WO1997012693A1

WO1997012693A1 - Method and device for handling powder in powder coating plants

Info

Publication number: WO1997012693A1
Application number: PCT/SE1996/001263
Authority: WO
Inventors: Jaan KÄREM
Original assignee: Herberts Powder Coatings Ab
Priority date: 1995-10-05
Filing date: 1996-10-04
Publication date: 1997-04-10
Also published as: SE9503448D0; AU7234096A

Abstract

Method and device for handling of powder in powder coating plants which comprise a number of spray guns (14) or the like. For the powder supply to the guns there is arranged an uptaking device (3) for powder from containers (1) for fresh powder, as well as a collecting device (12) for powder which has not been used in the spraying process for coating the work pieces (15). The supply of fresh powder and collected powder to a blending device (9) is done in predetermined proportions, within certain predetermined limits of tolerance, independently of the supply of said return powder in relation to the consumption in the spraying process. If, however, a surplus of return powder arises, this is allowed to accumulate, and when a deficit of return powder occurs, an influence on the spraying process is triggered so that it is interrupted or indicated for manual adjustment.

Description

TITLE:

Method and device for handling powder in powder coating plants.

TECHNICAL FIELD:

The invention relates to a method and a device for handling powder in powder coating plants, so that the powder may be supplied to powder spraying equipment in a rational manner.

BACKGROUND OF THE INVENTION:

According to a previously known coating method, the surface coating material, which is based on a heat-fusible polymer, is applied in a pulverous state by means of spraying. After the spray application, the powder is caused to temporarily adhere to the object, which is to be coated, by means of electrostatic forces or in another way, and until the powder is melted by heat and is caused to form a homogenous surface coating. In this method, after the delivery from a manufacturer, the powder is supplied to the spraying equipment by means of firstly being transferred from a transport container to a storage vessel associated with the spraying equipment. Thereafter, the powder is taken up by means of a suction device and is transferred from this to the spraying equipment.

When performing the spray application of the powder, a certain portion of the same will not stick to any object and can be collected in the space where the spraying takes place. It is possible to return this powder to the spraying process, whereby the amount of waste powder may be reduced. This implies that the system for powder supply should be arranged to take up powder from delivery packages, as well as from the spraying plant in a recycling system. Such a system is disclosed in EP Al 0 184 994 (Frei) . Therein, a method is suggested in which the powder, which is superfluous in the spraying process, is collected in a sealed powder container, which powder is periodically transferred to a purification plant and thereafter is blended with freshly delivered powder, fresh powder. This implies a discontinuous process, with manual handling as a prerequisite, which is hardly rational. Furthermore, it cannot be utilized for powder coating where high quality demands are set, something which normally occurs when demands are made on the aesthetic quality of the coating, consequently, on the whole, when all coating of products iε concerned. The blending of return powder will namely, to some extent, change the appearance of the coating, a change which however would be acceptable if the result is uniform, which implies that the proportion of fresh powder and return powder should be kept within comparatively narrow limits. A perhaps greater disadvantage may be that the spraying process and the spraying equipment have to be adjusted if a varied proportion of return powder occurs in a spraying process. Fresh powder and previously sprayed return powder often have different properties with respect to the electric, static charge which is utilized in order to retain the powder on the object which is to be coated. If adjustments are not made, this may for instance give rise to a varying layer thickness, depending on the proportion of return powder.

Hitherto there has consequently existed a problem in utilizing surplus powder arising in the spraying process in an economic way, as completely as possible and in a rational way, and so that a uniform coating result is obtained without having to perform continuous supervision and adjustment of the spraying plant. SUMMARY OF THE INVENTION:

The invention has as its object to provide a method and a device for the handling of the powder in the spraying process, so that the powder handling in the same may be executed in a rational way, with the smallest possible influence on the environment, and so that the prescribed quality requirements concerning the coating result are fulfilled and the risk of rejection iε reduced. Thus, an important object is to utilize the powder as completely as possible.

