EP0950733B1 - Method and installation for the forming of an airlay fiber web - Google Patents

Abstract

To produce a non woven fabric (V), the carded fibers are deposited on to a permeable conveyor belt (7a) by an air flow after they have been aligned (5). The fiber material is passed through a carding process (4) using a carding drum (4h) with a number of peripheral units (4e,4f) to separate and align the fibers in parallel. On leaving the carding drum (4h), the fibers are taken by the leading doffer cylinder (5a) at the carding drum (4h) surface with a rotation significantly slower then the carding drum, and in the opposite direction. The doffer cylinder has a clothing with the points aligned to the rear, against its direction of rotation. An Independent claim is included for an assembly with a carding stage (4), a conveyor (7a) at the air flow station (8), and a system to guide the air flow to project the carded fibers on to the conveyor. The fiber alignment station (5) gives a constant fiber flow to a final rotating cylinder (6) for delivery into the air stream. Preferred Features: The fiber alignment station (5) takes the fibers from the carding drum (4h) to gather them into a condensed web. The fiber alignment station (5) has at least a leading doffer cylinder (5a), and a second condensing cylinder (5b) at the circumference of the doffer (5a), rotating at a slower speed than the doffer and in the opposite direction and with a clothing where the points are aligned to the rear against its direction of rotation. Or the condensing cylinder (5b) rotates in the same direction as the doffer (5a), with a clothing where the points are aligned forwards against its direction of rotation. The delivery cylinder (6) is at the circumference of the condensing cylinder (5b), rotating at a higher or the same speed and in the same direction. Its clothing has points aligned forwards, in the direction of rotation. Or the delivery cylinder rotates at a high speed, and against the rotation of the condensing cylinder (5b), with clothing points aligned forwards in its direction of rotation. The assembly can have two fiber alignment stations (5), in parallel. With a single delivery cylinder (6), the second condensing cylinder (5b) is at its circumference. The air flow from the pneumatic unit (8) is directed towards the carding drum (4h) to assist in detaching the fibers from it. The delivery cylinder (6) has a rotary speed which is sufficient to detach the fibers from its surface by centrifugal forces.

Description

The present invention relates to the field of manufacturing a veil fibrous by air. More specifically, it relates to a process for forming a fibrous veil by dispersion and projection of fibers individualized, by means of an air flow, on a training surface and transporting the veil, the fibers having also been previously carded. The invention also relates to an installation for setting implementing this process.

We have known for many years a technique of forming a fibrous veil, by air, which is commonly known as " airlay " technique. This technique is characterized by the dispersion and projection of individual fibers, by means of an air flow, on a surface which is breathable and which allows the formation and transport of the fibrous web. The individualized fibers undergo during their course in the air flow a random dispersion, which is commonly called "random" effect , and which contributes to obtaining a better isotropy of the mechanical properties of the fibrous veil.

In the implementation of this "airlay" technique, the degree processing of fibers plays a major role on the homogeneity of the veil obtained. We understand that the more the fibers are individualized before being injected into the air flow, and the less there are risk that the fibrous veil ultimately contains residues or bundles of agglutinated fibers, which visually result in the presence of spots localized in the veil, and which affect the uniformity of the veil.

To prepare the fibers before their injection into the air flow "airlay", it has been known for many years to make a fiber carding operation upstream of this air flow. This carding operation is generally carried out by means of a carding system comprising at least one cylinder carding, which is equipped on its periphery with combing means having for function of individualizing and orienting each other substantially in parallel to the others the fibers situated on the periphery of the carding cylinder. AT By way of nonlimiting example, these combing means can so usual be constituted by a worker roller associated with a roller stripper, or more often by several successive pairs of these two types of rollers; These combing means can also be present in the form of a fixed fairing comprising a plurality of carding points, and commonly called carding plate. At the end of combing means arranged at the periphery of the carding cylinder, obtains fibers which are plated on the surface of the carding cylinder by being individualized and oriented substantially parallel to each other to others in the longitudinal direction, corresponding to the direction of progression of matter.

According to a first known method, combining upstream carding fibers and the "airlay" technique of forming a veil, we create the flow "airlay" air for the dispersion and projection of the fibers so that air flow is oriented substantially tangentially to the last cylinder carding system and comes into contact with the surface of this cylinder. This first process has already been described in numerous publications and corresponds for example to the solutions proposed in the European patent application EP-A-0.093.585 (CHICOPEE) or in the international patent application WO96 / 06964 (HERGETH HOLLINGSWORTH GMBH). In this first process, the fibers are detached from the carding cylinder both under the effect of the air flow and under the effect of centrifugal force, knowing that to achieve the function carding machine, the last carding cylinder rotates at high speed high. The air flow therefore has a double function: it helps detachment fibers from the surface of the carding cylinder; he directs the fibers, by randomly redirecting to a distant collecting surface breathable, for the formation and transport of the fibrous veil. In the particular variant of the international patent application WO96 / 06964, the dispersion of the fibers is further improved by the presence of an additional rotary cylinder (referenced 20 on the figures of application WO96 / 06964) driven at high speed in the direction reverse of the last carding cylinder (referenced 8 in the figures of the WO96 / 06964), and placed on the path of the fibers in the flow of air.

