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Grinding wheel dressing method - Patent Review 4027648
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Grinding wheel dressing method
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United States Patent4027648
Link to this pagehttp://www.wikipatents.com/4027648.html
Inventor(s)Bonnice; Phillip E. (Worthington, OH)
AbstractA cubic boron nitride, diamond or similar grinding wheel is dressed by
applying a dressing slurry comprising a multiplicity of inorganic crystals
dispersed in a normally fluid carrier medium against the rotating wheel to
form a layer of dressing slurry on the surface of the wheel and then
pinching the slurry between the wheel and a metal piece until dressing is
substantially complete.
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Inventor
Bonnice; Phillip E. (Worthington, OH)
Owner/Assignee
General Electric Company (Columbus, OH)
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Company News
Publication Date
June 7, 1977
Application Number
05/681,603 $10B$5B - $10B$2B - $5B$500M - $2B$100M - $500M$10M - $100M$1M - $10M$500K - $1M$100K - $500K< $100K[No votes]
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Technical Review
Claims
I claim:
1. A method of dressing a bonded, rigid grinding wheel on a high speed
grinding machine comprising the steps setting the wheel against a metal
piece at substantially zero clearance, rotating the wheel at normal
grinding speed of the machine, applying a wheel dressing slurry comprising
a multiplicity of abrasive crystals dispersed in a normally fluid carrier
medium to the moving surface of said grinding wheel by forcing said wheel
dressing slurry through a conduit in a dressing shoe having a metal
dressing face in substantially zero clearance to said wheel surface,
whereby the dressing slurry is spread on the surface of the wheel, and
abrading said wheel surface having said slurry spread thereon against said
metal dressing face to remove selected portions of the surface of said
wheel.
2. A method as defined in claim 1 wherein said grinding wheel is a diamond
grinding wheel.
3. A method as defined in claim 1 wherein said grinding wheel is a cubic
boron nitride grinding wheel.
4. A method as defined in claim 1 wherein said abrasive crystals are
aluminum oxide crystals.
5. A method as defined in claim 4 wherein said aluminum oxide crystals
range from 60 to 1000 grit size.
6. A method as defined in claim 1 wherein said liquid carrier medium is a
hydrocarbon medium of automotive grease viscosity.
7. A method as defined in claim 1 wherein said wheel dressing slurry has a
paste-like consistency, comprises a multiplicity of 60 to 250 grit
aluminum oxide crystals dispersed in a hydrocarbon automotive grease at a
mix ratio of 0.1 to 6 parts by volume of crystals per 1 part by volume of
said grease.
Claims
Description
This invention relates to a method for dressing abrasive-containing
grinding wheels.
BACKGROUND OF THE INVENTION
In machine grinding operations, it is necessary to dress the face of the
grinding wheel to assure the proper shape of the part to be ground (the
workpiece) and to prepare or restore the surface of the grinding wheel to
optimize its cutting ability and to insure that the quality of the finish
imparted to a workpiece is high.
Conventionally, grinding wheels are dressed with a variety of tools, such
as steel cutters, abrasive wheels, or techniques such as crush dressing
are used. One means for dressing wheels in the past comprises using a
rigid stick of abrasive material bonded in a hard matrix. These depend on
the mechanical strength and hardness of the matrix and require continuous,
forced application to break the conventional bonding material back away
from the diamond, cubic boron nitride, aluminum oxide, silicon carbide or
other materials used as the abrading materials in the wheels. See, for
example, Abrams, U.S. Pat. No. 3,508,533.
Conventional sticks must be used with considerable force and this leads to
economic losses caused by breakage and possible injury to the operator.
Moreover, the force necessary with conventional sticks precludes their use
in dressing form wheels, where force destroys the form.
