Note: Descriptions are shown in the official language in which they were submitted.
Background of the Invention
The present invention relates to an abrasive grain, to a method
of producing such grain, and to abrasive products incorporating such
grain.
Abrasives based on substantially pure alumina or alumina modified
with 0.25% to 6% additions of minor impurity phases, or residual
impurity phases derived from the original starting materials, have
proved to be the most versatile and commerc;ally ;mportant abrasive
systems. They find application in the most diverse types of grinding
operation involving the more common types of metal.
Although the levels of ;mpur;ty are qu;te low the;r influence
on the abrasives' grinding performance can be most dramatic and
significant. By changing the impurities, cooling and solidification
rate of the fused mass of material, a range of "alumina abrasives"
has been developed over the years. The individual types have unique
combinations of properties, e.g. hardness, toughness, frictional
characteristics, microstructure, fracture properties, thermal
behaviour, etc., which have made each type ideally suited to a
specific area or field of grinding applications using coated and
bonded abrasive products containing them.
Until recently no commercially competitive material has been
available which offered grinding properties superior to those of
substantially pure aluminas, particularly in applications where the
contact pressures were low to moderate.
Attempts have been made to alloy alumina with other oxides at
much higher levels than had previously been used. The material
showing distinct promise of success was zirconia.
Such attempts met with some success when at least 10% by weight
of zirconia was fused with aluminium oxide and when the fused
zirconia-alumina mixture was rapidly solidified.
U.S. Patent 3,156,545 to Kistler et al discloses that an
abrasive having a grinding removal rate comparable to the removal
rate of alumina can be prepared by rapidly cooling a composition
containing about 15% to 60% by Yolume of glass, such as silicon
dioxide, to form a glassy matrix in which particles of zirconia and
alumina are embedded. The resulting abrasive, however, was not
49~
.
substantially superior to alumina in steel removal rate.
Other alumina-zirconia alloys have, however, been disclosed in
subsequent U.S. and British Patents wherein high purity alumina and
zirconia are used. The products disclosed in these patents do show
substantial improvements ;n performance, in specific areas, over
alumina.
For example U.S. Patent 3,181,939 to Marshall and Roschuk
discloses that high strength abrasives can be obtained when from 10
to about 60% by weight of zir~onia is fused wi~h alpha alumina and the
resulting fusion is rapidly cooled. The patent discloses that such
abrasives are suitable for steel snagging operations, (i.e. high
pressure aperations) where high strength is required. The patent,
however, indicates that ~he alpha alumina should be o~ high pur;ty,
usually at least 99.8% by weight aluminium oxide, and further
indicates that the purity of the zirconia should be preferably at
least 99%.
As disclosed in U.S. Patent 3,891,408 to Rowse and Watson 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.
U.S. Patent 3,891,408 to Rowse and Watson ~eaches the very rapid
crystallization of eutectic and near eutectic molten mixes of
aluminium oxide and zirconium oxide. They believe the optimum eutectic
composition and performance in moderate pressure applications occurs
at 43% by weight of zirconia, but in any eYent the amount of zlrconia
in their abrasive grain is 35-50% by weight. The zirconia in their
material is in the Form of rods (or platelets) which, on the average,
are less than 3000 angs~roms in diameter, and preferably at least
25% by weight of the zirconia is in the tetragonal crystal form. The
solidified melt is made up of cells or colonies, typically 40 microns
or less across their width. Groups of cells having identical orien-
ta~ion of microstructure form grains which typically include 2 to
100 or more cells or colonies. In crush~ng the material fractures
along grain and cell boundaries. The abrasive grits produced are
described as having very high strength combined with highly desirable
microfracture properties.
The novel and unexpected feature alleged for abrasives produced
. .
,
. `
.
~L11;399~i9
in accordance with U.S. Patent 3,891,408 was that when produced at or
near the eutectic composition they were outstandingly useful in "light
duty applieations". Abrasive grits produced in accordance w;th U.S.
Patent 3,891,408 gave improvements in excess of 100% of prior art
standards when incorporated in coated abrasive products and tested
in low or moderate pressure applications. When such grits were
incorporated into bonded products substantial improvements were obtained
in low to ~oderate pressure applications.
The properties of the abrasive grains produced in accordance with
U.S~ Patent 3,8919408 are to be contrasted with the use of lower
zirconia levels, e.g. 25% which leads to very tough abrasives which
find utility in high pressure operations such as snagging operations.
Summary of the Invention
It has now been discovered that despite the teaching of U.S.
Patent 3,891,408 highly effective alumina-zirconia abrasives having
low to moderate pressure performance similar to or better than those
produced at or near the eutectic composition, can be produced using
lower amounts of zirconia than contemplated in U.S. Patent 3,891,408
by incorporating sufficient titania or a reduced form thereof in the
abrasive.
According to a first aspect of the present invention there is
provided an abrasive grain comprising 27 to 35% by weight zirconia,
titanium dioxide or a reduced form thereof in an amount on analysis
expressed as the oxide of 1 to 10% by weight, impurities, if any, in
a total amount on analysis expressed as the oxides of not greater than
3~ by weight, and a balance of alumina.
