GB2060420A - Improvements in or relating to the production of foam - Google Patents

Abstract

Apparatus for mixing a foaming agent with air and water comprises a tube (16) containing a series of masses (e.g. 22, 22A) of material which form a labyrinth, these masses being spaced apart along the length of the tube. The masses are of lead shot, or metal or plastics filaments held between perforated plates. The lengths of the masses progressively decrease towards the outlet end. The foam produced is suitable for mixing with cementitous material. <IMAGE>

Description

SPECIFICATION Improvements in or relating to the production of cementitious materials This invention relates to the production of aerated cementitious material (cement and concrete). For this purpose a foaming agent such as "Aphrosol" (Registered Tade Mark) is mixed with water and air to form a foam as is used for fire fighting. This foam is then mixed with cement and if desired sand and other filler.

It is known to mix sand, cement, water and a foaming agent, in a rotary concrete mixing container into which compressed air is introduced but it is difficult to produce a homogenous mix in this manner and the mixture does not produce a stable aerated mixture. Consequently aerated concrete produced in this manner cannot be pumped through a hose as the air bubbles tend to break down rapidly.

It is also known to produce fire fighting foam by mixing air and a solution of foaming agent in a nozzle containing steel wool but this gives a large increase in volume with large air cells which if mixed with cement or cement and filler results in a mix which loses its aerated texture if pumped through a hose or if batches are dropped onto each other in a shuttering. For cement or concrete mixes a stable foam is required which has a high consistency or viscosity.

According to the present invention an apparatus for mixing a foaming agent with air and water comprising a tubular member containing a series of masses of material which form a labyrinth, these masses being separated from each other by spaces. The material is preferably lead shot but may be metal or synthetic plastics filaments and may be similar to the materials used as pot scourers. The water, foaming agent and gas can be passed through such a device without being forced back to the inlet openings by back pressure caused by the expanding foam.

Preferably the water, foaming agent and gas enter the device through a nozzle into a conical chamber having its small end adjacent the inlet nozzle.

Desirably the air at a correct pressure, foaming agent and water are fed into one end of the device and the foam passes out of the other end either into a storage container or if desired directly into a mixing apparatus where it is mixed with cement and if desired with sand, fuel, ash, aggregates and/or other filler.

The invention will be further described by way of example with reference to the accompanying diagrammatic drawing wherein Figure 1 is a vertical section of a device made in accordance with the invention and Figures 2, 3 and 4 are details to be described.

The device comprises a metal casing in the form of a tube 10 having a conical inlet chamber 11 screwed onto one end and a part conical outlet chamber 12 screwed on to the other end. The large end of the chamber 11 is attached to the tube and has the same diameter as the tube. The inlet chamber 11 has an extension 1 3 into which is fed a solution of the foaming agent in water. An inlet nozzle 1 5 in the extension 13 in the small end of the chamber 11 serves for introduction of compressed air.

A perforated gauze plate 1 7 extends across the inlet chamber 11 at its large end and a perforated bulkhead 18 lies against the plate 1 7. At some distance from the bulkhead 1 8 is another gauze plate 1 7A and perforated bulkhead 1 8A so that between the plate 1 7A and the bulkhead 18 is a chamber 22 which is filled with lead shot of a size normal in shot gun cartridges.

At intervals along the tube are similar plates 17A; 18A; 17B; 18B; 17C; 18C; 17D; 18D; 17E; 18E; 17F; 18hand 17G, thus forming chambers 22A, 22B, 22C filled with lead shot and separated from each other by empty chambers 23, 23A, 23B.

The empty chambers have the plates and bulkheads at their opposite ends separated by spacer tubes 24, 24A, 24B.

Compressed air and solution is freely mixed in chamber 11 and forced through the lead shot labyrinth 22, emerging as a stable foam with cells of about 100--60 microns. The object of a short length of labyrinth is to allow foam to be made with the minimum of back pressure thus preventing solution from being forced back up the air line and into compressor. The foam having been made cannot, again due to back pressure, be forced back through into the air line.

Further reduction in size of the foam cells occurs by passing foam through the labyrinth with 22A into the expansion chamber 23A, again reducing the cell size at 22B and yet again at 22C when cells of 20-40 microns are produced. The length of labyrinths is shortened as the foam becomes more stable setting up back pressure, i.e.

thechambers are progressively shorter towards the outlet.

Cold or warm air is fed into the device from a pressure reducing valve at 50 to 120 p.s.i. and an aqueous solution of foam forming material for example "Niceral" or "Brixol" (e.g. 2.5 to 3.5% solution) is fed in from a gear pump at 90-100 p.s.i. The foamed material has an evenly aerated texture something like shaving cream and is very stable so that when mixed with cement or cement and filler it can be pumped through a hose without breaking down the aertated condition of the mixture.

The device results in a foam with very small air cells and the volume of which can be reduced to only 3 to 12 or general 6 to 8 times the volume of the incoming solution whereas fire fighting foam has a much greater volume. The volume and stability of the aerated material is also dependent to some extent on the choice of foaming agent.

For example "Brixol" (made by Robert Wilson s Company Limited of Belfast) is suitable. A simple test of any foaming agent will enable a suitable one to be selected on the basis of the following criteria: (a) a foaming agent used in the invention should produce foam which, when placed in one's hand, will not readily disintegrate.

(b) the foam should withstand hand mixing with a trowel with a parcel of sand and cement and water without breaking down (separation of the water) (c) the foam should withstand continuous mixing with sand, cement and water (d) should withstand pumping through a two inches diameter hose pipe dver 100 feet and not collapse when ruled off and levelled.

The length of the device is also important and it should be at least 20 inches long. Normally a device 30 inches long and two and a half inches diameter is suitable.

Also the pressure of the infeed is important. A gas e.g. air pressure of 50 to 120 p.s.i. can be used e.g. 60 to 80. The foam solution fed in can be at a pressure greater than the air pressure e.g.

55 to 150 p.s.i. e.g. 80 to 120. Commonly 100 p.s.i. is used.

Claims (9)

1. An apparatus for mixing a foaming agent with air and water comprising a tube containing a series of masses of material which form a labyrinth, these masses being spaced apart along the length of the tube.

2. An apparatus as claimed in claim 1 wherein the material is lead shot.

3. An apparatus as claimed in claim 1 wherein the material is metal or plastic filaments.

4. An apparatus as claimed in claims 1,2 or 3 wherein a nozzle for entry of compressed air enters at the small end of a conical chamber the large end of which is connected to the tube and has the same diameter as the tube, the small end of the chamber being arranged to receive foam solution.

5. An apparatus as claimed in any of the preceding claims wherein the masses are contained within perforated plates supported by perforated bulkheads separated from each other by spaces.

6. An apparatus as claimed in any of the preceding claims wherein the length of the masses along the tube are progressively shorter towards the outlet end.

7. An apparatus as claimed in claim 1 substantially as described with reference to the accompanying drawing.

8. A method of using the apparatus of claim 4 wherein compressed air is fed to the nozzle at 50 to 120 p.s.i. and the foam solution is fed to the chamber at a pressure of 55 to 1 50 p.s.i. but greater than the air pressure.

9. A method as claimed in claim 8 substantially as described.