U.S. patent number RE31,883 [Application Number 05/859,243] was granted by the patent office on 1985-05-14 for resinoid grinding wheels containing nickel-coated cubic boron nitride particles.
This patent grant is currently assigned to General Electric Company. Invention is credited to William A. Berecki, Harold P. Bovenkerk.
United States Patent |
RE31,883 |
Bovenkerk , et al. |
May 14, 1985 |
Resinoid grinding wheels containing nickel-coated cubic boron
nitride particles
Abstract
An improved resinoid grinding wheel particularly useful for the
wet or dry grinding of hardened steels and steel alloys utilizes
nickel-coated cubic boron nitride particles as the abrasive
medium.
Inventors: |
Bovenkerk; Harold P.
(Worthington, OH), Berecki; William A. (Columbus, OH) |
Assignee: |
General Electric Company
(Worthington, OH)
|
Family
ID: |
27127511 |
Appl.
No.: |
05/859,243 |
Filed: |
December 9, 1977 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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Reissue of: |
885630 |
Dec 16, 1969 |
03645706 |
Feb 29, 1972 |
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Current U.S.
Class: |
51/295; 51/298;
51/309 |
Current CPC
Class: |
B24D
3/00 (20130101); B24D 3/28 (20130101); C09K
3/1445 (20130101); B24D 18/0009 (20130101); B24D
18/00 (20130101) |
Current International
Class: |
B24D
3/20 (20060101); B24D 18/00 (20060101); B24D
3/28 (20060101); B24D 3/00 (20060101); C09K
3/14 (20060101); B24D 017/00 () |
Field of
Search: |
;51/295,298,309,307 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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698428 |
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Nov 1967 |
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BE |
|
724829 |
|
Feb 1969 |
|
BE |
|
Primary Examiner: Derrington; James
Attorney, Agent or Firm: Morgan, Finnegan, Pine, Foley &
Lee
Claims
What we claim as new and desire to secure by Letters Patent of the
United States is:
1. In a grinding wheel for hardened steel and steel alloys, an
abrasive surface consisting of nickel-coated cubic boron nitride
particles, the nickel constituting from 30 to 80 weight percent of
the coated particles, said coated particles being embedded in a
matrix of resinous material selected from the group consisting of
phenol-formaldehyde, urea-formaldehyde, melamine-formaldehyde,
epoxy, polyester, polyamide and polyimide resins, and mixtures
thereof.Iadd., said wheel being formed in a mold by pressing to a
stop.Iaddend..
2. A grinding wheel as claimed in claim 1 wherein the resinous
material is phenol formaldehyde.
3. A grinding wheel as claimed in claim 1 wherein the resinous
material is a polyimide.
4. A method of making an abrasive wheel for hardened steel and
steel alloys comprising applying a coating of nickel to a quantity
of cubic boron nitride particles, the nickel constituting about 30
to 80 weight percent of the coated particles, mixing said coated
particles with resinous material, selected from the group
consisting of phenol-formaldehyde, urea-formaldehyde,
melamine-formaldehyde, epoxy, polyester, polyamide and polyimide
resins, and mixtures thereof and forming the coated cubic boron
nitride resinous material mixture as the abrasive surface of a
grinding wheel .Iadd.in a mold by pressing to a stop.Iaddend..
5. A .Iadd.method of making an abrasive .Iaddend.grinding wheel as
claimed in claim 4 wherein the resinous material is phenol
formaldehyde.
6. A .Iadd.method of making an abrasive .Iaddend.grinding wheel as
claimed in claim 4 wherein the resinous material is a polyimide
.Iadd.and said pressing to a stop step is carried out at 5000
p.s.i..Iaddend.. .Iadd.7. A method of grinding hardened steel and
steel alloys comprising the steps of: providing an abrasive
grinding wheel whose surface comprises nickel-coated cubic boron
nitride particles, the nickel constituting about 30 to 80 weight
percent of the coated particle, in a matrix of resinous material
selected from the group consisting of phenol-formaldehyde,
urea-formaldehyde, melamine-formaldehyde, epoxy, polyester,
polyamide and polyimide resins, and mixtures thereof, said wheel
being formed in a mold by pressing to a stop; providing a hardened
steel or steel alloy workpiece; rotating said grinding wheel; and
contacting said workpiece with said rotating abrasive surface,
whereby said surface abrades said workpiece..Iaddend. .Iadd.8. The
method of claim 7, wherein said resinous material is phenol
formaldehyde..Iaddend. .Iadd.9. The method of claim 7, wherein said
resinous material is a polyimide..Iaddend.