A second method has already been proposed in international patent application WO97 / 20976 (El DUPONT DE NEMOURS AND COMPANY) combining upstream carding of the fibers and the "airlay" technique for forming a web. This process is characterized by the implementation between the last carding cylinder of the carding system and the air flow "airlay" of a rotary dispersing cylinder, driven at high speed, and having the function of ejecting into the flow air "airlay" the fibers under the effect of centrifugal force. In this second method, the fibers are detached from the periphery of the dispersing cylinder only under the effect of centrifugal force, without assistance from the "airlay" air flow. In a first variant illustrated in FIG. 1 of this publication, the dispersing cylinder (reference 50) directly picks up the fibers at the periphery of the carding cylinder (referenced 40). In another variant shown in Figure 3 of this publication, there is interposed between the dispersing cylinder (50) and the carding cylinder (40), a transfer cylinder referenced (48), and also commonly called " communicator ". This cylinder has the simple function of taking up the fibers at the periphery of the last carding cylinder, and of transferring them as they are to the dispersing cylinder, without subjecting them to any transformation, and in particular without modifying their parallel orientation.

The first and second processes mentioned above are interesting in what they allow to obtain a satisfactory degree of working fibers, by a judicious adjustment, and perfectly mastered to date, of the action of the carding organs. However, we find in practice that it is not enough to obtain a high rate of working of the fibers alone to obtain a homogeneous fibrous veil, and that ultimately the predominant factor affecting the quality of the fibrous veil lies in the random dispersion of the fibers by the "airlay" air flow on the surface of training and transport of the veil. The parameters affecting this random dispersion are numerous and poorly controlled to date. Among these parameters, we find in particular the nature and length of the fibers, the speed, width and orientation of the airlay "airlay", the speed of rotation of the last cylinder (carding cylinder for publications EP-A-0.093.585 and WO96 / 06964; dispersing cylinder for publication WO97 / 20976). Adjustment of parameters affecting dispersion random fibers is therefore extremely delicate, and cannot definitive be done only experimentally, for a type of fiber given, by successive tests by checking the homogeneity of the veil got. Besides the aforementioned drawback which is common to the first and second process, and which is linked to the preponderance of dispersion random fibers under the action of airflow "airlay" to obtain of a homogeneous veil, the first method has the disadvantage additional to require a very powerful "airlay" air flow to allow the spotting of fibers, which in practice are very strongly linked to the last carding cylinder. Or the implementation of an air flow powerful causes air turbulence, which is difficult to to master, and which ultimately harm the homogeneity of the fibrous veil obtained, in particular by creating preferential groupings of fibers in the form of packages.

In the implementation of the second method, the air flow "airlay" does not function to detach the fibers from the periphery of a cylinder, and in this case the dispersing cylinder, and it can therefore advantageously be lower compared to the first process cited above. The counterpart is the obligation to train a cylinder at very high speed (dispersing cylinder), which from an energy point of view is expensive, and is more delicate from a mechanical point of view, in particular due to the vibrational phenomena that can be generated on the cylinder. In addition, this second method recommended in the application for international patent WO97 / 20976 also has a drawback additional, which is linked to the choice of the peripheral lining of the dispersing cylinder. Indeed, the peripheral lining of the cylinder disperser must meet two contradictory constraints. She must on the one hand be aggressive enough to allow a recovery effective fibers at the periphery of the upstream cylinder (carding cylinder in the first variant, or "communicating" cylinder in the second variant), and thereby avoid damaging engorgement of this upstream cylinder, while being on the other hand not very aggressive to allow the fibers to be ejected under centrifugal force, and to avoid retention of fibers at the periphery of the dispersing cylinder. So we are forced to choose for the teeth of the lining of the dispersing cylinder an opening angle and a density of teeth which allow to obtain a compromise between these two contradictory constraints. This choice for the the dispersing cylinder lining is therefore very delicate and furthermore limit.

The present invention provides a new training process a fibrous veil, which is similar to the first and second processes aforementioned in that it combines an "airlay" technique of forming a fibrous veil to an upstream preparation of the fibers by carding, but which has the advantage over these two known methods of rendering the random dispersion of the fibers under the action of the "airlay" air flow less preponderant for obtaining a homogeneous fibrous veil.

The process of the invention is known in particular by one or the other of the aforementioned publications in that a fibrous veil is formed on a training and transport surface, dispersing and projecting on this surface individualized fibers by means of an air flow, and in that the fibers are subjected to a carding operation beforehand when they are introduced into the air flow.

According to an essential characteristic of the process of the invention, between the carding operation and the introduction of the fibers into the air flow, one acts on the flow of fibers by means of one or more systems regulators to make this fiber flow more regular.

