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 foam projection nozzle.

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

[0003] Viscose foams are valued for this reason; they are enriched with a gelling agent that increases their physical stability and makes them less prone to flowing over even steeply inclined or vertical surfaces. These two characteristics allow the foam to act for a sufficient time on the surface being treated. Examples are given in FR 2 841 802 A1. One of their drawbacks is that they are difficult to manufacture from a liquid foaming solution, precisely because of the high viscosity of this solution. Foam-generating equipment is generally designed for conventional foams and is not suitable for viscose foams.In particular, they do not allow us to guarantee a high overrun of the foam produced, i.e. a low liquid fraction in the foam (for example less than 10% by volume); a lower overrun 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] It has been observed, in particular, that even when high-expansion foams are produced, they are generally degraded as they pass through the ejection nozzle of the equipment. This causes some of the bubbles to burst and some of the contained gas to dissipate, thereby increasing the liquid fraction of the modified foam as well as the diameter of the remaining bubbles. Degradation can also occur along the paths leading to the nozzle, upstream of the nozzle, on long paths or paths with abrupt or significant changes in direction, which have the same detrimental effect of causing some of the bubbles to burst.

[0005] A typical foam projection nozzle is described in document WO 2005 / 025755 A; it comprises a jet of the liquid to be foamed, followed by a nozzle with multiple fine openings that divide the jet and thus form the foam just as it exits the device. However, it is not certain that this device allows for the production of high-expansion foams, or even that the expansion can be regulated or stabilized. In particular, the upstream section with the wide opening of the nozzle allows the liquid to pass through without a change of state, and the foam formation depends solely on the downstream section with fine openings, which is excluded from the invention.

[0006] US5344079 A describes a different device, where the foam projection device terminates at a single, wide-opening ejection nozzle. An ejection nozzle with such an opening is found in the invention. However, the nozzle opening in this document is still intended to create the foam itself, thus also producing the mixture of the gaseous and liquid fractions of the foam. The device further includes, just upstream of the nozzle, a spin passage device for the liquid, 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 rebound of the droplets off the wall of the opening. In the invention, the ejection opening and a mixer are adjacent but separate, so that a suitable mixer can be used to provide high expansion ratios to the foams.

[0007] US4421788 A describes a foam spray device comprising a single wide-aperture nozzle and a mixer (18) upstream of the nozzle, from which it is separated by a flexible lance (22). The device is not intended for the production of high-expansion foams (on the contrary, a high-density foam appears to be desired), and a significant decrease in foam expansion is expected as the foam flows through the lance. Finally, the nozzle has a conical shape that imposes a significant constriction on the foam flow just before the opening, which may also impair expansion.

[0008] One object of the invention is to project foams, in particular special high viscosity foams, which retain a satisfactory degree of expansion at the exit of a lance of a projection device, without being degraded on the way 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 out of the nozzle and the rest of the apparatus.

[0010] In general form, the invention relates to a foam projection nozzle, through which is a passage having a central axis corresponding to a direction of flow of the foam or of foam constituents from an upstream to a downstream, comprising a nozzle body encompassing a mixer of the foam constituents, forming the foam, and a tip downstream of the mixer, the tip containing an 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 main opposite sides connected to each other by short rounded connecting sides than the main sides, the main sides being everywhere separated by at least 2.5mm; the end of the passage widening towards the downstream direction of flow, at angles of no more than 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 point of connection, in a cross-section of the bore.

[0011] It has been observed that this particular nozzle opening design prevents significant degradation of viscous foams passing through the nozzle. This is achieved by limiting bubble bursting thanks to the sufficient width available for their passage and the gradually widening shape of the opening, which allows the foam to progressively transition to free-flowing conditions in the outside atmosphere. It has also been observed that the direct or nearly direct connection between the mixer and the ejection opening, with the mixer integrated into the nozzle body of the foam ejector in a way that minimizes foam travel distances to the outlet, helps maintain a high degree of foam expansion within the mixer. The same advantage can be attributed to the complete or near absence of flow cross-sectional variations up to the nozzle opening.

