EP2907581B1

EP2907581B1 - Swirl device for nozzles

Info

Publication number: EP2907581B1
Application number: EP14154925.3A
Authority: EP
Inventors: Federico Tonini
Original assignee: PNR Italia Srl
Current assignee: PNR Italia Srl
Priority date: 2014-02-12
Filing date: 2014-02-12
Publication date: 2017-12-27
Anticipated expiration: 2034-02-12
Also published as: EP2907581A1; WO2015121354A1

Description

The present invention relates to a device for imparting a swirling motion to the particles of a liquid, and specifically relates to a swirl device, according to the preamble of claim 1. Document DE 3718971 A1 discloses the preamble of claim 1. The different types of spray nozzles can be classified based on different features, the most important of which is the type of spray produced. Based on the shape of the spray, spray nozzles are divided into flat spray nozzles, in which the drops delivered from the orifice form a fan-shaped spray, hollow cone nozzles, in which the drops delivered from the orifice form a conical spray, where the drops are distributed only on the outer surface, and full cone nozzles, in which the drops delivered from the orifice of the nozzle form a cone with a well-defined opening angle. In this last case, the inner volume of the conical spray is filled by the drops in movement according to a more or less uniform distribution. These types of spray nozzles can be applied to various industrial sectors, such as for painting, for washing materials, for cooling surfaces, for waste treatment and for a variety of other applications.
Generally, a full cone spray nozzle is characterized by two components: the swirl chamber of the fluid and the swirl device. The swirl chamber represents the body of the nozzle comprising a cavity inside which the fluid assumes a rotary motion, while the swirl device, which is coupled to this chamber, performs the function of directing, through its geometry, the drops of the fluid so that upon delivery from the nozzle they assume the form of a cone-shaped spray.
More specifically, a spray of this type is obtained by conveying toward the outlet orifice of the nozzle a vein of fluid in rotation that moves along a duct generally cylindrical in shape and rotates about the axis of the duct. The fluid flows through a swirl device that imparts a given rotation speed thereon.
Based on the features of the swirl device, the fluid delivered from the orifice, subjected to centrifugal force, is divided into drops that will uniformly fill the inner volume of the cone that defines the delivered spray. Naturally, in order to obtain uniform filling of drops inside the cone, the drops in proximity of the rotation axis of said cone must be subjected to a centrifugal force of a lesser value with respect to the force to which the drops in proximity of the outer edges of the cone are subjected. Ideally, the centrifugal force acting on the delivered spray must vary linearly, decreasing until it reaches zero on the axis of the cone.
Swirl devices of various types are known in the prior art. One of these is normally produced by a cylindrical body, i.e. by a disc, of diameter variable according to the dimensions and hence the flow rate of the nozzle, provided with at least two helical inclined slots that oblige the fluid particles to assume a rotary motion. Figs. 1A-1C show a prior art swirl device 100 viewed from three different angles, from above (Fig. 1A), in an axonometric view (Fig. 1B) and in a side view (Fig. 1C). From the figures it can be noted that this swirl device 100 is provided with four peripheral slots 101 that define four ducts that extend longitudinally along the cylindrical body. In this case, the slots 101 have been produced using milling processes. In addition to the lateral slots 101, a central hole 102 is also provided. The purpose of this hole 102 is essentially to enable a part of the fluid to interfere with the fluid delivered from the lateral ducts 101 so as to have a slight rotation speed also in the center of the swirl chamber.
In structures of this type, the presence of a central hole is fundamental. In fact, without this hole the spray produced would be seriously lacking in drops of fluid in the central area thereof.
Although simple and functional, swirl devices of this type have some drawbacks.
Firstly, the presence of a central hole produced in this way could cause malfunctioning of the device if this hole were to become clogged. In fact, the use of highly viscous liquids, such as some paints, over time could cause partial or total clogging of the hole due to the accumulation of liquid particles therein. Naturally, this would have a negative impact on the distribution of the drops of fluid delivered from the nozzle, which would consequently lack uniformity. Moreover, as clearly shown in Fig. 1C, this type of swirl device 100 comprises a profile 103 with undercut with regard to lateral ducts 101. In other words, the lateral ducts 101 have an open rectilinear profile that is not parallel to the axial direction of the swirl device and the fluid particles that enter them are unable to pass through the swirl device parallel to the axis of the cylindrical body without necessarily colliding with the inclined walls 104 of these ducts 101. In this way, the fluid particles are obliged to flow a given direction in inside the lateral ducts 101 so as to determine a discrete distribution of the fluid delivered, through the central hole 102 or through the lateral ducts 101.
