Note: Descriptions are shown in the official language in which they were submitted.
BACKGROUND O~ THE INVENTION
This invention is related to the separation of fine
particles from a liquid coolant employed in a lens grinding
process. More particluarly, this invention is directed to a method
and a filtration system for improved separation of the fine
particles from the liquid coolant.
PRIOR ART
In the manufacture oflenses, a pieces of lens-forming
material, either glass or transparent plastic, is caused to come
into contact with an abrasive disc to form a curved surface on
the material in accordance with a prescription or specification.
Presently, two types of machines are used in forming
lenses - generators and edgers. A generator is a machine used
for ginding the front and back surfaces of a lens. As to an
edger, this machine is for grinding the edge or perimeter of
the lensso as to fit the lens to a particular frame selected
by the customer.
In the genreating or edging processes, because of the
grinding operation, a liquid coolant is needed for lubrication
purposes as well as for removing the heat generated by the
frictional contact between the lens material and the abrasive
disc. The coolant is usually delivered in the form of a
continuous spray directed at the surface being formed. Further
more, the coolant is generally stored in a container which
is connected to a pumping mear~s. After the coolant has been
sprayed onto the lens material, it is allowed to flow into the
storage tank where it is drawn into the input port of the
pumping means and circulated to the lens material again.
The grindi`ng operation creates fine particles of the
lens material and removes some of the abrasives from the abra-
sive disc. These particles are introduced into the liquid cool-
ant. The amount of such particles accumulated in the coolant
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increases wi~h the number of lenses ground when the same batch
of coolant ~s used. The presence of these particles in the
coolant should be kept at a minimum since they may cause scratch-
ing of the surface of the lens being formed.
To alleviate the problems caused by a high accumulation
ofthe fine particles in the coolant, most of the major manu-
facturers of lens generating or edging machines have suggested
changing the coolant after a specific period of time or after a
certain number of lenses has been formed with the same batch of
coolant. The proposed number of lenses formed is 30n to 400 lenses,
whereas the suggested period of time is two weeks. For example,
-according to the instruction manuals, and repair guide for edgers
(edging machines) manufactured by Shuron, Lemay and AIT
Industries, the operator of the machine is to change the coolant ;
after 300 - 400 lenses have been formed. In the edgers made by
Shuron and AIT Industries, the coolant is stored in a container `
lined with a bag formed of a non-porous material, such as
polyethylene. When it is necessary to change the coolant,
the used coolant and the bag are replaced. It must be noted that
the above manufacturers who are three of the five major
manufacturers of lens making mahines in the world, da not
suggest the use of a filter to separate the particles from the
coolant nor are filters provided by the manufacturers. They
merely suggest that the coolant be changed periodically. Further-
more, the use of polyethylene bags is undesirable for the
following reason. When replacing the coolant, both the bag
and the coolant are disposed of. The disposal of these wet `;
bags must be conducted with care since such bags have been known
to form methane gas at landfills, thus causing harm to the
environment.
Despite the failure of the manufacturers to provide
filters, users of the machines have used filters to separate
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the particles fxom the coolant. For example, in the lens forming
process utilized by Bausch & Lomb~ one of the ~ajor producers
of lenses ;n this country, ~ilter bags made of cotton duck, a
woven fabric, with a napped surface are used. Upon its return
to the storage tank, the coolant flows through the filter bag
prior to being pumped back to the grinding chamber. The bags
are efficient in removing approximately 50~ of the particles.
An operator has to remove, manually, the particles which have not
been collected by the filter. This manual cleaning procedure
is not only time consuming, but also exposes the operator to
a health hazard, since the fine particles may be difficult to
remove from a person's skin because of their small size. The
above discussion clearly shows that there is a present and urgent
need for an efficient filter system for use in connection with
lens forming processes.
On the other hand, it is noted that-the use of a
filter medium in cutting tool coolant supply system is known,
as exemplified by the following references.
U.S. Patent 2,364,41~ discloses a grinding machine
having oil as the cooling medium. To insure the delivery of
a clean coolant to the grinding wheel and the work, this patent
teaches the use of filter unit consisting of a pail partially
filled with small rhomboidal or lozenge-shaped cast iron pieces
or with crushed stone, with crushed stone being preferred. The
use of a non-woven fabric as the filtration medium has not been
mentioned in this patent.
