WO1992004135A1

WO1992004135A1 - Method and device for screening earth, gravel and the like

Info

Publication number: WO1992004135A1
Application number: PCT/SE1991/000565
Authority: WO
Inventors: Dagny Carlsson
Original assignee: Dagny Carlsson
Priority date: 1990-08-31
Filing date: 1991-08-29
Publication date: 1992-03-19
Also published as: EP0544806B1; AU8523791A; DE69121203T2; SE9002778D0; EP0544806A1; SE9002778L; SE466839B; ATE140883T1; DE69121203D1

Abstract

In a method for screening earth, gravel and the like containing comparatively large-size objects (1) and finer material (2), the material (1, 2) is moved into a screening drum (3) through an opening (13), whereupon the drum is rotated in a first direction, the large-size objects being retained in the drum (3) and the finer material being forced out of the drum through a screening element (8). When the drum is rotated in the opposite direction after the screening has been completed, the large-size objects are discharged from the drum through the opening (13). The drum is rotatably mounted on a frame (5) which is connected to the front loader (7) of a tractor (6). A pocket provided inside the drum retains the large-size objects (1) when the drum is rotated in the first direction . When the drum is rotated in the opposite direction, the large-size objects (1) are allowed to leave the pocket and are discharged from the drum (3) through the opening (13).

Description

METHOD AND DEVICE FOR SCREENING EARTH, GRAVEL

AND THE LIKE

The present invention relates to the screening of such materials as earth, gravel and the like containing comparatively large-size objects, such as stones, root vegetables and the like, which are to be separated from the finer material. More precisely, the invention concerns a method and a device of the type recited in the preambles of appended claims 1 and 4, respectively, use being made of a rotatable screening drum which preferably is connect¬ ed to a working machine, e.g. a tractor with a front loader.

This invention is based on the screening technique disclosed in EP-B1-0,178,656 (corresponding to SE-B-

454,096). This prior-art technique employs a substantially grate-type screening basket which is connected to the front loader of a tractor and which, during screening, is rotated by means of a rotary shaft extending in the main direction of travel of the tractor. This prior-art screen¬ ing device does, however, suffer from a number of draw¬ backs which chiefly are related to the alignment of the rotary shaft and its sole mounting point.

As appears from Fig. 4 of the above SE specification, the bearings of the screening basket will be subjected to a breaking action (observed in actual practice) when the basket is being loaded, which causes problems, especially when a considerable pushing force is required or when the front edge of the screening basket inadvertently encounters stones that are stuck in the ground. Another disadvantage is that it is difficult for the operator when sitting in the driver's seat of the tractor to supervise the screening work, since the rear part of the screening basket is a solid piece and therefore hides the screening comr tment (s?e Fig. 5 of the SE specification). Also, the forwardly-directed rotary shaft usually necessitates that the width of the screening basket be smaller than the track gauge of the tractor, since the forces generated by the rotational motion of the basket might otherwise jeop¬ ardise the stability of the tractor sideways. It has been found in practical use that the width of the screening basket should not exceed 1.7 m.

Thus, there is a demand for a screening device which, by relying on a different principle of rotation, obviates these disadvantages. Efforts have previously been made to meet this demand, and e.g. GB-A-1,512,206 and EP-A- 0,047,041 disclose screening devices which are equipped with grate-type, rotatable screening drums which are dis¬ posed transverse to the main direction of travel of the working machine. However, these drums have to be opened when to be fed with material, and closed to prevent the material from falling out of the drum during its rotation. Thus, the drums have to be provided with movable grating sections which are operated by means of hydraulic units. As a result, such grate-type screening devices become unnecessarily heavy and complicated, as well as liable to stoppages. In addition, the required operating equipment makes the construction more expensive.

Other background art is US-A-4,005,755 which relates to a machine which can be connected to a front loader and is adapted to take up and screen earth. This machine com- prises a housing which essentially consists of two inte¬ gral end walls and a front grating. Inside the housing, there is an endless chain drive whose transverse elements have substantially the same width as the housing. Also this machine suffers from drawbacks similar to those dis- cussed above. Thus, there is a considerable risk that stones become wedged in the complicated chain drive. Fur¬ ther, the machine has a large number of movable parts, which is far from being an advantage.

