Coal Age

DEC 2018

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.

Issue link:

Contents of this Issue


Page 25 of 59

24 December 2018 blasting continued to use long rows with many holes yet narrow patterns (minimum number of rows) in order to maximize the throw. In order to determine optimal bench width, a site-specific study should be conduct- ed analyzing the cast percentage achiev- able versus the economic considerations of the overburden excavation and the coal production. At a certain point, small bench widths can provide problems op- erating equipment and slow down the process of coal removal. Bench Height-to-Pit Width Ratio The final bench height ratio that will be discussed in this article is the Bench Height to Pit Width, which will work in tandem with the Bench Height-to-Blast Width Ratio. In this situation, reductions in Pit Width (or excavation width) will be considered on the casting effectiveness. The pit width will strongly influence how far the material being cast will have to be thrown. The narrower the pit width, the higher the casting effectiveness. Figure 6 shows a site-specific graphic that was made to illustrate the differences in cast- ing effectiveness compared to pit width and the powder factor used on-site. It can be seen that with a bench height equal to the pit width, the casting is much better than when the bench height is half of the pit width. It is critical to understand that the blast width and pit width will, in gener- al, be the same. The blast width is typi- cally set based on the pit width, and the pit width is set based on the equipment used and the area needed for excavation of overburden and coal. When a mine is already in operation, this pit width should be fully analyzed and when pos- sible minimized in order to facilitate bet- ter casting and a more efficient opera- tion. When a new operation is specifying equipment, it is critical to understand the relationships between blast width, pit width, and bench height to ensure that the proper equipment for extraction of the coal is specified so the pit width is not too large and proper estimates can be made for cast percentages. To optimize the casting effectiveness based on these parameters and others, mines should have site-specific models developed to ensure they are minimizing their overall costs. These models should be developed using two factor studies to understand the full-scale interaction of variables. Timing The last design variable that will be ana- lyzed is the timing of the blast. In today's new electronic detonators, especially in large boreholes where the increased cost is minimal compared to total blast cost, give blasters and mines the ability to refine and tune in cast effectiveness, fragmentation, ground vibration, and numerous other blast outcomes. How- ever, many using electronic caps are not benefitting from the full effectiveness of the caps because site-specific studies have not been completed and true un- COMPANY PROFILE-PAID ADVERTISEMENT For over forty years, Polydeck Screen Corporation has been the leading provider of modular screening solutions for the aggregate, coal, and mining industries. Their extensive selection of screen media, frame systems, and accessories has helped companies save time, increase production output, extend screen service life and improve worker safety. Their screen media product lines include: Polydex ® – Modular polyurethane screen media in 1' x 1' and 1' x 2' sizes that feature the most extensive range of opening sizes, shapes and configurations available today. Since all polyurethane screen panels are made with a high quality injection molding process, surface features like dams and restricted flow bars are an integral part of the panel, not a glued or bolted on option. Rubberdex ® – Modular rubber screen media in 1' X 2' sizes that are available in several material compounds for flexibility or stiffness, microbial resistance or high temperature applications. Rubberdex ® panels are also injection molded under extreme high pressure to ensure homogeneous construction for optimum performance. Armadex™ – Bolt-down rubber solutions for the most abrasive, abusive scalping appli- cations. Armadex™ products incorporate a proprietary injection molding process to pro- vide extended wear life that outperform existing competitive options. Fully customizable in sizes up to 48" x 96" and 52" x 96" and up to 4" thick. Metaldex™ – New line of modular steel sections with polyurethane borders that can be used on Polydeck's PipeTop II™ stringer system. Available with either pin-style or PolySnap ® fastenings, the Metaldex™ line features high-strength welded wire in a va- riety of openings. This is a specialty product primarily used on targeted areas of a screen deck to achieve higher production results. All Polydeck screening solutions are accomplished through a philosophy of partnering with their customers to develop products and solutions that exceed the performance, durability and productivity of existing industry options while maintaining the highest standards of quality and customer service. And, as always, Polydeck screening solutions are backed by the most comprehensive Performance Guarantee in the industry. Polydeck Screen Corporation

Articles in this issue

Links on this page

Archives of this issue

view archives of Coal Age - DEC 2018