GB2056294A

GB2056294A - Producing foamed material

Info

Publication number: GB2056294A
Application number: GB7936844A
Authority: GB
Original assignee: ZYKLOS MASCHINENBAU GmbH
Current assignee: ZYKLOS MASCHINENBAU GmbH
Priority date: 1978-10-26
Filing date: 1979-10-24
Publication date: 1981-03-18
Also published as: GB2056294B; DE2846605A1; FR2439615A1

Abstract

In a method of producing a foamed material, such as foamed concrete, the material to be foamed is located in a mixing trough 2 and is mixed by means of rotatable vanes 15, the vanes being so arranged as to cause the material to swirl around each vane thereby causing a cone or vortex to be formed in the material in the central region between the vanes, the foam producing material then being injected into the core of the cone or vortex. The trough 2 may be freely rotatable and the axis of rotation of the vanes is offset from the axis of the trough. <IMAGE>

Description

SPECIFICATION Method and apparatus for producing foamfilled material The present invention relates to an apparatus and to a method of producing foam-filled material, more especially foamed concrete, in which the foam produced by a foam generator is added to the material contained in a mixer.

It is known to use an auxiliary tool rotating at a relatively high speed in concrete in a concrete mixer which has, located around its shaft, a tube which is connected to a positive or negative pressure source. By so doing, it is possible to introduce gas or air into the mixed material for cooling or drying purposes or to alter the chemical structure thereof. For the introduction of foam, however, this method cannot be used because the high speeds of the tools, coupled with the properties of the material being processed such as mortar or concrete, causes vibrational forces and material collisions to occur, which burst the small bubbles of the foam.

Attempts have also been made to introduce the foam from the downstream side of a fixed blade projecting into the material. The foam introduced into the cavity formed behind the shovel, is however, burst by the material as it collapses during mixing.

The present invention therefore seeks to provide a method and an apparatus for introducing foam into a material to be mixed in such a manner that the foamed properties are retained and the foam uniformly permeates the whole material.

Thus, it should be possible to charge large quantities of foam into the material, even to the extent of multiples of the volume of the material itself, thereby rendering the material light but uniformly stable.

According to the present invention, there is provided a method of producing a foam-filled material, particularly foamed concrete comprising the steps of locating material to be mixed in a mixing chamber, mixing the material by utilising rotatable mixing vanes in such a manner as to cause the material to be initially conveyed outwardly from the axes of rotation of the vanes into the edge regions of the chamber and thence returns inwardly so that the material executes a swirling, generally forward in the direction of rotation, movement about the vane, thereby causing a cone or vortex to be formed in the central region between the vanes and injecting a foaming material into the core of the cone or vortex.

It has been shown that the relatively small amount of movement in the vortex created by the low speed of rotation of the mixing vanes and the vacuum prevailing in the vortex or cane prevents disintegration of the foam, the foam being absorbed by the edge regions of the material being mixed from whence it is distributed undamaged, uniformly throughout the material.

The proportion of water required thereby remains small.

A particularly suitable apparatus for carrying out such a method comprises a trough-shaped chamber for receiving the material to be mixed, a plurality of rotatable mixing vanes being mounted on a common drive shaft so that the vanes extend into the chamber, the shaft extending perpendicularly to, but eccentrically of, the chamber such that, in use, the vanes rotate the material so as to define a cone or vortex in the region below the free end of the shaft, and means for supplying a foaming agent into the cone or vortex thus formed whereby the foam is entrained by the swirling material. This apparatus is a relatively simple structure and is well suited not only for producing concrete foam but also for other types of foam.A desired contribution to the production of a suitable foam is provided if the speed of rotation of the mixing vanes is limited to a value below which the foam bubbles contained in the material are not burst. This speed is preferably less than 10 m/s, desirably less than 5 m/s, measured at the outer edge of the vanes. The measurement being taken at this point is important because the material particles move into and out of contact with the mixing vanes. A mixer in accordance with the present invention is easy to operate, is relatively reliable and appears to be less prone to breakdown than known mixers.

The foam is rapidly, but thoroughly, mixed with the components of the mixture and the trough is readily accessible for cieaning.

The invention will be further described, by way of example, with reference to the accompanying drawings, in which: Fig. 1 is a vertical section through a mixer in accordance with the present invention, and Fig. 2 is a plan view, partially broken away and partially in section of the mixer shown in Fig. 1.

In Fig. 1 there is shown a trough 2 which is freely rotatably mounted on a frame 1 by means of a bearing 3. An opening 4 is provided in the base of the trough 2 which opening is closed by a plate 5 when the contents of the trough are being mixed.

The plate 5 is mounted on a pivotable arm 6, the movement of which uncovers the opening 4 and permits the contents of the trough to be emptied.

