WO1997047447A1

WO1997047447A1 - Mixing apparatus

Info

Publication number: WO1997047447A1
Application number: PCT/GB1997/001588
Authority: WO
Inventors: Anthony Samuel Morgan George; William Thomas Williams
Original assignee: Maxene Limited
Priority date: 1996-06-13
Filing date: 1997-06-12
Publication date: 1997-12-18
Also published as: GB9612426D0; AU3099197A

Abstract

Mixing apparatus is provided which has particular application for mixing sand and cement to produce an aerated cement. The apparatus includes a mixing vessel (10) which has an inlet (14) for solids at one end and an outlet (16) for mixed products at the other end. Liquids for mixing into the solids are introduced intermediate the ends of the vessel, and the liquid, mainly water, is introduced with foaming agent after foaming has taken place. Within the vessel there are rotatable mixing means (18) which include an outer mixing element (18B) and an inner mixing element (26) rotatable at different speeds. The outer element is a spiral plate (22) extending from one end of the vessel to the other, the inner element (26) extends between the liquid inlet and the outlet. The apparatus also includes a conveyor system (52) for introducing metered amounts of the solid components into the inlet end.

Description

MIXING APPARATUS

This invention relates to mixing apparatus and particularly to such apparatus for mixing sand and cement and other products to produce an aerated cement or concrete products.

Various proposals have been made for suitable mixing apparatus which produces a fully aerated product and an object of the present invention is to provide an improved apparatus.

According to one aspect of the invention there is provided mixing apparatus which comprises a mixing vessel, a solids inlet for introducing solids, such as sand and cement, into the vessel and located towards one end of the vessel, an outlet for mixed products located towards the other end of the vessel, a liquids inlet for introducing liquid, including water, into the vessel and located intermediate the solids inlet and the outlet, rotatable mixing means rotatable within the vessel, a source of compressed air, and drive means for the rotatable mixing means, the vessel having a generally cylindrical internal shape, the mixing means comprising an outer rotatable mixing element and an inner rotatable mixing element, the mixing elements being rotatable at different speeds from one another about the axis of the vessel, the outer mixing element being a spiral plate extending between said solids inlet and said outlet and said inner mixing element extending at least between the liquid inlet and said outlet, the solids and liquid being mixed together with air to form an aerated mixture discharged from said outlet.

Preferably the outer mixing element takes the form of a spiral plate which may be in two portions of which a conveying portion extends between said solids inlet and said liquid inlet and a mixing portion extends between the liquid inlet and the outlet. The mixing portion may include a spiral plate having an outer edge adjacent to the wall of the vessel and an inner edge spaced radially outwards from the axis of the vessel.

The inner mixing element may be spaced radially inwardly of the outer mixing element and may take the form of a spirally extending rod. The outer mixing element may rotate at a slower speed than the inner mixing element, for example in the ratio of 1 : 1.5.

Preferably air from the compressed air source is mixed with a foaming agent to cause aeration of the mixture. Conveniently the mixing of air and foaming agent takes place outside the vessel and the mixture is introduced with the liquid in the form of water.

There may be provided common drive means driving an output shaft to the outer mixing element and an output shaft to the inner mixing element, the shafts rotating at different speeds. Drive to the outer mixing element may be through axially extending bars connected to the outer part of a spiral plate. Between the solids inlet and the liquid inlet the outer element may be attached to a shaft co-axial with the vessel.

The inner mixing element is preferably mounted on a shaft co-axial with the vessel and extending through the shaft for the outer mixing element.

The vessel may have its axis inclined to the horizontal, the outlet being at a higher level than the inlet.

According to another aspect of the invention there is provided mixing apparatus comprising a mixing vessel, a solids inlet for introducing solid products into the vessel and located towards one end of the vessel, an outlet for mixed products located towards the end of the vessel remote from the solids inlet, a liquid inlet for introducing liquid into the vessel and located intermediate the solids inlet and the outlet, rotatable mixing means rotatable within the vessel, drive means for the mixing means, feed means for feeding solids to the solids inlet including a conveyor belt having cross members upstanding from the conveying run of the conveyor belt on which solids are conveyed to the solids inlet.

Preferably there is provided feed means for different products, such as sand and cement, which are spaced from each other in the axial direction of the vessel feeding into a common solids inlet. The conveyor belt has an inlet end at which product is fed onto the conveyor belt, preferably from a hopper, and an outlet end located at a higher level than the inlet end.

