 3. New Design for Autogenous Mill for Ores of Different Minerals. |
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Fig.1. Autogenous Mill of a New Design
 Schematic Outline (Sketch) |
Studying of the experience in operation of different types of grinding equipment allowed us to modify method of material grinding and, based on it, propose new design for Autogenous Mills for which Russian and Uzbek patents were issued. Grinding process in the mill is a result of interaction between pieces (particles) of ground material in counter-current flows. At the same time need in mill balls and internal mill lining is no longer relevant. Foundation for mill installation is not also required.
One of the version of the mill design (Fig.1) includes housing and installed in it two hollow conical caps (bowls) rotating in opposite directions around vertical axis and located so that they form work chamber with annular discharging slot. The upper bowl has an axial charging opening.
Material grinding in such mill is realised as follows. |
Material destined for grinding is delivered under
gravity force through the charging opening in
the upper bowl into the work chamber formed by
internal conical surfaces of upper and lower bowls,
revolving in opposite directions. At that, owing
to friction forces, material in work chamber is
captured by revolving bowls; particles of material
are separated into two portions rotating in opposite
directions. An active zone is formed on the boundary
between these two portions of material. In that
zone particles of material move about one another,
interact with each other and become ground, spending
accumulated kinetic energy for friction, impact
load and chipping crushing action.
Particles of final (required) lump size leave
active zone for discharging slot as follows.
To move the single particle, revolving together
with other particles of material, from internal
zone to the discharging slot in peripheral zone
of the work chamber, shear thrusts (shearing actions)
of centrifugal forces should exceed exertions
of friction and cohesion forces which not let
the particle go away from other particles. In
revolving material, including the particles of
different lump size, shearing actions can reach
critical value first of all for small particles.
Therefore the process similar to material filtration
through a granular filter-bed takes place, with
movement of fine fraction to periphery and coarse
fraction concentration in the central part of
the revolving material. This process is promoted
by opposite rotation of the material and continuous
feeding material delivery (under gravity force)
into active zone where material self-grinding
and its separating in lump size (classifying)
mainly occurs.
Particles of ready (final) lump size in full rotating
ore volume under action of centrifugal forces
move to the periphery. When ready material reaches
internal conical surfaces of bowls, it under centrifugal
forces, produced as a result of interaction between
material and bowl surfaces, moves along the internal
bowl surfaces upstream or downstream to the annular
discharging slot and goes out through it from
the work chamber.
Lump size of ready class is determined by en empirically
selected frequency of bowl rotation, and by the
width of discharging slot.
Technological efficiency of the mill has been
tested in numerous experimental studies. Results
of experiments have shown that this mill is significantly
more efficient than mills currently being used
at the ore milling plants.
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