HK1088050A1 - Device for dry-forming a web of fibers with an innovative suction box and associated method - Google Patents

Abstract

The device comprises: a fiber distribution head (3); a forming wire (9) movable underneath the said head in a feeding direction (f 9); a suction box (7) located on the opposite side of the forming wire (9) to the head (3) and connected to a suction system. The suction box (7) is divided transversely with respect to the direction of feeding of the forming wire (9) into at least two longitudinal sections, extending in the direction of feeding of the forming wire. Moreover, control members (29) are envisaged for controlling suction in each of the longitudinal sections in an independent manner with respect to the other longitudinal sections.

Description

Device for dry-forming a fibrous web with an innovative suction box and associated method

Technical Field

The invention relates to an apparatus for dry-forming a fibrous web, of the type comprising: a fiber distribution head; a forming wire movable under the distribution head; suction boxes arranged on the opposite side of the forming wire with respect to the head and connected to a suction system.

The invention relates in particular to a suction box of a novel form for a device of this type.

According to various aspects, the present invention relates to a method of dry-forming a fibrous web.

According to a further aspect, the invention relates to a suction box for an apparatus for dry-forming a fibrous web.

Background

For the production of webs or sheets of fibrous material, in particular paper (absorbent or tissue paper), a method and a machine are generally used which distribute a slurry of cellulose fibers on a forming wire in order to form a thin web. The web is then dried by absorbing water and then passing over heated rollers or other drying devices.

Recently a new method has emerged for the manufacture of paper, in particular absorbent paper of considerable thickness, for example for the manufacture of sanitary articles such as baby diapers or feminine sanitary napkins. The method envisages distributing the web supplied by the air flow over a forming wire. This process is known as an "airlaid" process.

In order to implement a dry preparation process, various devices have been designed in order to obtain a fiber distribution as uniform as possible and to overcome many of the drawbacks and problems involved with this new technology.

In general, airlaying envisages suspending the fibers in an air flow and depositing them on a forming wire, below which a suction is generated to convey the fibers supplied from a forming head located above. The fibers are distributed in the air stream by using various techniques.

The first category of devices envisages the use of forming heads having a screen with a mesh structure at the bottom, through which the fibres are drawn by an air flow. The forming wire moves under a screen which closes the bottom of the forming head and on which the fibers are deposited to form the web. The impeller rotating about a vertical axis, i.e. perpendicular to the forming wire and to the axis of the screen, is arranged above the bottom closing screen of the forming head. The fibers are drawn up by the air flow through the closing screen of the forming head and deposited on the forming wire. Examples of devices prepared in this way are described in GB-1499687, GB-1559274, US-A-3581706, US-A-4014635, US-A-4157724, US-A-4276248, US-A-4285647, US-4335066, US-A-4351793, US-A-4482308, US-A-4494278, US-A-4627953, US-A-5527171, US-A-5471712, WO-A-9105100, WO-A-9522656, WO-A-9610663, WO-A-9954537 and EP-B-616056.

A second type of device for the fibres in the air flow drawn through the forming wire envisages the use of one or more perforated pipes having an axis parallel to the forming wire. The fibers drawn by the gas stream emerge from the orifices in the tube and are deposited on the underlying forming wire advancing in the feed direction. ｃA former head of this type is described in EP- ｃA-032772. A pair of tubes with parallel axes is arranged in the upper part of the forming wire. The tube has apertured walls through which the fibers carried by the gas stream inside the tube emerge. In order to allow the fibers to emerge more easily and to prevent the holes from clogging, a rotating shaft equipped with radial tips is arranged and has an axis parallel to the axis of the tube. The radial tips also have the function of breaking up any fibre agglomerates formed in the conveying gas stream. Devices based essentially on the same principle are described in US-A-4352649, WO-A-8701403 and EP-B-188454. In these devices the forming head has no bottom closing screen and both the air flow and the suspended fibres are confined inside the holed wall duct, which has the function of the closing screen of the forming head of the first type described above.

US-A-6233787 describes an apparatus for dry-forming A fibrous web in which A head receiving A gas stream with suspended fibers is arranged above A forming wire. The head has, in a lower portion, a series of shafts or rollers having axes parallel to each other and to the forming wire and extending transversely with respect to the feeding direction of the forming wire. The aforementioned shafts or rollers have radial tips or stems extending to substantially close the bottom opening of the head, forming a kind of wall capable of passing, which allows the passage of the fibers sucked by the air flow sucked from below the forming wire.

EP- ｃA-159618 describes ｃA device for dry-forming ｃA fibrous web comprising ｃA forming head located in the upper part of ｃA forming wire through which ｃA gas stream is sucked which sucks the fibres. The bottom of the forming head is closed by a stationary screen with perforations to allow the fibers to pass through the screen. A plurality of rollers having axes parallel to the forming wire and perpendicular to the feeding direction of the forming wire are arranged above the fixed screen. Said rolls are equipped with radial tips and are mounted on a continuous conveyor which causes a translational movement parallel to the direction of feed of the forming wire.

A co-pending international patent application PCT/IT02/00657, filed on 2002, 10, 15, in the name of the owner of the present application, describes a head for making a gas-forming wire that is particularly effective in terms of uniformity of the distribution of the fibers.