The foaming unit may include a chamber containing metal fibres to create foam which is then introduced through the liquid inlet into the vessel.

Further features of the invention will appear from the following description of an embodiment of the invention given by way of example only and with reference to the drawings, in which:

Fig 1 is a side elevation of mixing apparatus with part of the mixing vessel broken away to show the interior,

Fig 2 is a plan view of a conveyor system for feeding solid materials to the mixing apparatus, and

Fig 3 is a side elevation of the arrangement of Fig 2.

Referring to the drawings and firstly to Fig 1 there is shown a mixing apparatus comprising a cylindrical mixing vessel 10 having its central longitudinal axis inclined to the horizontal, in this case at about 13 degrees to the horizontal, so that one end 11, the inlet end, is lower than the other end 12, the outlet end.

Towards the inlet end 11 is located a hopper 14 for the introduction of solid material, in particular sand and cement, into the vessel 11 through an inlet in the base of the hopper 14.

Towards the opposite end of the vessel 10 is located an outlet 16 for mixed material and intermediate the inlet end 11 and outlet end 12 is an inlet 17 for introducing liquid for mixing with the solid material.

Within the vessel 10 is located mixing means including a mixing element 18, termed the outer mixing element, and a mixing element 19, termed the inner mixing element. The outer mixing element 18 is in two portions, 18 A and 18B, the portion 18A extending between the inlet from the hopper 14 and the liquid inlet 17, and the portion 18B extending between the liquid inlet 17 and the outlet 16.

The mixing element portion 18A comprises a hollow shaft 20 mounted in bearings (not shown) at the inlet end 11 of the vessel 10, and around the shaft 20 is located a spiral plate 22 which extends between near the inner surface of the vessel 10 and the shaft 20, there being a small clearance of, say, 5 mm between the outer edge of the spiral plate 22 and the inner wall of the cylinder 10. The spiral plate 22 extends beyond the liquids inlet 17 towards the outlet 16 but is diminished in its radial direction in this region so that it extends from the inner surface of the vessel 10 a limited extent to accommodate the inner mixing element 19.

Longitudinally extending bars 23 are located around the axis of the vessel, there being three bars 23 displaced 120 degrees to one another about said axis. The bars 23 are located adjacent to the inner wall of the vessel 10 and are secured to the spiral plates 22 as they intersect the plates, thereby serving to support the plates particularly over the region between the inlet 17 and the outlet 16 where the plates 22 are not supported on an inner shaft as at 20.

The inner mixing element 19 includes a shaft 25 extending along the axis of the vessel 10 and, located about the shaft 25, is arranged a spirally extending bar 26 spaced from and supported on the shaft 25 by radially extending connectors 27. The shaft 25 is of smaller radius than the shaft 20 and extends through the shaft 20 from one end of the vessel 10 to the other, there being bearing means (not shown) between the shafts 25 and 20 and at the end of the shaft 25 adjacent the outlet 16.

A drive motor 29 is common to the mixing elements 18 and 19 and has an output shaft 30 carrying a pair of drive wheels 31 and 32 of different sizes. Drive is transmitted from the drive wheels 31 and 32 by drive belts or chains 33 and 34 respectively to drive wheels 35 and 36, also of different sizes. Hence the motor imparts drive to the drive wheels 35 and 36 at different speeds. Such drive is transmitted from the drive wheel 36 to the shaft 25 of the inner mixing element 19 and from the drive wheel 35 to the outer mixing element 18 through shaft 37. The shaft 37 is connected to the outer mixing element through a drive arrangement (not shown) whereby drive is imparted to the longitudinal bars 23. The bars 23 impart rotation to the spiral plate 22 and to the shaft 20.

There is also shown in Fig 1 an arrangement whereby liquid is introduced into the vessel 10 through the inlet 17 in the form of a water and foaming agent mixture giving rise to foam which is introduced into the vessel 10 for mixture with the solid materials introduced from the hopper 14.

The liquid feed arrangement includes a source of water 40, a water pump 41, a source of foaming agent 42, and a source of compressed air 43. The water pump 41 conveys water from the water source 40 to a dosing pump 44 and foaming agent from the foaming agent source 42 is also conveyed to the dosing pump 44. The dosing pump mixes the water and foaming agent in the desired proportions and conveys the mixture towards a valve 45 from which the mixture is directed towards a chamber 47.

