In the world of aggregate production, controlling the shape of coarse aggregates is essential for achieving desired strength, workability, and overall performance in construction projects. One of the most critical aspects of shape control is managing the content of needle and flake particles. These elongated and flat particles can negatively impact the final quality of aggregates if not carefully monitored.
If you’re new to the crushing or aggregate production industry, the terminology can be a bit confusing. In simple terms, “coarse aggregate” refers to larger pieces of rock or gravel that are used as the foundation of concrete, asphalt, and many other construction materials. Within these aggregates, you might hear about “needle” or “flake” particles. Needle particles are elongated and thin—imagine small rods—while flake particles are flat and plate-like. Having too many of these elongated or flat shapes can compromise the strength, workability, and durability of construction materials. Understanding how to control the proportion of needle and flake particles is therefore crucial for producing high-quality aggregate.
The quality control measures for the needle and flake particle content in coarse aggregates primarily depend on selecting the right crushing equipment and adjusting the block size of the raw feed materials during production.
Influence of Raw Material Composition
Different raw materials vary in mineral composition and internal structure, affecting the size and grading of the crushed output.
Hard quartz sandstone and certain intrusive igneous rocks tend to produce higher amounts of needle and flake particles. Conversely, medium-hardness limestone and dolomitic limestone typically result in fewer needle and flake particles.
Choice of Crusher
Extensive experimental data show that the type of crusher significantly influences the proportion of needle and flake particles.
Jaw crushers generally yield a slightly higher content of needle-like and flaky particles compared to cone crushers.
Crushing Stages and Ratios
Needle and flake content is highest after coarse crushing, decreases after medium crushing, and is lowest after fine crushing.
A higher crushing ratio—meaning more significant size reduction in a single stage—tends to increase the proportion of needle-flake particles.
Optimizing the Crushing Process
To improve aggregate shape, consider reducing the block size before coarse crushing.
Wherever possible, transform small to medium rocks from coarse and medium crushing into sand.
Reserve smaller rocks from the fine crushing stage for the finished coarse aggregate. This strategy helps keep needle and flake particle content under strict control.
By carefully selecting equipment, adjusting crushing stages and ratios, and managing raw material feed sizes, producers can significantly reduce needle and flake content in coarse aggregates. This approach not only enhances the quality of the final product but also ensures better performance in various construction applications.
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