Moreover, it should also be noted that the presence of profiles 103 with undercut precludes the use of production processes other than milling, such as plastic injection molding or lost wax molding. Therefore, swirl devices of this type are not suitable for production in large batches and at limited costs, as required by industry today, as production using milling processes does not adapt well to being performed using automated machinery and on materials other than metals.
Moreover, as the lateral ducts must necessarily be obtained by milling, they will have a square or rectangular section. Further, as their total open surface area must necessarily have the same order of magnitude as the delivery orifice, their number will be limited by considerations of proportionality between the volume of the fluid rotating in the chamber and the volume delivered from the orifice. Consequently, only a discrete part of the outer fraction of the fluid present downstream of the swirl device will be accelerated in rotary motion, thus causing a substantial lack of uniformity in the values of the rotational speed in each cross section of the swirl chamber downstream of the swirl device, such as to generate strong turbulence, further increased by the injection of a vein of fluid through the central hole of the swirl device.
An object of the present invention is to overcome the aforesaid problems of prior art swirl devices and to provide device that is easy to produce in large batches and produces a full cone fluid spray having the greatest possible uniformity.
Another object of the present invention is to provide a swirl device that can be made of plastic material, through a molding process.
Yet another object of the present invention is to provide a method for producing a swirl device made of plastic material by molding.
These objects are achieved by a device for imparting a swirling motion to the particles of a fluid comprising the features of claim 1, and by a method for producing said device comprising the features of claim 13.
The device according to the present invention comprises a cylindrical body having a circular base. This cylindrical body, or this disc, will thus have a first base and a second base, opposite the first, circular in shape. On the first base, the cylindrical body comprises a plurality of openings arranged circularly around its longitudinal axis and defining a plurality of inlet openings. Each inlet opening delimits at least one duct that extends longitudinally through the cylindrical body to an opening arranged on the second base and that define an outlet opening. The fluid particles flow through this duct so that, upon delivery from the duct, they assume a rotary motion such as to form a cone-shaped spray. According to the present invention, the duct is delimited by at least one plane, inclined with respect to the longitudinal axis of the cylindrical body, which extends from the inlet opening, on the first base, to the outlet opening, on the second base, and adapted to divert the fluid particles with respect to the axial direction. In particular, the end of this inclined plane at the outlet opening is contained inside the perimeter of the inlet opening that is projected orthogonally on the second base so that said duct comprises a profile with no undercut.
According to the present invention, the full cone spray is guaranteed by the structure of the ducts associated with the plurality of openings, as the respective inclined planes assume a helical configuration about the axis of the cylindrical body.
Moreover, the particular configuration of the ducts for directing the fluid particles according to the present invention ensure that the swirl device has no profiles with undercut.
In fact, if the inclined plane of the duct comprises one end at the outlet opening that is contained inside the perimeter of the inlet opening projected orthogonally on the base containing this outlet opening, this means that a profile with no undercut is created between the inlet opening and the outlet opening. In other words, the fluid particles are not obliged to flow through specific ducts but can also find alternative paths. In principle, some of the fluid particles are able to pass through the cylindrical body longitudinally without colliding with any inclined plane. This leads to improved operation of the device. Unlike swirl devices described in the prior art, the distribution of the fluid delivered from the device is not discrete but continuous, thus creating a more uniform spray. Moreover, this considerably reduces the effects of turbulence at the outlet, which, as is known, causes a general loss of rotational energy of the particles, reducing the efficacy of the spray nozzle with which the swirl device is coupled.
The absence of profiles with undercut also makes it possible to use production processes other than milling. In fact, the device according to the present invention can be produced through a molding process, for example plastic injection molding. This has the enormous advantage of being able to produce this device using automation and in large batches, enabling production costs to be reduced. Moreover, the use of molding processes means that the device is easier to reproduce.
Further, the possibility of using molding processes to produce this device considerably increases design and production flexibility of ducts for diverting liquid particles. In fact, the geometry and the magnitude of the ducts are not limited by the instruments used to produce them - such as rotary milling tools - and therefore the geometry of the device can be more easily varied, so as to obtain the desired distributions with any geometry of the swirl chamber downstream.
