Note: Descriptions are shown in the official language in which they were submitted.
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SEALING MEMBER FOR A FILTER PRESS
The present invention relates to a sealing member for
filter presses or the like in which the material to be
treated is led in between two wires, whereby the sealing
5 member prevents the material from being discharged sideways
from between the wires. The sealing member according to the
invention is especially suitable for filter presses used for
thlckening of pulp or sludge.
The sealing member of the present invention will be
10 described below in connection with a filter press which
comprises a top wire unit and a bottom wire unit, and the
pulp to be thickened is fed in between these units. The
wires are supported by a plurality of successive rolls in
~uch a manner that the distance between the wires becomes
15 narrower in the longitudinal direction of the machine. The
` wire-supporting rolls are preferably so disposed that the
pressing zone includes several press nips which contribute
to the thickening of pulp i.e. by liquid being pressed out
of the pulp through the wires. As a result of being pressed
20 ln ~uch a narrowing space, the pulp is naturally itself
~ pron- to dlscharge crosswlse relative to the direction of
!~ - extenslon of the machine, in whlch case a side sealing
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arrangement is necessary for the pulp which 18 to be
thlckened unlformly and, what i8 most lmportant, which is
25 not to be discharged from the sides of the press out of the
pre~slng zone.
Finnish patent application 840841 discloses a typical
prlor art sealing member for a wedge section of dewatering
machlnes i.e. for a pressing zone. The sealing member is in
30 the flrst pl~ce dlsposed between said wires in the edge zone
o~ the press wires. The sealing member itself comprises one
or two sQaling ledges having the same thickness from one
side to the other, which sealing ledge/ledges is/are bent
bRtw en the wir-9 or attached in a U-Rhap- b~tween the wires
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by means of specific members. Both types of members arecharacterized in that the ledges used are entirely of the
same thickness from one side to the other and that their
outermost parts are fixed between metal or equivalent
5 frames, said frames being perpendicular to the plane of the
wire and attached to one another with bolts. These
arranqements have been possible, however, only at the wider
end of the filter section where the distance between the
wires i8 several centimetres. However, for a large part of
10 the pressing zone, the distance between the wires is less
than 20 mm, and in the area close to the end even less than
10 mm. In the areas, the sealing member has no space between
the wires for metal frames or a bolt to connect the frames,
and the sealing ledge has to be left free and curved having
15 the same thickness from one side to the other, the pressure
on which ledge easily bends it outwards so as to widen the
efficient area between the wires towards the rear end of the
press, whereby the pressing/thickening effect of the edge
~ections will no longer be the same as in the centerline of
20 the press. In the worst case, the sealing member will break
and the pulp will be freely discharged to the sides of the
machine.
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one of the drawbacks of prior art sealing members is, for
example, their short lifetime of approximately two weeks,
25 because no material that would endure friction and other
strains has been found. On the other hand, no company with
strong enough product development potential has been
interested in developing material suitable for this very
.
purpose because the market, with respect to product
30 development costs, is very limited. Such sealing members are
complicated in structure since they have a great number of
~eparate parts. Their lateral stiffness is poor, in other
word~ they have to be very well 6u.pported which means that
support members must be disposed very close together.
35 Furthermore, since the above-mentioned sealing members are
plates with the same thickness from one side to the other,
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their sealing characteristic is not as good as it should be
because the tip of the sealing lip is as stiff as the rest
of the sealing ledge and therefore the tip does not readily
respond to the movements of the wire surface. On the other
5 hand, a sealing ledge having the same thickness from one
side to the other and which bends for as wide part as
possible under the pulp pressure against the wire surfaces,
results in a greater wearing of the sealing ledge.
The drawbacks of the prior art side sealing arrangements
10 described above were eliminated by a sealing arrangement
according to Finnish patent 76703 which is characterized in
that it comprises a back portion communicating with two lips
leaving a space between the lips with the width of said
space changing in the longitudinal direction of the sealing
15 member, and a support member disposed into communication
with the back portion of the sealing members and to the
opposite side of the back side respective to the space
between the lips and substantially at the level in the
"depth-direction" of the space.
~; 20 That sealing member was much more durable, cheaper to
manufacture and easier to replace than the earlier
arrangements.
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However, the flexible plastic and rubber materials used
?~`,,`, in the arrangement according to the above-mentioned patent
25 have proved to be a bottleneck because, in the long run,
they become brittle, their tip area begins to crackland they
gradually lose their sealing ability. It has to be noted,
however, that their lifetime is in any event manifold in
comparison with prior art seals, but as it is not as long as
30 de~ired, a totally new arrangement has been developed for
~'~ sidQ ~ealing of filter presses. lt has been established that
steel sQals, which were previously completely condemned,
~ bring about the best result when designed properly, and
1~ dimensioned and installed in a correct manner. Formerly
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steel was not used because of the fear that it soon wears
out the wire at contact surfaces. According to the former
concept, the contact between the wire and the steel sealing
had to be linear in order to maintain the web width
5 constant.
According to the present invention, it is possible, if
desired, to maintain the web width constant and at the same
time the contact surface between the wire and the sealing is
large in area. Furthermore, the contact angle between the
10 sealing and the wire is acute, thereby resulting in a
wiping, gentle contact between them.
The sealing arrangement according to the present
invention is characterized in that the depth of the space
between the two sealing elements, which communicate with the ~ ;
15 sealing member and are disposed between two moving plane
surfaces, is reduced at the level of the pulp web in the
direction of movement of the pulp web.
