Aggregates Manager Digital Magazine
Issue link: http://read.dmtmag.com/i/632397
Get Great Fragmentation OPERATIONS Drilling & T he goal of drilling and blasting is more than just putting rock onto the ground for the processing plant. Many mine operators do not make efforts to optimize the drilling and blasting process until they run into problems, such as excessive oversize, which requires addition- al processing maneuvers such as breaking, or an abundance of fi nes, which can affect crusher wear parts and also creates waste. "The goal with every shot should be to improve production and effi - ciency in the plant," says Billy Zim- merman, senior blasting technician for Luck Stone. "It is a balancing act, through shot design, powder factor, and loading techniques — which are 90 percent of how your shot turns out — and fi ne tuning with timing, to create uniformity in your shot." The shot will affect the amount and size of material for the plant, and it should be optimized to achieve the best fragmentation size for loading and hauling, for crushing processes, and for helping to meet product specifi cations at the lowest cost, according to Andrew Heine- mann, manager of geology and mine engineering at Benchmark Resourc- es. "Generally, drilling and blasting has the highest effect on the cost to produce the fi nal product," he adds. Matthew Boatman, president of General Drilling agrees. "Paying for professional drilling and blasting can reap benefi ts in the processing plant," Boatman says. "Better drilling and blasting will result in a more effi cient plant. This will improve the production and quality of your ma- terial in the plant, and it will lower your costs overall." Reduced overall mining and pro- cessing cost is infl uenced by the drill and blast design — specifi cally the drill-hole diameter, drill-hole spacing, type of blasting agent and initiation, subdrilling, stemming, burden width, and timing. These are the variables in a drill and blast design that can be controlled and adjusted to optimize fragmentation at the lowest cost, effectively lowering the overall cost of mining and processing. Heinemann says an important parameter that often is linked to the distribution of explosive energy in the blast is the drill-hole diameter. It controls the distribution of energy in the blast and, therefore, affects fragmentation. "Large diameters are often associated with expansion of drilling patterns; however, large holes intersect fewer in-situ blocks of rock, resulting in more oversized material, especially in the case of jointed rock," he says. Typically, the drill-hole diameter changes depending on the geology or the type of drill machine. Similarly, changing the bench height (e.g., for a new loading ma- chine) affects all dependent parame- ters or the fragmentation size of the blast muck pile. Modifying a drill- hole diameter, a bench height, or a product size tends to change all oth- er relevant blast design parameters. Comparative calculations in every case allow the designer to determine the optimum cost parameters. AGGREGATES MANAGER Fines can affect equipment wear and also create waste. The amount of fi nes generated by a blast is infl uenced by the explosive properties, priming methods, rock properties, blast geometry, and delay timing on the oc- currence and extent of the fracture process. To reduce fi nes, the proper explosive type, blast parameters, ini- tiation sequence, and charge distribution must be used. The cheapest cost in making rock is at the face, through drilling and blasting. The better the drilling and blast- ing process is in an operation, the lower the costs will be due to effi cient loading, hauling, and crushing. Poor drilling and blasting practices, however, can increase expenses, as the material will require additional han- dling to move it through the plant. Effects on processing costs Reduction of fi nes 1 4