GB1561802A - Strands and netting and screens made thereof - Google Patents

Description

(54) IMPROVED STRANDS AND NETTING AND SCREENS MADE THEREOF (71) I, YURIKO KAI of 1918, 5-Chome, Hakataekiminami, Hakata-Ku, Fukuoka-Shi, Fukuoka-Ken, 812, Japan, a Japanese citizen, do hereby declare the invention, for which I pray that a patent may be granted to me, and the method by which it is to be performed, to be particularly described in and by the following statements: The present invention relates generally to screens of netting or screening mesh which is intended to be incorporated in apparatus or devices designed to sift finer materials which are intermingled with coarser materials, as for example, ores.

Prior art screens for sifting apparatus and other uses in industry has generally been formed of interlaced or woven metallic strands. When used to sift certain materials, such as ores or other hard substances, the noise produced, as such materials are passed across the screening area, may be objectionably loud. Such noise can be produced either by the material bouncing across the metallic strands of the screen, or by the material causing the wire strands to rub against each other.

Another objection to the metal screens of the prior art is that the metallic wires can abrade the material being passed over the screening and some instances such abrasion may not be desired. Alternatively if the material being sifted is very hard the metal screening itself may become abraded. In addition, such prior art metal screens may require a considerable amount of time on the part of service personnel to be mounted, removed or repaired. Further, such screens can become plugged or deformed by the materials being sieved, thereby adversely 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 a deformed part of the screen.In addition, it is well known that prior art metal screens do not ordinarily last for a long period of time when subjected to intensive use in a sifting process, being subject to rust or other deterioration, not only in use, but even when placed in storage. Lastly, metallic screens are normally heavy and thus add greatly to the weight of sifting frames or mountings so that they may be inconvenient to hand.

It is difficult to desolve blocking and to remove clogging from the mesh openings and to obtain accurate screening, to avoid the generation of waves at frequencies hazardous to the human body, and also to achieve a long life span.

The present invention seeks to obviate the problems engendered by metallic screens utilised in prior art sifting apparatus as hereinabove described.

Accordingly the present invention consists in a screen for a sieve adapted to sift particles of a predetermined size, said screen comprising: first and second layers of strands, each of said strands comprising an elongated element having at least its outer exposed surface constituted of an abrasionresisting organic elastomer, the strands of said first layer being laid parallel to, and spaced by a first predetermined distance from, each other in a plane; and the strands of said second layer being laid over, and orthogonally 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; the said elastomer surfaces of the strands of both layers being fused 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 cooled, thereby to fix the crossing strands permanently relative to each other to define mesh openings of predetermined configurations and dimensions, the area of the mesh openings being at least 43% of the total area of the screen.

The present invention also consists in a sieve for separating material incorporating a screen as set forth above, and comprising a pair of parallel members to which the strands of said first layer are connected whereby the strands of said second layer extend parallel to said members and to the direction of travel of the material to be sieved when the sieve is in operation.

In the special case of a netting or screening having large openings, the mesh may be constructed with metal strands with the surface of each metal strand being covered with an abrasion-resisting organic elastomer. A metallic net constructed in this way is thus covered on its entire surface with an abrasion-resisting organic elastomer. The elastomer contacting points of the coverings may then be heated to fuse or melt together the thus contacting organic elastomer points. Where such coverings are provided they should be sufficiently thick to insure durability in accordance with the shaping of the openings.

In addition to arranging the strands to provide square or rectangular openings in the manner hereinabove explained, the net may be reinforced by placing metallic strands of smaller cross section than the cross sections of the strands utilized to form the netting or screening, 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 approximate square openings and other sizes of the net 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 interval distance of the transverse strands, 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 polygonal cross section of a large sectional area in order to insure sufficient durability to the transverse strands, when made of an abrasion-resisting organic elastomer, and may be arranged to keep the space ratio of the net, forming the opening of each other rectangular shape.During screening the strands are caused to vibrate; the strands in upper layer guide and help the movement of the object to be screened.

When utilized for sifting ore, the ore pebbles which may arrive at the opening part of the net, will snap back 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. Eventually, the upper strands of the net cause the advance of particles to be concentrated and operate to promote the efficiency of the riddle, rapidly in the longitudinal direction to make screening accurate, and in that the occurrence of sound waves at frequencies hazardous to the human body, being minimized and the life span of net be able to sufficiently be extended. As the transverse strands may be constituted of strands with cores, and as such be rigid, they do not loosen.Even if the strands without cores are used, by employing urethane elastomers having small percent elongatlons, the same kind of eflect may be attained because of their high abrasion-resisting characteristics-even superior to piano wires-and its non-loosening property.

It will be readily appreciated by those persons skilled in the art that a screen constructed in accordance with the present invention, particularly when employed in a sifting device or apparatus, offers many advantages over prior art screens in that, when sifting of material occurs, the noise level is significantly reduced; resistance to abrasion is improved both in respect of the material being sifted 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 its use and/or storage; the screen construction is readily adaptable for mass production; and its mounting, removal, maintenance and repair is greatly facilitated so as to require a minimum of time and labor.In addition, because of the resilience of the elastomer of the strands or their coatings, vibration of the sifting screen better enables particles of the proper screen size to pass through the screen openings and not to become clogged in the mesh, as is so frequently the case with prior art metal screening. Thus, the screening of the present invention offers many advantages over metallic screening of the prior art.

