SCREENING DEVICE AND METHOD FOR SEPARATING DRY GRANULAR MATERIAL

Abstract

The present invention relates to a screening device for separating dry granular material into a fine fraction and a coarse fraction. The device comprises a drum screen defined by an open rotatable frame, which frame defines a circumferential wall, and a sheet-like screen arranged over the circumferential wall of the frame, a driving device by means of which the drum screen is rotatably driven, a feed opening at a short end of the drum screen and a discharge opening at the opposite short end of the drum screen. The screening device comprises a vibration device which rotates along with the drum screen, which vibration device comprises one or more vibrating elements mounted to the drum screen, which set the drum screen vibrating in use. The invention further relates to the screening of granular material using such a device.

Claims

1. A screening device configured for separating dry granular material into a fine fraction and a coarse fraction, said device comprising a drum screen defined by a substantially open frame that is rotatable about an axis of rotation that extends at least substantially parallel to a central axis of the drum screen, which frame defines a possibly virtual circumferential wall, and a sheet-like screen arranged over the circumferential wall of the frame, which screen has a mesh width that ranges at least substantially between a maximum grain size of grains for the fine fraction and a minimum grain size of grains for the coarse fraction, a driving device by means of which the drum screen is rotatably driven about the axis of rotation in use, a feed opening at a short end of the drum screen, through which dry granular material to be separated is supplied in use, and a discharge opening at the opposite short end of the drum screen, through which the coarse fraction of screened material is discharged in use, and a vibration device which rotates along with the drum screen, which vibration device comprises one or more vibrating elements mounted to the drum screen, which set the drum screen vibrating in use.

2. The screening device according to claim 1, wherein the one or more vibrating elements are mounted to the inner side of the drum screen.

3. The screening device according to claim 1, wherein the mesh width ranges between 1.0-1,000 m.

4. The screening device according to claim 1 wherein the vibration device is configured to vibrate at a frequency in the ultrasonic range.

5. The screening device according to claim 1 further comprising guide means which guide material in the drum screen in a conveying direction from the feed opening to the discharge opening during rotation of the drum screen, wherein the guide means comprise a spiral present on the inner side of the drum screen.

6. The screening device according to claim 1 wherein the axis of rotation extends at an angle which ranges from 15 to +15 relative to the horizontal.

7. The screening device according to claim 1 wherein the drum screen is provided with a hollow drive shaft for rotatably driving the drum screen, wherein wiring for driving the vibration device that rotates along with the drum extends through the hollow shaft.

8. The screening device according to claim 1 wherein one or more sliding contacts are provided for energising the vibration device via the wiring.

9. The screening device according to claim 1 wherein the frame defines a cylinder.

10. The screening device according to claim 1 wherein the screen comprises a screen cloth.

11. The screening device according to claim 1 wherein the screening device comprises a heating device that is wound around the drum screen.

12. The screening device according to claim 1 wherein the drum screen is surrounded by a housing.

13. The screening device according to claim 1 wherein the screening device comprises a feeding device for conveying material to be screened to the feed opening, which feeding device comprises a metering device for the metered supply of material to be screened to the feed opening.

14. A method for separating dry granular material into a fine fraction and a coarse fraction, comprising the steps of: a) supplying dry granular material to be separated to a feed opening on a short side of a rotating drum screen provided with a screen wall having a specific mesh width; b) conveying material present in the drum screen from the feed opening in the direction of a discharge opening located on a short side opposite the feed opening during rotation of the drum screen, during which transport relatively fine granular material falls through the screen wall into the drum screen, and c) discharging relatively coarse granular material at the discharge opening, wherein a vibration device that rotates along with the drum screen, which vibration device is configured to vibrate at a frequency in the ultrasonic range and comprises one or more vibrating elements mounted to the drum screen, sets the drum screen vibrating in step b).

15. The method according to claim 14, wherein the drum screen forms part of a screening device according to claim 1.

16. The screening device according to claim 2, wherein the mesh width ranges between 1.0-1,000 m.

17. The screening device according to claim 2 wherein the vibration device is configured to vibrate at a frequency in the ultrasonic range.

18. The screening device according to claim 3 wherein the vibration device is configured to vibrate at a frequency in the ultrasonic range.

19. The screening device according to claim 16 wherein the vibration device is configured to vibrate at a frequency in the ultrasonic range.

20. The screening device according to claim 2 further comprising guide means which guide material in the drum screen in a conveying direction from the feed opening to the discharge opening during rotation of the drum screen, wherein the guide means comprise a spiral present on the inner side of the drum screen.

