Classifications

• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21F—PAPER-MAKING MACHINES; METHODS OF PRODUCING PAPER THEREON
  • D21F1/00—Wet end of machines for making continuous webs of paper
  • D21F1/02—Head boxes of Fourdrinier machines
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21F—PAPER-MAKING MACHINES; METHODS OF PRODUCING PAPER THEREON
  • D21F1/00—Wet end of machines for making continuous webs of paper
  • D21F1/02—Head boxes of Fourdrinier machines
  • D21F1/028—Details of the nozzle section

Definitions

• the present invention relates to a method of ensuring the flatness of a vane that is detachably mounted in a headbox by means of a mounting arrangement which includes a plurality of engagement members that are connected to the vane at its upstream end portion, and a longitudinal groove for receiving the engagement members of the vane, said groove having inner, downstream and upstream support walls, that face towards said engagement members for cooperation therewith, said vane being affected during operation by shearing forces caused by stock flowing along the vane, and by retaining forces exerted on the vane by the mounting arrangement.
• the invention also relates to a headbox for delivering a jet of stock to a forming zone in a former for wet forming of a fiber web, including
• said mounting arrangement including
• the invention also relates to an arrangement for detachably mounting a vane to an anchoring element of a turbulence generator of a headbox for delivering a jet of stock to a forming zone in a former for wet forming a fiber web, including
• said mounting arrangement including - a plurality of engagement members that are connected to the vane at its upstream end portion, and
• an elongate structural element having a longitudinal groove for receiving the engagement members of the vane, said groove having inner, parallel, downstream and upstream support walls that face towards said engagement members for cooperation therewith.
• a known headbox of the type described above has engagement members in the form of oblong engagement bodies or engagement dowels arranged in a row at the upstream end portion of the vane, and extending in the cross machine direction.
• the engagement dowels have parts protruding from the vane to cooperate with the support walls of the connection bar.
• the vane is influenced during operation both by a shearing force in the machine direction, caused by stock flows along the vane, as well as a retaining force directed against the machine direction, exerted on the engagement dowels by the support wall situated downstream, the retaining force being intended during operation to be distributed uniformly between the engagement dowels.
• the retaining force may be distributed non-uniformly between the engagement dowels so that the shearing force on the vane gives rise to local compressive stresses in the cross machine direction in the downstream end portion of the vane.
• compressive stresses arise the vane buckles, making its downstream end portion uneven, which is not desirable, particularly at a separating-vane that separates two layers of stock, since good layering of stock is dependent on a flat separating-vane. If the separating-vane is not flat, streaks having a grammage different from the rest of the paper web may appear, for instance.
• the above-mentioned compressive stresses may arise as a result of variations in the placing of the engagement dowels within a predetermined tolerance interval.
• the placing of the engagement dowels within the tolerance interval may, for instance, deviate from an ideal placing in such a way that certain engagement dowels are downstream of the other engagement dowels, in which case the retaining force will be distributed in an uncontrolled manner between the engagement dowels, with the risk of compressive stresses appearing in the downstream end portion of the vane, resulting in buckling.
• Compressive stresses may also appear in a vane consisting of a plastic material, e.g. glassfiber-reinforced epoxy resin, and having reduced thickness in the machine direction so that the downstream end portion of the vane is relatively thin in relation to the upstream end portion.
• a vane of plastic material absorbs water from the surroundings both during storage prior to mounting, and also after mounting in the headbox, when the vane absorbs liquid from the stocks.
• the thinner downstream end portion of the vane will become saturated earlier than the thicker upstream end portion of the vane.
• the downstream end portion As the downstream end portion becomes saturated in the direction away from the downstream edge, the downstream end portion lengthens in the cross machine direction, whereas the thicker, unsaturated upstream end portion of the vane retains its dimensions.
• the object of the present invention is to essentially reduce the problems mentioned above and to provide a method which will efficiently ensure the flatness of a vane .
• the method in accordance with the invention is characterized by mounting at least one outer engagement member or an outer group of two or more engagement members in the proximity of each side edge of the vane, and said two outer engagement members or said two outer groups of engagement members cooperating during operation for at least one specific period of time, as the only engagement members, with the downstream support wall to take up said shearing forces, whereby tensile stresses are arising in a downstream end portion of the vane in the cross machine direction.
