Most typically, a feed hopper is handled by a crane, and when lowered over the feed chute to the ball mill, the bottom is opened and balls flow into the ball mill along with the ore feed.

Depending on the size of the mill and whether or not there is a trommel on the mill discharge, you can throw (hand-bomb) balls in from the discharge end of the mill, or you can install a 6" long radius pipe that will let you roll the ball into the mill, this can save on the muscle building, but needs to be a mobile structure so it can be removed during relining.  If the balls are small you can place them on the feed conveyor, AFTER the belt scale, but don't do this with anything over 50mm the impact of it falling in the feed shute will cause damage unless additional support is added.

A friend sent me this:

Grinding media management in ball mills

Grinding ball additions

Grinding balls should be added each shift. Mill performance is negatively impacted when the mill is not drawing power at targeted level. This results in coarser grind size or loss in throughput.

The grinding balls can be added onto the mill feed conveyor when the mill is running. This addition should be spaced over time to prevent overloading a section of the belt, plugging the feed, etc. If the mill is fed with a spout feeder this is no problem. If the mill is fed with a spout feeder, they should not be fed directly using this unit. In such case, there should be separate central pipe for use.  

The mill should develop and maintain a grinding media wear value (kg media per tonne ore processed). This can be used in combination with tracking mill feed tonnes in order to determine a target media addition for each shift. The monitoring of power draw and periodic mill observation are used to fine tune the estimated media consumption rate and allow for variation in ore hardness, grinding media quality, etc.

Target for ball loading

The mill staff should establish a target volumetric loading of balls for the ball mills. There will be a power draw associated with this charge. Note this should take into consideration the installed motor and any limits placed on the motor. In some cases, undersized motors have been installed or motors are derated due to site-specific occurrences.

During mill shutdowns, the mills should be periodically surveyed and the actual charge level observed. There is guidance in Moly Cop tools for doing this (spreadsheet: Media Charge level), where three methods are supported:

• Free height
• Chord length
• Number of exposed lifters

Charge monitoring

A control chart of mill power draw should be maintained. If the power draw is too low, additional balls should be added. If the power draw exceeds the upper limit, ball additions should be ceased.

Prior to mill shutdowns, the operators should occasionally grind out the mill for a short period of time. This is simply stopping mill feed and observing power draw. The power draw should increase in this time to a consistent level. Ball charging should be increased or decreased depending on the observed power and results from actual charge level measurement.