The paper testing laboratory at Innventia is equipped with a pressing and drying simulator which can replicate some of the phenomena occurring in the pressing and drying sections of a paper or board machine. The system is based on a  servohudraulic laboratory platen press that is monitored by a computer.

When simulating wet pressing one can vary the loading intensity (maximum load 40 kN), the duration and shape of the press impulse applied to the sample. The press nip can be configured either as a double-felted or single-felted press nip.

The sheet can be transferred into the drying part of the simulator directly after pressing, within less than 2 s after the press pulse. Here the sample is clamped with the help of a pair of heated, circular, porous rings in order to obtain complete restraining during drying. The sample is then dried by pressing heated, perforated surfaces on both sides of the wet sample. The heated surfaces consisted of a steel plate, with a special pattern of openings. The surfaces are mounted on the top of two beakers, which can be heated with hot air with the temperature of up to 250°C.

During drying, the heated surfaces are pressed against the wet sample for a certain time, and then lifted off the sample for the same time to allow for evaporation. The surfaces are rotated before being pressed onto the sample for the same time as in the previous position, lifted off the sample and rotated again. Given this special procedure, the sample is heated by conduction every second drying pulse. In the remaining time, water can evaporate from the surface of the sample. The total drying time for a sample is of the same order of magnitude as that in a drying section of a paper or board machine.

Wet pressing experiments at Innventia.