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
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D29/00—Filters with filtering elements stationary during filtration, e.g. pressure or suction filters, not covered by groups B01D24/00 - B01D27/00; Filtering elements therefor
  • B01D29/11—Filters with filtering elements stationary during filtration, e.g. pressure or suction filters, not covered by groups B01D24/00 - B01D27/00; Filtering elements therefor with bag, cage, hose, tube, sleeve or like filtering elements
  • B01D29/13—Supported filter elements
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B07—SEPARATING SOLIDS FROM SOLIDS; SORTING
  • B07B—SEPARATING SOLIDS FROM SOLIDS BY SIEVING, SCREENING, SIFTING OR BY USING GAS CURRENTS; SEPARATING BY OTHER DRY METHODS APPLICABLE TO BULK MATERIAL, e.g. LOOSE ARTICLES FIT TO BE HANDLED LIKE BULK MATERIAL
  • B07B1/00—Sieving, screening, sifting, or sorting solid materials using networks, gratings, grids, or the like
  • B07B1/46—Constructional details of screens in general; Cleaning or heating of screens
  • B07B1/4609—Constructional details of screens in general; Cleaning or heating of screens constructional details of screening surfaces or meshes
  • B07B1/4618—Manufacturing of screening surfaces
• • 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
• • 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
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T29/00—Metal working
  • Y10T29/49—Method of mechanical manufacture
  • Y10T29/49826—Assembling or joining
  • Y10T29/49947—Assembling or joining by applying separate fastener

Definitions

• the present invention relates to a method of manufacturing a screen cylinder, and a screen cylinder that is particularly suitable for screening, filtering, fractionating, or sorting cellulose pulp or fiber suspensions of the pulp and paper industry, or other similar suspensions.
• the present invention relates more particularly to screening or filtering devices of the type comprising a plurality of screen wires positioned at a small spacing parallel to each other, the plurality of screen wires forming a screening or filtering surface facing the pulp or fiber suspension to be screened and adjacent wires forming screening openings therebetween allowing an accept portion of the pulp or fiber suspension to flow therethrough.
• EP-A1 - 0 929 714 discusses a screening device in which the screen wires are fixed on the downstream side of the wires to transversely extending notches in solid support elements, i.e. support rings or support bars.
• the support elements which form the supports for the screen wires, are formed of solid bars, mainly rectangular but sometimes round or rounded in their cross section and most typically positioned perpendicular to the screen wires.
• the above-mentioned EP-A1 -0 929 714 discloses a wire screen where the support ring is of specific construction, i.e. it is a U- shaped bar, to which the screen wires are attached by means of deformation in notches machined transverse to the support bar.
• the screen wires are generally fastened to the support bars by a welding process which gives rise to a number of disadvantages such as variability distortion, thermal stresses and burrs.
• the heat induced by the welding often causes distortion of the wires and changes in the screening opening width between adjacent wires. It is therefore difficult to get completely uniform screening openings, which means that the efficiency of the screen suffers.
• Today, when the desired width of screening openings may be as small as 0.1 mm, or even smaller, only minimal distortions (if any) are acceptable.
• the thermal stresses and the burrs may also lead to failure in operation due to the loading on the screening device in the user's process.
• Such loading may be either in the form of a constant load or a cyclic loading giving rise to failure by fatigue. Burrs may also catch fibers of the suspension, leading to gradual clogging of the screen or filter, or the formation of so-called strings of fibers attached to each other which are very detrimental in the user's process.
• the next problem to solve is to find out how the screen wires could be fastened to the support rods or bars such that the fastening by means of welding would not bring any additional problems.
• the welding has been a reliable and simple way of securing the screen wires in the notches in the support rods or bars in such a manner that the wires would not be able to move in the notch.
• a so called keyhole notch has been tested for replacing the welding.
• the keyhole notch or opening is machined either entirely inside the support element, or ring or bar, or machined such that the keyhole is open at one side of the support element or bar or ring. In both cases the wire is able to move in the notch only in the direction of its longitudinal axis.
• the keyhole either clamps the wire substantially tightly, or allows the wire to be slid into the keyhole in the direction of the longitudinal axis of the wire.
• the keyhole prevents the screen wire from moving in the direction of the pressure pulses created during the screening i.e. in the direction substantially perpendicular to the screen wires.
