EP0767006A1 - Method and apparatus for feeding powder to a powder spraying device - Google Patents

Abstract

The method has the fluidisation occurring in a twin chambered device (2), the first chamber (3 )receiving the compressed air that then passes through a "frit" to the second chamber(4). The powder in the second chamber leaves the device from the nozzle (11) and is charged up. The powder is filled through the hole (9) which can be closed off. Apart from the nozzle and the air inlet and outlet valves (17,19), the fluidisation takes place in a closed chamber, the valves being used to maintain the correct pressure proportions. Additional mechanical energy is passed to the fluidised bed of the second chamber in the form of vibration.

Description

The invention relates to a method for spraying a fluidized powder according to the preamble of claim 1. Furthermore, the invention relates to a device for performing the method.

Such a method and an associated device are known from DE-A 12 34 802 and are used, for example, for electrostatic painting. The known device for powder spraying has a first chamber, into which an additional compressed air is introduced, which enters a second chamber via a frit (a pore partition). A powder suspended in air is fed to the second chamber via a line and further swirled with the additional compressed air emerging from the frit and guided in countercurrent. The powder particles emerging from the second chamber are electrically charged with the aid of electrodes which are arranged in the region of a powder / air outlet opening and are connected to a high-voltage generator and which form an electrostatic field.

According to one embodiment, a third feed line is used in the known device, which carries air and has an improving effect on the powder / air output in the powder / air outlet area. The powder / air outlet is always open; The spraying process is controlled by controlling or regulating the flow rates of air and the air / powder mixture.

Other devices for powder spraying, but which do not work with a two-chamber arrangement of the type described above, are from the documents DE-C1 35 29 703 and EP-A1-05 74 305 known. The device known from EP-A1-05 74 305 contains a rotating baffle in the air / powder outlet area to improve the powder distribution.

All of the above-mentioned methods and devices have in common that a relatively large amount of air is used to convey and spray the powder, and the powder discharge rate, the powder jet adjustability and controllability of the powder discharge are unsatisfactory.

The invention is based on the object of specifying a method and a device for powder spraying, by means of which a high, easily controllable ejection rate can be achieved and the powder jet can be specifically oriented.

This object is achieved by a method for powder spraying according to the preamble of claim 1 by the characterizing features. A device suitable for carrying out the method and advantageous refinements are specified in further claims and can be found in the following on the basis of the exemplary embodiments illustrated in the drawing figures.

In the method according to the invention, powder is fluidized in a closed container and a powder cloud with relatively no air content emerges. The powder exit rate can advantageously be determined by regulating easily measurable air pressures. No level measurements are required. There is no loss of powder during the switch-on or switch-off process.

Fig. 1

Pulversprüheinrichtung,

Fig. 2

Pulveraustrittsdüse,

Fig. 3

Ausschnitt aus einer Sprüheinrichtung mit geöffneter Düse,

Fig. 4

Ausschnitt aus einer Sprüheinrichtung mit geschlossener Düse,

Fig. 5 bis 7

Formen von Pulverwolken,

Fig. 8 und 9

Sprüheinrichtung mit alternativer Düsengestaltung,

Fig. 10 und 11

Sprüheinrichtung mit rotierendem Prallkörper,

Fig. 12

Sprüheinrichtung mit rotierendem Prallkörper und rotierenden Elektroden und

Fig. 13

Anordnung mit ringförmiger Elektrode.

Show it:

Fig. 1

Powder spraying device,

Fig. 2

Powder outlet nozzle,

Fig. 3

Detail from a spray device with an open nozzle,

Fig. 4

Detail from a spray device with a closed nozzle,

5 to 7

Shapes of powder clouds,

8 and 9

Spraying device with alternative nozzle design,

10 and 11

Spraying device with rotating impact body,

Fig. 12

Spraying device with rotating impact body and rotating electrodes and

Fig. 13

Arrangement with an annular electrode.

1 shows a powder spraying device 1, which essentially consists of a closed container 2 with a first chamber 3 and a second chamber 4. A compressed air supply line 5 opens into the first chamber 3. Compressed air 7 enters the second chamber 4 through a frit 6. Powder 8 is located in the second chamber 4 and can be filled through a powder supply opening 9.

The air 7, which is passed through the frit 6 into the powder 8 and fluidizes it, can exit again through an air outlet opening 10 on the container 2 above the fluidized powder bed 8.

