DE102006055823A1 - Method for detecting a tear of a fibrous web in a dryer section of a machine for producing the fibrous web and drying wire for carrying out the method - Google Patents

Abstract

The invention relates to a method for detecting a tear of a fibrous web (3) in a dryer section (2) of a machine (1) for producing the fibrous web (3), wherein the fibrous web (3) by means of at least one drying wire (5) through the dryer section (3). 2), wherein the tear is detected by at least one device (8) for web tear detection and wherein a tee (9) for the fibrous web (3) is activated by the device (8) for web tear detection. The inventive method is characterized in that a drying wire (5) with at least one characteristic color pattern (10) is used, which is reliably detected in the event of tearing of the fibrous web (3) by the device (8) for web tear detection. Furthermore, the invention relates to a drying wire (5) for a dryer section (2) of a machine (1) for producing a fibrous web (3), in particular for carrying out the method according to the invention.

Description

The The invention relates to a method for detecting a tear of a Fibrous web in a dryer section of a machine for production the fibrous web, wherein the fibrous web by means of at least a drying wire is passed through the dryer section, the demolition detected by at least one device for web tear detection is and wherein a tee for the fibrous web through the device for web tear detection is activated.

Farther The invention relates to a dryer fabric for a dryer section of a Machine for producing a fibrous web, in particular for carrying out the inventive method.

at the production of all, essentially paper grades formed from pulp suspensions is the fast and reliable Recording of the pulp web breaks during production is extremely important to damage from To prevent parts of the machine for producing the fibrous web.

At Places where the fibrous web is in free-flow, can Railway breaks very reliable be detected, for example by light barriers.

light barriers However, are not suitable in situations where the fibrous web on one also as a railway carrier serving covering, such as a forming fabric, a press felt or a drying wire, rests. Usually come here optical Systems, for example laser or optical waveguide sensors, for Use in which a detector and a light or radiation source the device for web break detection on the same side of Fibrous web are attached.

there Various methods for web tear detection are known.

Thus, in the known method "color recognition" the color difference between the fibrous web and the dryer fabric is used to detect the web break 1 is an example of the waveform of an optical device for web tear detection in the occurrence of a web break in a color intensity-time diagram (Ft diagram) outlined. When exceeding or falling below a predetermined tripping threshold value S (dashed line) of the color intensity F, a signal is given to a stripping device. For example, the trigger threshold value S for the signal to the tee device may be 50% of the color intensity F. This method works especially well with a distinct color difference, such as between a white fibrous web and a green dryer wire.

One Disadvantage of color detection systems is that these all the more unreliable become, the smaller the color difference between fibrous web and Drying screen is. This is for example in machines for manufacturing of cardboard or packaging papers, where brownish paper or board webs rest on red or amber dry sieves, the case. Here can no longer clearly differentiated between fibrous web and dryer fabric become. This will either lead to a web break detection without Demolition or demolition without web break detection. The former leads to one unnecessary Production stoppage and thus financial losses for the operator of the car the latter involves the risk of damaging the machine.

moreover can Deteriorate dryer fabrics with increasing service life, causing the actual color of the dryer through the dirt deposits is covered. In such cases it has been proven that a color detection system as well no longer reliable works.

One Another known method is the "detection of changes in light scattering (pseudo-texture recognition) ", where light is on the structured Drying screen is scattered differently than on the fibrous web. This Difference is used to detect web breaks.

It has also turned out to be pseudo-structural recognition systems also not reliable function. This is probably due to dirt in the dryer or on the transparency of the still partially moist fibrous web due.

Of the Invention is therefore based on the object, a method and a To develop the dryer fabric of the aforementioned types in such a way that compared to the prior art, a more reliable Detection of web breaks in particular single-row dryer sections a machine for producing a fibrous web is made possible.

These Task is according to the invention in a Method of the type mentioned solved in that a drying wire with at least one charateristic color pattern is used, which in the case of the tearing of the fibrous web from the device to Rail break detection reliably recorded becomes.

The inventive task is completely solved in this way.

By the use of at least one characteristic color pattern, which less vulnerable across from Dirt on the dryer fabric or discoloration of the fibrous web and / or the dryer fabric, the reliability of the detection of the Tear off the fibrous web markedly improved, especially in Regard to the conventional ones Method.

moreover will be compared with the conventional ones Process according to the invention now monitored more than one characteristic color. By the combination the two color measurements become the reliability of the demolition detection in turn improved.