According to a feature of the present invention, in order to maintain the tension of the net or screen in the transverse direction, each end of the transverse strands may be secured by a metal fitting, such as solderless terminal or a fitting. A nut having an inside screw thread is tightened between the upper clamping plate and the lower clamping plate and is secured, for example, by means of a bolt, nut or rivet. Furthermore, the inner edge of the lower clamping plate may be 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 clamping plate when the screen net is set up and vibrated as the material being screened is passed thereover.

Moreover, when the screen net is clamped 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 of a suitable strip of abrasion resisting organic elastomer may be secured on the upper surface of the upper clamping plate by fusion or some other suitable method.

In order that the present invention may be more readily understood, various embodiments thereof will now be described by way of example and with reference to the accompanying drawings, in which: Figures IA and IB 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 embodiment 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 4 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 sieve; Figures 6A through 61 show different cross-sectional configurations of abrasion resisting organic covers for wires; Figures 7A, 7B and 7C are a plan view, and two side elevations, respectively, of an embodiment of this invention in which its transverse strands have cores; 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;; Figure 10 is an enlarged and cross sectional view of a portion of the sieve shown in Figure 8, illustrating the means to anchor the net or screen; Figures I IA and 11 B are a plan view and a side view, respectively, of another embodiment of the present invention; Figure 12 is a perspective view of a sieve incorporating a net or screen; wherein traverse elastomer covered strands also extend through additional longitudinal strands; Figures 13A and 13B are a plan view and a side view, respectively, 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 15A and 15B are cross sectional views of a net or screen in which wires illustrated in the Figures 14A, 14B and 14C are provided with coverings of an abrasion-resisting organic elastomer; Figure 15C is an enlarged cross sectional view of a portion of the net or screen shown in Figures 15A and 15B; Figure 16 is a perspective view of a tube or trommel in which is installed a net or screen of the type shown in Figures 15A and 15B;; Figures 17A and 17B are a plan view and a side view, respectively, of a net or screen constructed with metallic wires which have square cross sections; Figures 1 8A and 1 8B are cross sectional views of the net illustrated 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 invention; Figures 19B 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 still another embodiment of the present invention;; Figure 21 is an enlarged view of a portion of the sieve shown in Figure 20; Figures 22A and 22B are cross sectional views illustrating means for mounting netting or screening in a sieve in accordance with the present invention; Figures 23A and 23B are plan views of other embodiments of the present invention, illustrating two means for mounting exposed strand cores comprising fine wires; Figure 23C is a plan view of the metal spacer shown in Figure 23A.

Referring to Figures 1A and 1B of the accompanying drawings, a screen or net constructed in accordance with the present invention comprises a plurality of equidistantly spaced parallel, horizontal strands 1 laid in a common plane to constitute one layer over which is laid a second layer of equidistantly spaced parallel strands 2 which extend at right angles to the strands 1.As used in this specification, the word "strand" includes not only thin, elongated elements such as solid or twisted metallic wires, filaments, twisted chemical or naturally spun fibers and metallic rods or bars of small cross section or diameter, but also includes elongated, thin elements of rubber, elastomer and any metallic or other thin elongated element which is mixed or coated with any of such elastomers; or thin, elongated elements thereof and strips of any of such elements or elastomers. In this connection the term "abrasion-resisting organic elastomer" should be deemed to include without limitation, natural rubber, synthetic rubber, chemical polymerizing materials as, for example, isoprene, neoprene, and a product which is sold under the trademark "S.B.R.", and polyurethane elastomers, which have abrasionresisting properties.

After the layer of strands 2 has been laid over the layer of strands 1, as shown in Figures 1A and 1B, the two layers are subjected to sufficient heating to cause all points of contact of the strands 2 with the strands 1 to melt and fuse together. As a result of the commencement of melting and fusing of the elastomer content or coating of the two strands, when the strands cool, the crossing strands will become fixed relative to each other to form a net or screen in the pattern in which they have been thus laid.

In the embodiments of the invention shown in Figures 2A, 2B, 3A and 3B, fewer and more widely spaced strands 2 are provided than in the embodiment of Figures 1A and 1B, with the result that in the case of the embodiments of Figures 2A, 2B, 3A and 3B, the interstitial openings or mesh defined by the crossing strands 1 and 2 will be observed to be elongated rectangles and not the squares shown in the embodiment of Figures 1A and 1B. Thus the exact structure of the mesh of the screen may be preselected with reference to the relative 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-resisting organic elastomer, such as a urethane elastomer or an abrasion-resisting 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 laid to cross strands 1 at right angles. The spacing between the strands of each of the layers is such as to define the required size of mesh openings, and the two layers of strands are secured together by heating to cause them to fuse at their contact or crossing points in the manner previously described. As can be seen in Fig. 7C the strands 1 have cores.

The net or screen thus constructed may be incorporated in an automatic vibrating sieve device of the type shown in Figures 8 and 10. Such incorporation may be accomplished by inserting 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 sieve. 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 orifice D"' in the channel D and through another orifice C" in the wall C. By virtue of the arrangement of the spring G, washer H and nut I shown in Figure 10, it may be seen that the channel D may be drawn toward the wall C by tightening of the nut I on the screw E.Thereby, the transverse strands 1 may be brought into tension from both of their ends, while the longitudinal strands 2 will be unaffected by such tensioning.