The device according to the present invention can be produced using different materials, such as plastic materials (PVC, PTFE, thermoplastic and the like).
The device according to the present invention comprises a maximum diameter of a value that depends on the dimensions of the nozzle and which, by way of example, can be between 20 mm and 600 mm.
According to a preferred embodiment of the present invention, the surface area of the inclined plane in proximity of the center of the cylindrical body, i.e. of its rotational axis, is smaller than the surface area of the inclined plane in proximity of the edge of said cylindrical body. In this way, it is possible to obtain a more uniform distribution of the fluid particles delivered from the device and hence from the spray nozzle. The role of the inclined plane is to divert the fluid particles that collide with it, supporting them. In other words, the surface area of this inclined plane offers a support that "thrusts" the particles, so that they assume a certain speed about the axis of the cylinder. The larger the surface area of the plane is, the greater the thrust, and consequently the speed of the particles, will be. According to the features of the device of the present invention, the particles diverted in proximity of the cylindrical axis will therefore have a lower speed than the speed of the particles diverted in proximity of the edge of the cylinder. In this way, when delivered from the orifice of the spray nozzle, the fluid particles will fill, with the greatest possible uniformity, the inside of the cone-shaped spray. It is interesting to note that through an appropriate geometrical configuration of the device, i.e. of the surface area of the inclined plane or of the inclined planes that define the ducts inside the cylindrical body, it is possible to obtain homogeneous and uniform distribution of the fluid particles inside the cone delivered even without a central hole in the cylindrical body.
According to another preferred embodiment of the present invention, the inclined plane forms an angle of between 60 degrees and 20 degrees, preferably 40 degrees, with the longitudinal axis of the cylindrical body. Through this inclination, the particles are thrust optimally toward the outlet of the device and therefore of the orifice of the spray nozzle, it being possible to obtain different peripheral speeds of the vein of fluid and therefore different opening angles of the cone-shaped spray.
According to a further preferred embodiment of the present invention, the area delimited by the inlet opening on the first base is different with respect to the area delimited by the outlet opening on the second base. In particular, the area delimited by the inlet opening on the first base can be larger than the area delimited by the outlet opening on the second base. In this way, it is possible to obtain greater control of the delivery direction of the fluid particles. It should be noted that a configuration of this kind cannot be obtained through currently used milling processes or the like.
According to another preferred embodiment of the present invention, the width of the inlet opening in proximity of the center of the cylindrical body, i.e. of its rotational axis, is smaller than the width of the inlet opening in proximity of the edge of said cylindrical body. This embodiment combines perfectly with the one described previously, according to which the surface area of the inclined plane decreases moving away from the edge toward the center of the cylindrical body. In fact, in this way, it is possible to further control the speed of the particles being delivered so as to obtain uniform filling of the cone-shaped spray. According to a preferred embodiment of the present invention, the duct is delimited by a second plane, opposite the inclined plane and not parallel thereto. This second plane can be parallel to the axis of the cylindrical body or oblique with respect thereto and extends, just as the inclined plane, from the inlet opening on the first base to the outlet opening on the second base. Preferably, this second plane converges toward the inclined plane opposite it, so that the point of convergence lies outside the cylindrical body.
According to another preferred embodiment of the present invention, the cylindrical body is provided with a raised edge, or collar, arranged along the outer circumference of the first base of the cylindrical body. In this way, it is possible to couple, or mount, the device with/on the body of the nozzle with greater precision, without requiring to modify this latter. Moreover, with this collar it is possible to obtain a standard device that can be mounted on any type of nozzle, regardless of the different geometrical configurations of the inlet and outlet openings and of the ducts inside the cylindrical body. This raised edge can comprise a value in length of between 10 mm and 4 mm, preferably 5 mm.
According to a further preferred embodiment of the present invention, a single opening extends along the width of a radius of the cylindrical body. In particular, several openings can be produced around the axis of the cylinder, but with a single opening that extends along the radius of the cylinder, for example in the form of a triangle, or of a segment, with the tip converging into the tip of the triangle that defines a second opening opposite thereto. In this way, the fluid particles can be diverted continuously from the edge to the center of the device and the variation of the centrifugal force takes place more uniformly to approximate a linear variation.
According to a preferred embodiment of the present invention, the inclined plane is defined by a fin that extends from the edge toward the center of the cylindrical body and in the lower part is tapered toward the center of said cylindrical body. In this way, the absolute speed of the fluid particles along the radius decreases moving from the edge toward the center of the cylindrical body, while the angular speed remains unchanged.
