Note: Descriptions are shown in the official language in which they were submitted.
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APPARATUS FOR PULPING PAPER
This invention relates to apparatus for
pulping paper making stock at relatively high con-
sistencies, and more particularly to paper pulping
apparatus in which a vaned rotor is utilized to
circulate the stock within a tub.
Paper pulping apparatus typically includes
a tub having a bottom wall and a cylindrical side
wall extending upwardly therefrom, a vaned rotor
centrally mounted on the bottom wall for rotation
within the tub, and a screen or valve means located
in or near the bottom wall to provide means for
removal of the pulped paper stock. The rotor vanes
include leading faces which are shaped and sized to
contact stock near the bottom wall of the tub and
propel it radially outwardly from the rotor against
the side wall, which directs the stock upwardly.
The rising stock flows to the center of the tub and
then downwardly toward the rotating vanes. Thus
durin9 pulping operation, the stock is caused to
flow in a generally clrcular pattern, and the reduc-
tion in size of the individual particles of paper
stock is due largely if not exclusively to the high
sheer forces between particles of stock created by
this flow pattern.
Many pulping devices of this construction
presently in use are limited in application to paper
making stock having a relatively low consistency,
typically in the range of 4-7% solids content If
the consistency of the stock is raised appreciably
above about 7~, the density of viscosity of the
stock is such that it does not easily flow downwardly
between the spinning vanes of the rotor. The vanes
will displace an initial quantity of pulp outwardly,
but cavitation will when occur since the displaced
pulp is not replaced by downwardly flowing pulp.
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In order to perform a pulping process upon
stock having a consistency in excess of about 10~,
special rotors have been developed. For example, in
the Blakly et al. U.S. Patent Application Serial No.
407,371, filed August 12,-1982 and commonly assigned,
a high consistency pulping apparatus is disclosed
having a rotor with a vertically oriented and axially
aligned feeding screw. The rotor induces vanes in
the form of circumferentially-extendin~ members with
a half-crescent shape which are disposed about the
periphery of a disk-shaped plate. The feeding screw
is mounted in the center of the plate and includes a
cylindrically-shaped body having a base which is
spaced from the rotor vanes, and a helical screw
flight which extends along the body and terminates
at a squared end above the disk-shaped plate support-
ing the vanes.
When rotated in a tub containing stock at
12-13% consistency, the feeding screw guides the
stock downwardly to the region oE the rotor vanes
which then propel it outwardly against the walls of
the tub. The higher consistency stock climbs the
walls o the tub, and baf1es are employed to direct
the pulp downwardly toward the tub center.
The potential advantages ox high censistency
pulping devices have been well recognized. For
example, since the density of the stock is consider-
ably higher for pulp stock having a consistency of
; about 14% than for stock having a consistency of
about 7~, the shear stresses created during a high
consistency pulping operation are significantly
greater, so that the time required to perform a
pulping operation with high consistency stock may be
the same or even less than the time required for
`~ 35 pulping the same volume of low consistency stock in
the same pulping tub.
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lowever, there often exist inherent disad-
vantages with high consistency pulping devices of
the type previously described. For example, since
the helical screw flight ox the feeding screw termi-
nates above the base of the rotor and is spaced fromthe rotor vanes, there may exist a tendency for the
high density stock to collect and form a wedge
between the underside of the trailing portion of the
screw flight and the portion of the rotor base
immediately beneath it. Another disadvantage is
that there does not exist means to guide the stock
from the squared trailing portion of the screw
flight to the working faces of the vanes, so that
voids may be created surrounding the working faces
of the vanes.
Accordingly, there is a need for a high
consistency pulping apparatus having a rotor which
minimizes the likelihood ox cavitation. There is
al90 a need for a high consistency pulping apparatus
in which the rotor provldes means for guiding the
high density stock in a smooth and uninterrupted
path from a location adjacent the center of the
rotor to the working faces of the vanes without the
stock becoming wedged between the screw slight and
rotor vane
The present invention provides an apparatus
for pulping paper making stock which is capable of
pulping relatively high consistency stock, that is,
stock in a range of approximately 10-25% solids, in
a manner that creates the necessary circular flow
patterns to generate the high shear forces between
paper particles in order to perform the pulping
operation in a minimum amount of time. Another
advantage of the invention is that it includes a
rotor that is designed to minimiæe the likelihood of
cavitation ancl the likelihood of stock collecting on
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the rotor to obstruct the downward and outward flow
of stock to the vanes.
