EP1109631A1

EP1109631A1 - Process and device for treating surfaces

Info

Publication number: EP1109631A1
Application number: EP99936646A
Authority: EP
Inventors: Urho Anttonen
Original assignee: Individual
Current assignee: Individual
Priority date: 1998-08-07
Filing date: 1999-08-06
Publication date: 2001-06-27
Also published as: AU5167099A; WO2000010739A1; WO2000010739B1; FI981716A0

Abstract

The invention relates to a process for treating surfaces by means of a mixture of air and powder introduced through a powder nozzle (46), whereby the velocity of the outflow of the powder particles used from the powder nozzle (46) is substantially less than 40 m/s. Furthermore, the invention is related to a device for treating surfaces comprising a pressure unit (52) and a multi-nozzle tool (40) comprising at least two powder nozzles (46). Additionally, the invention relates to the use of the process and/or device according to the invention for powder-based painting/coating of surfaces along with or without a process for cleaning, whereby the surface to be treated is pretreated with a suitable base coat liquid and while said base coat liquid is still wet, by utilizing the method and the device according to the invention, powder paint/coating agent is sprayed to attach onto/react with the base coat liquid spread on the surface to form the final coat of paint/coating.

Description

PROCESS AND DEVICE FOR TREATING SURFACES

This invention relates to an improved process for treating surfaces. It is also related to a device for practicing said process.

The removal of graffiti markings and other difficult dirt, e.g. soot etc., from various surface structures, such as walls of houses, bridges and other buildings, surfaces of various machines or other equipment, and the removal of different kinds of protective coatings from surfaces is nowadays in most cases performed by using various solvents and/or high- pressure washing (whereby commonly used pressure ranges from 75 to 100 bar). Often hot water is used as an aid in the washing. Removing dirt from surfaces is carried out also e.g. by means of sand-blasting with or without a washing liquid, by using a wire brush or various scrapers combined with chemicals having an effect on the dirt. It is also known to clean surfaces by means of so-called dry methods of surface treatment, i.e. methods whereby air with powder mixed therein is used. In connection with this invention the term powder is used to refer to a powder consisting of particles. The known dry methods of surface treatment are based on the idea that powder particles moved by air hit the surface to be cleaned with a great amount of energy. This is accomplished e.g. so that the powder is mixed ready into a high-pressure air flow, i.e. the powder and the air are already in a pressurized space and then directed to the surface to be cleaned through a so-called powder nozzle. Another way of dry cleaning a surface is to guide pressurized air into a tool where the flow of pressurized air is restricted suitable with a so-called air nozzle for instance to a pressure of 5-15 bar and even above, and mixing then the desired powder into said air flow, said mixture of air and powder being then directed to the surface to be cleaned through a suitable powder nozzle. In these methods, the velocity of the outflow from the powder nozzle is great and often within the range of 100 m/s or above (sand-blasting), whereby the kinetic energy of the powder particles hitting the surface to be cleaned is high and the working or "cleaning" effect is powerful. The purpose of the powder in the known methods of dry cleaning surfaces is to process the surface to be cleaned by applying a strong abrasive force. The acting powders used are often either quartz sand, silicon carbide or aluminum oxide. In the following the general term surface is used to refer to all above mentioned surface structures of buildings, machines and equipment.

Prior art dirt removal methods have several disadvantages. They are often complicated or cumbersome to implement, expensive (some of them) and time-consuming. Furthermore, several known cleaning methods are so "effective" that they easily damage more sensitive surfaces in particular. The cleaning often also leaves a distinct trace on the cleaned surface.

Several cleaning methods also involve many environmentally harmful factors. Uncontrolled release - and even a partial release - of cleaning agents (e.g. solvents, sand etc.) and waste material coming off the surface during the cleaning is an environmental problem. In certain methods the cleaning agents used have to be recovered because they are environmentally damaging compounds. Publication WO 93/10917, for instance, discloses a special embodiment to be used in connection with cleaning e.g. airplane surfaces whereby high- velocity water-soluble sodium sulfate particles are used to clean sensitive hard surfaces. On page 4 in said publication it is presented for instance that the invention is related to the removal of coatings from sensitive surfaces by applying a high- velocity water-containing fluid stream to the surface, preferably substantially a water- saturated compressed air stream under a pressure of 10-100 psi and containing as a blasting medium crystalline sodium sulfate having an average particle size of about 50 to 1000 microns, preferably about 150 to 500 microns.

Some cleaning methods, particularly chemical ones and those applying a high surface pressure to the surface to be cleaned weaken the properties of the surface to be cleaned in comparison with its original condition - especially the weather-resistance of the surface is generally weakened. In these cases the cleaned surface needs a finishing treatment and/or the entire surface has to be coated again, which naturally is expensive and time-consuming. Usually the coating is performed by other people and other companies than those performing the actual cleaning. The finishing treatment - usually painting - is carried out by utilizing in each case a suitable method of painting, e.g. spray painting or using a paintbrush. This easily leads to delays and changes in schedules which can be further influenced by weather conditions. The orderer of the work finds this annoying. Several mechanical cleaning methods also involve many problems caused by dust and noise and sometimes conventional coating/painting methods entail typically problems with splashes etc.

A common problem with prior art methods is that in addition to the removal of the dirt, the surface to be cleaned is affected so that it is usually is damaged or worn in harmful way.

It is an objective of the present invention to eliminate the above mentioned disadvantages and to provide an improved process for treating surfaces. A purpose in particular is to provide an improved process for cleaning surfaces. Another purpose is to provide a new kind of process for coating/painting surfaces. Yet a further objective of the invention is to provide a device for practicing the process in accordance with the invention. Additionally, the use of the device according to the invention for cleaning and/or coating/painting surfaces is an objective of our invention. These objectives are achieved by the characteristic features of the invention disclosed mainly in the characterizing portions of the appended patent claims.

The process for treating surfaces according to the invention is based on the low-velocity movement of the cleaning/coating compounds, e.g. particles of cleaning or coating powder. According to the invention, a basic idea of the cleaning treatment of surfaces is that the treatment should be actively focused to affect substantially the dirt to be removed or the coating and not to damage the structure of the surface and/or a possible filler/coating layer (such as color substance, filler material or binding agent) of the surface structure underneath the dirt. When the cleaning is aimed to affect the actual dirt only, the indirect result is that the surface underneath the dirt remains as genuine as possible, as it was originally. This new idea according to the invention is derived from the insight that the process for cleaning is both gentle and controlled unlike prior art methods which in the first place are "effective" and "fast" and have the purpose of treating the surface to be cleaned in a strongly abrasive manner.

