Gravity separator
Schwerkraftsichtung means that particle populations under gravity by size or density classified are. Sifting is a classification process that is used in many areas of industry. This method makes use of the different sinking speeds of particles of different sizes. In terms of fluid mechanics, three forces act on a particle during the sighting: gravity, drag force and buoyancy force. The particles with different sinking speeds are transported to different points in the classifier and are finally discharged upwards or downwards.
The riser separator
A riser sifter is the simplest type of sifter. The particles to be sifted are fed to a pipe through which there is flow from below. Particles that have a lower sink rate than the classifying air speed are discharged upwards as fine material; Particles with a higher sinking speed pass the classifier downwards as coarse material.
The zigzag sifter
A zig / zag sifter is a form of gravity sifter and is a combination of cross and countercurrent sifter. As can be seen in the illustration (right), the feed material in the classifier is divided into coarse and fine fractions. The sighting takes place in each spike by comparing the different sinking speeds of the particles. The selectivity of such a zig / zag sifter therefore depends on the number of points, but also on the geometry of the viewing channel.
Studies have shown that the following ratio applies to the area of the viewing channel:
The best separation results should be achieved with a length-to-width ratio of 3 1/3.
The angle at which the prongs are bent is optimally 120 °. If the intervention is chosen to be equal to zero, a coherent main flow results in the classifier.
Riser pipe
ZZ sifter
Viewing channel
angle
