RU2658522C1 - Device for cleaning surfaces - Google Patents

Abstract

FIELD: machine building.

SUBSTANCE: invention relates to apparatus for cleaning surfaces. Apparatus comprises a housing including a reservoir for abrasive material and a first channel for a compressed air flow that passes close to the said reservoir along the entire length of the said reservoir. Apparatus comprises a mixing valve connected to the said reservoir for mixing the said abrasive material with the said compressed air.

EFFECT: long-lasting and constant spraying of the abrasive material is ensured.

8 cl, 19 dwg

Description

FIELD OF THE INVENTION

[01] The present invention relates to an apparatus for cleaning metallic and non-metallic surfaces.

State of the art

[02] It is known to use apparatus for cleaning surfaces using a process known as sandblasting.

[03] Sandblasting involves applying a stream of compressed air and abrasive material to the surface to be treated in order to remove the surface layer of the material. Alternatively, sandblasting can be used to create inscriptions or images on marble, stone, wood or glass.

[04] Conventional cleaning apparatuses include an abrasive tank connected through a mixing valve to a mixing chamber into which a predetermined stream of compressed air, typically produced by a compressor, enters. A spray gun equipped with control means for spraying through an appropriate nozzle a stream of air and abrasive material is connected to the mixing chamber through an appropriate channel.

[05] US 2014/0065933 describes a type of cleaning apparatus comprising a hopper connected at its apex to a skeleton for containing sand material. At the bottom of the hopper is a mixing chamber designed to receive sand material and air. A vertical air access channel is inserted into the chamber, connected to an air control system. The chamber is connected via an outlet channel to a spray gun in such a way as to allow passage of air and sand. The channel for water supplied by means of a suitable pump is also connected to the gun in order to provide a spray of air, sand and water through a nozzle located at one end of the spray gun.

[06] WO 2008/035236 discloses yet another apparatus for cleaning surfaces, comprising a reservoir for storing abrasive material and a channel for the flow of compressed air that passes near the reservoir. A mixing valve is connected to a reservoir for mixing abrasive material with compressed air. This mixing valve is connected to the spray gun with a stream of compressed air and abrasive material through the connecting means.

[07] Cleaning devices typically use flint abrasives. As an alternative, carbonates are used, for example baking soda, which is environmentally preferable and particularly effective, since this leaves the base unchanged, even in the case of polished surfaces.

[08] In addition, cleaning machines are designed to work with baking soda or with mineral materials or plant materials, and since these materials have very different physical, mechanical and particle size characteristics, various types of machines are required.

[09] This is a drawback in practical use and entails high costs for ensuring the functioning of many different devices.

[10] An additional problem in this area is the fact that abrasive material, in particular material consisting of small grains, tends to adhere to the walls of the tank, especially at the edge located around the perimeter of the base of the tank, with subsequent loss of material, and violation of continuity in the flow of abrasive materials dispensed from the tank.

[11] Occlusion was also observed in the mixing valve, making it difficult to continue spraying and lengthening working hours.

Disclosure of invention

[12] The objective of the present invention is to solve these problems, to develop an apparatus for cleaning surfaces that provide continuous and constant spraying of material from a spray gun, whenever necessary, as well as proper storage inside the appropriate tank of the selected material.

[13] Another objective of the present invention is the creation of a portable apparatus for cleaning surfaces, which facilitates the transportation and maneuverability of such an apparatus.

[14] Another objective of the present invention is to create an apparatus that is simple in design and operation concept, certainly reliable in operation, universal in use, and also relatively economical.

[15] The above objectives are achieved, in accordance with the present invention, using the apparatus for cleaning surfaces according to claim 1.

[16] The apparatus for cleaning surfaces includes a mixing valve for mixing abrasive material with a stream of compressed air.

[17] The mixing valve comprises a first inlet for passing a stream of compressed air and a central channel that extends along a central axis and forms a mixing chamber.

[18] The central channel is connected to the first inlet channel.

[19] The mixing valve comprises a second inlet passage for the passage of abrasive material in communication with the central channel. The second inlet channel extends along a longitudinal axis inclined at an acute angle with respect to the central axis of the central channel.

[20] Preferably, such an acute angle is in the range between 30 ° and 45 °.

[21] A mixing valve is connected to the abrasive tank.

[22] The apparatus includes a housing that includes the aforementioned tank, and a first channel for compressed air flow that passes near the tank along the entire length of the tank. The channel is designed to provide a stream of compressed air both directly inside the tank, to enable efficient storage of abrasive material inside the tank, and in the direction of the mixing valve.

