More balls with small size results in fine powder. As a thumb rule powder to be milled should be taken as 25% of total ball weight. If the quantity of charge is very less then milling balls will start to collide with each other and no milling will take place. Ball size depends on initial size of charge and ranges from 10mm-150mm dia. For particular material and initial size the ball size must be optimized. Please refer the link below and see if it works for you and other method is hit and trial.
https://www.google.co.in/url?sa=t&source=web&rct=j&ei=fmrOVOXUGJD58QWvjIG4CQ&url=http://www.911metallurgist.com/blog/calculate-and-select-ball-mill-ball-size-for-optimum-grinding&ved=0CDUQFjAF&usg=AFQjCNFXhH6lxRRx2FpLWXhK3jP8ps6gGg&sig2=lgagkYTXOhHc6B1CmXG65w
More balls with small size results in fine powder. As a thumb rule powder to be milled should be taken as 25% of total ball weight. If the quantity of charge is very less then milling balls will start to collide with each other and no milling will take place. Ball size depends on initial size of charge and ranges from 10mm-150mm dia. For particular material and initial size the ball size must be optimized. Please refer the link below and see if it works for you and other method is hit and trial.
https://www.google.co.in/url?sa=t&source=web&rct=j&ei=fmrOVOXUGJD58QWvjIG4CQ&url=http://www.911metallurgist.com/blog/calculate-and-select-ball-mill-ball-size-for-optimum-grinding&ved=0CDUQFjAF&usg=AFQjCNFXhH6lxRRx2FpLWXhK3jP8ps6gGg&sig2=lgagkYTXOhHc6B1CmXG65w
The ball size to be decided based on the impact energy requirement. Bigger balls helps in size reduction if the feed particles are bigger in size like chunks. If the powder is feed for milling then smaller ball size is preferred for homogeneous mixing and milling by avoiding local impact between the balls.
There should be atleast 25% empty place in the milling jar after feeding balls and the material while high energy impact. There is no such thumb rule for powder to ball ratio. It is generally decided based on the nature of materials to me milled and the required Pulverization force needs to be generated. Usually, based on the requirement ball size, ball to material weight ratio, milling time, RPM these parameters can be varied to optimize the process.
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