Reasons for steel ball out of roundness in ball mill

　　Many mining, metallurgical, and cement enterprises often encounter the phenomenon of steel balls being out of round during the use of ball mills, which brings many unnecessary troubles to their production and operation activities.

　　Generally speaking, the definition of out of roundness of ball mill steel balls is that after 2000 hours of use, if the out of roundness of the ball mill steel balls is detected to be greater than 7%, it is considered out of roundness. (Out of circle=(maximum diameter - minimum diameter) ÷ average diameter x 100%)

　　There are the following reasons for a steel ball being out of round:

　　1. Steel balls with unqualified chemical composition; The composition of the raw materials used does not meet the standards, and they are purchased from small steel mills.

　　2. There are many impurities in steel; Excessive inclusions in steel can affect the quality and use of steel balls.

　　3. The heat treatment process is incorrect, the stress is not eliminated, and the residual austenite is too high (usually 15% -30% residual). During use, austenite heats up and transforms into martensite, causing volume expansion and increased internal stress. After 900 to 1000 hours, the phenomenon becomes severe;

　　4. The imperfect production process of steel balls results in incomplete quenching and tempering during the heat treatment process. The phenomenon of high hardness on one side and low hardness on the other side of the steel balls is generally referred to as the "yin-yang surface". The uneven hardness makes the steel balls wear differently during use, with high hardness wearing slowly and low hardness wearing quickly, resulting in the phenomenon of steel balls losing their roundness.

　　5. The hardness, temperature, moisture content, mill speed, lining structure, and gradation of raw materials (grinding materials) all have an impact; This has a certain impact, but not very significant.

　　6. Grinding process conditions and mill operating conditions (metal corrosiveness and fragility of incoming materials, grindability, hardness of incoming materials, particle size of incoming materials, and fineness of outgoing finished products)