These and other objects of the invention are attained by means of a blending and supply device for the powder supply to the spraying equipment, whereby the method is directed to a utilization of the device in order to reach a high- grade utilization of the return powder.

DESCRIPTION OF THE DRAWINGS:

In the following, the invention will be described with reference to an embodiment. Reference is made to the attached drawings in which

Fig.l shows a block diagram of a plant for powder spraying when powder coating; and

Fig. 2 shows a device for transportation o f the powder from the powder source to a spraying equipment.

PREFERRED EMBODIMENT:

A method for supply of powder and consumption of the powder in a spraying plant for powder coating in connection with powder varnishing is presumed to comprise the following steps: 1. Filling powder into transport containers, at the powder manufacturer's, which are preferably arranged for direct withdrawal of powder when used.

2. Transportation of the containers to the consumer, i.e. a powder coating plant.

3. Connection of the containers, at the powder consumer's, to a withdrawal system, preferably for transfer of the powder directly from the transport container to consumption in a powder spraying plant.

4. Continuous withdrawal of powder during transfer to the consumption plant.

5. As superfluous, unused powder arises in the spraying plant, transferring this in order to feed it into the spraying plant together with freεhly delivered powder from said container.

6. When larger series with continuous consumption of a larger amount of powder are concerned, a successive supply of the required additional powder quantity from additional deliveries.

The equipment required for this method and its function will now be described in the following, with reference to the drawings.

As mentioned by way of introduction, one of the main objects of the invention is to attain a utilization of the return powder which is as complete as possible under present conditions and quality requirements. Thus, the following particulars muεt be determined in order to arrive at a solution: 1. Determination of data for the powder streams in different plants and in normally occurring coating operations. It may be expected that the ratio between the flow of fresh powder and return powder may vary within certain limits, from supply of solely fresh powder (powder which not has been used in the process iε discarded), to a blend between fresh powder and return powder with the latter in a comparatively high proportion. These proportions, as well as the occurring volumes/weights of powder, are determined. These values should constitute a base for the ranges within which a buffer-blending container should be designed to operate and be adjusted for.

2. Determination of the regulation process. In the first- mentioned case, where no return powder is added, only a regulation of the supplied amount of fresh powder is required so that a εuitable level is maintained in the buffer container. In all caseε where a blend of freεh powder and return powder shall be utilized, the difficulty arises in adapting the proportion of return powder in εuch a way that, during the complete courεe of the εpraying process, the same proportion of fresh powder and return powder is supplied, something which is one of the main objects of the system. If too high a quantity of return powder in relation to the accumulation thereof is set, the proportion of return powder would become reduced in relation to the set value. If, on the other hand, too low a value is set, the return powder will be accumulated and be only partially returned into the spraying process. Consequently, there must be means for the calculation of how the proportions of fresh powder and return powder should be set. Such means may be standard values for adjustment in different typical cases or calculation formulas based on certain factors related to the spraying, which determine the outturn of the return powder, or any form of calibration method with measurement of the proportions of fresh powder and return powder during a short test series. All methods may be applied individually in different coating cases, or in certain caseε in combination with each other.

Since a pre-εetting may become approximate, εaid condition, with too low an accumulation of return powder in order to meet the set proportion may occur, or inversely that too large an amount of return powder will need to be consumed at the set proportion. Thus, the syεtem may be provided with an automatic regulation which reduces, respectively increaseε the proportion of return powder within εet toleranceε, so that a balance between produced return powder and the supply ariseε. Such a regulation may have to be complemented with an alarm function, εo that εupervising personnel can observe that a set proportion is changed. An alarm is definitively required if, in spite of said regulation, the toleranceε cannot be met.

