GB2133393A - Apparatus for storing and dispensing powdered material - Google Patents

Abstract

A container 1 holding bulk cement 7 has a screw conveyor 8 which extends downwards into the container 1 within a surrounding tube 12, which is in turn surrounded by an air-permeable fabric sleeve 27. Compressed air is supplied through a pipe 33 to the space within the sleeve 27 and the air flowing through the sleeve fluidises the cement surrounding the sleeve. The whole of the screw conveyor assembly is pivotally mounted on trunnions 15 and can be swung by a driving mechanism 20-25 from one side of the container 1 to the other. By fluidising the cement surrounding the conveyor and causing the conveyor to sweep through the container in this way, the whole contents of the container can be drawn in through the open bottom end 13 of the tube 12 and be discharged through a flexible pipe 9. By providing the movable conveyor, the container 1 can be made of a much larger capacity than a hopper with sloping sides which occupies the same area in plan. <IMAGE>

Description

SPECIFICATION Apparatus for storing and dispensing powdered material In apparatus, such as concrete weigh batching plant, in which powdered material such as bulk cement has to be stored and then dispensed, it is generally necessary to store the powdered material in a bottom-opening hopper. Because fine powdered material such as cement has a steep angle of repose, it is necessary for the hopper to have sides which slope steeply down to its bottom outlet opening. If, as is the case in concrete weigh batching plant, the powdered material must be delivered at a level above the bottom of the hopper, it is common to provide a screw conveyor in a surrounding tube. The tube is fixed in position and has an inlet opening at its bottom which is situated within the bottom of the hopper.

Owing to the necessity for providing the hopper with steeply sloping sides to ensure that the whole contents of powdered material in the hopper flows under gravity to the bottom of the hopper, the space utilisation of the hopper is very low. That is to say the overall capacity of the hopper is much less than the plan area occupied by the hopper multiplied by the overall height of the hopper. It is generally not practicable to fit other parts of a weigh batching plant in particular into the spaces surrounding the sloping sides of the hopper and in consequence a great deal of space is commonly wasted.

With mobile apparatus, and in particular with mobile concrete weigh batching plant, it is important that the apparatus as a whole should be constructed as compactly as possible and it is most desirable therefore to be able to use a storage container which makes better use of the available space than does a hopper with steeply sloping sides.

With this aim in view, according to this invention, apparatus for storing and dispensing fine powdered material, for example bulk cement, comprises a container for the material, a screw conveyor which extends downwards into the container within a surrounding tube which has an inlet opening at its bottom and a discharge opening at or near its top, an air-permeable sleeve, which surrounds and is radially spaced from the tube, means for supplying air under pressure to the space between the tube and the sleeve so that in use the air flows through the sleeve and fluidises the powdered material surrounding the sleeve, and means for moving the conveyor with its surrounding tube and sleeve transversely to the axis of the conveyor to cause the inlet to move over the bottom of the container and enable the conveyor to move material from any position along a path adjacent the bottom of the container.

The provision of the air-permeable sleeve surrounding the tube which, when air flows through it, fluidises the powdered material, firstly causes the fluidised material to flow downwards to the inlet opening at the bottom of the tube and secondly, and this is most important, owing to the fluidisation of the powdered material around the sleeve, enables the assembly consisting of the conveyor, the tube and the sleeve to make its transverse movement from one part of the container to another. Without the fluidisation of the powdered material around the sleeve, the powdered material would of course pack tightly around the tube surrounding the conveyor and this would make transverse movement of the conveyor from one part of the container to another impossible.

If it is necessary to obtain the maximum storage capacity from a particular plan area and height available for the container, the container may be provided with a flat bottom and vertical sides and it may, for example, be in the form of a rectangular prism.

In this case the conveyor is preferably mounted vertically and if the width of the container is not more than twice the diameter of the sleeve which surrounds the conveyor, the conveyor together with its surrounding tube and sleeve may be mounted so that it can move transversely along a straight line path parallel to the longitudinal centre line of the container. If, however, the container is of substantially greater width than the diameter of the air-permeable sleeve, for example if the container is substantially square in plan, it is necessary for the conveyor assembly to be mounted so that it is movable in two directions transverse to each other, that is to say that it can move both along and across the container. In this way the bottom of the tube can be made to traverse the whole of the area of the flat bottom of the container.

Where it is not necessary to obtain the maximum possible volume of the container within a given plan area and height, it is much simpier, and accordingly preferable, to provide the container with a bottom which is part-circular as seen in vertical section and the conveyor with its surrounding tube and sleeve are then mounted pivotally to enable the bottom of the tube to be swung along a path close to and following the bottom of the container.

With the conveyor and its surrounding tube and sleeve mounted pivotally in this way, the driving mechanism for moving the conveyor may be made much simpler and therefore less expensive than if the conveyor has to be moved along a straight line path and particularly if the conveyor has to be movable in two directions transverse to each other.

