Crushing Size Reduction ratio

In these operations the value is achieved at the fine end, say below 100 micron (150 mesh). Normally the size reduction by crushing is of limited importance besides the top size of the product going to grinding. This means that the number of crushing stages can be reduced depending on the feed size accepted by primary grinding stage.

Calculation of reduction ratio

All crushers have a limited reduction ratio meaning that size reduction will take place in stages. The number of stages is guided by the size of the feed and the requested product.

Selection of crushers

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. spiral chute

Primary crusher type


cone crusher
For soft feed (below Mohs5) a horizontal Impactor (HSI) is normally the first option if capacity is not too high.

For harder feed there is a choice between a gyratory or a jaw crusher.

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 type

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 �C 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.

Final crushing stage �C more than just crushing

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).

VSI �C 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.

Wet crushing prior to grinding

WaterFlush is a patented wet crushing process for producing a flakier finer product from specially designed cone crushers. The method is intended for mining applications comprising secondary crushing, sand manufacturing and fine crushing of ore prior to leaching.

The typically crusher discharge is a slurry of 30 to 70% solids. The flakier feed brakes easily in the following grinding mill.

WaterFlush can be an alternative to conventional crushing prior to grinding in applications with critical-size-build-up problems in the grinding circuits of type AG/SAG and Pebble mills.