CA1168162A - Screening apparatus - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

A sieve screen, for separating and/or deliquefying particulate material such as aggregates, comprises a plurality of apertured wire sieve elements secured together and/or to an underlying support structure by attachment means of synthetic plastics, rubber or other elastomeric material. Such an arrangement allows advantages of traditional sieve media, such as woven wire, perforated plate or wedge wire, to be realized in combination with those of newer materials, such as synthetic plastics. The attachment means comprise edge fitments or collars for individual metal sieve elements.

Description

~ he invention relates -to screening apparatus;
particularly for sizing and/or deliquefying particulate materials, such as aggregates, and is especially5 but not exclusively~ applicable to screenin~ apparatus having a flat or cambered sieve screen surface~
~ raditional materials for such scree~ing machines have included perforated metal plate~ looped or welded wedge-section wire, woven wire9 and welded meshO More recently, however~ sieve screens have been made o~
~ 10 sgnthetic plastics material9 such as pol~urethane~ either as one or more apertured plates stretched across the bed `~ of the machine, or as a plurality of separa-te screen modules which can be replaced individually. ~he selection of synthetic plastics screens in preference to tradi-tional metal scree~s is due mainly to their high wear resistance and quiet operation, the latter espeically when screening dry material~
: However, in some applications traditional metal "
screens may be preferred clue to their special charac-teristics. ~or example, in screening sticky materials, slurriesq and those with a high fines content, wear ra-te and noise may be o~ les~er im~ortance than resistance to blinding, high accuracy and maximum open area~
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- _ 3 _ ~ An object of the present invention is to provide screening apparatus ; for sizing and/or deliquefying aggregates which allows realisation of advantages of both synthetic plastics and traditional metal screening media.
According to the present invention there is provided a sieve screen for si~ing and/or deliquefying particulate material, comprising a plurality of apertured metal sieve elements and attachment means of synthetic plastics, ruhber or elastomeric material cooperating with edge portions of each sieve element to secure the elements together and/or to an underlying support structure, wherein the attachment means comprises a separate collar for each element and completely surrounding the element.
The sieve screen may comprise a plurality of similar modules, each comprising at least one said apertured metal sieve elements and associated synthetic plastics attachment means.
The metal sieve element may be secured to the attachment means by way of metal flanges~, tongues or other protrusions projecting from the periphery of the element, conveniently to a groove or slots in the attachment means.
In one embodiment the flange or tongue members extend in a plane which is substantially parallel to the screening surface. The flange or tongue member may then conveniently comprise one flange of a member of "L"
shaped cross-section, the other flange being secured to the apertured portion of the metal sieve element.
Alternatively the metal flange or tongue mem~ers may project downwardly from the periphery of the sieve element, i.e~ away from -that surface o~ the element which will be uppermost in use~
'rhe lower part of the or each depending flange or tongue may be lipped, curved, beaded or o-therwise :Eormed to positively engage the slot or groove so as -to resist remsval therefrom~
In a preferred embodiment, each sieve element comprises a plurality of wire~, typically of wedge-section~
~ecur0d side-by-side b-~ transverse ribs~ Flanges or tongue : 10 members which eætend in the direction of the ribs are secured to the ends of the wires, for example b~ welding, simi~ar members extending parallel to the wires ma~ then be secured to the e~ds of the transverse ribs or/and to the endmost wire adjacent that edge of -the element~
Preferabl~ the flange member~ ex*end co~tinuously alo~g each side of the element~ Where the element i~ of ~: cor~ered shape, ~or example recta~gular, with one or more : ~ ~langed members secured to each side thereof, adjacent flanged members may also be secured together at the corner.
Gon~enie~tly the flanged mem~er comprises a continuous ring around the eleme~t.
'~he attachment means may e3tend releasably around the entire peripher~ of the metal ~ieve element and have depending formatio~s to engage the support structure, for example lug~ to e~gage a lipped groove in the ~upport framer he attachment mean~ may be formed ~ a unitary member, , ~

