Petroleum coke

After a total dry grinding time of 5 minutes, sample starts sticking lightly to bowl and grinding balls.

This uses to happen 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.

To reach a better fineness, it is possible to separate sticking fine ground particles (by sieving or sifting) and proceed grinding the coarse particles.

Also anti-sticking-agents (like e.g. Aerosil) can be used to delay a sticking of sample. A grinding in suspension will be capable grinding the complete sample way finer.

30mm Ø grinding balls have been used instead of 20 mm Ø as shown in result 1. With their higher weight, 30 mm Ø grinding balls might be able to achieve a better fineness in dry grinding.

After a total of 5 minutes of dry grinding, sample use to stick a little stronger to bowl and grinding balls as shown in result 1. The fineness has been improved and 99,7 % of sample is able to pass the used test sieve with 180µm mesh on Vibratory Sieve Shaker ANALYSETTE 3 Pro.

As written in result 1 – by grinding in suspension, all sample can be ground much finer.