Rubber Screen For A Vibrating Sieve

Abstract

A rubber screen for use in a vibrating sieve for separating smaller particles of a substance from larger particles thereof, which screen comprises a body having a plurality of apertures and containing reinforcing members embedded therein and oriented laterally to the flow direction of the substance being sifted. An abrasion-resistive coating may be applied to one or both surfaces of the rubber screen.

Parent Case Text

This is a continuation-in-part application of application Ser. No. 34,654 filed May 5, 1970, now abandoned.

Description

This invention relates to a rubber sieve, and more particularly to a rubber screen for a vibrating sieve to be used in ore-dressing plants of various mines and steel mills. The present invention is directed to an improvement of a rubber screen to be used as a horizontal or inclined mesh in a vibrating sieve device through which the finer particles of a pulverized or granulated substance are passed to separate them from the coarser particles. The rubber screen may consist of any suitable rubber-like resilient material.

A metallic wire screen has heretofore been used as the mesh element of a vibrating sieve device. Such metallic wire screen has shortcomings in that it generates considerable noise during operation, its service-life is comparatively short due to its wearing, it rusts, and the mesh becomes clogged.

To mitigate such difficulties of known metallic wire screens, it has been proposed to use a rubber screen consisting of rubber-like resilient material. Known rubber screens, however, are susceptible to vibration of large amplitude, which cause various inconveniences in practical operations.

Therefore, an object of the present invention is to obviate such difficulties of known metallic wire screens and rubber screens, by providing an improved rubber screen which is free from any of such difficulties.

For a better understanding of the invention, reference is made to the accompanying drawings, in which:

FIG. 1 is a perspective view of a known vibrating sieve using a metallic wire screen;

FIG. 2 is a vertical cross section of the vibrating sieve of FIG. 1, taken at right angles to the direction of the flow of material being sifted thereby;

FIG. 3 is a perspective view of the wire screen in the vibrating sieve;

FIG. 4 is a vertical sectional view of a known vibrating sieve using a rubber screen, taken at right angles to the direction of the flow of material being sifted thereby;

FIG. 5a is an enlarged fragmentary sectional view of a joint portion of the rubber screen of the device of FIG. 4, taken along the flowing direction of the material being sifted thereby;

FIG. 5b is a view showing the details of the joint portion;

FIGS. 6a, 6b, and 6c are plan views of different rubber screens, according to the present invention;

FIG. 7a is a vertical sectional view of a rubber screen according to the present invention, taken at right angles to the direction of the flow of material being sifted thereby;

FIGS. 7b to 7f are enlarged fragmentary sectional views, illustrating different constructions of the mounting portion of a rubber screen of the present invention;

FIG. 8 is a perspective view of a vibrating sieve incorporating a rubber screen, according to the present invention;

FIG. 9a is a partial enlarged sectional view of one of the joint portions of a rubber screen according to the present invention, taken along the flow direction of the material being sifted thereby; and

FIG. 9b is an enlarged fragmentary sectional view of the joint portion.

Like parts are designated by like numerals throughout the drawings.

In a known vibrating sieve with a metallic wire screen, as shown in FIG. 1, the metallic wire screen 1 with crossing metallic wires is supported by a number of longitudinal frame members 3 carried by lateral frame members 2. The "longitudinal" direction is parallel to the flow direction of the material being sifted by the sieve, as shown by the arrow A of FIG. 1, while the "lateral" direction is perpendicular to the flow direction Side edges 1' of the metallic wire screen 1, as shown in FIG. 3, are bent along the lower edge of each clamping bar 4, as best can be seen from FIG. 2. The clamping bars 4 are then fastened to two side walls 9, respectively, by means of bolts 5 and nuts 6. A holding bar 11 is disposed on the screen 1 along the central axis thereof, which holding bar 11 is secured to the central member 3' of the longitudinal frame members 3 by a suitable fastening means 10, so as to securely hold the screen 1 on the frame members. In the illustrated example, the fastening means 10 includes stud bolts projecting from the central longitudinal frame member 3' and nuts engaging the stud bolts, respectively. Retaining bars 7 are integrally formed on the side plates 9, for preventing the clamping bars 4 from slipping along the side plates during the vibration. Each side plate 9 includes a suitable ledge 8 for stably supporting the longitudinal side edge of the screen 1, which ledge may be made by an angle steel.