In Fig. 1, a powder εpraying plant, iε εchematically εhown as a block diagram, wherein the invention is applied. In Fig. 1, a container for recently delivered, fresh powder is denoted by reference numeral 1. As earlier mentioned, this is conveniently a transport container, so that the powder, when consumed, may be drawn out directly without any refilling into any special container in the plant. As such, the container iε provided with a nipple 5 through which a εuction device 3 may be inεerted. This will be further described in connection with the detailed device in Fig. 2. A suction device in a probe form, of the type which may be utilized in the preεent invention, iε diεclosed in for instance US A 5 271 695 (Biεchof et al). As is indicated in the drawing, the container 1 iε poεitioned diagonally, εo that a corner thereof formε a lowest point towards which the powder may flow down as it is consumed by withdrawal via the device 3. The powder which has been drawn up is transported to an inlet 8 of a buffer and blending container 9 by means of a pipe 6, which will also be described in connection with Fig. 2.

To the container 9 there is also connected an inlet 10 from a pipe 11 for return powder. The second end of the pipe 11 is connected to a collecting device 12 such as a channel in a spray booth 13. In the wall of this there are inserted a number of powder spray guns for the coating of work pieces 15, which travel past the spray guns by means of a conveyor. As mentioned earlier, use is made of a potential difference between the powder, which has been charged inside the guns, and the work piece in order to retain the powder before it melts in a subsequent heat treatment. The spray gunε are εupplied with powder from the blending container 9, which for thiε purpoεe has an outlet 16 which is connected to the gunε 14 by meanε of a pipe 17.

Compreεεed air iε utilized for tranεportation of the powder from the suction device 3 and from the collecting device 12 to the blending container 9, and further to the guns 14. The compresεed air iε generated in a unit 18 which, by meanε of pipeε 19-21, is connected to the deεcribed unitε.

The device for transferring powder from the transport containers to the spraying plant is shown in greater detail in Fig. 2. On the far left of the drawing, the delivery container 1 is depicted, placed in said position with the nipple 5 turned upwards. A pipe 22 is brought through the nipple to the suction device 3. This is εhown in section and it is thereby evident that its outer pipe 22 encloseε an additional pipe 24, whereby a duct 25 iε formed inεide the pipe 24, and an annular duct 26 is formed between the pipes 22 and 24. The duct 25 discharges at the outer end of the pipe 22 in an opening 27, and the duct 26 dischargeε on the outside of the pipe 22 in a plurality of openings 28 around the end of the pipe.

On a head 30 of the suction device 3 there is provided both a hose connection 31, which is connnected to the duct 25, and a hose connection 32, which is connected to the duct 26. The hose connection 32 is intended to be connected via the pipe 19 to the source 18 of compressed air, which consequently may εtream out through the holes 28 via the duct 26.

The hose connection 31 is connected to the hose pipe 6, in which a negative pressure is produced, whereby a suction effect arises at the opening 27. Another suction hoεe, the pipe 11, iε connected to the collecting device 12 for return powder which during the powder εpraying haε not εtuck to any object to be coated. In Fig. 2, thiε iε indicated with a furrow, to the bottom of which the hose 11 iε connected.

In Fig. 2 the buffer and blending device 9 is also shown which can blend powder from different sources and forms a buffer stock for the powder. In this device both the hoses 6 and 11 are connected to an ejector device 38 for achieving the negative pressure in the hoses. This is εhown in section in order to indicate how this negative preεεure may be attained. Thuε, the ends of the inlet pipes 8 and 9, to which the hoses 6 and 11 are connected, are enclosed by conical sleeves 41 and 42. The narrower ends of these are turned away from the ends of the inlet pipes 8 and 9 and diεcharge into outlet pipes 43 and 44. The inlet pipes 20 and 21, which are connectable to said source of compressed air 18, are connected to the wider ends of the sleeves 41, 42, which with bottoms enclose the inlet pipes 6 and 11, respectively. The pipes 43 and 44 discharge into a conical buffer container 48, for which the device 38 constitutes a lid. From the bottom of the container, the outlet pipe 16 startε, which in the εame way as the pipes 8 and 10 is enclosed by conical sleeves 50 with a compressed air connection 51 and said outlet pipe 16. The pipe 16 is intended, by means of the hose pipe 17, to be connected to one or several powder spray guns 14. These guns will not be described herein, but such are previously known. As a rule, they are designed to provide the sprayed powder with an electrostatic charge by means of which the powder, when sprayed out by compressed air, is well distributed in the room and forms a cloud which may encompasε the object which is to be coated. Moreover, the electrostatic charge is frequently used in order to get the powder to temporarily εtick to the object until homogenization and final adhesion of the powder material on the object occur by heating, εo that the powder granules melt. It is previously known to achieve the electrostatic charge in two ways: either by supplying a high voltage to the gun, or by furnishing it with channels of a material which, by means of friction, provides the powder with an electric charge.