In a particular configuration, the maximum length of the fin is less than the radius of the cylindrical body. In this way, a central hole is defined at the center of the cylindrical body. However, unlike devices known in the prior art, this central hole is much less subject to clogging as it is in communication with the duct defined by the fin. Alternatively, at least two openings can extend in width along a radius of the cylindrical body. For example, several openings can be provided along a single radius, so as to define several ducts along the same radius. In this way, it is possible to design the device more easily according to the different distribution requirements of the spray of fluid. For example, it would be possible to design a device in which inlet openings of different width are arranged along circumferences of different radii, where the openings in proximity of the edge will naturally have a greater width than those in proximity of the center, i.e. of the rotational axis of the cylindrical body. At the same time, it would be possible to produce a device with a plurality of openings so close to the center of the cylindrical body that the presence of a central hole is no longer necessary.
The great flexibility of design of devices of this type makes it possible to produce structures that could not be obtained with other processes. Besides being able to produce a plurality of openings and consequently of ducts of different magnitude and geometry inside the same device as described above, it would also be possible, for example, to produce a device with a limited number of openings, for example only one or two, each of which defines a plurality of ducts with a same or different geometry arranged circularly about the rotational axis of the device.
The method according to the present invention enables production of the device according to any one of the preceding configurations through injection molding of plastic materials, through lost wax investment casting or through a metal injection molding process. As mentioned previously, this has the advantage of being able to produce the swirl device using automation and in large batches, enabling a reduction in production costs. Moreover, the use of molding processes means that the device is more easily reproduced. These and other aspects of the present invention will be more apparent in the light of the following description of some preferred embodiments described below.

Figs. 1A-1C.: show a schematic representation of a prior art swirl device viewed from above (1A), obliquely from the side (1B) and in cross section (1C);
Figs. 2A-2D.: shows a schematic representation of a device according to a preferred embodiment of the present invention viewed from above (2A), in a perspective view (2B), from below (2C) and in a cross section along the trajectory A-A of Fig. 1C (2D) ;
Fig. 3: shows a schematic representation of a device according to a variant of the embodiment of the Figs. 2A-2D; and
Figs. 4A-4E.: show a schematic representation of a device according to another preferred embodiment of the present invention viewed from above (4A), in a perspective view (4B), according to a detail of Fig. 1B (4C), from below (4D) and in side view (4E).

Figs. 2A and 2B show a schematic representation of a device 10 according to a preferred embodiment of the present invention viewed from above and in a perspective view. The device 10 has the form of a cylindrical body having a first circular base b1 and a second circular base b2. On the first base b1, the device 10 comprises a plurality of inlet openings 11 arranged circularly about the rotational axis Ar of the device 10 and equidistant from one another, each in the form of a triangular segment with the tip facing the axis Ar. Each opening 11 delimits a duct 12 that extends from the inlet opening 11 to the outlet opening 13. In particular, each duct 12 comprises an inclined plane 14 the purpose of which is to divert the fluid particles entering through the inlet opening 11 and delivering them through the outlet opening 13 imparting thereon a rotary motion about the axis Ar. The inclined plane 14 of each duct 12 comprises a first end 15 at the inlet opening 11, on the first base b1 and a second end 16 at the outlet opening 13 on the second base b2. As can be noted from Fig. 2A, by observing the device orthogonally from above, part of the outlet opening 13 is visible from the inlet opening 11. In other words, each duct 12 comprises a profile with no undercut. In fact, if the perimeter of the inlet opening 11, in the shape of a triangular segment, is projected orthogonally on the second base b2, the end 16 of the inclined plane 14 is contained inside this perimeter.
Moreover, Figs. 2A-2D show that the surface area of the inclined plane 14 in proximity of the center of the device 10, i.e. of the axis Ar, is smaller than the surface area in proximity of the edge of the device 10. More specifically, the inclined plane 14 is defined by a fin that extends from the edge toward the axis Ar and in the lower part is tapered toward the axis Ar. In fact, as can be noted from Figs. 2C and 2D, which show the device 10 viewed from below, the length of the end 16 on the base b2 is less than the length of the end 15 on the first base b1. Opposite the inclined plane 14, the device 10 comprises for each duct 12 a second inclined plane 17 (visible in Fig. 2B). The second inclined plane 17 also extends from the inlet opening 11 on the first base b1 to the outlet opening 13 on the second base b2 defining the duct 12 and has the purpose of directing the fluid particles outside the device 10 with greater precision. The second inclined plane 17 is not parallel to the inclined plane 14, or parallel to the axis Ar, and converges toward the inclined plane 14 in a point outside the device 10 so that an outlet opening 13 having a smaller surface area than the inlet opening 11 is determined. Moreover, Figs. 2A-2B show that the device 10 comprises a central opening 18 and that the inlet openings 11 converge into this central opening 18.