One object of the present invention is, therefore, to eliminate the above inconveniences by providing a simple, quick and efficient method for screening earth, gravel and the like, without necessitating any complicated equipment. Another iject of the invention is to provide a device for screening earth, grε /el and the like, which obviates the above inconveniences and which is of simple construction and has but a few movable parts. Yet another object of the invention is to provide a screening device having simple and reliable drivinr means and capable of efficiently taking up the forces to which it is subjected during the screening operation.

A further object of the invention is to provide a screening device easily connectible to a working machine, preferably to the front loader of a tractor vehicle, so that the device, by simple operation, can be moved into the earth or gravel to be screened and receive a suitable amount of material. These objects, as well as other objects that will appear from the following description, have now been achieved by a method according to the invention, which is of the type stated by way of introduction and which fur¬ ther comprises the features recited in the characterising clause of claim 1.

These objects are also achieved by a device which is of the type stated by way of introduction and which fur¬ ther has the features recited in the characterising clause of claim 4. Preferred variants and embodiments of the invention are recited in the appended subclaims.

To put it briefly, the invention is based on the idea of moving a screening drum which forms part of the device and is disposed transverse to the main direction of travel of the working machine, into the earth to be screened and then raising it and rotating it in a first direction o effect screening. The drum is thereafter rotated in the opposite direction, whereby the large-size objects retain¬ ed in the drum are automatically discharged therefrom. Thus, there is no need of any devices for closing the inlet opening of the drum, as is the case in prior-art screening devices of similar kinds where e.g. hydrau- lically-operated grating and gates are used for opening and closing the inlet opening.

The invention and its many advantages will be described in more detail below with reference to the accompanying drawings showing some embodiments. In the drawings,

Fig. 1 is a schematic perspective view showing a screening device according to the invention obliquely from in front, Figs 2-5 are schematic cross-sections of a screening drum forming part of the device and shown in different operational positions.

Fig. 6 is a perspective view obliquely from in front and Fig. 7 is a perspective view obliquely from below of a slightly modified screening drum which has been discon¬ nected from the other equipment.

Fig. 1 illustrates a device designed in accordance with the invention for screening such materials as earth, gravel and the like. In this case, the material to be screened is a mixture of relatively large objects 1 in the form of stones, and fine-grained material 2 in the form of earth. The main component of the screening device is a screening drum generally designated 3 which, by means of a substantially horizontal rotary shaft 4, is mounted on a frame 5. The frame 5, which is of known type (see, for instance, GB-A-1,512,206), is in conventional manner provided with means for connection to a working machine, in this case the front loader 7 of a tractor 6. Thus, the frame 5 and the drum 3 mounted thereon can be lifted, lowered and tilted by means of the front loader 7.

The screening drum 3 may be regarded as a body of revolution with respect to the axis of rotation or rotary shaft 4, and the circumferential surface of the drum 3 mainly consists of a curved screening element 8, one transverse edge of which is connected to a reinforcing metal sheet 9 in one piece (see Figs 6 and 7) and the other free, transverse edge of which extends into the drum 3. Further, the drum 3 has two integral vertical end walls 10, 11 of sheet metal, between which extend the curved screening element 8 and the flat reinforcing sheet 9. Both the screening element 8 and the reinforcing sheet 9 are connected, preferably by welding, to each other and to the periphery of the respective end wall 10, 11.

A driving unit 12, which is mounted on the frame 5 and arranged on the outside of the end wall 11, rotates the rotary shaft 4 and, consequently, the er*--lre drum 3 mounted thereon. The driving unit 12 prefer-,_^ly is a known hydraulic motor connected to one end of the rotary shaft 4. If need be, there may, of course, be arranged a hydraulic motor at each end of the rotary shaft 4. In the embodiment shown, the rotary shaft 4 is, hcv-ever, freely mounted on the forwardly-directed part of the frame 5 at the end wall 10 (not shown). For greater clarity, hydrau¬ lic lines and other equipment forming part of the hydrau¬ lic system are not shown in Fig. 1.

