On the role of evaporation processes during impulse pressing of paper

This thesis presents the main results of a laboratory investigation of the mode of dewatering of wet paper webs during an impulse pressing event. We tried to study this issue by two independent sets of experiments performed on a laboratory press simulator.

We found indications that a displacement dewatering mechanism can assist wet pressing and evaporative drying in accounting for the high dewatering rates observed during impulse pressing of paper. Yet, this mechanism seems to be grammage dependent and we found that a minimum basis weight of approximately 120 g/m2 is required for its existence.

We propose that this kind of “impulse effect” should be interpreted as an example of the “flashing-assisted displacement dewatering” originally proposed by Lucisano (2000).

Additionally we tested a patented solution to prevent or repair delamination in connection to impulse pressing of wet paper. It is proposed that the use of multiple press pulses with carefully controlled profile should be e ective in this respect. The results of our measurements clearly show that paper samples experienced internal flashing even after five consecutive pulses. Yet, it should be pointed out that we did not measure the mechanical properties of sheets treated with multiple pulses and that additional work is required in this respect.

Author: Petrini, Joachim

Source: LuleƄ University of Technology

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