From the above it is clear that particular attention has been paid so far to the head designed for distributing the fibres on the forming wire in order to obtain the desired uniformity of the distribution of the fibres in the final product. On the other hand, less attention is directed to the design of the suction box placed under the forming wire and opposite the head from which the fibers are delivered. The suction box is generally of a very simple form, without having specific features that allow the quality of the product leaving the device to be improved.

Disclosure of Invention

The object of the present invention is to provide an apparatus for producing a fibrous web using the so-called airlaid dry technique, which allows to obtain particular benefits in terms of uniformity of the thickness and distribution of the fibers, through a specific advantageous form of suction box.

These and further objects and advantages, which will become apparent to those skilled in the art upon a reading of the following text, are substantially achieved by an apparatus comprising: a fiber distribution head; a forming wire movable in a feed direction under the distribution head; suction box located on the opposite side of the forming wire with respect to the head and connected to a suction system. According to the invention, it is characterized in that: the suction box is divided transversely with respect to the feeding direction of the forming wire into at least two longitudinal sections extending in the feeding direction. Furthermore, the control element is adapted to control the suction in each of said longitudinal sections in an independent manner with respect to the other longitudinal sections.

In this way it is possible to have a variable degree of suction, i.e. vacuum, from one part to the other, thus having the possibility of optimizing the fibre distribution profile in the transverse direction in the final product. For example, it is possible to compensate for a greater or smaller flow of fibres from the distribution head located above by increasing or decreasing the suction in different parts of the tank, so that the finished product has the same density of fibres or the same thickness or the same basis weight along the whole cross section.

On the contrary, when it is desired to obtain a product having a non-uniform transverse distribution of quantity, thickness or density, it is still possible to obtain by suitably adjusting the suction in the different portions into which the suction box is transversely divided.

The different sections into which the suction box is transversely divided may all be connected to a single suction duct, with shutter valves or gates arranged between the different sections, i.e. reducing the suction cross section, in order to vary the suction conditions inside each section of the box. However, according to a preferred embodiment of the invention, each of said longitudinal sections into which the suction box is transversely divided is connected to its own independent suction duct. A respective fan may be associated with each of these ducts. Thus, for example, the possibility of more effectively and rapidly adjusting the suction in the different sectors is obtained, using an electronic system for controlling the different motor operating conditions for actuating the various fans. On the other hand, when each longitudinal portion of the tank is connected to a single suction duct by means of shutter doors or valves, each door or valve can be associated with an actuator connected to an electronic actuation and control system.

In both cases it is possible to form a control-i.e. feedback-loop by providing a series of sensors arranged downstream of the suction box and the distribution head of the forming device, which detect a control parameter, such as the thickness or the basis weight of the web. On the basis of the signal generated by the sensor or sensors and compared with predetermined values of the control parameter, it is possible to generate a feedback signal for adjusting the shutter valve or gate or the actuation motors of the different fans associated with the longitudinal portion into which the suction box is divided. The following possibilities are not excluded: for example by envisaging a plurality of fans and suction ducts less than the overall number of sections into which the box is transversely divided, the possibility of combining a throttle valve or gate with a separate suction duct and motor for the different fans, and the possibility of dividing one or more of said suction ducts into sections, each equipped with its own shutter valve or gate with its own operating actuator.

Advantageously, the different suction ducts are connected to the respective longitudinal portions of the suction box at the ends thereof located downstream with respect to the feeding direction of the forming wire. In this way, as will be clear from the following, an optimal operation of the suction box is obtained, since the suction air flow has a velocity with a component parallel to the feeding direction of the forming wire.

According to a practical embodiment, the suction box is divided into longitudinal sections by longitudinal partition walls extending upwards from the bottom of the box up to a height less than the plane of lie of the forming wire. In this way, the risk of the web having discontinuities with respect to each partition wall is avoided. But also the distance between the plane of lie of the forming wire and the partition wall is sufficiently small to enable different suction conditions at different longitudinal sections of the suction box.

According to a modified embodiment of the invention, the suction box is further divided into at least two transverse zones arranged adjacent to each other in the feeding direction of the forming wire, by means of a partition wall which is transverse (i.e. substantially perpendicular to the feeding direction of the forming wire) and which extends from a zone close to the plane of lie of the forming wire towards the bottom of the suction box, while keeping the transverse partition wall separated from the box bottom. Furthermore, an adjustable shutter element is associated with each of said lateral zones for regulating the air flow sucked into each of said zones. Thereby enabling to increase the effectiveness of the whole device.

In fact, considering a single portion of the forming wire, as it passes between the head and the suction box, more and more fibres are deposited thereon, said fibres increasing the head loss in the fibre-conveying gas flow (i.e. the air flow) which passes from inside the head through the forming wire and is sucked into the suction box, depositing the fibres on the forming wire. In conventional devices, this loss of head results in a diminishing efficiency in making the web, since the greater the thickness of the fibers already deposited on the forming wire, the smaller the amount of fibers that are continuously deposited during the remaining movement of the forming wire through the device. This is a result of less air flow through the forming wire and the web already partially made thereon, caused by increased head loss.