The process for treating surfaces according to the invention is preformed dry, i.e. the carrier material of the powder particles is air or some other suitable gas or gas mixture. Appropriate recovery and purifying units are connected with the device according to the process of our invention in order to treat the used powder and resulting dirt. Thus loading the nature and harmful releases can be avoided.

Another aspect of the invention is to use the process and device according to the invention also for a finishing treatment subsequent to the cleaning. By utilizing the solution provided by our invention, differences in shade between the cleaned surface and the clean "old" surface are small when compared with the results of the existing methods of cleaning. In order to have the desired result, the orderer of the cleaning often wishes to have the entire surface treated/painted even because of minor differences in color. The surface can be finished to appear exactly as desired by utilizing the finishing treatment according to our invention. By means of the solution provided by the invention, the cleaning and the finishing can be performed as subsequent steps, and moreover, by using the one and the same device. The powder-based painting/coating process of our invention can naturally be used as a separate method, without the cleaning aspect provided by our invention.

A finishing treatment of this kind can be performed for instance as follows: After cleaning the surface, the clean surface is pretreated with a suitable base coat liquid and while said base coat liquid is still wet, by utilizing the process and device according to the invention, powder paint/coating agent is sprayed to attach onto/react with the base coat liquid on the surface to form the final coat of paint/coating.

The solution provided by our invention can be utilized in the removal of graffiti markings and other difficult dirt, e.g. soot, stains of organic growth etc., from various surface structures such as walls of houses, bridges and other buildings, surfaces of various machines or other equipment, and removal of different kinds of protective coatings from surfaces. It can preferably be used in connection with the finishing of cleaned surfaces with a suitable coating such as powder paint. By utilizing the one and the same device according to the invention it is also possible to treat the surfaces both by cleaning and finishing, e.g. by using powder paint. The process for treating surfaces according to the invention is based on the low-velocity movement of the cleaning/coating compounds, e.g. particles of cleaning or coating powder, whereby all activity is directed to affect the surface itself, i.e. for instance the dirt on the surface and not the structures underneath the dirt. When treating sensitive surfaces, very small flow rates of mixture of powder and air is used per nozzle, and thus the solution according to the invention creates rather a cloud of powder than a spray of powder on the surface to be treated. By utilizing low pressure and a solution according to the invention based among other factors on a nozzle technique comprising several pairs of nozzles, the construction of which can be modified, an effective contact with the surface can be made. This is further assisted by the fact that the powder that has hit the surface and the dirt coming off the surface are withdrawn preferably to the recycling and to a new work cycle by means of a special suction member with a suction collar arranged therein. Using an effective withdrawing particle spray also ensures that the particles that have hit the surface do not get in the way of new particles and prevent them from making an effective contact with the surface to be treated. Effective withdrawal also ensures that releases into the environment can be avoided. The flow rate of the withdrawal is chosen preferably so that all mixture of air and powder directed to the surface and the material coming off the surface can be withdrawn to the recycling/purification/regeneration. This also means that the solution according to our invention can preferably be utilized indoors as well where the advantages of the solution become clearly emphasized.

The cleaning particles may be e.g. acrylic plastic particles (diameters typically approx. 0.05 μm - approx. 420 μm, dustfree), aluminum oxide particles (diameters typically approx. 0.05 μm - approx. 420 μm, dustfree), silicon carbide (diameters typically approx. 0.005 μm - approx. 280 μm, dustfree), glass beads (diameters typically approx. 0.05 μm - approx. 150-220 μm, dustfree), quartz sand powder (the particle size of which being preferably approx. 0.005 μm - approx 300 μm, dustfree) etc. which in the following are referred to by using the general term powder. Suitable generally available commercial powders can be used in the painting and coating.

Both the process for cleaning and the process for coating according to the invention can be practiced by using a device that comprises a pressure unit and a tool that is a special kind of a multi-nozzle tool comprising at least two powder nozzles. The multi-nozzle tool preferably comprises at least two pairs of nozzles, through which the mixture of powder and air or some other gas is directed to the surface to be treated. A pair of nozzles is comprised of an air nozzle which is positioned first in the direction of the air flow followed by a powder nozzle. Preferably the multi-nozzle tool has 2-10 pairs of nozzles. If necessary, the air nozzles respectively as well as the powder nozzles respectively in these pairs of nozzles can be arranged to have different inner diameters. Also the distance of the powder nozzles from the surface to be treated can vary. Further, the directions of the powder sprays that are determined by the angle position of the air nozzle and the powder nozzle in relation to each other can be non-parallel, i.e. the powder sprays from the multi- nozzle tool may hit the surface to be treated at different angles. A channel for powder is provided in the vicinity of each air nozzle, through which powder channel the powder is withdrawn into the air flow that is supplied through the air nozzle. The mixture of air and powder is then supplied through the powder nozzle to the surface to be treated. The structure of the multi-nozzle tool is described in more detail below in the description of the Figures.

In addition to the multi-nozzle tool and the pressure unit, the device preferably comprises a suction element and a cyclone element operating as a filtering/retreatment unit for the cleaning powder and the dirt coming off the surface. The same filtering-retreatment unit is used to regenerate the powder to be used as coating and at the same time, to remove possible dust particles that are formed during the coating when the powder hits the surface to be treated . This means that the "excess" coating powder that was not attached to the surface in the coating process can be purified and reused. This minimizes effectively the load on the environment.

