by N G Nair Manager (Mines) Malanjkhand Copper Project Malanjkhand Copper Project,
Khetri Copper Complex and Malanjkhand Copper Project
http://www.geocities.com/hrdngnair/malanjkhand6.html
Nair Profile
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A Geologist from Malanjkhand India
http://hrdnair16.blogspot.com/
R PUROHIT CHIEF MANAGER (MINES) KHETRI COPPER MINES, HINDUSTAN COPPER LIMITED. KHETRINAGAR, JHUNJHUNU DIST. RAJASTHAN STATE, INDIA.
In hole delay systems prove a predetermined time interval between each downline initiation and detonation of the corresponding explosive charge. A suitable time delay ensures that the initiation signal time has reached the detonators within each charge before it or adjacent charges begin to disrupt the surrounding rock mass. This minimizes the risk of downlines being physically damaged or cut off by ground moment during the blast, and permits the use of longer inter-row delays where required for improved blast performance.
In general it is recommended that all blast holes should contain two or more primers. This multipoint initiation provides security against disruption of the explosive column provides security against disruption of the column by ground moment, or proGood fragmentation in Primary blasts-key to reduced overall costs
It is very important that enterprises engaged in excavation for mining or construction purposes consider the total cost before finalizing drilling and blasting parameters. It is often observed that mining and construction projects attempt to increase the power factor to reduce input cost without realizing explosives consumption and or using expanded drill patterns. Attempts are made to reduce blasting cost without realizing the negative effects of a poor blast on the efficiency of downstream operations.
Cascading effects of post blast poor fragmentation and tight muck piles are:
· Loading machines encounter frequent digging conditions in the muck pile.
· Poor fill factor of loading machine bucket.
· Severe wear and tear of loading machines.
· More frequent breakdowns – example: rope breaking. Bucket teeth breakage.
· Loading machines waste time segregating boulders: losses in productivity, dumpers remains idle, higher turnaround time – poor utilization of dumpers.
· Damage to dumper body caused by huge / heavy boulders.
· Big boulders reduce carrying capacity – low hauling efficiency / productivity.
· Boulder can roll off the dumper and fall on haul road – a potential safety hazard.
· Where crushing is involved, poor efficiency of crushers.
· Frequent jams in crusher chute.
· Severe wear and tear of crusher parts.
· Frequent breakdowns.
Increased costs of maintenance, spares and repairs (loaders, dumpers and crusher)
Higher energy cost and fuel cost (leading, hauling and crushing)
Above are the hidden costs, which get affected due to poor blasts results. More and more operators are now adopting the Mine to Mill concept, looking at the total cost of operations. Blasting, loading, hauling and crushing are inter-related variables in the total cost equation.
Development during the last decade – Electronic delay Detonator
The aspects explained above have prompted the development of the Electronic Delay Detonator. Advancement of the Electronic have made possible the use of miniaturized microchip outside or inside the detonator shell.
In Hole Delay system
In hole delay system provide a predetermined time interval between each downline initiation and detonation of the corresponding explosive charge. A suitable time delay ensures that the initiation signal has reached the detonators within each charge before it or adjacent charges begin to disrupt the surrounding rock mass. This minimizes the risk of downlines being physically damaged or cut off by ground moment during the blast, and permits the use of longer inter-row delays where required for improved blast performance.
In general it is recommended that all blast holes should contain two or more primers. This multipoint initiation provides security against disruption of the explosive column by ground moment, or water penetration, etc. where the primary delay in the charge is number ‘N” e.g. 600 ms the insurance delay will be number ‘N”1 ie 650 ms to provide single point initiation under normal circumstances.
POWDER FACTOR AND EXPLOSIVES DISTRIBUTION
The powder factor (PF) is the mass of explosive (in Kilogram) used to break each cubic meter of solid rock. If the powder factor is expressed in Kg/tones it is important to quantify the figure with a statement of material density. Powder factor can be over emphasized as a design criterion in blasting. Since powder factors are defined by the mass of the explosive rather than it’s different strength may not be possible. Therefore energy factor is a more useful design tool.
SLEEP TIME IN BLAST HOLES
Sleep time is defined as the time between charging and firing of a shot. The sleep time of an explosive is important because the explosive is often charged into unfavorable conditions. Unfavorable conditions such as heat, cold, humidity and water cause the explosives is due to water. Explosives must be charged carefully and fired at the earliest practicable time. In some operations, this could be weeks after charging, but load-and-shout firing eliminates a number of possible processes of detonation. As the sleep time is dependent many factors, an Orica technical services representative should be consulted if the blast has to sleep for a long period.
MAGAZINES
Storage of Explosive
The storage of explosives is governed by regulations, and a Magazine License is required to store explosives and detonators. When building a new magazine, the proposal (with the construction details and location) should be approved prior to construction, to ensure that a license is granted.
A Mining Engineer from Copper Mines in India
NARAYANAN NAIR