One technique which avoids the need for rigid sticks is shown in Giardini
et al., U.S. Pat. No. 3,167,893 who used a high speed fluid jet ejected
against the moving grinding wheel surface. This requires a multiplicity of
pumps and apparatus of a very specialized design. Another technique which
avoids the need for rigid sticks is shown in Kuris et al., U.S. Pat. No.
3,123,951 who applied an ultrasonically cavitated fluid to the moving
surface of the grinding wheel. This too required non-conventional
apparatus which is generally too expensive for routine manufacturing use.
In general, also, the prior art methods require rather prolonged periods of
time for dressing to be completed.
A new method has now been discovered which avoids all of the
above-mentioned disadvantages. In addition, the method is simple enough
for even experienced operators to use it; the wheels, especially larger
wheels of 10 inch and greater diameter, are left free cutting and open
around the entire periphery; the dressing operation can be conducted in a
"hands off" fashion for safety of the operator and to reduce operator
error; the procedure is adaptable to a variety of machine types, wheel and
bond designs, grinding modes; the technique is capable of providing both
trueing and dressing in a single operation; and much more rapid dressing
is routinely achieved.
SUMMARY OF THE INVENTION
According to the present invention, a cubic boron nitride, diamond, silicon
carbide, aluminum oxide, or obviously equivalent, grinding wheel is
dressed by means of applying a dressing slurry comprising a multiplicity
of inorganic crystals dispersed in a normally fluid carrier medium against
the rotating wheel to form a layer of dressing slurry on the surface of
the wheel and then pinching the slurry between the wheel and a metal piece
until dressing is substantially complete. In one preferred embodiment, the
wheel dressing slurry is applied by transfer from a surface layer on said
metal piece. In a second preferred embodiment, the wheel dressing slurry
is applied by forcing it through at least one conduit in a dressing shoe
having a metal dressing face in substantially zero clearance to the wheel
surface.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention may be more readily understood by reference to the
accompanying drawings in which:
FIG. 1 is a schematic view showing dressing a wheel in a surface grinding
embodiment according to this invention;
FIG. 2 is a perspective view, semi-schematic in nature of a grinding wheel
and dressing shoe for application of a dressing slurry according to this
invention;
FIG. 3 illustrates an alternate design of a dressing shoe adapted for rigid
mounting to a grinder table; and
FIG. 4 shows, in greater detail, a dressing shoe of the type illustrated in
FIG. 2.
DETAILED DESCRIPTION OF THE INVENTION
All of the following sizes, speeds and materials are illustrative only.
Referring to FIG. 1, a number of dressing slurries are made by mixing
aluminum oxide grit of size 60, 80, 150 and 220, into a liquid carrier
medium comprising hydrocarbon-based automotive grease (Mobilux No. 2) to
provide concentrations of 25, 50 and 75 weight %, and small amounts of SAE
10 hydrocarbon oil and are spread to 1/8-3/16" thickness on M-2 HRC 62,
4" .times. 6" steel block 6. Wheel 4 comprising a 14" .times. 1/2",
100/120 mesh cubic boron nitride abrasive surfaced wheel, 25 v/o, is
mounted in a G&L #370, Q grinder (not shown). Wheel 4 is rotated at a 5500
SFPM speed and the table (not shown) bearing block 6 is moved at a speed
of 2 ft./min., for dressing. The wheel is brought into zero clearance with
block 4 and successive climb grinding passes are taken across the piece.
Climb grinding, wherein the work and the wheel travel is in the same
direction, is necessary to provide a "pinching" action on layer 12 of
slurry. No coolant is used. By the time the wheel has traversed the 4"
width of block, 4, the wheel is fully open. With a slurry comprising a 1:1
mix of 80 grit Al.sub.2 O.sub.3 and grease, total time required is 10
minutes. Test grinding on a piece of Rene' 80 indicates an excellent
finish and no burning, confirming that the wheel has been efficiently
dressed.
In contrast, the use of aluminum oxide rigid stick dressers (G & K hardness
sticks) fails to open the wheel even after 30 minutes.
