Condition monitoring and diagnostic of an extruder motor and its gearbox vibration problem.

Abstract

Reliable production plants are vital in today's economy as they have a direct impact on the productivity, profitability and overall prosperity of industrial nations, the income of which depends on their industries and the products they create and export. Reliability depends on regular condition monitoring and plant maintenance and, more importantly, the tools and technologies being designed, developed and used. Excess vibration is one source of plant failure and this can have many root causes, ranging from dynamic incompatibility between different elements of machinery or their foundations to other causes resulting from general wear and tear. Prediction or detection of the source or causes of these unwanted problems is challenging and requires sophisticated tools and theories as well as experience and expertise. Moreover, classical vibration monitoring on its own cannot predict the root causes of failures that are due to operating conditions, especially when severe or abnormal service conditions are present. Under such conditions, the systems may behave in a completely different or unpredictable manner: active excitation forces/loads and the resulting displacements can make the system behave in a non-linear fashion. Here, an industrial case study that involves the non-destructive evaluation of an extruder motor due to excessive vibration is presented. A novel dynamic design verification (DDV) procedure for non-destructive monitoring and resonant vibration identification, which relies on a combination of experimental modal analysis (EMA), operating deflection shapes (ODS) and linear elastic finite element analysis (FEA), is used to assess the structural integrity and dynamic behaviour of an extruder motor and associated subsystems. The analyses conclude that the root cause of the high vibration is not the result of wear and tear of the motors but is due to a weakness in the motor support structures and concrete foundation supporting the extruder motor. Based on the performed analyses, structural dynamic modifications (additional supports) applied to the non-drive end of the motor have been considered and their effects on the system are analysed. It was concluded that this modification shifted the lowest natural frequency away from the operating speed and effectively reduced vibration to a safe level.