In the first and second methods of the prior art, the fibers that come from the cylinder last carding cylinder are very strongly individualized and oriented substantially parallel to each other to others, because of the carding action they underwent; they form what is commonly called a "parallel" veil, which presents very weak cohesion in the transverse direction. Now we see in practice that this carding action ultimately results in the production of a very irregular and non-homogeneous fiber web, even the flow material at the entrance of the card is constant. This can be explained by the on the one hand that the fibers being carded are strongly stretched, which causes the appearance of "holes" in the parallel veil from the carding, and on the other hand by the fact that the fibers have a time of more or less important course in the carding system, which mainly depends on their length; the shortest fibers are carded faster, while longer fibers have tendency compared to being retained longer in carding organs. Thus, in the first and second methods of the prior art, the rate of introduction of the fibers into the "airlay" air flow is completely irregular, which may explain, according to the applicant the preponderance of the action of random dispersion of the fibers by the flux airlay air to obtain a homogeneous fibrous veil. On the contrary in the process of the invention, by supplying the airflow "airlay" with a smoother fiber flow, the dispersion is advantageously made randomness of the fibers by the less preponderant "airlay" air flow for obtaining a homogeneous fibrous veil. In the process of the invention, it is also advantageously possible to act on the homogeneity and thereby the isotropy of the "airlay" fibrous veil obtained on the formation surface and transport, by acting directly on the flow of the veil fibers parallel from carding, which is easier.

According to a preferred embodiment of the method of the invention, on the one hand to carry out the fiber carding operation on implements a carding system which is intended to be supplied of fibrous material, and which includes a carding cylinder at the outlet equipped on its periphery with means having the function of individualizing and orient the fibers substantially parallel to each other located on the periphery of the carding cylinder, and on the other hand for to make the flow of fibers from the carding cylinder more regular, we implements at least one first comb cylinder which is arranged to the periphery of the carding cylinder, which is intended to be driven in rotation with a circumferential speed strictly lower than that of the carding cylinder and in a direction of rotation opposite to that of the carding cylinder, and which is coated on its periphery with a lining the teeth or points of which point backwards, that is to say the opposite of its direction of rotation. In this variant the comb cylinder acts as a regulating barrier to the fibers coming from the carding cylinder, by ensuring the recovery of only part of the fibers at the periphery of the carding cylinder, and regulating the flow of fibers. The speed of rotation of this combing cylinder will be fixed according to the flow of fibers desired output from this cylinder.

• un système de cardage qui est prévu pour être alimenté en matière fibreuse, et qui comporte en sortie un cylindre de cardage équipé sur sa périphérie de moyens ayant pour fonction d'individualiser et d'orienter sensiblement parallèlement les unes aux autres les fibres situées sur la périphérie du cylindre de cardage,
• une surface de formation et de transport du voile fibreux, qui est associée à des moyens de formation d'un flux d'air,
• et des moyens de reprise et d'introduction dans la zone du flux d'air de toute ou partie des fibres situées à la périphérie du cylindre de cardage, le flux d'air ayant pour fonction de disperser et de projeter ces fibres sur la surface de formation et de transport,

Another subject of the invention is an installation for implementing the above-mentioned method. This installation is known, in particular from international patent application WO 97/20976, in that it implements:

• a carding system which is designed to be supplied with fibrous material, and which comprises at the outlet a carding cylinder equipped on its periphery with means having the function of individualizing and orienting substantially parallel to each other the fibers located on the periphery of the carding cylinder,
• a surface for forming and transporting the fibrous web, which is associated with means for forming an air flow,
• and means for taking up and introducing all or part of the fibers located at the periphery of the carding cylinder into the air flow zone, the air flow having the function of dispersing and projecting these fibers onto the surface training and transportation,

• au moins un système régulateur qui a pour fonction de reprendre une partie seulement des fibres individualisées à la périphérie du cylindre de cardage, et qui est conçu pour délivrer en sortie des fibres avec un débit plus régulier,
• et un cylindre de sortie rotatif, qui a pour fonction de reprendre les fibres issues du système régulateur, et les amener dans le flux d'air.

Typically according to the invention, the means for taking up and introducing the fibers into the air flow comprise:

• at least one regulating system which has the function of taking up only part of the fibers individualized at the periphery of the carding cylinder, and which is designed to deliver fibers at the outlet with a more regular flow,
• and a rotary outlet cylinder, which has the function of taking the fibers from the regulating system, and bringing them into the air flow.

• la figure 1 est une représentation schématique d'une ligne de production d'un voile fibreux, par voie aéraulique selon la technique "airlay", mettant en oeuvre une installation de l'invention réalisée conformément à une première variante de réalisation ;
• la figure 2 une représentation schématique d'une ligne de production d'un voile fibreux, par voie aéraulique selon la technique "airlay", mettant en oeuvre une installation de l'invention réalisée conformément à une deuxième variante de réalisation;
• la figure 3 représente de manière plus précise les cylindres des systèmes régulateurs et le cylindre de sortie de la ligne de production de la figure 1, en faisant apparaítre notamment l'orientation des pointes des garnitures respectives de ces cylindres ;

Other characteristics and advantages of the invention will appear more clearly on reading the description below of two particular variant embodiments of the invention, which description is given by way of non-limiting example and with reference to the accompanying drawings on which:

• Figure 1 is a schematic representation of a production line of a fibrous web, by air using the "airlay" technique, implementing an installation of the invention carried out in accordance with a first embodiment;
• Figure 2 a schematic representation of a production line of a fibrous web, by air using the "airlay" technique, implementing an installation of the invention produced in accordance with a second alternative embodiment;
• Figure 3 shows more precisely the cylinders of the regulating systems and the output cylinder of the production line of Figure 1, showing in particular the orientation of the tips of the respective linings of these cylinders;

The production line for a fibrous web of FIG. 1 includes a traditional loader-weigher 1 which feeds, via a conveyor 2, an installation 3 which is carried out in accordance with the invention and which makes it possible to form at the outlet a fibrous veil V, by ventilation using the "airlay" technique.

