Material grinding (also called attrition milling) is the process by which materials are mechanically broken into fine granules, and it is an essential step in many industrial processes. Grinding machinery can be used to reduce the particulate size of various materials, but is most commonly recognized for its uses in the mining industry to extract valuable metals, such as gold and silver, from surrounding host rock.
Although material grinding machines are used to achieve one general purpose — physically grinding pieces of material into smaller pieces of material — there are a variety of equipment types used to accomplish this. Some major types of mills used for industrial grinding include ball mills, vibratory mills, and rod mills. In addition, there are both wet and dry milling processes, which are typically chosen based on the resultant properties required for the material to be ground.
In general, the materials in attrition mills are ground via mechanical means, i.e., by physically crushing the material into smaller pieces. In ball mills, the material is loaded into a drum alongside a number of milling balls; the drum is rotated on a horizontal axis, causing the material and the balls to collide and consequently abrading the material. Vibratory mills work in a similar way but use vibration (typically in addition to rotation) to crush the material.
Material grinding machines can be applied to various industrial processes. As mentioned, the mining industry commonly uses milling machines to extract desired elements from the less desirable surrounding materials. However, grinding machines can be used for a variety of purposes outside of the mining industry. For example, mechanical attrition can be used to change the reaction of processes; for example, smaller particle size increases the surface area, which can improve the reaction speed or reduce the temperature at which a reaction occurs more quickly.
Moreover, attrition milling can be used to create nanostructured materials in a cost-effective and straightforward way. However, it’s worth noting that the creation of nanostructured materials from mechanical milling requires the consideration of the balance between the plastic deformation and the dislocation motion of the material; as this can affect whether milling is an appropriate means to attain nanoscale materials.
As mentioned above for the creation of nanomaterials, some materials are difficult to grind to a very fine particulate size using purely mechanical means. Thus, in some cases, such as for organic substances, like pigments, wet milling can be used to reduce the particle size further than possible via dry milling. For wet milling, a slurry is created, so as the material is mechanically crushed, it is also dispersing into the liquid medium; the liquid could be subsequently evaporated, depending on the material requirements.
The General Kinematics VIBRA-DRUM® Grinding Mill is a high-energy vibratory drum mill that can be used to grind various materials, including cement, iron oxides, precious metals, shale, and slag. Its unique ability to recover high value precious metals and industrial minerals that are too abrasive for other grinding technology offerings. In addition, the VIBRA-DRUM® Grinding Mill is smaller and more cost-effective than many standard single-barrel grinding drums. To find out more about this equipment or other Grinding and Attrition solutions, contact the technical experts at General Kinematics.