In order to achieve the object of the invention, i.e. to obtain a controlled proportioning of fresh powder from the delivery container and return powder from the box while utilizing the return powder in an economic way, the device is provided with a control εystem. The components of this are evident from Fig. 1. Consequently, regulating means 60, 61, for regulating the powder stream into the device 9, are inserted next to the connections 8 and 10 or inside the pipes leading thereto. Furthermore, a sensor 62, adapted to detect the powder level in the container 48, is connected to the device 9. An additional sensor 63 is arranged in the spray booth 13 and its collecting device 12 for return powder in order to detect the temporary supply of return powder, i.e. the powder which haε not stuck on any workpiece but has accumulated in the booth.

The means are, preferably in an electrical way, connected to a control system which, however, is not shown in the drawing, but the function of which will be described in the following. The following control functionε εhould be effected:

1. Controlling that a certain minimum weight/level is maintained in the container 48 and that a maximum quantity/level is not exceeded and that a minimum quantity/level is not fallen short of. The minimum level iε determined by the fact that a εufficient powder quantity for feeding the gunε εhould be preεent in the container with respect to the variations which may occur in the consumption and the slownesε of the εupply which may prevail. If, namely, the conεu ption relatively unexpectedly would rise, a larger buffer quantity must be found in the container. This is especially the case if a rapid increaεe of the supply cannot be brought about. There may also be interruptionε of the supply, for instance when changing the delivery container by moving over the suction device 3. On the other hand, the container may never reach such a degree of filling that, should an interruption or a reduction of the output of powder occur, no space for a certain additional filling is required before the supply has been terminated.

The sensor 62 may either be arranged for measuring the powder level in the container or the temporary weight of the container. The level measurement may be done with a photo-senεor or by meaεurement by meanε of an air εtream. When measuring with an air stream, one measurement pipe may discharge at the minimum level and one at the maximum level. Thereby, it can be detected if these levels are exceeded or fallen short of by means of the resistance the air meets, at the muzzles of the pipes, when streaming out.

2. When supplying fresh powder and return powder to the blending device 9 by means of the regulating means 60 and

61 under control from the sensor 62 via the control gear, the function is, thereby, that the supply is choked when the maximum level has been reached and increased when the minimum level has been reached. This may in its most simple way be done by means of starting and stoppimg of the regulating meanε which let the powder through, or in a more εophiεticated way with continuouε detection of the oεcillations between the minimum and maximum level, so that a synchronization of the supply capacity of the regulating means may be done with the temporary consumption. Such a more continuouε filling process may probably be preferable in order to achieve stable blending conditions.

Furthermore, the regulating means should be synchronized so that when they regulate the supply of powder to the container, this is alwayε done in certain proportions between return powder and freεh powder. These proportionε must be possible to set from no admixture of return powder at all to the highest proportion of return powder which may be anticipated. The adjustment means may thereby be arranged solely for manual adjustment or, as mentioned in the following, also for automatic regulation.

