Aggregate materials, encompassing sand, gravel, and crushed stone, form the foundational components for a vast array of construction projects, from residential improvements to major highways and bridges. These materials are extensively mined, making them the most extracted resources worldwide. For aggregates to be suitable for high-quality applications such as concrete production, drainage systems, and septic systems, they must be meticulously cleaned to remove impurities like dirt, clay, silt, shale, coal, soft stone, roots, and organic debris. Unwashed aggregates, particularly those with high clay content, can lead to issues such as cracking in concrete or clogging in drainage systems.
Dewatering screens are essential components in wet processing, primarily used to remove moisture from fine aggregates prior to stockpiling. They are single-deck, adjustable-incline, linear-motion screens that efficiently dewater sand products.
Dewatering screens typically handle feed sizes up to 10 mm and utilize polyurethane screen media ranging from #10 to #60 mesh. They are designed to produce a finished product with an approximate moisture content of 8–15% by weight. While some applications can achieve surface moisture as low as 7%, finer materials, such as those that are 100% passing 100 mesh (150 µm), may dewater to a drip-free consistency, which is conveyable and stackable, but can still retain a surface moisture content exceeding 20%. This observation reveals a fundamental technical trade-off: although dewatering screens are highly effective, their absolute efficiency in moisture reduction is inversely proportional to the fineness of the particles. For ultra-fine materials, achieving extremely low moisture targets may necessitate additional or complementary dewatering stages, and the term “drip-free” should be interpreted within the context of the aggregate’s particle size distribution.
Available screen sizes range from 1200 mm (4′) wide x 2400 mm (8′) long to 1800 mm (6′) wide x 4000 mm (13′) long, with processing rates reaching up to 210 mtph (230 stph) on a single unit. Power requirements vary by model, for instance, from 2×2.88 kW to 2×7.35 kW at 50Hz.
Hydrocyclones are fundamental to fine particle classification in wet processing, offering a compact and efficient solution for separating solids from liquids.
Hydrocyclones are precisely engineered for specific separation thresholds, defining the cut-off point between desired oversize and undersize particles. Key factors influencing their selection and sizing include the densities of both solids and liquids, the required flow rate to process, the percentage of circulating load (overflow/underflow), the desired overflow particle size (grind), and the required percentage of solids in both the overflow and underflow streams. They are commonly employed for desliming, dewatering, and sizing particles generally finer than 4 mesh (5mm). Typical recovery rates in aggregate applications for 2.7 specific gravity particles are +200 mesh (75µm). In fines recovery applications, hydrocyclones can capture particles down to 400 mesh (38µm) at 2.7 SG, with specialty applications achieving recoveries down to 625 mesh (20µm) at 2.7 SG.
Bucket wheels are a type of sand classification system designed for efficient dewatering and fine sand recovery.
Bucket wheel diameters typically range from 2.6m to 3.5m, with varying numbers of buckets (e.g., 36 to 48). The bucket wheel speed is characteristically very low, operating at 0-3 rpm, which facilitates relatively fine splits, approximately 200 mesh. For models integrating an auger screw, specifications include screw diameters (e.g., 2.1m) and lengths (e.g., 2.6m to 4m), with screw speeds typically ranging from 0-11 rpm. Design features often include long settlement areas and large weir areas, engineered to enhance the retention of +63 micron particles. These units can be powered by an electric supply or mechanically coupled to other processing machines.
Bucket wheels are characterized by lower capital and operating costs, reduced power consumption, and increased drainage time, resulting in a drier product with 10-15% residual water content. They also significantly reduce the loss of saleable material to ponds and feature robust construction for durability.
Common applications include processing concrete, mortar, and asphalt sands, quarry dust/crushed fines, lake and beach sands, silica sand, golf course sands, filter bed sands, recycled materials, and iron ore.
Log washers are robust machines designed for aggressive scrubbing and cleaning of coarse aggregates, particularly those contaminated with tough, insoluble materials.