[23] The apparatus includes a transport element mounted inside the tank at a lower location, having a hollow conical shape, asymmetric about the axis of rotation.

[24] It is preferable that the conveying element on its upper part forms a collecting hole for the abrasive material contained in the tank, as well as an opposite eccentrically located hole to which said abrasive material is supplied.

[25] Alternatively, the apparatus comprises a second channel that extends inside said tank along a longitudinal direction substantially parallel to said first channel, for supplying compressed air to said second inlet channel of the mixing valve so as to facilitate passage of said abrasive material in a direction mentioned mixing valve and reduce the phenomenon of occlusion.

[26] Preferably, the second channel comprises an inlet portion protruding relative to said abrasive material contained in said reservoir so as to allow inlet of a portion of compressed air into said second channel, and an outlet section inserted in an outlet that is connected to said second inlet a mixing valve channel for supplying compressed air to the second inlet channel.

[27] The spraying means is connected to a mixing valve.

[28] Preferably, the spraying means has at one end a spray nozzle for spraying a stream of compressed air mixed with abrasive material onto the surface to be treated.

[29] Preferably, the spray nozzle comprises a hollow cylindrical body having an inlet and an opposed outlet.

[30] Preferably, the spray nozzle comprises a narrowed cross section, from which the guide channel has a shape that expands in the direction of the final section to allow the flow of compressed air and abrasive material to exit.

[31] Preferably, the guide channel expands at an acute angle with respect to the longitudinal axis of the spray nozzle so as to spray a substantially conical stream having a uniform distribution of abrasive material over the volume of the stream.

[32] Preferably, the acute angle is in the range between 2 ° and 8 °.

[33] Alternatively, the guide channel may have a substantially cylindrical shape, and this configuration allows you to get a stream of exhaust air containing particles of abrasive material having a higher propagation speed.

[34] Preferably, the corresponding shutter member is located coaxially with respect to the second inlet of the mixing valve. The shutter is connected to the control valve, which allows you to adjust, with the use of the control valve connected to it, the cross section of this second inlet channel and, accordingly, the amount of abrasive material mixed with the flow of compressed air.

Description of drawings

[35] The details of the invention should be more apparent from the detailed description of a preferred embodiment of a surface cleaning apparatus according to the invention, illustrated by way of example in the accompanying drawings, in which:

in FIG. 1 shows a perspective view of the apparatus;

in FIG. 2 shows a vertical cross sectional view of an apparatus in accordance with the present invention;

in FIG. 3 shows a bottom view of the apparatus;

in FIG. 4 and 5 show, respectively, sections of the apparatus in planes IV-IV and V-V in FIG. 1 in accordance with the present invention;

in FIG. 6 is a longitudinal sectional view of an apparatus in accordance with an embodiment of the invention;

in FIG. 7, 8, 9 show respectively a perspective view, a side view and a top view of a part of the apparatus shown in figure 6;

in FIG. 10 is a longitudinal sectional view of an apparatus in accordance with another embodiment of the invention at the apparatus loading step;

FIG. 11 is an exploded perspective view of parts of the apparatus shown in FIG. 10;

in FIG. 12 is an exploded perspective view of a mixing valve of an apparatus in accordance with the present invention;

in FIG. 13 is an exploded perspective view of another embodiment of a mixing valve;

in FIG. 14 is an enlarged side view of a detail of the mixing valve shown in FIG. 12 labeled D;

in FIG. 15 is a cross-sectional view of the part shown in FIG. fourteen;

in FIG. 16 is a front view of an apparatus detail;

in FIG. 17 shows a sectional view of the above-mentioned part of the apparatus in the plane XVII-XVII;

in FIG. 18 is a longitudinal sectional view of yet another apparatus part;

in FIG. 19 is a longitudinal sectional view of another embodiment of the above part.

The best example of carrying out the invention

[36] With reference to individual drawings, the apparatus for cleaning surfaces in general, in accordance with the present invention, is indicated by a reference numeral 1.

[37] The apparatus 1 comprises a reservoir 2 for containing abrasive material, closed on top by a lid 3, equipped with a filling hole 4 for filling and further replenishing the material.

[38] Under the lid 3, the spring-loaded door 3 is positioned so as to hermetically close the filler hole 4 and to open the lid 3 exclusively in the direction inward of the tank 2.