Description
BACKGROUND OF THE INVENTION
Boron nitride is a compound which comes in a "soft" form and in two
"hard" forms. In the "soft" form it is a material which
crystallizes in the hexagonal system and cleaves readily in a
manner similar to graphite and molybdenum disulfide. Like these
materials it is a good dry lubricant.
If boron nitride is subjected to ultrahigh pressures and elevated
temperatures, it is converted to a cubic crystal similar to the
crystal of zincblende to produce one of its "hard" forms. The
preparation of this form of boron nitride is disclosed and claimed
in Wentorf U.S. Pat. No. 2,947,617 which is assigned to the same
assignee as the present invention.
If "soft" boron nitride is subjected to pressures of at least about
113 kilobars preferably at a temperature somewhat higher than room
temperature, it is converted to a densely packed form of "hard"
boron nitride possessing the same hexagonal crystal structure as
the mineral wurtzite. This form of "hard" boron nitride is
disclosed and claimed in Bundy et al. U.S. Pat. No. 3,212,851 which
also is assigned to the same assignee as the present invention.
The zincblende form of boron nitride was discovered some years
before the wurtzite form. Both the zincblende and wurtzite forms
are useful in the practice of this invention and it is intended
that the wurtzite form be included in the term "cubic boron
nitride".
The discovery of cubic boron nitride occurred several years after
the discovery of a reproducible synthesis for diamond. Initially it
was thought that cubic boron nitride was as hard as diamond but
additional investigations revealed that cubic boron nitride is a
close second to diamond in hardness. Both are considerably harder
than other abrasive materials.
Synthetic diamond became commercially available as an abrasive in
1957. It was early established that the abrasive qualities of
synthetic diamond were superior to those of natural diamond. The
disparity in favor of synthetic has steadily increased as processes
for tailoring the product to specific applications have been
developed.
From the inception of its commercialization, synthetic diamond has
been a growing industry. Its use in a resin-bonded wheel for
grinding tungsten carbides has brought about great economies in the
finishing of carbide tools. Its use in a metal bond has resulted in
saws which bring about great improvement in the cutting of natural
stones and ceramics.
When cubic boron nitride was first discovered, it was thought that
it would have widespread usage due to its hardness and other
properties. For instance, cubic boron nitride can withstand
temperatures of 2,500.degree. F. whereas diamond begins to burn at
1,600.degree. F. Nevertheless, cubic boron nitride proved to be
inferior to diamond as an abrasive for tungsten carbides, ceramics,
and natural stones. It offered advantages over diamond in the
cutting of hardened steels and steel alloys but neither diamond nor
cubic boron nitride was competitive with such abrasives as aluminum
oxide for hardened steels and steel alloys. Thus, although cubic
boron nitride is 21/2 times as hard as aluminum oxide, its cost per
gram would inherently be about the same as the cost per kilogram of
aluminum oxide. Even though other cost factors such as labor, wheel
dressing, etc., favored cubic boron nitride, the disparity in
material cost was too great for cubic boron nitride to compete in
the aluminum oxide market.
In 1967, metal-coated diamond was introduced to the market for use
in resinoid grinding wheels. Typically, the use of metal-coated
diamond extended the effectiveness of grinding wheels by a factor
of two. Such wheels are described in Lindstrom and Lundblad South
African Pat. No. 66/5310 advertised on Mar. 8, 1967 and assigned to
Allmanna Svenska Elektriska Aktiebolaget. Another document
describing metal-coated diamond resinoid wheels is Sacco South
African Pat. No. 67/2576 of the Norton Company.
The Sacco patent pointed out that it had been known to coat
aluminum oxide abrasive grains with nickel to achieve improved
bonding of abrasive particles in a resinoid wheel. In addition, the
patent postulated that the greater heat conductivity of heat
capacity of diamond coated with metal prevented rapid deterioration
of the resin matrix in the vicinity of the abrasive grit thereby
allowing for longer retention of the abrasive grit in the resin
matrix.
