Abstrict A gyratory crusher has two crushing shells (4 5) defining between
them a crushing gap (6). In operation, the crushing gap is adjusted
as a function of the determined crushing-shell wear calculated on
the basis of reference data on the established rate of wear of the
crushing shells (4 5) in previous crushing operations involving
the same or a similar raw material. To adjust the particle size
distribution of the crushed goods and obtain the desired particle
size distribution curve, the crusher is operated with brief periods
of alternatingly different settings of the width of the crushing
gap (6) and/or with alternating crushing power or crushing force.
Claims We claim:
1. A method for controlling a gyratory crusher having a frame supporting
a crushing head (3) with a first crushing shell (4), and a second
crushing shell (5) defining, together with the first crushing shell
(4), a crushing gap (6) whose width is adjustable by changing the
relative position of the first and the second crushing shell (4
5) in the axial direction by means of a hydraulic adjusting device
(15), the material to be crushed being introduced into the crushing
gap (6), and a driving device (10) causing the crushing head (3)
to execute a gyratory pendulum movement, said method comprising
the steps of adjusting the particle size distribution of the crushed
goods to the desired particle size distribution curve by operating
the crusher, such that the width of the crushing gap (6), periodically
and with preset operational time periods, changes between two crushing
gap settings, at least one of the two crushing gaps being determined
by a preset selected gap width (6) and at least one being determined
by a preset, selected maximum crushing power or maximum crushing
force; and, readjusting the relative positions of the crushing shells
(4 5) during the operational time periods by simultaneously monitoring
the relative axial position of the crushing head (3) in relation
to the frame of the crusher, and monitoring the set maximum crushing
power or crushing force.
2. A method as set forth in claim 1 comprising the step of operating
said crusher during the operational time periods with a set maximum
crushing power or crushing force while monitoring the relative axial
position of the crushing head (3) in relation to a frame (16) of
the crusher to avoid any direct contact between the two crushing
shells (4 5).
3. A method as set forth in claim 2 comprising the steps of controlling
the crusher during the operational time periods by selecting maximum
crushing power or maximum crushing force in such a manner that the
axial position of the crushing head (3) in relation to the frame
(16) of the crusher is readjusted to compensate for wear calculated
on the basis of reference data on the established rate of wear on
previous crushing operations involving the same or a similar raw
material.
4. A method as set forth in claim 1 comprising the steps of operating
the crusher with alternating periods of different crushing force
settings that are maintained by variations of the width of the crushing
gap (6).
5. A method as set forth in claim 1 comprising the steps of controlling
the crusher, during said operational time periods with maximum crushing
power or maximum crushing force selected in such a manner that the
axial position of the crushing head (3) in relation to the frame
(16) of the crusher is readjusted to compensate for wear calculated
on the basis of reference data on established wear ratios in previous
crushing operations involving the same or a similar raw material.
6. A method as set forth in claim 1 comprising the steps of monitoring,
during operation of the crusher, the axial position of the crushing
head (3) in relation to a frame (16) of the crusher to avoid any
direct contact between the two crushing shells (4 5), and by operating
the crusher with periods in which the crushing force is substantially
maintained by variations of the width of the crushing gap (6).
7. A method as set forth in claim 1 comprising the steps of operating
the crusher with periods of substantially constant crushing power
being maintained by variation of the width of the crushing gap (6).
8. A method as set forth in claim 7 comprising the steps of monitoring,
during operation of the crusher, the axial position of the crushing
head (3) in relation to a frame (16) of the crusher to avoid any
direct contact between the two crushing shells (4 5) and further
characterized by readjusting, during the operational period with
substantially constant crushing power and the operational period
with set width of the crushing gap (6), the relative position of
the crushing shells (4 5) by simultaneous monitoring of the axial
position of the crushing head (3) in relation to the frame (16)
of the crusher and monitoring of the set maximum crushing power,
and readjustment of the axial position of the crushing head (3)
in relation to the frame (16) of the crusher on the basis of reference
data from previous crushing operations involving the same or a similar
raw material.
9. A method as set forth in claim 7 comprising the steps of monitoring,
during operation of the crusher, the axial position of the crushing
head (3) in relation to a frame (16) of the crusher to avoid any
direct contact between the two crushing shells (4 5) and by readjusting,
during the operational period with set width of the crushing gap
(6), the relative position of the crushing shells (4 5) by simultaneous
monitoring of the axial position of the crushing head (3) in relation
to the frame (16) of the crusher and monitoring of the set maximum
crushing power, and readjustment of the axial position of the crushing
head (3) in relation to the frame (16) of the crusher on the basis
of reference data from previous crushing operations involving the
same or a similar raw material.
