U.S. patent number 3,594,963 [Application Number 04/870,712] was granted by the patent office on 1971-07-27 for grinding pad.
This patent grant is currently assigned to Univis, Inc.. Invention is credited to George A. Beasley.
United States Patent |
3,594,963 |
Beasley |
July 27, 1971 |
GRINDING PAD
Abstract
The method of providing a replaceable grinding pad for a
lens-grinding tool, having a surface thereon for grinding optical
and ophthalmic lenses. The pad is formed about the
curve-determining surface of the grinding tool, thus providing the
grinding surface of the pad with substantially the same curvature
as that of the tool. The pad is formed by interposing a sheet metal
blank between the tool and a die member of an elastic material and
thereafter deforming the blank with the tool by depressing it into
the elastic material, whereby to form a grinding pad having the
same configuration as that of the tool.
Inventors: |
Beasley; George A. (Fort
Lauderdale, FL) |
Assignee: |
Univis, Inc. (Fort Lauderdale,
FL)
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Family
ID: |
25355954 |
Appl.
No.: |
04/870,712 |
Filed: |
July 17, 1969 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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662379 |
Aug 22, 1967 |
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Current U.S.
Class: |
51/293; 29/421.1;
29/445; 451/527; 451/42 |
Current CPC
Class: |
B24D
18/0009 (20130101); B24B 13/01 (20130101); Y10T
29/49805 (20150115); Y10T 29/49861 (20150115) |
Current International
Class: |
B24D
18/00 (20060101); B24B 13/00 (20060101); B24B
13/01 (20060101); B24d 011/02 () |
Field of
Search: |
;72/54,57,60,63,465
;51/284,294 ;76/107 ;51/293,297 ;29/421,445 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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204,365 |
|
Nov 1956 |
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AU |
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716,480 |
|
Jan 1942 |
|
DT |
|
Primary Examiner: Herbst; Richard J.
Parent Case Text
This is a divisional application based upon parent application Ser.
No. 662,379 filed Aug. 22, 1967, and entitled "GRINDING PAD."
Claims
I claim:
1. The method of assembling a replaceable lens-grinding pad to a
lens-grinding tool having a selected curved surface thereon
cooperable in grinding a surface on a lens to a related prescribed
curvature, comprising the steps of: interposing a lens-grinding pad
blank between a body of compressible elastic material and a
lens-grinding tool and in alignment with the curved surface of said
lens-grinding tool, causing relative movement between the curved
surface of the tool and the elastic material to press the pad blank
into the elastic material and to deform the pad blank into
conformity with the curved surface of the tool whereupon the pad
blank has impressed thereon a curvature substantially corresponding
with that of the curved surface of the tool, and simultaneously
removably securing the deformed pad blank to the tool for grinding
the prescribed curvature on the lens by the use of the deformed pad
blank on the tool.
2. The invention in accordance with claim 1 wherein the deformed
pad blank is secured to the tool by interposing a cement between
the pad blank and the curved surface of the tool.
3. The invention in accordance with claim 1 wherein the deformed
pad blank is secured to the tool by bending peripheral surfaces of
the pad blank into frictional engagement with surfaces of the
tool.
4. The invention in accordance with claim 1 wherein the
lens-grinding pad blank is initially provided from a substantially
flat sheet of deformable metal.
5. The invention in accordance with claim 4 wherein slots are
provided in the flat pad blank for enhancing the grinding operation
of the deformed pad blank secured to the tool.
6. The invention in accordance with claim 1 wherein the curved
surface of the tool is concave and a substantially hemispherical
dome is provided on part of the elastic material extending in the
direction of the tool, the radius of the dome being smaller than
the shortest radius of the curved surface of the tool.
7. The invention in accordance with claim 1 wherein the elastic
material is a polyurethane elastomer placed in a die block.
8. The invention in accordance with claim 1 wherein the grinding
tool is coupled with a hydraulic press, and the tool is
hydraulically moved against the pad blank and hydraulically presses
the pad blank into the elastic material.
9. The invention in accordance with claim 1 wherein initially the
pad blank is deformed by pressing it into an elastic material by a
mandrel having a spherical pad blank engaging surface, and
thereafter the spherically shaped pad blank is deformed by and
secured to said grinding tool with the curved surface thereof being
toric.