Fig. 2D represents a cross section along the straight line A-A of the device 10 shown in Fig. 2C. From this figure it can be seen that the inclined plane 14 forms an angle of around 40 degrees with respect to the axis Ar.
Fig. 3 represents a variation of the device 10 shown in Figs. 2A-2D. This device 10' comprises, in addition to all the features of the device 10, a raised edge 19 that extends in height from the first base b1.
Figs. 4A and 4B show a schematic representation of a device 10 according to a second preferred embodiment of the present invention viewed from above and obliquely from the side.
The device 20 has the form of a cylindrical body having a first circular base b1 and a second circular base b2. On the first base b1, the device 20 comprises a plurality of inlet openings 21, 21', 21" arranged circularly about the rotational axis Ar of the device 20. The inlet openings 21, 21', 21" have a rectangular shape on the base plane and are arranged along three different circumferences. In particular, the surface area of the inlet openings 21 in proximity of the edge of the device 20 is larger than the surface area of the inlet openings 21" in proximity of the axis Ar, while the surface area of the inlet openings 21' arranged at a distance from the axis Ar between the openings 21 and 21" is larger than the surface area of the inlet openings 21" but smaller than the surface area of the inlet openings 21. Likewise, the surface area of the outlet openings 23 in proximity of the edge of the device 20 is larger than the surface area of the outlet openings 23" in proximity of the axis Ar, while the surface area of the outlet openings 23' arranged at a distance from the axis Ar between the openings 23 and 23" is larger than the surface area of the outlet openings 23" but smaller than the surface area of the outlet openings 23 (Fig. 4D).
Each opening 21, 21', 21" respectively delimits a duct 22, 22', 22" that extends from the inlet opening 21, 21', 21" to the outlet opening 23, 23', 23''. In particular, each duct 22, 22', 22" comprises an inclined plane 24, 24', 24" the purpose of which is to divert the fluid particles entering through the inlet opening 21, 21', 21" and deliver them through the outlet opening 23, 23', 23" imparting a rotary motion thereto about the axis Ar. The inclined plane 24, 24', 24" of each duct 22, 22', 22" comprises a first end 25, 25', 25" at the inlet opening 21, 21', 21", on the first base b1 and a second end 26, 26', 26" at the outlet opening 23, 23', 23''. As can be noted from Fig. 4A, by observing the device orthogonally from above, part of the outlet opening 23, 23', 23" is visible from the inlet opening 21, 21', 21". In other words, each duct 22, 22', 22" comprises a profile with no undercut. In fact, if the perimeter of the inlet opening 21, 21', 21", rectangular in shape, is projected orthogonally on the second base b2, the end 26, 26', 26" of the inclined plane 24, 24', 24" is contained inside this perimeter.
Moreover, Figs. 4A-4D show that the surface area of the inclined plane 24" in the ducts 22" in proximity of the center of the device 20, i.e. of the axis Ar, is smaller than the surface area of the inclined plane 24 in the ducts 22 in proximity of the edge of the device 20 and that the surface area of the inclined plane 24' in the ducts 22' arranged at a distance from the axis Ar between the ducts 22 and 22" is larger than the surface area of the inclined plane 24" in the ducts 22" but smaller than the surface area of the inclined plane 24 in the ducts 22.
Opposite the inclined plane 24, 24', 24", the device 20 comprises a second inclined plane 27, 27', 27" for each duct 22, 22', 22" (visible in Fig. 4B). The second inclined plane 27, 27', 27" also extends from the inlet opening 21, 21', 21" on the first base b1 to the outlet opening 23, 23', 23" on the second base b2 defining the duct 22, 22', 22" and has the purpose of directing the fluid particles outside the device 20 with greater precision. The second inclined plane 27, 27', 27" is not parallel to the inclined plane 24, 24', 24" and is parallel to the axis Ar. More specifically, the plane 27, 27', 27" converges toward the inclined plane 24, 24', 24" in a point outside the device 20 so as to determine an outlet opening 23, 23', 23" having a smaller surface area at the inlet opening 21, 21', 21''.