Since the suction in the transverse portions arranged consecutively in the wire feeding direction inside the suction box can be adjusted, it is possible to exert a greater intensity of the suction action in the region of the box situated further downstream with respect to the feeding direction of the forming wire. This gradual increase in suction compensates for the increased head loss across the thickness of the fibers gradually formed on the forming wire, so that the final portion of the suction box also contributes substantially to the formation of the fibrous web. This allows to increase the feeding speed of the forming wire and thus the productivity of the final device.

This measure of increasing the efficiency of the suction box (by dividing the box itself into lateral zones) can also be taken as the only measure, independently of the measure of dividing the box into longitudinal sections. This excludes the advantage of being able to adjust the dosing or lateral distribution of thickness, but will nevertheless increase the efficiency of the device in terms of productivity. When the box is divided into sections or zones arranged consecutively in the feeding direction of the forming wire only by means of transverse walls, these transverse partition walls may also extend to the bottom of the box, in which case separate suction ducts will be envisaged for each transverse zone into which the box is divided. It is also conceivable in this case for the shutter mechanism or element to be formed by a valve arranged on the suction duct, or for a separate fan to be used for each lateral zone. However, since it is sufficient to manually adjust the suction conditions in each section or lateral zone of the box at the start of production, an automatic adjustment system is not necessary in this case.

In a possible embodiment of the invention, the throttling elements associated with the transverse zones into which the suction box is divided each comprise a wall oscillating about a transverse oscillation axis and divided into a number of portions corresponding to the number of longitudinal portions into which the suction box is divided.

Adjustment is made by a lever associated with each swing wall having a locking mechanism to secure the wall in a desired position.

In a known manner, the suction box may have a plurality of transverse profiled parts on which the forming wire can be placed. These profiled parts may advantageously be interchangeable so that they can be replaced when worn. They may be arranged approximately in correspondence with the transverse partition walls which divide the tank into transverse zones.

Advantageously, it can be envisaged that an auxiliary suction box is arranged downstream of the suction box with respect to the feeding direction of the forming wire. Whereas the main suction box extends in the feeding direction of the forming wire for a length corresponding to the dimension of the head of the device in this direction, the auxiliary suction box extends outside the area acted on by the head of the device and has the main function of holding the web formed on the forming wire until it enters the subsequent work station of the production line. The subsequent stations may consist of a station for curing the fibres or a new fibre distribution device for preparing a second layer of fibres on the web.

The auxiliary suction box can also be divided transversely into longitudinal sections in a similar way to what has been envisaged in the main suction box. Each of these sections, which may be defined by a respective suction opening, may be associated with a suction adjustment member for adjusting the suction in an independent manner for the different openings and therefore for the different longitudinal sections into which the auxiliary tank is divided.

According to a different aspect, the invention envisages a process for dry-forming a fibrous web comprising the steps of:

-generating fibres suspended in an air flow, typically air;

-creating suction of said air flow across the forming wire on which said fibres are deposited to produce a web.

According to the invention, the suction is divided transversely with respect to the feeding direction into longitudinal sections extending parallel to the feeding direction of the forming wire, and the suction in each of said longitudinal sections is adjusted in an independent manner with respect to the other longitudinal sections.

Further advantageous features and embodiments of the device and method according to the invention are indicated in the appended dependent claims.

The invention also relates to a suction box for an apparatus for dry-forming a fibrous web, comprising a forming wire advancing in a machine direction, characterized in that the suction box is divided transversely with respect to the machine direction into at least two longitudinal sections extending in the machine direction; and a control element for controlling the suction in each of said longitudinal sections in an independent manner with respect to the other longitudinal sections.

Drawings

The invention will be better understood with reference to the following description and to the accompanying drawings which illustrate practical non-limiting embodiments of the invention. In particular, like numerals indicate like or corresponding parts throughout the several views:

FIG. 1 shows a side view of the device;

FIG. 2 shows a longitudinal section through the main suction box and the auxiliary suction box along II-II of FIG. 3;

figure 3 shows a perspective view of the suction box with the forming wire partially removed;

FIG. 4 shows a front view along IV-IV in FIG. 2;

FIG. 5 shows a cross-section along V-V in FIG. 2;

fig. 6 shows an enlargement of the detail indicated by VI in fig. 5;

FIG. 7 shows a cross-section along VII-VII in FIG. 6;

FIG. 8 shows a cross-section along VIII-VIII in FIG. 4;

FIG. 9 shows a partial cross-section along IX-IX in FIG. 5; and

fig. 10 shows a partial cross-section along X-X in fig. 5.

Detailed Description

Fig. 1 shows in its entirety a process for dry-forming (using the so-called airlaid technique) a fibrous web, for example cellulose fibers. The device, indicated as a whole by 1, comprises an upper part or head, indicated as a whole by 3, and a bottom 5, which bottom 5 comprises, as a main element therein, a suction box 7. A forming wire 9 passes between the head 3 and the suction box 7, on which forming wire 9 a fibrous web, schematically indicated with 11, is prepared (see figure 1).

The forming wire 9 defines a closed path, of which only the part defined by the two drive rollers 13 and 15 is shown in fig. 1. The direction of feed of the forming wire along this path is indicated by the arrow f 9. The arrow f9 also defines the so-called machine direction, i.e. the direction in which the material being prepared advances.