3. Automatic adaption of the proportion of return powder according to the supply of such. As earlier mentioned, it may be difficult to calculate how large the outturn of unused powder in the booth will be in a certain spraying process. A manual adjustment of the proportions may therefore give either a too high or a too low consumption of return powder in relation to the outturn. A control of how the outturn of the return powder stands, in relation to the consumption during the spraying process, is provided by the sensor 63. When a surplus of return powder occurs, the proportion of return powder should be increased during automatic regulation of the proportions, and when the return powder supply is imperfect in relation to the set proportion, the quantity should be reduced so that a balance is maintained. If, however, the proportion is changed above a certain tolerance level, the quality of the coating may be affected. Thus, there must be poεεibilitieε to adjust these tolerances.

It may also be the case that, in order to maintain a certain quality, it is desired to have the return powder admixed in a certain proportion, with narrow tolerances. This may lead to an output which is lower than the supply of return powder. Aε earlier mentioned, one can refrain completely from the admixture of return powder in certain εpraying proceεεeε in order to achieve a very accurate quality. Under such settings, it cannot be avoided that return powder is accumulated and must, in that case, be transported away from the booth for other uses or rejection.

If, however, it is desired to utilize the return powder to the highest posεible extent, a fixed proportion of thiε εhould be set and alεo, in order to εeek to reach a balance between the εupply and the output, the toleranceε within which thiε proportion should be allowed to fluctuate. As mentioned earlier, the determination of these set points may be done by utilizing tables with experience valueε from certain typical cases, by utilizing calculation formulas and/or by test spraying in order to calibrate the settings.

The sensor 63 may be designed according to a principle similar to the sensor 62 for the quantity in the container

48. Thus, meanε for tranεporting return powder which falls out to a measurement container, from which the powder is transported to the spray guns, may be arranged. Thereby, as earlier described, means of a similar type may be arranged for measuring oscillations between a maximum and a minimum level. When the maximum level is exceeded, the control gear thereby controls the regulating means 60, 61 in order to increase the proportion of return powder, and in order to reduce it when the minimum level is fallen εhort of. If the minimum level cannot be maintained, as well as if the maximum level is constantly exceeded in spite of changes of the proportion within the tolerance limits, there should be an alarm in order to summon control staff so that necessary adjustments in order to maintain a regulated quality can be made.

There may also be a need for a device for cooling the powder down. The powder may namely, because of friction during its transportation, be heated up so that an agglomeration is brought about, which jeopardizes the spraying process. This may be avoided if the powder is kept at a low temperature.

Such a cooling down may of courεe be done in many different wayε and in different sections of the system. A convenient way iε to keep the compressed air entering through the connections 46, 47 and 51 at an appropriately low temperature.

If freshly added powder and return powder are to be blended, this should be done as intimately as posεible. The container 48 should thereby be designed as a blending chamber. In Fig. 2, it is indicated how the pipes 43 and 44 are curved at their ends so that the entering powder forms a vortex in which the particles are intimately blended. It is desirable that the container 48 has a volume as small as posεible. When a εpraying εerieε is finished, there will, namely, always be powder left in the container which may not find any further use and thus must be discarded.

If ionized air is to be used for the final evacuation and cleaning of the transport container 1, this may be supplied through an intermediate nipple 55, see Fig. 2. This is inserted into the container nipple 5 and encloεeε the pipe 22 of the device 3. By meanε of a hoεe connection 56, the ionized air is blown in and streams out through openings 57 along the walls of the container. Powder residues are thereby neutralized and fall down towards the lower portion of the container and may be drawn out. The device 23 may be arranged to start the air-flushing when the container startε to become empty. The εinking-down of the pipe 22, aε the powder iε conεumed, may be utiliεed for thiε purpoεe.