or from a plurality of separate parts, for example two I~shaped parts which, fitted o~to the edges of the elemen-t~
form a comple-te collar. Such a plurality of separate par-ts may be separable from the metal sieve element, their engagement with the support structure and/or adjacent modules when installed9 bei~g arranged to maintain~ even e~lance, their interfitmen-t with the elements.
~he at-tachment mea~s ma~ be moulded directly onto the s edges~ e.g. flanges, of the metal sieve eleme~t t especially where the metal sieve elemen-t is made of apertured plate or wire mesha Where the sieve element is of looped or welded wed~e ~ire or the like, however, such direct moulding ma~
require steps -to be taken to limit penetration of the sieve aper-tures by the plastics material, for example by providing removable inserts in the apertures ad~acent the edges of the sieve element during moulding~
~he sieve elements ma~ comprise looped wedge wires secured to~ether b~ tie rods, an~ of -the various known rod end fitments being employed, such as nuts on threaded tie rods or rivetted ferrules~ ~hen, instead of a peripheral flange being provided, the ends of the tie rods may proaect beyond the edge of the metal sieve element and locate in recesses in opposed side parts of the attachment means. ~he endmost aligned loops o~ the element then pre~erably seat in grooves in the other ~1 r, :L~6~

opposed side parts of the attachment means. Advantageously the cross-section of at least a medial part of each groove is such as to retain the respective loops therein.
The aforesaid support structure of the screening apparatus may comprise a plurality of parallel support bars, the metal sieve elements being supported above and between the bars by the associated attachment means cooperating with a grid or lattice-like support frame of metal and/or synthetic plastics material, conveniently supported by the support bars, which preferably are aligned with cross-members of the lattice-work frame.
Embodiments of the invention will now be described by way of example only and with reference to the accompanying drawings, in which:-Figure 1 is a perspective partial view of one embodiment in which a sieve screen comprising a plurality of sieve elements is attached to a support frame in t.he form of a lattice;
Figure 2 is an exploded view of one of the screen modules of Figure 1 comprising a metal sieve element and surrounding synthetic plastics attachment collar;
Figure 3 is a partial cross-section on the line XX of Figure 2, with the metal sieve elem~nt and synthetic plastics attachment collar assembled together;
Figure 4 is a sectional view corresponding to Figure 3 but on the line ZZ of Figure 2;
Figures 5) 6 and 7 are views correspond.ing to Figures 2, 3 and 4 but of a second embodiment;
Figures 8 and 9 are detail views of a part of a metal sieve element;

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Figures 10 and 11 illustrate attachment of ~he metal elements of Figures 9 and 10 to a support; and Figure 12 is a partial sectional view of a modification applicable to the embodiments of Figures 8 and 9.
For convenience, in the drawings corresponding components in different views are identified by the same reference numeral.
Referring to Figure 1, a screening machine has a plurality of screen modules 10 assem~l!cd edge-to-edge to form a screening surface 12.
The modules 10 are secured to an underlying support frame in the form of a square lattice or grid 14. Each module obscures one hole 16 of the lattice, which is itself supported by :

,, ' ,:, support bars 189 of inverted "~" section, which extend longitudinally of ths bed o~ the machine and coincide with the cross~members of the lattice 140 The support bars 18 are carried by beams 20 which extend across the bed of the machine. If desired the heights o~ the support bars 18 ma~ increase towards the middle of the machine to cam~er -the screening surface~ At each longitudinal edge of the scree~ing surface a wedge~shaped pol~uretha~e wear strip 22 is provided betwee~ the machine side plates 24 and the adjacent screen modules so as to present an inclined surface 25 to di~ert aggregate i~wardly to the screening surface.
As sho~ in Figure 2~ each screen module 10 comprlses a metal sieve elemsnt 26 made up~of a pluralit~
o~ looped wedge-section wires 2~ secured side-by-side~
the looped being -thicker or "~og~;led" in known manner to define sleve apertures ~etween the wires~ ~hreaded tie rods 30 ex*end throu~h aligned loops of the wires - 28, ~hich are clamped together b~ ~uts 32 screwed onto opposite ends of the tie rods~ Alternative end fitme~ts, such a~ fer~ules, might be emplo~ed.
~ he sieve element 26 fits into a r~cta~gular attach ment collar 34 of s~nthetic plas~ics material, ~uch as pol~urethane. I~ the upper surface 36 of the collar is a ~quare recess 37 equal in ~ize to the wedge .~
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wire part o~ the element so as to acco~nodate the lat-ter with the upper surface of the wires level with that 36 of the collar 340 Opposite sides 38 and 40 of the attachment collar 34 each have a series of fiv0 register-ing holes 42~ immediatel~ beneath -the bottom of the recess 37 and spaced apart to accommodate -the ends o~ the tie rods 30 a~d associated nuts 320 As shown in ~igure 3, the holes 42 are stepped at 44, and dimensioned to conPorm to the tie rods and nuts~
~he other opposed sides ~6 and 48 of the a-ttac~men-t collar 34 have upwardly-opening grooves 50 and 52, respectively, to accommodate the endmost rows 54 and 56 of aligned loops of the wires 28~ As shown in Figure 4, - -the ~rooves 50 a~d 52 are of circul æ section and extend around a maaor portion of each loop to secure together that side o~ the attachment collar and the sieve element~
l ~he tie rods and nuts aæsociated with the endmost aligned il loops of wires are also acoommodated in holes 42 suitabl~
;~ aligned with the grooves 50.
i 20 It is envisaged -tha-t the looped wedge-wire sieve element might be pro~ided with a peripheral ~lange or tongues, extending outwardly or downwardl~ to engage in a suitable disposed groove or slots in the attachme~t collar 34. ~he flange or tongues might be welded to the wires 28 and~or to the tie rods 30, ~hich ~ight ex*end through ~uita~ly aligned holes in the flange.

