Note: Descriptions are shown in the official language in which they were submitted.
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TITLE
LAMINATED SCREEN PLATE
This invention relates to screen plates, particularly in the mining and
associated
industries.
S BACKC,ROUND
In the mining and associated industries screen plates are used to separate
smaller
grades of the material passing over the n plate or breaker screens, which may
either be a flat vibratory piste or an arcuate plate do form portion of a
rotating
cylindrical drum.
Conventionally screen plates comprise a metal plate having a plurality of
holes
there through of the required size, which may be in one example of the order
of
50mm square to permit material of smaller size to pass there through from
larger
rocks and boulders passing over the screen plate. In one example breaker
screens form the screening surface of a large rotating drum of a diameter of
some 5
1 S meters with a screening length about 17 meters, the drum having a
throughput of
about 2 million tonnes per month.
The screen plates are typically metal plates 50mm thick with 50mrn square
holes
forming the perforated plate. Each plate is typically about 1.8 meters square
weighing over 1 tonne. The wearing surtace of the perforated plate has a hard
facing of plasma transfer arc welded tungsten carbide to a depth of 2-3 mm. In
use
the impact of large rocks of up to 300mm diameter causes spalling of the hard
and
brittle tungsten carbide thereby adversely affecting service life.
Hence it is an object of the invention to overcome one or more of the
deficiencies
of the prior wear resistant screen plates.
Z 5 A further object of the invention is to provide a material separation
member having
abrasion resistant qualities.
A further object of the invention is to provide a material separation member
possessing a wear resistant surface provided with perforations.
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A further object is to provide a mineral separation member constructed in such
a
way that the surface between the holes is covered by an assembly of wear
plates
that protirds ail surfaces in contact with the material passing through.
BRIEF STATEMENT OF THE INVENTION
S Thus there is provided aooonding to the invention a scxeen plate of
multllayer
construction comprising a structural member, referred to henceforth as a
carrier plate,
containing a plurality of openings and provided with a protective layer of
highly
wear resistant material with openings corresponding with those in the carrier
plate.
Preferably the carrier plate is a metal steel date.
Preferably the abrasion resistant material is in the form of a plurality of a
bi~metallic
composite parts, each consisting of an alloy white iron brazed to a mild steel
backing plebe, and in tum welded to the underlying carrier plate.
Preferably the abrasion resistant protective layer consists of a multiplicity
of
relatively small plates shaped and arranged on the carrier plate in such a way
that
they form a mosaic with the openings in it that match those in the carrier
plate.
Preferably the abrasion resistant plates overlap the edges of the holes.
Preferably the abrasive resistant plates are abrasive resistant white iron
brazed to
a mild steel base.
Preferably the abrasive resistant plates are welded to the carrier plate
around the
ZO holes to the under surface of the abrasive resistant members.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a developed plan view of a curved carrier plate showing the holes
in the
plate,
Figure 2 is a anss sectional view of the carrier plate of Figure 1,
2 S Figure 3 is a cross section of portion of the screen plate with abrasion
resistant
plates welded thereon,
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Figure 4 is a plan view of portion of the screen plate with the abrasion
resistant
plates in position,
Figure 5a, b, c. d. e. f. g. h. i show various shaped abrasion resistant
plates,
Figure 6 shows a preferred screen plate with square holes surrounded by
abrasion
n3sistant plates,
Fgure 7 is a cross-sectional view of the screen plate,
Figure 8 shows an example of one of the abrasion resistant plates, and
Figure 9 shows an example of a larger abrasion resistant plafie grooved to
facilitate
deliberate breaking into one or more smaller abrasion resistant plates,
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring t4 Figures I to 5 of the drawings the screen plate 1 comprises a
carrier
plate 2 having a plurality of screening holes 3 there through. In the example
the
screen plate is one of a plurality of curved screen plates to form a drum
through
which the material to be screened passes. Figure 1 shows a developed plan of a
1 S carrier plate while Figure 2 shows a typical Gross section of a curved
carrier plate.
The carrier plate 2 has a plurality of bolt holes 4 whereby the screen plate
can be
bolted to the structure supporting the Screen plate, in this case to the drum
sb~u~ure. 'me area extending diagonally across the babe with no screening
holes is due tv the substructure in the screen drum. Depending on the
structure of
the screen drum screening holes may cover the whole surface and also if the
screen plate is used as a flat sa een in other installations the holes may be
across
the whole plate, or have areas with no holes depending upon the supporting
shvcd~re.
