Abstract
The invention relates to a former head of the kind which is used for forming, such as dry forming, of a fibrous web, where fibres are supplied to the former head mixed with air via at least one injection inlet. The former head comprising: a) a roller being rotatable in a rotation direction around a rotation axis and comprising: a roller surface surrounding the rotation axis, and a plurality of projections extending outwardly, such as radially outwardly, from the roller surface, b) a screen extending along at least part of the roller surface above the rotation axis, the roller surface and the screen defining therebetween a peripheral gap, and c) the injection inlet, wherein the injection inlet is positioned to conduct the mixture of the fibres and air into the peripheral gap in a delivery direction opposite or substantial opposite to the rotation direction of the roller.
Claims
1. A former head for forming a fibrous web, where fibers are supplied to the former head mixed with air via at least one injection inlet, the former head comprising: a) a roller being rotatable in a rotation direction around a rotation axis and comprising: a roller surface surrounding the rotation axis, and a plurality of first projections extending outwardly, such as radially outwardly, from the roller surface, b) a screen extending along at least part of the roller surface above the rotation axis, the roller surface and the screen defining therebetween a peripheral gap, and c) the injection inlet being positioned to conduct the mixture of the fibres and air into the peripheral gap in a delivery direction, wherein said delivery direction is opposite to the rotation direction of the roller, and said screen comprising a plurality of air inlets being configured for communicating with the peripheral gap and arranged before the injection inlet when viewed in the rotation direction of the roller.
2. The former head according to claim 1, wherein each air inlet comprises one or more perforated plates arranged along the circumference of the screen and said perforated plates being slidable relative to the screen between an open and a closed position.
3. The former head according to claim 1, wherein each air inlet comprises one or more manifold arranged along the circumference of the screen or each air inlet comprises one or more air blasting units arranged on the screen.
4. The former head according to claim 1, wherein the plurality of first projections are formed by needles, needle strips, a carding plate, carding plate segments, carding wires, blade flails, a rasping plate, or rasping plate segments.
5. The former head according to claim 1, wherein an underside of the screen is provided with a plurality of second projections extending outwardly, such as radially outwardly, from the underside of the screen.
6. The former head according to claim 1, wherein the screen comprises an injection opening extending along the rotation axis of the roller, the injection opening in the screen at least partially or fully dividing the screen into two portions, a first portion extending from the injection opening and along the rotation direction of the roller and a second portion extending from the injection opening and in a direction opposite of the rotation direction of the roller.
7. The former head according to claim 1, wherein the underside of the first portion of the screen comprises a first group of the plurality of second projections.
8. The former head according to claim 1, wherein the peripheral gap has a decreasing width seen from the injection inlet and in the rotation direction of the roller.
9. The former head according to claim 1, wherein the plurality of first projections and the plurality of second projections on both the roller surface and the underside of the screen are needles, the width of the peripheral gap and a length of the needles on the underside of the screen and a length of the needles on the roller surface of the roller being adapted to provide a needle overlap of the needles extending from the underside of the screen and from the roller surface.
10. The former head according to claim 1, further comprising a perforated plate extending along at least part of the roller surface below the rotation axis and being shaped substantially like the periphery of the roller surface, preferably extending in continuation of the screen.
11. An apparatus for depositing fibres fibers on a forming wire comprising: at least one former head according to any one or more of claim 1, and a forming wire configured to move in a direction and for receiving the fibres from the at least one former head.
12. The former head according to claim 1, wherein the plurality of second projections are formed by needles, needle strips, a carding claim plate, carding plate segments, carding wires, a rasping plate, or rasping plate segments.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0058] The invention will now be explained in further details with reference to the figures showing an aspect thereof.