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Figures 5, 6 and 7 illustrate the screen module 80 of a ~econd embodiment of the invention~ ~he screen module 80 is in~ended to fit a screenlng machine having a support ~rame 14~ supports 18 and beams 20 as disclosed in Figure 1~
~ach screen module 80 shown in ~igure 5 differs from those disclosed in ~igure 2 in that, instead of a metal sieve element made up of a plurality of looped wedge-sectio~ wires the screen module 80 comprise6 a rectangular metal sieve element 82 made up o~ a pluralit~
; o~ straight wedge-section wires 84 secured side-by-side .~ b~ spaced transverse ribs 86 (see Figures 6 and 7) extending across substantially the entire width o~ the ~-j element 82~ ~he ribs 86 are of rectangular cross-section , .
and are secured~ conveniently b~ resistance welding~ to : the undersides of the wires 84~
~he edges of the sieve eleIQen~ 82 are bounded by ~ metal ~lange members 907 92, 94 and 96, respectivelyO
I ~ach member is of "~" shaped cross-section and has one flange secured to the wire(s) 84 so that its other flange .1 extends outward1y from the element and generall~
parallel to the uppermost surface thereof.
~he two flange members 90 and 94 extending across the wires 84 are welded to an endmost one o~ the transverse rib~ 86~ (see Figure 6) which is secured to the wires 84 immediat~ly adaacent their ends~ Alternativel~ the flange ¦ members 90 and 94 could be welded directly to some or all I o~ the respective adjacent ends of the wires 84~
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The o-ther two flange members 92 and 96 ex*end across and are welded to some or all of, the opposite ends of the transverse ribs 86. If desired~ the~e flange members may also be secured direc-tly to the wire 84i (see Fîgure 7) adaacen-t the ends of -the ribs 86~
Ends of the flange members 90, 92, 94 and 96 are secured, e,g9 welded, to each other at the corners of the element to form a continuous ring. As can be seen from Figure 5, the ends oP the members 90, 92~ 94 and 96 are ; 10 mitred so -that -the corners oP the assembled element 82 are -truncated~ as at 97~
It will be appreciated that the flange members 90 96 could be at~ached to a sieve element of a diPPere~t t~pe e.g. the looped wedge wire t~pe desc,ribed with rePerence to ~igure 29 or woven mesh~ perforated plate or other apertured metalO
~ he sieve element 82 fits into a rectangular attachmen-t collar 98 of synthetie plastics materialq for example polyurethane. In the upper surface 100 of the collar i9 a square reeess 102 equal in length and width to the upper part of the sieve eleme~ 82 i.e~ as measured across the vertical flanges of members 90-96~ At a depth e~ual to the vertical flanges, the recess 102 opens into a slot 104, exte~ding into the collar and parallel to the plane oP the sieve eleme~t. ~he slot 104 is dimensioned ,~ .