• d'une carde 4,
• de deux systèmes régulateurs 5 délivrant deux voiles condensés en parallèle,
• d'un cylindre de sortie 6 permettant la reprise des deux voiles condensés délivrés en parallèle par les deux systèmes régulateurs 5,
• d'un convoyeur 7 comportant une courroie qui est perméable à l'air, qui est conçue pour entraínée dans le sens de la flèche F, avec une vitesse linéaire,de préférence réglable, et dont la portion rectiligne supérieure 7a fait office de surface de formation et de transport du voile fibreux V ,
• de moyens 8 permettant de créer un flux d'air "airlay" qui est orienté transversalement et en direction de la portion rectiligne supérieure 7a de la courroie du convoyeur 7.

In the particular example of FIG. 1, the installation 3 is made up:

• of a card 4,
• two regulating systems 5 delivering two condensed sails in parallel,
• an outlet cylinder 6 allowing the recovery of the two condensed sails delivered in parallel by the two regulating systems 5,
• a conveyor 7 comprising a belt which is breathable, which is designed to be driven in the direction of arrow F, with a linear speed, preferably adjustable, and whose upper rectilinear portion 7 has acted as a surface forming and transporting the fibrous web V,
• means 8 making it possible to create an “airlay” air flow which is oriented transversely and in the direction of the upper rectilinear portion 7 a of the conveyor belt 7.

The structure and operation of card 4 are traditional and will therefore not be explained in detail. In FIG. 1, the card 3 comprises a card entry constituted by a trough 4 a , a food roller 4 b and a breaker cylinder 4 c . The breaker cylinder 4 c supplies a first rotary carding cylinder 4 d , which is commonly known as the front end, and the surface of which is usually coated with a card lining or any other equivalent means enabling it to take up the fibers. from the periphery of the breaker cylinder 4 c . Usually, the carding cylinder 4 d is further provided on its periphery with combing means making it possible to work the fibers taken from the card lining of this cylinder, so as to individualize and parallelize them. In the particular example illustrated, these combing means consist of several successive pairs of a stripper roller 4 e and a worker roller 4 f . Downstream of these combing means, the fibers are taken from the periphery of the first carding cylinder 4 d and transferred in the state to a second rotary carding cylinder 4 h , by a transfer cylinder 4 g , also called a communicator. The second carding cylinder, also commonly called "large drum" or "main drum" is also coated with a carding lining or the like allowing it to take up the fibers at the periphery of the 4 g communicator, and is provided on its periphery with combing means (4 e , 4 f ) identical to those equipping the first carding cylinder 4 d .

The invention is not limited to a method or an installation using a card having the particular configuration of card 4 which has just been described with reference to FIG. 1. In particular, depending on the type of fibers to be open and the desired degree of processing of these fibers, it is possible to envisage using a longer card implementing at least three successive carding cylinders, or on the contrary a shorter card implementing a single carding cylinder. Furthermore, the rollers 4 e and 4 f could be arranged by being juxtaposed one behind the other in an alternating manner, according to a configuration commonly called "Garnett". The cleaning and working rollers (4 e , 4 f ) at the periphery of each carding cylinder could also be replaced by any means of different structure, but fulfilling the same function, that is to say having the function, in association with the carding cylinder, to individualize and parallelize the fibers on the periphery of the carding cylinder. In particular, these rollers could be replaced by static plates, commonly called "carding plates", mounted on the periphery of the carding cylinder and comprising a plurality of carding points in the form, for example, of grooves or grooves. For the aforementioned reasons, the invention therefore applies to any process and any installation for forming a fibrous web by air, generally using at least one rotary carding cylinder equipped on its periphery. means having the function of individualizing and orienting substantially parallel to one another the fibers on the periphery of the carding cylinder.