Pivotally mounted on the frame 1 about an axle 7 is a bridge structure 8. The bridge structure 8 includes an upright portion 9 and a drive motor 10 together with its requisite switching, control and regulating devices, the function of which will be described hereinafter. The upright portion 9 is adjoined by a bearing portion or arm 11 which carries a bearing 12 in which a hollow shaft 13 is received. The shaft 1 3 latter supports four arms 14, each arm 14 carrying one or more mixing vanes 1 5. The arms 14 have a downwardly extending portion so as to permit the vanes to extend adjacent to the base of the trough 2, and the vanes are so disposed as to brush against the side wall 1 7 of the trough.The vanes are flat and are so dimensioned that a major proportion of their front faces are constantly immersed in the material to be mixed and thus sweep substantially the entire region between the shaft 1 3 and the side wall 1 7 of the trough 2 nearest thereto. They are adjustable in a direction transverse to their direction of movement so as to be able to set up components of centrifugal movement in the material.

At its upper end the shaft 13 supports a belt pulley 18 and the motor 10 supports a second belt pulley 19. The two belt pulleys 18 and 1 9 are operatively connected by a belt 20. A feed conduit 21 passes through the hollow interior of the shaft 13 which conduit is mounted at its upper end in a head portion 22. A further conduit 23, emanating from a foam generator, (not shown) communicates through the interior of the feed conduit 21. The feed conduit extends to adjacent the base of the trough 2.

A further guide vane 24, which is vertically adjustable, is also mounted on the bearing arm 11. This vane 24 does not extend to the base 1 6 of the trough 2 and thus, during mixing, leaves a region close to the base 1 6 exposed.

In operation, the trough is charged with material 25 to be mixed, such as concrete. The vanes 1 5 rotate in the direction of the arrow 26 (Fig. 2), engage the material and convey it to adjacent the base 1 6 both outwardly and in the general direction of rotation, as is shown by the arrows 27 and 28 in Figs. 1 and 2. The material flowing along the base 1 6 causes the trough 2 to be rotated in the same direction of rotation as the vanes 1 5. The material thus leaves and re-enters the region of the mixing vanes 1 5 without impact or reversal of direction.

The material which is conveyed outwardly by the mixing vanes 1 5 becomes somewhat dammed between the side wall 1 7 and the guide vane 24 but then flows back downwardly towards the central region of the area swept by the mixing vanes 1 5 as is shown by the arrows 29 and 30.

This flow produces a funnel-like cone or vortex 31 in the material in the region of the extension of the shaft. At this point, a reduced pressure prevails since, subject to the influence of the rotating mixing vanes 15 and the rotating base 16, the materials begin to flow outwardly again.

Much of the material passes under the guide vane 24 and flows over the entire area of the base 1 6 but due to the rotation of the trough 2, is continuously subjected to the above-described flow movement. Since the mixing vanes have relatively large front faces, they convey the material effectively and force it outwardly at a considerable rate even though their rotational speed is slow. The rotational speed is maintained low so that the bubbles formed in the material by the foam are not burst by the mixing vanes 1 5, especially by the outer edges of the vanes. This speed of rotation should not exceed 10 m/s and desirably should be less than 5 m/s measured at the outer edge of the mixing vanes 1 5.

The feed conduit 21 is adjusted so that it projects into the cone or vortex 31 and terminates either just above or just below the material surface. If foam supplied through the conduits 23 and 21 into the material in the region of the cone or vortex it is passed into the mixture at low pressure and is progressively conveyed. The foam is thus uniformly distributed in the material to give it a loose foamed structure. The bubbles of the foam are retained and evenly enveloped by a bonding agent contained in the material which, in the case of concrete, is cement. Thus, after the mixture has set a lighter, uniformly soiid foamed concrete is produced.

A probe 32 is expediently secured to the bearing arm 11, which probe projects into the region of the material being mixed, or is even immersed therein, at a point where the material is flowing uniformly when mixing is taking place, that is to say, in a region in which the height of the material remains substantially constant. A lead connects the probe to a control device 33 which, in turn, controls the quantity of foam, water or solid material supplied to the trough.

The probe may detect the height of the material, the liquid content, the viscosity or the density of the material or combination of these parameters. These parameters are, of course, dependent upon the quantity of material employed and/or the proportion of foam; absorbed. In this manner, the supply of solids, water and foam to the mixture can be regulated so that the completed mix constantly has the pre-selected desired consistency.

When the material has been completely mixed, the mixer continues to operate but the guide vane 24 is lowered and the plate 5 is pivoted away from the opening 4. The material is thereby conducted to the opening 4 and flows downwardly into a collection vessel (not shown).

The supply conduit 21 need not pass through the hollow shaft 13. Indeed the foam may be supplied directly through the interior of the shaft 13. In such a case, the lower end of the shaft 13 is caused to terminate closely above the cone or vortex 31.

The method of the present invention, regardless of the finer details of the construction of the mixer, can expediently be used whenever a material is mixed by stirring so as to form a zone of lower pressure into which the foam may be introduced.

The method may be employed with any material which has a suitable consistency and which contains a bonding agent which, in the manner of cement, envelopes the bubbles of the foam and which subsequently sets. Thus, the method may be employed for making mortar, plaster or plastics material compositions.

