Note: Descriptions are shown in the official language in which they were submitted.
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` 1 IP-2956
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DOUBLE-DRUM ~OOD CHIPPER APPARATUS
BACKGRO~ND O~ THE INVENTION
This invention relates to an apparatus for obtaining
wood chips Erom logs, particularly logs which have been
debarked The invention further relates to a process for
obtaining wooa chips of uniform thickness from logs.
I SUMMARY OF THE INVENTION
~1
In the papermaking industry, it is often convenient
to form wood pulp using wood chips. Chips of unifor~n thick-
ness are preferredO Wood chips may be obtained by operating
upon logs, particularly debarked logs, by means of knives
which move relative to the surface of the logs. Workers in
this art have evolved a variety of chipping devices,
including so-called drum chippers, i.e., rota-ting drums whose
periphery or whose peripheries are provided with projecting
kn;ves. Drum chippers, sometimes termed peripheral chippers,
have the potential to produce uniform thickness chips with
minimum fiber damage, but the single-drum models of prior
constructions have inherent problems. The basic features of
a typical such-drum chipper are shown in U.S. Patent
2 IP-2956
3,757,839 issued to Stanley Vanek, hereby incorporated by
reference. As can be seen from Figure 2 of that patent, if the
log to be chipped drops onto the drum from a position to the
right of axle (3) it will tend to bounce, due to the lifting
forces exerted on it by the knives moving upward. Log bounciny
results in chips of various thickness. Logs that pass down~Jardly,
to the left of rotatiny drum (2) into the horn-angle between the
drum and the anvil wall (13) tend to rotate around their axes.
This rotation also produces variable thickness chips. When the
last remaining portion of a log reaches the exit of the chipper,
being the opening between the drum and the anvil, long slivers of
wood escape from the chipping zone and drop along with the other
chips onto a conveyor beneath the chipper. The slivers can be as
long as the space between knives on the drum on a line parallel
to its axis (12 inches to 18 inches, or more) and as thick as the
clearance between the drum's surface and the anvil (1/2 inch to
3/8 inch, or more).
The problem with logs bouncing on the surface of the drum
was realized and addressed ln U.S. patent 3,155,130, issued to
Logan et al, hereby incorporated by reference. In an attempt to
provide a steady feed of logs to the chipper drum, a pull-down
conveyor was installed in the log hopper as shown in Figure 2.
Actually, in the few models sold to mills, pull-down conveyors
were mounted on both sidewalls of the hoppers, also as shown in
this patent. This increased the cost of the chippers and only
partially solved the bouncing problem.
SUMMARY OF THE INVENTION
According to the practice of this invention, a novel
apparatus and method is disclosed which substantially eliminates
the problem of log bouncing. Further, according to the practice
of this invention, the problem of slivers of
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3 IP-2~56
wood escaping between the drum and the anvil o the dr~m is
substantially solved, to thereby insure the production of
wood chips of substantially uniform thickness.
The full nature of the invention will be ~nders~ood
from the accompanying drawings and the followiny dcscription
and claims It should be understood that references in the
following description to front, rear, upper and lower are for
convenience for description and such terms are not intended
to be used in a limiting sense.
BRIEF DESCRIPTION OF THE DRAWINGS
Figurel is a transverse cross-sectional view
illustrating the double-drum wood chipper apparatus of this
invention.
Figure 2 is a partial plan view of the rotating drums
illustrated at Figure 1, according to a first embodiment of
the drums.
Figure 3 is a view similar to Figure 2, showing a
second drum modification.
Figure 4 is a oartial transverse cross-sectional view
showing the drum configuration of Figure 3.
Figure 5 is a partial transverse cross-sectional view
illustrating the cutting or chipping action of the apparatus
illustrated at Figure 1, taken along section 5-5 of Figure 2.
Figure 6 is a perspective view of the drum carried
knives of this invention.
Figure 7 is a plan view of the knife of Figure 6.
Figure 8 is a front elevational view of Figure 7.
Figure 9 is a side elevational view of the knife of
Figure 7 taken at right angles to the longitudinal axis of
the knife.
Figure 10 illustrates the cutting action to form the
wood chips in the embodiment of Figure 1.
Figure 11 illustrates the cutting action to form the
wood chips in the embodiment of Figure 3.
