You need to know the properties of the material that you are dealing with. Perhaps the very important characteristic when dealing with reducing the size of a material is its hardness. Almost all of the size reduction equipment techniques involve creating new areas of the surface material. This means that additional energy is needed in order to break the bond of the particles. The Mohs scale is one way of expressing the hardness of a material. Diamond is deemed 10 in the Mohs scale while talcum is on level 1. It is also essential to determine whether the material is brittle or tough. Materials that are brittle are much easier to fracture.
There are other characteristics that you have to consider like the bulk density, moisture content, temperature sensitivity, abrasiveness, distribution of the particle-size and explosiveness. You also need to check the flow properties of the material as it can be a major factor in a smooth process. There are plenty of size-reduction processes that are continuous but usually have choke points where flow interruption and bridging occur. For example, size reduction equipment that is often fed with chutes might experience an interruption in its process flow. Though the feed flows well, the crushed product will at some point compact and will have a difficulty flowing. Storage bins which are intermediate might worsen the flow issues by causing bridging and compaction.
It is critical to know the desired particle-size of a product for every feed material. In mining, if materials are reduced to very fine particles, it can interfere and cause problem in the separation process like in froth flotation. This will usually result in the loss of precious components. In other operations however, the primary target might be to create very tiny particles. For example, in the process of sugar grinding tiny particles are agglomerated in order to increase the share of particles which are larger.
Size-reducing machines rely heavily on impact or compression. The compression is applied through moving jaws, gyratory cone or rolls. The discharge size is adjustable and is set using the clearance. Equipments which are impact-based usually use media or hammers. Rolls are capable of producing very tiny particles. In flour milling, the rolls are typically used where the crushing method yields different sizes of particles and which allows the separation of flours that are purified. The moisture content is also vital. For example, the bran tends to remain in larger pieces since it is soft while the endosperm is brittle and easily fractures into smaller particles.