Note: Descriptions are shown in the official language in which they were submitted.
CA 02871182 2014-11-14
"A DEPRESSED-CENTRE GRINDING WHEEL"
TECHNICAL FIELD
The present invention relates to a grinding wheel, in
particular a depressed-centre grinding wheel made of at least
a compacted abrasive material.
PRIOR ART
As is known, grinding wheels exist of a disc-shaped type
having a depressed centre, or centres that are flat, conical,
semi-flexible, dimpled or not dimpled, exhibiting an external
diameter that is substantially comprised between 20 and 230
mm, especially used on electric portable grinding machines, or
high-speed compressed air grinding machines (60-100 m/s
peripheral velocity), also known as sanders, able to perform
burring and/or cutting operations, which are essentially
constituted by an abrasive mixture reinforced with armatures
constituted by one or more textile meshes, one or more annular
metal elements, commonly known as washers or sleeves, which
delimit the fixing hole of the grinding wheel to the shaft of
the grinding machine, and possibly bear a paper label, or
commonly used adherent rating plate stuck on one of the two
faces of the grinding wheel (in depressed-centre grinding
wheels usually the convex face).
The abrasive mixture is generally constituted by grains of
abrasive material (silicon carbide, light green, dark green,
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black, corundum, modified corundums with zirconium, semi-
friable, dark brown, white, pink, ruby, with ceramic, mono-
crystalline, sol-gel abrasives or sintered ceramics, or other
like materials) having a predefined granulometry (normally
measured in meshes) which are mixed with resins, for example
phenolic, liquid and/or powder and possibly modified with
epoxy resins, and/or others, possibly modified with organic
compounds and/or vegetal or synthetic compounds, and other
types of polyamide resins, etc., with the use of additives and
fillers.
The reinforcing meshes are normally textiles with fibreglass
threads, but might also be other types of fibre such as
carbon, Kevlar or another; the meshes have a height of about
1.5 m, are first immersed in a solution of liquid resins and
solvents, squeezed between pairs of rollers and dried in
special ovens internally of which the resin dries without
polymerizing (polymerization is completed later in the firing
oven together with the firing of the grinding wheel).
The meshes, thus-impregnated with resin and dried, are used
for the blanking (or other method) of the mesh discs required
for reinforcing the grinding wheels.
The meshes can be pre-glued to a paper sheet or a slim polymer
material sheet, or to labels.
The annular defining elements delimiting the attaching hole of
the grinding wheel are constituted by a circular annulus
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plate, or another shape such as square or polygonal, from an
internal hole of which a cylindrical or non-cylindrical
appendage emerges; the plate adheres to one of the two faces
of the grinding wheel, while the hollow appendage inserts in
the hole of the grinding wheel, delimiting the internal wall
thereof.
The labels are made of paper or foil or another synthetic
material and normally are circular-annulus shaped (though they
could be of any other shape), and can occupy either the whole
face of the grinding wheel or a limited area of the face on
which the identifying and information data of the grinding
wheel are reported.
Flat grinding wheels (in particular reference is made to a
cutting disc and not a burring disc) exhibit the whole
circular annulus projecting externally of the annular elements
which delimit the attaching hole potentially active in the
cutting operations, and which can therefore exhibit a depth
that is substantially equal to the radial thickness of the
circular annulus (except the part of the blocking flanges
which block the grinding wheel on the rotary shaft of the
grinding machine, which normally have an external diameter of
42 mm), and/or the grinding wheel can be used for a large
number of cutting operations.
Flat grinding wheels, however, exhibit a high flexibility and
therefore low precision in the cutting operations and a low
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resistance to inappropriate uses and stresses. Further, as
they are not very rigid, they can be subject to flutter during
rotation, which makes precision cuts difficult to carry out.
To obviate this drawback, grinding wheels with a central
depression have been realised, in which at the central zone
proximal to the attaching hole a cupola is formed, as shown in
figure 1, which illustrates a depressed-centre cutting
grinding wheel of known type.
Depressed-centre grinding wheels have the advantage, with
respect to flat grinding wheels, of having a three-dimensional
shape and therefore of providing a greater rigidity, stability
and precision.
The main disadvantage of the depressed-centre grinding wheels
is that the cupola, or cap, which generally extends over a
conspicuous radial tract of the grinding wheel (in practice,
it normally exhibits an external diameter of about 65 mm, so
that the attaching flange, which has a standard external
diameter of 42 mm, of
the grinding machine can be
accommodated in the concave part of the cupola) and therefore
does not enable the cut to be as deep as with a flat grinding
wheel and/or does not enable making a same number of total
cuts as with a flat grinding wheel.
This forces the user to replace depressed-centre grinding
wheels frequently as they are no longer fit for use, with a
subsequent effect on costs for the users. Flat discs on the
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other hand can be used for a longer time as they do not have the cupola
interfering with
pushing the cut more deeply.
