CA1160597A - Strands and netting and screens made thereof - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
A screen for a sieve for sifting particles of a pre-determined size from a loose ore conglomerate has an upper layer of longitudinal straight strands each comprising glass fibre core covered by an abrasion-resisting organic elastomer and having a circular cross-section, the strands being parallel to and spaced from each other in a first plane and a lower layer of similar straight spaced parallel strands perpendicular to the strands of the upper layer and contacting the latter at crossing points. The elastomer surfaces of the strands of both layers are secured together at the crossing points by the strands having been heated sufficiently to produce a predetermined degree of melting of the surfaces and thereafter pressed, thereby to fix the crossing strands permanently relative to each other to define mesh openings of predetermined configurations and dimensions the screen having a space ratio of at least 60%, and the strands of the lower layer being tensioned. The use of glass fibre cores counteracts the generation of low frequency noise when the screen is in use and makes the screen light and flexible.

Description

1 16~)5~

BACKGRO~ND OF T~l~ INV~NTION

1. Field of The Invention This invention relates generally -to the manufacture of netting or screening mesh and particularly to screening which i~ intended to be incorporated in apparatus or devices designed to accomplish sift-ing out finer materials which are intermingled with coarser materials, as for example, ores.

2. Description of The Prior Art Prior art screening which has been particularly constructed for sifting apparatus and other uses in industry has generally been formed of interlaced or woven metallic strands. ~hen used to sift certain materials, such as ore or other hard substances, as such materials are passed across a prior art screened area, the noise produced may be objectionably loud. Such objectionable noise can be produced either by the mater;al bouncing across the metallic .trands of the screen, or by such material causing the contactirlg wire strands to rub against each other.
Another objection to metal screening of tne prior art is tha-t the metallic wires can abrade the material being passed over the screening where, in some instances, such abrasion may not be des;red. If the material being s:ifted is very hard, however, the metal screening itself may become abraded. In addition, such prior art metal screening may ~- tequi~e~
~eq~r~ a considerable amount of time on the part of service personnel to mount, remove or repair the metallic screening in sifting apparatus installations. Further, such screening can become plugged or deformed with respect to the ma-terials being screened, therehy adversely - 2 - .

l 1~0597 affecting the efficiency of the sifting process by, for example, permitting an undersized piece of ore to be retained on the screen or permitting an oversized piece of ore to pass through the screen where deformation has occurred. In ad-dition, it is well known that prior art metal screening does not ordinarily last for a long period of time when it is subjected to intensive use in a sifting process, being subject to rust or other deterioration, not only through such use, but even when placed in storage. Lastly, metallic screening is ordinarily heavy and necessarily adds greatly to the weight of sifting frames or mountings so that it may be inconvenient to handle.
It is a difficult matter to remove blocking and cloggings from the mesh openings and to make screening accurate, and not to transmit waves of hazardous frequencies to human bodies, and also to provide long life spans.

~ 3 -~ .~

l 160597 SUMMARY OF TH~ INVENTION
The present invention seeks to obvlate the problems engendered by metallic screening utilized in prior art sifting apparatus as hereinabove described. According to the present invention, the screening is constructed of abrasion-resisting organic elastomer strands. Such strands may be either extruded filaments, strings, rods or bars of such an elastomer, including natural rubber, synthetic rubber, synthetic polymer or other related compounds which are abrasion-resisting, but thermal plastic or thermo setting. One example of such a polymer might be a thermo-plastic urethane elastomer.
Alternatively, the strand could comprise a metal filament or wire, either solid or twisted, with another metal filament or wire, or with a filament of such an elastomer, or a rod or bar, coated with such an elastomer.
With prior art screens, the noise produced may be ob~ectionably loud. Such ob~ectionable noise can be produced either by the material bouncing across the metallic strands of the screen, or by such materlal causing the contacting wire strands to rub against each other.
Another ob~ection to metal screening of the prior art is that the metallic wires can abrade the material being passed over the screening where, in some instances, such abrasion may not be desired. If the materlal being sifted is very hard, however, the metal screening ltself may become abraded. In addition, such prior art metal screening may require a consider-able amaunt of time on the part of service personnel to mount, remove ar repair the metallic screening in sifting apparatus installations. Further, such screening can become plugged or deformed with respect to the materials being screened, thereby adversely affecting ~`

1 ~60a9~
the efficiency of the sifting process by, for example, permit-ting an undersized piece of ore to be retained on the screen or permitting an oversized piece of ore to pass through the screen where deformation has occurred. In addition, it is well known that prior art metal screening does not ordinarily last for a long period of time when it is subjected to intensive use in a sifting process, being subject to rest or other deterioration, not only through such use, but even when placed in storage.
Lastly, metallic screening is ordinarily heavy and necessarily adds greatly to the weight of sifting frames or mountings so that it may be inconvenient to handle.
According to the present invention, there is provided a screen for a sieve adapted to sift O~lt from a loose ore conglomerate, particles of a predetermined size, the screen comprising a fi.rst layer of straight strands, each of the strands comprising an elongated element having at least its outer exposed surface constituted of an abrasion-resisting organic elastomer, the strands being laid parallel to, and spaced by a first predetermined distance from, each other in a plane; a second layer of similar straight strands, the second layer of strands being laid upon perpendicularly with respect to the strands of the said first layer to contact the latter strands at crossing points, each of the strands of the second layer being parallel to, and spaced by a second predetermined distance from, each other; the said elastomer surfaces of the strands of both layers being fused together at their said cros-sing points by the contacting strands having been heated suf-ficiently to produce a predetermined degree of melting of the surfaces at the contact points, and thereafter cooled, thereby to fix the crossing strands permanently relative to each other to define mesh openings of predetermined configurations and dimensions.

