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22 www.coalage.com December 2018 blasting continued allow for much greater percent casting. This is one approach to increasing the powder factor, however, this is rather elementary and can lead to poor results in practice. Instead, a blast should be de- signed for specific results and the ques- tion then becomes how can the design of the blast be adapted to facilitate this increased powder factor? When fragmentation is a major con- sideration, it is known that the spacing should always be larger than the burden. However, with cast blasting the spacing will oftentimes be equal to or less than the burden. This will lead to a splitting action between boreholes, which is poor on fragmentation, but will allow the gas pressure on neighboring holes to work together to throw the material much farther. In this way, one can in- crease the powder factor to the desired levels. This will, in general, work to im- prove cast percentage, but other design criteria also have major influences on cast percentages. Stemming Oftentimes, the im- portance of stem- ming is downplayed in its ability to im- prove blast perfor- mance, specifically in the throw of ma- terial. It is a relative- ly simple procedure to place gravel in the top of the bore- hole. Proper stem- ming in a borehole can lead to in- creased blast per- formance by 30%, which leads to an increase in casting efficiency by ap- proximately 5%. This simple pro- cedure can lead to millions of dollars of savings per year. COMPANY PROFILE-PAID ADVERTISEMENT For more than 65 years, Derrick Corporation has been leading the indus- try in the design and manufacture of high-frequency vibrating machines and screen surfaces. With a pioneering spirit driving innovative solutions, the organi- zation is continuously in the forefront advancing the field of fine particle sep- aration technology. Known worldwide for their high-capacity and superior sepa- ration 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 10 mm to 38 µm. A Global Family Focused on Pioneering Separation Technology Derrick's global family, comprised of employees, sales representatives, and distributers, is strategically positioned worldwide to provide superior customer service and technical support to custom- ers around the globe. The company has a reputation for solving tough fine screening problems, increasing efficiency, and ultimate- ly increasing profits for its customers. Combining its large suite of wet and dry screening products with its highly skilled technical staff and an in-house testing facility, Derrick provides its customers with optimize solutions and demonstrates the solution's effectiveness under actual field conditions on full-size machines. Testing is performed using state of the art equipment and each test is videotaped to document test programs. Fine Screening Solutions Derrick has success stories in nearly every mining application that requires fine screening. Its proven fine particle separation technology has been benefi - cial in coal, copper ore, gold, industrial minerals, fertilizers, iron ore, plastics, silica sand, and many other fine screen- ing applications, creating more efficient processes, saving energy, and increasing profits for the processors. Derrick Corporation, founded in 1951, is a family owned and operated company headquartered in Buffalo, New York. Visit Derrick.com to discover more about its line of fine separation machines and read case studies that demonstrate the impact Derrick has had on the global mining industry. Figure 5—Bench height-to-blast width ratio comparisons.