This drawback is more severely felt in cutting grinding wheels which exhibit
relatively
small external diameters, as all depressed-centre grinding wheels have a
cupola with
an external diameter that is greater than 60 mm and therefore this cupola is
more
"unwieldy" in discs having a smaller diameter.
An aim of the present invention is to obviate the above-mentioned drawbacks in
the
prior art, with a solution that is simple, rational and relatively
inexpensive.
The aims are attained by the advantageous aspect of the invention reported
hereinafter.
DESCRIPTION OF THE INVENTION
The invention relates in particular to a depressed-centre grinding wheel
comprising at
least a circular cutting annulus made of a substantially planar compacted
abrasive
material lying on a plane that is perpendicular to the rotation axis of the
grinding wheel
and a concave central portion provided with a central through-hole for
attachment.
In the invention, the internal diameter of the circular annulus coinciding
with the external
diameter of the concave portion is not greater than 55 mm.
With this solution, given a same external radius of the grinding wheel, the
wheel exhibits
a larger active cutting portion and therefore a greater depth of cut and/or it
can be used
to perform a greater number of cuts.
In an aspect of the invention, the external diameter of the circular annulus
is
substantially comprised between 100 and 230 mm, preferably between 100 and 125
mm.
Another further aspect of the invention relates to a depressed-centre grinding
wheel
comprising a disc-shaped element obtained by pressing a mixture of a loose
powder of
abrasive material mixed with a binder, wherein the disc-shaped element
comprises:
at least a circular cutting annulus made of a substantially planar compacted
abrasive
material lying on a plane that is perpendicular to the rotation axis of the
grinding wheel;
and
Date Recue/Date Received 2020-12-23
a concave central portion obtained by deforming the disc-shaped element and
provided
with a central through-hole for attachment,
wherein the external diameter of the circular annulus is comprised between 100
mm
and 125 mm and the internal diameter of the circular annulus, coinciding with
the
external diameter of the concave portion, is not greater than 55 mm, wherein
the
concave portion comprises a substantially planar first central section and a
concave cap
wall, and wherein an inclination of the cap wall is substantially comprised
between 400
and 70 .
Another further aspect of the invention relates to the grinding wheel defined
hereinabove, wherein the external diameter of the concave portion is
substantially
comprised between 45 mm and 55 mm.
Another further aspect of the invention relates to the grinding wheel defined
hereinabove, wherein the external diameter of the concave portion is
substantially 55
mm.
Another further aspect of the invention relates to the grinding wheel defined
hereinabove, wherein the grinding wheel comprises at least a reinforcing mesh
sunk
into the abrasive material.
Another further aspect of the invention relates to the grinding wheel defined
hereinabove, wherein the inclination of the cap wall is substantially 60 .
In these grinding wheel formats, the increase in radial thickness of the
circular annulus,
with a subsequent reduction of the external diameter of the circular cap part,
enables a
significant increase in the active cutting portion of small-dimension grinding
wheels,
which among other things are the most widely-used because they are easier to
handle
and cost less.
The concave portion advantageously comprises a first central section that is
substantially planar and a concave cap, in which the inclination of the cap
wall is
substantially comprised between 40 to 70 .
Another further aspect of the invention relates to a method for realizing a
depressed-
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Date Recue/Date Received 2020-12-23
centre grinding wheel, as defined hereinabove, which comprises steps of:
- raw-moulding a substantially planar semi-finished grinding wheel;
- deforming the central portion of the semi-finished grinding wheel, so as
to define
a depressed concave portion having an external diameter that is substantially
identical to an internal diameter of the external planar circular annulus of
the
undeformed semi-finished grinding wheel, where the external diameter of the
concave portion is not greater than 55 mm.
Another further aspect of the invention relates to a method for realizing a
depressed-
centre grinding wheel as defined hereinabove, which comprises steps of:
- raw-moulding a substantially planar semi-finished grinding wheel;
- deforming the central portion of the semi-finished grinding wheel, so as
to define
a depressed concave portion having an external diameter that is substantially
identical to an internal diameter of an external planar circular annulus of
the
undeformed semi-finished grinding wheel, wherein the external diameter of the
concave portion is not greater than 55 mm, wherein the concave portion
comprises a substantially planar first central section and a concave cap wall,
and
wherein an inclination of the cap wall is substantially comprised between 400
and
70 .
Another further aspect of the invention relates to the method defined
hereinabove,
wherein the method comprises a step of firing the deformed semi-finished
grinding
wheel.
Furthermore, following the deformation, the deformed semi-finished grinding
wheel is
subjected to a firing step, for example at appropriate firing temperatures
which enable
polymerization of the binding resin that binds the abrasive mixture together.
