Method and Device for Applying a Coating Medium in a Machine Used for Producing a Fiber Web

Abstract

Disclosed is a machine for producing a paper web, cardboard web, or other fiber web (1), comprising a press section (2) which is provided with at least one press nip (5) formed by two squeeze rollers (3, 4) and in which a device (6, 7) for applying a medium, particularly starch, is disposed. The fiber web (1) can be guided through the press nip (5) along with a band (8). The inventive machine is characterized in that the device (6, 7) rests against at least one of the squeeze rollers (3, 4) for indirectly applying the medium to the fiber web (1).

Description

The invention relates to a machine for the production of a fibrous web of paper, card or other material which has at least one pressing section consisting of a pressure nip formed by two press rollers in which a device for the application of a medium and, in particular, of starch is arranged, where the fibrous web together with a belt can be passed through the pressure nip.

In DE 100 33 213 A1 a process and a device are described for a one- or two-sided application of a liquid to paste-like medium, preferably of starch, onto a material web, preferably of paper or card and, in particular, of corrugated board where first of all the material web is provided with a one- or two-sided application and then first passes through a pressure nip. According to one exemplary embodiment, the starch is applied by application rollers. The disadvantage of this solution is that no closed web guidance system is provided ahead of the application unit. As a consequence of free draws and of the still low tensile strength of the fibrous web within the pressing section an increased number of breaks occur during the production process, particularly when the relative weight per unit area is low, for example, when less than 125 g/cm². Furthermore, there arises the risk of deposits of the applied medium forming on a unit provided after the application device.

WO 99/22067 deals with a process and a device for applying a paste-like application medium onto a moving material web, where firstly the material web is formed in a twin wire zone of a paper machine and where an application device is used to apply a liquid or paste-like application medium to at least one side of the material web. To that end, a further application device is arranged after a press element of the pressing section for the application of a liquid or paste-like application medium onto the material web.

A process and a device for the treatment of a paper or card web in a pressing section is known from WO 00/55423. A first application device sprays an application medium onto the web while this is led by a felt over a suction roll. A second application device sprays an application medium onto the surface of a transfer belt from which the application medium is then transferred to the web. Both application devices are arranged ahead of the first pressure nip.

It is the object of the invention to create a machine which exhibits a pressing section with the capability of applying an application medium and, in particular, starch while simultaneously exhibiting a compact design.

This object is achieved according to the invention by a machine of the type described at the outset in such a manner that the device is attached to at least one of the press rollers for the purpose of indirect application to the fibrous web.

In comparison with the prior art, the combination at one place of the pressing of the fibrous web with the application facility for an application medium creates a more compact design of the machine in the area of the pressing section, whereby a higher degree of operational reliability is guaranteed.

One embodiment of the invention which is particularly advantageous involves the fitting of the at least one device for application to the mantle surface of one of the press rollers and the medium applied to the mantle surface being able to be transferred to the fibrous web in the pressure nip. The press roller to which the application device is attached can also be, in particular, a shoe press roll. The shoe press roll working in association with a conventional cylindrical press roller can be positioned on either the underside or top side of that press roller. The press rolls can be arranged either vertically or inclined with respect to one another.

Additionally, it is advantageous to provide a conditioning device or a cleaning device at the press roller. Such a cleaning device comprises, for example, a spray unit to apply water and, in particular, water in combination with a chemical auxiliary material and/or a doctor or a brush to remove deposits from the press roller.

In another advantageous configuration of the pressing section, provision is made that the at least one device for applying medium to a belt is fitted, in particular in the area of the mantle surface of one of the press rollers and that the medium applied to the mantle surface can be transferred to the fibrous web in the pressure nip.

It is also of advantage to fit a conditioning device or a cleaning device to the belt and this can be of the same design as a cleaning device fitted to a press roller.

Speedy drying of the applied medium is achieved if a drying unit for drying the applied medium on the fibrous web is arranged after the pressure nip with respect to the direction of movement of the web.

According to the invention, two different backwater circulation systems can be used. The backwater in the first circulation system originates from the de-watering section and is re-circulated just ahead of the head box. Water arising from a second backwater circulation system is treated in, for example, a rotary disc filter and used, for example, as spray water. The water enriched with starch from the pressing section is not, however, led to either of these two backwater systems but, rather, to a suitable location in the starch preparation process.

In a further advantageous embodiment of the invention provision is made that a further application device for the application of a medium and, in particular, of starch is arranged in one of the drying sections following the pressing section.