Log washer feed material should ideally be pre-screened to ensure the top size does not exceed a nominal 100mm (4”) and to eliminate all material smaller than 10mm (3/8”). Available in various sizes, log washers offer capacities ranging from 50 mtph to 365 mtph. Tube lengths typically vary from 9175 mm (30’) to 10820 mm (35’), providing extended scrubbing retention time essential for difficult materials. Power requirements generally range from 90kW to 200kW. They feature heavy-duty, 2-stage helical gear reducers designed to achieve high torque output at low spiral speeds, ensuring effective scrubbing. Paddles are often designed with a 2-piece, bolt-on configuration, featuring replaceable wear shoes (e.g., HiCR chrome or manganese) for extended operational life and simplified maintenance. Log washers are explicitly designed for the washing and separation of aggregates by breaking down heavy plastic clay, conglomerates, and certain types of soft stone. This specificity indicates that their design, particularly the aggressive scrubbing action and extended retention time, is meticulously optimized for these particularly difficult-to-remove contaminants. This functional specialization differentiates them from other washing equipment, implying that for highly contaminated feed materials, a log washer is not merely an option but a crucial, even necessary, component to achieve the required material quality, thus defining a specialized role within the broader wet processing circuit.
Log washers are ideally suited for washing ores with high mud content (exceeding 20%), such as manganese, iron, limestone, tungsten, tin, and silica sand ore.
Fine material washers, often referred to as sand screws or spiral classifiers, are crucial for processing fine aggregates, ensuring their cleanliness and proper classification.
Fine material washers are capable of accepting feed material sizes up to 10mm. They can achieve high production capacities, with some models capable of processing up to 725 mtph (800 stph). These machines are available in both single and twin screw configurations to suit various throughput requirements. Models vary in screw diameter and tube length (e.g., from 917×7769 mm / 36”x25′ to 1675×10760 mm / 66”x35′). Power requirements typically range from 15 kW to 2×45 kW. Water capacity is a critical specification, varying significantly based on the target mesh size (e.g., 100, 150, 200 mesh) and the specific model. These washers can classify material up to 50 mesh (300 microns), featuring a large pool area designed for maximum fines retention. Fine material washers are designed to achieve both “maximum fines retention” and “great achievement in dewatering”. This highlights a critical and delicate balance in their operation. While retaining valuable fines (which are often essential for producing high-quality concrete sand) is crucial for maximizing product yield, these finer particles inherently tend to retain more moisture. The engineering challenge lies in optimizing the design of the large pool area and the dewatering mechanism to simultaneously achieve both objectives, thereby maximizing both the quantity and the desired quality of the final product.
The comprehensive analysis of wet processing and washing technologies underscores their critical importance in modern aggregate production. These processes are not merely about cleaning but involve sophisticated engineering to classify, dewater, and enhance the quality of materials for diverse construction applications.
Polygonmach’s commitment to providing a wide array of advanced wet processing solutions positions the company as a key partner in the aggregates industry. The company’s offerings, including dewatering screens, hydrocyclones, bucket wheels, log washers, and fine material washers, demonstrate a strategic approach to addressing various client needs, from high-volume dewatering to aggressive clay disintegration and precise fines classification. The emphasis on robust construction, efficiency, and environmental responsibility across its product lines aligns with the evolving demands of the global market.
The industry’s shift towards more sophisticated, integrated solutions, as evidenced by the increasing preference for cyclone-based systems over traditional bucket wheels in certain applications, highlights a continuous drive for greater efficiency and environmental compliance. Polygonmach’s ability to offer both established and advanced technologies, and to integrate them into comprehensive processing circuits, ensures that clients can select optimal solutions tailored to their specific project requirements, feed material characteristics, and regulatory environments. This adaptability and focus on integrated systems enable Polygonmach to deliver not just individual machines, but complete, efficient, and sustainable wet processing solutions that contribute significantly to product quality, operational cost-effectiveness, and environmental protection.