Nozzle for spraying foam

Abstract

This nozzle comprises a nozzle body (22) terminating in a foam ejection tip (26). The foam has been pre-formed by mixing its liquid and gaseous components in a mixer located just upstream of the tip, within the nozzle body (22). The ejection passage (25) through the tip has oblong sections, the principal sides of which are at least 2.5 mm apart throughout, and it gradually widens towards the outlet. The expansion (low liquid fraction) of the foam delivered by the mixer does not decrease significantly until it reaches the ejection opening. Application to devices for projecting foams, particularly viscous foams, onto exterior surfaces.

Description

[0001] The present invention relates to a nozzle for projecting a foam.

[0002] It will be useful in particular in decontamination or depollution work, in which foams must be projected onto large surfaces which may be steeply inclined or vertical, belonging for example to buildings or other immobile structures, possibly difficult to access, and remain on these surfaces for a time long enough to act on the polluting products, without running or degrading in any other way.

[0003] For this purpose, so-called viscosified foams are appreciated, i.e., those enriched with a gelling agent that increases the physical stability of the foams and makes them less likely to flow on even very inclined or vertical surfaces. These two characteristics allow the foam to act for a sufficient time on the surface to be treated that they cover. Examples are given in FR 2 841 802 A1. One of their disadvantages is that they are difficult to manufacture from a foaming solution in the liquid state, precisely because of the high viscosity of this solution. Foam generating devices are generally intended for conventional foams, and they are not suitable for viscosified foams.In particular, they do not guarantee a high expansion of the foam produced in a sustainable manner, i.e. a low liquid fraction in the foam (for example less than 10% by volume); a lower expansion has the disadvantage of using an excess of liquid products for the same volume of foam, and of producing fewer small, more durable bubbles.

[0004] In particular, it has been found that, even when foams with a high expansion are produced, they are generally degraded when passing through the ejection nozzle of the devices, which burst some of the bubbles and dissipate some of the gas included, which increases the liquid fraction of the modified foam as well as the diameter of the remaining bubbles. They can also be degraded on the paths leading to the nozzle, upstream of it, on long paths or paths with sudden or significant variations in direction, which have the same unfavorable effect of bursting some of the bubbles.

[0005] A typical foam projection nozzle is described in WO 2005 / 025755 A; it comprises a passage for projecting a jet of the liquid to be foamed, then a nozzle with multiple fine openings which divide the jet and thus form the foam just at the outlet of the device. However, it is not certain that this device makes it possible to produce foams with high expansion, or even that the expansion can be adjusted or stabilized. In particular, the upstream part with a wide opening of the nozzle allows the liquid to pass without changing its state, and the formation of foam depends only on the downstream part with fine openings, excluded in the invention.

[0006] US5344079 A describes a different device, where the foam projection device ends at a single wide-opening ejection nozzle. An ejection nozzle with such an opening is found in the invention. But the nozzle opening of this document is still intended to create the foam by itself, thus also producing the mixture of the gaseous and liquid fractions of the foam. The device also comprises, just upstream of the nozzle, a liquid spinning device ("spin passage"), in which the liquid is atomized and from which it emerges as a mist of droplets, but which is not a mixer: the foam is formed by the droplets bouncing off the wall of the opening. In the invention, the ejection opening and a mixer are adjacent but separate, in order to be able to use a mixer adapted to provide high overruns to the foams.

[0007] US4421788 A describes a foam projector device further comprising a single wide-opening nozzle, and a mixer (18) upstream of the nozzle, from which it is separated by a flexible lance (22). The device is not dedicated to the production of high-expansion foams (on the contrary, high-density foam seems to be sought) and a significant drop in the expansion of the foam as it flows into the lance is to be expected. Finally, the nozzle has a conical shape which imposes a significant constriction on the foam flow just before opening, which can also impair expansion.

[0008] An object of the invention is to project foams, in particular special high viscosity foams, which retain a satisfactory degree of expansion at the outlet of a lance of a projection device, without being degraded on the path leading to the ejection nozzle of the device or through this nozzle.

[0009] Other objects of the invention are to easily and reliably produce foams having the desired degree of expansion from their liquid and gaseous constituents by means of a suitable mixer, and to pass these foams directly into the ejection opening, minimizing their paths to eject them from the nozzle and the rest of the apparatus.