According to a second aspect of the invention there is provided a
method of producing an abrasive grain as defined in the preceding
paragraph from a melt which on solidification gives a grain of the
defined composition, wherein the solidification to produce the grain
is effected ~n under three minutes by contacting the melt with a
suitable heat sink material.
The present invention also provides abrasive products, for
example coated abrasive products or bonded abrasive products which
incorporate the abrasive grain of the invention.
,
,
``` ~Il~6~
-- 4 --
Detailed Description
The amounts of titania or the reduced form thereof and the amounts
of impurities in the abrasive grain of the invention g;ven above are
the analyses expressed as oxides. This is conventional practice in
abrasive technology but does not mean to say that the titanium or
impurities, if any, are necessarily present as oxides and indeed th;s
may well not be the case as will be seen from the following description.
Ne~ertheless, conventional analy~ical techniques for abrasive products
determine, and express, the amounts of the various components as oxides
and this pract;ce is adopted herein. In fact, the general procedure is
to determine the amoun~s of the various components, excluding alumina,
as oxides, and to express the balance of the composition as being of
alumina and it is on this basis that the analy~ical figures ~or abrasive
grains are quoted herein.
In the following description it is to be understood that references
to the amount o~ titania or reduced form thereof or impurities in the
abrasive grain are the analytical figures expressed as oxides.
The amount of titanium dioxide or reduced form thereof (which may
for example be suboxide, oxycarbide or carbide) present in the abrasive
20 grain of the invention is from 1 to 10% by weight, preferably from 1
to 5% by weight. Although such high levels of titanice, or reduced
form thereof, have been found to be detrimental to the performance, in
common grinding operations, of abrasive grains with an approximately
eutectic compos;tion of zircon;a and alum;na, they surprisingly enhance
25 the low to moderate pressure performance of abras;ve grains which
include 27 to 35% by weight of zirconia. The mechanism by wh;ch the
titanium dioxide or reduced form thereof provides this improvenlent of
properties is uncertain but may be due to an enhancement of frictional
characteristics and rate at which heat is generated when in contact
with the metal, which would thermally assist the penetration of the
abrasiYe into the metal.
The impurit;es, if any, which are present in the grain are either
the residual impur;t;es introduced with the starting materials or
additions which have deliberately been made. Such additions may be
made, for example, to assist refining, e.g. iron and carbon are added
to bauxite fusions to reduce and control silica and iron oxide le~els.
.
~L6~
--5--
It is in fact common practice to add materials to adjust the
final analysis or to combine undesirable phases to facilitate
their removal by precipitation to the base of ~he furnace, or
volatilization from the surface of the melt.
Since it is economically not possible to remove all impuri-
ties completely, the abrasive grain of the invention may contain
certain impurities which can critically affect and can detract
from its performance. It is essential that such materials be
kept within certain limits. Such materials are alkalis (soda,
potash, lithia) alkaline earths, silica and ferric o~ide. These
may be present individually, in combination with one another,
or in combination with the major phases, or exist in reduced
forms such as carbides, nitrides or even free metals.
The potency of such detrimental impurities is variable.
Alkalis, particularly soda, have a devastatingly detrimental
effect on performance. Silica is also detrimental at the zir-
conia levels used in the present abrasives but is less harmful
than alkalis. Alkaline earths are more easily avoided in the
final composition but are thought to be similar or less detri-
mental than silica. It should be noted that at zirconia levels
higher than those used in the present invention, for example at
the eutectic zirconia alumina composition, silica may in fact be
a beneficial ingredient.
Thus, in the final composition the level of the other minor
impurity phases should be kept to the minimum economic levels.
These are dictated by the choice, cost availability and quality
of the sources of alumina and zirconia and the extent to which
they can be favorablly modified economically by the fusion tech-
nique employed. Irrespective of the material sources or the
fusion technique imposed the final composition should preferably
not contain more than 0.1~ Na20 or more than 1.5% SiO2 and pre-
fexably below 1~ SiO2. At these upper limits of Na20 and SiO2
the~r deleterious effect is not too gre~t and in part can be
neutralized by adjusting the titania levels. Additionally, the
combined weight percentage of MgO, CaO and Fe203 should not
exceed 1.5%
The abrasive grain of the invention may be produced by
rapidly solidifying an alumina-zirconia co-fusion which addi-
tionally includes the required titanium dioxide or reduced form
thereof, and possibly also impurities, and which on solidification
gives an abrasive grain in accordance with the invention.
Solidification is effected by contacting the co-fusion with a
heat sink material and should take place in under 3 minutes,
more preferably in under 1 minute, most desirably in under 20
seconds. The heat sink material, or cooling vehicle, may take
the form of metallic balls, metallic rods or plates, or lumps
of prefused abrasive material, onto which the co-fusion is poured.
One important criteria for the cooling vehicle is that it
has a configuration, size and mass that it forms voids or spaces
into which, and surfaces onto which, the molten material can
gain access. In so doing, the cooling vehicle should expose a
sufficiently large surface area to the molten mass to achieve
solidification of the melt within the specified time of 3 minutes
and preferably well below 1 minute of the molten material contacting
the surface provided by the cooling vehicle. At the very high rate
of heat transfer the cooling vehicle should be capable of absorbing
the thermal energy involved without melting or severe deterioration
of its properties to enable the cooling vehicle to be used repeatedly.
