U.S. patent number 3,918,220 [Application Number 05/446,918] was granted by the patent office on 1975-11-11 for method of grinding a surface of a workpiece and a tool for carrying out the method.
This patent grant is currently assigned to Ryton Machine Tools (Coventry) Limited. Invention is credited to Kenneth James Jury, Brian John Mottram.
United States Patent |
3,918,220 |
Jury , et al. |
November 11, 1975 |
Method of grinding a surface of a workpiece and a tool for carrying
out the method
Abstract
Grinding a surface of a workpiece with abrasive particles by
impregnating a pad of reticulated foam-like material with the
abrasive particles, whereby the abrasive particles occupy
interstices in the foam-like material, the abrasive particles and
the foam-like material respectively having hardnesses greater and
less than that of the workpiece surface; effecting relative rubbing
movement between the pad and the workpiece, whereby the foam-like
material will be worn away during the rubbing movement to expose
fresh abrasive particles in the rubbing surface of the pad and to
open interstices in the foam-like material of the pad to the
rubbing surface thereof, and applying a liquid to the rubbing
surface of the pad, whereby material worn away from the pad and the
workpiece during the rubbing action will be washed from the rubbing
surface of the pad, through the opened interstices in the pad of
foam-like material. Only some of the interstices in the pad are
occupied by abrasive particles and those interstices which are not
occupied by abrasive particles intercommunicate to define a
continuous throughway extending between the rubbing surface of the
pad and a face thereof remote from said rubbing surface, thereby to
define a path through which said washing liquid can flow to or from
the rubbing surface.
Inventors: |
Jury; Kenneth James (Coventry,
EN), Mottram; Brian John (Coventry, EN) |
Assignee: |
Ryton Machine Tools (Coventry)
Limited (Coventry, EN)
|
Family
ID: |
10399159 |
Appl.
No.: |
05/446,918 |
Filed: |
February 28, 1974 |
Foreign Application Priority Data
|
|
|
|
|
Aug 9, 1973 [UK] |
|
|
37809/73 |
|
Current U.S.
Class: |
451/59; 451/490;
51/295; 51/296; 451/164; 451/168; 451/174; 451/488; 451/526 |
Current CPC
Class: |
B24D
99/00 (20130101); B24D 15/00 (20130101) |
Current International
Class: |
B24D
15/00 (20060101); B24D 17/00 (20060101); B24B
001/00 (); B24B 007/00 (); B24D 011/00 (); B24B
055/02 () |
Field of
Search: |
;51/293,295-298,394,281R,328,391,392,393,401,402,358,59R,62,68,356 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Simpson; Othell M.
Attorney, Agent or Firm: Connors; Edward F.
Claims
What we claim as our invention and desire to secure by Letter
Patent of the United States is:
1. A method of grinding a surface of a workpiece with abrasive
particles consisting in the steps of impregnating a pad of
reticulated foam-like material having a plurality of interstices
therein with said abrasive particles, said abrasive particles
occupying only some of said interstices, said abrasive particles
and said foam-like material respectively having hardnesses greater
and less than that of the workpiece surface and those interstices
which are unoccupied by said abrasive particles intercommunicating
to define a continuous throughway extending between a rubbing
surface of the pad and a face thereof remote from said rubbing
surface, thereby to define a path through said pad for washing
liquid applied thereto, effecting relative rubbing movement between
said pad and the workpiece, whereby said foam-like material will be
worn away during the rubbing movement to expose fresh abrasive
particles and said unoccupied interstices in said rubbing surface
of said pad, and applying said washing liquid to said rubbing
surface of said pad, whereby material worn away from said pad and
from the workpiece during the rubbing action will be washed from
said rubbing surface of said pad by said washing liquid flowing
through said unoccupied interstices in said pad.
2. A method of grinding according to claim 1 in which said washing
liquid is injected through said unoccupied interstices from said
face of said pad remote from said rubbing face thereof and said
washing liquid is allowed to flow away from said rubbing face
through said exposed unoccupied interstices therein.