• U.S. Patents 5,090,721 and 5,094,360 suggest the attachment of screen wires by means of a certain keyhole cross section into notches in the support bar having the same keyhole form.
• the screen wires are inserted in the notches while the support bars are straight, i.e. not bent.
• the support bars are straight, i.e. not bent.
• the keyhole fastening together with the clamping feature has been improved with a number of suggestions known better in the industry. In other words, gluing, soldering, welding etc. have been suggested to ensure the keyhole fastening.
• a small gap is formed between the surfaces of the screen wire and the notch. Such a gap would indicate that the ring is not in full mechanical contact with the wire and not providing full strength.
• the gap is also apt to start collecting one or more fibers therein, which may result in the formation of a string of fibers that loosens from the gap from time and again and when possibly entering the paper making wire would reduce the quality of the end product.
• the heating of a lateral face of a support ring is a challenging task as it should be done such that the effects of the heating are the same all over an individual support ring as well as over each and every support ring.
• the heating of the screen wires should be avoided, in other words, though a lateral side face of a support ring is heated, the necessary high level of heating should not extend to the area of the screen wires.
• the support elements are in the form of individual rings arranged axially from each other. At least one of the support rings is heated after the assembly of the screen wires such that its diameter is permanently reduced whereby it clamps the screen wires in openings/notches in the support ring.
• Characterizing features of the method of manufacturing a screen cylinder being formed of at least a number of screen wires with a screening slot therebetween, and substantially circular support rings, said support rings having a first rim area provided with openings/notches into which said screen wires are installed, and a second rim area opposite to said first rim area, are
• a characterizing feature of the screen cylinder being formed of at least a number of screen wires leaving a screening slot therebetween, and of substantially circular support rings, said support rings having a first rim area provided with openings/notches into which said screen wires are installed, and a second rim area opposite to said first rim area, is that that at least one of said support rings is heated essentially evenly and uniformly at its second rim area after the installation of the screen wires such that its diameter is first expanded in substantially radial direction and thereafter reduced from its original diameter, the support ring thereby clamping the screen wires in said notches.
• Figure 1 illustrates schematically a wire screen cylinder of prior art
• Figure 2 illustrates schematically various embodiments of keyholes arranged, for instance machined, in the prior art support elements
• Figures 3 and 4 illustrate a preferred embodiment of the support element- screen wire combination of the present invention
• Figure 5 is a somewhat closer representation of a support ring in accordance with a preferred embodiment of the present invention.
• Fig. 1 shows in a very schematic and simplified manner a wedge wire screen cylinder 1 of prior art, i.e. the screen wires and the support ring have not been sketched in scale, and neither the screening slot size nor the number of screen wires relate to any existing screen drum or screen cylinder.
• the screen cylinder of Fig. 1 is shown as a radial cross section above one of its support rings. Additionally, the end rings, or the top and bottom rings of the screen cylinder are not shown.
• the prior art screen cylinder 1 is made of substantially axially-oriented screen wires 10, so-called wedge wires (originally the wire cross-section resembled a wedge, and most often still do) which are fastened, on one hand, to support elements 20 and, on the other hand, at their axial ends either directly or via the axially outermost support rings to the end rings situated at opposite ends of the screen cylinder.
• the wedge wire screen cylinder is of the so-called outflow type like in Fig. 1 . This means that the accept flow through the screening slots between the wires is from the inside of the screen cylinder to the outside thereof.
• the screen wires are normally attached to the radially inner rim of the support elements i.e. support rings.
• inflow type wedge-wire screen cylinders whereby the structure is opposite to that explained above.
• the distance between the adjacent screen wires 10 defines screening slots 15.
• the slot width is normally about 0.1 - 0.3 mm depending on the application of the screen cylinder 1 .
• both narrower and clearly larger slot widths are used.
• the circular support elements or support rings 20 are arranged along the length of the screen wires in such a manner that the axial distance between the support elements is about 20 to 100 mm depending again on the size and the application of the screen cylinder 1 .
• the axial distance between adjacent support elements is typically, but not always, constant along the length of the cylinder.
• the height or the thickness (in the axial direction of the screen cylinder) of the support element is normally about 3 to 10 mm and radial width from about 15 to about 50 mm. However, the dimensions may also vary from the above-mentioned ones in some special circumstances.
