Porcelaine

With a maximum length of ~20 mm, we recommend using 30 mm Ø grinding balls for a first pre grinding step.

After the first 2 minutes of dry grinding, sample started to stick stronger to the bowl of the grinding wall. This uses to happen after the majority of particles reached a fineness of < 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 a further comminution, we recommend grinding in suspension. For this, we added 50 ml of water and ground the sample for a total of 10 minutes.

To avoid over pressure, we ground the sample in steps of 2 minutes, followed by a programmed pausing time of 4 minutes. After several cycles, the outside temperature of the bowl should be checked (remain below 80°C); grinding time or programmed pausing time might be readjusted afterwards.

This is counting for all following grinding trails too.

After 10 minutes, the fineness has been checked with our Laser Particle Sizer ANALYSETTE 22 NanoTec plus.

Largest particles which could be found use to be about 60-80 µm. Because this use to be close to the maximum fineness of 30 mm grinding balls, we switched the grinding balls to 5 mm Ø to achieve a good grinding result (see result 2).

Grinding balls have been switched to 5 mm diameter in this trial.

Typically, we recommend to use 20x bigger grinding balls as present particle size. With up to 80 µm particles, a direct usage of 1 mm grinding balls can be problematic. Possibly also 3 mm Ø can be used for a direct grinding without skipping the balls a further time as shown in result 3.

Viscosity of ground sample has been like yoghurt. An optimum grinding viscosity use to be present, when the slurry use to be motor oil like. To achieve this again, we added 10 ml of water before we proceeded grinding.

We kept on grinding for further 35 minutes until a total grinding time of 45 minutes has been reached. The fineness has been checked with our Laser Particle Sizer ANALYSETTE 22 NanoTec plus again.

This time, a d50 < 1,72 µm has been reached. Finest grinding results will be achieved with 1 mm Ø grinding balls with classic line ball mills. Because a fineness of d50 < 0,5 µm is requested, a further change in ball size should be performed (see result 3).

To reach a maximum fineness, we changed the grinding balls to 1 mm Ø before this trial has been started. This balls size still use to be accelerated properly for a good comminution of particles. Small grinding ball diameters are only recommend for a usage with premium line planetary mills (like e.g. 0,5 or 0,1 mm Ø for premium planetary mill with a g-force up to 95).

We kept on grinding for further 45 minutes (total 90 min) and finally for a total of 120 minutes. Fineness of both grinding results has been almost equal. For this, after 90 minutes of grinding, the best achievable grinding result has been present.

With our Laser Particle Sizer ANALYSETTE 22 NanoTec plus, a d50 < 1,03 µm has been detected (a typical result for a classic line planetary mill). This is a typical grinding result with classic line planetary mills.

Grinding process has been aborted and sample got packed.