[0010] In a general form, the invention relates to a nozzle for projecting a foam, crossed by a passage having a central axis corresponding to a direction of flow of the foam or of constituents of the foam from an upstream to a downstream, characterized in that it comprises a nozzle body including a mixer of the constituents of the foam, forming the foam, and a nozzle downstream of the mixer, the nozzle containing one end of the passage, belonging to the passage, downstream of the direction of flow; the end of the passage having cross-sections, perpendicular to the central axis, comprising two opposite main sides and connected to each other by connecting sides shorter than the main sides, the main sides being everywhere at least 2.5 mm apart; the end of the passage widening downstream of the flow direction, at angles of at most 30° between a wall of the end of the passage and the central axis; the mixer being placed in a bore belonging to the passage, connected directly to the end of the passage; the cross-section of the end of the passage being geometrically inscribed, at the location of the connection, in a cross-section of the bore.

[0011] It was found that this particular shape of nozzle opening avoided significantly degrading the viscosified foams passing through the nozzle, by limiting the bursting of bubbles thanks to the sufficient width offered to their passage and to the gradually flared shape of the opening, which offers the foam a gradual passage towards the conditions of free flow in the external atmosphere. It was also found that the direct or almost direct connection between the mixer and the ejection opening, the mixer being included in the nozzle body of the foam ejector with an arrangement which avoids long paths of the foam to the outlet, contributed to maintaining at a high degree the expansion of the foam produced in the mixer. The same advantage can be attributed to the complete or almost complete absence of variations in the cross-section of the flow up to the opening of the nozzle.

[0012] According to some optional improvements: the principal sides of at least some of the cross-sections are curvilinear and diverge from each other towards midpoints of the principal sides, where they are at least 4 mm apart; the bore is cylindrical and rectilinear.

[0013] Particularly advantageous for obtaining high foam expansion: the mixer comprises a cage limited by a tube, two obstacles at two opposite ends of the tube and arranged in succession along the central axis, and at least one solid body freely movable in the cage and retained in the cage by the obstacles; the at least one solid body consists of at least one rigid ball; the obstacles are grids.

[0014] And the integration of the nozzle with the rest of a foam manufacturing or generation device, allowing to obtain a possibly significant flow of foam, is better if the tubular part has a thread connecting to a supply duct for the foam constituents.

[0015] Another aspect of the invention is the application of the nozzle according to any one of the preceding claims to methods of projecting viscosified foams onto exterior surfaces.

[0016] The invention will now be described in its various aspects, characteristics and advantages, by means of the following figures, which illustrate a particular embodiment, given for purely illustrative purposes: there Figure 1 is a diagram of a foam projection apparatus equipped with an embodiment of the invention; the Figure 2 , the projection nozzle body according to section II-II of the figure 6 ; there Figure 3 represents the mixer; the Figure 4 represents the end of the projection lance; the Figure 5 represents the nozzle body according to the VV section of the figure 6 ; there Figure 6 represents the nozzle ejection tip viewed from the front.

[0017] Referring to the figure 1 , a foam generating apparatus to which the nozzle is added is described; the nozzle could obviously be placed on other apparatus. This comprises a reservoir 1 of foaming solution in the liquid state, a bottle 2 of compressed air, a pressure gauge 3, a main pressure regulator 4, a pneumatic pump 5, a mixer 6, a foam ejection nozzle 7 (which is therefore the subject of the invention), a chassis 8. A first conduit 11 connects an outlet orifice of the reservoir 1 and passes through the pneumatic pump 5. A second conduit 14 connects an outlet orifice of the bottle 2 to the main pressure regulator 4, then merges with the first conduit 11 at a junction 15 downstream of the discharge orifice of the pneumatic pump 5. The air circulating in the second conduit 14 is slightly compressed at constant pressure (7 bars for example).The pressure gauge 3 is connected by a pressure tapping conduit 20 to the second conduit 14, upstream of the main regulator 4, and it therefore makes it possible to measure the gas pressure at the outlet of the bottle 2 and to evaluate the filling of the latter.

[0018] The frame 8 carries the tank 1, the bottle 2, the main regulator 4, the pneumatic pump 5, the first conduit 11 and the second conduit 14. The frame 8 can be vertical and belong to a backpack carried by the operator of the device; it can also be a rolling cart, for example. The foam ejection nozzle 7 is not fixed to the frame 8, but is located at the end of a flexible lance 21, which the operator holds. The lance 21 connects to the first conduit 11 and to the second conduit 14 at the location of the junction 15. The mixer 6, according to the invention, is adjacent to the nozzle 7 and to the foam ejection opening. It is even placed in a nozzle body 22 described below; it is not fixed to the frame 8, and it is located downstream of the entire lance 21.