In the particular example of FIG. 1, each regulating system 5 is constituted by two successive cylinders 5 a and 5 b . The first roller 5a is of the type doffer cylinder, is disposed at the periphery of the second carding cylinder 4 h, and is adapted to be rotated together with a strictly lower circumferential speed than the carding cylinder 4 h, and in a direction of rotation opposite to that of the second carding cylinder 4 h . This cylinder 5 a is coated on its periphery with a lining comprising a multitude of points allowing the fibers to be taken up at the periphery of the carding cylinder 4 h . If one refers to FIG. 3, these points referenced 5 ′ a are oriented towards the rear, that is to say are oriented opposite to the direction of rotation of the cylinder 5 a and form with respect to the tangent to cylinder 5 has an angle A which is greater than 90 °. These points can be replaced by any equivalent means, and in particular by teeth or the like having the same orientation. The second cylinder 5b is disposed at the periphery of the first roller 5a and is provided to be rotated with a circumferential speed lower than that of the first roller 5a. In the example of Figure 1, the cylinder 5b is intended to be rotated in the opposite direction of the first roller 5a; in this case, the cylinder 5 b is coated on its periphery with a lining comprising a multitude of teeth or points 5 ′ b which are oriented towards the rear, that is to say if we refer to the Figure 3, which are oriented opposite the direction of rotation of the cylinder 5 b and form with respect to the tangent to the cylinder 5 b an angle B which is greater than 90 °.

The cylinders 5b of each regulating system 5 are arranged at the periphery of the single outlet cylinder 6. This outlet cylinder 6 is designed to be rotated with a circumferential speed greater than or equal to the circumferential speed of each cylinder 5 b and in the same direction of rotation. If one refers to Figure 3, the cylinder 6 is provided on its periphery with a covering whose tips 6a or teeth are directed forwardly with an angle of opening less than 90 ° C.

The means 8 for forming the “airlay” air flow mainly comprise a fan 9, the outlet of which is connected to a blowing channel 10, oriented substantially transversely to the forming and transport surface 7 has fibrous web V. In the 'particular example of Figure 1, this blowing channel 10 consists of an upper portion 10 a whose section is slightly decreasing, and which extends from the outlet of the fan 9 to the periphery of the outlet cylinder 6 , and a lower portion 10 b which extends the upper portion 10 a from the periphery of the outlet cylinder 6. This upper portion 10 b has a section which widens from the periphery of the outlet cylinder 6, and s 'extends to near the formation and transport surface 7 has the fibrous web V. Opposite the fan 9 is mounted a suction box 11, which preferably extends at least over the entire width L of the output section of the inner portion 10 b of the blow channel 10, the surface of forming and conveying 7a of the web V being interposed between this suction box 11 and the output of the blowing channel 10. In the example of Figure 1, the suction box 11 extends far beyond the outlet of the blowing channel 10, so as to allow effective maintenance of the fibrous web F on the surface 7 a during transport.

In operation, the second cylinder 5 b of each regulator system 5 is rotated with a circumferential speed which is smaller than the first cylinder 5a, which cylinder 5 a is further rotated with a circumferential speed that is strictly less to that of the second carding cylinder 4 h . The outlet cylinder 6 is rotated with a circumferential speed which is greater than or equal to that of the second cylinders 5b of each regulator system 5.

On the periphery of the second carding cylinder 4 h , downstream of the combing means (4 e , 4 f ), a very light fibrous veil is obtained, which is commonly called "parallel veil", and the fibers of which are very highly individualized and oriented substantially parallel to each other in the machine direction, that is to say along the circumference of the carding cylinder 4 h . This veil has very low mechanical strength in the transverse direction and is in practice pressed against the periphery of the carding cylinder 4 h , while being positioned in the bottom of the peripheral lining of this cylinder (FIG. 3). Taking into account the respective circumferential speeds of the cylinders 4 h , 5 a , 5 b and 6, and the orientation of the tips or teeth of their linings, the constituent fibers of the parallel web disposed at the periphery of the second carding cylinder 4 h undergo the following treatments. The first cylinder 5 a of the upper regulating system 5 takes up only part of these fibers, and redirects them by breaking their parallelism. This first cylinder 5 a is the main regulating member, which essentially acts on the flow of fibers so as to make this flow of fibers more regular. The reoriented veil from this first cylinder is therefore more homogeneous than the parallel veil from the periphery of the 4 h carding cylinder. The entire fibers of this web is resumed at the periphery of the first cylinder 5, by the second cylinder 5b, which has the effect of raising fibers, and thereby blurring and condense more strongly the veil. As shown schematically in Figure 3, the second cylinder 5b stores in its peripheral lining a large amount of fiber. In parallel, the cylinders 5 a and 5 b of the lower regulating system 5 carry out the same operations on the residual fibers of the periphery of the carding cylinder 4 h which have not been taken up by the upper regulating system 5. At the output of the two regulating systems 5, two condensed webs are obtained in parallel arranged at the periphery respectively of the second cylinders 5 b . These two condensed webs are taken up by the outlet cylinder 6, to be conveyed in the form of a single condensed web as far as the blowing channel 10 in which the air flow "airlay" is created.

In the contact zone between the airflow "airlay" and the periphery of the outlet cylinder 6, the fibers of the condensed web on the periphery of the outlet cylinder 6 are detached from this cylinder, are dispersed randomly in the channel blower 10, and are individually projected on the surface 7a of the conveyor being divided into a zone 12 for forming the fibrous web V, that if one refers to Figure 1 extends over a distance d in the direction advancement of the conveyor belt. The outlet of this zone 12, a fibrous web is obtained V "airlay" whose fibers have been reoriented in the three directions, that is to say in the longitudinal and transverse directions of the surface 7a of the conveyor, and in the direction perpendicular to the plane of this surface 7 a (thickness of the web V). This veil has improved homogeneity and isotropy compared to the parallel veil from the second 4 h carding cylinder. The density and the thickness of the fibrous web V will depend on the linear speed of the surface 7 a , that is to say on the linear speed of the conveyor 7.

