METHOD FOR SCREENING SOIL AND A SCREENING DEVICE The invention relates to a screening device and a method for screening of soil removed from the ground and transporting it off the site by means of a scoop or a similar soil- processing device and in which method screening is carried out by means of a screening device connected to the scoop and soil removed with the scoop under the water surface by means of the scoop motion, whereby soil and water are moved towards the screening device, essentially deviating from the horizontal and most suitably located in an essentially tilted or vertical direction, and through it into the scoop and the soil gained into the scoop is sucked by means of a pump and removed into an outlet tube.

Previously known is, among other things a, screening device as above described from Finnish patent publication 94729, where a horizontal screening device comprises several shafts rotatable side by side and furnished with discs. The distance between shafts and the size of discs are so chosen that the discs are partly overlapping each other. The soil to be screened is lifted onto to the screening table and the soil material that has penetrated the screen is transported away from the screen underside.

Further, from the Finnish utility model registration 1803 a screen coop is known, in the bottom plate of which there is in the rear part an opening, into which shafts rotatable side by side are placed and shafts are furnished with discs. Soil is taken into the scoop, the scoop is lifted up and rotation of shafts started. The soil that has penetrated the screen falls from scoop, while not penetrated soil remains in it. On screening the scoop is kept for instance over the platform of a lorry. The soil that has not penetrated the screen is emptied elsewhere tilting the scoop.

The screening method and device according publication 94729 is intended for screening of soil transported in different ways to the screening device and lifted onto the screen table, whereby screening takes place by means of gravitation through the horizontal screen table. Soil that has not penetrated the screen must be removed from the screen table every now and then.

A screening method and screening device according to utility model 1803 connected to a

working machine can itself take soil, the working machine must then be driven to the screening site, where screening takes place in the working machine scoop by means of gravitation a scoopful at a time.

The disadvantage of above presented methods is their limited scope of screening by gravitation, whereby the screen table or a similar screening shaft assembly must be horizontal, because of which, among other things, by means of a scoop screen according to utility model 1803 screening may be started only when the scoop has been lifted up and kept there in place, in order to take the screened outcome in safe-keeping. Screening is not possible at the same time soil is taken with the scoop from the ground.

In the solution or publication FI-94729 separate machines are needed to gain and to move soil over to the screen table.

However, it is by means of above described methods and equipment not possible to carry out processing and screening of underwater soil and to transport screened material.

Therefore, a new method and screening device were developed, by means of which screening can be carried out surprisingly at once under water on the bottom, at same time soil is being loosened off. The method according to the invention is characterized in that screening is carried out by rotating the shafts of the screening device, which is formed of several shafts side by side and of discs fixed to them at a distance from each other, while at the same time by means of the said pump soil and water is sucked through said screening device.

The screening device in accordance with the invention is characterized in that the screening device is formed of several rotatable shafts side by side and of discs fixed to them overlapping each other and at a distance from and in respect to each other.

The advantage of the invention is that especially by removing soil on dredging the watercourses it is possible to keep the scoop connected to the working machine all the time or at least mainly in the bottom, to move it in bottom direction during working and at the same time to screen bottom soil and remove screened soil from the bottom without lifting up the scoop. On dredging the watercourse bottom, that is removing layers from it,

the layers are often of a sediment one wants to get mixed in the water as little as possible during dredging. In some cases the sediments even contain poisons. The important advantage is that the dredging scoop can be in slow motion during working in the bottom, and also when sucking water by pump into the scoop, the removed soil and water moves through the screen to the pump and to the outlet tube without the bottom soil getting hardly mixed at all in the water of the watercourse. The screen separates soil, which cannot be let to the pump and the outlet tube. Separation takes place during working without lifting up the scoop apparatus from bottom. When the screening device is in a position deviating from the horizontal, it can while working with the scoop, carry out screening. The screen device can clean itself and the construction is so made that the screening device rejects pieces, which cannot penetrate the screen.

By known suction dredging blocks often are formed in the grating in front of the screen by plastic bags, ends of boards, scrap metal etc. and clearing the screen of them means interruptions in work. Blocks appear especially on dredging of rivers, city canals and harbours. In the invention the screening device clears itself and thus interruptions due to blocks are minimized.

In the following the invention is disclosed with reference to the enclosed drawing, where Fig. 1 is the scoop and the screening device according to the invention in working position.

Fig. 2 is the scoop with the screening device in it viewed from the front Fig. 3 is the scoop and the screening device in profile.

Figure 1 shows bottom dredging of a watercourse by scoop equipment 1 connected, for, instance, to arm 2 of a dredge floating on the surface. Further, the scoop equipment can be turned with respect to arm 2 by means of cylinder 6. The scoop apparatus comprises a pump 4 and for it a motor 5 and also an outlet tube 3. Scoop equipment 1 is open only from its front edge, whereby soil gets into the scoop, when the scoop is moved on the bottom at a certain depth. Pump 4 sucks through the same open portion water and soil into the scoop. Working causes very little mixing of the soil in the surrounding water. Scoop apparatus 1 needs not to be lifted up in between. Its transfers to new motion are also done under water close to the bottom. Greater objects do not remain in the scoop, but the more

or less vertical assembly of the screening device rejects greater pieces and moves them away either sidewards or upwards.

Figure 2 shows the location of screening device in the scoop. The screening device has shafts 9 and discs 12 fitted to them. Furthermore, discs 12 are partly overlapping. Shafts 9 are rotated in the same direction by means of a rotating means inside box 7 and a driving motor 15. There are in the upper and lower part additional ribs 10. Shafts 9 can be fitted horizontally or vertically. Vertically assembled screening device rejects bigger pieces better sidewards.

In figure 3 discs 12 of the screening device are visible as a section view, in this case the vertical assembly. The screening device can even be tilted, especially backward, with other words, the upper part backward towards pump 4.

In addition, high pressure water jets can be fitted for screening device cleaning and also if there is hard clay in the bottom. By means of water jets, among other things, hard clods of clay in front of the screening device can be crushed, which otherwise would not penetrate the screen. Also between the discs clay may get stuck and rotate so that the penetration power of the screen deteriorates. The water jet scan also be directed to clean the screen.

In the figure the water jet nozzle parts are protected by projecting parts 8. Nozzle tubes 13 run from distributor pipe 16 and are turn towards the screening device.