In the forward direction in Fig. 1 with respect to the main direction of travel of the tractor 6 (indicated by an arrow), the circumferential surface of the drum 3 is formed with an inlet opening 13 for the mater,al to be screened. The opening 13 is defined by the front edge of the reinforcing sheet 9, the forwardly-directed edge of the end walls 10, 11, and the extension of the screening element 8 directed into the drum 3, as will be discussed in more detail below. For screening, the drum 3 is moved, by means of the tractor 6, in the direction indicated by the arrow into the earth 1, 2 until a suitable amount of material has been fed into the drum 3 through the opening 13. When the drum 3 is moved into the earth 1, 2, the rotary shaft 4 is either locked by a pressure-reducing valve or a non-return valve (not shown) in the hydraulic system, e.g. in the hydraulic motor 12, or l^acked mecha- nically by a locking means (not shown) which is mounted on the frame 5 and can be operatively applied against the outside of the drum 3. When a suitable amount of material has been fed into the drum 3, this is lifted and slightly tilted rearwards towards the tractor 6, which then takes the drum 3 to the screening site where the drum is rotated in a manner to be described further below. Fig. 2 shows the drum 3 in the lifted screening posi¬ tion in which the frame 5 is tilted forwards-downwards. The screening drum 3 is rotated towards the tractor 6 in the direction indicated by the arrow, so that the fine material, i.e. the earth 2, is forced out of the drum 3 through the screening element 8, which preferably is a netting or grating. The large-size objects, i.e. the stones 1, that cannot pass through the screening element 8, are retained in the drum 3 by a wall 14 which is an extension of the screening element 8 and is directed into the drum. The wall 14 located in front of the opening 13 forms in the drum 3 a pocket 15 which, when the drum is rotated in the first direction, serves to retain the stones 1 inside the drum 3.

As appears from Fig. 3, the stones 1 are caused, when the drum is rotated further in the first direction, to roll away from the pocket 15 and via the wall 14 associated therewith to pass towards the inside of the reinforcing sheet 9. Thus, the pocket 15 and the wall 14 efficiently prevent the stones 1 from dropping out through the opening 13. It is, in addition, highly advantageous that the stones 1 impinge upon the reinforcing sheet 9, since this protects the screening element 8, which here is a netting. The reinforcing sheet 9 preferably has an angled portion 16 (see Fig. 2) which extends a distance onto the curved screening element 8 which thus is further protected from the impact by the stones 1.

To direct the stones 1 as desired when the drum rotates, the wall 14 is preferably arranged essentially midway between the rotary shaft 4 and the opening 13. To ensure that no stones 1 bounce out of the drum 3, the inner free transverse edge of the wall 14 advantageously extends beyond the plane passing through the centre of the rotary shaft 4 and the point of intersection between the front edge of the reinforcing sheet 9 and the front, bottom corners of the end walls 10, 11. However, the e transverse edge of the wall 14 has to be located at a _ω-s- tance from the inside of the drum 3, i.e. at a distance from the inside of the reinforcing sheet 9. It should be pointed out that the free transverse edge of the wall 14 preferably is perfectly parallel to the rotary shaft 4, as are of course the two transverse edges of the reinforcing sheet 9.

After the screening operation has been completed, only stones 1 remain in the drum 3, as shown in Fig. 4, and they are efficiently retained therein by the wa 1 14 and the inner pocket 15. The drum 3 is preferably stopped in this position, whereuron it is taken, by the tractor 6, to an emptying station wnere it is rotated in the opposite direction, as illustrated by the arrow in Fig. 4. During the rotational motion of the drum, the stones 1 are allowed to leave the pocket 15, and the drum 3 is, after being turned a limited distance, situated in the emptying position shown in Fig. 5, where the stones 1 slide on the sheet 9 and out of the drum 3 through the opening 13. The drum 3 is preferably stopped in this emptying position, or is slightly turned further clockwise (with respect to Fig. 5) to be completely emptied. Naturally, the frame 5 can be further tilted and/or shaken should any material have got stuck in the drum 3.

