Patent Application
20090283236
1. Field of the Invention
The invention relates to an apparatus to produce a fibrous web having a three-dimensional surface structure, especially a paper, cardboard or tissue web and which is equipped with a headbox, a forming element, especially a forming roll, a structured fabric and a dewatering fabric, whereby the structured fabric and the dewatering fabric run together and form a stock infeed nip and are carried over the forming element whereby the structured fabric is the inside fabric and the dewatering fabric is the outside fabric and whereby fibrous suspension is fed into the stock infeed nip by way of the headbox. An apparatus of this type is described, for example in WO 2005/075737 A1.
2. Description of the Related Art
With an apparatus of this type problems regarding the running characteristics or runability can occur, especially at higher machine speeds. In view of the circumstance that the structured fabric, which may, for example, be a woven wire instead of a felt on which the fibrous web is formed, carries a large volume of water along with it and is open—in other words is highly permeable—and based on the fact that the basis weight of the fibrous web is very low, a very large volume of water is drawn through the fibrous web into the area of the outfeed nip between the forming element, or respectively the forming roll, and the structured fabric running off the forming roll. As can be seen from the layout in
As can be seen in
As can be seen in
An additional disadvantage is that the water which was removed from the fibrous web 24 in the manner described also contains fibers and fines which accumulate on the top surface or inside surface of the structured fabric 14. If a suction box, especially for wet embossing, is provided inside the loop of the permeable structured fabric 14, then fibers and fines can also accumulate on the front side of such a suction box.
An additional disadvantage of the aforementioned devices of the type described consists in that the guide rollers which are located inside the loop of the structured fabric clog within a very short time period with fibers and fines. This results in the production machinery having to be shut down at short intervals for cleaning purposes which inevitably leads to corresponding production losses.
What is needed in the art is an improved apparatus of the type mentioned at the beginning whereby the aforementioned disadvantages are eliminated. In particular, the runability and efficiency of the apparatus are to be increased.
The present invention provides that in the area of the outfeed nip which is formed between the forming element and the structured fabric running off the forming element at least one catch pan is provided for water, fibers, fines, and/or other substances accumulating in the area of this outfeed nip.
Considerably higher runnability and higher efficiency of the apparatus result due to this configuration. The catch pan located in the area of the outfeed nip ensures that water drops no longer get onto the structured fabric. The invention is particularly applicable in tissue production, as described in WO 2005/075737 A1.
The catch pan includes preferably an outlet and a wall section in order to catch water accumulating in the area of the outfeed nip and to direct it to the outlet.
The outlet is advantageously connected to a vacuum source.
According to one practical advantageous embodiment of the inventive apparatus, the catch pan includes a base section with one side facing the structured fabric, whereby on this side of the base section which is facing the structured fabric at least one suction equipped orifice is provided.
Preferably several suction equipped orifices are provided on the side of the base section facing the structured fabric.
In this arrangement the at least one orifice is advantageously connected with a vacuum chamber which is provided in the base section. This vacuum chamber is advantageously connected with a vacuum source.
The at least one orifice can be especially in the embodiment of a bore, a slot or a similar form.
The structured fabric may possess a progression having a horizontal component in the area adjacent to the forming element. This arrangement also ensures that no water drops get onto the top surface of the structured fabric thanks to the catch pan which is located in the area of the outfeed nip.
The structured fabric is preferably designed as an open or permeable fabric.
In this arrangement this structured fabric possesses advantageously a permeability of >200 cfm, especially >400 cfm and preferably >600 cfm (cfm=cubic feet per minute).
Viewed in direction of web travel at least one suction equipped embossing unit is provided following the forming element and is located on that side of the permeable structured fabric which faces away from the fibrous web and through which the fibrous web is sucked into the structure of the structured fabric.
It is especially advantageous in this arrangement if the suction equipped embossing unit includes a base section with one side facing the permeable structured fabric and a front edge on the fabric side when viewed in the direction of web travel, and if the embossing unit is equipped with at least one suction channel located in the area of the front edge of the base section, in order to suck off contaminants, water drops, fines, fibers, and/or similar substances which are carried along by the permeable structured fabric.
On the side of the base section of the suction equipped embossing unit facing the structured fabric, at least one suction equipped orifice is advantageously provided which can be connected with a vacuum chamber that is provided in the base section of the embossing unit. In this arrangement this vacuum chamber of the embossing unit is advantageously connected with a vacuum source.
The suction channel and the orifice are preferably connected with the same vacuum chamber of the embossing unit.
It is also particularly advantageous if at least one embossing unit is located in an area where the dry content of the fibrous web is <35%.
The apparatus includes preferably a drying unit with a suction roll and a hood allocated to it.
The fibrous web is hereby preferably routed over the suction roll, together with the permeable structured fabric, whereby the fibrous web is positioned between the permeable structured fabric and the suction roll.
The permeable structured fabric and the fibrous web are advantageously pressed against the suction roll by a permeable press belt.
The specific pressing pressure produced by the permeable press belt is hereby preferably ≦1.5 bar and especially ≦1 bar.
It is also of particular advantage if additionally a dewatering fabric which is located between the suction roll and the permeable structured fabric is routed around the suction roll.
It is also of particular advantage if, subsequent to the drying device, the fibrous web is run through a press nip which is formed between a drying cylinder, especially a Yankee-cylinder, and a press element.
Preferably at least one suction equipped embossing unit is provided between the forming element and the drying device.