U.S. Patent 2,671,561 discloses a sediment removing and
filtering apparatus for machine tools such as lathes, grinders
and shapers. According to this patent, the coolant is fed into
a tank having baffle walls at the entrance and exit ports thereof
to prevent the sediment from being discharged therefrom. An
endless conveyor belt traverses the bottom wall portion of the
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, . . . .
tank to remo~e the sediment. However, it is noted that this
patent does not teach the utilization oE a non~woven fabric as
a filter medium.
U.S. Patent 2,765,916 is directed to a filtering
means for removing scrap and suspended solids from a liquid such
as cuttingoll or coolant used in a machine. A strainer means
such as a screen or a perforated sheet metal is used for filter-
ing the coolant. The use of non-woven fabrics as a filtering
means is not disclosed in this patent.
U.S. Patent 3,341,983 discloses an apparatus for
continuously clarifying machine tool coolants. The apparatus
taught in this patent includes a vortex separator wherein the
differential in the flow velocity of the coolant is used to
remove the particles. This patent does not teach the use of a
filtering medium.
- U.S. Patent 3,455,457 discloses a filtering device for
contaminated liquid coolant from a machine tool. The filter
unit disclosed in this patent comprises a cartridge made of
cellulose fibers impregnated with resin, the fibers being bonded
in position by the resinous impregnation and polymerization. In
addition, stainless steel mesh cartridges may also be used as the
filter unit. It is noted that the cellulosic filter, as shown
at column 2, lines 53 through 57 of this patent, has an
initial degree of filtration as low as five microns. As to the
stainless steel mesh cartridge, the initial degree of filtration
can be as low as one micron, as indicated at column 2, lines
57 through 60.
U.S. Patent 3,651,607 discloses a self-contained waste
collector usable in a manufacturing operation. A filter bag is
used for separating the shavings. It is taught in this patent
that the filter bag is made of cloth or similar disposable
material.
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U.S. patent 3,830,373 is directed to a drainage tube
wth a re$training sc~een. The screen may be fabricated of spun
bonded filamentary mate~i~al. As indicated at column 2, lines 32
through 38 of this patent, the screen is for pre~enting water-
borne particles above ~ pa~ticular size from entering the tube.
U.S. Patent 3,841,488 discloses an 06cillating strainer
for a cutting tool coolant supply systemfo~a machine tool. A
screen is utilized as the strainer. The use of a fabric as a
filtering medium is not taught in this patent.
From the above discussion, it is clear that filters
are used in machine tools for separating particles or shavings
from the coolant. The filters employed are usually made of
cloth or a metal screen. However, it must be noted that the
use of a filter made of a non-woven fabric in a lens generating
or edging process has never been disclosed or suggested in the
above-cited references.
SUMM~RY OF THE INVENTION
The present invention provides a method whereby the
fine particles entrained in the liquid coolant in a lens
generating or edging device can be efficiently and economically
removed prior to the return of the cleaned liquid coolant to
the grinding chamber without exposing the operator to any health
hazards.
According to the present invention, the entrained fine
particles can be separated at a substantially increased
efficiency by passing the liquid coolant through a filter medium
made of a non-woven fabric comprising synthetic filaments having
a denier of from about 3.5 to about 5.0, the fabric having a
density of from about 0.3 oz. to about 2.0 oz. per square yard,
the reduction in the liquid coolant flow rate caused by the
filter medium being less than 1% wherein a cake of -the particles
~s formed on the surface ofthe medium into which the coolant
.
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enters to ~rovide an effective filter system.
B~IEF DESCRIPTION ~F THE DRAWINGS
. . .
Figure 1 shows a lens grinding system wherein the
present invention is applied.
Figure 2 shows a metkod of attaching a filter bag to
a coolant container used in a lens grinding device.
Figure 3 shows a multiple filter bag tray which may
be used in a lens grinding device.
Figure 4 shows a cross-sectional view along line 4-4'
in Figure 3.
