Note: Descriptions are shown in the official language in which they were submitted.
85615003
Using a knife as a chipper knife, profiling knife or hacker knife
The invention relates to the use of a knife of the type specified in the
preamble of claim 1
for the processing of wet wood and/or raw wood.
In the case of knives for machining wood or wood-like materials there is
generally a
pronounced interest in reducing or avoiding wear and maximizing service life.
This is
attempted in many areas of application by using cutting inserts of high
hardness
materials. Such high-hardness inserts are especially widely used in the fine
machining of
dry wood, fiberboard or the like; the cutting inserts are then soldered in a
conventional
manner to a knife body. The high-hardness materials known for this purpose are
considered to be very wear-resistant, but also shock-sensitive. In the said
application,
therefore, work is done with sufficiently low tooth pitches so that the impact
loads acting
on the individual cutting inserts are low. In such circumstances, very high
cutting speeds
and yet long service life can be achieved.
Different conditions can be found, however, in the processing of wet or raw
wood. For
example, in sawmills, the raw wood delivered from forestry is processed in
several
process steps. Sawn timber is produced from the raw wood in large machines,
wherein
the wood waste is further processed into wood chips. Such machines are
equipped with
special knives, for example profiling, chipper and/or hacker knives. Due to
the very high
tooth pitches such knives are exposed to high wear and extremely high impact
loads.
From DE 1 724 727 U a chipper knife is known which has a cutting insert of
hard metal
to increase the wear resistance. The cutting insert is welded onto the
supporting body of
the hacker knife. Again, it is disadvantageous that the cutting inserts tend
to break due to
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the high impact loads. Experts therefore currently assume that highly hardened
cutting
inserts in chipper knives, profiling knives or hacker knives cannot withstand
the impact
loads encountered and therefore are unsuitable for processing wet wood and/or
raw
wood.
The object of the invention is to be able to perform the processing of wet
wood and/or
raw wood with increased service life.
This object is achieved by the use of a knife having the features of claim 1.
The knife according to the invention comprises a blade base body and at least
one cutting
insert with a cutting edge. The cutting insert is supported by the blade body
and is fixed
to the blade body by a soldered joint with a copper solder. The knife thus
configured is
used according to the invention for the processing of wet wood and/or raw
wood.
The invention is based on the finding that, contrary to the technical
preconception of the
experts, a high-hardness cutting insert can safely be subjected to significant
operational
impact loads, provided that certain conditions are met. It was in fact
recognized that it
was not the impact load itself, but a resulting bending deformation of the
cutting insert
with local zones of tensile stress which was responsible for premature failure
of the
cutting insert.
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Specifically, the knife engages in the workpiece, acts on the cutting insert,
and there in
particular exerts a cutting force on the cutting edge. This cutting force
presses the cutting
insert against the blade body. In this process, the cutting insert undergoes
deformation
due to elastic compliance of the support thereof, which leads to bending
stresses in the
cutting insert.
In conventional soldering, in which a nearly full-surface soldered joint of
the base body
and cutting insert is present, with commonly used silver solder, a soldering
gap with a
certain gap thickness arises between the cutting insert and blade body in the
context of
the known manufacturing process, wherein the soldering gap is filled with the
soldering
material. Due to its flexibility in conjunction with the gap thickness, the
comparatively
soft solder material produces a resilient bedding of the cutting insert, which
allows the
previously described bending deformation of the cutting insert. The inherent
tensile
stresses resulting from the bending deformation are additive with operational
bending
stresses and lead to component failure or cutting edge fracture.
For knives with welded cutting inserts, the compliance of the bedding is
limited to the
compliance of the less soft weld, which is why the operational bending
stresses are
lower. However, it should be noted that welded cutting inserts are not full-
surface, but
are instead attached to the knife body like a frame. For example, cutting
forces can cause
the cutting insert to lift off from the knife body in the center and create
bending stresses
on the welds. In addition, welded knives have high thermally-induced residual
tensile
stresses at the joints of the knife body and the cutting insert as a result of
the welding
process. These residual tensile stresses are additive with the bending
stresses as well as
with the operational bending stresses and lead to component failure or cutting
edge
breakage.
