Abstrict A method for controlling a crushing gap width of a gyratory crusher
of the kind including a crusher head is disclosed. The crusher head
of the crusher is driven by a power unit and is positionally adjustable
in relation to a crusher shell by a hydraulic motor. The hydraulic
motor moves the crusher head of the crusher, thereby adjusting the
crushing gap width. A power consumption of the crusher, pressure
load on the crusher head, and the width of the crushing gap are
determined continuously. The crushing gap width is controlled by
being adjusted when the gap width is, above a pre-determined minimum
gap width value, substantially in accordance with a control function
which depends on both the power consumption and the pressure load,
and which is so selected as to provide an intended crushing effect
the material being crushed.
Claims I claim:
1. A method for controlling a crushing gap width between a crusher
head and a crusher shell of a gyratory crusher, said crusher head
being adjustable in relation to the crusher shell by a hydraulic
motor for adjusting said crushing gap width, comprising the steps
of:
driving the crusher head by a power unit,
continuously determining power consumption of the crusher,
continuously determining pressure load acting on the crusher head,
continuously determining the width of the crushing gap,
selecting a gap width control function which is conditionally dependent
on both the power consumption and the pressure load to provide an
intended crushing effect on material being crushed,
calculating a preferred gap width in accordance with said control
function, and
adjusting the crushing gap width, when the crushing gap width is
above a pre-determined minimum crushing gap width, so that said
crushing gap width is adjusted to said preferred gap width calculated
in accordance with said control function by means of said hydraulic
motor and physical contact between the crusher head and the crusher
shell is prevented.
2. The method according to claim 1 wherein the step of adjusting
the crushing gap width occurs only when said width has deviated
from a preferred gap width calculated in accordance with said control
function by a pre-determined extent and for a pre-determined length
of time.
3. The method according to claim 2 wherein said pre-determined
extent lies within the range of 2-15% of the preferred gap width.
4. The method according to claim 2 wherein said pre-determined
length of time is 3-10 seconds.
5. The method according to claim 1 and further comprising the
step of
starting the gyratory crusher up at a pre-determined crushing gap
width which exceeds the pre-determined minimum crushing gap width.
6. The method according to claim 5 and further comprising the
steps of
imparting to the crusher head a gyratory movement having an eccentric
radius, and starting the crusher up at a pre-determined crushing
gap width which amounts to 25-50% of said eccentric radius.
7. The method according to claim 1 and further comprising the
steps of:
using a hydraulic piston-cylinder device as said hydraulic motor,
measuring said width by means of a position sensor which includes
a first part stationary in relation to a cylinder casing of said
piston-cylinder device, and a second part which is stationary in
relation to a piston of said piston-cylinder device, and
transmitting a position signal characteristic of the positions
of said parts in relation to one another, and therewith characteristic
of the position of the crusher head, from said position sensor to
means for calculating a preferred gap width.
8. A method for controlling a crushing gap width between a crusher
head and a crusher shell of a gyratory crusher, said crusher head
being adjustable in relation to the crusher shell by a hydraulic
motor for adjusting said crushing gap width, comprising the steps
of
driving the crushing head by a power unit,
continuously determining power consumption of the crusher, pressure
load acting on the crusher head, and the width of the crushing gap,
selecting a gap width control function which is conditionally dependent
on both the power consumption and pressure load determined so as
to provide an intended crushing effect on material being crushed,
and
adjusting the crushing gap width, when the crushing gap width is
above a pre-determined minimum crushing gap width value to prevent
physical contact between the crusher head and the crusher shell,
in accordance with said control function, said control function
being expressed by the formula ##EQU2## S.sub.B is the crushing
gap width to which the crushing gap is adjusted in mm,
E is the power output of the power unit in kW,
P, Q and R are constants determined from a power consumption curve,
a is an exponent and C.sub.T is a constant, both being determined
from a pressure load curve,
T is pressure in MPa of hydraulic fluid in said hydraulic motor,
T.sub.o is a pressure calculation limit in MPa, and
I is a minimum crushing gap width value in mm.
