Note: Descriptions are shown in the official language in which they were submitted.
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Cutting machine with a sharpening unit for a blade, sharpening method and
blade for
said machine
Description
Technical Field
The present invention relates to a method to sharpen disk-shaped cutting
blades with a continuous cutting edge, and in particular to sharpen disk-
shaped
blades destined to cut rolls of web material such as paper, tissue paper,
toilet tissue,
kitchen towel and the like.
The present invention also relates to a sharpening unit for disk-shaped
blades,
in particular for cutting machines destined to cut rolls of web material or
the like, and
cutting machines comprising said sharpening unit.
Moreover, the invention relates to a blade particularly suitable to be used
with
the method of the present invention.
State of the Art
Cutting machines are commonly used in the paper converting industry to pro-
duce small rolls from logs of wound paper, which have an axial length which is
a
multiple of the axial length of the finished products, corresponding to the
axial di-
mension of the reels of paper coming from paper mills.
The cutting machines commonly used to cut logs of paper or other wound
web materials are provided with a unit rotating about an axis usually parallel
to the
direction of feed of the logs to be cut or slightly slanting in respect of it.
These logs
are fed along one or more channels parallel to one another to be subjected to
the ac-
tion of a rotating disk-shaped cutting blade carried by the rotating unit. The
disk-
shaped blade rotates about an axis in turn parallel to the direction of feed
of the elon-
gated products to be cut. Traditionally, machines of this type have
intermittent or
continuous feed (with variable or constant speed) of the logs. Examples of
cutting
machines of this type are described in US-RE-30598; EP-B-0507750, US-A-
3213731, EP-B-0609668, US-A-5315907.
The disk-shaped cutting blades used for this purpose are usually biconical in
shape. That is, they are thicker in proximity to the axis and gradually
decrease in
thickness from the axis towards the edge. The cutting edge is formed of a
bevel
symmetrical in respect of the median plane orthogonal to the axis of the tool.
The blade must be sharpened frequently to restore the cutting edge especially
as it is produced with steels of limited hardness and toughness, such as high
speed
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steels. Pairs of grinding wheels, motorized or more frequently drawn by the
move-
ment of the tool, are used for sharpening; these act in an approximately
symmetrical
manner on the two sides of the cutting bevel of the blade. The diameter of the
blade
is in this way gradually reduced from the original dimension to a minimum
dimen-
sion of diameter, beyond which the blade must be replaced. The cutting edge be-
comes blunted and damaged rather quickly and must be sharpened frequently,
which
causes relatively rapid consumption of the blade, due to the wear caused by
each
sharpening operation. This makes it necessary to use high initial diameters,
in order
to reduce the number of replacements required and above all to amortize the
cost of
each blade against a sufficient quantity of cut product.
The dimension of the product to be cut and of the hub to support the disk-
shaped cutting blade make it impossible..to go below a minimum dimension of di-
ameter.
The biconical shape of the tool produces a great deal of friction between the
tool and the material to be cut. Moreover, to produce a biconically shaped
tool, a
large amount of initial raw material is required, as the biconical shape is
obtained
principally through grinding.
To decrease these drawbacks blades have been designed with a cutting edge
defined by two asymmetrical sides, one of which is hardened by facing the
cutting
profile with hard oxides. A blade of this type is described in WO-A-0021722.
The
purpose of this known blade is to increase the quantity of logs cut during the
life of
the blade, to reduce the number of sharpenings required during the useful life
of the
blade and to reduce the variation in blade diameter due to wear caused by
sharpen-
ing. However, this blade _did not attain the expected results in terms of
duration, de-
crease in wear and reduction of sharpening frequency.
Obiects and summary of the invention
The object of the present invention is to provide a circular blade with a con-
tinuous cutting edge, which overcomes the drawbacks of prior art blades. A
further
object of the pxesent invention is to produce a sharpening unut that makes it
possible
to sharpen the blade efficiently decreasing wear and avoiding the need for
substantial
excursions of the sharpening grinding wheels to compensate for wear of the
blade re-
suiting from frequent sharpening operations.
