Method and device for making wet laid non wovens

Method for producing wet-laid non-woven fabrics, with which an aqueous suspension comprising fibres is laid down on a screen and is dewatered using suction boxes under the screen to form a sheet of non-woven web which is removed from the screen and guided to at least one subsequent treatment unit before the non-woven web can be wound, and transferring of the non-woven web from the screen to the at least one subsequent treatment unit and/or transferring of the non-woven web to interfaces between treatment units on the start of production and/or after an interruption in production, using a web feed, wherein web is fed via a temporarily closed draw of a free draw between the screen and the at least one subsequent treatment unit and/or of a free draw at an interface between treatment units, and the respective temporarily closed draw is produced via air flows, which lift off an end feeding strip as part of the running non-woven web by blowing, adhere same to a transport path device by generating negative pressure and lift up same at the following treatment unit by suction.

The invention relates to a method and to a device for making wet laid non wovens.

It is known from DE 24 37 611 A1 that in the case of methods and devices for making wet laid non wovens the non woven that is formed on the wire upon having been removed from the wire is either guided in a free transfer to the subsequent unit, or in the case of the so-called closed transfer, is removed from the wire by way of a felt-wrapped roller, whereupon the web is transferred to the subsequent unit on the lower side of this pick-up felt.

Both types of transfer have disadvantages. Transferring the non woven to the subsequent treatment unit or onto a transportation belt in a free transfer has the disadvantage that the non woven web must have a significant initial wet strength in order to sustain the removing from the wire cloth and the free transfer up to the subsequent unit without rupturing. Even when the web does not rupture, the web, as a result of the latter adhering to the wire cloth, in the removal from the wire is exposed to substantial tensile stresses, on account of which stresses in terms of elongation that have to be equalized by modifying the speed of the subsequent units arise.

The closed transfer with the aid of a pick-up felt requires good adhesion of the non woven web to the lower side of the felt while the former is running. To this end, the pick-up felt must have an adequate moisture content. Moreover, the non woven web according to experience must comprise a significant proportion of cellulose and have paper-like characteristics, because the adhesion in the case of inadequate moisture in the pick-up felt is substandard such the non woven web is released from the pick-up felt and causes operational malfunctions.

In order for these disadvantages to be avoided, it is provided according to DE 24 37 611 A1 that the non woven web that is laid down on an inclined wire in a suspension sump and is dewatered by suction boxes below the wire runs from this wire directly, without the intervention of intermediate elements, onto a dryer surface that is located below the wire. However, such a solution is not suitable when the non woven web prior to drying is to be solidified, for example by means of hydroentanglement, or by means of the application of a binding agent.

To this extent, a further attempt in terms of a solution is in avoiding free transfers by compromises in the disposal of the machine components, for example on top of one another.

In the production of wet non wovens, water is used for forming fibers to a planar structure or to a wet non woven, respectively. The fibers in the water herein are guided over a wire. While the water is suctioned through the wire, the fibers are deposited on the wire. This process stage is referred to as the sheet formation. Depending on the type of the fiber, the non woven upon sheet formation still contains significantly more water than fibers. Water continues to be extracted from the non woven by way of vacuum heads, but the web at the junction that follows the wire and is usually formed by an inclined wire former is nevertheless not a stable product but a loose fiber composite.

For the reasons set forth, it is therefore advantageous to start at the full speed of the former. The required web consistency for producing a fiber composite that has an adequate inherent strength in order to be transferred to the next conveyor belt, or to the next treatment unit, or to the next machine component, respectively, can only be generated when the former operates at full speed. As has already been explained above, free transfers between the treatment units were commonplace in the case of low production speeds. For safety reasons, said free transfers are no longer possible as production speeds have increased, in particular not for the web feeding.

Proceeding from this prior art, the subject matter of the present invention is based on the object of providing a method and a device for making wet non wovens, said method and device improving the web feed at the production start and/or upon a production interruption.

This object is achieved by the claimed features.

It is achieved on account thereof, that for the production of wet laid non wovens and while using a wire installation the required treatment units/machine components can be disposed sequentially in known manner. Free transfers are provided between the wire installation and the at least one subsequent treatment unit. This is advantageous in particular when all treatment units/machine components for an operating mode that is optimized in terms of economy and energy are to be equipped with dissimilar wire belts. This is the case in particular, for example, when the production of a wet laid non woven comprises an inclined wire former, a hydroentanglement installation, and a dewatering belt. The junction that is provided between these treatment units as far as possible should not compromise one another such that free transfers to this extent are advantageous.