The configuration of the forming head 3 may be of any kind and may advantageously be made as described in the international patent application PCT/IT02/00657 filed by the present applicant. It must be understood, however, that other configurations of the head are possible, since the advantages offered by the suction head according to the invention in terms of increase in product quality and yield can also be used with equivalent results in connection with the forming heads of the conventional type. In general, the characteristics of the suction box can be combined with heads made according to different techniques, so that the specific structure of the head 3 is not relevant to the description of the invention and therefore not illustrated here.

The head 3 rests on the structure of the underlying part at four support points 4 (see in particular figures 1 and 3), the height of the support points 4 being adjustable by means of motorized jacks 6.

As can be seen in particular in the cross-section according to fig. 2, the suction box 7 has a bottom which is at least partially inclined from the top downwards in the feeding direction of the forming wire 9. At the downstream end (with respect to the feeding direction of the wire 9), the suction box 7 is connected to three suction ducts indicated by 17, 19 and 21. The three suction ducts are connected to three respective fans, each equipped with its own motor, and only schematically shown in fig. 4 and indicated here by 23, 25 and 27. The three motors of the fans 23, 25 and 27 are connected to a central control unit, schematically indicated with 29, which is in turn connected to one or a series of sensors, schematically indicated with 31, arranged along the path of the forming wire 9 downstream of the head 3 of the device 1 for detecting the thickness or the quantity of the wire 11 leaving said device. This arrangement allows the device to be controlled in a manner to be described below. Basically, it is possible to envisage using sensors in linear array or matrix to detect the development of the transverse profile (i.e. in a direction perpendicular to the direction of feed of the forming wire 9) of one or more parameters of the web 11 produced by the device 1, such as basis weight, thickness, density or other parameters.

Each suction duct 17, 19, 21 is connected to a respective longitudinal portion of the suction box 7 divided by a longitudinal partition wall 33. As can be seen in particular in the cross-sections of fig. 2 and 5, these partition walls extend from the bottom of the suction box 7 up to a height that does not reach the plane of lie of the forming wire 9. In this way, three longitudinal portions are created inside the suction box 7, arranged alongside each other in the transverse direction, i.e. perpendicular to the feeding direction of the forming wire 9. In each of the three longitudinal sections, it is possible to establish suction conditions that can be adjusted independently of the suction conditions in the remaining longitudinal sections by increasing or decreasing the flow rate of the corresponding fan 23, 25 or 27.

When the apparatus is in operation, a gas flow is generated between the forming head 3 and the suction box 7, which contains the fibers in suspension intended to form a web on the forming wire 9. This air flow is drawn through the structure of the forming wire 9 and the fibres are deposited on the forming wire due to the vacuum conditions created inside the suction box 7. By increasing or decreasing the suction inside each of the three longitudinal sections into which the suction box is divided by the walls 33, it is possible to increase or decrease the flow rate of the gas flow and, consequently, the quantity of fibers deposited along the three longitudinal sections into which the forming wire is ideally divided with respect to the longitudinal section into which the suction box 7 is divided.

It must be understood that the longitudinal section into which the suction box 7 is divided can also be different from three. For example four, five or more longitudinal sections are conceivable. It is also possible to envisage a division into only two longitudinal sections. By increasing the number of portions into which the suction box is divided by the longitudinal walls 33, the complexity of the suction box is increased, but on the other hand the possibility of adjusting the suction conditions in the transverse direction is also increased-and thus the desired transverse distribution, i.e. the desired development, of the controlled parameters in the transverse direction, such as the thickness, basis weight or density of the web formed, is obtained with greater precision.

By means of the thickness or quantitative sensor 31, it is possible to detect the transverse profile, i.e. the progress, of the measured parameter (thickness, quantitative or other parameter of the web 11 produced) in the transverse direction and to transmit the detected values to the central control unit 29. These values can be compared with predetermined values of said parameters, which can also be modified by the operator. On the basis of the error signal resulting from this comparison, the suction conditions of the fans 23, 25 and 27 can be modified. In this way, the thickness or basis weight of the web 11 can be kept substantially constant in the cross direction. Alternatively, it is possible to produce a web having a cross-directional distribution of variable caliper or basis weight or density as desired, for example a greater caliper or greater basis weight in one of its longitudinal portions and a lesser caliper or lesser basis weight in a different longitudinal portion.

As can be observed in particular in the cross-section according to fig. 2, a suction air flow having a component parallel to the feeding direction f9 of the forming wire is formed inside the suction box 7, since the suction ducts 17, 19 and 21 are connected to the suction box 7 at the downstream end of the suction box 7 with respect to the feeding direction of the forming wire 9. This facilitates the distribution of the fibres contained in the air flow and supplied by the head 3.

In the region of the suction box 7, the forming wire 9 is supported by a plurality of transverse profiled parts 41 shown in detail in cross-section according to fig. 9 and 10. Each profiled part 41 is supported at its ends by respective blocks 43 screwed into the support frame of the suction box 7 by screws 45, the two longitudinal beams of the support frame of the suction box 7 being indicated by 47. As can be seen in the section according to fig. 2, transverse walls 51 are provided in correspondence of the four profiled parts 41, said walls dividing the suction box 7 into five transverse zones arranged in succession in the longitudinal movement direction of the forming wire 9. The four transverse walls 51 are supported by cross beams 53 also fixed to the blocks 43. The transverse partition wall 51 has a relatively limited downward extension and the transverse partition wall 51 extends over an intermediate height with its bottom edge at a considerable distance from the bottom of the suction box 7. This is so to avoid obstruction of suction through the suction ducts 17, 19, 21.