It will be recognized by those persons skilled in the art that Figure 8 discloses 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 particles or pebbles (not shown) are rolled downwardly along the screen mostly between the strands 2 and over the strands 1. As such rolling occurs, the pebbles or particles which are smaller 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 end of the screening to be deposited in another area or receptacle (also not shown). Thereby, the two different sizes of particles or pebbles may be sorted out.Since size difference may mean a difference in mineral content, screens constructed as described herein may greatly improve the desired sorting out of the different size pebbles in the course of an ore concentrating process. Because of the resiliency of the abrasion-resisting organic elastomer strands of which the screening is constructed, ore pebbles of a size which might be stopped in but not pass through openings in a prior art metal wire screen will be caused either to fall through the openings, if they are small enough in size, or to be bounced out of the mesh openings so as not to block the same. Thus an ore sieve constructed of screening as described herein may attain a high degree of efficiency. Further contributing to such efficiency is the placement of the strands 2 along the lines of travel of the pebbles.By so disposing the strands 2, a plurality of channels are effectively created along which the ore pebbles may be more rapidly moved during the sifting process. Because the transverse strands are tensioned to a rigid state, 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 coreless,if a urethane elastomer having a small percent of elongation, when tensioned, is employed, such coreless strands will still be effective because of their high abrasion-resisting capacity, as compared with strands of the type used for piano wire.

The next used in one example was that shown in Fig. IA, 1B and comprising two kinds with different meshes. The strands were made of urethane elastomer.

After 60 day's use as a sieve dealing with particulate matter in flowing water, in case of the strands with 10 mm diameter, 0.2 mm was damaged, and in case of strands with 8 mm diameter, 0.2 mm was damaged likewise. This result shows that the product according to this invention has high durability. Furthermore, blocking of the openings was very rare. They could be repaired, maintained and stocked easily.

The results of the comparison of abrasion-resisting ability and other physical properties between a net constructed in accordance with the present invention and conventional ones are shown in Table 1. As can be understood from examining this table, the net according to the present invention is superior to the conventional ones referred to in Table 1.

TABLE 1 The result of comparison between the strands according to this invention and conventional one

Strand according this invention Conventional strand Measured under Abrasion- Wire used the condition Urethane resisting for Item defined by Dimension elastomer rubber Brass Steel piano Remarks Hardness Japanese Industrial Shore Standard (J.I.S.) hardness HS HS HS K-6301 degree 85** 80** 24* 32* 55* Tensile J.I.S. K-6301 kg/cm2 400** 180** 35* 60* 100* strength kg/mm2 kg/mm2 kg/mm2 Percentage J.I.S. K-6301 % 600** 550** - - elongation Resistance to tear off J.I.S. K-6301 kg/cm2 80** 40** - - Thickness Thickness abrassived ratio 1.0 4.0 15.0 7.02 - in case that abrassived for sand brast the rate of abrassive of urethane elastomer regard as 1 Thickness abrassived in sand Thickness abrassived ratio 1.0 12.0 - 16.3 4.0 ditto Note: In the table *Hardness of metals is based on Japanese Industrial Standard (J.I.S.) Z-2246, and tensile strength of metals is based on J.I.S.Z-2241. **Hardness, tensile strength, percentage elongation and resistance to tear off of this invented strands is based on J.I.S. K-6301.

Table 2. As can be understood from this table, 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 for the same strand interval.

TABLE 2 The aperture area or space ratio by percentage of the nets according to this invention and conventional net (an example) aperture area or space ratio by percentage

Diameter I Screen according to Knitted cross Strand this invention Metal rubber section interval (cored strand) screen screen 2.6 5mm 43% 43% 39% 3 lornrn 49% 49% 35% 4 15 mm 62% 62% 42% 6 25 mm 65% 65% 46% 8 30 mm 64% 64% 44% 8 35 mm 66% 66% 46% 10 40 rrn 64% 64% 45% 10 50 mum 67% 67% 45% When large aperture area is desired, those structures given in Fig. 2A, 2B and 3 may be chosen. The structure of the net can be chosen as to the priority between accuracy and efficiency of riddle.

Referring to Fig. 6A6I, some cushion-like structures for receiving strands are shown. In each of structures a strand of abrasionTresisting elastic organic material is inserted to receiving groove B of the cushion A, the cushion A being made of the same kind of abrasion-resisting elastic organic material. Then this is welded to form single wire. Alternatively the strand could comprise twisted metal wires or mono-filament of synthetic resin with small expansibility. As in the previous examples the strand is placed in the receiving groove B and can be used as a strand of a netting after being welded together. The shape of the cross section of the structures A can be of any desired form. Composite strands of this kind can be used in the embodiments shown in Figs. 1, 2 and 3.These composite strands can be used in.the embodiments shown in Figs. 7A, 7B, 7C, 8 and 9. Here, the transverse strands I are urethane elastomer with a core and having dimensions similar to those given in Table 1, form the lower part of the screening. The upper part of the screening is formed by the strands 2 without a core and of urethane elastomer, the strands 2 forming the longitudinal lines.