• the headbox and the mounting arrangement in accordance with the invention are characterized in that said plurality of engagement members include at least one outer engagement member or an outer group of two or more engagement members in the proximity of each side edge of the vane, said two outer engagement members or said two outer groups of engagement members are arranged during operation for at least one specific period of time, as the only engagement members, to cooperate with the downstream support wall to take up the shearing forces generated in the vane by the flowing stocks, and in that an inner area of the upstream end portion defined by the two outer engagement members and the two outer groups of engagement members, respectively, is free from engagement members or has inner engagement members which, at least in the unloaded state of the vane are located upstream of said downstream support wall so that the vane within and downstream of said inner area is arranged to be able to move freely in the machine direction in relation to said downstream support wall during said period of time or part thereof .
• Figure 1 is a sectional view in machine direction of a part of a multilayer headbox mounted to deliver a multilayer jet of stock into a gap leading to a forming zone in a twin wire former of roll type.
• Figure 2 is a sectional view of an arrangement for mounting one of the vanes in the slice chamber of the headbox in connection with a group of turbulence channels in the headbox according to Figure 1.
• Figure 3 is a view from above of an unloaded vane of metal, and shows parts of a conventional mounting arrangement .
• Figure 4 is a view from above of a vane in accordance with Figure 3 during operation.
• Figure 5 is a view from above of a vane of moisture-absorbing plastic material and shows parts of a conventional mounting arrangement.
• Figure 6 is a sectional view along the line VI-VI in Figure 5.
• Figure 7 is a view from above of an unloaded vane, and shows parts of a mounting arrangement in accordance with a first embodiment of the invention.
• Figure 8 is a view from above of the vane in accordance with Figure 7 during operation.
• Figure 9 is a view from above of an unloaded vane and shows parts of a mounting arrangement in accordance with a second embodiment of the invention.
• Figure 10 is a view from above of the vane in accordance with Figure 9 during operation.
• Figure 11 is a view from above of an unloaded vane and shows parts of a mounting arrangement in accordance with a third embodiment of the invention.
• Figure 12 is a view from above of the vane in accordance with Figure 11 during operation.
• Figure 13 is a view from above of an unloaded vane and shows parts of a mounting arrangement in accordance with a fourth embodiment of the invention.
• Figure 14 is a view from above of the vane in accordance with Figure 13 during operation.
• FIG. 1 shows schematically a headbox designed to deliver a three-layer jet of stock into a gap 1 leading to a forming zone in a twin wire former of roll type.
• the twin wire former has an inner forming wire 2 , a rotatable forming roll 3, an outer forming wire 4 and a rotatable breast roll 5.
• the headbox has a turbulence generator including a group of turbulence channels 6 and a slice 7 arranged downstream of the turbulence channels 6 and containing a chamber 8 that converges from its upstream end in the direction of the flow of stock and terminates in a slice opening 9 at its downstream end.
• the turbulence channels 6 are arranged in three sections for supplying three different stocks, for instance, into the slice chamber 8.
• the lower section and the middle section each have two rows of turbulence channels 6 arranged close together, while the upper section has three such rows of turbulence channels 6.
• the rows of turbulence channels 6 extend in the cross machine direction and adjacent rows of turbulence channels 6 are separated by elongate stable anchoring elements 10 extending in the cross machine direction.
• the anchoring element 10 has an elongate, through engagement groove 11 (see Figure 2) , with a side opening 12 facing the slice chamber 8.
• the group of turbulence channels 6 is connected at its upstream end to a feeding system (not shown) comprising three stores of stock and suitable flow spreaders for uniform distribution of each stock to the rows of turbulence channels 6 in the associated section and uniform distribution of the stock within each row of turbulence channels 6.
• the headbox has six vanes 14 which divide the slice chamber 8 into seven converging channels 15 communicating with the rows of turbulence channels 6.
• Two of the vanes 14 constitute stock-separating vanes 14a that are arranged to separate the three stocks from each other and extend through the slice opening 9 a predetermined distance to form a jet which thus consists of three layers.
• the stock-separating vanes 14a also have turbulence-generating function.
• the other vanes are only turbulence vanes 14b having their free ends situated inside the slice chamber at a predetermined distance from the slice opening 9.
• the vanes 14 are relatively rigid and may consist of a metal material, usually titanium, or a plastic material, usually glassfiber-reinforced or carbonfiber-reinforced epoxy resin.
• the vanes 14 are sufficiently stiff to support various pressures and velocities of the flows of stock.
• Each vane 14 is arranged to be detachably mounted to said anchoring element 10 by means of an mounting arrangement comprising an elongate structural element 16 and engagement members 22 arranged in the upstream end portion 21 of the vane 14.
• the structural element 16 consists of a connection bar and the engagement members 22 of cylindrical engagement dowels (see Figure 2) disposed at right angles to the plane of the vane 14.
