GB2071065A

GB2071065A - Hopper feed out mechanism

Info

Publication number: GB2071065A
Application number: GB8105900A
Authority: GB
Original assignee: Conveyor & Elevator Co 1936 Lt
Current assignee: Conveyor & Elevator Co 1936 Lt
Priority date: 1980-03-08
Filing date: 1981-02-25
Publication date: 1981-09-16
Also published as: GB2071065B

Abstract

A tapered bottom hopper (10) has a parallel close-bladed or ribbon feed screw (14) of constant pitch mounted therein for feeding dry powdered or particulate materials to an orifice (13) at the base of the hopper (10). A ribbon screw (15) also of constant pitch is mounted coaxially with the feed screw (14) and is tapered so as to lie close to the tapered wall (12) of the hopper (10). The ribbon screw (15) feeds material away from the orifice (13) and to the top of the feed screw (14). By this means material compaction is avoided and a good constant feed out of material from the hopper (10) is achieved. <IMAGE>

Description

SPECIFICATION Hopper feed out mechanism This invention relates to apparatus for feeding materials, in particular dry powdered or particulate materials, from tapered bottom hoppers.

Many such materials tend to compact in the lower region of a tapered bottom hopper and do not readily flow from the orifice at the base of the hopper. It is therefore customary to provide a feed screw in the hopper to feed the material to and through such orifice. However, the use of such feed screws with certain materials, such as flour, cement, chalk, pulverised coal, gypsum, ground lime, sawdust and the like, tends to create a hole equal in diameter to the screw in the centre of the material, whilst the material surrounding the hole remains stationary within the hopper.

Various means have been proposed in an attempt to overcome this problem. It is known to mount the hopper and feed screw on resilient mountings and to provide means for vibrating the assembly. However with certain materials as mentioned above such vibration often aggravates the problem as the vibration tends to increase the compaction of the material.

It is also known to blow air into the material within the hopper in order to prevent such compaction.

Whilst such a method does alleviate the compaction problem it is difficult to obtain a steady predetermined delivery rate of material from the hopper with this method. Also there is then created the problem of separating the air from the material and recirculating or exhausting the air, which if exhausted to atmosphere must be filtered and possibly purified. In consequence the method is costly both to operate and as regards the provision of the ancilliary equipment.

It is also known to provide stirring or agitating means in the form of arms extending radially from the screw in order to alleviate the compaction problem. However such means, if they are to have any effect, require the provision of a considerable power supply, and in consequence the operating costs of such devices are prohibitive having regard to the limited success achieved by such devices in use.

It is an object of the present invention to provide means whereby such materials as aforesaid may be delivered at a predetermined measured rate from a tapered bottom hopper without the disadvantages of the prior art devices.

The invention provides apparatus for delivering dry or substantially dry powdered or particulate materials from a tapered bottom hopper comprising a first feed screw operable to feed said material in a direction axially thereof and a second feed screw surrounding said first feed screw and operable to feed said material in a direction opposed to that of said first feed screw.

Preferably said second screw is tapered in the axial direction thereof, in which case the taper preferably corresponds with the taper of the hopper to which the apparatus is to be applied whereby the periphery of the second screw in use lies parallel with and adjacent the tapering walls of the hopper.

The two screws may be coaxial and may be driven by a common drive means. In this case the screws are of opposite hand. Alternatively, the screws may be driven independently of each other. In this case they may be driven in the same rotational direction and be of opposite hand or they may be driven in opposing rotational directions and be of the same hand. The second screw may be driven at a slower speed of rotation than said first screw.

The first screw may be a parallel, close bladed or ribbon spiral and of constant pitch. The second screw comprises a ribbon spiral which may be tapered as aforesaid and may be of constant pitch or may be of varying pitch along its length. Preferably the flights of the two screws are continuous over the axial extent of said screws.

One embodiment of apparatus according to the invention will now be described with reference to the accompanying drawing, the single figure of which illustrates a tapered bottom hopper 10 having material delivering apparatus 11 mounted therein. The hopper 10 has a conically tapered bottom section 12 and an orifice 13 at the lower end thereof on the axis of the cone. Mounted within the hopper 10 and coaxial therewith is the delivering apparatus 11 comprising a first screw 14 and a second screw 15.

The first screw 14 is a parallel, close bladed spiral of contant pitch. The dimensions of the screw 14 and the speed of rotation thereof are chosen to provide the desired predetermined delivery rate of material from the hopper 10. The screw 14 is driven by means of an electric motor 16.

Mounted on the shaft 17 of screw 14 is the second screw 15, which is a ribbon spiral having a conical taper corresponding with the taper of the bottom section 12 of the hopper 10. The ribbon screw flight 15 is attached to shaft 17 by arms 18 so that the two screws are driven in rotation collectively by the drive motor 16, the screw flight 15 being closely adjacent the walls of the tapered bottom section 12 of the hopper 10. The hands of the screws 14 and 15 are opposed since their directions of rotation are the same. In the embodiment shown the screw 15 is of constant pitch and hence increasing helix angle towards orifice 13.

In use the device operates as follows. The material is put into the hopper and the motor 16 is then started. Screw 14 begins to feed the material disposed within its flight towards the orifice 13, thus tending to create a void in the centre of the material.

