Abstract
Six US coals and a crystalline quartz were tested in an instrumented laboratory high-pressure grinding rolls machine equipped with 100-mm-diam. rolls. The machine was choke-fed to maximize the capacity. As expected, the specific capacity decreased with increased grinding pressure for each material tested. Among the six coals, there were significant differences in the critical angle of nip, the effective feed porosity and the variation of strain at the gap relative to the grinding pressure. Although a precise correlation was not obtained, the overall effect of these factors was that, at a given grinding pressure, the specific capacity increased as the Hardgrove grindability index of the coal increased. The relationship between the specific capacity and the grinding pressure for a given coal was independent of feed size down to 150 µm. However, smaller feed sizes produced anomalous results, and the flow within the feed hopper was restricted.
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Abbreviations
- D:
-
diameter of rolls (m)
- f(P):
-
a function of grinding pressure, P
- F:
-
mass rate of flow through the rolls (kg/s)
- k:
-
pressure at standard relative strain in the Rosin-Rammler equation (Pa or MPa)
- L:
-
length of rolls (m)
- m:
-
specific capacity factor (-)
- n:
-
exponent in the Rosin-Rammler equation, Eq. (13) (-)
- P:
-
grinding pressure (Pa or MPa)
- t:
-
time to pass sample, rolls half full to half empty (s)
- u:
-
peripheral velocity of the rolls (m/s)
- x:
-
horizontal width between the rollers (m)
- xc:
-
width between the rolls at αc (m)
- xg:
-
width of the gap between the rolls (m)
- α:
-
angle defined in Fig. 2, 0 ≤ α ≤ αc (rads)
- αc:
-
critical angle of nip (rads)
- εg:
-
strain at the gap (-)
- εm:
-
the strain at the gap if the bed were compressed to zero porosity (-)
- Φ:
-
horizontal force on the rolls (N)
- ρ:
-
true solid density (kg/m3)
- θc:
-
porosity of the bed at the critical angle of nip (-)
- θg:
-
porosity of the bed at the gap (-)
References
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SME nonmeeting paper 94–650.
Discussion of this peer-reviewed and approved paper is invited and must be submitted, in duplicate, prior to August 31, 1995.
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Austin, L.G., Trubeljal, M.P. & von Seebach, H.M. Capacity of high-pressure grinding rolls. Mining, Metallurgy & Exploration 12, 65–73 (1995). https://doi.org/10.1007/BF03403080
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DOI: https://doi.org/10.1007/BF03403080