Failure analysis and effects of redesign of a polypropylene yarn twisting machine

Presented in this paper are the results pertaining to technical condition diagnostics, redesign, and analysis of its effects for a complex mechanical system of a polypropylene yarn twisting machine. Twelve twisting machines were installed on a polypropylene yarn production line. Due to design flaws and manufacturing errors, the winches were soon prone to failures and an unacceptable level of vibrations. Owing to insufficient structure rigidness, errors in design, manufacturing errors, and a high level of vibrations, the majority of twisting machines developed cracks in their foundation framework. FEM analysis was used with experimentally measured displacements in the crack zone to define stress distribution. Also shown in this paper is the method for measurement and analysis of the vibration signal during the winch run-up, with the aim to determine resonance zones and a condition analysis of the twisting machine framework. In order to make the winches fully operational, a redesign of the mechanical structure was performed. The level of vibration was measured again at the characteristic framework parts, and FEM analysis of the foundation framework was used to analyse the effects of the redesign. The vibration measurements and the results of FEM analysis proved that the redesign was successful, showing that the measures undertaken made this system fully operational again.

► Machine condition diagnostics, redesign, and analysis of its effects were considered.
► Low rigidness, vibrations, design and manufacture errors caused foundation cracks.
► Analyses before and after the redesign showed that Von-Mises stress was reduced.
► Analysis of vibration measurements showed that the redesign was very successful.
► Crack zone displacements-loads relationship allows analysis of technical systems.