With the use of copper solder according to the invention, the above
difficulties are
avoided. Since the hard-soldered joint with copper solder has very low
flexibility
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compared to other hard-soldered joints, in particular because of its
comparatively small
solder gap thickness, the cutting insert is supported against the cutting
forces in a much
less yielding manner by the copper solder. Due to the stiffer support, bending
stresses in
the cutting insert, resulting in particular from abruptly applied cutting
forces, are reduced.
In addition, the joining temperature differences in hard-soldered joints with
copper solder
are significantly lower compared to the joining temperature differences of
welded cutting
inserts. Due to the comparatively low temperature changes in the joining
region, the
formation of residual tensile stresses is essentially avoided. During welding,
localized
heating also occurs, which also leads to residual stresses in the material
during the
cooling process. Overall, it has been achieved that the special material
properties of high-
hardness materials in cutting inserts are much better taken into account:
These materials
are very wear-resistant and have a very high compressive strength, but are
sensitive to
tensile stress. According to the invention, it has now been achieved that the
bending
stresses in the cutting inserts are kept within limits, even at high impact
loads, so that it is
possible to work with increased tooth pitch and correspondingly increased
impact load.
In any case, this alone enables their use for the processing of wet wood
and/or raw wood,
especially for use as a chipper knife, profiling knife or hacker knife, and
leads to
significantly higher service life compared to the use of conventional knives.
Raw wood is
the wood of felled, debranched and topped trees that have not undergone
further
processing. Wet wood is damp, undried wood. In wood processing, wet wood is
also
referred to as green wood. Chipper knives, profiling knives and hacker knives
have in
common the fact that they are used at high feed rates and large tooth pitches.
Advantageously, the tooth pitch is at least 5 mm, in particular at least 8 mm,
preferably at
least 10 mm. In this process, in contrast to dry wood processing, very high
impact loads
occur. However, these can be withstood because of the embodiment according to
the
invention, so that overall very economical use with rapid work progress and
nevertheless
long service life has become possible.
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The soldered joint between the at least one cutting insert and the blade body
is
advantageously a high-temperature vacuum soldered joint. In high-temperature
vacuum
soldering, the cutting insert is soldered to the blade body with copper solder
at a
temperature of at least 750 C in an oven under vacuum. In this case, there is
uniform and
thorough heat input up to the soldering temperature in the entire knife.
Warping of the
knife and thermally induced stresses are very low. In addition, the vacuum
serves to
prevent oxidation, which eliminates the need for a separate flux.
It is advantageously provided that the copper solder has a mass fraction of
copper of at
least 99%. Preferably, the copper solder is pure copper. Copper solder with a
high mass
fraction of copper has particularly good machinability.
The at least one cutting insert is preferably formed of a material from the
group of
substances comprising uncoated hard metal, coated hard metal, cutting
ceramics,
superhard cutting materials, natural diamond, PCD, MCD, CVD-D, CBN. As a
result, the
cutting insert has a high hardness and is particularly resistant to abrasive
wear.
Advantageously, the knife comprises at least one additional cutting insert.
Also, the at
least one additional cutting insert is fixed on the blade body by means of the
soldered
joint with the copper solder according to the invention. The cutting contour
formed by
the cutting edges of the cutting inserts is angled in a preferred variant. The
design of a
complex cutting edge or a long cutting edge is made possible by the
arrangement of
several cutting inserts to each other. The geometry of such cutting edges can
be designed
differently, for example, to reduce cutting forces or to create a targeted
workpiece surface
or chip geometry. In an advantageous alternative, the cutting edges of the
cutting inserts
together form a continuous, linear cutting contour. In the formation of long,
in particular
straight cutting edges by a plurality of cutting elements, the different
coefficients of
expansion of cutting elements and blade body are taken into account. By using
several
and therefore smaller cutting edges, the thermally induced residual stress
within the
individual cutting edges can be reduced.