Alternatively, or in addition at least one suction equipped embossing device can also be provided between the drying device and the press nip which is formed between the drying cylinder the press element.
According to a preferred design variation of the inventive apparatus at least one cleaning device is allocated to at least one guide roll which is located inside the loop of the structured fabric.
The cleaning device can specifically include a doctor blade, a catch pan and/or a similar device.
The machine operating speed is preferably >900 m/min. and preferably >1200 m/min.
The structured fabric is preferably in the embodiment of a woven wire.
The basis weight of the fibrous web is preferably <40 g/m2, preferably <25 g/m2.
The invention is applicable especially in the production of tissue, as described in WO 2005/075737 A1.
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 apparatus 30 includes a headbox 34, a forming element, especially a forming roll 36, a preferably permeable structured fabric 38 and a dewatering fabric 40.
In this arrangement the structured fabric 38 and the dewatering fabric 40 run together and form a stock infeed nip 42. They are run over the forming roll 36 whereby the structured fabric 38 is the inside fabric and the dewatering fabric 40 is the outside fabric. The fibrous stock suspension is fed into the stock infeed nip 42 by way of the headbox 34.
As can be seen especially also in
Immediately following the forming roll 36, the outside dewatering fabric 40 which is not in contact with the forming roll 36 is again separated from the fibrous web 32 and the permeable structured fabric 38 which supports the web.
The catch pan 46 includes an outlet 48 and a wall section 50 in order to collect water accumulating in the area of the outfeed nip 44 and to direct it to the outlet 48.
The outlet 48 is connected with a vacuum source, for example through a discharge pipe 52 or a similar component.
As can be seen especially in
The orifices 58 adjacent to the structured fabric 38 are connected with a vacuum chamber 60 which is located in the base section 54 and which can be connected to a vacuum source.
The orifices 58 can for example be in the form of bores, slots or similar forms. In the illustrated design variation the structured fabric 38 progresses diagonally downward in the area adjacent to the forming roll 36. Hence, its progression possesses a horizontal component. As already mentioned, the structured fabric 38 is preferably designed as an open or permeable fabric.
After the forming roll 36 when viewed in direction of web travel L at least one suction equipped embossing unit 62 can be provided which is located on the side of the permeable structured fabric 38 facing away from the fibrous web 32 and through which the fibrous web 32 is sucked into the structure of the structure fabric 38 (compare
As can be seen especially in
In addition at least one suction equipped orifice 72 is provided on the side 66 of the base section 64 of the suction equipped embossing unit 62 which faces the structured fabric 38. This orifice 72 is connected with a vacuum chamber 74 which is located in the base section 64 of the embossing unit 62. The vacuum chamber 74 is advantageously connected with a vacuum source.
In the current design example the suction channel 70 and the orifice 72 are connected with the same vacuum chamber 74 of the embossing unit 62.
Preferably at least one embossing unit 62 is located in an area where the dry content of the fibrous web 32 is <35%.
In the illustration according to
As can be seen in
A suction equipped embossing unit 62 of this type is necessary to produce a fibrous web or tissue web with a three-dimensional surface structure. It supports the formation of the three-dimensional voluminous form of the fibrous web, especially a tissue web, whereby the fibrous web is sucked into the structure of the structured fabric, preferably at a dry content of less than 35%. In order to produce the referred to fibrous web one, or also several, such suction-equipped embossing units 62 may be provided. In order to avoid accumulation of fibers and fines at the front edge of the embossing unit, the suction channel 70 is provided through which contaminants, especially dust or similar substances, water drops, fines and fibers which are carried along by the structured fabric are sucked off.
As can be seen in
In this layout the fibrous web 32 is carried over the suction roll 84 together with the permeable structured fabric 38, whereby the fibrous web 32 is located between the permeable structured fabric 38 and the suction roll 84.
The permeable structured fabric 38 and the fibrous web 32 can be pressed by a permeable press belt 88 against the suction roll 84. A specific pressing pressure generated by the permeable press belt 88 of ≦1.5 bar and especially ≦1 bar is preferred.
In addition, a dewatering fabric 90 which is located between the suction roll 84 and the permeable structured fabric 38 can be routed around the suction roll 84.
In this arrangement therefore, hot air may especially flow successively from the hood 86 through the permeable press belt 88, the permeable structured fabric 38, the fibrous web 32 and the dewatering fabric 90 into the suction zone 92 of the suction roll 84. For this purpose the hood 86 is located, at least substantially in the area of the suction zone 92 of the suction roll 84.
Following the drying device 82 the fibrous web 32 is run through a press nip 98 which is formed between a dryer cylinder 94, especially a Yankee-cylinder and a press element 96. As illustrated, the press element 96 can be in the embodiment, for example, of a press roll.
In the current design example at least one suction equipped embossing unit 62 each is provided between the forming roll 36 and the drying device 82, as well as between the drying device 82 and the press nip 98.
It is also especially advantageous if a cleaning device 102 is allocated to at least one guide roll 100, including the press roll 96 which are located inside the loop of the structured fabric 38. Such a cleaning device 102 could for example include a doctor blade 104, a catch pan 106 and/or a similar device.
The structured fabric 38 can especially be in the embodiment of a woven wire.
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.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2006 062 236.7 | Dec 2006 | DE | national |
This is a continuation of PCT application No. PCT/EP2007/064201, entitled “APPARATUS FOR PRODUCING A FIBROUS WEB”, filed Dec. 19, 2007 which is incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/EP2007/064201 | Dec 2007 | US |
| Child | 12487974 | US |
