Note: Descriptions are shown in the official language in which they were submitted.
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MOBILE SCREENING UNIT
field of the invention
The present invention relates to a screening unit. More particularly, the
present
invention relates to a mobile screening unit for screening bulk material
containing
particles of different sizes into at least three different piles, each pile
containing
particles of substantially the same size,
Background of the invention
It is well known in the art that there are several technologies for screening
bulk
material composed of products such as moulds, composts, wood residues,
aggregates, etc. These technologies include the use of rotating screeners,
star
screeners, vibrating screeners, etc. The rotating screeners and the star
screeners
are much more performant with organic products, such as moulds, composts and
wood residues for example, for obtaining end products of small granular sizes
(1/2" and less, for example) and at high production rates (approximately 150
cubic yards/hour and more, for example). However, these types of screeners are
not compatible with inputs of great dimensions such as big rocks, big wooden
pieces or big cement blocks, because the latter can easily damage the screens
of
the rotating screeners or damage the stars and the shafts of the star
screeners.
Also known in the art are vibrating screeners which can be used for accepting
the
above-mentioned larger-sized products. These types of screeners are known to
be efficient for screening aggregates However, their production capacity for
obtaining end products of small granular sizes from organic materials is
fairly
limited. Also, the screens or the perforated plates used with these vibrating
screeners often get plugged up when the bulk material to be screened is humid.
In order to avoid the damaging of their rotating screeners or star screeners
which
are mostly used for screening organic material, several manufacturers will
often
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Use a vibrating screen placed over the material reserve used for feeding their
rotating or star screeners. This vibrating screen is primarily used for
carrying out
a primary screening of the inputs of great dimensions in order to then direct
the
bulk material, free of large debris, into the rotating screener, or star
screener.
However, in the prior art, the direction of flow of the bulk material onto the
vibrating screen is perpendicular to that of the reserve and that of the
rotating
screener, thus is perpendicular to the longitudinal axis of the screening unit
machine. This limits drastically the length allowable for the vibrating screen
due to
the maximal dimensions allowed for the screening unit for travelling on the
road.
In fact, the length of the screener is then limited to the width of the
screening unit
machine which is itself limited to 8'6" or 8"3" in most countries in order to
be
legally allowed to travel on the roads.
Since the length of the vibrating screener or of the vibrating screen is
limited, the
amount of material that can be unloaded therein with a loader or an excavator
is
also therefore limited. In fact, if the amount of material unloaded is too
great, it
causes an overflow of bulk material outside the vibrating screener at the
bottom
thereof because the retention time of the material is not sufficient enough
for it to
flow completely through the screen. An important amount of small-sized and
medium-sized product finds itself thus with the large-sized products of the
bulk
material. One must thus decrease the amount of bulk material unloaded onto the
vibrating screener or the vibrating screen in order to obtain a suitable
classification. Furthermore, the debris of great dimensions slide to the
bottom of
the vibrating screen, close to the location where the loader must position
itself for
unloading the bulk material on the same. The operator of the loader must thus
clean this area at frequent intervals in order to be able to feed the machine
in a
suitable and safe manner. All of the above factors lead to a decrease in
screening
productivity.
Furthermore, there exist vibrating screeners provided with two stages of
screening which enable to accept inputs of great dimensions at the upper stage
and carry out a selection of precise granular size at the lower stage.
However, the
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25='i 1-20'02 CA0101 ~
3
capacity of production of products in bulk and the capacity of screening of
humid
products is not as important with this type of screener as with star screeners
or
rotating screeners. ~ - _
,5 Known to the applicant are the following U.S. and foreign patents
which.describe
different screening processes and apparatuses: 517,724; 2,115,110; 2,36fi,222;
2,703,fi49; 2,864,561; 3,322,354; 4,256,572; 4,363,725; 4,86'1,481; 4,956,078;
4,983,280; 5,097,6'(0; 5,100,537; 5,106,490; 5,120,433; 5,234,564; 212642
{Australia); 64987 (lreland); 74896 {lreland); 285 882 {Germany); '(,553,667
i 10 (London);1488026 (U.S.S.R.).