Description

[0025] The present invention will now be discussed in more detail with reference to the appended figures of preferred embodiments of a screening device according to the present invention, in which:

[0026] FIG. 1 is a perspective side view of a part of a screening device according to the present invention;

[0027] FIG. 2 is a schematic side view of an alternative embodiment of a screening device according to the present invention; and

[0028] FIG. 3 is a perspective view of a vibrating element mounted to a screening device according to the present invention.

[0029] With reference now to FIG. 1, there is shown a perspective view of a screening device according to the present invention, a housing of which has been left out of the figure. The screening device of FIG. 1 comprises a drum screen 1, which is defined by a ring 11, which defines a feed opening 11a, a ring 12, which defines a discharge opening 12a, four elongate connecting elements 13 (only three of which are shown in FIG. 1), which extend between the ring 11 and the ring 12, and a spiral wound frame element 14 defining a cylinder, which is formed by arches extending between the respective connecting elements 13. The rings 11, 12, the connecting elements 13 and the frame elements 14 jointly form a frame of the drum screen 1. Stretched around the arches is a metal screen mesh as a sheet-like screen having a mesh width that corresponds to the material to be screened, in this case 60 m. The screen mesh 19 is only shown in part in FIG. 1. A hollow drive shaft 16, which extends horizontally in this exemplary embodiment, is connected, via connecting rods 5, to the connecting elements 13 as a rotary shaft forming part of a driving device (not shown). Provided on the side of the end at the feed opening is a slip ring construction 3 which is connected, via wiring (not shown in FIG. 1) within the hollow drive shaft 16 and connecting pieces 17, to vibrating elements 6 of a vibration device so as to cause them to vibrate at a frequency in the ultrasonic range. Located near the feed opening defined by the ring 11 is a supply pipe 2 for material to be screened. The supply pipe opens into the drum screen 1 via a metering device 4, which extends beyond the ring 11 to within the drum screen 1.

[0030] During operation, granular material to be screened by the screening device is introduced into the drum screen 1 via the supply pipe 2 and the metering device 4 and through the feed opening 11a. The material to be separated may consist of crushed concrete, for example, in particular concrete that has been crushed into its original materials, viz. pebbles, sand and cement, from which the pebbles have already been removed. The granular material may for example have been obtained by means of crushing device, using the method described in WO 2011/142663, page 9, line 7page 13, line 34. In the drum screen 1, the granular material to be screened drops onto the inner side of the screen mesh 19. The drive shaft 16 is rotatably driven and in turn drives the drum screen 1 in the direction indicated by arrow Q, so that granular material to be screened is conveyed over the screen mesh 19 in the direction of the discharge opening 12a by the frame element 14. Via the slip ring construction 3, wiring (not shown) extending from the slip ring 3 through the hollow drive shaft 16 and the connecting pieces 17, the vibrating elements 6 are energised and set vibrating. The vibrating elements 6 transmit a vibrating motion to the drum screen 1. The vibrating elements 6 are mounted to the connecting elements 6 and thus rotate along with the rotating drum screen 1. In FIG. 1, the vibrating element 6a is present on a lower part (in this figure) of the drum on which material to be screened is present. By causing the vibrating elements 6a-6d to vibrate during rotation of the drum screen 1, the screen mesh 19 is also set vibrating. Granular material to be screened that is present on the screen mesh 19 is thus set in motion in a direction perpendicular to the screen mesh, so that a more effective separation can take place. The person skilled in the field of screening granular material may be presumed to know that vibrating a screen bottom will contribute toward obtaining a good separation of material to be screened. In FIG. 1, the vibrating element 6c is present on an upper part (in this figure) of the drum screen 1. Vibration of the vibrating element 6c will cause granular material which sticks to the screen mesh 19 at the bottom side of the drum screen 1 or is stuck in the mesh of the screen mesh 19, and which has been carried along with the screen mesh 19 in upward direction, to come loose from the screen mesh 19, so that the meshes will be open again when they are present at the bottom of the drum screen 1 again (after a half revolution) and material to be screened is present thereon. This, too, contributes toward obtaining a better through-flow through the meshes in question of relatively small particles of granular material to be screened. The grains from the material to be screened that are larger than the meshes of the screen mesh 19 are conveyed in the direction of the discharge opening 19 by the frame element 14 during rotation of the drum screen 1, at which discharge opening the relatively coarse granular material drops from the drum screen 1 and is discharged through a discharge opening (not shown in FIG. 1) of a housing of the screening device.