The velocity of the outflow of powder particles from the powder nozzle at a certain pressure depends on the material properties of the powder particles used, such as the density, size and shape. Various surfaces to be treated, e.g. stone, metal, brick, concrete, marble, wood etc., and also the properties of the surface to be treated, for instance the extent of fouling, the properties of any other coating to be removed or the properties of the new intended coating, require a powder material and an intensity of treatment that has to be suited for each surface. The intensity of treatment is used here to refer to a combination of the properties of the material of the powder used and the amount of mechanical additional energy given to said powder particles. In connection with our invention the amount of additional energy given to the powder particles is measured by the velocity that said powder particles have in average when flowing out of the powder nozzle. In the measurements relating to our invention we have measured an average velocity of various powder particles leaving the powder nozzle within the range of 10 mm from the endface of the powder nozzle. The final result as regards the quality of the surface to be treated, both in powder cleaning and powder coating, is a combination of several factors. The velocity of powder particles when leaving the powder nozzle is a variable that measures best the energy bound in the powder particles used in the treatment of surfaces. With different powder materials this energy naturally varies even if the velocity of the outflow of the particles from the powder nozzle were the same. Also the suction near the surface to be treated and the features of the surface nozzle of the tool itself influence the effect of the final physical behavior of the particles on the surface to be treated and the effect of the particles on said surface. The features of the surface nozzle and its significance is disclosed below in connection with the description of the figures. The combination of the velocity of the powder spray, the actual powder material, the intensity of the suction used and the position of the suction used as well as the features of the surface nozzle create a counterpressure to the powder used, changing the direct spray from the powder nozzle into a cloud-like particle formation, said cloud of powder particles further producing a desired result on the surface the be treated e.g. in connection with powder cleaning or powder coating.

We have obtained good results when in connection with the process according to the invention the velocity of the outflow of powder particles from the powder nozzle is substantially less than 65 m/s and preferably less that 55 m/s. For most of the powders used, the velocity of powder particles that have proven to be suitable is within the range of 5 to 50 m/s and very preferably within the range of 15 to 45 m/s. Also the velocity of powder particles within the range of 15 to 35 m/s have given good results. When practicing the process in accordance with our invention, the distance of the powder nozzles from the surface to be treated is preferably substantially less than approx. 10 cm and preferably within the range of approx. 3 to 5 cm.

When utilizing the process according to our invention, e.g. powder nozzles are used having the cross-sectional area of the inner surface preferably < 39 mm² or with circular inner cross-sections the diameter being approx. < 7 mm; preferably the cross-sectional area of the inner surface of the powder nozzles is approx. 7-29 mm² and with circular cross- sections, the inner diameter is approx. 3-6 mm. The cross-sectional area of the inner surface of the air nozzles is preferably < approx. 7mm² and with circular cross-sections, the inner diameters are < approx. 3 mm and preferably the cross-sectional area of the inner diameter of the air nozzle is within the range of approx. 0.8 -3 mm², or with circular cross- sections, the inner diameter is within the range of 1 to 2 mm. The flow rate to be used is determined by the nozzle combination used and the surface to be treated. The amount of air used is thus typically approx. 30-300 1/min/air nozzle. Preferably, the amount of air used per nozzle is less than approx. 280 1/min/air nozzle and very preferably approx. 30- 280 1/min/air nozzle. Good results were obtained when using a gas flow of 50-250 1/min/air nozzle.

Good results were obtained when e.g. graffiti markings on a so-called exposed-aggregate concrete (a great amount of coarse particles of stone on the surface) were removed by using dust-free powder of glass beads and silicon carbide having a diameter of approx. 0.06-0.18 mm. Three nozzles were utilized, the operating pressure in the nozzles was approx. 5 bar, the diameter of the air nozzles was 2 mm and the diameter of the powder nozzles was 6 mm. Thus the flow rate was approx. 150 1/min/air nozzle. By using these values, the average velocity of the powder particles measured was approx. 25 m/s. Hence, the ratio of the cross-sectional area of the inner surface of the powder nozzle and the cross- sectional area of the inner surface of the air nozzle was approx. 9:1. According to our invention, collecting the cleaning powder and dirt by means of a method based on suction for retreatment enables the use of low pressure in a nozzle. The movement of the powder into the multi-nozzle tool and inside it towards the surface to be cleaned is facilitated by the suction directed to the powder through the suction collar in the suction member with the purpose of collecting the used powder and dirt. Due to efficient withdrawal used during the cleaning, no waste from the cleaning agent or the dirt from the cleaned surface is released into the environment.

The process for cleaning surfaces and a device for practicing said process is described in detail with reference to the accompanying figures illustrating solutions according to the invention. However, the invention is not intended to be limited to these solutions.

Figures 1 illustrate a device for cleaning surfaces arranged inside an easily movable transport unit,

Figure 2 is a schematic assembly drawing of a multi-nozzle tool, Figure 3 is a schematic assembly drawing of another multi-nozzle tool, Figure 4a is a partial cross-sectional view of a suction element and Figure 4b is a partial cross-sectional view of a cyclone element.

Figures 1 illustrate a suction element 10 and a cyclone element 20 of the device for cleaning surfaces, both elements being arranged inside an easily movable transport unit 1. In Figure la the transport unit 1 is seen from the front and in Figure lb from behind. Reference number 5 refers to the cover of the transport unit 1, reference number 3 refers to the wheels of the transport unit 1 and reference number 4 refers to the handle of the transport unit 1. Openings are arranged onto the back walls of the transport unit through which openings pipes/hoses and wires for the suction and cyclone elements can be easily combined with the multi-nozzle tool and necessary outside sources of power and pressurized air. These openings are referred to by using the reference numbers for the pipes and wires that go through the openings, said members being described in detail below. Also the suction element 10 and the cyclone element 20 of the transport unit are explained in detail in Figures 4a and 4b.

Figure 2 illustrates a multi-nozzle tool 40 according to the invention in a schematic assembly drawing. The body 41 of the multi-nozzle tool 40 is comprised of e.g. a so-called spray gun. In connection with the body 41, a pressure balancing cylinder 42 is arranged that is e.g. conical in shape. It is preferably arranged detachable to the body 41 e.g. by means of a threaded joint. In connection with the pressure balancing cylinder 42, a frame structure 43 for air nozzles is arranged, said frame structure 43 being provided with at least two air nozzles 47. The operational principle of an individual air nozzle is presented beside the frame structure 43 for the air nozzles. The inner diameters of the air nozzles used in our invention are typically < approx. 2 mm. In contact with the frame structure 43 for the air nozzles, a frame structure 44 for the powder nozzles is arranged, said frame structure 44 being provided with at least two powder nozzles 46. Beside the frame structure 44 for the powder nozzle, the operational principle of an individual powder nozzle 46 is presented. The inner diameters of the powder nozzles used in our invention are at the maximum approx. 7 mm and typically < approx. 6 mm. Frame structures 44 and 43 can be attached to the pressure balancing cylinder in some suitable manner, preferably with a joint that can be opened. In the example of Figure 2 they are attached by means of a bolted joint 45.

