Parts of olive trees and citrus fruits dried

In our first trial, we took a small amount of sample D and tried grinding with sintered corundum. It has shown that 20 mm Ø grinding balls use to comminute the present sample slowly. After a total milling time of 8 minutes, most of the sample has been ground, but still a few longer fibers (> 2 mm long) could be found. After 15 minutes of grinding, the sample appears to be very fine. Only a few fibers can be spotted with use to be too big. We are guessing that already 90 % might be able to pass a 200 µm sieve mesh. We packed a small sample quantity (~ 1,5 ml) of ground material for demonstration.

We ground the rest of sample to a total of 30 minutes. Afterwards, no big particles could be spotted. We are guessing that 95-99 % of the ground sample will be able to pass a 200 µm mesh test sieve.

We also like to mention that sintered corundum as grinding material will be beneficial for grinding of organic samples as given, but with its ruff surface, higher abrasion of aluminum oxide (compared to other materials) will be found afterwards.

The wooden parts of Sample A (olive tree) don’t use to be brittle enough for a grinding with 20 mm Ø grinding balls (checked in 80 ml grinding bowl previously - see packed sample for demonstration). Also 30 mm Ø grinding balls as we used for this trail did not lead to a comminution of sample.

A direct grinding of such a sample is not possible with a planetary ball mill. The start size of material use to be too big. It might be possible that the sample can be ground properly after pre grinding to < 1 mm (see result 4 & 5).

It took about 30 seconds until the complete sample has been fed. Fine dust of sample use to stick lightly to the rotors ribs and the sieve ring by electrostatic charge. All sample has been ground successfully. A grinding of higher amounts is possible (up to 50 g with the standard collecting pan).

Sample which has been ground this way can be used for a fine grinding with this machine too (see result 6). A very fine grinding of higher amounts is possible with e.g. our Planetary Mono Mill PULVERISETTE 6 classic line (see result 4 & 5) too.

After pre grinding to < 1mm start size in result 3, sample can be used for a fine grinding in this trial.

After 2 minutes of grinding, the majority of sample already use to be < 200 µm as desired. After a total grinding time of 5 minutes, no bigger particles can be spotted. It appears that minimum 95-99 % of particles use to be as small as desired. We took about 3 g of sample for demonstration and proceeded grinding for 8 minutes without visible changes in fineness. So 5 minutes of grinding should be fulfilling.

For a grinding of higher amounts, also grinding bowls made of 250 ml and 500 ml total volume are available (for useful sample amounts of ~ 125 – 225 ml).

Zirconium oxide as we used for bowl and balls in this trial has a smooth surface. For this, less abrasion will be found compared to a grinding in sintered corundum, but this material will have disadvantages in grinding of organic materials.

Sample which should be ground in zirconium oxide must be dry, brittle and small enough. If sample tends to be more slippery (oily), the sample might need to be ground in sintered corundum.

In this case, pre ground sample which is < 1 mm can be ground successfully with the bowl and balls made of zirconium oxide.

Large samples should not be fed directly to fine sieves like 0,2 mm or smaller, for this, sample has been pre ground to < 1 mm (see result 3). Afterwards, sample can be fed a second time for fine grinding with e.g. 0,2 mm sieve ring as shown in this trial.

The complete sample has been fed within 90 seconds. During the feeding of sample, fine sample dust escaped the feeding funnel and has been removed by placing the tube of a vacuum cleaner next to the feeding funnel.

For a grinding of higher amounts (100 ml as desired), we would recommend using the accessories for grinding large quantities. By using this accessories, also fine dust which escapes the feeding funnel will be minimized because of optimized air flow.

After all sample has been fed, we found ground sample which was sticking by electrostatic charge to the collecting pan as well as to the outside of the sieve ring and the ribs of the impact rotor.

Because the higher amounts of fine electrostatic charged dust, sample starts to build up behind the sieve rings openings. By grinding of higher amounts, the openings might also became closed when the accessories for grinding large quantities will be used. We are guessing that minimum 1-2 cleaning steps might be required if 100 ml of sample should be ground.

The dry pamace sample (C) don’t use to be brittle enough for a grinding with 20 mm Ø grinding balls (checked in 80 ml grinding bowl previously - see packed sample for demonstration). Also 30 mm Ø grinding balls as we used for this trail did not lead to a comminution of sample.

A direct grinding of such a sample is not possible with a planetary ball mill. The start size of material use to be too big. It might be possible that the sample can be ground properly after pre grinding to < 1 mm.

Just like the wood pieces, the sample might contain too much lignin. We are guessing that after a pre grinding to e.g. < 1 mm, it should be possible to grind the sample to fine powder.

Usually ground particles will show a d50 smaller as the half of the trapezoidal perforations of the used sieve ring. With a 0,5 mm sieve ring, the majority of particles should be < 250 µm.

The exploration of fine dust which use to escape the feeding funnel is minimal. Even higher amounts of sample can be ground. For amounts > 50 g, we use to recommend working with accessories for grinding large quantities.

Also the pulp of oranges sample can be ground successfully with a 0,5 mm sieve ring. Sieve ring and rotor use to remain free of residues, a grinding of higher amounts is possible.

The rest of orange pulp sample has been pre ground with 1 mm sieve ring (analogue result 3) and has been used for fine grinding with this trial.

Just like in previous mentioned trials, fine ground sample dust escapes the feeding funnel and will be removed by placing the tube of a vacuum cleaner next to the funnel. After grinding, a small layer of electrostatic charged sample use to be attached to the outside of the sieve ring.

All perforations of the sieve ring use to be free, but by grinding of higher amounts, dust might build up and lead to a closure of openings. It is possible that the accessories for grinding large quantities might be beneficial regarding exploration of dust and closing of the sieve rings openings.