Summary of the invention
An object of the present invention is to provide a mobile screening unit which
15 would overcome some of the above-mentioned problems, and would thus be an
improvement over the mobile screening units known in the prior art.
In accordance with the invention, the above object .is achieved by a mobile
screening unit for screening bulk material, said screening unit being
characterized
20 in that it comprises:
i - an elongated mobile support frame having a longitudinal axis;
- a first screener mounted to the support frame and extending
longitudinally thereon, the first screener having:
an inlet for receiving bulk material containing large-sized,
25 medium-sized, and small-sized particles,
a first outlet for releasing large-sized particles, and
a second outlet for releasing medium-sized and small-sized
particles, the first screener being used for screening the bulk material
along a first direction substantially parallel to the longitudinal axis of the
30 support frame;
- a second screener mounted to the support frame and extending
longitudinally thereon, the second screener having:
AMENDED SHEET
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an inlet for receiving medium-sized and small-sized particles
conveyed from the first screener,
a first outlet for releasing medium-sized particles, and
a second outlet for releasing small-sized particles, the second
screener being used for screening the medium-sized particles from
the small-sized particles along a second direction substantially parallel
to the longitudinal axis of the support frame;
- a feeding hopper mounted to the support frame for accumulating
bulk material, the feeding hopper having an inlet for receiving bulk material
and
an outlet for releasing bulk material;
- a feeding conveyor positioned to receive the bulk material released
from the outlet of the feeding hopper and convey the same in the first
direction
to the inlet of the first screener; and
- a transition conveyor mounted to the support frame and extending
longitudinally thereon, the transition conveyor being positioned to receive
the
medium-sized and small-sized particles released from the second outlet of the
first screener and convey the same in the second direction to the inlet of the
second screener.
Also according to the present invention, there is provided a screening method
for screening bulk material, said method being characterized in that it
comprises
the steps of:
a) accumulating into a feeding hopper bulk material containing large-
sized, medium-sized, and small-sized particles;
b) receiving in a first screener the bulk material from the feeding
hopper;
c) screening the large-sized particles from the medium-sized and the
small-sized particles along a first longitudinal direction;
d) conveying the medium-sized and small-sized particles along a
direction parallel to said first longitudinal direction;
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4a
e) receiving the medium-sized and small-sized particles conveyed in
step (d); and
f) screening the medium-sized particles from the small-sized particles
along a second longitudinal direction substantially parallel to the first
longitudinal
direction.
Preferably, step (b) comprises the step of receiving the bulk material in a
direction substantially parallel to the first longitudinal direction.
Preferably also, step (e) comprises the step of receiving the medium-sized and
the small-sized particles in a direction substantially parallel to the second
longitudinal direction.
The invention and its advantages will be better understood upon reading the
following non-restrictive description of a preferred embodiment thereof, made
with reference with the accomaanving drawings.
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Brief description of the drawings
Figure 1 is a side elevational view of the mobile screening unit according to
a
preferred embodiment of the invention, the mobile screening unit being shown
in
5 a transportation configuration.
Figure 2 is the same side view as in Figure 1, showing the mobile screening
unit
in a working configuration.
Figure 3 is a top view of the mobile screening unit shown in Figure 2,
Figure 4 is a perspective view of a vibrating screener suitable for use with
the
mobile screening unit of Figure 1.
Figure 5 is a partial top view of a disc screener suitable for use with the
mobile
screening unit of Figure 1.
Figure 6 is a perspective view of a star screener suitable for use with the
mobile
screening unit of Figure 1.
Figure 7 is a perspective view of a rotating screener suitable for use with
the
mobile screening unit of Figure 1.
