The paper testing laboratory at Innventia is equipped with a pressing and drying simulator, which can replicate some of the phenomena that occur in the pressing and drying sections of a paper or board machine. The system is based on a servohudraulic laboratory platen press, which is monitored by a computer.
When simulating wet pressing, the loading intensity (maximum load 40 kN) and the duration and shape of the press impulse applied to the sample can be varied. 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 two seconds of the press pulse. Here, the sample is clamped with 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 consist of a steel plate, with a special pattern of openings. The surfaces are mounted on top of two beakers, which can be heated with hot air with a temperature of up to 250°C.
During drying, the heated surfaces are pressed against the wet sample for a certain length of time, and are then lifted off the sample for the same length of time to allow for evaporation. The surfaces are rotated before being pressed onto the sample for the same length of 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.