9. The method according to claim 8 wherein the step of adjusting
the crushing gap width occurs only when said width has deviated
from a preferred gap width calculated in accordance with said control
function by a pre-determined extent and for a pre-determined length
of time.
10. The method according to claim 9 wherein said pre-determined
extent lies within the range of 2-15% of the preferred gap width.
11. The method according to claim 9 wherein said pre-determined
length of time is 3-10 seconds.
12. The method according to claim 8 and further comprising the
step of
starting the gyratory crusher up at a pre-determined crushing gap
width which exceeds the pre-determined minimum crushing gap width.
13. The method according to claim 12 and further comprising the
steps of
imparting to the crusher head a gyratory movement having an eccentric
radius, and
starting the crusher up at a pre-determined crushing gap width
which amounts to 25-50% of said eccentric radius.
14. The method according to claim 8 and further comprising the
steps of:
using a hydraulic piston-cylinder device as said hydraulic motor,
measuring said width by means of a position sensor which includes
a first part stationary in relation to a cylinder casing of said
piston-cylinder device, and a second part which is stationary in
relation to a piston of said piston-cylinder device, and transmitting
a position signal characteristic of the positions of said parts
in relation to one another, and therewith characteristic of the
position of the crusher head, from said position sensor to means
for calculating a preferred gap width.
Description The present invention relates to a method for controlling the crushing
gap width of a gyratory crusher of the kind which includes a crusher
head which is driven by a power unit and which for the purpose of
adjusting the crushing gap can be adjusted positionally in relation
to a crusher shell by means of a hydraulic motor, the method comprising
continuously determining the power consumption of the crusher, the
pressure load acting on the crusher head, and the width of the crushing
gap, and controlling the crushing gap width, above a pre-determined
minimum gap width value, in dependence on said power consumption
and said pressure load.
Such a method is previously known from, e.g., SE-B-411 102. According
to this publication the crushing gap width is adjusted, or regulated,
indirectly by determining a minimum value and a maximum value for
the power consumption of the power unit; alternatively, or in addition
thereto, determining a minimum value and a maximum value for the
pressure load on the crusher head; measuring the power consumed
and optionally the pressure load during a crushing operation; increasing
the crushing gap width stepwise, when the maximum value for the
power consumption or the pressure load is exceeded over a given
period of time, until the power consumption or pressure load has
fallen and lies immediately beneath said maximum value; decreasing
the crushing gap width again, until the maximum value for the power
consumption and/or the pressure load is exceeded; and then again
increasing the gap width, and so on. Thus, according to SE-B-411
102 the crushing gap width is, in principle, constantly set to the
smallest possible value permitted by the maximum power consumption
value and/or the maximum pressure load value. The aforesaid maximum
values thus also constitute set-point values.
In accordance with a further development of the known method, the
crushing gap is controlled indirectly by determining respective
upper and lower limit values for the power consumption of the power
unit, for the pressure load on the crusher head, and for the width
of the crushing gap, and measuring the power consumed by the crusher,
the pressure load, and the width of the crushing gap while the crusher
is at work. If the upper limit value for either the power consumption
or the pressure load is exceeded for a given period of time and
the prevailing gap width is smaller than the upper limit value for
the gap width, the width of the crushing gap is increased stepwise
until the prevailing power consumption and the prevailing pressure
load lie beneath said upper limit values therefor. If the lower
limit value for either the power consumption or the pressure load
is not exceeded for a given period of time and the prevailing gap
width exceeds the lower limit value for the gap width, the gap width
is decreased stepwise until the prevailing gap width is equal to
said lower limit value, or until said lower limit values for power
consumption and pressure load are exceeded before said gap width
has reached its lower limit value. Thus, the gap width of this alternative
embodiment is also adjusted so as to lie constantly as close to
the lower gap limit as is allowed by the limit values for the power
consumption and pressure load.
