REPLACEABLE WEARING SURFACE FOR A SEALING ARRANGEMENT

Abstract: The invention relates to a replaceable wearing surface for a sealing arrangement on drum end walls on press drums in presses which dewater fibre suspensions radially into the drum through the shell of the drum. The invention is characterized in that the wearing surface for the sealing arrangement (4) comprises a wear ring (5) and holder members (8), the wear ring (5) being provided, on the side which faces into the drum from the drum end wall after mounting, with locking members (6) which are arranged parallel to the drum axis and are preferably in the form of knob-shaped locking members (6), the arms (9) of the holder members (8) being designed so as, when mounted by being pushed in in the radial direction of the press drum, to engage the locking member (6), and the holder members being fastened to the drum end wall (14) by suitable fixing members, if appropriate comprising bolt connections.

Description: REPLACEABLE WEARING SURFACE FOR A SEALING ARRANGEMENT TECHNICAL FIELD The invention relates to a replaceable wearing surface for a sealing arrangement according to the precharacterizing clause of Patent Claim 1. STATE OF THE ART In presses for dewatering liquid suspensions, in particular fibre suspensions, where the presses have at least one rotatable screening drum and the dewatering takes place radially into the drum(s), the suspended material is dewatered by the liquid in the suspension passing through a perforated or slotted, often cloth- covered, surface shell of the drum(s) which is (are) arranged partly submerged in a trough containing the liquid suspension. The suspended material then forms a cake or a web on the outside of the surface, which may be cloth-covered, and is removed. New liquid suspension and, if appropriate, treatment liquid are supplied to the trough as liquid and solid material are removed by the dru (s) . The construction of such presses requires that the suspension is not allowed to escape over the end walls of the drum(s). For this reason, sealing arrangements are necessary between the drum(s) and the trough. The sealing between the trough and the drum(s) is effected between a stationary surface and a surface in continuous motion, that is to say between generally annular or circular-segment-shaped sealing elements arranged on the trough and an annular sealing element on the drum end walls on the rotating drum(s) . This means that, on account of the rotation of the drum(s) and a certain inevitable penetration of suspended material between the sealing surfaces, the sealing surfaces are subjected to wear, for which reason the sealing elements with their sealing surfaces or what are known as wearing surfaces must be easily replaceable, which means that the method of fastening the sealing elements on m particular the drum end walls is important. The known art for fastening sealing elements on the drum end walls involves fastening by welding and/or by radial or axial screw connections through the wearing surfaces, or by shrinking, all of these fastening methods having disadvantages. It is not suitable, for example, to fasten them on the drum end walls by welding because this leads to thermal stresses m the sealing elements with dimensional changes as a consequence and moreover destroys any surface finish of the wearing surface of the sealing elements, which results m a shortened life. Nor is it suitable to fasten them by screw connections, made axially m relation to the drum, through the wearing surfaces on the drum end wall because this on the one hand reduces the area of the wearing surfaces or alternatively means that the area must be increased and on the other hand means that the material m them must be made thicker m order to accommodate the head of the screw m the screw connection. In most cases, this means that the entire wear ring has to be replaced m spite of only a few per cent of the thickness having been worn down, which results m each replacement of the wearing surface being extremely expensive. Nor is it suitable to fasten them on the drum end walls by designing them as cover-like arrangements fastened to or on the drum shell because this reduces the dewatering surface area of the drum and moreover results m a connection which is unsuitable m terms of forces. Shrinking is not suitable either as an alternative fastening method because secure shrinking of a large thin ring is very exacting as far as tools and tolerances are concerned, which makes this method expens ive . PCT/SE98/01247 describes a sealing element in the form of a segmented sealing ring for a drum end wall intended inter alia for axial sealing between the drum end walls and a trough. The sealing ring segments are fastened by axial screw connections and welded joints. In this case, use is made of screw connections, made axially in relation to the drum, through the wearing surfaces on the drum end wall, which reduces the area of the wearing surfaces. It also results in it being necessary to demount the drum, or alternatively the parts of the housing against which the end wall seals, in order for it to be possible to demount the seal. SE-C 501 710 and SE 93 02 898-3 describe other types of sealing arrangements in the same type of press, where sealing arrangements are arranged between a submersible part of the trough and a rigidly arranged part of the trough, that is to say between two parts which are stationary in relation to one another during continuous operation. SE-C 380 300 shows diagrammatically another seal with specific seal components without going into their construction in greater detail. In the type of press concerned, the sealing is important as the liquids which are pressed out of the fibre suspension are