Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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TTR21 FLARED POCKETS FOR CENTRIFUGAL GRINDERS
This invention relates generally to centrifugal
grinders of the kind disclosed and claimed in my earlier
U.S. Patent No. 4,474,335, issued October 2, 1984. The
present invention relates more particularly to an
improvement in the shape of the pocket or pockets
provided in the rotor of a centrifugal grinder, along
which wood chips and the like pass to be pressed by
centrifugal force against the internal grinding surface
of the stationary grinding stone.
BACKGROUND OF THIS INVENTION
It is generally appreciated in the wood pulp
industry that, when grinding wood chips, it is very
desirable to orient the grain of the chips parallel to
the stone surface for the actual grinding operationO A
typical wood chip may measure about 1" x 1", with a
thickness of 1/8" to ~". The grain runs parallel to one
of the larger dimensions. When a wood chip is ground by
lying against the grinding stone with lts largest
surface, i.e. with the grain oriented substantially
- parallel with the surface of the grinding stone, it is
more likely whole fibres will be produced, rather than
small, broken fibre fragments. Generally speaking, the
larger the fibres, the better the quality of the
resulting pulp.
GENERAL DESCRIPTION OF THIS INVENTION
The aim of an aspect of this invention is to
provide a pocket configuration within the rotor of an
internal centrifugal grinder which is such as to promote
a parallel chip orientation by the time the chip reaches
the grinding surface, i.e. an orientation in which the
chip grain extends substantially parallel to the
internal grinding surface.
I have discovered that by shaping the pocket or
pockets in the rotor in a particular way, the desirable
orientation of the chips can be to a large extent
achieved. It will be understood that it is not a
practical goal to seek the proper orientation of all of
the wood chips. Because the chips are oriented in a
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random fashion initially, it is unlikely that in any
given time span a uniform parallel orientation can be
achieved for all of the chips. However, I have found
that the pocket configuration provided herein allows
better than three quarters of typical wood chips to
assume, by the time they reach the grinding surface, an
orientation in which they are parallel to the grinding
surface and to each other.
More particularly, this invention provides an
improvement in a centrifugal grinder having an internal
grinding surface shaped as a surface of revolution, and
a rotor mounted within the surface for rotation about
the axis thereof, the rotor defining a generally axial
inlet passageway for material to be ground. At least
one pocket extends generally outwardly from the axis of
the rotor toward the grinding surface, and the present
improvement provides a configuration for the pocket
wherein the cross-section of the pocket widens at an
increasing rate away from the rotor axis.
GENERAL DESCRIPTION OF THE DRAWINGS
_ _
Three embodiments of this invention are illustrated
schematically in the accompanying drawings which show
the essential geometry without all of the accessory
components, like numerals denoting like parts throughout
the several views, and in which:
- Figure 1 is a longitudinal section through a first
embodiment;
Figure 2 is a transverse section taken at the line
A-A in Figure l;
Figure 3 is a longitudinal section through a second
embodiment;
Figure 4 is a transverse section taken at the line
A-A in Figure 3;
Figure 5 is a longitudinal section through a third
embodiment;
Figure 6 is a transverse section taken at the line
A-A in Figure 5;
Figure 7 is a longitudinal sectional view through a
prior art construction;
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Figure 8 is a transverse view taken at the line A-A
in Figure 7; and
Figure 9 is a graphical representation of the rates
at which the cross-sectional area of a pocket increases
away from the axis of the rotor.
DETAILED DESCRIPTION OF THE DRAWINGS
.
Attention is first directed to Figures 7 and 8,
which shows the prior art construction.
In the prior art construction, a grinding stone 10
defines an internal grinding surface 12 shaped as a
surface of revolution, and more particularly as a
cylinder having an axis shown at the line 14. Looking
at Figure 8, a rotor 16 is provided, the rotor being
mounted within the surface 12 for rotation about the
axis 14. The rotor 16 defines a generally axial inlet
passageway 18 for material such as wood chips to be
ground, and two pockets 20 and 22, each extending
generally outwardly away from the axis 14 of the rotor
and toward the grinding surface 12. In the construction
shown in Figures 7 and 8, the two pockets 20 and 22
extend in diametrically opposite directions, and are
thus spaced at 180 from each other.
It will be noted in Figure 8 that each pocket 20,
22 is defined between generally rectilinear but slightly
diverging walls 24. Figure 7 shows a cross section at
right angles to the section of Figure 8, also cutting
through the pockets 20 and 22. It will be seen that the
pockets are defined by parallel walls 26 and 28,
transverse to the axis 14.
