Coating processes – Measuring – testing – or indicating
Reexamination Certificate
1999-01-08
2001-01-09
Bareford, Katherine A. (Department: 1762)
Coating processes
Measuring, testing, or indicating
C427S010000, C427S356000, C118S665000, C118S712000, C118S713000, C118S126000, C118S410000, C118S413000
Reexamination Certificate
active
06171642
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for direct or indirect application of a liquid or viscous medium onto a moving material web, specifically a paper or cardboard web.
2. Description of the Related Art
In the paper producing industry, coating mediums are applied in the thickness range of one micrometer when applying coating or glue. The coating mediums take the form of glue, starch substance, pigment medium or conventional coating ink. It is very important that the layers applied to the paper web display a uniform profile, both in cross direction and in longitudinal direction in order to meet the high quality requirements put on paper by the paper manufacturer's customers and end users. A multitude of factors influence the thickness and quality of the applied layers. It is therefore easily understandable that, with conventional paper web widths of 10 m or wider, conventional machine speeds of up to 2000 m/min. or higher, and the associated large machinery required for paper production, disturbing factors may arise which would have a negative influence upon the coating result. These factors would include temperature related deformations of machinery components, mechanical wear and tear of doctoring elements, fluctuations of consistency of the coating medium, contaminations, etc. In order to gain control over these disturbing influences, modern paper production lines are equipped with sophisticated electronics which conduct measurements at many different locations within the production sequence. On the basis of these measurements, a control center, usually a process computer, triggers suitable control elements through which a targeted control can be exercised over the individual operating parameters of the machines. For example, it is quite common to measure the actual cross profile of the applied coating layer and, in the event of unevenness in the coating profile, to regulate the contact pressure and/or the angle of attack of a doctoring element by adjusting screws or hydraulic actuators.
All previously known solutions for elimination of defects in the coating result, that is, elimination of fluctuations from a desired coating result, have in common that, depending on the type of adjustment, one or more operating parameters are adjusted gradually relative to the observed defect until the defect in the coating result is no longer observed. The operating parameter or parameters will then remain at the newly adjusted values until possibly another defect is observed which would make necessary further adjustments of the operating parameter or parameters. This method is effective and corresponds with well known principles of control engineering.
Disturbing factors occasionally arise in a production run whose negative effects upon the coating result cannot be eliminated by the continuous adjustment of one or several operating parameters. If dirt particles, clumps of coating medium, fluff, dust particles or pulp fibers from the paper web adhere to exposed locations on an applicator unit in a machine for paper production, for example a nozzle gap of a free jet applicator, the resulting impairments of the coating result cannot be corrected easily by gradual adjustments of appropriate operating parameters. Specifically, this is often not possible in a relatively short time period, which is why large amounts of reject paper must be expected.
SUMMARY OF THE INVENTION
The current invention is based in the technical problem to cite a method which enables a speedy correction of coating result defects, even when dealing with the aforementioned disturbing factors, resulting in a lesser amount of rejected, unusable material. A layer of the coating medium is applied to the material web by use of an applicator unit. The coating result is then checked for deviations from the desired coating result, whereby at least one applicator operating parameter is influenced in the event of such deviations being discovered.
In order to correct the deviations, at least one applicator unit operating parameter is adjusted within a short time period—with the web running—from an initial operating parameter value which is in effect prior to having noticed the deviations. If required, the adjustment process is repeated and subsequently reset at least approximately equal to the initial parameter value.
Under the method offered by the current invention, a defect that is considerably larger compared to the defect that is to be corrected is momentarily accepted, when the operating parameter is adjusted from its initial parameter value. This adjustment does not serve to reduce the observed deviation and approximation of a desired value per se, but is intended only to enable the removal of the disturbing factor. Thus, none of the defects in the coating result caused by such disturbance factors are observed any longer following the readjustment of the operating parameter to the original value.
Sufficiently strong adjustment of suitable operating parameters—such as contact pressure of a doctoring element, the flow pressure of the application medium, the opening cross profile of a discharge opening for the application medium, etc.—may, for example, allow dirt particles, fluff or clumps to be washed away and the coating medium to again be applied uniformly across the entire width of the material web. Actually, the incorrect coating caused by the short-term adjustment of the operating parameter results in a certain amount of reject. However, since fast trouble shooting is possible, this waste is extremely small compared to such adjustment procedures wherein an operating parameter is adjusted step by step in the sense of a convergency toward a desired value. An adjustment time of a few tenths of a second, as well as one of several seconds, may, for example, be viewed as a short-term adjustment of the selected operating parameter.
In the event of particularly stubborn contaminants, an appropriately longer adjustment period may be required. In each instance, the operating value is then essentially reset to its initial value, which differentiates the method of the current invention from conventional corrective measures. Since the correction of deviations is made with a moving material web, no operational shut down, which would massively increase the production costs, is necessary.
It is possible to delay the resetting of the operating parameter to its initial parameter value until the desired coating result has been achieved. Consequently, one form of the method of the current invention provides that the operating parameter, following its adjustment, is reset to the original parameter value, dependent on observing at least reduced deviations. It is then ensured that the cause of the observed deviations in the coating result has been completely removed.
Alternatively, provisions may be made that, following its adjustment, the operating parameter is reset to its original parameter value, independent of observing at least reduced deviations. Specifically, the operating parameter, following its adjustment, can be reset to the original parameter value after a predetermined time period. In this instance, it is not verified whether the adjustment of the operating parameter has already resulted in the desired result before resetting the operating parameter. If necessary, the adjustment of the operating parameter needs to be repeated if a single adjustment procedure has not achieved the desired result.
A preferred form of the operational method of the current invention provides that, when checking the coating results, the material web is checked for the presence of defective application zones in the applied layer. In such defective application zones, the coating medium has not been applied or has been applied only in insufficient quantities. Such defective application zones, for example, occur in free jet applicators and take the form of longitudinal streaking in the direction of the material web flow, when solid particles cause localized obstruction of the jet nozzle of the
Bareford Katherine A.
Taylor & Aust P.C.
Voith Sulzer Papiertechnik Patent GmbH
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