3
Figure 3b) of the unified material from the input feed. After
each turn of grinding, the mass of material below 0.1 mm
(Q1) was removed from the grinding product, and the
remaining sample Q2 was replenished with the portion of
material Q1 from the unified input feed.
The obtained crushing data was used in determination
of a series of mathematical models based on the specific
pressing force and the feed moisture as independent vari-
ables. Following values (dependent variables) were the sub-
ject of modeling:
• Bond work index Wi,
• Specific energy consumption Esp,
• Throughput Q,
• Crushing intensity expressed through crushing
ratios,
• Generation of fines below 0.1 mm in HPGR product.
Statistical verification of individual coefficients in
models in terms of their significance and potential auto-
correlation was also provided. Statistical significance for all
variables in models was tested on the confidence level (1
– a) =95%. The correlation between pairs of individual
variables was calculated with using of r-Pearson’s linear cor-
relation coefficient r. Statistical significance of each calcu-
lated coefficient r was verified by means of dedicated test
based on t-Student theoretical distribution.
RESULTS OF INVESTIGATIONS
Evaluation of HPGR Products
In the first stage of investigations a general fineness of
HPGR products in terms of achieved crushing ratios was
analyzed. Specific calculations were carried out with using
of formula (3).
S d
D
x
x
x =(3)
Where x denotes the characteristic particle, i.e., average –
50% (d50 and D50), 80% (d80 and D80), Dx denotes
particles in feed, dx – particles in product.
Results presented in Table 2 indicate that the pressure
in HPGR device generally had more significant impact on
the breakage intensity of HPGR products than the mois-
ture content. Additionally, while together with increasing
of Fsp, the breakage intensity increases as well, a higher
moisture content results in less significant decrease in val-
ues of crushing ratio. These relationships are true for all
analysed ratios. It may indicate that HPGR device operat-
ing at higher pressure values produces fines more effectively
than coarser particles.
The above relationship was also confirmed through
analysis of yield of finest particles (below 100 mm). Moisture
has an inverse impact on the yield of fines, because lower
contents of finest particles can be observed in HPGR prod-
uct with higher moisture content (Figure 4).
Productivity characteristics obtained during the test-
ing programme were presented in Table 1. Analysis of this
parameter shows that together with increasing operational
pressure, the throughput (Q) decreases. It can be also
noticed that together with increasing the moisture of the
feed material, throughput also decreases. This may be due
to a potentially higher slip of the feed material on the rolls,
especially since tests were performed for the plain surface
of both rolls. For the highest moisture content, it could be
observed the lowest decrease in Q value.
Evaluation of Energetic Aspects
One of the main aims of investigations was to evaluate
potential energy effects obtained for changeable pressure in
HPGR and moisture content of the material and for this
Table 2. Results of experiments
Pressure
Fsp, [N/mm2]
Moisture
content
M, [%]S20 S50 S80
3.3 0 8.86 5.12 3.2
3.3 2 7.66 5.1 3.18
3.3 4 6.99 4.88 3.1
4.3 0 14.19 7.49 4.32
4.3 2 10.98 6.57 3.62
4.3 4 10.65 5.63 3.34
5.3 0 15.72 8.31 4.64
5.3 2 15.36 8.22 4.66
5.3 4 13.93 8.11 4.68
Figure 4. Yields of –100 microns in HPGR products
Figure 3b) of the unified material from the input feed. After
each turn of grinding, the mass of material below 0.1 mm
(Q1) was removed from the grinding product, and the
remaining sample Q2 was replenished with the portion of
material Q1 from the unified input feed.
The obtained crushing data was used in determination
of a series of mathematical models based on the specific
pressing force and the feed moisture as independent vari-
ables. Following values (dependent variables) were the sub-
ject of modeling:
• Bond work index Wi,
• Specific energy consumption Esp,
• Throughput Q,
• Crushing intensity expressed through crushing
ratios,
• Generation of fines below 0.1 mm in HPGR product.
Statistical verification of individual coefficients in
models in terms of their significance and potential auto-
correlation was also provided. Statistical significance for all
variables in models was tested on the confidence level (1
– a) =95%. The correlation between pairs of individual
variables was calculated with using of r-Pearson’s linear cor-
relation coefficient r. Statistical significance of each calcu-
lated coefficient r was verified by means of dedicated test
based on t-Student theoretical distribution.
RESULTS OF INVESTIGATIONS
Evaluation of HPGR Products
In the first stage of investigations a general fineness of
HPGR products in terms of achieved crushing ratios was
analyzed. Specific calculations were carried out with using
of formula (3).
S d
D
x
x
x =(3)
Where x denotes the characteristic particle, i.e., average –
50% (d50 and D50), 80% (d80 and D80), Dx denotes
particles in feed, dx – particles in product.
Results presented in Table 2 indicate that the pressure
in HPGR device generally had more significant impact on
the breakage intensity of HPGR products than the mois-
ture content. Additionally, while together with increasing
of Fsp, the breakage intensity increases as well, a higher
moisture content results in less significant decrease in val-
ues of crushing ratio. These relationships are true for all
analysed ratios. It may indicate that HPGR device operat-
ing at higher pressure values produces fines more effectively
than coarser particles.
The above relationship was also confirmed through
analysis of yield of finest particles (below 100 mm). Moisture
has an inverse impact on the yield of fines, because lower
contents of finest particles can be observed in HPGR prod-
uct with higher moisture content (Figure 4).
Productivity characteristics obtained during the test-
ing programme were presented in Table 1. Analysis of this
parameter shows that together with increasing operational
pressure, the throughput (Q) decreases. It can be also
noticed that together with increasing the moisture of the
feed material, throughput also decreases. This may be due
to a potentially higher slip of the feed material on the rolls,
especially since tests were performed for the plain surface
of both rolls. For the highest moisture content, it could be
observed the lowest decrease in Q value.
Evaluation of Energetic Aspects
One of the main aims of investigations was to evaluate
potential energy effects obtained for changeable pressure in
HPGR and moisture content of the material and for this
Table 2. Results of experiments
Pressure
Fsp, [N/mm2]
Moisture
content
M, [%]S20 S50 S80
3.3 0 8.86 5.12 3.2
3.3 2 7.66 5.1 3.18
3.3 4 6.99 4.88 3.1
4.3 0 14.19 7.49 4.32
4.3 2 10.98 6.57 3.62
4.3 4 10.65 5.63 3.34
5.3 0 15.72 8.31 4.64
5.3 2 15.36 8.22 4.66
5.3 4 13.93 8.11 4.68
Figure 4. Yields of –100 microns in HPGR products