3. A grinding tool comprising a pad of reticulated foam-like
material having a plurality of interstices therein of which
interstices only some are impregnated with abrasive particles, said
abrasive particles and said foam-like material respectively having
hardnesses greater and less than that of the surface of a workpiece
which is to be ground, and those interstices which are unoccupied
by said abrasive particles intercommunicating to define a
continuous throughway extending between a rubbing surface of the
pad and a face thereof remote from said rubbing surface, thereby to
define a path through said pad for washing liquid applied thereto,
whereby on effecting relative rubbing movement between said pad and
the workpiece said foam-like material will be worn away during the
rubbing movement to expose fresh abrasive particles and said
unoccupied interstices in the rubbing surface of said pad, and a
support member in which said pad of foam-like material is mounted,
said support member having a port therein through which said
washing liquid is passed, said port communicating with said
continuous throughway defined in said pad, whereby material worn
away from said pad and from the workpiece during the rubbing action
will be washed from said rubbing surface of said pad by said
washing liquid flowing through said unoccupied interstices in said
pad.
4. A grinding tool as claimed in claim 3 in which said pad is
shaped to conform with the surface of the workpiece to be
ground.
5. A grinding tool as claimed in claim 4 in which said pad is
pre-shaped before the impregnation of interstices therein with said
abrasive particles.
Description
The invention relates to a method of grinding the surface of a
workpiece with abrasive particles and a tool for carrying out the
method. The term "grinding" as used herein is intended to means any
grinding action by abrasive particles and includes fine surface
finishing and polishing where the grit size is very small.
A disadvantage of known grinding tools is that the grinding surface
of the tool rapidly becomes clogged with material from the tool and
the workpiece surface, thereby impairing the efficiency of grinding
and the finish of the workpiece surface. An object of the invention
is to provide a method and a tool by which the grinding surface of
the tool is kept clear of material removed from the tool and the
workpiece, thereby prolonging the effective life of the tool and
improving the finish of the workpiece surface and also permitting
the relative speeds of movement of the tool and the workpiece to be
higher and for the grinding to be effected at greater pressure than
hitherto.
According to the invention, a method of grinding a surface of a
workpiece with abrasive particles consists in the steps of
impregnating a pad of reticulated foam-like material with the
abrasive particles, whereby the abrasive particles occupy
interstices in the foam-like material, the abrasive particles and
the foam-like material respectively having hardnesses greater and
less than that of the workpiece surface; effecting relative rubbing
movement between the pad and the workpiece, whereby the foam-like
material will be worn away during the rubbing movement to expose
fresh abrasive particles in the rubbing surface of the pad and to
open interstices in the foam-like material of the pad to the
rubbing surface thereof, and applying a liquid to the rubbing
surface of the pad, whereby material worn away from the pad and the
workpiece during the rubbing action will be washed from the rubbing
surface of the pad, through the opened interstices in the pad of
foam-like material.
Preferably only some of the interstices in the pad are occupied by
abrasive particles and those interstices which are not occupied by
abrasive particles intercommunicate to define a continuous
throughway extending between the rubbing surface of the pad and a
face thereof remote from said rubbing surface, thereby to define a
path through which said washing liquid can flow to or from the
rubbing surface.
Conveniently said washing liquid is injected through the unoccupied
interstices from a face of the pad remote from the rubbing face
thereof and the liquid is allowed to flow away from the rubbing
face through the opened interstices therein.
The invention also includes a grinding tool comprising a pad of
reticulated foam-like material impregnated with abrasive particles,
whereby the abrasive particles occupy interstices in the foam-like
material, the abrasive particles and the foam-like material
respectively having hardnesses greater and less than that of the
surface of the workpiece which is to be ground, whereby the
foam-like material will be worn away during the rubbing movement to
expose fresh abrasive particles in the rubbing surface of the pad
and to open interstices in the foam-like material leading from the
rubbing surface of the pad to convey liquid applied to the rubbing
surface of the pad to wash away from the rubbing surface of the pad
material worn from the pad and the workpiece during the rubbing
action through the opened interstices in the pad.