Description
BACKGROUND OF THE INVENTION
Optical and ophthalmic lenses are commercially produced by grinding
a lens blank precisely to a predetermined curvature thus imparting
the desired optical qualities to the lens. The grinding is
generally performed by use of a tool made of cast iron or the like
which is provided with a lapping surface having a curvature
precisely corresponding to the curvature desired to be impressed
upon the lens blank surfaces. During the grinding process, an
abrasive slurry is deposited over the lapping surface and a
relative rotary, oscillatory or combination rotary and oscillatory
motion is imparted between the lens blank and lapping surface. As
will readily be appreciated, since the lapping surface of the
grinding tool as well as the lens blank is subjected to the
abrasive action of the slurry, it will wear fairly rapidly, thus
requiring truing or refinishing at frequent intervals to restore
the lapping surface to the desired curvature. It is therefore
desirable to provide a replaceable grinding surface for use with
such a grinding tool and heretofore several attempts have been made
at providing an adequate replaceable pad having such a grinding
surface thereon. However, all of these attempts have met with one
objection or another. The principal difficulties were those of
forming the pad accurately to curve, maintaining adequate adhesion
of the pad to the tool, and the too short working life of such
pads.
SUMMARY OF THE INVENTION
It is therefore a principal object of this invention to provide an
economical and efficient replaceable grinding pad for a
lens-grinding tool which is easily replaceable, accurate in
curvature and can be positively secured to the grinding tool and
the method of fabricating and replacing such pads.
This and other objects and advantages are most effectively attained
by producing a grinding pad directly over the curve-determining
surface of the grinding tool. A flat blank of metal or other
suitable material is interposed between this surface of the
grinding tool and a die block filled with an elastic material. The
tool is then forced against the blank into the elastic material
under relatively high pressure, thus deforming the blank to conform
to the curvature of the surface.
In the preferred embodiment of the present invention, the pad is
somewhat smaller than the curve-defining surface of the tool and a
pressure sensitive adhesive coating or contact cement can be used
between the tool and pad to provide securement during use.
In the manufacture of pads for grinding toric lenses it has been
found that the formation of an intermediate, spherical, shell may
be required before the final toric shape can be formed if the sheet
metal blank from which the pad is to be formed is relatively thick
or inflexible. Thus, in the manner described above, a flat metal
blank is interposed between the spherical end of a mandrel and a
die block filled with an elastic material. The mandrel is then
pressed against the blank into the elastic material thus deforming
the blank into a spherical shell. The shell is then interposed
between a grinding tool having the desired toric curvature and a
die block filled with an elastic material. The grinding tool is
forced against the shell into the elastic material thereby causing
the shell to deform to the desired toric shape. The intermediate
spherical shell may be manufactured somewhat larger than the toric
lap of the grinding tool. In this case, when the final grinding pad
is produced, the excess material may be conveniently bent to form a
peripheral retaining rim adapted to secure the grinding pad to the
grinding lap during use.
As was previously stated, an abrasive slurry is spread over the
grinding surface of the tool during use. The tool may thus be used
for grinding or polishing lenses, dependent on the particle size
and abrasiveness of the slurry used. In order to evenly distribute
this slurry over the lapping surface, the metal blank may be
provided with a series of cutouts or slots which serve as feed
channels when the pad is affixed to the grinding tool. The slots,
when properly positioned and shaped, are also utilized to assure a
grinding pad which possesses a wear pattern that results in its
curvature remaining substantially unchanged throughout its life and
which will enable the grinding of wave-free lenses.
