Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
~7~
Thie invention relates to methods and means
~or use in the ~inishing o~ lens sur~aces. The
invention has been developed in relation to the finishin~
o~ spectacle lenses but is o~ general a~plication to
lens finishing.
The present methods of manufacturing
- spectacle lense~ normally involve a rough grinding
operation, a fine grinding operation and a polishing
operation in which the ~inely ground sur~ace is
brought to a high degree of optical perfection. The
~ine grinding operation is normally referred to as a
finishing operation and is usually accomplished b~v
brineing the lens surface into contact with a cast-iron
~orming tool which has an operative surface accuratel~v
formed to a configuration complementary to that of the
desired lens surface configuration. A slurry containing
; an abrasive medium in the ~orm o~ particles of predetermined
size is then applied to the space between the tool and the
lens and oscillation of the tool relative to the lens is
e~fected to perform controlled abrasion Or the lens
surfaceO
Although the above method is widely used9 it
has the disadvantage that the æurface of the tool i 8
abraded in use so that it no longer has the required
sur~ace configuration~ It is accordingly common
practice to use a replaceable facing for the ~orming
tool, the facing comprising a sheet o~ thin ~oraminous
material which is shaped to con~orm to the presented
~ace o~ the tool and is secured adhesively to the tool
in intimate engagement ~ith said presented ~aceO At
the end o~ the finished operation, the facing sheet is
detached ~rom the tool and discarded.
2 -
~ 8
Desplte the advantages provided by the use
o~ a replaceable facing sheet w~ich is used once only
and then dlscarded, there are a number of disad~an-tages
o~ the abo~e method, not the least of which ls ~he cost
of providing a new facing sheet ~or each lens ~lnlshing
operation. In addition the application and removal o~
the ~acing sheet for each finishlng operatlon i8 a
tlme-consuming, expensive procedure and it is deslrable
that there should be some means of pro~idlng facing
sheets which can be used for a conslderable number of
~ini~hing operations and which are, ~or each ~inl~hing
operation for whlch they can be used~ considerably less
expensive than the faoing sheets at present in use
According to one aspect of the invention there
is provided a flnl~hing means compris1ng a ~orming tool
ha~lng a presented ~ace of predetermined contaur
related to the requlred contour of the workpiece to
be flnished, and a sheet of ~oraminous ma~erlal attaohed
to the forming tool so as to co~er the presented face
thereof 9 which foraminous material has a solid impregnant
incorporating abrasi~e particles~ each o~ the in~erstices
of the foraminous material containlng a multiplicity of
said abrasive particles.
According to another aspec~ of the lnvention
there is provided a facing for attachment to a ~in1shing
tool for use in the ~inishing of a lens surface,
comprising a support member of foramlnous material
~upporting an abrasi~e-loa~ed solld carrier comprl~ir.g
an impregnant in each of the interstices o~ the foraminous
material9 each o~ the lnterstices contain~ng a
multipllclty of abraslYe partlcle~.
The ~oraminou~ material may be a ~ire me~hD
,J~
1~7(~L8
g.t mild steel mesh, aluminlum mesh or Gopper mesh
and the solid impregnant, which serve~ a~ a carrier for
the abrasl~e particles and ~llls ~he interstices of the
mesh7 may be of P synthetic plastics material; ln
particular a resiliently de~ormable thermoplastic
material. Alternatl~ely, the impregnant may be a
metal ha.~ing a melting point substantially lower than ~he
metal from whlch the mesh is formed. As a further
alternatl~e, the impregnant may be a sintPred metal
product, the slntering temperature of whlch is
.,
.- .
, ,
.'. . . ' . . , - ~ ' . .
. .
. . . ~ ' -
107C1~8
substanti~lly lo~rer than the meltin~ point of the
metal formin~ the mesh. The prererred abrasive
material is industrial diamonds of small particle
size within the ran~e of, for example, from 8 to ~5
mlcrons, or from 10 to 20 microns. However, other
abrasive materials or mixtures may be employed.
- Tools to which sheets of foraminous material
have already been attached may be supplied to a lens
~inisher or sheets of foraminous materials may be
supplied to a manufac~urer of finishing tools for
attachment thereto. Thus, according to a second aspect
of the invention, a facing for attachment to a
finishing tool for use in the finishing of a lens
surface comprises a sheet of foraminous material the
interstices of which are filled with an abrasive-loaded
solid carrierO
The forming tool will be of predetermined
contour in dependence on the contour of the spectacle
lens or other workpiece ~o be finished and the facing
sheet, which is initially of flat form, is caused to
- adopt the curvature of the presented face of the
~orming tool by pressing it against said face using~if
desired, a forming tool having a sur~ace con~i~uration
generally complementary to that of said face. The
facing sheet may be continuous but can be formed with
a number of radiating-slDts extendinF to the periphery
of the sheet to facilitate outward flow of slurry
during a finishing operation. The facing can be
bonded to the forming tool by means of an adhesive such
as an epoxy resin or can be attached thereto by
mechanical clamp elements.