[0059] FIG. 1 illustrates a cross sectional view of a former head according to the invention,
[0060] FIG. 2 illustrates a close-up of a needle overlap, as seen down towards the horizontal plane HP of FIG. 1
[0061] FIG. 3 illustrates a close-up of an air inlet being used as an airlock,
[0062] FIG. 4 illustrates a cross sectional view of a roller,
[0063] FIG. 5 illustrates a roller comprising blade flail,
[0064] FIG. 6 illustrates a carding plate segment,
[0065] FIG. 7 illustrates a rasping plate,
[0066] FIG. 8 illustrates a carding wire,
[0067] FIG. 9 illustrates an end view of the former head illustrated in FIG. 1,
[0068] FIG. 10 illustrates a cross sectional view of a former head having a perforated plate extending along a bottom part of the roller,
[0069] FIG. 11 illustrates a cross sectional view of a former head having a peripheral gap with a varying width,
[0070] FIG. 12 illustrates a perspective view of an injection inlet,
[0071] FIG. 13 illustrates an example of wall plates provided between the former head and the former wire,
[0072] FIG. 14 illustrates a cross sectional view of an apparatus according to the invention comprising a former head according to the invention,
[0073] FIGS. 15A-15B illustrate a former head according to the invention,
[0074] FIGS. 16A-16B illustrate a former head having at least one manifold arranged on the circumference of the screen,
[0075] FIGS. 17A-17B illustrate a former heads according to a third embodiment, where a having at least one blasting unit arranged on the screen.
[0076] FIG. 18 illustrates a flow diagram.
[0077] FIGS. 19A-19B depict a sample produced by using a former head according to the invention.
DETAILED DESCRIPTION
[0078] The invention relates to a former head 1 of the kind is used for forming a fibrous web, such as in a dry forming process. Fibres are supplied to the former head 1, normally in an entangled form, suspended in an airstream. The airstream with the fibres enters the former head 1 via at least one former head injection inlet 2, in a delivery direction DD opposite the rotation direction RD of a roller 10.
[0079] Referring to FIG. 1, the former head 1 according to the invention is shown as comprising the roller 10 which is generally cylindrical and which extends between two roller ends 12, 12′, shown in FIG. 4. The roller 10 is mounted for rotation in the rotation direction RD around a rotation axis A, and an air impervious structure referred to in the following as screen 20 covers or extends along at least part of an upper side of the roller 10, in the shown example along at least a portion of the roller 10 above a horizontal plane HP extending through the rotation axis A.
[0080] In the presently illustrated embodiment the entire upper side of the roller 10 is covered by the screen 20 which has an injection opening 24 through which the mixture of fibres and air is supplied via the injection inlet 2. The injection opening 24 in the screen 20 is arranged at a level above the aforementioned horizontal plane HP. The screen 20, or an underside 21 of the screen 20, is shaped to provide a peripheral gap 22 between the underside 21 of the screen 20 and the surface 11 of the roller 10. In the presently illustrated embodiment the provided peripheral gap 22 has a constant or substantially constant width W.
[0081] The roller 10 is provided with a plurality of projections 13 extending radially outwardly from the roller surface 11. In the presently illustrated embodiment the plurality of projections 13 are twenty-four rows of pointed needles/pins, or twenty-four needle strips extending along the length L, shown in FIG. 4, of the roller 10 parallel with the rotation axis A, also shown in FIG. 4, wherein each needle has a length LR. The number of rows of needles or needle strips may vary from a minimum of e.g. four rows of needles or needle strips to as many as may be fitted on the roller surface 11. The rows of needles or needle strips may in the presently illustrated embodiment arranged on the roller surface 11 with a constant or substantially constant distance in-between each row of needles or needle strips and in-between the individual needles.
[0082] In the presently illustrated embodiment the delivery direction DD of the mixture of fibre and air and thus the orientation of the injection inlet 2 is parallel with a vertical plan VP extending through the rotation axis A. The delivery direction DD may vertically downward or substantially vertically downward. As an alternative and as shown in broken line in FIG. 10, the delivery direction DD, and thereby the orientation of the injection inlet 2, may be inclined relative to a plane parallel with the vertical plane VP, with the delivery direction DD remaining opposite or substantially counter to the rotation direction RD of the roller 10. This is in order to ensure in any case that as the flow of air with fibres enters the peripheral gap 22 the entangled fibres will collide with the plurality of projections 13 moving in a direction against the flow of fibres, thereby proving a strong impacting force on the fibres. As shown in FIG. 11, by the term “substantially counter to the rotation direction RD of the roller 10” is meant that an angle α between a plane P extending through the rotation axis A of the roller 10 and towards or through the outlet of the injection inlet 24 and the delivery direction DD is less than 180 degrees.