Where this is convenient, the container may be cylindrical with its axis upright and in this case the container is preferably provided with a partspherical bottom. The conveyor with its surrounding tube and sleeve are then preferably universally pivotally mounted so that the bottom opening can be moved to any position over the part-spherical bottom of the container by a tilting movement of the conveyor.

The air-permeable sleeve, which is preferably of circular cross-section with its wall at a constant distance from the wall of the tube, which is also of circular section, may be made of fine metal mesh or finely perforated metal. Where, however, the container is intended to hold finely powdered material, such as bulk cement, it is important for the opening through the sleeve to be so fine that the powdered material does not pass through them into the space between the sleeve and the tube when compressed air is not being supplied to the inside of the sleeve. For this purpose, the sleeve is preferably of a textile fabric and a heavy cotton material has been found to be very satisfactory. When the sleeve is made of textile fabric or other flexible material, it is preferably supported from the tube by a series of axially spaced perforated rings which surround and are fixed to the tube.The perforated rings allow the compressed air, which is preferably supplied to the top of the space between the sleeve and the tube, to flow downwards and then outwards through the sleeve along the whole length of the sleeve. The bottom of the space between the tube and the sleeve is preferably closed and this enabies the powdered material at the bottom of the tube to settle into a solid mass which is picked up by the screw conveyor. In some cases, though, where the powdered material tends to be cohesive, the bottom of the space may be bounded by a wall which is also air-permeable. In this case the air flowing through the bottom wall stirs up the powdered material at the bottom of the tube and may assist in its entrainment by the end of the screw conveyor.

The inlet opening at the bottom of the tube may be in the side wall of the tube, but preferably the lower end of the tube is open to form the inlet opening and the screw conveyor projects beyond the lower end of the tube.

An example of an apparatus in accordance with the invention is illustrated diagrammatically in the accompanying drawings in which: Figure 1 is a vertical section through the apparatus passing through the axis of rotation of the screw conveyor; Figure 2 is a sectional plan on the line Il-Il in Figure 1; and, Figure 3 is another sectional plan on the line Ill-Ill in Figure 1.

The apparatus shown in the drawings is intended for storing and dispensing cement in a concrete weigh-batching plant. The apparatus comprises a tank-like container 1, which is fabricated out of steel plate and is rectangular as seen in plan. The container has an arcuate bottom 2 and is supported by an annular concrete footing 3 in the ground 4. The container is supported from the footing 3 by a skirt 5 with a bottom flange 6 which is seated on the footing. The container is filled with bulk cement 7.

A screw conveyor 8 extends downwards into the container 1 and dispenses the bulk cement through a flexible pipe 9.

The screw conveyor has a central driving shaft 10 on which a conveyor screw 11 is fixed and the conveyor screw 11 is surrounded by a cylindrical steel tube 12 which has an open bottom end 13 through which the lower end of the shaft 10 and the conveyor screw 11 projects. The open bottom end 13 of the tube 12 forms an inlet of the screw conveyor and an outlet 1 4 of the conveyor leads from near the upper end of the tube 12 to the flexible pipe 9.

The screw conveyor 8 is pivotally mounted on trunnions, one of which is shown at 1 5 and which are in turn supported by brackets at the two sides of the container 1, one of the brackets being shown at 16. The common axis of the trunnions 1 5 passes through the centre of curvature of the bottom 2 so that the screw conveyor 8 can swung backwards and forwards from left to right and right to left with the lower ends of the shaft 10 and the conveyor screw 11 moving along a pati close to the bottom 2.

The conveyor shaft 10 is driven by an electric motor 17 through a reduction gear box 1 8 which is supported from the upper end of the tube 12 by supports 19. The swinging movement of the screw conveyor 8 is brought about by a reversible electric motor 20 which drives a shaft 21 through a reduction gear box 22. The reduction gear box 22 together with the motor 20 and the shaft 21 are supported from a cover plate 23 of the container 1 by a pedestal 24. The shaft 21 has a worm 25 at its right-hand end and the worm meshes with a pinion 26 which is fixed to the trunnion 1 5. The direction of rotation of the motor 20 is automatically reversed at each end of the swing of the screw conveyor 8 as the screw conveyor approaches the side walls of the container 1.

The tube 1 2 is surrounded by an air-permeable heavy cotton fabric sleeve 27, which is supported, and held spaced, from the tube 12 by an annular top plate 28, an annular bottom plate 29 and a series of annular intermediate plates 30 which are provided with perforations 31. An annular space 32 is thus formed between the tube 12 and the sleeve 27. A pipe 33 extends through the top plate 28 for the supply of compressed air to the space 32. Compressed air, which, in use, is supplied through the pipe 33 flows downwards through the space 32 and then outwards through the airpermeable fabric sleeve 27 as indicated by the series of small arrows. The air flowing outwards through the sleeve 27 fluidises the cement 7 surrounding the sleeve 27 and most of this fluidising air then leaves the container 1 through a filter 34 provided in the cover plate 23. The filter 34 can, incidentally, be removed to provide an opening for filling the container 1 with bulk cement.

