5
PSD Distribution Analysis
As mentioned earlier, along with the resultant particle from
coal cutting, the specific energy was also collected during
the process. The dust concentration was collected and ana-
lyzed using the NMAM method, and then laser diffraction
was used to analyze smaller fines retained by the installed
vacuum filter. The larger fines not retained by the filter,
along with the larger chips, were further analyzed to see the
behavior of coal at a broader spectrum. The larger fines and
the larger chips were made to pass through a 1-inch mesh
size. The retained samples were spread out on a board with
a white background to be virtually sieved. As the passing
particles were very fine to be analyzed for the virtual siev-
ing, the amount of the material generated was measured
based on the weight of the material.
It was configured that larger chips and larger fines
were directly related to macro-rock mechanics, which is
influenced by both cutting geometry and bit condition.
However, the smaller fines and dust concentration were
much more a result of micro-rock mechanics, which is
influenced by the bit wear condition. That is why the test
matrix was designed so that the influence of penetration and
bit condition on the resultant larger fines and chips were
analyzed. For the dust concentration analysis, the focus was
constrained to the influence of bit wear conditions.
RESULTS
Specific Energy-Penetration
The results in Table 1 show an apparent positive relationship
between penetration depth and all three forces (drag, nor-
mal, and side forces) with the same radius (0.028 inches)
and spacing (3 inches). The drag force increases the most
from 639 lbf to 1596 lbf when the penetration depth goes
up from 0.2 to 0.5 inches, then the normal force (which
increases the least) from 549 lbf to 1371 lbf and finally the
side force (which rises the least) from 128 lbf to 319 lbf.
That relation indicates that cutting at a deeper penetration
into the material requires much more force across all direc-
tions, with the most effective resistance being in the drag
direction. The ultimate relationship can be seen as a linear
nature of the relationships among the variables, which sug-
gests a controlled increase in resultant force with penetra-
tion depth.
Specific Energy-Bit Condition
Figure 7 and 8 indicate a strong correlation between bit
wear and cutting forces/specific energy in abrasive coal
mining. The bigger the bit radius, the more wear the tip of
Figure 5. Two L-square rulers are placed on opposite sides of
the rock where the fractured rock remaining on the surface is
collected for particle size distribution analysis
Table 1. SE for soft bituminous
Radius
(inches)
Spacing
(inches)
Penetration
(inches)
Drag Force
(lbf)
Normal
Force (lbf)
Side Force
(lbf)
SE
(hp-hr/
yd3)
SE
(kwh/
m3)
0.028 3 0.2 639 549 128 2.087 1.56
0.028 3 0.4 1277 1098 255 2.085 1.56
0.028 3 0.5 1596 1371 319 2.085 1.55
0
200
400
600
800
1000
1200
1400
1600
1800
0.2 0.4 0.5
Penetration (inches)
Drag Force (lbf) Normal Force (lbf) Side Force (lbf)
Figure 6. Forces vs Penetration depth
)fbl(secroF
PSD Distribution Analysis
As mentioned earlier, along with the resultant particle from
coal cutting, the specific energy was also collected during
the process. The dust concentration was collected and ana-
lyzed using the NMAM method, and then laser diffraction
was used to analyze smaller fines retained by the installed
vacuum filter. The larger fines not retained by the filter,
along with the larger chips, were further analyzed to see the
behavior of coal at a broader spectrum. The larger fines and
the larger chips were made to pass through a 1-inch mesh
size. The retained samples were spread out on a board with
a white background to be virtually sieved. As the passing
particles were very fine to be analyzed for the virtual siev-
ing, the amount of the material generated was measured
based on the weight of the material.
It was configured that larger chips and larger fines
were directly related to macro-rock mechanics, which is
influenced by both cutting geometry and bit condition.
However, the smaller fines and dust concentration were
much more a result of micro-rock mechanics, which is
influenced by the bit wear condition. That is why the test
matrix was designed so that the influence of penetration and
bit condition on the resultant larger fines and chips were
analyzed. For the dust concentration analysis, the focus was
constrained to the influence of bit wear conditions.
RESULTS
Specific Energy-Penetration
The results in Table 1 show an apparent positive relationship
between penetration depth and all three forces (drag, nor-
mal, and side forces) with the same radius (0.028 inches)
and spacing (3 inches). The drag force increases the most
from 639 lbf to 1596 lbf when the penetration depth goes
up from 0.2 to 0.5 inches, then the normal force (which
increases the least) from 549 lbf to 1371 lbf and finally the
side force (which rises the least) from 128 lbf to 319 lbf.
That relation indicates that cutting at a deeper penetration
into the material requires much more force across all direc-
tions, with the most effective resistance being in the drag
direction. The ultimate relationship can be seen as a linear
nature of the relationships among the variables, which sug-
gests a controlled increase in resultant force with penetra-
tion depth.
Specific Energy-Bit Condition
Figure 7 and 8 indicate a strong correlation between bit
wear and cutting forces/specific energy in abrasive coal
mining. The bigger the bit radius, the more wear the tip of
Figure 5. Two L-square rulers are placed on opposite sides of
the rock where the fractured rock remaining on the surface is
collected for particle size distribution analysis
Table 1. SE for soft bituminous
Radius
(inches)
Spacing
(inches)
Penetration
(inches)
Drag Force
(lbf)
Normal
Force (lbf)
Side Force
(lbf)
SE
(hp-hr/
yd3)
SE
(kwh/
m3)
0.028 3 0.2 639 549 128 2.087 1.56
0.028 3 0.4 1277 1098 255 2.085 1.56
0.028 3 0.5 1596 1371 319 2.085 1.55
0
200
400
600
800
1000
1200
1400
1600
1800
0.2 0.4 0.5
Penetration (inches)
Drag Force (lbf) Normal Force (lbf) Side Force (lbf)
Figure 6. Forces vs Penetration depth
)fbl(secroF