Although the aforedescribed adjustment methods constitute an advance
in relation to manual control, it can prove uneconomical to adjust
the crushing gap width in a manner such that the crusher will constantly
operate at the smallest possible gap width or as close as possible
to the lower limit of a pre-determined gap width range with regard
to the permitted power consumption of the crusher and/or the permitted
pressure load on the crusher head. Considerable increases in production
can namely be achieved through the agency of so-called interaction,
i.e. a process in which crushing is effected by the mutual crushing
action of ingoing lumps of material, one against the other, and
in which the width of the crushing gap can thus be allowed to exceed
considerably the cross-dimensions of the crushed material.
An object of the present invention is to provide a novel and advantageous
control method which will ensure that crushing is achieved in the
manner intended within the whole of the possible power output and
the possible pressure load range of the crusher, thus in principle
from idling power to a maximum permitted power output and from a
state of no load on the crusher head to a state of maximum load
thereon.
It has been discovered, in accordance with the invention, that
for each combination of power output and pressure load there is
found a correspondng crushing gap width at which the crusher will
crush material in an intended manner, e.g. when crushing a given
ore the crusher will provide maximum production of a crushed product
within a given size range. Accordingly, it is proposed in accordance
with the invention that when carrying out a method of the aforesaid
kind the width of the crushing gap is maintained, above said minimum
value thereof, at a setting essentiallly in accordance with a control
function which is conditionally dependent on both the power consumption
and the pressure load, and which is so selected as to provide an
intended crushing effect on the material being crushed.
The easiest way to determine the control function for a given material
to be crushed in a specific crusher is to run crushing tests in
the crusher which is to be used or in a similar crusher, partly
under conditions in which the pressure load is negligible and does
not change to any appreciable extent when changes occur in the crushing
gap width, e.g. by feeding dry and well-screened material, i.e.
material which is essentially free from fines, to the crusher, and
partly under conditions in which the pressure load changes appreciably
when changes occur in the crushing gap width, e.g. by feeding moist
and non-screened material to the crusher. When carrying out crushing
tests with dry, well-screened material, the material input feed
is set at a constant value and the crushing gap width is set to
a value in which the desired crushing effect is obtained to the
highest extent possible, i.e. a crushing effect in which a maximum
amount of material lies within a given desired particle size range,
while recording the corresponding gap widths and power consumptions.
The fact as to whether or not the desired crushing effect has been
achieved to the best extent possible can be checked by examining
the crushed material. Crushing tests are then carried out with the
dry, well-screened material at other material input feeds and the
crushing gap width is again set to a value at which the desired
crushing effect is obtained to the best extent possible, while again
recording the corresponding gap widths and power consumptions. The
values recorded with regard to gap widths and corresponding power
consumptions can then be plotted to provide a curve which illustrates
how the gap width should be changed in response to changes in power
consumption if the desired crushing effect shall be obtained to
the best extent possible. When crushing corresponding material which
is moist and where screening is deficient or incomplete, the input
material feed is set to mutually different values and the crushing
gap width is adjusted at each of these values in a manner to obtain
the desired crushing effect to the best possible extent, while determining
the power consumed by the crusher motor at said values. By comparing
these gap widths with the gap widths applicable to the same power
consumption according to the curve representing the dry and well-screened
material, it is possible to determine the additional gap width required
when crushing moist and incompletely screened material in order
to maintain the desired crushing effect to the greatest possible
extent at varying pressure loads. These additional values can be
used to plot a curve showing how the gap width shall be changed
with changes in pressure load, if the desired crushing effect is
to be achieved to the best possible extent.