Figure 8 is a perspective view of a double-stage vibrating screener suitable
for
use with the mobile screening unit of Figure 1,
Detailed description of a preferred embodiment of the invention
In the following description, the same numeral references refer to similar
elements. The embodiments shown in the figures are preferred.
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Moreover, although the present invention was primarily designed for screening
bulk material relating to the fields of compost, construction and demolition,
contaminated soils, wood waste/top soil, peat moss and the like, etc., it
could be
used in different fields for other screening purposes, such as in the food or
the
agricultural industry for screening bulk material containing grains of
different sizes
for example, as apparent to a person skilled in the art. For this reason,
expressions such as "pieces" and/or "blocks" and any other references and/or
other expressions equivalent thereto should not be taken as to limit the scope
of
the present invention and include all other objects and all other purposes
with
which the present invention could be used and may be useful.
In addition, although the preferred embodiment of the mobile screening unit as
shown comprises various components such as a feeding hopper, piling
conveyors, retractable side panels, etc., not all of these components are
essential
to the invention and thus should not be taken in their restrictive sense, i.e.
should
not be taken as to limit the scope of the present invention. ft is to be
understood,
as also apparent to a person skilled in the art, that other suitable
components and
cooperations thereinbetween may be used for the mobile screening unit
according to the present invention, as will be explained hereinafter, without
departing from the scope of the invention.
Furthermore, although the preferred embodiment of the first and second
screeners of the mobile screening unit as shown in the accompanying drawings
consist of a vibrating screener and a rotating screener respectively, it is
also to be
understood that the terms "vibrating" and "rotating" should not be taken in
their
restrictive sense, i.e. should not be taken as to limit the scope of the
present
invention, since other suitable screeners may be used respectively for the
first
and the second screener of the mobile screening unit depending on the
particular
applications of the mobile screening unit and the desired screening of the
different types of particles composing the bulk material, as also apparent to
a
person skilled in the art. For example, the first and second screeners may be
any
one of the following; a vibrating screener, a disc screener, a star screener,
a
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7
rotating screener, a satellite screener, a gyratory screener, or a double-
stage
vibrating screener, depending on the intended applications of the mobile
screening unit, as apparent to a person skilled in the art.
Moreover, expressions such as "large", "great", and "big" as well as any
equivalent expressions and/or compound words thereof, may be used
interchangeably in the context of the present description. The same applies
for
any other mutually equivalent expressions, such as "medium" and "average" for
example, as well as "small" and "fine", as also apparent to a person skilled
in the
art.
Finally, it is to be understood that the expression "particles", as used in
the
context of the present description, refers to various types of
objects/substances
which may be screened with the present invention, as also apparent to a person
skilled in the art and as will be explained hereinafter.
Broadly described, and referring to figures 1 to 3, the screening unit 1
illustrated
in the accompanying drawings is a mobile screening unit 1 for screening bulk
material 3 containing at least large-sized, medium-sized, and small-sized
particles 5,7,9. The screening unit 1 comprises a first screener 11, a second
screener 13, and an elongated mobile support frame 15 having a longitudinal
axis
17. The first screener 11 is mounted to the support frame 15 and extends
longitudinally thereon. The first screener 11 has an inlet 19 for receiving
the bulk
material 3, a first outlet 21 for releasing large-sized particles 5, and a
second
outlet 23 for releasing medium-sized and small-sized particles 7,9. The first
screener 11 is used for screening the bulk material 3 along a first direction
25
substantially parallel to the longitudinal axis 17 of the support frame 15, as
better
shown in figure 3. The second screener 13 is also mounted to the support frame
15 and extends longitudinally thereon. The second screener 13 has an inlet 27
for
receiving medium-sized and small-sized particles 7,9 conveyed from the first
screener 11, a first outlet 29 for releasing medium-sized particles 7, and a
second
outlet 31 for releasing small-sized particles 9. The second screener 13 is
used for
CA 02425408 2005-06-29
screening the medium-sized particles 7 from the small-sized particles 9 along
a
second direction 33 substantially parallel to the longitudinal axis 17 of the
support
frame 15, as also better shown in figure 3.