10. A method as set forth in claim 7 comprising the steps of monitoring,
during operation of the crusher, the axial position of the crushing
head (3) in relation to a frame (16) of the crusher to avoid any
direct contact between the two crushing shells (4 5) and by so
controlling the crusher, during operational periods with a relatively
broad crushing gap (6), either set at a predetermined value or maintained
at such a setting that it gives the desired set crushing motor power,
that the relative position of the crushing shells (4 5) is readjusted
by simultaneous monitoring of the axial position of the crushing
head (3) in relation to the frame (16) of the crusher and monitoring
of the set limit for the crushing motor power, such controlling
of the crusher being performed by readjustment of the axial position
of the crushing head (3) in relation to the frame (16) of the crusher
to compensate for wear calculated on the basis of reference data
on the established rate of wear on previous crushing operations
involving the same or a similar raw material.
Description The present invention relates to a method for controlling a gyratory
crusher so as to maintain a substantially constant crushing gap
or to adjust the particle size distribution of the crushed goods,
or both to maintain a substantially constant crushing gap and to
adjust the particle distribution of the crushed goods.
The invention relates to a gyratory crusher having a crushing head
with a first crushing shell, and a second crushing shell defining,
together with the first crushing shell, a crushing gap whose width
is adjustable by changing the relative position of the first and
the second crushing shell in the axial direction by means of a hydraulic
adjusting device, the material to be crushed being introduced into
the crushing gap and a driving device causing the crushing head
to execute a gyratory pendulum movement.
In the operation of such gyratory crushers, the crushing head is
so adjusted that a certain predetermined width of the gap between
the first, inner crushing shell and the second, outer crushing shell
is obtained. The adjustment operation is performed manually and
in such a manner that there is a certain safety margin up to maximum
permissible crusher load. Since the load on the crusher will vary
during the crushing operation, too narrow a gap would involve the
risk of overload on the crusher with ensuing damage. As crushing
proceeds, the shell surfaces are worn, which increases the gap width,
thereby reducing productivity. To counteract this development, the
axial position of the crushing head is adjusted gradually, either
manually or automatically, to obtain the gap width as originally
set.
Swedish Patent Specification 8601504-7 (SE-B-456798) teaches a
method for controlling such a gyratory crusher in order to avoid
damage caused by caking in the crushing chamber between the outer
and the inner crushing shell. Caking may arise if the material is
supplied incorrectly or if the composition of the material supplied
is not right (e.g. if the material contains too much moisture or
too many pieces of stone which are harder than the remaining material).
Thus, caking may cause high, but brief load peaks resulting in brief
pressure increases, so-called pressure surges. Prior-art crushers
are therefore equipped with a load-relieving system dealing with
such temporary load peaks. In the above Swedish patent, such a system
for dealing with temporary load peaks is combined with adjustment
based on a determined value of the number of pressure surges in
the hydraulic fluid of the adjusting device that exceed a predetermined
pressure level in a given period of time, the relative position
of the crushing shells being changed depending on this value to
increase the width of the crushing gap if the calculated number
of pressure surges exceeds a predetermined sum.
PCT Publication WO87/01305 discloses a readjustment of the width
of the crushing gap by now and then bringing the crushing shells
together to obtain a reference value for the subsequent adjustment
of the crushing gap during the next operational period. Thus, this
publication merely describes conventional calibration of a cone
crusher during a crushing operation.
EP-A-0 429 237 discloses a safety device for preventing overload
of the cone crusher with ensuing damage. In this device, the upper
part of the chamber housing of the crusher is pressed downwards
towards the main frame of the crusher. If there is an overload,
the downwardly-directed force is relieved by temporarily raising
the upper part of the chamber housing of the crusher. The use of
this safety device does not involve any controlled variation of
the crushing force.
Swedish Published Application 8601353-9 (SE-B456138) and the corresponding
U.S. Pat. No. 4856716 disclose a method for operating a cone crusher,
in which the power consumption, the pressure load on the crushing
head and the width of the crushing gap are continuously measured.
The measured values are then used for maintaining the width of the
crushing gap on a level above a determined minimum value by correlating
the power consumption and the pressure load in accordance with a
set formula.
