GB2318069A - Foam for use in the manufacture of an aerated concrete or polymer - Google Patents

Abstract

The foam is produced by passing a mixture of air, water and foaming agent through a series of tortuous passages in five mixing chambers. A mixture 27 of water and foaming agent enters the first chamber 25 via pipe 13 where it meets air 26 from pipe 14. This mixture passes through holes 32 in a closed pipe 29 into second chamber 30 from where it passes through perforated plate 37 and through packed stainless steel wool 36 in third chamber 35. Passing through a second perforated plate 37 the mixture continues into fourth chamber 39 formed from stainless steel eyelets 38 packed into pipe 40 and on through fifth chamber 42 which is packed with a further quantity of steel wool 36. The foam for use in the manufacture of an aerated concrete or polymer can then be inspected through transparent tube 43.

Description

IMPROVEMENTS IN OR RELATING TO THE MANUFACTURE OF FOAMS AND THEIR USES This specification relates to an apparatus and method for the manufacture of foams, in particular, air-water foams and the use of such foams in, for example, aerated concrete, aerated filled polymers, etc.

The addition of air to concrete during manufacture has been practised for a considerable time. One method is to insert a lance into the concrete in the mixer and blow air in through small holes. As the mixture is churned in the rotating mixer, the bubbles are distributed through the concrete and remain while the mixture is poured or cast. Disadvantages of this method are that the bubbles may not be distributed evenly through out the whole of the mixture and, during the mixing, some bubbles may coalesce to form larger ones creating 'voids'.

Fig. 1 shows a typical section through concrete made using this method. Bubbles 1 are shown, in concrete matrix 2. Bubbles 1, though shown fairly evenly distributed, are of uneven size and irregular shape and, where they approach closely, cracks 4 can form between the adjacent bubbles 1. In some cases, such cracks can propagate 5 and become major points of weakness.

It is known that concrete, like most such inorganic materials, is weak in tension and bending, though strong in compression. Thus, while a matrix such as shown in Fig. 1, may be perfectly adequate for some applications, e.g. making the blocks used for the internal walls of bungalows, etc., it would be unsuitable for more arduous duties such as for building high walls, or use as lintels, etc. Blocks for such domestic applications must be able to withstand an edge load of 4N, industrial blocks must withstand 7N and structural blocks 10N. Unless very high quality control can be provided, aerated concrete cannot be made consistently to these higher standards, unfortunately high quality is expensive and cannot always be justified.

Builders would clearly prefer to have a single quality of block for all applications and would like this to be the lighter aerated one, which has better insulating properties, but this has not previously been an economical proposition.

The presence of bubbles 1 and cracks 4, 5 also makes blocks, with a matrix as shown in Fig. 1, susceptible to absorbing water by capillary action. This is another reason why the presently available blocks have serious limitations.

The ideal type of structure is shown in Fig. 2, to a higher level of magnification than that of Fig. 1. Here the bubbles 3 are much smaller and are herein termed 'microbubbles' and thus are given a different reference numeral. Because they are so small, the surface tension draws them into spheres, as shown. Microbubbles 3 are uniformly distributed throughout matrix 2. Because they are so small, there is less likelihood of them coalescing and forming larger bubbles. Though cracks 4 could form between two microbubbles which happen to be almost touching, the likelihood of a crack propagating 5 is much reduced due to the more even microbubble distribution and their inherent strength, which they impart to the matrix..

Other methods of making aerated concrete have been developed, including making the foam separately and adding it to the mix, but subsequent research has shown that the bubbles in the foam are not small enough to have long-term stability. Despite development of foam making equipment and foaming agents, it has not hitherto proved possible to produce a foam with a sufficiently small bubble size and the inherent strength to withstand the mixing process. Most foams are produced with a range of sizes and the larger bubbles coalesce, particularly during the churning action of mixing.