Compressed air from the source of compressed air 43, usually a compressor, is directed to a valve 48 controlling the supply of compressed air to the chamber 47. The chamber 47 is a generally cylindrical chamber having within the chamber wire wool 46 or other metal filament or fibre so that, as the water and foaming agent mixture enters the chamber with the compressed air, the mixture is caused to foam producing a large quantity of small bubbles of air constituting foam which is directed to the inlet 17 and into the vessel 10.

It will be seen that water from the source of water 40 may also be directed by a pump 49 to wet the solids material in the hopper 14.

Upon the introduction of the liquid through the inlet 17 the liquid in the form of foam is mixed with the solid materials from the hopper 14 by the action of the mixing elements 18 and 19 over the region of the vessel 10 between the inlet 17 and the outlet 16. Due to the action of the mixing elements the liquid foam and solid materials are thoroughly mixed and the foam is thoroughly and evenly distributed so that a homogeneous mixture is discharged through the outlet 16. There may be provided at the liquid inlet 17 an atomising gun (not shown) whereby the foam is distributed amongst the solids.

Other materials can be added to the liquid or foam according to requirements such as dyes, stabilisers and accelerators. The foaming agent may be of any convenient kind but preferably is a foaming agent containing protein which has been found to provide stable foam. Means may be provided (not shown) for ensuring an adequate supply of water, foaming agent and compressed air.

Referring now particularly to Figs 2 and 3 there is shown the feed arrangement for the solids. In this case there are two components of solid materials each with its own feed arrangement, a feed 50 for cement and a feed 51 for sand. Due to the different relative quantities of cement and sand the capacity of the cement feed arrangement 50 can be lower than the capacity of the sand feed arrangement 51.

In each case the feed arrangement comprises an endless conveyor belt 52, 53 and each conveyor belt has cross members 54 which are upstanding from the conveying runs 52A and 53A of the respective belts and are spaced apart from one another along the belts. The cross members 54 extend outwardly of the associated belt by a pre-determined amount selected according to the desired rate of feed and speed of the belt. The sand or cement occupies the space between successive members 54 up to the height of the members 54.

Each belt passes around rollers 56,57 at the output and input ends of the conveyors respectively. A drive motor 58 drives the rollers 56 from a common drive arrangement 57 so that the conveyors may be driven at the same speed.

At the inlet ends of the feed arrangements there are provided feed hoppers 60 and 61 to contain cement and sand respectively. The hoppers are open at their lower ends to release cement and sand onto the conveyor belts 52 and 53 between the cross members 54 but the sides of the hoppers are closed to prevent the contents spilling. At the upstream sides of the hoppers there is provided an opening the height of the upstanding members 54 so that excess sand and cement is not discharged. This results in the belts carrying a pre-determined quantity of cement or sand determined by the width of the belts and the heights of the members 54. Thus the quantities of cement and sand delivered by the conveyors is pre¬ determined according to the speeds of the conveyors. If desired it will be possible to increase the speeds of the conveyors or to replace the cross members 54 to give a deeper bed of material on the conveyors and thereby increase the rate of feed.

The conveyors 50, 51 deliver their respective products into the hopper 14 for discharge into the vessel 10 and it will be appreciated that the respective quantities of cement and sand are controlled to give the desired mixture. Similarly the quantity of water and foaming agents discharged at the inlet 17 is matched to the amount of sand and cement discharged into the vessel 10.

The apparatus is controlled by control means by which the mixing action and the proportions of the various components in the mix are controlled. In some cases a greater quantity of foam is required and in some cases the sand and cement proportions will be different. To determine the quantity of mixture being made the revolutions of the mixing elements may be counted and the drive motor speed monitored.

After the mixture has been discharged from the vessel it may be conveyed under gravity or by a suitable pump to the point at which it is to be used. A peristaltic pump may be used.

By way of example it has been found that satisfactory results have been achieved when the outer mixing element 18 and the inner mixing element 19 have speeds in the ratio of 1 : 1.5. Moreover the speed of the outer mixing element may be around 100 r.p.m.

Over the conveying portion of the outer mixing element 18, i.e. between the solids inlet and the liquid inlet 17 the pitch of the spiral plate 22 may be about 125 mm and over the region between the inlet 17 and the outlet 16 the pitch may be 90 mm.

For the inner mixing element 19 it has been found that a radial clearance of some 5 mm may be provided between the rod 26 and the inner diameter of the plate 22. The rods 26 may have a diameter of 16 mm and the length of the vessel 10 may be some 1,400 mm.

