SE514412C2 - Method and apparatus for forming a fibrous web - Google Patents

Abstract

Method for forming multiply paper or board product, where all the plies are formed by means of roll forming of the type where the fibre suspension jet is introduced in the twin-wire nip at such a speed that the outer wire of the tensioned wires (2; 10; 17) is deflected while maintaining a substantially constant tension during the deflection of the outer wire, by the fact that the outer wire is supported by a rotating support (5; 14; 19), at least one of which being resiliently or displaceably mounted to compensate for said deflection. The forming of each ply occurs over only one forming roll (4; 11; 18), wherein the wire winding angle ( alpha ) over the forming rolls is at least 110 DEG , that the forming rolls are located alternatingly in two planes, that for the forming roll (rolls) in the upper plane the wires leave the roll in a lower quadrant (G, H) where the paper web follows the outer wire, and for the forming roll in the lower plane the wires leave the roll in an upper quadrant (E, F), where in this case the paper web also follows the outer wire.

Description

25 30 in 2 2. Co-shaping of all the layers in a forming unit using a multilayer irrigation box. Forming the layers on top of each other in a sequential process, i.e. forming the second layer on top of the first layer and the third layer on top of the second layer, etc. The present invention relates to this category.

Separate forming is usually performed with a multi-fourdrinier machine. Hybrid forming or double wire forming (see eg DE 44 02 273 A1) can also be applied. The increase in dewatering capacity provided by two or more forming units can also be used for increased production rates and / or reduced formation concentration for improved sheet properties. However, all variants of separate molding have one problem in common, namely the layer adhesion, which generally limits the strength of the multilayer product in the z-direction. Starch or another binder must often be sprayed on the layers before they are glued together.

However, since double wire forming would be preferred for speeds above 1000 rn / min, in order to avoid unstable surfaces and achieve higher drainage capacity, the problem of layer adhesion is exacerbated. This is because the layer formed with double wire forming has two wire sides with poor bonding ability, in contrast to a fourdriner layer, which has a wire side and a top side with better bonding ability.

Joining a multilayer product with a multilayer box can also be applied.

Examples of multilayer boxes are described in EP 0 681 057 A2 and in GB 2 019 465.

With this method, however, the dewatering capacity is limited to that provided by a single dewatering unit. Therefore, this principle is not suitable for high speed molding of moderate to high basis weights at low molding concentrations. In addition, to date, it has proved difficult to achieve acceptable co-shaping coating properties.

Multilayer forming in a sequential process has traditionally been applied to the formation of a two-layer linerboard using a second headbox located some distance downstream of a fourdrinier wire with drainage of the topsheet through the base layer formed upstream of the second headbox. The problem of layer adhesion is mainly avoided by depositing the top layer on top of the preformed layer. This means that the strength of the multilayer product in the z-direction is determined by the strength of the individual layers in the z-direction rather than by the layer adhesion. However, the formation of a top layer on top of a base layer on a fourdrinier wire entails fl your disadvantages.

It is sufficient to consider disadvantages with regard to drainage capacity and the serious basis weight variations which depend on the surface area and which occur in particular above 1000 m / min.

Dewatering in a double virazon created by the wire carrying the base layer and an additional pathless wire, through which the top layer is mainly dewatered, has been applied briefly or the second headbox in units that rely mainly on vacuum-generated dewatering (see e.g. Attwood (1991) "Mu1ti-ply forming", Pulp and Paper Manufacture Vol. 7 Paper Machine Operations, TAPPI &CPPA; p.250-25l). Dewatering through the previously formed layer is thus mainly avoided, whereby an improved dewatering efficiency is achieved. Dewatering of the top layer by a web-free wire is also advantageous in terms of purity and formation of the top layer, because a separate handling of the backwater from the top layer is possible and because an influence on the structure of the base layer on the top layer is mainly avoided.

However, the capacity of these units is limited and they are typically used on multilayer board machines that are slower than 600 m / min.