According to one embodiment of the present
invention, a rotor particularly adapted for use in
pulping paper making stock at high consistencies is
characterized by a rotor body adapted for mounting
on a vertically extending drive shaft, a plurality
of vanes extending outwardly from the rotor body,
and a feed screw mounted centrally of the rotor body
and extending upwardly therefrom. The feed screw
has a conical body with helical flights extending
along its length. When the rotor is rotated within
a tub filled with paper making stock, the conical
body and flights cooperate to guide stock downwardly
and outwardly toward the vanes.
The downward and outward movement of the
pulp resulting from the rotation of the weed screw
causes the pulp to slow directly to the faces of the
vanes and red-lces the likelihood of the stock col-
lecting on the rotor between the feed screw and
vanes. Furthermore, this elow path ensures that
stock flows clownwardly between vines so that the
entire face of each vane can provide the maximum
pumping action for which it was designed.
In a preferred embodlment, the conical body
of the feed screw includes a base sized such that
its periphery is adjacent the root portions of the
rotor vanes. The trailing end of the screw flight
blends into the working face of a vane to form a
continuous surface therewith. In another embodiment,
the flight of the feed screw includes a trailing
edge which tapers in width and terminates at the
periphery of the base adjacent a vane root. Thus,
the combination of the feed screw with the rotor
; 35 provides a guiding surface along which the stock mAy
travel which extends from the upper tip of the feed
screw to the outer tip of the rotoe vane.
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The present invention preferably ;ncludes a
tub having a bottom wall and a cylindrical side wall
extending upwardly therefrom, and the rotor body is
centrally mounted on the bottom wall for rotation in
a vertical axis.
The feed screw is sized such that, when
mounted to the rotor body, its height above the
bottom wall of the pulping tub approximates the
intended depth of the stock within the tub. When
rotated, the rotor of the preferred embodiment
causes the stock within the tub to flow in the
previously described circular pattern such that the
level of the stock at the center of the tub is below
the level of the stock at the side wall, thereby
exposing the tip of the feed screw. When the Eeed
screw and stock are in this configuration, the feed
screw provides a means of escape for any air which
is present in the vicinity of the vanes, thus further
reducing the likelihood oE cavitation.
Another advantage of the construction of
the present invention over prior art high consistency
pulping devices is that the lnvention can utilize
prior art rotors which previously were capable of
functioning only in low consistency pulping opera-
tions. By sizing the feed screw such that the
periphery of the base and trailing portion of the
flight are substantially contiguous with the faces
of the vanes, the feed screw can be retrofitted to a
prior art rotor, such as the rotor disclosed in the
Couture U.S. Patent No. 3,88g,885. However, due to
the nature of high consistency paper making stock,
it is preferable although not necessary to utilize a
` rotor having between three and six vanes, since it
is difficult to cause high consistency pulp to flow
between the relatively narrow spaces existing between
the vanes of rotors having more than six vanes. In
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rotors having more than three of four vanes, it is
also preferably to utilize a fced screw having
multiple flights so that the stock can be urged
downwardly and outwardly in a relatively balanced
pattern about the periphery of the rotor.
Accordingly, it is an object of the present
invention to provide an apparatus for pulping paper
making stock at high consistencies which minimizes
the likelihood of cavitation; an apparatus which
provides a continuous path along which stock may
travel from an upper portion of the pulping tub to
the outer tip of the vane; and an apparatus for
pulping high consistency stock which can be made by
modifying low consistency systems.
