Mobile Crushing and Sand-Making Equipment: Pros and Cons of Three Sand-Making Processes

Mobile crushing and sand-making equipment are essential in producing high-quality sand and gravel aggregates for construction, infrastructure, and industrial applications. The choice of sand-making process—dry, semi-dry, or wet—significantly impacts production efficiency, sand quality, operational costs, and environmental footprint. Below, we explore the advantages and disadvantages of each method, along with practical measures to enhance equipment performance and output quality.

1. Dry Sand-Making Process

Process Overview

The dry sand-making process is a water-free method designed to produce artificial sand efficiently. Key steps include:

• Raw Material Preparation: Crushed stone is controlled to a particle size range of 5-40mm and fed into the sand-making machine.
• Screening and Recycling: Screening equipment separates fine crushed stone (2-5mm) and larger particles (>5mm), returning them to the sand-making machine for further processing.
• Fine Material Classification: Particles below 2.5mm are subdivided into two grades: <0.6mm and 0.6-2.5mm. An air classifier removes excess stone powder from the <0.6mm fraction.
• Mixing: The three resulting material types (2.5-5mm, 0.6-2.5mm, and <0.6mm) are blended uniformly to meet artificial sand quality standards.

Additional Considerations

• Dust management is critical, requiring shielding and rainproof measures during processing.
• Installing an alloy rubber sweeper at the belt conveyor head enhances stone powder recovery, reducing waste.

Advantages

• Water Conservation: Eliminates water usage, making it ideal for arid regions or projects with strict water regulations.
• Cost Efficiency: Lower operational costs due to no need for water supply or wastewater treatment.

Disadvantages

• Dust Generation: Requires robust dust control systems, such as enclosures or air filtration, to mitigate environmental and health concerns.
• Powder Recovery Needs: Additional equipment may be necessary to reclaim stone powder effectively.

Best Use Case

The dry method suits water-scarce environments or projects where dust suppression technologies are readily available, such as urban construction sites with advanced air quality controls.

2. Semi-Dry Sand-Making Process

Process Overview

The semi-dry method balances water usage and quality control, accommodating a variety of raw materials. It involves:

• Raw Material Inputs: Three types of materials enter the sand-making silo:
  • Coarse aggregates (5-40mm) from primary crushing and grading.
  • Returned aggregates (2.5-40mm) from the sand screening building.
  • Dewatered slag (2.5-5mm) from screening and dewatering finished coarse aggregates.
• Mud Content Control: The process effectively manages mud content through grading and dewatering.
• Finished Sand Composition: Includes:
  • Coarse bone sand (<5mm) from grading and screening.
  • Fine sand (<2.5mm) recovered from wastewater after grading coarse aggregates.
  • Additional fine sand (<2.5mm) from processing.

Additional Considerations

• The semi-dry process can be adapted as primarily dry-based or wet-based, depending on raw material quality.
• It requires significant wastewater treatment, which adds complexity and cost.

Advantages

• Versatility: Handles materials with high mud content or softer rock types effectively.
• Quality Stability: Produces consistent sand quality with minimal dust pollution compared to the dry method.
• Adaptability: Suitable for diverse raw materials, enhancing its applicability across projects.

Disadvantages

• Wastewater Treatment: Generates substantial wastewater, necessitating costly treatment systems.
• Process Complexity: Requires careful management of multiple material streams and treatment stages.

Best Use Case

This method is ideal for projects with variable material quality, such as quarries with mixed rock types, where moderate water usage is feasible and wastewater treatment infrastructure is available.

3. Wet Sand-Making Process

Process Overview

Commonly used in hydropower projects in China, the wet method leverages water to achieve high-purity sand. The process includes:

• Closed-Loop System: Combines inspection screening and vertical shaft impact crushing.
• Screening Setup: Uses 5mm and 3mm screens on the inspection surface.
• Material Flow:
  • Particles <3mm from rod mill processing go directly to the finished sand silo after dewatering and grading.
  • Particles 3-5mm are returned to the rod mill for further grinding.
  • Particles >5mm are sent back for additional crushing.
• Purification: Specialized equipment treats muddy wastewater to ensure environmental compliance.

Additional Considerations

• The process excels at removing mud and impurities, producing exceptionally clean sand.
• High water usage demands robust treatment systems to manage runoff and sludge.

Advantages

• High Cleanliness: Produces premium-quality sand with minimal impurities, ideal for high-specification concrete.
• Effective Mud Removal: Water washing ensures thorough cleaning of raw materials.

Disadvantages

• Water Intensive: Consumes significant amounts of water, posing challenges in water-scarce regions.
• Treatment Costs: Wastewater treatment increases operational expenses and requires additional infrastructure.

Best Use Case

The wet method is best for projects prioritizing sand purity, such as hydropower or large-scale infrastructure developments, where water availability and treatment facilities are not constraints.

Measures to Improve Sand-Making Equipment Quality

To optimize the performance of mobile crushing and sand-making equipment, consider these practical enhancements:

1. Addressing Powder Wrapping in Coarse Aggregates

• Rinsing Process: Incorporate water rinsing in the system to remove powder coatings from aggregates, improving their quality for concrete production.
• Specialized Equipment: Use long spiral classifiers to wash and grade stones ≤5mm, effectively removing clay and soil.
• Material Challenges: For sources with tuff interlayers or hard-to-clean rocks, secondary crushing can exacerbate powder wrapping, necessitating tailored washing processes to keep mud content within acceptable limits.

2. Optimizing Particle Size Distribution

• Balanced Grading: High-quality graded sand reduces cement usage and boosts concrete strength. Poorly graded sand (too coarse or too fine) affects workability:
  • Coarse Sand: Leads to poor cohesion and segregation.
  • Fine Sand: Increases cement demand, raising costs and potentially weakening concrete.
• Goal: Achieve a balanced particle size distribution to enhance concrete performance while minimizing material costs.

Additional Insights: Why Process Selection Matters

Choosing the right sand-making process is not just about equipment capabilities—it influences:

• Operational Efficiency: The dry method minimizes resource use, while wet and semi-dry methods prioritize quality over simplicity.
• Environmental Impact: Water-free dry processes reduce ecological strain, whereas wet methods require careful wastewater management to avoid pollution.
• Cost Management: Balancing initial investment (e.g., dust control or treatment systems) with long-term savings (e.g., reduced cement use) is key.
• Equipment Longevity: Advanced wear parts and automated controls can extend machine life across all methods, reducing downtime and maintenance costs.

Technological Enhancements

Modern mobile crushing equipment benefits from:

• Precision Screening: Improved separation technologies enhance particle consistency.
• Durable Materials: Wear-resistant components (e.g., manganese steel) withstand abrasive conditions.
• Automation: Real-time process monitoring optimizes output and reduces human error.