l 160597 In addition to arranging the strands to provide square or rectangular openings, the screen may be reinforced by placin~
metallic strands of smaller cross section than the cross sections of the strands utilized to form the netting or screeniny, but having an abrasion-resisting covering of an organic elastomer or strands of such an elastomer, at each of one or more corners of each opening, thereby to define small triangles in the netting.
During the sifting operation, the strands around the approximately square openings are vibrated and the strands in the upper layer guide the progress of the object being sifted.
Moreover, the longitudinally extending strands in the upper layer may serve to guide the progress of the material to be screened, thereby further improving the efficiency in sifting. The longitudinal strands may be arranged at equal intervals, which are two or several times the equal interual distance of the transverse strandq, and the transverse strands may be fixed to each other by holding and melting in order to maintain their locations at or off the center portion of cored longitudinal strands when the latter strands may be employed.
Such longitudinal strands may have a circular or polygonalcross section of a large sectional area in order to ensure sufficient l 160597 durability to the transverse strands, when made of an abrasion-resisting organic elastomer, and may be arranged to keep the space rati.o oi the net, forming the opening of each other rectangular shape. During screening~
a p~rc~ t e, those strands located around the mesh of a square or an arprc~ ely square ~t the strands made of abrasion-re-sisting organic elastomer are caused to vibrate and the strands in upper layer guide and hel.p the move-men-t of the object to be screened.
When util.iYed for sifting ore, the ore pebbles which rnay arrive at the openi.ng part of the ne-t, will snap bacl~ through the vibration of the net itself or will fall through the openings because of the spring of the strands, thereby avoiding blocking of the net openings. Thus, the purpose of the screening is attained with high efficiency. Eventua:Lly, the upper strands of the net cause the advance of particles to be concen-trated and operte to promote the e~`fici.ency of the riddle, rapi(lly in -the longitudi.nll direction to make screeninlr,.lccurate, and in that the occur-rence of sound waves at fre~uerlcies ha%ar(icnli to the hum.-l-l ho(ly, be:i.ng minimi%ed and the l:iie span Or net be able to sm:rf:ic:i.erlt;ly be oxtended.
As the transverse st:rllnds may be constitute(i of strallds w:ith CO~'C`5, alld a5 such be rigid, they do not l.oosen. I~vc~rl :i:r t.he strurlds w:i.l;hout cores are u-;ed, by employi.n& urettlane e1.astomters havi.nK ~;mal.l pel(ent elonga-tions, the sarne Icind of effect mLIy be atta:i.rled because of their high abrasion-resi;ting characteristics--everl superior to piano wi.res--and its non-loosening property.
It will be readily appreciated by those persons s~si].led in the art that a screen constructed in accordance with the present invention, particularly when employed in a sifting device or appara-t:us, offers many advantages over prior art screens in that, when slfting of material occurs, l 1~0597 the noise level is significarltly reduced; resistance to abrasion is improved both in resp~ct Or the ma.terial. being siIted as well as in respect of the surfaces of the strands which are contacted by such material; rusting is eliminated so that the screen should not deteriorate over a long period of time of i-ts u~e and/or storage;
the screen construction is readily adaptable for mass production; and its mounting, removal, mai.ntenance and repair is greatly faci]itated so as to require a minimum of time and labor. In addition, because of the resilience of the elastomer of the strarlds or their coaL:ings, vibration of the sift:ing screen be-tter enables particles of the proper screen size to pass through the screen openings and not to becorne clogged in the mesh, as is so frequently the ca6e witn prior art metal screening.
Thus, the screening Or the present invention offe.rs many advantages over metallic screening of the prior ar-t.
Accordi.ng to the present invelltion, in order to ma:intai.rl the tension of the net or screen in the transvcrse di.rection, each end of the transverse strands may be secured by a me~tal fitti.ng, such as solderless terminal or a fitting havi.ng one end to receive a strand arld the other resemblirlg a lin~s r-,Se. A nut having an inside screw thread i~ tightened betweerl the ~pper c:Larnping pl.ate and the :Lower c:Lall)pirlg pl.ate and i8 secured, for example, by means of` a bo].t, nut or rivet. Such tightening means also constitutes a feature o~` the preserlt invention. Thus, the inner edge of the lower clamping plate is bent down toward the center of the screen at a gentle slope. Thereby, the lower surfaces -towards the ends of the organic elastomer strands are prevented from being sheared by the inwardly protruding edge of the lower c~ampi.ng plate when the screen net is set up and vibrated as the material being screened is passed ~.

_ ~_ 1 16 ~ 7 thereover. Moreover, when the screen net is c~lamped and tightened between the upper clamping plate and the lower clamping plate and secured, for example, with a bolt and nut, a sheet or covering Or a suitable strip o~` abrasion refilstirlg organic elastomer rnay be secured on the upper surface of -the upper clampin~ plate by -.usion or some other suitable method.

~ 1~0597 BRIEF DESCRIPTION OF THE DRAWINGS
Figures lA and lB are a plan view and a side view, respectively, of a first embodiment of the present invention, in which the shape of each opening in the net or screen is substantially square, and net strands are made of an abrasion-resisting organic elastomer;
Figures 2A and 2B are similar views of another embodlment of the present invention, in which the shape of each opening in the net or screen is a rectangle whose length is twice the width of such opening;
Figures 3A and 3B are similar views of still another embodiment of the present invention, in which the shape of each opening in the net or screen is also rectangular, but with its length much greater than its width;

Figure 4A is a plan view of a net or screen, as shown in Figure 3, mounted in a sieve;
Figure 5 shows another embodiment of the present invention mounted in a siève;
Figures 6A through 6I show different cross-sectional configurations of abrasion resisting organic covers for wires;
Figures 7A, 7B and 7C are a plan view, and two side elevation6, respectively, of an embodiment of this invention in which its transverse strands are cored;
Figure 8 is a perspective view of a sieve in which the net or screen shown in Figures 7A, 7B and 7C has been installed;
Figure 9 is a plan view of another embodiment of the present invention and appears on the same sheet as Figures 6 and 7;
Figure 10 is an enlarged and cross sectional view of a portion of the sieve shown in Figure 8, illustratin6 the means to anchor the net or screen;
Figures llA and llB are a plan view arld a side view, respec-tively, of another embodiment of the present inventi.on;
Figure 12 is a perspective view of a sieve incorporating a net or screen; penetration through the -traverse elastomer covered strands instead of fusion;
Figures l~A and l~B are a plan view and a side view, respec-tively, of another embodiment of the present invention;
Figures 14A, 14B and 14C are a plan view and two side elevations, respectively, of a net constructed with metallic wires which have circular cross sections;
Figures ].5A and 15B are cross sec-tional views of a net or screen in which wires illustrated in the Figures 14A, 14B and ].4C are provided with coverings of an abrasion-resisting organic elastomer;
Figure 15C is an enlarged cros~s sectional view ot a pottion of the net or screerl shown in l/:igures 15A arld 1~;
~ `igrure ].6 :is a perspective view o.( a tuho or tromrrlel. in which is inst~lled a net or screen of the type shown in Fi.gllres 15A and 15B;
Figures 17A and :I.7B ~re a plan view and a side view, respectively, or` a net or screen constructed with metallic wires which have square cross sections;
Figures 18A and 18B are cross sectional views of the net illust-rated in Figures 17A and 17B with the wires covered with an abrasion-resisting organic elastomer in accordance with the present invention;
Figure 19A is a plan view of another embodiment of the present inven-tion;

_ ~_ .

l 160597 Figures l9B and 19C are cross sectional views taken on the lines a-a and b-b, respectively, of Figure 19A and looking in the direction of the arrows;
Figure 20 is a plan view showing a sieve with an arrangement of transverse strands constituted of an endless strand in s-till another embodiment of the present invention;
Figure 21 is an enlarged view of a por-ti.on of the sieve shown in Figure 20;
Figures 22A and 22B are cross sectional views illustrating means for moun-ting netting or screening in a sieve in accordance with the ~resent invention;
Figures 23A and 23B are plan views of o-ther embodiments of the present invention, illu~strating two means for mounting exposed str~nd cores comprising fine wires;
Figure 23C is a plan vi.ew of the metol spacer shown :in i~'igure 23A.

_ ~_ I 1~0~97 Ijk,~CRIPrlON 0~ TH~I PREEERRE~ ~hl',O~)~MENT

i~elerring to FiKures lA arld lB of l,lle accompanying drawings, a ~reen or nct constructed in accordance with the preserlt i.nventlon may comprise a pl.urality of equidistantly spaced parallel, horiYontal strands 1 laid in a cornmon plane to constitute one layer over whi.ch is laid a second layer of equidistantl.y spaced parallel, vertical strarlds 2. As used in this specification, the word "strand" incl.udes not only thin, elongated elements such as solid or twisted metallic wires, filaments, twiste~ chemical or naturally spun fibers and metallic rods or bars of small cross section or diameter, but also includes elongated, thin elements Or rubber, elastomer and any metallic or other thin elongcltell element which is mixed or coated with any of such elastomers;
or t~lin, elon~lted elements thereof and strips of any of such elements or elastomers. ln this conllection the term "abrasion-re,isting elastomer"
should ~e deemed t;o include without limitati.on, ncltural rubber, uynthetic rubber, chem.ical po:lymcri~.ing materials ils, .Lor exam~)le, L.;oprene, neo-prene, and polyurethane elastomers, which have abrasion-resisting pro-perties.
Al`ter the layer of stral-ds 2 has been l.a:;d over th~ l.ayer oE
strands 1, U3 showrl irl li`i.gures lA arld lB, the two l.ayes~s are ~ubjected to sufl`icient herlting to cause all points of contact oi` tlle strarlds 2 with the stran(ts 1 to melt or fuse. As a r~sult of the commencement of melting and fusing of the elastomer content or coating oL the -two strands, when the strands cool, the crossing strands w-i.11 become fixed relative to each other to form a net or screen in the patterrl in which they have been thus laid.

