WO1998006897A1 - Process for elimination of paper defects in continuous paper production - Google Patents

Abstract

A process for elimination of paper defects during continuous paper production which reduces time lost due to defect correction has the following steps: a) recognition and localization of the paper defect by means of sensors (5) directed at the running paper web (4); b) detection or calculation of the speed of the paper web (4) between the sensor (5) and a station (6) for defect correction positioned downstream from the sensor (5); c) on the basis of the speed of the paper web, calculation of the arrival time of the web segment with the paper defect at the station (6) for defect correction; d) before arrival of the web segment with the paper defect at the station (6) for defect correction, reduction of the web segment speed to a lower value than normal speed or to zero, e) automatic removal of the paper defect in station (6) for defect correction and f) restoring the web section to normal speed.

Description

 Process for eliminating paper defects in the continuous

Papermaking

The invention relates to a method for eliminating paper defects in continuous paper production. Continuously operating paper machines are made up of the stations headbox, wire section, press section, dryer section, drying smoothing unit and rewinder. In the headbox, the aqueous stock suspension is evenly distributed over the web width in order to ensure optimum sheet formation. In the subsequent wire section, the actual paper sheet is formed by a filtration process. The individual paper fibers are already fixed to their final position in a wet fleece. The excess water in the press section is then driven out of the paper fiber fleece by means of pressure. For this purpose, the paper web passes through a plurality of presses arranged one behind the other. After the subsequent drying, the paper web is smoothed, for which purpose a smoothing unit composed of two rollers is generally used, which, in addition to smoothing, compresses the paper and at the same time influences the paper thickness. Finally, the paper web is wound up on a drum.

Errors in the paper web can occur during the aforementioned production process. These can be holes or tears along the longitudinal edges of the paper web, as well as dark or light spots on the paper web. Furthermore, it can lead to unwanted pieces of fabric during manufacture, or folds in the running paper web. These errors usually disrupt the further transport of the paper web within the paper not pier machine. In contrast, in the downstream processing stations, for example in a subsequent coating machine or also in a printing press, the paper web may be torn or torn at the faulty locations. It is therefore necessary to eliminate such paper defects before the paper web enters a downstream processing stage.

Up to now, paper errors have been eliminated manually by marking the paper web for errors at the points at which errors are detected, and by braking the paper web in a downstream station when the paper web section marked in this way approaches that an operator can apply an adhesive to the fault location at creep speed. Depending on the type of error, the operator also removes the entire faulty paper web section and applies an adhesive point across the entire paper web width. This type of troubleshooting is time-consuming, since the speed of the paper roll and thus the entire paper web must be reduced to creep speed or even to a standstill in order to then manually eliminate the fault location. But even this time-consuming and therefore costly elimination is not sufficient to reliably rule out paper errors as the cause of the tear in subsequent processing stages.

The invention is based on the object of providing a method with which the time losses caused by eliminating errors in the paper web during paper production can be reduced.

To solve this problem, a method for eliminating paper defects in continuous paper production is proposed with the following steps:

a) detection and localization of the paper error by means of a detector aligned with the running paper web; b) detection or calculation of the speed of the paper web between the detector and a station located downstream of the detector for troubleshooting;

c) based on the speed of the paper web, calculating the time of arrival of the web section having the paper error in the troubleshooting station;

d) before the arrival of the web section having the paper error in the station for troubleshooting, reducing the speed of the web section to a value reduced to normal speed or to zero;

e) automatic removal of paper errors in the station for troubleshooting and

f) Increase the speed of the track section to normal speed.

According to the invention, therefore, only the paper defect is recognized and localized by means of conventional means, namely suitable detectors, the detection elements of which are aligned with the running paper web. In contrast to the means previously used, however, the speed of the paper web between the detector and a station located downstream of the detector is recorded or calculated for the purpose of troubleshooting. This speed is used to calculate the point in time at which the web section having the paper error arrives in the troubleshooting station, the speed of the web section being reduced to a value which is reduced compared to the normal speed or even completely to zero before this arrival. The station then automatically removes the paper error by means of suitable devices at the point in time which was calculated on the basis of the speed of the paper web. The speed of the track section is then increased again to normal values. In contrast to the known manual troubleshooting, it is not necessary to carefully and manually lower the paper web to the reduced speed required for troubleshooting. Rather, based on the knowledge gained by evaluating the detection signals, a decision is made within the system as to which speed the web section in the downstream station must have for troubleshooting to reliably remedy the paper errors. For this purpose, the detector can be set up not only to recognize and locate the paper defect, but also to determine its character, for example the type and contour of the paper defect and its localization with respect to the width of the paper web. All of this information can be used and evaluated within the system in order to set the speed of the track section within the station to the required value for troubleshooting. In this way, the time lost in paper production by eliminating faults in the paper web is reduced to the absolutely necessary minimum.