A further aspect of the invention relates to a grinding system which comprises
a
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Date Recue/Date Received 2020-12-23
grinding machine having a rotary shaft which can be inserted into a grinding
wheel, as
described above, (i.e. into the through-hole) and a coupling flange suitable
to be
inserted into the concave portion of the grinding wheel and having an external
diameter
substantially equal to 42 mm.
BRIEF DESCRIPTION OF THE DRAWINGS
Further characteristics and advantages of the invention will emerge from a
reading of
the description that follows, provided by way of non-limiting example, with
the aid of the
figures of the accompanying tables.
Figure 1 is a section view of a depressed-centre grinding wheel of the prior
art.
Figure 2 is a section view of a depressed-centre grinding wheel according to
the
present invention.
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Date Recue/Date Received 2020-12-23
CA 02871182 2014-11-14
=
BEST WAY OF CARRYING OUT THE INVENTION
With particular reference to the figures, reference numeral 10
denotes in its entirety a depressed-centre cutting wheel.
The grinding wheel 10 comprises an abrasive disc-shaped
element 11 which is attachable, substantially coaxially, to
the free end of a rotating shaft of a grinding machine.
The disc-shaped element 11 comprises at least a substantially
central through-hole 12 and a first convex face 13 defining
the back of the disc-shaped element.
The disc-shaped element 11 further comprises a second face 14
opposite the first face 13.
In particular, the disc-shaped element 11 is realized by at
least a layer of an abrasive mixture that is compacted and
stably bound by a binder resin.
In practice, the disc-shaped element 11 is obtained by
pressing a mixture of a loose powder of abrasive material, for
example abrasive material such as natural corundum, sand,
recycled artificial corundum or the like, abrasive so-gel or
sintered ceramic, corundum at zirconium, or other, and mixed
with a suitable binder, for example resin-based, such as
phenolic, liquid and/or powder resins possibly modified with
phenoxy epoxy resins and/or others, modified with organic
and/or vegetal or synthetic compounds, and other types of
poly-imide resins, etc...., and/or with additives and fillers.
The disc-shaped element 11 is constituted by an external
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peripheral circular annulus 15 and a disc-shaped internal cap
16 (or hub), both coaxial to the through-hole 12.
In practice, the disc-shaped cap 16, which comprises the
through-hole 12, extends radially externally from the circular
annulus 15.
The circular annulus 15 lies substantially in a perpendicular
plane to the axis of the grinding wheel 10 (axis of the
through-hole 12).
The circular annulus 15 of the abrasive mixture is the active
portion of the grinding wheel 10, i.e. the portion thereof
that is generally used for cutting.
The circular annulus 15 has an external diameter De, variable
during use, which defines the external diameter of the
grinding wheel 10 and an internal diameter Di, fixed, which
defines the external diameter of the circular cap 16.
The circular cap 16 has an external diameter substantially
equal to the internal diameter Di of the circular annulus 15
and an internal diameter substantially equal to the diameter
of the through-hole 12.
In particular, for the purposes of the present invention, the
external diameter of the circular cap 16, which substantially
coincides with the internal diameter Di of the circular
annulus 15, is substantially not greater than 60 mm (for
example, less than 57.5 mm).
The external diameter of the circular cap 16 is preferably
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substantially between 45 and 55 mm, so as to allow insertion
of a coupling flange in its concavity, able to fasten the
grinding wheel 10 to the rotary shaft of the grinding machine,
which generally exhibits a diameter of about 42 mm and, at the
same time, does not adversely affect either the radial
thickness of the active portion in the cutting action
(circular annulus 15) of the grinding wheel 10 or the
stability and resistance of the grinding wheel.
Advantageously, the external diameter of the circular cap 16
is substantially 55 mm.
This dimension has been found to be optimal for the aims set
out above.
The external diameter (De) of the circular annulus 15 is
between 100 and 230 mm.
In particular, the wheels 10 have standardized dimensions and
are classified according to the external diameter (De) of the
grinding wheel 10, which exhibit the following rated
dimensions:
De = 115 mm, 125 mm, 150 mm, 180 mm, 200 mm and 230 mm.
The external diameter (De) of the circular annulus 15 is
preferably between 100 and 155 mm and preferably between 115
and 150 mm.
In these formats (where the external diameter of the grinding
wheel 10 is between 100-155 mm, and in particular the standard
formats have external diameters of 115 mm and 125 mm) of
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grinding wheels 10, where the external diameter is smaller,
the peculiarity of the invention (i.e. the fact that the
external diameter of the circular cap 16 does not exceed 60
mm) is decidedly more advantageous, as it provides a
percentage active portion greater than the grinders (of the
same diameter) of the traditional type (as shown in figure 1),
given an identical sturdiness of the grinding wheel 10.
