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EXCON Special: Rotor Impact Mills for Sand Processing

SONTHOFEN/GERMANY, November 11, 2013 - At bauma 2013, BHS-Sonthofen has showcased its unique rotor impact mills, which are not manufactured by any other company in the world. They produce crushed sand with special characteristics that cannot be achieved in the same quality with any other machine: the grains are cubical, but their edges are rounded. Dry mortar produced with this type of sand is easier to use and makes concrete easier to pump.

Rotor impact mill, type RPM 1513 for throughput up to 75 t/h. | photo: BHS Sonthofen

Last year BHS-Sonthofen delivered numerous RPM-type rotor impact mills for new dry mortar factories in fast-growing Asia and the Middle East, further consolidating its position as market leader in machinery for producing dry mortar sands. BHS rotor impact mills employ a globally unique principle.
These rotor impact mills are increasingly being used for other applications than manufacturing sand for the dry mortar industry; for instance, they are being employed more and more frequently to make sand for ready-mixed concrete, as the concrete containing such sand has excellent pumping properties. Around the world, the number of rotor impact mills is also growing in the asphalt industry, in the manufacture of surfaces for sports facilities, as well as for grinding limestone, dolomite, gypsum, anhydrite and quick lime.
When it comes to crushing rocks, the rotor impact mill works best on slightly to moderately abrasive material. It can process feed sizes up to 56 mm. Larger feed sizes can be used for materials that are easy to crush, such as quick lime. Throughput can reach 75 t/h.

The hammers are wearing parts and can easily be replaced in just a few simple steps. h | photo: BHS Sonthofen

The horseshoe-shaped hammers in BHS rotor impact mills seem to be unrivaled. The input material is fed into the machine from above through the centrally-located feed tube. When it hits the rotor, it is accelerated outward at high speed by the centrifugal forces, where it is then caught by the horseshoe-shaped hammers, which impel it against the anvil ring of the annular housing.
The rock breaks upon impact and assumes its cubical form. Repelled by the anvil ring, which is available in toothed and smooth versions, the material hits the hammers again, is further crushed, and thrown back against the anvil ring. This repeats until the material is small enough to pass through the gap between the rotor and the anvil ring, and falls out through two discharge chutes.
The multi-phase crushing process serves to grind the edges of the particles, closely approximating the way sand is produced in nature. In practical applications, the rounded grain form makes it easier to process the material. For example, plaster made from this sand is easier to spread than if made from sand with sharp edges. The same effect makes the rotor impact mill an attractive choice for producing sand for ready-mixed concrete, which is then easier to pump.

The crushing chamber of the rotor impact mill features horseshoe-shaped hammers. | photo: BHS Sonthofen

The sand produced has a high proportion of grains sized between 0 and 2 mm. Compared to conventional impact mills, the rotor impact mill results in a considerably higher proportion of useful grains.
The gap between the horseshoe hammers and the anvil ring is adjustable and the peripheral speed of the rotor is variable, making the BHS rotor impact mill flexible for use in a wide range of applications. It also effectively processes fine off-spec gravel fractions, making it an efficient and future-proof solution.
The adjustable hammers can be installed and set manually without any special tools or lifting devices. They ensure the output grain-size curve of the BHS rotor impact mill remains constant over the entire service life of the wearing parts, maintaining a consistent quality of the final product.
The entire inlet cover can be pivoted for optimum accessibility, which greatly simplifies maintenance of the machine.
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