With an embodiment of the method it is proposed that the paper web passes through a further detector before it reaches the detector, and that the further detector carries out a preliminary or large detection of the paper error, whereas the detector for additional detection of the characteristic of the paper error, e.g. B. its type and contour is set up. In this way it is possible to operate the paper web and thus the paper machine in normal operation at a very high speed, since the further detector must only be set up to detect errors at all and to locate them temporarily. The measurement characteristic of this detector is therefore aimed at a fast detection, less at a detailed detection. Rather, details are captured by the detector upstream of the station for troubleshooting. Such details are the type of paper defect, its contour and the location of the paper defect with respect to the width of the paper web.

The time of arrival of the web section having the predetected paper defect at the detector is preferably calculated on the basis of the speed of the paper web on the way to the detector. In a further embodiment of the method, it is proposed that the speed of the web section containing the paper error is reduced to a value which is lower than the normal speed before the web section arrives at the detector. Furthermore, the speed which has already been reduced can be reduced to a value which is again reduced in comparison to it or to zero immediately before the path section arrives in the station for troubleshooting.

With the invention it is further proposed that the removal of the paper defect is carried out by covering the area of the defect with a rapidly hardening fluid. According to a first variant, the fluid can be applied by spraying on one or both sides onto the fault location. According to a second variant, the fluid can be applied to the flaw by roller application.

A fast-curing UV varnish is particularly suitable as the fluid.

The process is suitable for both on-line paper production and off-line paper production. In the first case, the station, detector and further detector are arranged along a continuous paper web, so that the automated removal of paper defects thus takes place at full paper web speed in the paper machine, while in the second case the further detector on a paper machine and station and detector along one of the paper machine downstream rewinders or pre-rollers are arranged. The rewinder or pre-winder represents the link between the paper machine and the coating machine.

Further details and advantages are explained below using an exemplary embodiment. Reference is made here to the attached drawing, on which a pre-roller is shown in a side view, which is arranged within the production process between the paper machine and the coating machine.

In the drawing, the drum 1 is shown on the right, on which the paper web wound at the end of the paper machine is located. This paper web can have paper defects at various points. The detection of this Paper errors already occur in the upstream paper machine, the location of the paper error with respect to the length of the paper web wound on the drum being stored internally in a control unit. After the drum 1 is clamped onto the pre-reel, the system already "knows" where there are defects within the length of the wound paper web. It is alternatively also possible to provide the drum 1 with a built-in memory element which contains the corresponding position data of the paper errors, e.g. B. an electronic chip arranged on the drum.

The paper web is drawn off the drum 1 in the pre-roller and then guided over a first deflection roller 2 and a second deflection roller 3. The paper web itself is shown in the drawing with the reference number 4.

Between the drum 1 and the deflection roller 2 there is a detector 5, which is constructed differently in terms of its detection characteristics than the further detector integrated in the upstream paper machine. While the further detector is only set up to detect paper defects even at high web speeds and at least roughly localize them with respect to the length of the web, the detector 5 attached to the pre-roller is set up to recognize the already predetected paper defects with regard to their exact character and the size and extent of the To locate paper error. Furthermore, sensitization to further properties of the paper defect can be provided, e.g. B. the detection of light / dark shades or warps and folds. On the basis of the measured values of the detector 5, a decision is then made within the system to what extent and in what way an error is rectified.

Since the rough localization of the paper error is already known on the basis of the measurement result of the further detector, the speed of the web section containing the paper error can be reduced to a value which is lower than the normal speed before this web section arrives at the detector 5. This has the advantage that the detector 5 already detects the arrival and the approximate localization of error signals is prepared, and can use the detailed recording of the error without delay.

The time of arrival of the web section having the predetected paper error at the detector 5 can, provided the paper web arrives from the paper machine directly and without interruption, also be calculated on the basis of the speed of the paper web on the way from the further detector to the detector 5.