The grinding tool may include a support member in which the pad of
reticulated foam-like material is mounted.
The pad may be shaped to conform with the surface of the workpiece
to be ground. Where the pad is shaped to conform with the surface
of the workpiece to be ground, the pad may be pre-shaped before its
impregnation with the abrasive particles.
The abrasive particles may be of any suitable hard material for
example diamond, a synthetic or natural substance usually used for
grinding, such as silicon nitride, silicon carbide or aluminium
oxide, or a hard alloy steel, such as a nickel-chromium alloy
steel.
The support member may be provided with an inlet or outlet port
through which said washing liquid is passed, the port communicating
with a continuous throughway defined in the pad and extending
between the rubbing surface of the pad and a face thereof remote
from said rubbing surface, the continuous throughway being defined
by intercommunicating interstices that are not occupied by abrasive
particles.
The invention also includes a method of manufacturing a grinding
tool as set out in any one of the five immediately preceding
paragraphs in which a reticulated foam-like material is impregnated
with the abrasive particles.
The abrasive particles may be injected into interstices of the
foam-like material under pressure together with a bonding material
which is then allowed to set to hold the abrasive particles in the
foam-like material. The bonding material may be a synthetic resin,
for example, of an epoxy type resin or it may for example be a
ceramic material.
Alternatively the abrasive particles may be injected into
interstices of the foam-like material and bonded to the foam-like
material by subjecting the latter to a sintering process.
Conveniently the abrasive particles may be distributed through the
foam-like material prior to sintering by vibrating the foam-like
material. The foam-like material is such that it will withstand
heating to the temperature required to sinter the abrasive
particles to the foam-like material.
In yet another method of manufacturing the pad of the grinding
tool, the abrasive particles may be secured to the foam-like
material by a metallic plating process and therefore prior to
injecting the abrasive particles into interstices in the foam-like
material, the walls of the interstices are given a metallic
plating. The plating process may be of any suitable kind. For
example it may be an electrolytic plating process, an electroless
plating process, that is the deposition of a metallic layer from a
metallic salt solution in which the pad together with impregnated
abrasive particles is immersed, or a vacuum deposition process.
Where the abrasive particles are particles of diamond, they would
be pre-coated with a metallic layer before being bonded by the
metallic plating process to the foam-like material. Alternatively
where the particles are of tungsten carbide or similar abrasive
material, they may not need to be pre-plated.
In yet another method of manufacturing the pad of the grinding
tool, the abrasive particles may be secured to the foam-like
material by a metallic flame-spraying process. The abrasive
particles may be injected into the interstices of the foam-like
material before applying the flame-spraying process. Alternatively,
the abrasive particles may be applied to the foam-like material in
the metal spray which will permeate through interstices in the
foam-like material. For example, the flame-spraying process may be
performed by a thermo-spray powder gun to which the abrasive
particles are supplied as in a thermo-spray or plasma spray
process, the abrasive particles being of such material that they do
not become molten in the flame.
In any of the foregoing methods of manufacturing the pad of the
grinding tool, a removable mask may be employed to limit the
injection of abrasive particles to certain regions of the pad.
By way of example, the polishing or grinding tools in accordance
with the invention, their construction and use will now be
described with reference to the accompanying drawings, in
which:
FIG. 1 is a diagram, to a large scale, of a pad forming the
tool;
FIGS. 2 to 5 are diagrams showing different ways of impregnating a
foam-like pad with abrasive particles;
FIG. 6 is a diagram showing generally the way in which a pad is
mounted and used to perform a polishing or grinding operation;
FIG. 7 is a cross-section through the pad, its mounting and a
workpiece on the plane VII--VII in FIG. 6;
FIG. 8 is a cross-section through a first practical embodiment of
tool in accordance with the invention;
FIG. 9 is a view of the tool in the direction of arrow IX in FIG.
