and 25 weight percent of 20
grit abrasive prepared in accordance with Example I.
EXAMPLE VIII
The procedure of Example VI is followed ex-
cept that the abrasive of Example IV is substituted
by a mixture consisting of 50 weight percent of 14
grit abrasive prepared in acccrdance with Example I, ~-
25 weight percent of 16 grit abrasive prepared in
accordance with Example I and 25 weight percent of
20 grit abrasive prepared in accordance with Example
IV.
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11137Z7
EXAMPLE IX
The wheels prepared in accordance with Examples
VI, VII and VIII are tested for performance by
running them on a Model CP3490 Chicago pneumatic
air grinder at a wheel speed of 6000 rpm using an
air pressure of 90 to 100 psi. The grinder is hand
held for 30 minutes in a position which allows the
wheel to grind a cast steel block.
The wheel and block are both weighed at the
start and finish of the 30 minute test period to
determine the total abrasive consumed. The results
are given in Table II.
TABLE II
WHEEL METAL REMOVED G. RATIO
TESTED PER MINUTE GMS METAL/GMS WHEEL
EXAMPLE VI 16.3 grams 8.7
(alumina)
EXAMPLE VII 27.9 grams 10.9
(bauxite-zirconia)
EXAMPLE VIII 27.9 grams 13.4
(bauxite-zirconia
and alumina blend)
This Example shows that the abrasive of the in-
vention is superior to alumina in grinding rate in the
wheels tested and can unexpectedl,y be combined with
alumina to obtain longer wheel life without sacrific-
ing grinding performance.
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