As can be noted from Figs. 4A-4D, the device 20 does not comprise any central hole. The function of the central hole is replaced in this case by the plurality of openings 21" which are arranged circularly at a distance in close proximity of the axis Ar.
Fig. 4C shows a detail of the device 20 and in particular of the ducts 22 in proximity of the edge of the device 20. This detail clearly shows the different magnitude between the inlet opening 21 and the outlet opening 23, and the profile with no undercut of the duct 22. Moreover, it can be noted how, while the ducts 22' and 22" are closed on four sides, the ducts 22, i.e. those in close proximity to the edge of the device 20, are delimited by three planes and are open on the outermost side.

Claims

Swirl device (10; 10'; 20) for nozzles adapted to impart a swirling motion to the particles of a fluid,
comprising a cylindrical body having a first circular base (b1) and a second circular base (b2) and comprising a plurality of openings arranged circularly about the longitudinal axis of the cylindrical body (Ar) on the first base (b1) that define a plurality of inlet openings (11; 21, 21', 21") separate from each other, wherein each inlet opening (11; 21, 21', 21") delimits at least one duct (12; 22, 22', 22") that extends longitudinally through the cylindrical body to a corresponding opening arranged on the second base (b2) that defines an outlet opening (13; 23, 23', 23") and through which the fluid particles flow so that, at the outlet of the duct (12; 22, 22', 22''), they assume a rotary motion such as to form a cone-shape spray,
characterized in that
each of said duct (12; 22, 22', 22") is delimited by at least one inclined plane (14; 24, 24', 24") with respect to the longitudinal axis (Ar) of the cylindrical body that extends from the inlet opening (11; 21, 21', 21") to the outlet opening (13; 23, 23', 23'') and adapted to divert the fluid particles, wherein the end (16; 26, 26', 26") of said inclined plane (14; 24, 24', 24") at the outlet opening (13; 23, 23', 23") is contained inside the perimeter of the inlet opening (11; 21, 21', 21") projected orthogonally on the second base (b2) and wherein the inclined plane (14) is defined by a fin that extends from the edge toward the axis (Ar) of the cylindrical body and in the lower part is tapered toward the axis (Ar) of said cylindrical body, so that said duct (12; 22, 22', 22") has no undercut.
Device (10; 10'; 20) according to claim 1, wherein the surface area of said inclined plane (14; 24, 24', 24") in proximity of the axis (Ar) of the cylindrical body is smaller than the surface area in proximity of the edge of said cylindrical body.
Device (10; 10'; 20) according to any one of the preceding claims, wherein the inclined plane (14; 24, 24', 24") forms an angle of between 60 and 20 degrees, preferably 40 degrees, with the longitudinal axis (Ar) of the cylindrical body.
Device (10; 10'; 20) according to any one of the preceding claims, wherein the area delimited by the inlet opening (11; 21, 21', 21") on the first base (b1) differs with respect to the area delimited by the outlet opening (13; 23, 23', 23") on the second base (b2).
Device (10; 10'; 20) according to claim 4, wherein the area delimited by the inlet opening (11; 21, 21', 21") on the first base (b1) is larger than the area delimited by the outlet opening (13; 23, 23', 23") on the second base (b2).
Device (10; 10'; 20) according to any one of the preceding claims, wherein the width of the inlet opening (11; 21, 21', 21") in proximity of the axis (Ar) of the cylindrical body is smaller than the width of the inlet opening (11; 21, 21', 21") in proximity of the edge of said cylindrical body.
Device (10; 10'; 20) according to any one of the preceding claims, wherein the duct (12; 22, 22', 22") is delimited by a second plane (17; 27, 27', 27"), opposite the inclined plane (14; 24, 24', 24") and not parallel thereto.
Device (10') according to any one of the preceding claims, wherein the cylindrical body is provided with a raised edge (19) arranged along the outer circumference of the first base (b1) of the cylindrical body.
Device (10; 10') according to one of claims 1 to 8, wherein the maximum length of the fin is less than the radius of the cylindrical body.
Device (20) according to any one of claims 1-9, wherein at least two openings (21, 21', 21") extend in width along a diameter of the cylindrical body.