8;
FIG. 10 is a section on the line X--X in FIG. 11 of a second
practical embodiment of tool in accordance with the invention;
FIG. 11 is a section on the line XI--XI in FIG. 10;
FIG. 12 is a view in the direction of arrow XII in FIG. 11 of the
pad employed in the tool shown in FIGS. 10 and 11, and
FIG. 13 is a view similar to FIG. 10 of a modification of the
second practical embodiment of the tool.
The tool essentially comprises a pad of reticulated foam-like
material having a multiplicity of randomly-disposed interstices
therein in which particles of abrasions are embedded. Such a
foam-like material is called "metal foam". Metal foam known by the
Registered Trade Mark RETIMET is described in British Patent
Specification No. 1,199,404 of Foam Metal Limited and is made from
a reticulated synthetic plastics foam which is coated throughout
the wall surfaces defining the interstices in the foam with metal
by, for example, electrodeposition after making the foam
electrically conductive. The plastics foam may be left within the
metal coating or it may be destroyed to leave the metallic coating
as a sketetal structure. The metallic coating may be of any metal
to which the abrasive particles which are to be embedded in the
interstices of the foam-like material, in accordance with this
invention, can be bonded as hereinafter described. For example,
nickel, copper and lead have been used. The foam-like material must
also have a hardness less than that of the abrasive particles and
that of the workpiece to be ground.
The abrasive particles may be of diamond, any natural or synthetic
material usually employed as a grinding material, such as silicon
oxide, silicon carbide, silicon nitride, aluminium oxide or boron
nitride, or a hard alloy steel, such as a nickel-chromium alloy
steel. The abrasive particles selected must have a hardness greater
than that of the foam-like material and the workpiece. The abrasive
particles are bonded in interstices of the pad of foam-like
material by any of the methods to be described hereinafter. When a
surface of the pad is rubbed against a surface of a workpiece by a
grinding movement, abrasive particles and particles of the
workpiece material will be separated from the rubbing surfaces of
the pad and the workpiece respectively and are washed away by a
liquid, for example, a coolant, the interstices in the pad are
opened by the removal of abrasive particles by the rubbing action
aiding the flow of the washing liquid to or from the rubbing
surfaces. The foam-like material will also be rubbed away and this
will open more interstices and will expose fresh abrasive particles
in the rubbing face of the pad. Thus throughout the grinding
operation a layer of fresh abrasive particles in the rubbing
surface will continually be exposed.
The impregnation of the interstices in the pad with abrasive
particles may be substantially complete, that is most interstices
contain an abrasive particle. Alternatively only some of the
interstices, for example, 70% are filled with abrasive particles,
the interstices containing abrasive particles being
randomly-disposed throughout the pad and the un-occupied
interstices communicating with one another to define continuous
throughways from a face of the block remote from the rubbing face
to the rubbing face. Before using the pad, it is mounted in or
secured to a mounting block or backing member. Where the pad is of
the kind which has been only partly impregnated with abrasive
particles, a face of the pad remote from the rubbing face, for
example the back face, communicates with a port in the mounting
block or backing member. The washing fluid is then passed through
the port and the un-occupied interstices to flow through the
rubbing surface of the pad and will from there wash away from the
rubbing surfaces particles from the pad and the workpiece.
Alternatively washing fluid supplied directly to the rubbing faces
may be retained within a seal enclosing the area of the rubbing
face and be removed through the un-occupied interstices in the
block and through the port in the mounting block or backing member.
Where the pad is of the kind that is substantially filled with
abrasive particles, it would be held in a mounting block or on a
backing plate side-by-side with a pad in which the interstices have
not been filled with abrasive particles, i.e., they have been left
un-occupied, washing liquid being passed through the interstices of
the latter pad between a port in the mounting block or backing
plate and the rubbing surfaces of the two pads.
