Classifying – separating – and assorting solids – Sifting – Plane sifters
Patent
1999-03-10
2000-12-05
Walsh, Donald P.
Classifying, separating, and assorting solids
Sifting
Plane sifters
209317, 209319, B07B 128
Patent
active
061554286
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to vibratory screening machines such as shale shakers used to separate mixtures of solids and liquids into the separate components such as mixtures which result from drilling of a bore hole or tunnel when a drilling fluid is used. Separation of the components permits re-use of the drilling fluid.
BACKGROUND TO THE INVENTION
There are many examples of such machines which essentially comprise a rigid supporting framework within which is resiliently mounted a box or basket containing one or more mesh screens onto which the mixture of solids and liquids is poured. To assist in the sieving action it is known to vibrate the box or basket so that the solid matter on the mesh screens is itself caused to vibrate. This causes clumps of fine material to break up, and if appropriate, pass through the mesh, together with the liquids, and for larger pieces of material which cannot pass through a mesh to migrate over the surface of the mesh to form part of the solids output of the machine.
By using a coarse mesh screen followed by a fine mesh screen so the process of screening is split into two steps in which liquid and fines (small solid particles) pass through the coarse mesh leaving the larger solid material thereon, and essentially the liquid alone is able to pass through the very fine mesh screen leaving the fines to be discharged from the second screen.
U.S. Pat. No. 4,167,478 describes a modular screening machine having at least one screen for separating particulate material according to size in which the screen box is driven so as to describe an elliptical movement at one end and a substantially rectilinear oscillatory movement at the other end.
U.S. Pat. No. 4,340,469 also describes a vibrating screening apparatus containing two screens which are vertically spaced above and below two independently rotatable shafts containing unbalanced weights so that when rotated the screen assembly is caused to move in a generally elliptical path. By choosing the position of the two shaft axes relative to the centre of gravity of the assembly, a rocking movement is introduced at the infeed end of the assembly.
U.S. Pat. No. 5,265,730 describes a further arrangement in which rotary eccentric vibrators are mounted outboard of the machine but act on the screen basket in such a way as to introduce an appropriate shaking movement.
In such machines the objective is twofold. On the one hand the material has to be vibrated so as to separate liquid from solids as far as possible, and to separate small solids from larger solids particularly where a degree of adhesion can exist as a result of the inherent characteristics of the materials concerned. On the other hand as soon as the liquid and solid separation has occurred, it is desirable to remove the solid material from the screens as quickly as possible to make way for further material which is usually desirably delivered for processing on a continuous basis.
Generally movement of solid material off the screen is achieved by incorporating into the motion a backwards and forwards component, as is known in the field of conveyors. This will cause particulate material to migrate along the length of a conveyor in response to an appropriate shaking movement. A drive for such a conveyor is described in U.S. Pat. No. 4,212,731 which also utilises two counter-rotating eccentric weights to generate the forces necessary to introduce conveyance of particulate material along the surface of the conveyor illustrated therein.
Whereas the rapid removal of solid material from the screen is obviously advantageous where a high throughput is required, if the rate of removal is too high the migrating solids and fines may carry too much of the liquid phase.
Whilst it has been found that improved efficiency, both in terms of screening and throughput, can be achieved using two screens, a first having a relatively coarse mesh and a second having a relatively fine mesh as aforesaid, the actual movement of each of the two screens in order to achieve optimum proces
REFERENCES:
patent: 5037536 (1991-08-01), Koch et al.
patent: 5265730 (1993-11-01), Norris
patent: 5683580 (1997-11-01), Young
Bailey Arthur Robert
Burnett George Alexander
Martin Brett C.
Rig Technology Limited
Walsh Donald P.
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