[0083] The screen 20 may additionally be provided with a plurality of projections 23, 23′, 23″ extending radially from the underside 21 of the screen 20 into the peripheral gap 22. The plurality of projections 23, 23, 23″ may be divided into two groups of projections. A first group of projections 23′ is provided on a first portion 20′ of the screen 20 extending from the injection opening 24 and along the rotation direction RD of the roller 10; this first group of projections 23′ assist in the disentanglement of the fibres. A further, second group of projections 23″ is provided on a second portion 20″ of the screen 20 extending from the injection opening 24 and opposite the rotation direction RD of the roller 10; this second group of projections 23″ assist in preventing the fibres from moving in a direction counter to the direction of rotation of the roller 10.
[0084] In the presently illustrated embodiment this plurality of projections 23, 23′, 23″ are rows of pointed needles/pins or needle strips running along the length of the screen 20 parallel with the rotation axis A of the roller 10. Eight rows of needles or needle strips are in the shown example arranged on the first portion 20′ of the screen 20 and three rows of needles or needle strips are arranged on the second portion 20″ of the screen 20. The needles/pins of each row of needles or needle strip are arranged at a mutual distance corresponding to the mutual distance between the needles in each row on the roller 10 to allow for the passage of the roller projections between the screen projections as the roller 10 rotates. The projections/needles 23, 23′, 23″ have a length LS, which may be the same for all projections, or which may differ.
[0085] Referring to FIG. 2, the needles/pins or needle strips on respectively the roller surface 11 and the underside of the screen 20 provides an overlap O to increase the separation/disentanglement of the fibres and/or the dispersion of the fibres in the air or airstream. As an alternative the underside 21 of the screen 11 may be a smooth surface (not shown), i.e. without any of the projections referred to.
[0086] Returning to FIG. 1, the second portion 20″ of the screen 10 may be provided with an air inlet 27 which provides an airlock, allowing an airstream to flow into the peripheral gap 22 in a supply direction SD towards or substantially towards the rotation axis A of the roller 10, wherein the latter airstream SD is guided to flow opposite the rotation direction RD of the roller 10 when hitting the roller 10 and/or entering the peripheral gap 22.
[0087] The second portion 20″ of the screen 20 may further be provided with an end piece 26 which also may be part of the airlock. Starting from the injection opening 24 in the screen 20 and looking against the rotation direction RD of the roller 10, the second group of projections 23″ is arranged closest to the injection opening 24 in the screen 20, the end piece 26 is arranged furthest from the injection opening 24 and the air inlet 27 is arranged there in-between, i.e. between the second group of projections 23″ and the end piece 26. As shown in FIG. 3 the air inlet 27 may comprise a perforated plate 28 being respectively openable and closable and being arranged in a second opening in the screen 20 extending along the entire length L or substantially the entire length L of the roller 10 parallel with the rotation axis A of the roller 10, shown in FIG. 4. As an alternative the plate 28 may comprise multiple sections of perforated plates 28 with holes a number of holes 281 (shown in FIG. 15b) arranged in one or multiple second openings in the screen 20. The end piece 26 protrudes into the peripheral gap 22 so that the width W of the peripheral gap 22 becomes equal or substantially equal to the length LR of the projections 13 on the roller 10, i.e. in the presently illustrated embodiment the length LR of the needles extending from the roller surface 11. A distance between the tip of the projections 13 and the end piece 26 may be about 1 mm.
[0088] The airlock comprising at least the air inlet 27 may assist in ensuring that the supplied fibres are conveyed in the rotation direction RD of the roller 10, to exit the peripheral gap 22 at a first exit opening 29 of the peripheral gap 22. The end piece 26 combined with the air flow SD additionally assist in clearing away fibres remaining on the roller 10 on leaving the gap 22 at exit 29. By using a suction box underneath the former head 1, it is possible to enhance the distribution of the fibres during the step of conveying the fibres onto the former wire 101. During the step of placing the fibres on the former wire, the former wire is able to convey the fibres in the conveying direction, preferably in a continually operation.
