Stage 1: Primary Crushing (Coarse Crushing)
The crushing process begins with primary crushing where large rocks extracted from quarries undergo their first size reduction. Massive stone boulders, typically measuring 1500-500mm in diameter, are fed into powerful primary crushers. The most common equipment for this stage includes:
- Jaw crushers: These utilize two vertical jaws where one is stationary while the other moves back and forth to crush material against the fixed jaw
- Gyratory crushers: These feature a conical head inside a conical shell that gyrates to compress and break rock
The primary crushing stage reduces the massive rock pieces to 400-125mm sized fragments—about the size of a basketball to a softball—suitable for the next processing phase. This stage sets the foundation for efficient downstream processing by creating manageable material sizes that secondary crushers can handle effectively.
Stage 2: Secondary Crushing (Intermediate Crushing)
Following primary crushing, the material proceeds to secondary crushing which further reduces the stone size to 100-50mm (about the size of a hen’s egg to a golf ball). Common machines for this stage include:
- Cone crushers: These compress rock between an eccentrically rotating spindle and concave liners
- Impact crushers: These use high-speed impact forces to fracture stone
Secondary crushers apply greater pressure to the stone than primary crushers but produce smaller output. This stage often involves the first screening operations to separate already adequately sized material from that needing further crushing. Proper secondary crushing ensures optimal feed size for the final crushing stages while maximizing production efficiency.
Stage 3: Tertiary Crushing (Fine Crushing)
Tertiary crushing represents the final size reduction stage in most quarry operations, producing material typically sized between 25-5mm. Equipment used includes:
- Vertical shaft impactors (VSIs): These accelerate rock at high speeds into crushing chambers for precise shaping
In this stage, operators emphasize producing cubically shaped particles required for high-quality concrete and asphalt applications. Many modern systems employ closed-circuit crushing where material is continuously screened and recirculated until the desired size is achieved. Tertiary crushing demands precise control to avoid creating excessive fines that might represent product losses in certain applications.
Stage 4: Screening and Classification
Screening operations occur throughout the crushing process but become particularly critical after tertiary crushing. Key components include:
- Vibrating screens: These separate material into different size fractions
Modern screening technology uses multiple deck screens to simultaneously produce several product sizes from a single feed stream. Efficient screening ensures proper sizing for downstream processes and helps maximize plant throughput by preventing adequately sized material from undergoing unnecessary crushing—a principle known as “pre-screening.”
Stage 5: Material Handling and Stockpiling
The final stage involves:
- Conveyor systems: These transport sized material efficiently
- Stockpile management: This ensures proper segregation of different product grades
Each stage in the stone crushing process plays a vital role in transforming raw quarry rock into the precisely graded aggregates essential for construction, road building, and other industrial applications. Modern crushing circuits integrate these stages seamlessly to optimize production efficiency while maintaining strict product quality standards.