EP0193075B1 - Process for making a multi-layer dewatering band endless, particularly a papermaker's wet-felt - Google Patents

Abstract

A method for seaming the ends of a papermaker's fabric during installation on papermaking equipment is disclosed. The method comprising the steps of: providing a base fabric having a batt needled thereto such that one end of the batt extends beyond the corresponding end of the base fabric to overlap the opposing end of the batt when the ends of the base fabric are joined; joining the base fabric to form a continuous belt; overlapping the extended end of the batt upon its opposite end; cutting the overlapping batt ends across the width of the fabric such that the opposing batt ends are configured to complement each other; combing each of the complementary batt ends such that the fiber dispersion of the batt material is decreased and the ends of the batt are lengthened; overlapping the combed batt ends; and needling the overlapping combed batt ends together and to the base fabric such that the batt material of each end of the batt is interdispersed with each other and the resultant material is essentially the same as the remainder of the fiber batt.

Description

The present invention relates to the connection of two sections of a composite wiping strip, and in particular of a wet-end felt for stationery.

Such a strip comprises on the one hand a canvas of woven, stiff and mechanically resistant threads, to withstand the tensioning forces of the strip and maintain intervals of passages for a liquid to be expelled, and on the other hand a sheet made up of fibers. fine and flexible intertwined to form a soft surface allowing to apply pressure to a deformable sheet to wring it without marking it.

If, to facilitate its manufacture or installation, this strip is installed on the rollers in open form but must then be looped over itself before its continuous use, or if sections of separate strips must succeed one another, the problem arises the connection of two sections. It can be resolved in a known manner with respect to the canvas. And it is also known to stop the plies of flexible fibers, at the two ends to be connected, so as to show, after the connection of the scrim, neither gap between these two plies nor overlap.

The object of the present invention is in particular to obtain good continuity between two such plies after the connection of the scrims.

It applies more particularly to the case where the composite wiping strip, two sections of which must be connected, is a stationery felt, which is advantageously manufactured and installed in the form of a strip having two ends, and which is then used, after connection of these ends, in the form of a tight band circulating in a closed loop. A felt thus connected can be called "junction felt".

In a stationery the almost liquid paper pulp is taken up by a permeable fabric circulating in closed loop and called "training fabric". On this canvas water flows from the paste, which then forms a sheet having a concentration of about 20% in dry matter (mainly cellulose fibers). This sheet then passes between spin rollers with the interposition of "wet end" felts. The pressure brings the water out of the sheet and this water flows through the interstices of these felts, which therefore must not be crushed under the pressure used. A dry matter content of the sheet is thus obtained, for example 45%.

The sheet is then transported, still on a felt circulating around rollers, in a drying zone where water is evacuated by evaporation under the action of heat, part of the steam passing through the felt.

It has long been known to use felts with a junction in the drying zone because on the one hand the sheet being dried is strong enough not to be easily irreversibly marked by its passage against the irregularity of the felt constituted by the junction area, and on the other hand the pressures applied by the rollers are relatively low, since they are not intended to perform a spin.

On the other hand, the risk of such marking is much greater in the "wet part" of the stationery because the paper is softer there and the pressures are stronger. This is why we have long used felts in this area without joining. The installation of these last presented however difficulties such that, to minimize them, one sometimes chose to use felt lighter and less stiff than it would have been suitable for the manufacture of paper. In addition, the manufacture of the felt in the tubular form prevented the loop from being given a length greater than twice the width of the loom which wove the canvas, which was sometimes troublesome.

We have therefore sought to use junction felts in this part too, and we have endeavored not to create any appreciable excess thickness or under-thickness of the felt in the connection zone. Methods are known for making the connection of the two scrims while respecting this condition. For example, in the case of a scrim formed by conventional weaving of long threads intertwined with wide threads, the ends of the long threads are provided, at weaving or after this, with loops forming longitudinal projections from from the end of each canvas. These loops are distributed across the width of the canvas. At the connection, the loops of one canvas are inserted between the loops of the other, and a transverse rod is passed through all these loops. This rod has a thickness comparable to that of the son in width of the entire canvas.

Other known connection methods can be used with different types of scrim.