In the embodiment of the invention illustrated in Figures 1 lA, IIB, 13A and 13B, the screening is constructed with mesh openings in the form of long rectangles. In this embodiment of the invention, the strands 1 may be made of a thermoplastic urethane elastomer and are arranged at equal intervals to provide a predetermined length of openings in the direction of travel of material to be sieved along the sieve. The strands 3, which may also be of the same elastomer, are secured to the transverse strands 1 by heating both sets of strands 1 and 3 to the point where they fuse together in the configuration shown in Figures 11B 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 1 lB and 13B, the longitudinal strands 3 are shown to have square cross sections, it will be understood by those skilled in the art that the cross sections of the longitudinal strands may be square, rectangular, polygonal or round.Desirably, the thicknesses (i.e., the cross sectional areas) of both the longitudinal and transverse strands 3, 1, 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 IIA, 11B, 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 thermo-plastic urethane elastomer and transverse strands or cords 4. The latter cross the strands 3 of the lower net at right angles thereto and pass below the strands 3 only at such points of crossing. Both the strands 3 and 4 are secured together by fusing at their crossing points. Strands 2 of the upper net are also arranged to cross at right angles with respect to strands I of the lower net with their spacing being the same or almost the same as those of the transverse line.The parenthesized numerals in Figures I IA and 11B denote parts of the upper net. The sifting screen thus structured by the upper and lower nets just described is illustrated in Figures 13A and 13B. The longitudinal strands 3 in the lower net and the crossing strands or cords 4, in the upper net are secured together by heating them to a temperature at which they fuse at their mutual cross points. However, while the strands 1 of the lower net may cross the strands 2 of the upper net at right angles, there will be a small vertical spacing or gap between them. Since, therefore, there is no contact between strands 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 of the sieve to handle a greater volume or ore particles or pebbles, or effect a more accurate sifting of the ore particles oF pebbles. The installation of such a two-layer screen may be accomplished in the same manner as that described above in connection with Figures 8 -and 10 of the drawings.

Referring to Figures 13A and 13B, it may be seen that the net has mesh of an extended long rectangular form. The strands 1 made of thermoplastic urethane elastomer are arrayed in equi-intervals corresponding to predetermined size as transverse lines. The strands 3 comprise thermoplastic urethane elastomer are 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 of both longitudinal and transverse strands should be such that they will wear away over approximately the same time period. Thus, for example, the longitudinal 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 sifting screen of the type just described, sifting is accomplished through the meshes defined by the strands of both the upper and lower nets or screens. Between the two layers there may be mesh openings thus defined which are both almost square at one level, and in the configuration of long rectangles, at another level. Ore pebbles or particles passing over the screen therefore, do not tend to get caught in the mesh openings to clog up the sifting screen because of both the resiliency of the strands and the particular sizes and configurations of the mesh openings which they define.

Ores having a large clay content, therefore, do not tend to clog up the sifting screen.

Fig. 12 is a perspective view of a sieve incorporating a net or screen; in which the traverse elastomer covered strands also extend through special longitudinal strands 3(4) which are also of abrasion-resisting elastomer.

Figure 16 illustrates the manner in which netting or screening constructed in accordance with the present invention may be employed to line the inside of a tube or trommel K.

In the embodiment of the invention illustrated in Figures 14A, 14B and 14C, the screen or net is constructed of transverse metal wires 5 having circular cross sections and longitudinal metal wires of the same cross sections. The wires 5 and 6 are so spaced and arranged to cross each other and to define square mesh openings, and may be secured to each other at each contact point by welding. While square mesh openings are thus shown and have been selected 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 intervals of spacing. In some instances, if large mesh openings are desired and heavy materials are to be sifted, rods or bars could be substituted fSo'r the wires 5 or 6 shown in Figures 14A, 14B and 14C.

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 utilized to define the mesh openings, the present invention contemplates that the external surfaces of the metallic wires or strands will be covered with an abrasion-resisting organic elastomer. Such covering may be accomplished either by using prefabricated cushions of abrasion-resisting organic elastomer in some configuration such as is illustrated in cross sections in Figures 6A through 61, with the ends of such coverings fused together at each contact points; or, alternatively, the metallic wire net may be covered directly with such an elastomer.In this manner, the final metallic wire netting which is covered with the abrasion-resistant organic elastomer will appear either as shown in Figures 15A, 15B and 15C, or, if the strands are provided with square cross sections as shown, for example, in Figures 17A, 18A and 18B. Obviously, the strands 5 and 6 could have any other polygonal cross section.

When it is desired to apply some type of covering, such as any of those illustrated in Figures 6A to 61, or others, to a metal bar or wire netting, a suitable groove B is provided in the covering A. Alternatively, a strand 5 or 6 could be inserted in the hollow core M of a cylindrical type covering A' before 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 mesh openings N may be modified by providing bridging strands 7 to extend across the corners formed by the intersections of the strands 5' and 6'. The strands 7 may be metal wires, each of which may be covered with an abrasion-resisting organic elastomer in the manner described above with reference to Figures 15A, 15B, 15C and 18A and 18B.

Thereby, the corners of the large mesh openings may be cut off at angles 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 particles, as well as to reinforce the net. This constitutes a special application of the present invention and should not be regarded as necessary for the practice thereof.

