Note: Descriptions are shown in the official language in which they were submitted.
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_GRADING PLANT
The invention relates to a grading plant comprising
a self-cleaning screen for lump materials retaining oversize
fractions compared wi-th a predetermined material size, the
screen being displaceable by means of a moving device backwards
from a horizontal sorting position to a vertical discharging
position, and forwards back to the sorting position, the screen
being guided in tracks with a horizontal portion and a curved
downwards directed portion in connection with the horizontal
portion.
Such grading plants are utilized to retain oversize
fractions of lump materials which are to be carried
through stone crushing plants and used e.g. for levelling
on bui]ding and constructions sites.
T~e operation of crushing plants may from time to time
be stopped during long periods caused by jamming of too big
blocks between the breaker plates. Removing of such blocks
may be very work consuming and take a long time during which
20 the production of the crushing plant will be strongly reduced.
Thus, a strong demand exists to provide equipment which can
sort out oversize fractions of rocks before the materials are
put into the crushing plant, thereby ensuring continuous
operation.
At constructions sites where lump materials are taken out
for later use as filling materials by levelling works, road
building, etc., it is desireable to be able to carry out a
safe construction of such base layers by as far as possible
using approximately homogeneous materials ensuring the
stability. By retaining undesired fractions, this may to a
great extent be achieved.
US-PS Nos. 2 396 954, 2 690 840 and 3 402 816 disclose
grading plants with screens pivoted upwards for discharging
retained fractions. The patent specifications disclose a screen
which may be pivoted about an axis at one end of the screen.
This means that the distance from the place where the sorted
fraction falls down to t~at place where the retained fraction
is discharged is comparatively small. Discharging of the
retained fraction demands by certain solutions a high amount
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of force, depending on the quantlty of the fraction which
is to be discharged. Discharg:Lng is ef~ec~ed ~y means of
engine and mechanical trans~issions or hydraulically.
US-PS 1 685 823 discloses a screen which is movable
on wheels along a track containing a horizontal p~rtion and
a curved portion, whereby the screen is pushed until the
wheels are in the curved part, whereby the retained fraction
is discharged and a spring is tensioned, which spring there-
upon moves the screen back to the star-ting position. As the
entire screen with its relativeiy large weight is pivoted so
that the center of gravity is displaced a considerable vertical
distance downwards, a disproportional strong spring is
required to absorb sufficient energy as to move the screen
back to the correct starting position.
N0-PS 117 159 discloses a screen with two pairs of
wheels where the pairs are guided in straight tracks forming
an acute angle relative to each other. This solution gives
an uncontrolled discharging of the screen, as the motion of
the screen towards the discharging position starts when the
weight on the protruding part of the screen exceeds a
certain value, whereas the returning motion of the screen
starts when the weight balance ùpon discharging of the
retained fraction is displaced so much that the center of
gravity no longer is located in the protruding part. To
start the discharging motion of the screen, the materials
preferably have to be put on the protruding part of the
screen.
The return motion of the screens according to the two
last mentioned patent specifications is not ensured to be
executed quite forwards to the sorting position.
It is an ob~ect of the present invention to provide a
grading plant which ensures effective discharging of the
retained fraction at a safe distance from the position where
the sorted fraction falls down and to ensure a correct return
motion of the screen to the starting position, combined with
a simple and rugged design.
The grading plant according to the invention is of the
type set forth above and is constructed as a portal where the
transportation lorry may be placed for collection of the
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sorted fractions. Basically, the invention provides a gradi.ng plant including
a self-cleaning screen for receiving lump materials and retaining oversize
fractions thereof a~ove a predetermined sizeJ movement means for displacing
the screen from a horizontal sorting position to a vertical discharging
position and back to the sorting position, and tracks for guiding the screen
during its displacement, said tracks having a horizontal portion and a
curved, downwardly directed portion connected to the horizontal portion,
comprising: a carriage, bearings for pivotally supporting the screen approxi-
mately in a lateral center of gravity axis in the sides of the carriage,
first wheels attached to th.e sides of the carriage in rolling engagement
with fixed horizontal beams of the grading plant below the sides of the
carriage to enable its horizontal displacement,and two second wheels attached
to the rear end of the screen and individually guided in the tracks provided
with each horizontal beam, the screen being in a position for discharging
the retained fractions when the second wheels are in a lower part of the
curved portion of the tracks, and in a sorting position when the second
wheels are in a forward part of the horizontal portion of the tracks.