Although the first and second directions 25, 33 as illustrated in the
accompanying
drawings are directed in opposite ways, for example in figure 3, the first
direction
25 points to the left whereas the second direction 33 points to the right, it
is worth
mentioning that the mobile screening unit 1 and the components thereof, namely
but not exclusively the first and second screeners 11, 13, may be disposed
otherwise so that both directions 25, 33 point towards the same way, as
apparent
to a person skilled in the art, so long as the directions 25, 33 are disposed
along
the longitudinal axis 17 of the support frame 15, according to the present
invention.
As shown in figures 1-3, the mobile screening unit 1 comprises a feeding
hopper
35 for accumulating the bulk material 3. The feeding hopper 35 is preferably
mounted to the support frame 15 and extends longitudinally thereon between the
first screener 11 and the second screener 13, as better shown in figures 2 and
3.
The feeding hopper 35 has an inlet 37 for receiving the bulk material 3 and an
outlet 39 for feeding the first screener 11. As also shown, the mobile
screening
unit 1 preferably also has a feeding conveyor 41 positioned to receive the
bulk
material 3 from the outlet 39 of the feeding hopper 35 and convey the same in
the
first direction 25 to the inlet 19 of the first screener 11. Preferably also,
the
feeding hopper 35 comprises retractable rear and lateral side panels 43.
Similarly to the above-mentioned, it is worth noting that although the feeding
hopper 35 is preferably mounted between the first screener 11 and the second
screener 13 as illustrated in the accompanying drawings, the mobile screening
unit 1 and the components thereof, namely but not exclusively the feeding
hopper
35, and the first and second screeners 11, 13, may be disposed otherwise by
suitable cooperations thereinbetween, i.e. the feeding hopper 35 need not be
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necessarily located between the first and second screeners 11, 13, as apparent
to a person skilled in the art.
As shown in figures 1 and 2, the feeding hopper 35 is preferably positioned in
the
central portion of the mobile screening unit 1. The feeding hopper 35 is
intended,
among other things, to receive and to accumulate the raw bulk material 3 to be
screened. The bulk material 3 may be loaded onto the feeding hopper 35 by
appropriate feeding means such as a loader, an excavator, a mechanical shovel
or even an auxiliary conveyor for example. Preferably also, the bulk material
3 is
in turn fed to the first screener 11 by the feeding hopper 35. The feeding
hopper
35 preferably comprises two lateral side panels 43 and a rear side panel 43
mounted over the feeding conveyor 41 which enables to feed the first screener
11
equally and continuously. The lateral side panels 43 and the rear side panel
43
are preferably provided with appropriate pivoting devices enabling them to be
folded back during transportation of the mobile screening unit 1 in order not
to
exceed the maximal height allowable for circulation on the roads. The side
panels
43 are deployed in the working position, as shown in figure 2, in order to
increase
the capacity of the feeding hopper 35. The direction of flow of the bulk
material 3
in the feeding hopper 35, on the feeding conveyor 41, is preferably done along
the longitudinal axis of the support frame 15 which enables the feeding hopper
35
to have side panels 43 having a length of at least 12'. This enables, among
other
things, to load the feeding hopper 35 by the side of the mobile screening unit
1
with most models of loading shovels known in the industry (the shovels of the
loaders used in the industry have generally a length located between 9' and
12').
Preferably also and as better shown in figures 1 and 2, the mobile screening
unit
1 also comprises a transition conveyor 45 mounted to the support frame 15 and
extending longitudinally thereon. The transition conveyor 45 is positioned to
receive the medium-sized and small-sized particles 7,9 released from the
second
outlet 23 of the first screener 11 and convey the same in the second direction
33
to the inlet 27 of the second screener 13.