Figures 22A and 22B (and 23A, 23B and 23C) illustrate 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 the embodiment of Figures 22A and 22B, a strip 14 of an abrasion-resisting organic elastomer may be provided to cover the upper surface of an upper clamping plate 12. This covering strip 14 may have an edge 16 which extends inwardly toward the center of the screen and beyond the inner edge 18 of the upper clamping plate 12.

Such a covering strip 14 serves not only to protect the upper clamping plate 12 and the metal fitting 17, but also to prevent the upper surface of the organic elastomer strand 1"' from being brought into contact with, and damaged by the inwardly extending end 18 of the upper clamping 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 strands 1"' from being damaged or deformed when the two clamping plates 11 and 12 are tightened together by the fitting 17. It will also be noted that the inner edge of the clamping plate 12 may extend further toward the center of the screen than the downwardly curved edge 13 of the lower clamping plate 11, thereby more effectively to prevent shearing of the lower surface of the transverse strand.

After the organic elastomer covering 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 inserted 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 with its inserted strand core end 5' may then be clamped between the upper metal clamping plate 12 and the lower metal clamping plate 11, both of which clamping plates may be drawn tightly together by means of the fitting 17. The 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 tightened by such devices as are shown in Figures 22A and 22B, the transverse strands 1"' should remain undamaged and not become loosened.

In the embodiment of the invention illustrated in Figures 20 and 21, the transverse strands 1" comprise a single cored strand of an abrasion-resisting organic elastomer, one end la of which may be secured to the bottom 8'a 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, 8', respectively, with the other end lb of the strand 1" terminating at, and being secured to, the upper top end of the side member 8'b. If the two side members 8, 8' are pulled apart from each other, they will effect a tightening of the strand 1". Longitudinal strands 2" may then be placed over the thus laced strand 1" with the crossing points being secured by fusing in the manner heretofore described.Alternatively, tightening of the strand 1" in its laced pattern may be accomplished by the means shown in Figure 10 with the shear preventing strip 14 and channel 15, illustrated in Figures 22A and 22B and discussed in connection with those Figures, being additionally provided.

In the embodiment of the invention illustrated in Figure 23A, the ends of the plurality of exposed cores 5" of strands 1"' may be brought together and inserted into a metal clamping member 19 to be secured therein. Such core ends may be .brazed into the element 19. In addition, a metallic or other type of spacing member 20 may be provided with a series of spaced grooves 21. Such grooves may be equidistantly spaced from each other or spaced at any other desired interval or intervals. When the exposed cores 5" are laid into the grooves 21 in the member 20, the desired spacing of the strands 1"' will be properly established and maintained.

Should it become desirable to prevent the wire cores of a net or screen from becoming separated from their organic elastomer coverings, after the transverse strands have been cut or otherwise formed to the required length and their organic elastomer coverings have been removed from the ends of such strands 1"' 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, of course, to cause such fusing of the strand coverings on the cores even without first stripping the coverings from the ends of the cores as shown in Figure 23A. Heating to cause such fusion could be provided by passing a sufficient electric current through the wire core to raise the temperature of the latter to somewhere between 250 to 3000 for a brief period.At such temperature range, a covering of, for example, urethane, will begin to melt and thereby fuse 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 strands, tension of the transverse strands may be better maintained in netting or screens of the type hereinabove described.

From the foregoing description of various embodiments, several common features will be apparent. Thus in the embodiments the surface portions at least of the strands of which the various nets or screens are composed consists of an abrasion-resistant organic elastomer body. Where necessary, elastomer-covered core strands consisting of core strands having no elongation property and an abrasion-resistant organic elastomer body can be used in such a manner that no slack may be produced in the transverse strands.

As the cores of cored strands there can be used, not merely metallic wires such as piano wires, but also a fibre material such as nylon (Du Pont's trade-name, polyamide system fibre), and daclon (also Du Pont's trade-name, polyester system fibre) possessing a small elongation property can be used.

Carbon fiber 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 3 shows some dimensions of glass-fibre core strands covered with an elastomer whose principal constituent is a polyurethane elastomer, together with the elastomer covering ratio and the space ratio.

TABLE 3 Space Ratios of the Cored Strands according to this in vention

A B A/B C D E Diameter of Cored Diameter Ratio of C Elastomer of Glass Elastomer Mesh (Mesh opening) Covered Fibre Core Covering Opening to Core Strand Space Ratio Strands Strands Ratio mm Diameter % 1.2# 0.8# 1.5 3#4 Approx. 3 Approximately 60% maintained 1.6# 0.8# 2.0 3#5 " 3 for each case.

This is 1.5#2.0 2.0# 1.2# 1.7 4#7 " 3 times that of known knitted 3.0# 1.2# 2.5 5#12 " 2#4 nets.

4#6# 2.0# 2#3 10#30 Approx. 2.5#5 8#10# 3.0# 2.7#3.3 20#45 " 2.5#5 12# 5.0# 2.4 30#150 " 2.5#10 16# 5.0# 3.2 30#150 Approx. 2#10 20# 10.0# 2.0 100#200 " 5#10 30# 10.0# 3.0 100#200 " 3#7 A: finished strands diamet er mm to be used net Mesh opening mm D= Strands diameter having core mm Screening was carried out with nets having, as shown in Table 3, mesh openings of which ranged from 3 mm to 200 mm.In conducting this experiment the abrasion-resistantd organic elastomer diameters ranged from 1.2-30 mm, the glass fibre core diameters from 0.8 to 10 mm, the diameters of the elastomer-covered strands ranged from 1.5-3.5 times the diameters of the core strands, and the space ratio of 60% was maintained.