Furthermore, a suction member 60 with a suction collar 61 is arranged in connection with the frame structure 44 for the powder nozzles. A suction conduit 62 is attached to said suction collar 61, through which suction conduit the used powder remaining inside the suction collar and the dirt coming off the surface are withdrawn to be treated in the suction element/cyclone element. In connection with the suction collar, a preferably detachable surface nozzle 63 is provided, which is e.g. a construction with brushes or the like, ensuring that the multi-nozzle tool 40 lies well in contact with the surface to be cleaned even if the surface is uneven. Preferably, brush-like surface nozzles of several types can be utilized whereby the optimal contact with the surface to be treated can be ensured by using a surface nozzle 63 most suitable for each surface. The suction member 60 can naturally be constructed in various ways and still function as desired, i.e. ensuring the recovery of the used powder and the dirt removed from the surface.

An inlet conduit 51 is provided in contact with the body 41, to which an inlet hose 511 for pressure medium - such as air or some other gas or gas mixture - is provided. The pressurized air entering the body is pressurized by means of a pressure unit 52 e.g. a compressor. The body comprises also a discharge conduit 49 for pressurized air through which conduit the powder pump (described in more detail in Fig 4b) receives with the pressurized air required. The discharge conduit 49 is arranged after a closing valve 53, and when pressurized air is fed to the multi-nozzle tool 40 itself, the powder pump 33 and a powder shaker 302 (see description below) arranged in connection with the closing valve 301 receive pressurized air for operation. The operational means of the closing valve is e.g. a trigger 54. In connection with the trigger 54 an operating wire 50 of the closing valve 301 is provided. (The structure of the closing valve is presented in more detail in Fig. 4b.)

The pressure balancing cylinder 42 provided in contact with the body 41 is arranged preferably detachable to the body 41 e.g. by means of a threaded joint. The diameter of the open inner space of the pressure balancing cylinder 42 increases so that positioned against the base of the frame structure 43 for the air nozzle, there is an open tube-like portion 421, said open space being placed against the base of the frame structure 43. The location of the feeding tubes 471 of the air nozzles 47 arranged in the frame structure 43 for the air nozzles can be determined in a desired way within the area defined by the diameter of the open tube-like portion 421 located against the base of the body 42 of the air nozzles of the pressure balancing cylinder.

An inlet conduit 48 for powder is arranged to the frame structure 43 for the air nozzles. A powder channel 481 leads from the inlet conduit 48 to the vicinity of each air nozzle. The powder to be fed in/withdrawn through powder channels 481 is mixed via said inlet conduit 48 with the pressurized air coming from the nozzles 47 after the nozzles 47, whereby the mixture of air and powder continues further in the mixing tubes 461 of the frame structure 44 for the powder nozzles, air and powder being mixed into each other in said mixing tubes. At least two powder nozzles 46 are arranged in contact with the mixing tubes 461, in the vicinity of the surface 462 at the end of the tubes, preferably somewhat below said surface. The surface 462 at the end of the mixing tubes 461 may also function as the end surface of a separate mixing tube 461. The mixing tube 461 may also be a hole drilled in the frame structure 44, whereby the surface 462 acts at the same time also as the endface of the frame structure 44.

Figure 3 is a schematic assembly drawing of another multi-nozzle tool 40. In this embodiment the pattern of the powder spray leaving the powder nozzle 46 and hitting the surface to be treated and the particle density of the pattern can be varied in different parts thereof so as to obtain the optimal contact with each surface to be treated. In this embodiment the distance of the powder nozzles 46 of the multi-nozzle tool 40 from the surface to be treated is varied according to the quality/profile of the surface to be treated so that the distance of different powder nozzles from the surface to be treated is set different i.e. the mixing tubes 461 are of different length if necessary. In this tool this idea has been practiced in such a way that the powder nozzles 46 are attached to the detachable mixing tubes 461. In this manner the length of the mixing tube 461 can be chosen as desired. In addition to this or instead of this, different flow rate outputs can be selected for various pairs of nozzles 47-46. This is brought into practice so that the pairs of nozzles furthermost on the sides have air and powder nozzles with smaller diameters than those in the pairs of nozzles inside the pattern of the powder spray.

In this embodiment the total of 7 pairs of nozzles are arranged on two peripheries within each other in the frame structure 44 for the powder nozzle of the multi-nozzle tool 40. Four of them are placed on the outer periphery and three on the inner periphery. The diameter of the air nozzles in a pair of nozzles on the outer periphery is set to 1.5 mm and correspondingly, the diameter of the powder nozzles is 4.5 mm. The diameter of the air nozzles in a pair of nozzles on the inner periphery of the powder spray is set to e.g. 2 mm and correspondingly, the diameter of the powder nozzles is 6 mm. In this way such density profile of the powder spray pattern is obtained that the density of the powder particles on the side area is smaller than in the center of the pattern. This is further intensified by the fact that the powder sprays from the inner periphery come from powder nozzles that are placed within a smaller distance from the surface to be treated than the powder sprays on the outer periphery. The powder sprays from the outer periphery, i.e. further away, are partially mixed with the powder sprays from the center part thus blending effectively the sharp edges of different sprays. In this way the edges of the powder sprays can be blended exactly as desired, i.e. the distinct edges of the treated surface and the untreated surface can effectively be avoided. By altering the dimensions of the inner diameters of the adjacent pairs of nozzles and the distance of the powder nozzles from the surface to be treated, an appropriate contact between the powder and various types of surfaces can be obtained. Thus, it is easy to accomplish by means of the solution provided by the invention a cloudlike mixture of powder and gas having a great particle density but yet being gentle, which is necessary with sensitive surfaces. The suction member 60 is mounted detachable on the frame structure 44 for the powder nozzles, e.g. by means of a screw joint 441.

