Sifting

How a Plansifter Increases the Quality of Plastic Granules

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The Right Sifting Conditions

By taking these findings into account, it became clear that the Fuchs Siftomat plansifter offers good conditions for sifting plastic granules, as the sifting movement has no vertical component. Additionally, the rectangular shape of the sifter has the advantage that, compared to circular units, the sifting width does not increase during the process.

Additionally, the developer subdivides the sifting surface, the perforated plate, into several segments with perforated and imperforated plates. Thus, it is possible to adjust the surface of the perforated plates to the required capacity by inserting only as many perforated segments as necessary. The rest of the segments are imperforated and sieve surfaces that are too large can be avoided.

The frequency of the plane circular sifter movement is kept as low as possible, without interfering with the conveying of the material to be sifted. The low frequency accelerates the process and prevents the long granules from getting into a vertical position and falling through the holes into the “good” products. By using a frequency converter the process can be adapted to the specific requirements and optimised.

For high throughputs requiring a fast transport of the material to be sieved, the slope of the sieve can be increased. Additionally, the sieve case and the sieves are modularly built. For cleaning the sieve case and changing the sieves, for instance in order to process other plastic granules, the sieves and the spacer frames can be removed and replaced very easily.

Summary

In order to avoid problems, the sifting surface should be as highly adapted as possible to the sifting capacity. Excessive frequencies of the sifting movement have a negative effect on the sifting quality. The thickness of the material layer on the sieve should be kept constant, in order to avoid ”jumping“ of the granules. The sifting movement should not have vertical components, which exacerbates the “jumping effect”.

* Daniel Baumann is CEO of Fuchs Machines Ltd, Granges-Paccot/Switzerland.

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