• the screen cylinder is often manufactured such that the screen wires 10 are fastened to support bars before the screen is rolled to a cylindrical form whereby the support bars form the support elements or support rings after the rolling. Sometimes the screen wires are fastened to the support elements after the bars have been bent and welded 22 to form circular rings, or to support elements cut from sheet metal.
• a common way of fastening and properly positioning the screen wires to the support elements or support rings is to use in the support elements 20 transverse notches or recesses or openings into which the screen wires 10 are inserted.
• Fig. 2 shows a few alternatives for the shape of the so-called keyhole or dovetail notch 30 in the support element 20 or support bar or support ring.
• a round (could as well be oval, rectangular, triangular or any other desired shape) opening in the support element has been illustrated as an example of openings fully surrounded by the support element material.
• the notches and openings have normally a few common features.
• the notch/opening 30 is normally machined at right angles to the bar, or element, whereby the notch axis is perpendicular to the longitudinal axis of the support element.
• the basic idea of the keyhole notch 30 (and naturally of an opening too) is to secure the screen wire in the notch 30 so that the screen wire cannot move except in the direction of the longitudinal axis of the wire, i.e. at right angles to the radial plane the support element is located in.
• so-called form locking is used.
• the movement of the screen wire in the direction of its longitudinal axis is not a desired feature either, but it can be utilized in the assembly of the screen cylinder.
• the support bars may be readily bent and welded to circular support rings 20 whereafter the wires are pushed manually, or forced by a hammer or by an automated device, in the notches 30.
• the size and shape of the notches 30 should be very close to the size and shape of the cross- section of the screen wire.
• the wires may be welded, glued or soldered to the support ring, or the wire may be deformed at the notch area so as to prevent its movement.
• all the discussed fastening methods are complicated, or they may create burrs, which collect fibers, or they may not provide a very precise or accurate slot width, or they may be otherwise not ideal for their desired purpose.
• FIG. 3 illustrates a partial radial cross-section of a screen cylinder in accordance with the present invention in an enlarged scale showing a support ring 20, its first rim area 24, its second rim area 26 and the cross-section of three screen wires 10 in one of their numerous preferred forms.
• the screen wires 10 have been installed in the notches machined in the first rim area 24 of the support ring.
• Fig. 4 is likewise a partial, now axial, cross-section of the screen cylinder showing a screen wire 10, the cross-section of the support ring 20, and the second rim area 26 opposite to the first rim area and the screen wire 10.
• the circumferential surface having the notches is called the first rim, and the opposite solid circumferential surface the second rim.
• Figure 4 also shows the centreline plane C L of the support ring 20, the plane extending in radial direction.
• a preferred, but of course not the only way of assembling a screen cylinder in accordance with the present invention is such that the support elements 20 in the form of circular rings with appropriate keyhole or dovetail notches in their first rim areas or corresponding openings are attached to a jig.
• the support rings may be made by rolling a bar to a circular ring and welding the ends together or by cutting the ring out of a metal plate. In the latter case, the support rings are thus made without a seam.
• the distance between adjacent support rings is of the order of 20 to 100 mm, just to give a rough example. In fact the distance varies in accordance with the screen cylinder size, the screen wire size, the forces being applied to the screen cylinder, its application, etc..
• screen wires 10 are pushed through the notches/openings 30 in the support rings 20.
• the notches or openings in all the rings are alike.
• the screen wires are fastened so that they cannot move in the direction of their longitudinal axis anymore. This is performed by means of heating the second rim area 26 of a support ring 20. In other words, the heating of the second rim area is performed as evenly and uniformly as possible such that the support ring expands thermally substantially in the radial plane or substantially in the radial direction i.e. without bending, twisting or tilting.
• the heating may be performed either by subjecting merely the surface of the second rim (radially outer or inner surface of the support ring) to heating or by subjecting both opposite substantially radially extending side faces of the support ring at the second rim area to heating or both. Uniform heating may also be possible by heating of the side of the support ring in certain situations where, for example, the support ring is thin and wide, and thus where the conductance of heat through the ring in the axial direction is much greater and faster than conductance of heat radially.
• both the axial surface of the rim and the side surfaces of the support ring extending substantially radially from the second rim inwards or outwards up to approximately the half of the radial dimension of the support ring as well as the contained volume. While the axial surface is most often planar, any other shape e.g. rounded or longitudinally/circumferentially grooved may be used.
• the first rim area extends from the first rim up to approximately the half of the radial dimension of the support ring.