[39] The abrasive material used differs depending on the type of work performed. Such a material may be, for example, a mineral or plant material, or a metal based material. Alternatively, carbonates, for example baking soda, can be used. The above materials can be used individually or, alternatively, in combination with each other, thereby creating a mixture. The grain size of the above materials may be larger, 0.06 mm, preferably within the range of 0.06-1.50 mm.

[40] The reservoir 2 comprises a hollow cylindrical body, preferably obtained by extrusion of aluminum, to make the apparatus easier, as well as to facilitate transportation, and possibly also carrying it on the shoulder.

[41] The reservoir 2 is connected in the upper part to the aforementioned lid 3 and in the lower part to the base 6 by means of connecting elements 7 containing a set of connecting rods that extend longitudinally along the entire length of the cylindrical body, so as to form a stable and durable a reservoir 2 capable of withstanding the high pressure reached in that reservoir.

[42] The connecting rods 7 are fixed at one end to the cover 3 using a screw type hook 8.

[43] At the opposite end, the connecting rods have appropriately made sections 7a, for example with threaded ends, for insertion into the corresponding seats 9 of an agreed shape, available on the base 6.

[44] The base 6 has an emptying hole 10 closed with a corresponding emptying valve 11.

[45] The base 6 also includes an outlet 12 for abrasive material and an additional outlet 13 for compressed air.

[46] A pair of legs 14 for supporting the apparatus 1 is connected to the front of the base 6.

[47] On the rear of the base 6, a pair of wheels 15 is mounted so as to facilitate transportation of the apparatus.

[48] The cover 3 and the base 6, for example, are made of a plate, preferably made of aluminum, which gives an additional weight reduction.

[49] The tank 2 has an upper part, designed to contain compressed air, which forms a pressure chamber, so as to exert constant pressure on the introduced material, and, accordingly, carry out proper storage of this material inside the tank 2.

[50] Inside the tank 2, at the bottom, there is a conveying element 16 having the shape of a hollow cone, asymmetric with respect to the axis of rotation.

[51] The transport element 16 at the top has a receiving hole 17 that coincides with the base of the cone, by which the material contained inside the tank 2 is collected and suitably directed to the eccentrically located hole 18 opposite the receiving hole 17 (see Fig. 6- 9). An eccentrically located hole 18 is located above the outlet 12.

[52] Adjacent to the tank 2, the first channel 19 extends along the entire length of the cylindrical body of the tank 2, while the first channel 19 communicates with the pressure chamber and is designed to allow compressed air to pass through.

[53] According to an embodiment of the invention, a second channel 20 is disposed within the tank 2, extending in the longitudinal direction substantially parallel to the first channel 19, for supplying compressed air towards the outlet 12.

[54] In more detail, the second channel 20 is equipped with an inlet portion 200 protruding relative to the abrasive material, that is, one that extends above the abrasive material contained in the tank 2, so as to allow access to a portion of the compressed air supplied to the chamber, inside this second channel 20.

[55] Such a channel 20 has an outlet portion 201 that is inserted into the abrasive outlet 12 to supply compressed air to the abrasive material inlet towards the mixing chamber, as is best explained below, in order to facilitate the passage of material in the aforementioned chamber and reduce the effects of occlusion (see Fig. 10).

[56] The first channel 19 comprises, in the upper part, a first transverse hole 21 s and a second transverse hole 22. A first hole 21 made on the aforementioned pressure chamber connects the outer part to the inside of the tank 2 (see FIG. 4), and the second hole 22 connects the outer part with a separate first channel 19 (see Fig. 5).

[57] In the aforementioned openings 21, 22, respectively, a valve 23 is used for introducing pressurized air both into the channel 19 and into the reservoir 2, as well as a safety valve 24 for venting air in case of overpressure in the reservoir 2.

[58] A configuration is possible in which the first channel 19 is provided with a third hole 25 located beneath the second hole 22, which connects the channel 19 to the outside. An outlet valve 26 is provided at the third opening 25 to provide for the release of pressurized air remaining in the tank 2 when spraying is stopped, as is best explained below (see FIG. 1). Thus, the operating time is reduced, since excess air is quickly discharged from the tank 2, and then the air pressure in the chamber of the apparatus 1, which is at rest, is rapidly restored.

[59] Compressed air is supplied by a compressor, which is not shown in the drawings, through a supply channel 27 communicating in the final section with an anti-condensation filter 28.