DETAILED DESCRIPTION OF THE INVENTION
It has b-een found that non-woven fabrics having
specific physical characteristics are highly efficient in
separating fine particles from the liquid coolant in lens
generating or edging processes.
According to the present invention, the contaminated
or particle-carrying coolant in the lens generating or edging
process is passed through a filtration system having particular !;
physical characteristics to separate, with high efficiency, the
~0 particles created by contacting a lens material with an abrasive
disc and deposited in the liquid coolant. After the filtration
step, the cleaned coolant is circulated back to the grinding
chamber. In general, the grinding chamber comprises a grinding
or abrasive disc, a clamping means for the lens material, a
driving means for the abrasive disc and a drainage pan into
which the liquid coolant, after having been sprayed onto the work,
can flow. The grlnding chamber is usually an enclosed area so
as to prevent the intro~uction of flne powders of the lens
material into the surrounding atmospnere.
3~ The present invention is applicable to lens generating
or edglng devlces whereln a liquid coolant lS used as a lubrlcant
as well as for removing heat produced by the grinding process.
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The coolant is s~rayed ~nto the work (the lens being ground) and
dra~ned into a storage tank. The coolant is then delivered to
the work by means of a pump.
As a result of the research conducted by the inventor,
it was found that while woven filter fabrics generally have an
efficiency of about 50%, non-woven fabrics have a much higher
efficiency. For particles having a size of 5 microns or larger,
it was found that by using the method of the present invention,
approximately 97% to 99% of the particles were removed. For
particles smaller than 5 microns, approximately 75% to 80% were
removed after the first passage of the coolant through the
filter. However, after several passages ofthe coolant, a layer
or cake of the particles was formed on the inlet surface of the
filter to improve the efficiency thereof. Consequently, the
removal of particles smaller than 5 microns approached 97% to
99~ after the build-up of the cake.
Suitable non-woven fabrics include those made of
synthetic filaments, such as polyamide, polyester, polyacetate,
polyolefin and polyurethane. Among these, polyamide and
polyester are preferred with polyamide being most preferred.
The non-woven fabrics suitable for application in this
invention should possess the following physical properties:
(a) Denier: The filaments of the fabric should range
from about 3.5 to about 5.0 denier, with 3.5 being
preferred;
(b) Density: from about 0.3 to about 2.0 oz. per square
yard, with from about 0.5 to about 1.5 oz. per square
yard being most preferred. The density of the fabric
selected depends on the flow rate through the fabric,
the higher flow rate, the lower the density; and
(c) Reduction in coolant flow rate through the filter
medium: less than about 1.0%. The filter medium
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should cause as low a reduct;on in flow rate
of the coolant as possible, preferably less than
about 1.0~. A high reduction by the filter may
cause the suppl~ of the liquia coolant to be
depleted, thus preventing delivery to the work,
a highly undesirable result.
The above-listed requirements (a), (b) and (c) are of
primary importance in the present invention. These requirements
must be satisfied in order to achieve the results provided by
0 this invention.
Among the numerous non-woven materials presently
available in the market, two appear to be particularly suitable
for the instant invention, viz. those supplied under the trade-
marks CEREX and REEMAY. CEREX is a spunbonded fabric manufactured
by Monsanto and is composed of continuous filaments of NYLON 6,6.
It is noted that the filaments in CEREX have a round cross-
sectional configuration. This material has been known to be appli-
cable in filtration processes. However, it must be noted that
the use of CEREX as a filtration medium for the liquid coolant
in a lens generating or edging process is unknown. As to REEMAY,
it is a non-woven material composed of spunbonded polyester fila-
ments having a tri-lobal cross-sectional configuration. Although
REEMAY has been known to be useful in filtration processes,
its application as a filtration medium for the liquid coolant
in a lens generating or edging process is not known.
Furthermore, it should be noted that CEREX and REEMAY
remain stiff even when wet, which facilitates replacement of
the filter bags.
With reference to the drawings, Figure 1 illustrates
how the present invention can be applied. In Figure 1, 10
generally refers to a lens gathering or edging device. The
lens gathering or edging device comprises a grinding chamber 12
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having connected thereto one end of a drainage pipe 14 and the
outlet pp~t 16 of the pump 18. The other end of the drainage
pipe ;s connected to a filter bag 20, the bag being located
inside a storage tank 22 for a liquid coolant 24. The inlet
port 26 of the pump is also connected to the storage tank. The
liquid coolant 12, after having been sprayed onto the work, is
permitted to flow into tank 22 by means of drain pipe 14.