• the support rings are made of stainless steel whereby the applicable heating temperature for the rings is about 450 - 1 100 degrees Celsius.
• the support ring After the second rim area of the ring is heated to a desired temperature, the support ring is allowed to cool down, preferably in room temperature, whereby the support ring starts retracting in a radial plane (again without bending, twisting or tilting in the axial direction) such that the second rim or the free rim of the support ring passes its original position.
• both the internal and the external diameter of the support ring become smaller than that before the heating.
• the second rim area Due to constraining thermal expansion of the support ring by its internal structure and the adjacent structure and to the lower temperature of the first rim area, the second rim area is not able to expand as much as the temperature raise would indicate, whereby the heated second rim area is subjected to compressive stresses resulting in plastic deformation of the second rim area.
• first a tensile stress is created at the second rim area, and then a compressive stress is created in the first rim area resulting in the deformation of the first rim area, which leads to the reduction of the diameter of the support ring compared to its diameter prior to the heating.
• the plastic deformations or the effect of heating may be verified as local variations in the metallurgical character of the support rings.
• the stresses remain in the ring such that approximately one half (30 - 70 % of the radial dimension) of the support ring i.e. the first rim area (the rim area including the notches for the screen wires) is subjected to compressive stresses and approximately another half (70 - 30 % of the radial dimension) i.e. the second rim area to tensile stresses.
• the result of all this is that while the screen wires were inserted in their notches in the support ring before the heating, the retraction of the support ring clamps the screen wires firmly in the notches.
• the shrinkage of the support ring in accordance with the present invention i.e. the reduction of the diameter of the support ring is of the order of 0,2 - 1 ,0 %, preferably more than 0,5 %, sometimes even above 1 ,0 %, which is, in fact, also the shrinkage of the notch or opening dimensions in the support ring.
• Performed experiments have shown that such shrinkage is sufficient for ensuring that the screen wires remain firmly in their notches, and cannot move in any direction, including also the longitudinal direction thereof.
• the even and uniform heating (and cooling) of the support rings in accordance with the present invention may be performed as many times as desired, whereby each heating/cooling cycle reduces the diameter of the support rings and increases the compressive force holding the screen wires in place in the notches.
• a few different heating means may be used, and secondly, the heating itself may be performed in a few different manners.
• the second rim area of a support ring may be heated by means of a heating torch.
• accurate control of the heating with a torch is very difficult. In other words, the area subjected to the heating is hard to adjust, as well as the temperature of the support ring.
• a heating torch can be used, as its use does not require any expensive investments whereby it is a cost-effective means of heating.
• Inductive heating can be controlled substantially accurately so that a desired heating pattern may be used.
• Laser may be mentioned as the third heating means.
• the controllability of laser is far better than that of the earlier heating means in view of both the area and the temperature.
• more traditional heating means may be employed such as electrical resistance or simple conduction for heating the support ring.
• heating of the support rings in the manufacture of a screen cylinder several different ways may be used. Firstly, it is possible that each and every support ring of a screen cylinder is heated in a similar manner, whereby all screen wire - support ring joints are identical. Secondly, it is also possible that all support rings are not heated in an identical manner. For instance, it is possible that odd support rings counted from an end of a screen cylinder are not heated at all or are heated less i.e. to a lower temperature by using reduced power than the even support rings.
• every second support ring has a smaller diameter than the adjacent support rings.
• the choice between the support rings heated with full power and with reduced power may be different. For instance one ring may be heated with full power, the next with reduced power, next with no heating etc., or one ring with full power, the next two rings with reduced power, next ring with full power, the next two with reduced power etc.
• Another option is to divide the second rim area of the support ring into several annular zones, and heat at least one zone at a time. For instance such that the zone I (closest to the edge of the second rim) of a support ring 20 is first heated on both sides of the support ring to a desired temperature (between 450 - 1 100 degrees Celsius), the ring 20 is allowed to cool for a while, whereafter the ring 20 is heated again but now at a zone II somewhat farther away from the edge of the second rim of the support ring 20. Performed tests have shown that the shrinkage of a support ring 20 heated, and cooled, in this two-stage manner is greater than that of a ring heated in a single stage.
• zone III in Fig. 5.
