Method and device for improving the paper quality in multilayer and multilayer papers

摘要

Improvement of multilayer paper quality in the wet working section of a paper machine entails at least two different quality pulps for paper strip mfr.; collection and recycling of dilute suspension drained from a screen in quite separate containers where at least most of a first pulp is drained through a first screen, corresp. for a second pulp and where the suspensions from each screen are separately gathered and reintroduced to the corresp. pulp i.e. paper layer. The appts. for the implementation comprises: appts. and pipework for gathering the separate dilute suspensions in accordance with quality levels and pipework for the re-introduction of the suspensions. Where a two-layer strip is formed by passing two pulp layers through a continuous double-sided screen, the gathering of the different dilute suspensions is carried out mainly in the screens' initial zone. In the formation of a triple layer sheet where the dilute suspension extracted from a first screen originates essentially from the outer layers it is reintroduced to them, while that from a later screen is reintroduced to the middle layer. The outer layers (S1, S3) can originate from approx. the same pulp and enclose a middle layer (S2).