~ ' 1 16~)597 In the ernbodiment.s of the invention sho~lrl in Fip;ures 2A, 2B, 3A and 3B, fewer and more widely spaced .strands are provided than in the embodiment of Figures lA and lB, with the result that in the case of the embodiments of Figures 2A, 2B, 3A and 3B, the interstitial openirlgs or mesh defined by the crossing strands 1 a:nd 2 will be observed to be long rectangles and not squares, as irl the Figures l.A and lB embodimen-t. It is a feature of the present ln-~ention that the exact structure of the mesh of the screen may be preselec-ted with reference to the re].ative importance between the accuracy and efficiency of the screening.
Referring -to the embodiment of the invention illustrated in Figures 7A, 7B and 7C, the transverse strands 1 may be made of an abrasion-resi.sting organic E~lastomer, such as a urethane el~-lstomer or an abrasion-res:i.sting rubber, and are disposed to constitute the bottom layer of the net or screen. Over this bottom layer, a layer of strands 2 may then be l.aid to cross s-trands 1 at right angles. The spacing between the strands of each of the layers is such as to define the required si~e of mesh openings, and -the two layers of strand6 are secured together by heating to cause them to fuxe at their contact or crossing points i.n the manner previ.ously descri.bed.
Tne net or screen thus constructed may be incorporated in an automatic vibratirlg sieve de~:ice of the type shown in Figures 8 and 10. Such incorporation may be accomplished by insertirLg the ends of the strands 1 in -the metal fittings F disposed on the shelf C' secured to the wall C which constitutes the side framing of the si.eve. A metal channel D is provided with one edge D' seated on -the inside of the wall C, and its other D" inserted between the -two wings F', F" of the metal fitting F. A screw E is then passed through an oriflce D"'i.n the channel D and ~,,, _ ~ _ \3 t 16U597 tnrough another orifice C" in the wall C. By virtue of the arrange-L

ment of the spring ~, washer ~l and nut I shown in Figure lO, i.t may be seen tha-t the channel D may be drawn toward the wa'Ll C by -tightelling of the nut I on the screw E. Thereby, the trarlsverse strands l may be brought into tensi.on from both of' their ends, while the longitudinal strands 2 will be unaffected by such tensionin6.
It will be recognized by those persons skilled in the art that Figure S disc],oses generally a type of screen adapted for use in an automatic vibrating sieve to accomplish the sifting of material such as, for example, crushed ore. In such a screen, the crushed ore par--ticles or pebbles (not shown) are rolled downwardly along the screen mostly between the strands 2 and over the strallds l. As such ro].ling occurs, the pebbles or particles which are small.er than the interstitial mesh openings will drop through such openings and onto some conveyor or other surface (not shown), while the particles which are larger than such openings will continue to roll down to the en(l o~` the sc.reening to be deposited in another area or rec:eptac]e (also not silown). Theret)y, the two different siæ,es of particles or pebbles may be sor~ted out. ~ince size difference may mean a d:i.rfererlce :i.n mirleral content, screerr; con-structed in accordance with the pre;ent .i~lvention may greltly improve the desired sorting out of the Aif:t`erent size pebb:les in the course of an ore concentrating process. Because of the resiliency of the abrasiorl-resisti.ng orgAIlic elastomer strands o:t` which the screening is constructed in accord-ance with the present invention, ore pebbles of a size which might be stopped in but not pass through openings in a prior art me-tal wire screen will be caused either to fall through the openings, if -they are small enough iIl size, or to be bounced out of the mesh openings so as not to block the . ,~ _ ~_ .. .

l 16V~97 sa.me. Thus an ore sieve constructed of' screening in accordance with the present inventiorI may attain a high de~ree of efficiency. Further contributing to such efl'iciency is the placement of the strarlds 2 along the lines of travel of the pebbles. By so disposing the strarIds 2, a plurality of channels are effectively created along which the ore pebbles may be more rapidly moved during the si~`ting process. Because tht transverse strands are tensioned to a rigid s-tate, such strands provide a minimum of impediment to the ore pebbles or particles as they move down between the longitudinal strands 2. Even should the transverse strands be eoreless, if a urethane elastomer having a small percent of elongation, when tensioned, is employed, such coreless str~itnds will still be effeetive because of their high abrasion-resistin~r capacity, as compared with s-trands of the type used for piano wire.
The net used is that shown in Fi~. :IA, lB a~ld comprising two kinds with di~ferent meslIes. Thc~ strands are made Or ure1;harIe e:Lastomer.
After 60 day's use as the screen with i'lowinI, water~ in case o r the wire with 10 mm diameter, 0.2 mm was daml~red, and in cnse Or the wire with 8 mm diameter, 0.2 mm WaG dUIrlrl~t`d lil;ewi5e~. ~rhiri re;-Ilt: shows that the product uceordirIG to tIIis inverltioll hu5 higher durubility thaIl eollvention<ll ~iteel one. I~ur(lletln()r~ blockinl; o~ thc O~t!llin~s didn't almost occur. They eould be rep~ired mairItairle(I und sLocked e~sily.
The results o~ the comparison of abrclsion-resistirl~r ability and other physical properties ~etween t}~e net accordinL~ to the present invention and conventional ones are shown In 'rable 1. As ont! under-stands lookin~ at this tabl?~ it is ~uperior to any conventionul one.

_ ~_ .. .. ~

~ 1~0~7 ~j O _ ~ ~ h _ _ .
R ~ C ~ ;~ 0 0D-~ ~ oN~ _ _ o N

C ~~ h ~2 N l N 0 ~ ~ y~ N ~; l l I~ ,_I ~) ~: ~ _U~, .Y, 7~
C ;~ ~ N N~ l l O l ~ ~

C ~ I h _. . _____ ,, O O h ~ H

F~ ~.~ ~ h ~ o~ o o o ~ ~1 H ui ~.~ ~ ' 9~
~ ~i ~1 .. .. .. .. o o U~ ~ D 0 ~ c o o ,i ~i h .

h _ 0 ~ ~ 0 ~ 0 ~ 1~

~j ~1 ~ . 0 H ~
~ P~l ~ N,~ ~ N~ d .~ ~ h~

A ~ ~ 0 ~1 O ~ ~ ~j H o o o L ~ ~ ~ ~

o~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
4~ .~ ~ U~ U~ U~ ~ ~ rd ~ 0~
O ~ ~ ~ ~ H H H .~ ~ ~ 1~ ~ ~
~1 . ~ 0 h ¦~ E~3 ~ 8` 8 _ __ _ 8 ~ ~ 0 ~

~r 1 ~60597 Table 2. As easily understood from this, the aperture area of the net according to this invention is larger than that of knitted screen, and the same as -that of metal screen.