Figure 4 a illustrates a suction element 10. The suction element 10 comprises a motor 11, a waste container 13 and a filter element 12. An inlet conduit 15 from the cyclone element 20 is arranged on the side of the waste container 13. Light fractions to be filtered in a filter element 12 are withdrawn through the inlet conduit 15 from the cyclone element 20 via connecting pipe 251. There is a sealing 17 between the motor 11 and the waste container 13. A sealing 16 is also mounted between the waste container 12 and the discharge conduit 14 thereof.

Figure 4 b shows a cyclone element 20. The cyclone element comprises a cover 21 and a sealing 36 thereof. The body of the cyclone element is marked with reference number 22. Thus, the body 22 forms a so-called cyclone to which reference is made in the later description of the device. A discharge conduit 25 of T-shape is attached to the body 22 and a plug 250 is placed detachable at one end of the branch tubing of the discharge conduit. The light fractions are directed from the cyclone 20 to the inlet conduit 15 of the suction element 10 through an intermediate pipe 251 positioned in contact with the other branch of said discharge conduit 25. A wire guide 26 is provided with the body 22, the operating wire 50 of the closing valve 301 being arranged inside said wire guide. Further, an inlet conduit 27 is arranged to the body 22, through which inlet conduit the used powder remaining inside the suction collar 61 of the suction member 60 and the dirt released from the surface are withdrawn via suction conduit 62 to be processed in the suction element 10 / cyclone element 20. Said suction conduit 62 is preferably placed to start from the suction collar 61 behind the endface of the powder nozzle 46 i.e. in such a way that the endface 46 of the powder nozzle is closer to the surface to be treated than the suction conduit 62. The velocity of the powder spray, the powder material itself, the intensity of the suction used and the location of the suction conduit 62 preferably behind the endface of the powder nozzle 46 as well as the features of the surface nozzle 63 create a counterpressure to the used powder changing the direct spray coming from the powder nozzle into a cloud-like particle formation, said cloud of powder particles creating a desired result on the surface to be treated e.g. in powder cleaning or coating. There is a powder container 32 under the body 22. A screen 28 is located in connection with the upper part of the powder container 32. The powder intended for the treatment in the cyclone element arrives via inlet conduit 27 first to a coarse screen 28 that collects coarse dirt. Lighter dirt moves further through the cyclone into the suction element 10 to be filtered. A filtering funnel 29 is placed below the coarse screen. The opening 38 at the bottom of the filtering funnel 29 is closed by means of a closing valve 301 of the closing mechanism 30. The coarse dirt remaining in the screen 28 is removed as follows: The cover of the body 22 is opened and the connecting tube 251 affixed to the conduit 25 is detached (said connecting tube being e.g. a tube made of some suitable material) and bent into the body 22 and the coarse dirt on the surface of the screen 28 is withdrawn by means of the connecting tube 251 into the waste container 13.

A pneumatic hose from the discharge conduit 49 for pressurized air belonging to the body 41 is arranged to the inlet conduit 34, through which pneumatic hose the powder pump 33 and a powder shaker 302 in connection with the closing valve 301 are provided with the pressurized air needed. The powder shaker 302 facilitates the movement of the powder in the powder container 32 into the powder pump 33. The feed tube 35 for powder from the powder pump 33 is arranged to an inlet conduit 48 for the feed tube for powder connected to the frame structure 43 for the air nozzles within the multi-nozzle tool 40.

A discharge base 24 and an associated sealing 39 are arranged at the bottom of the cyclone element 20.

When operating a multi-nozzle tool 40 by pulling down the trigger 54 and thus opening a closing valve 53, the multi-nozzle tool receives the pressurized air that it requires. Said pressurized air moves into the pressure balancing cylinder 42 and further into the frame structure 43 for the air nozzles, to which frame structure at least two air nozzles 47 are arranged. The pulling down of the trigger 54 also makes the operating wire 50 of the closing valve 301 to close the opening 38, and the access of the replacement air and particles through the opening 38 at the top of the cyclone element 20 into the powder container 32 and also into the powder pump 33 is prevented. The pressurized air needed in the powder pump 33 is obtained from the multi-nozzle tool via conduit 49, through which pressurized air flows as soon as the closing valve 53 is opened by means of the trigger 54.

When the multi-nozzle tool 40 is in operation, the powder needed is withdrawn from the powder container 32 by means of the powder pump 33 and guided along a feed tube 35 for powder into the inlet conduit 48 of the feed tube for powder arranged to the frame structure

43 for the air nozzles in the multi-nozzle tool 40. The powder is moved on from said conduit 48 via powder channels 481 by the effect of the pressurized air pushing forward and the suction withdrawing into the suction collar 61. The powder to be fed in/withdrawn through the powder channel 481 via said inlet conduit 48 is mixed with the pressurized air after the air nozzles 47 supplying said air, and the mixture of air and powder continues further in the mixing tubes 461 located in the frame structure 44. A powder nozzle 46 is placed in connection with each mixing tube 461, in the vicinity of the surface 462 at the end of the tubes, preferably somewhat below said surface. The multi-nozzle tool 40 thus preferably comprises at least two powder nozzles 46 and preferably each powder nozzle 46 has a separate air nozzle 47, together forming a pair of nozzles. Thus, a pair of nozzle comprises a powder nozzle 46 and an air nozzle 47.

The mixture of air and powder passing through said powder nozzles 46 is then directed to the surface to be treated, wherefrom the used powder and the dirt coming off the cleaned surface is withdrawn for further treatment, i.e. for regeneration. A suction conduit 62 is arranged to the suction collar 61, through which suction conduit the used powder remaining inside the suction collar and the dirt coming off the surface are withdrawn to be processed in the suction element/cyclone element. In connection with the suction collar, preferably a detachable surface nozzle 63 is arranged which is e.g. a construction with brushes or the like, ensuring that a good contact is obtained with the multi-nozzle tool 40 to the surface to be cleaned even if the surface is uneven.