A diagrammatic perspective view of a pad, to a large scale,
impregnated with abrasive particles is shown in FIG. 1. The pad 10
is a reticulated foam-like material having randomly-disposed
intercommunicating interstices 11 therein. Some of the interstices
are shown occupied by abrasive particles 12 bonded to the walls
defining the interstices at 13.
Several methods of impregnating a pad of the foam-like material
with abrasive particles are now described with reference to FIGS. 2
to 5.
FIG. 2 shows diagrammatically how a pad of pre-made foam metal is
impregnated with a mixture of abrasive particles, resin and
hardener, where the abrasive particles are to be held in
interstices in the foam metal by the resin. An openable mould 15
has a cavity 16 therein of a shape and size to receive the
pre-formed pad 17. The cavity has an inlet port 18 through which
the mixture is applied and an outlet port 19, fitting with a
controlling bleed screw 20 through which displaced air and, in some
cases, water is expelled during the impregnation. The inlet port 18
communicates with a ram 21 into the cylinder of which the mixture
is inserted through plug 22. The mixture of abrasive particles,
resin and hardener, together with water where an emulsion is easier
to inject, is inserted into the cylinder of the ram 21. The
preformed pad 17 of foam metal is placed in the cavity 16 and the
ram 21 is connected to the mould 15. The bleed screw 20 is suitably
adjusted and the ram is operated to displace the mixture into the
interstices of the foam metal. The mould 15 is opened and the pad
17 is removed and allowed to dry in air or is heated, thereby to
cure the resin. The extent of impregnation of abrasive particles in
the foam metal may be controlled by varying the volume ratio of the
total mixture to the cubic capacity of the foam metal, the ratio of
the volume of abrasive particles to the combined volume of resin
and hardener in the mixture, the pressure applied by the ram or the
time of application of the pressure or any combination of these
factors. For example where the preformed pad of foam metal is 10%
metal (or plastics wall coated with metal) and 90% air space, 85 %
of the total volume may be filled with the mixture (made from 70%
of the whole volume of abrasive particles, 10% of the whole volume
of resin and 5% of the whole volume of hardener). The resulting pad
will then have 5% of its total volume formed by un-occupied
interstices. It has been found that these interstices are
randomly-disposed throughout the pad and providing there are
sufficient un-occupied interstices these will be in communication
with one another in a random arrangement of throughways extending
between the faces of the pad.
FIG. 3 is a diagram similar to FIG. 2 showing a combined mould and
ram for impregnating a tubular preformed pad of foam metal. The pad
may be circular or rectangular in cross-sectional shape. A cylinder
25 defining the combined mould and ram cylinder has removable end
plates 26 and 27 and an internal bore of the outer shape of the
preformed pad. The cylinder 25 contains a piston 28 of appropriate
cross-sectional shape and a hub 29 shaped to define the internal
cross-sectional shape of the preformed pad. The preformed pad 30 is
placed in an annular space 31 between the cylinder 25 and the hub
29. As before, a bleed screw 32 controls flow of air or water
through a port 33 in the end plate 26 of the cylinder 25 and
communicating through a duct 34 with the annular space 31. The
mixture of abrasive particles, resin and hardener is inserted into
the cylinder adjacent the end of the pad 30 and hub 29 as shown at
36. The piston 28 and end plate 27 are placed in the positions
shown and pressure is applied to inject the mixture into the pad,
as described with reference to FIG. 2. The pad is then removed for
curing of the resin.
Instead of using a resin and hardener, the abrasive particles may
be mixed with a ceramic material which after injection into the
mould is allowed to harden or is fired.
