Selection of Crushers
In mineralprocessing plant, Knowing the number of crushing stages we can now start to
select the correct crusher for each reduction stage. Depending on operating
conditions, feed size, capacity, hardness etc, there are always some options.
For primary crushers, see below.
Stationary crushers
Mobile Crushers
Primary Crusher
For soft feed (below Mohs5) a horizontal Impactor (HSI) is normally the
first option if capacity is not too high.
Rule 1: Always use a jaw
crusher if you can, being the most cost effective alternative.
Rule 2: For low capacity
use jaw crusher and hydraulic hammer for oversize
Rule 3: For high
capacities use jaw crusher with big intake opening
Rule 4: For very high
capacities use gyratory crusher
Secondary Crusher
In a rock crushing circuit, the second stage normally starts to be of
importance for control of size and shape.
Because of this
the jaw crusher, in most cases, is disqualified as secondary crusher. Instead
the cone crusher is used more frequently. Also in comminution (crushing and
grinding) circuits for ore and minerals the cone crusher is frequently used as
the secondary stage.
Using a secondary HSI means as always a restriction in feed hardness.
Cone Crusher – A Powerful Concept
Compared to
other crushers the cone crusher has some advantages making them very suitable
for size reduction and shaping downstream a crushing circuit. Reason is the
crushing chamber and the possibilities to change feed and discharge openings
during operation.
•
Chamber intake to match feed size
•
Each machine size has different chamber options (other crusher types have not)
•
Each chamber has a certain feed size vs capacity relation
•
Increased Ecc. (at the same CSS) will give higher capacity, but also coarser
discharge
•
Decreased CSS will improve cubicity but will also reduce capacity and increase risk
for packing
Approx. size of discharge: From Cone 70-80%<CSS, From Gyratory
55-60%<CSS.
Final Crushing Stage
For many rock
and gravel crushing circuits the final crushing stage is of special interest.
The final sizing
and shaping will take place in this stage influencing the value of the final
product.
For hard rock circuits there are only two options, cone crushers or
Vertical Shaft Impactors (VSI).
Most common
VSI – A Rock on Rock autogeneous crushing Impactor
Horizontal
impactors normally use rock to metal impaction. This means a restriction in
crushing circuits with hard feed material, when wear can be dramatically high.
The VSI Impactor
of Barmac type is using a rock-to-rock impaction
technology where most of the design is protected by rock, see below. This means
that we can use the advantages of the impaction techniques also in hard rock operations.
The crushing
action takes place in the “rock cloud” in the crushing chamber, not against the
rock protection.
VSI – function
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