Minerals and Slag

Our jaw crushers are usually designed to pre-crush larger samples into a range of fineness, where samples can be fed to other types of mills for fine grinding.

With the smallest gap setting, the gap of the moving mill will open up > 2 mm. Typically this will result into particles up to ~ 8 mm length (depending on brittleness of sample).

Test wise, we used 600 grams of the provided M-slag sample and fed the small fragments three times into our jaw crusher. For the first test, about 30 seconds of grinding time was required until the entire sample has fallen into the collecting vessel.

As expected, a lot of particles about 5 mm length were spotted. For the second feeding step, about 25 seconds were required until the grinding sound vanished. Fine range of particles only seems to increased minimal.

A final feeding of sample required only 20 seconds until all sample passed the grinding chamber. Finally, we sieved out the complete output with our Vibratory Sieve Shaker ANALYSETTE 3 Pro and a test sieve of 500 µm mesh.

We found 291 g > 0,5 mm (with particles up to ~ 5 mm length) and 298 grams of sample < 0,5 mm (~ 49,4 % > 500 µm and 50,6 % < 500 µm).

We aborted the grinding process at this point and cleaned the grinding chamber rapidly by vacuuming with a soft brush.

We don’t expect that further feeding steps will improve the fineness significantly. To achieve a fineness of 95 % < 500 µm, we recommend different types of mills. For larger amounts of sample, we recommend using Disk Mill PULVERISETTE 13 (see result 2).

Also 600 grams of M-slag sample were fed into our Disk Mill PULVERISETTE 13 premium line. The gap between the disks was set to 0,05 mm. Also this type of mill is not capable to grind all samples < 50 µm because output only need to comply in one dimension to pass the grinding chamber. While the height of output particles uses to be about 0,05 mm (depending on 0-gap setting), fragments can be much longer and wider to pass the grinding chamber. Typically few percentages remain > 300 µm when a sample will be sieved out afterwards.

The start size of M-slag was slightly larger and particles might be capable to interlock in the feeding funnel. We recommend a slower feed rate, so there is no need to mobilize samples of this start size. It is also possible to use a Jaw Crusher PULVERISETTE 1 above the Disk Mill to pre crush even larger fragments, so sample will slide into the grinding chamber automatically.

It took about 3,5 minutes until all 600 grams of the slag were fed into the grinding chamber. Further 60 seconds were required until the grinding sound vanished completely.

The output inside the collecting vessel is much smaller than result 1 output. We took all output was sieved with 500 µm mesh test sieve. Rapidly the majority passed the test sieve and only a residue of 8,2 g of flat flakes (~ 1 mm max. length) was found on top of the 500 µm sieve. 580 grams was found inside the sieving pan. Therefore, in only one round, already > 98 % of sample was ground finer than 500 µm as desired. There is no need for a second feeding.

Fine sample dust uses to remain inside the grinding chamber by electrostatic charge. Cleaning was performed rapidly by vacuuming with a soft brush. For a much longer durability of grinding disks, we recommend using disks made of hardmetal tungsten carbide when higher batches of abrasive samples will be ground.

Next to a Disk Mill PULVERISETTE 13, also Planetary Mills or Vibrating Cup Mills might come into question to quickly grind such types of samples even finer. For both types, a pre crushing will be required before those mills can be used. Most likely also 500 grams of sample need to be split into min. 2 batches for comminution (because of limited vessel volume; only about 200-250 ml of sample volume can be used for this types of mills.