Failure behaviour of a tumble dryer

A tumble dryer is a rotating heated vessel used to fulfil a poly-condensation process of PETgranules. This step is very crucial in the entire production process of polymer fibres. System failure, causing production loss, cannot be afforded. Unfortunately, since a couple of years, the reactors suffer from severe cracking at weld details. To find the root cause(s) of this problem a detailed study of the vessel construction, the loads induced during the production process and the cracking has been performed. Hereby the influencing parameters and their importance could be determined. Based on this study it is put forward that fatigue, due to the exceptional translation of the granules in the vessel, is responsible for the cracking of the tumble dryer. Two main loading modes and corresponding crack locations could be determined: a cyclic changing torque causes the cracks on the outside of the vessel while the dynamic play of the moving granules around the heating elements is responsible for the cracks at the inside the tumble dryer. The root cause of the cracking problem has been determined but the actual mechanism causing the cracks, still needs to be quantified.