The aperture area by percentage of the nets according to this invention and conventional net.
Ian example) _ \ Aperture area by percentage . _ .. . __ . ,_ . .. , ~
Diameter Screen accordlng to Knltted cross-Strand this invention Metal Rubber section interval (cored strand) Screen Screen 2.65 mm 43% 43% 39%
.

3 10 mm 43% 49% 35%
415 mm 62~ 62% 42%
625 mm 65% 65% 46%
830 mm 64% 64% 44%
. .
835 mm 66% 66% 46%
. .. _ . _ . .
1040 mm 64% 64% 45~
.. .
1050 mm 67% 67% ~5%
_ When large aperture area is desired, those structures given in Fig. 2A, 2B and 3 may be chosen. According to this invention, the structure of the net can be chosen as to the priority between accuracy and efficiency of riddle.
Referring to Fig. 6A - 6I, some structures of cushion are shown.
The wire of abrasion-resisting elastic organic material is inserted to receiving groove B of the cushion A made of same kind of abrasion-resisting elastic organic material. Then this is welded -to form single wire. Or, me-tal wire, the rope comprising twisted metal wires, monofilament of synthetic resin with small e~pansibility or its twisted wire ~ 160~97 rope is put into the receiving groove B and can be used as a strand after being welded togethex. The shape of the cross section can be formed e.g. square, as desired.
Referring to Fig. 7A, 7B, 7C, 8, 9, the transverse wires 1 comprising thermoplastic urethane elastomer having core same as those given in Table 1 are put in the lower layer.
In the upper layer, the coreless strands 2 of the same material from longitudinal strand. Both strands cross perpendicularly.
Their intervals are roughly the same, or those of longitudinal lines are rather small, so as to form predetermined opening area. The strands of longitudinal and transverse strands are welded together at their crossing points. Fig. 9 shows a plan view and Fig. 7 shows a side view. The screen is mounted as an automatic vibrating screen is, as shown in Figs. 8 and 10.
Both ends of strands 1 are inserted into metal fittings F of the frame of the screen, and secured to plate D by screw E, and thereby the lower strands are tensioned through both ends, while the upper strands are free. In use, crushed ore particles, for example, roll on the upper strands 2, and those of under size pass through the square me~h formed by both upper and lower strands and fall. On the other hand, those of over size roll on the net further. Thus two kinds of particles are sorted and concentrated. In ore concentrating processes, since differences in size correspond to differences in mineral con-tent, such screening is an important step.

l~

1 lGa597 In the embodiment of the invention illustrated in Figures llA, llB, 13A and 13B, the screen is constructed with mesh openings in the form of long rectangle~. In this embodi-ment of the invention, the strands 1 may be made of a thermo-plastic urethane elastomer and are arranged at equal intervals to provide a predetermined length of openings in the direction of travel of the pebbles along the sieve. The strands 3, which may also be of the same elastomer, may be secured to the trans-verse strands 1 by heating both sets of strands 1 and 3 to the point where they fuse together in the configuration shown in Figures llB and 13B. After the strands 1 and 3 have been so disposed as illustrated in Figures 13A and 13B there may be seen to be formed rectangular mesh openings in which the transverse width is as much as several times that of the longitudinal length, or similar to the mesh configuration shown in Figures 2A and 3A. Alternatively, however, the strands disposition could be modified to make the longitudinal rectangle dimension longer than its transverse dimension. While, as also illustrated in Figures llB and 13B, the longitudinal strands _,~ _ ~0~

1 1~0~97 3 are shown to have square cross sections. It will be understood by those skilled ln the art that the cross sections of the longitudinal strands may be square, rectangular, polygonal or round. Desirably, the thickness (i.e.
the cross sectional areas) of both the longitudinal and transverse strands 3, l, respectively, should be such that, with use, they will become worn down at substantially the same rates. Because each of the ore pebbles or particles moves down a sieve, in almost continuous contact with at least a pair of longitudinal strands 2, whereas such pebbles may be bounced over the transverse strands 4, the wear on the longitudinal strands may tend to occur at a faster rate than on the transverse strands. For this reason, it is desirable to provide a greater thickness for the longitudinal strands 2 so that the durability of both the longitudinal and transverse strands will be substantially the same.
In the embodiments of Figures llA, llB, and 13A and 13B, provision is also made for an upper and lower net. The lower net comprises the transverse strands 1 and the longitudinal strands 3. The upper net comprises the longitudinal strands 2 of the thenno-plastlc urethane elastomer and transverse strands or cords 4. The latter crosses the strands 3 of the lower net perpendicularly and passes below the strands 3 only at such points of crossing. Both the strands 3 and 4 are secured toget~ler by fusing at their crossing points. Strands 2 of the upper net are also arranged to cross perpendicularly strands 1 of the lower net with their spacing being the same or almost the same as those of the transverse line. The parenthesized numerals ln Figures llA and llB denote parts of the upper net. The sifting screen thu~ structured by the upper and lower nets just described is illustrated in Figures 13A

and 13B. The longitudina:l strands 3 in the lower ne-t and t~e crossing strands or cords L~, in the upper net may be secured together by hea-ting them to a temperature at which they may fuse at their mutual cross points.
}lo~cver, while the strands 1 of the lower net may cross the strands 2 of the upper net perpendicularly, there will be a small vertical spacing or gap between them. Since, therefore, there is no contact between str~nds 1 and 2 at their crossing points, such crossing points are not secured by fusing. Thus, by providing or avoiding fused crosspoints of net strands, one may either increase the capacity Or the sieve to handle R greater volume or ore particles or pebbles, or effect a more accurate sifting of the ore particIes or pebbles. The ins-tallation of such a -two-layer screen may be accomplished in the same manner as that described above in connec-tion with Figures 8 and 10 of the drawings.
Referring to Figure 13, it may be seen that the net has mesh of an extended long rectangular form. The strands 1 made o~ thermoplastic urethane elastomer are arrayed in equi-intervals corresponding to pre-determined size as transverse lines. The rope 3 comprising thermoplastic ~r~ urethane elastomer ~ welded to the transverse wires so as to form rectangular openings similar to those shown in Figures 2 and 3, and the longitudinal strands may have square, rectangular or circular cross-sections. However, in Figure 13 square cross sections are shown. As mentioned above, the cross sectional areas o~` both longitlldirlal and transverse strands should be such that they will wear away o~er approxi-mately the same time period. Thus, for example, the longLtudinal strands may have larger cross-sectional areas than the transverse strands to result in some relative durability.
In operation, when crushed ores are placed upon a double layer 1 l~O~g7 ~1 ~ , ~

