Analysis of headbox structural strength : OptiFlo II TIS 2200

Abstract: Valmet is a world leading supplier of tissue machines. In the tissue industry the demand on the machines is high to be able to produce the finest paper for use in products such as toilet paper and napkins. The machine components need to perform to be able to produce a product of consistent quality. Many different properties of the tissue can be evaluated through manipulation of the fibre content. Layers of cellulose are added into the process through a headbox, which acts as nozzle which distributes the fibres and water along the machine width. The tissue machines can be around 6 metres wide which put high demands on structural rigidity of the machine components to be able to maintain a uniform product along the machine width. Crucial parts are calculated prior to manufacturing to make sure they fulfil stress and rigidity criteria. This thesis covers the development of such a computational model of a headbox. The aim was to create a model which will be accurate in terms of deflection but also fast to calculate using ANSYS Workbench software. Many simplifications were made in the model to speed up solving time such as: • Removal of non-structural parts • Mirror symmetry • Material manipulation to replace perforated structurally important itemsAlso contact formulations were showing a large effect on accuracy and solution time in the model.With applied simplifications the solver time was decreased by over 73% compared to the initial model. The computational model was used in the thesis to evaluate the current configuration of the transverse welds in the headbox when exposed to static load. The load was applied by internal pressure. An evaluation was desirable following a material change from austenitic stainless steel SS2343 to the LDX2101 of duplex grade. LDX2101 which have a significantly higher yield stress of near 500 MPa compared to 250 MPa for SS2343.For static evaluation the welds showed low stresses in welds throughout the headbox. This leaves room to possible optimization of weld applications by reduction to least recommended throat measure of 3mm. This reduction result in quicker manufacturing time and thereby lower manufacturing costs. Static calculations show possible reductions of 66% in application time.