to be or at least are intended to be used/recirculated in a closed system and are therefore to be recovered. Leakage in the presses means that great quantities of impure liquids have to be cleaned away around the machine and destroyed. BRIEF DESCRIPTION OF THE INVENTION The invention relates to a replaceable wearing surface for a sealing arrangement in presses with at least one rotatable press drum which dewaters fibre suspensions by the liquid in the suspension passing radially into the drum through a shell surface, which may be cloth- covered, on the drum(s), a cake or a web of the fibre material being formed on the outside of the shell surface which may be cloth-covered. The replaceable wearing surface for the sealing arrangement according to the invention constitutes part of an axial seal between the end walls of the press drum(s) and a trough in which the drum(s) is (are) partly submerged and relates to that part of this seal which is arranged on the drum end walls. The object of the invention is to provide a replaceable wearing surface for a sealing arrangement which is easily mountable and thus easily replaceable when the wearing surface has become unserviceable, and in which the problems of the known art described above relating to fastening the wearing surface in the sealing arrangement are eliminated. Accordingly, a sealing surface can be provided over the entire radial extent of the wear ring without fixing elements encroaching on the extent of the wearing surface. It is also the object of the invention to provide a sealing arrangement with a wearing surface which can be prepared in advance, for example by hard-metallization, where no finishing is required on replacement, which prolongs the life of the sealing arrangement. At the same time, the wearing surface part can be optimized for its function as a replaceable wear part. These objects are achieved by a sealing arrangement according to the characterizing part of Patent Claim 1. Further characteristics, aspects and advantages of the invention emerge from the patent claims below and the description following of some possible embodiments. The invention is described in greater detail with reference to figures according to the following list of figures. LIST OF FIGURES Fig. 1 shows a side view of one end of a press drum; Fig. 2 shows a detailed view of a replaceable wearing surface for a sealing arrangement according to the invention; Fig. 3 shows a holder member which constitutes part of the replaceable wearing surface for a sealing arrangement according to the invention; Fig. 4 shows a wear ring according to the invention in a side view divided into two sections; Fig. 5 shows a detailed view of a preferred alternative embodiment of Figure 2, and Fig. 6 shows an alternative embodiment of a knob- shaped locking member. DESCRIPTION OF SOME EMBODIMENTS OF THE INVENTION Fig. 1 shows a view of one end of a press drum 1 in a press which is used for dewatering a paper pulp suspension and is arranged so that the press drum 1 can rotate about a shaft 2 supported by a shaft end 3. The invention relates to an annular replaceable wearing surface for a sealing arrangement 4 on the drum end wall . Fig. 2 is a detailed view of a replaceable wearing surface for a sealing arrangement 4 according to the invention. This comprises a wear ring 5 which extends around the outer edge of the drum end wall 13, 14 and L-shaped holder members 8. The wear ring 5 has a wearing surface 7 and an opposite surface which, after mounting on the drum, faces radially into the drum from the drum end wall, this opposite surface being provided with knob-shaped members 6 arranged parallel to the drum axis. In one embodiment, the wear ring 5 is divided diametrically into two segments or halves, shown in Fig. 4 as two 180° segments 5a and 5b respectively, so as to be easily mountable, but can of course be complete or divided into more than two segments. The number of segments can vary depending on the size of the press drum, but is usually between 1 and 15. 15 segments give a coverage of 24° per segment. - 6 - An advantage of segmenting into a number of parts is that replacement of a wear ring can be effected by indexing the drum forwards step-by-step to a position in which only one sector of the end wall of the drum is exposed and there replacing the exposed segment. Fig. 3 shows in greater detail the L-shaped holder members 8. The first leg 9 of the L-shaped holder members is provided with a slot 10 which is designed so as to engage under the knob on the knob-shaped member 6 and in this way hold the wear ring 5 in position against the support element 13 and the end wall 14 of the drum and at the same time prevent the wear ring 5 from moving axially outwards from the drum 1. This first leg can have constant thickness but is preferably wedge-shaped, in other words slightly tapered, towards the outer end of the leg 9, so that the first leg has its minimum thickness at the outer end at the beginning of the slot 10. By means of such a wedge shape of the first leg 9, the wear ring 5 is clamped against the drum end wall 13, 14 with great force . The second leg 11 of the L-shaped holder member 8 is designed to be fastened to the drum end wall 13, 14 by a screw connection 12 directed radially outwards in relation to the drum axis and thus lock the holder member 8 in the appropriate position. If desired, the screws in the screw connection 12 can be secured by tack welds (not shown) or other types of locking element such as lock washers acting against the second leg 11 of the holder. A tack weld 20 can also be used as an extra means of securing the L-shaped holder to the drum end wall. The support element 13 can be a component which is separate from the drum end wall 14 