What is the working principle of a ball mill?

The ball mill is the most critical piece of equipment in the preparation of raw materials for aerated concrete, as it is used to grind materials such as lime, gypsum, sand, and slag. Only after the materials have been thoroughly ground to the required fineness can they be adequately mixed and properly interact with one another, thereby enabling the final product to achieve the desired strength. Grinding is a vital step in the production of aerated concrete, and the grinding process is highly energy-intensive; consequently, the ball mill is typically the equipment with the largest motor capacity in an aerated concrete plant.

A ball mill consists of a horizontal cylindrical shell, hollow inlet and outlet shafts, and a grinding head. The shell is a long cylinder internally fitted with grinding media; it is fabricated from steel plates and lined with steel liners that are securely fastened to the shell. The grinding media are typically steel balls of various diameters, loaded into the shell in specific proportions, though steel segments may also be used.

The selection of grinding media is based on the particle size of the material to be ground. The material is fed into the mill through a hollow shaft at the feed end and enters the cylindrical shell. As the mill rotates, the grinding media, under the combined action of inertia, centrifugal force, and friction, adhere to the inner surface of the shell lining and are carried along by the rotating shell. When they reach a certain height, their own gravitational force causes them to fall; in a projectile-like motion, the falling media strike and crush the material inside the shell. The material is uniformly fed into the first chamber of the mill via a hollow shaft and a spiral feeder, where it encounters either stepped or corrugated liners and is charged with steel balls of various sizes. The centrifugal force generated by the rotation of the cylinder lifts the balls to a certain height before they fall, delivering impact and grinding action on the material. After coarse grinding in the first chamber, the material passes through a single-layer partition plate into the second chamber, which is lined with flat liners and also contains steel balls for further fine grinding. Finally, the ground powder is discharged through a discharge grate, completing the grinding process.

During the rotation of the mill cylinder, the grinding media also experience a cascading motion, which exerts a grinding action on the feed material. To make effective use of this grinding action, when processing relatively coarse feed—typically around 20 mesh—the mill cylinder is divided into two sections by a partition plate, forming a two-chamber mill. In the first chamber, the steel balls crush the feed; in the second chamber, the steel media grind the material further. The finely ground product that meets the required fineness is discharged through the hollow discharge shaft. For materials with finer feed particles, such as No. 2 sand and slag, or coarse fly ash, the mill cylinder may be designed without a partition plate, functioning as a single-chamber tube mill, and the grinding media can consist solely of steel segments.

This machine is a horizontal cylindrical rotating unit driven by external gear transmission, featuring two chambers and a grid-type ball mill. Material is fed uniformly into the first chamber of the mill via a hollow feed shaft equipped with a spiral feeder. The first chamber is fitted with either stepped or corrugated liners and contains steel balls of various sizes; as the cylinder rotates, centrifugal force lifts the balls to a certain height before they fall, delivering impact and grinding action on the material. After coarse grinding in the first chamber, the material passes through a single-layer partition plate into the second chamber, which is lined with flat liners and also contains steel balls for further grinding. The ground powder is discharged through a discharge grate, completing the grinding process.