A further example of cooling method is, instead of pouring
the melt into a cooling vehicle, to intruduce a cooling vehicle
into the melt and to withdraw the cooling vehicle when a layer of
product has solidified thereon.
Once separated from the cooling vehicle, the solidified mass
may be subjected to the normal types of crushing procedures to
produce abrasive grits. The crushing procedure may comprise
primary jaw crushing, secondary roll crushing, canary milling or
hammer impact milling. The crushing technique used may be
varied to produce grits having different ~hapes. This is common
practice in the industry to extend the use of specific abrasive
compositions to as wide an area of abrasive products and appli-
cations as possible. For example a more friable weak elongated
sharp grit may be required in certain
. ,
- 7 -
coated abrasive applica~ions whereas a sharp but more "blocky"
tougher grain may be required in certain bonded abrasive applications.
The particle size of the abrasive grits produced may be between
6 to 1000 grit as defined by FEPA standards issued 1971-~2 or U.S.
Department of Commerce Commercial Standard CS271-S5 issued April 12,
1965. The grit size is preferably between 6 and about 180 and most
desirably is between about 14 and 80.
The abrasive grain of the invention may be utilized for the
production of coated abrasive products and bonded abr~sive products in
conventional manner. The inventive abrasive grain may be the sole
abrasive in such products, or may be used in conjunction with
conventional abrasives.
A more detailed description of the method of producing the abrasive
grain will now be g;ven by way of example only.
The alumina for the intended composition may be intorudced in the
form of bauxite or calcined alumina obtained from the Bayer process or
surplus abrasive grits con~aining a substantial quantity of alumina.
Bauxite used in the abrasive industry in addition to alumina usually
contains from about 3 to about 4.5 weight percent titanial from about
3 to about 8 weight percent silica, and from about 3 to about 10 weight
percent iron oxide (Fe203).
The bauxite may be synthetic bauxite, unpurified calcined bauxite
or only partially puri~ied bauxite, i.e. alumina made by the fusion and
reduction of calcined bauxite with metallic iron and carbon. When
unpurified calcined bauxite is used directly, iron and carbon should be
incorporated into the bauxite-zirconia fusion to remove iron oxide and
as much silica as possible titania may also be reduced to too low a
level in this system and further additions of titania may be necessary
to adjust the final analysis.
Synthetic bauxite is produced by combin;ng or mixing pure alumina
with desirable impurities such as titania which is then used in place
of the natural bauxite.
Pure alumina used herein may be surplus abrasive grits high in
alumina or calcined alumina obtained from the Bayer process. The
latter has two forms which differ in soda content: low soda calcined
:
,
.: :
,
$~39~
-- 8 --
alumina containing 0.1% or less Na20 by weight and normal calcined
alumina containing 0.5-0.3% Na20 by weight.
The zirconia required by the composition is preferably provided
in the form of Baddelyite ore which usually contains from:-
about 95 to 99 weight percent zirconia
about 0.3 to about 3 weight percent silica
about 0.5 to about 2 weight percent titania
about 0.5 to about 2 weight percent iron oxide.
Any hafnia present is inclusive in the weight percent figure
quoted for zirconia.
When compared with bauxite, ~he Baddelyite ore is found to
contain lower percentages of sil;ca, titania and iron oxide than
unpurified bauxite.
The zirconia may alternatively be provided by zirconia bubbles
made by smelting zircon ore or purified zirconia.
The titanium required by the composition which is not provided
by the residues obtained from the other starting materials is supplied
typically by commercially available grades of rutile which contain at
least 90% titan;a and preferably in excess of 95% titan;a.
The requisite proportions of the major starting materials are
usually pre blended with the necessary additions of carbon, usually
in the form of petroleum coke or graphite, and iron. The appropriate
quantities of oarbon and iron where the latter is required, can be
readily calculated by those skilled in the art. Should the level
of titanium fall below the required level during the fusion, additional
titania may be added as necessary during the fusion to readjust the
level to that required in the final product.
In the preferred embodiment the residual impurities in the
final composition irrespective of starting matPrials or fusion
technique employed should be kept to below the ~ollowing llmits:
silica below 1.5 weight percent9 preferably below 1.0 weight percent
and ideally below O.S weight percent; combined alkali (Na20) and
alkaline earths (CaO and MgO), prefera~ly below 1.0 weight percent
and ideally below Q.5 weight percent, of which soda should comprise
less ~han 0.1 weight percent.
3~
Fusion of the selected and preblended mixture of starting
materials is normally carried out in a carbon arc furnace at a
temperature normally in excess of 1800C.
When melted (fused), ref;ned and adjusted with respect to titania
where necessary~ the fused mixture is cast or poured ;nto a suitable
cool;ng vehicle wherein rapid cooling and solidification of the melt
takes place preferably within 1 minute desirably within 20 seconds
of the molten material contact;ng the cooling surfaces provided by
the cooling vehicle.