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The at least one cutting insert and the blade base define a soldering gap
whose width is
advantageously less than 0.1 mm, preferably less than 0.08 mm. Since the
stiffness of the
blade main body is greater than the stiffness of the copper solder, with a
smaller width of
the soldering gap the displacement of the cutting insert is also decreased
during the
cutting process. As a result, the bending stress is reduced to a minimum,
which is
associated with a corresponding increase in impact resistance.
Further features of the invention will become apparent from the further
claims, the
description and the drawing, in which exemplary embodiments of the invention
described
in detail below are illustrated. The following are shown:
Fig. 1 is a front view of a chipper disc with mounted knives,
Fig. 2 is a sectional view of the chipper disc according to Fig. 1
along the section
plane indicated by the arrows II-II in Fig. 1,
Fig. 3 is a perspective view of a chipper knife,
Fig. 4 is a front view of the chipper knife of Fig. 3,
Fig. 5 is a side view of a profiling knife with cutting insert,
Fig. 6 is a bottom view of the profiling knife of Fig. 5,
Fig. 7 is a schematic, partially enlarged view of the knife with
cutting insert
according to Fig. 5,
Fig. 8 is a schematic, partially enlarged view of the soldering gap of
the knife
according to Fig. 5, and
Fig. 9 is a perspective view of a variant of the knife according to
Figs. 5, 6 with a
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wider cutting insert divided into individual parts.
In Fig. 1, a chipper disc 10 is shown, which is used in a profiling-chipping
system, not
shown, for the production of plane-parallel surfaces of raw wood and/or wet
woods. With
this, the wood is conveyed through the profiling-chipping system and processed
by two
oppositely arranged chipper disks 10. The chipper discs 10 are each driven in
rotation by
a drive system in the direction of rotation 11 about the axis of rotation 9
thereof Upon
contact of the wood with the chipper discs 10, the wood is cut to a defined
geometry by
so-called profiling knives. At the same time, the residual wood is chopped
into chips by
so-called chipper knives in order to be used as raw material in the paper
industry.
The chipper disc 10 shown in Fig. 1 has a wood-facing, conically-shaped inner
side 12,
on which a plurality of blades 1 is arranged over the entire circumference of
the chipper
disc 10. Each knife 1 is fastened to the chipper disc 10 by means of a screw
16. The
knives 1 have a rear end 15 and a front end 14 with respect to the direction
of rotation 11,
wherein a cutting edge 4 is formed on the front end 14 of the knife 1. The
chipper disc 10
has a chip opening 13 for each knife 1. The chip opening 13 is arranged in the
direction
of rotation 11 of the chip disk 10 immediately in front of the knife 1. As a
result, the
chips that are formed when wood is cut on the cutting edge 4 of the knife 1
are
discharged through the chip opening 13.
As shown in Fig. 2, the chipper disc 10 has a tapered portion 17. Since two
chipper discs
10 are arranged opposite each other in operation, these form a kind of funnel-
shaped
passage through which the wood is pushed during processing. Upon contact of
the wood
with the chipper disks 10, the wood is cut in several steps across the funnel-
shaped
passage of the chipper disks 10 to a minimum width of the passageway. In the
exemplary
embodiment, the blades 1 mounted in the conical section of the chipper disk 10
are
designed as chipping knives. The chipper disc 10 also has on its inner side 12
a contact
surface 18, which also allows the mounting of a circular saw, not shown.
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The chipper disk 10 as well as the profiling-chipping system are merely
examples of the
use of a knife according to the invention. Fig. 3 shows a first exemplary
embodiment of
such a knife 1, namely a chipper knife 1 for the chipper disk 10 according to
Figs. 1 and
2. The knife 1, like the exemplary embodiment shown in Figs. 5 and 6, has two
legs 19
and an internal thread 20 (Fig. 4) on the knife base body 2. By means of the
legs 19 and
the internal thread 20, the knife 1 can be positioned and secured to a
corresponding
cutting system, specifically on the chipper disc 10 according to Figures 1 and
2. In an
alternative embodiment, the knife can also be attached to a cutting system in
other ways.
