Paper making and fiber liberation – Processes and products – With measuring – inspecting and/or testing
Reexamination Certificate
1999-05-11
2001-05-15
Silverman, Stanley S. (Department: 1731)
Paper making and fiber liberation
Processes and products
With measuring, inspecting and/or testing
C162S198000, C162SDIG004, C162SDIG004, C162S252000, C162S253000, C162S255000, C162S262000, C162S263000, C162S306000
Reexamination Certificate
active
06231722
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a method for monitoring the process of separation of a web, in which method the web is passed from a roll to a free draw of the web, in particular to the first free, unsupported draw of the web.
The invention also relates to a system for monitoring the process of separation of a web, which system is fitted in connection with the roll from which the web is passed to a free draw, in particular to the first free unsupported draw.
BACKGROUND OF THE INVENTION
In a press section of a paper machine, one of the most critical points with respect to runnability in the paper machine is the way the web behaves when it is separated from a centre roll. The separation of the web from the centre roll is especially important because the first free draw of the web is most often performed at this stage, that is to say the web is detached from the roll without support when it is especially susceptible to breaks if its properties and the factors affecting it have not been regulated correctly. The centre roll in the press has often constituted, as known per se, a critical point impairing runnability in the paper machine and it has limited the available maximum speed, even caused web breaks, and thereby reduced the efficiency of the paper machine.
Various factors affect the process of separation and the point of separation, i.e. the angle of separation, of the web. Among other things, properties of the web, linear loads of the press, draw differences in the press section, the wet end chemistry of the paper machine, the condition of the face of the centre roll, the operation of the doctor of the centre roll and the condition of jets used in connection with doctors, the selection of chemicals possibly used in connection therewith, all affect the separation point and, in addition, these factors are further partly dependent on one another. However, these factors influencing separation and indirectly also the operation of the doctor of the centre roll are not adequately known, because the effects of the factors influencing the process of separation may additionally appear with very different delays (from a second to weeks or months). Moreover, the effects may vary from one mill, process or moment to another. Since the process of separation has not been closely monitored, it has also not been possible to connect it with other process changes, and thus it has not been possible to establish right cause-to-effect ratios.
It is known from prior art to monitor the separation of the web by visually following an image of a video camera. However, this does not provide accurate information about the processes of separation but, instead, it gives random information because the monitoring of the separation process is based only on visual examination. Furthermore, the regulation measures possibly taken based on video camera monitoring have been mainly specific to a particular operator and based on the operator's personal analysis of the situation.
Thus, the monitoring of the separation of the web carried out by a video camera has not been accurate, and by means of it it has not been possible to monitor rapid changes in the separation process, nor has it been very simple to transfer the situations seen from it onto paper or into electric form to form proportional factors in a data collecting system of a paper machine, especially if normal sway of the separation process is large. Also, this arrangement provides the situation not farther away from the edge in the longitudinal direction of the roll but only at the edge of the web, which may cause miscalculations because the line of separation is not necessarily straight in the direction of the roll and, at the edge, there may occur disturbances that are not representative considering the whole web.
OBJECTS AND SUMMARY OF THE INVENTION
An object of the invention is to provide a method and an arrangement in which the behaviour of the web in separation may be closely monitored and, in addition, the factors influencing the process are monitored so as to establish the cause-to-effect ratios influencing the matter, which ratios may thus be efficiently observed and analysed, utilizing the obtained information in control.
An object of the invention is also to provide an arrangement which can be connected, when desired, to other information obtained from a paper machine.
With a view to achieving the objectives stated above and those that will come out later, the method according to the invention is mainly characterized in that, in the method, the point of separation of a web or a web point comparable thereto is measured when the web is passed from a roll to said free unsupported draw, and that, in the method, the draw difference, i.e. the speed difference, of the web across the separation point is measured, and that the results of measurement of the separation point and of the speed difference are transferred into a data collecting system and/or into an analysis system in order to establish the cause-to-effect ratios in the separation process.
The arrangement according to the invention, in turn, is mainly characterized in that the system comprises measurement members for measuring the point of separation of a web or a web point comparable thereto, measurement members for measuring the draw difference, i.e. the speed difference, of the web across the separation point, and a data collecting system and/or an analysis system, into which the results of measurement are transferred and in which, based on the measurement results, the factors affecting the separation process are established.
In accordance with the invention, several variables are simultaneously monitored and recorded, either all or, when desired, only certain ones at a time. The following factors may be monitored in the monitoring system in accordance with the invention:
1. draw difference of the web across the point of separation,
2. separation point of the web or a web point comparable thereto,
3. web tension after the separation point, for example, on a paper guide roll, preferably measured with a carbon fibre roll as a weighing roll or by means of a non-rotating tension measurement shoe,
4. variation in loading pressure; doctor vibration (for example, as variation in the pressure of a loading hose, which indicates, for instance, soiling of a roll),
5. moisture measurement immediately after a press section.
Since the variations in the separation of the web may result from a change in the properties of the web or in the face of a roll or in the liquid between them, it cannot be found out by monitoring only one of the above-mentioned variables 1-5 which of these three factors changes. Of course, most information is obtained by monitoring all the variables 1-5 simultaneously, but combinations of 1-4; 1-3; 1-2 and 4; 1-2 and 4-5 are also very useful. In order for the inventive idea to operate, the minimum requirement is to monitor the variables 1 and 2. The monitored factors are advantageously compared with other process and running parameters which are monitored in any case and/or intentionally on a paper machine, as known per se.
The draw difference is conventionally measured on all machines. The most important thing is to adjust the draw difference in terms of time to the same scale with measurement of the separation point.
In accordance with the invention, the point of separation of the web is monitored by means of an appropriate method, for instance, by means of a video+an image processing arrangement or by means of a linear camera and an image analysis associated therewith to establish the boundary between a dark and a light area, whereby it is seen where the separation point of the web is situated. The point of separation may also be measured by means of a laser measurement device, recording the separation point as invariable and regulating the draw difference. Other methods known per se for measuring the process are, of course, possible. Preferably, in connection with the invention, a distance measuring device based on the laser-Doppler method is used for m
Halpern Mark
Silverman Stanley S.
Steinberg & Raskin, P.C.
Valmet Corporation
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