The present invention represents an improvement of the invention
described in the above Swedish Patent Specification 8601504-7 (SE-B-456798)
and has, as one object, to provide safer and more effective control
of the operation of the crusher as well as an enhanced adjustability
in respect of the particle size distribution of the crushed goods.
This and other objects of the invention are achieved if the crusher
is operated in accordance with the method defined in the appended
claims.
In the inventive operation of a gyratory crusher having two crushing
shells defining between them a crushing gap, the width of the gap
is adjusted depending on the determined wear of the crushing shells.
The wear is calculated on the basis of reference data on the established
rate of wear of the crushing shells in previous crushing operations
involving the same or a similar raw material. To adjust the particle
size distribution of the crushed goods and obtain the desired particle
size distribution curve, the crusher may, in the method according
to the invention, be operated with brief periods of alternatingly
different settings of the width of the crushing gap and/or with
alternating crushing power or crushing force.
According to one aspect, the invention thus provides a method for
controlling a gyratory crusher of the type mentioned by way of introduction.
This aspect of the invention is distinguished by performing the
adjustment of the crushing gap depending on an estimated wear of
the crushing shells calculated on the basis of reference data on
the established rate of wear of the crushing shells in previous
crushing operations involving the same or a similar raw material.
According to this aspect of the invention, the gyratory crusher
is first calibrated, either by bringing the two shells of the crusher
into engagement with each other or by inserting a piece of lead
or some other spacing element between the shells. After a certain
period of crushing, another calibration is performed in the same
way to determine the axial displacement of the crushing head in
relation to the frame of the crusher required to regain the desired
width of the gap, thereby to enable determination of the rate of
wear under given crushing conditions. In the continued crushing
operation, the calculated rate of wear is then used as input data
for the control device of the crusher for automatically displacing
the crushing head in relation to the outer crushing shell to compensate
for the estimated wear. However, since the wear is not always the
same per unit of time, the adjustment should, by way of precaution,
be performed at a value slightly below the estimated value.
According to another aspect of the invention, the gyratory crusher
is controlled in such a manner that the particle size distribution
of the crushed goods is adjusted to the desired particle size distribution
curve. According to this aspect, the crusher is operated with alternating
brief periods of different settings of the width of the crushing
gap. For example, the crusher may be operated, during one operational
period, with a set maximum crushing power or crushing force and,
during another operational period, with a set constant width of
the crushing gap.
During the operational period with the set maximum crushing power
or crushing force, the axial position of the crushing head in relation
to the frame of the crusher should be monitored to avoid any direct
contact between the two crushing shells.
In an especially preferred embodiment of the invention, the relative
position of the crushing shells can be readjusted, during the operational
period with a set crushing power or crushing force and/or the operational
period with a set gap width, by simultaneous monitoring of the axial
position of the crushing head in relation to the frame of the crusher
and monitoring of the set maximum crushing power or crushing force,
and readjustment of the axial position of the crushing head in relation
to the frame of the crusher on the basis of reference data from
previous crushing operations involving the same or a similar raw
material.
The invention will be described in more detail below with reference
to the accompanying drawings, in which
FIG. 1 schematically illustrates a gyratory crusher with associated
driving, adjusting and control devices;
FIG. 2 contains a series of particle size distribution curves obtained
for different settings of the crushing gap at an approximately constant
gap width during the entire crushing operation; and
FIG. 3 is a diagram showing a desired as well as an attained particle
size distribution curve achievable by adjusting the crushing gap
in accordance with the invention.
In the embodiment illustrated, it is assumed that the position
of the crushing head (i.e. the position of the first crushing shell)
is changed when the relative position of the crushing shells is
altered, and that the width of the crushing gap is reduced when
the crushing head is lifted in the axial direction.
The gyratory crusher shown in FIG. 1 comprises a shaft 1 which
is eccentrically mounted at the lower end 2. At the upper end, the
shaft carries a crushing head 3. A first, inner crushing shell 4
is mounted on the outside of the crushing head. In the machine frame
16 a second, outer and annular crushing shell is mounted so as
to surround the inner crushing shell 4 with which it defines a crushing
chamber. This chamber is in the form of a gap 6 which in axial section,
as shown in FIG. 1 has a width that decreases downwards. The shaft
1 is vertically adjustable by means of a hydraulic adjusting device
15. The crusher also comprises a motor 10 which, in operation, causes
the shaft 1 and the crushing head 3 to execute a gyratory pendulum
movement, i.e. a movement during which the two crushing shells 4
5 approach one another along a rotating generatrix and move away
from one another along a diametrically opposed generatrix.