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Preferably also and as better shown in figures 1 and 2, the mobile screening
unit
1 comprises a recovering conveyor 47 mounted to the support frame 15 and
extending longitudinally thereon. The recovering conveyor 47 is positioned to
receive the small-sized particles 9 released from the second outlet 31 of the
5 second screener 13 and convey the same in the first direction 25 to an
outlet end
49 thereof.
Preferably also and as better shown in figures 2 and 3, the mobile screening
unit
1 also comprises a first piling conveyor 51 mounted to the support frame 15
for
10 receiving the small-sized particles 9 from the outlet end 49 of the
recovering
conveyor 47 and forming a pile 53 of small-sized particles 9 aside from the
support frame 15. The piling conveyor 51 is preferably movable with respect to
the support frame 15 between a folded position where it is folded against the
support frame 15 along the longitudinal axis 17 thereof and an extended
position
where it extends in perpendicular to the longitudinal axis 17 of the support
frame
15.
As better shown in figures 1-3, the mobile screening unit 1 preferably also
comprises a second piling conveyor 55 mounted to a rear end of the support
frame 15 for receiving the medium-sized particles 7 released from the first
outlet
29 of the second screener 13 and forming a pile 57 of medium-sized particles 7
at
the rear of the support frame 15, as better shown in figure 3. This piling
conveyor
55 is preferably movable between a folded position where it is folded against
the
rear end of the support frame 15, as better shown in figure 1, and an extended
position where it extends in the same line as the support frame 15, as better
shown in figure 2.
According to the particular embodiment of the invention illustrated in figures
1-3,
the first screener 11 preferably consists of a vibrating screener, such as the
one
illustrated in Figure 5, whereas the second screener 13 preferably consists of
a
rotating screener, such as the one illustrated in figure 7.
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In this particular case, the vibrating screener is preferably actuated by an
eccentric shaft with a counterbalancing weight and preferably comprises a
stage
of fingers 65 in order to carry out the primary screening of the large-sized
particles 5 contained in the bulk material 3, The stage in question of the
vibrating
screener is preferably composed of several sections of fingers 65 disposed in
a
cascading configuration, as better shown in figure 4, in order to create a
shaking
effect onto the bulk material 3 moving along the screener 11. Each section of
fingers 65 preferably contains a plurality of fingers 65 disposed in parallel
according to a desired spacing. Preferably, the bulk material 3 to be screened
is
unloaded directly at the inlet 19 of the first screener 11 on the first
section of
fingers 65 thereof by means of the feeding conveyor 41 cooperating with the
material reserve contained in the feeding hopper 35, thereby enabling a
constant
and continuous feeding of the first screener 11. It is worth mentioning though
that
the bulk material 3 can be unloaded directly at the inlet 19 of the first
screener 11
by other appropriate feeding means such as an excavator, a loader, a
mechanical
shovel or even an auxiliary conveyor for example. The direct loading onto the
first
screener 11 by these feeding means may be deemed more suitable if the bulk
material 3 to be screened might risk of blocking in the feeding hopper 35 or
either
damage it if it contains pieces which are excessively large andlor excessively
heavy.
The first screener is 11 intended, among other things, to remove from the bulk
material 3 the inputs of large dimensions, i,e. the large-sized particles 5,
such as
large rocks, stumps, cement blocks and other residues for example, before
conveying the rest of the material towards the second screener 13. The minimal
dimension of the large-sized particles 5 that one wishes to screen from the
bulk
material 3 with the first screener 11 is selected according to one's
particular
needs by adjusting the spatial restrictions imposed by the screening medium of
the first screener 11, such as for example, by varying the spacing between the
fingers 65 in the case of a vibrating screener. For example, in order to
screen
large-sized particles 5 having a minimal dimension of about 3" and more, the
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spacing between the fingers 65 of the vibrating screener could be selected
between approximately 2" and 3", as apparent to a person skilled in the art.