Roll forming according to Webster's method was introduced in its original form about four years ago (Us 1056319) and is well known from the field of high speed production of (single layer) printing paper. The forming takes place between two wires running over a rotating forming roll, by inserting the bone netting beam into the double wire nip at such a speed that the outer of the tensioned wires they fl are actuated while maintaining a substantially constant tension during the fl section of the outer wire, by the wire is supported by rotating supports, at least one of which is fi-resilient or dry-slidably mounted to compensate for the fl section. The dewatering rate is determined by the voltage of the outer wire divided by the instantaneous radius of curvature, and during roller dewatering the pressure increases rapidly during an initial phase, after which it flattens out to a plateau.

WO 99/09249 discloses a method and apparatus for multilayer forming using roll forming according to Webster's method to form a topsheet on top of a base coat. Preferably, roll forming according to Webster is applied to form all layers including the base shield. Two forming / dewatering rollers are shown for each forming unit.

According to one of the machine configurations shown, a long base wire runs through all dewatering units, which can cause problems regarding the wire stability when many dewatering units are used. According to another configuration shown, each wire runs over a maximum of two forming units. A problem with the latter configuration concerns the separation of one wire from the paper web and the other wire after the second roll in the forming units where the second dewatering roll lies over the first roll.

The separation takes place here by the outer wire over the second roller leaving it, while the paper web and the inner wire continue substantially horizontally towards the next forming unit. When separating one wire from the web and the other wire, there is a risk in the current dry matter area that pieces will come loose from the web. With a current configuration, pieces from the paper web can be thrown out of nips to fall onto the web due to gravity, which can lead to damage to the finished product and to web breakage.

Another disadvantage of previous machine constructions concerns the difficulty of achieving a sufficiently short fi in beam length after the headboxes for the second and the following layers.

The constituent wire comes substantially horizontally while the center of rotation of the breast roll is located substantially vertically above / below the center of the forming roll. The angle between the incoming wire and the connecting line between the center of rotation of the forming roll and the center of rotation of the breast roll (the "opening angle") is thus 90 ° in the construction described above. With a long free beam length, the beam tends to be broken up by instabilities before it hits the nip, which impairs the formation.

SUMMARY OF THE INVENTION The object of the invention is to provide a method for multilayering a paper or board product at high speed, which means a low investment cost while maintaining high drainage capacity and avoiding driveability problems related to pieces detached from the web during separation. of the one wire from the web and the other wire no. The rollers in the upper plane wire the roller in a lower quadrant, where the paper web follows the outer wire, and the forming roller (s) in the lower plane leave the roller in an upper quadrant, where also in this case the paper web follows. outer wire.

The wire enclosing angle should preferably be at least 120 ° in order to enable a high dewatering capacity.

In the forming rollers used for forming two and subsequent layers, according to a preferred embodiment variant, the wire with the incoming paper web is guided towards the respective forming roll at an angle of at least 10 °, preferably at least 15 ° relative to the horizontal plane. This allows space for the headboxes to avoid long free beam lengths.

The invention further relates to a device for forming a multilayer paper or board product which applies the above-mentioned method. Other features of the invention are set forth in the subclaims and in the description which follows. 10 15 20 25 30 Brief description of the drawings The invention will in the following be described in more detail with reference to an example of drying shown in the accompanying drawing.

Figure 1 schematically shows an example of a device for forming a three-layer web.

Figure 2 schematically illustrates the sectors where the wires leave the roller.

Figure 3 schematically illustrates the geometry around the headbox relative to the roller and incoming wires.

Description of exemplary connection A leg pin discharged from the headbox 1 is inserted into a nip created between two tensioned wires, an inner wire 2 and an outer wire 3, both of which enclose a rotating forming roller 4. The stock jet is inserted into the double wire nip at such a high speed that it exterior 3 of the tensioned viruses they ter are ectated as described in US-A-3,05 6,719, the contents of which are to be incorporated by reference into the present application. The tension on the outer wire 3 is kept substantially constant during the fl section, by being supported by a rotating support 5, which is resiliently or slidably mounted to compensate for said fl section. In order to reduce the cost of machine investment, the principle dewatering in each forming unit takes place over only one pre-roll 4, ie the wires run with the bersuspension / web in between over only one roll - the pre-roll 4. To achieve sufficient dewatering capacity, the outer wire 3 has an enclosing angle. be at least 110 ° and preferably at least 120 °. The roll diameter should be at least 1.2 m, preferably approx. 2 m.