[0031] FIG. 2 shows in schematic side view an alternative embodiment of a screening device according to the present invention. In FIG. 2, elements corresponding to elements from the screening device shown in FIG. 1 are indicated by the same reference numerals incremented by 30. FIG. 2 shows the screening device including a housing 50. Such a housing may also be provided around the drum screen 1 of FIG. 1. It is a casing made of metal or of plastic material, for example, which fully surrounds the drum screen 31, so that granular material that comes to float in the air during screening cannot, or at least not easily, find its way into the atmosphere surrounding the screening device other than through discharge openings 38, 39 specially provided for that purpose. The drum screen 31 of FIG. 2 is different from the drum screen 1 of FIG. 1 in that the frame element 14 is not spiral-shaped, but is configured as endless, annular arch elements 44 extending parallel to each other. The arch elements coincide with the inner wall of the drum so as not to form obstacles to material being conveyed toward the discharge opening 42a. The device shown in FIG. 2 is further different from the device shown in FIG. 1 in that the drum screen is pivotally connected to a tilting frame 40 via a tilt axis 51 and slopes down at an angle of inclination of 15 from the feed opening 41 to the discharge opening 42. The angle of inclination can be set between 15 and +15.

[0032] In use, granular material to be screened, in this example comprising unhydrated cement having a grain size <60 m and sand having a grain size >63 m, respectively, is introduced into the drum screen 31 via a supply pipe 32 and a metering device 34 and through a feed opening provided with a rotary lock 37. In the drum screen 31, the material to be screened drops onto a screen cloth 49 having a mesh size of 60 m, which is stretched around frame elements 44 and which is schematically indicated by means of a dotted line so as to symbolically represent meshes 49a in the screen cloth 49. The screen cloth 49 has been left out in FIG. 2 so as to provide a good view of other parts. It is stretched around the arch elements 44 of the drum screen 31 along the entire length of the drum screen 31. As a rule, the meshes 49a will be very small, but this depends on the composition of the material to be screened and on the difference in grain size between the fine fraction and the coarse fraction to be separated by the screening device. With the device shown in FIG. 3, material to be screened that has been introduced into the drum 31 is carried in the direction of the discharge opening 42, partially under the influence of the force of gravity, during rotation of the drum 31 driven by the hollow drive shaft 46. During this displacement, relatively small grains, mainly cement, will fall through the mesh screen 49 into the hopper 52. Relatively large grains, mainly sand, which do not fall through meshes of the screen cloth 49, are collected in the hopper 53. Relatively fine granular material (cement) that has fallen through the screen cloth 49 is subsequently discharged from the housing 50 via the rotary lock 38. Relatively coarse granular material (sand) that has not fallen through the screen cloth is discharged by the rotary lock 39. It will be understood that the vibrating elements 36a, 36b (and the vibrating elements 36c, 36d, which are not shown) have a positive effect on the screening result in the same manner as described with reference to FIG. 1.

[0033] FIG. 3 shows in perspective view a vibrating element 61 mounted to a screening device according to the present invention. Numeral 60 indicates a connecting element comparable to the connecting element 13, 43 of FIGS. 1 and 2. Attached to the part of the connecting element 60 that is shown in FIG. 3 are three sections 62 of a frame element (see 14, 44 in FIGS. 1 and 2). Furthermore, a spacer 64 is welded to the connecting element 60, to which spacer a vibrating element 61 is connected, which vibrating element is energised via a power supply that extends to the vibrating element 61 via a connecting piece 63 (see 17, 47 in FIGS. 1 and 2. In use, the vibrating element 63 is energised, so that it will vibrate at a frequency in the ultrasonic range. Via the spacer 64, the vibrating motion of the vibrating element 61 is transmitted to the connecting element 60, and thus to the drum screen of a screening device of which the drum screen forms part. In the present example, a vibration device is used which vibrates at a frequency in the ultrasonic range and which has an output of 50-16,000 Watt. The invention is not limited to this range, which partially overlaps the ultrasonic range.

[0034] In the figures and the above description the present invention is shown and described with reference to two embodiments thereof. It will be apparent that the scope of the invention is not limited to these embodiments, but that many variants, which may or may not be obvious to the skilled person, are conceivable within the scope of the present invention as defined in the appended claims. Thus it is conceivable to use a flexible screen cloth or any other known type of screen having a suitable mesh size instead of a metal screening wall.

[0035] In the figures and the above description, the present invention is shown and described with reference to the use thereof (voor van ??) in a screening device for separating or screening particles of cement and sand from crushed concrete. This should not be interpreted as being limitative, either. On the contrary, the range of application concerns all dry granular materials having different grain sizes, and in particular grain sizes whose (normal) distributions do not differ much from each other or overlap to a small extent, since the meshes cannot be made much larger than the grain size of the small fraction and the risk of clogging is relatively great.