Preferably, the movement means comprises two symmetrically
arranged wires each attached at one end to a bracket at a rear end of each
beam, guide discs for the wires attached to a front end of the carriage,
guide pulleys for the wires fixed relative to each beam at opposite sides
of a longitudinal axis of symmetry of the carriage, and a movable disengage-
ment lever connected to the other ends of the wires, whereby movement of the
lever away from the carriage causes tens:ion of the wires and, by pressure
exerted against the discs, displaces the carriage in a direction away from
the lever and towards the rear end of the beams.
Preferably also, the discs are individually mounted on two locking
means locking the carriage when the screen is in the sorting position, each
'B~
locking means comprising a plate pivotally mounted to the front end of the
carriage and having a hook biased by a spring, acting on the plate, into
engagement with a corresponding hook mounted on the beam, the locking means
releasing the carriage in response to the wires being tensioned by moving
the disengagement lever in a direction away from the carriage.
The grading plant may further comprise a return spring mounted on
the rear end of each beam for absorbing the kinetic energy of the carriage and
the retained fractions on the screen, and for releasing said energy to
return the discharged carriage back to its sorting position.
In another emhodiment, the movement means comprises a double-
acting hydraulic cylinder mounted on each beam in the longitudinal dirèction
thereof, and a piston of the cylinder connected to the carriage for implementing
a reciprocating motion of the carriage.
In the following the invention will be further described by way of
example with reference to the accompanying drawings) in which
Fig. 1 illustrates a side elevation of the grading plant;
Fig. 2 illustrates a plan view of the wire arrangement;
Fig. 3 shows a detail illustration of the plate of the locking
arrangement; and
Fig. 4 shows in perspective an embodiment with hydraulic cylinders
for the motion of the carriage.
A carriage 2 can roll on beams 1 by means of wheels 4. The
carriage 2 comprises a frame and has a screen 3 which is arranged within the
frame and is pivotally mounted in pivoting supports 13 in the center axis of
gravity. On the screen 3 are mounted two wheels 5 which can roll on a horizontal
portion 11 and a curved portion 12 as a continuation thereto of a track mounted
to each beam. Rock materials are filled into the screen 3 and the sorted
fraction is falling down through the screen on a su;table transportation
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4a
machine ~not shown~ below the heams 1, within the portal of the grading
plant. The loading machine e.g. a shovel loader, which has delivered the
materials on the screen, thereafter pulls a disengagement lever 6 to the
left in Fig. 1, whereby a wire 7 is tightened, a locking plate 16 is turned
towards the axis of symmetry of the grading plant, there~y releasing the
locking plate 16, whereafter the carriage 2 with its load is forced to the
right in Fig. 1, caused by the tightening of the wire 7 between a pulley
8 and a wire bracket 10, and against a disc 9 on the carriage. When the
carriage is moved to the right in Fig. 1, the screen will stay in the same
position by means of the wheel 5 until the wheel 5 enters the curved portion
12 of the track, whereby the screen will be turned to a position wherein
the upper surface of the screen forms an angle of less than 90 with the
horizontal plane. Hereby the retained fraction
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will fall down on the right side of the grading plant as
shown in Fig. 1. When the screen achieves its discharging
position, the carriage 2 will have compressed a return spring
20, whereafter the spring 20 gives off its absorbed energy
by pushing the carriage 2 back to the left in Fig. 1. The
spring 20 has absorbed the energy from the carriage with
the retained fraction, and this energy is sufficient to
bring the carriage 2 back to the starting position, where the
screen 3 is in the sorting position and where a hook 15
on the locking plate 16 engages another hook on the beam 1,
thereby locking the carriage in this position. As the
carriage 2 moves back to the starting position, the disc
will tighten the wire 7 and bring back the disengagement
lever 6 to its vertical initial position. ~hen the carriage
2 is in the starting position, a spring 17 will press the
locking plate 16 so as to bring the hook on the locking plate
away from the axis of symmetry of the grading plant to engage
another hook (not shown) on the beam.
In another embodiment~ two double-aCting hydraulic
cylinders 18 are used to moye the carriage ~ from the starting
position wherein the screen 3 is in the sorting position, to
the rear position wherein the screen 3 is in the discharging
position. Thereafter the hydraulic cylinders 18 move the
carriage back to the starting position. The hydraulic
cylinders 18 have a fixed working cycle consisting of a
reciprocating motion. This working cycle may be started by
means of radio control or by means of a signal from a
mechanically activated electric switch, e.g. by the loading
machine.
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