In some cases, the addition of foam results in a mix which is rather wet for certain applications, especially as it is normal to add extra water to give the required 'workability'.

There is thus a need for a means of producing a stable uniform microbubble foam which can be added to concrete during conventional mixing and subsequently cast in the normal manner. Such a foam should be capable of making the whole range of items currently produced from concrete, yet give enhanced properties which can be assured to exist evenly throughout the product. In particular, there is a need for a standard size of lightweight building block, which has adequate physical properties for all types of structural applications and which can be produced for an economical price. Ideally, the blocks will also have good insulating properties and resist absorbing water.

Such a foam would have other uses, for example, mixing with resin-filler mixtures prior to polymerisation to give a lighter material. Such materials are often called 'polymer concretes'.

According to the invention, there is provided apparatus for making foam, comprising: i. a source of air; ii. a source of water; iii. a source of a foaming agent; iv. a means of mixing said air, water and foaming agent to form a mixture; v. a means to pass said mixture through a foaming block to produce an essentially homogeneous, stable foam; and vi. providing said foam for use; characterised in that said air, water and foaming agent mixture is supplied at high pressure to said foaming block and said high pressure is used to drive said mixture through a series of tortuous passages to create a turbulent mixing regime giving an essentially homogeneous, stable foam.

According to a first variation of the apparatus of the invention, said series of tortuous passages includes holes.

According to a second variation of the apparatus of the invention, said series of tortuous passages includes the voids between strands of packed metal wool.

According to a third variation of the apparatus of the invention, said series of tortuous passages includes the voids between and/or through inert packings.

According to a fourth variation of the apparatus of the invention, said packings are short, metal tubes.

in a preferred design of the apparatus, the foaming agent and water are pre-mixed and pumped to the first chamber of the foaming block, where mixing with compressed air occurs. The mixture thus formed is passed through small holes at high pressure into a second mixing chamber. From here, the mixture passes into a third mixing chamber packed with stainless steel wool, so that the mixture faces tortuous paths between the individual strands of wool; this creates high shearing forces to break up the air bubbles into ever smaller sizes.

The mixture which leaves this chamber, passes into a fourth mixing chamber packed with short lengths of small diameter stainless metal tubes and undergoes further, though less violent mixing. Here, the localised volumes of mixture are larger than in the voids between the strands of wool so that 'localised bulk mixing' can take place rather than just local mixing in a very limited volume of mixture. The fifth and final mixing chamber contains further packed stainless steel wool to give the foam a final 'polish'.

The apparatus of the invention creates "microbubbles" by subjecting the air J water / foaming agent to very high shearing forces in a series of highly turbulent mixing regimes. Because several such regimens are used in series and the mixture has an extended residence time in each regime, very fine mixing occurs resulting in a very small and uniform bubble size. The first chamber is for coarse mixing. The second chamber provides for further bulk mixing to give uniformity on the macro-scale and is followed by micro-mixing in the tortuous passages between the strands of the wool in the third chamber. This process is repeated in the fourth and fifth chambers. The packing in the fourth chamber has larger voids (than between the strands of stainless steel wool); this allows 'mini-mixing', i.e. further macro-mixing, though on a smaller scale than in the second chamber. This is followed by a firrther passage through tightly packed stainless steel wool to give a final micro-mixing in the fifth chamber.

This 'series mixing', first on the macro-scale and then on the mini- and micro-scales, gives both the conditions and the residence time to achieve as near uniformity as practicable and the quality of the foam produced sets new standards in the process of foam manufacturing.

According to a fifth variation of the apparatus of the invention, said series of tortuous passages includes bends in the pipework.

it is known that changes in the direction of a flowing fluid cause turbulent mixing and the sharper the bend the more the turbulence. The incorporation of right angle (90;) bends between adjacent chambers further improves the quality of the foam produced.

