Understanding the Crushing Process and Jaw Crushers in the Mining Industry
Crushing is a fundamental principle of the mining and construction sectors that is used to
grind large rocks or ores into smaller chunks that are easy to handle. This is a very
important step due to a number of reasons that include making material easier to transport,
store and process. Crushing is important regardless of whether you want to attain a greater
surface area or isolate some important minerals or ready raw materials to be refined
further.
We will discuss the crushing process in this blog in depth, its various phases, the
functioning of jaw crushers and the main features which render it effective in its
operation.
What is the Crushing Process?
Crushing is the process of decreasing the size of large rocks or ores to make them useful in
their various applications. This is a mechanical process of reducing the size, also referred
to as size reduction or crushing, which is required in mining and construction. We could
have a more detailed look at the primary causes of crushing:
- Enhance Surface Area: Surface area of the material is augmented through crushing
and this renders it more favorable to further processing.
- Transportability and storage: The smaller sizes are easier to move around, manage
and store, leading to a cost reduction.
- Separation of Minerals: Mining involves crushing to recover precious minerals
among the wastes surrounding the mine.
- Ready to undergo further processing: The refined or enriched further processing
of the crushed product is ready.
Crushing typically occurs in three stages, depending on the desired size
of the material
- Primary Crushing: It is the initial crushing stage whereby the raw material is
crushed down to sizes of about 800-1500 mm in order to come out with sizes of about
150-300 mm.
- Secondary Crushing: This is the output of the primary crushing which has already
a relatively large size 150-300 mm that is recrushed to a final product measuring 50-80
mm.
- Tertiary crushing: The output of secondary stage ranging around 50 and 80 mm is
reduced further in size to produce the end product of 512 mm.
What is a Jaw Crusher?
Jaw crusher is yet another popular crusher with mining and construction industries. It is
largely used in primary and secondary crushing of hard abrasive materials.
Jaw crushers are particularly useful in processing huge blocks of materials. They operate by
crushing the material in place between two jaws, one of which is fixed and the other one is
not fixed. The movable jaw travels back and forth crushing the material between the two
surfaces.
How Do Jaw Crushers Work?
The operating mechanism of the jaw crusher is not complicated. It works on the principle of
carrying the fixed jaw stationary and the movable jaw has a swinging motion but with an
elliptical shape. The material is introduced into the top of the crusher and as the movable
jaw moves back and forward, it crushes the material between the two jaws. The crushed
material will then pass out of the bottom of the crusher.
The size of discharge is determined by the distance between the jaws and the distance between
the jaws is an important factor in determining the size of the output of the crushed
material.
Key Components of a Jaw Crusher
A jaw crusher is made up of various main parts which collude to the crushing work. Here are
the primary parts:
- Feed Chute: This is the opening on which the raw materials are loaded to the
crusher.
- Drive Flywheel: This provides the mechanical force to make the crusher drive.
- V-Belts: V-Belts are used to transfer the power of the motor to the flywheel.
- Motor Stand: This is used to keep the motor in position.
- Setting and Damping Group: It gives the option of control and the vibrations.
- Hydraulic Cylinder: It is utilized in order to adjust the distance between the
jaws.
- Toggle Plate: It is a part which extends the movable jaw to the pitman.
- Swing Jaw: The moving jaw which is crushing the material.
- Discharge: The location where the crushed material goes out.
- Fixed Jaw: This is the fixed jaw that aids in pleating the material.
Key Parameters of a Jaw Crusher
The efficiency and performance of a jaw crusher are defined by several technical parameters:
1. Gape Width (G):
The aperture at the opening of the top of the crusher.
2. Feed Size (b):
The diameter of material that can be supplied to the crusher.
3. Length of Area (L):
Normally, approximately twice the width of the gape.
4. Area Width (W):
Between 1.3 and 3 times the gape width.
5. Stroke (LT):
Minimal and maximum displacement of the lower jaw end.
It is the distinction between the Open Side Setting (OSS) and Closed Side Setting (CSS).
6. Size Reduction Ratio (R):
The ratio of the mouth side of the jaw to the gaping part of the jaws that is closest on
the
side of the jaw.
Typically ranges from 1/3 to 1/9.
A secondary crusher usually has a ratio of 1/4.
A primary crusher usually has a ratio of 1/3.
7. Nip Angle (θ):
Angle of the jaws which assists in holding the material inside during crushing.
It is the angle between the two jaws.
It helps the material to be gripped without slipping.
The value depends on size, hardness, and friability of the material.
Cannot be fixed as too large or too small universally.
Types of Jaw Crushers
Jaw crushers come in two types, which are determined by the direction of jaw movement:
1. Single-Toggle Jaw Crushers:
- Eccentric Shaft Movement: The moving jaw is attached to an eccentric shaft
and it
moves in an elliptical direction.
- Compression and Friction: The crushing is based on the pressure and friction
to
crush the material.
Applications: These crushers are commonly used in medium-hard materials in such
industries as aggregates and construction.
2. Double-Toggle Jaw Crushers:
- Non-Eccentric Pitman The movable jaw is of the type in which two toggle
plates are
engaged, and the crushing process is less frictional.
- More Durable The double-toggle jaw crushers are more resilient and durable.
- Best on Harder Materials These crushers are more applicable to highly
abrasive, or
hard material, but at a greater price.
Choosing Between Single-Toggle and Double-Toggle Jaw Crushers
In making comparison between jaw crushers of the same capacity, the two-toggle jaw crushers
are more costly but they last longer in operation because they are less prone to wear and
tear. Conversely, single-toggle jaw crushers are less expensive and are mostly applied on
aggregate.
Even though double-toggle crushers are more durable, single-toggle crushers are more typical
in industries where abrasive materials are less required, and cost-effective solutions are
needed.
Single-toggle jaw crushers have the moving jaw mounted on an eccentric shaft that is moved
by the pitman to which it is attached. The bottom of the movable jaw has a toggle plate of
the pitman. The compression of the toggle plate is between the movable jaw and the main
body.
This is required to ensure that any part of the moving jaw is in a elliptical orbit (four-bar
linkage movement). In this movement the movable jaw applies the pressure and friction forces
on the material to be crushed.
In double-Toggle jaw crushers, this is achieved by a non-eccentric fixed pitman that is
fitted at the top of the crusher. It possesses two removable toggle plates located on the
right and the left which is connected with the pitman which is attached to the driven
camshaft.
The Toggle plate on the left is attached to the jaw-supporting block and that on the right to
the main body.
The double-toggle jaw crushers action makes it possible to exert force on the material alone.
Comparing jaw crushers of the same capacity it is observed that, the double-toggle jaw
crushers are more expensive as compared to the normal jaw crushers. Due to this fact,
single-toggle jaw crushers are mostly used in aggregate industry whereas the double-toggle
jaw crushers are mostly used in crushing very hard and mighty abrasive material.
The double-toggle jaw crushers also have a higher working life since they do not experience
any force of friction.
