Stickies in weissen und braunen Stoffen : praxisrelevante Grundlagen zur messtechnischen Erfassung

Measurement technology plays a key role in the operation and optimization ofprocess lines as well as in ongoing machine development work. It is important, however, that measuring techniques keep pace with the continuous improvement in machines and processes, since only then can further improvements be achieved. With today's high demands imposed on the quality of stocks from secondary fibres, the measuring methods applied must be able to reliably detect even very small concentrations of disturbing substances in the finished stock. This applies particularly to the stickies content Fundamental statistics are presented for reliable stickies measurement, based on which the necessary sample volume can be determined for a certain stickies content Suitable graphic illustration ofthe data gained in this manner will provide additional information on the accuracy of the stickies measurement as well as on the stickies content throughout the entire preparation process. Statistical considerations show that for measured values with a confidence interval of ± 20 % and a statistical reliability of 80 %, sample masses of 100 g or more of fibre stock must be evaluated in some instances. Since this is often not practically possible with conventional methods for measuring stickies contents, an improved method for the identification ofmacrostickies is presented, based to a great extent on the methodics ofthe well known Escher Wyss method. This pick-up-method is fast and practical and its accuracy can be adjusted to the requirements of the user via the sample size. Based on twelve months of experience with the described statistics and pick-up measuring method, it was found that mis-interpretations due to inaccurate measuring results can be avoided and that reproducibility of measuring results is clearly higher than with conventional methods.