1 161~97 sifting screen of the type just descri.bed, sifting is accornp]ished through the mc~s}les defined by the stran(ls oL both t;he UppeI` and lower nets or screens. Between tne two layer.s tnere may be mesh openings thus defined which are bo-th a).rnost square at one level, and in the configuration of long rectangles, at another level. Ore pebbles or particles pacising over the screen.
Fig. 12 is a perspecti.ve view of a sleve inCGrpo.r.lting a net or screen; penetra-t.ion through the t;raverse el.astomer covered strands instead of fusion; specir-ll lon~-;itudin;ll s-tr~nds ~(4) are abras:iorl-resis-ting elastomer, therefore, do not tend to get caugllt in the mesh open~ gs to c106 up the sifting screen because of both the resi.liency of the strands and the particular siz~es and configura-tions of the mesh openings whi.ch -they define. Ores having a large clay conterlt, therefore~ do not tend to clog Up thc s:irting screen.
E'igure ]6 illustr~tes the manner i.n whic:h netting or screerli.ng constructed in accordance wi.th the pre,~ellt :i.rlvelltion Illay be employed -to lirle the inside oi` a tube or trornmel K.
In thc erllbodir!lerlt of the invcntion i:L].ustr.ltrd :in l~'-i.gllre:; :L4~, 14~3 ar~ C, the ~(roerl or net is con;tructed o.r trurliver.ie me-tal w:ires 'j havi.rlg circllLar cro:-.s sect;:ioll.s and lon6itl~ inal metal wites of the same cross sections. The wi.res 5 nnd 6 are so sp.lced arld ~rrangecl to cross each other and to define square mesll openings, and may be secured to each other at each contact point by welding. While square mesh openings al~ thus shown and have been se:Lected to handle a particular type of material to be sifted, obviously different -types of mesh openings may be defined by rearranging the crossing wires and changing their inter-vals of spacing. In some instances, if large mesh openings are desired and heavy _ j~_ materi.als are to be si~ted, rods or bar.s could be substitutc(l for the wires 5 or 6 shown in Figures 14A, l4B ar1d l4C.
Whatever the configuration of the mesh openings, and whether wires, rods or bars, secured together at their crossing points in the manner hereinabove described, are utili~ed to defi.ne the mesh openings, the present invention contemplates that the external surfaces of the metallic wires or strands will be covered with an abrasion-resis-ting organic elastomer. Such covering may be accomplished either by using prèfabricated cushions of abrasion-resisting organic elastolner in some configuration such as is illustrated in CI`OSS sections in Figures 6A

through 6I, wi.th the ends of such coverings fused toge~tht-~r at each pO; r,~
contact ~e~t~; or, ai.ternatively, the metallic wire net may be covered di.rectly with such an elastomer. In this manner, the final metallic wire netting which is covered with the abras:ion-resistant organi.c elastomer will appear eittler as shown in Figures l5A, l5B and l5C, or, if the strands are provided with square cros~ sectionC~ as shown, for ext-~n~p.1.e, i.n Figures 17A, loA and loB. Obviously, the ;trands 5 and 6 co1lld havi3 any other E~olygonal cross section.
Wher1 it is desired to apply some type o~ coverirlg, suct1 as any of those i'llustrated in Figures 6A througt1 6I, or others, to a me-ta'L bar or wire netti.ng, a suitabl.e groove B is provided in the covering A. Al-ternatively, a str~nd 5 or 6 cou].d be inserted in the hollow core M of a cylindr1cal type covering A' bei'ore or after the metal strand is welded to a crossing strand.
In the embodiment of the invention illustrated in Figures 19A, 19B and 19C, the configuration of the large rectangular mes~ openings N
may be modified by providing bridging s-trands 7 -to extend across the ~3 .

l 1~0597 corners Eormed by the intersectiorl, of the strands 5' and 6'. The strands 7 may be metal wires, each of which may be covered wi-th an abrasion-resisting organic elastomer in the manner described above with reference to Figures 15A7 15~, 15C and 18A and l&B. Thereby, the corners of the large mesh openings may be cut off at ang:les to restrict the size of particles or pebbles which can pass through the mesh openings N. Additionally, providing the bridging wires 7 may serve to improve the vibrating action upon the pebbles or parti.c]es, ~ n st, t4te S
as well as to reinforce the nct. Tl.i~ Lil~t-~ a special applica-tion of the present invention and should not be regarded as necessary for the practice thereof.
Figures 22A and 22B (and 23A, 23:B and 23C) il.lustrate a different manner of securing the ends of the transverse strands to form screening than that which has been discussed above in connection with Figures 8 and 10. Thus, in thc ernbodirnent of E`:ig~lres 22A and 22B, a strip 14 of an abrasion-resist:i.ng orgarlic el(lstorrler rnay be provided to cover the upper surface of an upper clampi.rlg p].ate 12. This covering strip 14 rnay have an edge :l6 which exl:erlds :inwardLy toward the center of the screen and beyond the inncr edge 18 o:l` the upper clarnping plate 12.
Such a covering str:ip :l.4 serves not onl.y to protect the u~per c:Larnping plate 12 and the metal fitting 17, but also lo prevent the upper surface of the organic elastomer s-trand 1 from bei.ng brought into contac-t with, and damaged by the inwardly extending end .L8 of the upper cl.amping plate 12. In addition, by providing an orificed abrasion-resisting elastomer channel 15 between the clamping plates 11 and 12, such channel 15 may serve to insulate the upper and lower surfaces of the covered s-trands 1 from being damaged or deformed when the two clamping plates 11 and 12 are . ..... .. .

l 1~0597 tightened together by the fitting 17. It will also be noted that the inner edge of the clamping plate 12 may extencl fur-ther toward the center of the screen than the downwardly curved edge 13 of the lowe~r clamping plate 11, thereby more effectlvely to prevent shearing of the lower surface of the transverse strand.
After the organic elas-tomer cc,verirlg has been removed from each end of the strand 1"' in the Figures 22A, 22B embodiment, thereby to expose the core 5', such core may be inser-ted through the orifice in a metal fitting similar to the solderless terminal or link fuse 19.
Such fitting could also be a nut having inside screw threads. This fitting :19 wi-th its inserted strarld core end 5' may then be clamped be-tween the upper metal clamping plate 12 and the lower metal c:Larnping plate 11, both of which clamping plates may be drawrl tigtltly together by means of the fitting 17. Ttle latter may comprise an elongated fastener 17' having a head 17" at one end and being threaded at the other end to receive a nut 17"' which may be tightened on such threaded end. When tighterlecd by such devices a5 are shown in E`;gures 22A and 22~3, the transverse strarlds 1"' shoulcd remain undamaged and not become loosened.
In the embodinen-t oF tne inventiorl illustrated in I~`igures 20 and 21, the transverse str~nd~ L" compri6e a single cored strand of an abrasion-resistirlg organic e~la;tomer, one end la of which may be secured to -the bott;om 8a' of the side member 8'. The cored strand is then laced back and forth between, and looped over pins or projecting elements 10, 10' on the side members 8,g', respectively, with the other end lb of the strand 1" terminating at, and being secured to, the upper end of the side member 8b'. If the two side members 8,8' are pulled apart from each ottler, they will effect a tightening of the strand 1". Longitudinal .`.~,~.
.~
_ ~ _ .. .. .....

