gbw-animation Pressure Distribution


purpose, advantages, inventor


comminution, material throughput, pressure distribution, modelling


plant configuration, roller wear, references


literature survey, references


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Pressure distribution in the gap between the rollers

The feed material is introduced into the compression zone and then compacted by the pressure load in this zone. The compression of the material bed can only take place by comminution of particles. If the particle bed is seen as a continuum then the compression condition would be associated to inhomogen three-dimensional state of stress which however can be neither measured nor calculated. What can be measured is the local impact of the grinding force onto the rollers [9, 15, 16]. and with this the average normal pressure and the average shear stress in the measurement area can be calculated. When the material transport is without slip then shear stress at the boundary layer has no impact on compaction and therefore also no impact on the comminution effect. Even with a slight slip, especially in the upper part of the compaction zone there should exist only a small effect. Therfore it can be hypothized that mainly the normal pressure determines the comminution.

grinding results for different materials

characteristic of different rollers

Pressure Distribution
literature pressure distribution, pressure diagrams, peripheral pressure distribution, axial pressuredistrib., effective pressure and specific grinding force, compression angle and specific throughput

Press Tests
tests with a molding press

mathematic model of the process

Signs and Symbols

Schematic presentation of variables used to describe the pressure distribution measurements / Dissertation U. Lubjuhn, TU Clausthal, 1992

The normal pressure is a function of the angle a and - starting at angle a0 - it increases with decreasing angle, hits a maximum in the shaft layer (or just before) and then declines sharply. The wear picture of rollers and the decreasing comminution effect towards the edges of the rollers are also indicators for an axial pressure decrease.

In the following test results are reported where pressure sensors at l = 0, 19 and 38 mm were used, correspondingly l = 0, 0,19 and 0,38, see picture above. Out of this the peripheral pressure distribution P(a, l = const.) and the axial pressure distribution p(a = const, l) are resulting. Variable parameters were the type of feed material, the graining and the circumferential speed. The appendix of the dissertation of U. Lubjuhn [25] gives an overview over the test conditions and contains all detailed test results. The number of pressure distribution measurements is shown in table 10 and 11. Additional informations regarding the axial pressure distribution can be taken from the so called stripe tests where throuput as well as particle size distribution were measured in dependence of the axial coordinate, see also experiment setup.


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