Classifying – separating – and assorting solids – Sifting – Plane sifters
Patent
1994-04-18
1995-08-22
Kashnikow, Andres
Classifying, separating, and assorting solids
Sifting
Plane sifters
2093665, B07B 128
Patent
active
054431638
DESCRIPTION:
BRIEF SUMMARY
APPARATUS FOR SCREENING GRANULAR MATERIALS
The present invention relates to vibrating screening apparatuses, which handle the material to be screened in a mainly vertical loose flow--in the following called Sizers. An example of such a Sizer is described, e.g. in the U.S. Pat. No. 3,710,940. In that case the loose flow of particles is created by the apertures of the classifying elements, below called screen cloths, being larger than the particles arriving on them. A loose flow of particles can also be achieved when a minor portion of them are larger than these apertures.
Conventional screening apparatuses have screen cloths where the apertures are usually smaller than a greater portion of the particles. In such a case it is much more difficult for the particles to pass the screen cloth: the particles form a bed on top of the screen cloth, which obstructs the movement of the particles. Particles, which have nearly the same size as the apertures may get stuck in the screen cloth.
Sizers depend upon the formation of such beds of particles being avoided as far as possible; by using several layers of often steeply sloping screen cloths, satisfactory separations are obtained, despite the apertures being large in relation to the separation size.
In practice, however, Sizers do suffer from beds being formed, normally when the flow of particles meets the first part of the screen cloths, where the flow is relatively concentrated. If such a bed is allowed to spread over a substantial segment of the screen cloth, the danger of reduced screening efficiency becomes imminent in that the congestin of the bed prevents the finer particles from working their way down through the screen cloths; they contaminate the coarser products.
The object of the present invention is to prevent the formaton of such beds, or, to segregate the particles in the beds.
This is achieved by the movement being more vigorous and basically perpendicular to the surface of the screen cloths at the inlet end of the Sizer, close to the first parts of the screen cloths, so that it agitates and segregates the flow of particles in this region, according to the characterizing parts of the claims.
The motion of Sizer has so far been linear and of approximately the same attitude (stroke, direction and frequency) over the entire Sizer. Such a vibration is normally created by two vibrator motors or eccentric elements, where the eccenters rotate in opposite directions, or by a linear magnetic vibrator.
The movement of the Sizer, according to this invention, must not be uniform. At the initial part of the screen cloths, it should be vigorous and approximately perpendicular to the surface of them so that the segregating action is enhanced. An elliptic motion could be advantageous, in that its direction of rotation can be varied, according to the screening duty. This motion has not the same impact as a linear motion and could, therefore, be larger and more effective.
Towards the outlet end of the Sizer, where the particles leave it, a more transporting and less agitating movement is to be preferred; it should be more horizontal, having a direction with an acute angle, relative to the surface of the screen cloths.
The invention will be described by way of examples with reference to the drawings:
FIG. 1 illustrates the principle of the invention;
FIG. 2 schematically illustrates a Sizer according to the invention in longitudinal section;
FIG. 3 illustrates the Sizer seen from the rear end;
FIG. 4 illustrates an external side view of the invention;
FIGS. 5 and 6 are diagrams showing the development of the cleanliness and recovery respectively;
FIG. 7 schematically illustrates another embodiment of the invention in the longitudinal section;
FIG. 8 illustrates an external side view of the embodiment shown in FIG. 7.
FIG. 1 illustrates the principle. 1 is a screen cloth, seen from the side. 2 indicates the general direction of the flow of particles arriving on the screen cloth. The primary part of the screen cloth, near its inlet end, moves, more or less, perpendicular
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Douglas Lisa
Fredrik Mogensen AB
Kashnikow Andres
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