Other objects and advantages of the present
invention will become apparent from the hollowing
description, the accompanying drawings and the
appendecl claims. In order that the invention may be
more readily understood, reference will now be made
to the accompanying drawings, in which:
i Fig. 1 is a perspective view of the pulping
apparatus of the preferred embodiment of the inven-
tion in which the tub wall has been cut away to show
the rotor;
Fig. 2 is a detail oE the rotor of Fig. l;
Fig. 3 is a side elevation in section of
the tub of Fig. 1 showing the flow pattern of pulp
stock during a pulping operation
Fig. 4 is an alternate embodiment of the
rotor of the invention; and
Fig. 5 is another embodiment of a rotor of
the invention.
i The pulper shown in Fig. 1 includes a tub
I; 10 having a cylindrical upper wall 12 and a bottom
wall comprising a plane center section 14 surrounded
by a frusto-conical portion 16~ As shown in Fig. 2,
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Serial No. 448,340 -7-
the center section 14 includes a perforated bed plate 18
for draining the pulped paper stock from the tub 10 after
the completion of the pulping operation. The tub 10 is
mounted on supports 20 above a gear drive 22 which is
directly driven by a motor 24. The cylindrical side wall
12 incudes baffles 26 which direct pulp stock flowing
upwardly against the wall outwardly toward the center of
the tub 10.
A rotor, generally designated 28, is mounted in
the center of the perforated bed plate 18 and is driven by
the motor 24 and gear drive 22. The rotor 28 includes a
rotor body 30 having a cover plate 32 and vane ring 34.
The vane ring 34 supports a plurality of vanes 36, alter-
nate ones of which are of increased thickness and function
as pumping vanes 38. The rotor ~28 as described thus far
is of a type well-known in the art and is commonly used in
pulping devices or defibering stock a between 5% and 8%
consistency. The structure and cooperation of the rotor
28 with the perorated bed plate 18 are described more
ully in the Couture U.S. Patent No. 3,889,885.
However, the rotor 28 of the present invention
differs significantly from prior art rotors in that it
includes a feed screw, generally designated 40. The feed
screw 40 includes a conical body 42 which is concentric
with the rotor body 30, and extends upwardly therefrom.
The rotor 28 may be cast as a single unit, or the feed
screw 40 and rotor body 30 may be fabricated separately
and then joined together. The conical body 42 includes a
rounded top 44 and a circular base 4~ which extends to the
root portions 48 of the pumping vanes 38.
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The feed screw 40 includes helical screw
flights 50, 52 which intertwine along the l.ength of
the conical body 42. Each of the screw flights 50,
52 is ribbon-shaped and includes a trailinq portion
54 which terminates at the bass 46 of the conical
body 42 adjacent the root ~8 of a vane 38. In the
embodiment shown in Figs. 1 and 2, the trailing
portions 54 are twisted so that their undersides 56
are contiguous with the face 58 of the pumping vane
38 so as to form a continuous surface therewith
The operation of the pumping apparatus is
best shown in Fig. 3. Prior to operation, the tub
10 is filled with paper making stock 60 which prefer-
ably is at a consistency of between 12~ and 25~
solids. The level o the stock within the tub l0
should approximate the height of the rounded top 44
of the feed screw ~0 above the center section 14.
Once the tub 10 is willed, the rotor 28 is rotated
in a countercloclcwise direction, indicated by arrows
shown in Figs. 2 and 3. When the rotational speed
j oE the rotor 28 has reached its intended operational
speed, the helical screw flights sn, 52 of the feed
screw 40 draw the stock 60 downwardly toward the
rotor body 30. it the same time, the stock is urged
outwardly by the lncreasing diameter oE the conical
body 42. Thus, the stock travels in a downward
helical path of increasing diameter, as indicated by
arrows B in Fig. 3.
Since the base 46 of the helical body 42
and the trailing portions 54 of the screw flights
are located adjacent the roots 48 of the vanes 38,
the stock 60 is guided directly to the faces 58 of
the pumping vanes 38. The downward and outward
motion imparted to the stock 60 by the cooperation
of the conical body 42 and flights 50, 52 places the
stock down between the vanes 36 and 33 so that it
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contacts the entire area of the vane face 58. Thus,
the efficiency of the vanes 38 is increased since
almost the entire vane face 58 contacts the pulp 60.
Once the pulp has contacted the vanes 38,
it is propelled outwardly in a generally radial
direction toward the frusto-conical portion 16, and
then upwardly against the wall 12 to the top of the
tub 10. The rising pulp encounters the baffles 26
which act to direct the pulp downwardly and inwardly
toward the center of the tub where it again is
directed toward the rotor body 30 by the feed screw
40. Due to the high consistency of the stock 60,
the depth of the upwardly rising stock at the peri-
phery of the tub 10 is greater than that at the tub
center. Therefore, during operation, the rounded
top 44 becosnes exposed and the feed screw provides a
channel or conduit for the escape of air from the
vicinity of the rotor body 30, thereby further
reducing the likelihood of cavitation. It is to be
understaod that the apparatus can be operated such
that the depth of stock in the tub may exceed the
height of the top 44, in which case the eeed screw
40 will convey air to the upper level of the stock,
where it will escape through the remaining stock to
the atmosphere.