The deεcribed εyεtem functionε in the following way: when a container iε to be connected to the εyεtem, it iε poεitioned in a rack so that the nipple is directed upwards. The nipple 5 is opened by removing a transport cloεure and the pipe 22 to the device 3 iε inεerted into the nipple 5. Thereafter, compreεεed air iε connected to the connection 32 and to the connection 46. This causes air to stream out from the holes 28 at the outer end of the pipe 22 which rests against the powder surface closest to the nipple when the container is filled.

The compressed air, through the connection 46 will stream around the pipe 39 in the chamber in the conical sleeve 41 and out through the pipe 43. Thereby, a negative presεure iε formed by means of ejector action in the hose 6 and the connection 31, and thereby in the duct 25 inside the inner pipe 24. By means of the compressed air which streams out through the openingε 28, the powder closest to the opening 27 iε fluidized and is transported by the negative presεure and is brought through the pipe 43 and into the container by the compressed air.

In case return powder also is to be added, this is done in a corresponding way by the addition of compressed air to the connection 47 and thereby suction through the hose 11.

From the container 48 into which the powder is brought, it is brought further on through the outlet pipe 16, in which a suction effect also arises by means of ejector action in the conical sleeve 50, and via the pipe 52 and up to the spray guns. Additional devices for further transportation of the powder may be necessary if the hose pipes are long and maybe also branched to several spray guns.

The described supply procesε for the powder is controlled in the way evident from the earlier deεcription of the control system with its regulating and senεor meanε.

In a spraying plant where long series of objects are coated in a continuous working manner, one must allow for the powder from several containers to be supplied succeεεively, since the containers, for handling reasons, muεt have a limited size and conveniently are size-claεsified according to a modular system. Thus, it becomes necessary to successively add new containers without having to make any interruptions to the spraying.

This may be achieved if several devices 3 are connected to the blending device 9 with the container 48. This may conveniently be done by means of connecting these devices by branching the hose 6, or by providing several ejector devices in the device 38. In the latter arrangements, the flow from the different devices 3 may be controlled by means of an appropriate proportioning of the supply of compressed air, andtherebythe output fromindividual containers. In order to obtain a continuous supply when transport containers are concerned, it is convenient if these may be transported forward in turn, whereby the first container is connected to a device 3 for supplying powder to the blending device 9. When only a minor amount of powder remains in this container, a device 3 is inserted into the next container in the transportation line for delivery of powder as soon as the supply from the first container has stopped, possibly also with a contemporaneous supply from this container during a final phase of its emptying process.

The powder in the container 48, however, constituteε a buffer quantity which preventε the εupply to the εpray guns from ceasing, even if the εupply from a tranεport container temporarily should be interrupted. Accordingly, an alternative posεibility is to provide a mechanism for the transfer of a single device 3 from one container, when a ceased flow indicateε it is empty, to a filled container. During the short interruption of the supply of fresh powder, however, an output is obtained by means of the buffer quantity which is left in the container 48. This quantity should, however, be as small aε poεεible.

In order to obtain an indication of when the tranεport container starts to be emptied, the head 30 of the suction device 3 may be provided with a sensor, see 54 in Fig. 3, for instance a switch for an electric control circuit. Thereby, an alarm or a control signal, indicating that a new container should be switched in, may be obtained when the pipe 22, because of the consumption of the powder, has sunk so deep into the container that the senεor 54 haε reached the nipple 5.

The pipe 22 may alεo be provided with the previously described intermediate nipple 55, with its compresεed air outlet 57 for air-flushing of the transport container during said final phase of the emptying of the container, so that powder residues are flushed down to the suction opening 27 for an evacuation which is as complete as possible. The sensor 54 or the like may be utilized for the activation of such flushing.