FIG. 4 shows a combined mould and resin similar to FIG. 3, but
intended for impregnating a block instead of a tubular pad and thus
not including the hub 29. Instead a mask 35 is located in the
cylinder 25 between the piston 28 and the pad 30. The mask has a
pattern of apertures formed therein whereby the mixture will only
be injected through the holes in the mask 35 and so the interstices
directly behind the apertures in the mask will be filled with the
mixture. According to the pressure applied and the time of
application, there will be a tendency for the mixture to permeate
into interstices behind the non-apertured parts of the mask, but
this tendency can be controlled. The use of a mask therefore
enables the interstices in some portion of the pad to be left
un-occupied.
FIG. 5 shows how a preformed pad can have abrasive particles
injected into it where the particles are to be secured in the pad
by sintering. A preformed pad 40 of foam metal is inserted into a
cavity 41 in a floating die 42. The bottom of the cavity is closed
by a fixed punch member 43. Abrasive particles mixed with a powder
which can be sintered to the abrasive particles and the foam metal
are poured into the cavity 41 on top of the pad 40 as shown at 46.
A top punch member 44 is then inserted into the cavity in the
floating die 42. The die is vibrated by an electro-magnetic
vibrator 45 to cause the mixture to permeate through the
interstices of the pad. Pressure is applied to the pad to effect
compression of the mixture therein. The impregnated pad is then
removed and placed in a sintering furnace where the metal powder
becomes sintered to the abrasive particles and to the metal
foam.
As aforesaid, other methods of impregnating and securing abrasive
particles in the pad of foam-like material may be employed. For
example the foam-like material may be plated, if not already coated
with a suitable metal, and the abrasive particles may be plated to
the metallic coating of the foam-like material by a plating process
which may be electrolytic, electroless or by vacuum deposition. A
mask may be used to limit the plating to only certain regions of
the pad.
Alternatively the abrasive particles may be introduced as a mixture
with a metal powder, as described with reference to FIG. 5 and then
be sintered by flame-spraying or a mixture of abrasive particles
and metal powder may be introduced by a flame gun as in a
flame-spraying process. A mask may be used to limit the
flame-spraying to certain areas of the pad.
The impregnated pad may be of any shape depending upon the grinding
operation to be performed. For example it may be a block having a
concave surface for polishing the cylindrical surface of a shaft or
it may be a flat pad for polishing a flat surface, it may be
annular or in the form of a rounded tool for polishing an internal
surface or it may be formed as a wheel. By way of example only, a
pad 50 is shown in FIGS. 6 and 7 having a concave rubbing face for
polishing the cylindrical surface of a shaft 51. The polishing may
be effected by relative rotation or transverse movement, relative
longitudinal vibration or feeding between the pad and the shaft
while pressure is applied to the pad.
The pad is held by a backing member to which it is secured, for
example by bonding, or it may be held in a mounting block. A
suitable backing member 52 is shown in FIGS. 6 and 7. The backing
member may have a port 53 therein communicating with a duct 54 to
which a liquid lubricant or coolant is applied. The liquid may be
water or any other suitable liquid. The liquid flows through
interstices in the pad that are not occupied by abrasive particles.
As these intercommunicate within the pad, as already described, the
liquid will flow through the pad to the rubbing surface 55 thereof
and will wash away particles of abrasive and foam metal worn away
from the pad and particles worn from the workpiece during the
rubbing action. Fresh abrasive particles are continually being
exposed in the rubbing surface 55 of the pad.
Three practical arrangements of mounting a pad for polishing a
cylindrical shaft or roll that the Applicants have employed are now
described with reference to FIGS. 8 and 9; FIGS. 10 to 12, and FIG.
13.