[0089] As an alternative to the embodiment illustrated in FIGS. 1 and 4, and now referring to FIGS. 5-8, the plurality of projections 13 on the roller may be replaced by blade flails or rows of blade flails as illustrated in FIG. 5, or a carding plate or carding plate segments as illustrated in FIG. 6, or a rasping plate or rasping plate segments as illustrated in FIG. 7, or carding wires as illustrated in FIG. 8. And the plurality of projections 23, 23′, 23″ on the screen 20 may be replaced by a carding plate or carding plate segments as illustrated in FIG. 6, or a rasping plate or rasping plate segments as illustrated in FIG. 7, or carding wires as illustrated in FIG. 8. Alternatively, the underside 21 of the screen 11 may be a smooth surface (not shown), i.e. without projections. The smooth surface may be a perforated smooth surface accommodating an air intake into the peripheral gap 22.
[0090] Now referring to FIG. 9, an end view of the former head 1 illustrated in FIG. 1 is shown wherein the former head 1 comprises two end walls 30 where in-between the screen 20 extends, one of the end walls 30 being shown in FIG. 1 and the other end wall 30 being shown in FIG. 9. The two end walls 30 enclose the roller 10 at each end 12, 12′ of the roller 10 (shown in FIG. 4) and provides together with the screen 20 a housing being open in the bottom and thus partly enclosing the roller 10. The orientation of the opening in the bottom may be slightly angled in order to turn or orientate the fibres from the fibre head 1 into the moving direction of the former wire 101, i.e. in the wire direction WD.
[0091] Now referring to FIG. 10, the former head 1 may be provided with a perforated plate 40 covering or extending along a lower part of the roller surface 11 below the horizontal plane HP extending through the rotation axis A. The perforated plate 40 may be shaped like the periphery of the roller surface 11 and/or substantially like the periphery of the roller surface 11 and/or extend in continuation of the underside 21 of the screen 20 from the first exit opening 29 of the peripheral gap 22 towards the end piece 26/second exit opening 31 of the peripheral gap 22.
[0092] Now referring to FIG. 11, the underside 21 of the first portion 20′ of the screen 20 may be arranged to have a varying distance R from the rotation axis A of the roller 10. The varying distance R may decrease from the injection opening 24 towards the first exit opening 29 such that the width W of the peripheral gap 22 between the roller surface 11 and the underside 21 of the screen 20 is decrease by up to e.g. 40% at the first exit opening 29 compared to the width of the peripheral gap 22 at the injection opening 24. To receive the projections on the roller 10 grooves may be formed in the underside 21. Alternatively, the projections may be bendable, allowing for the projections 13 on the roller 10 to be received in the peripheral gap 22 by bending.
[0093] Referring now to FIG. 14, an apparatus 100 according to the invention is shown comprising the former head 1 according to the invention and as described above, wherein the apparatus 100 further comprises a former wire 101 being moved conveying direction, i.e. in a wire direction WD, and a vacuum suction box 102 configured for sucking the fibres individualised by the former head 1 towards and onto the former wire 101. The screen 20 and the end walls 30 may extend towards or to the former wire 101. The wall plates 120 may be transparent in order to provide a visual view into the forming wire 101 being arranged below the former head 1.
[0094] The apparatus 100 may further comprise a first and a second web roller 130, 131 wherein the provided fibrous web may leave the former head by being transported between the second web roller 131 and the former wire 101. The first and second web roller 130, 131 may be moveable or adjustable towards and away from the former wire 101 by means of adjusting means such as pistons 232, also shown in FIG. 3. The first and second web roller 130, 131 may further prevent that the fibres below the former head 1 is blown around in a turbulent way by unwanted airflows entering between the former head 1 and/or the wall plates 120 and the former wire 101, so that a fibrous web having an irregular g/m2 profile is provided.
[0095] Referring to FIG. 12, the injection inlet 2 shown in the presently illustrated embodiment is compatible with a longitudinal injection opening 24 in the screen 20 of the former head 1. The injection inlet 2 may further be provided with regulating means 3 for regulation of the velocity of the mixture of fibres and air through the injection inlet 2 and/or for regulating the thickness/weight, such as the g/m.sup.2 profile, of the provided fibrous web.