High production speeds are demanded of modern inclined wire former, on the one hand; on the other hand, there are safety guidelines that rule out the operators intervening in the machine. Since the product is fed onto inclined wire production lines at full production speed, an automated solution is possible therefor according to the invention.

According to the invention, the temporarily closed transfers offer the possibility of permitting free transfers between the treatment units/machine components, on the one hand, and of assigning the temporarily closed transfers to an automated solution, on the other hand, in order for the non woven web to be able to be fed at comparatively high machine speeds.

It is advantageously utilized that the wet non wovens that are generated on a wire device, in particular when long fibers are used, have an adequate strength in order to be released from the wire of the wire device by compressed air.

It is therefore provided according to the invention for a web feeding device which is configured as a temporarily closed transfer to be provided at the junctions between the wire installation and a subsequent treatment unit, or at junctions between two neighboring treatment units, respectively. An end feeding strip of the non woven web that at the exit end of a wire belt of the wire installation is cut from the running web is acquired by the temporarily closed transfer. This strip by way of air flows of the temporarily closed transfer is transferred to the respective subsequent treatment unit. The same applies to the junctions between two respective neighboring treatment units, for example between the wire belt of a hydroentanglement unit and a downstream dewatering belt.

It is furthermore provided that the cut end feeding strip is lifted from the wire, so as to be transferred by compressed air to a transportation installation, for example. Using an air flow, this tape is caught by the subsequent treatment unit such that the transfer of the end feeding strip that is achieved forms a temporarily closed transfer. Essential herein are preferably controlled raising, transferring, and subsequent controlled picking up.

Further embodiments of the invention are to be derived from the description hereunder and from the dependent claims.

The invention relates to a method and to a device for making wet laid non wovens. A wet non wovens plant1that is provided in an exemplary manner to this end is illustrated inFIG. 1aandFIG. 1b.

Accordingly, a fiber suspension installation2, a wire installation3, at least one subsequent treatment unit4, and optionally a winder5are sequentially disposed. A hydroentanglement installation is provided as the at least one treatment unit4in the case of the wet non wovens plant1illustrated inFIG. 1aandFIG. 1b. Further treatment units6,7are furthermore provided. The treatment unit6is a drying wire, for example, and the treatment unit7is a dryer, for example.

The wire installation3is illustrated as an inclined wire former. Alternative configurations of the wire installation3can be used. A junction8is provided between the wire device3and the subsequent treatment unit4. For example, a junction9is provided between the treatment unit4and the treatment unit6. When the non woven web10is fed, both junctions8,9are configured as free transfers.

In the case of a production start, or upon a production interruption, it is necessary for the non woven web10to be fed in order for the spacing in the region of the junctions8,9to be overcome.

It has been established according to the invention that the non woven web10produced with wet non woven products on an inclined wire machine such as is illustrated in an exemplary manner as a wire installation3inFIG. 1ahas an adequate strength in order for the material to be taken from the wire11by blowing. This is highlighted inFIGS. 2 and 3in conjunction withFIG. 4.

The method according to the invention for making wet laid non wovens provides that an aqueous suspension having fibers is deposited onto a wire11of the wire installation3for the formation of a sheet of a non woven web10that is removed from the wire11and is dewatered by suction boxes12under the wire and, prior to the non woven web10being finally windable onto a roll23, is infed to at least one subsequent treatment unit4.

The non woven web in the case of a production start and/or upon a production interruption from the wire11to the at least one subsequent treatment unit4and/or at a junction9between two treatment units4,6is transferred with the aid of a web feeding13.

Referring toFIG. 2toFIG. 4, web feeding13is performed by way of a transfer that in each case is temporarily closed and is part of a transfer that is free per se between the wire11and the at least one following treatment unit4and/or of a free transfer at a junction9between treatment units4,6.

The transfer that in each case is temporarily closed of a web feed13is generated by way of air flows. These air flows act on an end feeding strip14which is cut by means of a cutting installation16which acts on the non woven web10at the exit side of the wire11. The end feeding strip14is severed from the remaining web15of the non woven web10by means of the cutting installation16. Web feeding is performed by way of the end feeding strip14, while the remaining web15drops into a pulper17.

