WO2009056682A1 - Tamis, cylindre tamiseur, tamis plat et procédés de fabrication de cylindre tamiseur - Google Patents

Tamis, cylindre tamiseur, tamis plat et procédés de fabrication de cylindre tamiseur Download PDF

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Publication number
WO2009056682A1
WO2009056682A1 PCT/FI2008/050613 FI2008050613W WO2009056682A1 WO 2009056682 A1 WO2009056682 A1 WO 2009056682A1 FI 2008050613 W FI2008050613 W FI 2008050613W WO 2009056682 A1 WO2009056682 A1 WO 2009056682A1
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WO
WIPO (PCT)
Prior art keywords
screen
apertures
screen cylinder
cylinder
wires
Prior art date
Application number
PCT/FI2008/050613
Other languages
English (en)
Inventor
Jukka Virtanen
Original Assignee
Metso Paper Inc.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Metso Paper Inc. filed Critical Metso Paper Inc.
Publication of WO2009056682A1 publication Critical patent/WO2009056682A1/fr

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Classifications

    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21D—TREATMENT OF THE MATERIALS BEFORE PASSING TO THE PAPER-MAKING MACHINE
    • D21D5/00—Purification of the pulp suspension by mechanical means; Apparatus therefor
    • D21D5/02—Straining or screening the pulp
    • D21D5/16—Cylinders and plates for screens