According to the invention, the forming is completed during roll dewatering. Thereafter, the fi plant structure is substantially fi xerated so that no significant redistribution of the fi bridges occurs as the web passes over additional drainage elements. A further consolidation of the web can then take place according to well-known methods such as gusset rollers, suction boxes and the like before the web enters the press section or other forming unit. The wires 2, 3 leave the roller 4 in an upper quadrant (see Fig. 2), in the example shown the upper upward quadrant E, where the paper web follows you with the outer wire 2. The separation of the outer wire 2 with the accompanying web from the inner wire 3 takes place by ensuring with a suction box 6, or in another way, that the web follows the outer wire after the forming roll 4.

Banana. here the outer wire 2 follows upwards and is then passed over a reversing roller 7. Because the web and the outer wire 2 are now transported above the inner wire 3, the risk of drivability problems has been reduced by following any web pieces that came loose during the separation following the inner wire 3, from which they are removed with a booze or the like. Wires 2,3 can also leave the roller in the upper downward quadrant F.

The wire 2 then transfers the formed base layer to a second forming unit. Further dewatering can take place over suction boxes 8. The second forming unit comprises an inlet box 9, a double wire nip formed by the wire 2, which may now form an inner wire, and an outer wire 10, and a forming roller 11.

To avoid high machine conglomerations, the forming rollers are alternately placed in two planes. The height difference between the external points of the forming rollers is then limited to preferably not more than 4-5 m. The first forming roll 4 over which the base layer is formed is thus placed in a lower plane while the second forming roll 11 is placed in an upper plane. In the second forming unit, a second web layer is formed on the moist base layer, which preferably has a dry content of 7-15% by weight. The headbox 9 emits a äld blast jet into the double wire nip created by viruses 2 and ll). Also in this case the radiation is applied at such a speed that the outer wire 10 de fl is ignored. The tension on the outer wire 10 is kept substantially constant during the fl section, by being supported by a rotating support 12, which is resiliently or slidably mounted to compensate for said fl section. The forming takes place in the same way as in the first forming unit. The wires 2, 3 leave the roller 4 in a lower downward quadrant H (see Fig. 2), where the paper web follows the outer wire 10 downwards. The separation of the outer wire 10 with the accompanying web from the inner wire 2 takes place by ensuring with a suction box 13, or in another way, that the web follows the outer wire or the forming roller 11.

Here, the web follows the outer wire 10 downwards and is then passed over a turning roller 14. Any web pieces that came loose during the separation and followed the outer wire 10 are removed downwards when the outer wire 10 and the web are redirected over the turning roller 14. Further dewatering of the web can take place over suction boxes 15. it is conceivable that the wires 2, 10 arm the roller a bit into the lower upward quadrant G.

For a roller rotating in the counterclockwise direction in the upper plane, the viral roller preferably learns in the in this case downward quadrant G (Fig. G. 2).

In the third forming unit, a third web layer is formed on top of the other two formed layers. The third forming unit is located on the same plane - the lower plane - as the first forming unit. The inlet box emits a äld supernatant jet into the double wire nip created by wires 10 and 17. Also in this case the jet is set at such a speed that the outer wire 17, which is supported by a resilient or displaceable rotating support 19, they fl are ignored.

In the same way as in the first forming unit, the wires 10, 17 leave the roller 18 in an upper quadrant E (see Fig. 2), where the paper web follows the outer wire 17. The separation of the outer wire 17 with the accompanying web from the inner wire 10 takes place by securing - set with a suction box 20, or in another way, that the web follows the outer wire 17 after the forming roll 18. The web follows the outer wire 17 upwards and is then passed over a turning roller 21. Any web pieces which come loose during the separation follow the inner wire 17, from which they are removed with a wire spray or the like.

For most slest drawer constructions, a requirement for a short free beam length means an opening angle of at least 110 °. In all forming stations, therefore, an increased space has been created for the headboxes 4, 11 and 18 by angling the wire with the incoming web in relation to the horizontal plane. Thus, the wire with the incoming web forms an angle ß of at least 10 ° to the horizontal plane. This avoids long free beam lengths while reducing the reduction of the wire enclosing angle on the forming roll. Of course, the invention is not limited to the form of drying shown and described, but a number of modifications are conceivable within the scope of the claims.