And a further advantage of the method according to the invention is that the at least one color pattern to be detected is substantially larger than the structures of the dryer fabric is thus less susceptible to soiling in the fabric Drying screen is.

With The term "color" is used in the context of the present Revelation Light with a specific wavelength or light from one certain wavelength range, such as the R channel in an RGB sensor. UV and IR radiation are included in it.

In a first preferred embodiment The characteristic color pattern of the dryer fabric is replaced by several different colored and preferably transverse to its direction aligned color stripes formed. The color stripes of the dryer fabric can have a variety of different colors. These too Multi-color bears to a significant improvement in the reliability of the demolition detection at.

Under Practical conditions will be the characteristic color pattern of Drying screen preferably formed by a plurality of differently colored threads. Thus, targeted in the production of the dryer and relatively inexpensive influence on his later Use be taken.

In first version For example, the characteristic color pattern is preferred in a woven dryer fabric through differently colored wefts generated. So can for the weft threads white polytetrafluoroethylene and for the warp threads red polyester can be used. The basic color of the dryer can be red, for example, every 30 cm can be a white color strip be present, with next to every fourth white color strip a black Color stripe is arranged. As a minimum width for the characteristic Color pattern is preferably a thread thickness of the weft thread used.

In second and alternative execution For example, the characteristic color pattern may be preferred in a spiral screen through differently colored Spirals are generated. Spiral screens made of differently colored spirals exist, are due to the nature of the production of spiral screens without much extra Extra effort and thus without considerable Additional costs monochrome seven to make. As a minimum width for the characteristic Color pattern in this case preferably a spiral thickness of the spiral is used.

Further can be the maximum width of the characteristic color pattern result in a preferred embodiment of the maximum permissible track length, on the machine for producing the fibrous web still no Damage caused before the teeper through the facility for Web break detection is activated. A typical value would be for Example 10 m track length, that means that The color pattern on the dryer should be repeated every 10 m at the latest. Color stripes that are much wider than 10 m would therefore no longer make sense do.

The Color stripes of the characteristic color pattern can be found in of course, of course vary. For example, a dryer can be 90 cm wide red and 10 cm wide white stripes consist.

Farther can the characteristic color pattern also by a subsequent coloring of the Drying screen, preferably by means of a thermography generated become. This provides the advantage that the same dryer fabrics, if necessary in larger quantities to lower unit costs prepared, usable due to different colorations for different cases can be made.

at the execution the method according to the invention can also be a dryer with a only partially arranged characteristic color patterns are used. The color stripes can So they only have a certain strip length, that means they have to be not necessarily over extend the entire width of the dryer fabric. This may be the case Provide advantage reduced manufacturing costs for the dryer fabric.

The detection of the tear of the fibrous web can be carried out according to the invention by means of various measuring methods: Thus, a point measurement, such as a laser beam, a light beam or the like, a line measurement, such as a line scan camera or the like, and / or a surface measurement, such as a CCD camera or the like, who uses the. All measurement methods are characterized by high reliability and good usability even in difficult environments.

Further can for detecting the tear of the fibrous web in a preferred execution a difference between a non-periodic, in particular stochastic signal of fibrous web and a periodic Signal of the characteristic color pattern can be used. It must So the color change of the color stripes or even by the color change caused periodic signal to be detected.

Of the recorded demolition of the fibrous web is preferred over a Fourier or power spectrum of the signal evaluated, with a for the Dry sieve characteristic frequency at least one tripping threshold is set. The characteristic tripping frequency results here from the width of the color strip and the speed of the fibrous web. In addition, it is advantageous if the characteristic frequency through the choice of the widths of the color strips is adjustable.

The inventive task is achieved in a dryer of the type mentioned fact that it is provided with at least one characteristic color pattern, which in the case of the tear of the fibrous web of a demolition detector reliable is detected.

The inventive task is completely solved in this way again and it results in the already mentioned inventive advantages.

Further Features of the dryer according to the invention and further advantages of the invention will become apparent from the following Description of preferred embodiments with reference to the drawing.

It demonstrate

1 an exemplary waveform of an optical device for web tear detection upon the occurrence of a web break;

2 a schematic representation of a portion of a machine for producing a fibrous web according to an embodiment of the invention;

3 an exemplary waveform of a solution according to the invention;

4 a detection of a tear of a fibrous web by a Fourier spectrum;

5 a fragmentary plan view of a formed from threads dryer fabric, which has a first embodiment of a characteristic color pattern, and

6 a fragmentary plan view of a formed of spiral filaments dryer fabric, which has a second embodiment of a characteristic color pattern.

