gbw-animation Throughput


purpose, advantages, inventor


comminution, material throughput, pressure distribution, modelling


plant configuration, roller wear, references


literature survey, references


Other Links
links to suppliers, universities and other institutions


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Test Results Throughput - Introduction

Since High Compression Roller Mills were introduced industrially in the year 1985 this new grinding technology - traced back to Schönert [1] - was widely spread all over the world for the dry or moist fine grinding of medium hard or brittle materials.

The reasons for this are savings in energy consumption up to 50 % compared to a ball mill, the low specific wear, the small overall installed size and less noise emissions.

grinding results for different materials

Exper. Setup
lab-scale mill, techn. data mill, intrumentation, feed materials, testing program, roller surface data, test execution

literature, decoupling of throughput and comminution, energy absorption, characteristic of different rollers, phenomenons, throughput results, elasticity, friction angle, specific throughput

Pressure Distribution
pressure diagrams

Press Tests
tests with a molding press

mathematic model of the process

Signs and Symbols

Test assembly with a lab-scale High Compression Roller Mill, Institute for Mineral Processing, Technical University of Clausthal (1989)

The advantages of the High Compression Roller Mill are a result of the determinated pressure load on the mill feed within a material bed between two rollers of the same size which are rotating with the same speed in the opposite direction, see sketch.

Principal sketch of a lab-scale High Compression Roller Mill

One of the rollers is bedded as a sideways movable roller within in the closed machine frame. In operation the gap width of the mill is adjusting itself depending on the roller with and the material properties.

The grinding force which is necessary for comminution is generated by hydraulic cylinders and transferred to the material bed by the movable roller. Due to the resulting high pressure in the gap between the rollers the material bed is building agglomerates (flakes). But these flakes can be destroyed with little energy in a following process step.

Because of the “material-bed” situation and the self adjusting gap the mill product can still contain not comminuted, coarse particles with a particle size up to the gap width. Therefore the High Compression Roller Mill is used as a pre-grinding equipment (upstream to another mill) or in a closed circuit with a classifier.

Despite of the numerous industrial applications the procedural questions which arise from this technology were only researched in some special cases. The material transport and the pressure distribution in the roller gap are in this connection two aspects which are important for the widening of the basics of engineering sciences as well as for the design and operation of High Compression Roller Mills.

The material transport is linked with acceleration and rearrangement processes in the material bed which determine the throughput behaviour of the mill. Whereas the pressure distribution characterizes the load on the mill feed. According to previous experiences throughput and comminution effect have only little interactions. Therefore both effects can be considered as independent.

The throughput is determined by the friction forces in the catchment area which again are depending on the weight, the streaming and the centrifugal forces in that area. Further on the properties of the bulk material like internal and external friction are influencing the entrainment of particles as well as the form fit and the momentum exchange between roller and particles resp. between particles inside the material bed.

The intensity of the material load is characterized by the maximum pressure which reaches normally between 80 MPa and 500 MPa. This pressure is predetermined by the grinding force - applied from outside - and by the width and the shape of the pressure distribution.

A complete description of the process can only be given with a precise knowledge of transport and load processes in the gap between the rollers. The doctorate of Lubjuhn, U. [25] contributes some ideas for a better understanding of these two important fields of comminution in a material bed.

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