DESCRIPTION OF THE DRAWINGS
In the accompanying drawings:
FIG. 1 is an exploded fragmentary side elevational sectional view
of a die block and press for manufacturing grinding pads in
accordance with the present invention;
FIG. 2 is a view similar to FIG. 1 after the pad is formed;
FIG. 3 is a side elevational sectional view of the pad produced in
FIG. 2;
FIG. 4 is a view similar to FIG. 1 wherein an intermediate
spherical shell is used as a workpiece for manufacturing toric
grinding pads in accordance with the alternate embodiment of the
present invention;
FIG. 5 is a view similar to FIG. 2 showing the actual production of
the toric pad;
FIG. 6 is a fragmentary side elevational sectional view of a
grinding tool having a grinding pad secured thereto by an adhesive
bonding agent;
FIG. 7 is a fragmentary side elevational sectional view of a
grinding tool having a grinding pad manufactured in accordance with
the alternate embodiment of the present invention disposed about
its lapping surface wherein the pad is provided with a peripheral
rim for retaining it to the grinding tool;
FIG. 7a is a bottom plan view of the grinding view of FIG. 7;
FIG. 8 is a fragmentary side elevational sectional view of a die
block and press for manufacturing concave grinding pads;
FIG. 9 is a plan view of a tool provided with a multiplicity of
depressed grooves covered by a grinding pad formed in accordance
with the present invention wherein the grooves in the tool have
become formed on the pad;
FIG. 10 is a plan view of a metal blank which is particularly well
suited for use in forming a replaceable pad for the grinding of
spherical surfaces;
FIG. 11 is a plan view of an embodiment of a metal blank
particularly suited for forming a replaceable pad for the grinding
of toric surfaces;
FIG. 12 is a plan view of another embodiment of a metal blank for
use in grinding toric surfaces;
FIG. 13 is a plan view of still another embodiment of a metal blank
for use in grinding toric surfaces;
FIG. 14 is a fragmentary elevational sectional view of a die block
and press for forming a continuous grinding pad about a grinding
wheel in accordance with the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Reference is now made to the drawings to FIG. 1 in particular,
wherein an apparatus 10 for practicing the method of the present
invention is shown. The apparatus 10 includes a tough elastic
material 12 confined within a die block 14. The elastic material
12, which may consist of a natural resilient elastomer such as
rubber or various rubber compounds, or a synthetic elastomer such
as polyurethane, serves to provide an opposite die for the pressing
member or mandrel 16 during the operative condition of the
apparatus. The pressing member 16 may be hydraulically operated
(the hydraulic equipment is not depicted) and, in accordance with
the present invention, the die portion 18 of the pressing member 16
may have a spherical, toric or any desired configuration and
curvature. The spacing between the die block 14 and pressing member
16 is such that the pressing member will be forced into the elastic
material 12 of the die block when the hydraulic press is made
operative.
In use, a flat grinding pad blank 20 which consists essentially of
a thin sheet of steel or other metal, is interposed between the
elastic material 12 and pressing member 16 and aligned relative to
the pressing member. In the preferred embodiment of the present
invention, the upper surface of the blank and the lower or die
portion 18 of the pressing member 16, which comprises the
curve-determining surface of a grinding tool, will have previously
been coated with a suitable contact cement of adequate bonding
strength to hold the pad in its formed configuration to the tool
and to withstand the stresses of abrasive grinding. The press is
then activated, causing the pressing member to advance toward the
die block thereby deforming the blank 20 to conform to the shape of
the lower portion 18 of the pressing member 16, and thereby forming
the assembly depicted in FIG. 6 consisting of the tool 38, adhesive
44 and pad 30.
The grinding pad of the present invention, may be formed over and
used with the individual grinding tools as depicted in FIGS. 6 and
7 or, it may be used in conjunction with a grinding wheel 52 as
depicted in FIG. 14. In the latter case, a succession of pads may
be formed about the periphery of the grinding wheel 52 in
end-to-end relationship in the same manner as that described above
using the wheel as the pressing member for each pad, or, a
continuous pad 30c may be formed by using a sufficiently long blank
56 and rolling the wheel 52 against the blank into an elastic wheel
54 under sufficient pressure to deform the blank in the manner
described above. The apparatus for practicing the latter method is
depicted in FIG. 14.
In one successful operation of the above-described process, cold
rolled, deep drawn sheet steel blanks having a maximum hardness of
Rockwell B55 and thickness of between 0.005 and 0.010 inch were
formed into pads under a pressure of between 20 and 25 tons. The
elastic material 12 contained within the die block 14 consisted of
Elasta Cast Polyurethane Elastomer, supplied by Acushnet Process
Company of New Bedford, Mass. Satisfactory results have also been
obtained with the use of a hydrostatic bag consisting of a
liquid-tight nonelastic cover filled with an incompressible fluid
as the elastic material. A suitable adhesive is that supplied by
the Minnesota Mining and Manufacturing Company as No. 1357 cement.
This is a contact cement which is supplied in liquid form and is
applied to the surfaces of the tool and pad to be contacted in
accordance with the manufacturer's instructions.
FIG. 8 depicts an apparatus for producing concave pads in
accordance with the present invention. The elastic material 12b
confined within the die block 14b includes a hemispheric dome 40
protruding toward the pressing member. The radius of the dome 40 is
smaller than the shortest radius intended to be formed on the pad
30b. In all other respects, the apparatus and method are the same
as that described above for the formation of convex pads.
An alternative method of practicing the present invention has been
found to be most useful in the manufacture of relatively thick pads
or pads from less flexible materials. In this alternate procedure,
a spherical, intermediate shell is first formed and thereafter, the
intermediate shell is further worked to the desired shape. Thus, in
the manner described above, a spherical shell 30a may be produced
by utilizing a die portion 18 having a spherical tool. Referring to
FIG. 4, the spherical shell 30a is thereafter interposed between a
second pressing member 16a and a die block 14a filled with an
elastic material. The die block used in this second step, may, of
course, be the same as that utilized in the initial step and serves
the same function.