strands 2" may then be placed over the thu., laced strand l" w1th the crossing points belng secured by fusing in the manner heretofore de-scribed. Alternatively~ tightening of -the strand l" in its laced pattern may be accomplished by the means shown in Figure lO w:Lth the shear preventing strip 14 and channel ]5, illustrated in Figures 22A
and 22B and discussed in connection with those Figures, being addi-tionally provided.
In the ernbodiment ot the invent3.0n illustrated in Figure 23A, the ends of the plurali.ty of exposed cores 5" of strands l"' may be brought to~ether and inserted into a metal clarnping mernber 19 to be secured therein. Such core ends rnay be bra:ised into the element 19.
In addition, a metal.1.ic or other type of spacing member 20 rnay be providecl with a seri.cs o:~ space(i grooves 21. Sucl-l grooves may be equidistantly spaced from each other or spaced at any othe:r desired interval or intervals. When the exposed cores 5" are 1.aii into the grooves 21 i.n the member 2(), the des.ired spacirlg of the strandc. l"' will be properly established and mairlta.ined.
~ hould it becorne desirab:Le to prevel~t the wire co:res of a net or scree.rl frorn becomi.rl~rr ;cparated from thci.r organic el~lstorller coveri.n~s, af-ter the trallsvcrse ~,trarlds have been cut or otherwise .t`ormed to the re~luired ler~gth and their orgr1nic el.astomeI co~erin~s have been removed from the ends Or such strands l"' to leave the exposed cores 5", as shown in Figure 23A, the strands may then be sufficiently heated to cause the organic elastomer coverings to fuse onto the cores. It would also be possible, o:t` course, -to cause such fusing of the strand coverings on the cores even without first stripping the coveri.ngs from the ends of the cores as shown in Figure 23A. Heating ~e 1 1605~17 to cause such fusion could be provi.ded by passing a suf`ficient electric current through the wi.re core to raise the temperature of the la-t-ter to somewhere between 250 to 300 for a brief period.
At such temperature range, a covering of, for example, urethane, will begin to melt and thereby i`use to the core. It has been found that where coverings are fused throughout the entire lengths of the strands without exposing the cores at the ends of the strarlds, tension of -the transverse strands may be better maintained in netting or screens of the type hereinabove described.

_ ~_ . , _ l 1~0~7 Now several embodiments o this invention will be described.
The surface portions at least of the strands of which the net is composed consists of an abrasion-resistant organic elastomer body. Where necessary, the so-called elastomer-covered core strands consisting of core strands having no elongation property and ~n abrasion-resistant organic elastomer body can be used in such a manner that no slack of the transverse strands may be produced.
As the core strands, not merely metallic wires such as piano wires, but also a fibre material such as nylon (Du Pont's tradename, polyamide system fibre) and polyester fibre processing a small elongation property can be used.
Carbon fibre strands reinforced with a resin material, such as polyester, epoxi-, polyamide-, phenol-,or polyethylene-resin (called sometimes FRT, FRTP, and FRTS) and coated and adhered with a polyurethane, elastomer provide light and strong abrasion-resistant organic elastomer-covered core strands.

Although such carbon fibres are excellent in performance, the manufacturing cost is very expensive at present.
Table 1 shows an example of the glass-fibre core strands 1 1~()597 covered with an elastomer whose pri.ncipal cons.tituent is a pol~-urct;hclnt e lastomt r, to~ et;her wlth the elastomt r coverine ratio and the spae- ratio.

Table 3 Space Ratios of the Cored Strands aecordi.ng to this invention A _ A/B C D
Diameter Diameter Elastomer Mesh Ratio of C Spnee of Cored of Glass Covering Opening (Mesh opening) Ratio Elastomer Fibre Core Ratio mmto Core Strand %
Covered Strands Diame ter Strands _ _ __ 1. 2 eS O . 8 f~ l . 5 3 4 Approx . 3 Apilroxima te :l y 1.6 ,~ O.8 ~ 2.O .~~5 " 3 60i ma.int.lillecl 2.0 e~ 1.2 ~ 1.7 1~ ,~ " ,~ for eaeh ea. e.
3 . O ~ 1 ,e~_ _ . 5 ... j- 12 .. ~ Tl ls i3 1. . 5 lJ-6 ~ 2.O ~ 2-) lO~30~pll~o~;. ,~.;_j 20 t~ s t~l~t 8 ~ 10 p~ 3 . 0 ~ .~ - ~ ~ 3 - 3 2 0-- ~ ~> " ~ o f ~ / ? I~ rl i t 12 f~ ~.O ~2.Il 3()-1 jO , .5-10 net s .
_.___ _ ___ __ __. _,.. ... ... - .. _.. :.. . _ .. _ . _.__ 16 ~5 . 0 ~ 3 . 2 3()~1.~0 Approx . ~ lO
20 f610. 0 ~:~ ~ . O 1.00~200 j- lO
3o ~ 10.()~ i 3.o - 100-20() 3-7 . _ ~
A: rinishcd strarl(:3J diameter mm to be u:;ed r et V _ Mesh o~)enin~ mm :;trclnds diun)eter h; vln~ eore mrn A, indieated in Table ~ , sereenin~ w s carried o~lt with the nets mt?sh openin~s Or which ranged from 3 rnm to 200 m;n. In eondue t-ing this experi.ment the abrasion-rt sistant or~anie elastomer di.ameters ranged from 1.2 - 30 mm, the glass ribre core diameters from o.8 to lO mm, the d1aMeters oL tht? c~.astoml r-covcred stral-d .; ral-lged from 1.5 _ 3.5 times the cli..l;neter . oi t3 e core strands, ant the space -- 3~--. ~

1 1~0~7 ratio of 60~ was maintained.
The mesh opening ratios andspace ratiosofthe nets accord-ing to the embodiments ofthis invention are listedin Table 3.
The space ratio is the ratio of the areaofan opening of the mesh to the area within the axesofthe strands defining that open-ing, expressed as a percentage.
According to the embodiments of this invention, the four sides ofeach mesh opening constitute two different levels with the upper and lower layer strands, each having acircular cross-section, whereas according to the conventional knit nets, the foursides ofeach mesh opening are substan-tially in a plane. This very difference is the cause for permitting the space ratios according to this invention to be taken greater than those ofthe prior art nets. This difference plays animportant role for the marked im-provements in both screening and workability.
The thickness ratio of the elastomer-covered strands used for the two layer strands was also investigated. ~ur test results with other embodimentsoftaking the elastomer thickness of the upper layer elastomer-covered strands one to five times that of the lower layer elastomer-covered strands have verified that the thicknessesofthe orderofone to three times provide a favorable effect. Since the upper layer strands have naturally ahigher con-tact ratio withtheobject to be processed than the lower layer strands, awell-balanced durability life span for both layers can be exPected from this order of thicknesses.
However, this ratio shouldbe subject to change with the kindofobject to be processedor the operating circumstances, etc.
With each of the embodiments using the glass-fibre core strands shown in Table 3, the ratio of the diameterofthe core strands to the diameter of the elastomer-covered strands was in-vestigated.