When using the multi-nozzle tool the cleaning powder moves from the powder container 32 into the multi-nozzle tool 40 and further to the surface to be treated and further via the suction collar 61 and suction conduit 62 into the body 22 to be processed. During the operation the closing valve 301 is closed and the connection between the space in the body 22 and the powder container 32 is shut. Thus, the powder container receives no replacement air from the space in the container 22. Only after when the cleaning is discontinued will the closing valve 301 open and the used and purified powder can flow into the powder container 32. The replacement air needed for the powder container 32 is supplied preferably near the powder pump 33. This is carried out so that a pneumatic hose 341 from the discharge conduit 49 for pressurized air provided to the body 41 arranged to the inlet conduit 34 is located inside the powder container 32 to pass inside a protective cover 342 all the way to the powder pump 33. The protective cover 342 is fixed to the wall of the powder container in such a way that the necessary replacement air can be withdrawn via joint 343 between the pneumatic hose 341 leading to the powder pump and the protective cover. Now the replacement air can be brought substantially close to the powder pump 33 whereby said air is mixed with the powder pumped by the powder pump 33 as efficiently as possible.

When the trigger 54 is released and the operation of the multi-nozzle tool 40 is discontinued the flow of the pressurized air operating the powder pump 33 is stopped and the powder pump 33 is turned off. When releasing the trigger 54, an opening 38 at the bottom of the filtering funnel 29 is opened as the closing valve 301 of the closing mechanism 30 opens. The cleaning powder accumulated in the funnel 29 flows into the powder container 32 for reuse. Dirt particles, both large and small ones, removed during the cleaning are extracted from the used cleaning powder by means of a coarse screen 28 and cyclone element 22 and suction element 10.

When new cleaning powder is to be added into the powder container 32, e.g. the tube connected to the suction conduit 62 can be detached and new cleaning powder withdrawn from e.g. a sack. The new powder then flows through a tube attached to the conduit 27 into the body 22 through a screen 28 into the funnel 29. By means of an inlet conduit 27 arranged to the body 22 the used powder remaining inside the suction collar 61 and the dirt coming off the surface are withdrawn through the suction conduit 62 to be processed in the suction element 10 /cyclone element 20. New cleaning powder can be easily added into the device by opening the cover 21 and pouring new cleaning powder into the funnel 29 e.g. directly from a sack. When the type of the cleaning powder or the covering powder needs to be changed, the discharge base 24 of the powder container located at the bottom of the cyclone element 20 is opened and the cleaning powder in the powder container 32 is poured into a suitable tank and the new type of cleaning powder is poured into the powder container 32. Several powder containers 32 can be arranged in connection with the cyclone element, whereby it is possible to use different material or powders having different particle sizes at different stages of cleaning and covering. A solution of this kind diversifies the use of the process according to our invention and facilitates the use of the device according to the invention. For instance, the cleaning powder and paint/coating powder can be "loaded" into the transport unit 1 at the same time, which further diversifies and increases the operation possibilities of the device for cleaning/coating.

The process according to the invention can, if so desired, be applied also to the finishing of the surface after the cleaning. This kind of finishing would be e.g. a powder-based painting/coating. In this case after the cleaning, the preferably clean surface to be treated is treated with a suitable base coat liquid, and while said base coat liquid is still wet, by utilizing the process and device according to the invention, e.g. powder paint is sprayed onto the surface, to attach to/react with the base coat liquid spread on the clean surface and to form the final coat of paint or coating. The velocity of the outflow of the powder particles from the powder nozzle 46 in the powder coating is preferably within the range of 5 to 50 m/s depending on the physical properties of the coating particles used, such as their density and particle size. Also possible chemical reactivity with the base coat liquid used influences the applied velocity of the outflow of particles from the particle nozzle.

When using the above mentioned powder-based finishing treatment it is easy to modify for instance the color or the roughness of the surface to be exactly as desired by varying the amount/composition of the powder to be used. Good results have been obtained e.g. by recovering pigment dust coming off the surface to be treated into the waste container 13 of the suction element 10 and mixing it with the powder to be used as the new coating material, e.g. powder paint. This kind of shading ensures that the differences in the shade between the old untreated surface and the new cleaned and finished surface remain as small as possible. In practice this "patination" has proven very successful and by means of it, such a result can be obtained that one will not even notice that the surface has been treated. In the solution according to our invention not even expensive pigment coating goes to waste, because all or almost all powder particles can be recovered by withdrawal and reused. By practicing the solution according to our invention it is also possible to avoid pollution and burdening the environment in any way.

Due to the low velocity of the outflow of the powder particles and the short distance between the powder nozzles and the surface to be treated, the need for the pressure of spray is low. The pressure of spray applied and the intensity of the withdrawal is adjusted so that the impact velocity of the powder particles hitting the surface to be treated is as desired. Since there are several pairs of nozzles in the multi-nozzle tool it is possible to cover such an area with one sweep of the multi-nozzle tool that the cleaning/coating progresses effectively despite the above mentioned low flow rate of the mixture of powder particles and air. Owing to the short distance between the multi-nozzle tool and the surface to be treated, the density of the particles in the mixture of powder particles and air is, however, great when hitting the surface to be treated. The desired impact velocity can be obtained by using several different combinations comprising the powder nozzle, the distance of the powder nozzles from the surface to be treated, the air nozzle, the operational pressure of the air nozzle, and the flow rate. Furthermore, the distance of the multi-nozzle tool and an individual powder nozzle from the surface to be treated can vary within a distance range preferable to said tools. As stated above, directions of the powder sprays determined by the angle position of the air nozzle 47 and the powder nozzle 46 can be non-parallel, i.e. the powder sprays from the multi-nozzle tool 40 may hit the surface at different angles. The air nozzles 47, the mixing tubes 461 positioned thereafter and the powder nozzles 46 at the end of the mixing tubes can be preferably arranged so that at least one powder spray leaving the multi-nozzle tool positioned perpendicularly towards the surface to be treated has an non-perpendicular impact angle in relation to said surface. Preferably the powder sprays furthest on the sides are parallel and hit the surface to be treated perpendicularly when the multi-nozzle tool is positioned perpendicularly in relation to the said surface. In such case the sprays from the powder nozzles positioned in the center are preferably non-parallel when meeting the surface to be treated. This kind of arrangement of the angle positions of the nozzles is advantageous in cases where the surface to be treated has granules or is uneven, around which there will easily be shades that could not be treated if all powder sprays hit the surface to be treated perpendicularly. Should all powder sprays hit the surface to be treated in a perpendicular position, the tool would need to be turned in order to have all areas of the surface treated and then the contact of the surface nozzle 63 of the suction member 60 with the surface to be treated might be impaired to such an extent that powder and removed dirt could escape. Thus, preferably at least one of the powder sprays from the multi-nozzle tool has a different impact angle in relation to the surface to be treated in comparison with the other sprays coming from the multi-nozzle tool.

