GB2092479A - Sieving apparatus - Google Patents

Abstract

Sieving apparatus comprises a closed container 10 partitioned by a horizontal sieve screen 20 into a cylindrical upper part and a generally conical lower part. Material to be sieved is fed tangentially to the container 10 from a supply hopper 30 through an inlet in the upper part, and fines are conveyed through an outlet in the lower part to a collection hopper 40 for subsequent discharge. A fan unit 43 draws air through the apparatus from the supply hopper 30 to the collection hopper 40 to entrain the material to be sieved and the fines while the container 10 and screen 20 are vibrated to assist the sieving process. <IMAGE>

Description

SPECIFICATION Sieving apparatus This invention relates to sieving apparatus.

Numerous types of sieving apparatus for sieving dry particulate material are known which employ mechanical agitation of the sieving screen to produce a bulk turbulence in the material to be sieved on top of the sieve screen. This turbulence however produces dust which enters the air surrounding the apparatus.

The invention provides sieving apparatus for sieving dry particulate material comprising a base, a closed container mounted on the base for allowing vibratory movement of the container relative to the base, a sieve screen mounted in the container so as to partition the interior of the container into upper and lower parts, the container having an inlet to the upper part on one side of the screen and an outlet from the lower part on the other side of the screen, means for vibrating the container and screen relative to the base to produce, in use, turbulence of material being sieved, a feed pipe for providing a gas-tight feed path for material to be sieved from a supply vessel to the container inlet, and means for producing a gas flow along the feed pipe and through the screen such as to entrain particulate material along the feed pipe from the supply vessel to the upper part of the container.

The sieve is preferably arranged generally horizontally, the gas flow producing means comprising a fan arranged to suck air down through the screen.

The apparatus may include the supply vessel which is preferably a supply hopper having an inlet in communication with ambient air.

The apparatus preferably further comprises a collection hopper having a discharge outlet for the discharge of accumulated fines, an inlet in gas-tight communication with the container outlet for incoming gas with entrained fines and a gas outlet connected to the gas flow producing means so that the fines are entrained by the gas flow so as to be conveyed to the collection hopper. An outlet pipe may be connected between the container outlet and the collection hopper inlet.

The upper part of the container may comprise a generally upright cylinder sealed at its upper end, the sieve screen being generally circular, and the lower part of the container may comprise a funnel for collecting fines passing through the screen. The container inlet is preferably situated in the side wall of the cylinder, the feed pipe being arranged such that the material to be sieved enters the container substantially tangentially to the cylinder.

The apparatus may further comprise ultrasonic vibrator means operable to effect ultrasonic vibrations of the screen. Such vibrator means preferably comprises an ultrasonic probe connected directly to the screen.

An embodiment of the invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure lisa schematic elevation of sieving apparatus embodying the invention; and Figure 2 is a plan view of part of the apparatus of Figure 1.

The sieving apparatus shown in Figure 1 comprises a sieving machine generally designated 5 having a closed container 10 supported on a base 11 for vibratory movement relative thereto. This support may be by means of a plurality of resilient mounting blocks such as are well known in the art. The base is mounted in turn on a trolley 12 for ease of transport of the machine. The container is vibrated relative to the base by a pair of out-of-balance weight assemblies 14 and 15 driven through a flexible transmission, such as a belt and pulley arrangement, by an electric motor (not shown) attached to the base 11. The weight assemblies 14 and 15 act on a frame 13 to which the container 10 is fastened by means of clamps (not shown).The weight assemblies typically rotate at speeds in the range 500 to 3000 revolutions per minute producing oscillations of the container 10 of 0.125"to 1" in amplitude.

A sieve screen 20 is mounted in the container 10 such as to partition the interior of the container into upper and lower parts. The upper part comprises a generally upright cylinder 21 closed at its upper end by a top plate 22, while the lower part comprises a conical funnel 24 the constricted end of which leads to an outlet 25 of the container 10. The upper part may be removed on releasing the clamps to give access to the screen 20.

Material to be sieved is supplied from a supply hopper 30 into which sacks of unsieved material can be emptied from a bag platform 31. The supply hopper 30 has an outlet 33 to which is attached a flexible feed pipe 34 for feeding unsieved material to the container 10. The pipe 34 enters the cylinder 21 generally tangentially as shown in Figure 2.

The fines (material which has passed through the sieve screen 20) is conveyed along a second flexible pipe 35 to a collection hopper 40 for the accumulation of the fines. The collection hopper 40 may be emptied periodically through a discharge outlet 41 openble by means of a jack 42. An electric extractor fan unit 43 is connected by a tube 44 to an air outlet of the hopper 40 so as to extract air therefrom. This outlet is covered by a bag filter 45 to prevent fines reaching the fan unit 43. Some fines inevitably settle on the bag filter 45 and vibrator means may therefore be provided for cleaning the filter.

