SCREEN

Abstract: The invention relates to a screen, provided with a plurality of rotatable screening members, which are spaced transversally with respect to the proceeding direction of the material to be screened, designed for the fine screening of material. According to the invention the screening members (3, 21, 31, 32) are in cross section essentially deviant from circular form, in order to achieve essentially vertical and horizontal motional components for the material to be treated on the screen (2, 20); and that the screening members (3, 21, 31, 32) are mutually installed so that the screen aperture (11, 27) formed by two adjacent screening members (3, 21, 31, 32) can be kept essentially in the same size throughout the screening process.

Description: SCREEN The present invention relates to a screen used in the fine screening of solid material, such as rock material and coal, provided with a plurality of successive, rotatable screening members suitably spaced in the proceeding direction of the material . Many material treatment processes require that for instance the coarsest and finest particles are removed of the material under treatment, in which case the said material is essentially a fraction between two limit measures. Thus an essentially desired size grade is obtained for the material. Consequently, several different screens have been developed for sieving material into an advantageus particle size for the next treatment stage. Usually the screens are arranged in an inclined position, so that the material to be screened passes over the screen by force of gravitation, or the screens are provided with vibrators, which set the material into motion on the screen. There are also developed roller screens, as in the FI patent 56,131, comprising several rotatable transversal rollers. By means of these rollers, material is made to pass over the screen. Moreover, the roller screen of the FI patent 56,131 is adjustable, i.e. the distance between the rollers is increased in the proceeding direction of the material in order to adjust the overflow, so that essentially all pellets forming the overflow are larger than those separated therefrom and returned to pelleting. The rotatable rollers of the FI patent 56,131 set the material to be screened only and essentially into horizontal motion, in which case the material either rolls or slides on top of the rollers. Thus vertical motion, which is advantageous for screening and normally obtained by means of a vibrator, is not created in the process. The object of the present invention is to eliminate some of the drawbacks of the prior art and to achieve an improved screen which is more secure in operation, and where an essentially vertical motional component also is obtained for the material to be screened by means of suitably shaping the screening members . The essential novel features of the invention are apparent from the appended patent claims . According to the invention, the screen is provided with a plurality of suitably spaced rotatable screening members arranged transversally with respect to the proceeding direction of the material. In cross-section, the screening members essentially deviate from circular shape, but in such a fashion that at least 50% of the cross-sectional circumference is curved. In addition, the screening members are essentially symmetrical in relation to their rotating axis. Moreover, the screening members are coupled to each other, so that the distance between two successive screening members remains essentially the same at the different stages of screening. By means of the cross-sectional surface of the screening members of the invention, which shape deviates from a circle, two different motional components are achieved for the material which is fed and proceeded on the screen, i.e. both an essentially horizontal and an essentially vertical motional component. By means of these two motional components, the material located on the screen can be made to change its direction at different stages. Thus for instance an elongate particle that could not be screened with an essentially horizontal motion only, can now be screened owing to the alternating motion created by the screening members, which essentially increases screening efficiency with the screen of the present invention. The screening members of the screen of the present invention are for example essentially elliptical in cross-section, so that the whole cross-sectional circumference of the screening member is curved. The cross-section of a screening member may also be a circle, which is removed of essentially equal-sized segments located symmetrically with respect to the rotating axis of the screening member, the number of these segments being advantageously two or three. Thus at least 50% of the cross-sectional circumference is curved and is composed of circular curves . According to the invention, the screening members are arranged in an advantageous fashion with respect to each other, so that two successive screening members are turned at an angle of essentially 90° in relation to each other. Thus, for instance when the screening members are elliptical in cross-section, every second member is essentially in horizontal position, and every second member essentially in vertical position. While the material proceeds on the surface of the screening members of the screen, the particles are set to an essentially rising or lowering motion due to the effect of the screening members, so that both the horizontal and vertical motional components affect the material to be screened, and the single particles contained therein. The screening members of the screen of the invention are further installed so, that the screen aperture in between two successive screening members is equal-sized in all intervals throughout the screen. Moreover, two successive screening members are synchronized by means of a gearing member, so that the screen aperture remains essentially the same throughout the screening process, owing to the advantageous cross-sectional symmetry of the screening members . The screen of the present invention is meant for the fine screening of the material to be screened, in which case the screen aperture is advantageously of the order 4 - 25 mm. When the material is desired to be screened into several fractions, two or more screens with different screen apertures can be connected, so that they form a screen trac of several screens. These screens are advantageously operated either with one and the same or with several different actuator devices. The invention is explained in more detail below, with reference to the appended drawings, where figure 1 illustrates a preferred embodiment of the invention, seen in a partial side-view cross-section, figure 2 illustrates the coupling of the screening members of the preferred embodiment of figure 1, seen from the top, figure 3 illustrates another preferred embodiment of the invention, seen in a partial side-view cross-section, figure 4 illustrates the coupling of the screening members of the preferred embodiment of figure 3, seen from the top, figure 5 further illustrates an advantageous cross-section of the screening member of the invention, and figure 6 further illustrates an advantageous cross-section of the screening member of the invention. According to figures 1 and 2, the material conveyed on the conveyor belt 1 is fed onto the screen 2. The screen 2 is provided with screening members 3 arranged transversally to the proceeding direction of the material, spaced at a distance determined by the screen aperture 11. The screening members 3 are essentially elliptical in cross-section, and the screening members 3 are mutually installed so that every second member 3 is essentially in vertical position, and every second member 3 is essentially in horizontal position, i.e. in alternate members, the long axis of the ellipse is in turns in vertical or in horizontal position. The screening members 3 are interconnected, so that at the end of the screening member 3 (figure 2) there is installed a sprocket 5 by intermediation of a gearing 4. The sprockets 5 are further connected to each other by intermediation of roller chains 6. The rotation of the roller chains 6 is achieved by means of the actuator arrangement 7. For the underflow of the screen 2, there is provided a hopper 8 underneath the screen 2, through which hopper 8 the fine material that has penetrated the screen proceeds to an underflow conveyor belt 9 located below the hopper 8. For the screen overflow, there is provided a conveyor belt 10 at the end of the screen with respect to the proceeding direction of the material. When the screen 2 of the invention is in operation, material to be screened is fed onto the screen 2 from the conveyor belt 1. The screening members 3 are rotated by means of the actuator arrangement 7, so that the screen aperture 11 in between two screening members 3 remains essentially equal during the whole screening process. The essentially vertical and horizontal screening members 3 shift the material to be screened forward on the screen, and essentially give the material both vertical and horizontal motional components. Thus the efficiency of the screening can be essentially increased. The fine material located on the screen 2 falls in between the screening members 3 to the hopper 8 and further to the conveyor belt 9 of the screen underflow. That part of the material that does not fall in the underflow proceeds into the overflow of the screen 2 and further to the conveyor belt 10. In figures 3 and 4, the screening members 21 are spaced according to an interval determined by the screen aperture 27. In order to operate the screening members 21, at the end of each member 21 there is installed a sprocket 23 by intermediation of a gearing 22. The sprockets 23 are interconnected by a roller chain 24. The roller chain 24 is further arranged to pass around a special return roller 25. The actuator arrangement 26 of the screen 20 is connected to the return roller 25 according to the drawing. As for the material treatment, the screen of figures 3 and 4 essentially corresponds to the preferred embodiment illustrated in figures 1 and 2. In figure 5, the screening member 31 is in cross-section composed of two opposite circular curves and two connecting, parallel linear parts. According to the invention, two adjacent screening members 31 are advantageously installed, with respect to each other, so that the parallel linear parts of the cross-sectional surface of the screening member 31 are alternatingly either essentially in vertical position or essentially in horizontal position. The cross-sectional shape of the screening member 32 of figure 6 is advantageously achieved so, that from a circular cross-sectional surface, there are removed, symmetrically with respect to the rotating axis of the screening member 32, three segments, in which case the cross-sectional surface is formed of both curved and linear parts, and the proportion of the curved parts is at least 50% of the whole cross-sectional circumference. Although several preferred embodiments of the invention are described in the above specification, it is obvious that the invention can be modified even to a large extent within the scope of the appended patent claims. Similarly, for instance the location of the actuator arrangement of the screen can vary in the different applications . The actuator arrangement can be operated either through specific gearing, or the actuator arrangement can be connected to some known sprocket, or each screening member may obtain its rotatory force from a power transmission axis running along the side of the screening members, which axis is connected to the screening member by means of sprocket gearing. Moreover, the cross-section of the screening members may vary within the scope of the appended patent claims.