The Sacco patent gave examples of five resinoid wheels using
diamond abrasives coated with various metals. The improvement in
grinding ratio versus wheels made with uncoated diamond varied from
37 percent to 280 percent. Thus, the most-improved wheels removed
3.8 times as much material from workpieces as did wheels made with
uncoated diamond from similar workpieces. These levels of
improvement are typical of what has been achieved by metal-coated
diamond.
SUMMARY OF THE INVENTION
In accordance with the present invention it has been discovered
that a resinoid grinding wheel employing abrasive particles of
cubic boron nitride coated with nickel to the extent of 30 to 80
weight percent of the coated particles is much more effective than
a similar wheel in which the particles are uncoated.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The resinoid grinding wheel of the present invention is
characterized by the use of nickel-coated cubic boron nitride
particles as the abrasive medium. The use of such abrasive
particles does not necessitate other alterations in wheel structure
and so the resinoid wheel may otherwise be of conventional
construction. This statement is not intended to mean that
nickel-coated cubic boron nitride wheels do not give improved
performance with certain resins or with particular methods of
fabrication.
In a typical preparation of a resin-bonded nickel-coated cubic
boron nitride grinding wheel, a mixture of granulated resin,
nickel-coated cubic boron nitride particles and filler is placed in
a grinding wheel mold, a molding pressure appropriate to the
particular resin--usually of the order of several thousand pounds
per square inch--is applied and the mold is heated to a temperature
sufficient to make the resin granules deform plastically and to
cure in cases where the resin used is heat-curable.
The resin most frequently used in resin-bonded grinding wheels is a
phenol-formaldehyde reaction product. However, other resins or
organic polymers may be used such as melamine or urea-formaldehyde
resins, epoxy resins, polyesters, polyamides, and polyimides.
Polyimides in particular have shown promising results. Typically,
the abrasive surface of nickel-coated cubic boron nitride grinding
wheels will contain about 25 percent by volume of abrasive.
There is no novel technology involved in applying a nickel coating
to the cubic boron nitride particles nor is the size of the
particles critical to the success of the invention. It is desirable
that the entire surface of particles be coated and that the weight
of the coating be 30 to 80 percent of the combined weight of the
particle and coating. Generally, the particle size will range from
60 mesh to 325 mesh but larger or smaller particles may be used to
advantage depending upon service requirements.
Typical processes for applying a nickel coating to cubic boron
nitride particles are by electroless deposition, well known in the
art, but sputtering as disclosed and claimed in Vanderslice U.S.
Pat. No. 3,351,543, which is assigned to the same assignee as the
present invention, or by high vacuum deposition from a filament
composed of nickel. In the latter case, it is necessary to agitate
the cubic boron nitride particles in order to insure a nickel
coating on all surfaces. After a thin film of nickel has been
applied by one process, the film may be built up by another process
such as conventional electrolytic deposition from an electrolyte
solution. It is not necessary that the nickel have an extremely
tenacious bond with the cubic boron nitride substrate.
The following is a typical procedure for formulating a resin-bonded
cubic boron nitride grinding wheel:
1. Weight out the material as follows: 40 volume percent
nickel-coated cubic boron nitride using density of 5.29 g./cc.; 39
volume percent phenolic resin using a density of 1.28 g./cc. (The
phenolic resin powder is preferably less than 100 mesh). 21 volume
percent filler composed of silicon carbide approximately 20 microns
in size using 3.22 g./cc. as the density.
2. Premix or blend in a mortar and pestle the resin and filler
until homogeneous. Mix cubic boron nitride with 1 percent of a
wetting agent which is typically furfural. Combine cubic boron
nitride, furfural and resin filler mixture and lightly mix with
mortar and pestle until homogeneous.
3. Load mixture into mold cavity, hot press on heated platen press
at 350.degree. F. and 10,000 p.s.i. for 30 minutes. The molding
process is typically done to a stop rather than at constant
pressure using the amount of mixture to completely fill the cavity
based on the above density calculation.