The metallic wire screen 1 in such vibrating sieve produces noise of considerably high level during the sifting operation. Besides, individual metallic wires forming the screen 1 wear fairly quickly, if the screen is used for sifting hard particles or granules of ore, resulting in a short service life. It is susceptible to rust or corrosion, as well as clogging, which also lead to short service life.

In order to mitigate such difficulties of the known metallic wire screen, it has been proposed to use a rubber screen made of rubber or rubber-like resilient material. FIG. 4 illustrates a vibrating sieve using a rubber screen of known construction. In the figure, a rubber screen 12 comprises a rubber sheet with a plurality of apertures 13, through which fine particles to be sifted fall down. Ribs r are integrally formed at the opposite edges of the screen 12 extending in parallel with the flow direction of material, being sifted, to facilitate the mounting of the screen to the side plates 9 by means of clamping bars 4. A suitable tension is preferably applied to the screen 12 when it is mounted on the sieve. In operation, a pulverized or granulated material to be sifted is fed onto the rubber screen 12, while vertically reciprocating or vibrating the screen (e.g., along a circular or elliptic path, two-dimensionally or three-dimensionally), so that fine particles with a diameter smaller than that of the aperture 13 fall through the apertures 13. Thus, the finer particles of the substance thus fed are separated from coarser particles.

The known rubber screen, however, has the following drawbacks. During the sifting operation, the rubber screen 12 itself vibrates while forming nodes at the clamping bars 4 and a holding bar 11. Such vibration of the rubber screen 12 is shown by two-dot-dash lines in FIG. 4. The amplitude of such vibration of the rubber screen can become very large under certain conditions. If a light substance with a comparatively small specific gravity, e.g., coke particles, is sifted by such sieve, light particles of the substance are apt to be thrown out of the screen over the side plates 9. In practice, additional holding bars 14 are secured to longitudinal frame members 3, so as to suppress the amplitude of such vibration of the rubber screen per se, by fastening the rubber screen to the frame members not only at the central portion thereof but also at other intermediate positions, as shown in FIG. 4. The additional holding bars 14, however, reduce the effective surface area of the rubber screen 12 to lessen the sifting efficiency. The use of the additional parts inevitably increases the cost of the sieve device, and requires extra man-hours for replacement of the rubber screen in case of any breakage in the rubber screen. Accordingly, the use of such additional holding bars 14 is not preferable.

If no extra holding bars 14 are added, the pulverized or granulated substance flowing on the rubber screen tends to concentrate in spaces between adjacent longitudinal frame members 3, inclusive of the central member 3'. If the substance being sifted has a comparatively large specific gravity, such flow of the substance on the screen tends to cause a considerably large tension in the rubber screen at such portions where it engages frame members 3 and 3'. As a result, the wear of the rubber screen is accelerated at such portions by the tension thus generated, and the rubber screen 12 is often torn out at such portions.

Sometimes, it is desirable to have a long sieve. To this end, a desired elongated sieve is preferably made by connecting a number of comparatively short rubber screen units, because partial replacement is easier than the total replacement of a long unitary screen in the case of breakage. With conventional rubber screens, the joint portion of short screen units for producing such long screen is made by overlaying the edge portions of the adjacent short screen units, as shown in FIGS. 5a and 5b. Accordingly, there are formed a number of bumps Q on the sifting surface of the long rubber screen. The bumps Q not only disturb the smooth flow of substance being sifted to hamper the sifting efficiency, but also cause the particles of the substance to strike such bumps to increase the wear of the rubber screen. As a matter of fact, such long rubber screen is often broken at such joint portions.

Therefore, an object of the present invention is to obviate the aforesaid difficulties of known metallic wire screens and the known rubber screens by providing an improved rubber screen.

FIG. 6a shows an embodiment of the rubber screen, according to the present invention. A rubber screen 12 of the present invention includes a plurality of inextensible, flexible and continuous reinforcing members 15 completely buried therein, which reinforcing members extend at right angles to the flow direction A of the substance being sifted thereby and which members 15 are placed under tension. In the embodiment of FIG. 6a, the flexible reinforcing member 15 under tension are buried at or in the proximity of the opposite edges e, e' of the rubber screen, lateral to the flow direction A, and at the suitable portions between the edges e and e'. The reinforcing members can be made of any suitable flexible and inextensible material, such as steel ropes, steel wires, steel members, other organic or inorganic cords, and the like. Although the reinforcing members 15 in the embodiment of FIG. 6a are disposed at right angles to the flow direction A of the substance being sifted, the invention is not restricted to such disposition. In fact, any suitable disposition of the reinforcing members 15 is possible relative to the flow direction A, for instance, at a slanted relation to the flow direction A. A plurality of screening apertures 13 are bored through the rubber screen 12, but such apertures are not provided where the reinforcing members 15 are buried.