Definitions

  • the invention relates to a screen cylinder for purifying or classifying pulp mixture, in which screen cylinder there are screen wires forming a cylindrical screening surface of the screen cylinder.
  • the invention further relates to a method for manufacturing a screen cylinder intended for purifying or classifying pulp mixture, the method comprising mounting screen wires, forming the screening surface of the screen cylinder, side by side on support bars, bending the support bars into rings and connecting the ends of the support bars bent into rings such that the screen wires form a screening surface in the axial direction of the screen cylinder.
  • the invention further relates to a second method for manufacturing a screen cylinder intended for purifying or classifying pulp mixture, the method comprising mounting screen wires, forming the screening surface of the screen cylinder, side by side on support bars, bending the support bars into rings and connecting the ends of the support bars bent into rings such that the screen wires form a screening surface in the axial direction of the screen cylinder.
  • the invention further relates to a flat screen for purifying or classifying pulp mixture, the flat screen comprising wires forming a planar screening surface of the screen.
  • the invention further relates to a screen for purifying or classifying pulp mixture, the screen comprising screen wires forming the screening surface.
  • Screen cylinders are used, among other things, for purifying and classifying pulp mixtures.
  • Screen cylinders formed of screen wires are typically manufactured by attaching parallel screen wires, forming the screening surface of the screen cylinder, side by side close to one another to form a cylindrical shape such that a slot of desired magnitude, i.e. a screen slot, will be provided therebetween. This may be performed, for instance, by attaching the screen wires first either by laser welding or hard soldering directly to the surface of the support bars or to grooves provided in the support bars for the screen wires. Subsequently the produced planar screen panel is bent into a cylindrical shape by rolling the support bars into rings. The ends of the support bars that have been bent into rings are connected to one another by welding, for instance. Around the support bars it is further possible to mount particular supporting rims to reinforce the structure of the screen cylinder.
  • the screen wires of the screen cylinder form the screening surface of the screen cylinder comprising structures through which the fluid in the pulp mixture and the portion of fibres defined by the size of said structures may flow from the screen cylinder feed side to the screen cylinder accept side and further onwards in the pulp making process.
  • the pulp mixture is fed into the screen cylinder through one end thereof and the portion of pulp mixture that has not flown from the screen cylinder feed side to the screen cylinder accept side will be discharged from the opposite end of the screen cylinder for further processing.
  • the object of the present invention is to provide a novel screen cylinder and a novel method for manufacturing a screen cylinder.
  • the screen cylinder of the invention is characterized in that at least one screen wire comprises apertures formed through at least one side of the screen wire, through which apertures the fluid in the pulp mixture and the portion of fibres defined by the aperture size may flow from the feed side of the screen cylinder to the accept side of the screen cylinder.
  • the method of the invention for manufacturing the screen cylinder is characterized in that in a screen cylinder manufacturing step there are formed apertures through at least one side of at least one screen wire, through which apertures the fluid in the pulp mixture and the portion of fibres defined by the aperture size may flow from the screen cylinder feed side to the screen cylinder accept side.
  • the second method of the invention for manufacturing a screen cylinder is characterized by mounting screen wires, which form the screening surface of the screen cylinder, side by side close to one another in support bars of the screen cylinder, in which screen wires there are provided in advance in a screen wire manufacturing step apertures through at least one side of the screen wire, through which apertures the fluid in the pulp mixture and part of the fibres defined by the aperture size may flow from the screen cylinder feed side to the screen cylinder accept side.
  • the flat screen of the invention is characterized in that at least one screen wire comprises apertures formed through at least one side of the screen wire, through which apertures the fluid in the pulp mixture and the portion of the fibres defined by the aperture size may flow from the screen cylinder feed side to the screen cylinder accept side.
  • the screen of the invention is characterized in that at least one screen wire of the screening surface comprises apertures formed through at least one side of the screen wire, through which apertures the fluid in the pulp mixture and the portion of the fibres defined by the aperture size may flow from the screen cylinder feed side to the screen cylinder accept side.
  • the screen cylinder for purifying or classifying a pulp mixture comprises screen wires forming a cylindrical screening surface of the screen cylinder. Further, at least one screen wire of the screen cylinder comprises apertures formed through at least one side of the screen wire, through which apertures the fluid in the pulp mixture and the portion of the fibres defined by the aperture size may flow from the screen cylinder feed side to the screen cylinder accept side.
  • the presented screen cylinder combines the structure that resembles the structure of a conventional perforated screen cylinder and a modern manufacturing technique of a wire screen cylinder.
  • the presented screen cylinder typically provides a structure that resembles the structure of a perforated screen cylinder having a good fractioning capability with an efficient manufacturing technique characteristic of a wire screen cylinder, when screen wires are placed side by side one close to the other such that there will be no particular screen slot between the screen wires, but all the flow from the screen cylinder feed side to the screen cylinder accept side passes through said apertures provided in the screen wire sides.
