Classifying – separating – and assorting solids – Sifting – Concave and convex sifters
Patent
1996-03-10
1998-06-16
Milef, Boris
Classifying, separating, and assorting solids
Sifting
Concave and convex sifters
209382, B07B 106
Patent
active
057656967
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to an improved sieve screen deck and more particular to a sieve screen deck in which the sieve screen is rapped in a novel manner to prevent blockage or blinding of the screen. The novel screen rapping mechanism is simple to make and install, and may improve the efficiency of operations of the sieve screen deck.
Known sieve screen decks are used to separate oversized and undersized particles from one another or to separate liquids from solids, or both simultaneously. Typically, a sieve screen deck comprises a frame, a sieve screen mounted on the frame and vibration means on the frame or the screen to cause the screen to vibrate. Originally, the screen was connected rigidly to the frame at either end, however, in more recent designs the ends of the screen are connected to the frame through flexible members which allow the screen to vibrate more freely and thus improve the screening action of the sieve screen deck.
It is known that the sieving action of such a screen deck may be enhanced by vibrating and/or rapping the screen, that is, by applying repeated impacts to one face of the screen or to the screen frame. Rapping is normally done by connecting a rapping bar to the underside of the sieve screen and positioning on the frame, or on the ground beneath the frame, a mechanical impacting means which imparts blows in rapid succession to the rapping bar or vibrates the complete screen and frame.
Whilst known rapping arrangements provide some alleviation to the problem of blinding of the sieve screen, it would be desirable to provide a more effective rapping action.
The present invention provides a sieve screen deck comprising:
a frame;
a sieve screen resiliently mounted to the frame so as to allow a limited amount of movement between the sieve screen and the frame, the sieve screen having flexible side walls; and
a rapping mechanism having a ram fixed at one end relative to the frame and acting at its other end on a drive shaft via a crank arm, the drive shaft extending across the sieve screen and being rotatably journalled in the respective side walls of the sieve screen, the rapping mechanism also having a rapping bar connected to the drive shaft by resilient elongate arms;
means actuating the ram to cause it to move the rapping mechanism at intervals from a rest position wherein the rapping bar is spaced a short distance from the sieve screen and the sieve screen is supported by the frame, to a primed position wherein the rapping bar is spaced further away from the sieve screen and a predetermined distance above its rest position and the screen is raised relative to the frame and thereafter to release the mechanism to allow the rapping bar and the sieve screen to fall back to the rest position with such force that the rapping bar will cause the resilient arms to bend sufficiently to cause the rapping bar to strike the sieve screen.
In use, the ram is driven so as to exert an upward force on the crank arm to rotate the shaft and move the rapping bar upwards and away from the screen. The upward force exerted on the crank arm and an inertial or centrifugal force resulting from the rotational movement of the rapping bar causes a resultant upwardly directed force to be exerted on the shaft which is sufficient to move the sieve screen upwards relative to the frame. When the ram is released, the sieve screen will move under gravity back to a rest position relative to the frame to provide a first rap of the screen, and the rapping bar will also move downwards under gravity, the momentum of the rapping bar being sufficient to flex the resilient elongate arms and allow the rapping bar to move beyond its rest position and impact with the screen to provide a second rap in a flicking manner on the screen.
Preferably, the rapping mechanism is positioned above the sieve screen and the rapping bar impacts with the upper surface of the sieve screen.
Preferably, the ram is an hydraulic ram or a pneumatic ram having a cylinder and a piston driving a telescopic rod. Further, the ram preferably ha
REFERENCES:
patent: 4288320 (1981-09-01), Wilson
patent: 4505812 (1985-03-01), Lees
patent: 4575420 (1986-03-01), Blachetta et al.
Milef Boris
Minpro Australia N.L.
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