1. Primary crusher –Jaw crusher and Gyratory crusher 2. Secondary crusher –Cone crusher and Roll crusher 3. Tertiary crusher – Rod mill and Ball mill
S.R.P* 5TH TERM- CONSTRUCTION EQUIPMENT MANAGEMENT Page 32 If it is a single process, excessive fines will be generated and normally there is a limited market
for fines.
As stone passes through the crusher, the reduction in size can be expressed as the reduction ratio, i.e. the ratio of the crusher feed size to the product size.
Crushing equipment selection The kind of stone to be crushed The required capacity of the plant The maximum size of the feed stones The method of feeding the crusher The required size ranges of the product By compaction method
Jaw crusher
A jaw or toggle crusher consists of a set of vertical jaws, one jaw being fixed and the other being moved back and forth.
The jaws are farther apart at the top than at the bottom, forming a tapered chute so that the material is crushed progressively smaller and smaller as it travels downward until it is small enough to escape from the bottom opening.
The movement of the jaw can be quite small, since complete crushing is not performed in one stroke.
The inertia required to crush the material is provided by a weighted flywheel that moves a shaft creating an eccentric motion that causes the closing of the gap.
Machines operate by allowing stone to flow into the space between the two jaws, one is stationary while the other is movable.
The movable jaw is capable of exerting a pressure sufficiently high to crush the hardest rock. Jaw crushers are designed with the toggle as the weakest part.
This toggle will break if the machine encounters an uncrushable object.
Single and double toggle jaw crushers are constructed of heavy duty fabricated plate frames with reinforcing ribs throughout.
The crusher‘s components are of high strength design to accept high power draw.
Manganese steel is used for both fixed and movable jaw faces. Heavy flywheels allow crushing peaks on tough materials
Double Toggle jaw crushers may feature hydraulic toggle adjusting mechanisms.
Single toggle
When the eccentric shaft of the single toggle crusher
is rotated, it gives the movable jaw both a vertical and horizontal motion
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Double Toggle
The Blake type is a double –toggle jaw crusher The movable jaw is suspended from the shaft
Rotating an eccentric shaft actuates the two toggles and these produce the crushing action.
Size of Jaw and Roll crusher product
The figure below represents the percent of material passing or retained on screens having the size openings indicated.
To read the chart selects the vertical line corresponding to the crusher setting.
Then move down this line to the number that indicates the size of the screen opening.
From the size of the screen opening proceed horizontally to the left to determine the percent of material passing through the screen or to the right to determine the percent of material retained on the screen.
Q .1 A jaw crusher with a closed setting of 3 inches is fed at the rate of 50 tons/hr. Determine the amount of stone produced in tons per hour within the following size ranges; in excess of 2 inch, between 2 and 1 inch, between 1 and ¼ inch, and less than ¼ inch.
The amount retained on a 2 inch screen is 42% of 50, which is 21 tons per hr. The amount in each of the size ranges is determined as
S.R.P* 5TH TERM- CONSTRUCTION EQUIPMENT MANAGEMENT Page 34 Size range(in) Percent passing screens Percent in size range Total output of crusher (tph)
Amount produced in size range (tph) Over 2 100-58 42 50 21.0 2 - 1 58-33 25 50 12.5 1 – ¼ 33-11 22 50 11.0 ¼ - 0 11- 0 11 50 5.5 Total 100% 50.0 Gyratory crusher
A gyratory crusher is similar in basic concept to a jaw crusher, consisting of a concave surface and a conical head; both surfaces are typically lined with manganese steel surfaces.
The inner cone has a slight circular movement, but does not rotate; the movement is generated by an eccentric
arrangement.
As with the jaw crusher, material travels downward between the two surfaces being progressively crushed until it is small enough to fall out through the gap between the two surfaces.
A Gyratory Crusher is one of the main types of primary crushers in a mine or ore processing plant. Gyratory crushers are designated in size by the size of the receiving opening.
Gyratory crushers can be used for primary or secondary crushing. The crushing action is caused by the closing of the gap between the mantle line (movable) mounted on the central vertical spindle and the concave liners (fixed) mounted on the main
frame of the crusher.
The gap is opened and closed by an eccentric on the bottom of the spindle that causes the central vertical spindle to gyrate. The vertical spindle is free to rotate around its own axis.
Impact crushers
Impact crushers involve the use of impact rather than
pressure to crush material.
The material is contained within a cage, with openings on the bottom, end, or side of the desired size to allow pulverized material to escape.
This type of crusher is usually used with soft and non-
abrasive material such as coal, seeds, limestone, gypsum or soft metallic ores. The stones are broken the by application of high speed impact forces.
Speed of rotation is important to the effective operations of these crushers as the energy available for impact varies as the square of rotational speed
S.R.P* 5TH TERM- CONSTRUCTION EQUIPMENT MANAGEMENT Page 35
Cone crusher
Used as secondary crusher
Capable of producing large quantities of uniformly fine crushed stone
The conical head on the stone crusher is usually made of manganese steel
The maximum diameter of the crusher head can be used to designate the size of the cone crusher.
A cone cutter differs from a gyratory crusher in these aspects
It has a shorter cone
It has a smaller receiving opening It rotates at a higher speed
It produces a more uniformly sized stone Reduction ratio of the major type of crushers Roll crusher
Used for producing additional reductions in the size
A roll crusher consists of heavy cast iron frame equipped with either one or more hard steel rolls each mounted on a separate horizontal shaft.
Feed size
The maximum size of the material that fed to a roll crusher is directly proportional to the diameter of the rolls.
The maximum size particles that can be crushed are determined as follows
A = 0.085 R +C
A is the maximum size feed R is the radius of the rolls
C is the roll setting or the size of the finished product
Capacity of the roll crusher
The capacity of the roll crusher will vary with the type of stone
size of feed
size of the finished product
S.R.P* 5TH TERM- CONSTRUCTION EQUIPMENT MANAGEMENT Page 36 Capacity of the roll crusher in tonnes/hr =
CW¶RN 864
Q is the probable capacity in tons per hour C is the distance between rolls in inches R is the radius of the roll in inches N is the speed of the roll in rpm W is the width of the roll in inches.
Advantages
It produces more per hour of material of specified size considering weight of crusher. It can handle any material for hardest to softest.
It is cheaper in initial cost and in installation. Less operation and maintenance.
It consumes less power. It produces uniform material Uniform wearing of the surface.