In a stable operating state, the amount of material entering the ball mill should be equal to the amount exiting. If, due to some reason (such as increased return sand or increased raw ore), the amount of material fed into the mill exceeds its maximum allowable throughput capacity and cannot be discharged, it gradually accumulates inside the mill, causing it to lose its grinding function. This phenomenon is called “bloating.”
Bloating not only causes the mill to lose (or reduce) its grinding effect on the ore, disrupting stable grinding operation, but also causes fluctuations in feed concentration and fineness in subsequent beneficiation operations, affecting their normal progress. Furthermore, severe bloating can lead to damage to the mill. For example, in a severely bloated overflow mill, large pieces of ore and steel balls will be ejected from both the feed and discharge ports, a phenomenon known as “front ejection and rear pull.” Grate-type ball mills discharge a large amount of slurry containing ore and steel balls from the feed inlet. Especially during closed-circuit grinding, both types of mills cause a large amount of steel balls and ore chunks to enter the return sand box. This results in large pieces of ore and steel balls violently impacting the spoon-type feeder, damaging the feeder and return sand box, causing the spoon head to detach, or the screws connecting the feeder and the hollow shaft to deform or shear off, disrupting the concentricity of the feeder and the hollow shaft. In severe cases, this can cause the ball mill to vibrate or jump, and the bearings and gears can be damaged by the impact load. Therefore, it is crucial to be highly responsible during the operation of the grinding mill to prevent “bloating.”