The foam thus produced is extremely stable and will retain its aerated form for severai hours at ieast. This is the prime inventive feature of the disciosure and such foam has many uses According to the invention, there is provided a method of making foam and products containing foam, comprising the steps of - i. providing a source of air; ii. providing a source of water; iii. providing a source ot a roaming agent; iv. mixing said air, water and foaming agent to form a mixture; v. passing said mixture through a foaming block where high shear stresses are generated on said mixture to create an essentially homogeneous stable foam; and vi. using said foam to manufacture products.

According to a first variation of the method of the invention, the foam is added to cement during mixing to produce aerated concrete.

According to a second variation of the method of the invention, other additives are introduced to the concrete during mixing.

According; to a third variation of the method of the invention, the means of manufacturing said products is casting the aerated concrete into moulds.

One variation of the method of the invention provides for pre-determined quantities of water, cement, foam and fillers, e.g. sand; aggregate, etc., to be placed in a concrete mixer and churned to produce the desired composition which is then delivered for use, e.g. pouring into moulds, for foundations etc. The process of mixing the concrete does not destroy the foam but incorporates it uniformly into the final product, where it remains, as foam, during setting to give a concrete uniformly aerated with microbubbles.

Because of its high and uniformly distributed microbubble air content, concrete made by the method of the invention, is lighter, stronger and has better thermal insulating properties than currently available aerated concretes. The presence of the foam enhances workability of the concrete and gives a product which is ideal for all types of traditional and standard uses. The presence of the foam means that no additional water is required make the mixture 'workable' so that no settling occurs once working of the mixture has stopped. It is particularly well suited for making thermally insulating, water resistant building blocks.

According to a fourth variation of the apparatus of the invention, the foam is mixed with an aqueous resin and, if required; a filler(s) to produce a uniform composition prior to polymerisation.

A preferred variation of the method of the invention provides for the foam to be mixed with aqueous-based resin and filler(s) systems to produce composite materials. It is preferred to premix the resin and foam prior to adding the filler. The reason for this is that a more uniform mixture results if the constituents being mixed are of roughly similar volumes. Thus, if equal volumes of resin and foam are premixed into a 'mousse', the resulting 'double volume' can be mixed more uniformly with the greater volume of filler (roughly a 1:3 volumetric ratio) than would be the case without foam (i.e. a 1:6 ratio).

The increase in volume provided by the foam reduces the bulk density of the composite but does not materially weaken it as the microbubbles tend to collect in the interstitial spaces between the particles of filler, thus freeing resin to bond to the surfaces of the particles and secure them to each other.

For a clearer understanding of the invention and to show how the same may be put into effect, reference will now be made, by way of example only, to the following drawings in which: Figure 1 is a microsection of a presently available aerated concrete (Prior Art); Figure 2 is a microsection of an ideal aerated concrete structure; Figure 3 is a block diagram of the process of making aerated concrete according to the invention.

Figure 4 is a sectional elevation of the foarning block according to the invention, Figure 4A is a sectional elevation of an alternative first mixing chamber.

Figure 5 is a block diagram of the method of mixing water and foaming agent and supplying them to foaming block 15; Figure 6 is a side elevation of the mixing finger used in the second mixing chamber 30; Figure 7 is a perspective view of the 'eyelet' packings used in the fourth mixing chamber of the foaming block 15.

Figure 8 is a diagrammatic section through a concrete mixture having the 'ideal' cement-water ratio.

Figure 9 is a diagrammatic section through a concrete mixture having a higher cement-water ratio.

Figure 10 is a diagrammatic section through an aerated concrete mixture having the 'ideal' cement-water ratio and containing a microbubble foam.

Figure 11 is a side elevation of a mould newly filled with concrete.

Figure 12 is a side elevation of a mould some time after filling with concrete.

In the following description, the same reference numeral is used for the same component or different components fulfilling identical functions. The description uses the application of the foam to produce aerated concrete a an example, but similar principles apply to the manufacture of aerated resin-filler composite materials.