It is believed that any cooling me~hod or vehicle may be used
wherein the melted composition is cast or poured upon a heat sink
having high heat conductivity, i.e. preferably in excess of about
0.05 calories per second per square cen~imeter per cm per degree
centigrade at about 1200C, and wherein the maximum distance through
the cast or poured material to the nearest heat sink surface is
preferably less than about 2 and more preferably less than about 0.5
centimeters.
Heat sink materials, such as lumps of previously solidified
composition, which have lower conductiYities may be used provided
that the thickness of the cast or poured melted composition ~s
substantially smaller, e.g. in the case of lumps of previously
solidified material, less than 0.7 and preferably about 0.3 cm.
Suitable 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 also because of its low
cost and availability. Another example of commercially feasible
heat sink material is cast iron. Examples of further possible good
heat sink materials are chromium, nickel, 2irconium and their alloys,
although they may be too expensive for commercial use.
After solidification, the resulting composition is comminuted to
the desired grain size and grit shape. Such comminuting is achieved
using combinations of jaw crushing, impact crushing or roll crushing9
i.e. standard techniques to the industry.
The zirconia in the resulting abrasive has been usually found to
be between 10 to 40% in the tetragonal crystal form. Usually the
higher the residual silica level the lower the amount of the zirconia
obtained in the tetragonal crystal form.
lo - :
Overall the microstructure obtained consists of two parts-
1. primary alumina crystals which are embedded in,
2. a suppor~ing alumina-zirconia eutectic matrix.
The volume fraction of primary aluminaJcrystals ~s about 40% at
5 a zirconia content of 34 weight percent and about 52% by volume of
primary alumina crystals when the zirconia content is 27 weight
percent.
At the optimum eutectic compos;tion cited in U.S. Patent 3,891,408
there would be little or not primary alumina crystals present,
theoretically there would be none. At the upper limit of zirconia
cited in U.S. Patent 3,891,408 of 50% by weight zirconia9 the
abrasive will contain primary ~irconia crystals. The preferred embodi-
ment of U.S. Patent 3,891,408, thus produces a microstruGture which is
predominantly pure and which consists, as far as possible9 entirely of
eutectic cells or colonies.
The microstructure of the current invention thus differs in this
important respect in that it desirably contains about 40 to 52 volume
percent of primary alum;na crystals and must also additionally contain
from 1 to 10 weight percent of titania or a reduced form thereof.
The primary alumina crystals in the current invention vary in size
from about 5 to 50 microns and are predominantly finer than 30 ~icrons.
Often they exhibit a dendritic type of orientated structure in which
separation both between the dentrites and groups of dendrites occurs
by virtue of the presence of the eutectic matrix.
The zirconia in the matrix exists as rods or platelets inter-
spersed in an alumina rich background phase. The diameter of the
rods or thickness of the platelets is thought to be 200 4000 Angstroms.
Typically the inter rod spacing averages less than 3000 Angstroms with
appreciably finer spacings existing which often cannot be clearly
resolved by the scanning electron microscope.
The matrix consists of groups of rods or platelets of zirconia
having a high degree of orientation which divide the matrix between
the primary alumina crystals into a series of eutectic colonies or
domains. The size of the colonies or domains typically varies between
5 and 30 microns.
The important or vital t;tania phase or a reduced form thereof,
is thought to exist in soli~ solut;on with the primary alumina crystals,
~3~
-- 11
but it is considered that the maJor aMount exists at the inter-
face between the primary alumina crystals and eutectic matrix and
particularly at t~le interface between the eutectic colonies or
domains comprising the eutectic matrix in which the primary
S alumina crystals are embedded. The other residual impurities are
also thought to be located at these latter two sites where they
exist individually or in combination with each other or the major
phases present including the titania.
The invention will be further described by way of example
only with reference to the fol]owing Examples.
In the examples which follow the fol]owing fusion technique
and means of rapid solidification have been used.
Fusions were carried out using a 100 K.V.A. single phase
t`usion facility. This uses two 3" diameter graphite electrodes
adjustable between 4" to 10" spacing and also adjustable with
respect to height. Preblended mix Or the specific composition
to be examined is introduced into the case of the furnace and
fusion started by laying a graphite track between the electrodes
when spaced 4" apart.
Once the initial pool of molten material had been obtained
additional mix was pro~ressively added in increments and the
height and spacing of the electrodes ad~usted~ relative to the
melt, to maintain a current of 600 to 1000 amps at a voltage of
~5-90 volts.
~5 Furnacing was continued in this manner for about 30 to 40
minutes after which time the first casting was made. The
electrodes were lifted above the surface of the me]t and after
about 2 minutes delay the molten material was poured into a mold
containing 1" diameter steel balls or a rod mold having 1"
diameter steel rods with a 0~19" inter rod spacing.
The quantity of material produced by each casting was about
20 to 40 lbs and a number of castings were carried out for each
specific composition.
, ~
~ A -
The cast and solidified material produced by the above
procedure was cornminute~ to yield abrasive grits. Typically
the material was jaw crushed to yield about 8 grit and finer
product whic~l was then secondary roll crushed to yield a 16 grit
and finer stock material. After coarse rnagneting to remove free
iron contamination from the crushing equipment, the stock
material was accurately sieved into
~ j..
- 12 -
cross matched grit sizes for product manufacture and physical and
chemical analysis. This yielded 16 grit to 80 grit these being the
most popular sizes for subsequent grinding tests. Commercially a
complete grit si~e range would be produced.