  • At least one screen wire comprises apertures provided through the side directed against the feed flow direction of the pulp mixture, through which apertures the fluid in the pulp mixture and the portion of fibres defined by the aperture size may flow from the screen cylinder feed side to the screen cylinder accept side. Said disposition of the apertures gives the screen cylinder a good fractionating accuracy, in particular, if the surface of the screen wire that is directed to the screen cylinder feed side is inclined and ascending towards the feeding direction of the pulp mixture, whereby said inclined surface guides large particles away from vicinity of the apertures.
  • the screen wires are arranged adjacently at a distance from one another such that between the adjacent screen wires there will be provided a slot such that the fluid in the pulp mixture and the portion of the fibres defined by the apertures and the slot size may flow from the screen cylinder feed side to the screen cylinder accept side both via the slots between the screen wires and via said apertures.
  • Figure 1 shows a schematic cross-sectional view of a general basic structure of a screen cylinder, seen from the end of the screen cylinder,
  • Figure 2 shows schematically a screen cylinder, seen from the end of the screen wires and crosscut
  • Figure 3 shows schematically the screen cylinder of Figure 2, seen in the direction of a screening surface
  • Figure 4 shows schematically a second screen cylinder, seen from the end of the screen wires and crosscut
  • Figure 5 shows schematically the screen cylinder of Figure 4, seen in the direction of the screening surface
  • Figure 6 shows schematically a third screen cylinder, seen from the end of the screen wires and crosscut
  • Figure 7 shows schematically the screen cylinder of Figure 6, seen in the direction of the screening surface
  • Figure 8 shows schematically a fourth screen cylinder, seen from the end of the screen wires and crosscut
  • Figure 9 shows schematically the screen cylinder of Figure 8, seen in the direction of the screening surface
  • Figure 10 shows schematically a fifth screen cylinder, seen from the end of the screen wires and crosscut
  • Figure 11 shows schematically the screen cylinder of Figure 10, seen in the direction of the screening surface
  • Figure 12 shows schematically a flat screen seen from the end of the screen wires and crosscut
  • Figure 13 shows schematically the flat screen of Figure 12, seen in the direction of the screening surface
  • Figure 14 shows schematically a sixth screen cylinder, seen from the end of the screen wires and crosscut,
  • Figure 15 shows schematically a seventh screen cylinder, seen from the end of the screen wires and crosscut
  • Figure 16 shows schematically an eighth screen cylinder, seen from the end of the screen wires and crosscut, and
  • Figure 17 shows schematically the screen cylinder of Figure 16, seen in the direction of the screening surface.
  • Figure 1 shows schematically a general basic structure of a screen cylinder in the axial direction of the screen cylinder, i.e. seen from the end of the screen cylinder and crosscut. Throughout the inner circumference of the screen cylinder 1 there are arranged screen wires 3 side by side that constitute the screening surface 2 of the screen cylinder 1.
  • the screen wires 3 are typically mounted on support bars 4 prior to bending the support bars 4 into rings such that a screen cylinder 1 of a suitable size in diameter is produced.
  • the ends 4' and 4" of the support bars 4 are attached to one another by welding at an attachment point 4a such that the support bars 4 form a ring- shaped structure.
  • Support bars 4 are located in the axial direction of the screen cylinder 1 , i.e. in the longitudinal direction of the screen cylinder, at suitable intervals such that the screen wires 3 will keep sufficiently rigidly and firmly in place.
  • the screen wires 3 may be secured to the surface of the support bars 4, for instance, either by hard soldering or laser welding. It is also possible that on the inner surface of the support bars 4, i.e.
  • FIG. 1 shows schematically support rims 5 arranged around the support bars 4, which support rims are intended to further reinforce the structure of the screen cylinder 1.
  • the support rims 5 may be arranged either around all the support bars 4 of the screen cylinder 1 or only around some of the support bars 4.
  • the interior of the screen cylinder 1 constitutes the feed side 6 of the screen cylinder 1 , where the pulp mixture to be purified or classified is fed and the exterior of the screen cylinder 1 constitutes an accept side 7 of the screen cylinder 1 , where the fibres of desired magnitude are able to flow or move along with the fluid through the screening surface 2.
  • the interior of the screen cylinder 1 constitutes the accept side of the screen cylinder 1 and the exterior of the screen cylinder 1 constitutes the feed side 6 of the screen cylinder.
  • the pulp mixture to be purified or classified is fed into the screen cylinder 1 through one end, i.e.
  • Figure 2 shows schematically a screen cylinder 1 seen from the end of a screen wire 3 and crosscut along the line A - A of Figure 3, and Figure 3 shows schematically the screen cylinder 1 of Figure 2 seen in the direction of the screening surface 2.
  • Figures 2 and 3 show two screen wires 3 of the screen cylinder 1.
  • Figure 2 does not show a support bar 4.
  • the feed flow direction of the pulp mixture in the screen cylinder 1 is indicated by arrow F.
  • the screen wire 3 comprises a feed side surface 3a directed to the feed side 6 of the screen cylinder 1 , an accept side surface 3b directed to the accept side 7 of the screen cylinder 1 , a first side 3c of the screen wire 1 directed against the feed flow direction F of the pulp mixture and a second side 3d of the screen wire 1 in the same direction with the feed flow direction F of the pulp mixture.
  • the feed side surface 3a of the screen wire 3 directed to the feed side of the screen cylinder 1 is formed to be inclined such that the feed side surface 3a of the screen wire 1 is an ascending surface in the feed flow direction F of the pulp mixture. Thanks to the screen wire's 3 feed side surface 3a ascending in the feed flow direction F of the pulp mixture the screening surface 2 of the screen cylinder 1 forms a gradual screening surface 2 whose advantages will be discussed later.
  • the first side 3c and the second side 3d of the screen wire 3 are formed such that when proceeding along the first side 3c and the second side 3d of the screen wire from the feed side of the screen cylinder 1 towards the accept side of the screen cylinder 1 , the sides 3c and 3d are arranged, for at least part in the elevational direction of the screen wire 3, to orient towards the centre line of the screen wire 3.
  • the screen wire 3 is formed such that the upper part of the screen wire 3 is broader than its lower part.
  • the accept side surface 3b of the screen wires 3 is, in turn, formed to be an arc of a semi-circle, which contributes to the flow of pulp mixture from the accept channel 8 to the accept side 7 of the screen cylinder.