To protect the surtaoe of the carrier plate abrasion resistant plates (ARP) 5
are
2 5 welded between the holes as shown in Flgure 4. As shown in the Figures
each of
the ARP are so shaped and dimensioned to overlap the edges of the holes in the
carrier plate, the holes teeing shown by dotted lines. The ARP 5 protect the
edges of the holes of the carrier plate.
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Each of the ARP 5 comprise a highly abrasive resistant material 6 such as
white
iron brazed to a backing plate 7 of mild steel, examples of this material are
sold
under the registered trade marks DOMITE and L~4MINITE. These are welded to
the carrier plate by welding from underneath into the overlapping portion by a
S bead of weld 8 extending around the edge of the hole 3, as shown is Figure
3,
and the under surtace of the backing plate 7. Preferably the edge of the hole
3 is
chamfered or bevelled to provide a greater area for welding.
In the example shown the ARP may be produced in various shapes to cover the
spaces between the holes. The majority of these would be the shape A,
however around the edges the shapes can vary as illustrated in Figures 4 and
5.
Also it is noted some of the shapes such as C, D and E are produced in right
and
left hand v~rsions.
With the oonstructlon of this invention, if any of the ARP become
unserviceable for
any reason, the ARP can be removed by grinding out the weld, and welding in a
1 S new ARP. This results in less downtime than in the prior systems where the
entire
plate weighing over one tonne has to be removed and replaced.
A preferred version of the invention is shown in Fgures 6, 7 and 8. The
carrier
plate 10 has spaced square holes 11 flame cut therein. in this embodiment the
ARP are rectangular and are sized to overlap the adjacent holes 11 to protect
the
edges of the holes as in the previous embodiment. The edges of the holes are
bevelled or chamfered to receive the welding bead welding the ARP to the
Carrier
plate 10.
Referring now to Figure 9, there is shown a larger ARP In the form of four ARP
of A
shape separated by grooves 12. In this way one or more ARP can be separated
2 S from the others by deliberate fracturing along the groove or grooves 12.
Although
the A shape is illustrated it is realised the concept can be applied to other
shapes,
particularly the shape shown in Figures 6, 7 and 8.
The larger grooved ARP thus covers a greater area resulting in reduced
welding.
There are a reduced number of gaps between each ARP thereby decreasing the
exposure of preferential wear in the gap of each opening. Less items per
assembly are required and the cast in grooves provide the ability to mould
into the
curvature of the carrier plate.
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While two embodiments of the Invention are described It is to be realised that
the
invention is not limited to these embodiments for the invention can be applied
to
quite a range of different applications where abrasive resistant screens are
required. Thus the hole sizes and shapes can vary, also th thickness of the
carrier
5 or base plate can vary depending upon the particular desired application of
use of
the screen plate. Also as described the invention can be applied ~ flat or
a,rrved
surfaces.
The ARP are welded to the base or carrier plate by welding the overlapping
portion to the bevelled edges of the holes in the base plate. Thus the size of
the
screen plate is determined by the spacing of the ARP, the size of the holes in
the
base plate being determined by the degree of overlap of the ARP over the
holes:
Thus each ARP is individually welds to the base or carrier plate and thus if
one or
more of the ARP are very severely damaged, they can be removed by grinding
out the weld and replaced. This then requires less down time compared with the
existing equipment where the whole panel has to be removed and replaced.
The ARP has definite advantages over the tungsten carbide plasma coating due
to the greater thickness of the white iron alloy a feature which ensures that
the
sidewalls of the screen openings are of the same wear resistant material as
the
surface, thus presenting a more durable edge to the screen openings than the
thin
layer of hard facing material which is known to spall away and expose the mild
steel
sub-strafe. During use the tungsten carbide plasma coating becomes damaged
particularly around the edge of the sd'een hole thus exposing the mild steel
carrier
plate which is thus exposed to abrasive attack. Also the ARP extend over the
edge of the hole in the carrier plate and thus the mild steel carrier plate Is
protected
from abrasive attack.
Although various embodiment of the invention have been described, the
invention
is not to be limited thereto but can include variations and modifications
falling within
the spirit and scope of the invention.
