Analysis and Optimization of Paper Machine Clothings

Paper Machine Clothings

The basic principles of the paper manufacturing  process are the same today as they were almost 500 years ago. The only difference is that forming, pressing and drying are optimized and fast processes within modern paper machines. Starting with a fibrous suspension (1 percent dry solids content), the emerging paper web is transported through the paper machine on clothings at a speed of up to 2,000 m / min (120 km / h). Along with the transport of the paper web, these mostly textile structures also have the important task of supporting the dewatering of the paper.

Press Nip Simulation

The behaviour of press felts is analyzed and simulated at the Fraunhofer ITWM. This type of clothing is an essential component of the mechanical dewatering within the press section of the paper machine. The optimised dewatering in the press reduces the use of thermal energy in the drying section, which considerably reduces energy costs and the impact on the environment.

Simulation einer Durchströmung eines virtuellen Pressfilzes
© Fraunhofer ITWM
Simulation einer Durchströmung eines virtuellen Pressfilzes. Der Pressfilz ist dabei aus einer Faserlage (dunkelgelb), einem Gewebe (rot und hellgelb) und einer Membran (blau) aufgebaut. In der Membran und der Gewebelage sieht man in der Darstellung deutlich die höhere Strömungsgeschwindigkeiten (rot) bedingt durch die geringere Porosität.

The mechanical dewatering is a complex fluid dynamical process which is influenced by effects ranging from the micro-scale to the macro-scale. These dimensions refer to textile structures up to press rollers with 1 m diameter. Accordingly, the analysis is also done by a multi-scale simulation.


Multi-scale Simulation of Paper Machine Clothings

The starting point of the micro-scale analysis is a flow simulation by means of the GeoDict software developed at the Fraunhofer ITWM. In the pursued approach, GeoDict provides the capability of analysing both real and virtually created press felt structures.
By means of the software a multitude of machine parameters can be combined on the macro scale with the data acquired from the micro-simulation. In addition to the dewatering performance, this simulation also provides better insight into the dynamics of mechanical dewatering in order to support new developments. Along with the analysis of existing press felts and paper machines, the simulation also provides the capability of testing innovations in the early stage of development. In doing so, the artificial generation of virtual and innovative structures with the corresponding dewatering simulation guarantees a technological advantage.