6
the pick is (from 0.028 inches new to 0.201 inches worn),
and the larger the increase in all force components and
required specific energy. The drag force rises approximately
100% from new (3,835 lbf) to worn (7,670 lbf) and the
specific energy also increases in the same way, from 1.879
to 3.757 hp-hr/yd3. This identical increase in forces and
specific energy associated with bit wear, with the same spac-
ing (4 inches) and penetration (1 inch), shows that bit wear
creates increased operational forces and a greatly reduced
energy efficiency. The bit’s gradual deformation as the
radius grows suggests that periodic bit replacement should
be integral to cutting performance and energy efficiency
during abrasive coal mining operations.
PSD of Larger Particles
Bit Wear Condition
New Bit: The particle size distribution is somewhat uni-
form in the case of the new bit, with a maximum concentra-
tion (13 particles) between 200–300mm and a significant
number of particles were in between 300–400mm and
1000mm. This would imply that the new bit condition
cut less rough, leaving a reasonable distribution of parti-
cle sizes. The cumulative percentage graph peaks as high
as 400mm. It descends gradually down to about 80% of
particles below 500mm, thus proving that it is efficient in
cutting rocks and has a very controlled distribution.
Table 2. SE of bit abrasive coal
Bit
Condition
Radius
(inches)
Spacing
(inches)
Penetration
(inches)
Drag
Force (lbf)
Normal
Force
(lbf)
Side
Force
(lbf)
SE
(hp-hr/
yd3)
SE
(kwh/
m3)
New 0.028 4 1 3,835 3,295 767 1.879 1.40
Moderate 0.114 4 1 5,485 4,712 1,097 2.687 2.00
Worn 0.201 4 1 7,670 6,590 1,534 3.757 2.80
0
0.5
1
1.5
2
2.5
3
3.5
4
New Moderate Worn
Figure 7. Specific energy vs bit conditions
0
2,000
4,000
6,000
8,000
10,000
New Moderate Worn
Drag Force (lbf)
Normal Force (lbf)
Side Force (lbf)
Figure 8. Forces vs bit condition
0 5
13
11 8 1 3 3 0 1
11
0
20
40
60
80
100
120
Particle size(mm)
cumulative cumulative %
0
5
13
11
8
1 3 3 0 1
11
Particle size (mm)
Figure 9. Particle size distribution of new bit
SE
Forces
(lbf) Cumulative
%
srebmuNelcitraP
the pick is (from 0.028 inches new to 0.201 inches worn),
and the larger the increase in all force components and
required specific energy. The drag force rises approximately
100% from new (3,835 lbf) to worn (7,670 lbf) and the
specific energy also increases in the same way, from 1.879
to 3.757 hp-hr/yd3. This identical increase in forces and
specific energy associated with bit wear, with the same spac-
ing (4 inches) and penetration (1 inch), shows that bit wear
creates increased operational forces and a greatly reduced
energy efficiency. The bit’s gradual deformation as the
radius grows suggests that periodic bit replacement should
be integral to cutting performance and energy efficiency
during abrasive coal mining operations.
PSD of Larger Particles
Bit Wear Condition
New Bit: The particle size distribution is somewhat uni-
form in the case of the new bit, with a maximum concentra-
tion (13 particles) between 200–300mm and a significant
number of particles were in between 300–400mm and
1000mm. This would imply that the new bit condition
cut less rough, leaving a reasonable distribution of parti-
cle sizes. The cumulative percentage graph peaks as high
as 400mm. It descends gradually down to about 80% of
particles below 500mm, thus proving that it is efficient in
cutting rocks and has a very controlled distribution.
Table 2. SE of bit abrasive coal
Bit
Condition
Radius
(inches)
Spacing
(inches)
Penetration
(inches)
Drag
Force (lbf)
Normal
Force
(lbf)
Side
Force
(lbf)
SE
(hp-hr/
yd3)
SE
(kwh/
m3)
New 0.028 4 1 3,835 3,295 767 1.879 1.40
Moderate 0.114 4 1 5,485 4,712 1,097 2.687 2.00
Worn 0.201 4 1 7,670 6,590 1,534 3.757 2.80
0
0.5
1
1.5
2
2.5
3
3.5
4
New Moderate Worn
Figure 7. Specific energy vs bit conditions
0
2,000
4,000
6,000
8,000
10,000
New Moderate Worn
Drag Force (lbf)
Normal Force (lbf)
Side Force (lbf)
Figure 8. Forces vs bit condition
0 5
13
11 8 1 3 3 0 1
11
0
20
40
60
80
100
120
Particle size(mm)
cumulative cumulative %
0
5
13
11
8
1 3 3 0 1
11
Particle size (mm)
Figure 9. Particle size distribution of new bit
SE
Forces
(lbf) Cumulative
%
srebmuNelcitraP