Improvements relating to vibratory sifters

Abstract: A sifter comprises a screen (10) mounted for vibratory movement in three dimensions having a rotational component and upward and downward components, the screen having means (18) for collecting undersized particles therebelow and a discharge aperture (34) formed therethrough at its peripherly for oversized particles.

Description: This invention relates to vibratory sifters, the term "sifters" being used in a broad sense to include the various sieves, screens and the like by which the materials can be screened, graded or separated. The term "material" is intended to describe solids, liquids, items or any other substances tobe separated by size. In certain current vibratory sifters, material to be separated is supplied to the top of the vibrating screen, oversize material being retained on the top of the screen while undersized material passes through the screen. Oversized material is removed from the periphery of the screen, normally by way of an opening in a peripheral wall surrounding the screen. Arrangements of this nature have been disadvantageous in that oversize material often tends to accumulate on the peripheral wall especially around the discharge aperture, thereby reducing its efficient discharge. United States Patent 4315817 discloses a vibratory system in which the vibrating means imparts a linear, that is essentially a linear back and forth vibration to a screen. Oversized material which has not passed through the screen moves off the edge of a screen and over a flat non-perforate surface before falling through a discharge opening. As a result of this the oversize material has to follow a path, after the screening operation, which is at least as great as the width of the non-perforate surface. This extra travel can result in deterioration of oversized particles that is, contamination by undersized particles. It extends the length of time occupied by the screening operation and consequently results in increased energy consumption. Specification No. GB-A-2085760 also discloses a vibratory material separator. It is an object of the present invention to obviate or mitigate these disadvantages. According to the present invention there is provided a sifter comprising a resiliently supported circular chamber having a screen fitted in the base, means for subjecting the chamber and screen to a vibro gyratory action having a three dimensional motion of a rotational character having upward and downward components in the movement, means for collecting undersized material passing through the screen and an aperture through the screen adjacent to and inside the periphery of the chamber through which oversized materials from the top of the screen are dischargeable directly below the chamber. Preferably the apparatus comprises a plurality of vertically spaced screen each having a discharge aperture for oversized particles adjacent to and inside its periphery. Preferably a discharge chute for oversize material is located beneath the or each aperture, directing oversize material away from the centre of the sifter. Preferably the collecting means for undersize material has an inclined base and a discharge at the periphery of the sifter. Preferably the screen comprises a mesh supported by a peripheral tensioning frame to which the mesh is bonded or otherwise fixed. Further according to the present invention there is provided a vibratory sifter screen comprising a peripheral tensioning frame supporting a mesh which has an aperture for oversize material being sifted adjacent to and inside the peripheral frame. Preferably a further frame member is attached to the peripheral frame to define said aperture. Preferably the mesh is bonded or otherwise fixed to said peripheral and further frames. An embodiment of the present invention will now be described by way of example only with reference to the accompanying drawings in which:- Fig. 1 shows a perspective view of a separating screen for a sifter, Fig. 2 shows a plan of a sifter, Fig. 3 shows a sectional elevation on the lines A B of a sifter, and Fig. 3A shows an enlarged sectional elevation of part of the sifter. A vibratory sifter comprises a cylindrical base support 10 on which is supported by an annular series of compression springs 12 a vibratory assembly comprising a cylinderical sifter chamber 14 in which is mounted a sifter screen 16 above a collecting pan 18 for undersize material passing through the screen, the pan 18 having a peripheral discharge chute 20 extending through the side wall of the chamber 14. The chamber 14 extends upwardly from a base member 22 having a central mounting ring 24. An electric vibrator motor 26 is supported by and below the ring 24. The motor shaft projects above and below the motor casing and is fitted with relatively angularly adjustable eccentric weights 28, 30. Due to the provision of these weights and to the resilient mounting of the sifting chamber 14, rotation of the motor imparts to the chamber a vibro-gyratory action in the form of a high frequency rotary oscillation about the central axis of the motor and chamber with an upward and downward component of movement. This causes vibration of the material on the screen with an outwardly spiral motion. Under size particles fall through the screen to be collected in the collecting pan 18 and discharged by way of the chute 20, whereas oversized particles remain on top of the screen and move towards its periphery. Fig. 1 shows a perspective view of a circular screen. The screen comprises a circular peripheral tensioning frame 30 having a mesh 32 bonded, clamped or otherwise fixed to it. Within the outer periphery of the frame 30 there is provided in the screen an aperture 34 which is reinforced by an arcuate member 36 welded or otherwise attached to the frame 30. Oversized particles at the periphery of the screen fall through the aperture 34 and it will be realised that, unlike earlier vibratory sifters of this nature where oversize material is discharged over the edge of the screen 30, oversize material discharges effectively through the screen. Fig. 3 and 3A show that discharge chute 38 for over size material is located below the aperture 34. and that the screen is replaceable, for example, for cleaning purposes, by removably attaching in the chamber 14 between an upper section 14A and a lower section 14B, the sections being clamped together by any suitable means. Various modifications can be made without departing from the scope of the invention. For example, a multiple progressive sifting operation can be achieved by fitting one above the other in the sifting chamber 14, a plurality of screens, the mesh size of which decreases progressively downwards, each screen having fitted therebelow a discharge chute 38 for over size material, each leading to a separate collecting means, the undersize material falling through an upper screen to the next below screen where it is subject to a further sifting operation, the lowermost screen being provided with a collecting pan 18 and discharge chute 20, for undersize materials passing through the lowermost screen. Various other modifications can be made without departing from the scope of the invention. For example, the compression springs 12 on which the vibrating chamber is mounted may be replaced by rubber bushes or any other resilient assemblies. Alternative vibrating means may be provided so long as they impart to materials on the screen a movement causing undersize material to pass through the screen and oversized material to pass to the edge of the screen.

Claims: A sifter comprising a resiliently supported circular chamber (14) having a screen (10) fitted in its base, means (12,24,26,28,30) for subjecting the chamber and screen to a vibro-gyratory action having a three dimensional motion of rotational character having upward and downward components in the movement, means (18) for collecting undersized material passing through the screen characterised in that an aperture (34) is provided through the screen adjacent to and inside the periphery of the chamber (14) through which oversized materials from the top of the screen are dischargeable directly below the chamber. A sifter as claimed in Claim 1, characterised in that there is provided a plurality of vertically spaced screens (10) each having a discharge aperture (34) for oversized particles adjacent to and inside its periphery. A sifter as claimed in Claim 1 or Claim 2, characterised in that a discharge chute (38) for oversized material is located beneath the or each aperture (34), directing oversize material away from the centre of the sifter. A sifter as claimed in Claim 3, characterised in that the collecting means (18) for undersize material has an inclined base and a discharge (20) at the periphery of the sifter. A sifter as claimed in any one of the preceding claims, characterised in that the screen (10) comprises a mesh (32) supported by a peripheral tensioning frame (30) to which the mesh (32) is bonded or otherwise fixed. A vibratory sifter screen, characterised in that it comprises a peripheral tensioning frame (10) supporting a mesh (32 )which has an aperture (34) for oversize material being sifted adjacent to and inside the peripheral frame (30). A vibratory sifter screen as claimed in Claim 6, characterised in that a further frame member (36) is attached to the peripheral frame (30) to define said aperture (34). A vibratory sifter screen as claimed in Claim 7, characterised in that the mesh (32) is bonded to said peripheral and further frames (30,36).

Inventors: EMMETT PETER, EMMETT, PETER
Applicants: WILLIAM BOULTON VIBRO ENERGY L, WILLIAM BOULTON VIBRO ENERGY LIMITED
Application year: 1990
Main classification: B07B1
IPC codes: B07B1