In the 2 is a side view of a schematic section of a dryer section 2 a general with 1 designated machine for producing a fibrous web 3 shown.

In a conventional manner, the dryer section fulfills 2 inside the machine 1 the function of a manufactured and / or processed fibrous web 3 To remove moisture, that is to dry it.

I'm in the 2 As shown, this is done by contact drying, with a in the drawing from the left to be supplied fibrous web 3 by direct contact with a plurality of drying cylinders 4 on the one hand and one the drying cylinders 4 circulating endless drying wire 5 on the other hand is dried.

In the 2 are two dryer fabrics 5 shown in their complete circulation path, each of the dryer fabrics 5 each a group of drying cylinders 4 circulates. More exactly, every drying wire runs 5 in the field of drying cylinders 4 wavy up and down, with the drying wire 5 on the wave mountain of a drying cylinder 4 is deflected and in the trough of a suction roll of a respective vacuum device 6 is diverted. After leaving the last drying cylinder 4 the corresponding group becomes the dryer fabric 5 over several guide rollers 7 back to the first drying cylinder 4 returned to the group.

To carry out the method according to the invention for detecting a tear of a fibrous web 3 in the dryer section 2 the machine 1 for the production of the fibrous web 3 is for each group of drying cylinders 4 at least one symbolically indicated device 8th provided for web tear detection, which will be described later. Moreover, for each group of drying cylinders 4 at least one only schematically indicated tee 9 for the fibrous web 3 provided by the institution 8th is activated for web break detection.

Further, in each group of drying cylinders 4 a woven from threads fabric dryer 5 with at least one characteristic color pattern 10 used, which in case of demolition of the fiber material web 3 from the institution 8th is reliably detected for web break detection.

For the detection of the tear of the fibrous web 3 either a point measurement such as a laser beam, a light beam or the like, a line measurement such as a line scan camera or the like, and / or an area measurement such as a CCD camera or the like are used. Since these preferred measuring methods are known to the person skilled in the art, their further description is not discussed here. This is how to capture the tear of the fibrous web 3 So a difference between a non-periodic, especially stochastic signal of the fibrous web 3 and a periodic signal of the characteristic color pattern 10 used. To detect a break, the color change of the characteristic color pattern must be 10 or also by the color change of the characteristic color pattern 10 caused periodic signal to be detected.

The recorded outline of the fibrous web 3 is evaluated via a Fourier or Powerspektrum the signal, with one for the drying wire 5 characteristic frequency f at least one trigger threshold S is set (see. 4 ).

The characteristic triggering frequency results from the width of the characteristic color pattern 10 and the velocity v (arrow) of the fibrous web 3 ,

The 3 shows an exemplary waveform of a solution according to the invention in a color intensity-time diagram (Ft diagram).

When a predetermined tripping threshold S (dashed line) of the color intensity F is exceeded, a signal is applied to the signal in the 2 indicated tee 9 the corresponding group of drying cylinders 4 given. Thus, the trigger threshold S for the signal to the tee device, for example, at 50% of the color intensity F lie. After the pulp web has been torn off, the different colors, in the present case the two colors 1 and 2, of the characteristic color pattern are recorded.

The 4 shows a detection of a tear of a fibrous web by a Fourier spectrum, once in the situation before demolition (left) and once in the situation after the demolition (right). In the respective intensity-frequency diagram (If diagram), the characteristic frequency f of the corresponding color pattern is shown. On the other hand, in the situation before demolition, the characteristic frequency f does not exceed the tripping threshold value S. On the other hand, in the situation after demolition, the characteristic frequency f exceeds the tripping threshold value S at least once, thereby applying a signal to that in the 2 indicated tee 9 the corresponding group of drying cylinders 4 is generated.

The 5 shows a fragmentary plan view of one of threads 11 formed dryer fabric 5 which is a first embodiment of a characteristic color pattern 10 having. And the 6 shows a partial plan view of a spiral threads 12 formed dryer fabric 5 which is a second embodiment of a characteristic color pattern 10 having.

