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Jet airstream sifter (Cross Flow Sifter)
Sifting in 3 fractions with separating efficiency of 80 - 90 %, especially suitable for abrasive products.
Function
The feed stock to be separated into three fractions is metered into the sifter in fluidised condition via a pneumatic tube. Through a central inlet tube the product (diagram, item 1) falls onto a rotating dish (diagram, item 2). The special shape of the dish and accelerating forces cause the product flow (diagram, item 3) to move towards the outer edge of the dish where it is seized by special blades, further accelerated and dispersed. In the peripheral zone of the dish the product evens out over the dish circumference and is flung into the sifting zone at a defined, adjustable speed transversely to a generated sifting air stream (diagram, item 4). The particles move on trajectories that fan out depending on the balance between centrifugal forces, air resistance and gravity. The sifting air flowing in from the top at a uniform speed via the ring circumference of the sifting zone deflects the trajectories of fine particles stronger downwards than those of medium or coarse grained particles. Two replaceable separator blades adjustable in height (diagram, item 5) divide the trajectory fan into three fractions, i.e. fine, medium and coarse (diagram, items 6, 7 and 8).
Design features
The sifter consists of a steel housing made of two separate parts. The connecting flanges for the sifting air as well as a central, axially arranged product feed tube are located on the sifter upper part. The lower part contains the rotating dish (made of wear-resistant chilled cast material / diagram, item 2) and the height adjustable, wear-resistant separator blades (diagram, item 5). The sifter is driven by an external electric motor arranged at a right angle to the sifter axis. The sifter bottom features connecting flanges for a Y-piece (fine and medium grain fractions) and for a removal system (such as a rotary valve) to discharge the coarse grain fraction.
Advantages
The grain size fractions can be infinitely adjusted over a wide range via the dish speed and sifting air velocity. Height adjustable separator blades of different geometries allow the separation range to be adapted to the specific task. Wit the Jet Airstream Sifter, materials can be separated into three fractions (fine, medium and coarse) in a single unit. The split housing provides for fast and easy replacement of wearing parts thus reducing the necessary maintenance effort. The external drive motor has also proved to be advantageous in practical operation. The compact multi-chamber sifter housing can be suspended (in a steel structure) or set up. Optionally, the sifter housing can be provided with an anti-wear lining so that abrasive products can also be handled without any problem. The stable and constant sifting air flow and the acceleration / dispersion of the product that is independent of the air flow makes the Jet Airstream Sifter insensitive to throughput fluctuations. Adjustment of the sifting product and sifting air result in size fractions free from stray particles.
Typical Applications
The Grenzebach BSH Jet Airstream Sifter is suitable both for classifying bulk materials and for separating fines without stray coarse particles in all sectors of solids process engineering. Below are some typical examples:
- Non-metallic minerals industry: limestone, aluminium oxide, ceramics, asbestos, bauxite, dolomite, feldspar, kaolin, quartz, talc.
- Chemical industry: aluminium hydroxide, ammonium carbonate, sodium carbonate, pigments, titanium slag, abrasives.
- Primary industry: activated carbon, sulphur, salts
- Food processing industry: sugar, cocoa, powdered milk, starch.
Limits of Application
The Jet Airstream Sifter can be used for particle sizes up to 3 mm and is suitable for classifying or dedusting powders at 20 - 150 µm. Depending on the application and sifter type, throughput rates of 3,000 - 50,000 kg/h are possible, at product temperatures of up to some 130 °C.
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