  • the accept side surface 3b of the screen wire 3 may also be straight, acute-angled or of some other shape, of course.
  • the screen wires 3 shown in Figures 2 to 9 are so-called profiled screen wires 3 in shape, and they are thus arranged one beside the other such that the upper part of the first side 3c of the screen wire 3 coming behind in the feed flow direction F of the pulp mixture is arranged to come close to the upper part of the second side 3d of the screen wire 3 ahead in the feed flow direction F of the pulp mixture.
  • Said apertures 9 are provided in the first side 3c of the screen wire 3, in other words, such that the apertures 9 are open in the direction against the feed flow direction F of the pulp mixture, i.e. at the apertures 9 the screen wire 3 comprises no screen wire manufacturing material between the aperture 9 and the second side 3d of the adjacent screen wire in the feed flow direction F of the pulp mixture.
  • the fluid in the pulp mixture to be purified or classified and the fibres belonging to the class defined by the size of apertures 9, i.e. the portion of fibres 9 defined by the apertures 9 may flow through the apertures 9 from the feed side 6 of the screen cylinder 1 to the accept side 7 at the same time as slivers, excessively large fibres, fibre bunches and other matter to be separated remain in the feed side of the screen cylinder 1 to be removed from the screen cylinder 1 for further processing.
  • the apertures 9 in the first sides 3c of the screen wires are semi-circular in cross section and form semi-circular screen apertures in the screening surface 2 of the screen cylinder 1 , when the screen wires 3 are placed in the manner shown in Figures 2 to 9 side by side close to one another on the side directed to the feed side 6 of the feed cylinder 1 such that there will remain no screen slot characteristic of a conventional wire cylinder between the screen wires 3.
  • Figure 4 shows schematically a second screen cylinder 1 , seen from the end of the screen cylinder 1 and crosscut along the crosscut line B - B appearing in Figure 5, and Figure 5 shows schematically the screen cylinder 1 of Figure 4 seen in the direction of the screening surface 2.
  • Figure 4 does not show a support bar 4.
  • the screen cylinder 1 of Figures 4 and 5 corresponds to the screen cylinder 1 of Figures 2 and 3 in all other respects but in the screen cylinder 1 of Figures 4 and 5 the apertures 9, i.e. the screen apertures of the screening surface 2 in the screen cylinder 1 , have semi-oval cross sections.
  • the presented screen cylinder combines the structure resembling the structure of a conventional perforated cylinder and the modern manufacturing technique of a wire cylinder.
  • the presented screen cylinder thus provides a structure that resembles the structure of a perforated cylinder typically having a good fractioning capability with an efficient manufacturing technique characteristic of wire cylinders. It is considered that the best characteristic of the perforated screen cylinders is typically a good fractioning capability and an important characteristic is a large, open area, which is now possible to implement by an efficient manufacturing technique characteristic of wire screen cylinders.
  • the screen wires 3 it is thus possible to machine or otherwise produce apertures of desired size and shape, through which part of the water and fibres in the pulp mixture to be fed into the screen cylinder 1 is able to flow from the feed side 6 of the screen cylinder 1 to the accept side 7 of the screen cylinder 1.
  • Said apertures 9 may be machined in the screen wires 3, for instance, by milling prior to mounting the screen wires 3 in connection with the support bars 4 or after the screen wires 3 have been mounted in connection with the support bars 4 but prior to bending the support bars 4 into rings.
  • the apertures 9 in the first side of the screen wire 3 may be produced also in connection with mangling, in general cold rolling, of the screen wire 3, in advance while manufacturing the screen wire 3 before the screen wires 3 for the screen cylinder 1 are cut to size corresponding the length of the screen cylinder 1 to be manufactured.
  • the presented solution has also an advantage that the solution allows screen cylinders with smaller perforations to be manufactured more economically than before, because previously perforations had to be produced in a completely solid screen cylinder made of a plate by cumbersome and time-consuming manufacturing techniques, such as drilling, electron jets or laser beams.
  • the aperture 9 may be semi-circular or semi-oval in cross section.
  • the cross sectional shape of the aperture 9 is not limited to these shapes, but the shape and size of the cross section of the aperture 9 may vary.
  • the apertures 9 are very close to one another in the longitudinal direction L of the screen wire 3, but the spacing therebetween in the longitudinal direction L of the screen wire 3 may be even larger, as schematically shown in Figure 7.
  • the spacing between the apertures 9 in the longitudinal direction of the screen wire 3 may also be different in the feed end of the screen cylinder from that in the discharge end.
  • the cross sections of the apertures 9 may also be different in size in the feed end and in the discharge end of the screen cylinder 1 and the cross sectional area of the apertures 9 may also become larger when proceeding along the aperture 9 from the feed side 6 to the accept side 7 of the screen cylinder 1.
  • the size of the apertures 9 may be reduced and the spacing therebetween in the longitudinal direction L of the screen wire 3 may be reduced towards the discharge end of the screen cylinder 1 , where the pulp is more tainted and contains a proportionally larger amount of large particles and slivers, which will thus remain on the screening surface 2, i.e. on the classifying surface, and will not be allowed to the accept side 7 of the screen cylinder 1 , which improves pulp fractioning.
  • Figure 6 shows schematically a third screen cylinder 1 , seen from the end of the screen cylinder 1 and crosscut along the line C - C in Figure 7, and Figure 7 shows schematically the screen cylinder 1 of Figure 6, seen in the direction of the screening surface 2.
  • the screen cylinder 1 of Figures 6 and 7 in the second side 3d of the screen wires 3, i.e. in the side that is in the same direction with the feed flow direction F of the pulp mixture, there are provided apertures 9, or channels 9 side by side close to one another in the longitudinal direction indicated by L of the screen wires 3, which apertures extend from the feed side 6 of the screen cylinder 1 to the accept channel 8.