Both illustrated dryer fabrics 5 are outstandingly suitable for carrying out the method according to the invention. So is every dryer 5 with at least one characteristic color pattern 10 provided, which in the case of the tear of the fibrous web 3 from a demolition detector of the device 8th is reliably detected for web break detection (see. 2 ).

The characteristic color pattern 10 every one in the 5 shown dryer fabric 5 consists of several differently colored and preferably transversely to the direction L (arrow) aligned color stripes 13 , which in turn preferably consists of a plurality of preferably differently colored threads 14 consist. Exemplary is only a color strip 13 shown, consisting of seven differently colored threads 14 consists. This can be different threads 14 of course the same color.

This is the characteristic color pattern 10 at the woven dryer 5 of the 5 from seven preferably differently colored weft threads 14 , The weft threads 14 are made of white polytetrafluoroethylene and the warp threads 15 made of red polyester. Alternatively and not explicitly shown, the drying wire 5 have the basic color red and every 30 cm have a white color stripe, where next to each fourth white color strip is a black color stripe.

Furthermore, the characteristic color pattern has 10 in a woven dryer 5 a minimum width Bmin in the range of a thread thickness DF of the weft thread 14 on.

On the other hand, there is the dryer screen designed as a spiral screen 5 of the 6 the characteristic color pattern 10 through differently colored spirals 16 , This shows the characteristic color pattern 10 a minimum width Bmin in the region of a spiral thickness DS of the spiral 16 on.

In both embodiments, the characteristic color pattern 10 a maximum width Bmax, which results from the maximum permissible track length on the machine 1 for the production of the fibrous web 3 still no harm done before the teeper 9 through the device 8th is activated for web break detection (cf. 2 ).

Moreover, the color stripes 13 vary in width. That's how the dryer fabric works 5 for example, from 90 cm wide red and 10 cm wide white stripes 13 consist. The characteristic color pattern 10 Alternatively, it can also be made from a subsequent dyeing of the dryer fabric 5 , preferably by means of a thermography known in the art, and it may also only partially on the drying wire 5 to be available. In other words: the color stripes 13 may have a certain length, that is, they do not necessarily have to be over the entire transverse width of the dryer fabric 5 extend.

In summary It should be noted that by the invention, a method and a Dryer fabric of the aforementioned types are developed in such a way that compared to the prior art, a more reliable Detection of web breaks in particular single-row dryer sections a machine for producing a fibrous web is made possible.

1

machine for producing a fibrous web

2

drying section

3

Fibrous web

4

drying cylinders

5

dryer

6

Vacuum device

7

leadership

8th

Facility for web break detection

9

cutting device

10

characteristic color pattern

11

thread

12

spiral thread

13

color stripes

14

weft

15

warp

16

spiral

Bmax

maximum width

Bmin

minimal width

DF

thread thickness

DS

spiral thickness

F

color intensity

f

frequency

I

intensity

L

direction (Arrow)

S

triggering

t

Time

v

speed (Arrow)

Claims (27)

