Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
2135146
CHIPPER RNIFE
This invention relates to a knife used in a
wood chipper such as a rotatable disc type with a
plurality of circumferentially spaced chip openings
through the disc.
Wood chippers having rotatable cutters, or
drums, or rotatable chipping discs with openings
through which chips may pass, and fitted with double-
edged knives are known in the art.
A single reshaping of the knife blade,
involving the removal of material from one or both of
the edge surfaces forming the cutting edges of a
double-edged knife (known in the art as counter
grinding), is often the only reshaping or resharpening
of a knife blade bèfore it is discarded.
One aspect of the geometry of knives is that
knives having a large wedge angle, i.e., the angle
between the two surfàces converging to the cutting
edge, remain sharper longer and therefore are more
popular. However, the larger wedge angle6 are more
likely to cut a chip by shearing the chip from the
incoming material rather than by cleavage. More force
is required to sever chips by shearing than by
cleavage, and thus more power is required for operation
of a disc chipper having knives with larger wedge
angles.
~ Another problem i6 the penetration of chip
particles between the knife and the knife holding means
beneath the knife, typically a counter knife, that can
cause excessive pressure on the knife which may bend
it.
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The invention provides a novel knife and
knife-holding means for a chipper. The knife i6
double-edged, each cutting edge comprising an upper
surface, preferably a standing bevel, and an under
surface converging and intersecting to form a cutting
edge. Additionally the knife includes a chip-
deflecting surface forming the part of the under
surface remote from the cutting edge which deflects and
breaks chip material cut by the knife cutting edge.
The benefits of the invention can be provided
in a chipper knife having a cutting edge formed by the
intersection of an upper surface and an under surface
and having a bottom, by the improvement comprising a
chip-deflecting surface extending between the under
surface and the bottom of the knif-e and forming a
depression with the under surface for breaking chips
and deflecting them prior to passing beyond the bottom
- surface of the knife.
The chip-deflecting surface breaks chips and
deflects them so as to plevenL the penetration of chip
particles between the knife and the knife holding means
beneath the knife, such as a counter knife, and
preferably so that the chips do not strike the knife
holding means which decreases wear on the knife holding
means.
Means for holding the knife can be provided
in a chipper knife having a cutting edge formed by the
intersection of an upper surface and an under surface,
... . .-,_~. ,
- and the knife having a bottom, in combination with
knife holding means beneath the knife and having a top,
by the i ,ov~ ?nt comprising the chipper knife having
in its bottom a groove extending parallel to its
~ . '~
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cutting edge, the knife holding means having in its top
a groove parallel to said chipper knife groove, and a
key fitting in said chipper knife groove and said knife
holding means groove for securing the chipper knife to
the knife holding means against --ve --t of the chipper
knife relative to the knife holding means in a
direction transversely of said grooves.
In drawings which illustrate emko~ s of
the invention:
FIG. 1 is a cross section of a reusable knife
and its associated holding means;
FIG. 2 is an enlarged cross section of a
knife and its associated holding means;
FIG. 3 is a partial top plan of the counter
knife used in the knife holding means of FIG. 1.
The knife of the present invention is
illustrated as being used in a disc type wood or log
chipper as shown in FIG. 1, but it could be used in a
drum chipper or rotary knife chipper. The materials to
be chipped, such as logs, are fed at an angle to the
rotating disc. The chips pass through radially
elongated openings 106 in the disc 92 adjàcent to the
knives to be expelled from the chipper.
Each knife ~s- ~ly includes a knife 10 or
radial series of knives placed end to end, and knife
holding means including knife seat 70, counter knife
30, and knife clamp 50. Each knife A~' - bly is lodged
in a recess 94 in disc 92 adjacent to a radially
elongated opening 106 through the disc. ~he knife seat
has an elongated body with a platform 72 thereon for
placement of the counter knife 30, and a support 74 for
" ~ the knife clamp 50. The platform 72 has in it a blind
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bore threaded to receive a fastener such as a cap screw
104 for mounting the counter knife.
The counter knife 30 has a bottom surface 36
in contact with the knife seat platform 72, a top
surface 34 for engagement by the bottom surface 13 of
the knife body 10, an inner end 40 abutting a shoulder
in the knife seat platform 72, a recess 42 to receive
the head of the mounting screw 104, and longitu~inal
recesses 46 for placement of interlocking means or keys
90 engaged between knife 10 and counter knife 30.
The grooves 46 in the top 34 of the counter
knife 30 are preferably of rectangular cross section
and are arranged in sets. Typically each outer set
closer to the ends 44' of the counter knife includes
grooves 46' and each inner set farther from the ends
44' of the counter knife includes grooves 46" as shown
in FIG. 3. The grooves 46' and 46N of both sets are
parallel to the edge 42' of the counter knife
underlying the knife and to the main longitu~inAI axis
of the counter knife. The grooves 46" of the inner set
are staggered in relation to the grooves 46' of the
outer set of grooves. The distance between ad~acent
grooves of each set can be very small, such as
approximately 1j8 of an inch on centers and the
distance between the centers of the grooves in one set
and the centers of the grooves in the other set
transversely of the groove length will be 1/16 of an
inch as shown in FIG. 3. The different sets of y~Go~es
46' and 46" represent different positions for the knife
that i6 interlocked with the counter knife by keys 90
fitting in the grooves 23 in the bottom 13 of the knife
so as to permit position changes corresponding to small
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amounts of material, about 1/16 of an inch, to be
removed from the knife cutting edges during
- resharpening.
