granite

After 20 minutes of grinding, sample starts sticking to bowl and balls.

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

To achieve a better output in dry grinding, it is possible sieving out desired fraction and only grinding the coarse fraction until a sticking of sample occurs again.

For this, we sieved dry ground sample with our Vibratory Sieve Shaker ANALYSETTE 3 Pro and used fraction > 63µm for a further dry grinding of 5 minutes. Sample started sticking after totally 25 minutes. A fineness of 87% < 63µm has been achieved.

Because sample use to fill the bowl almost to the maximum, we recommend grinding maximum 100g of sample with such bowl volumes.

After 15 minutes of grinding, complete sample has been sieved with our Vibratory Sieve Shaker ANALYSETTE 3 Pro. Coarse fraction > 63µm has been fed and ground a second time for 5 minutes (totally 20 minutes).

Afterwards, a fineness of 95% < 63µm has been detected.

Some general information: granite use to be quite hard compared to agate (used as desired). We would recommend using zirconium oxide for bowl and balls which will be much harder as agate and will be faster in grinding because of its density of ~ 5,7g/ml instead of ~ 2,65g /ml in agate.

To avoid sticking of sample, a grinding in suspension is recommended. Then 100% < 63µm is achievable in one step.