Modal analysis and acoustic noise characterization of a grain crusher.

Abstract

Noise is one of the most important physical factors occurring in private farmers' working environment. Hazardous noise exposures and hearing loss have been documented among farmers and farm workers for many years. In most cases, reducing the amplitude of vibratory motion of elements in a machine will reduce the noise generated by the machine element. The authors present the results on studies performed on a grain crusher with the aim of optimizing their acoustic behaviour. The dynamic behaviour of a grain crusher was investigated by identification of its natural frequency and damping parameters. The study was conducted using the experimental modal analysis technique. The excitation was generated at one single point by a vibration exciter, and the response signals were acquired by an accelerometers fixed at different points of the grain crusher. The modal parameters were determined from a set of frequency response measurements between a reference point and a number of measurement points of the structure. The introduced structural modifications reduced the noise level by 3dB (A)5 dB[lin]) for the hopper component frequencies related to the vibration of the hopper (180 Hz) and the crusher support structure (240 to 480 Hz). The level of these components determines the level of noise at the operator's work station for the average conditions of filling the hopper with grain. The total noise level at the crusher operator was reduced by 2.6 dB (A). Reducing the amplitude of vibratory motion of the elements in a machine will reduce the noise generated by the machine element. The obtained results confirm that structural dynamic modification is an effective tool for changing the dynamical properties of vibrating systems.