Agitator ball mill

Principle of an agitator ball mill

The agitator ball mill ( also: agitator mill or agitator mill ) is a special form of the ball mill . Agitator ball mills consist of a vertically or horizontally arranged, mostly cylindrical container, which is 70-90 % filled with grinding media , which are mostly made of steel, glass or wear-resistant ceramic materials. An agitator with suitable agitating elements (rods or discs) or a smooth-walled agitator ensures the intensive movement of the grinding media. The grinding stock suspension is pumped continuously through the grinding chamber. The suspended solids are comminuted or dispersed between the grinding media by impact and shear forces. At the outlet of the mill, the grinding stock and grinding media are separated using a suitable separation system. Starting from a few micrometers, suspended particles can be comminuted down to the range with mean fineness ( grain sizes ) of <50 nm.

Horizontal agitator ball mill

Horizontal cylindrical grinding container that is filled with grinding beads and grist. For wet grinding of free- flowing suspensions . An agitator ball mill is used in the manufacture of paint to finely grind color pigments ( paint mill ). The paint runs through a large cylinder that is divided into several levels with spheres of different sizes. These balls grind the paint particles.

Another piece of equipment for crushing paint particles is the three-roller mill . This type of mill can be used universally and is used for grinding minerals and colors. This agitator ball mill is also often used in chemistry, pharmacy and laboratories.

Vertical agitator ball mill

Standing cylindrical grinding container, which is filled with grinding beads and grist. The agitator is located in the container, which sets the bed in rotation. Depending on the material to be ground, the mill can be designed to be protected against wear . A distinction is made between dry and wet operating modes . This type of mill is used in areas in which certain finenesses must be produced economically in large quantities.

Dry grinding

This process is used to grind mineral fillers. Common applications are the crushing of limestone , quartz or titanium oxide . In the food industry, this type of mill is used to grind grain flour . Here, the starch is broken down and the water absorption of the cereal flours is increased.

Wet grinding

This process is used to grind highly concentrated limestone slurries such as those used in the paper industry for coating paper. But this process is also used to produce mineral fillers or glazes.

Energy input

The comminution of particle agglomerates can be described by the stress intensity BI and the stress number BZ . The product of stress intensity and stress number is proportional to the "specific energy" which is introduced into the ground material during the entire dispersion process in order to break up the agglomerates. The two key figures enable the product fineness to be estimated in an agitator ball mill.

${\displaystyle BI=d_{MK}^{3}\cdot \rho _{MK}\cdot v^{2}}$

With the diameter of the grinding media, density of the grinding media and the speed of the agitator of the mill. ${\displaystyle d_{MK}^{3}}$ ${\displaystyle \rho _{MK}}$ ${\displaystyle v}$

${\displaystyle BZ\sim {\frac {n\cdot t}{d_{MK}}}}$

Here is the rotation of the agitator and the time of the dispersing process. ${\displaystyle n}$ ${\displaystyle t}$

Individual evidence

1. ↑ A. Kwade, L.Blecher, J. Schwedes, Stress intensity and movement of the grinding media in agitator mills, Chemie Ingenieur Technik (69) 1997.
2. ^ Sabine Walther, doctoral thesis 2011, University of Erlangen-Nuremberg.