Thus, the method according to the invention for screening material is clearly illustrated in Figs 1-5. The material 1, 2 is fed into the drum 3, which is first brought to a screening position, in which it is rotated in a first direction, the stones 1 being retained in the drum 3. Then, the drum 3 is brought to an emptying position, in which it is rotated in the opposite direction, so that the stones 1 are removed from the pocket 15 and discharged from the drum 3 through the opening 13. In practical tests, the screening device of this embodiment has proved to be particularly efficient. In the tests, the drum was rotated at a speed of about 7-15 rpm, and especially good results were obtained at a speed of about 10-12 rpm. During each screening cycle, the drum was rotated about 4-5 revolutions in the first direction, and about 0.5-1 revolution in the opposite direction. All in all, this represents a shorter screening cycle than could be achieved in prior-art screening devices of similar type.

Generally, a screening drum of this type should, to the largest possible extent, consist of a screening ele¬ ment. The practical tests mentioned above have shown that the drum is especially effective if about 70% of its cir- cumferential surface is made up of the screening element, about 15% thereof is made up of the reinforcing sheet, and about 15% thereof is made up the opening. It will, how¬ ever, be appreciated that these percentage figures are nothing but exemplifying target values. Figs 6 and 7 illustrate a slightly modified screening drum generally designated 3' which has been disconnected from the other equipment and whose drive shaft has been removed. For reasons of manufacture, the netting-type screening element 8 extends slightly beyond the two end walls 10, 11. Further, the front edge of the reinforcing sheet 9 is bevelled, which makes it easier to move the drum 3' into the material to be screened. The bevelled portion is designated 17.

Figs 6 and 7 also illustrate a vertical partition 18 which is arranged in the drum 3' and essentially has a stiffening function. The partition 18 may be replaced with a similar structure, e.g. spoke-like struts, arranged between the drive shaft and the netting. In narrow drums, the partition as well as the rotary shaft may be dispensed with. If desired, the screening element 8 may also be replaceable in accordance with the contemplated degree of screening (diffeiant mesh widths). Also, the entire drum 3' may be replaceable.

Compared with the prior art, the screening device according to the invention confers several major advan- tages, some of which have been discussed earlier in the text. Owing to the fact that the drum 3 is disposed transversely and mounted at two points on the frame 5, the pushing forces generated when the drum is being loaded are taken up very effectively. Also, the robust construction results in excellent force absorption when the drum 3 is rotated. In the tractor 6, the operator has a clear view into the drum 3 all the time, and may thus supervise the entire screening operation.

It should also be added that the screening drum 3, 3' can be much wider than e.g. the screening device described in EP-B1-0,178,656 discussed by way of introduction. The inlet opening of the screening drum 3, 3' may advan¬ tageously have a width of up to about 3.0 m. Another con¬ siderable advantage to be emphasised is that the screening drum 3, 3' proper does not cor ain any movable parts at all. Further, the driving means are simple and of standard design.

Finally, it should be pointed out that the invention is by no means restricted to the embodiments discussed above, and that several modifications of the invention are conceivable within the scope of the appended claims. Thus, the screening device may, for instance, be connect¬ ed to other working machines, and other frames, stands and driving means may be used. Further, the screening concept of the invention can be applied to other mate¬ rials than thosε referred to herein.

Claims

1. Method for screening such materials as earth, gra- vel and the like containing comparatively large-size objects (1), such as stones, root vegetables and the like, which are to be separated from the finer material (2), in which method is used a screening drum (3) which is rotat- able about a substantially horizontal axis of rotation (4) and which has a circumferential surface mainly consisting of a screening element (8) and further having an inlet opening (13) for the material to be screened, said drum (3) being first moved into said material so that a suit¬ able amount thereof is fed into the drum (3) through the opening (13), whereupon the drum (3) is brought to a screening position, in which it is rotated about its axis of rotation (4), such that the material contained in the drum is set in motion, the large-size objects (1) remain¬ ing in the drum (3) and the finer material (2) being forc- ed out of the drum (3) through said screening element (8), c h a r a c t e r i s e d in that the drum (3) when in said screening position is rotated in a first direction, the large-size objects (1) being retained in the drum (3) by means of a pocket (14, 15) provided therein, and that the drum (3), after the finer material (2) has been forced out of the drum (3) through the screening element (8), is brought to an emptying position, in which it is rotated in the opposite direction, whereby the large-size objects (1) are removed from said pocket (14, 15) and discharged from the drum (3) through said opening (13).

