1. Field of the Invention
This invention relates to a machine for producing a fibrous web, in particular a paper web, paperboard web or tissue web, having a former on which the fibrous web is formed on a structured belt and is dewatered between said structured belt and a forming belt, and having a drying apparatus for the further dewatering of the fibrous web, through which the fibrous web is guided together with the structured belt and in which hot air flows through the permeable structured belt and the fibrous web. Such a machine is described for example in WO 2005/075737 A1.
2. Description of the Related Art
Also known already from WO 00/75423 A1 is a so-called printed forming fabric.
Such a printed forming fabric can be used for example on conventional tissue machines. However, there is no advantage in using a printed forming fabric for an application on such conventional tissue machines because the sheet is pressed 100% and the volume is too small to produce a micro-embossed and macro-embossed sheet on the machine. A suitable processing plant is required for embossing the sheet.
A printed forming fabric can also be used on a TAD machine (TAD=Through Air Drying) where the volume and the sheet absorption capacity are 50 to 100% greater than on conventional machines.
As can be seen from
Because a vacuum is applied to an already formed fibrous web with a consistency of over 20%, the fibers are stretched into the depressions, as the result of which the sheet thickness is reduced and only a small part of the fibers remains protected inside the structure of the belt, whereby the fibers in question are those which are not pressed in order to achieve a certain quality (cf.
With such a micro-embossing and macro-embossing on the machine it would be possible to avoid performing such an embossing on the processing plant and hence compressing the sheet and sacrificing quality.
On a TAD machine, quality is thus produced in the TAD zone. The negative draw (˜0.8 V) on such a machine serves to produce quality but destroys the embossing effect. Also evident in
What is needed in the art is a machine of the type initially referred to which in terms of the quality, volume and water absorption capacity of the produced fibrous web is comparable to a TAD machine.
The present invention provides that the forming belt is formed by a printed forming fabric or a dimensional structured paper (DSP) fabric with zonally different permeability. The printed forming fabric can be in particular such a printed forming fabric as described in WO 00/75423 A1.
Disclosed according to the invention is therefore a machine for producing a fibrous web, in particular a paper web, paperboard web or tissue web, which includes a former on which the fibrous web is formed on a structured belt and is dewatered between said structured belt and a printed forming fabric or DSP fabric with zonally different permeability, and a drying apparatus for the further dewatering of the fibrous web, through which the fibrous web is then guided together with the structured belt and in which hot air flows through the permeable structured belt and the fibrous web.
Because the produced fibrous web is already wet-structured on the machine, it is no longer necessary for the web to be embossed further upon passing through an expensive processing plant in order to press the micro and macro structures into the fibrous web. In particular this avoids having to press the structure into the already dried fibrous web in a processing plant, which would entail compressing the web, as the result of which the quality, volume and absorption capacity would be reduced.
The printed forming fabric or DSP fabric can be formed by a forming fabric whose surface coming into contact with the fibrous suspension is coated with local lines, dots and/or the like.
In this case the coating material can include for example plastic, rubber and/or the like.
If the coating material includes plastic, then it includes expediently polyethylene, polyamide, polyurethane and/or the like.
As already mentioned, the printed forming fabric used can be constructed as described in WO 00/75423 A1.
Advantageously the printed forming fabric or DSP fabric is provided for a macro-embossing of the fibrous web and the structured belt for a micro-embossing of the fibrous web.
It is an advantage in particular for the fibrous web to be formed with a consistency in the range from around 0.15 to around 0.35% on the structured belt.
On a practical embodiment of the inventive machine, the fibrous web is dewatered further in the drying apparatus between the structured belt and a dewatering belt, whereby the hot air flows through the permeable structured belt, the fibrous web and the dewatering belt in succession.
The drying apparatus includes advantageously an evacuated device such as in particular a suction roller, over which the structured belt, the fibrous web and, if required, the dewatering belt are guided.
The structured belt, the fibrous web and, if required, the dewatering belt can be pressed by way of a permeable press belt against the evacuated device. In this case the hot air can flow first through the permeable press belt and then through the fibrous web.
The drying apparatus includes expediently a hot air hood.
Advantageously this hot air hood lies at least essentially opposite a suction zone of the evacuated device.
It is an advantage in particular for a press nip for the fibrous web, extended in the web running direction, to be formed above the evacuated device.
On a preferred practical embodiment of the inventive machine, the fibrous web is guided together with the structured belt directly after the drying apparatus through a press nip formed between a drying cylinder, in particular a Yankee cylinder, and a press element.
In this case provision can be made for a way to crépe the dry fibrous web in the region of the drying cylinder.
The machine can be used preferably for producing tissue paper.
According to the invention the fibrous web is dewatered between a structured belt or embossing belt and a printed forming fabric or DSP fabric. A further dewatering of the fibrous web takes place expediently between the structured belt and a dewatering belt. The fibrous web is dewatered by way of the dewatering belt which lies opposite the structured belt. The dewatering takes place by way of an air current, in particular a hot air current, and a mechanical pressure field, which can be created by way of a permeable press belt. The air current extends from the permeable press belt to the dewatering belt. The belts, which lie in sandwich fashion one above the other, form a press nip, which is extended in the web running direction, above an evacuated device such as in particular a suction roller. The maximum peak pressure in this case can be 40 times lower than on a conventional press, whereby said extended press nip is charged with air in addition. The fibrous web is carried and/or protected by the structured web and advantageously passed on to a Yankee drying apparatus. The fibrous web is dried further and dry-créped by said drying apparatus which includes for example a Yankee cylinder and a hood.
