Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
~?3~ 4047-519
CHIPPER KNIFE
_ackqround and SummarY oE the Invention
This invention relates to chipper apparatus, and more
particularly, to chipper apparatus which includes a rotating
chipper disc and one or more knives mounted on this disc
operable to produce wood chips on the feeding of wood material
against the disc. The invention more specifically is directed
to a novel construction for a double-edged chipper knife usable
in such apparatus.
In recent years, so-called double-edged chipper
knives have become increasingly popular, since through turning
of the knife a convenien-t way is provided for replacing the
cutting edge which is used in the chipper withou-t having to
grind an edge. Furthermore, such knives lend themselves to use
in a returnable system, wherein after dulling of both edges,
they are returned or thrown away with the elimination of any
grinding by the ~Iser.
While the advantages of double-edged knives are
recognized, certain problems have been experienced with knife
constructions known to date. Certain knives, for instance,
have a geometry which is somewhat complex, introducing problems
in making the knife and in properly mounting it on the chipper
disc. A problem of general concern is that with many knife
constructions, and during use, wood particles, resins, etc.
tend to build up between the knife and the structure mounting
it, causing displacement of the knife in its mounting and
overheating of the knife. Furthermore, any system which relies
upon clamping onto certain blade surfaces in a knife introduces
a problem, in that should it be desired to change the angle of
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these blade surfaces, such also requires a change in the clamping
structure which is used to clamp onto the knife in the chipper.
Another problem which has been encountered is the tendency for a
knife, when such twists in its mounting during use, to bend or
break the mounting structure which clamps it in place on the
chipper.
A general object of this invention is to provide an
improved double-edged knife for a chipper with a construction
taking care of many of the difficulties discussed a~ove.
A more specific object is to provide a double-edged
chipper knife which lends itself to being securely mounted in a
chipper disc, but nevertheless, is devoid of the complex geometry
characterizing certain prior art knives.
Another object is to provide a double-edged chipper knife
which has a back side in part surfaced by blade surfaces, and in
part surfaced by a bearing surface which is the surface utilized
in clamping the knife in place.
A further feature and object of the invention is a knife
which features an elongate key-receiving channel on one of its
sides relied upon to anchor the knife in place on the chipper disc,
and organized in such a manner as to inhibit build up of wood
residues between the knife and the structure mounting it.
Another object is to provide a chipper knife including
an elongate knife body bounded on opposite margins by elongate
cutting edges lying in a plane and ha~ing a back side extending
between the cutting edges and a front side extending between the
cutting edges, said back side being formed by a pair of back knife
surfaces extending inwardly on the knife body from respective
cutting edges and inclined at a common acute angle with respect to
a plane bisecting the knife disposed normal to the plane of the
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cutting edges and further being formed by a bearing surface which
extends between and joins said back knife surfaces, the front side
of the knife being formed by a pair of front lcnife surfaces
extending inwardly on the knife from respective cutting ~dgPs at
a common acute angle with respect to respective back knife surfaces
and further being formed by an elongate key-retaining channel
indented inwardly into the knife body and extending longitudinally
of the knife body intermediate the knife edges, the back knife
surfaces having substantially equal widths and the front knif~
surfaces having substantially equal widths, the width of said key-
retaining channel approximately equalling the width of a front
knife surface and the width of said bearing surface approximately
equalling the width of a back knife surface.
Brief Description of the Drawinas
These and other objects ancl advantages are attained by
the invention, which is described hereinbelow in conjunction with
the accompanying drawings, wherein:
Fig. 1 is a view looking at the front of a chipper disc
and illustrating knives and a mounting for these knives supporting
the knives on the disc;
Fig. 2 is an enlarged cross-sectional view, kaken
generally along the line 2-2 in Fig. 1, and showing further details
of a knife as contemplated and its mounting on the chipper disc;
Fig. 3 is a cross-sectional view of a double-edged knife
as contemplated, on an even larger scale;
Fig. 4 is a schematic illustration of a knife mounting
which tends to produce overly thick chips;
Fig. 5 is a schematic illustration of a mounting tending
to produce overly thin chips; and
Fig. 6 is a view, similar to portions of Fig. 2, but
having various dimensions indicated therein.