• the order of heating may also be changed. In other words, it is possible to start the heating on zones II or III, and then advance towards zone I. Also, it is possible to perform the two-stage, or in more general terms, multi-stage heating for the entire second rim area, whereby the second rim area is first heated to a desired temperature, allowed to cool down, then reheated, and again allowed to cool down.
• the discussed heating sequence may be repeated as many times as desired to reach the optimal shrinkage of the support ring.
• the clamping force i.e. the friction force preventing the screen wires from sliding in their longitudinal direction in their notches can be maximized.
• the installation of the screen wires in their notches/openings may be made easier by allowing a slightly larger assembly tolerance without still sacrificing the friction force.
• the heating is performed in a similar manner and at the same time on the opposite side of the support ring, too. In other words, the support ring is heated on its both lateral sides simultaneously, and with the same power.
• a way to express the way the heating is done is to say that the heating of the support ring is performed evenly and uniformly, i.e.
• the present invention is applicable to the manufacture of both an outflow screen cylinder and an inflow screen cylinder.
• the means used for heating the support rings when manufacturing an inflow screen cylinder have to be positioned inside the screen cylinder. Therefore the description already above discusses the first and second rim areas of the support ring, the first rim area including the notches and the second rim area being the heated one opposite to the first rim area.
• the first rim area is the radially outer rim area, and the second rim area the radially inner one
• the first rim area is the radially inner one
• the second rim area the radially outer one.
• the screen cylinder of the present invention may not only be used as a stand-alone screen cylinder but also as a functional screen element of a screen drum having a reinforcing support shell against which the second rims of the support rings of the screen cylinder are positioned. Such a screen drum structure has been discussed in more detail in US 5,200,072.
• an option to consider concerning the heating is whether to subject either the entire rim area or an annular zone of the second rim area of the support ring, or a segment of the second rim area or of a zone of the second rim area of the support ring to the heating. It is quite natural that by means of inductive heating it is possible to heat the entire second rim area of the support ring at a time or to subject only an annular zone (for instance I, II or III), or a segment at a time to heating. Also, it is easy to understand that the heating of the entire rim area of the support ring by means of heating torches is hardly possible, or at least difficult due to high amount of heat spreading all over the surroundings. At least a risk of heating of the screen wires is high when using heating torches, whereby proper insulation of the screen wires from the heat is worth consideration. As to the laser, it can be used for both total heating or segmented heating, as desired.
• heating torches or similarly working local heating means are used, a preferable way of treating the support rings is to first position the screen cylinder, after all the wires are inserted, and properly positioned in the axial direction, into the notches of all support rings, on rolls, bring heating means in their heating position and rotate the cylinder to heat a certain area of one or more support rings.
• the limiting factor is the size of the heating means i.e. because the support rings are substantially close to each other there may not be enough room for the heating means to heat all the support rings simultaneously.
• Another option, which is especially suitable when the heating means is by using a laser, is to use an arm running in parallel with the screen cylinder axis and having a desired number of laser heating elements positioned such that they heat both lateral faces of desired number of support rings. Now by moving the arm in relation to the screen cylinder in a radial and/or in a circumferential direction a desired heating pattern on the faces of the support rings is formed and each support ring is subjected to identical heating, unless the heating energies of some laser heating elements are adjusted to result in non-uniform shrinking of some support rings.

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• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Manufacturing & Machinery (AREA)
• Paper (AREA)
• Combined Means For Separation Of Solids (AREA)
• Wire Processing (AREA)
• Filtering Materials (AREA)
• Separation Of Solids By Using Liquids Or Pneumatic Power (AREA)

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• 2010
  • 2010-10-06 FI FI20106029A patent/FI124683B/fi active IP Right Grant
• 2011
  • 2011-10-05 EP EP11775811.0A patent/EP2625333B1/en active Active
  • 2011-10-05 CN CN201180048348.2A patent/CN103298997B/zh active Active
  • 2011-10-05 KR KR1020137010977A patent/KR101750904B1/ko active Active
  • 2011-10-05 WO PCT/FI2011/050859 patent/WO2012045911A1/en not_active Ceased
  • 2011-10-05 BR BR112013007579-1A patent/BR112013007579B1/pt active IP Right Grant
  • 2011-10-05 US US13/823,324 patent/US9290886B2/en active Active
  • 2011-10-05 CA CA2811636A patent/CA2811636C/en active Active
  • 2011-10-05 JP JP2013532236A patent/JP5951617B2/ja active Active

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