and ring-shaped, preferably divided diametrically into two or more segments, or halves, so as to be easily mountable, but can also be in the form of a complete ring. The support element 13 can also be an integral part of the drum end wall 14. Figure 4 indicates a number of positions 6pl-6p6 for the knob-shaped member 6 over a quarter of the circumference of the wear ring. The knob-shaped member which is arranged in a position 6pl closest to the division between the two halves 5a and 5b respectively is preferably to be arranged as close to the division as possible. Figure 4 shows six positions for the knob- shaped member, which gives eleven positions for each half 5a and 5b respectively. In wash presses of relatively great diameter, use is of course made of more knob-shaped members, and the total number can vary from four to fifty knob-shaped members, preferably one for every or every other drainage cell in the drum. Normally, there are thirty drainage cells in the drum, and therefore fifteen or thirty knob-shaped members. Figure 5 shows an alternative embodiment of the holders, in which the L shape of the holders has been replaced by a slightly wedge-shaped flat bar 8b. In this simplified variant, the arm/wedge 9b is pressed out radially under the knob 6, after which the flat bar is fastened to the end wall part 14 by means of a tack weld 21. This embodiment makes it possible to avoid the drilling and threading operations for fixing screws, which increase the cost. Another advantage is that adequate clamping force is developed against the wear ring when a second leg does not bear against drum end wall portions 14. Figure 6 shows an alternative embodiment of a knob- shaped locking member 6. In this case, the knob-shaped locking member has a tapered surface 6a on the inside of the knob, against which the locking arm engages. The taper can therefore be formed on the inside of the knob — o — or on the arm 9 or on both. In a preferred embodiment, the sealing arrangement 4 is arranged in a special dewatering press, what is known as a wash press, for a paper pulp suspension. The wash press comprises two counter-rotating press drums arranged partly submerged in a trough. The rotation of the drums forces the pulp web formed up between the two drums, pressing it simultaneously in the nip between them. The fact that it is a wash press means that treatment liquid is also supplied to the press, preferably the trough, in order to reduce the concentration of any undesirable loose and/or finely divided material there may be in the pulp suspension supplied. A seal 15 arranged on the end walls of the trough interacts with the wearing surface 7 on the wear ring 5. The seal 15 is not the subject of this invention but is described in greater detail in Swedish Patent Application SE-A 9902308-7 entitled "Sealing arrangement for pulp dewatering arrangement" filed at around the same time as this application. As a result of the special design of the replaceable wearing surface for the sealing arrangement according to the invention, the wear ring 5 can be made radially wider, and the area of the wearing surface 7 is thus also increased in comparison with the embodiment according to the known art. The larger wearing surface 7 of the wear ring 5 means that the seal 15 can be arranged so as to act along different radii on the wear ring, for example the position 15' . Alternatively, the seal 15 can lie eccentrically in relation to the drum end wall so as to prevent the seal 15 lying and wearing in the same groove on the wearing surface 7 throughout the entire revolution. The invention can be varied in a number of ways within the scope of the patent claims. For example, the knob- shaped members of the wear ring can be replaced by radially directed grooves in the wear ring itself, which are open radially inwards and in which the arms of an L-shaped holder 9 or flat-bar-shaped holder 9b engage . The knob 6 can also be replaced by a U-shaped part, into which the wedge is driven. With an L-shaped holder, the second leg of the holder can also be angled inwards towards the drum, seen from the drum end wall. The essential feature of the invention is that the leg 9, 9b of the holder 8, 8b can be slipped in towards the wear ring from a radially retracted position and then out towards a radially external position in which it locks the wear ring in the axial direction of the drum. The taper of the leg 9, 9b of the holder can also be replaced by a corresponding taper on interacting surfaces on the knob 6 or by interacting surfaces in corresponding radially directed grooves in the wear ring itself. The leg 9, 9b of the holder can also be given the shape of a curved convex spring which, under spring action from the leg 9, 9b itself, presses the wear ring into position by spring force. The taper of the leg 9 in the L-shaped variant can also be sufficiently marked that the wear ring 5 is pressed into a fixed position before the second leg 11 of the holder comes into contact with the drum end wall 14. In the flat-bar-shaped variant 8b, the correct clamping force is ensured by a certain minimum, but limited, projection on that end of the holder facing away from the groove remaining after pressing in. The knob-shaped members 6 can also be fastened to the wear ring by key-shaped locking recesses arranged in the wear ring, which interact in a conventional manner with congruent key-shaped projections on one end of the members 6, so that this end can be introduced into the keyhole in the wear ring and rotated through 90° into a positive-locking position. The other end of the members can then also have a rectangular or oval shape so that the slot 10 interacts with the member so that rotation in the keyhole in the wear ring is prevented.