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Detailed Description of a Preferred Embodiment
Referring now to the drawings, illustrated in Fig. 1
at 10 is a chipper disc which is substantially circular in
outline, has a substantially flat disc surface 12 forming the
face of the disc, and which is mounted in the chipper apparatus
for powered rotatlon about its axis 14. Arranged with such
extending generally radially on the chipper disc are multiple
kniEe assemblies designated generally at 16. ~lthough three
such assemblies are shown, it should be obvious that the number
and relative spacing of these knife assemblies are subject to
variation with different si~es and types of chipper apparatus.
Each of the knife assemblies 16 is illustrated as
having three knives disposed end to end and indicated at 20,
20A, and 20B, such being aligned with each other in the
assembly. Again r it should be understood that the number of
knives in a knife assembly will vary according to the individual
installation.
During use, the chipper disc is rotated in the
direction shown by the arrow in Fig. 1 r or in a counter
clockwise direction, which is the direction of travel of the
disc. Immediately in advance of the knives in a knife assembly
is an opening 22 provided in the disc. During operation of the
chipper and with the advancing of a log or other wood against
the chipper disc, the knives in a knife assembly shave wood
chips from the wood, with such then traveling through an opening
22 to be expelled from the chipper.
Considering now in more detail the construction of a
knife, and referring to Fig. 3 which illustrates the knife in
cross section, such includes a knife body 30 bounded along
opposite margins by elongate cutting edges indicated at 32 and
34. That part of the knife which appears at the top of Fig. 3
is referred to as the back side of the knife, and the opposite
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side or the side adjacent the bottom of Fig. 3, the front side
of the knife.
The back side of the knife is defined by a pair of
back knife surEaces 36, 38 extending inwardly on the knife body
from respective cutting edges. These may have substantially
equal widths and ordinarily are planar and are inclined at a
common acute angle wi-th respect to a plane, indica-ted at 40,
which bisects the knife body and extends normal to the plane 41
defined by cutting edges 32, 34. In the particular embodiment
of the invention illustrated, this angle is around 35 degrees,
although the angle will vary depending on the chipper and the
type of chips desired. Extending between and joining with these
back knife surfaces is what is referred to as a bearing surface
44, whîch may be planar and ordinarily parallel to the plane o
the two cutting edges. With the knife being symmetrical when
viewed in a transverse cross section, plane 40 described bisects
bearing surface 44.
The opposite or front side of the knife is defined by
a pair of so called front knife surfaces 46, 48, which in the
embodiment of the invention shown are flat and occupy a common
plane paralleling plane 41. Between these front knife surfaces
and extending the length of the knife body is a key-receiving
channel 50. Such is defined by side edges 52, 54 disposed
normal to the plane of the knife edges, a floor 56 which
generally parallels the plane of the kniEe edges, and
preferably, rounds 58, 60 providing a smooth continuation
between the side edges of the channel and its floor 56. With
the knife body having symmetry in cross section, knife surfaces
46, 48 have equal width and key-receiving channel 50 is bisected
by plane 40 earlier described.
In a preferred embodiment of tbe invention, each
knife surface 46, 48 is relief ground along the outer margin
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thereof which meets with a cutting edge. Thus, the knife
surfaces include relief surEace portions shown in Fig. 3 at 62
and 64. The remaining surface portions of the two knife
surfaces are flat, and preferably extend in a co~non plane,
these remaining surface portions forming a major portion,
normally 70% or more, of each knife surface. This plane, with
surfaces 36, 38 inclined at 35 degrees relative to bisecting
plane 40, inclines at an acute angle, i.e, 35 degrees, relative
to surfaces 36, 38. A relief surface portion inclines inwardly
on the knife body in a direction extending toward a cutting edge
and relative to the plane of the major portion of the knife
surface at a slight acute angle, typically~ ranging from four to
seven degrees tshown at 65 in Fig. 2). Thus, while a knife
surface is essentially planar in a preEerred embodiment, it is
not entirely so, by reason of the slight inclination of a relief
surface portion.
A knife of -the type described is mounted in a kniEe
assembly utilizing the mounting structure shown in Fig. 2.
Specifically~ this structure includes what is referred to as a
base 68 and a clamp 70, these supporting a knife with the knife
clamped therebetween.
Further describing the base, such includes a holder
72 provided along one edge with a ridge 74. The opposite edge
of the holder is formed with an inclined shelf 76 and surfaced,
where such faces the direction of travel of the knife assembly
(which is to the left in Fig. 2), with a surface 78 which is
inclined with respect to the plane of the disc surface which
includes the knie assembly ~shown at 79 in Fig. 2).