In operation, the crusher is controlled by a control device 11
which, at an input 12', receives input signals from a transducer
12 arranged at the motor and measuring the load on the motor. At
an input 13', the control device 11 receives signals from a pressure
transducer 13 sensing the pressure of the hydraulic fluid in the
adjusting device 15. At an input 14', the control device 11 in addition
receives signals from a level transducer 14 sensing the vertical
position of the shaft 1 in relation to the machine frame.
When the crusher is to be put in operation, a calibration is first
performed. Thus, the pump 18 pumps hydraulic fluid into the tank
7 until the shaft 1 has reached its vertically lowermost position.
In this position, the distance between the crushing head 1 and a
fixed point in the machine frame is measured. The measured value
is then supplied to the control unit as representing the distance
corresponding to the signal from the level transducer 14. Subsequently,
hydraulic fluid is pumped into the system from the tank 7 until
the inner shell 4 is applied against the outer shell 5. When the
inner shell thus comes into contact with the outer shell, there
is a pressure surge in the hydraulic fluid which is recorded by
the pressure transducer 13. In this position, the above distance
is measured and supplied to the control unit as representing the
signal from the level transducer 14 for this position. Knowing the
gap angle between the inner shell 4 and the outer shell 5 one may
then determine, with the aid of the two calibration values measured,
the gap width for any position of the shaft 1.
In this method, calibration is based on a position in which the
inner and the outer shell touch each other. However, it is possible
to base calibration on a position in which the crushing shells do
not touch but in which a set gap width has been established by measuring
with the aid of a piece of lead or some other spacing element introduced
into the gap. Otherwise, calibration is performed in a similar manner.
When the method according to the invention is utilised to achieve
automatic calibration and to maintain the crushing gap substantially
constant during the crushing operation, the wear of the crushing
shells is calculated. This is done by determining the distance of
displacement from the first manual calibration to the next manual
calibration (compared with the same reference gap) and taking into
consideration the time the crusher has operated under load (i.e.
not idling). Then, the displacement measured is divided by the operating
time, giving a measurement of the rate of displacement or wear,
e.g. in millimeters per hour.
With the knowledge of how much the shaft 1 has to be displaced
per unit of time owing to wear, the control unit 11 is, in continued
operation, caused to automatically compensate for the wear at regular
intervals, once per hour. For safety reasons, wear compensation
should not be carried out to the full, since the wear of the crushing
shells may vary with time. This is so because the abrading properties
of the crushed material are not constant, the size distribution
of the supplied material varies or the load of the crusher is not
constant. Several factors may concur.
After the first occasion of calculation mentioned above, the circuits
of the control unit are connected for automatic calibration. The
control unit adjusts the axial position of the crushing head depending
on the rate of displacement or wear measured. As a matter of precaution,
compensation may be carried out by a factor of e.g. 0.3 or 0.5 of
the estimated wear.
After a certain period of operation, another manual calibration
is performed to obtain a second occasion of calculation. The control
unit may be programmed not to make any new calculation prognoses
until there has been a displacement of e.g. 10 mm from the preceding
prognosis. If this manual calibration shows that the rate of wear
is lower than expected, the safety margins can be reduced so that
compensation for the estimated wear can be increased in subsequent
operation. If, on the other hand, the wear, and consequently the
rate of displacement, varies considerably with time (e.g. if different
types of goods or goods having highly varying properties are being
crushed), the safety factor may perhaps never be raised above e.g.
0.3. It may even be necessary to interrupt automatic calibration.
Naturally, manual calibrations can be performed whenever desired,
but calculations and subsequent check-ups should always be carried
out after a predetermined minimum distance of displacement (10 mm
in the above example) if measuring errors are not to have an adverse
effect on the result.
The automatic calibration described above is advantageous in that
it eliminates a common inconvenience, namely that the actual gap
increases as the shells are worn, despite the fact that the gap
set by the control device remains the same. In prior-art techniques,
the set gap is only correct for a brief period after calibration.
If automatic calibration is performed in accordance with the invention,
the control device 11 will gradually lift the main shaft 1 and reduce
the gap 6 such that the desired, set gap is maintained for a much
longer period of time. Thus, the actual gap will not increase as
rapidly as before, and much fewer manual calibrations of the gyratory
crusher are thus required when using the invention.