The substantial length of the first screener 11, made possible thanks to its
positioning along the longitudinal axis of the length of the screening unit
machine,
and the shaking effect created by the sections of fingers 65 positioned on
different levels, combine to increase the retention of the bulk material 3 on
the
vibrating screener and thus allow to maximize the quantity of material that
passes
through the fingers 65 of the vibrating screener, It is therefore possible to
obtain
an important production capacity while minimizing the losses of material (i.e.
medium and small-sized particles 7,9 which would otherwise get undesirably
screened along with the large-sized particles 5) at the exit of the vibrating
screener before conveying the rest of the material towards the second screener
13.
The large-sized particles 5 which do not pass through the fingers 65 of the
vibrating screener progress on the top of the latter until the end of the
screener
11, thanks to its oscillatory movement, and fall either directly at the front
of the
screener 11 in order to form a moderately-sized pile of large-sized particles
5, or
into a suitable piling conveyor (not shown) in order to be able to form a
greater
pile of large-sized particles 5, further away from the front end of the
support frame
15 so as to not interfere with the mobile screening unit 1. The resulting pile
of
large-sized particles 5 can, among other things, be used for commercial or
recycling purposes.
Furthermore, the mobile screening unit 1 according to the present invention is
devised so that the medium-sized and small-sized particles 7,9 that pass
through
the screening media of the first screener 11, such as the fingers of a
vibrating
screener for example, fall directly onto the transition conveyor 45. This
conveyor
45 is primarily intended to convey the material exempt of large-sized
particles 5
towards the second screener 13, along a direction substantially parallel to
the
longitudinal axis of the support frame 15~ As mentioned earlier, the second
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screener 13 may consist of a star screener, a rotating screener, a vibrating
screener or any other type of suitable screener, as apparent to person skilled
in
the art. The object of the second screener 13 is to separate the medium-sized
particles 7 from the small-sized particles 9 at an important production rate
and
without damaging the screening medium of the second screener 13 which is
generally, by virtue of its intended purpose, more fragile than that of the
first
screener 11. Indeed, the screening media of screeners intended to screen
coarser particles is often more robust than the screening media of screeners
intended to screen finer particles.
After the primary screening, the material released from the first screener 11
is
preferably exempt of any large-sized particles 5, so that the secondary
screening
can be easily carried out by a rotating screener for example, without risking
damaging the screening screens thereof. The secondary screening may also be
carried out by means of a star screener such as the one shown in figure 6 for
example, without the risk of damaging the stars or the star shafts thereof.
Moreover, the secondary screening may be carried out by means of another
vibrating screener for example. This latter approach turns out to be more
efficient
and quicker than with a rotating screener or a star screener when the material
to
be screened contains aggregates. Moreover, it is worth mentioning that the
second screener 13 may also be a double-stage screener, such as the one
shown in figure 8, comprising a first screening floor for screening the medium-
sized particles 7 from the small-sized particles 9 and a second screening
floor to
further screen the small-sized particles 9 into coarser small-sized particles
and
finer small-sized particles, thereby enabling the mobile screening unit 1 to
screen
bulk material 3 into four different categories,
Hence, It can be easily understood from the above-discussed that both the
first
screener 11 and the second screener 13 may be selected from the group
consisting of a vibrating screener, a disc screener, a star screener, a heavy-
duty
star screener, a rotating screener, a satellite screener, a gyratory screener,
and a
double-stage vibrating screener, depending on the applications intended for
the
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14
mobile screening unit 1, and the nature of the particles 5,7,9 being screened,
as
apparent to a person skilled in the art. A vibrating screener is also known as
a
'°screen box" and a rotating screener is also known as a "trommel
screener". All of
the above-mentioned types of screeners are well known in the art and thus,
their
working principles need not to be explained herein.
Since both the first and second screeners 11,13 are disposed substantially
along
the longitudinal axis 17 of the support frame 15 so as to enable increased
screening lengths thereof, and therefore enable increased screening capacities
thereof, and since the large-sized particles 5 of the bulk material 3 are
removed
at the first screener 11, the present invention enables to obtain an increased
screening rate at the second screener stage, than what is possible with the
mobile screening units known in the prior art which have screeners disposed
otherwise.