Whatever the process used for the connection of the scrim, it appeared essential, to make a felt with junction usable as felt of wet part, to also ensure without appreciable irregularity the connection of the plies of flexible fibers. A process designed precisely to ensure such a connection is the subject of patent document EP-A -0 108 733 (Nordiskafilt AB). This process can be described by assuming that the length and width of the felt are horizontal and its thickness vertical, the web whose connection is described being above the canvas. The internal cohesion of this sheet and its attachment to the stiffer canvas are conventionally achieved by needling. According to this method, the sheet of flexible fibers is extended, during the manufacture of a first of the two sections of the felt to be connected, beyond the future connection line of the scrims. Obviously, not only can it not be attached to the canvas at this time in the area of this sheet beyond this connection line, but it is also omitted, or deleted, in an area below this line. A flexible flap is thus produced which can be raised to move it away from the canvas and allow the operations of connecting the canvas. This flap extends longitudinally on either side of the connecting line of the canvas. The free end of this flap and the tablecloth on

the second section to be connected are cut, over the entire thickness of the sheets and over the entire width of the felt, so that, when the connection of the canvas has been made and when the flap is lowered to cover the connection line of the canvas , the edge of the flap coincides with the edge of the second ply to be connected, that is to say that of the second section of the felt, along a ply connecting line. This avoids any excess or any defect in the ply material in the vicinity of the connection.

The inventor of this known method indicates that the connection line of the plies is disposed behind that of connection of the scrims, with respect to the direction of circulation of the felt in service. It indeed appears desirable that, when the felt passes between two pressure rollers, the force component applied provisionally rearward by these rollers does not risk displacing the free end of the flap towards its attachment to the rest of the first ply , which would form a fold that would mark the sheet of paper. Still for the same purpose, it is indicated that after connecting the canvas and putting the flap in its final position, needling is carried out to fix the flap to the canvas on either side of the connecting line of the canvas. It is also indicated, as an alternative, that the flap can be glued to the canvas. Apparently always for the same purpose, the figures in the document above show that the plane of cut and connection of the two layers is inclined relative to the vertical, that is to say that the line of connection of the layers appears more in rear at the upper part of the sheets than at their lower part, and that there is in fact a sheet connection zone whose longitudinal extension appears to be of the order of half the thickness of the sheets.

Although these various precautions are useful and may seem to the skilled person to resolve the problem entirely, their effect remains imperfect, that is to say that certain sheets of paper or the like produced with the help of such a felt receive a mark due to the connection of the ends of the felt of wet part thus constituted.

The present invention more particularly aims to avoid the damaging effects that may have in service the irregularities of a composite wiping strip, in particular of a stationery felt, in a connection zone between two successive sections of this strip. .

It relates to a connection zone, this strip comprising on the one hand a woven scrim (40) made up of strong and relatively large and stiff threads to withstand the forces applied to the strip parallel to its surface and to maintain intervals for easy circulation of a liquid even in the presence of a spin pressure perpendicular to this surface,

- This strip further comprising a ply (42) made of relatively fine and flexible fibers to form a soft and permeable support surface even in the presence of said spin pressure, the cohesion of this ply and its attachment to the canvas being obtained by needling, the surface density of the ply being the same for these two sections,

• - réalisation d'un premier et d'un deuxième tronçons de bande à raccorder, avec un premier (44) et un deuxième (48) canevas pourvus de moyens de raccordement mutuel (54) à leurs extrémités selon une ligne de raccordement de canevas, et avec une première (46) et une deuxième (50) nappes aiguilletées sur ces canevas, respectivement, un tronçon de longueur extrême d'au moins la première nappe étant séparé de son canevas pour former un rabat (52) qui peut être soulevé pour dégager la ligne de raccordement des canevas, -raccordement des deux canevas (44, 48) selon cette ligne de raccordement, chaque dit rabat (52) étant soulevé,
• - abaissement de chaque dit rabat pour couvrir la ligne de raccordement de canevas,
• - les extrémités des deux dites nappes ayant été préparées, au cours d'une étape antérieure oe préparation, pour que, après cet abaissement, la densité surfacique de matière de nappe soit constante dans la zone de raccordement et égale à celle des nappes des deux dits tronçons à distance dans cette zone, avec recouvrement de ces deux nappes sur une zone de raccordement de nappes présentant une extension longitudinale, - et aiguilletage final d'un rabat sur le canevas sous-jacent pour l'y fixer,
• - ce procédé étant caractérisé par le fait que l'extension longitudinale de ladite zone de raccordement de nappes (ZR) est au moins égale au double de l'épaisseur de ces nappes, ladite étape d'aiguilletage final du rabat étant effectuée également dans cette zone de raccordement de nappes, de manière à donner une cohésion propre à une nappe continue (42) constituée par lesdites première et deuxième nappes, et à éviter une variation locale de la compressibilité de la nappe.