However, not just any combination of air and powder nozzles is functional. When utilizing a certain operational pressure, the ratio of the cross-sectional areas of the air nozzles and powder nozzles is to be such that the powder utilized is withdrawn into the gas flow leaving the air nozzle. This withdrawal of powder into the gas flow can be intensified by arranging a suitable withdrawal which is usually applied in the tool close to the surface to be treated.

The process according to the invention can be used to replace traditional methods of sand- blasting and grinding in connection with e.g. automobile, metal and construction industries. It is excellent for removing graffiti markings and e.g. air-pollution related dirt etc. from walls of buildings. By utilizing the coating treatment, e.g. powder painting, according to our invention the surface can be finished to appear exactly as desired. The cleaning and finishing can be performed as subsequent steps and moreover, by using the one and the same device. The powder-based painting/coating process of our invention can naturally be used as a separate method, without the cleaning aspect also provided by our invention.

The invention has been described above by presenting one preferable embodiment. The invention is not limited to this embodiment, but as is obvious to a person skilled in the art, it is to cover various alternative and optional modifications relating to the configuration and possibilities within the spirit and scope of the appended patent claims.

Claims

CLAIMS:

1. Process for treating surfaces with a mixture of powder and air or some other gas, whereby the mixture of powder and air or some other gas is directed to the surface to be treated by means of a powder nozzle (46), characterized in that an average velocity of the outflow of the powder particles to be used from the powder nozzle (46) is substantially less than 65 m/s.

2. Process according to claim 1, characterized in that the velocity of the outflow of the powder particles to be used from the powder nozzle (46) is preferably less that 55 m/s.

3. Process according to claim 1 or 2, characterized in that the velocity of the outflow of the powder particles to be used from the powder nozzle (46) is preferably within the range of 5 to 50 m/s and very preferably within the range of 15 to 45 m/s.

4. Process according to claim 1 or 2, characterized in that the velocity of the outflow of the powder particles to be used from the powder nozzle (46) is preferably within the range of 15 to 35 m/s.

5. Process according to any of claims 1-4, characterized in that the gas to be used, e.g. air, is directed into an air nozzle (47) after which the powder used is mixed therein, whereafter the mixture of gas and powder is directed through the powder nozzle (46) to the surface to be treated and that the gas flow per air nozzle (47) is less than approx. 300 1/min/nozzle.

6. Process according to any of the preceding claims 1-5, characterized in that the amount of the gas flow used per air nozzle (47) is less than approx. 280 1/min/nozzle.

7. Process according to any of the preceding claims 1-6, characterized in that the amount of the gas flow used per air nozzle (47) is within the range of 30-280 1/min/nozzle and very preferably approx. 50-250 1/min/nozzle.

8. Process according to any of the preceding claims, characterized in that the distance of the powder particles used flowing out of the powder nozzle/s (46) from the surface to be treated is substantially less than approx. 10 cm and preferably within the range of approx. 3 to 5 cm.

9. Process according to any of the preceding claims, characterized in that the powder is subjected further to sub-atmospheric pressure facilitating the movement of the powder in the tool, said sub-atmospheric pressure being directed substantially to the vicinity of the surface to be treated and said sub-atmospheric pressure being used to withdraw loose particles near the surface under treatment to the recovery e.g. to be regenerated in a purifying unit (10, 20).

10. Process according to any of the preceding claims, characterized in that a surface is treated with a mixture of powder and air or some other gas, and that the mixture of powder and air or some other gas is directed to the surface to be treated by means of a multi-nozzle tool (40) comprising at least two pairs of nozzles (46, 47) that are comprised of an air nozzle (47) and a powder nozzle (46) and that

- the cross-sectional area of the inner surface of the air nozzles (47) is preferably < approx. 7 mm² and with circular cross-sections, the inner diameters are < approx. 3 mm, and preferably the cross-sectional area of the inner surface of the air nozzle (47) is approx. 0.8- 3 mm² or with circular cross-sections, the inner diameter is approx. 1-2 mm, and that

- a mixture of gas and powder is sprayed through the powder nozzles (46) whereby the cross-sectional area of the inner surface of the powder nozzle (46) is preferably < approx. 39 mm² or with circular inner cross-sections, the diameter is < approx. 7 mm, and preferably, the cross-sectional area of the inner surface of the powder nozzle (46) is approx. 7-29 mm² and with circular cross-sections, the inner diameter is in the range of approx. 3-6 mm.

11. Process according to any of the preceding claims, characterized in that at least one powder spray leaving the multi-nozzle tool positioned towards the surface to be treated has a different impact angle in comparison with the impact angle of the other powder sprays leaving the multi-nozzle tool and directed towards to the surface to be treated.

12. Process according to any of the preceding claims, characterized in that the surface is treated with a mixture comprising at least two of the powders listed below:

- acrylic plastic powder, the particle size of which being preferably approx. 0.05 ╬╝m - approx. 420 ╬╝m;

- aluminum oxide powder, the particle size of which being preferably approx. 0.05 ╬╝m - approx. 420 ╬╝m, dustfree;

- silicon carbide, the particle size of which being preferably approx. 0.005 ╬╝m - approx. 280 ╬╝m; - powder of glass beads, the particle size of which being preferably approx. 0.05 ╬╝m - approx. 150-220 ╬╝m;

- quartz sand powder, the particle size of which being preferably approx. 0.005 ╬╝m - approx. 300 ╬╝m; said powders very preferably being dustfree.

13. Process according to any of the preceding claims 1-11, characterized in that the surface is treated with a powder of glass beads and silicon carbide, said powder being preferably dust-free and having the diameter of the powder particles approx. 0.06-0.18 mm.

14. Process according to any of the preceding claims 1-11, characterized in that the surface to be treated is treated with a suitable base coat liquid, and while said base coat liquid is still wet, by utilizing the process and device according to the invention, e.g. powder paint or some other powder-like coating is sprayed onto the surface to attach to/react with the base coat liquid spread on the surface and to form the final coat of paint/coating, and that the velocity of the outflow of the powder particles used from the powder nozzle (46) is preferably within the range of 5 to 50 m/s.