In practice, even in these formats, in which the external
diameter De is 115, 125 and 150 mm) the ratio between the
internal diameter Di and the external diameter De of the
circular annulus 15 is substantially less than
The circular cap 16 includes a first internal portion 161 that
is substantially planar, parallel and coaxial to the circular
annulus 15, and a cap wall 162 (coaxial with the circular
annulus 15), connecting the first internal portion 161 and the
circular annulus 15.
Advantageously, the cap wall 162 of the concave circular cap
16 has an inclination substantially comprised between 40 and
70 , preferably 60 .
In practice, the cap wall 162 radially occupies a radial
portion substantially identical to the distance of the rise
that it defines (i.e. the axial distance between the first
internal portion 161 and the circular annulus 15, which are
substantially parallel).
The abrasive mixture has a granulometry of substantially
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between 120 and 12 mesh (however abrasive mixtures of a
greater or smaller particle size than the above-described
range recorded can be used, according to requirements).
The layer of abrasive mixture can have a thickness of around 3
mm or less, though this could be greater or smaller than 3 mm,
depending on requirements.
The grinding wheel 10 comprises, for example, at least a
reinforcement mesh 17, schematically illustrated in figure 2,
incorporated in the layer of abrasive mixture.
The reinforcing mesh 17 is for example disc-shaped and
substantially coplanar to at least the first face 14 of the
disc-shaped element 11.
The grinding wheel 10 can have a plurality of reinforcing
meshes 17 and a plurality of layers of abrasive material of
different nature, according to needs.
By appropriately selecting the ratio between the grain size of
the abrasive mixture used, which depends on the intended use
of the grinding wheel, and the opening of the meshes of/and
reinforcing mesh/es 17, the penetration of the mixture through
the mesh thereof can be advantageously optimised.
A label 18 can be placed on the first face 14, i.e. the back
of the wheel 10, illustrated schematically in figure 2; the
label can be paper or foil or other like material.
The abrasive mixtures of the layer of abrasive mixture, as
well as the reinforcing mesh 17 and the label 18, are of a
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type widely known in the industry.
The label 18 can otherwise be applied once the grinding wheel
has been fired/polymerised, by gluing or applying self-
adhesive labels, by screening, pad printing, spraying or
5 another form of stencil painting.
Lastly, the grinding wheel 10 includes one or more metal
annular elements, commonly known as washers or sleeves 19,
which delimit the attachment hole of the grinding wheel 10 to
the pivot of the grinding machine.
10 The washer 19 is fixed to the first face 13 (or label) of the
disc-shaped element 11 and, for example, extends radially
substantially over the entire disc-shaped cap 16 exhibiting
the concave shape.
The washer 19 comprises a hollow central shank 190 that
inserts substantially snugly in the through-hole 12 and which
exhibits an axial thickness that is substantially identical to
(or slightly smaller than) the axial thickness of the grinding
wheel 10 (the layer of abrasive mixture that constitutes the
disc-shaped element 11).
The method for realising a grinding wheel 10 as described
above comprises a step of raw-moulding a semi-finished
grinding wheel that is substantially planar, i.e. so that the
not-yet-concave central area that will form the disc-shaped
cap 16 is substantially coplanar to the disc-shaped circular
annulus 15.
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The substantially planar raw moulding grinding wheel 10 is
realized using a mould able to press the abrasive mixture
together with the binder resin and give it the desired disc-
shape.
Once the semi-finished grinding wheel has been formed the
forming method continues by deforming the central portion of
the grinding wheel, so as to define the disc-shaped cap 16
having an external diameter substantially equal to the
internal diameter Di of the circular annulus 15, wherein the
external diameter of the disc-shaped cap is substantially less
than 60 mm.
The step of deforming the semi-finished grinding wheel is
advantageously done by inserting the grinding wheel into a
mould, the bottom die of which (and/or the punch) is shaped
such as to impart the desired shape to the grinding wheel.
Finally, the grinding wheel 10 thus-formed (i.e. deformed) is
subjected to a heat treatment of firing, for example in
special polymerization oven, where the polymerization is
completed of the binder resin that solidifies and stably
retains the abrasive mixture that constitutes the disc-shaped
element 11.
In practice, the grinding wheel 10 is subjected to a thermal
cycle which involves the insertion thereof in an oven at a
temperature of substantially between 120 and 220 C for a
time substantially comprised between 1 and 50 hours, or it can
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be fired in situ in the heated mould suitable for forming of
the 10 depressed-centre grinding wheel.
The invention as it is conceived is susceptible to numerous
modifications and variants, all falling within the scope of the
inventive concept.
Further, all the details can be replaced by other technically-equivalent
elements.
In practice, the materials used, as well as the contingent shapes and
dimensions, can be any according to requirements, without forsaking the
scope of protection of the following claims.