- this process comprising the following steps:

• - production of a first and a second strip section to be connected, with a first (44) and a second (48) canvas provided with mutual connection means (54) at their ends along a canvas connection line, and with a first (46) and a second (50) needled plies on these scrims, respectively, a section of extreme length of at least the first ply being separated from its scrim to form a flap (52) which can be lifted to clear the connecting line of the scrims, connection of the two scrims (44, 48) along this connecting line, each said flap (52) being raised,
• - lowering of each said flap to cover the canvas connection line,
• the ends of the two said plies having been prepared, during a previous stage of preparation, so that, after this lowering, the surface density of the ply material is constant in the connection zone and equal to that of the plies of the two said sections at a distance in this zone, with overlap of these two plies on a zone of connection of plies having a longitudinal extension, - and final needling of a flap on the underlying canvas to fix it there,
• - This process being characterized by the fact that the longitudinal extension of said ply connection zone (ZR) is at least equal to twice the thickness of these plies, said final needling step of the flap also being carried out in this ply connection zone, so as to give a specific cohesion to a continuous ply (42) constituted by said first and second plies, and to avoid a local variation in the compressibility of the ply.

The reference numbers in parentheses refer by way of example to the attached figures. According to the present invention, it has also appeared advantageous to adopt, at least in certain cases, the following more specific provisions:

- According to a first embodiment of the invention, during said step of preparing the layers, each of said first and second (50) layers is first cut so that the edges of these two layers can come into coincidence if each said flap was lowered (52, 78, 80), then each of the ends of the sheet thus formed is combed by teeth driven into the thickness of the sheet and moving longitudinally towards the free end of this sheet, this combing being started on an extreme section of the ply of length at least equal to the thickness of this section and continued to lengthen the ply by at least this thickness, so as to create or lengthen said ply connection zone and to locally remove at least partially the entanglement of the fibers of these sections, to allow said final needling to exert its action under conditions similar to those of the formation and fixing of said first and second plies, and thus to confer more homogeneous compressibility on said continuous ply resulting from this final needling.

- According to a second embodiment of the invention, possibly complementary to the first, each of said first and second plies is constituted by the superposition of several layers (70, 72, 74, 76) occupying a succession of levels and fixed the to each other by needling, this process being characterized by the fact that during the said step of preparing the plies, these layers are cut according to the connecting lines of the layers distributed longitudinally over the said zone for connecting the plies, the needling of these layers the one on the other having been previously omitted in the connection area.

With the aid of the attached diagrammatic figures, a description will be given more particularly below, by way of nonlimiting example, of how the invention can be implemented. It should be understood that the elements described and shown can, without departing from the scope of the invention, be replaced by other elements ensuring the same technical functions. When the same element is represented in several figures, it is designated therein by the same reference sign.

Figure 1 shows the wet end of a stationery making newsprint, the direction of view being parallel to the axes of the spin rollers.

Figures 2, 3, 4 and 5 show side views of the connection area of a wet-end felt used in the stationery of Figure 1, in successive stages of the first embodiment of the method according to the invention , to connect two end sections of this felt previously engaged on the rollers of Figure 1, to form a felt closed loop of this figure.

Figures 6 and 7 show side and partial top views, respectively, of a needling apparatus for effecting the final sharpening of the method according to the invention.

Figures 8, 9 and 10 show views similar to those of Figures 2, 3, 4 and 5, but according to the second previously mentioned embodiment of the invention.

The modes of implementation which will be described more particularly include the provisions previously mentioned according to the invention.

In accordance with FIG. 1, a stationery producing newspaper paper has the following provisions:

A permeable fabric 2 circulates on rollers such as 4 and 6 after having taken liquid paper pulp from which the water has flowed. It thus forms an inconsistent sheet 8 whose dry matter content is of the order of 20% and which arrives according to arrow 10.

It is taken from this canvas by a felt of wet part 12, by means of a roller 14. A first pair of pressure rollers 16, 18 ensures a first spin. A second wet-end felt 20 separates this sheet from the roller 18. A second pair of rollers 22, 24 provides a second spin. The sheet is driven by the roller 24, of polished granite, to a third pressing zone formed by this roller and a roller 26 on which a third felt 28 circulates.

Its concentration of dry matter is thus brought to around 45%. Rollers 30, 32, 34 direct the sheet 8, along an arrow 36, to a drying zone, not shown.

The speed of circulation can go up to 2000 meters per minute. The pressures ensuring the spin can go up to 1100 kN per centimeter of width of the felt between rollers whose diameter can be between 0.4 and 2 m approximately. They cannot be reduced under penalty of reducing the efficiency of the spin and increasing the energy consumption in the drying zone which follows it. Under these conditions, any appreciable variation in thickness of the felt causes an indelible mark on the sheet 8.

