Grinding & Classification Circuits

Grinding & Classification Circuits

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Oversize Ballmill Discharge (1 reply)

4 months ago
Steve 4 months ago

We recently converted our metso 18X11 steel lined Rodmill to rubber lined trommel discharge Ballmill to improve grinding efficiency and increase throughput. Our rodmill used to run 120 tons/hr at a critical speed of 61.5% with rods diameter of 3".  However after converting, we are having difficulties running at more than 80 tons/hr. When we run more than 80 tons/hr, we have a lot of oversize loading up the trommel and spilling on the floor. We have rocks literally the size of the feed discharging from the ballmill. We commission the mill after converting with a blend of balls ranging from 3" to 1" and we are currently running at 36% charge. The mill is fully charge and we cannot add more. Moreover, with the mill fully charge, ballmill amps is 98, not even nearly close to the amps we had when it was a rodmill (130 amps when fully charged). We tried several solids density from 70% to 82% solids but in vain. Please note that we still have the mill running at 61.5% critical speed. Our intent was to use 3" grinding balls. but I am now considering 3.5" and even 4". Our feed top size is supposed to be half inch. For the most part we get that feed size, with few oversize here and there but not a lot. The mill is direct drive, so I cannot play with speed. any idea how to handle this problem?

4 months ago
SmartDog 4 months ago
1 like by mpelera

There are many factors that impact on mill sizing and performance that you do not mention, particular grindability, desired product size, open or closed circuit, wet or dry grinding, what material you are grinding, and others.  First off, a ball mill will generally draw less power than a rod mill, so that is not surprising.  Next with a 1/2" feed size, 3" balls may be too large, and going larger may aggravate the issue.

also ball mills generally work better in closed loop system, while rod mills often work in open circuits.

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