MONITORING GRINDING PARAMETERS BY SIGNAL MEASUREMENTS FOR AN INDUSTRIAL BALL MILL

Mechanical grinding emits a high-intensity vibration signal that conta ins information on the mill operating state. Vibration signals from th e mill are presented in the form of both mechanical vibration and acou stic pressure. To apply these source signals to monitoring of grinding parameters, industrial scale grinding tests were performed with an ir on ore at LKAB, Malmberget. Three operating parameters were considered : the feed rate, the mill feed size and the pulp density of mill disch arge. The measured response parameters were the ground product size, t he power draw and the pulp temperature. The source signals of the time -domain waveforms were simultaneously sensed by accelerometer and micr ophone so as to obtain a ''stereograph'' of grinding. The signals were first stored on a DAT recorder and then converted into digital format by an oscilloscope. The digitised waveforms were transformed into fre quency-domain spectra by power spectral estimation. The variations on the power spectra can be described by a few ''latent'' variables deriv ed by principal component analysis. Finally, close relations were esta blished between key grinding parameters and ''latent'' variables by mu ltiple regression. Using signal measurements, an automatic and efficie nt strategy can be developed to monitor operating parameters for the c ontrol system in a ball grinding circuit.