ANGULARLY DISPOSED BLADES FOR A CYLINDRICAL SUSPENSION CLASSIFIER

LAMES INCLINABLES A ANGLES VARIABLES POUR CLASSIFICATEUR CYLINDRIQUE PAR SUSPENSION

English Abstract

ABSTRACT OF THE DISCLOSURE
A classifying apparatus for a suspension, especially for
a pulp suspension, having a screen drum, means for feeding the
suspension to one side of the screen drum, for removing thickened
suspension from the same side of the screen drum and liquid from
the opposite side of the screen drum, blades inclined in relation
to their direction of rotation so that any one of the ends of the
inclined blades is substantially on the same screen drum line
parallel to the screen drum axis as the opposite end of some
other blade and fitted to sweep at least one surface of the screen
drum, and driving means for moving the screen drum or the blades
in relation to each other.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. Classifying apparatus for a suspension such as pulp suspension,
comprising a screen drum, means for feeding the suspension to a first side
of the screen drum, means for removing the reject or thickened suspension
from said first side of the screen drum, and means for removing the accept
or liquid from the other side of the screen drum, a set of longitudinal
blades fitted to sweep at least said first side of the screen drum to create
pressure impulses for removing the reject suspension from the screen, driving
means for effecting relative rotational movement between said blades and the
screen drum about the axis thereof; the blades being so arranged at an inclined
angle to their direction of rotation relative to the screen drum about said
axis that the end portion of each blade at one end of the drum lies substanti-
ally on the same line parallel to the axis of the screen drum as the end
portion of another blade at the opposite end of the screen drum.
2. Classifying apparatus as claimed in claim 1, wherein said other
blade is a next adjacent blade.
3. Classifying apparatus as claimed in claim 1, wherein at one end
of the screen drum there is provided an inlet for feeding suspension into
the screen drum and at its opposite end there is provided an outlet for
removing the reject or thickened suspension from the screen drum, the end
portion of each blade nearest said outlet being arranged to move behind the
opposite end of said blade in the direction of rotation.
4. Classifying apparatus as claimed in claim 1, 2 or 3 wherein the
screen drum is fixedly fitted to a housing which has an outlet for removing
the accept or liquid.
5. Classifying apparatus as claimed in claim 1, 2 or 3, wherein
opposite ends of adjacent blades are separated by or overlap by an amount

not exceeding 5° of a circle.
6. An improved classifying apparatus for a suspension, especially for
a pulp suspension, comprising:
a generally cylindrical stationary screen drum having a central axis and a
plurality of apertures formed therein along a portion of its axial extent
through which accept suspension material can pass;
means at both ends of said screen drum for supporting said drum;
means for feeding the suspension to one side of the screen drum;
means for removing reject or thickened suspension from said one side of
said screen drum;
means for removing accept suspension or liquid from the opposite side of
said screen drum;
sweeping means for generating hydraulic impulses to detach solids attached
to said drum;
said sweeping means comprising a plurality of inclined blades;
blade support means for supporting said inclined blades for rotation in a
predetermined direction about the central axis of said drum so that said blades
are inclined relative to said axis and to their direction of rotation and so
that said blades sweep a surface of the screen drum; and
driving means connected to said blade support means for supporting to
establish motion of said blades relative to said surface, said blade support
means being arranged to establish the angle of inclination of said blades so
that the end portion of each of said blades near one end of said drum overlaps
an end portion of at least one other of said blades near the other end of said
drum with respect to an axial line along said drum, said overlap being sufficient
to dampen said hydraulic impulses and lying axially within said portion of said
drum in which said apertures are formed to permit the accept suspension material
to pass therethrough.
7. A classifying apparatus according to claim 6 wherein the angular extent

of blade overlap, relative to said axial line, is no greater than about 5°.
8. A classifying apparatus according to claim 6 wherein:
said means for removing accept suspension includes a mantle surrounding
and fixedly attached to said drum, said mantle having an outlet for carrying
accept away from the region outside of said drum;
said means for feeding includes an inlet conduit for delivering suspension
into the interior of said drum at one axial end thereof; and
said means for removing reject includes an outlet conduit at the opposite
axial end of said drum;
and wherein said inclination of said blades and said predetermined direction
of rotation are chosen such that the blade ends closest to said outlet
conduit pass said line after the ends of the same blades closest to said
inlet conduit to convey the reject suspension toward said outlet conduit.

