Secondary Blasting
Secondary Blasting -in open cast mines during the blasting in the high benches are broken. Many times the required fragmentation is not formed and large lumps are created. These large lumps or blocks are not handy and these blocks create loading problems by machines. To breaking of such big blocks into desire fragments by re-blasting is known as Secondary blasting.
Method of secondary Blasting-
1.Pop shooting.
2.Plaster shooting.
3.Snake shooting.
1.Pop shooting- in pop shooting a small hole of 30 mm dia is made in the block. the lenth of hole is approx 0.3-0.4m. these holes are charged with small priming cartridge. And these holes are blasted. Due to Blasting the block is broken to pieces. The Blasted material is scattered and the desired fragmentation are achieved.
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| Pop shooting |
Advantages of pop shooting-
1.there are no much sound.
2.Explosive consumption is less as compared to other method.
Disadvantages-
1. Fly rock problem is more.
2. Workers and drilling cost are required.
2.Plaster shooting- in this case of secondary blasting the surface of the block or lumps is dressed slightly and and make a small area plane on the top of the block. The slab of explosive or cartridge is placed on the plane area on the top of block. And this slab of explosive is covered with thick mud on its top. When such a charge of explosive is blasted, due to shattering effect of the explosive the cracks are developed in the block. After the block can be splitted in small and handy block along the plane of cracks.
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| Plaster shooting |
Advantages of plaster shooting-
1. No drilling is necessary.
2.No fly rock problem.
3.The whole process take less time compare to other method.
Disadvantages-
1.More noise is create.
2.Explosive consumption is high compare to other method.
3.Snake Shooting- in this case the explosive is not placed on the block top of the block. But small space is made below the big block. The explosive charged is placed at this space below the block such the explosive charge is almost touching the block. The charge of explosive is covered by thick layer of mud as far as possible including the possible side. When such a charge of explosive is blasted under the big block or lumps the detonation waves of explosive charge travel in all direction including the open side. While the waves traveling in the block cause cracks in the block. Thus big block is broken into small block.
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| Snake shooting |
Advantages of snake shooting-
1.No fly rock problem.
2.No drilling is required.
3.No waste of time and money in drilling operations.
Disadvantages of pop shooting-
1.Explosive consumption is high.
2.Most of explosive energy is lost through open space.
3.More noise is created due to such blasted.