The paper error is eliminated in a station 6 which, in the exemplary embodiment, is located between the deflection roller 2 and the deflection roller 3. There is a spray head 7 aligned with the paper web 4, via which a fast-curing UV varnish is sprayed onto the flaw. Alternatively, the fluid can also be applied via rollers. The order can, as shown in the drawing, be one-sided or both-sided. As an alternative to a quick-curing UV varnish, it is also possible to use a suitable plastic adhesive. It is crucial that the fluid by itself has the property of covering the area of the defect in a flat and film-forming manner, and in this way protecting the paper in the area of the paper defect during further processing, for example in a coating machine or in a printing press. The agent used should be used in the process of dissolving paper, e.g. B. in committee processing or waste paper recycling can easily be separated from the paper.

The application of the fluid in station 6 takes place automatically, ie without human intervention. For this purpose, the exact time must be known at which the web section with the paper defect arrives in the working area of the spray head 7. The decisive factor here is the speed at which the paper web and thus also the defective web section moves from the detectors to the spray head 7. Therefore, the speed of the paper web between the detector 5 and the station 6 spatially downstream of the detector 5 is detected or calculated, and the exact time of the arrival of the web section having the paper defect in the station 6 is calculated on the basis of the determined speed. Within the control of the spray head 7, the result of the detector is also found 5 measurements taken into account, ie the spray head 7 does not work in all cases over the entire width of the paper web, but only in the region detected as defective with regard to the longitudinal direction of the web and the width of the web. The spray head 7 is therefore advantageously composed of a large number of individual spray nozzles, which are arranged across the width of the paper web and can be controlled individually.

Even before the arrival of the web section having the paper defect at station 6, the speed of the paper web is reduced to a value which is reduced from normal speed or to zero. After the station 6 has passed and the drying process can be considered complete, the speed of the paper web is raised again to the normal value.

The drawing shows the method for an application off line, i. H. the further detector is already in the paper machine and the station 6 and the detector 5 are arranged in the preliminary roller. However, an on-line method application is also possible, with the station, detector and further detector being located along a continuous paper web, for example in a combined paper and coating machine.

The detectors work optically across the entire width of the paper web. Infrared photo detectors or CCD line cameras can be used.

B e z u g s z e i c h e n l i s t e

1 drum

2 deflection roller

3 deflection roller

Paper web

5 detector

6 station

7 spray head

Claims

Patent claims 1 . Procedure for eliminating paper defects in continuous paper making, with the following steps: a) detection and localization of the paper error by means of a detector (5) aligned with the running paper web (4); b) detecting or calculating the speed of the paper web (4) between the detector (5) and a station (6) spatially downstream of the detector (5) for troubleshooting; c) based on the speed of the paper web (4) calculation of the time of arrival of the web section having the paper defect in the station (6) for troubleshooting; d) before the arrival of the web section having the paper error in the station (6) for troubleshooting, reducing the speed of the web section to a value which is reduced compared to the normal speed or to zero; e) automatic removal of the paper error in the station (6) for troubleshooting and f) raising the speed of the web section to normal speed. 2. The method according to claim 1, characterized in that the paper web, before it reaches the detector (5), passes through a further detector, and that the further detector carries out a preliminary or rough detection of the paper error, whereas the detector (5) for additional Detection of the characteristics of the paper error, e.g. B. its type and contour is set up. 3. The method according to claim 2, characterized in that the time of arrival of the web section having the predetected paper defect on the detector (5) is calculated on the basis of the speed of the paper web (4) on the way to the detector (5). 4. The method according to claim 3, characterized in that the speed of the web section containing the paper defect still before the arrival of the web section at the detector (5) is reduced to a value which is lower than the normal speed. 5. The method according to claim 4, characterized in that the already reduced speed immediately before the arrival of the web section in the station (6) for troubleshooting is reduced to a further reduced value or to zero. 6. The method according to any one of the preceding claims, characterized in that the elimination of the paper error is carried out by covering the area of the defect with a rapidly hardening fluid. 7. The method according to claim 6, characterized in that the fluid is sprayed on one or both sides of the fault location. 8. The method according to claim 6, characterized in that the fluid is applied by roller application to the fault location. 9. The method according to claim 6, 7 or 8, characterized by a fast-curing UV varnish as a fluid. 1 0. The method according to any one of the preceding claims, characterized in that the station, detector and further detector are arranged along a continuous paper web (method on line), the automated removal of paper errors thus takes place at full paper web speed in the paper machine. 1 1. Method according to one of the preceding claims, characterized in that the further detector on a paper machine and station (6) and detector (5) are arranged along a rewinder or pre-winder downstream of the paper machine (method off line).