Claims: CLAIMS 1. A screen, provided with a plurality of rotatable screening members, which are spaced transversally with respect to the proceeding direction of the material to be screened, designed for the fine screening of material, c h a r a c t e r i z e d in that the screening members (3, 21, 31, 32) are in cross-section essentially deviant from circular form, in order to achieve essentially vertical and horizontal motional components for the material to be treated on the screen (2, 20) ; and that the screening members (3, 21, 31, 32) are mutually installed so that the screen aperture (11, 27) formed by two adjacent screening members (3, 21, 31, 32) can be kept essentially in the same size throughout the screening process. 2. The screen of claim 1, c h a r a c t e r i z e d in that at least 50% of the cross-sectional circumference of the screening member (3, 21, 31, 32) has a circular form. 3. The screen of claim 1 or 2, c h a r a c t e r i z e d in that the screening member (3, 21, 31, 32) is essentially symmetrical in cross-section with respect to its rotating axis. 4. The screen of claim 1, 2 or 3, c h a r a c t e r ¬ i z e d in that the screening member (3, 21) is essentially elliptical in cross-section. 5. The screen of claim 1, 2 or 3, c h a r a c t e r ¬ i z e d in that the cross-section of the screening members (31, 32) is composed of at least two corresponding circular curves and at least two parallel parts connecting these circular curves . 6. The screen of any of the preceding claims, c h a r ¬ a c t e r i z e d in that two adjacent screening members (3, 21, 31, 32) are installed as turned at an angle of essentially 90° with respect to each other. 7. The screen of any of the preceding claims, c h a r ¬ a c t e r i z e d in that in order to rotate the screening member (3, 21, 31, 32) , the screening members (3, 21, 31, 32) are interconnected by means of at least one chain (6, 24) . 8. The screen of any of the preceding claims, c h a r ¬ a c t e r i z e d in that in order to rotate the screening member (3, 21, 31, 32), two adjacent screening members (3, 21, 31, 32) are interconnected by a chain (6) .

Inventors: MEHTO PETRI, MEHTO, PETRI
Applicants: MEHTO PETRI, ROXON OY, MEHTO, PETRI
Application year: 1993
Main classification: B07B1
IPC codes: B07B1