In the embodiments of this invention previously, the four sides of each mesh opening have two different levels because of the upper and lower layer strands, whereas according to the conventional knitted nets, the four sides of each mesh opening lie substantially in a single plane. This difference is the cause for permitting the space ratios previously described to be made greater than those of the prior art nets. This difference, allowing a space ratio of at least 43%, and in many cases at least 60%, plays an important role for the improvements obtained in both screening and workability.

The thickness ratio between the upper and lower strands of the screenings described herein was also investigated. Tests with various embodiments were carried out by making the elastomer thickness of the upper layer elastomercovered strands vary from one to five times that of the lower layer elastomercovered strands. These tests verified that the thicknesses in the ratio of the order of one to three times provide a favorable result. Since the upper layer strands have naturally a higher contact ratio with the material being processed than the lower layer strands, a well-balanced durability life span for both layers can be expected from this order of thicknesses.

However, this ratio is subject to change with the kind of object to be processed or the operating circumstances, etc.

With each of the embodiments using the glass-fibre core strands shown in Table 3, the ratio of the diameter of the cores of the strands to the diameter of the complete elastomer-covered strands was also investigated.

It was discovered that the optimum ratios of the external strand diameter to the glass fibre core ranged between 1.5 to 3.5. The optimum ratios where the elastomer strand diameters are small and the mesh openings are fine should preferably be between 1.5 and 20. This ratio should be subject to variation with the kind of object to be processed or the operating conditions, the optimal value ranging between 1.3 to 3.5.

In conducting the tests of all embodiments shown in Table 3, which maintained the space ratio of 60%, the average side dimension of the square or rectangular mesh openings varied from 2 to 10 times the average diameter of the strands or wires. The mesh openings should preferably be of the dimensions equal to 2~7 times the diameter of the organic elastomer-covered strands of which the net is composed. The recommendable ratio for the fine mesh openings should be from 2 to 4, while that for the large mesh openings of 100 mm or above should be from 3 to 7. Of course, these ratios must be suitably adjusted depending on the object to be processed or the operating conditions.

Table 4A shows the results of a series of measurements made regarding nets of different kinds, including some embodying the present invention.

Table 4B shows the results of weighing different kinds of nets were investigated as an important reference problem. The weight of the net with 100 mm mesh openings made of conventional steel wires SWRH42A (conforming to the Japanese Industrial Standard, JIS-G 3506-1971, C 0.39~0.46%, Si 0.150.35%, Mn 0.30.6%, both P and S - less than 0.04%) was 13 kg/m2. The 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 weight of the net with 100 mm mesh openings constituted of the glass fibre core strands covered with an abrasive-resistant organic elastomer having an overall diameter of 10 mm was 4 kg/m2. This corresponds to only 30% of the weight of the steel wire net and 20% of that of the stainless steel perforated plate.

The total weight of the net constituted of the strands of the SWRH42A material, 10 mm in the strand diameter, and 100 mm in mesh openings was 286 kg and that of the net using the stainless perforated sheet was 440 kg.

In contrast, a net embodying the present invention weighed only 88 kg.

This feature of lightweight offers marked advantages in transportation, administration, storage, repair, and installation, as well as in workability.

With the conventional screen nets such as steel nets, increasing the mesh opening ratios was invariably accompanied by the defect of deteriorating the durability and shortening the serviceable life. This problem has been solved by this invention as has been described by reference to the embodiments indicated in Table 4A, 4B.

Trommels or sieves have been used for screening lime stone, ore, crushed stones for mixing concrete.

Presented below are the results of investigations for several embodiments of nets for use with concrete mixing trommels having diameters of 900-1500 mm and lengths of 3,000-10,000 mm.

The description will be limited to the trommel net dimensions of a cylindrical form having the diameter of 1,000 mm, the length of 7,000 mm, and the area of 22 m2.

TABLE 4A Practical Measured Space Ratio to Strand Diameter

Diameter Rubber Opening Ratio of Steel Net Net of Net Elastomer Mesh Opening Opening embodying Strands Opening Ratio Ratio present mm# mm % % invention, % 3 10 59 48 59 4 15 62 43 62 6 25 65 48 65 8 30 64 45 64 8 35 66 44 66 10 40 64 53 64 10 45 53 53 67 TABLE 4B Practical Weight of Net or Instead Material

A B C D E Diameter Weight of Weight Weight of Net Elastomer Mesh of of embodying Strands Opening Steel Net Rubber Net the invention mm mm kg/m2 kg/m2 kg/m2 2 6 6.7 13.1 2.4 3 10 10.0 22.2 3.4 4 15 13.0 25.0 4.3 5 20 13.4 25.5 4.5 6 25 15.8 30.1 5.3 8 30 20.6 32.1 6.9 Area of mesh opening (m2) Space Ratio = x 100 Area of 4 centre of strands diameter around mesh opening (mD Trommels using the nets embodying the present invention are advantageous in operation over those using the conventional nets in the following respects: (1) reduction in the power cost, (2) installation costs of power transmission, distribution, and substation facilities. The administration and maintenance costs can also be greatly reduced. (3) transportation and storage costs are reduced.