• the connection bar 16, consisting of metal, e.g. bronze, is the same length as the width of the vane 14 and includes in the following order an engagement part 17 situated downstream, a flexible waist part 18, and an engagement part 19 situated upstream and forming a pivot.
• the engagement part 17 is provided with an elongate, through groove 20 to receive the upstream end portion 21 of the vane 14 and its engagement dowels
• H- TJ Pi r 3 CD 3 3 o 3 •» 0 ⁇ r hi ⁇ - ⁇ rt 0 O SD ⁇ ⁇ CQ ⁇ SD ⁇ - ⁇ - 3 m CQ O H- H- rt hj i 3 rt ⁇ - ⁇ - 3 ⁇ - ⁇ rt 3 Hi CQ rt CQ 3 rt rt 3 Pi a
• the positions of the engagement dowels 22 in relation to the downstream support wall 25 may vary.
• This is illustrated in Figure 3 in that the engagement dowel 22e is situated downstream, i.e. closer to the downstream support wall 25 than the other engagement dowels 22.
• Figure 4 shows the vane 14, made of metal, during operation where shearing forces caused by the stocks flowing along the vane 14 press the engagement dowels 22 towards the downstream support wall 25.
• the shearing forces act along the surfaces of the vane 14 and are illustrated in Figure 4 by downwardly directed force arrows designated F s .
• the retaining forces exerted by the downstream support wall 25 on the engagement dowels 22 are illustrated by upwardly directed force arrows designated F r .
• buckling may arise in a vane made of a moisture-absorbing plastic material and having narrowing thickness in the machine direction, as a result of the thinner, downstream end portion of the vane becoming saturated earlier than the thicker upstream end portion of the vane.
• a vane 14 is described in the following with reference to Figures 5 and 6 where the vane 14 is shown in unloaded state after, for instance, a certain operating period when it has been in contact with the flowing stocks.
• the downstream end portion 33 of the vane 14 becomes saturated in the direction away from the downstream edge 30, the downstream end portion 33 becomes stretched in the cross machine direction, while the thicker, unsaturated upstream end portion 21 of the vane 14 retains its dimensions.
• Figure 7 shows an unloaded vane 14 with parts of a mounting arrangement in accordance with a first embodiment of the invention.
• Figure 8 shows the same vane 14 during operation.
• the vane 14 is symmetrical with respect to its centre line 34, which coincides with the machine direction.
• An outer engagement dowel 22a is arranged in the proximity of each side edge 31, 32 of the vane 14, for cooperation with the downstream support wall
• Figure 9 shows an unloaded vane 14 with parts of a mounting arrangement in accordance with a second embodiment of the invention where three engagement dowels 22b, forming an outer group 36, are arranged in the proximity of each side edge 31, 32 of the vane 14.
• the engagement dowels 22b are arranged adjacent each other in a row in the cross machine direction.
• the inner area 35 of the upstream end portion 21 of the vane, extending between the two outer groups 36 is free from engagement dowels so that said inner area ' 35 of the vane 14, as well as the area downstream of this, are arranged to be able to move freely in the machine direction in relation to the downstream support wall 25.
• the bending moment M]- bends the vane 14 in its plane, stretches the downstream edge 30 of the vane 14 and generates tensile stresses S ⁇ in the cross machine direction in the downstream end portion 33 of the vane 14. The displacement arises under the same circumstances as those described for the vane in accordance with Figure 7.
• FIG 11 shows an unloaded vane 14 with parts of a mounting arrangement in accordance with a third embodiment of the invention, which is more suitable for high stock-flow velocities , than the embodiments described previously.
• the vane 14 is provided with engagement dowels 22b, arranged in outer groups 36, as in the second embodiment described in connection with Figures 9 and 10, as well as engagement dowels 22c arranged in two inner groups 37 with three engagement dowels 22c in each group 37.
• the inner groups 37 of engagement dowels 22c are arranged at a predetermined distance from the outer groups 36.
• Each inner group 37 of engagement dowels 22c is arranged at a predetermined distance from the downstream support wall 25, e.g. about 5 mm.
• a first period of time commences with the stocks starting to flow through the headbox and finishes, e.g. when the inner groups 37 of engagement dowels 22c come into contact with the downstream support wall 25 in that the inner area 35 has been displaced in the machine direction under the influence of the shearing forces F s from the stocks, whereupon the downstream edge 30 of the vane 14 is stretched and a tensile stress S ⁇ in the cross machine direction is built up in the downstream end portion 33 of the vane 14. At the end of the period of time the machine speed has a predetermined value.
• each inner group 37 of engagement dowels 22c in relation to the downstream support wall 25 and to the outer group 36 of engagement dowels 22b is decisive for each stock flow rate.
• the inner part-area 35a, defined by the inner groups 37 of engagement dowels 22c moves forwards in machine direction, the movement being limited by the displaced position when there is a risk of compressive stresses appearing in the downstream end portion 33 of the vane 14.
• the swelling phenomenon must also be taken into account in choosing maximum stock flow rate or machine speed and determining the positions of the inner groups 37 of engagement dowels 22c.