Yet another object of the present invention is to produce a method of sharpen-
ing that is simpler and more efficient sharpening than prior art methods, and
a cutting
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machine that implements said method.
Essentially, according to a first aspect, the present invention relates to a
disk- .
shaped blade to cut logs of wound web materials, comprising an axis of
rotation and
a cutting bevel, with a continuous cutting edge, defined by a first side and
by a sec-
. and side, the first side having a greater radial extension, and at least
said first side
having surface hardening treatment. Characteristically, according to the
invention,
the surface treatment has a penetration depth or a thickness of at least 30
microme-
ters and preferably more of less equal to or greater than 80 micrometers and
even
more preferably equal to or greater than 90 micrometers and even more
preferably
equal to around 100 micrometers or more.
In the context of the present description and of the attached claims, by
surface
treatment it is understood either a treatment which provides for the
penetration of at-
oms or molecules of a material inside the base structure of the blade (such as
a nitrid-
ing or carburizing, for example), or also a deposit - on the base material
forming the
blade - of a layer of harder material, such as a layer of carbides, a layer of
ceramic
material or of other hardening material, having a suitable thickness.
The penetration depth of the treatment or, generally speaking, the treatment
thickness, is such as to ensure that the bevel formed by sharpening has a
portion in-
tegrally formed in the thickness of the surface hardening, being it provided
by pene-
tration or by deposit.
Advantageously and preferably, at least the first side of the bevel has a sur-
face hardness equal to or greater than 70 HRC (Rockwell Hardness C) and
preferably
equal to or greater than around 72 HRC and even up to 73 HRC.
Advantageously, the blade is produced in alloy steel, such as molybdenum
chrome steel, and at least the surface of the first side is treated by
controlled nitrid-
ing, such as by Nitreg~ surface treatment.
Nitreg~ treatment is a special thermochemical nitriding treatment for harden-
ing the surface of steels. For a description of the process see A.M. Staines,
«NI-
TREG-A New Devel~ment in Gaseous Nitridin~», published by Nitriding Ser-
vices Ltd, Telford, Shropshire, UK. Nitriding treatments of this type are
described in
US-A-4391654, US-A-5,228,929, US-2002/0104587A1, EP-A-1229143. The treat-
ment in question makes it possible to attain high degrees of hardness
maintaining a
high level of toughness in the material treated.
When the blade is new, that is before being sharpened for the first time, the
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two sides defining the cutting bevel may have symmetrical inclinations, that
is they
may define the same angle in respect of the lying plane of the cutting edge.
However,
it is preferable for the first side to have a lesser inclination than the
second side in re-
spect of the lying plane of the cutting edge. This makes it possible, as shall
become
clear hereunder, to position the sharpening grinding wheels in symmetrical
positions
and to produce, during the life of the blade, a cutting edge symmetrical in
respect of
the lying plane. For example, the difference in inclination between the first
and the
second side is at least 1° and preferably between axound 1.5°
and around 2.5° and
even more preferably around 2°. According to an advantageous
embodiment, the first
. side can have a zero inclination with respect to the median plane of the
blade, i.e.
with respect to the lying plane of the cutting edge of the blade.
When the blade is new, that is before wear determined by successive sharpen-
ings, the cutting edge may lie on a lying plane that does not coincide with
the plane
of the center line of the blade and, in respect of this, is moved towards the
second
side.
The disk-shaped blade may be biconical in shape, that is with a body delirn-
ited by two opposed conical surfaces, with a wide aperture. Nonetheless,
according
to a preferred embodiment of the invention, the body of the blade is delimited
by two
planes essentially parallel to each other and essentially orthogonal to the
axis of rota-
tion of the blade.
According to a different aspect, the present invention relates to a sharpening
unit to sharpen a disk-shaped blade, with. a cutting bevel with a continuous
circular
cutting edge, and comprising a first grinding wheel and a second grinding
wheel act-
ing on a first side and on a second side of said bevel. Characteristically,
according to
the invention, the first grinding wheel has a finer grain than the second
grinding
wheel. Moreover, the inclination of the first grinding wheel is not paxallel
to the re-
spective first side of the bevel of the blade, while the inclination of the
second grind-
ing wheel is essentially parallel to he second side of said bevel.
