Pit & Quarry, February 2019
DRILLING BLASTING using a set powder factor or pattern are not recommended It is now understand that spacing is a major factor for both the fragmentation and throw of a blast As Ash stated in his 1963 paper It can be generally assumed that uniformity of sizing is a direct result of the KS ratio If on firing a single hole the rock is satisfactorily broken and cleanly removed without excessive displacement it may be assumed the burden is satisfactory Too often blasters reduce the burden rather than extend the spacing in their desire to eliminate boulders or to make rock sizing more uniform SUMMARY Most blasting difficulties occur because of a lack in understanding of how rock is broken and the use of improper charge placement and initiation timing practices Weve explored the basics of blast design for a typical rock with the exception of blast timing from 1963 through today The old standards that Ash recommended in 1963 were KB 20 to 40 KH 15 to 4 KJ 03 minimum KT 05 to 10 KS 10 to 20 These ratios continue to give blasters basic starting points for blast design but these are rather large ranges for design Methods exist today to key in on much more exact numbers and ranges depending on the goals for fragmentation and throw relying on the advice of those like Ash who developed these original rules of thumb As Ash once stated The standards will be found to be quite convenient and Engineered for Accuracy B u i l t to Endure Trusted to Last WY15 Conveyor Belt Scale too close for the timing fines will occur between boreholes with boulders in the burden of the blast Should the spacing be too far for the timing large boulders will be found between boreholes and sawtooth effects can form on the back wall Today it is understood that not only does the timing influence the borehole interaction but the stiffness ratio of a blast will have a major influence on the spacing A sliding scale exists where the higher the stiffness ratio up to a stiffness ratio of 4 the larger the spacing can be At a stiffness ratio of 4 the spacing becomes constant and the changes are then only based on the hole to hole timing of the blast This allows the blaster to key in the spacing for a specific blast based on the different design variables The interaction between timing spacing and bench height are all reasons that simply WY10 Conveyor Belt Scale HY15 Conveyor Belt Scale WF10 Weigh Belt Feeder Control Gates Data Collection Stop by talk to our experienced professionals about a solution for your weighing material handling needs February 12th 14th 2019 indianapolis indiana tecweigh com 8005364880 Booth 38058 68 PIT QUARRY February 2019 pitandquarry com
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