Rod Mils can accept feed up to approximately 25 mm and are generally selected to grind products in the -4 mm to -0.5 mm range. Grinding action is by line contact between rods which extends the length of the mill.
Large feed particles spread the rods at the feed end and in so doing allow preferential grinding of the coarse fraction.
A minimum amount of fines are created and a relatively uniform sized grading is produced.
Rod Mills are usually operated in open circuit. Most rod mill applications involve wet grinding where material is reduced in size from crusher product size to a size suitable for ball mill feed. Rod milling in the size range utilised is more efficient than primary ball milling, in that the desired product is obtained at a lower cost per ton. To avoid breakage or tangling of rods, the L/D ratio of rod mills is kept within the limits 1.3/1 to 2/1.
We supply the 3 most common rod mill types:
Overflow Rod Mill
An overflow mill is constructed with a feed opening at one end and a discharge opening at the other,
both on the axis of the mill. Material leaves the mill by overflowing at the discharge end. Used for producing
the finer end of the product range.
End Peripheral Discharge Mill
The end peripheral discharge mill’s steeper gradient produces shorter retention time and thus a coarser
product than the overflow type. Product is discharged through port openings equally spaced around the
periphery of the shell at the discharge end. Grinding may be accomplished wet or dry. End peripheral discharge
is used to good advantage in damp grinding of coke or steelwork sinter plants.
Centre Peripheral Discharge Mill
Feed is from both ends and is discharged at the centre through discharge ports, equally spaced around
the mill periphery. The ports are in a separate ring between the shell halves. The fact that the particles only travel half the mill length makes the CPD rod mill an outstanding unit for coarse grinding and rapid removal of finished material.