WO2011032807A1

WO2011032807A1 - Method and device for conveying and distributing powders in a gas stream

Info

Publication number: WO2011032807A1
Application number: PCT/EP2010/062304
Authority: WO
Inventors: Eckart Theophile
Original assignee: Reinhausen Plasma Gmbh
Priority date: 2009-09-15
Filing date: 2010-08-24
Publication date: 2011-03-24
Also published as: EP2477751B1; EP2477751A1; DE102009041338A1

Abstract

In order to enable the conveyance of extremely fine powders with uniform distribution in the gas stream and to prevent or resolve agglomerations of the powder, according to the invention a closed container (2) is filled up to a maximum fill level (4) with powder (5), the powder is impinged in a periodic sequence via at least one gas inlet (3), but preferably four gas inlets, with a gas that is under overpressure, and the whirled up powder/gas mixture (7) flows out of the container via at least one outlet (6), preferably two outlets, arranged above the maximum fill level of the container.

Description

Method and device for conveying and distributing

Powders in a gas stream

The invention relates to a method and apparatus for conveying and distributing powders in a gas stream.

Such methods and conveyors come to the feeder

metered quantities of fine-grained powders, especially for coatings, used. Powder deposits and

Agglomerations of the powder in the conveyor and the

Powder flow paths must be avoided.

The promotion of extremely fine powders with grain sizes of less than 10 [im is virtually impossible with known conveyors. Below this grain size take the

Adhesive forces between the powder particles significantly. The surface of the particles increases considerably in relation to the volume. A cube with an edge length of 1 cm has a surface of 0.006 m ² . The same volume filled with particles of five nanometers edge length, however, has a surface area of 2,400 m ² . The large increase in surface forces hinders the promotion of such small particles. Only by permanent energy coupling, in particular high flow velocities, which are associated with a high gas or air consumption, can

Agglomeration of the powder / gas mixture can be avoided. High gas flow rates, however, are in different

downstream work processes, such as in plasma coating processes or laser

Coating processes, disadvantageous. In addition, high gas flow rates require a higher energy input for the promotion. There are also downstream processes where the powder / gas mixture requires the use of inert gases. Due to the high cost of inert gases, a reduction of gas consumption is also for this reason

desirable. DE 44 23 197 discloses a powder pump for powder for spray coating of articles in a rod-like manner

elongated shape. On one end, the powder pump has a powder suction, is sucked through the powder from an open-topped powder container and conveyed through an inner tube of the powder pump to a consumer. The promotion itself is done by generating a vacuum in the powder pump. The vacuum is created with an injector nozzle located near the powder suction port.

DE 10 2006 002 582 A1 discloses a powder conveyor with a fluidising unit. The fluidizing unit is arranged at the end of a powder suction pipe of the powder conveyor and blows in the intake of the Pulveransaugrohrs fluidizing air in the powder supply, so that the powder can be fluidized and thus easier to be sucked and transported. The fluidising unit is above and concentric with the

Pulveransaugöffnung arranged. As a result, a screen-shaped fluidized powder region forms around the

Intake port around out. The promotion takes place by means of a working with compressed air injector, which at the

Fluidising unit opposite end of the

Pulveransaugrohres is connected. A fluidization takes place directly below the Pulveransaugöffnung

not by design. Although the annular

Fluidization improves the suction of the powder, the constancy of the amount of powder is not optimal during suction. Furthermore, agglomerates of the powder are insufficiently dissolved and mostly directly through the

Aspirated powder intake. This leads to problems, in particular in downstream coating processes which require a constant layer thickness. Based on this prior art, the invention is based on the object, a method for conveying and To provide dispersing powders in a gas stream, which allows the promotion of extremely fine powders, especially those with a particle size of less than 10 [im, with small amounts of gas, are nevertheless avoided in the agglomeration of the powder or dissolved and at the same time

uniform distribution of the powder in the gas stream is achieved. Furthermore, a simple structure conveyor for the promotion and distribution of extremely fine powders in a gas stream is proposed.

This object is achieved in a method of the type mentioned above in that a closed container is filled up to a maximum level with powder, the powder via at least one gas inlet, but preferably four gas inlets with a pressurized gas in a periodic sequence applied will and that

fluidized powder / gas mixture over at least one

Outlet, preferably two above the maximum level of the container arranged outlets from the container

flows.