Parallel to each transverse wall 51 and to the vertical transverse portion of the outer wall defining the suction box 7, there extends a shaft 57 for supporting and mounting in a swinging manner five doors or walls 59, which doors or walls 59 can rotate about the shaft 57 to assume different angular positions between the vertical position shown in figure 2 and the horizontal position. Each wall 59 is formed of three portions aligned along axis 57. These portions, arranged adjacent to each other, define slits in the wall 59 at points corresponding to the longitudinal partition walls 33, said longitudinal partition walls 33 dividing the suction box 7 into three longitudinal portions.

Depending on the angular position assumed by each wall 59, the suction cross-section between two consecutive transverse walls 51-or between one of said transverse walls and the outer transverse wall of the suction box 7-can vary independently of the other partition walls. In this way, the zone located below the forming wire 9 and corresponding to the suction box 7 is divided into five transverse zones, in each of which the suction can be reduced to a greater or lesser extent with respect to the other adjacent transverse zones.

By controlling the swinging movement of the wall 59 by the levers 61, each of the levers 61 can be fixed at a predetermined angular position independently of the angular positions at which the remaining levers 61 are fixed. This allows manual adjustment of the throttle of each of the lateral zones into which the suction box is divided. Manual adjustment of the throttling is sufficient for the purpose intended for this adjustment. In fact, the above-mentioned division for obtaining a continuous adjustment of the thickness or the quantity of the web produced by means of a feedback loop, as opposed to the division into longitudinal portions, has the sole purpose of dividing the suction box 7 into transverse zones as follows: the suction from the more upstream to the more downstream zone of the suction box is adjusted along the feeding direction of the forming wire 9 in order to compensate for the greater pressure drop through the forming wire and the assembly formed by the fibrous layer produced on the forming wire.

Thus, the further downstream lateral zone of the suction box 7 with the maximum thickness of fibres will be fully open, i.e. the corresponding wall 59 will be in a generally vertical position. The remaining walls of the transverse region situated further upstream in each case will gradually become more and more closed, i.e. more inclined with respect to the vertical. The wall 59 hinged adjacent to the rear outer wall of the suction box will be the wall normally in the most closed position.

Although the possibility of adjusting these throttling conditions can be envisaged, for example when the type of fibre used varies, it is generally sufficient to set these different degrees of throttling manually. But also an automatic or in any case servo-assisted adjustment of the throttling of the lateral zones of the tank.

As can be seen in particular in the cross-sections according to fig. 7, 9 and 10, the configuration of the block 43 for supporting the profiled part 41 and for locking the shaft 57, and the configuration of the cross-beam 53 supporting the wall 59 and the transverse wall 51, enable replacement of the worn profiled part 41 to be carried out without dismantling the wall 51 and the wall 59. It is in fact sufficient to unscrew the screws 45 which lock the corresponding block 43 on one of the two sides of the suction box and to remove said block, in order to allow the removal of the worn profiled part 41 and the replacement of a new profiled part which will be locked in position by the reinsertion of the block 43.

In addition to the block 43 and at a spaced position relative to the block 43, the insert 44 is also fixed to the longitudinal beam 47. The inserts 44 and the blocks 43 form respective continuous longitudinal surfaces on both sides of the suction box 7, on which the steel plate 67 is fixed, on which the longitudinal edges of the forming wire 9 rest and on which the longitudinal edges slide on the steel plate 67. These plates can be interchanged without dismantling the remaining parts of the structure and in any case have a limited degree of wear due to the hardness of the material from which they are made.

An auxiliary suction box, indicated as a whole with 81, is arranged downstream of the suction box 7 in the feeding direction of the forming wire 9. As can be seen in particular in the perspective view of fig. 3, on the downstream side with respect to the feeding direction of the forming wire 9, three suction ports 83 are formed in the auxiliary suction box 81, which three suction ports 83 are arranged adjacent to each other in the transverse direction, i.e. in the direction perpendicular with respect to the feeding direction of the forming wire 9. In contrast to the design of the main suction box 7, the interior of the auxiliary suction box 81 is not divided into longitudinal sections by a partition wall. However, providing three suction ports arranged side by side with each other allows (by varying the suction conditions within each of said ports) to have suction conditions that are variable in the transverse direction of the cavity.

The three suction ports 83 are connected to a single suction duct 85 by means of three gate valves or gates schematically indicated by 87 (see in particular figures 3 and 4). The valve 87 may be adjusted manually or automatically. At the same time, inside the auxiliary suction box 81, the forming wire 9 is supported by the profiled part 41 in a similar way to that envisaged in the main suction box 7.

It is understood that the drawing only shows one possible embodiment of the invention, the form and arrangement of which may be varied without thereby departing from the idea forming the basis of the invention. The reference numerals appearing in the appended claims have the sole purpose of facilitating reading in the light of the foregoing description and the attached drawings, and do not in any way limit the scope of protection of the invention.