For installation or replacement work, it will be obvious that nets embodying the present invention are advantageous over any other conventional nets.

Additional tests were also carried out with different types of screens in an oscillating sieve to determine the operational effectiveness and degree of probability of blocking of the nets embodying the present invention. The results of these tests are shown in Table 5.

TABLE 5 Blocking & Life (Usable Span) of various sieve nets in an Oscillating Screen Sieve

Conventional Steel Nets Rubber Net of the (l) (2) (3) Net Invention Diam-eter of 1.2 1.2 5.0 13.0 5.0 Strands (mm) (thickness) Mesh Opening (mm) 3.0 3.0 15.0 15.0 15.0 Rotation Speed (r.p.m.) 1,000 800 800 1,000 500 1,100 Vibration Amplitude (mm) 10.0 5.0 10--15 10^12 5 Blocking Net Net Net Net No Status unusable blocked blocked blocked blocking blocking mostly at all Usable Period (months) 3~5 3-5 5 3~5 315 > 20 As will be obvious from the above table, the embodiment of a net according to the present invention offers markedly easy working conditions, small rotation speed and vibration amplitude, reduced power cost and requires only small scale power facilities.

Further, the net embodying the present invention has proven to have outstanding features over the conventional nets, such as, lightweight, larger opening ratios, longer durable life spans of the order of 5 to 7 times those of the conventional nets.

In this test operation of the net embodying the present invention was stopped after it had been used for 20 consecutive months in the sieve. It was discovered, however, that the net was still repairable, maintained the same performance as at the time of installation.

Another important advantage of the use of the net according to this invention is the possibility of prevention of public hazard due to sound waves. According to a survey, the audible noise heard by normal persons from operation of the net used in the test decreased markedly when compared to conventional nets. Furthermore the production of inaudible or low-frequency sound waves of frequencies less than 20 Hz.

When one considers that low-frequency sound waves are hazardous to the human body, it can easily be imaginedthat the use of the net -according to this invention serves greatly for the prevention of environmental hazards.

There are a few theories which are conceivable for clarifying the causes for the reduced occurrence of low-frequency sound waves from the net according to this invention -- the air vibration theory, the metallic wire vibration theory, and the resonance theory. The measurement method for such hazardous low-frequency sound waves has not yet been established.

It has been verified by our experiment that use of the net according to this invention constituted of abrasion-resistant organic elastomer covered strands consisting of the glass fibre core strands and a polyurethane elastomer plays a dominant role for reducing the production of hazardous low-frequency noise.

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 the inherent surface smoothness and thermo-plasticity or thermossetting ability, of the abrasion-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 tobe 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 transportation. Since the exposed portions of the strands are abrasion-resisting organic elastomers, the sieve screening will not rust so that it will 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 sifting noise will be found to be significantly reduced. More importantly, however, sieves constructed of strands in accordance with the present invention as hereinabove disclosed, 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 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.

The various embodiments of nets or screens herein described are formed of crossing strands of an abrasion-resisting organic element, and the sieves are constructed with such netting or screening. The strands may be either cored or coreless. Where a core is provided it may consist of some type of metallic wire, inorganic fibre or organic polymerized elongationless strands, either solid or formed of monofilament or twisted strands. The net or screen is formed by arranging one set of strands in a plane parallel to each other and spaced apart by predetermined distances and placing a second set of strands, spaced at the same or other predetermined distances parallel to each other, transverse to and on the first set of strands. The two sets of strands are caused to adhere to predetermined points of contact by heating to a temperature at which the contacting elastomers fuse to each other.Netting or screening so formed may be employed to construct screening, such as may be employed in sieves, particularly for sifting out finer materials from coarser materials. Such sieve construction may be accomplished by inserting the ends of one set of strands of the netting in clamping plates and drawing said plates apart from each other by tightening them against walls spaced from each other.

A net or screen can screen without blocking, it has a long life, it can advance the object elastically and speedy, and it does not cause hazardous sound waves.

Among other of its advantages are:- its lightweight and ease of handling; no possibility of the production of rust or corrosion; ease of transportation, storage, administration, installation, replacement, and repair; the capability of making the opening ratio large; long durability; and improvements in workability and screening.

WHAT I CLAIM IS: 1. A screen for a sieve adapted to sift particles of a predetermined size, said screen comprising: first and second layers of strands, each of said strands comprising an elongated element having at least its outer exposed surface constituted of an abrasionresisting organic elastomer, the strnads of said first layer being laid parallel to, and spaced by a first predetermined distance from, each other in a plane; and the strands of said second layer being laid over, and orthogonally 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; the said elastomer surfaces of the strands of both layers being fused 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 crossing points, and thereafter cooled, thereby to fix the crossing strands permanently relative to each other to define mesh openings of predetermined configurations and dimensions, the area of the mesh openings being at least 43% of the total area of the screen.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (21)