An important advanta~e of the invention is
-- 4 --
7~
that the inherent ~lexibility Or a sheet of foraminous
material such as mild steel mesh enables the ~acing
sheet to be caused to adopt the required configuration
without requiring any complex ~ormin~ operations and~
if the abrasive impre~nant is diamond particles, a
forming ~ool equipped with a diamond-impregnated facing
sheet can be used for a very large number of ~inishing
operations thereby af~ording considerable coæt-saving
advantages as compared with the use of a replaceable
non-impregnated sheet of wire mesh which is used for
just one ~inishing operation and is then discarded.
The invention will now be described by way
o~ example with re~erence to the accompanying drawings
which illustrate one embodiment o~ the invention and in
which:-
Figure 1 is a side viev~ o~ a ~orming tool ~or
use in lens polishing with a ~acing sheet attached thereto,
Figure 2 illustrates an initial stage in the
manufacture o~ a facing sheet,an~
Figure 3 illustrates a subsequent stage in
the manufacture of the facing æheet.
As shown in Figure 1, the forming tool 10 has
a metal body portion 11 provided with formations 12 to
permit mounting of the tool on a supporting arm of a
standard lens polishing machine. The upper surface of
the tool is o~ arcuate ~orm and is accurately shaped to
conform to the curvature to be ~ormed on a lens blank
and a ~acing sheet 13 of mild steel mesh impregnated
with an abrasi~e in the manner described below is
attached to the tool 10 60 as to cover said arcuate
upper æur~ace.
In carrying out a ~inishing operation, a
lens blank (not shown~ is attached to a holder o~
the poli~hing machine and is ~ositioned upon the
~acin~ sheet 13. An oscillating movement is then
applied to the tool 10 and the lens blank is also
caused to move relative to the machine whilst a
slurry 1~ fed on to $he racin~ sheet 80 that the
scrubbing actlon generated by movement of the tool
10 and the lens blank serves to abrade the surface
o~ the blank B0 that it is caused to correspond
precisely to the confi~uration o~ the presented
sur~ace of the facing sheet 13.
Turning next to Figure 2, this shows a ~lat
wire mesh disc 14, formed from mild steel mesh, which
is placed within a mould 15 on top of a plun~er 16
which rests on a distance piece 17. After the disc 14
has been placed in position, the space 18 within the
mould 1S is ~illed with a mixture o~ bonding powder
and abrasive particles, the mixture bein~ levelled off
flush with the upper surface o~ the mould 15 using a
metal scraper such that any surplus material drops into
a collection tray for subsequent use.
A~ter the space 18 has been filled ~ith said
mixture, the mixture is subjected to a controlled degree
of compression by pressing a plunger 19 downwardly
within the mould 15. The distance piece 17 is then
remo~ed and the plun~ers 19 and 16 are mo~ed into the
po~ition shown in Figure 3 in which the distances by
whlch the t~o plunger6 pro~ect ~rom the mould are equal.
The ~pparatus i6 then placed in a hydraulic press and
3 the t~o pluneers urged together with a pressure o~
; between 2 and 3 tons per sq. in.
The pressed disc is then sub~ected to a
~ 8
sinterlng treatment and this may lnvolve placing the
pre~sed disc in a fhrnace at the requlred sintering
temparature in a hydrogen atmosphere~ ~he disc being
maintained 1n the f~ ace for a period o~ time
depending on the requlred degree of grain gro~h
(which determi~es the poroslty of the dlsc)o In an
alternative ~intering process~ ~he mould 15, together
with two plungers 16 and 199 ls placed in a ~urnace
of the required temperature in a hydrogen atmosphereO
As soon as the mould has been heated to the furnace
temperature, it is remo~ed and replaced in the hydraullc
press, the disc then being pressed again with a pressure
of between 2 and 3 tons per sq in. ~th the applied
pres~ure maintalned whilst the dlsc is cooling. me
second sintering process discussed abo~e gives a more
dense product, i.e. the disc has a lower degree o~ poroslty.
The size o~ the distance plece 17 ls
calculated to ensure that the space 18 is of the required
; Yolume. The ratio o~ the volume o~ the loose po~nder
to the volume o~ the final sintered product ls normally
about 3 to 1 but this will depend upon the mesh size of
the metal powder and o~ the sintering characterlstlcs
thereo~. The bonding material may be an alloy
comprising 70% by weight copper, 27S6 by weight cobalt
and 3S6 by welght tin. The material may be of 300
mesh size and i6 mi~ed with industrial diamonds of the
appropriate particle slze with the quantity of
industrial dlamonds such as to provide the requlred
concentration, 4.4 carat per cm3 of the final ~roduct
representing 100 co~centratlon.
m e particular bonding materlal d~scussed
above is rather hard and has a slntering tcmperature
~? . ".
70~18
; of about 900C. An alternative bont~in~ material
comprises a copper/tin alloy containing 85~. by
weight co~per and 15~ by weight tin anfl this material
ha~ a sintering temperature of about 700 C.
After the sinterine treatment has been
er~ected, the product which is obtained consists of
mild steel wire mesh the lnterstices of which are
filled with the bonding material which is impre~nated
with abrasive particles, i~e. the industrial diamondsg
and this ensures that the profile of the article i~
ma~ntained when it is used to carry out a series Or
lens polishing operations. The disc of impregnated
wire mesh is attached to a forming tool so as to be in
intimate face-to-face engagement therev~ith antl such
attachment may be e~fected either by means of mechanical
clamping device or by the use of a suitable adhesive
such as an epoxy resin.
Wha$ we claim is:-