EXAMPLE 1
A series of such fusions were carried out in the manner described
above. The starting material and mix compositions used are listed
in Table No. 1.
Table No. 1.
Starting Materials Low Soda Alumina Synthetic Bauxite
Compositions ~Wt.%) _ Compositions (Wt.%)
F35? F358 F359 F360 F361 F362 F363 F364
Low Soda Calcined 65.5 63.0 69.5 67.0 64.7 62.2 68.65 66.18
Alumina (+99% A1203)
Baddeleyite Ore
(98% ZrO2) 32 32 28 28 32 32 28 23
Rutile
(95% TiO2) 2.5 5.0 2.5 5.0 2.5 5.0 2.5 5.0
Silica (98% SiO2) ~ 0.6 0.58 0.64 0.62
Ferric Oxide
(87~ Fe203) - _ - - 0.2 0.19 0.21 0.20
100.0 100.0 _100.0 100.0 100.0 99.7 100.0 100.0_
Fine Graphite
addition 1.0 1.2 1.0 1.2 1.0 1.2 1.0 1.2
25 NOTE: The graphite additions appear excessive but this is not the
case since a large proportion is oxidized in the crust and
does not en~er the melt. The ~igures used are those found
to give satisfactory results and were empirically determined
on a trial and error basis. A much coarser source of carbon
would appreciably reduce the quantities required.
The mix compositions in Table No. 1 after fus~on, castin~ into a 1"
rod mold as previously described and when solidified crushed ~n the
~L163~
- 13 -
manner previously indicated gave the following % chemical analyses
listed in Table No. 2.
Table No. 2.
% ANALYSIS
5usion Number Zr2 A1203 TiO2 CaO Fe2~3 SiO2 Na20
F357 31.5 65.96 1.82 0.04 0.15 0.5 0.03
F358 31.2 65.07 3.35 0.01 0.05 0.3 0.02
F359 28.6 65.22 1.82 0.01 0.01 0.3 0.04
F360 29.0 65.15 3.26 0.04 0.01 0.5 0.04
F361 31.9 65.55 1.67 0.01 0.04 0.8 0.03
F362 32.0 63.73 3.28 0.04 0.01 0.9 0.04
F363 29.1 68.40 1.73 0.02 0.02 0.7 0.03
F364 29.0 66.77 3.26 0.03 0.02 0.9 0.02
EXAMPLE ?
Accurately matched grit splits in 36 grit of the compositions
specified in Example 1 and produced by the methods described previously
were incorporated into coated abrasive belts. A sample of conventional
brown fused alumina produced by the fusion and refining of bauxite
as manufactured by The Carborundum Co., Ltd., Manchester, England,
and in the quality designated G52E which is widely used in such
coated abrasive belts was also made into belts. The grit size of
the G52E was accurately cross matched to the experimental compositions
F357 to F364.
In order to eliminate variables regarding levels of dust on the
different grains and possible var;ations in their electrostatic
projection properties all grains were washed to remove the dust followed
by a surface ~reatment to guarantee standard surface electrical
conductivities.
The treated grains were then Plectrostatically projected onto a
flexible backing material across a projection gap of about 25 mm
using a l9KV DC projection voltage over a time period of about 20
seconds.
The flexible backing mater~al was a 4/1 sateen weave polyester
cloth approximately 103 x 40 threads per square inch, which had
previously been coated with a maker adhesive mix cons;sting of a
,
~14-
commercial one stage liquid phenolic resin with a phenol to
formaldehyde ratio of approximately 1:1.6 designated S363 as
manufactured by The Carborundum Co. Ltd., Manchester. The
resin also contained ground limestone of an average particle
size of approximately 17-25 microns. The proportion of resin
to ground lirnestone was 58 percent resin by weight and 42~
limestone by weight. Additionally the maker adhesive also
contained a wetting agent MANOXOL O.T. 9 a trademark
designating the compound sodi um di-octyl sulpho-succinates at a
level of 0.1 percent by weight. The maker adhesive had a
viscosity of approximately 8 poise at the coating temperature.
A typical make weight of 0.28 Kg/m was used for 36 grit.
The cloth with the adhering abrasive grit at a
concentration of approximately O.9Kg/m2 was then carefully
dried for 1 hour (min) at 75C, plus 3 hours minimum at
gOC .
A sizer co~a~t is then applied to the grain surface to
partially fill in the gap between the projected abrasive grits
to improve their adhesion and bond strengths. The sizer weight
used is approxin~ately 0.65Kg/m2. The composition of the
sizer is basically the same as the maker adhesive but has 1-1/2
percent addition by weight of the thixotropic agent PYROGENE, a
trademark for Kieselsaure. This prevents the sizer coat from
"running" during the final drying and curing.
A typical cure after sizing is a minimum of 1 hour at
75C and minimum 3 hours at 90C and a minimum 1 hour at
96C and a minimum 1 hour at 100C and minimum 12 to 14
hours at 107C.
After curing the product is placed in a humid
atmosphere of +95 percent RH for 24 hours minimum. After which
time the product is flexed in three directions at 45 to
facilitate easy handling during the manufacture in the form of
belts. Abrasive belts 82" x 2" wide are made from the coated
abrasive material by the usual techniques.