Claims (66)

1. An apparatus for dry-forming a web (11) comprising: a fibre distribution head (3); a forming wire (9) movable under said head in a feeding direction (f 9); a suction box (7) arranged on the opposite side of the forming wire (9) with respect to the head (3) and connected to a suction system; wherein: said suction box (7) being transversely divided with respect to the feeding direction of the forming wire (9) into at least two longitudinal portions extending in the feeding direction of the forming wire; each of said longitudinal portions being connected to a suction duct (17, 19, 21) separate from the other longitudinal portions; and an air suction control member (29) for controlling the air suction in each of said longitudinal portions in an independent manner with respect to the other longitudinal portions, characterized in that a respective fan (23, 25, 27) is associated with each of said air suction ducts.

2. A device as claimed in claim 1, wherein each of said suction ducts is connected to a respective longitudinal portion of a suction box at the end of the suction box downstream with respect to the feeding direction of said forming wire (9).

3. The apparatus according to claim 1, characterized in that at least one sensor (31) determining the cross-directional distribution of at least one parameter of the web (11) is arranged downstream of the suction box, the suction in the longitudinal section being adjusted according to said cross-directional distribution, said at least one parameter being selected from the group consisting of: a thickness of the web, a basis weight of the web, and a density of the web.

4. The apparatus according to claim 2, characterized in that at least one sensor (31) determining the cross-directional distribution of at least one parameter of the web (11) is arranged downstream of the suction box, the suction in the longitudinal section being adjusted according to said cross-directional distribution, said at least one parameter being selected from the group consisting of: a thickness of the web, a basis weight of the web, and a density of the web.

5. A device according to claim 3, characterized in that it comprises a central control unit connected to said sensor and to said inspiration control element.

6. The apparatus of claim 3 wherein the parameter whose cross-machine direction profile is sensed by the sensor is the web thickness.

7. The apparatus of claim 4 wherein the parameter whose cross-machine direction profile is sensed by the sensor is the web thickness.

8. The apparatus of claim 5 wherein the parameter whose cross-machine direction profile is sensed by the sensor is the web thickness.

9. The apparatus of claim 3 wherein the parameter whose cross-directional profile is sensed by the sensor is a basis weight of the web.

10. The apparatus according to any of claims 4-8, wherein the parameter whose cross-directional distribution is detected by the sensor is a basis weight of the web.

11. The apparatus according to claim 1, characterized in that said suction box (7) is divided into said longitudinal sections by longitudinal partitions (33), said longitudinal partitions (33) extending from the bottom of said suction box upwards to a level lower than the plane of lie of said forming wire (9).

12. Apparatus according to any of claims 2-9, characterized in that the suction box (7) is divided into said longitudinal sections by longitudinal partition walls (33), said longitudinal partition walls (33) extending from the bottom of the suction box upwards to a level below the plane of lie of the forming wire (9).

13. Device according to claim 1, characterized in that the suction box is further divided into at least two transverse zones by means of a partition wall (51), which partition wall (51) is arranged in a transverse direction with respect to the feeding direction of the forming wire and extends from a zone close to the plane of lie of the forming wire towards the bottom of the suction box, while the partition wall (51) remains mutually separated from the bottom of the suction box.

14. Apparatus according to any of claims 2-9 and 11, characterized in that the suction box is further divided into at least two transverse zones by means of a partition wall (51), which partition wall (51) is arranged in a transverse direction with respect to the feeding direction of the forming wire and extends from a zone close to the plane of lie of the forming wire towards the bottom of the suction box, while the partition wall (51) remains mutually separated from the bottom of the suction box.

15. The device according to claim 13, characterized in that an adjustable throttling element (59) is associated with each of said lateral zones in order to regulate the air flow sucked into each of said lateral zones.

16. The device according to claim 14, characterized in that an adjustable throttling element (59) is associated with each of said lateral zones in order to regulate the air flow sucked into each of said lateral zones.

17. The device according to claim 15, characterised in that each of said throttling elements comprises a wall (59) oscillating about an oscillation axis (57) and divided into a plurality of portions corresponding to the number of longitudinal portions into which the suction box is divided.

18. An apparatus according to claim 16, wherein each of said throttling elements comprises a wall (59) oscillating about an oscillation axis (57) and divided into a plurality of portions corresponding to the number of longitudinal portions into which the suction box is divided.

19. Device according to claim 17, characterised in that an adjusting lever (61) and a mechanism for locking the adjusting lever in a selected position are associated with each oscillating wall.

20. Device according to claim 18, characterised in that an adjusting lever (61) and a mechanism for locking the adjusting lever in a selected position are associated with each oscillating wall.

21. The apparatus as claimed in claim 17, wherein each of said axes of oscillation lies substantially in correspondence of the transverse partition wall and extends parallel thereto.

22. The apparatus as claimed in claim 19, wherein each of said axes of oscillation lies substantially in correspondence of the transverse partition wall and extends parallel thereto.

23. Apparatus according to any one of claims 1-9 and 11, characterized in that said suction box has a plurality of transverse profiled elements (41) for supporting the forming wire.