4. Cool mold and strip rim and hub from mold cavity. Post-cure
phenolic at 375.degree. F. Raise temperature at the rate of
25.degree. per hour. Hold 375.degree. F. for 12 hours. Cool at the
rate of 25.degree. per hour. Total time: 36 hours.
As those skilled in the art are aware, formulations and treatments
may be varied widely to meet specific service requirements. For
example, when a polyimide resin is substituted for the phenolic
resin, the mold pressure is reduced to about 5,000 pounds per
square inch, the molding temperature is about 500.degree. F., the
time in the mold is 10-15 minutes, and the postmold treatment is
about 21/2 hours at about 475.degree. F. Accordingly, the
procedures outlined above are given for purposes of illustration
only and should not be considered as limiting the invention.
Resin-bonded nickel-coated cubic boron nitride wheels have
performed wet and dry grinding of Type A2 steel, which is commonly
used for dies, high speed cutting tool steels, etc.; Type T-15
steel which has a high tungsten content; and Type M-2 steel which
has molybdenum as the principal alloying ingredient. Table I below
gives performance figures for an M-2 steel comparing nickel-coated
cubic boron nitride wheels with uncoated cubic boron nitride
wheels. The term "grinding ratio" is the unit volume of work
material removed per unit volume of wheel wear.
TABLE I ______________________________________ WET SURFACE GRINDING
Percent Coating Performance Level Down- Improvement (Weight feed
Grind- Over Similar Borazon Mesh % Per ing Uncoated Wheel No. Size
Nickel) Pass Ratio Wheel ______________________________________
ASD-177 80/100 0 .001 273 -- ASD-175 80/100 59.6 .001 891
.[.226.]..Iadd. 227.Iaddend. ASD-177 80/100 0 .002 29 -- ASD-175
80/100 59.6 .002 367 1165 B1A1-5-170 140/170 0 .001 109 -- ASD-182
140/170 64.6 .001 655 .[.502.]..Iadd. 501.Iaddend. B1Al-5-170
140/170 0 .002 15 -- ASD-182 140/170 64.6 .002 139 .[.828.]..Iadd.
827.Iaddend. ______________________________________
It will be noted from Table 1 that the minimum improvement brought
about by applying a coating of nickel to the cubic boron nitride
particles was .[.226.]. .Iadd.227 .Iaddend.percent. Even more
spectacular is the relative performance improvement gained with
nickel-coated cubic boron nitride where the material removal rate
is doubled by increasing the downfeed from 0.001 to 0.002 inch. At
the increased material removed rate conditions the grinding ratio
achieved with the coated versus uncoated abrasive is .[.365.].
.Iadd.367 .Iaddend.and 29, respectively. In this case, the
performance improvement is 1,165 percent. In fact, the grinding
ratio achieved at 0.002 inch downfeed with the coated cubic boron
nitride abrasive is considerably higher than that of the uncoated
cubic boron nitride abrasive at 0.001 inch downfeed. Thus, the
wheel wear of coated cubic boron nitride at double the material
removal rate is less than the wheel wear of uncoated cubic boron
nitride at half that material removal rate.
Table II below gives comparative test results on four additional
samples of M-2 steel having a Rockwell C hardness of 60 and also
four samples of A-2 steel having a Rockwell C hardness of 61:
TABLE II ______________________________________ WET SURFACE
GRINDING Coating Level Down- (% feed Grind- Percent of Borazon
Wheel Ma- Weight Per ing Performance and Mesh Size terial Nickel)
Pass Ratio Improvement ______________________________________
R5090, 100/120 M-2 0 .001" 160 -- R5091, 100/120 M-2 60 .001" 593
.[.270.]..Iadd. 271.Iaddend. R5090, 100/120 M-2 0 .002" 16 --
R5091, 100/120 M-2 60 .002" 340 .[.2010.]..Iadd. 2,025.Iaddend.
R5090, 100/120 A-2 0 .001" 25 -- R5091, 100/120 A-2 60 .001" 175
600 R5090, 100/120 A-2 0 .002" 12 -- R5091, 100/120 A-2 60 .002"
35* .[.190.]..Iadd. 192.Iaddend.