A series of belts incorporating the experimental
abrasives F357-F364 as listed in Table No. 2 and G52E
conventional fused alumina were prepared in this manner.
The belts produced were then evaluated on a
conventional heavy duty floor backstand belt tester using mild
steel workpieces in the form of rolled 3/4" x 3/4" x 1/8" angle
cross section by about 48" long. In the test the belt is
placed on the backstand in the normal manner and the workpiece
so positioned so that the 3/4" x 3/4" x 1/8" section engases
the belt just below the horizontal diameter of the contact
wheel.
The abrasive belt is driven at 4500 surface feet per minute
over a contact wheel of 14 inches in diameter. 16 lbs dead weight
infeed force is applied to the workpiece and 50 contacts of 2.25
seconds duration with a 10 second interval between each of the
50 contacts comprises a grinding cycle. The amount of metal removed
(i.e. ground) in each grinding cycle ;s measured and testing is
continued unt;l the metal removed ;n a cycle fa11s to below 66 gms.
The total we;ght of material removed by the belt and the total
weight lost by the belt thus def;ne the relative performance
ability of each belt when tested in this manner.
The abrasive belts gave the following results listed in
Table No. 3.
Table No. 3.
Abrasive 1st Test Series 2nd Test Series
Metal Belt Metal Belt -
Removed Loss Removed boss
(gms) (gms) (gms) (gms)
F357 1888 12 1292 9.0
F358 1265 10 1189 10.0
F359 1470 11 1279 10.0
F360 1848 13 Not Tested~
F361 1408 12 1154 10.0
F362 1768 19 1361 11.5
F363 1462 12 1119 11.0
F364 Not Tested------- 1267 12.0
G52E (conventional
A1203) 571 9 415 8
The large performance advantage of the abrasives of the current
invention over conventional fused alumina is clearly apparent.
Improvements of 100 to 230% are being obta;ned. The difference between
the two series was due to the different contact times used. Each
gr;nding cycle of the 1st test series was 50 con~acts of 2.25 seconds
whereas each grinding cycle of the 2nd series was 50 contacts of 2
seconds duration.
3~
~16-
EXAMPLE 3
The test data produced for belts is obtained in what
the "industry" refers to as a low cut frequency operation,
i.e., the number of times each cutting point makes contact with
the workpiece per second is comparatively low. Cut frequency
for belts depending on the land to groove ratio of contact
wheels used is typically 1 to 10 per second. In order to
assess the merits of the novel abrasive compositions in high
cut frequency coated abrasive applications tests were also
carried out in which the abrasives were incorporated into 7"
diameter coated abrasive discs. Here the cut frequency per
grit can be as high as 100 per second.
Essentially the same procedures were carried out as
detailed in Example 2, except that the abrasive grits were
projected onto a heavy duty fiber backing material.
The maker coat for discs was a commercial one stage
liquid phenolic resin with phenol to formaldehyde ratio of
1:1.55, designated CL32 as manufactured by The Carborundum Co.
Ltd. at Manchester. A 15 percent by weîght of "Ethane Diol" is
added to the CL32 and also crushed limestone in the ratio of 9
parts by weight Calcium Carbonate powder to 11 parts by weight
of CL32. Wetting agent MANOXOL "OT" and water are added to
give a coating viscosity of 17 poise. The make weight used is
0.53 Kg/m . The grain weight projected electrostatically
onto the maker coat is 1.4 Kg/m2. (Depending on the specific
gravity the grain weight is modified to a constant volume
basis.)
The projection voltage of 19 KV DC across a 25 mm gap
and time of 20 seconds are used.
The coated product at this stage is dried for a
minimum of 3 hours at 90C.
A sizer coat is then applied which comprises 35 parts
by weight of a one stage commercial liquid phenolic resin with
a phenol to formaldehyde ratio of 1 to 1.6, designated CL151
and manufactured by the Carborundum Co. Ltd., Manchester; 65
parts by weight of cryolite filler; and in addition 2-1/2 parts
by weight of Denox, a trademark for iron oxide-pigment grade,
and 0.1 parts MANOXOL "OT" wetting agent. The si~er weight
used is about 0.69 Kg/m2.
~ . .. ~
~ .
~6~
- 17 -
The product is dried and cured for a minimum of 4 hours at
90C plus 14-16 hours at 107C, followed by humidification at
+95% relative humidity for 24 hours and ball flexed in the stanclard
manner used in the industry. 7" diameter discs were stamped out
of the coated abrasive product in the normaJl manner.
Accurately cross matched grit splits in 36 grit of the abrasive
compositions listed in Table No. 1 and also conventional fused alumina
designated G52E as indicated in Example 2, were incorporated into 7"
diameter coated abrasive discs in the manner described.
The discs produced were mounted on an alum;nium alloy back up
pad which was faced with 1/16-1/8" thick insertion rubber. The
disc was so arranged as to contact the end of a 8" diameter mild steel
tube having a 1/4" wall thickness and initial length of 10 inches.