Detachably mounted on the holder as by screws 80 is a
counter-knife or key element 82 Such extends the length of the
knife and sits within shelf 76 of the holder. Formed along the
forward margins of the counter-knife, which is the upper margin
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as illustrated in Fig. 3, is an elongate key portion 84, and
downwardly and to the right from this key portion a support
surface 86. The key portion projects from the side of the
counter-knife which faces the knife. Counter-knife 82 further
includes an inclined wear or fender surface 88 extending along
the underside thereof at its forward margin. Bounding the
forward margin of key portion 84 is a forward edge or surface
90, and this edge joins with fender surface 88. Edge surface 90
joins through a round 92 with a surface 94.
Clamp 70 extends ~long the length of the knife above
the knife. Such is notched along one edge by notch 98 which
fits over ridge 74 of the holder. Along the underside of the
clamp adjacent its opposite edge or toe 99 is a flat expanse
referred to as a clamping surface 100. The clamp and holder are
secured together and to the chipper disc by fasteners such as
the one shown at 102. Reference may be had to U.S. 4,669,516
for further details of the mounting of such an assembly on a
chipper disc.
With a knife mounted in place on a chipper disc
utilizing the holder, counter-knife, and clamp illustrated in
Fiy. 2., the knife becomes positioned with one of its cutting
edges (edge 32 in Fig. 2) positioned beyond the plane 79 of the
cutter disc r and with this cutting edge and adjacent portions oE
the knife protruding over an opening 22 in the chipper disc.
The knife is positioned with its front side facing the direction
of travel of the disc, and with the plane o its front knife
surface inclined at an acute angle with respect to the plane of
the disc surface where such extends rearwardly from the cutting
edge, or put in another way, where the plane recedes from the
cutting edge. The knife is firmly clamped in position, with
clamping surface 100 of the clamp clamped Eirmly against bearing
surface 44 of the knife. Key portion 84 of the counter-knife
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seats within channel 50 provided on the front side of the knife.
Edge surface 90 of the key portion bears against side edge 52 of
channel 50. A forward portion of surface 94 of the key portion
bears against a orward portion of floor 56 in the knife. The
knife is additionally supported while in its clamped position
with surface 86 bearing against the relief surEace in tha knife
which is adjacent the cutting edge of the knife opposi-te edge
32, i.e., edge 34 in Fig. 2.
As so positioned, the knife is firmly held from
twisting on itself, and forces tending to break or bend the
clamp where such bears against the bearing surface of the knife
are minimized. This is because when the exposed cutting edge of
the knife meets resistance tending to cause it to twist in its
mounting, such forces are resisted by toe 99 and adjacent
surface portions of the clamp spaced a substantial distance from
where the knife is supported adjacent its edge 34. Put in
another way, the operative moment arm for the forces exerted on
the protruding cutting edge in the knife is nearly the same as
the operative moment arm for forces resisting turning, a feature
not present in many prior art constructions.
It should also be noted that the knife surfaces on
the back side of the knife are not used in clamping the knife in
place. This means that the inclination of these back surfaces
may be changed as desired to fit the particular operating
conditions under which the chipper disc is used without
affecting how the knife is held in place.
I~ should be further noted, and since edges 52, 5~
defining channel 50 are normal or substantially normal to front
knife surfaces 46, 48r there is minimal tendency for debris to
wor~ between the counter-knife and kni~e. The front side of the
knife which extends from Eorward edge 32 inclines at an acute
angle relative to the plane of the disc surface in a direction
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receding from this edge and meets wear surface 88 in the
counter-knife. This wear surEace of the counter-knife also
inclines at an acute angle relative to the plane of the disc
surface in a direction receding from edge 32, this acute angle
being somewhat greater than the first-mentioned acute angle.
Thus, material cut by the kniEe with opera-tion of the chipper
moves down along a front knife surface, i.e., surface 46 in
Fig. 3, thence to travel over surface 88 of the counter-knife
until finally deflected out of the chipper disc assembly.
Material, if such is to work between the counter-knife and
knife, must travel at substantially a right-angle path on
leaving front knife surface 46.
