Granite

We used grinding disks made of zirconium oxide for this trial, this way, no discoloration will happen. If small abrasion of steel can be tolerated, grinding disks made of steel will be much cheaper. We are guessing that even in steel, very high amounts of granite can be ground before the disks need to be replaced.

Always depending on the brittleness of sample, we are guessing that a gap setting of ~ 0,25 mm which result in particles with a max. length of ~ 800 µm.

We found an output of 88 g after the first minute of grinding. A total output of 190 g have been found after 3 minutes. Usually the last 50 g of sample need a longer time to get out of the machine. For this, sound stopped after a total of almost 5 min. We are guessing that a grinding of 800 g of sample as requested can be realized within 10-12 minutes.

Usually, about 7 ± 3 g of sample use to remain inside of the grinding chamber. Small pieces might lie in front of the feeding funnel or on the ribs of the fixed disk. Residues can be brushed off easily.

We determined the fineness of particles by sieving an aliquot with our Vibratory Sieve Shaker ANALYSETTE 3 Pro and test sieves of 400 & 800 µm meshes.

We found 0,2% > 800 µm; 11,8 % 400-800 µm and 88 % already < 400 µm.

Possibly the output of desired fraction can be improved by stepwise grinding. A first grinding trial with 0,5 mm or bigger gap can be prepared (see result 2). After separation of desired fraction (by sieving or sifting), the coarse fraction can be ground with a lower gap setting again.

With this test, we want to determine the particle size when a gap of 0,5 mm will be chosen for grinding.

After grinding, we used a Vibratory Sieve Shaker ANALYSETTE 3 Pro and determined the particle size by sieving of an aliquot. We found: ~ 5 % > 800 µm; 43,2 % 400-800 µm and 51,8 % < 400 µm.

It has shown that still only a small amount of sample use to be > 800 µm. It might be possible that the grinding can be improved by adjusting an even bigger gap of e.g. 0,7 mm. We are guessing that > 60 % might get ground to the desired fraction by stepwise grinding.

With a brittle sample and the fast spinning Cross Beater Mill PULVERISETTE 16, resulting particles use to be much finer as the bottom sieve which has been inserted. In our first trial, we ground 250 g of sample within 20 seconds. It appears that the majority of particles use to be finer as 500 µm.

For this, we repeated the trial with a 2,0 mm bottom sieve additionally (see result 4).

With the bottom sieve with 2,0 mm trapezoidal perforation, sample particles with a few particles with a max. length above 1 mm can be found.

By sieving an aliquot with our Vibratory Sieve Shaker ANALYSETTE 3 Pro, we determined particles of: 31,6 % > 800 µm; 21 % 400-800 µm and 46,3 % < 400 µm.

Typically higher amount of residues will stay inside of the grinding chamber. Attached by electrostatic charge and lying loose on the ribs of the grinding insert.

Cleaning can be done by vacuuming with a stronger brush.

Possibly the output can be maximized when a grinding will be done in two steps. After a first grinding with e.g. 2,0 mm sieve insert, the desired fraction can be separated by sieving or sifting. Afterwards, the fraction above 800 µm can be ground a second time.