Ore material size control

In beneficiation plant, With size control we understand the process of separating solids into two or more products on basis of their size. This can be done dry or wet. neither crushers nor grinding mills are too precise in their size reduction job and a lot of size fractions are misplaced. By using optimum size control the result can be improved both regarding capacity, size and particle shape.
Size Control by Duties
To prevent undersize in the feed from blocking the next size reduction stage(scalping)
To prevent oversize from moving into the next size reduction or operation stage(circuit sizing)
To prepare a sized product (product sizing)
Size Control by Methods
In mineral processing practices we have two methods dominating size control processes:-Screening using a geometrical pattern for size control.
-Classification using particle motion for size control.


Screens
Performance of screens will fall back on three main parameters:
Motion – Inclination – Screening Media
Screen Motions
Screening by Stratification
By building up a material bed on a screen deck the material will stratify when the motion of the screen will reduce the internal friction in the material. This means that the finer particles can pass between the larger ones giving a sharp separation.



Screening by free fall
If we use the double inclination used for stratification (from 10-15 up to 20-30 degrees) we are in free fall, meaning that no particle layer can build up on the screen deck. The particles will now be sized directly via the screening media, giving a higher capacity, (or a more compact installation), but also less sharpness in separation. Optimal use when a large amount of fines shall be removed fastly.
Screen Types
There are many types of screens, but they can be reduced to the four types shown below. Of these types approx.80 % used worldwide are of type single inclination, stratification screens. The other are of type double, triple or multiple inclination, where screening by stratification and free fall are combined for different applications.
Single inclination
• Stratification screen

• Circular (15 deg.)
• Linear 0-5 (deg.)
• Still the leader in selective screening
Double inclination
• Free fall
• Compact - high capacity paid for by lower selectivity
• Typical in circuit screening
Triple inclination
• Combine capacity and selectivity
• Typical control screen for advanced product fractions
Multiple inclination (banana screen)
• Effective ”Thin-layer” screen
• Popular in coal and metallic mining
Selection of Screening Media
Selection of the correct size and type of screen is important. Equally important is the selection of the screening media. This refers not only to a correct aperture related to the ”cut size ”, but also to the wear in operation of these screens. Below a short selection guide to screening media can be found.
Rubber or Polyurethane?

What type of panel

What thickness?
General rule for min. Thickness
What hole size? (Inclined deck)
General guideline for wire mesh:
Required product size plus 5 – 10%
General guideline for PU panels:
Required product size plus 15 – 20%

General guideline for rubber panels:
Required product size plus 25 – 30%

What type of hole?
Particle Size – Mesh or Micron?
Sinonine technology team

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