VIBRATION CHARACTERISTICS IN A LARGE-SCALE BALL MILL

Vibration signal measurements have been widely used on condition monit oring in mechanical industries. Similarly, the vibration signal can be applied for monitoring the variations of the processing parameters in the ball mill. The vibration sources were mainly the movement of the grinding charge, which was changed along the rotating axis of the mill body. The location and orientation of the vibration sensor were there fore the key factors to obtain the real signals from ball grinding. Th e vibration measurements were performed on an industrial scale ball mi ll located in LKAB, Malmberget, under commercial scale operation. Afte r data acquisition and digital signal processing, it was found that th e lower frequencies on the spectra were independent of the sensor loca tion. The high frequencies were dependent on both the location and ori entation of the sensor. Simple correlation analysis on all spectra dat a shows that the vibration signals are highly correlated from differen t sensor locations and orientations. Two vibration sensors should be s ituated at different orientations for each location. The first three f actors from factor analysis account for 91.8% of variations of the ori ginal spectra. After rotation of the factor loading by equamax transfo rm, three factors are mainly related to three orthogonal sensor orient ations. It is therefore recommended to use three vibration sensors to map out the whole vibration signals from grinding.