The forming of the web in a paper machine is a highly dynamic process in which the dynamic mechanical properties of the web in the x, y, and z directions are each of central importance for both the process operation and the properties of the final product. The properties in the x and y directions, such as the dynamic tensile stiffness and stress relaxation, affect control of the draw in open draws, web flutter, and stress variation. The dynamic mechanical properties in the z direction affect the behavior of the web in the press section and the post-press dry solids content. All these features are also related to the properties of the final product.
Laboratory research on the dynamic mechanical behavior of wet webs has been carried out with special equipment designed to simulate the paper production process, particularly its dynamic characteristics. The draw and press simulators have been built to monitor and handle properties related to the dynamic mechanical behavior of paper. The draw simulator has been used to study dynamic tensile stiffness and visco-elastic component of the web during drying. The press simulator has been used to monitor the compressibility and pressure in the web as a function of different press impulses and wet pressing temperature.