[60] An anti-condensation filter 28 is located below the compressed air flow control valve 29, for example of a pneumatic type, which is connected to the connecting channel 30. The connecting channel 30 is connected at the opposite end to a pressure regulator 31 connected to the compressed air valve 23.

[61] Compressed air can reach pressures above 0.2 bar, preferably in the range of 0.2 bar to 10 bar.

[62] The mixing valve 31 is connected to the reservoir 2 and is designed to receive abrasive material, and, in the case of a second channel 20, also pressurized air through the outlet 12, and a separate stream of compressed air through another outlet opening 13 available on the end portion of the channel 19. In particular, the mixing valve 31 is located below the base 6.

[63] The mixing valve 31 includes a housing 32, within which a first inlet channel 33 for the passage of compressed air is formed, communicating via a central channel 34 with a second inlet channel 35 for abrasive material or abrasive material with compressed air.

[64] The central channel 34 extends along the central axis B in the transverse direction, preferably orthogonal to the first inlet channel 33, and forms a mixing chamber for compressed air and abrasive material.

[65] At one end, the central channel 34 forms a connecting portion 36 for connecting the mixing valve 31 using the connecting element 37 to the flexible rubber tube 38.

[66] The connecting portion 36 inside is threaded, while the corresponding portion of the mating form 37a of the connecting element 37 can be inserted by screwing (see Fig. 12, 14e, 15).

[67] Alternatively, the connecting element 37 is attached to the valve 31 through appropriate means for connecting. In particular, the connecting portion 36 has a thread made on its inner surface so that it can be connected by screwing to the aforementioned attachment means 39 (see FIG. 13).

[68] The attachment means 39 includes a female threaded coupler having a shape consistent with the shape of the connecting portion 36, aligned with the connecting member 37, and assembled, abutting against the housing 32 of the mixing valve 31. Between the sleeve 39 and element 37 has a seal 40 inserted, for example, such as an o-ring.

[69] The connecting element 37 is made of a material having high hardness and abrasion resistance, for example, steel or tungsten carbide.

[70] The second inlet channel 35 extends from the outlet 12 to the central channel 34 along the longitudinal axis A, inclined at an acute angle with respect to the central axis B of the central channel 34.

[71] The acute angle a is preferably in the range of 30 ° to 45 ° (see FIG. 17), at which optimal results are achieved for a constant flow out.

[72] In the second inlet channel 35, a corresponding shutter member 41 is placed, which makes it possible to regulate, by activating the control valve 42 connected to it, the cross section of this second inlet channel 35 and, accordingly, the amount of abrasive material mixed with the compressed air stream.

[73] It is preferable that to provide optimal abrasion resistance, the shutter member 41 is made of steel.

[74] A flexible tube 38 is connected on one side to a connecting member 37, and at the opposite end to a corresponding spraying means 43, which is, for example, a spraying gun 44.

[75] The spray gun 44 contains a number of elements not shown for simplicity, suitably assembled in such a way as to give the spray gun 44 itself an ergonomic configuration. These elements are preferably produced by extrusion from aluminum.

[76] The spray gun 44 has at one end a spray nozzle 45 by which a jet of air and abrasive material is sprayed onto the surface to be treated.

[77] The spray nozzle 45 comprises a hollow cylindrical body 46 having an inlet 47 and an opposing outlet 48 for the flow of air and abrasive material.

[78] Preferably, the spray nozzle 45 is made of a material having high hardness and abrasion resistance, preferably tungsten carbide.

[79] The spray nozzle 45 comprises a section 49 tapering in cross section, from which the thickness of the cylindrical body 46 gradually decreases to the outlet end 48, thereby forming a flow guide channel 50.

[80] More specifically, the guide channel 50 expands at an acute angle β with respect to the longitudinal axis C of the spray nozzle 45 so as to form a channel, essentially conical, expanding in the exit direction, for a stream of compressed air and abrasive material. Due to this shape, the distribution of the outgoing material is especially homogeneous, which leads to the formation of a jet, essentially conical in shape, with a uniform distribution of the material over the volume occupied by the stream (see Fig. 18).

[81] The diverging angle β is preferably in the range of 2 ° to 8 °, in which uniformity of distribution is optimal.

[82] Starting from the tapering portion 49, the nozzle 45 forms, towards the entrance, on the side opposite to the side of the outlet channel 50, a tapering inlet channel 51 so as to obtain, in combination with the aforementioned portions of the nozzle 45, a Venturi effect.

[83] In practice, the thickness of the cylindrical body 46 is gradually reduced toward the inlet 47, thereby forming a converging inlet 51, for entering the flow of compressed air and abrasive material.

