The trend towards lower basis weights presents a set of challenges for production. First, the economical production of lighter weight grades requires higher machine speeds. Second, producing board from lower grade recycled furnish often causes quality problems, and, finally, the end product still needs be strong.
Over the past twenty years fluting and linerboard basis weights have decreased significantly (Fig.1) . To compensate for this, it has been necessary to increase machine speeds proportionately. This is already evident in the higher design speeds of new installations.
While basis weights have decreased, the use of recycled fiber as the furnish for containerboard has increased. Economic pressures require cost reductions, which has led to the use of mixed waste instead of high quality OCC. This, in turn, has increased the ash content of the furnish (Fig.2).
The increase in ash content is often compensated by the use of a film size press. As is well known, ash does not make hydrogen bonds and thus does not contribute to strength. With furnish of strong fiber, a film size press is naturally not needed. Furnish made using mixed waste often comes with a high ash content, and so a film size press is necessary. This paper describes the outline of Metso new concept for fluting and linerboard.
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