[0019] According to the figure 2 , the nozzle body 22 comprising the nozzle 7 is unitary, in the form of a cylinder, and crossed from one side to the other by a passage 23. The passage 23 comprises a main part, which is a cylindrical bore 24, which is immediately followed downstream by one end of the passage 25 of more complex shape which will be described later, and constitutes the ejection opening of the nozzle 7. The bore 24 is formed in a tubular part of the nozzle body 22. The mixer 6 is placed in the bore 24 and occupies all or part of its length. The foam or its constituents pass through the passage 23 in a flow direction from left to right on the figure 2 , which represents the arrow on a central axis XX of the nozzle body 22 and the passage 23, and the nozzle 7 comprises at its downstream end a nozzle 26, which contains the end of the passage 25. The foam is ejected from the nozzle 7 by the nozzle 26 forming a plume 27 preferably in the shape of a flattened cone, capable of covering large widths of surfaces to be treated by flaring outwards.

[0020] Mixer 6 is shown in figure 3 . It comprises two flat grids 28 following one another in the bore 24 and occupying its entire section, two sealing joints 29 to which the grids 28 are respectively fixed and which serve as support for the wall of the bore 24, and spherical and rigid balls 30 free to move between the grids 28. It has been found that the balls 30, being both mobile and in small number, able to move independently of each other and constantly during manufacture, without forming superimposed layers which would reduce their mobility, were able to efficiently produce viscosified foams thanks to the low pressure losses and the intensity of the agitation which they produce in the liquid constituents.The seals 29 serve to hold the grids 28 in place and to form between them a cage 31, still delimited by the wall of the bore 24, and in which the balls 30 are retained while occupying only a small part of the volume of the cage 31. They also force all the fluids circulating in the bore 24 to pass through the interior of the cage 31. The mixer 6 thus defined can occupy the entire volume of the bore 24 or almost, that is to say that the upstream grid 28 is close to the inlet of the bore 24, and the downstream grid 28 rests on the rear face of the end piece 26. The mixer 6 and the ejection opening are then directly connected.

[0021] There figure 4 shows that the lance 21 is joined to a rear end of a barrel 33 of a gun 32 held by the operator of the apparatus. The opposite end of the barrel 33 carries a thread 34 to which the nozzle body 22 is screwed. The operator opens the lance 21 and triggers the projection of foam by pressing a trigger 35 of the gun 32.

[0022] There figure 5 is a sectional representation of the nozzle body 22, which fully illustrates the passage 23 and in particular represents an internal thread 36 which is used to screw the nozzle 7 onto the thread 34 at the end of the barrel 33.

[0023] We will now describe the tip 26 particularly by means of the figure 6 The end of the passage 25 is approximately conical, continuously widening downstream of the flow direction with a moderate slope: its wall makes angles of less than approximately 30° with the central axis XX, as represented by figures 2 And 5The cross sections (perpendicular to the direction of flow of the fluids in the nozzle 7, in the central axis XX) of the end of the passage 25 are oblong, that is to say strongly elongated in a transverse direction (vertical to the figure 6 ) relative to the other transverse (horizontal) direction.

[0024] There figure 6 represents the outline of an internal cross-section Si of the end of the passage 25, by which the end of the passage 25 connects to the bore 24, and the outline of an external cross-section Se, by which it opens onto a front face 37, directed towards the surface to be covered with foam, of the nozzle 7. The cross-sections such as Si and Se (with progressive variations in shape for the intermediate cross-sections) are generally composed of two main sides Li or Le, of generally vertical orientations to the figure 6 , which are connected by rounded edges Ri and Re. The main sides, such as Li or Le, are all arranged symmetrically with respect to the central axis XX. Their shape is purely curvilinear, which is the case of the main sides Li of the inner cross-section Si, or partially or completely rectilinear, which is the case of the main sides Le of the outer cross-section Se. The opposite main sides are always spaced apart by a distance greater than about 2.5 mm (here F = 3 mm to E = 5 mm at the ends and in the center of the lateral sides Li of the inner cross-section Si, which is the narrowest), in order to provide a sufficient passage width for the foam bubbles and to prevent, as far as possible, them from bursting when leaving the nozzle 7. In addition, the contour of the inner cross-section Si is geometrically inscribed, that is to say included, in the contour of the bore 24.