There may also be means for measuring the water content of the sand delivered to the apparatus whereby the amount of added water may be monitored. It may be possible to adjust the angle at which the axis of the vessel 10 is arranged to the horizontal. For example with lower densities of solid material the angle may be increased.

Although the apparatus has been described in relation to the mixing of sand, cement and foaming agent it could also be used for other liquids, solids and mixtures.

Claims

1. Mixing apparatus comprising a mixing vessel, a solids inlet for introducing solids, such as sand and cement, into the vessel and located towards one end of the vessel, an outlet for mixed products located towards the other end of the vessel, a liquids inlet for introducing liquid, including water, into the vessel and located intermediate the solids inlet and the outlet, rotatable mixing means rotatable within the vessel, a source of compressed air, and drive means for the rotatable mixing means, the vessel having a generally cylindrical internal shape, the mixing means comprising an outer rotatable mixing element and an inner rotatable mixing element, the mixing elements being rotatable at different speeds from one another about the axis of the vessel, the outer mixing element being a spiral plate extending between said solids inlet and said outlet and said inner mixing element extending at least between the liquid inlet and said outlet, the solids and liquid being mixed together with air to form an aerated mixture discharged from said outlet.

2. Mixing apparatus according to Claim 1 wherein the outer mixing element takes the form of a spiral plate which may be in two portions of which a conveying portion extends between said solids inlet and said liquid inlet and a mixing portion extends between the liquid inlet and the outlet.

3. Mixing apparatus according to Claim 2 wherein the mixing portion includes a spiral plate having an outer edge adjacent to the wall of the vessel and an inner edge spaced radially outwards from the axis of the vessel.

4. Mixing apparatus according to any one of Claims 1-3 wherein the inner mixing element is spaced radially inwardly of the outer mixing element.

5. Mixing apparatus according to Claim 4 wherein the mixing element takes the form of a spirally extending rod.

6. Mixing apparatus according to any of the preceding claims wherein the outer mixing element rotates at a slower speed than the inner mixing element.

7. Mixing apparatus according to Claim 6 wherein the speeds of the outer and inner mixing elements are different and in the ratio of 1 : 1.5.

8. Mixing apparatus according to any one of the preceding claims wherein air from the compressed air source is mixed with foaming agent to cause aeration of the mixture.

9. Mixing apparatus according to Claim 8 wherein the mixing of air and foaming agent takes place outside the vessel and the mixture of air, foaming agent and water is introduced at said liquids inlet.

10. Mixing apparatus according to any one of the preceding claims comprising common drive means driving an output shaft to the outer mixing element and an output shaft to the inner mixing element, the shafts rotating at different speeds.

11. Mixing apparatus according to Claim 9 or 10 wherein compressed air, water and foaming agent are introduced into a chamber containing fibres to create foam prior to introduction to the vessel through the liquids inlet.

12. Mixing apparatus according to any one of the preceding claims wherein drive to the outer mixing element is through axially extending bars connected to the outer part of a spiral plate.

13. Mixing apparatus according to any one of the preceding claims wherein the outer element is attached to a shaft coaxial with the vessel between the solids inlet and the liquid outlet.

14. Mixing apparatus according to any one of the preceding claims wherein the inner mixing element is mounted on a shaft coaxial with the vessel and extending through a shaft for the outer mixing element.

15. Mixing apparatus according to any one of the preceding claims wherein the vessel has its axis inclined to the horizontal, the outlet being at a higher level than the inlet.

16. Mixing apparatus according to any of the preceding claims comprising feed means for feeding solids to the solids inlet including a conveyor belt having cross members upstanding from the conveying run of the conveyor belt on which solids are conveyed to the solids inlet.

17. Mixing apparatus comprising a mixing vessel, a solids inlet for introducing solid products into the vessel and located towards one end of the vessel, an outlet for mixed products located towards the end of the vessel remote from the solids inlet, a liquid inlet for introducing liquid into the vessel and located intermediate the solids inlet and the outlet, rotatable mixing means rotatable within the vessel, drive means for the mixing means, feed means for feeding solids to the solids inlet including a conveyor belt having cross members upstanding from the conveying run of the conveyor belt on which solids are conveyed to the solids inlet.

18. Mixing apparatus according to Claim 17 comprising feed means for different products, such as sand and cement, which are spaced from each other in the axial direction of the vessel and feed into a common solids inlet.

19. Mixing apparatus according to Claim 17 or 18 wherein the conveyor belt has an inlet end at which product is fed onto the conveyor belt and an outlet end located at a higher level than the inlet end.