Filber-Samples (Hops and other)

All 3 air-dried samples were brittle enough to be ground with our Variable Speed Rotor Mill PULVERISETTE 14 premium line (converted into a cutting mill). With start sizes up to ~ 30 mm, a pre-cutting would be required, before finest sieve shell sets could be used.

We used the largest sample 3 for this trial. About 50 grams (1 liter of compressed bulk sample material) was used for this pre-cutting trial. The mill was equipped with cutting mill conversion, a sieve shell set with 0,5 mm trapezoidal perforations was used and our high-performance cyclone separator with sample exhauster were equipped to remove such lightweight sample material out of the grinding chamber.

The mill was started with max. speed 18.000 and fed the sample. The sound of grinding was typical and after only 60 seconds, the sample was fed and ground. The grinding chamber was free of residues because of the active air flow of the cyclone separator. There was not significant clogging of sieve shell perforations. Even higher amounts of sample could be ground this way.

The grinding chamber was cleaned rapidly by vacuuming with a soft brush (required about 1-2 minutes).

The fine grinding was performed with the results 02 (< 0,2 mm) and result 03 ( < 0,12 mm).

Pre-cut sample of result 01 was used for this trial. We exchanged the sieve shell holder against one, who was equipped with a 0,2 mm sieve-shell set.

30 grams of the < 0,5 mm pre-cut sample were prepared and ground within 80 seconds at 18.000 rpm speed setting without problems. Also with such a fine sieve shell set, the sound of grinding was typical and vanished directly after the last sample fragment was fed.

The mill was stopped after 1:20 minutes. The sieve shell perforations were not significantly clogged and a grinding of higher amounts of sample should be possible, too.

Please keep in mind to grind only as fine as required, not as fine as possible. This way, you can safe plenty of processing and cleaning time and minimizes abrasion inside your sample.

After this trial, the cleaning was performed rapidly by vacuuming with a soft brush.

With our last test with our Variable Speed Rotor Mill PULVERISETTE 14 premium line, we ground pre-cut sample with a sieve shell set with 0,12 mm trapezoidal perforations.

The 19,5 grams of sample were fed slowly into the mill. The sound of grinding was typical and vanished rapidly after the last fragment was fed. After ~ 80 seconds, all sample was fed and ground. The perforations of the sieve shells remained free and a grinding of 50 grams should still be possible in one batch.

For an intensive cleaning of the equipment, all grinding parts were placed into our ultrasonic cleaner. After a few minutes of treatment, the equipment was flushed with fresh water and dried off.

Finest sieve shell sets are available with 80 µm trapezoidal perforations. Those can be clogged easily and even with very low feeding rates; ground fibers are capable to pass the openings longitudinal.

If you like to achieve an absolute maximum < 100 µm fine, we would recommend using a Vibrating Cup Mill PULVERISETTE 9.

Sample 2 was picked to demonstrate the grinding with our Vibrating Cup Mill PULVERISETTE 9. Next to steel or hardmetal tungsten carbide (up to 250 ml capacity), also a metal free grinding is possible with zirconium oxide and agate equipment.

We used a 100 ml grinding set made of zirconium oxide to perform our test. Without problems, about 13 grams of sample were fed between housing, ring and core.

We ground the sample for one minute at 1500 rpm. The sample was ground to a fine powder; the sample was not sticking strongly yet and we proceeded grinding for a second minute.

Now the sample became compressed lightly and a longer dry grinding is not recommended anymore. Typically, a d50 < 20 µm might be present with this level of fineness. Finer results are possible when a grinding would be proceeded in suspension (e.g. with proper solvents or water).

The sample was brushed off best possible and packed. The grinding set was cleaned by comminution of a proper portion of sand and water for a minute. The sand is taking off last residues of sample rapidly. Finally, the grinding set was flushed with fresh water and dried off.