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4 IP-295
DETAILED DESCRIPTION OF THE INVENTION
Referring now to Figure 1 of the drawings~ the
numeral 10 denotes generally the double-drum wood chipper
apparatus of this invention and includes a housing having
horizontal wall portions 12, parallel, vertical walls 14 and
pa~allel, vertical lower walls 16. Vertically extending
walls 14 define a hopper denoted generally by the numeral 20
for holding a supply of logs each identified by the numeral
22. The reader will understand that the logs are positioned
within hopper 20 with their longitudinal axes perpendicular
to the plane of the paper.
The numeral 24 denotes one of a pair of oppositely
rotating, hollow drums, the drums each being open at at least
one end. The numeral 26 denotes any one of a plurality of
cutting knives suitabiy carried on the cylindrical wall of
the drum. The numeral ~7 denotes any one of a plurality of
wood chip receiving apertures extendiny completely through
the hollow drum 24, each aperture 27 being placed in front of
~relative to the direction of drum rotation) and contiguous
to an associated cutting knife 26. Drum 24 is suitably
mounted on shaft 28, the shaft rotating about an axis denoted
by the numeral 30. The numeral 34 denotes the other one of
the pair of oppositely rotating drums, drum 3~ similarly
carrying a plurality of angularly spaced cutting knives 36,
each of the latter having an associated through aperture 37
for the reception of wood chips as will later be described.
Drum 34 is suitably mounted on rotating shaft 33, the latter
rotating about an axis indicated by the numeral 40~ The
numeral ~5 denotes the nip zone between the arums. hs shown
at Figure l, an imaginary line between the lower~ost portion
15 of either hopper wall 14 and the axis of rotation of
either shaft 30, 40 makes an angle of 10 (5 to 15 being
the preferred range) with the vertical. The walls 14 are
IP-2956
thus between the shafts 30, ~0 thereby insuring that any log
contacting a drum surface will tend to fall towards nip 25.
As indicated by the curved arrows, the drums rotate in
opposite direction such that their facing surfaces at nip
zone 25 both travel downwardly.
Referring now to Figure 2 of the drawings~ a partial
plan view of the drums shown atFigure 1 is illustrated. The
cutting knives are arranged and positioned in straight r~ws
on the circumference o the drum, each row being parallel to
an immediately adjacent row, the rows being parallel with
respect to the axis of rotation of the drum, being axis 30
with respect to drum 24 and axis 40 with respect to drum 34.
From a consideration of Figure 2 it will be seen that the
knives of any one row of either drum would be interdigitated
with the Xnives of any next adjacent row, if these two
adjacent rows were rotated so as to come together.
Referring now to Figure 3, an alternative knife
mounting configuration is illustrated. The drum and knife
construction themselves are the same as that described with
respect to Figures 1 and 2, except that the knives on each
drum are arranged in a plurality of helical paths. Thus, the
numeral 40 at Fiqure 3 denotes any one of a plurality of
helical paths on the drum s~rfaces along whi~h and on which
knives 26, 36, are positioned. As easily seen at Figure 3,
the helices of the two dru~s are interdigitated, i.e.l
spaced from each other relative to the parallel axes of the
drums. As indicated at Figure 4, at the nip 25 between rolls
24 and 34, homologous or corresponding knives on opposite
sides of the nip are at substantially the same angular posi-
tions, as distinguished from the embodiment of Figure 2
wherein, at the nip 25, the knives alternate (are interdigi~
tated) at any given axial location along the drums.
Referring now to Figure 5 of the drawings, the
cutting action of the knives and the formation of chips in
the nip 25 is illustrated. One portion of a log 22 is
illustratea as extending into the nip 25 between the rolls.
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6 IP-2956
Knife 26-A on drum 24 is seen as cutting into a portion of
log 22. Knife 36-A of drum 34 is, likewise, seen as cutting
into a portion of log 22, but from the opposite side. Knife
26-B has cut completely through its corresponding portion oE
log 22 to thereby define a complete chip 220, this chip
illustrated as having passed almost completely through the
aperture 27 which is associated with knife 26-B. The reader
will readily imagine that with continued rotation of the
drums in the indicated direction, a corresponding wood chip
would be formed by knife 36-A, this chip passing through
opening 37 associated with that knife and falling into the
interior of drum 34. Thus, the interior of each of drums 24
and 34 continuously receive a supply of wood chips from
apertures 27 and 37, respectively.