The workpiece is angled vertically about 2-3 from horizontal and
in the horizontal plane about 1 to 2 from normal. The workpiece
rotates at 70 surface feet per minute and the disc at a peripheral
velocity of 10,000 sur~ace feet per minute. The disc is applied to the
workpiece under a dead weight force of 50 pounds.
The disc grinds the workpiece for a contact period o~ 15 seconds
after which time the workp;ece is removed, weighed9 watercooled and
dried. Repeated con~acts to this pattern are carried out until the
quantity of metal removed in a 15 second contact falls below 20 gms.
at which time the total metal removed and total disc loss are taken
as the measure of the abrasive's performance. Tests carried out in
this manner on the F357-364 series and standard alumina G52E gave the
following results listed in Table No. 4.
Table No. 4.
Abrasive Metal Disc
Removed Loss
(~ms) (~ms)
F357~ 1004 2.73
F358 Low Soda Alumina 918 2.88
F359 1071 2.80
F360 1171 4.05
F361 637 1.93
F362 735 2.68
F363 Synthetic Bauxite 660 2.17
F364 810 2.60
G52E (Standard Fused A1203) 537 2.20
,
.
- 18
The abrasives of the current invent;on are aga;n shown to be
superior to conventional standard fused alumina G52E. Improvements
up to 118% are obtained.
EXAMPLE 4
To compare the performance of abrasives of the current invention
in bonded products two further fusions were carried out as described
previously using the following mix compos;tions given in Table 5.
Table No. 5.
Mix Composition Fusion Numbers
F365 F366
Synthetic ) Low Soda
) Alumina A1203 66.7% Wt. 64.2% Wt.
Bauxite )Rutile 2.5 5.0
Compositions)
)Silica 0.6 0.6
)Ferric Oxide 0.2 0.2
Baddelyite 30.0 30.0
100.0 100.0
Fine Graphite 1~0% 1.2%
The analyses of the finished abrasive grits are listed in
Table 6.
Table No. 6.
F365 F366
A1203 68.72 Wt.% 65.25 Wt.%
zro2 28.60 30.20
TiO2 1.76 3.24
CaO 0.04 0.02
Fe203 0.14 0.24
SiO2 ~.76 1.08
Na20 ~ 0.10 ~ 0.10
(Gain on Ignition 0.29% 0.35%
~tlOOs and finer 1300C for 2 hours)
Specific Gravity 4.42 gm/cc 4.47 gm/cc
- 19 -
The abrasive grits produced were accurately cross matched for
shape and size distribution to a conventional fused brown alumina
abrasive obtained by the fusion of bauxite which is widely used in
bonded abrasive products and which is designated E.D.R.
Wheel Formulations
Grit splits used in the test wheels were:-
64.0% - 24 t 2~ Mesh
36.0% - 28 + 32 Mesh
The bonded abrasive mix formulations used were:
EDR F365 F366
Abrasive 76.02 Wt.% 78.02 Wt.% 78.20 Wt.%
Bonded Blend 22 17.10 15.68 15.54
CS 303 1.71 1.57 1.55
CL50 5.17 4.74 4.70
15 NOTE: The different weight percentages are the adjustments made
to allow for the difference specific gravities of F365 and
F366 compared to that of EDR (which is 3.95 gms/cc). These
ensure that the volume of abras;ve to bonding phase is kept
constant.
The bond blend consists of a fine powdered mixture of CS222 resin
at 36.9 wt. percent and 63.1% of a combination of whiting and potassium
aluminium flouride fillers.
The CL50 is a one stage liquid phenolic resole having a phenol
formaldehyde ratio of 1:1.2. The CS303 is a powdered phenolic novolac
having a phenol formaldehyde ratio of l O.9S. The CS222 is a powdered
phenolic novolac having a phenol formaldehyde ra~io of 1:0.71.
The mix procedurP is to wet up the grain using the CL50 and then
to add to the bond blend 22 to build up the bond coating on the wetted
grain. Add the CS303 as a dusting powder to complete the mix and
give a free flowing mix ready for molding.
Wheels
The above mixes were used to make type 27 depressed center wheels
of 7" diameter and 1/4" thickness containing one internal reinforcing
woven glass fabric located at the center and one external back face
3~ reinforcing woven glass fabric. The wheels were molded in the
conventional manner to give pressed wheel densities of:-
4~
- 20 -
EDR F365 F366
Hard Grade 39.5 gm/in3 43.07 gm/in 43.45 gm/in
Soft Grade 38.0 41.57 41.95
The variations in molding density aga;n-~re to allow for basic
differences in abrasive specific grav;ties, i.e. volume of abrasive
to bond in the pressed wheels are ;dentical for a specific grade.
The wheels are clamped together in stacks using metal spacers
shaped to the geometry of ~he wheels and are cured in this state.
The cure cycle is approximately 27 hours up to 355F and a soak at 355F
for 10 hours. The cured wheels are edged accurately to 7" diameter
and checked for cured density prior to testing.
The type 27 depressed center wheels of 7" diameter were tested
on a machine designed specifically for evaluating this type of
product.