24. The apparatus of claim 23, wherein the transverse profiled members are interchangeable.

25. Device according to claim 13, characterized in that said suction box has a plurality of transverse profiled elements (41) for supporting the forming wire, and in that said transverse profiled elements (41) are arranged substantially in correspondence of said transverse partition walls (51).

26. Device according to claim 24, characterized in that each of said interchangeable profiled parts (41) is fixed by means of a pair of blocks (43) which can be detached and fixed along the longitudinal edges of said suction box.

27. A device according to claim 26, characterised in that the suction box is further divided into at least two transverse zones by means of a partition wall (51), which partition wall (51) is arranged in a transverse direction with respect to the feeding direction of the forming wire and extends from a zone close to the plane of lie of the forming wire towards the bottom of the suction box, while the partition wall (51) remains mutually separated from the bottom of the suction box; an adjustable throttling element (59) is associated with each of said lateral zones to regulate the air flow sucked into each of said lateral zones; each of said throttling elements comprises a wall (59) oscillating about an oscillation axis (57) and divided into a plurality of portions corresponding to the number of longitudinal portions into which the suction box is divided; each of said oscillation axes being disposed substantially in correspondence with the transverse partition wall and extending parallel thereto; and each pair of blocks fixes a respective transverse partition wall and a respective oscillation axis of a corresponding throttling element.

28. Apparatus according to any one of claims 1-9 and 11, characterized in that the cross section of the suction box increases progressively from upstream to downstream in the feeding direction of the forming wire.

29. An apparatus according to any one of claims 1-9 and 11, characterized in that an auxiliary suction box (81) is arranged downstream of the suction box with respect to the feeding direction of the forming wire.

30. Apparatus according to claim 29, characterized in that said auxiliary suction box is associated with a plurality of suction openings (83) for generating suction flows in the feeding direction of the forming wire.

31. Device according to claim 30, characterized in that the number of suction openings is equal to the number of longitudinal sections into which the suction chamber (7) is divided.

32. A device according to claim 30, characterised in that an aspiration adjustment member (87) for adjusting the aspiration for the different orifices in an independent manner is associated with each aspiration orifice.

33. Device according to claim 32, characterized in that said suction openings are connected to a single auxiliary suction duct (85) and in that a valve which is adjusted independently of the valves of the other suction openings is associated with each of said suction openings.

34. A process for dry-forming a fibrous web comprising the steps of:

-generating a fibre suspension in the gas flow;

-producing suction of said gaseous flow across a forming wire on which said fibers are deposited, said wire being prepared, said forming wire moving in a feeding direction;

-dividing the suction transversely with respect to the feeding direction into longitudinal portions extending parallel to the feeding direction and adjusting the suction in each of said longitudinal portions in an independent manner with respect to the other longitudinal portions;

characterised in that said suction into each longitudinal section is generated by a separate fan.

35. The method of claim 34, wherein a cross-directional profile of at least one parameter of the web produced on said forming wire is sensed, and suction in each of said machine direction sections is adjusted in accordance with said cross-directional profile, said at least one parameter being selected from the group consisting of: a thickness of the web, a basis weight of the web, and a density of the web.

36. The method of claim 35, wherein the parameter is a web thickness.

37. The method of claim 35 wherein the parameter is basis weight of the web.

38. The method of claim 35, wherein:

-setting an inspiration condition for each of said longitudinal portions;

-detecting said transverse profile;

-comparing the detected transverse profile with a predetermined transverse profile;

-generating a feedback signal for modifying the inspiration conditions in one or more of said longitudinal sections on the basis of the difference between the detected transversal profile and the predetermined transversal profile.

39. The method of claim 36, wherein:

-setting an inspiration condition for each of said longitudinal portions;

-detecting said transverse profile;

-comparing the detected transverse profile with a predetermined transverse profile;

-generating a feedback signal for modifying the inspiration conditions in one or more of said longitudinal sections on the basis of the difference between the detected transversal profile and the predetermined transversal profile.

40. The method of claim 37, wherein:

-setting an inspiration condition for each of said longitudinal portions;

-detecting said transverse profile;

-comparing the detected transverse profile with a predetermined transverse profile;

-generating a feedback signal for modifying the inspiration conditions in one or more of said longitudinal sections on the basis of the difference between the detected transversal profile and the predetermined transversal profile.

41. A method as claimed in any one of claims 34 to 40, characterized by dividing the zone located below said forming wire into a plurality of transverse zones arranged side by side with each other, and adjusting the suction conditions in each of said transverse zones.

42. A method as set forth in claim 41, characterized in that the suction conditions in each of said transverse zones are adjusted so as to compensate for the greater drop in air flow pressure in the direction of feed of the forming wire due to the accumulation of fibers on said forming wire.

43. A method as claimed in claim 41, characterized by reducing suction in each of said transverse zones in the direction of feed of the forming wire.

44. A method according to any one of claims 34 to 40, wherein said suction is generated in each longitudinal portion of a suction box at the end of the box that is downstream with respect to the feeding direction of the forming wire.

45. A suction box (7) for an apparatus for dry-forming a fibrous web, comprising a forming wire advancing in a machine direction, wherein: the suction box is divided transversely with respect to the machine direction into at least two longitudinal sections extending in the machine direction; an aspiration control member (29) for controlling aspiration in each of said longitudinal portions in an independent manner with respect to the other longitudinal portions; each of said longitudinal portions being connected to a suction duct (17, 19, 21) separate from the other longitudinal portions; characterised in that a separate fan (23, 25, 27) is associated with each of said suction ducts.