With the embodiment shown in Figs. 1, 2 and
3, the conical body 42, the flights 50, 52 and the
vane faces 58 combine to provide a substantially
continuous pathway which positively guides the stock
from the top of the feed screw 40 to the outer tips
of the rotor vane faces 58. Since the trailing
portions 54 of the screw flights blend into the vane
faces 58, there are no pockets or gaps which may
;~ collect pulp or form voids, so that the generated
flow of pulp is much smoother than with prior art
rotors having feed screws whose flights are not
contiguous with th. vane roots 48.
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One of the advantages of the present inven-
tion is that a previously existiny low consistency
pulpiny apparatus may be converted Jo perform the
highly efficient high consistency pulping operation
of the present invention with a minimum of expense.
For example, the rotor 28A shown in Fig. 4 includes
a rotor body 30A in which a weed screw 40A has been
attached to the cover plate 32A by a bolted flange
62 which extends outwardly from the peripherylbase
46A of the conical body 42A. The design of the
rotor 28A differs from the rotor 28 shown in Figs.
1-3 in that the periphery of the base 46A is not
immediately adjacent the vane roots 48A of the
pumping vanes 38A. Furthermore, the trailing por-
tions 54A of the screw fliyhts 50A, 52A are not
contiguous with the vane roots 48A. Rather, the
trailing portions 54A taper in width until they
terminate at a point 64 locateci at the base 46A of
the conical body 42A.
Since the feed screw 40A cannot be fabri-
cated easily such that its trailing portions 5~A
blend into the vane faces 58A of the pre-existing
rotor 2~A, it is desirable to taper the width of the
trailiny portions to a point 64 to reduce the like-
: 25 lihood that pulp stock will become wedged in the
space between the underside of the trailing portions
and the cover plate 32A or other portions of the
rotor body 30A. Despite the fact that the conical
body 42A and screw flights 50A, 52A are not immedi-
ately adjacent the vane roots 48A, the feed screw
40A will still impart a downward and outward motion
' to the pulp stock within a tub which directs it to
:~ the faces 5~3A of the vanes 3~A. This motion mini-
: mizes the likelihood that pump stock will collect or
stagnate in the central area of the rotor body 30A
and not flow to the pumping vanes 38A.
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Another application of the invention is
shown in Fig. 5 in which a rotor 28B includes a
rotor body 30B having four vanes 36B, each of which
includes a pumping face 58B. The vanes 36B are
mounted on a generally frusto-conical shaped vane
ring 34B. Rotor bodies 30B of this type are general-
ly used in pulping operations where the consistency
of the pulp stock is between 5% and 8~ solids.
A feed screw 40B is mounted to the central
portion of the rotor body 30B and includes screw
flights 50B, 52B which intertwine about the conical
body 42B and terminate immediately adjacent the vane
roots 48B. Each of the trailing portions 54B of the
screw flights 50B, 52B taper in width in a manner
similar to that of the embodiment of Fig. 4 and
terminate at a point 64B on the base 46B of the
conical body 42B.
Since the base 46B end points 64B are
located immedlately adjacent the vane roots 48B, the
outer edges 66 o the trailing portions 5qB cotnbine
wlth the upper edges 68 oE the pumping faces 58B to
orm continuous edges therewith. Ayain, while the
trailing portions 54B ox the screw flights 50B, 52B
do not blend into the pumping Eaces 58B, the location
of the trailing portions and the base 46B of the
conical body 42B combine to provide a continuous
path for the paper stock which guides the stock
directly to the pumping faces 58B of the vanes 36B.
While the forms of apparatus herein
; 30 described constitute preferred embodiments of the
invention, it is to be understood that the invention
is not limited to these precise forms of apparatus,
and that changes may be made therein without depart-
ing from the scope of the invention as defined in
the appended claims.
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