WO1991008059A1

WO1991008059A1 - Sifting apparatus

Info

Publication number: WO1991008059A1
Application number: PCT/GB1990/001773
Authority: WO
Inventors: Lee Crompton
Original assignee: Individual
Current assignee: Individual
Priority date: 1989-11-23
Filing date: 1990-11-16
Publication date: 1991-06-13
Anticipated expiration: 1992-05-23
Also published as: AU6725890A; GB8926520D0

Abstract

A sifting apparatus for particulate and/or granular materials comprises means such as a feed hopper (1) for feeding a powder material to be sifted to a sifting screen (3). Rotatable paddle means (4) is provided within the sifting screen for agitating the powder and air is supplied to the sifting screen by means such as an auger (9) rotating within a tube (11), so as to fluidise the powder within the screen (3) and to carry the powder through the screen. Sifted powder is removed from the apparatus by the fluidising air while material that is unable to pass through the screen (3) is removed from the apparatus by the means for supplying the air, for example by reversing the direction of rotation of the auger (9).

Description

SIFTING APPARATUS

The present invention relates to a sifting .apparatus for sifting particulate and/or granular materials.

Currently available sifting apparatus for powders generally employs a broom to force particulate material through a screen. However, such apparatus is prone to mechanical failure and is difficult to clean and maintain and often requires regular attention by a skilled fitter rather than brief intervention by the operator. This is undesirable from the point of view of lost production time and in respect of the employment of greater numbers of skilled workers than would otherwise be necessary.

It is an object of the present invention to provide a sifting apparatus which is simple and reliable in operation and which is easy to clean and maintain.

According to the present invention there is provided a sifting apparatus which comprises:

means for feeding a powder material to be sifted to a sifting screen;

rotatable paddle means provided within the sifting screen or agitating the powder; means for supplying air to the sifting screen so as to fluidise the powder within the screen and to carry the powder through the screen; and

means for removing sifted powder from the apparatus,

wherein the means for supplying air is operable to remove from the sifting screen material that is unable to pass therethrough.

The feeding means may comprise a hopper.

The sifting screen may be conical in shape.

The paddle means may have two paddles and may be substantially V-shaped so as to fit within a conical sifting screen.

The means for supplying air may comprise an auger rotatable with the paddle means and mounted within a tube, such that rotation of the auger within the tube draws air along the tube and into the sifting screen. Rotation of the auger, and thus the paddle means, is preferably reversible such that rotation of the auger in 'the reverse direction carries material that is unable to pass through the sifting screen along the tube and discharges such material from the apparatus. Means may be provided for rotating the paddle means at different speeds.

For a better understanding of the present invention and to show more clearly how it may be carried into effect reference will now be made, by way of example, to the accompanying figure which is a diagrammatic illustration of one embodiment of a sifting apparatus according to the present invention.

The sifting apparatus shown in the figure comprises a feed hopper 1 and a product bin 2 releasably connected to the feed hopper. A stationary conical sifting screen 3, for example of metal such as stainless steel, is located in an aperture between the feed hopper and the product bin and has a mesh size that is suited to the material to be sifted. I have found that 030 perforations are suitable for many materials. Alternative mesh sizes that have proved satisfactory include screens with 1 mm and 2 mm diameter perforations.

Rotatable within the sifting screen 3 is a V-shaped paddle assembly 4. The illustrated paddle assembly is formed with two paddles, but any suitable number of paddles may be provided. The paddle assembly may be rotated through a drive shaft 5 mounted in bearing 6 and connected to a motor 7 by way of a drive belt 8. Motor 7 may be, for example, a 3-phase squirrel cage AC motor, the speed of which can be varied by an AC inverter drive unit (not shown in detail) from 0 rpm to twice the rated rDm of the motor. The motor

7 is reversible under control of the drive unit, with the reverse and forward speeds being separately adjustable. However, if desired, the speed and direction of drive can be controlled by other means such as a separate gear arrangement.

Secured to the paddle assembly 4 and rotatable therewith is an auger 9. The auger 9 extends through the product bin 2 and the free end of the auger is rotatably mounted in a bearing 10. Auger 9 is positioned within a tube 11 which communicates with ambient atmosphere by way of a pipe 12. The product bin 2 is provided with a product outlet 13.