The wheel is mounted in the machine which rotates the wheel at
6,000 r.p.m. The mild steel workpiece in the form of ~" x 4" x 1/4"
thick plate is clamped beneath the wheel such that the wheel traverses
backwards and forwards along the 1/4" x 8" edge. The test wheel
under a dead weight force of 13 lbs is presented to the workpiece at
an angle typical of that used in "off-hand" grinding. There is a
"rocking motion" imparted to the test piece which simulates the tilting
movement used by an operator using a portable grinder. This "rocking
motion" traverses the workpiece under the wheel at a rate of about
30ft per minute.
The test involves measuring the metal removed and wheel loss
incurred during 2 minutes contacts of wheel and metal. The test is
continued until the metal removal obtained falls below 30 gms for a
2 minute contact. The data generated expresses $he relative
performance of the abrasives tested in terms of average metal removal
rate, grinding ratio and quality factor. The grinding ratio is the
total metal removed divided by the equivalent weight loss of the wheel.
To allow for differences ;n wheel density due to abrasive specific
gravity differences all wheel losses are standardized to the volume
equivalent of standard fused alumina wheels (i.e. equivalent weight
loss).
The results obtained for F365 and F366~ and standard EDR fused
alumina are given in Table No. 7.
6;;~
Table No. 7.
Abrasive Wheel Average G.R. Q.F.
Grade Metal Removal (MRR x GR)
Rate (gm/m;n)
S EDR (STD Fused Soft 24.97 13.64 341
Alum;na) Hard 24.66 13.05 322
F365 Soft 27.87 16.74 467
Hard 27.64 20.64 571
F366 Soft 27.65 20.07 555
Hard 27.38 27.10 742
The data clearly shows the superior performance of the current
abrasives over standard fused alumina in a bonded abrasive product.
It also clearly indicates the improvement made by increasing the titania
content from 1.76% in F365 to 3.24X in F366. Performance as indicated
by QF have been obtained with F366 which are up to 130% superior to
standard fused alumina.
The above Examples have clearly demonstrated the superior low to
intermediate pressure performance of abrasives of the current invention
when incorporated into coated and bonded abrasive products and when
compared to similar products containing conventional fused aluminas
under a variety of conditions. The abrasives of the current invention
gave up to 230% improvements in coated products and in excess of 100%
in bonded products.
In order to give an indication of the performance of alumina
~irconia eutectic abrasives containing 40 43% by weight zirconia and
produced according to U.S. Patent 39891,408 to Rowse and Watson,
performance of a commercially available alumina zirconia eutectic
abrasive was compared with conventional fused alumina.
EXAMPLE 5
When the commercially available eutectic abrasive was cross
matched for grit size and shape and incorporated into ooated abrasive
belts as produced in Example 2 and tested as in that Example 4 gave
the results listed in Table No. 8.
~63~435~
.
- 22 -
Table No. 8.
1st Test Series 2nd Test Series
Abrasive Metal Belt Metal Belt
Removal Loss ' Removal Loss
(gms) (gms) (gms~ (gms)
Commercial Eutectic
(40-43% ZrO2) 1699 8 1236 10
Standard G52E
Conventional Fused
Alumina 571 9 415 8
The performance of the eutectic abrasive was about 200% superior
to conventional fused alumina.
NOTE: 1st test series used 50 contacts of 2.25 seconds/cycle
2nd test series used 50 contacts of 2.0 seconds/cycle
EXAMPLE 6
When the commercially available alumina zirconia eutectic abrasive
was cross matched for grit size and shape and incorporated into coated
abrasive discs as produced in Example 3 and when tested as described
in that Example 7 the results listed in Table No. 9 were obtained.
Table No. 9.
Abrasive Metal Removed Disc Loss
(gms~ (gms)
Commercial Alumina 984 2.75
Zirconia Eutectic
G52E Standard Fused 537 2.20
Alumina
The commercial eutectic abrasive gave an 83% improv ment when
compared with standard fused alumina.
EXAMPLE 7
When the commercial alumina zirconia eutectic abrasive was cross
matched for grit size and shape and incorporated in type 27 depressed
center wheels as produced in Example 4 and when tested as described in
that Example the results listed in Table 10 were obtained. (The
specific gravity of the eutectic abrasive was accounted for in terms of
mix formulations and pressed wheel densities.)
~,~6~4~
- 23 -
Table No. 10.
Abrasive Wheel Average G.R. Q.F.
GradeMetal Removal
Rate (gm/mi
Commercial Alumina
Zirconia Eutectic Soft 28.15 21.14 595
Hard 23.70 32.19 763
Std. Fused Alumina
E.D.R. Soft 24.97 13.64 341
Hard 24.66 13.05 322
The eutectic abrasive's performance is 74 to 137% superior to
standard fused alumina.
The performance advantage over standard fused alumina of the
commercially available alumina zirconia abrasive, embodying the maior
claims and teachings of U.S. Patent 3~891,408 are similars equal or
in certain instances inferior to those of the current invention. The
novel and unexpected feature of the current invention was that it is
produced outside the compositional limits and structural features
claimed to optimize low to moderate pressure performance of the
alumina zirconia system as cited in U.S. Patent 3,891,408. The ability
to achieve equivalent or superior performance is made possible by the
presence of the titania or reduced form thereof. The ability to reduce
the zirconia content and still maintain excellent performance can
reduce raw material costs significantly.