The die portion 18a used in this second pressing step consists of a
tool having the desired toric or spherical curvature and thus, when
the apparatus 10a is activated to the position shown in FIG. 5, the
shell 32 so produced will conform to the toric or spherical
curvature of the tool 18a.
In the alternative embodiment as depicted in FIGS. 4 and 5, the
intermediate spherical shell 30a produced during the initial
pressing process is somewhat larger than the grinding tool serving
as the die portion 18a in the second pressing step. Thus, as shown
in FIGS. 5, 7 and 7a, when the second pressing step is completed,
the retaining rim 34 will be formed out of the excess material.
This rim 34 serves to secure the shell 32 about the grinding tool
38 by frictionally engaging the sidewall of the grinding tool.
It can thus be appreciated that the deformed blank forms a pad
about the grinding surface of the grinding tool 38 and the outer
surface 42 of the pad thereby serves as a replaceable grinding
surface for the grinding tool 38. When the grinding surface of the
grinding pad wears out through the abrasive action of the slurry
used in the lens-grinding operation, the entire pad can easily be
removed from the grinding tool and a new pad substituted therefor
in one of the manners described above.
The surface blank 20 from which the grinding pad is formed may be
made from sheet steel or from any material having the appropriate
softness for forming and having suitable properties for glass
grinding. Stamped sheet steel blanks of thicknesses varying between
0.005 and 0.010 inch have produced particularly successful results.
By providing the blank 20 with a multiplicity of slots and cutouts
in various geometrical arrays, desirable wear and slurry
distribution characteristics may be imparted to the grinding pad
produced from such a blank. Particularly, it is desirable to
produce an grinding pad that possesses a wear pattern that results
in the curvature remaining substantially uncharged during its life
and one which will permit the grinding of wave-free lenses. FIGS.
10 through 13 depict various forms that the blank 20 may take prior
to its formation into a grinding pad and with which successful
results have been obtained.
FIG. 9 depicts a tool provided with a multiplicity of depressed
grooves 46 covered with a grinding pad 20a formed thereon in
accordance with the present invention in which the grooves have
become formed in the pad by the elastic action of the elastic
material 12. The depressed grooves serve as channels for
distributing the grinding slurry.
The pad 20b depicted in FIG. 10 is particularly well suited for
forming spherical grinding pads. It is substantially circular and
symmetric about the diameter defined by slots 48b and 49b. A
multiplicity of slots extending radially inwardly is provided
including the T-shaped slot which include portions 51b parallel to
the axis of symmetry and portion 50b perpendicular to the axis.
The irregularly shaped pad depicted in FIG. 11 and intended for the
grinding of toric lens surfaces, is also symmetrical about the
major axis which runs through the middle of slot 48c and also
includes a multiplicity of inwardly directed slots and cutouts
including slots 49c parallel to the major axis and slots 50c and
cutout 51c which are directed toward the center of the pad. The pad
is substantially octagonally shaped with opposite sides 53 and 55
through which the major and minor axis pass provided with V-shaped
cutouts directed toward the center. The cutouts located in sides
55c and 55c' extend from one end of the respective side to the
other while the cutouts located in sides 53c and 53c' terminate
intermediate the ends.
The pad 20d depicted in FIG. 12, also intended for use in grinding
toric surfaces is a substantially rectangular member having major
and minor axis and a series of slurry distributing slots 48d
disposed symmetrically about a diagonal. The slots extend inwardly
intermittently beginning one one side of the axis of symmetry and
then the other.
The pad 20e depicted in FIG. 13 is similar to that of FIG. 12 with
the exception that slots 48e are substantially parallel to the
minor axis.
In addition to (with the distribution of slurry, the cutouts
described above serve to facilitate the precise conforming of the
pad to the tool during the pressing step. It has been found that
with the use of such cutouts, the force necessary to properly form
the pad has been reduced from between 20 and 25 tones (without
cutouts) to between 5 and 10 ton with cutouts).
Thus it can be appreciated by one skilled in the art that the
teachings as set forth above provide an economic and efficient
method of making replaceable grinding pads for a lens-grinding tool
which are accurate and inexpensive. It should be understood that
modifications may be made in the illustrated and described
embodiments of my invention without departing from my invention as
set forth in the accompanying claims.
* * * * *