For metal concentrator managers, selecting between an overflow ball mill and a grid-type ball mill is not a matter of "which is better," but "which is more suitable." The right choice depends on a comprehensive analysis of grinding fineness requirements, production efficiency goals, and long-term operational costs—all of which can be quantified through specific data and scenarios.
The first and most critical factor is grinding fineness. This indicator directly determines the mill type: if the subsequent process (such as flotation or leaching) requires fine-grained ore (fineness <0.2mm), the overflow ball mill is the clear choice. For example, in a copper concentrator, flotation requires copper sulfide ore particles to be ground to 0.074-0.15mm to ensure that copper minerals are fully exposed and can react with flotation reagents. In this case, the overflow mill’s ability to stably control fineness below 0.2mm and its low risk of producing overly coarse particles (which would reduce flotation recovery) make it irreplaceable. Conversely, if the task is coarse grinding (fineness >0.2mm) as the first stage of two-stage continuous grinding, the grid-type mill is superior. Take an iron ore concentrator as an example: the first-stage grinding needs to reduce ore particles from 20-30mm to 0.3-0.5mm (greater than 0.2mm) for subsequent separation by magnetic separators. The grid-type mill’s forced discharge ensures that these coarse particles are quickly discharged, avoiding over-grinding and improving the overall efficiency of the two-stage grinding process.
The second factor is production efficiency requirements. If the concentrator has a high throughput target (e.g., processing 5,000 tons of ore per day), the grid-type mill’s 10%-25% higher productivity becomes a key advantage. Let’s calculate: suppose an overflow mill with a diameter of 3.2m and length of 4.5m has a daily output of 800 tons when processing iron ore. A grid-type mill of the same specifications can produce 880-1,000 tons per day—this 80-200 ton increase can directly help the concentrator meet its production targets without increasing the number of mills. However, if the concentrator’s throughput requirement is low (e.g., 200 tons per day) and the priority is to reduce maintenance costs, the overflow mill is more suitable. Its simple structure means that maintenance costs (such as replacing worn parts and labor) are 20%-30% lower than those of the grid-type mill, reducing long-term operational burdens.
The third factor is energy consumption and cost balance. While the grid-type mill has higher productivity, it also consumes more power—usually 15%-20% more than the overflow mill of the same specifications. For a concentrator with high electricity costs (e.g.,0.15perkWh),thisdifferencecanaddupsignificantly.Forexample,a3.2m×4.5mgrid−typemillconsumesabout280kWhperhour,whileanoverflowmillofthesamesizeconsumesabout230kWhperhour.Overayearof3,000operatinghours,thegrid−typemillwouldincuranadditional
22,500 in electricity costs. Therefore, if the concentrator’s profit margin is narrow, the overflow mill’s lower energy consumption may be more cost-effective, even if its productivity is slightly lower.
Finally, process matching must be considered. In a closed-circuit grinding process (where ground ore is classified by a hydrocyclone, and coarse particles are returned to the mill for regrinding), the combined-type ore feeder of the overflow mill (which handles both coarse-grained feeding and backfill processing) is more compatible. In an open-circuit grinding process (where ore is ground once without classification), the grid-type mill’s forced discharge and high productivity make it a better fit.
By integrating these four factors—grinding fineness, production efficiency, energy cost, and process matching—concentrator managers can make a data-driven choice that maximizes grinding efficiency and minimizes operational costs.
