Vision Pulp Analyzer The papermaking process is largely automated but the pulp production and especially its quality control lack accurate methods of characterising the papermaking properties of pulp. The development of the Vision Pulp Analyser (VPA) process microscope is an effort to meet the challenge of bringing on-line efficient measuring equipment to the market. The VPA measurements provide a link between the quality of the microscopic components of pulp and the strength properties of paper.
Continuously increasing customer demands and quality requirements of the printing papers set new challenges for the paper industry. Better surface, strength and optical properties of the paper, with a lower base weight are constant demands in the tightening paper markets. These demands force scientists to consider the raw material, i.e. wood pulp, in a new way, and also to develop new techniques for pulp and paper research. Typically, in a paper mill, wood pulp is considered as a particle collective, and its papermaking potential is characterised with one or two bulk measurements. The refining process disassembles wood chips into fibers and microscopic fragments, forming papermaking pulp. The most important control parameters in the refining process are specific energy consumption (MWh per ton of pulp) and refining temperature. In the refin-ing process, the fibers are delaminated and fibrillated according to the refining conditions and applied energy. Both their physical and chemical structure is changed. The ability of fibers to bond depends mainly on their flexibility and degree of fibrillation. Flexible and well-fibrillated fibers with a high specific surface area are bonded more easily to each other than stiff and low-fibrillated fibers.
Tensile strength prediction Tensile strength is one of the most interesting properties of paper, not predictable by freeness. The fibrill content has a correlation with the strength properties of a sheet. Fibrilles act as a glue within a web. In the following figures are the results from a test in which the fibrill content and whole pulp laboratory handsheet tensile index were correlated. The results shown in the figures support the assumption that the fibrillar content is an indicator of tensile strength.
Tear index prediction The tear index
is largely explained by fiber length. However, a better prediction can
be obtained if the image processing results are also utilized.
Discussion The pulp samples were collected from three mills at six different processing stages. There was variation in the raw material, too. These facts make the results even more interesting: the experiment was close to real-life processing conditions, contrary to a laboratory experi-ment of controlled changes in variables. The results imply that the suggested VPA indices are useful and robust in predicting the quality factors of the final paper product . The results have been interesting enough to start a prototype development work by an equipment vendor. Contact infornation:
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