The periodic loading of the powder with the pressurized gas causes the powder to be swirled up into the free space above the powder and distributed there. At the same time, the pressure pulses dissolve any agglomerates of the powder. The inside of the closed

Container due to the gas inlet adjusting overpressure above the ambient pressure causes that so

fluidized powder / gas mixture arranged in the direction of each above the maximum level of the container

Outlet emanates.

An optimal distribution of the powder in the gas space above the powder level is characterized by a low-frequency

Application of the powder in a range of 1 Hz to 100 Hz achieved. The overpressure of the closed container (Pressure vessel) introduced gas is preferably in the range of 100 mbar to 5 bar.

A higher delivery rate is achieved in that the powder is acted upon by several, in particular four gas inlets with the gas under pressure.

The distribution of the powder in the gas and the dissolution of existing agglomerates can be improved by passing the powder over several consecutive times

controlled gas inlets with the gas is applied.

Preferably, the gas pressure pulses act without temporal

Interruptions between two consecutive gas pressure pulses on the powder. If the gas inlets evenly over the circumference of the container, preferably in one

Container level, are arranged, the admission takes place circumferentially around the container.

A further improvement in the swirling and distribution of the powder in the space above the powder in the container is achieved when the application of one or more

several gas jets at an angle of at most 45 degrees to the surface of the powder. It is assumed that the surface of the powder bed in the

Essentially is just.

For powders that tend to agglomerate strong, in an advantageous embodiment of the invention, the level of the powder is kept in the closed container constantly above a minimum level and the powder below the minimum level via at least one standing in contact with the powder gas inlet directly with gas

applied. As a result, the pressure pulses are particularly effectively transferred to the powder and dissolved as a result, the agglomerates extremely effective. The pressurized gas flows through the powder into the overlying one Free space and promotes the fluidized by the pressure pulses powder / gas mixture toward each outlet.

The outlet can be connected in an advantageous embodiment of the invention with a hose, with which the powder / gas mixture another process, in particular a

Coating process is supplied.

In order to ensure continuous powder delivery, in an advantageous embodiment of the invention, the powder is replenished from a refill container via an inlet into the container. The refill container is under the same overpressure as the closed container, is refilled in the. Preferably, the level of the powder is kept in the closed container constantly above a minimum level.

A preferred device for carrying out the method results from the features of claim 9.

A particularly effective periodic loading of the

Powder is carried out with pressurized gas

preferably by means of a directed gas jet. to

Generation of the directed gas jet, each gas inlet is located at a particular in the interior of the container projecting, but at least in the interior of the container opening nozzle. In order to ensure the application of the powder at an angle of at most 45 degrees to the surface of the powder, the nozzle has a corresponding

Angle of attack.

The closed container for receiving the powder is designed in particular circular-cylindrical. The gas inlets are in a plane of the circular cylindrical container

preferably arranged over its circumference, so that the Center angle between all gas inlets

matches.

The individual inlets are with the help of

Control means, in particular a valve control, periodically exposed to gas. The individual inlets can be subjected to gas in succession or partially overlapping in time or in a temporally overlapping manner. In the latter case, all gas inlets are simultaneously exposed to gas in a periodic sequence.

Furthermore, the circulating admission over several

Inlets, depending on the nature of the powder to be pumped and the required flow, with short

Interruptions take place so that, at least temporarily, gas does not enter the container via any of the inlets.

In order to produce a spiral flow of the powder / gas mixture in the container in the direction of its outlet, in one embodiment of the invention at least one nozzle is arranged parallel to a secant with respect to the circular bottom of the container, the secant being at a distance from the latter Center runs. To ensure continuous operation of the conveyor, the closed container is over

Piping connected to a refill container for the powder, wherein from the preferably larger

Refill container powder automatically runs into the closed container for the distribution and conveying of the powder. To exclude exceeding the maximum level during automatic refilling, the mouth is located in the interior of the container

extending pipe just below the maximum level of the container. The invention will be explained in more detail with reference to the figures. Show it:

Figure la is a schematic plan view and Figure lb is a schematic side view of a first

Embodiment of a device according to the invention for conveying and distributing powders in a gas stream;

Figure 2a is a plan view of a second

Embodiment of a device according to the invention with a substantially

tangential gas supply;

Figure 2b is a plan view of a third

Embodiment of a device according to the invention with a plurality of distributed over the circumference arranged gas inlets;

Figure 3 is a schematic side view of a fourth

Embodiment of a device according to the invention with arranged at a pitch angle gas inlets nozzles;