[0025] According to the invention, the foam is formed not far from the outlet of the apparatus by the mixing of air and the foaming solution, passing through the mixer 6. The grids 28, and especially the balls 30, are very effective in obtaining a foam with high expansion, that is to say with a low liquid fraction. The end of the passage 25 in the nozzle 26 has a shape which gives the plume 27 flattened and flaring, thus able to easily cover entire strips of the surface by a simple sweep of the lance 21. It also has an opening width and conditions of direct connection with the bore 24 which reduce to very little the proportion of foam bubbles which burst after leaving the mixer 6 and produce a degradation of the foam by increasing its liquid fraction.The high foam expansion, promoted by the mixer 6 and maintained by the nozzle 7 as well as by the shortness of the foam's path to the outlet of the nozzle 26, is sought among other things for viscosified foams with high expansion.

[0026] Some additional indications, of a concrete nature, are given below to describe more fully a particular example of this realization of the device and its performances.

[0027] Mixer 6: diameter and length of cage 31: from 10 to 100 mm and from 10 to 400 mm; Rigid balls 30: from 1 to 40, from 2 to 20 mm in diameter; Nozzle body 22: external diameter ∅ and length: 35mm and 100mm; Bore 24: diameter and length: 25mm and 80mm; Cross sections of the end of the bore ( figure 6): A=25mm, B=31mm, C=2mm, D=15mm, E=5mm, F=3mm; Foaming solution: water, with Glucopon 215UP [BASF] at 10g / l, and Xanthan Gum (G1253) [Sigma Aldrich] at 3g / l; Layer projected on vertical surface: 10m 2< , 1cm thick, in 120s; sliding speed less than 1cm / min. In the case where the foam is used to fill a volume, the foam holding time is at least 120min; Expansion of the foam obtained: approximately 16.7 (approximately 100 liters of foam produced for 6 liters consumed of the foaming solution).

[0028] A similar test with another nozzle, belonging to the known art, produced a foam of much lower expansion.

[0029] The balls 30 could be replaced by another solid body freely movable in the cage 31, and their number could also be different, only one solid body being possible.

[0030] And the shapes of the tip 26 may also differ from those proposed here, the advantageous embodiments therefore comprising a sufficient opening width to avoid too many bubbles bursting and moderately progressive opening section changes.

Claims

1. Foam projection nozzle, traversed by a passage (23) having a central axis (XX) corresponding to a direction of flow of the foam or foam constituents from an upstream to a downstream point, characterized in thatIt comprises a nozzle body (22) encompassing a mixer (6) of the foam constituents, forming the foam, and a nozzle (26) downstream of the mixer, the nozzle containing an end of the passage (25), belonging to the passage (23), downstream of the flow direction; the end of the passage (25) having cross-sections, perpendicular to the central axis (XX), comprising two opposite principal sides (Li, Le) connected to each other by connecting sides (Ri, Re) shorter than the principal sides, the principal sides being everywhere separated by at least 2.5 mm; the end of the passage (25) widening downstream of the flow direction, at angles of at most 30° between a wall of the end of the passage and the central axis (XX); the mixer (6) being placed in a bore (24) belonging to the passage (23), connected directly to the end of the passage (25);the cross-section of the end of the passage being geometrically inscribed, at the point of connection, in a cross-section of the bore (24).; 2. Foam projection nozzle according to claim 1, characterized in that the principal sides (Li) of at least some of the cross sections of the end of the passage (25) are curvilinear and diverge from each other towards midpoints of the principal sides, where they are at least 4mm apart.

3. Foam projection nozzle according to any one of claims 1 or 2, characterized in that the hole (24) is cylindrical and straight.

4. Foam projection nozzle according to any one of claims 1 to 3, characterized in thatthe mixer comprises a cage (31) limited by a tube, two obstacles (28) at two opposite ends of the tube and arranged in succession along the central axis (XX), and at least one solid body (30) freely movable in the cage and held in the cage by the obstacles.

5. Foam projection nozzle according to claim 4, characterized in that at least one solid body consists of at least one rigid ball.

6. Foam projection nozzle according to any one of claims 4 or 5, characterized in that The obstacles are grids.

7. Foam projection nozzle according to claim 3, characterized in that the drilling (24) has a circular cross-section, and the passage (23) has a uniform and straight direction in the nozzle body (22).

8. Foam projection nozzle according to any one of claims 1 to 7, characterized in thatthe passage (23) has, at one end, a thread (36) for connection to a conduit (33) for supplying the constituents of the foam.

9. Application of the nozzle according to any one of the preceding claims to methods of projecting viscosified foams onto external surfaces.