Simulation of structure-borne sound from a ball mill

Abstract

Ball mills are the grinding equipment in the mineral and chemical processing industry. Many spherical objects called media are put into a mill with material, and the mill is rotated. In the mill, material is grounded by collision force due to contact between the material and the media. During operation, the mill vibrates and emits sound. The vibration and sound of mills contain information related to inside of the mill and are useful for operation control. If the relationship between the internal state and the information contained in vibration and sound is clarified, we are able to estimate the internal state of the mill. In this study, we develop simulation models for analysis of structure-borne sound from a ball mill during operation. At first, the motion of the balls in the mill reproduces by discrete element method. The simulation calculates collision force between the ball and the mill wall. Then, the collision force is applied as input force of vibration analysis by finite element method. The vibration response of mill wall is calculated. Finally, the radiated sound pressure is analyzed based on the result of the vibration analysis. The mill is divided into small element, and each element is regarded as a point source of sound. The simulations are performed under the different rotational speed condition. When the rotational speed increases, the velocity of collision with the mill wall also increases. As the result, the amplitude of mill wall vibration and sound pressure increase. Moreover, the sound pressure shows an influence of rotational speed more clearly than vibration displacement of mill wall.