According to the present invention, the material exempt of large-sized
particles 5
which exits the first screener 11 is then conveyed to the second screener 13
along a direction substantially parallel to the longitudinal axis 17 of the
support
frame 15 in order to separate the medium-sized particles 7 from the small-
sized
particles 9 more adequately and at a high screening rate, preferably at a rate
of
150 cubic yards/hour and more, The small-sized particles 9 which pass through
the screening media of the second screener 13 (bed of stars, screens, sections
of
fingers, etc,, depending on the type of second screener 13 being used) are
then
picked up by the recovering conveyor 47 that preferably passes under the
secondary screener, as better shown in figures 1 and 2. As explained earlier,
the
recovering conveyor 47 then preferably unloads itself at its outlet end 49
onto a
piling conveyor 51 of small-sized particles. In the transportation
configuration of
the mobile screening unit 1 as shown in figure 1, the piling conveyor 51 of
small-
sized particles 9 preferably folds itself towards the front of the support
frame 15
along the longitudinal axis thereof. In the working configuration of the
mobile
screening unit 1 as shown in figure 2, the piling conveyor 51 preferably
unfolds
itself perpendicularly to the longitudinal axis 17 of the support frame 15 in
order to
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distance the piling of the small-sized particles 9 so as to produce a
substantially-
sized pile 53 of small-sized particles 9 which will be far away enough from
the
mobile screening unit 1 so as to not interfere therewith,
5 The medium-sized particles 7 that do not pass through the screening medium
of
the second screener 13 are rejected at the end of the latter in order to then
be
preferably picked up by the piling conveyor 55 of medium-sized particles 7
located along the longitudinal axis of the screening unit machine, at the rear
end
of the support frame 15, as better shown in figure 2. The piling conveyor 55
10 preferably folds itself at the rear end of the support frame 15 for
transportation
purposes, as better shown in figure 1. In order to distance the piling of the
medium-sized particles 7 far away enough from the mobile screening unit 1 the
piling conveyor 55 unfolds itself at the rear of the support frame 15 in the
working
position, as shown in figure 2. This configuration helps to create a larger
pile of
15 medium-sized particles than would be possible if no piling conveyor 55 was
used.
When the screening cycle of the mobile screening unit 1 is over, the bulk
material
is then classified into at least three different piles, each pile containing
particles of
substantially the same size, as better shown in figure 3. The first pile 58
contains
large-sized particles 5 and is preferably located at the front of the mobile
screening unit 1, at the exit of the first screener 11, The second pile 57
contains
medium-sized particles 7 and is preferably located at the rear of the mobile
screening unit 1, at the exit of the second screener 13. The third pile 53
consists
of small-sized particles 9, and is preferably located perpendicularly to the
middle
of the support frame 15 on the side of the mobile screening unit 1,
As better shown in figure 1, the support frame 15 preferably comprises a
coupling
device 59 for removably coupling the support frame 15 to hauling means (not
shown) and a wheeled assembly 61 operatively connected to the support frame
15 for allowing transportation of the screening unit 1 by the hauling means,
such
as a tractor-trailer for example. Indeed, the mobile screening unit 1
preferably
comprises a set of axles and wheels, a suspension system, a suitable braking
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system, and signaling devices, all of which are preferably compliant for safe
transportation on roads and highways. The mobile screening unit 1 in its
transportation configuration, as shown in figure 1, preferably complies also
with
road requirements in terms of length, width and height allowable, by virtue of
its
foldable components, as well as due to the longitudinal disposition of the
first and
second screeners 11,13,
As also shown in figure 1, when the mobile screening unit 1 is in the
transportation configuration, the piling conveyor 51 of small-sized particles
9 is
folded back along the longitudinal axis 17 of the support frame 15, the piling
conveyor 55 of medium-sized particles is folded back on itself at the rear end
of
the support frame 15, and the side panels 43 of the feeding hopper 35 are also
folded back in order to comply with the maximum height, length and width
dimensions required by the Highway Code.
