This study on the effects of particle filling and size on the ball load behaviour and powerudin a dry mill was initiated at the University of the Witwatersrand in 2003. The aim of theudstudy was to make available a better understanding of the underlying causes in theuddifferent power draws that occur in mills when ore particles are being added to the balludload. This mimics the process of filling an industrial grinding mill after a grind out hasudbeen performed. Typically after a grind out, the mill operator would refill the mill with oreudup to the point where maximum mill power draw is registered. At maximum power drawudit is assumed that the void spaces within the ball load are filled with ore particles andudthat the charge is well mixed.udIn order to conduct the study an inductive proximity probe was used to measure theuddynamics of the load behaviour. This novel technique in measuring load behaviour wasudchosen due to the fact that the probe could sense the presence of steel ballsudindependent of the presence of particles in the mill. The probe’s response to a loadudcomprised of steel balls only at the fillings of 15-45% and mill speeds of 60 – 105%udindicate that the various changes in load behaviour such as cataracting, centrifuging,udball packing and toe and shoulder responses were easily distinguished in probesudresponses. Further tests were conducted in a mill with a 20% ball filling with increasingudcoarse or fine silica sand particle filling from 0 – 150% at the mill speeds of 63-98% ofudthe critical mill speed. These tests clearly reveal radial segregation of coarse silicaudsand, increased ball cataracting and centrifuging of just silica sand or a combination ofudballs and silica sand. The impacts of these phenomena have been discussed withudreference to industrial mills.udThe physical parameters defining the load provided by the inductive probe made itudinteresting to make use of Morrell’s C model to simulate the power drawn by the mill.udModifications to Morrell’s model were made thus leading to a modification in the toe andudshoulder model and proposals for a segregated charge model, a centrifuged chargeudmodel and a particle pool model. Furthermore a modelling study based on the torquearmudmodelling approach was conducted. Here Moys power model was used to studyudthe effect increasing coarse and fine particle filling has on the power drawn by a mill. Audliner model was proposed to define N* as a function of particle filling. In both modellingudcases the models were used to account for the various conditions arising within the loadudas particle filling and mill speed increases.
展开▼
