Granulator
Cutting mills are used for pre-shredding and homogenizing medium-hard to soft and elastic materials. A distinction is made between knife and cutting mills.
Knife mill
These are constructed like kitchen mixers and are mainly used to shred and homogenize organic samples. Oily or moist materials can also be processed.
To do this, the grist is placed in a plastic, glass or steel container. A knife cylinder is used in the middle, which holds two vertically offset knives arranged at right angles to the direction of rotation. The knives are accelerated to very high speeds (up to 10,000 min −1 ), which then shreds the material very quickly.
For various bulky samples that lose their volume as a result of shredding, for example lettuce, there are special lids that ensure that the material can still be caught by the knives.
Granulator
Cutting mills are floor-standing devices that use rotor knives and stator knives to shred the material to be ground by shearing. The material usually falls from above through a funnel into the grinding chamber, where it is picked up by the rotor and ground between it and the fixed cutting plates. There is also a sieve in the lower part of the grinding chamber; only material that has reached the required fineness passes through and then falls into the collecting container or suction pan.
Sieves are available in different sizes and designs, depending on how finely the material is to be crushed.
Cutting mills are available in different designs. They differ in the speed of rotation of the cutting rotor, which depends on the cutting speed. As a rule, a cutting speed of 7 to 15 m / s is achieved in a cutting mill. The cutting speed depends on the material to be ground.
In addition, various rotors are offered in which the rotor knives are arranged either parallel or in a spiral shape (parallel or tangential cut rotor). A parallel cut rotor, however, has the disadvantage that the parallel cut tends to lead to crushing or crushing of fragments. As a result, the material is more likely to break and this creates a greater proportion of dust. A so-called scissors cut rotor (tangential cut rotor) clearly achieves better cutting results. This relates to both the quality of the granules and the undesirable dust content in the granules.
A further development of the scissor cut rotor are the V-cut rotor or cross-scissor cut rotor. In the case of the V-cut rotor, an accumulation of material can be observed due to greater wear on the blades and the sieve in the center of the cutting mill. The cross-shear cutting rotor distributes the material evenly over the entire grinding chamber thanks to its alternating rows of inclined rotor blades.