[0096] Referring now to FIGS. 15a-17b, the former head 1 may be connected to an apparatus 100 identical to the apparatus shown in FIG. 14. In all the embodiments shown in FIGS. 15a-17b, the former head 1 is positioned above the former wire 101 and a suction box 102 is configured for applying suction underneath the former head 1. By using a suction box underneath the former wire and the former head, it is possible to enhance the distribution of the fibres during the step of conveying the fibres onto the former wire 101 as the former wire moves the fibers in the conveying direction, i.e. in a wire direction WD. Fibres are supplied to the former head 1, normally in an entangled form, suspended in an airstream. The airstream with the fibres enters the former head 1 via at least one former head injection inlet 2, in a delivery direction DD opposite the rotation direction RD of a roller 10.
[0097] FIGS. 15A-15B show, the former head 1 according to first embodiment of the invention used for forming of fibrous web. The air inlet 27 comprises at least one perforated plate 28, preferably three perforated plates 28 as shown in FIG. 15b. The perforated plate 28 can be arranged along the circumference of the screen 20 and each perforated plate 28 is slidable relative to the screen 20 between an open and a closed position. Each perforated plate 28 may include a number of holes 281 having a diameter of 1-10 mm, preferable 2-8 mm, most preferably 2-5 mm.
[0098] In FIG. 15a, the air inlets 27 are designated as with the reference numbers 27a to 27d. Air inlet 27a represents a first preferred position for the air inlet, air inlet 27b represents a second preferred position for the air inlet, air inlet 27c represents a third preferred position for the air inlet, and air inlet 27d represents a fourth preferred position for the air inlet. Each of the air inlets 27a, 27b, 27c, 27d allows an airstream to flow into the peripheral gap 22 in the supply direction SD towards or substantially towards the rotation axis A of the roller 10. The supply direction SD of the airstream will depend on the position of the individual air inlet. As shown in FIG. 15A, it is possible to position one air inlet 27a along the circumference of the screen 20 or arrange one or more air inlets 27b, 27c on the surface of the former head injection inlet 2. The airstream SD is guided to flow in the rotation direction RD of the roller 10 when encountering the roller 10 and/or entering the peripheral gap 22. In a fourth preferred position for the air inlet 27d, it is also possible to arrange the air inlet 27d at the second portion 20″ of the screen 20. The airstream SD enters through the air inlet 27d, where the airstream SD will be guided to flow in the opposite direction of the rotation direction RD of the roller 10 when encountering the roller 10 and/or entering the peripheral gap 22. Beside the above mentioned positions for the air inlet, it is also possible to combine the air inlets 27a with air inlets 27b, air inlets 27a with air inlets 27c, air inlets 27a with air inlets 27d etc. The screen 20 would have a number of apertures for allowing the flow of air to enter the peripheral gap 22 and the number of apertures and position of the apertures corresponds to the number and position of the air inlet.
[0099] The air inlets 27 would as mentioned before be operable between an open and a closed position by movement of the least one perforated plate 28 arranged at the air inlet 27. Movement of the perforated plate 28 can either be achieved by a manual operation performed by a machine operator or by an actuator being connected to the controller of the apparatus 100.
[0100] The airstream DD containing the fibres can be construed as the primary airstream and the airstream SD can be construed as a secondary airstream. The airstream DD enters the former head 1 via at least one former head injection inlet 2, in a delivery direction DD opposite the rotation direction RD of a roller 10.
[0101] FIGS. 16A-16B show a second embodiment of the former head 1 according to the present invention used for forming of fibrous web, where one or more air inlet can be arranged along the circumference of the former head 1. In the second embodiment of the former head, the air inlets are formed as a number of air inlet manifolds via a number of holes for allowing air to be blown into the former head 1. The air inlet manifolds are designated as with the reference numbers 204a, 204b, 204c, 204d. The air inlet manifold 204a represents a first preferred position for the air inlet, the air inlet manifold 204b represents a second preferred position for the air inlet, the air inlet manifold 204c represents a third preferred position for the air inlet, and the air inlet manifold 204d represents a fourth preferred position for the air inlet.
