Introduction to Jaw Crushers in Cement Industry
Jaw crushers are a fundamental part of the cement industry, used primarily for the initial size reduction of raw materials. The primary goal is to reduce large rocks or ores into smaller, manageable pieces that can be further processed in subsequent stages. This process is crucial for preparing the raw materials for the next steps in cement production, such as grinding and mixing.
Components of a Jaw Crusher
A jaw crusher consists of several key components:
- Feed Chute
- Drive Flywheel
- V-belts
- Electric Motor
- Motor Stand
- Settings and Damping Group
- Hydraulic Cylinder
- Toggle Plate
- Swing Jaw
- Discharge Area
- Fixed Jaw
Working Principle
The working principle of a jaw crusher is based on the reciprocating movement of the movable jaw that compresses and crushes the material between itself and the fixed jaw.
- Feeding Material: The material to be crushed is fed into the top of the crusher through a feed chute.
- Compression: As the material enters the zone between the jaws, it gets compressed by the reciprocating movement of the movable jaw against the fixed jaw.
- Crushing Action: The moving jaw moves back and forth against the fixed jaw, applying both pressure and friction forces to break down large chunks into smaller pieces.
- Discharge: Once crushed, the material is discharged from the bottom of the crusher when there is enough space created by the moving jaw’s backward motion.
Mechanism Types
There are two main types of mechanisms used in jaw crushers:
- Single-toggle Jaw Crushers:
- In single-toggle jaw crushers, an eccentric shaft drives a pitman connected to a toggle plate at one end and supported by bearings at both ends.
- This mechanism ensures that any point on the moving jaw moves in an elliptical orbit.
- The single-toggle design allows for both pressure and friction forces to be applied to crush materials.
- Double-toggle Jaw Crushers:
- In double-toggle jaw crushers, two toggle plates are linked to a pitman mounted on a non-eccentric shaft situated at the top.
- This mechanism only applies pressure on materials without involving friction forces.
- Double-toggle designs are more suitable for very hard and highly abrasive materials due to their longer lifecycle.
Technical Parameters
Several technical parameters influence how effectively a jaw crusher operates:
- Gape Width (G): The width between jaws where material enters.
- Maximum Feed Size (b): Typically desired to be between 80% and 90% of inlet width.
- Area Length (L): Generally around double gape width.
- Area Width (W): Varies between 1.3 and 3 times gape width.
- Open Side Setting (OSS) & Closed Side Setting (CSS): Determines maximum and minimum distances between jaws during operation.
- Stroke (LT): Difference between OSS and CSS; indicates movability range of lower end of movable jaw.
- Size Reduction Ratio (R): Ratio of gape width to near side opening; varies from 1/3 to 1/9 but generally around 1/3 for primary crushing.
- Nip Angle (θ): Angle between jaws ensuring material grip without slipping; ranges from 18°–24° in primary crushing up to a maximum of 33°.