When using the invention, the control device 11 may also control
the crushing operation by maintaining a specific, selected crushing
power or crushing force. If, in this type of operation, use is made
of the above automatic compensation for wear, more time may elapse
between successive manual calibrations of the gap.
The control technique may be utilised if one wishes to obtain an
essentially constant size of the product as well as automatic compensation
for wear. If so, the crushing procedure begins with manual adjustment
of the gap until the desired product has been obtained. Then, power
and force are read, and the resulting values are then inputted as
maximum permissible power and force. The control device 11 will
then operate at the set power and force and automatic wear compensation
meaning that the control device 11 adjusts the main shaft 1 upwards
to compensate for the wear and to maintain the load.
When the invention is used for affecting the particle size distribution
of the crushed goods, the crusher should be operated during brief
periods of alternatingly different settings of the width of the
crushing gap 6. This aspect of the invention will be described in
more detail below.
If a gyratory crusher is operated with an essentially constant
crushing gap during the crushing operation, particle size distribution
curves of the type shown in FIG. 2 are obtained. If, for instance,
the gap is 24 mm, the particle size distribution curve farthest
to the right can be obtained during an operational period. Likewise,
the other curves can be obtained with gap widths of, respectively,
1 mm, 18 mm, 15 mm and 12 mm. When the gap width is altered, the
general shape of the curves is thus basically maintained, but there
is an anticlockwise angular rotation when the crushing gap is reduced.
However, one often desires to obtain particle size distribution
curves of completely different shapes and types, which may depend
on the purpose of the crushed product. The invention provides the
possibility of affecting the particle size distribution of the crushed
product by periodic alterations of the operational conditions.
FIG. 3 shows a desired particle size distribution curve for a product,
indicated by a full line. Such a curve cannot be obtained by crushing
with a constant gap in accordance with FIG. 2. However, the idea
is to combine two or more product yields into a new desired product
yield. In the method according to the invention, this can be achieved
by causing the control device to periodically change the gap width
between two set positions. These positions can be obtained by switching
between two different types of operational periods, namely a first
operational period in which the automatic setting system strives
to maintain constant a specific set high crushing power for a high
degree of crushing of the material through a comparatively narrow
crushing gap, and a second operational period in which the automatic
setting system strives to maintain constant a specific comparatively
broad set gap for a lower degree of crushing of the material. The
control device 11 can be programmed so as to provide switching between
these two operational positions at desired points of time. For instance,
the highest possible power and force can be allowed during one period
to give maximum crushing. The yield obtained during this period
may then contain enough fine material, while there is a lack of
coarse material. More coarse material can be produced by running
the second operational period with a larger gap than in the preceding
period. If the crusher is allowed to work for e.g. 60 s with the
narrow gap and 45 s with the broader gap, this results in two different
product yields which are physically separated immediately after
the crusher. After the customary few intermediate storages and reloadings,
the two yields are, however, mixed into a single product having
the desired distribution of fine and coarse material. The durations
of the different operational periods should be chosen while taking
into consideration the handling of the crushed goods after crushing,
as well as the agitation and mixing achieved during handling. Durations
of 30-120 s may be suitable, depending on the aimed-at particle
size distribution curve.
According to this aspect of the invention, the crusher can thus
be operated with a set high crushing power or crushing force during
the one operational period and operated with a set crushing gap
width during the other operational period. Alternatively, the crusher
may, during the one operational period, be operated with a set narrow
crushing gap and, during another operational period, be operated
with a broad crushing gap. In both instances, the crusher can be
operated while monitoring the axial position of the crushing head
in relation to the frame of the crusher in order to avoid any direct
contact between the two crushing shells. A third possibility is
to operate the crusher during different periods of alternating high
and low crushing power or crushing force.
In the above examples, use is made of two different sets of operation
parameters in the modification of the particle size distribution
of the crushed goods. If desired, use may, of course, be made of
three or more different sets of operation parameters to obtain additional
advantages.
Preferably, the crusher is however preset, during the operational
period with set maximum crushing power or crushing force, at a specific
chosen gap width. The relative position of the crushing shells is
then readjusted by simultaneous monitoring of the axial position
of the crushing head in relation to the frame of the crusher and
monitoring of the set maximum crushing power or crushing force,
as well as by readjustment of the axial position of the crushing
head in relation to the frame of the crusher on the basis of reference
data from previous crushing operations involving the same or a similar
raw material. |