It is also within the scope of the present invention for the supply conduit to be separate from the drive shaft. Thus, the conduit may terminate laterally of the shaft beyond the arms 14 and the vanes 15, the foam being injected between the rotating components into the cone or vortex. The method may constitute one of a series of mixing operations.

Thus, in a first stage, a binder or bonding agent and a liquid, such as cement and water respectively, may be thoroughly mixed at a high rotational speed of the mixing vanes to form cement glue. In a second stage, small-grained material such as sand, may be admixed therewith.

In a third stage, coarse-grained material such as gravel may be added. At least in the third stage, the speed of the mixing vanes are reduced to the speed specified hereinbefore and the foam is charged therein. The completely mixed material may then be discharged.

It may also be advantageous for the control device 33 to be supplied with signals which are dependent on the speed of rotation of the mixing vanes 1 5 or of the speed of the drive motor 10.

The quantity of foam supplied to the mixture would, in such case, also be dependent on these speeds.

The pressure in the core region of the cone or vortex is lower than the static pressure which would prevail in a material not being displaced.

Due to the flow velocities, this pressure will also be lower than atmospheric pressure.

Claims

1. A method of producing a foam-filled material, particularly foamed concrete comprising the steps of locating material to be mixed in a mixing chamber, mixing the material by utilising rotatable mixing vanes in such a manner as to cause the material to be initially conveyed outwardly from the axes of rotation of the vanes into the edge regions of the chamber and thence returns inwardly so that the material executes a swirling, generally forward in the direction of rotation, movement about the vane, thereby causing a cone or vortex to be formed in the central region between the vanes and injecting a foaming material into the core of the cone or vortex.

2. A method as claimed in claim 1, wherein the configuration and speed of rotation of the mixer and the quantity of material charged therein are so selected that a region of reduced pressure exists in the core of the cone or vortex.

3. A method as claimed in claim 1 or 2, wherein the speed of rotation of the mixing vanes, measured at the outer edge of the vanes, is maintained below a value at which the foam bubbles contained in the material are burst.

4. A method as claimed in claim 3, wherein the speed of rotation of the mixing vanes does not exceed 10 metres per second.

5. A method as claimed in claim 4 wherein the speed of rotation of the mixing vanes does not exceed 5 metres per second.

6. A method as claimed in any preceding claim wherein the amount of foam supplied to the mixture is controlled in dependence upon the speed of rotation of the mixture and/or the properties of the material.

7. A method as claimed in claim 6, wherein said control is effected automatically.

8. A method of producing a foam-filled material substantially as hereinbefore described.

9. An apparatus for carrying out a method as claimed in any one of claims 1 to 8, comprising a trough-shaped chamber for receiving the material to be mixed, a plurality of rotatable mixing vanes being mounted on a common drive shaft so that the vanes extend into the chamber, the shaft extending perpendicularly to, but eccentrically of, the chamber such that, in use, the vanes rotate the material so as to define a cone or vortex in the region below the free end of the shaft, and means for supplying a foaming agent into the cone or vortex thus formed whereby the foam is entrained by the swirling material.

10. An apparatus as claimed in claim 9 wherein the trough is freely rotatable.

11. An apparatus as claimed in claim 9 or 10 wherein four mixing vanes are provided.

12. An apparatus as claimed in any one of claims 9 to 11 wherein the supply means include a supply conduit which is co-axial with the drive shaft.

13. An apparatus as claimed in any one of claims 10 to 12 wherein the trough and the mixing vanes are rotatable in the same direction of rotation.

14. An apparatus as claimed in claim 13 wherein the trough is caused to rotate by the pressure of the material pressing thereagainst due to the rotation of the mixing vanes.

15. An apparatus as claimed in any one of claims 9 to 1 4 wherein a major portion of the mixing vanes are, in use, constantly immersed in the material to be mixed, the vanes being so dimensioned as to sweep over substantially the entire space between the shaft and the wall of the chamber nearest thereto, the vanes being shallow and being disposed obliquely to their direction of movement so as to produce centrifugally directed components of movement in the material.

16. An apparatus as claimed in any one of the claims 9 to 11 or 13 to 15, wherein the shaft supporting the mixing vanes is hollow, and the foam is introduced into the cone or vortex produced in the mixture through said hollow interior.

1 7. An apparatus as claimed in claim 12 or any one of claims 1 3 to 1 5 when appendant to claim 1 2 wherein the drive shaft, drive means therefor and the supply conduit are mounted on a bridge member spanning the chamber, the bridge being adapted to be pivotally moved so as to expose the chamber.

18. An apparatus as claimed in claim 17, wherein a probe is mounted on the bridge member which, during the mixing, monitors one or more parameters of the mixture and is connected to a control device, the control device controlling the quantity of foam supplied to the mixture.

19. An apparatus as claimed in claim 1 8 wherein the probe monitors the water content of the mixture.

20. An apparatus for producing a foam-filled mixture constructed and arranged to operate substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.