Ore material size classification
For size control
of particles finer than 1 mm, we are moving out of the practical range of
conventional screens. Classification is the process of separating particles by
size into two or more products according to their behaviour in air or water
(liquids). Classification methods
• Wet classification with Hydrocyclones using separation by centrifugal force covering the size
range of 100 –10
micron (typical)
• Wet classification with Spiral classifiers using separation by gravity covering the size range of
100- 1000 micron (typical)
• Dry classification using separation by centrifugal force
covering the range of 150 –5 micron (typical).
Wet classification – fundamentals
If a particle
has no interference from other particles it moves faster than a particle
surrounded by other particles due to increased density and viscosity of the
slurry. This is called free and hindered movement and is valid both for gravity and centrifugal
classification.
Hydrocyclone
Centrifugal
forces classify solids by size (mass). High mass particles closer to outer wall
reporting to underflow .Low mass particles closer to the centre reporting to
overflow.
Hydrocyclone design
1. Vortex finder
2. Inlet head
3. Spigots
(apex)
4. Overflow
elbow
5. Feed inlet
6. Barrel
7. Cones
8. Cone
extension
Hydrocyclone applications
Although the
hydrocyclone by nature is a size controlling machine the number of applications
in mineral are many
•
Classification in grinding(ball mill)
circuits
•
Dewatering and thickening
•
Desliming and washing
•
Enrichment of heavy minerals
Spiral Classifier
By combining a
gravity settler of rectangular section with a sloped transport spiral for the
sediment - we have got a spiral classifier.
Spiral Classifier – Design
The design of a
spiral classifier is simple and robust with few moving parts. A reliable
machine for tough classification duties in the 100-1000 micron range.
Spiral Classifier design features:
•
Replaceable wear shoes,
•
Submerged bearing for spiral
•
Tank options and adjustable weir for full flexibility in pool area and
classification cut point (cp)
Spiral Classifier-applications
As for the
hydrocyclone this size control machine has many practical applications in mineral processing
•
Closed circuit grinding (primary classification with cyclone as secondary)
•
Dewatering
•
Sand recovery
•
De-sliming
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