EP0415686A2

EP0415686A2 - Sealing member for a filter press

Info

Publication number: EP0415686A2
Application number: EP90309356A
Authority: EP
Inventors: Matti Haakana; Raimo Kohonen; Jukka Heino
Original assignee: Ahlstrom Corp
Current assignee: Ahlstrom Corp
Priority date: 1989-08-31
Filing date: 1990-08-24
Publication date: 1991-03-06
Also published as: FI83480B; JPH03219168A; FI83480C; CA2024342A1; FI894079A0; EP0415686A3

Abstract

The present invention relates to a sealing member preferably for sealing of the sides of the pressing zone of filter presses used in the pulp and paper industry. The sealing member according to the present invention solves the problems mentioned above because the sealing members (36, 38), made of practically permanent material which is ideal as to its friction properties relative to the wire surfaces, are constructed to form a single sealing member (30) together with the support members (32, 34), which sealing member (30) allows bending thereof conforming to the movements of the press wires, but prevents the tendency of the sealing member to bend, which tendency is caused by the pressure of pulp.

Description

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 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 thickening of pulp or sludge.
The sealing member of the present invention will be 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 such a manner that the distance between thw wires becomes narrower in the longitudinal direction of the machine. The wire-supporting rolls are preferably so disposed that the presing 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 in such a narrowing space, the pulp is naturally itself prone to discharge crosswwise relative to the direction of extension of the machine, in which case a side sealing arrangement is necessary for the pulp which is to be thickened uniformly and, what is most important, which is not to be discharged from the sides of the press out of the pressing zone.
Finnish patent application 840841 discloses a typical prior art sealing member for a wedge section of dewatering machines i.e. for a pressing zone. The sealing member is in the first place disposed between said wires in the edge zone of the press wires. The sealing member itself comprises one or two sealing ledges having the same thickness from one side to the other, which sealing ledge/ledges is/are bent between the wires or attached in a U-shape between the wires by means of specific members. Both types of members are characterized 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 frames, said frames being perpendicular to the plane of the wire and attached to one another with bolts. These arrangements have been possible, however, only at the wider end of the filter section where the distance between the wires is several centimeters. However, for a large part of 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 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 sections will no longer be the same as in the centerline of the press. In the worst case, the sealing member will break and the pulp will be freely discharged to the sides of the machine.
One of the drawbacks of prior art sealing members is, for example, their short lifetime of approximately two weeks, 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 development costs, is very limited. Such sealing members are complicated in structure since they have a great number of separate parts. Their lateral stiffness is poor, in other words they have to be very well supported which means that support members must be disposed very close together. Furthermore, since the above-mentioned sealing members are plates with the same thickness from one side to the other, 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 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 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 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.
That sealing member was much more durable, cheaper to manufacture and easier to replace than the earlier arrangements.
However, the flexible plastic and rubber materials used in the arrangement according to the above-mentioned patent have proved to be a bottleneck because, in the long run, they become brittle, their tip area begins to crack and 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 sealings, but as it is not as long as desired, a totally new arrangement has been developed for side sealing of filter presses. It has been established that steel sealings, which were previously completely condemned, bring about the best result when designed properly, and dimensioned and installed in a correct manner. Formerly 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 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 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 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, 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 invention;
Fig. 2 a is an end view of a sealing member according 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
Fig. 3 is a top view of an embodiment according to Fig. 2.

In accordance with Fi. 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 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 top wire 14 is supported in the pressing zone 16 by a group of rolls 22 which group is substantially vertically adjustable and 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 adjustbly displaceable by means of adjusting means 24 at its opposite end. The tension regulation of the wire 14 is effected by a wire turning roll 26. The distance between the top and bottom wires is substantially constant at the pulp inlet end but adjustable at the opposite end. The pressing zone is preferably arranged so as to become narrower like a wedge to correspond 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 is an end view of a sealing member 30, which comprises support members 32, 34 and sealing elements 36, 38 pressed between said support members by means of screws or bolts 40. It is a characteristic of the invention that 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 the 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 steel, which, according to Fig. 2a is bent so as to form an angle β between the sealing elements 36 and 38 clamped together. Thus, each sealing element is preferably subjected to the extent of bending of β/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 the Finnish patent 76703 referred to as the prior art and the basis of the present invention, in which patent said angle changes evenly along the whole length of the sealing. A characteristic feature of the invention which brings about an acute contact angle between the sealing and the wire, i.e. a gently wiping contact, is 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 (arrow B in Fig. 3), whereby the distance between the tips of the sealing elements 36 and 38 is correspondingly reduced as well as the distance between the wires.
Fig. 3 also shows how the edge of the sealing element 36, which edge contacts the top wire moving in the direction of arrow B, approaches the support member 32. In other words, the contact surface between said edge and the wire is not linear but a plane surface, the width of the plane conforming to the change of width of the sealing element 36 in the projection in the direction of the wire plane. For the same reason, the contact angle between the sealing element and the wire is acute and the way of contact is wiping.
Fig. 2b illustrates a second preferred embodiment of the invention, in which embodiment the tip parts of the sealing elements are bent to conform to the planes of the wires, whereby the contact with the wire becomes more gentle and also the area of the contact surface larger than in the embodiment of Fig. 2a.
The object of 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 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 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 means 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. Spring steel has been found to be most suitable for this purpose. However, some other material with suitable stiffness and friction properties 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 sealing member. In test apparatuses, specific quick- disconnect 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 completely new type of sealing member has been developed for such points of operation where a stationary sealing of varying dimensions is needed which may be disposed between two movable surfaces. The sealing member according to the invention eliminates or minimizes the weaknesses of the prior art solutions by simplifying the member to the utmost thereby enabling fast manufacture and replacement thereof.
Where technical features mentioned in any claim herein are followed by reference symbols, those reference symbols are included solely for the purpose of increasing the intelligibility of the claims.

Claims

1. A sealing member intended for use between two plane surfaces which surfaces move relative to said sealing member and the distance therebetween changes in the longitudinal direction of the sealing member, said sealing member being attached at its support structure to the frame of a machine in such a manner that the two sealing elements connected to said sealing member leave a space therebetween and are disposed between said plane surfaces, characterized in that the depth of said space between the two sealing members at the level of the pulp web is reduced in the direction of movement of the pulp web.

2. A sealing member as claimed in claim 1, characterized in that the bottom angle β of the space between the two sealing members remains constant along the whole length of the sealing member (30).

3. A sealing member as claimed in claim 1, characterized in that the sealing elements (36, 38) define the space therebetween, the width of said sealing elements counted from the support structure to the tip of the sealing element becomes narrower in the direction of movement of the pulp web.

4. A sealing member as claimed in claim 1, characterized in that the support structure of the sealing member (30) is formed on two ledges (32, 34) arranged in the direction of the pulp web level, between which ledges one edge of the sealing elements (36, 38) is pressed.

5. A sealing member as claimed in claim 1, characterized in that the part of edge of the sealing members (36, 38) which part lies against the wire is bent substantially to the level of the wire.

6. A sealing member as claimed in claim 1, characterized in that the material of the sealing member (36, 38) is metal, preferably steel.