  • Said apertures 9 are provided in the second side 3d of the screen wire 3 such that the apertures 9 are open in the same direction with the feed flow direction F of the pulp mixture.
  • the apertures in the second sides 3d of the screen wires 3 are semi-oval apertures in cross section that form semi-oval screen apertures on the screening surface 2 of the screen cylinder 1 , when the screen wires 3 are placed side by side close to one another on the side directed to the feed side 6 of the screen cylinder 1 , as shown in Figures 2 to 9, such that between the screen wires 3 there will be no screen slot typical of conventional wire cylinders.
  • the apertures 9 are provided in the screen wire's 3 first side 3c, which is directed against the feed flow direction F of the pulp mixture.
  • the screen wire 3 being a profiled screen wire 3, in which the feed side surface 3a of the screen wire 3 is ascending in the feed flow direction F of the pulp mixture, the step or ridge between the feed side surfaces 3a of two successive screen wires throws large particles con- tained in the pulp mixture away from the vicinity of the apertures 9, whereby the separation efficiency of the screen cylinder 1 improves. If the apertures 9 are placed as shown in Figures 6 and 7 at the highest point on the feed side surface 3a of the screen wire 3, the quality of pulp may slightly deteriorate as compared with the embodiment of Figures 2 to 5.
  • Figure 8 shows schematically a fourth screen cylinder 1 , seen from the end of the screen cylinder 1 and crosscut along the line D - D of Figure 9, and Figure 9 shows schematically the screen cylinder 1 of Figure 8 seen in the direction of the screening surface 2.
  • the screen cylinder 1 of Figures 8 and 9 in both the first side 3c and the second side 3d of the screen wire 3 there are provided apertures 9 or channels 9 in the longitudinal direction of the screen wires 3 indicated by arrow L, which apertures extend from the feed side 6 of the screen cylinder 1 to the accept channel 8.
  • the apertures 9 in different sides 3c, 3d of the screen wire 3 may be of the same or different size, as shown in Figures 8 and 9.
  • apertures 9 are provided on both sides 3c and 3d of the screen wire 3
  • the apertures 9 on sides 3c and 3d are advantageously provided in offset locations in the longitudinal direction L of the screen wires 3 in order that the screen wire 3 would not break in use or in order that larger apertures 9 could be made.
  • Figure 10 shows schematically a fifth screen cylinder 1 , seen from the end of the screen cylinder 1 and crosscut along the line E - E of Figure 11
  • Figure 11 shows schematically the screen cylinder 1 of Figure 10, seen in the direction of the screening surface 2.
  • the structure of the screen cylinder 1 of Figures 10 and 11 resembles the screen cylinder 1 of Figures 2 and 3, in which the first side of the screen wires 3 comprises apertures 9, but in addition to apertures 9, there is provided a slot 10, i.e. a screen slot 10, typical of conventional wire cylinders.
  • the fluid in the pulp mixture fed into the screen cylinder 1 and the portion of fibres defined by the size of the apertures 9 and the slots 10 may flow through the apertures 9 and the slots 10 from the feed side 6 to the accept side 7 of the screen cylinder 1.
  • the screen cylinder 11 of Figures 10 and 11 thus comprises both apertures 9 in the first side 3c of the screen wires 3 and slots 10 between the screen wires.
  • the best characteristic of the slot screen cylinders is good sliver reduction, which has been more difficult to achieve with conventional perforated screen cylinders.
  • By providing a screen cylinder having both apertures 9 and slots 10 in the manner shown in Figures 10 and 11 it is possible to combine good characteristics of both perforated and slot screen cylinders, and hence to provide a higher yield without the quality being any lower.
  • a screen cylinder may also be made of screen wires that are not profiled as the screen wires shown in Figures 2 to 11 , whereby a flat screening surface will be achieved.
  • the screen wires may be rectangular, quadrangular or triangular in cross section, for instance.
  • the apertures may be provided in one or both sides of the screen wire, for instance, alternately, whereby it is possible to form larger apertures of any shape, and thus a screen cylinder having apertures and flat screening surface will be provided.
  • a screen cylinder having circular apertures will be provided.
  • the screen wires 3 of the screen cylinder 1 run in the axial direction of the screen cylinder 1 , but the screen cylinder may also be manufactured such that the screen wires 3 run in the circumferential direction of the screen cylinder 1 and the support bars 3 run in the axial direction of the screen cylinder.
  • the screen cylinder 1 should be understood in a broad sense such that the cylindrical screening surface 2 of the screen cylinder 1 may be a cylinder or a truncated cone in shape, i.e. the term screen cylinder refers to both screen structures having a cylindrical shape and screen structures of having a truncated cone shape.
  • Figure 12 shows schematically a flat screen 11 , i.e. a planar screen plate, seen from the end of the screen wires 3 and crosscut along the line G - G appearing in Figure 13, and Figure 13 shows schematically the flat screen 11 of Figure 12, seen in the direction of the screening surface 2.
  • the flat screen 11 of Figures 12 and 13 comprises rectangular screen wires 3 having no particular profiling on the surface directed to the feed side of the flat screen 1 , which wires constitute a planar screening surface 2 such that the screen wires 3 form a planar screen structure and, for at least a portion of the screen wire surface 3a, the surfaces of the screen wires 3 belong to said pla- nar screening surface 2.
  • the screen wires 3 On both sides 3c, 3d of the screen wires 3 there are provided semi-circular apertures 9 such that in combination the apertures 9 of the screen wires 3 placed one against the other form circular screen apertures, through which the fluid in the pulp mixture to be purified or classified and the portion of fibres defined by the size of the apertures 9 may flow from the feed side 6 of the screen cylinder 1 to the accept side 7 of the screen cylinder 1.
  • the feed flow direction of the pulp mixture is towards the screening surface 2, as indicated by arrow F.
  • the feed flow direction of the pulp mixture may also be in the direction of the planar structure of the flat screen, however.
  • the flat screen 11 may be manufactured in a manner resembling that of a screen cylinder by mounting screen wires 3 to attachment grooves provided in a support bar 4 and by attaching the screen wires to said grooves by welding or soldering.