Attached to the end of the drain pipe is a filter bag 20 formed
of a non-woven fabric. The bag may be secured to the drain
pipe by means of a tie wire or a conventional hose clamp 28.
The coolant flows through the filter bag leaving the fine
particles entrapped therein. The coolant is then drawn into the
inlet port 26 of the pump 18 which delivers the substantially
particle-free coolant to the grinding chamber 12. It is noted
that although Figure 1 shows the tank 22 is placed within the
lens generating or edging device 10, the tank may be located
outside the device, if necessary. In addition, instead of being
attached to the drain pipe, the filter bag 31 may be clamped to
a large circular ring 30, as shown inFigure 2. The ring is
provided with four lugs 32 through which S-hooks 34 are
anchored for attaching the ring to a container 36. Container 36
can be of any shape, although a square one is shown inthe
drawing. The drain pipe from the grinding chamber is placed
inside the bag whereas the inlet port of the pump is placed
between the exterior of the bag and the interior of the container,
when the lens generating or edging device is in use.
Figures3 and 4 show a device whereby a series of bags
may be used. As shown in Figure 3, a tray 40 is provided with
a bottom wall 42 and four side walls 44 to form a box-like con-
tainer wïth an open top portion. The bottom wall 42 is providedwith a plurality of openings 46. It is noted that eight
openings are shown in the drawing but any convenient number of
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openings can be used. Longitudinal partition wall 48 and lateral
partition wall$50, 52 and 54 are provided to divide the tray
- into compartments, each havin~ an opening in the center thereof.
The partition walls 50, 52 and 54 have different heights, with
wall 50 being the tallest andwall 54 the shortest.
As shown in Figure 4, a circular flanged collar 56 is
inserted into opening 46. The open end of a filter bag is -~
inserted through opening 46 and folded over lip 58 of collar 56.
A hose clamp of tie wire is then used to hold the bag tightly -
in place. Each of the openings is fitted with a filter bag as
shown above.
When in use, the tray is placed on top of a container.
Contaminated liquid coolant is fed into the compartment having
~ the tallestpartition wall. The filtered coolant is then
ç pumped to the grinding chamber. As the bag becomes clogged
after being in operation for a period of time, the liquid coolant
overflows into the adjacent compartment until all of the bags in ~ ;
s the tray are used. At that time, a new tray may be inserted
or the individual bags fitted onto the used tray may be replaced.
- Although it has been shown in the drawings that the
; filter medium is located between the drain pipe and the inlet
port of thepumping device, the bag may be placed at other
locations deemed convenient by one of ordinary skill in the art.
For example, the filter medium may be located immediately below
the grinding chamber, i.e. at the inlet of the drain pipe
rather than at the outlet. As long as the contaminated coolant
is passed through the filter medium prior to being sprayed onto
the lens material in the grinding chamber, the results desired
in this ~nvention can be obtained.
The present filter medium which is effective in
removing fine particles of lens materials such as glass and
transparent plastics, from the coolant, should be replaced every
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600 lenses, atthe maximum. Continued use of the coolant
beyond 600 lenses may bring forth undesirable results, such as
scratching of the lens.
At the present time, the liquid coolant used in most
- edgers comprises a water soluble coolant. As to generators,
about 10% thereof use water soluble coolants, the remainder
require oil based coolants. However, governmental regulations
require that by 1985, water soluble coolants be used in all
generators. The change from oil to water as the coolant is
necessitated for saftey reasons. In the grinding chamber, which
is a substantially enclosed area, a small portion of the oil
- coolant exists in the form of a fine mist, as the result of the
heat generated in the grinding operation. When the operator
opens the cover to the grinding chamber upon the completion
, of a grinding process, the sudden availablity of oxygen may cause
the hot oil mist to flash, thus causing injury to the operator.