[84] According to another embodiment of the invention, the thickness of the cylindrical body 46, starting from the aforementioned tapered portion 49 towards the outlet 48, remains unchanged, respectively, the formed guide channel 50 has a substantially cylindrical shape (see FIG. 19). In this case, the configuration of the guide channel 50 allows you to get an outgoing air stream containing particles of abrasive material with a higher propagation speed. This type of flow is suitable when a particularly aggressive treatment is required for the surface.

[85] The spray gun 44 is also equipped with appropriate control means 52, which can be controlled by the user to enable or disable the spraying of compressed air and abrasive material through the spray nozzle 45.

[86] In particular, this control means 52 is connected to the flow control valve 29 by means of connecting means 53, for example, of the type of connecting tubes, to send control signals to the valve 29 to set it to the closing or opening position.

[87] Preferably, the control means 52 comprises a lever element that is manually actuated.

[88] The operation of the apparatus for cleaning surfaces is easily understood from the foregoing description.

[89] When the compressor is started, the compressed air stream enters from the supply channel 27 through an anti-condensation filter 28, sequentially, to the compressed air flow control valve 29 and the pressure control gear 31, to the inlet valve 23, from which the flow is distributed into the first channel 19 and into the tank 2. In particular, compressed air occupies the upper part of the tank so as to exert constant pressure on the material. In the event that a second channel 20 is provided, compressed air also enters the second channel 20 and facilitates the flow of abrasive material from the tank 2 into the second inlet channel 35 to the central channel 34 of the mixing valve 31, where it is mixed accordingly with the stream of compressed air entering through the first channel 19.

[90] A stream of compressed air and abrasive material mixed in the mixing valve 31 is transported through a flexible tube 38 to a spray gun 44, which, when activated by the operator, sprays the jet onto the surface to be treated.

[91] When the user wants to stop the flowing stream of compressed air and abrasive material, he activates the spray gun control means 52. The control means 52 sends a control signal to the flow control valve 29 so as to set it to the closing position and thereby stop it the passage of compressed air from the compressor to the inlet valve 23.

[92] The excess air remaining in the tank 2, after spraying is automatically removed through the exhaust valve 26, which allows you to quickly restore the atmospheric air pressure in idle mode in the chamber of the tank 2, and then makes the device ready for operational use.

[93] The apparatus for cleaning surfaces thus reaches a state that provides a continuous and stable ejection of material from the spray gun whenever necessary.

[94] It has been observed in practice that the inclination of the second inlet channel of the mixing valve relative to the central channel at an angle ranging from 30 ° to 45 ° can significantly reduce the occurrence of occlusion of the abrasive material, which ensures a constant flow of material in the direction of the mixing chamber. In addition, in an embodiment of the invention containing the second channel, the supply of abrasive material to the mixing valve is facilitated by the aforementioned second channel, which introduces compressed air into the supply channel for the abrasive material, thereby significantly reducing occlusion phenomena, which often occur mainly when using abrasive material having reduced grain size.

[95] Thus, uninterrupted flow of abrasive material and compressed air from the mixing valve is ensured, followed by optimization of the processing time.

[96] It was also noted that the inclination of the guide channel of the nozzle of the spray gun is optimal from the point of view of uniformity of the product jet at the outlet. The abrasive material is actually evenly distributed over the volume of the obtained conical stream, thereby ensuring uniform distribution of the abrasive material over the surface to be treated.

[97] Another important aspect is the fact that the uniform draft created by the air supplied to the pressure chamber makes the outflow of material from the tank in the direction of the mixing chamber constant and ensures proper storage of the material in the tank.

[98] In this regard, a significant contribution to the continuity of the aforementioned flow is caused by the use of a conveying element, which avoids the problems of adhesion of the material to the tank, in particular, at the edge located around the perimeter of the base of the tank, facilitating the outflow of material in the direction of the outlet.

[99] This aspect has a particular advantage in the case of using a material consisting of reduced grain size and low pressure used for compression in relation to the material, as well as if it is often necessary to change the type of abrasive material used and thus to minimize adhesion material to the tank to facilitate its replacement.

[100] Another aspect that should be emphasized is that the apparatus allows to reduce the execution time of the work, in particular, the time of the release of excess compressed air and, accordingly, the time required between two subsequent sprayings, thanks to the exhaust valve, which allows you to quickly release air remaining in the tank at the end of each spray. This also saves abrasive material, since, in the absence of such a valve, excess air is blown out at the end of each spraying through the nozzle of the spray gun along with the abrasive material. At the same time, reducing the time of this release increases user safety, as the jet exiting the spray gun stops in less time.