Method for detecting a tear of a fibrous web ( 3 ) in a dryer section ( 2 ) of a machine ( 1 ) for producing the fibrous web ( 3 ), whereby the fibrous web ( 3 ) by means of at least one drying wire ( 5 ) through the dryer section ( 2 ), the demolition being carried out by at least one device ( 8th ) is detected for web tear detection and wherein a tee device ( 9 ) for the fibrous web ( 3 ) by the institution ( 8th ) is activated for web tear detection, characterized in that a drying wire ( 5 ) with at least one characteristic color pattern ( 10 ), which in the case of the tearing of the fibrous web ( 3 ) of the institution ( 8th ) is reliably detected for web tear detection. Method according to claim 2, characterized in that the characteristic color pattern ( 10 ) of the drying wire ( 5 ) by a plurality of differently colored and preferably transversely to the running direction (L) aligned color stripes ( 13 ) is formed. Method according to claim 1 or 2, characterized in that the characteristic color pattern ( 10 ) of the drying wire ( 5 ) by several differently colored threads ( 11 ; 12 ) is formed. Method according to claim 3, characterized in that the characteristic color pattern ( 10 ) in a woven dryer fabric ( 5 ) by differently colored weft threads ( 14 ) is produced. Method according to claim 4, characterized in that for the weft threads ( 14 ) white polytetrafluoroethylene and for the warp threads ( 15 ) is used red polyester. Method according to claim 4 or 5, characterized in that the minimum width (Bmin) for the characteristic color pattern (Bmin) 10 ) a thread thickness (DF) of the weft thread ( 14 ) is used. Method according to claim 3, characterized in that the characteristic color pattern ( 10 ) in a spiral screen by differently colored spirals ( 16 ) is produced. Method according to claim 7, characterized in that the minimal width (Bmin) for the characteristic color pattern (Bmin) 10 ) a spiral thickness (DS) of the spiral ( 16 ) is used. Method according to one of claims 6 or 8, characterized in that the maximum width (Bmax) of the characteristic color pattern ( 10 ) is the maximum permissible track length on the machine ( 1 ) for producing the fibrous web ( 3 ) caused no damage before the tee ( 9 ) by the institution ( 8th ) is activated for web tear detection. Method according to one of the preceding claims, characterized in that the characteristic color pattern ( 10 ) by a subsequent coloring of the drying wire ( 5 ), preferably by means of a thermography. Method according to one of the preceding claims, characterized in that a drying wire ( 5 ) with a characteristic color pattern arranged only in regions ( 10 ) is used. Method according to one of the preceding claims, characterized in that for detecting the tear of the fibrous web ( 3 ) a point measurement such as a laser beam, a light beam or the like is used. Method according to one of the preceding claims, characterized in that for detecting the tear of the fibrous web ( 3 ) a line measurement such as a line scan camera or the like is used. Method according to one of the preceding claims, characterized in that for detecting the tear of the fibrous web ( 3 ) an area measurement such as a CCD camera or the like is used. Method according to one of the preceding claims, characterized in that for detecting the tear of the fibrous web ( 3 ) a difference between a non-periodic, in particular stochastic signal of the fibrous web ( 3 ) and a periodic signal of the characteristic color pattern ( 10 ) is used. A method according to claim 15, characterized in that the detected outline of the fibrous web ( 3 ) is evaluated via a Fourier or Powerspektrum of the signal, wherein at one for the drying wire ( 5 ) characteristic frequency at least one triggering threshold (S) is set. Drying wire ( 5 ) for a dryer section ( 2 ) of a machine ( 1 ) for producing a fibrous web ( 3 ), in particular for carrying out the method according to one of the preceding claims, characterized in that it has at least one characteristic color pattern ( 10 ), which in the case of the tearing of the fibrous web ( 3 ) of the institution ( 8th ) is reliably detected for web tear detection. Drying wire ( 5 ) according to claim 17, characterized in that the characteristic color pattern ( 10 ) of the drying wire ( 5 ) of a plurality of differently colored and preferably transversely to the running direction (L) aligned color strips ( 13 ) consists. Drying wire ( 5 ) according to claim 17 or 18, characterized in that the characteristic color pattern ( 10 ) of the drying wire ( 5 ) of several differently colored threads ( 11 ; 12 ) consists. Drying wire ( 5 ) according to claim 19, characterized in that the characteristic color pattern ( 10 ) in a woven dryer fabric ( 5 ) of differently colored weft threads ( 14 ) consists. Drying wire ( 5 ) according to claim 20, characterized in that the weft threads ( 14 ) of white polytetrafluoroethylene and the warp threads ( 15 ) are made of red polyester. Drying wire ( 5 ) according to claim 20 or 21, characterized in that the characteristic color pattern ( 10 ) a minimum width (Bmin) in the range of a thread thickness (DF) of the weft thread ( 14 ) having. Drying wire ( 5 ) according to claim 19, characterized in that the characteristic color pattern ( 10 ) in a spiral screen by differently colored spirals ( 16 ) consists. Drying wire ( 5 ) according to claim 23, characterized in that the characteristic color pattern ( 10 ) has a minimum width (Bmin) in the region of a spiral thickness (DS) of the spiral (FIG. 16 ) having. Drying wire ( 5 ) according to one of claims 22 or 24, characterized in that the characteristic color pattern ( 10 ) has a maximum width (Bmax), which results from the maximum permissible track length, which on the machine ( 1 ) for producing the fibrous web ( 3 ) caused no damage before the tee ( 9 ) by the institution ( 8th ) is activated for web tear detection. Drying wire ( 5 ) according to one of claims 17 to 25, characterized in that the characteristic color pattern ( 10 ) from a subsequent coloring of the drying wire ( 5 ), preferably by means of a thermography. Drying wire ( 5 ) according to one of claims 17 to 26, characterized in that a drying wire ( 5 ) a characteristic color pattern arranged only in regions ( 10 ) having.