15. Process according to any of the preceding claims, characterized in that by means of a suction conduit (62) the powder is subjected to sub-atmospheric pressure in the suction member (60) preferably in such a way that the endface of the powder nozzle (46) is closer to the surface to be treated than the suction conduit (62), whereby the velocity of the powder spray, the powder material itself, the intensity of the suction used and the location of the suction conduit (62) preferably behind the endface of the powder nozzle (46) as well as the properties of the surface nozzle (63) together create a counterpressure to the powder used changing the direct spray from the powder nozzles into a cloud-like particle formation, said cloud of powder particles creating a desired result on the surface to be treated e.g. in powder cleaning or coating.

16. Device for treating surfaces comprising a pressure unit (52) and a tool, characterized in that the tool is a multi-nozzle tool (40) comprising at least two powder nozzles (46).

17. Device according to claim 16, characterized in that the multi-nozzle tool 40 comprises at least two pairs of nozzles (47, 46) that are comprised of an air nozzle (47) and a powder nozzle (46) and that - the cross-sectional area of the inner surface of the air nozzles (47) is preferably < approx. 7 mm² and with circular cross-sections the inner diameters are < approx. 3 mm, and preferably the cross-sectional area of the inner surface of the air nozzle (47) is approx. 0.8- 3 mm² or with circular cross-sections, the inner diameter is approx. 1-2 mm, and that - the cross-sectional area of the inner surface of the powder nozzle (46) is < approx. 39 mm² or with circular inner cross-sections the diameter is < approx. 7 mm, and preferably the cross-sectional area of the inner surface of the powder nozzle (46) is approx. 7-29 mm² and with circular cross-sections, the inner diameter is in the range of approx. 3-6 mm.

18. Device according to claim 17, characterized in that the multi-nozzle tool (40) has preferably 2-10 pairs of nozzles (47, 46).

19. Device according to claim 16, 17, or 18, characterized in that in contact with the frame structure (44) for the powder nozzles of the multi-nozzle tool (40), at least two powder nozzles (46) are provided at a distance from the surface to be treated.

20. Device according to claim 15, 16 or 17, characterized in that there are at least two pairs of nozzles (47, 46) arranged to the multi-nozzle tool (40), said pairs of nozzles having different nozzle diameters, i.e. two pairs of nozzles having air nozzles (47) with the inner diameters of 1.5 mm and the corresponding powder nozzles (46) with the inner diameters of 4.5 mm, and two pairs of nozzles (47, 46) having air nozzles (47) with the inner diameters of 2 mm and the corresponding powder nozzles (46) with the inner diameters of 6 mm.

21. Device according to any of the preceding claims 16-20 comprising further a cyclone element (20), in connection with which there are a coarse screen (28), a powder pump (33) and a powder container (32), and a suction element (10), in connection with which a motor (11), waste container (13) and a screening element (12) are arranged, characterized in that the multi-nozzle tool (40) also comprises

a body (41), with an associated inlet conduit (51), to which an inlet hose 511 of pressure medium - such as air or some other gas or gas mixture - is provided, and said body (41) further comprising a discharge conduit (49) for pressurized air through which conduit the powder pump (33) receives the pressurized air required,

a discharge conduit (49) arranged after a closing valve (53),

a closing valve (53) with a operating wire (50) of the closing valve (301) provided in connection with the operational means of the closing valve,

a frame structure (43) for air nozzles to which at least two air nozzles (47) are arranged,

a frame structure (44) for the powder nozzles positioned in connection with the frame structure (43) for the air nozzles, said frame structure (44) being provided with at least two powder nozzles (46),

an inlet conduit (48) for powder arranged to the frame structure (43) for the air nozzles, and a powder channel (481) leading from the inlet conduit (48) to the vicinity of each air nozzle, through which powder channel the powder to be fed in/withdrawn is mixed with the pressurized air coming from nozzles (47) after the nozzles (47),

mixing tubes (461) located in the frame structure (44) for the powder nozzles, in which mixing tubes the air and powder are mixed into each other and through which mixing tubes the mixture of air and powder moves further to the powder nozzles (46) that direct the mixture of air and powder to the surface to be treated,

a suction member (60) in connection with the frame structure (44) for the powder nozzles comprising a suction collar (61) and a suction conduit (62) arranged in contact therewith, through which suction conduit the used powder remaining inside the suction collar and the dirt possibly coming off the surface are withdrawn to be processed in the suction element (10) /cyclone element (20), and a surface nozzle (63) in connection with the suction collar ensuring that a good contact is obtained with the multi-nozzle tool (40) to the surface to be cleaned even if the surface is uneven.

22. Device according to any of claims 16-21, characterized in that that the endface of the powder nozzle (46) is preferably closer to the surface to be cleaned than the suction conduit (62) whereby the velocity of the powder spray, the powder material itself, the intensity of the suction used and the location of the suction conduit (62) preferably behind the endface of the powder nozzle (46) as well as the properties of the surface nozzle (63) together create a counterpressure to the used powder changing the direct spray from the powder nozzles into a cloud-like particle formation, said cloud of powder particles creating a desired result on the surface to be treated e.g. in powder cleaning or coating.

23. Process according to any of claims 16-22, characterized in that at least one powder spray leaving the multi-nozzle tool positioned towards the surface to be treated has a different impact angle in comparison with the impact angle of the other powder sprays leaving the multi-nozzle tool and directed towards the surface to be treated.

24. Device according to any of claims 16-23, characterized in that it preferably also comprises a transport unit (1) inside which the suction element (10) and the cyclone element (20) can be arranged, thus providing easy transportation of the cleaning device.

25. Use of the process and device according to any of preceding claims for removing graffiti markings and other difficult dirt (e.g. soot, stains of organic growth etc.) from surfaces and for removal of different kinds of protective coverings from various kind of surfaces.

26. Use of a device according to any of claims 17-25 for powder-based painting/coating of surfaces along with or without a process for cleaning, whereby the surface to be treated is pretreated with a suitable base coat liquid and while said base coat liquid is still wet, by utilizing the device according to the invention, powder paint/coating agent is sprayed to attach onto/react with the base coat liquid spread on the surface to form the final coat of paint/coating.