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Blogging articlesWet Screening: Linear or Rotaspiral Screens?
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The Rotaspiral screen is a rotary drum screen with a build in spiral to remove oversize fast.
Rotaspirals use steel mesh with a high open area. The mesh is neutral and allows a higher throughput through the mesh than Polyester Linear Screen cloths.
Steel mesh cut points are more accurate. PSS devised a very simple mesh installation method for fast replacement on very abrasive slurries mesh life in excess of 6 months is normal.
The drum is suspended on two shafts with wheels on top, one of which is driven by a gearbox and motor.
Rotaspirals only have 4 bearings.
Feed is introduced inside the drum using a HDPE feed pipe with distribution holes.
The mesh is cleaned on the top downwards using a spray bar, and the wash water collected and guided to the last spiral.
The Rotaspiral can be used for sizing applications and screen down to 75 – 100 microns.
For sizing applications the meshes are slotted in a ratio of 1 : 4 to prevent “pegging” or “blinding”
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Linear Screens are efficient because the woodchips fall flat and do not move hence cannot pass through the mesh.
Rotaspirals turn and a woodchip is deposited/tumbles a few times, hence in theory not as efficient as Linear Screens.
However a woodchip on a Linear Screen can splash to the side, they can pass over the side of the cloth to the underflow. This cannot happen on a Rotaspiral Screen.
Particles larger than the Rotaspiral aperture cannot by pass to the underflow.
Rotaspirals are more efficient than Linear Screens on carbon scavenging duties.
Linear Screens are more efficient than Rotaspiral Screens on a Woodchip/Splinter Screen duty.
The Rotaspiral is cheaper and easier to maintain and requires much less attention.
Gold Mines prefer Linear Screen for woodchip removal – Gold Mines should use Rotaspiral Screens for Carbon Scavenging.
Platinum Mines prefer Rotaspiral Screens because they can cope with high flows and very abrasive (Chromium) slurries and the efficiency are acceptable and better than Linear screens on these duties
1. Berzillius Stolberg – GMBH Rotaspirals: 2 of RS 1.2 – 1.8
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2. Montana Winery – New Zealand Rotaspirals: 2 of RS 0.8 – 1.0
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3. Anglo Platinum - SA Rotaspirals: 1 of RS 1.2 – 1.8
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4. Lonmin Platinum - SA Rotaspirals: 1 of RS 1.2 – 1.8
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5. MMS - Russia Rotaspirals: 4 of RS 1.6 – 3.0
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6. MAED – Talas GM - Ukraine Rotaspirals: 2 of RS 1.6 – 3.0
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7. Siyanda Chrome - SA Rotaspirals: 1 of RS 1.6 – 3.0
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8. Aquarius Platinum – SA Rotaspirals: 1 of RS 0.8 – 3.0
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9. Bindura Nickel – Zimbabwe Rotaspirals: 1 of RS 1.6 – 3.0
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10. Chrome-Tech Holdings – Lonmin SA Rotaspirals: 1 of RS 1.2 – 1.8
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11. Outotec (Filters) Oy – Finland Outotec has standardized on PSS Rotaspiral
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12. Apogee Silvell Mine – Bolivia Rotaspirals: 1 x RS 0.8 – 1.0
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13. AngloGold Ashanti – Savuka Mine Rotaspirals: 1 x RS 0.8 – 1.0 |
Experience & References: Berzillius GMBH
The Rotaspiral Fine Screen is a new development in fine screening technology, which may be reminiscent of trommel screens of previous times. There are, however, significant differences in design and application. During November 2001, Particle Separation Systems (PSS) delivered two Rotaspirals to Berzillius Stolberg GmbH of Germany to separate fines from granulated slag in the lead smelter. Feed rate to the parallel Rotaspirals (1,2m ø model RS12-18 with 1.1 kW drive) is between 15 and 20 t/h each. The QSL furnace at Stolberg produces granulated slag with a particle size of less than 2 mm with about 10% minus 200 micron. The fines have an economic metal content and this portion can be profitably recycled to the smelter. It was thought that vibrating screens would not perform well in this application. Alternatively, hydro-separators were not able to provide a clear cut, recovering too many coarse particles with the fines because of gravity and shape effects. This would have resulted in recycle of nearly 30% of the slag instead of the target of less than 10%.
PSS have recently started marketing Rotaspirals, which were developed in South Africa initially for platinum mineral processing. The design of the Rotaspiral allows cut points down to 100 micron. The unique woven stainless steel mesh specification is designed to maintain clean and precise apertures. Recovery of fines is +95% and wear rates are negligible because of the low velocities between mesh and particles. An axial spiral inside the screen provides fast transport of the oversize, and high velocity sprays at multiple points guarantee a sharp separation. Additional benefits of this technology include the low energy demand and negligible noise levels.
R BUISMAN
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