ENERGY ASPECTS OF BALL MILL GRINDING K.Okaya, Oum je Hyun and Y.Okano Summary Grinding performances of a dry batch ball mill were investigated in relation to mill power measured, changing such variables as ball size, mill rotational speed, ball and material loadings, geometry or number of lifter bars and grinding time. Introduction ln the field of study on 'comminution' ther e appear some kinds of polari z ation, i.e. macro-micro, software- ha r dware and practice-theory and so on. For instance, numerous papers are available on of practical mathematical modelling or simulation ball mill grinding circuits. Few discussion, howev e r, viewpoint h as of been energy made in those consumption on papers from the basis of the its quantitative measurement. On the other hand so-called 'fracture of a single particle' phenomena have been investigat ed exclusively from this point of view in other papers concerned. Th e authors, therefo re , are trying to fill the gap of this type and conducted so far some experimental wo rk on a labo ratory scale ball mill system facilitating precise m ea sur e ments of torqu e. Experimental Fig.l and and a block Batch tests Fig. 2 show respectively a photograph diagram of only have the experimental system used. been carried out wit.hin the extent of this pape r, although the system can be applied to continu ous ones planned to be in nea r future. A series of bat ch ba ll mill grinding processes was thus performed with predetermined input variables 406
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ENERGY ASPECTS OF BALL MILL GRINDING
K.Okaya, Oum je Hyun and Y.Okano
Summary
Grinding performances of a dry batch ball mill
were investigated in relation to mill power measured,
changing such variables as ball size, mill rotational
speed, ball and material loadings, geometry or number
of lifter bars and grinding time.
Introduction
ln the field of study on 'comminution' there appear
some kinds of polari zation, i.e. macro-micro, software
ha r dware and practice-theory and so on.
For instance, numerous papers are available on
of practical mathematical modelling or simulation
ball mill grinding circuits. Few discussion,
howeve r,
viewpoint
h as
of
been
energy
made in those
consumption on
papers from
the basis of
the
its
quantitative measurement. On the other hand
so-called 'fracture o f a single particle' phenomena
have been investigated exclusively from this point
of view in other papers concerned.
Th e authors, therefo re , are trying to fill the
gap of this type and conducted so far some experimental
work on a laboratory scale ball mill system
facilitating precise measure ments of torque .
Experimental
Fig.l and
and a block
Batch tests
Fig. 2 show respectively a photograph
diagram o f
only have
the experimental system used.
been carried out wit.hin the
extent of this pape r , although the system can be
applied to continuo u s ones planned to be conduct~d
in near future.
A series of bat c h ba ll mill grinding processes
was thus performed with predetermined input variables
406
Fig.l:Photograph of the system
ball size, ball and material loadings, mill rotational
speed, number of lifter bars and grinding time. Then
output variables of torque values and finenesa, of
products were determined. The fineness was assessed
by the surface area from Blaine method and size
distribution from standard sieves or L & N MICROTRAC
(a light scattering method ).
4
Results and Discussion
l motor
2 transmission
3 torque detector
4 mill dr um (30cm
5 amplifier
6 recorder
Fig.2:Block diagram of the system
Variation of mill power with rotational speed
This item has been investigate d by other
X 30cm)
investigators /1/. In this study , however, in arder
to get additional information the effect of ball size
was observed, As illustrated in Fiq. 3 in case of
no lifter, i. e. smooth lining, within a conside rably
wide range of rotational speed and an )rdinary extent
of ball loading, an almost identical variation curv•!
was obtained for small bal ls of 23mm and large onE s
of 32mm. At higher rotational spee :b . however, a
407
steeper decrease in power was shown in case of the
balls of smaller size. It is thought to be probably
because of inter ball layer slippage.
700
100
ball diameter 23 mm 32 mm -----
100 N/Nc [-)
Fig.3: Power variation with rotational speed
Figure s in the diagram correspond to J value, and solid and dotted lines to Db=23mm and 32mm respectively.
150
Effect of lifter bars to mill power
In all the experiments where power was measured
changing the number of lifter bars and the ball loading
mill power was much more increased in using the smaller
balls (Fig.4). Furthermore mill power maximum ?Oints
always shifted towards the smaller rotational speed
side on abscissa. It must be mentioned, however,
that the lifte r bars applied here have a somewhat
exaggerate d dimension, i.e. a rectangular cross section
Of 23mm height X 40mm Wicth.
Fig.4: Effect of lifter bars to mill power i n case of lO bars
Figures , solid and dotted lines i ndicate the sarne as noticed in Fig.3