Choosing the right grinding media to ensure reliable, consistent performance for your bulk material preparation can be a challenge. When choosing, be sure to consider the following factors:
Sphericity: When grinding media that is perfectly spherical is used in your mill, all gaps that form between them will be the same size. Once the media is no longer spherical, the force of the fluid or powder is not exerted equally; this can cause media to “tumble” in the mill, leading to some gaps being large and some small. The liquid or powder vehicle in the premix then naturally flows more through the large gaps. The shear force is not high enough to do any deagglomeration, and mill efficiency suffers.
Size: As most of the work in a grinding mill such as a ball mill, horizontal mill, vertical mill is done by squeezing the material through the gaps between the media, we can assume that the more gaps, the more effective the milling. In order to increase the number of gaps, you will need to increase the number of beads or cylinders. However, to maintain the amount of media that is loaded, the only option is to decrease the size of the media – for example, the diameter of the beads.
Density: In a media or bead mill, denser media accelerates at a slower rate than less dense media so the velocity has to be increased by increasing the speed of the agitator or the mill itself. It also loses energy more slowly once energized. The media will impact and impinge the grinding shell wall and sink energy to the mill wall before being drawn into the recumbent flow of the mill. This causes grinding shell wear and puts undue stress on the mill cooling system if the correct media is not selected.
Media Surface: Irregular surfaces on grinding media can have an additive effect on the milling process, caused by surface cavitation as the fluid under process is forced around the bead. This causes accelerated mill wear because of the increased abrasion on the irregular surfaces and also causes accelerated wear on the media itself.