Fig. 3 shows the principle of the process of making aerated concrete in block diagram form. A source of primary power 6 is used to drive a compressor 9 supplying air 8 through pipe 14 to foaming block 15. Power source 6 also drives a pump 11 passing a mixture of water 10 and foaming agent 12 through pipe 13 to foaming block 15.

Electrical connections 7 are shown from primary power source 6 to compressor 9 and pump 11. A further connection 7 is shown to source 12 of the foaming agent as this could alternatively be added directly to foaming block 15 via a metering pump. Other methods of pre-mixing are equally possible. Any suitable source of power 6 may be used. For small scale applications, mobile petrol, or diesel, powered generators are appropriate while for larger factory applications, mains power is preferred.

In foaming block 15, a mechanically strong foam is produced and passed through pipe 16 to concrete mixer 17 where cement 18 and other additives 19 are introduced.

Mincer 17 is a conventional concrete mixer and may be of an appropriate size for the duty required; i.e. mixing small or large batches. The concrete produced is passed 20 for use 21, e.g. pouring into foundations, or manufacturing of concrete products.

Fig. 4 shows the detail of foaming block 15. The mixture of water and foaming agent enters 27 first mixing chamber 25 via pipe 13 where it meets air 26 from pipe 14. Both these streams 26, 27 enter at the sam high pressure; 6.8 bar (100 psi) has been used for the experimental purposes and a high pressure of this sort of magnitude is required to drive the mixture through foaming block 15. The coarse mixture 49 from first mixing chamber 25 passes into mixing finger 29. This unit has been colloquially termed the 'bullet' and consists of a sealed pipe 29 having a number of small holes 32; this apparatus will be described in more detail hereinafter.

Holes 32 are very small in diameter so that the air/water/foaming agent mixture issues at considerable velocity 50 (Fig. 6) into second mixing chamber 30. Chamber 30 is the annular space formed between bullet 29 and pipe 31. A great deal of turbulence is caused by this violent process, which breaks down large air bubbles into much smaller ones and distributes them throughout the liquid.

The mixture passes out of pipe 31 through a first perforated plate 37 into third mixing chamber 35, which is packed with stainless steel wool 36. The mixture passes round bend 33, through the tortuous passages between the packed strands of stainless steel wool 36 and round a further bend 33 before leaving via a second perforated plate 37.

As the mixture must follow very sinuous paths through the wool 36, the size of air bubble will be considerably reduced during its passage through third mixing chamber 35.

The mixture now enters a fourth mixing chamber 39 formed from stainless steel eyelets 38 packed into pipe 40. Here the flow regime is slightly less tortuous but nevertheless, there is still a high degree of turbulence created and further bubble size reduction occurs. From fourth mixing chamber 39, the mixture passes through a third perforated plate 37, round another bend 33 and into fifth mixing chamber 42. Chamber 42 is the internal volume of pipe 41 and the two bends 33 and is packed with a further quantity of stainless steel wool 36. The passage of the mixture through fifth mixing chamber 41 gives the foam a final 'polish' before it leaves, via fourth perforated plate 37, as a uniform mixture which (for a foam) is mechanically strong.

The final section of foam block 15 is transparent pipe 43 which allows the operator a visual check on the quality of the foam. Adjustable valves 22 are provided in both inlet pipes 13 and 14 so that the relative flows of air 26 and water/foaming agent 27 can be adjusted. Once these have been pre-set, there should be little need for further adjustment and, in some applications, valves 22 may be replaced by appropriately sized orifice plates (not shown). Simple on/offvalves 23 are provided to admit the air and liquid in their pre-set proportions. Non-return valves 24 are provided to prevent backflow along either pipe 13 or 14. Various types of non-return valve 24 are possible and the type shown consists of balls 24A pressed against seatings 24B via springs 24C located by stops 24D. The skilled person will know that fluids at 6.8 bar (100 psi) pressure are potentially very dangerous and must be handled properly with safe equipment; this is one reason why non-return valves 24 are provided.