If one were to calculate the cross-sectional area
of the pockets 20 and 22 by determining, for different
radii beginning at the wall of the passageway 18 and
ending at the surface 12, the surface area of a series
of theoretical cylinders lying within the pocket, the
cylinders having the increasing radii, then one would
arrive at the line identified by the numeral 27 in
Figure 9, the line being also labelled "Fig. 4". As can
be seen, this line is essentially a straight line, due
to the fact that the walls of the pockets 20 and 22 are
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almost parallel in both directions. Because there is a
very slight divergence as can be seen in the section of
Figure 8, the cross-sectional area increases slightly in
the outward direction, as indicated by the slight upward
slope of the line 27 in the graph of Figure 9.
However, I have determined that a mere divergence
by itself is not sufficient to encourage a large-scale
re-orientation of the wood chips so that they lie, ir.
the main, parallel to the grinding surface by the time
they reach the latter. In order to accomplish this
large-scale re-orientation, it is necessary to ensure
that the transverse section of the pocket widens at an
increasing rate away from the rotor axis, and this is
best accomplished by providing a flared configuration as
seen in Figures 1 through 6.
Attention is first directed to Figures 1 and 2,
illustrating the first embodiment of this invention. As
can be seen, in Figure 1, the grinding stone 10 is again
provided, with an internal cylindrical grinding surface
12. A rotor 30 is provided, rotatable about the axis 14
of the stone 10, the rotor 30 shaped to define an axial
passageway 18a which opens into two oppositely extending
pockets 32 and 34. As can be seen in Figure 1, each
pocket 32, 34 is defined between walls 36 and 38 which
widen at an increasing rate away from the axis 14. The
section through the wall 36 is thus a curve, as is the
section through the wall 38.
Referring to Figure 2, the dimension of each pocket
32, 34 in the direction transverse to the section of
Figure 1 also widens at an increasing rate. The pocket
32 is defined between a flat wall 40 and a strongly
curved wall 42, and the same is true for the pocket 34.
The strongly curved wall 42 in each case is the trailing
wall in the sense of rotation, which in the view of
Figure 2 is counter-clockwise.
If one were to utilize the precise geometry shown
in Figures 1 and 2, and perform the same calculations as
were done to arrive at the line 27 in Figure 9, one
would arrive at the line identified by the numeral 44 in
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Figure 9, which is also labelled as "lst Embodiment".
As can be seen, the slope of the line 44 increases at a
progressive rate from the left to the right, which
corresponds to increasing distance away from the axis
14. The angle alpha drawn adjacent the line 44 in
Figure 9 represents the slope of the line 44 at the
leftward extremity, whereas the angle beta drawn at the
upper right in Figure 9 represents the slope of the line
44 at the rightward extremity. The distance Dl in
Figure 9 is proportional to the tangent of the angle
alpha, whereas D2 is proportional to the tangent of the
angle beta. It can be seen that D2, in effect a measure
of the slope of the line 44 at the rightward end, is at
least 8 times as large as Dl, which is the slope at the
leftward end.
It is pointed out that the curves in Figure 9 are
not measured in any specific units, but-are accurate in
terms of showing the relative rate of increase of the
cross section away from the axis.
Attention is now directed to Figures 3 and 4, which
are similar to Figures 1 and 2, but are directed to the
second embodiment of this invention. In order to avoid
repetition, it is not necessary to again identify all
parts of the structure. It will be noted that the
Figure 4 section is substantially identical to the
Figure 2 section, but that the section represented in
Figure 3 differs from that represented in Figure 1 in
that the Figure 3 section cuts through flat, parallel
walls. Thus, the section of Figure 3 is very similar to
the prior art section of Figure 7.
In the embodiment illustrated in Figures 3 and 4,
the widening takes place only in the transverse plane,
which is cut by the section of Figure 4, and no widening
takes place in the longitudinal plane represented by
Figure 3. Nonetheless, as can be seen by referring to
the line 48 in Figure 9, there is again a progressive
increase of the cross section of the pocket in the
direction away from the axis 14, such that the rate of
increase at the outer extremity of the pocket is
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greater than the rate of increase at the inside. This
again is represented by the curved nature of the line
48, with a steeper slope at the right than at the leftO
Finally, attention is directed to the third
embodiment illustrated in Figure 5 and 6. It will be
noted that the longitudinal section of Figure 5 is
substantially the same as that of Figure 3 for the
second embodiment, but that the transverse section shown
in Figure 6 includes a double flare with two rounded
walls 50 for each of the pockets 51 and 52. This more
greatly exaggerates the flare, so that the rate at which
each pocket widens away from the axis 14 is greater than
in either of the two earlier embodiments. This is
particularly seen with reference to the line 55 in
Figure 9, which is also labelled "3rd Embod.".
While three embodiments of this invention have been
illustrated in the accompanying drawings and described
hereinabove, it will be evident to those skilled in the
art that changes and modifications may be made thereto
~o without departing from the essence of this invention, as
set forth in the appended claims.