Figure 4 is a diagram for illustrating the

inventive method for conveying and distributing powders in a gas stream using a device according to. Figure 2b;

Figures 5a, a fifth embodiment of a

Device according to the invention with a

Refill container for continuous operation as well FIG. 6 shows the connection of a device according to the invention

Device to a downstream

Plasma coating process. The apparatus shown in Figure 1 for conveying and

Distributing powders in a gas stream, hereinafter referred to as "powder conveyor" (1), essentially consists of a closed container (2), which via a gas inlet (3) with means not shown for gas supply

connected is. The container (2) is up to a maximum

Level (4) filled with a fine powder (5), which is a subsequent process, in particular a

Coating process, to be supplied. Above the maximum level (4) of the container (2), an outlet (6) for a powder / gas mixture (7) is arranged. The outlet (6) is in particular with a connection for a

Hose line (19) equipped for forwarding the powder / gas mixture (7) to the downstream process. The means connected to the gas inlet (3) for

Gas supply comprise as control means for the periodic control of the gas, in particular a valve control with which a pressurized gas in a periodic sequence via the gas inlet (3) in the interior of the container (2) is inserted. The valve control operates, for example, at a frequency of 10 Hz. The height of the gas pressure is determined such that the pressure inside the container (2) is higher than the ambient pressure, with pressure losses in a possibly connected to the powder outlet

Hose line to be considered to the mouth. The introduced gas is preferably an inert gas to prevent dust explosions in the container (2)

prevent. In the illustrated embodiment, the gas inlet (3) opens directly into the powder (5). In addition to this favorite direct introduction of the gas into the powder (5), it is also possible to arrange the gas inlets (3) above the maximum level (4) of the powder (5), so that the gas impinges on the surface (9) of the powder (5) ,

The powder conveyor (1) according to Figure 2a differs from the powder conveyor of Figure 1 in that the

Gas inlet (3) on a nozzle (10) which is parallel to a secant (11) with respect to the circular bottom (12) of the container (2). This type of gas introduction into the container (2) produces a spiral flow (13) of the powder / gas mixture (7) in the container (2). The channel (8) having the outlet (6), as can be seen in Figure 2a, is also aligned parallel to a secant with respect to the circular bottom (12) of the container (2).

FIG. 2b shows a preferred embodiment of the invention

Powder conveyor (1) according to the invention with four offset by 90 degrees to each other, but arranged in a plane, gas inlets (3a - d) and two outlets (6a - b) for the powder / gas mixture (7). The periodic admission of the gas inlets (3a-d) with the gas under overpressure can take place simultaneously. Preferably, the

Gas inlets (3a - d), however, temporally successive acted upon by the pressurized gas gas, so that the outgoing of the gas supply unit pressure pulses to the container (2) rotate.

FIG. 3 shows a modification of the device according to FIG. 1. The powder conveyor (1) differs essentially in that it has two nozzles (10) projecting into the interior of the container (2) with an angle of incidence (14) of approximately 25 degrees to that Bottom (12) of the container (2) having the

Gas inlets (3a - b) have. This angle of attack improves the dissolution of agglomerates in the fine powder (5). The method according to the invention for conveying and distributing powders in a gas stream with the aid of the preferred apparatus according to FIG. 2b will be explained in more detail below with reference to FIG.

From a refilling container (15) not shown in FIG. 4 b), the container (2) is filled with powder (5) via a pipe (16) up to the maximum level (4). The powder (5) is acted upon by the four gas inlets (3a-d) in chronological succession. In the diagram of Figure 4 c) can be seen how the gas inlets (3a - d) without

One after the other, introduce the pressurized gas into the tank (2) one after the other. By the application of gas, the powder (5) is fluidized, wherein in the

Free space above the surface (9) of the powder (5) forms the powder / gas mixture (7), which over the two

diametrically opposed outlets (6a, b) from the

Tray (2) flows out. The successive ones

continuous loading of the powder (5) with the

Pressure impulses from the four gas inlets (3a-d) improve the delivery rate with low gas consumption. Furthermore, the continuous, periodic causes

Actuation of the powder (5) via several gas inlets (3a-d) optimum dissolution of existing agglomerates.