Once set up, the operator should only have to start compressor 9 and pump 11 and open on/off valves 23 to activate the foam block. As soon as helshe is satisfied with the quality of the foam in pipe 43, the required volume of foam is pumped through pipe 16 into mixer 17.

It will be seen that the method of producing the foam is a series process in that the mixture passes through five consecutive chambers during which the bubble size is progressively reduced. The quality of the final foam can best be compared to that of shaving foam, which retains its structure for a considerable time, despite being massaged onto the skin and scraped off with the razor.

In order to appreciate the improvement that this foam offers over that previously available, as described with reference to the prior art (Fig. 1), it is appropriate to compare shaving foam with the foam produced using normal dishwashing liquid. The bubbles in the dishwashing liquid foam are basically large in size with a wide size range.

This foam is only stable for a short time, typically a few minutes. in contrast, the bubbles in shaving foam cannot be seen with the naked eye and the foam retains its consistency for hours.

To manufacture concrete according to the invention, foam from pipe 16 is placed in mixer 17 and cement 18 added. Further additives 19, e.g. sand, aggregate etc., are introduced until the concrete has the desired consistency. Other ingredients 19, e.g.

acrylic fillers, may be added to produce any of the specialist concretes which can made by any of the conventional processes currently available. Because the foam is stable, the microbubbles 3 retain their identity and are mixed as uniformly through the concrete as is the liquid itself. The concrete is then transferred 20 for use 21. Typical uses could be for the manufacture of building blocks, roof tiles, lintels or other structural items, as well as for casting items such as flower pots, garden statues, fountains, etc.

Fig. 5 shows a preferred method of pre-mix ng the water 10 and foaming agent 12 by adding them to a holding tank 45, preferably with a lid. The mixture is drawn through pipe 47 and an in-line filter 46 to pump 11 and thence via pipe 13 to foaming block 15.

Fig. 6 shows the detail of 'bullet' 29. It consists of a sealed tube 29 through which a number of small holes 32 are drilled. Holes 32 are, preferably, only about 1.2 mm (3/64 inch) in diameter, so that the mixture 50 exits from them at high velocity creating considerable turbulence in the second mixing chamber 30. Bullet 29 is mounted on a plate 28 fast between pipe 31 and first mixing chamber 25 and is shown welded/brazed 48 into plate 28. Bullet 29 and plate 28 are made of non-corrodable materials, e.g.

stainless steel or copper.

Fig. 7 shows a perspective view of an 'eyelet' 38 which consists of a short length of small diameter stainless steel tube 38A with a flange 38B. Eyelets 38 are obtainable in bulk and are a suitable packing for fourth mixing chamber 39.

The materials used in the apparatus of the invention are non-corrodable and electrochemically compatible, or electrically insulated from each other. Suitable materials are copper, brass, stainless steel and polymers; The person skilled in the art will know which are suitable materials for each individual component and which combinations of metals are acceptable in an aqueous environment. One factor to be borne in mind is the high inlet pressure to foaming block 15. This very high pressure [6.8 bar (100 psi)] is required to drive the mixture through the two sets of packed wool 36, 36 at an economic flow rate and to generate sufficient turbulence to break up the bubbles 1 into microbubbles 3. The size of microbubbles 3 is not known, but it is felt that they are probably in the micron range (1 pm = 104 m). It is known that the smaller bubbles are, the stronger they are.

It will be noted that the final section 43 foaming block 15 is made of transparent material, preferably a polymer. Though there is a high inlet pressure to foam block 15, the pressure drops through holes 32, chambers 35, 39 and 42 are considerable so that, when the mixture reaches pipe 43, the pressure has fallen to a low level and will not burst plastic pipe 43. There are no valves, or restrictions, downstream of pipe 43.

