Rotor mill
Rotor mills are used for the coarse or fine comminution and deagglomeration of soft, medium-hard and fibrous, brittle materials. Grinding is carried out by means of a rotor , which crushes the materials using impact, shear and impact forces .
Executions
Rotor mills are available as floor-standing or table-top units. They differ greatly in their design and mode of operation, but are summarized under the umbrella term rotor mills.
Rotor Beater Mills (Impact Mills)
Rotor beater mills are floor-standing devices in which the rotor is placed in the center of the grinding chamber on a shaft. In addition, a ring sieve is placed in the grinding chamber. There the regrind is ground between the rotor and the sieve insert. The size of the holes in the ring sieve therefore determines the final fineness of the material, as it is only discharged once it has passed through the ring sieve. There are also different versions of the rotor beater mills: They differ in the speed of the rotor, which can be between 3000 and over 8000 revolutions per minute. It is also possible to install additional baffle plates in the screen frame so that the material is exposed to further impact forces.
Centrifugal mill
Centrifugal mills are table-top devices in which the grinding chamber consists of a removable cassette, the rotor is placed in the middle of the cassette, the ring sieve is placed around the rotor. Here, too, the grist passes through the funnel to the center of the rotor and is carried to the outside by centrifugal forces. There it meets the wedge-shaped rotor teeth, which rotate at a speed of more than 100 km / h. The material is pre-shredded by the impact. It is then finely comminuted by the shearing action between the rotor and the ring sieve. So it is a two-stage shredding process. Due to the higher speed (6,000 to 22,000 revolutions per minute) compared to the rotor beater mill, the centrifugal mill introduces more energy in a shorter time. For the grinding result, this has the consequence that the material
- can be crushed more finely than with a rotor beater mill.
- is subject to greater stress and may therefore heat up (deformation work and friction are converted into heat).
- has a very short residence time in the grinding chamber, which in turn counteracts heating.
Due to the relatively gentle processing, the properties to be determined are usually retained. When searching for highly volatile substances, it helps to freeze the sample in liquid nitrogen beforehand. In the same way, viscoplastic samples can also be embrittled and comminuted.
In addition to the rotor and sieve ring structure described, there are other inserts so that the mill can be converted into a pin or cutting mill.
Ring sieves
Ring sieves are an important part of all rotor mills, as they determine the final fineness. Ring sieves are therefore offered with different hole sizes from a few micrometers to one centimeter.
practice
In practice, rotor mills are very versatile devices. Their application spectrum ranges from the grinding of a few grams to a few kilograms. With some devices, all parts in contact with the product can be completely removed and sterilized. This enables extremely clean work without cross-contamination. Areas of application for centrifugal mills are, for example, the pharmacy and traditional Chinese medicine, but they are also represented at research institutions, to name just a few examples. A rotor beater mill comes for. B. is used when the sample volume increases, as it usually has a higher throughput than the centrifugal mill.
Individual evidence
- ↑ http://www.herbasinica.de/down/Kurier-40.pdf ( Page no longer available , search in web archives ) Info: The link was automatically marked as defective. Please check the link according to the instructions and then remove this notice.
- ↑ http://www.analytik-news.de/Fachartikel/Volltext/fritsch34.pdf
- ↑ Koutsomitopoulou, AF, et al .: Preparation and characterization of olive pit powder as a filler to PLA-matrix bio-composites. Powder Technology 255 (2014): pp. 10-16.
