Determined by theses factors to match a proper bearing , such as  the diameter of the ball mill, the hardness of the ore, the particle size of the ore of the ball mill, the hardness (quality) of the steel ball, and the speed of the ball mill. When the model of the ball mill is determined, the speed of the ball mill is  determined as well. The hardness of the ore is measurable. The ore particle size of the goal mill is determined by changing the size of the grid screen.

How to add steel balls to the ball mill in proportion to the size of the steel balls?

The rules of perennial practice and theoretical experience are as follows: 

Generally, the newly installed ball mill has a running-in process. During the running-in process, the amount of steel balls is only added  80%  accounting for the maximum ball load of the ball mill for the first time. 

The proportion can be added according to the size of the steel ball (Φ120mm, Φ100mm, Φ80mm, Φ60mm, Φ40mm). 

The amount of addded steel balls need to follow a main rule , different ball mill models have different total ball sizes.

For example, MQG1500×3000 ball mill (processing capacity 100-150 tons) has a maximum ball load of 9.5-10 tons. Stainless Steel Bearings Manufacturer--QuanJiao BoYang bearing Co.,Ltd  advises the adding amount propotion are like this, the large balls (120mm and 100mm) accounted for 30%-40% , the medium balls 80mm accounted for 40%-30%, and the  small balls (60 and 40mm) accounted for 30% when adding the balls at the first time  .