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After 10 minutes of dry grinding, sample starts sticking lightly 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. Depending on the iron content, also magnetic properties might cause a sticking.
An aliquot of sample has been sieved out with our Vibratory Sieve Shaker ANALYSETTE 3 to determine the fineness. About 85,7% use to be < 63µm as desired.
For dry grinding, it will be possible improving the ratio by sieving out the complete sample and proceed grinding coarse fraction until sticking occurs again.
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