The fluidized powder 8 is removed from the area of the fluid bed through a pipe 25 and is led out through a nozzle 11 arranged laterally on the container 2 and closable with a closing device 13.

In the powder outlet area 12, needles are arranged as corona electrodes 14, which are connected to a high-voltage source (not shown) and which charge the emerging powder particles.

The shape of the emerging powder cloud 15 can be determined by the nozzle 11 and additional impact bodies 16, 22 (see also FIGS. 10 to 14). The shape and arrangement of the electrodes 14 can be adapted to this.

The air supply can be influenced with the aid of a controllable air inlet valve 17 and the air supply rate can be measured with the aid of a flow meter 18. The outlet opening 10 for fluidizing air is closed off by a controllable outlet valve 19, with which a defined flow resistance can be set.

The air pressure p ₁ in the first chamber 3 and the air pressure p ₄ above the powder bed 8 can be regulated via the valves 17 and 19 with the aid of a control and regulating device, not shown. The pressures p ₁ and p _{4 are} measured using suitable pressure sensors. The ambient air pressure is denoted by p ₀ . With p ₂ the air pressure above the frit 6 and thus immediately below the fluidized powder bed is designated. The pressure drop p ₁ -p ₂ depends on the selected frit 6 and must be taken into account when dimensioning.

P ₃ denotes the pressure inside the container 2 at the powder outlet opening 11, which can be adjusted by regulating the pressures p ₁ and p ₄ .

, durch die Gestalt der Düse 11, d.h. durch deren Strömungswiderstand, von den Parametern des Pulvers, sowie vom Fluidisierungszustand bestimmt.The amount of powder flowing out and the speed of the particles as they exit is determined by the differential pressure ${\text{Δp = p}}_{\text{3rd}}{\text{- p}}_{\text{0}}$

, determined by the shape of the nozzle 11, ie by its flow resistance, by the parameters of the powder, and by the fluidization state.

Since on the walls of the chamber, e.g. Irregularities in the fluidization caused by bubbles cannot be avoided, the powder is tapped from the interior of the chamber 4 through a pipe 25 attached to the nozzle 11. This ensures a high level of uniformity of the powder output.

Since only pressures and an air flow rate need to be measured and controlled (no fill levels), the powder output rate can be set and controlled very well. High output rates in the range of 100 g / min to 1000 g / min can be achieved. The control behavior of the device is very good, since fluidization and spraying take place in a single device. Since there is no hose connection between the fluidization chamber 4 and the nozzle 11, there are no fluctuations in the powder output and no powder losses when switching on and off.

The fluidization can advantageously be operated near the loosening point; then the air / powder ratio of the sprayed powder is minimal. This also ensures a high level of uniformity of the powder output.

The shape of the powder cloud 15 is u. a. can be influenced by the shape of the nozzle 11 and the powder outlet area 12. 2 shows a possible design of the nozzle 11 and the outlet area 12 with dimensions given in millimeters by way of example. FIGS. 3 and 4 show sections of the powder spraying device 1, the nozzle 11 shown in FIG. 2 with the closing device 13 being shown in the open or closed position.

5 shows a top view of a typical cylindrical container 2 with an emerging powder cloud 15. By designing the nozzle 11 and the outlet area 12 accordingly, a different configuration of the powder cloud 15 can also be achieved, as shown in FIG. 6. In Fig. 7 it is shown that the design of the container 2 can also be adapted to a desired shape of the cloud 15.

A simple possibility for nozzle design is shown in FIGS. 8 and 9, an orifice 20 with different nozzle openings 21 being shown.

A particularly broad and uniform powder cloud can also be achieved with the aid of an impact body (deflector) which - as is shown schematically with reference to FIGS. 10 and 11 - can also be designed as an impact body 22 rotating about an axis 23. An associated drive device 24, including ball bearings 31 and drive belts 32 for the rotating impact body 22 is only indicated in the drawing. A different design of the powder outlet area 12 is shown in FIGS. 10 and 11. In FIG. 11, a jacket 33 is placed around the impact body 22, so that a rotating gap is created, through which the shape of the powder cloud can be additionally influenced.

The spray device 1 according to FIG. 1 can be operated in such a way that powder 8 is filled in and then the filling opening 9 is closed. The powder can then be sprayed until a minimum powder level, which is in the region of the nozzle 11, is reached.

Figures 12 to 14 show further options for designing the powder outlet area.

12 shows an arrangement in which both a rotating impact body 22 and rotating high-voltage electrodes 14 are present. The rotatable arrangement of the components 22, 14 is indicated by the ball bearing 31 and the drive belt 32.