As illustrated in Fig. 4 in conjunction with a
conventional knife "K" and counter-knife "C", cut material, on
traveling from leg "L" along the front side of the knife and
thence against the leading surface of the counter-knife, is
deflected by the counter-knife surface away from the knife
proper with material breaking apart and the formation of chips.
In Fig. 4, the counter-knife is too far back from the leading
edge of the chipper knife, which tends to result in chips being
produced having greater thickness than desired. A converse
situation is illustrated in Fig. 5 where the counter-knife "C"
is positioned in a relatively extended position on the chipper
knife, and with this positioning, chips tend to form which are
too thin. This discussion emphasizes the importance of the
position of the counter-knife and its leading surface with
respect to the chipper knife. With the usual woods processed in
America, and to obtain desired chip size, the width of the
exposed front side of the chipper knife might range from 0.4 to
0.6", which with the chipper knife of the invention translates
to a front knife surface having a width of this dimension ~with
the knife mounted, surface 88 of the counter-knife becomes
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located where the front knife surface terminates by reason of
joining with a side edge of the key-retaining channel).
Referring to Fig. 2, cutting edge 32 of the chipper
knife is the one that is performing the cutting, and front knife
surface 46 the surface Eending chips away after being cut.
With surfaces 36, 46 in a specific embodiment
defining an angle of 35 degrees as earlier described (this angle
usually is within the range of 30 to 40 degrees), and with the
knife constructed so that surface 88 of the counter-knife
appears directly at the termination of the front knife surface,
the back knife surface normally will have a width at least as
great as the width of the front knife surface. In Fig. 6, the
width of the front knife surfaces is indicated at FKSW and the
width of a back knife surface at BXSW, and it will be noted that
the width BKSW slightly exceeds the width FKSW.
With the knie deriving a good deal of its support
from adjacent the edge which is not serving as the cutting edge,
and with it desirable, as earlier explained, that this portion
of the knife be well back of toe 99, the width of the
key-retaining channel shown at CW in Fig. 6 will approximate
closely the wi~th of a front knife surface FKSWo More broadly
stated, the width of the key-retaining channel should preferably
be 50 percent or more of the width of the front knife surface.
In Fig. 6, the width of the bearing sur~ace in the
knife is indicated at BSW. This bearing surface width in the
embodiment illustrated approximates the width of a back knife
surface, i.e., the width BKSW, and thus only slightly exceeds
the width oE the key-retaining channel or CW. In this way, the
knife is held from fluttering, as would be the case if the
bearing surEace width was minimal, and the knife were supported
on its back side well rearwardly of where supported on its front
or underside. The support of the bearing surface does not
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extend well beyond where -the knife is supported on its underside
by the key in the counter-knife, since with this type of support
and with the knife mounted in place, it would tend to turn in
its mounting, affecting the pitch angle of the knife and the
ability of the knife (the angle defined by surEace 36 and plane
79 in ~ig. 2 and typically about 2 degrees~ to pull into the
wood during the cutting operation. More broadly stated,
optimally the bearing surface width is within the range of 50 to
150 percent of the width of a front knife surface in the knife.
During operation of the chipper, any wear which
occurs on material moving past the exposed blade surface of the
knife and thence over the counter-knife occurs for the most part
in surface 88 of the counter-knife. If wear becomes excessive
in this area, it is a relatively easy matter to replace the
counter-knife to provide a new wear surface~
When one of the edges in a knife becomes dull through
usage, the clamp mounting for the knife may be loosened and the
knife removed. If the knife is then turned end-for-end and then
remounted in the clamp mounting, this places its opposite edge
in a cutting position. In its newly mounted position, the front
side of the knife still faces forwardly and the back side
rearwardly.
A knife configured as herein disclosed may be
constructed which operates very efficiently and effectively in
producing the chips desired, but which has a relatively small
edge-to-edge dimensionO For instance, a commercial embodiment
o~ the knife has been constructed configured as illustrated
which has a total width edge-to-edge of approximately 1~". This
is particularly advantageous in a so-called throw-away system,
where the knives after dulling of both edges are scrapped, as it
tends to minimize the initial cost of the knife, making such
handling cost-efective. A knife having a width of 3" or 4"
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might perform in a proper manner, but the amount of material
required to make such a knife would make the knife impractical
in a truly throw-away system.
While there has been described herein a sp~ciEic
embodiment of the invention, obviously variations and
modifications are possible without departing from the invention.
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