Size: The smaller the media
particles, the smaller the particle size of the final product.
The grinding media particles should be substantially larger than
the largest pieces of material to be ground.
Density: The media should be
denser than the material being ground. It becomes a problem if
the grinding media floats on top of the material to be ground.
Hardness: The grinding media
needs to be durable enough to grind the material, but, where
possible, not so tough that it also wears down the tumbler.
Composition: Various grinding
applications have special requirements. Some of these
requirements are based on some of the grinding media being in the
finished product, while others are based on how the media will
react with the material being ground.
Where the color of the finished
product is important, the color and material of the grinding
media must be considered.
Where low contamination is
important, the grinding media may be selected for ease of
separation from the finished product (e.g., steel dust produced
from stainless steel media can be magnetically separated from
non-ferrous products). An alternative to separation is to use
media of the same material as the product being ground.
Flammable products have a
tendency to become explosive in powder form. Steel media may
spark, becoming an ignition source for these products. Either
wet-grinding, or non-sparking media such
as ceramic or lead must be selected.
Some media, such as iron, may
react with corrosive materials. For this reason, stainless
steel, ceramic, and flint grinding media may each be
used when corrosive substances are present during grinding.