Claims

CLAIMS :

1. Method for handling of powder in powder coating plants which comprise a number of powder spray guns (14) or the like for the supply of powder to which there is arranged an uptaking device (3) for powder from containers, preferably delivery containers (1) for fresh powder, as well as from a collecting device (12) for powder which has not been used in the spraying process for the coating of work pieces (15), with pipeε (6, 11) arranged for tranεportation of powder from said container and collecting device, respectively, to a buffer and blending device (9) for blending the fresh powder and the collected return powder, and also with means (16) for transporting the powder blend to the spray guns (14) or the like, c h a r a c t e r i z e d i n that the εupply of fresh powder and return powder to the blending device (9) is done in predetermined proportions, within certain predetermined limits of tolerance, in such independence of the supply of return powder in relation to the consumption in the spraying process that the limits of tolerance of the predetermined proportion are not exceeded during the spraying process by means of allowing the return powder to accumulate, when a surpluε of thiε prevailε, and triggering an influence on the εpraying process, when a deficit of return powder prevails, so that it is interrupted or indicated in order to be manually adjusted.

2. Device for carrying out the method according to claim 1 for the handling of powder in powder coating plants, in which both fresh powder as well as collected, unused powder in the spraying process in question is utilized for the supply to the powder spray guns (14) or similar application means of the plant, c h a r a c t e r i z e d i n that a buffer and blending device (9) is arranged to receive powder from a container (1) for fresh powder and from a collecting device (12) for return powder from the spraying process, and is arranged for blending fresh powder and return powder, and also for output to the powder spray guns or the like, whereby a control system is arranged to be adjustable to different proportions of fresh powder and return powder, while maintaining certain limits of tolerance for these proportionε with the control gear connected to sensor means (62) for the detection of a maximum and a minimum quantity, respectively, in a powder container (48) being a part of the buffer and blending device (9), and to regulating meanε (60,61) for the regulation of the quantity of fresh powder and return powder supplied to the container while maintaining the set proportion within the limits of tolerance with the control system additionally arranged, by means of the regulating means, to control the powder supply so that the quantity detected by means of said sensor is maintained within the maximum and minimum values, and also εensor means (63) for the detection of the supply of return powder at its accumulation in the spraying proceεs, with the control system thereby arranged to be influenced in such a way by a certain exceeded maximum quantity, when accumulation of return powder occurs, respectively when the minimum supply of return powder is fallen εhort of, that the proportion of return powder supplied to the buffer and blending device, by meanε of the regulating means, is primarily changed within the predetermined limits of tolerance towards reaching a balance between supply and consumption of return powder, and secondly in order to achieve an influence on the coating process by interrupting the same or by activating an alarm device or the like.

3. Device according to claim 2, c h a r a c t e r i z e d i n that the buffer and blending device (9) is arranged for intimate blending of fresh powder and return powder, preferably by means of vortex formation.

4. Device according to claim 3, c h a r a c t e r i z e d i n that an uptaking device (3) in the form of a probe for drawing up powder from a container (1) for fresh powder, preferably a delivery container, said collecting device (12) for return powder from the spraying process, pipes (6, 11) and compressed-air driven means (46, 47) for transportation of powder from uptaking device 3 and collection device (12), reεpectively, to the buffer and blending device (9), whereby the buffer and blending device iε connected to εaid pipeε for freεh powder and return powder by the meanε (60, 61) for regulation of the supplied powder quantity in a predetermined proportion within predetermined limits of tolerance, and also with the buffer and blending device provided with a container (48) for powder, and said sensor (62) connected to the container for the detection of maximum and minimum quantities of powder, respectively, output devices (50) and pipes (17) for supply of powder from the container (48) to the powder spray guns (14) or the like, at the collection device (12) for return powder said sensor means (63) of the spraying process for detection of the accumulation of return powder and said control gear which is arranged, by means of the regulating means, to control the supply of powder to the buffer and blending device, so that the maximum and minimum quantities detected by the sensor are not exceeded or fallen short off and that the supply of powder at the collecting device measured out under influence of the sensor in such a way that the proportion of return powder, by means of the regulating means, is raised when exceeding a certain accumulated quantity of return powder meaεured out by means of said sensor, and reducing the proportion of return powder when a certain limit for the supply of return powder is fallen short of.