2. The method of claim 1, c h a r a c t e r i s ¬ e d in that the drum (3) is rotated at a speed of about 7-15 rpm, preferably about 10-12 rpm.

3. The method of claim 1 or 2, c h a r a c t e r - i s e d in that the drum (3) is rotated about 4-5 revo¬ lutions in the first direction and about 0.5-1 revolution in the opposite direction during every screening cycle. 11 4. Device for screening such materials as earth, gravel and the like containing comparatively large-size objects (1), such as stones, root vegetables and the like, which are to be separated from the finer material (2), said device including a frame (5) with means for connection to a working machine (6), preferably to the front loader of a tractor, and a screening drum (3) which is mounted on said frame (5) and rotatable by a driving unit (12) and which has a circumferential surface mainly consisting of a screening element (8) and further having an inlet opening (13) for the material to be screened, the axis of rotation

(4) of the drum (3) being substantially horizontal and transverse to the main direction of travel of the working machine (6), c h a r a c t e r i s e d in that the drum (3) has an interior pocket (14, 15) which is arranged inwardly of the opening (13) and associated with the screening element (8) and which, when the drum (3) is rotated in a first direction, serves to retain the large-size objects (1) in the drum (3) while the finer material (2) leaves the drum (3) through the screening element (8), and which, when the d. m (3) is rotated in the opposite direction and after the screening has been completed, allows the large-size objects (1) to leave the drum (3) through the opening (13).

5. The device of claim 4, c h a r a c t e r i s ¬ e d in that the pocket (14, 15) has an obliquely inwardly inclined wall (14) which is substantially parallel to the axis of rotation or rotary shaft (4) and arranged between said axis or shaft and the opening (13), and which has a free, transverse edge located within the drum (3) at a distance from the in .de thereof.

6. The device ox claim 5, c h a r a c t e r i s ¬ e in that the wall (14) forms an extension of the screening element (8) of the drum (3) that project „nto said drum (3), said screening element consisting of a netting or grating.

7. The device of claim 5 or 6, c h a r a c t e r ¬ s e d in that the drum (3) comprises two opposing ver¬ tical end walls (10, 11) which are interconnected by means of the rotary shaft (4) extending therebetween, and by means of the screening element (8) extending between the peripheries of the ends walls (10, 11), the drum (3) being further provided, on its circumferential surface, with a reinforcing metal sheet (9) which extends between the end walls (10, 11) and is connected thereto, and which has a first transverse edge which is located on the circumferen¬ tial surface of the drum and is parallel to the rotary shaft (4) and which is connected to the screening element (8), and a free second transverse edge which also is parallel to the rotary shaft (4) and defines the opening (13) which in addition is defined by the end walls (10, 11) and the wall (14).

8. The device of claim 7, c h a r a c t e r i s ¬ e d in that the wall (14) is so directed into the drum (3) that the major portion of the material contained therein, in particular the large-size objects (1), im¬ pinge upon the reinforcing sheet (9) when the drum (3) is rotated.

9. The device of claim 7 or 8, c h a r a c t e r ¬ i s e d in that about 70% of the circumferential surface of the screening drum (3) is made up of the screening element (8), about 15% thereof is made up of the reinforc¬ ing sheet (9), and about 15% thereof is made up of the opening (13).

10. The device of any one of claims 4-9, c h a r - a c t e r i s e d in that the driving unit (12) is a hydraulic motor mounted on the frame (5) and connected to the rotary shaft (4).