Student number : 0318567G
School of Chemical and Metallurgical Engineering
Faculty of Engineering / Comminution is an important process in mineral processing, power plants, cement
production and pharmaceutical industries. It is costly and an inefficient process in
terms of energy requirements and steel consumption related to grinding media and
liners.
Spherical grinding media are predominantly used in final stages of ore grinding. The
spherical balls change shape through breakage and wear. Though this is universal in
milling, its contribution and effect on milling kinetics, load behaviour and mill power
is not fully established. One area that is usually ignored is the relationship between
media shape and mill power.
The objective of this dissertation was to investigate how media shape affects
grinding. Ball size distribution inside an industrial mill was analysed in terms of
shapes and sizes. Load behaviour, mill power and breakage as affected by media
shapes were studied in a pilot laboratory mill. An inductive proximity probe, light
emitting diode, phototransistor and video photographs were used to determine the
load orientation in terms of toe and shoulder positions. A load beam was used to
measure the torque exerted by the charge.
The variation in load orientation and mill power with speed among different media
shapes was observed. Higher shoulder positions were noted with cylpebs than with
worn and spherical balls. The power increased to a maximum with increasing mill
speed for all media shapes reaching its peak at different mill speeds for the three
shapes studied.
Variations of breakage rates with media shapes were found; higher breakage rates
were noted with spherical media but the differences narrows with decreasing feed size
and increasing material fractional filling U. Considering that worn balls in an industrial mill charge constitute about 15 to 40
percent and that the highest difference in breakage rate observed being nine percent
for purely one shape charge; it is very doubtful whether it is worthwhile in attempting
to develop techniques for removing worn balls from the mill.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:wits/oai:wiredspace.wits.ac.za:10539/1506 |
| Date | 31 October 2006 |
| Creators | Lameck, Niyoshaka Nistlaba Stanley |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | 1073957 bytes, application/pdf, application/pdf |
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