Wet Rod Mill

The main advantages of wet rod mills compared to ball mills include: 1) Narrower product particle size distribution with less overgrinding, typically keeping -200 mesh content below 20%; 2) Better suited for processing clay-prone ores, reducing efficiency losses caused by clay formation; 3) Lower energy consumption, typically 15-20% less than same-specification ball mills; 4) More suitable as primary or pre-grinding equipment, improving overall grinding efficiency by 15-25% when forming a composite grinding system with downstream ball mills; 5) Simpler cylinder structure with lower maintenance costs.

Wet rod mills typically handle feed sizes of 15-25mm, with maximum acceptance up to 30mm. The reasonable feed size range depends on cylinder diameter, generally recommended not to exceed 1/40-1/60 of the cylinder diameter. Compared to ball mills, rod mills can accept larger feed sizes. If the feed is too large, it increases rod consumption and energy consumption, potentially causing rod bending; if the feed is too fine, it fails to fully leverage the advantages of rod mills, decreasing efficiency.

Rod media proportions for wet rod mills should be determined based on ore hardness, feed size, and required product size. Typically, a mixed rod configuration is used, with new installations having rod diameter distributions of: Ø100-120mm at 15-20%, Ø80-100mm at 30-40%, Ø60-80mm at 30-40%, and Ø40-60mm at 10-15%. For harder ores, increase the proportion of larger diameter rods, while for finer product sizes, increase the proportion of smaller diameter rods. When adding supplementary rods, generally only larger diameter rods are added, allowing the mill to naturally form a reasonable rod diameter distribution.

Wet rod mills are suitable for processing various ores with Mohs hardness of 3-9, but achieve highest efficiency with medium hardness ores (Mohs hardness 4-7). For higher hardness ores (such as quartzite, granite, etc.), rod mills can still be used, but should be equipped with appropriately increased rod loading rate and reduced feed size. For softer ores, the advantages of rod mills are particularly evident, significantly reducing overgrinding while lowering energy consumption. Rod mills are especially suitable for processing clay-prone ores; the stronger the clay-forming tendency, the more apparent the advantages of rod mills over ball mills.

The optimal operating conditions for wet rod mills include: 1) Rod loading rate of 35-40%, which can be slightly higher for initial installation and stabilize during operation; 2) Slurry concentration typically 65-72% solids content, adjusted according to ore properties; 3) Rotation speed generally 65-72% of critical speed, lower than ball mills; 4) Uniform and continuous feeding, avoiding overload or idle operation; 5) Maintaining appropriate classification efficiency, typically controlling the recirculation ratio at 200-300%; 6) Maintaining appropriate grinding media surface condition, neither too smooth nor too rough. Following these conditions achieves optimal grinding efficiency and minimal energy consumption.

Rod consumption in wet rod mills typically ranges between 250-500 grams per ton of ore processed, depending on ore hardness, grinding fineness, and operating conditions. Compared to ball mills, rod mills typically have 10-20% lower media consumption. Rod costs are slightly higher than steel balls, but due to lower overall consumption, unit grinding costs are typically lower than ball mills. Additionally, rod mills use 15-20% less energy than ball mills, with slightly lower maintenance costs. Overall, wet rod mills' total operating costs are typically 10-15% lower than ball mills of equivalent processing capacity.

Wet rod mill maintenance includes: 1) Daily inspections: monitoring bearing temperature, lubricant condition, reducer performance, and rod loading, recording at least once per shift; 2) Regular maintenance: checking liner wear conditions and cleaning feeding and discharge devices and screens every 500-1,000 hours; 3) Rod replenishment: typically adding rods every 1-2 weeks based on power changes and production conditions to maintain stable loading rate; 4) Major overhaul: performed every 8,000-12,000 hours to replace liners and service bearings and transmission components. Proper maintenance can extend rod mill service life beyond 20 years while maintaining stable production efficiency.

Rod entanglement is a common issue in wet rod mills, with solutions including: 1) Maintaining appropriate rotation speed, typically 65-72% of critical speed, avoiding excessive speed; 2) Maintaining appropriate rod loading rate, not exceeding 40%; 3) Maintaining appropriate feed rate, avoiding idle operation or severe overloading; 4) Using quality rod media with good straightness and uniform hardness; 5) Controlling appropriate slurry concentration, typically 65-72% solids content; 6) Regularly adding new rods while gradually phasing out deformed rods; 7) Using wave-shaped liner design to increase friction and reduce rod slippage; 8) If problems are severe, stopping the mill to clean and replace bent rods. These measures significantly reduce the frequency of rod entanglement.

Wet rod mills can be used as standalone grinding equipment, but are typically most suitable as coarse grinding or primary grinding equipment. When used as standalone grinding equipment, the most suitable grinding product size is 0.5-3mm, with product content finer than 200 mesh (74 microns) preferably not exceeding 30%. For processes with lower fineness requirements, such as certain non-metallic mineral processing and chemical raw material pretreatment, wet rod mills can definitely be used as standalone grinding equipment. However, for processes requiring finer grinding products, it's recommended to configure rod mills with ball mills in series to leverage their respective advantages for optimal economic benefits.