As soon as the supply of powder (5) falls below the maximum fill level (4) to a minimum fill level (17) as a result of the continuous removal of the powder / gas mixture through the two outlets (6a, b), as illustrated in FIG is refilled, powder from the above the container (2) arranged refill container (15). The

Piping (16) for refilling the powder extends into the interior of the container (2), wherein the mouth, as can be seen in particular from Figure 5a, just below the maximum level (4) of the container (2). To that To ensure automatic refilling, is the powder supply (18) in the refill (15) below

the same pressure that also prevails inside the container (2).

FIG. 6 shows an example of application of the powder conveyor (1) according to the invention. The outlet (6) of the powder conveyor (1) is connected via a hose line (19) to a jet generator (20) for generating a bundled plasma jet by arc discharge. In the plasma jet (21) of the jet generator (20), the powder / gas mixture (7) in the region of its outlet (22)) is introduced. The finely divided powder (5) is deposited with the plasma jet (21) on the surface (23) of an object (24).

LIST OF REFERENCE NUMBERS

No. Designation

1 powder conveyor

2 containers

3, 3 a - d gas inlet, gas inlets

4 maximum level

5 powders

6, 6 a - b From 1as s, from 1äs se

7 powder / gas mixture

8 channel

9 surface

10 nozzles

11 sec

12 floor

13 flow

14 angle of attack

15 refill containers

16 pipeline

17 minimum level

18 powder supply

19 hose line

20 beam generator

21 plasma jet

22 From 1as s

23 surface

24 object

Claims

Claims:

1. A method for conveying and distributing powders in a gas stream, characterized in that a closed container (2) at most up to a maximum level (4) is filled with the powder (5),

the powder (5) is acted upon by at least one gas inlet (3) with a pressurized gas in a periodic sequence and

the fluidized powder / gas mixture (7) flows out of the container (2) via at least one outlet (6) arranged above the maximum filling level (4) of the container (2).

2. The method according to claim 1, characterized in that the powder (5) is acted upon at a frequency in the range of 1 Hz to 100 Hz with the gas.

3. The method according to claim 1 or 2, characterized in that the powder (5) via a plurality of gas inlets (3a - d) is acted upon by the gas under pressure. 4. The method according to claim 3, characterized in that the powder (5) is applied in chronological succession via the gas inlets (3a - d) with the gas.

5. The method according to one or more of claims 1 to 4, characterized in that the application of a

Gas jet or multiple gas jets under one

Incident of maximum 45 ° to the surface (9) of the powder (5). Method according to one or more of claims 1 to 4, characterized in that the level of the powder (5) in the closed container (2) constantly above a minimum level (17) held and the powder (5) below the minimum level (17 ) above

at least one gas inlet (3) in contact with the powder (5) is directly exposed to gas.

Method according to one or more of claims 1 to 6, characterized in that the overpressure of the gas is in the range of 100 mbar to 5 bar.

Method according to one or more of claims 1 to 7, characterized in that powder (5) consists of a

Refill (15) is refilled via an inlet into the container (2) during the promotion and distribution of the powder in the gas stream.

Device for conveying and distributing powders in a gas stream, in particular according to claim 1, characterized in that a closed container (2) which can be filled up to a maximum level (4) with powder (5) has at least one gas inlet, which is provided with means for

Gas supply is connected,

- means for gas supply control means for

periodic control of the gas at each gas inlet (3, 3a-d), above the maximum level (4) of the container (2) at least one outlet (6, 6a-b) for a

Powder / gas mixture (7) is arranged and each gas inlet (3, 3a-d) is located below each outlet (6, 6a-b).

10. The device according to claim 9, characterized in that each gas inlet (3, 3a - d) is located in each case one in particular in the interior of the container projecting nozzle (10).

11. The device according to claim 10, characterized in that each nozzle (10) has an angle of at most 45 ⁰ to a bottom surface of the container (2).

12. Device according to one of claims 9 to 12, characterized in that the container (2) is circular cylindrical.

13. Device according to one of claims 9 to 12, characterized in that a plurality of gas inlets (3, 3a-d) are arranged uniformly distributed over the circumference of the container (2).

14. Device according to one of claims 9 to 12, characterized in that at least one nozzle (10) parallel to a secant (11) with respect to the circular bottom (12) of the container (2) extends at a distance from the latter

Center runs.

15. Device according to one of claims 9 to 14, characterized in that the container (2) via a

Pipe (16) with a refill container (15) for the

Powder (5) is connected. Apparatus according to claim 15, characterized in that the pipe (16) is in the interior of the

Container (2) extends and whose mouth is below the maximum level (4) of the container (2)