The invention relates to a double layered paper making forming fabric with a coarse structured running side and a fine structured paper side.
Since long time the paper makers request that in the manufacturing of paper making forming fabrics the paper side, i.e. the paper making surface of the paper making forming fabric, should be provided with an as small meshed structure as possible to obtain an optimal fiber depository at a high as possible retention and a complete absence of marking, while the running side of the paper making forming fabric should be provided with coarse meshes to achieve a good dewatering of the pulp, whereby furthermore the susceptibility to pollution should be reduced and the cleaning possibilities should be improved. Additionally the running side should be sufficiently wear resistant by respective built-in-materials, so that at least the life time usual nowadays for double layered forming fabrics is achieved.
For the attainment of the above quality features of double layered paper making forming fabrics considerable progresses have been made in the last years, but no fabrics could have been manufactured which are adequate in their entirety to the modern, quick and efficient but also more sensitive printing processes to that extent that they can deliver papers of highest quality. Even the so-called composite forming fabrics, comprising two complete fabrics connected to one another could not completely fulfill as yet the requirements of the requested paper qualities.
In this context attention is drawn for instance to U.S. Pat. No. 4,112,982 disclosing two-layered forming fabrics which are characterized by transverse or cross floatings on the paper side and a coarse structure of the running side by means of relatively thick cross threads of a relative low number. The practice has shown in this connection that only cross threads of a similar thickness can be interwoven with the fine longitudinal threads of the known double layered fabric on the running side thereof and that by increasing the diameter of the cross threads the weft runner quality is lost more and more. That means, the distance between the wear plane provided by the cross thread floatings and the plane of the longitudinal thread knuckles is getting less and less. That is the reason why the longitudinal threads are exposed too early to the wearing so that a quick loss of the stability in the longitudinal direction will occur leading finally to a tearing in transverse direction of the fabric and a reduced running time.