The two grinding wheels are advantageously equipped with a movement to
move them towards and away from the blade in a direction essentially parallel
to
their respective rotation axis. The object of this movement is to position the
grinding
wheels in the operating and non-operating position respectively and also to
recover
wear of the blade caused by the successive sharpening operations.
The grinding wheel with larger grain is used to perform the actual sharpening
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and acts on the side of the bevel that, following initial sharpening, loses
the surface
hardening treatment. On the contrary, the first grinding wheel, with extremely
fme
grain, acts on the side of the bevel destined to preserve the surface
hardening treat-
ment and acts simply to remove any burrs from the cutting edge, while also
support-
s ing the blade to prevent flexure caused by the pressure exerted by the
second grind-
ing wheel. The two grinding wheels rnay start to operate simultaneously.
Nonethe-
less, to obtain optimal operation of the sharpening unit, the finest grinding
wheel
starts to operate before the grinding wheel with the larger grain and leaves
the oper-
sting position with a delay. Preferably, the delay.with which the first
grinding wheel
disengages from the blade in respect of the moment at which the second
grinding
wheel ceases to act on the' bevel of the blade is equal to at least one
complete turn of
the blade. This ensures that any burrs are eliminated from the cutting edge.
'The inclination of the first grinding wheel allows it to operate only in prox
imity to the cutting edge, that is at the tip of the bevel, and not along the
entire exten
t S' sion of the side of the bevel. The thickness of surface treatment on the
blade, the fact
that the grinding wheel is not aggressive and its angular position in respect
of the
side of the bevel mean that the cutting edge, that is the line of intersection
of the two
sides and the surface ' area of the blade immediately adjacent to , this line
remain
within the thickness of the material of the blade that has been subjected to
the surface
hardening treatment,. Independently of whether it is formed by a deposit or by
the
penetration of particles --e.g. by thermal treatment - in the structure of the
base ma-
terial forming the blade.
The grinding wheels may be idle and hence drawn in rotation by the rotating
blade. Nonetheless, they are preferably motorized. The motorized grinding
wheels
may be pressed against the blade with less pressure, thus making it possible
to obtain
a smoother ground surface. Mixed solutions may also be used in which one
grinding
wheel is drawn and the other motorized or in which there are more than two
grinding
wheels, some motorized and others drawn.
Preferably, according to a particularly advantageous embodiment of the in
vention, the inclinations of the two grinding wheels are equal and opposite in
respect
of the lying plane of the cutting edge of the blade.
According to another aspect, the present invention relates to a cutting ma-
chine to cut logs of wound web material, comprising: a feed path of the logs
to be
cut; at least a disk-shaped blade rotating about an axis of rotation and
having a cut-
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ting bevel, with a continuous cutting edge, said bevel being defined by a
first side
and by a second side, the first side having a greater radial extension in
respect of the
second side, and at least said first side having a surface hardening
treatment; a sharp-
ening unit for the blade, with at least a first grinding wheel acting on the
first side
and a second grinding wheel acting on the second side. Characteristically,
according
to the invention, the first grinding wheel has a finer grain than the second
grinding .
wheel; and the inclination of the first grinding wheel is greater than the
inclination of
the first side of the bevel in respect of a lying plane of the cutting edge of
the blade,
while the inclination of the second grinding wheel is essentially parallel to
the second
side of said bevel. In this way the first grinding wheel acts only on the
terminal part
of the bevel, that is the part nearest to the cutting edge, while the second
blade acts
on the entire radial extension of the bevel.
Advantageously, the inclination of the first grinding wheel in respect of the
first side of the bevel and the thickness of.the hardening treatment may allow
the cut
ting edge of the blade to remain within the volume that has been subj ected to
the
hardening treatment.