There follows below a more detailed explanation of the invention by means of exemplary embodiments. These show:

FIG. 1 a pressing section in which an application is made to both sides of the fibrous web ahead of the pressure nip,

FIG. 2 the pressing section according to FIG. 1, in which an application is made solely at the shoe press roller, and

FIG. 3 the pressing section according to FIG. 1, in which an application is made solely at the press roller combined with a section of a subsequent drying section.

After a fibrous web 1 (FIG. 1) has passed through a wire part an application medium and, in particular, starch is applied to both sides of it in a pressure nip 5 formed in a pressing section 2 by a press roller 3 and a shoe press roller 4. The application devices 6, 7 perform this activity. The application device 6 carries the application medium to the mantle surface of the press roller 3 while the application device 7 applies the application medium to a felt or a belt 8. Preferably, the medium is applied to the belt 8 in the area of the mantle surface of the shoe press roller 4 but this can also take place at some earlier point.

Finally, the fibrous web 1 accepts the application medium on both sides in the pressure nip 5. Then a drying unit 9, for example a radiant drying unit, arranged close to the fibrous web 1 after the pressure nip 5 dries the application medium.

For cleaning, cleaning or conditioning devices 10 or 11 are arranged both at the mantle surface of the press roller 3 and at the belt 8. In each case, a cleaning liquid is applied. Together with, for example, the support of a mechanical cleaning device, in each instance this removes impurities from the mantle surface or from the belt 8. Preferably, the conditioning device 11 also comprises a doctor 12.

Furthermore, a tensioning device 13 and a controller 14 are provided for the belt 8. The fibrous web 1 is subjected to vacuum extraction by a suction roll 15 through a transfer belt 16 and is then led forward through a drying section with drying cylinders 17.

In an alternative version (FIG. 2) the fibrous web 1 receives only a one-sided application of medium by the application device 7 via the belt 8. A further drying unit 18 is arranged between the suction roll 15 and the drying cylinder 17.

In a further configuration of the invention (FIG. 3) only one application is made to the press roller 3 via the application device 6. Furthermore, the design of the pressing section 2 is the same as shown in FIG. 1 or 2. In a drying section 19 which follows the pressing section 2, the said drying section comprising the drying cylinders 18 and suction-type guide rolls 20, an application of medium is similarly made on the under-side of the fibrous web 2 by a further application device 21. The application device 21 consists of a spray unit 22 which first applies the medium to the mantle surface of a transfer roll 23; from this roll the medium is transferred to the fibrous web 1.

The transfer roll 23 is fitted with a conditioning or cleaning unit 24. Contaminated cleaning liquid flowing away from the transfer roll 23 is led to a discharge channel 25.

Claims

1. A machine for the production of a fibrous web (1) of paper, card or other material which has at least one pressing section (2) comprising a pressure nip (5) formed by two press rollers (3, 4) in which a device (6, 7) for the application of a medium is arranged, where the fibrous web (1) together with a belt (8) can be passed through the pressure nip (5), and wherein the device (6, 7) is fitted to at least one of the press rollers (3, 4) for indirect application onto the fibrous web (1).

2. The machine as claimed in claim 1, wherein the at least one device (6, 7) for application is fitted to a mantle surface of one of the press rollers (3, 4), and wherein the medium applied to the mantle surface can be transferred to the fibrous web (1) in the pressure nip (5).

3. The machine as claimed in claim 2, wherein a conditioning device (10) is fitted to the press roller (3).

4. The machine as claimed in claim 1, wherein the at least one device (6, 7) for applying medium to a belt (8) is fitted in the area of a mantle surface of one the press rollers (4), and wherein the medium applied to the mantle surface can be transferred to the fibrous web (1) in the pressure nip (5).

5. The machine as claimed in claim 4, whereina conditioning device (11) is fitted to the belt (8).

6. The machine as claimed in claim 1, whereina drying unit (9, 18) for drying the applied medium on the fibrous web is arranged after the pressure nip (5) with respect to a direction of movement of the web.

7. The machine as claimed in claim 1, wherein a further application device (21) for the application of a medium onto the fibrous web (1) is arranged in a drying section (19) following the pressing section (2).

8. The machine as claimed in claim 1, wherein the device for application of a medium comprises a device for application of starch.

9. The machine as claimed in claim 7, wherein the further application device for application of a medium comprises a further application device for application of a starch.