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to receive9 and pre~erably grip, the outwardly-directed flanges of the elementO
It should be no^ted that the projecting flange need not extend alo~g the en-tire side of the element~ It is envisaged that a plurality of discrete flanges or tongues might be provided spaced around the periphery of the element~
~he slo-t 104 might still be continuous, al-though a more robust construction might be achieved where a corresponding pluralit~ of slots were provided~ each complementar~ -to the associated one of the discrete flanges or tongues.
The sieve elements ~ illustrated in Figure 8 and 9 have downwardly~projecting peripheral flanges 112~ each comprising a strip of metal welded to the edge of the -~ element so that its upper edge if level with the upper surface of the element and its lower edge projects below : the lower cross-rods 86. ~he sieve element shown in `i Figure 8 has onl~ two flanges extending one at each opposite edge o~ the element and pa~allel to the wires 84 Each flange i~ welded to the end~ of the cross~rods 86 as at 114, If desired. the i~ller surface of the metal strip fla~ge could also be welded to -the endmost wire.
l`he sieve eleme~t sho~ in Figure 9 is similar to that shown in Figure 8, but has flanges at all four edges of the element~ The flanges 116 extending parallel to the cross-rods 86 are ~Jelded to the e~ds of the wires 8 .~h. "~
and/or at their ends to the adjacent flanges ~4~.
~ he downwardly-proaecting portion 115 of the flar~ge is intended to fit into a vertical slot in the synthetic plastics attachment means~ relying upon the resilience of the material to grip and retain the fla~ge therei~
Improved security of the element in the attachment mea~s ma~ be obtained by suitable shaping of the depending portion of the flange~ for example by curving it i~wardly, as i~dicated by broken lines i~ Figure 8~
to form a lip 118~ which can the~ u~derengage a suitabls lug of the attachment means Where the elastic-ity of the attachment collar will enable it to be stretched sufficiently for fitting on~o -the sieve elemen~, the collar ma~J be moulded as a separate unitary member. Alternatively the collar may be for~ed by a plurality of parts~ for example two "~"
shaped parts which7 when assembled onto the edges o~ the ~ metal sieve element, will form a complete oollar. It i~ is also en~isaged that the attachme~t means might be 1 20 provided on onl~ two~ opposed~ sides of the sieve element, especiall~ where the latter is self-supporting e g.
looped or welded wedge wire, perforated plate, or woveu wirer Installation of the module on-to the support frame, ¦ with its outer ed~ abutting adjacent modules as shown in Figure ~ or Figure 7, will usuall~ ensure that the i 6~ .

attachment means, whether unitL~ry or not, does not di~
engage from the sieve element~ Specifically, that part of the collar above the slot 104 is prevented from flexing outwardly, to release the f]ange, by virtue of its abutting again~t the corresponding part of the ad~acent collar.
~he attachment collar has a peripheral depending skirt 1069 (not visible in Figure 23 the inner surface of which is undercut to form an i~wardl~ directed lug 108q which e~gage~ beneath a corresponding lip 110 ; ~ormed b~ an undercut sidewall of a groove 66 in the associated cross-member of the su.pport frame 14~ As can be seen from Figure 4, each groove 66 is of generally shaped cross-section to secure together the edges of two adjacent modulesh ~he inner surface 68 of the skirt 60 beneath the lug 62 ~lopes outwardl~ to assist flexing of the skirt and/or ~roove wall during installation b~ appl~ing downward~ pressure to the moduleO
The opposite edges of each attachment collar which, in use, will lie parallel to the material flow direction ma~ have upstanding lips 70, having inner wall~ 810ping upwardl~ and outwardl~ and vertical outer walls so that ~ the lip~ 70 o~ adjacent modules abut to form a truncated ; 25 triangul~r rib which serves to divert the material being ,~ ' ~LS~L~Z

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screened away from the aoint and towards the apertured portions of -the sieve elemen-ts~
Tlhe provision of a depe~ding skirt and grooved support frame is especially advantageous where the su-pport frame is at least partially of synthetic plastics material.
It should be appreciated, however, that alternative attachment means might be employed to secure the elements to the support frame~ ~or example~ discrete spigots or pegs might dèpend a-t intervals from the attachment collar to engage i~ corresponding holes i~ the support frame~
~: perhaps with pairs of spigots of adjacent modules i~ the same hole~ Alter~atively the edges of the attachment collars might have several semi-cylindrical recesses, stepped so that whe~ the edges of ad~acent modules are juxtaposed, the recesses form co~terbored holes through which headed spigots or studs are inserted to secure the modules to the support frame.
It should be noted that these alternative attachmen-t means could also be adap-ted to secure the edges of the metal sieve elements to the sy~thetic plastics attachme~t strips~
It is also envisaged that the synthetic plastics attachme~t means might be adapted to secure the modules to each other as well as, or even instead of, to the under-lying support structure~ ~hu~ the outer edges of the ,~ , ~L~l6~