1 1 ~0597 It was di.scovercd that the optimurn rltios of the diameter of the glass fibre core rarlged between 1.5 to ,.5. The optimum ratios where the ela~tomer itrclnd diam~ters are small an(l the mesh openings are fine should urc.rcrably bc bctwcell l..5 arld 20. This rati.o should be subjcct to variatloll with thc kind of object to bc processed or the operating conditlon; thc optj.ma1 Yalue ranginC~ b-etween 1.3 to 3-5.
In conducting the teits oi` all embodirnenls shown i~ Tabl.e 3.
which maintaine~ the space ratio of 60%, thc average sicle dimension of the r~.quare or rcctangu].lr mesh openin~s varied from 2 to 10 time.s the average diameter of the strands or wires. The mesh openings shou1d preferably be of the dimensions equa1 to 2 - 7 times the diameter of the organic elastomer-covered strands of which the net is composed. The recommendable ratio :ror the fine mesh openings should be from 2 to 4, while thl~: for the lar~e mesh opcnirl~5 of 100 mm or above should be from 3 to 7. 01` coursc, these ratios must be ruitably ad;jllsted dcpending on the o~ject to be procer~.~.ed or the operating con(li.ticnr.
Then~ ;cc T~bLc 2A and 21~, weights of a ~ew kirlds of nets were i.nvestig;lte(l as all i.m~ortlllt rc.~ererl(e problem. The wcight of the net wi.th 100 mm mc-.h opcni.ngr; mr.ldc of corl~crltional steel wi.res SWR~l42A (conrorming to thc ]IS Stalldc~rcl JlS-G ~506-1971, C 0.39 -o.46%, si 0.15 ~ 0.35',S, ~ln 0.3 - 0.6%, both P and S - less than 0.0l~%) was 13 kg/m2~ T~e weight of a perforated plate with 100 mm square punched holes, 6 mm thick, made of a stainless steel material was 20 kg/m2.
In contrast the wcight of the net with 100 mm mesh openings 3t 1 lB0597 constituted of the glass fibre core str~-lnds covcred with an abrasive-re.s~ tant or~anlc elastomcr havin~ an ovcrall diamctel of 10 mm was 1~ k~/m2. Thl.s corresponds to only 3C~ of thc wci.ght of the steel wi.re nct ar-ml 20/o of that of thc stainlcss steel per-forated platc~
This feature of liGhtwei~lt offers marked advantages in transportation, administration, storat,e, repair, and instal.l.ation, as well as in workability. Thc feature also displays the outstarlding improvements in incrcasin~ its durable li:fe s~n and in rcducing the power costs.
With the conventiol1al screen ncts such a~; steel nets, increasing the mesh openin~r rat:ios waci invari.ably accompanied by the defect of detcrioratin~ the durabi.l.i.ty and shortcllin~, the crviceabl.e ;Ifc.
'rhis problom h:ls bccll so1.vc(l by tilis invention as has bcen dcicribed by reference to the cmbo(li.mcnts indicated in Table 4~, 4R~
Trommels or sieves have been u~ed for screening lime stone, ore, crushed stones for mixin~ concrete.
Pre~;ented below are our investi6ati.on resul.ts for several embociments of nets .for use with concrete mi.xillg trommels having diameters ol` 900 - lSoo mm alld lcn~;ths Or ~,ooo ~ lo,ooo mm.
The description will be limitcd to thc trommcl net dimensions of a cylindrical form havin~ tllc diamcter o~ 1,000 mm, the length of 7,000 mm, and the area o r 22 m2.

3~

1 ~0597 Taole 4A ~ractical Mcas~lred Space Ratio t !~ S trand 'i Diameter -Diameter Mesh Steel Net R~bberI Net of this of OpeningO~)ening NetInvention, Elastomer Ratio Opening Openin~ Rati.o Strand 5 Ratio mm~ mm % . % %
3 lo 59 '~859 l~ 15 62 L~ 3 62 6 25 G5 ___ _ ___ __ 8 30 61~ 1~5 ~I~
8 35 G6 ~"; 66 __. ___ ~ ~ _ _. __ __ ~
o l~(~ 64 53 64 T.~ble 413 Rractic~ll Wei~ht o~` Net or InF,tead Materi11 ._ A _ - C E
_ _ ,__ ~
Diametor Mesh Wei~ht Wei~ht Wei~ht of Opc~ , ~lastomer Str~nd,s mm mm ~ n2 k ~ m ~cg/m2 __ _.
2 6 6.7 13.1 2.4 3 lo lo.o 22.2 ,.l~
L~ 15 13.0 25.0 ~ 3 _ _ ~ ____ . _ _ I
` 20 . 13.~ 25.5 1~.5 6 25 15.8 30.1 5 3 8 3o 20.6 ~2.1 6.9 Area of mesh o~enin (m2) O
S~ace Ratio = l - g - x lC
,~rca of ~ ccntre Or stranc~s diametcr around mesh oepnin~ (m'-) ~- A

Z 1 160aZ97 No~.~ the ~leights of various nets having the area ~Ind tbe speeiI'iecl values ~n Table 4B will be eompared.
The total wei~ht of thc net eonstituted of the strands of the S~R}11~2A material, 10 rnrn in the strarld diameter, and lOO ~
in mesh opcninZ,s waS 20~ '<g and th.lt o~ the net usi.rlg the st:lin-less perforated sheet wai I~Llo kg.
In eontrast, the net accordinlr to this invention weigllcd onl.y 88 Ic6.
Trommels usi.nZ, t;hc nets aceordillg to this invention are advant;ageous in opcration over thor.e using the eonventional nets in the following rospeets: (1) reduction in the power eost, (2) install.ation eosts of power transmission, distribution, and sub-station facilit.ies. Tllc admilli.strtltion and maintenarlee eosts can a]so bc gretltly rcdllcel~Z. (3) tran~spoltation und storage costs become ineY~pensive.
The net aeeording to this inverlti.orl, whcn brolcen down into several p~rts~ clln be tralu~iportc(l l)y a ].i.gllt trtlek insteacl a heclvy traelc as usecZ` ror c;lrryi.llZ~ tll~ tZrolccn-dowll part.i O` a COnVellt:i.Orl net .
Çor~ stcl~].titi.(>lT OT' I c~l.l\c~rllcllt. wo~k, ~t wiil.l bc o~?vious th~t tnc nct accorrlirlg to thi; in~tcrltlon is ac'vtlntal,eolls over any other eonvelltiorlal net r; ~
Some te ts were e~r~ rled on otllcr prr~ctice of the underr:~ention, in thc case of usene.i; to ZJseillatinlg sieve.
The prcsent inverltion condlleted tl te.st for delZonstrrlting bloeking and workabi;ity of the nets aeeording to the embodiments of this invention. Our invest;igation rcsults I'or attesting the 3 ~ ~

limitint, con(litions for tnc occurrence of blockirlg is tabulated below, in connectiGrl with Oscillatirlg Screen to sieve.

Tab]e 5 Blocking & Life (lJsable Span) to Oscillating Screen to Sieve _ Coventional Steel Ncts RubbcrNet o~ the I (1)(2)I (3) NetInvention Diameter of 2 13.0 O
Strands (mm) 1.2 1. 5.0 (thickness) 5-_ _~ ~ ~ __ __ Mesh Opening 3.0 ~.0 l~.O l.~.O 15 0 ____ __~ ______ _. _ _ _ (r.p m.)1,000 800 SOO 1,100 500 __ _~__ __ ~ .~ ____ Vibration 10.0 5.0 10-15 10-12 5 Ampl~tude (mrn) __. ._ _ ____ _.... _.. ____. ~ _.
Net Net Net Net No Blocking Status unusable blocke(i bloclcecl blocked bloeking blocking rno-,tly at al.l __ ___ __ _ _ __ _ . _ ._ ____ ~_ _ _ Usable Period 3-5 3~5 3~5 3~5 > 20 (months) _ _ _ _ __ __ ~ ; wil.l be obvious ~`rom the test data, thc! net aeeording to this inventi.on offers markedly easy worki.ng conditions, srnall rotation specd and vibratioll am~litu(le, reduc~ed power cost and re(luirer; only small seale power fac:ilities.
Further, the net aceordinlJ to this inventi.on has proven to ve outstanding features over the conventioTlal nets, such as, lightweight, larger opening ratios, lont,er durable life spans of the order of 5 to 7 times those of the conventional nets.
Operation of the net a(:cording to thi.s test was stopped _ ~ _ 3~

