page_title: Trommel screen
section_title: Particle rotational velocity behaviour
hierarchical_section_title: Trommel screen / Design and heuristics / Particle rotational velocity behaviour
caption_attribution_description: English: Relationship between the velocities and the sieve behavior of particles
context_page_description: A trommel screen, also known as a rotary screen, is a mechanical screening machine used to separate materials, mainly in the mineral and solid-waste processing industries. It consists of a perforated cylindrical drum that is normally elevated at an angle at the feed end. Physical size separation is achieved as the feed material spirals down the rotating drum, where the undersized material smaller than the screen apertures passes through the screen, while the oversized material exits at the other end of the drum.
context_section_description: Considering the mesh sizes of the rotating drum are larger than particle sizes as shown in Figure 7, the particle motion velocity  can be broken down into two velocity components consisting of the vertical component  and horizontal component  . Denoting  to be the angle between the particle motion and vertical component, the vertical and horizontal velocities can now be written as:
  When , the particles escape through the mesh in the rotating drum. However if , the particles are retained within the rotating drum. Larger granules will be retained inside the trommel screen until the desired aperture is met and follows the same particle behaviour.
caption: Figure 7: Relationship between the velocities and the sieve behaviour of particles
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