In the particular variant of the installation of FIG. 1, the stain removal of the fibers from the periphery of the outlet cylinder 6 is obtained under the combined effects of the "airlay" air flow which comes into contact with the periphery of this cylinder and centrifugal force imparted to the fibers due to the rotation of the outlet cylinder 6. Preferably, the air flow "airlay" is created relative to the outlet cylinder 6 so that it enters the lining of this cylinder, so as to obtain the maximum efficiency for stain removal of the fibers. The fibers break off further more easily that the airflow "airlay" is oriented in a direction substantially tangential to the periphery of the outlet cylinder 6, and the teeth or spikes 6a of the liner of this cylinder outlet 6 are oriented in the direction of this airflow "airlay". In this variant, the air flow speeds "airlay" in the blowing channel 10, at the outlet cylinder 6, are preferably greater than the circumferential speed of the outlet cylinder 6, so that the air flow best assist in stain removal of fibers. It is up to the person skilled in the art to provide the air flow required for the fan 9, as a function of the circumferential speed of the cylinder 6, as well as the volume and the section of the blowing channel 10, in order to obtain the speeds d air required.

In another alternative embodiment, it is possible to envisage implement an output cylinder 6 which is driven with a speed high enough rotation that the stain removal of the fibers from the periphery of this cylinder could occur under the exclusive effect of the centrifugal force. In this case, the air velocities in the blowing 10 at the outlet cylinder 6 may be less than the circumferential speed of the output cylinder 6. Also in this other variant, it is not necessary that the airflow "airlay" crosses the lining of the outlet cylinder 6; this "airlay" air flow can be created so you just come to "lick" the ends of the tips or teeth of the cylinder of the outlet cylinder 6. To the extreme with a speed sufficient circumferential, it is conceivable that the air flow "airlay" does not come into contact with the outlet cylinder lining, but either slightly distant from the periphery of this filling.

In a specific embodiment given purely by way of nonlimiting illustration of the invention, the line in FIG. 1 was intended to produce a fibrous web from polyester fibers, having a titration of 1.7 dtex and an average length about 38mm. The diameter of the second carding cylinder 4 h was 900mm, and this cylinder was rotated at a speed of about 1500 m / minute; the diameter of the first comb cylinder 5a of each regulator system 5 was 500mm, and this cylinder was rotated at a speed of the order of 300 m / minute; the lining of each first cylinder 5 a had a density of points (or teeth) of approximately 46 points / cm ² and the opening angle A of these points or teeth was approximately 140 °; the diameter of the second condenser cylinder 5b of each regulator system 5 was 350 mm, and this cylinder was rotated at a speed of the order of 150 m / minute; the lining of each second cylinder 5 a had a density of tips (or teeth) of about 23 tips / cm ² and the opening angle B of these tips or teeth was about 140 °; the diameter of the outlet cylinder 6 was 500mm, and this cylinder was rotated at a speed between 150 m / minute and 3000 m / minute; the lining of this outlet cylinder 6 had a density of tips (or teeth) between 23 and 31 tips / cm ² , and the opening angle C of these tips or teeth was about 90 °.

The installation of the invention which has just been described with reference to Figures 1 and 3 has several advantages. The main advantage derives from the implementation, between the outlet of the card 4 and the "airlay" air flow, of at least one regulating system 5 advantageously making it possible to supply the blowing channel 10 with a flow of fibers which on the one hand is more regular compared to the flow of fibers at the output of carding machine 4, and which on the other hand can be adjusted mainly by adjusting the rotational speeds of the combing rollers 5 has regulating systems 5. It is thus possible by acting in particular on the speed of rotation of the combing cylinders 5 a of each regulating system 5, to modify the homogeneity and the isotropy of the fibrous veil V obtained at the outlet, and incidentally to improve the homogeneity and the isotropy of this sail. Comparatively in the solutions of the prior art, efforts to date have constantly been made to act on the “airlay” air flow directly on the parallel web coming from the card. For example, in European patent application EP-A-0.093.585 (CHICOPEE) or in international patent application WO 96/06964 (HERGETH HOLLINGSWORTH GMBH), the "airlay" air flow acts directly on the last cylinder of carding, which is the equivalent of the second carding cylinder 4h of the installation of FIG. 1. In the international patent application WO97 / 20976 (El DUPONT DE NEMOURS AND COMPANY), the air flow "airlay" acts on fibers which come from the periphery of a dispersing cylinder arranged downstream of the carding outlet; the fact remains that in this publication, the parallel orientation of the fibers during their transfer from the carding outlet to this dispersing cylinder has not been modified. It follows that in these solutions of the prior art, it is essentially the random effect of dispersion of the fibers in the air flow "airlay" which conditions the homogeneity and the isotropy of the fibrous veil obtained, and this random scattering effect must also be all the more effective as the fiber feed rate at the inlet of the blowing channel in the solutions of the prior art is very irregular. In the solution of the invention, the effect of random dispersion of the fibers in the “airlay” air flow continues to play a role in the homogeneity and the isotropy of the fibrous veil V obtained; however, this effect is less preponderant than in the previous solutions, and it is possible to act more easily on the homogeneity and the isotropy of the veil V, and thereby more easily improve the homogeneity and the isotropy of this veil, by judiciously regulating the flow of fibers by means of regulating systems.

