Coal Age

MAR 2019

Coal Age Magazine - For more than 100 years, Coal Age has been the magazine that readers can trust for guidance and insight on this important industry.

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March 2019 www.coalage.com 31 blasting continued www.Derrick.com 5-Deck Stack Sizer ® Multi-Deck Dry Sizer For more than 60 years, Derrick ® Corporation has been leading the industry in the design and manufacture of high-frequency vibratory screening machines and patented screen surfaces. With a pioneering spirit driving innovative solutions, the organization is continuously in the forefront advancing the field of fine particle separation technology. Known worldwide for their high-capacity and superior separation efficiency, Derrick products are used successfully around the world. Its advanced technology allows processors to screen a wide variety of wet or dry fine materials in the range of 6.2 mm to 38 μm. Discover more visit: Hall/Booth: B2.137 to prevent splitting between bore- holes and proper radial cracking and flexural failure. When delays are put in between boreholes, the spac- ing is brought closer together as the increase in time between bore- holes detonating changes the stress fields between boreholes. Pulling the spacing closer together then al- lows the boreholes to have effective utilization where all rock is nicely fragmentated, but a splitting action does not occur between boreholes. These spacing variations then also change based on the bench height, and in Figure 2, the com- parison between firing boreholes instantaneously (blue line) or with delays between holes (orange line) can be observed. It can be seen that depending on the stiffness ratio, an instantaneous blast can have a powder factor that is more than 30% lower than that of a delayed blast. By changing nothing more than the hole-to-hole timing, the powder factor will radically change due to the change in spacing from a proper design. If a mine switched to an in- stantaneous blasting sequence and held the same spacing, in order to maintain the same powder factor, they would dramatically increase their drill and blast costs and the re- sult would be poor fragmentation. Conclusion The Powder Factor Design approach- es of the 1600s and 1700s serve no purpose in today's modern blasting industry. The use of powder-factor design can be, at best, considered a pure guess at the blast variables. While it can be more refined based on experience of the blaster, this experience is limited to situations where the rock type, rock structure, bench height, and timing all remain the same. The powder factor design is a design approach that leads to in- creased drill and blast costs at sites and poor performance of the blast in terms of fragmentation, throw and environmental impacts. In today's 21 st century, modern design approaches exist that work based off of the actual rock breakage mechanisms. In design methodolo- gies such as the Independent Vari- able Konya Design, each variable is independently changed to account for the desired performance of the blast and how changes to that vari- able affect the final performance of the blast. Modern design approach- es as such should be utilized and powder factor should be left as a tool for economic analysis and left as a historical design approach used by blasters in the 18 th century. Calvin Konya is the founder of Pre- cision Blasting Services. Anthony Konya serves as project engineer for PBS. www.idc-pbs.com.

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