With such an inventive machine, a structured fibrous web comparable to a TAD product is produced. The same high quality is obtained without an elaborate and expensive TAD machine being required. The cost can be reduced to approximately 40%, whereby less equipment and less work are needed. The machine can be kept simpler in design, whereby its operation and maintenance are also simplified. The entire outlay including energy, sheathing, chemicals etc. is reduced to approximately 35%.
It is also an advantage in particular that on the inventive machine the fibrous web is formed on a structured belt, whereby the forming can begin with a very low consistency of for example between 0.15 and 0.35% and the same structured belt carries the fibers, protected inside its structure, from the headbox to the point of transfer into the Yankee drying unit. In the Yankee drying unit, only those fibers in the knuckle area of the structured belt are pressed. The protected fibers inside the structure of the structured belt remain unpressed in order to obtain the corresponding quality. The depressions of the structured belt are filled with the largest possible amount of fibers, as this represents the mass of unpressed fibers which accounts for the high quality of the end product. The printed forming fabric or DSP fabric is thus a forming belt with which the depressions of the structured belt are sure to remain filled with the largest possible amount of fibers.
Because the produced fibrous web is already structured, it is no longer necessary for the fibrous web to be embossed further upon passing through an expensive processing plant in order to press the micro and macro structures into the web. This avoids having to press the structure into the dry fibrous web in a processing plant which compresses the web and reduces the quality, volume and absorption capacity accordingly.
It has turned out that with the inventive machine, the micro-embossing can take place within the machine without compressing the fibers on the structured or embossing belt and the macro-embossing can take place by using the special printed forming fabric, as described for example in WO 00/75423 A1. In principle it is also possible, as previously explained, to use a DSP fabric with different permeability. Hence instead of a conventional embossing, a shift of fibers takes place according to the invention in the forming zone. The advantage of this is, among other things, that the intimacy between the belts over the evacuated device, in particular a suction roller, is not lost. The evacuated device or suction roller accounts accordingly for a maximum dewatering and a maximum increase in dry content.
In addition, the printed forming fabric or DSP fabric can be exchanged far more quickly than the structured belt, should an operation of the machine with a different macro-embossing (marking) be required.
Hence it is possible with the inventive machine to obtain a high paper quality while avoiding additional elaborate and expensive processing machines for the micro-embossing and macro-embossing.
The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention will be better understood by reference to the following description of embodiments of the invention taken in conjunction with the accompanying drawings, wherein:
Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate one embodiment of the invention, and such exemplifications are not to be construed as limiting the scope of the invention in any manner.
Referring now to the drawings, and more particularly to
The machine 20 includes a former 24, on which the fibrous web 22 is formed on a structured belt 26 and is dewatered between said structured belt and a forming belt which is formed by a printed forming fabric 28 or a DSP fabric with zonally different permeability.
The machine 20 includes in addition a drying apparatus 30 for the further dewatering of the fibrous web 22, through which the fibrous web 22 is guided together with the structured belt 26 and in which hot air flows through the permeable structured belt 26 and the fibrous web 22.
The printed forming fabric 28 or DSP fabric can be formed in particular by a forming fabric whose surface coming into contact with the fibrous suspension is coated with local lines, dots and/or the like. The coating material can be included in particular plastic, rubber and/or the like. For example, the coating material can include for example polyethylene, polyamide, polyurethane and/or the like.
The printed forming fabric 28 used can be for example such a printed forming fabric as is described in WO 00/75423 A1.
The machine 20 includes a headbox 32 and a forming element such as in particular a forming roller 34 over which the structured belt 26 and the printed forming fabric 28 or DSP fabric are guided.
In this case the structured belt 26 or DSP fabric and the printed forming fabric 28 converge to form a fiber intake nip 36, whereby they are guided with the structured belt 26 as the inner belt and with the printed forming fabric 28 or DSP fabric as the outer belt over the forming roller 34. Fibrous suspension is fed by way of the headbox 32 into the fiber intake nip 36.
After the forming roller 34, looking in the web running direction L, it is possible to provide at least one evacuated embossing device 38 which is arranged on the side of the permeable structured belt 26 facing away from the fibrous web 22 and by way of which the fibrous web 22 is sucked into the structure of the structured belt 26.
As can be seen from
For this purpose the drying apparatus 30 includes an evacuated device, in particular a suction roller 42, over which the structured belt 26, the fibrous web 22 and the dewatering belt are guided.
In this case the structured belt 26, the fibrous web 22 and the dewatering belt 40 can be pressed by way of a permeable press belt 44 against the suction roller 42. Hence in the case in question, drying air, in particular hot air, flows through the permeable press belt 44, the structured belt 26 and the fibrous web 22 in succession.
In the case in question the drying apparatus 30 includes a hot air hood 46, which can lie at least essentially opposite a suction zone of the suction roller 42.
Hence above the suction roller 42 there is formed a press gap which is extended in the web running direction L and is charged, at least in some regions, simultaneously with hot air.
The fibrous web 22 is guided together with the structured belt 26 directly after the drying apparatus 30 through a press nip 52 formed between a drying cylinder 48, in particular a Yankee cylinder, and a press element 50, in this case for example a press roller. In addition, provision can be made for a way to crépe the dry fibrous web 22 in the region of the drying cylinder or Yankee cylinder.
As is evident from
The printed forming fabric 28 or DSP fabric is provided for a macro-embossing of the fibrous web 22 and the structured belt 26 for a micro-embossing of the fibrous web 22.
The fibrous web 22 can be formed in particular with a consistency in a range from around 0.15 to around 0.35% on the structured belt 26.
While this invention has been described with respect to at least one embodiment, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.
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