Claims: PATENT CLAIMS 1. Replaceable wearing surface for a sealing arrangement on drum end walls on press drums m presses which dewater fibre suspensions radially into the drum through the shell of the drum, c h a r a c t e r i z e d i n that the sealing arrangement (4) comprises a wear ring (5) and holder members (8), the wear ring (5) being provided, on the side which faces into the drum from the drum end wall after mounting, with locking members (6) which act m the axial direction of the drum, the holder member (8) being provided with at least one radially directed arm (9) which is designed so as, when mounted by being pressed out m the radial direction of the drum, to interact with the locking member (6) to secure the wear ring m the axial direction against the drum end wall (13, 14), and the holder members (8) comprising at least one interacting fixing connection (12, 20 or 21) for fastening the holder member to the drum end wall (14) . 2. Replaceable wearing surface for a sealing arrangement according to Claim 1, c a r a c te r i z e d i n that the arm (9) is arranged so as to interact with the locking member (6) via a wedge-shaped surface (6a) which lies m a plane parallel to the end wall of the drum. 3. Replaceable wearing surface for a sealing arrangement according to Claim 2, c h a r a c t e r i z e d i n that the wedge-shaped surface (6a) is arranged on the locking member (6) . 4. Replaceable wearing surface for a sealing arrangement according to Claim 2, c h a r a c t e r i z e d i n that the wedge-shaped surface (6a) is arranged on the arm (9), with its minimum thickness at the outer end of the arm, seen in the radial direction of the drum. 5. Replaceable wearing surface for a sealing arrangement according to Claim 3 or 4, c h a r a c t e r i z e d i n that the arm of the holder member (8) is provided with a radially directed slot (10) which is open at the outer end of the arm (9), seen in the radial direction of the drum. 6. Replaceable wearing surface for a sealing arrangement according to Claim 5, c h a r a c t e r i z e d i n that the wear ring (5) is provided, on the side which faces inwards from the drum end wall after mounting, with knob-shaped members (6) which are arranged parallel to the drum axis and with which the slotted (10) arm (9) engages under the knob ( 6) . 7. Replaceable wearing surface for a sealing arrangement according to Claim 6, c h a r a c t e r i z e d i n that the knob-shaped members (6) are arranged in a number of positions (6pl- 6p6) in the circumferential direction over the circumference of the wear ring, the total number of knob-shaped members ranging from four to fifty, preferably fifteen to thirty. 8. Replaceable wearing surface for a sealing arrangement according to any one of the preceding claims, c h a r a c t e r i z e d i n that the holder member (8) is plate-shaped in the plane of the arm, and the arm is fastened to the drum end wall (14) by means of a weld (21) . 9. Replaceable wearing surface for a sealing arrangement according to any one of the preceding claims, c h a r a c t e r i z e d i n that the holder member (8) is L-shaped, with the arm constituting a first leg (9) extending in the radial direction of the drum, and a second leg (11) arranged parallel to the axis of the drum. 10. Replaceable wearing surface for a sealing arrangement according to Claim 9, c h a r a c t e r i z e d i n that the second leg (11) of the L-shaped holder members (8) is designed so as to be fastened to the drum end wall (14) by a fixing connection (12), preferably a screw connection, which connection comprises fixing elements which are mounted outwardly in the radial direction of the drum when the second leg (11) of the holder member is fastened to the drum end wall (14) . 11. Replaceable wearing surface for a sealing arrangement according to any one of the preceding claims, c h a r a c t e r i z e d i n that the wear ring (5) is divided diametrically into at least two circular- segment-like parts (5a, 5b) . 12. Replaceable wearing surface for a sealing arrangement according to any one of the preceding claims, c h a r a c t e r i z e d i n that the entire surface (7) of the wear ring (5) on the side which faces outwards from the drum end wall after mounting is plane, arranged parallel to the drum end wall and exposed for bearing against a sealing element (15, 15' ) .

Inventors: HANSSON STEFAN, HANSSON, STEFAN
Applicants: HANSSON STEFAN, KVAERNER PULPING TECH, HANSSON, STEFAN, KVAERNER PULPING AB
Application year: 2000
Main classification: D21C9
IPC codes: B01D33, D21C9, D21F3