During the development of mixing block 15, straight sections of pipe 31, 34, 40, 41 and 43 were used, but the quality of foam produced was not as good as when the four right angled bends 33 were introduced. It is well known that a right angled bend creates considerable turbulence in the fluid flowing in the pipe so that it is concluded that bends 33 play a significant part in the final quality of foam produced, in conjunction with bullet 29, stainless steel wool packing 36, 36 and eyelets 38. Another advantage of bends 33 is to reduce the overall length of foam block 15. This is particularly useful if the apparatus of the invention is portable, i.e. apparatus with an overall length of 50 cm is easier to manage than if it is over lm long.

The diameter of the piping preferred for the foam block is 35-40 mm and the length of each of the straight sections is 100-250 mm.

In order to understand the method of use of the invention and the benefits resulting therefrom, reference will now be made to practical examples. In the table below, figures are given for masses of ingredients to make a normal type of concrete, suitable for the manufacture of building blocks. Comparisons are given for the 'ideal' mix, a normal 'practical' mix and the mix according to the invention.

I 'IDEAL NORMAL MIX ACCORDING MZ' 'PRACTICAL' MIX TO INVENTION WATER (kg) 3.6 4.8 3.6 CEMENT (kg) 12.0 12.0 12.0 WATER: CEMENT 0.3 i 0.4 0.3 RATIO FOAM 10% by volume* FILLER Nature and mass depend on particular applications (OP1lONAL) ) TABLE 1: FORMULAE FOR CONCRETE MIXES * The volume of foam is a percentage of the total volume of the mix, i.e.

including fillers, if present. 10% is a typical figure but may be varied for each application. For example, 5% foam will enhance the properties of the mix to a small, but significant, extent, while 30% will give a mechanically weak mix suitable for bulk infilling, e.g. where little stress is present.

To prepare a mix, it is normal to place the cement and water in the mixer and thoroughly churn the two together. Then, if required, the filler is added. Fillers are commonly sand, aggregate, acrylic materials, etc. or mixtures of these. After a further period of churning, the concrete is ready for use, e.g. to pour into moulds.

In the method of the invention, foam (prepared as hereinbefore described) is added to the cement-water mix before adding any fillers. The addition of fillers and subsequent churning does not destroy the microbubbles or cause them to coalesce into larger ones.

The reason for this is explained by the following theory. Tests have shown that Angus S90 foaming agent from Angus Fire Products of Bentham, Lancashire used at the rate of 9g / litre (1.5 ounces I gallon) gives the most satisfactory foam.

Very small bubbles adopt a spherical form due to the effects of surface tension. The surface area S of a sphere is given by the formula S = 4sf and its volume V is given by V = 4war3/3 . The ratio of these is Surface 4war2 3 ~ = ~ Volume 47per3 r 3 This shows that the relative effect of the surface tension per unit of volume is inversely proportional to the radius of the bubble. For example: for a bubble with a radius of 30 Zm the ratio is S: V :: 3: 30 = 1: 10 for a bubble with a radius of 3 um the ratio is S: V :: 3:3 = 1:1 i.e. as the size decreases, the relative importance of the surface tension increases.

Thus, very small bubbles will always tend to become spherical. With bubbles in the micron (or micrometer) range such as are believed to be produced by the method of the invention, the surface tension is a considerable magnitude per unit volume of microbubble. It should be noted that the concrete mixture acts like a fluid so that the pressure acts unifonnly inwards all round the surface of the microbubbles; this applies whether or not the mixture contains a particulate filler or is a pure cement and water basis. With the very small size of the microbubbles, the surface tension is (relatively) so much larger than the forces acting on touching bubbles to cause them to coalesce so that each bubble will preferentially retain its identity; this is true whether the mixture is static, i.e. has been cast, or still in motion, i.e. being churned in a mixer or worked with a trowel, etc.