Yet another aspect of the present invention relates to a method to sharpen a
disk-shaped blade rotating about an axis of rotation, said blade having a
cutting
bevel, with a continuous cutting edge, said bevel being defined by a first
side and by
. a second side, the first side having a greater radial extension than the
second side,
and at least said first side having a surface fardening treatment. According
to the
method a first grinding wheel acts on the first side and a second grinding
wheel acts
on the second side. Characteristically, according to the invention: the first
grinding
wheel has a finer grain than the second grinding wheel; the first grinding
wheel is
moved against the first side of the blade with an inclination slightly greater
than the
inclination of the first side, in respect of. a laying plane of the cutting
edge of the
blade; and the second grinding wheel is moved against the second side of the
bevel
with inclination essentially corresponding to the inclination of said second
side in re-
spect of said laying plane.
Further advantageous characteristics and embodiments of the blade, the
sharpening unit, the cutting machine and the sharpening method according to
the in-
vention are indicated in the appended dependent claims.
Brief description of the drawings
The invention shall now be better understood by following the description
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and appended drawing, which shows a non-limiting practical example of the
inven-
tion. In the drawing:
Figure 1 shows a summary side view of a cutting machine according to the
invention;
Figure 2 shows a front view according to II-II in Figure 1;
Figure 2A shows a development in the plane of the control cam in Figure 2;
Figure 3 shows a side view and part section according to III-III in Figure 2;
Figure 4 shows a partly enlarged section of a detail of Figure 3;
Figure 5 shows a front view of a cutting blade;
Figures 6A and 6B shows two enlarged local sections according to a radial
plane of the cutting bevel of the blade in Figure 5, respectively of the new
blade and
of the completely worn blade;
Figure 7 shows a-greatly enlarged view of the cutting bevel and of the cutting
edge of the blade during use and after at least a first sharpening;
Figure 8 shows an enlarged view of the arrangement of the sharpening grind-
ing wheels of one of the sharpening units of the cutting machine;
Figure 9 shows a longitudinal section of one of the two grinding wheels with
the respective operating mechanism; and
Figure 10 shows a part cross-section according to X-X in Figure 9.
Detailed description of the preferred embodiment of the invention
Figure 1 schematically shows (limited to its front part) a cutting machine, as
a
whole indicated with 1, to which the present invention is applied. The machine
has a
feed path of the logs to be cut, indicated with L, which are pushed by pushers
3 se-
cured to a flexible chain element or the like 5, driven about a driving wheel
sup-
ported by a fixed structure 7. Only one dxiving wheel, indicated with 9, is
visible in
Figure 1, while the other is at the rear end of the cutting machine, not
shown. In ac
tual fact, as known to those skilled in the art, there are more than one
flexible ele
ments 5 in parallel to feed several rows of logs L according to parallel
paths. In the
example shown four channels are provided for simultaneous feed of four logs L
posi
tinned side by side,
The flexible elements 5 associated with the various parallel feed channels of
the logs may be motorized separately from one another to stagger the movement
of
logs in each feed channel.
The number 11 generically indicates a cutting head that, by means of a sup-
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port 13, carries a rotating unit 17. The unit 17 rotates about a horizontal
axis A-A
parallel to the direction fL of feed of the logs L. In the example shown,
three disk-
shaped blades 19A, 19B and 19C are mounted on the rotating unit 17, disposed
at
120° from one another about the axis A-A, as can be seen in particular
in Figure 2.
Each of the rotating disk-shaped blades 19A, 19B and 19C rotates about its own
axis
of rotation B-B parallel to the axis A-A and to the direction of feed fL of
the logs L.
The number 21 indicates a motor that, by means of a belt 23, transmits rota-
tory motion to the rotating unit 17. A second motor 25 is positioned on the
support
13 of the rotating unit 17 and, by means of a belt 27, supplies rotatory
motion to a
shaft that drives disk-shaped blades 19A, 19B and 19C in rotation by means of
a
transmission to be described hereunder. By means of a belt 31, a third motor
29
drives the driving wheel 9 of the rotating element 5 in rotation. As mentioned
above,
as several parallel channels may be provided for feeding the logs L that are
cut sepa-
rately to form the small rolls R, a driving wheel 9 may be associated with
each chan-
nel, with its own motor unit 29 suitably controlled as a function of the
angular posi-
tion of the rotating unit 17. The number 35 indicates a programmable control
unit
that synchronizes the angular position of the unit 17 with the feed movement
of the
flexible elements) 5 acting on the motors) 29.