Another advantage of the invention lies in the greater ease of detaching the condensed web from the periphery of the cylinder outlet 6, compared to the solutions of the prior art. So when the "airlay" air flow assists in spotting fibers from the periphery of the outlet cylinder 6, it is possible to implement an air flow less powerful, compared for example to the solution of publications EP-A-0.093.585 (CHICOPEE) and WO96 / 06964 (HERGETH HOLLINGSWORTH GMBH); when the stain removal of the fibers from the periphery of the outlet cylinder is obtained exclusively under the effect of centrifugal force, it is advantageously possible to obtain this stain removal of fibers with a lower circumferential speed to the output cylinder, compared for example to the speed circumferential which is necessary for the dispersing cylinder of the solution described in publication WO97 / 20976 (E.l. DUPONT DE NEMOURS AND COMPANY).

An additional advantage of the solution of the invention, compared for example to the solution recommended in publication WO97 / 20976 (El DUPONT DE NEMOURS AND COMPANY) lies in the possibility of opting for a slightly aggressive packing for the outlet cylinder ( lower density of the teeth or points of the lining and greater opening angle of these teeth or points relative to the tangent of the cylinder), and in particular less aggressive than the lining which must be used for the dispersing cylinder of the publication WO97 / 20976. This is explained by the fact that the resumption of the condensed veil at the outlet of each regulating system 5 is very easy to carry out, knowing that the fibers of this veil have been straightened and are not located in the bottom of the lining of this cylinder, unlike for example the fibers located on the periphery of the carding cylinder 4 h . However, the ability to use a slightly aggressive lining advantageously contributes to facilitating the spotting of the fibers from the periphery of the outlet cylinder 6.

The production line for a fibrous web, by air, of FIG. 2 differs from that of FIG. 1, only by the direction of rotation of the second cylinder 5 b of each regulating system 5. This direction of rotation is reversed relative to the direction of rotation of the outlet displacement 6. As a result, the teeth or points of each second cylinder 5 b are no longer oriented towards the rear as in the variant of FIG. 1, but are oriented towards the front . For this reason, in order to allow fibers to be taken up by the outlet cylinder 6, it is necessary in this variant that the circumferential speed of the outlet cylinder 6 be strictly greater than that of the second cylinder 5b . The variant of FIG. 2 has all the advantages of the variant of FIG. 1, and also has the additional advantage of avoiding a reversal of the condensed veil during the passage of this veil between the second cylinder 5b and the cylinder of exit 6.

The invention is not limited to the particular variant embodiments of FIGS. 1 and 2. It is notably possible to envisage using more than two regulating systems 5 in parallel, and distributed over the periphery of the carding cylinder 4 h ; the structure of a regulating system is not limited to the implementation of two successive cylinders 5 a and 5 b ; in particular, it will be possible to use a regulating system consisting solely of one or more combing cylinders 5 a and not comprising a condensing cylinder; in general, we can use instead of the two cylinders 5 a and 5 b , any structure ensuring the same function, that is to say ensuring the recovery of only part of the fibers at the periphery of the carding cylinder 4 h , and making it possible to improve the regularity of the flow of fibers, prior to their dispersion by the "airlay" air flow. In another variant, it is conceivable to provide an additional cylinder commonly known as a counter-drum, arranged tangentially both to the carding cylinder 4 h and to the first combing cylinder 5 a and driven in the same direction of rotation as the carding cylinder , and thereby with a direction of rotation opposite to that of the comb cylinder 5 a . It is also possible to eliminate the outlet cylinder 6, in particular when the installation comprises a single regulating system, and to make the air flow act "airlay" directly on the condensed web on the periphery of the second cylinder 5 b of each regulating system 5.

Claims (17)