[101] In addition, it was noted that the presence of an exhaust valve significantly reduces the turbulence that can occur in the compressed air inlet valve, which leads to the accumulation of abrasive material in the compressed air supply circuit, in particular, in the pressure control device.

[102] The present invention also relates to the field of creating a versatile apparatus that can be used for materials having various mechanical, physical and particle size characteristics, thanks to the aforementioned mixing valve, which allows the amount of abrasive material mixed by means of the control valve to be appropriately dosed.

[103] The apparatus for cleaning surfaces is also easily transported, mainly due to the use of materials such as aluminum, which greatly facilitates the overall weight of the apparatus and also makes possible an alternative way to use it. In the case of an embodiment of the invention in a small apparatus, the operator can easily bear the weight of the apparatus, for example, by loading it on his shoulder.

[104] Ergonomic features of the spray gun also give the unit ease of movement.

[105] Another aspect that should be emphasized is the use of materials with high hardness and abrasion resistance, in particular tungsten carbide, for the implementation of elements such as valves, spray nozzles and connecting elements, especially those subject to abrasive phenomena. Thus, the device is given greater reliability and durability.

[106] The apparatus described as an example allows for numerous modifications and variations in accordance with various requirements.

[107] In practice, in the practice of the present invention, the materials used, as well as the shape and dimensions, may vary depending on requirements.

[108] If the technical characteristics indicated in any claim are indicated by reference numerals, such reference numerals were included only for the purpose of enhancing understanding of these paragraphs, and, accordingly, they should not be considered as limiting in any way the scope of protection of each element identifiable reference numbers for purposes of explanation.

Claims (15)

1. Apparatus for cleaning surfaces containing a housing (1) comprising a reservoir (2) for containing abrasive material therein, and a first channel (19) for a stream of compressed air that extends adjacent to said reservoir (2) along the entire length of said reservoir (2); a mixing valve (31) connected to said reservoir (2) for mixing said abrasive material with said compressed air; a spray device (43) for connecting to said mixing valve (31); wherein said first channel (19) is designed to provide a stream of said compressed air both directly to said reservoir (2), so as to ensure efficient storage of said abrasive material inside said reservoir (2), and to said mixing valve (31) , characterized in that said mixing valve (31) comprises a first inlet channel (33) for passing a stream of said compressed air, a central channel (34) extending along the central axis (B), forming a mixing chamber and connecting to said first inlet channel (33); a second inlet channel (35) for passing said abrasive material in communication with said central channel (33), extending along a longitudinal axis (A) inclined relative to said central axis (B) of said central channel (33) at an acute angle (α), and characterized in that it comprises a conveying element (16) mounted inside said reservoir (2) at a lower location having a hollow conical shape asymmetric about its axis of rotation. 2. The apparatus according to claim 1, characterized in that said transporting element (16) forms in the upper part a receiving hole (17) for said abrasive material contained in said reservoir (2) and an opposite eccentrically located opening (18) in the direction of which the said abrasive material is supplied. 3. The apparatus according to claim 1, characterized in that the said acute angle (α) is in the range from 30 to 45 °. 4. Apparatus according to any one of the preceding paragraphs, characterized in that said spray device (43) has at one end a spray nozzle (45) for spraying a stream of compressed air mixed with said abrasive material onto a surface to be treated containing hollow a cylindrical body (46) having an inlet (47) and an opposed outlet (48). 5. The apparatus according to claim 4, characterized in that said spray nozzle (45) comprises a section (49) having a narrowing of the cross section, from which a guide channel (50) having a shape expanding in the direction of said outlet (48), formed for said stream of compressed air and abrasive material. 6. The apparatus according to claim 5, characterized in that said guide channel (50) expands at an acute angle (β) with respect to the longitudinal axis (C) of said spray nozzle (45) so as to spray a stream having essentially , a cone shape with a uniform distribution of said abrasive material throughout the volume of said jet. 7. The apparatus according to claim 6, characterized in that the said acute angle (β) is in the range from 2 to 8 °. 8. The apparatus according to any one of the preceding paragraphs, characterized in that it comprises a shutter element (41) located inside the said second inlet channel (35) connected to the control valve (42), which makes it possible to regulate when the said control valve is activated ( 42), a cross section of said second inlet channel (35).

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