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

[0013] This is particularly advantageous for obtaining high-expansion foam: The mixer comprises a cage bounded by a tube, two obstacles at two opposite ends of the tube arranged in succession along the central axis, and at least one solid body freely movable in the cage and held 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 for a potentially large flow rate of foam, is better if the tubular part has a thread for connecting to a supply conduit 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 external 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 thereof, given for purely illustrative purposes: there Figure 1 is a diagram of a foam projection device 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 tip 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 as seen 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 apparatus comprises a reservoir 1 of liquid foaming solution, a compressed air cylinder 2, 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), and a frame 8. A first conduit 11 connects an outlet port of the reservoir 1 and passes through the pneumatic pump 5. A second conduit 14 connects an outlet port of the cylinder 2 to the main pressure regulator 4, then joins the first conduit 11 at a junction 15 downstream of the discharge port of the pneumatic pump 5. The air flowing in the second conduit 14 is slightly compressed at a constant pressure (7 bar, 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 allows the gas pressure at the outlet of the cylinder 2 to be measured and the filling of the latter to be assessed.

[0018] The frame 8 supports the reservoir 1, the cylinder 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 part of a backpack worn by the device operator; it can also be a rolling cart, for example. The foam ejection nozzle 7 is not attached to the frame 8, but is located at the end of a flexible lance 21, held by the operator. The lance 21 connects to the first conduit 11 and the second conduit 14 at the junction 15. The mixer 6, according to the invention, is adjacent to the nozzle 7 and the foam ejection opening. It is even located within a nozzle body 22 described below; it is not attached to the frame 8, and it is situated downstream of the entire lance 21.

[0019] According to the figure 2 The nozzle body 22, which includes the nozzle 7, is a single, cylindrical unit, traversed through and through by a passage 23. The passage 23 comprises a main portion, a cylindrical bore 24, immediately followed downstream by one end of the more complexly shaped passage 25, which will be described later, and constitutes the ejection opening of the nozzle 7. The bore 24 is formed in a tubular portion of the nozzle body 22. The mixer 6 is positioned within the bore 24 and occupies all or part of its length. The foam or its constituents flow through the passage 23 in a left-to-right direction over 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 includes at its downstream end a tip 26, which contains the end of the passage 25. The foam is ejected from the nozzle 7 by the tip 26 forming a plume 27 preferably in the shape of a flattened cone, suitable for covering large widths of surfaces to be treated by flaring outwards.

[0020] Mixer 6 is shown in the figure 3 It comprises two flat grids 28 following one another in the bore 24 and occupying its entire cross-section, two sealing gaskets 29 to which the grids 28 are respectively fixed and which serve as support for them against the wall of the bore 24, and rigid spherical balls 30 free to move between the grids 28. It has been found that the balls 30, being both mobile and few in number, able to move independently of each other and continuously during manufacturing, without forming superimposed layers which would reduce their mobility, were able to efficiently produce viscous foams thanks to the low pressure losses and the intensity of the agitation which they produce in the liquid constituents.The sealing gaskets 29 serve to hold the grids 28 in place and to form between them a cage 31, further delimited by the wall of the bore 24, and in which the balls 30 are retained, 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 inside of the cage 31. The mixer 6 thus defined can occupy all or almost all of the volume of the bore 24, that is to say that the upstream grid 28 is close to the inlet of the bore 24, and the downstream grid 28 rests against the rear face of the nozzle 26. The mixer 6 and the ejection opening are then directly connected.