In use of the sifting apparatus shown in the figure, feed material is supplied to the feed hopper 1 and the motor 7 is energised so as to rotate the drive shaft 5, paddle assembly 4 and auger 9 in such a direction that air is drawn through the pipe 12 and carried along the tube 11 by the auger 9 and fed into the base of the conical sifting screen 3. Feed material flows under gravity through the feed hopper 1 and into the sifting screen 3 where it is fluidised and cooled by the incoming air. The paddle assembly 4 agitates the feed material within and against the sifting screen to break up any agglomerates. Particles that are sufficiently small pass through the screen into the product bin 2 with the fluidising air and through the product outlet 13.

Particles that are too large to pass through the sifting screen accumulate therein until the feed material in the feed hopper 1 is exhausted.

The sifting apparatus is controlled in a cycle which comprises a sequence of operating steps in which the motor

7 and auger 9 are run in their forward direction for a first selectable time of, say, 20 minutes at the conclusion of which the feed hopper 1 is arranged to be empty. The motor 7 and auger 9 are then stopped for a second selectable time of, say, 2 seconds inter al ia to allow any material in the screen to settle, and are then run in reverse for a third selectable time of, say, 10 seconds.

Rotation of the auger in the reverse direction may be at a lower speed than in the forward direction because fluidisation of the particles is no longer necessary.

Rotation of the auger 9 in the reverse direction carries the rejected material along the tube 11 and discharges it through the pipe 12 thereby cleaning the sifter without the need for any dismantling of the apparatus.

Control of the apparatus and the associated equipment such as supply of material to the feed hopper 1 may be carried out by way of a programmable logic control system (not shown in detail) which incorporates memory capacity for preset data and user selectable data. The control system may be programmed in any suitable way, such as directly by way of one or more of a touch key pad, pushbuttons, selector switches, thumbwheel switches, potentiometers or the like mounted on a control panel, and/or indirectly by way of digital signals or data highway signals. Such a control system can also provide fault and/or running information both locally and remotely.

I have found that the sifting apparatus is particularly efficient and can be used for a wide range of materials such as powdered pharmacueticals and cosmetics, powdered foods, powdered chemicals and powdered ingredients for paints. The variable speed motor 7 allows adjustment of the rotational speed of the paddles and the auger to suite any particulate material.

Maintenance or replacement of various components, for example to handle a different material or a different colour paint, can be carried out in a simple manner by removing and replacing the product bin. If it is necessary to change the sifting screen and/or the auger, these operations can readily be carried out after the product bin has been removed.

Claims

CLAI MS

1. A sifting apparatus which comprises:

>

5 means for feeding a powder material to be sifted to a sifting screen;

rotatable paddle means provided within the sifting screen for agitating the powder; 10 means for supplying ai to the sifting screen so as to fluidise the powder within the screen and to carry the powder through the screen; and

15 means for removing sifted powder from the apparatus,

wherein the means for supplying air is operable to remove from the sifting screen material that is unable to pass therethrough. 20

2. A sifting apparatus as claimed in claim 1, wherein the feeding means comprises a hopper.

3. A sifting apparatus as claimed in claim 1 or 2, 25 wherein the sifting screen is conical in shape.

4. A sifting apparatus as claimed in claim 1, 2 or 3, wherein the paddle means includes two paddles.

5. A sifting apparatus as claimed in any one of claims 1 to 4, wherein the paddle means is substantially V-shaped so as to fit within a conical sifting screen.

6. A sifting apparatus as claimed in any one of claims 1 to 5, wherein the means for supplying air comprises an auger rotatable with the paddle means and mounted within a tube, such that rotation of the auger within the tube draws air along the tube and into the sifting screen.

7. A sifting apparatus as claimed in claim 6, wherein rotation of the auger, and thus the paddle means, is reversible such that rotation of the auger in the reverse direction carries material that is unable to pass through the sifting screen along the tube and discharges such material from the apparatus.

8. A sifting apparatus as claimed in any one of claims 1 to 7 and including means for rotating the paddle means at different speeds.

9. A sifting apparatus substantially as hereinbefore described with reference to, and as shown in, the accompanying drawing.