46. Suction box according to claim 45, characterized in that each of said suction ducts is connected to a respective longitudinal portion of the suction box at its downstream end with respect to the feeding direction of said forming wire (9).

47. Suction box according to claim 45, characterised in that it is divided into said longitudinal sections by longitudinal partitions (33), said longitudinal partitions (33) extending from the bottom of the suction box up to a level lower than the plane of lie of said forming wire (9).

48. A suction box according to claim 46, characterized in that it is divided into said longitudinal sections by longitudinal partition walls (33), said longitudinal partition walls (33) extending from the bottom of the suction box up to a level below the plane of lie of said forming wire (9).

49. A suction box according to claim 45, characterized in that the suction box is further divided into at least two transverse zones by means of a partition wall (51), said partition wall (51) being arranged in the transverse direction with respect to the machine direction and extending from a zone close to the plane of lie of the forming wire towards the bottom of the suction box, while the partition wall (51) remains mutually separated from the bottom of the suction box.

50. A suction box according to claim 46, characterized in that the suction box is further divided into at least two transverse zones by means of a partition wall (51), said partition wall (51) being arranged in the transverse direction with respect to the machine direction and extending from a zone close to the plane of lie of the forming wire towards the bottom of the suction box, while the partition wall (51) remains mutually separated from the bottom of the suction box.

51. A suction box according to claim 47, characterized in that the suction box is further divided into at least two transverse zones by means of a partition wall (51), said partition wall (51) being arranged in the transverse direction with respect to the machine direction and extending from a zone close to the plane of lie of the forming wire towards the bottom of the suction box, while the partition wall (51) remains mutually separated from the bottom of the suction box.

52. Suction box according to claim 49, 50 or 51, characterized in that an adjustable throttling element (59) is associated with each of said lateral zones for adjusting the air flow sucked into each of said lateral zones.

53. Suction box according to claim 52, characterized in that each of said throttling elements comprises a wall (59) oscillating about an oscillation axis (57) and divided into a plurality of portions corresponding to the number of longitudinal portions into which the suction box is divided.

54. Suction box according to claim 53, characterized in that an adjusting lever (61) and a mechanism for locking the adjusting lever in a selected position are associated with each oscillating partition wall.

55. Suction box according to claim 53, characterized in that each of said oscillation axes is placed substantially in correspondence of a transversal partition wall and extends parallel thereto.

56. Suction box according to any one of claims 45 to 48, characterized in that it has a plurality of transverse profiled parts (41) for supporting a forming wire.

57. Suction box according to claim 56, characterized in that said transverse profiled parts are interchangeable.

58. A suction box according to claim 56, characterized in that the suction box is further divided into at least two transverse zones by means of a partition wall (51), said partition wall (51) being arranged in a transverse direction with respect to the machine direction and extending from a zone close to the plane of lie of the forming wire towards the bottom of the suction box, while the partition wall (51) remains mutually separated from the bottom of the suction box; and the transverse profiled element (41) is arranged substantially in correspondence of the transverse partition wall (51).

59. Suction box according to claim 57, characterized in that each of said interchangeable profiled parts (41) is fixed by a pair of blocks (43) which can be detached and fixed along the longitudinal edges of the suction box.

60. A suction box according to claim 59, characterized in that the suction box is further divided into at least two lateral zones by means of a partition wall (51), said partition wall (51) being arranged in the lateral direction with respect to the machine direction and extending from a zone close to the plane of lie of the forming wire towards the bottom of the suction box, while the partition wall (51) remains mutually separated from the bottom of the suction box; an adjustable throttling element (59) is associated with each of said lateral zones for adjusting the air flow sucked into each of said lateral zones; each of said throttling elements comprises a wall (59) oscillating about an oscillation axis (57) and divided into a plurality of portions corresponding to the number of longitudinal portions into which the suction box is divided; each of said oscillation axes being disposed substantially in correspondence with the transverse partition wall and extending parallel thereto; and each pair of blocks fixes a respective transverse partition wall and a respective oscillation axis of a corresponding throttling element.

61. Suction box according to any one of claims 45 to 51, characterized in that the cross-section of the suction box increases gradually from upstream to downstream in the feeding direction of the forming wire.

62. Suction box according to any one of claims 45 to 51, characterized in that it is associated with an auxiliary suction box (81) arranged downstream of said suction box with respect to the feeding direction of the forming wire.

63. A suction box according to claim 62, characterized in that said auxiliary suction box is associated with a plurality of suction ports (83) for generating suction flows in the feeding direction of the forming wire.

64. Suction box according to claim 63, characterised in that the number of suction openings is equal to the number of longitudinal sections into which the suction box (7) is divided.

65. Suction box according to claim 63, characterized in that a suction adjustment member (87) for adjusting the suction independently for the different mouths is associated with each suction mouth.

66. A suction box according to claim 65, characterized in that the suction mouths are connected to a single auxiliary suction duct (85) and each of the suction mouths is associated with a valve which is regulated independently of the other suction mouths.