Influence Of Delay Time Between Holes Interval Of Limestone Mine Bench Blasting On Ore Powder Rate And Its Application

In the step blasting production process of aggregate mines,due to factors such as the complexity of the ore body's endowment conditions,it is easy to have a situation where the blasting effect is not good.Excessive rock mass after blasting will directly affect the shoveling efficiency and increase the cost of secondary crushing.Excessive fine ore rate will lead to the loss of ore,reduce the economic benefits of the enterprise,and deteriorate the working environment and affect the health of employees.Therefore,it is of great significance to study the problem of blasting block size in the blasting and mining of aggregate mines,to reduce the mining cost,improve the production environment and improve the utilization rate of mine resources.The reasonable choice of millisecond delay blasting interval time can make full use of the energy generated by explosive explosion,achieve good blasting and crushing effect,improve blasting block size,reduce large block rate and fine ore rate.Taking the bench blasting of an open-air limestone mine as the engineering background,based on the rock blasting and breaking mechanism,and analyzing the mechanism of powder ore formation according to the actual situation of on-site blasting,the theoretical calculation formula of millisecond delay interval between holes was derived;Indoor pendulum impact test under dynamic load;use ANSYS/LS-DYNA finite element software to simulate the blasting effect under different millisecond delay blasting conditions between different holes,optimize the millisecond delay interval of step blasting,and apply it to mine production practice In addition,the sieving method and Split-Desktop block analysis are used to analyze and compare the fine ore ratio before and after optimization,to verify the rationality of the delay time interval,and to achieve the purpose of improving the blasting effect and reducing the fine ore ratio.And get the following result:(1)In the indoor pendulum impact test of limestone under impact dynamic load,as the angle between the pendulum and the vertical direction increases,the impact incident energy increases.The higher the degree of limestone fragmentation,the larger the diameter of the rock fragments.As the number of fragments decreases,the number of fragments in the rock sample increases.The crushing energy consumption and crushing energy density of the limestone samples both increase linearly with the increase of incident energy.Dynamic compressive strength increases with increasing energy density.The pulverization rate generated by the crushing increases exponentially with the increase of energy density,and the average size of rock fragments decreases exponentially with the increase of energy density.(2)In the numerical simulation calculation of step blasting,under the five working conditions of 0ms,25 ms,50ms,75 ms,and 100 ms,the effective stress calculation results show that as the millisecond delay interval between holes increases,the gun hole is extremely deep.The blasting and crushing effect of some rock masses gradually deteriorates,and the root bed is easy to be produced.The blasting and crushing effect of the rock mass at the top of the step slope gradually deteriorates,and large blocks are prone to be produced.The time interval of millisecond delay interval corresponding to the working condition with good blasting and crushing effect of rock mass should be0ms-25 ms.(3)In the millisecond delay blasting interval of 0-25 ms,under the six working conditions of 0ms,5ms,10 ms,15ms,20 ms,and 25 ms,the volume of the crushing circle area at 20 ms is the smallest,and the amount of fines generated is relatively Less;the effective stress peak and particle vibration peak velocity of the same unit all decrease with the increase of the millisecond delay interval;from the gun hole to the bottom of the gun hole,both the effective stress peak and particle vibration peak velocity First decrease and then increase,then decrease and increase.The existence of joints attenuated the peaks of explosive stress waves and particle vibration velocity.The step blasting effect is the best and the amount of millisecond delay interval corresponding to less ore production should be 20 ms,which is in line with the theoretically calculated millisecond delay interval.(4)In the field blasting pulverization rate screening statistics and Split-Desktop block analysis test,the relationship between the amount of fine ore produced and the rate of fine ore is always: the surface of the explosion pile < the middle of the explosion pile < the middle of the explosion pile < the bottom of the explosion pile.After the hole millisecond delay interval is optimized from 50 ms to 20 ms,the fine ore rate in each area of the explosion pile decreased by 2.74%,5.62% and 10.00%,respectively,and the overall fine ore rate of the explosion pile decreased by 6.12%;large blocks of rock in each area of the blast pile and the average size of the entire blast pile also decreased accordingly.The millisecond delay interval is set to 20 ms.The application to mine blasting production can better reduce the fine ore rate.