According to FIG. 2, a felt such as the felt 12 which receives a sheet which is still very moist and soft comprises a scrim 40 consisting for example of polyamide threads whose diameter is of the order of 0.8 mm, and a ply 42, 3 mm thick for example in the absence of compression, and made up of needled fibers on themselves and then on the canvas. These fibers are also made of polyamide and have, for example, a diameter of less than 0.1 mm. The density of the sheet is for example 0.230 g / cm ³ . This felt is delivered to the stationery and installed around the rollers in the form of an open strip of the desired length. This length is not limited by the dimensions of the weaving looms that make the canvas. These two felt end sections are then connected to form a closed loop which is subsequently tensioned.

With reference to the direction of movement of the felt in service, a first of these sections of felt comprises a first canvas 44 and a first ply 46, the second section of felt comprising a second canvas 48, and a second ply 50. A flap 52 is formed at the end of the first ply, omitting the needling of the ply on the canvas over the corresponding length. These layers are formed with a length that is initially excess.

The end of each of the two scrims was formed with loops such as 54 distributed along the width of the felt with their centers arranged along a scaffold connection line. To connect the two scrims, the flap 52 is raised, their two connecting lines are brought into coincidence, the loops of one section passing between those of the other, and a connecting rod 56 is introduced into all these loops according to the common connection line. This rod will generally be stiffer than the wide threads of the canvas. Its diameter is for example 1 mm. The weaving of the canvas and this rod are chosen so that the thickness of the canvas is little changed in the connection area. Other known connection methods can be used, for example in the case where the canvas consists of propellers whose axes are arranged along its width, which follow one another for a long time.

linearly by interpenetrating and which are joined by stiff wires extending parallel to their axes in the interpenetration zones. In this case, the connecting rod can be identical to these stiff wires.

Known means are used to ensure mutual blocking of the various threads of the canvas, to prevent the latter from coming apart.

When the connection of the canvas has been made, the flap 52 and the end of the second ply 50 are cut, for example with a razor blade, possibly going slightly forwards while going down, according to two cutting planes parallel to the width of the felt and such that, if the flap is lowered, the two cutting planes, and therefore the two edges of the two plies in these planes, come into coincidence.

Then combing or carding is carried out. As previously mentioned and as shown by the arrows 58, using a brush or comb 60, this in the same way on the ends of the flap and of the second sheet. The two plies are thus lengthened, giving them a density which decreases towards the free end, and at the same time reducing the entanglement of the fibers and the cohesion of the ply. The situation shown in FIG. 3 is thus obtained.

According to Figure 4 the flap is lowered and pressed on the combed end of the second sheet.

The above-mentioned final needling operation is shown in FIGS. 5, 6 and 7. It is carried out using a portable jigsaw 62 on the market. In place of the saw blade of this apparatus, a board 64 of 1.5 x 2.5 cm has been mounted in which two rows of three vertical needles such as 66 projecting down have been fixed. The vertical reciprocating movement has, for example, an amplitude of 3 cm and the needles in the high position have their tips about 1 cm above the continuous ply being formed. These needles are of the type usually used for needling, for example with a triangular section and edges deformed locally to form barbs which entrain the fibers in their vertical movement to entangle them.

This needling is carried out over the entire connection zone until a thickness and compressibility of the ply are approximately equal to those of the ply on either side over the whole of this zone. This thickness and compressibility vary together and can be properly appreciated by passing your fingers over and next to this area. The guide plate 68 of the device 62 ensures the verticality of the needling.

The final needling with three distinct functions: one is the fixing of the flap to the canvas, the other is the restoration of the mechanical continuity of the web with respect to horizontal forces, and the third is the standardization of the vertical compressibility of the sheet.

In FIG. 5, the ply overlap zone is shown in ZR, the longitudinal extension of this overlap zone being at least twice the thickness of the ply.

According to the second embodiment of the invention previously mentioned, the sheet comprises several layers, each of which is formed from several needled webs one on the other. These layers are laid on the canvas previously described. The number of these layers is typically two as shown, but may be three. There are more precisely two first layers of first and second level 70 and 72 respectively, above the first canvas 44, and two second layers of first and second level 74 and 76 respectively, above the second canvas 48.

The needling of the first two layers 70 and 72 has been omitted in an area which should form with these two layers two first and second level flaps 78 and 80, which allow access to the scrim connection line. The needling of the second second level layer 76 has also been omitted to allow this layer to be raised to cut it without cutting the second first level layer.

The connection of the two sections of canvas 44 and 48 is carried out as in the first embodiment described above.

