sweet grass (Miscanthus)

In our first trial, we wanted to testify a direct grindability of sample with sieve rings with small trapezoidal perforated openings.

Usually, up to 3 cm long pieces might be pre ground with e.g. 2 mm sieve rings, before a fine grinding step will follow. But the sent miscanthus sample use to be very lightweight. So probably a direct grinding will be possible. Usually the majority of ground particles will show a fineness half as big, as the trapezoidal perforation of the sieve ring. For a 0,2 mm sieve ring, d50 < 0,1 mm is expected to be found.

Within one minute of grinding, up to 12 g of sample can be ground. A bit of fine dust uses to escape the feeding funnel during grinding. Also the rotor speed will be slowed down after large particles have been fed.

Fine ground sample use to stick on the outside of the used sieve ring, but all openings appears to be free of residues. A grinding of higher amounts should be possible.

Probably the usage of the optional impact bar might improve the grinding result (see result 2).

In our second trial, we started grinding with the impact bar and a sieve ring with 0,2 mm trapezoidal perforation. First 15 g of sample have been ground within 55 seconds. Grinding sound use to be smooth, only very small amount of dust escapes the feeding funnel. The remaining 35 g of sample (for a total grinding of 50 g as desired) have been fine directly without a cleaning step in between. After a total grinding time of 2 minutes and 40 seconds, the complete amount of 50 g of sample has been ground.

Only a few stems use to be intact, between the impact bars ribs. The sieve rings openings use to remain free of sample. If higher amounts should be ground, we recommend using the accessories for grinding large quantities.

A classification of ground particles by length is not possible with one of the machines in our portfolio. With a vibratory sieve shaker, long particles will be lifted and are able to pass the sieve mesh longitudinal.

To reduce this effect, we only sieved with lowered amplitude (1,5 mm). More suitable might be a planar moving sieve shaker where sample will only slide over the mesh of the test sieves.

To testify, only 5 g of the voluminous ground sample have been sieved. Up to 20-25 g of sample might be sieved in one batch.

Weight of sieves has been checked after 10 minutes and after 20 minutes. It has shown that the weight does not differ significantly. For this, 10 minutes might be suitable to sieve out the used sample amount.

Following particle distribution has been found after 10 minutes of sieving:

37,65 % < 50 µm; 28,63 % 50-100 µm; 23,33 % 100-160 µm; 5,10 % 160-200 µm and 5,29 % > 200 µm.

As mentioned, found fractions show particles which use to be way longer as the test sieves mesh.