An autogenous mill, also known as a media-free mill, uses the material itself as the crushing medium. It does not require the addition of steel balls (though a small amount may be added in special cases), and its high grinding ratio greatly simplifies the crushing and grinding process. Ore crushing relies on the impact force of the ore’s free fall, the mutual abrasion between particles, and the instantaneous stress caused by the sudden change from a pressure state to a tension state, thus avoiding over-crushing.
Under fixed specifications and rotational speed, the feed rate and the ratio of large and small ore pieces directly affect the grinding process and should be carefully considered during production. Production practice shows that a material filling rate between 30% and 40% is ideal. If the feed rate is not well controlled, fluctuations in the material level within the autogenous mill can lead to either “overfilling” (excessive material level) or “underfilling” (excessive material level). Therefore, it is essential to maintain stability in both the quantity and particle size distribution of the ore feed during production. Furthermore, both must be stable simultaneously. If only the quantity remains stable while the particle size distribution is inappropriate, production will become abnormal. Regarding the particle size distribution, large pieces of ore should not be insufficient. In special circumstances where large pieces of ore are insufficient, a small amount of large steel balls can be added. Too much large piece of ore is also undesirable, but too little will also result in unsatisfactory production. The appropriate particle size distribution should be determined through experiments and production practice, based on the specific properties of the ore.