1. A method of producing a fiber web by the airlay technique, in which a fiber web (V) is formed on a forming and transport surface (7a) by dispersing and projecting individualized fibers onto said surface by means of an air flow, and in which the fibers are subjected to a carding operation prior to being inserted into the air flow, the method being characterized in that between the carding operating and the insertion of the fibers into the air flow, action is taken on the fiber feed rate by means of one or more regulator systems (5) so as to make said fiber feed rate more regular.
2. A method according to claim 1, characterized in that to perform the fiber carding operation, a carding system (4) is implemented which is designed to be fed with fiber material, and which has at its outlet a carding cylinder (4h) fitted at its periphery with means (4e, 4f) having the functions of individualizing the fibers situated on the periphery of the carding cylinder and of orienting them substantially parallel to one another, and in that to make the feed rate of fibers from the carding cylinder (4h) more regular, at least a first combing cylinder (5a) is implemented which is disposed at the periphery of the carding cylinder (4h), which combing cylinder is designed to be rotated to have a circumferential speed that is strictly less than that of the carding cylinder (4h) and in a direction of rotation opposite to that of the carding cylinder (4h), and which is coated on its periphery with a covering whose teeth or spikes (5'a) point backwards, i.e. in the direction opposite to its direction of rotation.
3. A method according to claim 2, characterized in that the fibers are dispersed in the airlay airflow by means of a rotary outlet cylinder (6) that is rotated to have a circumferential speed that is strictly greater than that of the cylinder preceding it.
4. A method according to claim 3, characterized in that the outlet cylinder (6) ) is rotated at a speed of rotation that is high enough for the fibers to become detached from its periphery solely under the effect of centrifugal force.
5. A method according to claim 3 or 4, characterized in that the outlet cylinder (6) is coated on its periphery with a covering whose teeth or spikes (6a) point forwards, i.e. in the direction of its rotation.
6. An installation for forming a fiber web by the airlay technique, the installation implementing:

   a carding system (4) which is designed to be fed with fiber material and which has at its outlet a carding cylinder (4h) fitted on its periphery with means (4e, 4f) having the functions of individualizing the fibers situated on the periphery of the carding cylinder and of orienting them substantially parallel to one another;

   a surface (7a) for forming and transporting the fiber web, which surface is associated with means (8) for forming a flow of air; and

   means for taking up all or some of the fibers situated at the periphery of the carding cylinder and inserting them into the air flow, the function of the air flow being to disperse the fibers and project them onto the forming and transport surface;

      the installation being characterized in that the means for taking up the fibers and inserting them into the air flow comprise:

   at least one regulator system (5) having the function of taking up a portion only of the fibers individualized at the periphery of the carding cylinder (4h) and designed to output fibers at a more regular rate; and

   a rotary outlet cylinder (6) having the function of taking up the fibers from the regulator system (5) and bringing them into the air flow.
7. An installation according to claim 6, characterized in that a regulator system (5) has the additional function of reorienting the fibers taken up from the periphery of the carding cylinder (4h) so as to output a condensed web.
8. An installation according to claim 6 or 7, characterized in that a regulator system (5) comprises at least one combing, first cylinder (5a) which is disposed at the periphery of the carding cylinder (4h), which is designed to be rotated to have a circumferential speed that is strictly less than that of the carding cylinder (4h) and in a direction of rotation opposite that of the carding cylinder (4h), and which is coated on its periphery with a covering having teeth or spikes (5'a) that point backwards, i.e. in the direction opposite to its direction of rotation.
9. An installation according to claims 7 and 8, characterized in that a regulator system (5) includes a condenser, second cylinder (5b) which is disposed at the periphery of the combing, first cylinder (5a) which is designed to be rotated to have a circumferential speed that is less than or equal to that of the combing, first cylinder (5a).
10. An installation according to claim 9, characterized in that the condenser, second cylinder (5b) is designed to be rotated in the opposite direction to the first cylinder (5a) and is coated on its periphery in a covering whose teeth or spikes (5'b) point backwards, i.e. in the direction opposite to its direction of rotation.
11. An installation according to claim 9, characterized in that the condenser, second cylinder (5b) is designed to be rotated in the same direction of rotation as the combing, first cylinder (5a), and is coated on its periphery with a covering whose teeth or spikes point forwards, i.e. in the direction of rotation of the cylinder.
12. An installation according to claim 10, characterized in that the outlet cylinder (6) is disposed at the periphery of the condenser, second cylinder (5b) of a regulator system (5), is rotated to have a circumferential speed greater than or equal to that of the second cylinder (5b) and in the same direction of rotation as the second cylinder, and is coated on its periphery with a covering whose teeth or spikes (6a) point forwards, i.e. in the direction of its rotation.
13. An installation according to claim 11, characterized in that the outlet cylinder (6) is disposed at the periphery of the condenser, second cylinder (5b) of a regulator system (5), is designed to be rotated to have a circumferential speed that is strictly greater than that of the second cylinder (5b) and in the direction of rotation opposite to that of the second cylinder (5b), and is provided at its periphery with a covering whose teeth or spikes point forwards, i.e. in the same direction as its direction of rotation.
14. An installation according to any one of claims 6 to 13, characterized in that it comprises at least two regulator systems (5) in parallel.
15. An installation according to claim 14, characterized in that it has a single outlet cylinder (6), with the condenser second cylinder (5b) of each regulator system (5) being disposed at the periphery of said single outlet cylinder (6).
16. An installation according to any one of claims 6 to 15, characterized in that the means (8) for forming a flow of air for dispersing and projecting fibers are designed so that the air flow comes into contact with the periphery of the outlet cylinder (6), and assists in detaching the fibers from the periphery of said cylinder.
17. An installation according to any one of claims6 to 15, characterized in that the outlet cylinder (6) is designed to be rotated at a speed of rotation that is high enough for the fibers to become detached from its periphery solely under the effect of centrifugal force.

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