• the tensile stress that still exists in the downstream end portion 33 of the vane can be utilized to compensate the compressive stresses deriving from the swelling.
• a suitable distance between two adjacent outer and inner groups 36, 37 may be about 2000 mm.
• the inner groups 37 of engagement dowels 22c may be situated about 5 mm from the downstream support wall 25, seen in unloaded state of the vane 14.
• the engagement dowels in each group 36, 37 are preferably placed about 50 mm from each other. It is preferable to arrange the engagement dowels 22b and 22c within each group 36, 37 so that the distance to the downstream support wall 25 increases in two adjacent engagement dowels in the direction from the closest side edge
• a suitable increase in this distance is about 0.1 mm.
• the invention is not limited to three engagement dowels 22 in each group. More or fewer, e.g. two or four engagement dowels 22, may be used in each group. Neither is the invention limited to two inner groups 37 of engagement dowels 22. It is thus possible, for instance, to place additional inner groups of engagement dowels 22, spaced from the support wall 25, between the outer and inner groups 36, 37.
• Figure 13 shows an unloaded vane 14 with parts of a mounting arrangement in accordance with a fourth embodiment of the invention, the engagement dowels 22 being arranged in a row along a curved line extending between the side edges 31, 32 and symmetrical about the centre line 34.
• the engagement dowels 22 are arranged with uniform spacing but in accordance with an alternative embodiment (not shown) the spaces may be different and distributed in a regular pattern, e.g. groups of engagement dowels with equal distance between them within the group and equal but greater distance between the groups.
• a certain number e.g.
• engagement dowels situated nearest a side edge 31, 32 may be considered to be included in an outer group of engagement dowels, whereas the other engagement dowels may be considered to constitute separate inner engagement dowels situated one after the other, or to form inner groups of engagement dowels, depending on the shape of the curved line and the distance between the engagement dowels as mentioned above.
• a period of time commences at the moment when the stocks start flowing through the headbox and extends to the moment when the engagement dowels 22 closest to the centre line 34 also come into contact with the downstream support wall 25 as a result of the influence of the shearing forces F s from the stocks, whereupon the downstream edge 30 is stretched and a tensile force S ⁇ in the cross machine direction is built up in the downstream end portion during this period of time, as illustrated in Figure 14.
• the vane consists of a plastic material, is narrowing and can no longer be moved forwards within the central area, there may be such a large excess of tensile stress in the downstream end portion at the end of said period of time that remaining swelling gives compressive stresses that are balanced by said excess of tensile stress. If the tensile stress decreases to zero and the vane is still not saturated, i.e. the swelling is going on, said maximum machine speed must be reduced in a corresponding degree.
• the engagement dowels are arranged in a row along a curved line which, when the vane is unloaded, has a certain extension in the machine direction.
• the inner engagement dowels situated nearest the centre line of the vane will cooperate with the support wall situated upstream of the groove and will absorb support forces therefrom.
• the support forces will bend the vane in its plane, stretch the downstream edge of the vane and generate tensile stresses in the cross machine direction in the downstream end portion of the vane. These tensile stresses ensure that the vane is flat right at the start-up phase of the headbox, i.e. before the stocks have had time to influence the vane.
• the engagement dowels 22 can move freely, i.e. without influence from outer retaining forces from engagement dowels, in the machine direction in relation to the downstream support wall 25 during said period of time or part thereof.
• the engagement dowels 22 By arranging the engagement dowels 22 in the manner described above they create, during operation, shearing forces F s acting on the vane 14, together with the retaining forces F r acting on the engagement dowels 22 a bending moment M ⁇ , which under normal operating conditions always bends the vane 14 in its plane and generates tensile stresses S ⁇ in the cross machine direction in the downstream end portion 33 of the vane 14.
• the placing of the engagement dowels 22 in accordance with the principle of the invention prevents that the compressive stresses described previously will arise in the downstream end portion 33 of the vane 14.
• a characteristic feature of the invention is thus that compressive stresses are prevented in the vane, which compressive stresses may cause the vane to buckle so that the stock layering may be affected in an unfavourable manner.
• engagement members in the form of engagement dowels 22.
• the invention can be realized with other types of engagement members.
• the engagement members being designed as a plurality of discrete elements such as engagement dowels, they may consist of a continuous engagement element cooperating with said downstream support wall in accordance with the principles of the invention.
• the vane 14 may be attached directly to the anchoring element 10, for instance, which then has the same function as the elongate connection bar 16 and has a groove with support walls similar to that in the connection bar.

