Hard Coal

With a start size of 5-10 mm, the size is small enough for a direct feeding to Disk Mill PULVERISETTE 13. A pre crushing with a jaw crusher as requested is not necessary for such a sample.

We ground the sample with an output of ~ 180 g/min. When grinding chamber will not been filled at the end of the grinding process, output will become lower.

After grinding of ~ 1,4 kg of sample, only a small amount of sample use to be left inside the grinding chamber. Cleaning can be performed rapidly by vacuuming with a soft brush.

The gap between the disks uses to be free of residue, so even higher amounts of sample can be ground this way.

With a disk mill, particles only need to be reduced in one dimension to pass the gap. With a gap of 100 µm (smallest possible setting with Disk Mill PULVERISETTE 13 classic line), longer and wider particles can be found.

We determined the achieved fineness by sieving an aliquot of sample with our Vibratory Sieve Shaker ANALYSETTE 3 Pro and a test sieve of 200 µm mesh. It has shown that 41 % of sample is able to pass the test sieve.

We used a rotor with inserts and knives and made of hardmetal tungsten carbide (WC) for a much longer durability than a standard rotor with knives made of steel.

With the optional cyclone separator, fine sample dust will be removed and exportation will be avoided. Also an additional chilling effect and a faster output of sample will be provided (because of the cyclones air flow of ~ 2800 liter per minute).

Even higher amounts of sample can be ground this way. After 165 seconds, only a bit of sample remains loose inside of the grinding chamber and can be removed easily by vacuuming with a soft brush. It is also possible to run the machine a little longer (e.g. ~ 60 seconds) to minimize the reside of the grinding chamber.

By sieving an aliquot of sample, about 77,6 % of sample is able to pass a 200 µm test sieve.

Smaller sieve cassettes are available on special request, but next smaller 200 µm sieve cassette has been tried for grinding without success. The sample was lying on top of the sieve cassettes openings and blocked the air flow of the cyclone separator. Even switching off and on of the cyclone did not improve the result. Sticking sample staid on top of the sieve cassette and did not get removed. Only a few grams of output have been generated (and got disposed). Probably a grinding might be possible after a pre drying step.

With a Cross Beater Mill PULVERISETTE 16 and a 0,5 mm sieve cassette, sample can be ground in higher amounts. After 30 seconds, all sample got ground. Only a minimum amount of sample use to remain loose inside the grinding chamber. A grinding of up to 2,5 kg as requested might be possible.

Fine sample dust can escape the feeding funnel. To avoid dust exploration, we placed the tube of a vacuum cleaner next to its opening.

By sieving the sample with a 200 µm test sieve and a Vibratory Sieve Shaker ANALYSETTE 3 Pro, we determined 72,1 % which is able to pass the mesh of the test sieve.

Finest grinding result has been achieved in our last trial with Cross Beater Mill PULVERISETTE 16 and a bottom sieve of 0,2 mm trapezoidal perforation. Like result 3, we placed a vacuum cleaner next to the opening of the feeding funnel to avoid dust exploration.

After 2 minutes, we generated an output of ~ 380 g. It has shown that the ribs of the grinding insert start closing slowly. Also some openings of the bottom sieve use to be blocked with sample too. We are guessing that a grinding of up to 2,5 kg of sample can only be performed batch wise. We are guessing that minimum 3 cleaning steps will be required for a grinding of 2,5 kg of sample.