Another means of practicing the invention as an alternative to surface
grinding is shown in FIG. 2. As is seen, a formed metal dressing face 20
in a dressing applicator 22 is set against wheel 4. Slurry for dressing of
the type described above is forced under air pressure from suitable
storage reservoir 24 through a suitable conduit 26, e.g., plastic tubing
to one or more holes in dressing face 20 at the leading edge of the radius
to permit the slurry to enter the dressing zone. A more detailed
illustration of a suitable dressing applicator 22 is shown in FIG. 4 in
which body 21 is formed to fit the operator's hand, conduit 28 is bored
through the handle, and the supply of slurry is adapted to pass through
plastic conduit 26, bored conduit 28 and thence into the plurality of
holes 30 bored through cast iron or steel dressing face 20. A suitable
hole 30 diameter is 1/16 inch.
The apparatus according to FIGS. 2 and 3 comprised a 12" .times. 1", 25
v/o, 80/100 boron nitride wheel, mounted in a G & L 370 Q grinder and
operated with a wheel speed of 5500 SFPM. The slurry is a 1:1 mix of 60
grit Al.sub.2 O.sub.3 in hydrocarbon grease (Mobilux .multidot.2). The
block 20 in dressing applicator 22 is fabricated from nodular cast iron,
65 Brinell hardness.
Wheel 4 is first trued with a diamond nib and is completely glazed prior to
start of dressing. The grinder is set to traverse across the block slowly
allowing overlap on each side of about 1/2 wheel width.
The wheel is found to be fully open after 5 minutes, but observation was
that this could probably have been done in half that time.
A comparison dressing test (with the same wheel after re-trueing and
glazing) was made using an aluminum oxide stick of `G` hardness 220 grit,
followed by a `K` hardness 220 grit stick. The `G` stick is consumed in 5
minutes, and the `K` stick is 75% consumed in 15 minutes. The wheel
appears moderately open after this 20 minute period.
Grinding results using wheels dressed according to this invention in terms
of spindle power and surface finish are set forth in Table I:
Table I
______________________________________
Grinding Power Requirements and Surface Finish
______________________________________
Downfeed Spindle Power (KW)
Surface Finish (AA)
(by hand)
Stick Slurry Stick Slurry
______________________________________
.001 2.0 .3
.002 2.8 1.1 15 60
______________________________________
It is seen that the slurry dressed wheel according to this invention is
superior in providing exceptionally low power draw and rough surface
finish. This strongly suggests that some crystal loss at the surface may
have occurred in the slurry dressed wheel and demonstrates the ability to
true as well as dress in a single operation.
In another embodiment, adapted for cylindrical grinding of large wheels,
the slurry is fed through a device which can be rigidly mounted on a
grinder. For example, it can be mounted in the existing machine nib
holder. One such unit is illustrated in FIG. 3 and comprises mounting
plate 34, extension 32, wear plate 20, conduit 28 and holes 30. The
perforated plate 20 is removable so that it can be replaced when
necessary. The unit can also accommodate a resin bonded diamond nib as a
trueing tool when forming the wheel is to be a first step.
In using a rigidly mounted dressing fixture, abrasive is delivered from a
pressurized reservoir, like that shown in FIG. 2. In one method, a 16-
.times. 2" cubic boron nitride abrasive wheel, 80/100 mesh, 25 v/o is
mounted in a grinder (Cincinnati Cylindrical) and rotated at 5500 SFPM. A
slurry of 1:1 mix 120 grit Al.sub.2 O.sub.3 in grease (Mobilux #2) is fed
at 10 psi, against nib 30 mounted through plate 34 on a table (not shown)
moving at 2 ft./min. Dressing face 20 comprises 1020 steel HRB 24.