However screw 15 begins to feed the material adjacent the walls of the bottom section 12 of hopper 10 upwardly away from orifice 13. Due to the weight of material above, movement of material upwardly from the lower regions is resisted, and in consequence such material moves somewhat laterally to fill the void being created by the screw 14. In this way the screw 14 is continuously supplied with material which it feeds towards orifice 13. The dimensions of the screw 15, in particular the width thereof, are chosen, having regard to the rotational speed at which it is to be driven, to provide that material is fed to screw 14 by screw 15 at least at the rate of feed of material by screw 14 at that rotational speed.

By means of the apparatus of the present invention, a constant predetermined rate of feed of material from the hopper is provided.

The screw 15 is supported from shaft 17 by the minimum practical number of arms 18 so as to keep the power requirements for rotation of screw 15 to a minimum.

In the case that screw 15 is driven independently of screw 14, the former may be driven at a slower rate of rotation that the latter in order to reduce the power requirements further, since the large diameter of the former relative to the latter in most cases will provide a sufficient supply of material from the outer to the inner screw under such circumstances.

The motor 16 is preferably a variable speed motor whereby the apparatus is suitable for use in the delivery of different materials, having different fluidity characteristics, from the hopper 10.

In the embodiment shown the screws 14, 15 are continuous over their complete axial extent and are of equal axial extent. However, part screws could be provided although in the case of screw 15 if an interrupted screw were to be provided this would create a need for more arms 18 and thus increase the non-productive power requirements of the device.

Also screw 15 is shown as being of constant pitch but is could be of varying pitch along its length whilst preferably being of increasing helix angle towards the orifice 13.

Also the tapered bottom section 12 of hopper 10 is shown as being conical whereas other configurations of tapered bottom section may be provided. In any such case the taper of screw 15 preferably corresponds with the taper of the hopper.

The orifice 13 of the hopper 10 is provided with a bush 19 which is of an internal diameter such that it is contacted by the periphery of the flights of screw 14. In this way the shaft 17 is supported at its lower end. The bush 19 may be of a graphite impregnated plastics material in order to reduce friction and wear of the screw 14. The bush 19 may be readily replaceable when it becomes worn.

Alternatively, and in particular for use with cohe sive materials, the feed screw 14 may be a parallel ribbon screw so as to prevent 'filleting' at the root of the flight by such cohesive material from reducing the capacity of the screw.

The helix angles of the screws are chosen to suit the material being handled, being generally shallow er for dry powder materials than for cohesive materials so as to provide for constant delivery of the material through the orifice.

Claims

1. Apparatus for delivering dry or substantially dry powdered or particulate materials from a ta pered bottom hopper, comprising a first feed screw operable to feed said material in a direction axially thereof and a second feed screw surrounding said first feed screw and operable to feed said material in a direction opposed to that of said first feed screw.

2. Apparatus according to claim 1 wherein said second screw is tapered in the axial direction thereof.

3. Apparatus according to claim 2 wherein said second screw is of increasing helix angle in direction from the larger towards the small end thereof.

4. Apparatus according to claim 3 wherein said second screw is of constant pitch.

5. Apparatus according to any one of claims 1 to 4 wherein said second screw is a ribbon screw.

6. Apparatus according to claim 5 wherein said screws are disposed coaxially.

7. Apparatus according to any one of claims 1 to 6 wherein said first screw is a parallel close-bladed or ribbon spiral.

8. Apparatus according to any one of claims 1 to 7 wherein said first screw is of constant pitch.

9. Apparatus according to any one of claims 1 to 8 wherein each screw has a flight which is continuous over its axial extent.

10. Atapered bottom hopper having an orifice at the base thereof and having mounted therein means for delivering dry or substantially dry powdered or particulate materials from said hopper, said delivery means comprising a first feed screw operable to feed said material towards said orifice and a second feed screw surrounding said first feed screw and operable to feed said material in a direction away from said orifice.

11. A hopper according to claim 10 wherein said screws are mounted in a tapering walled section thereof and said second screw has a taper in the axial direction thereof corresponding with the taper of said tapering walls whereby the periphery of said second screw lies parallel with and adjacent said tapering walls.

12. A hopper according to claim 11 wherein said screws are mounted coaxially and said second screw is a ribbon screw.

13. A hopper according to claim 12 wherein said second screw is of constant pitch.

14. A hopper according to claims 12 or claim 13 wherein said first screw is a parallel close-bladed or ribbon spiral of constant pitch.

15. A hopper according to any one of claims 12 to 14 wherein said screws are of opposite hand and means are provided for driving said screws in the same rotational direction.

16. A hopper according to any one of claims 12 to 14 wherein said screws are of the same hand and means are provided for driving said screws in opposed rotational directions.

17. A hopper according to claim 15 or claim 16 wherein said driving means are adapted to drive said second screw at a slower speed than said first screw.

18. A hopper according to any one of claims 15 to 17 wherein said driving means comprises a common motor drivingly engaged with both screws.

19. A hopper according to any one of claims 10 to 18 wherein said orifice has a bush located therein and adapted to support said first screw rotatably within an internal bore of said bush.

20. A hopper according to claim 19 wherein said bush is of a graphite impregnated plastics material.

21. A tapered bottom hopper for delivering dry or substantially dry powdered or particulate material therefrom substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.