Referring to Table I above, it will be noted that the normal 'practical' mix contains 30% more water than the other two mixtures. This is because the additional water is necessary to improve 'workability' of the mix. The effect of this is illustrated with reference to Figs. 8 and 9. Fig. 8 shows two planes of filler particles 51 and 52 in a cement water matrix 53. When a shearing force is applied, as shown by arrows 54, the two planes cannot easily move as projections on the particles overlap and interfere with the adjacent plane. Fig. 9 shows the effect of adding the extra 30% water. Here, the planes of particles 51 and 52 are separated and, when shear force 54 is applied, the two planes of particles 51 and 52 can slide past each other as indicated by dashed line 54 & Here, the effect of the extra water is shown 53 by the increased space between the two planes 51 and 52. For clarity, the spacing bet

it is important to note that, because of their inherent strength, the microbubbles retain their identity throughout the churning in the mixer, working, e.g. casting into a mould; or trowelling, etc., and during the setting and hardening processes, so that the microstructure ofthe final block represents that shown in Fig. 10 (with the microbubbles 3 unifonnly distributed between the particles 51, 52 in all three planes, as explained previously).

Advantages of the aerated concrete made with the foam of the invention are:1. Better Mechanical Pronerties: Because the microbubbles 3 retain their identities, they do not coalesce to form larger, irregularly shaped bubbles which are mechanically weak and lead to crack propagation. The uniform distribution of microbubbles acts like a form of 'dispersion hardening' to 'reinforce' the matrix. This is in addition to mechanical effects of additions such as acrylics, or fibres, etc. Because the use of microbubbles 3 gives a workable mixture at the 'ideal' water cement ratio, settling, and voids caused by water evaporation from within the matrix, do not occur after casting and this also improves the mechanical properties.

2. Better Thermal Properties: The presence of microbubbles 3 reduces the thermal conductivity of building blocks and thus improves their insulating properties; this is of particular benefit when used for building construction.

Because of the lower thermal conductivity, such blocks perform better when exposed to a fire, i.e. they have greater resistance to the effect ofthe heat and flame before failure occurs and such failure should be more progressive through the block than with ones which do not have a uniform microbubble content.

3. Better Woitibility: Because microbubbles 3 act like 'ballbearings', they give the required workability with the 'ideal' composition so that concrete prepared by the method described is easier to use. Because there is no excess water present, surface finishes are better.

4. Greater Volume of Mii: As shown in Fig. 10, the addition of microbubbles 3 increases the volume of the mix so that more products can be obtained from the same mass of concrete.

5. Use of Material: Concrete prepared by the method described may be used with all current additives and manufacturing methods.

6. Use on Site: Portable units of the apparatus of the invention may be used to enable the manufacture and casting of concrete to be carried out on site, e.g. for floors and walls in new building. Conventional reinforcing members may be incorporated in the casting.

7. Use in Factories: Permanent installations of the apparatus of the invention inside buildings may be used for the manufacture of concrete products, e.g. blocks, tiles, pipes, statues, etc. as a part of a production line, etc. Products made by such processes may be cured in autoclaves, or by natural processes, as required.

An in-line filter 46 is shown in pipe 47 to emphasise the importance of using clean water. Experiments have shown that warm water improves the quality of the foam and this work is continuing. Most foaming agents are organic in nature and experiments are being undertaken with mixtures of agents and with inorganic additives, e.g. for hard or soft waters.

The principle of the use of stainless steel wool has been explained as the key to achieving microbubbles but other conventional mixing means may be used in less critical areas of the foaming block. Fig. SA shows the use of venturis to promote the initial mixing in first mixing chamber 25. Here, high pressure water 10 enters via one venturi 58 and compressed air 14 via another 59. The vacuum effect of the flow of water in venturi 58 is used (wholly or partly) to draw in foaming agent, at a preset rate, via pipe 12 into the throat, where it is mixed thoroughly with the water. it is known that the afflux from a venturi is highly turbulent and consequently an extremely good mixing environment. Thus the foaming agent 12 is given a very good preliminary mixing with water 10 in venturi 58 before the efflux from both venturis 58 and 59 meet in first mixing chamber 25. As shown in Fig. SA, venturis 58 and 59 are angled inwards so that their separate effluxes immediately interact to promote good mixing.