Thus, instead of the legs 19, for example, a hole or a slot may be formed on
the blade 1
for attachment. Furthermore, for example, a clamping site of the knife for
attachment to a
cutting system is possible. The knife 1 comprises a first cutting insert 3
with a cutting
edge 4 and an optional additional cutting insert 3' with an associated cutting
edge 4'. The
cutting inserts 3, 3' are arranged at the front end 14 of the blade 1 and
fixed on the blade
body 2 by means of a soldered joint 5 using copper solder 6. The cutting
inserts 3, 3'
contact each other, wherein the cutting edges 4, 4' form a cutting contour 22.
For the
formation of the soldered joint and the copper solder 6 used, the same applies
mutatis
mutandis to what is said below for the exemplary embodiments according to
Figs. 5 to 9.
As shown in Fig. 4, the cutting contour 22 is made to be angled. In the front
view of the
knife 1, i.e., in the direction from the front end 14 to the rear end 15 of
the knife 1, the
cutting edges 4 and 4' form an angle a. In order to be able to carry the
additional cutting
insert 3', the blade base body 2 has a thickening 23 at the front end 14 on
the one leg side,
on which the additional cutting insert 3' is arranged. The additional cutting
insert 3' is
held on the thickening of the knife body 2.
In connection with Figs. 1 to 4, a chipper disc 10 with associated chipper
knives 1 has
been described. However, profiling lines for processing of raw wood and/or wet
wood
often also have so-called profiling units, which are connected to the chipper
discs 10, and
process the longitudinal edges of the surfaces produced by the chipper discs
10.
According to the invention, knives 1 are also used in such profiling units
according to the
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invention, not shown here, namely in the form of profiling knives. Figs. 5 and
6 show a
second exemplary embodiment of a knife 1 according to the invention, which is
designed
as such a profiling knife. The knife 1 comprises a knife base 2 and a cutting
insert 3 with
a cutting edge 4. The cutting insert 3 is arranged on the front end 14 of the
blade 1 with
respect to the direction of rotation and is fastened on the blade base body 2
by means of a
soldered joint 5. On the blade body 2, an internal thread 20 is formed, via
which the knife
1 is positioned on a corresponding cutting device in its longitudinal
direction. According
to Fig. 6, the knife body 2 has two legs 19, between which in the assembled
state
fastening screws pass through and fix the knife 1 in the set position thereof.
In Figs. 7 and 8, the cutting region of the knife 1 according to Figs. 5 and 6
is shown
schematically in a longitudinal section. In this case, the cutting insert 3
and the knife
body 2 define a soldering gap 8 for the soldered joint 5. The soldering gap 8
has a width
a, which corresponds to the distance between the blade main body 2 and the
cutting insert
3. In the exemplary embodiment, the maximum width a of the soldering gap 8 is
at most
0.1 mm, preferably at most 0.07 mm. In the soldering gap 8 between the blade
body 2
and the cutting insert 3, copper solder 6 is present, which connects the blade
body 2 with
the cutting insert 3 by positive substance jointing. In this case, the copper
solder 6 is in
contact with the blade body 2 and the cutting insert 3 and forms the soldered
joint 5.
In all of the illustrated exemplary embodiments, soldered joint 5 is formed as
a high
temperature-vacuum soldered joint. Accordingly, the soldering process for
fixing the
cutting insert 3 on the blade body 2 takes place under exclusion of air in a
vacuum. In
this process, the knife 1 is heated gradually in an oven under vacuum to a
heat soaking
temperature of less than 750 C. Subsequently, the temperature is increased to
a soldering
temperature of greater than 750 C for melting the copper solder 6. The copper
solder 6 is
distributed in the soldering gap 8 by capillary action, followed by diffusion
of the copper
solder 6 into the surfaces of the blade base 2 and the cutting insert 3. After
subsequent
cooling of the blade 1, the soldered joint is complete.