Opposing end portions 16 (FIG. 7) of each reinforcing member 15 extend sideways from the side edges of the sifting portion of the rubber screen 12, to form ribs r and r'. The ribs r, r' thus extended can be bent along the lower edges of the clamping bars 4, as described hereinbefore referring to the metallic wire screen 1 of FIG. 1. The rib r or r' thus formed may be provided with a rubber coating, as shown in FIG. 7c. Alternatively, each end portion 16 of the reinforcing member 15 can be looped, so as to surround a holding core 17 for constructing a solid rib r or r', as shown in FIGS. 7a and 7b. To strengthen the rib portions, it is possible to fasten the core 17 to the reinforcing members 15 by suitable bolts or fasteners (not shown).

In the preferred embodiment of FIGS. 6a, the holding cores 17 extend in parallel to the flow direction A along the opposing edges of the screen 12, so as to connect the reinforcing member 15 in the rubber screen 12 by means of the ribs r and r', which ribs extend integrally with the cores 17 over the full length of the rubber screen. It is possible to use short holding cores 17 at each end portion 16 of the individual reinforcing member 15, so as to form a separate rib r or r' at each end of the reinforcing member 15, as shown in FIG. 6b.

The rib portions r and r' are used to securely hold the rubber screen 12 to the side plates 9 by means of the clamping bars 4, as shown in FIG. 8. It should be understood that the ribs r and r' need not extend upwards in excess of the plane of the upper surface of the rubber screen 12. In fact, the top of the ribs r and r' can be flush with the top surface of the rubber screen 12, while forming longitudinal grooves 18 thereon, as shown in FIG. 7d. The longitudinal grooves 18 engage the lower edges of the corresponding clamping bars 4 for securely fastening the rubber screen 12 to the side plates 9.

FIGS. 7e and 7f illustrate another embodiment of the termination of flexible reinforcing members 15. The end portion 16 of each reinforcing member 15 is turned back so as to form a folded portion, as shown in FIG. 7e. The folded end portion of the reinforcing member 15 is inserted into a coacting aperture bored through a stopper plate 15a, so as to project the folded edge portion of the rienforcing member 15 slightly beyond the outer surface of the stopper plate, as shown in FIG. 7e. A stopper pin 15b is forced into a closed loop defined by the folded portion of the reinforcing member 15 and the stopper plate 15a. The size of the opening of the stopper plate 15 and the dimensions of the stopper pin 5b are such that, once the end assembly of the reinforcing member 15 thus fabricated is enclosed in the form of a rib r or r' by the rubber material of the rubber screen 12, as shown in FIG. 7e, the stopper plate 15a is integrally secured to the reinforcing member 15. Thus, the stopper plate 15a holds the reinforcing member 15 against a tension tending to pull the reinforcing member 15 away from the stopper plate 15 in a direction as shown by the arrow F of FIG. 7e. The embodiment of FIGS. 7e and 7f is particularly suitable for the reinforcing member 15 in the form of a strap.

With the construction of the ribs r and r', as shown in any one of FIGS. 7a to 7f, the flexible reinforcing members 15 buried in the rubber screen 12 can be tightly secured to the side plates 9, by means of the clamping bars 5 and the fastening means consisting of bolts 5 and nuts 6. If the length of each reinforcing member 15 is suitably determined, relative to the spacing between the side plates 9 of the sieve structure, it is possible to apply a proper tension to the reinforcing members 15 when they are fastened to the sieve. The direction of such tension applied to the reinforcing members 15 is apparently substantially lateral to the flow direction A, as long as the members 15 are disposed in the manner as shown in FIGS. 6a and 6b.