In addition, FIG. 12 shows an additional air duct 30, via which additional air 28 can be fed, which can escape through air nozzles 27 in the powder outlet area 12. With the additional air 28, an additional acceleration of the powder particles and shaping of the powder cloud can be achieved.

FIG. 13 shows an arrangement of, for example, a ring-shaped earth electrode 26 in the area between the wall of the container 2 and the impact body 22. At least a part of the ion current flows to the earth electrode 26, as a result of which the powder flow is crossed and an improved charging is achieved. In this case, the high-voltage electrodes 14 are attached to the rotating impact body 22. With this arrangement, at least part of the ion current flows from the high-voltage electrode to the earth electrode and the powder particles are forced to cross this ion current, whereby better charging is achieved.

Reference list

1

Powder spraying device

2nd

closed container

3rd

first chamber

4th

second chamber

5

Compressed air supply

6

Frit

7

Compressed air

8th

Powder, powder bed

9

Powder feed opening

10th

Air outlet opening

11

jet

12th

Powder exit area

13

Locking device

14

Corona electrode (needle electrodes)

15

Powder cloud

16

Impact body (general)

17th

Air inlet valve

18th

Flow meter

19th

Air outlet valve

20th

cover

21

Nozzle opening

22

rotating impact body

23

axis

24th

Drive device

25th

pipe

26

Earth electrode

27

Air vents

28

Additional air

29

rotating disc (with electrodes)

30th

Additional air duct

31

ball-bearing

32

Drive belt

33

coat

Claims (8)

A method of spraying a fluidized powder (8), wherein a) the fluidization takes place in a two-chamber device (2), in the first chamber (3) of which compressed air (7) is introduced, which is supplied to the second chamber (4) via a frit (6), and b) the fluidized powder (8) emerges from the two-chamber device (2) and is then electrically charged,
characterized in that c) powder (8) is poured into the second chamber (4) via a closable powder feed opening (9), d) the powder fluidization of the chamber (4) within a - apart from a nozzle (11) and air inlet and outlet valves (17, 19) - closed container (2) by regulating the position of the air inlet and outlet valves (17, 19) appropriate pressure conditions are maintained, and e) the fluidized powder (8) is removed from the area of the fluid bed and fed to the nozzle (11). A method according to claim 1, characterized in that additional mechanical energy is added to the fluid bed in the second chamber (4) by stirring or vibration in order to avoid that larger air bubbles form, rise and reach the nozzle (11). Device for performing the method according to claim 1 or 2, wherein a) a two-chamber device (2) is provided, in the first chamber (3) of which compressed air (7) can be fed, b) a frit (6) is arranged between the first chamber (3) and the second chamber (4), via which air (7) can pass from the first chamber (3) into the second chamber (4), and c) high-voltage electrodes (14) are arranged at the powder discharge point for charging,
characterized in that d) the two-chamber device is designed as a closed container (2), e) Powder can be filled into the second chamber (4) via a closable powder feed opening (9) and can be fluidized there by supplying air from the first chamber (3) while regulating the compressed air supply and discharge in a fluid bed, and f) there are means (25) for removing fluidized powder (8) from the area of the fluid bed and feeding them to the nozzle (11) which can be closed by means (13). Device according to claim 3, characterized in that an impact body (16, 22) is arranged in a powder outlet area (12) of the nozzle (11) and can also be designed to be rotatable with the aid of a drive device (24). Device according to one of claims 3 or 4, characterized in that high-voltage electrodes (14) for electrostatic charging are arranged on a rotating disc (29) in order to achieve a particularly uniform charging on the circumference of a powder cloud (15). Device according to claim 5, characterized in that an annular earth electrode (26) is arranged behind the rotating high-voltage electrodes (14), i.e. in a region between the outer wall of the container (2) and the high-voltage electrodes (14), to which at least a part of the Ion current flows and thereby crosses the powder flow and an improved charging is achieved. Device according to one of claims 3 to 6, characterized in that the fluidized powder (8) is removed from the fluid bed with the aid of a tube (25) which conducts the fluidized powder (8) to the nozzle (11) and prevents larger air bubbles rising to the housing wall reach the nozzle (11). Device according to one of claims 3 to 7, characterized in that air nozzles (27) open into the powder inlet area (12), exit via the additional air (28) and additionally accelerate the powder particles and can additionally form the powder cloud (15).

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