Crushing is the first mechanical stage in the comminution process for extracting and refining ore. It typically occurs in two or three stages, with primary crushing reducing ore sizes from 1.5m to 10-20cm using heavy-duty machines. Crushing can be done via open or closed circuits. Primary crushers, like jaw and gyratory crushers, are heavy-duty machines that reduce run of mine ore sizes for transport and feeding to secondary crushers. Jaw crushers consist of two plates that open and close to crush material, and come in blake, dodge, and universal styles that vary feed and discharge areas.

2. Presented by:
Muhammad Ali Mohsin (MME-16-04)

3. Crushing:
 Crushing is the first mechanical stage in
communation process for extraction and refining of
ore.
 It is generally a dry operation and is usually performed
in two or three stages.i.e primary,secondary and
tertiary stage.
 In Primary crushing the feed size of ore can be as
large as 1.5m and is reduced to 10-20cm in heavy duty
machines.

4. Crushing may be done in open circuit or closed circuit.
 In open-circuit crushing, undersize material from the
screen is combined with the crusher product and is then
routed to the next operation.
 In Closed-circuit crushing, the undersize from the screen
is the finished product.
 Following are the flow sheet diagrams of open & closed
circuit:

5. Open Circuit Closed Circuit

6. Primary crushers:
 Primary crushers are heavy-duty machines, used to
reduce the size of run of mine ore to make it suitable
for transport and for feeding the secondary crushers.
 They are always operated in open circuit, with or
without heavy-duty scalping screens (grizzlies).
 There are two main types of primary crusher in
metalliferous operations –jaw and gyratory crushers.

7. Jaw crusher
 Jaw crusher consists of two plates which open and shut
like animal jaws and the material fed into the jaws is
alternately nipped and released to fall further into the
crushing chamber.
 The jaws are set at an acute angle to each other, and
one jaw is pivoted so that it swings relative to the other
fixed jaw.

9. Types of jaw crusher
 Jaw crushers are classified by the method of pivoting the
swing jaw.
 In the blake jaw crusher the swing jaw is fixed at the top.
 It has fixed receiving area but variable discharge opening.
 In dodge jaw crusher the swing jaw is pivoted at the
bottom.
 It has variable feed area but fixed discharge opening.
 The Dodge crusher is restricted to laboratory use, where
close sizing is required, and is never used for heavy-duty
crushing as it chokes very easily.

10. In Universal jaw crusher the swing jaw is pivoted in
the middle.
It has variable feed and delivery area.

11. Blake crusher
 Blake crusher has two types i.e double toggle and
single toggle blake crusher.
 In Double toggle blake crusher the oscillating
movement of the swinging jaw is effected by vertical
movement of the pitman.
 In Single toggle blake crusher the swing jaw is
suspended on eccentric shaft.

12. Double toggle blake crusher Single toggle blake crusher

13. Jyratory crusher
 The gyratory consists of a long spindle carrying a hard
steel conical crushing element, the head, seated in an
eccentric sleeve.
 The spindle normally rotates b/w 85 to 150 rev/min.
 It sweepes out a conical path due to gyratory action of
the eccentric.
 Maximum movement of the head occurs near the
discharge, this tends to relieve choking.