The layers are cut at each level (Fig. 9) so that after lowering the flaps the apparent continuity of each layer is ensured, that is to say so that at each level the edge of the first layer comes coincidence with that of the second layer. The two cutting lines, that is to say the connecting lines of layers of the two levels are chosen at the ends of the envisaged connection zone, (or in the vicinity if the preferred arrangement is adopted below).

If there were, for example, three levels of layers, the connecting line of the intermediate level would be made in the middle of this area.

According to a preferred arrangement not shown, combing is carried out at each level as previously indicated in the first embodiment of the invention, which lengthens the connection area.

The flaps are completely lowered (Fig. 10) and the previously described final needling is carried out, which performs the same functions as above.

The present invention is particularly advantageous in the case of the production of cartons. A type of stationery felt used in this case is said to be "long taker" (in English "long bottom felt" or "long top felt").

It is used to form the cardboard sheet by circulating on a succession of pulp feed rollers. It is of a light type (1000 g / m ² maximum) to first ensure the drainage of the dough by simple gravity, that is to say without pressure. But it is also used for subsequent spinning.

In this case the formation of the flap, by razor cutting for example, is difficult to carry out and compromises the service life or even the quality of service of the felt, this because this flap has a fiber density too low to hold (for keep its shape and dimensions). In this case, the invention makes it possible to use a junction felt.

The invention also appears particularly useful in the case of the manufacture of cotton wool (very light sheet: 15 to 30 g / m ² ) because in this case the discontinuity, even moderate, brought about by a cut in the snap of a Junction felt can create a relatively large variation in the consistency of the sheet produced. The present invention allows in this case the use of a junction felt as a "lifter, boarder and frictionneur".

Claims (3)

1. A method for joining two sections of a composite dewatering belt, particularly a felt for use in the wet section of a papermaking plant, with joining a first and a second section of the belt, each of which comprising respectively,

- a first (44) or a second woven canvas cloth (48) constituted of resistant and relatively coarse and stiff threads capable of supporting the stresses applied to the belt parallelly to its surface and of maintaining passage ways for the easy circulation of a liquid, even with the presence of a dewatering pressure directed vertically onto said surface,

- and a first (46) or second layer (50), constituted of relatively fine and flexible fibres needled to the corresponding canvas cloth in order to constitute a soft and permeable supporting surface, even with the presence of said dewatering pressure, the two layers having a same layer thickness and surface density,

- with the method comprising the following steps:

- implementing junction means (54) at the ends of said first (44) and second canvas cloth (48) in order to enable their mutual joining along a junction line,

- forming of at least one flap (52) constituted of a longitudinal end portion of at least the first layer, said end section being separated from the corresponding canvas for being lifted in order to expose the junction line,

- joining the two canvas cloths (44, 48) along said junction line, with the flap (52) being lifted,

- lowering each flap to cover said junction line,

- with the ends of the two layers having been prepared during an earlier stage of preparation, so that, subsequent to said lowering, both of the layers overlap within a zone of overlapping layers having a longitudinal extension, and the surface density of the matter constituting the layers in that overlapping zone is constant and equal to said layer surface density,

- and final needling of a flap on the underlaying canvas for fixing it thereto,

- this method being characterized in that the longitudinal extension of said zone of the overlapping layers (ZR) is of a length at least equal to twice the layer thickness, and that the final needling step of the flap is also effectuated in said zone so as to form a continuous layer (42) free from local variation of compressibility.

2. A method according to claim 1, wherein each of said first and second layers is constituted of a succession of several sublayers (70, 72, 74, 76) occupying a succession of levels and fixed one to another by needling, characterized in that during the preparation phase of the layers, the sublayers are cut along junction lines of the sublayers distributed longitudinally along said overlapping zone of layers with the needling of the sublayers with each other having been omitted previously in that zone.

3. A method according to claim 1 or 2, characterized in that during said preparation phase of the layers, each of said first (46) and second layers (50) or else each of said sublayers (70, 72, 74, 76) is beforehand cut in such a manner that the cutting faces of these two layers or two sublayers of each level are able to meet in coincidence, when each of said flaps (52, 78, 80) is lowered; that then each of the ends of a layer or sublayer thus formed is subjected to combing by means of teeth sunk into the thickness of the layer or sublayer while displacing themselves longitudinally towards the free end of that layer or else that sublayer with the combing being started on an end of the layer or sublayer having a length being at least equal to the thickness of this section and being continued for elongating the layer by at least said thickness, such as to create and lengthen said overlapping zone of the layers and to make locally disappear the intermingling of the fibres of these sections at least partially, in order to enable said final needling to exercise its action under conditions that are analogous to those of the formation and fixing of said first and second layers, and to confer in this matter a more homogeneous compressibility to the continuous layer resulting from the final needling.

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