Göttsching and K.-B. Gräber

On the Influence of Paper Machine Wet End Performance on theVariations of Basis Weight and Other Paper Properties

Part l: Metrology and Methods of Evaluation

The publication comprising a series of articles starts with the discussion of metrological and mathematical aspects for the evaluation of variations of different paper properties and of hydraulic pressure variations in the paper machine wet end. In  the following, the results of investigations in different production units are discussed.

The present part l presents the test program. It is pointed out how necessary it is both for the mechanical engineer and the technologist to use a common language for the evaluation of paper machine performance and quality of the product. Subsequently, following a critical survey of previous metrology for the evaluation of the variations of basis weight, the applied metrology is described. Beside the semi-automatical IfP paper testing line covering seven primary properties of cross machine

and machine direction strips taken from paper webs, the newly developed automatical IfP weighing System is dealt with. Measurements underline the influence of the size of the tested sample area with respect to the magnitude of the variance of paper properties. Finally, the most important aspects of statistical handling of data according to the variance component analysis are desribed with the help of a graph and documented in the appendix.

On the Influence of Paper Mach ine Wet End Performance on the Variations of Basis Weight and other Paper Properties

Part II:  Measuring Technique and Data-Processing Methode. Evaluation of the Paper Machine Wet End Performance

The connection between pressure pulsations in the approach flow System and in the headbox of a paper machine and varia-tions of mass per unit area of the paper is reviewed and demon-strated by a simple model.

The basic testing setup is discussed in connection with the test-ing procedure applied. Likewise, the methods of time series analysis for presenting the data form pressure measurements and of measurements of mass per unit area are described and explained by means of examples. Hydraulic pulsations in the approach flow System can be identified by means of the Fourier analysis. Indications of the causes of the Variation by the mass per unit area in paper can be derived by either Fourier analysis or time series analysis.

On the Influence of Paper Machine Wet End Performance on the Variations of Basis Weight and other Paper Properties

Part III: Paper Machine Wet End Performance and Variations of Basis Weight

The possibility of metrological evaluation of a sheet forming system by means of the variance analysis on paper samples is investigated. In the case of basis weight, a gravimetrical and a radiometrical measuring method are compared and their influen-ce on the results of a variance analysis is discussed. The size of the measured area as well as kind and size of the sample are examined as influencing variables. A large-scale series of tests was performed on a paper machine with modifications of furnish and technological Parameters. It was found that the residual Variation as nonsystematic component — considering some few marginal conditions — can numerically characterize a sheet forming system with regard to the pa­per characteristic investigated.

For exemplification, two sheet forming systems of foudrinier paper machines are compared with regard to basis weight variation

On the Influence of Paper Machine Wet End Performance on the Variations of Basis Weight and other Paper Properties

Part IV: Paper Machine Wet End Performance and Variations of Different Paper Properties

With the help of the analysis of variance the influence of technical and pulp Parameters in a fourdrinier paper machine on the kind of distribution of some paper characteristics (basis weight, caliper, bulk, compressibility) of wood-free printing and writing paper is analysed. It is found that the variations of different characteristics are of different magnitude and — regarding their components — are not equally changed by variations of paper machine operation or pulp influences. A fundamental alteration of the sheet forming system by the replacement of a perforated roll type headbox by a high turbulence headbox sometimes changes the amplitude of variation of paper characteristics including its variance components, but partly also the tendency is fundamentally altered.