The aforesaid curves can be expressed mathematically and inserted
in a control function which calculates the preferred width toward
which the crushing gap should be adjusted when crushing the material
concerned, and the control function may also contain stipulations
concerning the minimum gap size, so as to prevent physical contact
of the crusher head with the crusher cone, and also data concerning
a pressure calculation limit which is dependent on the natural weight
of the head and on the weight of the material present in the crusher,
and from which the extent to which the pressure load contributes
to the gap width shall be initially calculated. Such a control function,
in accordance with which the gap width is adjusted, can be expressed,
e.g., by the formula ##EQU1## in which S.sub.B =the gap set point
value in mm
E=the power output of the crusher motor in kW
P=a constant
Q=a constant
R=a constant
a=an exponent
T=pressure in MPa
T.sub.o =the pressure calculation limit in MPa
C.sub.T =a constant
I=minimum gap width in mm,
the constants P, Q and R being determined from said power consumption
curve and the constants C.sub.T and the exponent a being determined
from said pressure load curve.
One important advantage afforded by the invention is that it is
not necessary to control accurately the flow of material to the
crusher or the lump or particle size distribution of the material,
provided that the crusher is allowed to work within the limits of
its capacity. In order to avoid continuous adjustments to the gap
width, the width of the gap is preferably not adjusted until the
prevailing gap width has deviated from the preferred gap width calculated
in accordance with the control function to a predetermined extent,
suitably within the range of 2-15%, and for a pre-determined length
of time, suitably from 3 to 10 seconds. Overloading of the crusher
is avoided by increasing the gap width beyond the values calculated
in accordance with the control function, when the power consumption
and/or the pressure load exceeds pre-determined maximum values,
thereby avoiding interruptions in production as a result of triggering
a motor cut-out device or the like.
If the power consumption of the crusher motor falls rapidly to
a level corresponding to idling power, e.g. due to a temporary interruption
in the supply of material to the crusher, the control function is
conveniently blocked so as to maintain the gap width at the value
that prevailed when idling power was reached, until the time when
the power consumption has again risen above the idling level, e.g.
by re-starting the feed of material to the crusher.
Similarly, after an interruption in operation, the crusher is preferably
started-up with a gap width which substantially exceeds the minimum
gap width and which preferably corresponds to 25-50% of the eccentric
radius of the crusher head.
The invention will now be described with reference to the accompanying
drawings, while disclosing additional characteristic features of
the invention and advantages afforded thereby.
FIG. 1 illustrates control curves which are intended for controlling
a fine crusher in accordance with the invention and which derive
from tests carried out.
FIG. 2 illustrates schematically a crushing plant that can be controlled
in accordance with the invention.
FIG. 3 is a detailed illustration of the method applied when determining
the position of the crusher head, and therewith the gap width.
FIG. 1 shows two curves derived from the abovementioned control
function, where
P=79.64
Q=1.128
R=320.3
T.sub.o =2 MPa
C.sub.T =0.5
a=2 and
I=2 mm
The control function was determined by crushing tests in accordance
with the method described above on sulphide ore which had been coarsely
crushed to a particle size below 100 mm and which emanated from
L.ang.ngdalsgruvan, Sweden. The crushing tests were carried out
in a crusher of the Hydrocone No. 460 type from Svedala Arbr.ang.
AB having an electric motor with an idling power of 24 kW and a
rated power output of 150 kW. The control function was compiled
in order to produce, irrespective of the input feed of the material
to the crusher, a product which is crushed essentially to a maximum
such as to be suited for further comminution in a rod mill. At a
power consumption and a pressure load in excess of 130 kW and 7
MPa, respectively, the gap width of the crusher was increased beyond
the values calculated in accordance with said control function,
in order to avoid the risk of damaging the motor or crusher. In
FIG. 1 the broken-line curve is the power curve, and the continuous
line curve is the pressure curve, whereas the upper limits for use
of the control curves are marked with horizontal dashes. Controlling
of a crushing process in accordance with the above results in a
superior capacity at vaying flows, varying moisture contents and
varying particle size distributions, and will also result in but
small wear on wear elements, since such elements are utilized over
substantially the whole of their working area. It will be understood
that control of the crusher in accordance with the pre-determined
function is effected automatically with the use of electronic control
equipment.