`~ The sealing member according to the present invention is
described in more detail in the following by way of example,
20 with reference to the accompanying drawings, in which
Fig. 1 is a schematic overall elevational view of a filter
press including a sealing member according to the
lnvention;
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Fig. 2 a is an end view of a sealing member accarding to
a preferred embodiment of the invention taken
along line A - A of Fig. 3;
:,:
Fig. 2 b is an end view of a sealing member according to
a second preferred embodiment of the invention;
and
30 Fig. 3 is a top view of an embodiment according to Fig. 2.
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In accordance with Fig. 1, a filter press including a
sealing member of the invention comprises a frame 10
provided with two wire sections, i.e. a bottom wire 12 and a
top wire 14. The bottom wire 12 is supported in the pressing
5 zone 16 by rolls 18, which rolls are disposed relatively
close to each other successively in the longitudinal
direction of the press. The tension regulation of the bottom
wire 12 is effected by adjusting the position of a wire
turning roll 20 in a substantially horizontal direction. The
10 top wire 14 i~ supported in the pressing zone 16 by a group
of rolls 22 which group is substantially vertically
ad~ustable an~ its pulp inlet end (on the right-hand side of
the figure) is pivoted to the frame 10, and the group is
arranged to be vertically adjustably displaceable by means
15 of ad~usting means 24 at its opposite end. The tension
regulation of the wire 14 is effected by a wire turning roll
26. The distancQ between the top and bottom wires is
substantially constant at the pulp inlet end but adjustable
at the opposite end. The pressing zone i8 preferably
~20 arranged so as to become narrower like a wedge to correspond
à`;to the real dimensions of the pressing zone. Both sides of
this pressing zone are provided with a sealing member
according to the invention.
Fig. 2 i9 an end view of a sealing member 30, which
6~2S comprises support members 32, 34 and sealing elements 36, 38
~`~pressed between said support members by means of screws or
bolt~ 40. It is a characteristic of the invention jthat,the
direction of the support members 32, 34 is substantially the
same as that of the wires 12 and 14, i.e. the direction of
~`30 tho pulp web plane. The support members 32 and 34 are
preferably metal ledges. The sealing elements 36 and 38 are
preferably comprised of steel plate, especially of spring
isteel, which, aocording to Fig. 2a is bent so as to form an
angle ~ between the sealing elements 36 and 38 clamped
.35 together. Thus, each sealing element is preferably
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subjected to the extent of bending of B/2. It is also
appreciated in Fig. 2a that the angle between the sealing
elements 36 and 38 remains unchanged along the whole length
of the sealing, unlike in the Finnish patent 76703 referred
5 to as the prior art and the basis of the present invention,
ln which patent said angle changes evenly along the whole
length of the sealing. A characteristic feature of the
lnvention which brings about an acute contact angle between
the sealing and the wire, i.e. a gently wiping contact, is
10 shown in both Fig. 2a and 3. Said figures 2a and 3 also
indicate how the width of the sealing elements 36 and 38 ;
counted from the turning point, i.e. from the inner edge of
the support members 32 and 34 to the tip of the sealing ~ -
member, decreases in the direction of movement of the wires
15 ~arrow B in Fig. 3), whereby the distance between the tips
of the ~ealing elements 36 and 38 is correspondingly reduced
~as well as the distance between the wires.
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Fig. 3 also show~ how the edge of the sealing element 36,
which edge contact~ the top wire moving in the direction of ;
-~ 20 arrow ~, approaches the ~upport member 32. In other words,
the contact surface between said edge and the wire i~ not
;; linear but a plane iurface, the width of the plane
`~ ~ ¢onforming to the change of width of the sealing element 36
in the pro~ection in the direction of the wire plane. For
~ ~25 the same reason, the contact angle between the sealing
P~ element and the wire is acute and the way of contact is
c~ wiping.
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t! ' Fig. 2b illustrates a second preferred embodiment of the
invention, in which embodiment the tip parts of the sealing
~0 elements are bent to conform to the planes of the wires,
~; whereby the contact with the wire becomes more gentle and
i~ also the area of the contact surface larger than in the
embodiment of Fig. 2a.
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The object of the support members 32 and 34 in itself is
to provide the sealing member with necessary lateral
stiffness which is very important in order that the width of
the pulp web to be thickened remains constant along the
5 whole length of the pressing zone and in order that the
sealing member need not be supported by support means to be
installed very close together, the number of which support
means being directly proportional to the amount of work
needed for the change of the sealing member. On the other
10 hand, the support means shown in the figures allows vertical
bending of the sealing member, which may in some cases occur
as the direction of the wires changes slightly. Such
bendings have not been allowed by prior art sealing members
because clamping means for sealing ledges, said clamping
15 mean,a being made of metal or equivalent material, have been
positioned so as to resist bending in said direction.
A preferable material for the sealing element in a
sealing member according to the invention is steel with such
friction properties as to match well the plastic wire.
20 Spring steel has been found to be most suitable for this
~` purpose. Nowever, some other material with suitable
tiffne~s and friction propertie,3 may be used as well. The
support member is preferably a flat metal bar which may be
readily arranged with clamping and support means for the
as ,sealing member. In test apparatuses, specific quick-
di,sconnect elements have been used as clamping and support
~, means for fast replacing of the sealing member.
As can be noted from the above description, a compl-tely
new type of sealing member ha,s been developed for such
30 points of operation where a ,3tatlonary sealing of varying
dlmensions i,s needed which may be disposed between two
movable surface,3, The sealing member according to the
invention eliminates or minimizes the weaknesses of the
prior art solutions by simplifying the member to the utmost
35 thereby enabling fast manufacture and replacement thereof.
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