2. -
OBJECTIVES
At the end of this chapter, participants will be
able to achieve:
• Fragmentation principles
•Evaluation of fragmentation
• Factors controlling fragment size
3. -
CONTENT
• Fragmentation Principles
• How to Quantify the Fragmentation
• Evaluation of Fragmentation in Tata Steel
West Bokaro
• Factors Affecting Fragment Size
4. -
INTRODUCTION
• The term ‘rock (or blast) fragmentation’ is an
index that is used to estimate the effect of
bench blasting in the mining industry.
• it is generally understood that both the stress
wave and the gas pressurization make
significant contributions to rock
fragmentation.
5. -
INTRODUCTION(contd.)
•It is well known that the rock fragmentation in
bench blasting is affected by blast condition
such as specific charge, spacing and burden etc.
6. -
BLASTING MECHANICS
Upon detonation, explosives affect rock by various
interrelated means.
Which are-
1.Detonation Shock Wave -an energy pulse is
generated and transmitted to the adjacent rock &
the rock immediately surrounding the borehole is
crushed to some extent.
2.Shock Wave Reflection -when the shock wave
reaches a free face, the outward-bending
compressive force releases, and the wave is
reflected back into the rock as a tension wave.
8. -
BLASTING MECHANICS (contd.)
3. Gas Pressure and Rock Movement –
1.Upon detonation the solid explosive is instantly
converted to superheated gas
2.Gas tries to occupy a space 10,000 to 20,000 times its
original solid volume
3.exerting a pressure that can exceed 1.5 million psi.
4.The fractured rock mass has a certain inertia which
the gas pressure must initially overcome to start rock
movement
5.Once inertia is overcome, the rock moves outward
away from the borehole at around 60 mph
9. -
Processes involved in primary
blasting of rock in bench blasting.
1. Face survey
- estimating overburden
2. Drilling the shot holes
- preparing charge hole
3. Charging with explosive
and stemming top
4. Detonating the explosive
5. Shot pile ready for loading
10. -
Secondary blasting
Blasting conducted to reduce the size of boulders
resulting from a primary blast which can then be
handled by the loading, hauling, and crushing
system.
Secondary fragmentation can be accomplished
by:
1. Drilling method - small diameter hole is drilled
into the oversize fragment and a hydraulic rock breaker
device inserted to split the rock .
11. -
Secondary blasting
2. Plaster blasting- An explosive charge may be packed
loosely into a crack or depression in the oversize fragment
then covered with a damp earth material and fired.
plaster
boulder
3. Pop shooting - blast hole is usually drilled near a crack
or depression in the rock, and is directed toward the
centre of the mass and then charged is filled in it and
12. -
OPTIMUM FRAGMENTATION
• Minimise oversize boulders (less secondary
breaking)
• Minimise ultra fines production
• Maximise Lump product
• Fragmentation enough to ensure efficient
digging and loading
• Muck pile loose enough for fast cycle times
and full buckets
18. -
How delay interval can help to achieve better
fragmentation in different conditions
The delay time between individual holes in a row:
i) The delay time between holes in a row should be
between 1 ms and 5 ms per foot of burden, with 3 ms yielding
good results in most instances.
ii) Where air blast is a problem or potential problem, the
delay time between holes in a row should be at least 2 ms per
foot of spacing.
iii) This will result in a blast progression along the face or
along a row of holes that is approximately half the speed of
sound (or less) and reduces the low frequency air blast
generated by face area movement or by surface area mounding.
iv) Where possible, corner holes at the end of rows
should be given extra delay time because of the greater
degree of fixation of the rock in those locations requires more
time for the rock blasted by previously fired adjacent holes to
move away.
19. -
Delay interval between rows:
i) The delay interval between rows should be from two to three times
longer than the delay interval between holes in a row.
ii) The last row in the shot should often be delayed slightly more than
preceding rows.
iii) This serves to allow rock in previously fired rows time to move out
and tends to reduce back-break in the rock behind the blast.
An additional hazard can exist where delay times (compared to burden
and spacing) are excessively long, causing cutoffs of the initiation system
or powder columns due to ground shift. Again, this needs to be analysed
on a case by case basis and accounted for during blast design
22. -
HOW TO QUANTIFY THE
FRAGMENTATION
1 . A commonly used method today to quantify
fragmentation is to use the mean fragment
size, often designated by k50.
•k50 is a figure which represents the screen size
through which 50% of the loosened rock would
pass if screened.
•This implies that a low value represents a fine
fragmentation and vice versa
23. -
HOW TO QUANTIFY THE
FRAGMENTATION
Another way to quantify the fragmentation is
by the oversize content.
•This could be expressed in percentage of the
broken material exceeding an acceptable stone
size.
The oversize content is a very good
complement to the k50 value as these two
values together will provide a much better
control of the fragmentation distribution
25. -
The formula can be rewritten as
The constant k is determined by test blasting
Method 2.
or ,
The constants k and a must be determined, preferably by test
blasting and regression analysis.
where v is particle velocity and K represents the initial energy
transferred from the explosive to the surrounding rock
And R represents the distance.
26. -
CALCULATION OF
FRAGMENTATION
Kuz-Ram Model
The Kuz-Ram model is probably the most widely used
approach for the prediction of rock fragmentation by
blasting. The unique feature of this model is that the
input data consists of the relevant blast design
parameters.
Three key equations are the backbone of this model:
• Kuznetsov’s Equation:
• Rosin- Rammler equation:
30. -
BOKAKO
Date of Blasting Powder factor (m3/Kg Explosive) Mean Particle size of muck pile
(cm)
DAY 1 2.12 47.18
DAY 2 2.23 49.63
DAY 3 2.0 44.51
DAY 4 1.7 37.83
DAY 5 1.6 35.60
DAY 6 1.9 42.28
DAY 7 2.18 48.51
DAY 8 2.0 44.51
DAY 9 2.0 44.51
DAY 10 2.1 46.73
33. -
REPORT OF TATA STEEL WEST
BOKAKO
Date of
Blasting
Powder factor (m3/Kg
Explosive)
Mean Particle size of
muck pile coal (cm)
DAY 1 4.5 16.02
DAY 2 4.3 15.45
DAY 3 4.3 15.45
DAY 4 4.3 15.45
DAY 5 4.1 14.87
DAY 6 4.4 15.90
DAY 7 4.6 16.08
DAY 8 4.3 15.45
DAY 9 4.3 15.45
DAY 10 4.3 15.45
35. -
WORK ON WIPFRAG SOFTWARE
We can get –
1) Mean particle size
2) Min & Max fragment size
3) standard deviation
and most importantly-
4) percentage of fragment of particular
size.
45. -
CONCLUSION
In this project so far we have read about different type
of rock fragmentation (i.e. primary & secondary) and
different stages involved in fragmentation of rock. This
project also projects the necessity of different type of
explosives & charge hole design for more power
output.
In project we have also learned about application of
KUZRAM model and WIPFRAG software.
This topic has void role in mining industry as it decides
the total output and profit of ore.