**WARNING** start of CLMS field may overlap end of DESC **. for use in ore-type sieves. Advantage is taken of the elasticity, strength, abrasion resistance and the inherent surface smoothness and thermo-plasticity or thermossetting ability, of the abrasion-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 tobe 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 transportation. Since the exposed portions of the strands are abrasion-resisting organic elastomers, the sieve screening will not rust so that it will 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 sifting noise will be found to be significantly reduced. More importantly, however, sieves constructed of strands in accordance with the present invention as hereinabove disclosed, 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 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. The various embodiments of nets or screens herein described are formed of crossing strands of an abrasion-resisting organic element, and the sieves are constructed with such netting or screening. The strands may be either cored or coreless. Where a core is provided it may consist of some type of metallic wire, inorganic fibre or organic polymerized elongationless strands, either solid or formed of monofilament or twisted strands. The net or screen is formed by arranging one set of strands in a plane parallel to each other and spaced apart by predetermined distances and placing a second set of strands, spaced at the same or other predetermined distances parallel to each other, transverse to and on the first set of strands. The two sets of strands are caused to adhere to predetermined points of contact by heating to a temperature at which the contacting elastomers fuse to each other.Netting or screening so formed may be employed to construct screening, such as may be employed in sieves, particularly for sifting out finer materials from coarser materials. Such sieve construction may be accomplished by inserting the ends of one set of strands of the netting in clamping plates and drawing said plates apart from each other by tightening them against walls spaced from each other. A net or screen can screen without blocking, it has a long life, it can advance the object elastically and speedy, and it does not cause hazardous sound waves. Among other of its advantages are:- its lightweight and ease of handling; no possibility of the production of rust or corrosion; ease of transportation, storage, administration, installation, replacement, and repair; the capability of making the opening ratio large; long durability; and improvements in workability and screening. WHAT I CLAIM IS:

1. A screen for a sieve adapted to sift particles of a predetermined size, said screen comprising: first and second layers of strands, each of said strands comprising an elongated element having at least its outer exposed surface constituted of an abrasionresisting organic elastomer, the strnads of said first layer being laid parallel to, and spaced by a first predetermined distance from, each other in a plane; and the strands of said second layer being laid over, and orthogonally 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; the said elastomer surfaces of the strands of both layers being fused 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 crossing points, and thereafter cooled, thereby to fix the crossing strands permanently relative to each other to define mesh openings of predetermined configurations and dimensions, the area of the mesh openings being at least 43% of the total area of the screen.

2. A screen as claimed in claim 1, wherein the strands of said second layer are

provided with a greater thickness of abrasion-resisting organic elastomer than strands of said first layer.

3. A screen as claimed in claim 1 or 2, wherein the strands of at least one of the two layers are constituted of strands having cores covered by an abrasion-resisting organic elastomer.

4. A screen as claimed in any one of the precedme claims, wherein the strands of both the first and second layers of strands are cored strands, the cores of which have been welded together at their crossing points and, after having been so welded together, are provided with coverings of an abrasion-resisting organic elastomer.

5. A screen as claimed in any one of the preceding claims, wherein at least one additional layer of strands is disposed below said first layer of strands at angles with respect to the strands of both said first and second layers to cross the stands 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.

6. A screen as claimed in any one of the preceding claims wherein the mesh openings defined by the intersecting first and second layers are oblong.

7. A screen as claimed in claim 3 or any one of claims 4 to 6, when dependent on claim 3, wherein the thickness of the elastomer is equivalent to 1540 percent of the diameter of said strands.

8. A screen as claimed in any one of the preceding claims, wherein the strands of said first and second layers comprise cores covered by an abrasion-resisting organic polymer, and the thickness of the polymer covering the cores of the strands of the second layer is from one to three times the thickness of the polymer covering the cores of the strands of said first layer.

9. A screen as claimed in any one of the preceding claims, wherein there is provided a second layer of orthogonally intersecting strands below the first mentioned screen, said layer also being formed from strands covered with an abrasion-resistive organic polymer.

10. A screen as claimed in claim 3 or any one of claims 4 to 9, when dependent on claim 3, wherein the cores of the strands having cores comprise either metallic wires, non-extensible organic polymer strands or inorganic fibre strands.

11. A sieve for separating material incorporating a screen as claimed in any one of the preceding claims, and comprising a pair of parallel members to which the strands of said first layer are connected whereby the strands of said first layer are connected whereby the strands of said second layer extend parallel to said members and to the direction of travel of the material to be sieved when the sieve is in operation.

12. A sieve as claimed in claim 11, comprising means for moving said members apart to tension the strands of said first layer.

13. A sieve as claimed in claim 12, wherein said first layer is formed by a single strand interlaced between anchor points on said parallel members.

14. A sieve as claimed in any one of claims 11 to 13, wherein each side member comprises upper and lower clamping plates operative to clamp said first layer therebetween.

15. A sieve as claimed in claim 14 and including strips of an organic elastomer disposed between the clamping members and the strands clamped therebetween.

16. A sieve as claimed in claim 14 or 15, wherein at least one bolt extending between each pair of clamping members, and an internally threaded nut curved on said bolt for adjusting the grip of said clamping members.

17. A sieve as claimed in claim 16, wherein the inner edge of each lower clamping member is curved towards the centre of the screen.

18. A screen for a sieve substantially as hereinbefore described with reference to any one of Figures 1 to 9, or I IA to l5C, or 17A to 19C of the accompanying drawings.

19. A sieve incorporating a screen as claimed in any one of the preceding claims.

20. A sieve substantially as hereinbefore described with reference to Figures 8, or 10 to 12 of the accompanying drawings.

21. A sieve substantially as hereinbefore described with reference to Figures 20 to 23B of the accompanying drawings.