According to the present invention, instead of using the aforesaid continuous reinforcing members 15 buried in the rubber screen, it is also possible to fulfill the object of the invention by using a rubber screen 12 made of a compound rubber material, such as fiber-reinforced rubber, which consists of rubber material and short fibers mixed therein. More particularly, 5 to 50 percent by volume of short fibers 15' of which length is about 5 mm to 50 mm are added to the rubber material, based on the total volume of the rubber screen, and the short fibers are oriented lateral to or at right angles to the flow direction A of the substance being sifted, as illustrated in FIG. 6c. The short fibers are, for instance, short metallic pieces, textile cut fibers, short textile yarns, short cords or organic or inorganic material, or the like. In the case of the rubber screen using such compound rubber material, the sectional shape of the rubber screen can be made the same as that of the rubber screen with the reinforcing members 15, as described hereinbefore referring to FIGS. 7a to 7d. In order to make such rubber screen, the compound rubber material containing the aforesaid amount of short fibers of the said dimension is thoroughly mixed by a rubber kneading roll, and the short fibers are oriented to the desired direction.

When the short fibers are added and oriented lateral to the flow direction A, the rubber screen 12 will have a comparatively high rigidity in a lateral direction relative to the flow-direction A, namely in the longitudinal direction of the short fibers 15'. The degree of the rigidity depends on the amount of the short fibers 15' added in the compound rubber. Accordingly, it is possible to provide rubber screens 12 having optimal rigidity for specific applications, such as for sifting light coke particles or heavy iron ore particles.

The rubber screen 12 made of such compound rubber material can be mounted on the sieve in the same manner as that of the rubber screen with the reinforcing members 15, as shown in FIG. 8. The opposing edges e and e' of the rubber screen 12 made of the compound rubber, which edges are lateral to the flow direction A of the material being sifted, are sometimes required to have a higher rigidity than that of the remaining portion of the rubber screen, for providing a perfect joint portion between adjacent rubber screens 12 of such construction. In this case, it is preferable to embed continuous reinforcing members 15 along the edges e and e', as shown in FIG. 9b. The material of the reinforcing member along the edge e or e' can be the same as that for those embedded in the intermediate portions of the rubber screen 12 without compound rubber, as described hereinbefore referring to FIGS. 6a and 6c.

Accordingly, with the rubber screen of the present invention, there will be no vibration of large amplitude in the rubber screen between the central holding bar and the side plates. The risk of dropping the particles which are being sifted, over the side plates, is completely eliminated. Besides, the number of the holding bars 11 necessary for holding the rubber screen of the present invention on the sieve can be minimized.

Furthermore, when it is desired to form a long rubber screen by connecting a plurality of unit screens, the rubber screens of the present invention are particularly advantageous. Referring to FIGS. 9a and 9b, at the connecting portion b of adjacent rubber screen units 12, the edges e, e of the abutting rubber screens 12 include reinforcing members 15 embedded therein, respectively. The abutting edges are slant cut, as best shown in FIG. 9b, relative to a vertical plane perpendicular to the flow direction A.

As a result, a smooth continuous surface is made on the long rubber screen by the connection of a plurality of the rubber screen units 12 of the present invention. Accordingly, bumps at the connecting portions of the adjacent rubber screen units, which have been experienced in conventional rubber screen as shown in FIGS. 5a and 5b, can completely be eliminated. Consequently, smooth flow of pulverized or granulated substance being sifted is ensured, and the sifting efficiency is considerably improved. The elimination of the bumps at the connecting portions of the adjacent rubber screen units results in the complete removal of the striking of the rubber screen by the substance being sifted, and the degree of the wear and tear is reduced, so that the service life of the rubber screen is also greatly improved.

In mounting the rubber screen 12 of the invention, it is preferable to stretch it in a direction lateral to the flow direction A of the material being sifted, so as to apply a suitable tension to the flexible but inextensible reinforcing members 15 or short fibers in the compound rubber. Such tension acts to reduce the vertical vibration of the reinforcing members, or the short fibers, at the longitudinal frame members 3 and 3', and accordingly the tension suppresses the vertical vibration of the rubber screen 12, so that elongation of the rubber screen surfaces due to such vertical vibrations is greatly reduced. As a result, the local wear of the rubber screen in the proximity of such frame members, which was experienced with conventional rubber screens, is also substantially eliminated. Thus, the wearing of the rubber screen becomes uniform over the entire span thereof. Such elimination of the local wear also contributes to the improvement of the service life of the rubber screen.

