Cement panel

For a feeding into the machine, maximum length should be < 6 cm. We used a hammer for a fast pre grinding of the 18 cm long panel.

Majority of sample has been found in the collecting vessel after 2 minutes. We interrupted the grinding process after a total of 4 minutes, because two pieces (almost intact) had been grating in the grinding chamber without a further size reduction. A pre comminution with a jaw crusher used to be suboptimal for such a sample (probably some other compounds have been added to stabilize the cement panel).

Equal fineness might be achieved by a manual comminution with a bigger hammer inside of a plastic bag, or a circular saw might be utilized for a rapid pre comminution as well.

With hardmetal tungsten carbide (desired material), only bowls up to 250 ml use to be available. For a grinding of higher amounts, 500 ml bowls are available in other materials like steel or zirconium oxide (with lower densities, 30 mm Ø balls might be required for a proper grinding result).

It is also possible using a Planetary Mill PULVERISETTE 5 with up to 4 bowl fasteners for a simultaneous grinding of a total of 240 g of sample in tungsten carbide as desired.

75 g of dry sample are used to fill the bowl to the maximum. After 30 seconds of grinding, sample volume collapses a bit and further 25 g sample can be fed. By further grinding, the volume of sample stays equally.

After 2 minutes of grinding, sample has been ground to a fine powder. The sample already starts sticking softly to bowl and balls.

This usually happens after the majority of particles reached a fineness of < 20-30 µm. Interacting forces between fine ground particles will become bigger as their own g-force. Therefore, particles will stick to each other and become compressed by the used grinding balls. These clusters of particles also contain bigger particles which will not be ground any further.

For this, pieces up to 100 µm can be found. A further grinding for a total of 5 minutes has achieved an almost equal result (with ~ 50 % of particles < 15 µm). See present particle size distribution, measured with Laser Particle Sizer ANALYSETTE 22 NanoTec plus after 2 minutes of dry grinding with meas. 62232 on separate page. Dry grinding result can be improved by separation of sticking fine fraction (e.g. sieving, classifying or sifting) and proceeding to grind coarse fraction until sticking occurs again.

To reach desired final fineneness, a grinding in suspension will be required (see result 3).

Because 2 minutes and 5 minutes of dry grinding in result 2 haven’t shown an improvement in grinding (result 2), a grinding in suspension is required for a further size reduction. For this, we added ~ 80 ml of isopropyl alcohol (IPA).

To avoid overpressure, we ground the sample in steps of 1 minute, followed by a programmed pausing time of 4 minutes. After several cycles, the outside temperature of the bowl should be checked (remain below 70 °C); grinding time or programmed pausing time might be readjusted afterwards. By using solvents with higher boiling points, grinding time can become increased (- or pausing time reduced).

After 10 minutes of grinding in suspension (totally 15 minutes), d50 has been reduced to < 9,3 µm (see particle size distribution on meas. no. 62244 on separate page). Because complete sample should be ground to < 10 µm, we recommend a change in grinding ball size to e.g. 2-5 mm Ø to speed up grinding process (see result 4).

General grinding comments of result 3 use to count for this trial as well.

To maintain an optimum grinding result, we had to add ~ 70 ml of isopropyl alcohol for achieving the proper viscosity (motor oil like).

After a total of 30 minutes of grinding time, already 80 % of sample particles are smaller as 10 µm (as desired). We proceeded grinding for totally 60 minutes.

Aftewards, fineness has been checked again with our Laser Particle Sizer ANALYSETTE 22 NanoTec plus: a d50 < 2,09 µm has been achieved (see meas. no. 62277 on separate page).

A longer grinding time is still possible to achieve a better endfineness.

We are guessing that about 95-98 % of sample might achieve < 10 µm after a total of 2 hours of grinding. A faster grinding result is expected, when 3 mm Ø will be used instead of 5 mm Ø; achievable endfineness with 3 mm Ø grinding balls should be finer as well.

Sample and grinding balls have been separated with a 2,0mm test sieve afterwards.