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

[0022] There figure 5 is a cross-sectional representation of the nozzle body 22, which fully illustrates the passage 23 and notably 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 tip 26 in particular by means of the figure 6 The end of passage 25 is approximately conical, widening continuously downstream of the flow direction with a moderate slope: its wall forms angles of less than approximately 30° with the central axis XX, as shown in the diagrams. figures 2 And 5The cross-sections (perpendicular to the direction of fluid flow in nozzle 7, along the central axis XX) of the end of passage 25 are oblong, that is, highly 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, through which the end of the passage 25 connects to the bore 24, and the outline of an external cross-section Se, through which it opens onto a front face 37, directed towards the surface to be covered with foam, of the nozzle 7. Cross-sections such as Si and Se (with progressive variations in shape for intermediate cross-sections) are generally composed of two main sides Li or Le, with 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 either purely curvilinear, as is the case for the main sides Li of the inner cross-section Si, or partially or completely rectilinear, as is the case for the main sides Le of the outer cross-section Se. Opposite main sides are always spaced more than approximately 2.5 mm apart (here F = 3 mm to E = 5 mm at the ends and center of the lateral sides Li of the inner cross-section Si, which is the narrowest), in order to provide sufficient passage width for the foam bubbles and to prevent, as far as possible, them from bursting when leaving the nozzle 7. Furthermore, the contour of the inner cross-section Si is geometrically inscribed, that is, included, within the contour of the bore 24.

[0025] According to the invention, the foam forms near the outlet of the device through the mixing of air and the foaming solution as it passes through the mixer 6. The grids 28, and especially the beads 30, are very effective in producing a high-expansion foam, i.e., one with a low liquid fraction. The end of the passage 25 in the nozzle 26 has a shape that produces the flattened and flared plume 27, thus easily covering entire sections of the surface with a simple sweep of the lance 21. It also has an opening width and direct connection with the orifice 24 that greatly reduces the proportion of foam bubbles that burst after exiting the mixer 6 and cause foam degradation by increasing its liquid fraction.The high expansion of the foam, favored by the mixer 6 and maintained by the nozzle 7 as well as by the short path of the foam to the exit of the nozzle 26, is sought among other things for viscous foams with high expansion.

[0026] Some additional details, of a concrete nature, are given below to describe more fully a particular example of this implementation of the device and its performance. Mixer 6: Cage diameter and length 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: Outer diameter Ø and length: 35 mm and 100 mm; Drilling 24: Diameter and length: 25 mm and 80 mm; Cross-sections of the drilled end ( 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; Coating sprayed onto a vertical surface: 10m², 1cm thick, in 120s; sliding speed less than 1cm / min. When the foam is used to fill a volume, the foam retention time is at least 120min; Expansion ratio of the resulting foam: approximately 16.7 (approximately 100 liters of foam produced for every 6 liters of foaming solution consumed).

[0027] A similar test with another nozzle, belonging to the known art, produced a foam of much lower expansion.

[0028] The balls 30 could be replaced by another freely movable solid body in the cage 31, and their number could also be different, only one solid body being possible.

[0029] And the shapes of the 26 tip can also differ from those offered here, the advantageous designs therefore including a sufficient opening width to avoid the bursting of too many bubbles and moderately progressive evolutions of opening sections.

Claims

1. Nozzle for spraying a foam, traversed by a passage (23) having a central axis (X-X) corresponding to a flow direction of the foam or foam constituents from upstream to downstream, comprising a nozzle body (22) containing a mixer (6) of the foam constituents, forming the foam, and a nozzle tip (26) downstream of the mixer, the nozzle tip containing one end (25) of the passage (23), belonging to the passage (23), downstream of the flow direction; the end (25) of the passage (23) having cross-sections, perpendicular to the central axis (X-X), comprising two main sides (Li, Le) opposite one another and connected to each other by rounded connecting sides (Ri, Re) shorter than the main sides, the main sides being at least 2.5 mm apart throughout; the end of the passage (25) widening downstream of the direction of flow, at angles of at most 30° between a wall of the end of the passage and the central axis (X-X); 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 connection point, in a cross-section of the bore (24).

2. Foam spray nozzle according to claim 1, characterized in that the main sides (Li) of at least some of the cross-sections of the end of the passage (25) are curved and diverge from one another towards the centers of the main sides, where they are at least 4 mm apart.

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

4. Foam spray nozzle according to any one of claims 1 to 3, characterized in that the 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 (X-X), and at least one solid body (30) freely movable in the cage and retained in the cage by the obstacles.

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

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

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

8. Foam spray nozzle according to any one of claims 1 to 7, characterized in that the passage (23) has, at one end, a thread (36) for connecting to a duct (33) supplying the foam constituents.

9. Application of the nozzle according to any one of the preceding claims to methods for spraying viscous foams onto external surfaces.

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