According to the invention, the end feeding strip14as part of the running non woven web10is lifted from the wire11by blowing by means of a compressed air installation18. The end feeding strip14, on account of negative pressure being generated on a transportation path installation19, is attached to a transportation path that is formed by the transportation path installation19and is picked up by suctioning on the respective subsequent treatment unit4. Suctioning on the subsequent treatment unit4is performed by means of a vacuum catching device21, for example.

The explanations pertaining to the web feeding13at the junction8apply in an analogous manner to the web feeding13at the junction9.

It has been established according to the invention that wet non woven products have an adequate strength when the latter have been dewatered on a wire installation3which is configured as an inclined wire machine, for example. This applies in particular also when long fibers are used for producing the non woven web. On account of this strength of the non woven web as produced by the wire installation3, the wire web for web feeding can be released from the wire11by compressed air from the compressed air installation18. The end feeding strip14that is raised from the wire11has sufficient stability in order to be transferred to the transportation path installation19by compressed air. The transportation path installation19inFIG. 2is illustrated as an air baffle. The transportation path installation19inFIG. 3is configured as a vacuum conveyor belt. By virtue of the air flows that exist, both transportation path installations19ofFIG. 2andFIG. 3form negative pressure preferably on the lower side of the transportation path installation19. On account thereof, it is possible for the raised end feeding strip14that is guided by way of the compressed air of the compressed air installation18to be moved to the subsequent treatment unit4. The end feeding strip14is picked up by the vacuum catching installation21on a wire belt20of the subsequent treatment unit4.

The transfer of the end feeding strip14thus achieved represents a temporarily closed transfer. To this extent, it is essential that controlled raising, transferring, and subsequent controlled picking up is possible on account of the configuration according to the invention.

As is illustrated inFIG. 1a, the treatment unit4is a hydroentanglement unit, for example. The end feeding strip14can be further stabilized by way of such hydroentanglement. On the free transfer subsequent to this hydroentanglement, at the junction9, the transfer of the end feeding strip can again be raised from the wire belt20of the treatment unit4by compressed air and, based on the same principle, by way of a transportation installation19that generates negative pressure can be transferred to a next wire belt22of a subsequent treatment unit6. According toFIG. 1a, this further treatment unit6is a vacuum dewatering unit, for example.

The end feeding strip14after the wire belt22of such vacuum dewatering is most often sufficiently stable in order to be able to be introduced into a rope cutter. Raising can again be performed by way of the wire belt by compressed air. The end feeding strip14can be caught by an air baffle or a further wire belt and be transferred to a rope cutter. The transfer of the end feeding strip14as described by way of the temporarily closed transfer can be readily carried out at production speeds between 200 and 250 m/min and more.

Once the end feeding strip14has been guided through the dryer, for example the treatment unit7, and a quality assurance unit25up to the winder5, the non woven web10on the wire installation3can be run at the full product width. After the wire installation3, the wet non woven herein is sufficiently stable in order to be guided also by way of the entire product width directly by way of a free transfer to the next treatment unit.

In the case of the production speeds just mentioned, any change in the raising of the non woven web can rapidly lead to web ruptures. Therefore, a variable vacuum suction box26that is displaceable along the wire belt11is preferably fitted below the wire belt11of the wire installation3. Once the non woven web runs at full width on the production line, the position of the product web lift can be defined with this vacuum suction box26precisely by way of an adjustment of the vacuum suction box26, on the one hand, and of the setting of the vacuum, on the other hand. The free transfer between the vacuum suction box26of the wire installation3and the vacuum catching installation21of the subsequent treatment unit4can thus be defined in a precise manner. Unequal raising of the product web is prevented. The product web tension between the two wire belts11,20is preferably controlled by way of a slack regulator. The same explanations apply to the junction9between two treatment units4,6.

According to the invention, the non woven web can be transferred in a more cost-effective manner as compared to conventional solutions, and the controlled free transfer moreover offers a cost-effective solution for guiding a product web.

The aforementioned slack control can be complemented by a control device for controlling lifting, transferring, and picking up an end feeding strip14at the junctions8,9having a web feeding13.