As a result, in order to protect the operator, the government
has orderedthe changeoverto water soluble coolants. The
anticipated changeover should not have any effects on the
applicabilitv of the present invention since the filter medium -
used herein is effective in both water soluble and oil coolants.
The temperature at which the instant invention may
be carried out is not particularly restricted, although most
generating and edging processes are carried out at room
temperatures (60F - 80F). The temperature range within which
the instant invention is opertive is from about 40F to about
400F.
It has also been found that the pore size of the
fabric has no effect on the efficiency of the filter medium.
It has also been found that the construction of the
filter bag is not particularly restricted. As an example, a
filter bag formed in the following mannerhas been found to be
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effective, A squareor rectangle sheet of the non-woven fabric
is folded along its center line. Two of the three edges so
formed which comprise two layers~ of the fabric are folded with
one layer overlappingthe other, to a width of about one inch.
The folds so formed are secured together by stitching to form a -
bag having an opening at one end and two sides sewn together.
It should be noted that the above construction merely represents
an e~ample. Any other convenient method of forming the filter
bags may be used.
The size or dimension of the filter bag can be varied.
However in order to facilitate safe handling and disposal, the
bag should be of such a size that when filled it can be easily
handled by an operator of average strength.
The inventor has also found that the high efficiency
' ofthe~present invention can be obtained by passing the particle-
carrying liquid coolant through a single layer of the filter
medium only once. Additional layers of the filter medium and
additional passes are not necessary. However, if the operator
so desires, additional passes and layers may be used.
The present inventor believes that the high efficiency
in separating the fine particles is due to the build-up of a
layer or cake of the particles on the surface of the filter
medium into which the contaminated or particle-carrying coolant
flows. This cake serves as an additional filtering medium for
the coolant, thus providing a filtration system with increased
efficiency. It must be noted that the invention merely offers
the above as a possible mechanism of the present invention. Such
mechanism should not be interpre-ted as the only one possible nor
does the inventor wish to be bound or limited thereto.
The present in~ention not only provides a highly
efficient method of removing fine particles from liquid coolants,
but also provides desirable results in the following areas:
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(1~ Cost. ~ilter bags of the present invention cost
approx;mateIy 1/3 to 6/7 of that of woven cloth bags.
In addition, as a result of the increased filtering
; efficiency when using the present filter bags, the useful life
of the abrasive disc is increasçd by at least 20%.
Most important of all, the savings incurred by the
present invention lie in the significantly decreased length of
time needed in replacing the used coolant. A decrease in labor
cost as much as 90% can be achieved by using the presentinvention.
10(2) Safety. In contrast to woven cloth filter bags
where the fine particles can penetrate the fabric so as to
accumulate on the outside surface, the present invention provides
filter bags wherein substantially all of the particles are
trapped on the interior surface thereof. Thus, an operator
will not be exposed to the fine particles of glass or plastic if
non-woven fabric is used to form the filter. A safer working
environment fbr the operator is therefore obtained.
(3) Environmental consideration. As has been
pointed out, non-woven polyethylene bags used for storing the
used coolant are undesirable since they may generate methane
gas when deposited in the wet form in a land fill, causing
undesirable effects to the environment. In contrast, the
non-woven material used in the present invention retains very
little water and is not known to degenerate into har~ful products
upon disposal.
To illustrate the advantages of employing the present
invention, the following example is included herein. The example
is for illustrative purposes and by no means restrict the
present invention.
EXAMPLE
A series of test runs were made with the following
filter bags for lens edging devices.
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Bag l; Cotton duek
Bag 2: CEREX~ 3.5 denier and a densit~v of l oz/sq.yd.
Bag 3: CEREX, 3.5 denier and a density of 1.5 oz/sq.yd.
The results wexe summarized as follows:
Filtration efficiency
of partieles having
diameter of 5 microns Time needed for replacing
or larger clogged bags
Bag l(Prior art) 50% 6 man-hours
Bag 2 97% l/20 man-hours
Bag 3 97% 1/20 man-hours
The results shown above clearly indicate that the
present invention is highly efficient in particles removal
(about 97%) as well as eeonomieal. The time needed to replace
used eoolants has been reduced to l/120 of that of the prior
art, which provides a sharp-reduction in the costs incurred
in forming the lens.
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