The width of the container in a direction perpendicular to the plane of the paper in Figure 1 is substantially twice the diameter of the sleeve 27 and accordingly the cement surrounding the sleeve 27 is fluidised across the full width of the container 1 in this direction.

In operation, with compressed air supplied through the pipe 33 as already described, the screw conveyor is set in operation and cement is conveyed by the bottom end of the conveyor screw 11 through the open bottom end 1 3 of the tube 12 and thence up the tube 12 and hence through the outlet 1 4 to the flexible pipe 9.

As the cement is conveyed away from the bottom of the container 1, further cement will, owing to its fluidisation, fall down into the bottom of the container and be conveyed away, but to ensure that the whole cement contents of the container 1 can be removed, the screw conveyor 8 is gradually swung in one direction or the other by means of the motor 20 acting through the reduction gear box 22, the shaft 21 and the worm and pinion 25,26. In general, discharge of the cement does not start with the conveyor 8 in the upright position shown, but with the conveyor swung either towards the right or to the left to its fullest extent with the bottom of the sleeve 27 adjacent one of the two side walls of the container 1. The conveyor 8 is then gradually swung from the side of the container 1 at which it starts to the opposite side of the container.When it reaches the opposite side of the container, substantially the whole of its cement contents has been removed.

The container 1 is then refilled with bulk cement and as the cement is required, the operation just described is repeated with the conveyor 8 being swung in an opposite direction.

The swinging movement of the conveyor 8, which is of course very slow, is permitted whilst keeping the container 1 closed except for the filter 34, by means of a corrugated rubber diaphragm 35 which has its outer periphery fixed to the edge of an opening through the cover plate 23 of the container 1 and its inner periphery fixed to the outer edge of the annular top plate 28 which bounds the top of the space 32 between the tube 12 and the sleeve 27.

In this example, the annular bottom plate 29 which bounds the bottom of the space 32 is imperforate so that the cement immediately below is not fluidised, but is packed quite tightly where it is picked up by the bottom end of the conveyor screw 11. If the container 1 is intended to hold powdered material which tends to pack together so tightly that the conveyor screw 11 cannot easily dig into it, the bottom plate 29 may be perforated. In this case its perforations are much smaller than the holes 31 in the plates 30 so that the powdered material does not tend to enter the space 32 when there is no compressed air supplied to the space. The air issuing from the perforations in the plate 29 fluidises the material at the bottom of the conveyor screw 11 to some extent and thus facilitates the picking up of the powdered material by the screw conveyor. In any case, since the filter 34 necessarily maintains some pressure in the air which has flowed through the sleeve 27 into the container, some of the air tends to pass upwards through the tube 12 and thus aerates the powdered material being moved by the screw conveyor to some extent and facilitates its flow through the outlet 14 and the flexible pipe 9.

Claims (9)

1. Apparatus for storing and dispensing fine powdered material, the apparatus comprising a container for the material, a screw conveyor which extends downwards into the container within a surrounding tube which has an inlet at its bottom and a discharge opening at or near its top, an airpermeable sleeve, which surrounds and is radially spaced from the tube, means for supplying air under pressure to the space between the tube and the sleeve so that, in use, the air flows through the sleeve and fluidises the powdered material surrounding the sleeve, and means for moving the conveyor within the surrounding tube and sleeve transversely to the axis of the conveyor to cause the inlet to move over the bottom of the container and enable the conveyor to move material from any position along a path adjacent the bottom of the container.

2. Apparatus according to Claim 1, in which the container has a bottom which is part-circular as seen in vertical section and the conveyor with its surrounding tube and sleeve are mounted pivotally to enable the bottom of the tube to be swung along a path close to the bottom of the container.

3. Apparatus according to Claim 2, in which the container is circular as seen in plan with a partspherical bottom and the conveyor with its surrounding tube and sleeve are universally pivotally mounted so that the bottom inlet can be moved to any position over the part-spherical bottom of the container by a tilting movement of the conveyor.

4. Apparatus according to Claim 1, in which the container has a flat bottom and upright sides and the conveyor is mounted with its axis upright.

5. Apparatus according to Claim 4, in which the container has a width of not more than twice the diameter of the sleeve and the conveyor with its surrounding tube sleeve is mounted so that it is movable transversely along a straight line path extending along the length of the container.

6. Apparatus according to Claim 4, in which the container is of substantially greater width than the diameter of the sleeve and the conveyor with its surrounding tube and sleeve is movable in two directions transverse to each other along and across the container.

7. Apparatus according to any one of the preceding Claims, in which the sleeve is of textile fabric and is supported from the tube by a series of perforated rings which surround, and are fixed to, the tube.

8. Apparatus according to any one of the preceding Claims, in which the lower end of the tube is open to form the inlet opening and the screw conveyor projects beyond the lower end of the tube.

9. Apparatus according to any one of the preceding Claims, in which the bottom of the space between the tube and the sleeve is closed.

1 0. Apparatus according to Claim 1, substantially as described with reference to the accompanying drawings.