Abstrict The amplitude of the variations in the power drawn by a crusher
motor is dependent on the crushing gap in the crusher, other parameters
such as ore feed rate etc. remaining constant. In accordance with
the invention, this phenomenon is used to set the crushing gap.
The power drawn by the motor is monitored and the amplitude of the
variations of the power drawn is used as a basis for determining
whether the existing crushing gap is too great or too small.
Claims I claim:
1. A method of maintaining a predetermined size of crushing gap
in an ore crusher of the type comprising crusher means defining
an adjustable crushing gap, and a driving motor for driving said
crusher means, said method comprising the steps of:
establishing a predetermined gap size,
measuring noise in the power drawn by said motor during a crushing
operation, which measured noise is indicative of the size of said
crushing gap,
setting said crushing gap at said predetermined gap size in accordance
with said measured noise, and
maintaining the crushing gap at said predetermined gap size.
2. A method of maintaining a predetermined size of crushing gap
in an ore crusher of the type comprising crusher means defining
an adjustable crushing gap, and a drive motor for driving said crusher
means, said method comprising the steps of:
establishing a predetermined gap size;
monitoring the power drawn by said motor during a crushing operation
while keeping parameters of ore size and ore feed rate substantially
constant;
measuring noise in the power drawn by the motor during such operation;
determining from the measured noise a measured size of said crushing
gap;
comparing said measured gap size with said predetermined gap size;
adjusting the size of said crushing gap in accordance with a difference
between said measured and predetermined gap sizes to maintain said
predetermined gap size; and
maintaining the crushing gap at said predetermined gap size.
3. A method of maintaining a predetermined size of crushing gap
in an ore crusher of the type comprising crusher means defining
an adjustable crushing gap, and a drive motor for driving said crusher
means, said method comprising the steps of:
establishing a predetermined gap size;
monitoring the power drawn by said motor during a crushing operation
while keeping parameters of ore size and ore feed rate substantially
constant;
measuring noise in the power drawn by the motor during such operation;
comparing said measured noise with a predetermined noise value
corresponding to said predetermined gap size;
adjusting the size of said crushing gap in accordance with a difference
between said measured noise and said predetermined noise value to
maintain said predetermined gap size; and
maintaining the crushing gap at said predetermined gap size.
4. In an ore crusher of the type comprising crusher means defining
an adjustable crushing gap and a drive motor for driving said crusher
means, the improvement comprising means for monitoring the power
drawn by said motor during a crushing operation, and for measuring
noise in the power drawn by the motor, and means for setting the
crushing gap size to a predetermined gap size in accordance with
the measured noise.
5. In an ore crusher of the type comprising crusher means defining
an adjustable crushing gap and a drive motor for driving said crusher
means, the improvement comprising:
means for monitoring the power drawn by said motor during a crushing
operation while keeping parameters of ore size and ore feed rate
substantially constant;
means for measuring noise in the power drawn by the motor during
such operation;
means for determining from the measured noise a measured size of
said crushing gap;
means for comparing said measured gap size with a predetermined
gap; and
means for adjusting the size of said crushing gap in accordance
with a difference between said measured and predetermined gap sizes
to maintain said predetermined gap size.
6. In an ore crusher of the type comprising crusher means defining
an adjustable crushing gap on a drive motor for driving said crusher
means, the improvement comprising:
means for monitoring the power drawn by said motor during a crushing
operation while keeping parameters of ore size and ore feed rate
substantially constant;
means for measuring noise in the power drawn by the motor during
such operation;
means for comparing the measured noise with a predetermined noise
value corresponding to a predetermined gap size; and
means for adjusting the size of said crushing gap in accordance
with a difference between said measured noise and said predetermined
noise value to maintain said predetermined gap size.
Description BACKGROUND TO THE INVENTION
This invention relates to the measuring and setting of the crushing
gap in crushers, such as gyrating disc or cone crushers.
At present, the crushing gap is ascertained by leading. In the
leading process, the crusher is stopped, and a lead body is dropped
into the gap on a string. When the crusher is restarted, the lead
is deformed to a thickness equal to the crushing gap. If the gap
so ascertained is incorrect, it is necessary to reset it, and then
to perform the leading process again to check the setting. The leading
process may have to be performed over and over again until an acceptable
gap is measured.
This unsophisticated, trial-and-error process has obvious drawbacks.
For instance, it implementation leads to considerable downtime and
the final result may still not be accurate. Also, it is not uncommon
for the operator to neglect to do his checks at the required frequent
intervals, with the result that the gap is often too great as wear
of the crusher takes place. This in turn means that the rock is
not crushed to the required size and may have to be returned for
a further pass, and attendant reduced production and efficiency.
