Classifying – separating – and assorting solids – Sifting – Drum sifters
Patent
1997-07-16
1999-07-13
Nguyen, Tuan N.
Classifying, separating, and assorting solids
Sifting
Drum sifters
209289, 2093654, 209386, 209387, B07B 126, B07B 142
Patent
active
059214007
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to an apparatus for sieving a particulate material into selected size fractions.
The present invention relates particularly, although by no means exclusively, to an apparatus for sieving diamonds into selected size fractions.
The conventional apparatus for sieving diamonds into selected size fractions comprises an assembly of vibrating screens that are arranged in a stack with the uppermost screen having the largest screen size and successive screens having progressively finer screen sizes.
The conventional apparatus is operated on a batch basis and, as a consequence, the apparatus generally is not compatible with upstream and downstream diamond processing steps which are usually operated on a continuous basis. Another disadvantage of the conventional apparatus is that the screens block readily due to diamonds becoming lodged in holes in the screens ("pegged"). As a consequence, pegged diamonds must be removed from the screen holes periodically to maintain optimum performance of the screens. In addition to this being a time-consuming and labour intensive exercise, there is generally a degradation of product caused by diamonds being broken during the de-pegging operation. Other disadvantages of the conventional apparatus are high noise and dust levels.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an apparatus for sieving diamonds into selected size fractions which alleviates the disadvantages of the conventional apparatus described in the preceding paragraph.
According to the present invention there is provided an apparatus for sieving a particulate material into selected size fractions comprising: fraction and an oversize fraction, the screen having an inlet and for introducing particulate material to the screen and an outlet and for discharging the oversize fraction; the screen; and in two directions.
The applicant has found that the motion of particulate material in the screen that is caused by the twin phase drive means substantially increases the path length of the particulate material in the screen and, thereby, greatly increases the opportunity for particles to pass through the screen.
In addition, the applicant has found that the overall motion of the particulate material in the screen caused by the combined effect of the twin phase drive means and the rotating/oscillating drive means increases the overall movement of particles in the screen and this minimises pegging of particulate material in the screen.
It is preferred that the twin phase drive means be coupled to the screen for driving the screen in two orthogonal directions.
It is preferred that the twin phase drive means be coupled to the screen for driving the screen in a vertical direction and an axial direction of the screen for imparting vertical and axial motion to the particulate material as the particulate material moves from the inlet end toward the outlet end.
It is preferred that the screen be supported with the axis of the screen horizontal.
With such an arrangement, it is preferred that the twin-phase drive means be coupled to the screen for driving the screen vertically and horizontally for imparting vertical and horizontal motion to the particulate material.
The horizontal motion of the particulate material which results from the drive applied to the screen may be in a forward direction only, i.e. in an axial direction towards the outlet end of the screen, or it may be such that there are components of forward and reverse motion.
It is noted that for each particle at various times there may be no imparted horizontal motion, with the only motion of the particles being vertical and rotational/oscillatory.
It is preferred that the rotating/oscillating drive means and the twin phase drive means be adapted to impart a tumbling motion to the particulate material so that the orientation of the particulate material with respect to the screen holes changes continually as the particulate material travels through or along the screen to increase the pr
REFERENCES:
patent: 2245650 (1941-06-01), Christopherson
patent: 2249109 (1941-07-01), Botimer
patent: 2804975 (1957-09-01), Liebhart et al.
patent: 4585354 (1986-04-01), Thesenfitz
patent: 4636304 (1987-01-01), Hoppe
patent: 4896835 (1990-01-01), Fahrenholz
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