  • the screen wires 3 may be attached to the grooves provided in the support bars 4 also by utilizing shape-locking, for instance, such that the support bars are produced in the shape of an arc of a circle and the grooves are provided in the outer circumference of the arc- shaped support bar, whereby, when the support bars are straightened, the screen wires mounted in the grooves will lock in the grooves of said support bars.
  • Figure 12 shows schematically a support bar 4 drawn in a broken line.
  • the support bars 4 may also be without the mounting grooves for the screen wires 3, whereby the screen wires 3 may be attached directly onto the support bars 4 by welding, for instance.
  • the flat screen may be applied, for instance, when manufactured in a circular shape in the flow direction of the pulp mixture placed in the upstream of the screen cylinder acting as a pre-purifying screen.
  • the flat screen may also be used in a separate screening device.
  • the shape of the apertures 9 in the screening surface of the flat screen 11 may also vary.
  • apertures 9 may be on one side of the screen wires alone.
  • the cross sectional shape of the screen wires 3 may be, apart from a rectangle, a square, a triangle or a circle, for instance, or they may have a profiled shape.
  • Screen cylinders 1 and flat screens 11 may be advantageously employed, apart from various screens, as pulper screen plates.
  • the diameter of the apertures may be 8 to 10 mm, for instance, and in screen plate applications in pulpers used in primary screening step the aperture size may be about 3 to 5 mm, for instance.
  • the thickness of the screen wires must be correspondingly increased such that in some applications the presented solutions does not necessarily give so great an economic advantage on the manufacturing costs over those achievable by the conventional screen applications separate from the pulpers.
  • the aperture size of the screening surface of the screens may be 0.5 to 3 mm, for instance, advantageously 1 to 2 mm.
  • the aperture size may be as small as 0.15 to 0.2 mm.
  • one or more, or possibly all the screen wires are provided with apertures either in one or both sides of the screen wire, through which apertures the fluid in the pulp mixture to be fed into the screen cylinder or the flat screen and the portion of fibres defined by the aperture size may flow from the feed side of the screen to the accept side of the screen cylinder.
  • Figure 14 further shows schematically a sixth screen cylinder 1 , seen from the end of the screen wires 3 and crosscut.
  • Figure 14 shows, by way of example, three of the screen wires 3 in the screen cylinder 1.
  • Figure 14 does not show a support bar 4.
  • An exemplary feed flow direction of the pulp mixture in the screen cylinder 1 is indicated by arrow F.
  • the screen wire 3 comprises a feed side surface 3a directed to the feed side 6 of the screen cylinder 1 , an accept side surface 3b directed to the accept side 7 of the screen cylinder 1 , a first side 3c of the screen wire 3 directed against the feed flow direction F of the pulp mixture and a second side 3d of the screen wire 3 directed in the same direction with the feed flow direction F of the pulp mixture.
  • the feed side surface 3a of the screen wire 3 directed to the feed side of the screen cylinder 1 is provided straight, whereby said screen wire 3 is neutral with respect to the feed flow direction of the pulp mixture, but the feed side surface 3a of the screen wire 3 of Figure 14 could also be given an ascending shape in the feed flow direction F in the same manner as is shown in Figure 2, for instance.
  • the first side 3c of the screen wire in accordance with Figure 14 comprises a first side flange 12 or a first side branch 12, and the second side 3d comprises a second side flange 12' or a second side branch 12'.
  • the side flanges 12 and 12' are thus placed at a distance from the feed side surface 3a and the accept side surface 3b of the screen wire 3 such that the screen wire 3 of Figure 14 forms a profiled screen wire 3 having a cross-like cross section.
  • the apertures 9 or the channels 9 are arranged in the side flanges 12 and 12' in the sides 3c and 3d of the screen wires 3 such that they extend from the feed side 6 of the screen cylinder 1 to the accept channel 8.
  • said apertures 9 may be provided in the side flanges 12 and 12' side by side in the above-described manner.
  • Apertures 9 are provided in the first side flange 12 such that the apertures 9 are open in the direction against the feed flow direction F of the pulp mixture, i.e. at the apertures 9 the screen wire 3 does not comprise screen wire manufacturing material between the aperture 9 and the second side flange 12' in the adjacent screen wire 3.
  • Apertures 9 are also provided in the second side flange 12' such that the apertures 9 are open in the feed flow direction F of the pulp mixture, i.e. at the apertures 9 the screen wire 3 does not comprise screen wire manufacturing material between the aperture 9 and the first side flange 12 in the adjacent screen wire 3.
  • the screen wires 3 are placed side by side to one another such that the side flanges of the screen wires will be in contact with one another on the finished screening surface such that a screening surface having apertures is formed.
  • Figure 15 shows schematically a seventh screen cylinder, seen from the end of the screen wires and crosscut.
  • the structure of the screen cylinder 1 in Figure 15 corresponds to that of the screen cylinder shown in Figure 14.
  • the structure of the screen cylinder in Figure 15 differs from the screen cylinder in Figure 14 in that the side flanges of the screen wires 3 are placed at a distance from one another such that, in addition to the apertures 9 provided in the sides 3c, 3d of the screen wire profile 3, the finished screening surface comprises slots 10 between the screen wires 10.
  • the apertures 9 may be, for instance, circular, as in Figure 13, or semi-circular, as in Figure 9, in shape. Also other cross-sectional shapes are applicable, for instance, oval or elliptical shape or halves of these shapes. It is possible that the apertures 9 in the screen wire 3 are located, as in Figures 14 and 15, in both side flanges 12, 12' of the screen wires 3 or only either in the first side flange 12 or in the second side flange 12'. The extent or depth of the apertures 9 in the longitudinal direction of the side flanges, i.e.
  • substantially in the feed flow direction F of the pulp mixture may be arranged such that the depth of the apertures 9 correspond to the length of the side flanges or such that they extend only to a portion of the length of the side flanges 12, 12' in accordance with Figures 14 and 15.