[0102] The air inlet manifolds may be connected to an air supplying source such as an air pressure system for delivering compressed air to the former head 1 of the apparatus, more specifically for delivering compressed air into the peripheral gap 22 of the screen 20. The air pressure system may be configured for regulation the air pressure, which can be achieved by a regulating element such as a valve. In the presently illustrated embodiment the provided peripheral gap 22 has a constant or substantially constant width W. Instead, the screen 20 may be formed with a decreasing width continually decreasing from the injection opening in the screen and in the rotation direction of the roller as shown in FIG. 11.
[0103] As shown in FIG. 16A, it is possible to position a number of air manifold 204a, 204d along the circumference of the screen 20 or position a number of air manifolds 204b, 204c on the surface of the former head injection inlet 2. The airstream SD is guided to flow in the rotation direction RD of the roller 10 and the airstream will be conveyed into peripheral gap 22. In a fourth preferred position for the air inlet 27d, it is also possible to arrange the air inlet 27d. The airstream SD is guided to flow in the opposite direction of the rotation direction RD of the roller 10 when encountering the roller 10 and/or entering the peripheral gap 22. Beside the above mentioned positions for the air inlet, it is also possible to combine the air inlets 204a with air inlets 27b, air inlets 27a with air inlets 27c, air inlets 27a with air inlets 27d etc.
[0104] The airstream DD containing the fibres can be construed as the primary airstream and the airstream SD can be construed as a secondary airstream. The airstream DD enters the former head 1 via at least one former head injection inlet 2, in a delivery direction DD opposite the rotation direction RD of a roller 10.
[0105] FIGS. 17A-17B show the former head 1 according to a third embodiment of the invention used for forming of fibrous web, where one or more air inlets can be arranged along the circumference of the former head 1. In the third embodiment of the former head, the air inlets are formed as a number of air blasting units for allowing air to be blown into the former head 1.
[0106] In FIG. 17a, the air blasting units are designated as with the reference numbers 206a, 206b, 206c. The air blasting unit 206a represents a first preferred position for the air inlet, the air blasting unit 206b represents a second preferred position for the air inlet, the air blasting unit 206c represents a third preferred position for the air inlet.
[0107] As shown in FIG. 17A, it is possible to position one or more air blasting units 206a 206c along the circumference of the screen 20 or arrange an air blasting unit 206b on the surface of the former head injection inlet 2. The airstream SD is guided to flow in the rotation direction RD of the roller 10 and the airstream will enter the peripheral gap 22. In a third preferred position for the air blasting unit 206c, it is also possible to arrange the air inlet 27d. The airstream SD is guided to flow in the opposite direction of the rotation direction RD of the roller 10 when encountering the roller 10 and/or entering the peripheral gap 22. Beside the above mentioned positions for the air inlet, it is also possible to combine the air inlets 27a with air inlets 27b, air inlets 27a with air inlets 27c, air inlets 27a with air inlets 27d etc.
[0108] Each of the air blasting units may be connected to an air supplying source such as a high pressure fan for delivering compressed air to the former head of the apparatus, more specifically for delivering compressed air into the peripheral gap 22 of the screen 20. The air pressure system may be configured for regulating the air pressure, which can be achieved by regulating the speed of the fan on the ventilator. In the presently illustrated embodiment the provided peripheral gap 22 has a constant or substantially constant width W. Instead, the screen 20 may be formed with a decreasing width continually decreasing from the injection opening in the screen and in the rotation direction of the roller as shown in FIG. 11.
[0109] Independent of the position of the air blasting unit 206a-206c, the air inlets are formed for allowing an airstream to flow into the peripheral gap 22 in the supply direction SD towards or substantially towards the rotation axis A of the roller 10. The supply direction SD of the airstream will depend on the position of the air inlet.
[0110] FIG. 18 illustrates a flow diagram for a specific hole size according to a preferred embodiment of the air inlet. As mentioned with reference to FIGS. 15A-15B, the air inlet 27 may comprise at least one perforated plate 28 with a number of holes 281. Each perforated plate 28 can be arranged along the circumference of the screen 20 and each perforated plate 28 is slidable relative to the screen 20 between an open and a closed position. Dependent on the diameter of the holes 281 in each perforated plate 28, the air flow into the peripheral gap 22 of the screen 20 will vary. As shown in the flow diagram, the best possible fibre dispersion was with an airflow in the region of 30 to 60 m/s and 0.4 to 1.0 bar.