Referring firstly to FIGS. 8 and 9, the pad comprises a plurality
of alternate elements 60, 61 clamped together side-by-side. The
elements 60 are made of foam metal which has been substantially
completely impregnated with abrasive particles, that is as many as
possible of the interstices in the pad have been filled with
abrasive particles; whereas the elements 61 are of un-impregnated
metal foam. The elements 60, 61 are clamped together to form a
lozenge-shaped insert between two metal plates 62 secured together
through the elements by screws. The insert is held in a
complementarily-shaped socket 65 in a mounting block 63 by a
retaining plate 64. The bottom of the socket 65 communicates with a
duct 66 to a port 67 to which a supply pipe for admitting liquid
coolant is connected. The rubbing faces 68 of the elements 60, 61
are shaped to conform to the surface of the shaft 69 or roll to be
polished. The mounting block is shown secured to a support 70 in
FIG. 8. The tool is used in rotating the shaft 69 while applying a
force on the support 70 to urge the pad into contact with the
surface of the shaft 69. The support 70 may also be moved parallel
to the axis of the shaft 69 to produce a relative reciprocation or
feeding movement longitudinally of the shaft 69. During the
polishing operation, the liquid coolant supplied to the mounting
block 63 passes through the interstices of the elements 61 to their
rubbing faces 68 and from there spreads all over the rubbing faces
68 of the elements of the whole insert to emerge from the periphery
of the insert adjacent the surface of the shaft 69. The liquid
coolant therefore washes away abrasive particles and particles of
the foam metal and also particles of the shaft worn away by the
polishing operation. During the polishing operation fresh abrasive
particles are continually being exposed in the rubbing faces 68 of
the elements 60.
Referring to FIGS. 10 to 12, a pad 70 of foam metal impregnated
with abrasive particles, as described hereinbefore, is bonded to a
curved backing plate 71 carried on a spigot 72 having a duct 73
therein communicating with a liquid coolant supply pipe 74. The
spigot 72 is held in a block 75 to which a pair of plates 76 are
pivoted by pins 77. The ends of the plates 76 remote from the pivot
pins 77 carry pins 78 to which the backing plate 71 is secured.
Coolant supplied through the pipe 74 passes to a hole 79 in the pad
and from there percolates through un-occupied interstices and along
the rubbing face of the pad to remove worn particles from the
rubbing face. Fresh abrasive particles are continually exposed in
the rubbing face as abrasive particles break away from the foam
metal and the latter is worn away. The abrasive particles may be
disposed throughout the pad provided sufficient un-occupied
interstices are left therein for the flow of coolant to the rubbing
face or they may be disposed only in certain regions of the pad
behind certain areas 80 of the rubbing face, as shown in FIG. 12.
This pattern of regions occupied by abrasive particles may be
produced by a mask, as hereinbefore described.
Finally, FIG. 13 shows a pad arrangement similar to that shown in
FIGS. 10 to 12 in which the pad 70 and backing plate 71 are
enveloped in a seal comprising a deformable tube 81 extending
around the periphery of the pad 70 and carried by a flexible skirt
82 secured to the plates 76. A coolant extraction pipe 83 extends
from the space within the seal to a coolant outlet pipe carried on
the block 75 and leading to an extractor pump (not shown). Thus
coolant after washing away the particles from the rubbing face is
carried together with the particles to the pump. The particles can
then be filtered from the coolant and the coolant
re-circulated.
As a modification of the arrangement shown in FIG. 13 the pad could
be provided with a region containing un-occupied interstices
separated from the remainder of the pad through which the coolant
can be returned, instead of the extraction pipe 83 being provided.
In a further modification the coolant could be applied directly
through the pipe 83, allowed to travel through opened interstices
in the rubbing face and then extracted through un-occupied
interstices in the pad to the hole 79 and from there extracted
through the duct 72 and pipe 74.
In the foregoing embodiments, as the abrasive particles at the
rubbing surface of the pad are continually exposed during the
polishing or grinding process and the materials worn away from the
tool and the workpiece are continually washed through the
interstices in the pad, the tool will not readily become clogged
and thus the effective life of the tool and the finish of the
workpiece will be improved. Furthermore the liquid will be
distributed throughout the rubbing surface of the pad and so the
speed of the grinding movement and the pressure applied to the tool
can be greater than hitherto, all these factors resulting in an
improved finish. By selecting different tools having pads
impregnated with abrasive particles of different hardness and grit
size, any desired surface finish can be produced.
* * * * *