  • the portion of the screen wire locating above the side flanges 12 and 12' as seen in Figures 14 and 15 or the top flange of the screen wire having a cross-like cross sectional profile may be relatively high as in Figures 14 and 15 in relation to the total height of the screen wire 3, but the top flange may also be very low.
  • the apertures 9 may extend in the longitudinal direction of the side flange also to the area of the vertical portion of the screen wire.
  • the screen wire 3 having a cross-like cross sectional shape as shown in Figures 14 and 15 cleans the screen effectively.
  • the top flange of the screen wire 3 brushes the surface of a rotor or foil preventing spinning formations.
  • the screen wire having a cross-like cross section generates, on the other hand, a strong turbulence in the feed flow of the screen or classifier and thus prevents accumulations on the surfaces of the screen wire 3 and thus prevents the screen cylinder or screen basket from being clogged.
  • the screen wire having a cross-like cross section enables a screen wire having large and high dimensions that resists well mechanical stresses. The mechanical resistance of the screen wire is further improved by the symmetrical structure of the screen wire.
  • the structure of the screen cylinder encompasses, however, relatively large open screening area.
  • the large, open screening area of the screening surface translates to large yield as the screen cylinder is used.
  • Figure 16 shows schematically an eighth screen cylinder 1 , seen from the end of the screen wires 3 and crosscut along the line H - H appearing in Figure 17, and Figure 17 shows schematically the screen cylinder 1 of Figure 16, seen in the direction of the screening surface.
  • Figures 16 and 17 show, by way of example, three of the screen wires 3 of the screen cylinder 1.
  • Figures 16 and 17 do not show the support bar 4.
  • the exemplary feed flow direction of the pulp mixture in the screen cylinder 1 is indicated by arrow F.
  • the screen wire 3 comprises a feed side surface 3a directed to the feed side 6 of the screen cylinder 1 , an accept side surface 3b directed to the accept side 7 of the screen cylinder 1 , a first side 3c of the screen wire 3 directed against the feed flow direction F of the pulp mixture and a second side 3d of the screen wire 3 directed in the same direction with the feed flow direction F of the pulp mixture.
  • the feed side surface 3a directed to the feed side of the screen cylinder 1 is formed wavy, but the feed side surface 3a of the feed side of the screen wire 3 could also be formed flat.
  • the first side 3c of the screen wire of Figure 16 comprises a first side flange 12 or a first side branch 12 and the second side 3d comprises a second side flange 12' or a second side branch 12' such that the portion of side flanges 12 and 12' that is directed substantially to the feed side of the screen cylinder 1 constitutes part of the feed side surface 3a of the screen wire 3.
  • the screen wire 3 of Figure 14 forms thus a profiled screen wire 3 having a substantially T-shaped cross section.
  • the apertures 9 or channels 9 are arranged in the side flanges 12 and 12' of the sides 3c and 3d of the screen wires 3 such that they extend from the feed side 6 of the screen cylinder 1 to the accept channel 8.
  • the apertures 9 are semi-circular and they are placed at different points in the sides 3c and 3d of the screen wire 3 in the longitudinal direction L of the screen wire 3, whereby a structure resisting well to mechanical stress is obtained.
  • Apertures 9 are formed in the first side flange 12 such that the apertures 9 are open in the direction against the feed flow direction F of the pulp mixture, i.e. at the apertures 9 the screen wire 3 does not comprise screen wire manufacturing material between the aperture 9 and the second side flange 12' of the adjacent screen wire 3.
  • Apertures 9 are also provided in the second side flange 12' such that the apertures 9 are open in the feed flow direction F of the pulp mixture, i.e.
  • the screen wire 3 does not comprise screen wire manufacturing material between the aperture 9 and the first side flange 12 of the adjacent screen wire.
  • the adjacent screen wires 3 may be placed in close contact with one another such that the adjacent screen wires' 3 apertures 9 facing one another are in the same line, whereby circular apertures will be provided in the finished screening surface, or in accordance with Figures 16 and 17, such that elongated, circular apertures will be provided in the finished screening surface due to screen slots 10 between the screen wires.
  • the screen cylinder consisting of screen wires having a T- shaped cross section is an alterative solution to the conventional perforated plate screen basket, in which a purifying, turbulent flow is provided by selecting a suitable shape for the feed side surface 3a of the screen wire 3.
  • the screen wire having a T-shaped cross section may provide a broad and high screen wire, which endures well mechanical stresses.
  • the symmetrical structure of the screen wire 3 improves the structural endurance of the screen wire and further of the whole screen cylinder.
  • the structure may comprise, however, a relatively large open screening area.
  • a suitable number of apertures of suitable size and depth for the purpose may also extend to the vertical portion of the T-profile.
  • the thickness or extent of the side flanges 12 and 12' may be slight, because the vertical portion of the screen wire 3 may be dimensioned to receive the major part of mechanical stress loading the screen wire 3.
  • the side flanges 12 and 12' having a thin structure resist the flow less than thick side flanges, whereby reduction in the thickness of the side flanges 12 and 12' makes it possible to increase the amount and proportion of accepted fractions flowing through the screening surface.
  • the corners of the screen wire 3 profile may be rounded, but they are often manufactured relatively sharp, because sharp edges produce more turbulence in the pulp mixture suspension flow.
  • the T-profile of Figures 16 and 17 comprises a substantially sharp-cornered profile. Relatively great turbulence is often desirable, because the material to be screened or classified can be kept in motion and the material is prevented from being stopped on the surfaces of the screen wire 3, and thus, clogging will be prevented.
  • a screen wire profile having apertures through at least one screen wire profile side or side flange is applied for providing a screen cylinder or a screening surface of a flat screen.
  • the screen wire profiles of the solution allow a cylindrical, conical or planar screening surface to be formed.
  • the screen wire profiles of the solution also allow a curved screening surface to be formed, whereby the solution may also be applied in the curved screens.