Even more serious in the case of diamond-bearing rock is the fact
that diamonds can be lost if the gap is too great.
Experiments conducted by the inventor revealed that the power drawn
by a gyradisc crusher during operation is not constant, even if
other operating parameters, such as ore feed rate and ore size,
are kept constant, but exhibits considerable variations. Furthermore,
it was found that the amplitude of the variations is greater if
the crushing gap is small than if the crushing gap is larger.
It is an object of the invention to use these findings in the measuring
and setting of the crusher's crushing gap.
SUMMARY OF THE INVENTION
In a method according to this invention, the crushing gap in a
crusher is set in dependence on the amplitude of the variations
in the power drawn by the crusher motor when operational.
In a preferred form, the method includes the following steps: monitoring
the power drawn by the motor, determining the actual crushing gap
by analysing the amplitude of the variations in the power drawn
by the motor, comparing the actual crushing gap with a predetermined
value, and adjusting the crushing gap according to whether, and
by how much, the actual gap differs from the predetermined value.
Alternatively, the method may include the following steps: monitoring
the power drawn by the motor, comparing the actual amplitude value,
and adjusting the crushing gap in accordance with whether, and by
how much, the actual amplitude differs from the predetermined value.
In this case, if the actual amplitude is greater than the predetermined
value, the crushing gap will be increased, and vice versa.
Preferably, the method of the invention is carried out continuously
and automatically i.e. the power drawn is monitored continuously,
and crushing gap adjustments are made automatically as required.
Preferred apparatus according to one embodiment of the invention
includes means for monitoring the power drawn by the crusher motor,
means for determining the actual crushing gap by analysing the amplitude
of the variations in the power drawn, means for comparing the actual
gap with a predetermined gap, and means for adjusting the actual
gap in accordance with whether, and by how much, the actual gap
differs from the predetermined gap.
Alternative apparatus may include means for monitoring the power
drawn, means for comparing the amplitude of the variations in the
power drawn with a predetermined amplitude value, and means for
adjusting the actual gap in accordance with whether, and by how
much, the actual amplitude differs from the predetermined value.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1a, 1b, 1c show graphs of the power drawn by a gyradisc crusher
for different crushing gap settings; and
FIG. 2 illustrates schematically how the crushing gap can be set
continuously to an optimum value.
DESCRIPTION OF AN EMBODIMENT
Referring firstly to FIG. 1 the power drawn characteristics recorded
by a chart recorder in three different experiments with increasing
crushing gaps are illustrated graphically in the form of waves representative
of the power drawn by a crusher motor. In each case, other operating
parameters, such as ore feed rate and ore size prior to crushing
are kept constant. Power drawn is on the vertical axis, and time
on the horizontal axis. In these experiments, the chart speed was
60 cm/h, and the graphs are at full scale. In the experiment represented
by graph (a), the crushing gap was 5 mm, in that represented by
graph (b) it was 7 mm, and in that represented by graph (c), it
was 11 mm.
A comparison of the graphs readily indicates that the smaller the
crushing gap, the greater the "noise" in the power drawn.
"Noise" is the variations in the power drawn, and is represented
by the wave amplitude of the graphs of FIGS. 1a, b, and c. Compare,
for instance, graph (a) with graph (c), where it is seen that the
amplitude of the variations in the power drawn is markedly greater
in the case of the smaller gap than in the case of the large gap.
The invention contemplates using this phenomenon in the measuring
of the actual gap and the resetting of that gap (if necessary) to
an optimum value. FIG. 2 illustrates schematically the basic components
in one form of apparatus which could be used to achieve this end.
In FIG. 2 a conventional crusher and motor combination is designated
by the reference numeral 10. During operation, the power drawn by
the motor is monitored continuously by a measuring instrument 12.
An instrument 14 analyses the incoming power drawn signals and produces
from them a measured gap signal which is indicative of the actual
crushing gap and which is dependent on the amplitude of the variations
in the power drawn by the motor. The measured gap signal is passed
to a gap controller 16 which compares the actual measured gap with
an ideal value and controls an on-line gap adjustment system 18
depending on whether, and by how much, its comparison reveals a
difference between the actual and ideal gap values. Preferably,
the gap adjustment system 18 will be capable of effecting continuous
fine adjustments to the gap setting, so maintaining the crushing
gap continuously at an optimum value.
Note that the apparatus shown schematically in FIG. 2 effects its
adjustments as a result of a comparison between a computed actual
gap value and an ideal gap value. It would also be possible to have
an apparatus which does not compute an actual gap value, but which
performs a direct comparison between the ideal amplitude of the
variations in the power drawn with an ideal amplitude value, and
then performs its adjusting function on the basis of that comparison. |