The invention also includes that one or more of the headboxes may be a multilayer box.

Claims (10)

10 15 20 25 30 10 Patent claims 1. l. A method for forming a multilayer paper or board product, wherein all the layers are formed by roll forming of the type in which a multilayer jet is inserted into a double wire nip at such a speed that the outer of the tensioned wires (2; 10; 17 ) is deflected while maintaining a substantially constant tension during the flection of the outer wire, by the outer wire being supported by rotating supports (5; 14; 19), at least one of which is resiliently or slidably mounted to compensate for said fl section, I characterized in that the formation of each layer takes place over only one forming roll (4; 11 1; 18), that the wire enclosing angle (α) above the forming rollers is at least 110 °, that the forming rollers are placed alternately in two planes, that for the forming roll ( the rollers) (11) in the upper plane the wires (2,10) leave the roller in a lower quadrant (G, H), where the paper web follows the outer wire (10), and for the forming roller (-rollers) (4; 1 8 ) in the lower plane the wires (2,3 ; 10, 17) leaves the roller in an upper quadrant (E, F), where also in this case the paper web follows the outer wire (2; 17). 2. A method according to claim 1, characterized in that the wire circumference angular angle over the forming rollers (4; l1; l8) is at least 120 °. Method according to claim 1 or 2, characterized in that at least in the forming rollers (11; 18) used for forming layer two and subsequent layers, the wire (2; 10) is guided with the incoming paper web towards the respective forming roll ( l1; 18) at an angle (ß) of at least 10 °, preferably at least 15 ° relative to the horizontal plane. Method according to one or more of the preceding claims, characterized in that for the forming roller (s) (4; 18) in the lower plane the wires (22,3; 10,17) leave the roller in an upper upward quadrant ( E). 10 15 20 25 30 11 Method according to one or more of the preceding claims, characterized in that for the forming roller (s) (11) in the upper plane the wires (2, 10) screen the roller in a lower downward quadrant (H). An apparatus for forming a multilayer web of paper or board, in particular for forming a topsheet on top of a base layer, for carrying out the method according to claim 1, and which as the only forming unit for forming the respective layer comprises a roll forming unit of the kind in which a äld supernatant beam is inserted into a double wire nip between two tensioned wires (2,3; 2, 10; 10, 17) at such a speed that the outer (2; 10; 17) of the tensioned wires they fl are ignited, the device further comprising means for to maintain a substantially constant tension during the deflection of the outer wire, by the outer wire being supported by rotating supports (5; 14; 19), at least one of which is resiliently or displaceably mounted to compensate for said de characterized in that only one forming roll (4; 11; 18) is provided for forming each layer, that the wire enclosing angle (α) over the forming rollers is at least 110 °, that the forming rollers are placed alternately in two planes, that for the forming roller (s) (11) in the upper plane the wires are arranged to leave the roller in a lower quadrant (G, H), where the paper web follows the outer wire (10), and for the forming roller (s) (4; l 8) in the lower plane the wires are arranged to leave the roller in an upper quadrant (E, F), where also in this case the paper web follows you with the outer wire (2; l7). Device for forming a multilayer web according to claim 6, characterized in that the wire enclosing angle over the forming rollers (4; l l; 18) is at least 120 °. Device according to claim 6 or 7, characterized in that at least at the forming rollers (11; 18) used for forming layers two and the following layers form the wire (2; 10) with the incoming paper web at the respective forming roll (11; 18) an angle (ß) of at least 10 °, preferably at least 15 °, relative to the horizontal plane. 10 12 Device according to one or more of Claims 6 to 8, characterized in that for the forming roller (s) (4; 18) in the lower plane the wires (2,3; 10,17) are arranged to lean the roller in an upper upward quadrant (E). Device according to one or more of Claims 6 to 9, characterized in that for the forming roller (s) (11) in the upper plane the wires (2,10) are arranged to leave the roller in a lower downward quadrant (H).