4.1 Influence of duration of the jigging process

The stratification is improved with increasing duration of the jigging process. The measured dependences seem to follow an exponential function (figure 4). Therefore only in the first seconds a clear effect can be indicated. Besides during the experiments becomes clear that this parameter is strongly connected with the state of the loosening of the material bed. If the process of loosening is not sufficient intensive, even a very long treatment cannot improve the results. Then the duration of the process plays nearly no role.

4.2 Influence of stroke

The stroke which is necessary for a sufficient fluidisation depends on the height of the material bed and the particle size. In the literature [5] an empirical equation is given for the dependence between the stroke and the maximum particle size:

h = 8.1· d00.6 (2)

h: stroke [mm]
d0: maximum particle size [mm]

The example of the material combination coal / concrete in figure 3 illustrates that a higher stroke results in a better stratification. If a stroke of 14 mm was applied no stratification at all could be achieved. Already an increase to 19 mm results in a good separation. The duration of the jigging process was 20 seconds in both cases.

Figure 3: Comparison of the achieved stratification

4.3 Influence of waveform of the oscillation

In table 4 the runs of experiments with the most interesting results with regard to the waveform are summarized for the material combination coal / concrete. In these experiments the parameters frequency (f = 1,0 s-1), height of the material bed (h = 45 mm) and particle size (1 - 4 mm) were constant while the stroke was varied in three levels.

The best separation was found if an oscillation type K7 combined with a high stroke of 22 mm was applied (Run 1). If the stroke is reduced to 14 mm with this type of oscillation only moderate effects are obtained (Run. 8). A very good separation was also found if the K5P type of oscillation was realized. In this case the influence of the stroke was smaller, that means the jigging process becomes more stable (Run 4, Run 6 and Run 7). The experiments with K3P and K8 type of oscillation (Run 3 and Run 5) show more unfavourable results. If the jigging process was operated with well established sinuous shaped curve K3 (Run 2) no separation could be obtained.

Table 4: Results of the jigging tests in dependence on the type of oscillation

The measured contents of foreign material in the bottom layer do not agree with visual evaluation in all runs. Nevertheless the runs with the K5P type of oscillation show lower contents of foreign material than the other runs.