As shown in figures 1 and 2, the support frame 15 also preferably comprises
hydraulic support legs 63 for stabilizing the support frame 15 of the mobile
screening unit 1 during stationary work operation of the screening unit 1.
As mentioned previously, it is worth mentioning once again that the second
screener 13 may be a double-stage screener comprising a first screening floor
for
screening the medium-sized particles 7 from the small-sized particles 9 and a
second screening floor to further screen the small-sized particles 9 into
coarser
small-sized particles and finer small-sized particles, thereby enabling the
mobile
screening unit 1 to screen bulk material 3 into four different categories.
According to the present invention, there is also provided a screening method
for
screening bulk material, the method comprising the steps of a) receiving bulk
material containing large-sized, medium-sized, and small-sized particles; b)
screening large-sized particles from medium-sized and small-sized particles
along a first longitudinal direction; c) receiving medium-sized and small-
sized
particles obtained in a step (a); and d) screening medium-sized particles from
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small-sized particles along a second longitudinal direction substantially
parallel to
the first longitudinal direction.
Preferably, step (a) comprises the step of receiving the bulk material in a
direction
substantially parallel to the first longitudinal direction. Preferably also,
step (c)
comprises the step of receiving medium-sized and small-sized particles in a
direction substantially parallel to the second longitudinal direction.
As may now be appreciated, the mobile screening unit 1 according to the
present
invention is an improvement over the prior art in that, as discussed
hereinabove,
both the first and second screeners 11,13 are disposed substantially along the
longitudinal axis 17 of the support frame 15 so as to eriable increased
screening
lengths thereof, and therefore enable increased screening capacities thereof,
and
since the large-sized particles 5 of the bulk material 3 are removed at the
first
screener 11, the present invention enables to obtain an increased screening
rate
at the second screener stage, than what is possible with the screening units
known in the prior art which have screeners disposed otherwise.
Furthermore, the mobile screening unit 1 according to the present invention is
also advantageous in that the flow of the bulk material 3 into the first
screener 11
is carried out in the same direction as the flow of the material in the
feeding
hopper 35, that is, substantially along the longitudinal axis 17 of the
support
frame 15. This enables to obtain a greater first screener length when compared
to
a screening unit having a first screener whose flow of material is done
perpendicularly to the flow of product in the material reserve (feeding
hopper) and
thus perpendicularly to the longitudinal axis of the machine. As discussed
previously for the prior art, a flow of material in a first screener done
perpendicularly to the flow of material in the material reserve will often
result in an
overflow of material in the first screener. The disposition of the first
screener 11
according to the present invention, and the screening carried out therealong,
as
explained hereinabove, overcome the above-mentioned problem associated to
the prior art.
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The mobile screening unit 1 according to the present invention is also
advantageous over the prior art in that the longitudinal disposition of the
first and
second screeners and of the conveyors allow for an easier maintenance, repair
and/or part replacement thereof.
The mobile screening unit 1 according to the present invention is also
advantageous over the prior art in that the longitudinal disposition of the
screeners and of the conveyors enable to increase substantially the length of
the
screeners, while respecting the maximal dimensions allowed by the Highway
Code, contrary to the machines whose first screener lengths are perpendicular
to
the longitudinal axis of the screening unit (the length of the screener is
thus
limited by the width of the screening unit).
Furthermore, this increase of the length of the screeners due to their
longitudinal
disposition according to the present invention enables to unload more material
at
once on the screeners while having an increased quality of screening, which
results in an increased production capacity and rate, without damaging the
screeners used to obtain particles of smaller sizes from bulk material
containing
large-sized particles, such as big rocks, stumps, cement blocks and the like.
Of course, numerous modifications could be made to the above-described
embodiments without departing from the scope of the invention as defined in
the
appended claims.