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The copper mass fraction of the copper solder 6 is at least 99%. In an
alternative
embodiment, however, it is also possible to use a copper alloy with a lower
copper
content, in particular of at least 50%, preferably at least 80%, preferably at
least 90%,
and corresponding additives as soldering material. The cutting insert 3
consists of a
coated or uncoated carbide. For even higher abrasion resistance, however, the
cutting
insert 3 can also consist of a cutting ceramic, super-hard cutting materials
or ultra-hard
cutting materials. These include, for example, natural diamond, PCD
(polycrystalline
diamond), MCD (monocrystalline diamond), CBN (polycrystalline cubic boron
nitride)
and CVD-D (chemical vapor deposition diamond). In the exemplary embodiment,
the
blade body 2 is made of steel. The use of other materials, such as powdered
metal, may
also be appropriate.
With further reference to Figs. 7 and 8, the conditions in operation, which
apply equally
to the exemplary embodiment according to Figs. 1 to 4 as well as to the
exemplary
embodiment according to Figs. 5 and 6, will become clear: During the cutting
operation,
the cutting insert 3 contacts the workpiece, not shown, in a contact region 21
at the end
adjoining the cutting edge 4. Here, in the contact region 21 on the cutting
insert 3, cutting
forces Fc are effective, pressing the cutting insert 3 via the intermediate
soldered joint 5
against the blade body 2 and leading to elastic deformations. If the cutting
forces Fc are
high enough, this can even lead to plastic deformation of the copper solder 6.
In any case,
deformation of the base of the cutting insert 3, in particular within the
layer of the copper
solder 6 by a deformation amount b takes place, wherein the deformation amount
b
represents a percentage of the width a of the soldering gap. The deformation
of the base
is accompanied by a corresponding deformation of the cutting insert 3, wherein
in the
cutting insert 3 corresponding bending deformations with compressive stresses
D and
tensile stresses Z occur. The hard cutting insert 3 is especially sensitive to
the bending-
induced tensile stresses Z. According to the invention, it has been possible
to reduce the
bending deformations and thus the tensile stresses Z in the cutting insert 3
to a minimum.
In particular, from the enlarged detail illustration according to Fig. 8, it
becomes clear
that the smaller the width a of the soldering gap, the smaller the deformation
amount b. It
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has been found that a sufficiently small width a of the soldering gap cannot
be achieved
with conventional soldering joints, but it can in accordance with the
invention with the
copper solder 6, which consequently results in a correspondingly small
deformation
measure b and correspondingly low tensile stresses Z. The bearing strength of
the cutting
insert 3 against particular impact or abruptly applied cutting forces Fc is
increased
accordingly, which allows the inventive use thereof for processing wet wood
and/or raw
wood with correspondingly large tooth pitches and associated large impact
loads. In this
case, the tooth pitch corresponds to the advance of a knife 1 into the
workpiece relative to
the preceding knife 1 in the direction of rotation. The knives according to
the invention
are suitable for use with a tooth pitch of 5 mm or more. However, it may also
be
appropriate to use the knife at a higher tooth pitch rate of 8 mm or more and
in particular
of at least 10 mm or more.
Fig. 9 shows in a perspective view a variant of the knife 1 according to Figs.
5, 6 with a
greater width compared to those. In the blade body 2, two U-shaped receptacles
for
mounting screws are formed. In addition to the one cutting insert 3 according
to Figs. 5,
6, by way of example further cutting inserts 3 are provided here, adding up to
a total of
six. Depending on the application and geometric design, however, different
total numbers
of cutting inserts 3 may also be appropriate. The cutting inserts 3 correspond
in their
geometric configuration and in their manner of attachment of the cutting
insert 3
according to Figs. 5 to 8. They are positioned without gaps next to each other
in such a
way that their cutting edges 4 complement each other to form a continuous,
linear cutting
contour 22. Functionally, a single, larger cutting edge is thus formed, which
is composed
of smaller individual cutting inserts. In the other features and reference
numerals, the
exemplary embodiment of Fig. 9 is consistent with the exemplary embodiments
described above.
Naturally, the above statements regarding profiling knives and chipper knives
apply
correspondingly for other knives 1, for example, for use as a hacking knife or
the like
wherever high impact loads are expected during operation. The mentioned hacker
knives
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are used on hacker machines. Such hacker machines are used for crushing raw
wood,
green wood and/or wood waste and produce mainly wood chips for the paper
industry.
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