The crushing plant illustrated in FIG. 2 includes a gyratory crusher
driven by an electric motor 1 and comprising a stationary, conicle
crusher shell 2 and a moveable, conicle crusher head 3. The crusher
head 3 is fixedly mounted on a post 4 the upper end of which is
journalled in a bearing (not shown) for axial movement while being
substantially immoveable in a radial direction. The bottom surface
of the post 4 rests, via a slide bearing 5 on the piston 6 of a
hydraulic piston-cylinder device, the cylinder of which is referenced
by numeral 7. The post 4 is journalled beneath the crusher head
3 in an eccentrically located opening in a journal device 8 which
is driven rotatably by means of the motor 1 via a transmission
shown generally at 9. When the bearing device 8 is rotated, the
crusher head 3 will therefore execute a gyratory movement, such
that the gap between the crusher shell 2 and the crusher head 3
will increase and decrease around the periphery of the head. The
journal device 8 may be made adjustable so as to enable the degree
of eccentricity of the opening receiving the post 4 to be changed,
and the post 4 together with the crusher head 3 can be raised and
lowered respectively, by feeding hydraulic fluid to and removing
hydraulic fluid from the cylinder 7 so as to adjust the width of
the crushing gap, by which is meant the smallest distance between
the outer surface of the crusher head 3 and the inner surface of
the crusher shell 2 as is conventionally meant in the parlance
of such crushers.
Located adjacent the upper part of the crusher shell is a shaft
10 through which material to be crushed is fed to the crusher. An
ultrasonic transmitter and receiver 11 12 monitors the supply of
material and detects any blocking of the shaft 10 and may also
be used for controlling the supply of material. The transmitter
and receiver are connected, via a conductor 13 to an electronic
unit 14 incorporated in an electronic control apparatus, and deliver
to the electronic unit signals which are characteristic of the state
of the shaft 10.
The reference 15 identifies a hydraulic-fluid tank which is connected
to the cylinder 7 via a conduit 16. Hydraulic fluid is fed to and
from the cylinder 7 by means of a pump 17 incorporated in the conduit
6. The pressure of the hydraulic fluid present in the cylinder 7
is continuously measured by means of a pressure meter 18 which
sends an analogue signal corresponding to the pressure load acting
on crusher head 3 to the electronic unit 14 via a conductor 19.
The reference 20 identifies a conventional so-called pressure accumulator,
which prevents the occurrence of unpermitted heavy pressure surges
in the hydraulic system, should, for instance, a broken-off digger
tooth or some other non-crushable object happen to pass through
the crusher.
An analogue signal corresponding to the power consumption of the
motor 1 is continuously determined sent to the electronic unit 14
via a conductor 21 whereas an analogue signal corresponding to
the position of the crusher head 3 in relation to the crusher shell
2 and thus corresponding to the width of the crushing gap, is similarly
continuously determined and sent to the electronic unit 14 over
a conductor 22. The reference 23 identifies a display and control
unit which is provided with means for selecting and programming
in a desired control function and to supply control signals to the
electronic unit 14 via a conductor 24 in response to the selected
control function, so that the electronic unit 14 in response to
said control function and in response to the signals arriving on
the conductors 19 21 22 produces a digital control signal on
a conductor 25 connected to the drive means of the pump 17. The
unit 23 receives, via a conductor 26 signals corresponding to given
states of the crusher plant, e.g. power consumption, pressure load,
crushing gap width etc., these signals being converted to visisble
data on the display part of the unit 23. It will be understood that
the control equipment for controlling the crusher plant in accordance
with the prevailing control function can be constructed in many
different ways, all of which can be readily realized by one skilled
in this art, and hence the control equipment will not be described
in detail here, particularly since the construction of such control
equipment, with the exception of the arrangement illustrated in
FIG. 3 forms no part of the present invention.