[0111] The measurement was obtained by supplying compressed air to a perforated plate at 0.1-1.0 bar. The diameter of the hole 281 in the perforated plate was in the range of 2-5 mm. The specific test result shown in FIG. 18 was obtained with a perforated plate having a hole diameter of 2 mm. The test was performed by using a manometer to measure the air inflow pressure of the compressed air flow at a position before the air flow passed through the hole in the perforated plate, so that it was possible to compare the air flow at four different measuring points after the compressed air had passed through the hole. The first graph A depicts a measurement obtained at a distance of 8 mm from the hole. The second graph B depicts a measurement obtained at a distance of 16 mm from the hole. The second graph B depicts a measurement obtained at a distance of 16 mm from the hole. The fourth graph D depicts a measurement obtained at a distance of 32 mm from the hole.
[0112] The test was performed on a former head having a setup as described with reference to FIGS. 15A, 16A and 17A.
[0113] In one specific test, the former head included two air inlets, where the air inlets were arranged at the positions 204a and 204b shown in FIG. 16A. Each of the air inlets included a manifold and a perforated plate (screen) arranged below the manifold. In the test set up, each of the perforated plates included a number of holes arranged in one row where the holes were arranged in a distance of one another.
[0114] FIG. 19A shows a fiber web formation 101 produced by a former head having two air inlets, where the airflow into the peripheral gap 22 of the screen 20 was disabled, so that an airflow through the air inlets 204a and 204b (shown in FIG. 16A was not possible. It is evident from FIG. 19A, that the fiber lumps consist of a lots of single fibers being entangled together and without an airflow through the air inlets web formation and appearance is not in the desired quality. FIG. 19B is showing an improved fiber web formation and appearance on the former wire 101, when an airflow is able to pass through the air inlets. By using two air inlets at the position 204a and 204b (see FIG. 16A), it is possible allow compressed air to be forced into the manifold at position 204a and 204b.
[0115] In the test, the fiber used was 100% fluff pulp, type GP 4822 (Cellulose fibers) and the pulp fibers are fiberized in a hammer mill and via air stream using a suction fan for the transport of fibers to the forming head. The process air temperature was 25 degree C. and humidity: 65%. The former head (forming head) had a working width of 600 mm. The produced fiber web at forming wire 101 had the following: 40 gram/m2 at capacity of 50 kg/h. The perforated plate arranged below the manifold includes a number of holes of ø3.0 mm arranged in one row in a direction being perpendicular to the wire direction WD at each of the air inlet positions 204a and 204b. The distance between each hole was 6.0 mm from center to center of each hole. In the test, the former head was installed with 166 holes per 1000 mm working width per position for each air inlet. The rotational speed (RPM) of the needle rotor was 2500 RPM (31 m/sec at the needle tip speed). Compressed air was delivered into the former head at 0,9 bar and the airflow in each nozzle according to FIG. 18 was set to 50 m/sec Even though the test was performed on a former head with air inlets positioned as shown in FIG. 16A, the same effect would also be achievable for a former head having air inlets as shown in FIG. 15A and FIG. 17A.
[0116] The present invention provides a teaching on how to obtain a better and more unified fibre distribution. According to the invention and the sample shown in FIG. 19B, small fiber lumps are dispersed in the process airflow inside the former head (forming head) and at the peripheral gap 22 (fiber inlet canal) of the screen 20. By using a number of air inlets, the end result is an even better fiber web formation and appearance at the forming wire 101. The air inlets could be arranged on the circumference of the screen or on the surface of the injection inlet 2 or any other position, where the air inlets could ensure a high airflow, hereby enabling that the fiber lumps would be dispersed in this position, by using compressed air. The fiber lumps Fb would be dispersed in the region XX shown in FIG. 16A. Each air inlet comprises a manifold and one or more perforated plates with holes positioned below the manifold.