As each knife in the upper portion of nip 25
approaches the narrowest part of the nip, it moves towards
the opposite drum surface. The opposite drum surface thus
functions as an anvil. The drums are rotating at the same
speed and there is no bouncing or rotating movement of the
logs with respect to either drum surface. The path of motion
of the cutting knives is such as to tend to pull the logs
down against the arums so that the logs can neither bounce
nor rotate. As indicated at Figure 1, some logs will be
consumed on the upper surfaces of the drums and will hence
never reach the nip zone 25.
~ s is conventional, the knives are oriented on the
drum surfaces in such a manner to yield a relief angle of
about 3 between the surace of the wood being cut by the
knife and that face of the knife opposite the knife-engaged
wood. This relief angle is indicated at Figure 5. The
manner of mounting the knives on the drums forms no part of
this invention and has accordingly not been illustrated. ~ny
conventional mounting manner may be employed.
Referring now to Eigures 6 - 9, the configuration of
the knife 26 is illustrated, this conf;guration being the
same, of course, for the knife 36 of drum 34. The leading,
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7 IP-~956
cutting edge of each knife, termed the parallel cutting ed~e
is denoted by edge A, B, while the face or surface of the
knife which is opposite to that portion of the logs and which
are cut by the parallel cutting edge of the knife is denoted
by the numeral 260. Cross cutting faces 262 are defined by
swept backed portions, the corners of which are denoted by B,
D, E, C. This face portion is swept back towards the rear of
the knife so that the angle oetween edges AB and BC is about
150, as indicated at Figure 7. Figure 9 also indicates the
(conventional) relief angle of 3 between swrface 260 and the
surface of the log which has been cut by the cutting edge of
the knife, this latter surface indicated by the arrow
extending from the cutting edge denoted by B at Figure 9.
Figure 9 also illustrates another important feature of this
invention. In addition to the relief angle of 3 between the
surface of the wood after cutting and the knife surface
trailing the cutting edge, to thereby insure that the wood
does not ride on the knife, a similar relief angle between
the wood and the cross cut knife surfaces 262 has been
identified in developing this invention. Namely, the leading
cutting edge BC of the cross cut knife must be swept back to
an angle of about 7~ as shown in Figure ~ between its edge
~C and the trailing surface 260 of the parallel-cutting
knife. This angle may be varied by as much as 2 in either
direction. This angle was found experimentally to produce
minimal fiber damage during formation of the wood chips. By
detaching the fibers fxom the wood with~the parallel-cutting
edge prior to cutting off the chips at an angle to the
fibers, the probability of producing longitudinal compression
failures in the fiber walls was avoided.
The angle at which the longitudinal axes of knives
are placed in the drum walls will now be apparentO Namely,
the surface 260 of each knife makes an angle of about 3 with
the tangent to the drum circumference at each knife location.
Accordingly, each knife is mounted in its corresponding drum
wall such at its surface 260 makes an angle of about 87 with
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8 IP-2956
a radius line from the center of rotation (20, 40l of the
respective drum. The angle which face 260 makes with the
underside of the knife ~being the cutting angle of parallel
cutting edge AB) is about 35, while the anyle face 262 ma~es
with the underside of i~s portion of the X~nife (being the
cutting angle of cross-cut edge BC) is about 30.
Referring now to Figures 10 and ll, an illustration
of the mode of formation and the general shape of the wood
chips for the two emboaiments aescribed is illustrated. In
Figure 10, two of the knives of one of the rolls 24, 34,
being on a single line (as illustrated at Figure 2) are
illustrated and immediately beneath them are end and top
views of these chips. The upper portion of Figure 10
indicates a following and interdigitated knife, on the the
same drum, with end and top views of a typical chip cut by
that knife indicated by the numeral 220.
Referring now to Figure ll, the left portion of the
Figure indicates any of the knives on drums 29, 34 arranged
in the helical pattern of Figure 3, with a typical wood chip
220 shown below this knife, both in end and top views,
respectively. The upper right hand portion of Figure 11
indicates a following knife, on the same helical ~3th and on
the same drum, and beneath this knife is also illustrated a
typical wood chip 220, also both in end and top views.
The interdigitation of and alignment between the
knives in the configuration of Figure 2 is indicated at
Figure 10 by the dashed vertical lines between the edges A, B
of the cutting faces of the knives. The single,
corresponding vertical dashed line of Figure ll indicates the
staggered relation of the knives on any heli~ 41 of the Xnife
configuration of the embodiment of Figure 3.