______________________________________ *Wheel R5091 was nearly
consumed by the time this test was begun and only one test point
could be run at .002" downfeed on A2 material. Consequently, the
grinding ratio attained is at best questionable and is included
only to show that an improvement over uncoated cubic baron nitride
was attained even with a wheel having an extremely thin layer of
abrasive remaining.
Table II shows that the performance improvement obtainable on M-2
steel is maintained on A-2 steel.
Table III below gives comparative performance figures covering the
dry grinding of samples of M-2 steel having a Rockwell C hardness
of 64 and T-15 steel having a Rockwell C hardness of 65:
TABLE III ______________________________________ DRY GRINDING
Coating Percent Level Performance (% Improvement Borazon Nickel
Infeed/ Grind- Over Similar Wheel and by Ma- Double- ing Uncoated
Mesh Size Weight terial pass Ratio Wheel
______________________________________ FC911, 60/80 0 M-2 .001" 126
-- FC928, 60/80 60 M-2 .001" 1849 .[.1370.]..Iadd. 1,367.Iaddend.
FC911, 60/80 0 M-2 .002" 19 -- FC928, 60/80 60 M-2 .002" 310
.[.1530 .]..Iadd. 1,532.Iaddend. FC911, 60/80 0 T-15 .001" 51 --
FC928, 60/80 60 T-15 .001" 145 .[.165.]..Iadd. 184.Iaddend. FC911,
60/80 0 T-15 .002" 60 -- FC928, 60/80 60 T-15 .002" 62 3
______________________________________
The results for M-2 steel shown in Table III further substantiate
the exceptional increase in performance attained by the use of
nickel-coated cubic boron nitride. In the case of T-15 steel, the
improvement was not so appreciable at an infeed of 0.001 inch and
at an infeed of 0.002 inch the grinding ratio was substantially the
same whether the nickel coating was or was not present. The T-15
results show that there are many factors which enter into
performance figures and the element of predictability is not very
high. In addition to such items as wheel diameter, wheel width,
wheel speed, etc., the feed rate and physical properties of the
workpiece play an important part in determining optimum grinding
conditions.
It was previously pointed out that cubic boron nitride is quite
inferior to diamond in cutting tungsten carbides. The reverse is
true, although not uniformly so, in the case of hardened steels and
steel alloys. Table IV below compares grinding ratios for aluminum
oxide, nickel-coated cubic boron nitride and nickel-coated diamond
on a number of hardened steels.
TABLE IV ______________________________________ WET SURFACE
GRINDING Percent Improvement Al.sub.2 O.sub.3 Nickel-Coated
Nickel-Coated Borazon Ma- Grinding Borazon Diamond Over terial
Ratio Grinding Ratio Grinding Ratio Diamond
______________________________________ M-2 4.5 1030 85
.[.1100.]..Iadd. 1,112.Iaddend. M-4 2.0 180 95 .[.90.]..Iadd.
89.Iaddend. T-15 .8 120 100 20 0-1 50 750 135 455 A-2 20 390 210 86
W-1 40 420 270 55 D-2 3.0 650 1000 -35
______________________________________
In Table IV, the M-4 material is a molybdenum alloy steel differing
from the M-2 material in having a higher carbon content and a
vanadium content of 4 percent instead of 2 percent.Iadd., tungsten
content of 5.5 percent versus 6.00 percent and molybdenum content
of 4.5 percent versus 5.00 percent .Iaddend..The O-1 material is a
oil hardened cold work tool steel. The W-1 material is a water
hardened tool steel. The D-2 material is a high carbon, high
chromium type of cold work tool steel.
Table IV shows that nickel-coated cubic boron nitride is superior
to nickel-coated diamond on all except the D-2 steel. In the case
of M-2 and O-1 steels, the superiority of cubic boron nitride is
dramatic and surprising. The reasons for the wide variation in
performance are not clearly understood at the present time.
However, as previously stated, the physical and chemical properties
of the workpiece play a large role in wheel effectiveness.
Table IV also gives grinding ratios for aluminum oxide, the most
commonly used commercial abrasive for hardened steels and steel
alloys. The vast superiority of nickel-coated cubic boron nitride
over aluminum oxide emphasizes the importance of this invention in
enabling cubic boron nitride to be competitive with aluminum oxide
in spite of the great cost and price differential between the
two.