Still other conventional rubber screens have utilized reinforcements of inflexible solid rods or bars. The performance used by the rubber screen of the present invention utilizing flexible but inextensible reinforcing members or cords 15 under tension is far superior to that achieved by the use of conventional rubber screens utilizing inflexible solid rods or bars, such as taught in Australian Pat. No. 108,053. Conventional rubber screens using inflexible solid rubber rods or bars as reinforcing members are frequently troubled by the tendency of the screen to become clogged. This clogging tendency is avoided by use of the screen of this invention, since the flexible reinforcing cords may flex when one or more screening holes are filled with a solid substance so as to prevent the solid substance from becoming lodged within the holes. The use of solid and inflexible rods or bars as reinforcing members does not permit such flexing and removal of the filling substance from the screening holes. Furthermore, the flexible reinforcing members 15 of the rubber screen of this invention, may allow certain parasitic oscillation of the rubber screen in response to sieving vibration, which oscillation acts to prevent the screen elements from being clogged. On the other hand, solid and inflexible rubber bars or rods may not allow the rubber screen to make such parasitic oscillation so that the screen holes are more easily clogged. Still another advantage of the flexible reinforcing members 15 of the present invention is that the rubber screen can be rolled so as to facilitate its transportation and insulation.

With the present invention, it is also possible to apply suitable abrasion resisting rubber layers on the front and back surfaces of the rubber screen, such as hard rubber layers and urethane rubber layers, for the purpose of improving the durability.

As described in the foregoing, according to the present invention, the performance characteristics of the rubber screen is considerably improved, together with its durability. Furthermore, the man-hours necessary for the replacement of the rubber screen in a vibration sieve is greatly saved, in the case of any breakage in the rubber screen. Thus, the present invention provides a remarkable contribution to the industry.

Claims

What is claimed is:

1. A rubber screen for use in a vibration sieve for separating smaller particles of a substance being sifted from larger particles thereof while passing said substance along the top surface of the rubber screen, comprising a planar body made of rubber-like resilient material and having a plurality of apertures bored therethrough for passing the smaller particles, a pair of mounting members integrally formed on opposite edges of the planar body, and elongated inextensible members made of flexible cords and embedded in the screen so as to extend between said opposite edges of the screen, each of said elongated inextensible members being continuous members tautly extending across the entire width of the planar body and across said opposite edges at right angles thereto, said mounting members including bent end portions of the continuous members, said mounting members further including stopper plates having small apertures and stopper pins, each of the continuous elongated inextensible members having end portions thereof so bent as to form a folded loop-like end portion, each said stopper pin extending through said loop-like end portion of the elongated inextensible member at an outer surface of the stopper plate relative to space between said opposite edges, the stopper plates thus coupled to the end portions of the elongated inextensible members being embedded in the rubber screen along opposite edges of the rubber screen.

2. A rubber screen for use in a vibration sieve for separating smaller particles of a substance being sifted from larger particles thereof while passing said substance along the top surface of the rubber screen, comprising a planar body made of rubber-like resilient material and having a plurality of apertures bored therethrough for passing the smaller particles, elongated flexible inextensible members embedded in the screen so as to extend between opposite edges of the screen, each of said elongated inextensible members having opposite ends thereof terminated in means for mounting said screen and allowing tensioning of said elongated inextensible members, and adjacent ones of said elongated inextensible members having a plurality of said apertures therebetween.

3. A rubber screen according to claim 2 further comprising cores in each of said mounting means, and wherein said elongated inextensible members are bent around said cores.

4. A rubber screen according to claim 3 wherein a plurality of said cores are provided in each opposite edge of the planar body, and wherein said mounting means are provided on said opposite edges only in the regions of said cores.

5. A rubber screen according to claim 2, wherein said inextensible members are continuous members extending across the entire width of the planar body and across said opposite edges at right angles thereto, said mounting means including bent end portions of the continuous members.

6. A rubber screen according to claim 5, wherein the continuous members are made of a material selected from the group consisting of steel ropes, steel wires, steel members, and fibrous cords.

7. A rubber screen according to claim 5, wherein the continuous members include at least two continuous members disposed along the opposite edges of the screen at right angles to said opposite edges of the rubber screen.

8. A rubber screen according to claim 5, wherein one set of the opposite edges of the rubber screen is bent upwards above the upper surface of the remaining portion of the rubber screen, so as to form said mounting means.

9. A rubber screen according to claim 5 and further comprising a pair of grooves formed on the upper surface thereof along one set of the opposing edges thereof, so as to constitute said mounting means.