Light infeeds are taken by hand at first to grind a contour into the plate
20. Plate 20 is set to overshoot the wheel about 1/2 diameter. The machine
is then put into the automatic mode and infeed 0.001" at both sides of
the wheel; slurry feed is minimal. This is continued until 0.075" infeed
is made then shifted to 0.002" infeed per pass. Slurry flow too is
increased. This is maintained for 0.080 to 0.100" infeed, and noticeable
sparking is seen to occur. Infeed is then stepped up again to 0.003" per
pass and continued to 0.080". The wheel and plate 20 are then inspected.
The wheel is found to be fully open, based on visual appearance, and
photomicrographs confirm this. The face plate 20 is about 2/3 used up and
only half (about 150 cc.) of the slurry is used. Total time for complete
dressing is 4 minutes.
For comparison, the wheel is again glazed and dressed instead with rigid
`G` and `K` dressing sticks. Total dressing time required is 45 minutes.
To further illustrate the efficiency of dressing grinding wheels according
to this invention, the procedure described above with reference to the
surface dressing embodiment of FIG. 1 is repeated with variety of dressing
compositions then power requirements and surface finishes are measured
during and after grinding at a wheel speed of 5500 SFPM, a table speed of
50 ft./min.; 0.100" crossfeed; and 0.002" downfeed. The results are set
forth in Table 2:
Table 2
______________________________________
Grinding Power Requirements and Surface Finish
______________________________________
Al.sub.2 O.sub.3 Max. KW
KW Total
Grit Concentration
KW Entire Last Watt- Final
Size w/o 1st Pass*
Test Pass Hours AA
______________________________________
60 25 3.0 3.0 2.0 114 34
" 50 2.0 2.2 2.0 109 19
" 75 1.5 1.5 1.2 74 50
150 25 -- -- -- -- --
" 50 -- -- -- -- --
" 75 1.7 2.9 2.6 118 17
220 25 -- -- -- -- --
" 50 -- -- -- -- --
" 75 4.3 4.3 3.0 185 18
______________________________________
*The 25 and 50% levels of the finer grit size are omitted since
preliminary trials indicated that more than one pass over the slurry will
be necessary to open the wheel
The KW Hour figure indicates wheel openness. The lower the number, the more
open the wheel. These results indicate that the best compromise for this
mesh size wheel (100/120) is found with the 150 grit Al.sub.2 O.sub.3
grit. This gives excellent finish at a reasonable level of power drawn.
Note that in the 60 grit series, there is good correlation between
Al.sub.2 O.sub.3 concentration and wattage. It appears that, in general,
for a given cubic boron nitride mesh wheel, e.g., a 100/120 wheel (a very
common size), a 120-150 grit Al.sub.2 O.sub.3 at 75% concentration gives
superior results. Grit size is U.S. Standard Sieve.
In one example of form grinding, a run is carried out on a 5" .times. 1/4"
resin bond wheel with a simple radius form. Slurry is spread over a block
of M-2 steel which has been grooved with the wheel during earlier grinds.
The glazed wheel is opened in only about 2 minutes, with no degradation of
the form.
It is thus evident that the present invention provides dressing methods
which are fast, efficient and convenient. Obviously, many modifications
will suggest themselves to those skilled in the art in view of the above
detailed description. For example, instead of automotive grease as a
carrier, other thickened oils, and naturally thick oils, such as Vaseline,
can be used to carry the grit particles. Instead of a cubic boron nitride
abrasive wheel, other abrasives can be used, such as diamond wheels.
Instead of aluminum oxide crystals, other grits can be slurried, such as
cubic boron nitride, diamond, silicon carbide, and the like. Instead of 80
grit, the crystals can range from 60 to 250 grit size. Instead of a 1:1
mix ratio, other ratios of mixes can be used in the slurries, such as 0.1
to 6 parts of crystals per 1 part of carrier medium. Wheel trueing can
comprise a preferred preliminary step, using a conventional wheel-forming
tool. All such obvious variations are within the full intended scope of
the invention as defined by the appended claims.
* * * * *
Description
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