Figures 2 and 3 show how the rotating unit 17, drawn in rotation by the hub
17A, internally supports three toothed wheels, positioned at 120° from
one another
about the axis A-A, indicated with 41 A, 41 B and 41 C. Said wheels mesh with
a cen-
tral toothed wheel 43 keyed onto a shaft 45 that receives its motion from the
motor
through the belt 27.
The toothed wheels 41A, 41B and 41C are keyed onto respective spindles
25 47A, 47B and 47C onto which toothed pulleys 49A, 49B and 49C are in turn
keyed.
Each of the toothed pulleys 49A, 49B, 49C transmits the motion supplied by the
mo-
tor 25, through toothed belts 51A, 51B, 51C, to the rotating disk-shaped
cutting
blades 19A, 19B a 19C.
As can be seen in the detail in Figure 4 for the blade 19C, the toothed belt
51A, 51B, 51C transmits motion to a toothed pulley 53A, 53B, 53C keyed onto an
axle 55A, 55B, 55C, on the opposite end of which the respective disk-shaped
blade
19A, 19B, 19C is keyed.
Each of the shafts is supported by bearings 57 in a respective sleeve 59A,
59B, 59C sliding on sliding bearings 61 mounted in a respective seat 63A, 63B,
63C
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provided in the rotating unit 17. The angular movement about the axis B-B of
each
sleeve 59A, 59B, 59C is prevented by a tab 58 integral with the respective
sleeve,
cooperating with wheels 60 supported idle in the sliding seat of the sleeve.
At the rear, that is on the opposite side in respect of the disk-shaped blade
19C, each sleeve 59A, 59B, 59C has an enlarged area 65A, 65B, 65C that houses
the
toothed pulley 53A, 53B, 53C respectively, and mounted idle on which is a
wheel
67A, 67B, 67C that constitutes the feeler for a fixed cam 71 extending in an
arc of
circumference, shown in particular in Figure 2 and in its development in the
plane in
Figure 2A.
The arc of circumference along which the cam 71 extends has its center on
the axis A-A of rotation- of the rotating unit 17 and extends in the lower
part of the
path of each disk-shaped blade 19A, 19B, 19C, i.e. in the zone in which the
blade is
inserted into the product to be cut.
Through the effect of the cam 71 and of the feeler 67A, 67B, 67C each sleeve
59A, 59B, 59C associated with the respective disk-shaped blade 19A, 19B, 19C
trav-
els with alternate motion according to the double arrow fl. Consequently, the
respec-
tive disk-shaped blade 19A, 19B, 19C are provided with the same motion. The
movement according to the arrow fl is parallel to the direction of feed of the
logs L
or other elongated products to be cut. Contact of the feeler 67A, 67B, 67C
with the
annular cam 71 is ensured by an arrangement of Belleville springs 72A, 72B,
72C
that act between the rotating unit 17 and the enlarged portion 65A, 65B, 65C
of the
sleeve 59A, 59B, 59C.
Along the lower arc of the circular~trajectory taken by each disk-shaped blade
19A, 19B, 19C, the blade is pushed forwards by the annular cam 71 that
overcomes
the compression strength of the respective Belleville springs 72A, 72B, 72C.
In this
way the blade that is operating at that time, i.e. inserted in the material
constituting
the logs) L to be cut, moves forward following the forward motion of the logs
L
along the feed path.
The forward movement is controlled by the ascending ramp 71A of the cam
71 (see Figure 2A). The forward motion starts before the respective blade 19A,
19B,
19C penetrates the material constituting the first of the logs to be cut, so
that at the
time in which contact with the blade starts it is already moving forward at
the same
speed as the material to be cut according to the arrow fL.
When the blade emerges from the logs) L, it is made to reverse by the
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springs 72 that maintain the feeler 67 in contact with the descending ramp 71D
of the
circular cam 71, which may be limited to a portion of the circumference
followed by
the feeler 67C, as in the upper stretch of travel the blade 19A, 19B or 19C
does not
require to follow the movement of the roll. Forward motion of the logs L is
con-
trolled in the same way described in EP-B-0507750.