Though not shown, valves 22, 23 are provided upstream of venturis 58 and 59, as previously described.

This is just one of the many known mixing techniques which are applicable to this invention.

Foam may also be combined with aqueous solutions of polymer systems, e.g. certain types of phenolic resins and water compatible fillers such as hollow ceramic microspheres. The combination of microbubbles and microspheres will give a mechanically strong composite with extremely low density. The foam, resin and fillers may be mixed, on either a continuous or batch basis, with the conventional types of equipment used for mixing non-aerated polymers and products manufactured from the mix using the conventional casting, extrusion, etc. techniques.

Claims (20)

What we claim is:

1. Apparatus for making foam, comprising: i. a source of air; ii. a source of water; iii. a source of a foaming agent; iv. a means of mixing said air, water and foaming agent to form a mixture; v. a means to pass said mixture through a foaming block to produce an essentially homogeneous, stable foam; and vi. providing said foam for use; characterised in that said air, water and foaming agent mixture is supplied at high pressure to said foaming block and said high pressure is used to drive said mixture through a series of tortuous passages to create a turbulent mionn8 regime giving an essentially homogeneous, stable foam.

2. Apparatus as claimed in claim 1, wherein said series of tortuous passages includes holes.

3. Apparatus as claimed in claim 1, wherein said series of tortuous passages includes the voids between strands of packed metal wool.

4. Apparatus as claimed in claim 3, wherein said packed metal wool is stainless steel wool.

5. Apparatus as claimed in claim I, wherein said series of tortuous passages includes the voids between and/or through inert packings.

6. Apparatus as claimed in claim 5, wherein said packings are short metal tubes.

7. Apparatus as claimed in any preceding claims, wherein the mixture is passed through pipework including bends.

8. Apparatus as claimed in any previous claim, wherein the means of mixing includes a venturi.

9. Apparatus for making foam as described in and by the above statement with reference to the accompanying drawings.

10. A method of making foam and products containing foam, comprising the steps of:- i. providing a source of air; ii. providing a source of water; iii. providing a source of a foaming agent; iv. mixing said air, water and foaming agent to form a mixture; v. passing said mixture through a foaming block where high shear stresses are generated on said mixture to create an essentially homogeneous stable foam; and vi. using said foam mixture to manufacture products.

11. A method of making foam as claimed in claim 10, and adding it to cement to make aerated concrete.

12. A method of making aerated concrete as claimed in claim 11, wherein other additives are mixed with the foam and the cement to create particular types of aerated concrete, aerated mortars etc.

13. A method of making aerated concrete as claimed in claims 11 or 12, wherein the means of mixing said foam with cement, and/or other additives is a concrete mixer or other suitable apparatus.

14. A method of making aerated concrete as claimed in claims 11 to 13, wherein the means of manufacturing said product(s) is casting the aerated concrete into moulds.

15. A method of making aerated concrete as claimed in claims 11 to 13, wherein the means of manufacturing said product(s) is by other methods.

16. A method of making foam as claimed in claim 10, and adding it to resin to make a polymerisable foam.

17. A method of making foam as claimed in claim 10, and adding it to resin and filler(s) to make a polymerisable composite material.

18. A method of making polymerisable materials as claimed in claims 16 or 17, on either a continuous or a batch basis, using conventional mixing techniques.

19. A method of making polymerisable materials as claimed in claim 18, and manufacturing products from said materials prior to polymerisation using conventional techniques.

20. A method of making foam, making materials incorporating said foam and products from said materials incorporating said foam as described in and by the attached statement with reference to the accompanying drawings.

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