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  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Paper (AREA)

Abstract

La présente invention concerne un cylindre tamiseur (1) pour épurer ou classifier un mélange de pâte. Le cylindre tamiseur (1) comprend des fils de tamis (3) qui forment une surface de tamisage cylindrique (2) du cylindre tamiseur (1), et au moins un fil de tamis (3) qui comprend des ouvertures (9) prévues à travers au moins un côté (3c, 3d) du fil de tamis (3). Le fluide du mélange de pâte et la portion de fibres définie par la taille des ouvertures (9) peuvent s'écouler à travers lesdites ouvertures, depuis le côté d'alimentation (6) du cylindre tamiseur (1) jusqu'au côté d'admission (7) du cylindre tamiseur (1). En outre, la présente invention concerne des procédés de fabrication d'un cylindre tamiseur (1), d'un tamis plat et d'un tamis.
PCT/FI2008/050613 2007-11-02 2008-10-30 Tamis, cylindre tamiseur, tamis plat et procédés de fabrication de cylindre tamiseur WO2009056682A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
FI20070833A FI20070833A0 (fi) 2007-11-02 2007-11-02 Sihti ja menetelmä sihdin valmistamiseksi
FI20070833 2007-11-02

Publications (1)

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WO2009056682A1 true WO2009056682A1 (fr) 2009-05-07

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Application Number Title Priority Date Filing Date
PCT/FI2008/050613 WO2009056682A1 (fr) 2007-11-02 2008-10-30 Tamis, cylindre tamiseur, tamis plat et procédés de fabrication de cylindre tamiseur

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FI (1) FI20070833A0 (fr)
WO (1) WO2009056682A1 (fr)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
AT13421U1 (de) * 2011-12-22 2013-12-15 Metso Paper Inc Siebtrommel

Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4828689A (en) * 1987-03-13 1989-05-09 Pierre Lamort Purifier screen of non-welded manufacture
US5387340A (en) * 1993-07-15 1995-02-07 Ackerman; Carl D. Wire filter element and method of manufacture
US5647128A (en) * 1994-12-28 1997-07-15 Aikawa Iron Works Co., Ltd. Method of manufacturing paper making screen plate
US5791495A (en) * 1996-03-11 1998-08-11 Beloit Technologies, Inc. Paper pulp screen cylinder
US6789681B2 (en) * 2000-02-19 2004-09-14 Voith Paper Patent Gmbh Screen for fiber suspensions and method for the manufacture thereof
US20050274667A1 (en) * 2004-06-10 2005-12-15 Giancarlo Dal Maso Method for manufacturing filtering baskets of fibres in aqueous suspension and a filtering basket manufactured with said method

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4828689A (en) * 1987-03-13 1989-05-09 Pierre Lamort Purifier screen of non-welded manufacture
US5387340A (en) * 1993-07-15 1995-02-07 Ackerman; Carl D. Wire filter element and method of manufacture
US5647128A (en) * 1994-12-28 1997-07-15 Aikawa Iron Works Co., Ltd. Method of manufacturing paper making screen plate
US5791495A (en) * 1996-03-11 1998-08-11 Beloit Technologies, Inc. Paper pulp screen cylinder
US6789681B2 (en) * 2000-02-19 2004-09-14 Voith Paper Patent Gmbh Screen for fiber suspensions and method for the manufacture thereof
US20050274667A1 (en) * 2004-06-10 2005-12-15 Giancarlo Dal Maso Method for manufacturing filtering baskets of fibres in aqueous suspension and a filtering basket manufactured with said method

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
AT13421U1 (de) * 2011-12-22 2013-12-15 Metso Paper Inc Siebtrommel

Also Published As

Publication number Publication date
FI20070833A0 (fi) 2007-11-02

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