The considerable length of the belts S1A, 51B and 51C provides the toothed
pulley 53A, 53B or 53C with sufficient freedom of movement in the axial
direction,
so that the respective disk-shaped blades may advance and reverse without
being ob-
structed by mechanical transmission of motion from the central axis. The
axial'exten-
sion of the toothed pulleys 53A, 53B, 53C and 49A, 49B, 49C may be greater
than
the height of the respective belts 51A, 51B, 51C to allow any minor sliding of
the
belts on the driving pulleys.
Integral with each sleeve 59A, 59B, 59C is a support 73A, 73B, 73C, each
carrying a sharpening unit 80 comprising a pair of grinding wheels 81, 83 to
sharpen
the respective rotating disk-shaped blades 19A, 198, 19C. Each grinding wheel
of
the pair of grinding wheels 81, 83 associated with each blade acts on one of
the two
sides of the cutting bevel of the blade, which will be described in detail
with refer-
ence to Figures 5 to 7.
The grinding wheels 81 and 83 may be motorized grinding wheels, that is
drawn in rotation by specific motors such as pneumatic motors, although it is
also
possible to use grinding wheels mounted idle and drawn in rotation through the
effect
of contact friction with the disk=shaped blade. Feed of compressed air to the
actua-
tors associated with the three pairs of grinding wheels 81, 83 may be supplied
by an
axial rotating distributor, not shown and of a per se known type.
The two grinding wheels 81, 83 of each sharpening unit 80 are also provided
with a movement parallel to their axis of rotation to be brought alternately
into con-
tact with and moved away from the respective rotating disk-shaped blade, as
sharp-
ening is not continuous but performed only at regular intervals as the blade
becomes
blunt and thus requires sharpened. The structure of the mechanisms that make
the
grinding wheels rotate and cause them to move towards and away from the respec-
tive blade will be described with reference to Figures 9 and 10. The
arrangement of
the two grinding wheels 81, 83 of each sharpening unit 80 is shown in
particular in
the enlarged detail in Figure 8.
Each of the blades 19A, 198, 19C is designed as shown in Figures 5 to 7,
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which show any one of the three blades 19A, 19B, 19C, indicated simply with
the
reference 19.
The blade 19 has a disk=shaped body delimited by two flat faces 201A, 201B
parallel to each other, and a circular cutting edge 203. Therefore,
essentially it has a
continuous thickness in the range of 1.5-4 mm and preferably between 2 and 3
mm,
in particular for example 2.5 mm.
The cutting edge 203 represents the final edge of a cutting bevel, indicated
as
a whole with 205. This cutting bevel is delimited by two sides 207 and 209.
The first
side 207 extends radially (i.e. in the direction of the radius of the disk-
shaped blade)
to a greater extent that the radial extension of the second side 209, in any
condition
of wear of the blade.
At least the side 207 has been subjected to surface hardening treatment. IN a
practical embodiment described here by way of example, said treatment is a con-
trolled nitriding thermal treatment, such as in particular Nitreg~ treatment.
In actual
~ fact, the entire surface of the blade may be subjected to this treatment, as
it is simpler
and less expensive to perform complete treatment than to mask the parts of the
blade
that do not require to be treated. Alternatively, the entire surface of the
blade rnay be
subjected to treatment, with the exception of the side of the cutting bevel on
which
the grinding wheel with the largest grain, destined to perform actual
sharpening, acts.
In this way the duration of the grinding wheel may be extended. The controlled
thermochemical nitriding treatment penetrates the base material of the blade
for a
depth T (Figure 7), for example of axound 100 micrometers. Alternatively, as
set
forth herein before, the surface hardening treatment can be provided in the
form of a
deposit of a harder material on the surface of the blade, or even in a
depressed area of
the blade body provided for the purpose of being filled up with said deposit.
Figure 6A shows the bevel of the blade before the first sharpening operation
with continuous surface treatment along its entire surface. In this initial
condition,
the cutting edge 203 lies on a lying plane PG parallel to the median plane PM
of the
blade, which is represented by the plane orthogonal to the axis B-B of
rotation and
equidistant from the faces 201A, 201B of the body of the blade. The lying
plane PG
of the cutting edge 203 is shifted, in respect of the median plane PM of the
blade,
towards the second side 209 of the bevel 205.