1 16~597 after it h1l been operat:ed f`or 20 conseculive months. It W.l;
diseovered however, that the net wa~ still repairable, main-tained the same performanee as at the time of in~tallatiorl.
Another important advarlta~e of the uie of the net aceordin~
to this inventi.on is the possibility of` prevention of publie hazard due to sc,und waves. Aecording to our survey, the audible noise heard by norrnal persorls from operLit~on of the net aceordin~?
to this invention decreased markedly an~ notably, the production of inaudible or low-fre~lueney sourld waves of frequencies lc5s tharl 20 ll~..
Whell one considerx that low-fre~uency sound waves are hazardous to t:he Illlrrlan l)o(ty~ one ean easily imagine that the use of the net aceording to this invention serves greltly for the prevention of envirorlmental ha arcls.
There are a few theori.es whierl ~re coneei.vll)le for e]arifyi tne enuses for tho l.east oceuIrenee of low-(rt?quency sound waves from the net leeording to this inventiorl - the air vibration thtnly, t.he metalli.e wire vibratiorl theory ln(l the resonarlee l.h U:)ly. The Ill~:';l'-n~rCmCrlt mcthod fOI' ~.uch h.'l'.'.ardOll'; IOW-'frCqllC~Cy ;ourl(l wav(?s rL~ ot yc~t b~ estL~l-li.51\~!d.
lt nas been vt~rified by our experimellt that use of the net :~ cordi~lg to this inventioll eonstituted o~ abrasion-resistant organic elastomer covered strands consisting of the gl.ass fibre eore strands an(l a polyuretllarle elastomer plays a dominant role for redueine th? production of ha~ardous l.ow-frequeney noise.

1 1~0597 It will be appreciated by persons skilled in the art that the present invention, as described in connection with the several embodiments hereinabove described with reference to the accompanying drawings, will produce a greatly improved screen for use in ore-type sieves. Advantage is taken of the elasticity, strength, abrasion resistance and thc inherent surface smoothness and thermo-plasticity or thermo-setting ability, of the abraslon-resisting organic elastomer strands or portions of the strands. With sieves constructed of strands in the manner hereinabove disclosed, the movement of pebbles or other particles to be sifted is greatly facilitated so as to produce a significant improvement in the efficiency of the sifting process.
Moreover, such sieves will be lighter in weight than prior art sieves;
they can be made smaller; and because of the flexibility of the strands, the sieve screens may even be foldable to facilitate storage and trans-portation. Since the exposed portions of the strands are abrasion-resisting organic elastomers, thc sieve screening will not rust so that it wil:L have a much longer life than prior art screens. In addition, screening so constructed may be more easily repaired and installed and such screening lends itself to mass production. In addition, the sift-ing noise will be found to be significantly reduced. More importantly, however, sieves constructed o strands in accordance with the present invention as hereinabove disclos0d, will be found to be much more accurate in sifting out particular sized particles and, because of the resiliency of the strands or their coverings, clogging of the screen will largely be avoided.
The present invention will be found to be applicable to many different types of net or screens, such as those having very fine mesh _ ~_ ...... ~.~.

1 16~9 i7 openings or very large openings, openings of different size rectangles, or of other polygonal openings. The present invention, therefore, will be found to be extremely useful in many fields and methods of utilization.

_~ _ . .

Claims (13)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A screen for a sieve adapted to sift out from a loose ore conglomerate, particles of a predetermined size, said screen comprising:
a first layer of straight strands, each of said strands comprising a glass fibre core having a covering of abrasion-resisting organic elastomer and having a circular cross-section, said strands being laid parallel to, and spaced by a first pre-determined distance from, each other in a first plane; and a second layer of similar straight strands, said second layer of strands being laid upon perpendicularly with respect to the strands of the said first layer to contact the latter strands at crossing points, each of the strands of said second layer being parallel to, and spaced by a second predetermined distance from, each other in a second plane;
said strands of the uppermost one of said layers ex-tending longitudinally of said screen; and the said elastomer surfaces of the strands of both layers being secured together at their said crossing points by said contacting strands having been heated sufficiently to pro-duce a predetermined degree of melting of said surfaces at said contact points, and thereafter pressed, thereby to fix the cross-ing strands permanently relative to each other to define mesh openings of predetermined configurations and dimensions.

2. A screen as claimed in claim 1, wherein said elongate elements consist of the abrasion-resistant organic elastomer.

3. A screen as claimed in claim 1 or 2, wherein at opposite side edges of the screen and parallel to said first layer of strands, a pair of oppositely facing walls are provided.

4. A screen as claimed in claim 1, wherein the strands of said first layer each have a core and the strands of said second layer consist of the abrasion-resistant organic elastomer.

5. A screen as claimed in claim 4, wherein the thick-ness of the elastomer of the strands of said first layer is equal to one to three times the thickness of the strands of said second layer.

6. A screen as claimed in claim 1, wherein the opposi-tely facing walls are fixed relative to each other, and the strands of the upper layer are provided with a greater thickness of abrasion-resisting organic elastomer than strands of the other lower layer.

7. A screen as claimed in claim 1, wherein the strands of both the first and second layers of strands comprise cores welded together at their crossing points and, after having been so welded together, provided with coverings of an abrasion-resisting organic elastomer.

8. A screen as claimed in claim 1, wherein at least one additional layer of strands is disposed below the first layer of strands at angles with respect to the strands of both said first and second layers to cross the strands of both layers near their mutual contacting points, thereby to define with said crossing strands of the first and second layers, small triangles near said contacting points.

9. A screen for a sieve adapted for use as a screen or a conveyor for selective screening and transportation of an object to be processed, comprising:
a first layer of straight transverse strands disposed in a plane;
a second layer of straight longitudinal strands dis-posed upon said first layer of said transverse strands so as to be in a different plane;
said strands each comprising a glass fibre core covered by an abrasion-resisting organic elastomer;
said transverse strands being disposed orthogonally to the direction of progression of said objects to be processed and parallel to each other and being spaced by a first predeter-mined interval distance from, and rigidly fixed with tension to the side plate body for supporting the screen;
said longitudinal strands having the same or larger thickness of elastomer than said elastomer of said transverse strands;
the said elastomer surfaces of the strands of both layers being secured together at their said crossing points by said contacting strands having been heated sufficiently to produce a predetermined degree of melting of said surfaces at said contact points, and thereafter pressed, thereby to fix the crossing strands permanently relative to each other to de-fine mesh openings of predetermined configurations and dimen-sions;
said screen having a space ratio of at least 60%; and means for tensioning the strands of said first layer, the strands of said second layer being untensioned.

10. A screen as claimed in claim 9, wherein said strands comprise cores of metallic wire, organic polymer or inorganic fibre.

11. A screen for a sieve or a trommel sieve, compris-ing:
a first layer of transverse strands in one plane;
a second layer of longitudinal strands disposed upon said first layer of said transverse strands and in a different plane;
said strands each comprising a glass fibre core having a covering of abrasion-resisting organic elastomer;
said transverse strands being disposed parallel to each other at predetermined intervals, and fastened, with tension, rigidly to supporting side plate members;
said longitudinal strands being disposed at predeter-mined equal intervals;
said elastomer comprising polyurethane;
said elastomer surfaces of both layer strands being fused together at their cross contacting surface points to define mesh openings of predetermined configurations having mesh opening side dimensions from two to seven times the strand diameters of said strands;

said strands having glass fibre cores; and said screen having a space ratio of at least 60%;
and means for tensioning the strands of said first layer, the strands of said second layer being untensioned.

12. A screen as claimed in claim ll, wherein the thickness of said abrasion-resisting organic elastomer is 1.3 -3.5 times the diameter of said fibre cores.

13. A screen as claimed in claim 11 or 12, wherein the elastomer thickness of the longitudinal strands is one to two times that of said elastomer of said transverse strands.