Landscapes

• Paper (AREA)
• Extrusion Moulding Of Plastics Or The Like (AREA)
• Agricultural Machines (AREA)
• Operation Control Of Excavators (AREA)
• Control Of Vehicle Engines Or Engines For Specific Uses (AREA)
• Turbine Rotor Nozzle Sealing (AREA)

Applications Claiming Priority (5)

Publications (2)

Family

ID=26655155

Family Applications (1)

Country Status (8)

Cited By (1)

Family Cites Families (1)

• 2001
  • 2001-06-18 JP JP2002504724A patent/JP2004501294A/ja active Pending
  • 2001-06-18 AU AU2001274758A patent/AU2001274758A1/en not_active Abandoned
  • 2001-06-18 CA CA002407913A patent/CA2407913C/fr not_active Expired - Fee Related
  • 2001-06-18 EP EP01941401A patent/EP1313911B1/fr not_active Expired - Lifetime
  • 2001-06-18 DE DE60130343T patent/DE60130343T2/de not_active Expired - Fee Related
  • 2001-06-18 WO PCT/SE2001/001368 patent/WO2001098583A1/fr active IP Right Grant
  • 2001-06-18 AT AT01941401T patent/ATE372411T1/de not_active IP Right Cessation
  • 2001-06-18 BR BR0111649-5A patent/BR0111649A/pt not_active Application Discontinuation

Non-Patent Citations (1)

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