After a knife edge has been resharpened, the
knife will be assembled with the counter knife as shown
in FIGS. 1 and 2 and two keys 90 will be placed in the
grooves 23 in the bottom 13 of the knife 10 and in
corresponding grooves 46' of the outer sets of yLooves
or in corresponding grooves 46" of the inner sets of
grooves in the top surface 34 of the counter knife 30,
depending upon the desired degree of projection of the
knife edge beyond the counter knife edge 42 as
indicated in FIG. 1. Initially the keys will be placed
in grooves 46' or 46" farther from the edge of the
counter knife, and the keys will be moved toward the
counter knife edge progressively, first in grooves 46',
then in grooves 46", then back to grooves 46', until
the knife edge has been resharpened as many times as
possible. At that point, the keys 90 will be located
in the grooves 46' closest to the edge of the counter
knife 30 as shown in FIG. 1.
The dash-dot lines extending to the left of
knife 10 in FIG. 1 represent the profile of a new knife
prior to any use or regrinding. Subsequent regrinds
make the knife narrower and naLLo~/er as both edges are
resharpened until it is reduced to the knife 10 shown
in solid lines in FIG. 1. Once the edges of the knife
shown in solid lines in ~IG. 1 are completely dulled,
the knife is discarded.
The double-edged knife 10 comprises an
elongated body having cutting edges on its opposite
edges. The body of the knife has a top surface 11 and
, '".',_ ,J''....
~_ ''.,''`~
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a bottom surface 13 as shown in FIG. 2. Each cutting
edge has an upper surface 15 or 15', preferably a
standing bevel at an obtuse angle to the top surface
11, which projects beyond and preferably is inclined
slightly relative to the plane of the disc. Each
- cutting edge additionally has an under surface 17 or
17', which may be an under bevel. The intersection of
the convergent upper and under surfaces forms the
cutting edge of the knife and the included angle
between the upper surface and the under surface defines
the wedge angle of the knife.
The knife further includes a chip-deflecting
- surface 21 or 21' between the under surface 17 or 17'
and the bottom surface 13 of the knife which terminates
- 15 in a heel remote from the cutting edge of the knife.
Such chip-deflecting surface 21 or 21' merges with the
under surface 17 or 17' of the knife so as to form a
depression which may be a reentrant angle as shown in
FIG. 2. The inclination of the under surface or under
20 bevel 17 or 17' in relation to the bottom surface 13
may vary from o degrees to 20 degrees, making the
included angle from 180 degrees to 160 degrees, and the
inclination of the chip-deflecting surface 21 or 21' to
the bottom surface 13 may vary from 20 degrees to 90
degrees, so that the included angle would be 160
degrees to 90 degrees as shown in FIG. 2, but should
always be greater than the angle be~ween the under
surface or under bevel 17 or 17' and the bottom surface
13 so that the surface 17 or 17' will be offset from
- 30 the bottom surface 13 of the knife. The depth of the
depression between the cutting edge and the heel of the
chip-deflecting surface 21 or 21' is approximately one-
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fifth to one-third of the thickness of the knife
between the heel of the chip-deflecting surface and the
upper surface 15.
The purpose of the chip-deflecting surface 21
or 21' is to break apart chips cut by the cutting edge
of the knife and to deflect the chips toward the
discharge slot 106 and away from the end surface 32 of
the knife holding means or counter knife beneath the
knife so as to prevent chip material from wedging into
the joint between the knife and the counter knife
beneath the knife. The knife holding means edge 42' is
set back from the chip-deflecting surface 21 or 21' so
as to i ni i ze the chip material striking the knife
holding means.
Additionally, the knife can include a fourth
surface 19 or 19' between the upper surface 15 and the
under surface 17 or 17' to increase the wedge angle of
` the knife locally at the apex of the cutting edge.
The knife is held in position by the knife
clamp 50 as shown in FIG. 1. The knife clamp has a
knife engagement surface 54 contacting the knife top
surface 11. The knife clamp is secured to the disc 92
by a fastener such as a screw 102 as shown in FIG. 1.
Following resharpening of the knife, the
interlocking means or keys 90 would be repositioned in
the grooves of the counter knife 30 shown in FIGS. 1
and 3 to advance the now narrower knife by moving the
knife laterally relative to its longit~inAl axiæ and
cutting edge. This process could be repeated each time
the knife cutting edges are resharpened. A plurality
- - ~ of grooves in the counter knife as shown in FIG. 3
.
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permit this process to be repea~ed as many times a5
tberç are grooves in a set 46' and in a set 46".
The degree of inclination of the chip-
deflecting surfaçe 21 could be al~ered during
resharpening of the cutting edge and thus affect the
breaking force and chip deflection provided by contaçt
of the chips with suçh surface. The setback of the
heel of the chip-deflecting surface from the cutting
edge could also be altered indepçndently of the degree
of narrowing of the knife effected by sharpening of the
cutting edge.