FIG. 3 illustrates in larger scale part of the piston-cylinder
device 6 7 illustrated in FIG. 2 and shows that the cylinder 7
comprises a lining 27 and an outer casing 28. The outer casing 28
is connected to a lower cylindrical end-wall 29 having provided
therein a channel 30 which connects the interior of the cylinder
with the hydraulic fluid conduit 16 illustrated in FIG. 2. The cylinder
7 is open at its top and the piston 6 located in the cylinder has
a considerable vertical extension and carries at its upper end surface
a part 31 shown in chain lines, of the slide bearing 5 described
with reference to FIG. 2 and intended for carrying the post 4 and
the crusher head 3. The piston 6 is hollow and comprises a cup-shaped
part 32 and a lid or cover member 33 which covers the downwardly
facing opening of the part 32. Seals 34 are provided peripherally
on the cover member 33 to prevent the leakage of oil between the
outer surface of the piston 6 and the inner surface of the lining
27. Due to the gyratory movement of the post-end resting against
the piston 6 via the journal 5 in combination with the heavy pressure
on the piston 6 caused by the weight of the post 4 and the crusher
head 3 and the pressure load on the crusher head during the crushing
operation, it is extremely difficult, however, to avoid leakage
of hydraulic fluid from the interior of the cylinder 7. Consequently,
it is not suitable to determine the position of the crusher head
3 and therewith the width of the crushing gap, by determining the
level of the hydraulic fluid in the tank 15 with the aid of a level
sensor, as in accordance with conventional procedures, since the
hydraulic fluid leaking from the interior of the cylinder 7 is not
returned to the tank 15 and consequently it is often necessary
to halt the crushing process in order to calibrate the level sensor
in relation to the prevailing or actual position of the crusher
head 3. This drawback is avoided with the arrangement according
to FIG. 3 in that the position of the crusher head 3 and therewith
the width of the crushing gap, is established by determining the
position of the piston 6 and the cylinder 7 in relation to one another.
This determination is not dependent on changes in the amount of
hydralic fluid in the hydraulic system due to leakages from or re-filling
of the system. A calibration need only be carried out at relatively
wide intervals, in order to compensate for wear on the wear surfaces
of the crusher shell and the crusher head. Thus, there is used in
the FIG. 3 embodiment a position indicator, generally referenced
35 which includes a first part 36 which is stationary in relation
to the cylinder casing 27 28 29 and a second part 37 which is
stationary in relation to the piston 6 and which is intended to
send to the electronic unit 14 via the conductor 22 shown in FIG.
2 a positional signal characteristic of the position of the two
parts 36 37 relative to one another and therewith characteristic
of the position of the crusher head 3. In the illustrated embodiment,
the position sensor includes a metal wire which is tensioned or
stretched in a protective tube 36 in the axial direction of said
tube and which is placed in vibration by means of a combined transmitter
and receiver carried by the cylinder end-wall 29 whereas the part
37 comprises a ring-shaped permanent magnet which encircles the
tube 36 and which is fitted to the cover member 33 of the piston
6 by means of a holder 39. The tube 36 extends through an opening
40 provided in the cover member 33 and into the interior of the
piston 6 the tube being accommodated within the piston in a further
tube 41 which is sealingly connected to the upwardly facing mouth
of the opening 40 and which is operative in preventing hydraulic
fluid from leaking into the interior of the piston 6. The arrangement
is such that the vibrations (the tones) transmitted and received
by the transmitter/receiver 38 are influenced by the magnet 37 such
that the vibrations (tones) become characteristic of the distance
between the transmitter/receiver 38 and the magnet 37. The transmitter
35 transmits an analogue signal to the electronic unit 14 via the
conductor 22 shown in FIG. 2 characteristic of said distance.
The invention is not restricted to the embodiment described above
with reference to the drawings, but can be realized in many ways
within the scope of the invention defined in the following claims. |