Two rock samples

In our application laboratory, we only provide Model II as classic line model which is equipped with riffled steel jaws. Those, but also standard jaws can be used for comminution of mineral samples.

The Jaw Crusher was set to its smallest grinding position (1.0) with standard kinematic setting. This way, a fed sample typically will be crushed to a height about 2 mm and a length about 8-10 mm (depending on sample properties).

The sample A was within ~ 30 seconds into the grinding chamber. The grinding sound vanished after a total grinding time of 70 seconds. The sound while grinding was typical smooth. Surely even more of sample can be fed this way.

The sample output which was found inside the collecting vessel was typical. As expected about 2-3 mm thick fragments can be found with a length up to ~ 10 mm for a few fragments.

Sample B was ground equally to result one. The stones were fed into the grinding chamber within 100 seconds. The grinding sound was harsher, compared to result one. The grinding sound started to vanish after ~ two minutes. After 140 seconds, no further grinding sound was recognized.

Also the sample B was ground to a thickness of ~ 2-3 mm with a max. fragment length up to ~ 10 mm.

Surely even higher amounts of sample can be ground this way, too. For an intensive cleaning of the used equipment, fine sample dust was removed rapidly by vacuuming with a soft brush.

For a comminution of higher amounts of sample, we recommend using a Disk Mill PULVERISETTE 13. Also with this type of mill, resulting fineness is influenced immensely by the properties of the fed type of sample. A sample only needs to comply the used gap setting in one dimension to pass the grinding chamber. This way, typically about 3x longer fragments will escape the grinding chamber. With a gap setting of 0,1 mm, we expect that about 5 % of sample might be found > 300 µm and no sample should be found > 500 µm with this setup.

We used the complete pre ground sample of result A (trial 1) and fed the sample into the feeding funnel.

The grinding sound was typical without any harsh sounds. After three minutes, the complete sample was transferred into the grinding chamber. The grinding sound starts to fade after about 5 minutes. After a total grinding time of 6 minutes, the grinding sound vanished completely and the machine was stopped.

The collecting vessel was filled almost completely. The sample is ground fine, with a few longer fragments we spotted. The sample was mixed and a small portion of sample was used to determine the level of fineness by sieving.

We sieved about 51 grams and determined 92,3 % < 500 µm as desired with still about 7,7 % > 500 µm fragments. The two sieving fractions got packed separately for demonstration.

Cleaning of the mill was performed rapidly by vacuuming with a soft brush. By standard, about 10 ± 5 grams of sample is left inside the grinding chamber by electrostatic charge, or remains on top of the fixed disk (can be transferred into the collecting vessel with a brush to minimize losses).

Because sample A still has shown fragments > 500 µm when a gap setting of 0,1 mm was adjusted, we ground the sample B with 0,05 mm (smallest gap setting for our premium line model).

The half of provided sample was used (1,35 kg) and fed into the funnel of the mill. The complete sample was transferred into the grinding chamber with 3 minutes as well. The output after seven minutes was 1,2 kg already. After a total grinding time of eight minutes, the output rose to 1,3 kg and after 8,5 minutes with only minimal grinding sound, the trial was interrupted.

We mixed the output sample and checked the particle size by sieving with our Vibratory Sieve Shaker ANALYSETTE 3 Pro and a test sieve of 500 µm mesh. With 186 g of sample, only 1,8 g remained on top of the 500 µm mesh after a few seconds. This comply to 99 % < 500 µm after this grinding test.

Cleaning was performed rapidly by vacuuming with a soft brush.

Because sample B wasn’t ground to 100 % < 500 µm, we used a Vibrating Cup Mill PULVERISETTE 9 for rapid comminution into fine powder.

Sample B (pre crushed with result 2) was used for this test. About 350 g of sample can be fed into the large 250 ml steel grinding set. With less of sample, more impact and faster grinding time should be found. The optimum speed setting can differ from sample to sample. Usually the best speed setting is about 1100-1500 rpm. We set the speed to 1400 rpm and ground the sample for the first two minutes.

Afterwards, a lot of sample was already slightly compressed between ring and housing. We found a few fragments up to ~ 1-2 mm length and haven’t checked the level of fineness by sieving yet.

We proceeded grinding for further two minutes and opened the grinding set after a total grinding time of four minutes. Now only powder was spotted and we checked the particle size distribution by sieving.

The complete sample passed the 500 µm test sieve without difficulties. The sample was not sticking yet to the grinding set; even longer grinding times can be applied to improve the result even finer.