Still in the condition of a nevv blade, represented in Figure 6A, the side 207
is
defined by a conical surface with axis coinciding with the axis B-B of
rotation of the
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blade and with an inclination a in respect of the lying plane PG of the
cutting edge
203. The angle a may for example be around 8°. The side 209 also has a
conical
form coaxial to the axis B-B and an inclination [3 in respect of the plane PG.
The an-
gle (3 is slightly greater than the angle a and may be for example equal to
10°. The
possibility is not excluded, however, that the angle cc is 0°.
In Figure 6B the blade is, shown in its condition of maximum wear. The sides
207, 209 still have the same inclination, although the side 207 now extends in
a ra-
dial direction for less than the side 209. Moreover, the lying plane PG of the
cutting
edge 203 is moved in respect of the median plane PM towards the first side 207
and
not towards the second side 209. As the relative dimensions of the two sides
vary as
the blade becomes worn, unless otherwise specified in the present text and in
the ap-
pended claims, reference is generally made to the dimensions of the new blade,
that
is before wear caused by initial sharpening.
The blade is produced in molybdenum chrome steel, such as X150CrMo12
steel, which with Nitreg~ treatment even reaches a hardness equal to 72-73 I-
iRC for
the penetration depth of the controlled nitriding treatment.
As shown in particular in the enlarged detail in Figure 8, the two grinding
wheels 81 and 83 are disposed with equal inclination and contrary in respect
of the
lying plane. PG of the cutting edge 203 of the blade 19, that is in respect of
a plane
orthogonal to the axis B-B of rotation of the blade 19. More specifically, the
two
grinding wheels are inclined by an angle (3 in respect of the lying plane of
the cutting
edge of the blade. This means that the grinding wheel 83, which acts on the
side 209
inclined by an angle (3 in respect of the plane PG, operates parallel to the
side and
performs the actual sharpening of the blade. Removal of material from the side
of the
blade by the second grinding wheel 83 does not alter the conical shape of the
side
209 of the bevel and its inclination in respect of the original inclination.
On the contrary, the first grinding wheel 81, which acts on the side 207 of
the
bevel 205, only touches the side in the area nearest the cutting edge, due to
the dif
ference in inclination between the side 207 (inclined by an angle a in respect
of the
plane PG) and the grinding wheel (inclined by an angle (3 in respect of this
plane).
The contact conditions between the sides of the bevel 205 and the two grinding
wheels are shown in the enlargement in Figure 7, where the two grinding wheels
81,
83 are indicated with a dashed line. As can be seen in Figure 7, due to the
slight dif
CA 02501183 2005-04-04
WO 2004/035273 - 13 - PCT/IT2003/000631
ference between the inclination of the side 207 and of the grinding wheel 81,
and due
to the considerable depth T of the surface hardening treatment, the cutting
edge 203
is produced wholly in a thickness of the material of the blade 19 subjected to
this
treatment. The cutting edge 203 and the portions of the sides of the bevel
immedi-
ately adjacent to this cutting edge always remain within the thickness that
has been
subjected to hardening notwithstanding the amount of wear on the blade.
Therefore,
the cutting edge is hardened on both sides. Moreover, thanks to the
symmetrical lay-
out of the grinding wheels 81, 83, it has a symmetrical section in respect of
its lying
plane PG, with consequent advantages in terms of dynamic stresses on the
blade.
The two grinding wheels 81 and 83 have markedly distinct abrasive charac-
teristics. In fact, as mentioned hereinbefore, the second grinding wheel 83 is
utilized
for the actual sharpening operation and consequently has a grain size suitable
for this
purpose. On the contrary, the function of the grinding wheel 81 is to support
the
blade against the stresses exerted by the grinding wheel 83 and to eliminate
any burrs
produced along the cutting edge 203 by said grinding wheel 83, although it
does not
actually perform any sharpening operations, but merely polishes the bevel.