Table V below compares the dry grinding ability of nickel-coated
cubic boron nitride vs. nickel-coated diamond vs. aluminum oxide on
three alloy steels.
TABLE V ______________________________________ DRY SURFACE GRINDING
Nickel- coated cubic Nickel- Improvement boron coated Percent
nitride diamond Al.sub.2 O.sub.3 nitride grinding grinding grinding
over diamond Material ratio ratio ratio and Al.sub.2 O.sub.3
______________________________________ M-2 1,200 10 10 11,900 M-42
900 10 10 8,900 T-15 500 10 10 4,900
______________________________________
The results listed in Table V are averaged and rounded off values
from a number of tests made under comparable conditions of
grinding. The M-42 material differed from the M-2 material in
having 1.5 percent tungsten vs. 6.00 percent of M-2; 9.5 percent
molybdenum vs. 5.00 percent for M-2; .Iadd.1.10 percent carbon vs.
0.85 percent for M-2; 1.15 percent vanadium vs. 2.0 percent for
M-2; 3.75 percent chromium vs. 4.00 percent for M-2; .Iaddend.and
8.00 percent cobalt vs. 0.00 percent for M-2. While Table IV shows
a striking improvement for nickel-coated cubic boron nitride over
nickel-coated diamond for most steels subject to wet grinding,
Table V shows even a more striking improvement in the case of dry
grinding. In fact, nickel-coated diamond is .[.no better than.].
.Iadd.only comparable to .Iaddend.aluminum oxide for the dry
grinding of tool steels and is greatly inferior to its performance
in wet grinding. This is in sharp contrast to nickel-coated cubic
boron nitride which is as good in dry grinding applications as it
is in wet grinding.
The data of Tables I-V show a surprising degree of superiority of
nickel-coated cubic boron nitride over uncoated borazon as well as
a surprising degree of superiority of nickel-coated cubic boron
nitride over nickel-coated diamond in the grinding of most tool
steels and steel alloys. Of particular interest and commercial
importance is the ability of nickel-coated cubic boron nitride to
grind alloy steels under dry grinding conditions. Nevertheless,
these data are also contradictory in certain respects for they show
that a superiority in grinding one material does not necessarily
carry over to another material or, if it does carry over, that the
degree of superiority is changed considerably. Diamond and cubic
boron nitride share in common only the properties of extreme
hardness and the cubic crystal system. (Both diamond and cubic
boron nitride can be superhard in a hexagonal form but this form of
both materials is relatively rare). From the standpoint of
elemental composition and chemistry there is no relationship
between the carbon of diamond and the boron nitride of cubic boron
nitride. As was heretofore mentioned, cubic boron nitride can
withstand temperatures of 2,500.degree. F. whereas diamond begins
to burn at 1,600.degree. F. Sacco contended that the improvement
brought about in resinoid wheels by the use of metal-coated diamond
was due to the improved bond between the resin and metal and the
different thermal properties of metal-coated diamond versus
uncoated diamond. The data of Tables I-V suggest that, at best,
Sacco's explanation is over-simplified and that there may be other,
more important factors presently unidentified which are
responsible. This is further borne out by the fact that
copper-coated cubic boron nitride did not produce a significantly
better grinding wheel for dry grinding than uncoated cubic boron
nitride. Copper-coated and cobalt-coated cubic boron nitride wheels
were superior to uncoated wheels for wet grinding but were inferior
to nickel-coated wheels.
It might be supposed that the combination of boron and nickel is
responsible for the results shown in Tables I-V. In order to test
this, three wheels were made with boron carbide abrasive. These
wheels were identical except that in one the abrasive had no
coating. In another, the abrasive had a coating of 49 percent by
weight of nickel and in the other, 58.8 percent nickel. All three
wheels were tested on M-2 steel. The uncoated wheel had a grinding
ratio of 1.00; the wheel with 49 percent nickel had a grinding
ratio of 1.01; and the wheel with 58.8 percent nickel had a
grinding ratio of 0.73. Thus, the experimental results achieved so
far do not provide a clear explanation of the principles underlying
the invention.
* * * * *