3.1 Test equipment and parameters

For the experiments a batch jig was developed and assembled. It consisted of the vibrating table with the fixed water tank. The third element was the jig screen, which was mounted at a stationary tripod. A 3.15 mm mesh screen was used as jig screen. The best height of the material bed on the screen was experimentally found out. It amounts to 45 mm.

Figure 1: Batch jig used in the experiments

The test equipment allows to vary the following parameters:

-Duration of the process between 0 and 120 seconds

-Height of the stroke between 14 and 22 mm

-Frequency between

-Waveform of the oscillation.

The focus of the experiments was directed on the influence of the waveform of the pulsation on the achieved stratification. From the literature follows that the influence of the waveform on the movement of the particles and the achieved stratification is not well understood till now [5]. On the one hand experiments show that an improvement of the separation can be obtained if asymmetrical oscillations are used. On the other hand a considerable number of authors point out that a harmonic oscillation is the better option. Sometimes it is even said that the amplitude and shape of the pulsation have only a very small influence if the stroke, the number of strokes and the water flow are adjusted properly [5].

2 three different diagrams “velocity versus time“ are compared which were adapt in these experiments. The well established sinuous shaped curve is shown in figure 2 a. The diagram acc. to figure 2 b shows a retarded downward flow. That is a characteristic feature of air pulsed jigs. Because of that the fluidized stage shall maintained for a rather long period. In the diagram proposed by Mayer [6] acc. to figure 2 c the material bed shall be hiked as a whole by a strong upward flow. The consolidation shall take place in the unmoved fluid.

Harmonic pulsation Asymmetrical pulsation

Figure 2: Examples of pulsation diagrams [5]

Altogether 13 different waveforms were tested in 52 series with 140 runs. The diagrams discussed in this paper are the asymmetrical pulsation, the asymmetrical pulsation with an additional impulse and the harmonic pulsation with an additional impulse (table 1). As a reference a simple harmonic oscillation was realized.

Table 1: Features of tested waveforms