There-
fore, it will have a much finer grain size than the grinding wheel 83 and will
not
abrade the surface layer of the side 207 that has been subjected to the
hardening
treatment, except to a negligible extent anti only in proximity of the cutting
edge, that
is at the tip of the bevel 205
Typically, with reference to DIN standards and ISO 6106-1979 standards, the
grinding wheel 81 may have diamond grains or equivalent and have an «extremely
fine» grain, that is from 7 to 46 (ISO standards), and preferably in proximity
or
equal to the minimum value 7, corresponding to a dimension of the sieve from
37 to
44 micrometers. The grinding wheel 83 may, on the contrary, be produced with
the
same type of abrasive and «fine» grain according to DIN and ISO 6106-1979
classification, that is between 45 and 91 (ISO standards), corresponding to
screen
meshes with dimensions between 53 and 74 micrometers. Preferably the grain
size of
this grinding wheel is around 70-80 (ISO).
With this arrangement wear of the blade caused by sharpening is very limited
and a considerably long useful life of the blade is obtained, greater than the
useful
life of traditional grinding wheels (in terms of number of cuts made), with a
limited
variation in the total diameter of the blade, for example of about 15-20 mm
for
blades with initial diameters usually between around S00 and 600 mm.
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In addition to a lower cost for expendable materials, this also has the advan-
tage of eliminating the need to provide the grinding wheels with a movement to
move them gradually towards the axis of the blades in order to recover wear,
and to
adjust the position of the blade in respect of the axis of rotation of the
unit carrying
it, as the variation in diameter resulting from wear can be recovered by the
simple
movement towards the blade and away there from, with which the grinding wheels
are periodically brought in the operating and non-operating position
respectively.
Figure 9 shows a longitudinal section of one of the grinding wheels 81 and of
the relative axial supporting and traversing and rotation system. The grinding
wheel
83 is mounted and rotation and travexse movement are controlled in the same
man-
net.
The grinding wheel 81 is keyed onto a shaft 85 supported by bearings 87 in a
bushing 89. The bushing slides on the sliding bearings 91 inside a supporting
sleeve
93 connected integral with the support 73C. At the opposite 'end in relation
to the po-
sition of the grinding wheel 81 the shaft 85 is connected to a hollow shaft 95
coupled
by a spline coupling 97 to the motor shaft 99 of a pneumatic or equivalent
motor 101.
The bushing 89 has a helical groove 103 that extends through an arc of helix
extremely reduced and inclined greatly in respect of the axis C-C of the shaft
85 of
the grinding wheel 81. A wheel 105 mounted idle on a spindle 106 supported by
the
support 93 engages in the helical groove 103. The arrangement of the groove
103 and
of the wheel 1 O5 may be inverted, with the groove integral with the
supporting sleeve
93 and the wheel integral with the bushing 89
With this arrangement angular oscillation about the axis C-C of the bushing
89 causes it to slide axially along the axis C-C through the effect of the
wheel 105
that acts as a tappet inside the helical channel 103 that acts as a
desmodromic cam.
Angular movement about the axis C-C of the bushing 89 is imparted by a pair
of piston-cylinder actuators 1 O8A, 108B paxallel to each other, visible in
particular in
the section in Figure 10. The cylinders of these actuators are integral with
the sup-
porting sleeve 93, while the rods extend inside the sleeve and their ends rest
on a lev-
eled surface 110 produced. on the bushing 89. By extending one of the two
actuators
lO8A, 108B and retracting the other this causes oscillation of the bushing 89
about
the axis C-C and consequently axial movement of the bushing and of the
grinding
wheel supported by it.
With an arrangement of this type it is possible to control, with great
precision,
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the pressure that each of the two grinding wheels 81, 83 exerts on the
respective side
of the corresponding disk-shaped blade 19A, 19B, 19C. This is obtained by
control-
ling the pressurized fluid inside the actuators 108A, 108B, In this way
sharpening of
the blades can be controlled accurately, limiting wear and at the same time
maintain-
ing optimal sharpening. -
It is understood that the drawing merely shows a non-limiting example of the
invention, which may vary in shapes and arrangements without however departing
from the scope of the concept on which the invention is based. Any reference
num-
bers in the appended claims are provided to facilitate their reading with
reference to
the description hereinbefore and the appended drawings, and do not limit the
scope
of protection.