collars might be castellated and the modules secured together by a rod or other elongate member extending through the inter-calated parts of adjacent modules.
It should be noted that the screen modules may cover more than one aperture of the lattice 14. In particular, a screen module may be any desired multiple of lattice apertures e.g. 4 by 41 4 by 1. If, as is envisaged, the screen module is attached only to the cross-members around its periphery, strip inserts may be installed in the grooves in intermediate cross-members, preferably conforming in cross-section to the groove, to prevent ingress and accummulation of the material passing through the superjacent sieve element.
Thus, it should be noted that the attachment means may itself be formed as a lattice or grid securing a plurality of the metal sieve elements together. Several such screen lattices might then be secured to a support frame as described herein-before.
As shoNn in Figure 10, juxtaposed flanges of adjacent elements are fitted into a common groove, the sides of the slot, being of resilient synthetic plastics material exerting a resili-entJ firm grip on the flanges.
Figure 11 illustrates a modification, wherein the grooves 136' in the attachment means have sidewalls undercut to provide lips 140, similar to those of the support frame 14, beneath which the curved flanges 118 of the metal elements engage to l~

secure the latter in position.
Figure 12 shows a preferred cross-section of the attach-ment means as fitted to the embodiments having a depending flange.
The attachment means has a vert;cal slot 150 of a depth equal to that of the flange 115 of the sieve element so that the upper edge of the attachment means is level with the screen surface. The inner wall 152 of the attachment means inclines downwardly and inw-ardly towards the middle of the sieve element, at an aDgle :` :

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of about 45~ its uppermost edge 154 coinciding with t'ne junction between the flange 115 and the transverse ribs 86. Consequen-tly the apertured portion of the sieve eleme~-t is not obstructed by the a~tachment mea~s 7 permîtting an open~area of as high as 92 per cent.
~he attachment means may be attached resiliently to the flange or, and preferably, moulded direc-tly onto the ~lange 115~ which may be indented or apertured as at 156 for ~dded security o~ attachme~tO
Various other modi~ications are envisagedO For example, metal sieve elements ha~ing outwardly-directed flanges could be laid upon a support ~rame with their - flanges supported by the cross-bars of the frame and clamped thereto by an attachment means in the form of a strip overlyin~ adjacent flanges of each adjacent pair of elements and secured to -the underlying cross-bar~ I~ desired, where tha support frame is metal~ a synthetic plastics strip could be provided be-tween the ~la~ges and -the support ~rame~
~he overlying strip might have integral depending studs or ribs to project between the auxtaposed ~la~ges a~d into a hole or slot in the cross-members.
Alternati~ely such strip might have cou~terbored h~les formed at i~tervals along its len~th and be secured by stuas or spigots passing through these holes and regîsteri~g holes in the support frame. Moreo~er two parallel strips with stepped semi-cylindric~l recesses ~ s~

might be combined to give the counterbored holes~, It is ~urther envisaged that the s~thetic plastics attachmen-t means migh-t be bonded to the peripher~ o~
the metal sieve element ~ for example to -the Elanges, 5 where provided, perhaps even to a Elat peripheral surface extendillg perpendicular to the plane of the element.
Irlstead of a flange, the metal sie~re element mij ht have a peripheral sidewall, e~tendirl~; generally perpendicular to the plane of the element, provided 10 (for example by de~ormation) with a ridge to eIlgage a recess in the s;srnthetic plastics attac~ment means.
'rhe recess ma;sT be preformed or ma~ be formed b~sr resilient deformation on inser*ion of the element.
It will be appreciated that the sieve element migh~
15 be of an;y traditional constructiic)n, for example welded or looped wedge wire, perforated plate, woven wlre, welded mesh.
Embodimexlts of the invention advantageously allow ad~ran~ages of tradi-tional screening media in particular 20 applicatiorl~ to be realised in combirlation with those of s;s~thetic plastics material such as lower rLoise level and modular constructio~ with replaceable eleme~ts.
~sr example, in dewatering coal or other slurr~ a wedge-wire t~pe sieve eleme~t can be used yet individual 25 screen modules, whe~L worn, can be replaced quickly and easil~y without special tool~