Description

10E~5;~48
.
~ e present invention relates to a classifying apparatu~ for
a suspension and especially for a pulp suspension, having a screen drum
which allows the accept or only liquid to pass through it and retains the
re~ect or the thickened suspension. The invention relates in particular
to a classifying apparatus having blades substantially parallel to the
screen drum, which sweep along the gcreen drum surface and form an angle
with the axis of the screen drum in order to generate hydraulic impulses
to promote the detaching of the solids attached to ~he screen drum sur-
face and their conveying towards the outlet.
Previously known are classifiers provided with a screen drum
in which the pulp to be screened is forced through screen apertures of
a certain size, whereby the accept pulp passes through the screen drum
and the reject pulp does not. In order that the screen drum not be
clogged, it has been provided with rotatlng blades which produce
hydraulic impulses to detach the clogging pulp from the surface of the
screen drum. Often, the blades have been fitted obliquely to the longi-
tudinal axis of the screen drum ln order to promote the movement of the
reject pulp in the desired direction, i.e., towards the re~ect outlet
pipe.
The screen drum cleaning impulse6 create hydraulic pulsation
in the pulp suspension being screened. This hydraulic pulsation has
proven detrimental, for example, when the ~creen classifiers have been
placed prior to the paper machine head bo~. The paper machine head box
has not ln all cases been capable of dampening the pulsation sufficiently,
but part of the pulsation has remained undampened and has caused pulp
density (surface weight) variation in the paper being manufactured,
mainly in its longitudinal direction.
The object of the pre6ent invention i~ to reduce the detrimental
pulsation caused by the blades, without reducing the effect of the
impulses which clean the screen drums.
According to one aspect of the present invention there is
provlded an improved classifying apparatus for a suspension, said appara-
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1085348 .
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tus comprising a screen drum, means for feeding the suspension to afirst side of the screen drum, means for removing the reject or thickened
suspension from said first side of the screen drum and means for removing
the accept or liquid from the other side of the screen drum, a set of
longitudinal blades fitted to sweep at least said first side of the screen
drum to create pressure impulses for removing the reject suspension from
the screen, driving means for effecting relative rotational movement between
said blades and the screen drum about the axis thereof; the blades being so
arranged at an inclined angle to their direction of rotation relative to the
screen drum about said axis that the end portion of each blade at one end of
the drum lies substantially on the same line parallel to the axis of the
screen drum as the end portion of another blade at the opposite end of the
sc.reen drum.
The best dampening of pulsation is achieved if each end of each
blade and respectlvely the opposite end of some other blade are exactly on
the same line of the screen drum, the line being parallel to the screen
drum axis. However, variations of a circle sector of approximately 5 degrees
can be allowed without substantially worsening the dampening of pulsation
achieved by the invention. According to the invention, the opposite end of
every second, third, or the next blade can also be on the same line, i.e.,
the blades partially overlap.
The invention is described below in more detail with reference
to the enclosed drawing, which depicts a side elevation, partially as a
cross section, of a preferred embodiment of the invention, by means of
which the hydraulic pulsation on the accept side has been reduced by 40%.
The pulp to be screened is fed in tangentially through an
inlet 1 in the upper part of the classifier shown in the drawing. From
the upper part of the classifier the pulp to be screened flows downwards
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~085348
through a vertical screen drum 2, whereby accept from the pulp suspension
passes through the apertures in the screen drum 2 into the annular space
between the screen drum 2 and the classifier mantle 3 and is removed from
there through an outlet 4. The reject pulp slnks to the bottom of the
classifier, from where it is removed through a reject outlet 5.
A shaft 7 rotated by a motor 6 has been fitted centrally and co-
axially inside the screen drum 2. Several blades 9 have been attached to the
shaft 7 by means of arms 8, the blades 9 extending obliquely from one end of
the screen drum 2 to the other end having been fitted to sweep the inner sur-
face of the screen drum 2 very closely so as to detach, by means of hydraulicimpulses, the pulp adhering to it.
In order to dampen the pulsations on the accept side, the blades 9
have been fitted according to the invention in such a position that each end of
each blade 9 is substantially on the same line 10 parallel to the shaft 7 as
the opposite end of the adjacent blade.
In an alternative embodiment, blades 9a (shown in phantom) may be
fitted on the outside of the screen drum either in place of or in addition to
blades 9 on the inside of the drum. If blades are fitted on both sides of the
drum means may be provided to rotate blades 9 in the opposite direction to the
direction of rotation of blades 9a.
In addition, the blades can be hollow and open towards the screen
drum so as to feed a rinsing liquid onto the screen drum or to remove through
the blades the pulp detached from the screen drum.
It is also evident that the pulp to be screened can be fed around
the screen drum and the accept removed from the inside of the screen drum and
that the blades can be stationary and the screen drum rotating. All that is
required is that there shall be relative rotational movement between the screen
drum and the blades.
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