It will be appreciated that with the discharge outlet 41 closed, the fan unit 43 causes an air flow right through the sieving apparatus from the supply hopper 30, along the pipe 34, through the sieve screen 20 and along the pipe 35 to the collection hopper 40. This air flow entrains particles of unsieved material from the hopper 30, conveying them to the container 10 for the sieving process, and similarly transports the fines along the pipe 35 to the collection hopper 40.

The upper part of the container 10 can be relieved of oversize material from time to time through an oversize material outlet 26 integral with the cylinder 21. A flexible valve 27 of an elastomer or similar material is attached to the outlet 26, the valve 27 being closed by sub-ambient pressure in the cylinder 21 while material is being sieved and opening when the pressure in the cylinder 21 is ambient or super-ambient which may be while fines are being discharged from the discharge outlet 41 of the collection hopper 40. Alternatively, the outlet may communicate with a sealed collecting chamber for oversize material, or indeed the outlet 26 can be omitted altogether in which case oversize material can be removed from the container 10 by removing the plate 22.

To increase the rate of sieving, an ultrasonic vibrator may be mounted in the funnel 24 to cause the screen 20 to vibrate ultrasonically, for example at between 10 and 20 kHz. Such a vibrator may have an ultrasonic probe secured firmly to the centre of the sieve screen 20.

An advantage of the aforedescribed embodiment of the invention is that the closed container in which the sieve screen is mounted effectively eliminates the escape of dust produced by the sieving process to the surrounding air. A further advantage is that the air flow through the apparatus performs the functions of increasing the rate of flow of fines through the sieve screen, conveying material to be sieved from the supply hopper and conveying the fines to the collection hopper. Thus the relative heights of the supply hopper, sieving machine and collection hopper do not affect the sieving process.

Claims (3)

1. Sieving apparatus for sieving dry particulate material comprising a base, a closed container mounted on the base for allowing vibratory movement of the container relative to the base, a sieve screen mounted in the container so as to partition the interior of the container into upper and lower parts, the container having an inlet to the upper part on one side of the screen and an outlet from the lower part on the other side of the screen, means for vibrating the container and screen relative to the base to produce, in use, turbulence of material being sieved, a feed pipe for providing a gas-tight feed path for material to be sieved from a supply vessel to the container inlet, and means for producing a gas flow along the feed pipe and through the screen such as to entrain particulate material along the feed pipe from the supply vessel to the upper part of the container.

2. Sieving apparatus as claimed in Claim 1 wherein the sieve is arranged generally horizontally, the gas flow producing means comprising a fan arranged to suck air down through the screen.

3. Sieving apparatus as claimed in either Claim 1 or Claim 2 wherein the supply vessel is a supply hopper.

3. Sieving apparatus as claimed in either Claim 1 or Claim 2 and including said supply vessel which is a supply hopper having an inlet in communication with ambient air.

4. Sieving apparatus as claimed in any preceding claim further comprising a collection hopper having a discharge outlet for the discharge of accumulated fines, an inlet in gas-tight communication with the container outlet for incoming gas with entrained fines and a gas outlet connected to the gas flow producing means so that the fines are entrained by the gas flow so as to be conveyed to the collection hopper.

5. Sieving apparatus as claimed Claim 4further comprising an outlet pipe connected between the container outlet and the collection hopper inlet.

6. Sieving apparatus as claimed in any preceding claim wherein the upper part of the container comprises a generally upright cylinder sealed at its upper end, the sieve screen being generally circular, and the lower part of the container comprises a funnel for collecting fines passing through the screen.

7. Sieving apparatus as claimed in Claim 6 wherein the container inlet is situated in the side wall of the cylinder, the feed pipe being arranged such that the material to be sieved enters the container substantially tangentially to the cylinder.

8. Sieving apparatus as claimed in any preceding claim wherein the container further has an outlet from the upper part on the one side of the screen for the discharge of oversize material from the container, the outlet from the upper part being closed during sieving.

9. Sieving apparatus as claimed in any preceding claim further comprising ultrasonic vibrator means operable to effect ultrasonic vibrations of the screen.

10. Sieving apparatus as claimed in Claim 8 wherein the ultrasonic vibrator means comprises an ultrasonic probe connected directly to the screen.

11. Sieving apparatus substantially as hereinbefore described with reference to and as shown in the accompanying drawings.

New claims or amendments to claims filed on 18th May1982 Superseded claims 1 and 3 New or amended claims:

1. Sieving apparatus for sieving dry particulate material comprising a base, a closed container mounted on the base for allowing vibratory movement of the container relative to the base, a sieve screen mounted in the container so as to partition the interior of the container into upper and lower parts, the container having an inlet to the upper part on one side of the screen and an outlet from the lower part on the other side of the screen, means for vibrating the container and screen relative to the base to produce, in use, turbulence of material being sieved, a supply vessel having an inlet in communication with ambient air, a feed pipe providing a gas-tight feed path for material to be sieved from the supply vessel to the container inlet, and means for producing a gas flow along the feed pipe and through the screen such as to entrain particulate material along the feed pipe from the supply vessel to the upper part of the container.