Particle Size Analysis rod-mill comminute 10mm granite chippings 23July2025

Updated mill: Rod-mill with new end-cover working well [video on my YouTube channel].

Mill now outwardly presents planar end-cover; secured by six threaded studs through six anchors on the outer shell of the mill against which nuts draw-up the cover.
The end-face of the shell has been made as flat as possible using manual grinding with a large angle-grinder.
Metal-to-metal contact of shell end-face to end-cover plate is close.

The ground / comminuted material

Batch test charge of 10mm granite chippings, dried for 1 hour at 110C.
Ground for 30 minutes with all rods in mill (as previously), so maximum rod size is 40mm.

The comminute sieved

The masses on each sieve were:

Aperture(microns) mass(g)
4760	0.5
2400	2
1200	136
600	960
300	820
150	564
75	406
-75	1016

The sum total of these masses is 3904.5 g (3.9045 kg)

Graphed...

Of the 23July2025 rod-mill comminution:

Observations / comments

On this 23July2025 rod-mill comminution of 10mm granite chippings - a "test grind":

• the size range is surely way too big?
• where are all these very-fines coming from?
• how does all this vary with grinding time?
• are those oversized "lifters" the problem?

Expanding on the latter point:
the "lifters" on the inside of the shell are vastly oversized. The comes from a misunderstanding. The "lifters" should be very few millimetres dimensions in height and width. "just" to ensure that the charge, of grinding medium / rods and charge / mineral cannot "skid" within the shell.

The "lifters" have been roughly cut back to about 20mm tall - still way too tall. The largest rods are 40mm diameter and it seems probable they are carried high in the mill regardless of mill rotational speed.

The oversized "lifters" cause the mill to always "cataract"; never "cascade"?
Should the mill work more in "cascading" mode than "cataracting" mode?

It is certainly correct that experience is accruing...

(R. Smith, 29Jul2025)