_ 20 '~' Similarly, readily replaceable screen modules may be provided with woven wire or other high open area sie~e elements such as are preferrad for damp material having a high fines content~
Efflbodiments of the invantion will generally be quieter in operation than conventio~al metal screens since the synthetic plastics attachment means may act as a shock absorber. It should be noted that the attachment means might be made from alternative material, for e~ample rubber or other elastomeric material.
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Moreover, the smaller size of sieve elamant employed in modular cons-truction will be less susceptible -to resonance and reverberation~ leading to reduced noise levels, particularly where the sieve element comprises perforated metal plate.
It is further envisaged that the attachment means migh~ be of wedge-shaped vertical cross-section so that ~he screening surface has a sa~ooth sectional profile 7 - the "steps" extending across the directîon of flow of .l 20 the material to be screened. This arra~gement is .1 particularly useful for scree~ing sluxriesO
Althou~h described with p~rticular. reference to flat-bed or cambered screens, the inve~tion also comprehends cylin~rical or conical screens, .~or example centrifugal apparatus and trommel æcreens.:

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Claims (17)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A sieve screen for sizing and/or deliquefying particulate material, comprising a plurality of apertured metal sieve elements and attachment means of synthetic plastics, rubber or elastomeric material cooperating with edge por-tions of each sieve element to secure the elements together and/or to an under-lying support structure, wherein the attachment means comprises a separate collar for each element and completely surrounding the element.

2. A sieve screen as claimed in claim 1, wherein the apertured metal sieve elements are rectangular and attachment means cooperate with at least two edges of the elements.

3. A sieve screen as claimed in claim 1 or 2, wherein the attachment means comprises two L-shaped members each cooperating with two adjacent edges of the element.

4. A sieve screen as claimed in claim 1, wherein the attachment means has depending portions engageable with a support structure underlying the elements to secure the latter thereto.

5. A sieve screen as claimed in claim 4, wherein the depending portions comprise an undercut rib or spigot member engageable with a lipped groove or hole of the support structure.

6. A sieve screen as claimed in claim 1, wherein the edge portions of each element comprise protrusions cooperating with grooves or slots in the attachment means to secure the element thereto.

7. A sieve screen as claimed in claim 6, wherein the protrusions project in a plane generally parallel to that of the element to engage in a sidewall part of the attachment.

8. A sieve screen as claimed in claim 6, wherein the protrusions project downwardly into the attachment means.

9. A sieve screen as claimed in claim 6, 7 or 8 wherein the protrusions comprise flanges extending along substantially the whole of each edge of the ele-ment or comprise a plurality of tongues spaced along the edge of the element.

10. A sieve screen as claimed in claim 6, wherein the protrusions comprise an external ridge on a peripheral wall of the element.

11. A sieve screen as claimed in claim 1, wherein each apertured metal sieve element comprises a plurality of wires extending parallel to, and spaced from, each other to define slit apertures between adjacent wires, said wires being secured together by a plurality of tie rods or bars extending across the element transversely to the length of the wires.

12. A sieve screen as claimed in claim 11, wherein the wires have formed therein loops extending in the plane of the wire and are secured together by a tie rod extending through aligned loops of different wires, end portions of the tie rods each extending beyond the end-most wire and into a recess in the attach-ment means and wherein a row of aligned said loops adjacent the edge of the ele-ment is retained in a complementarily-formed groove in the attachment means.

13. A sieve screen as claimed in claim 11, wherein the wires are straight and the tie rods or bars are welded directly to lowermost parts of the wires.

14. A sieve screen as claimed in claim 13, wherein strip members extending along respective opposite edges of the element parallel to the wires are welded to the ends of the tie rods or bars, the or a protrusion for securing the ele-ment to the attachment means comprising a flange portion of the strip depending below the tie rods or bars.

15. A sieve screen as claimed in claim 8 or 14, wherein the protrusions are arcuate in cross-section and engage a lip formed by a recessed sidewall of a groove or slot in the attachment means.

16. A sieve screen as claimed in claim 8 or 14, wherein the depending flange extends into a slot in the attachment means, which means has an inclined surface extending downwardly and inwardly from a position beneath the edge of the apertured part of the metal sieve element.

17. A sieve screen as claimed in claim 1, comprising a support frame in the form of a lattice-work having arms of metal and/or synthetic plastics mate-rial, the attachment means cooperating with the arms to secure the elements thereto.