EP0792694B1 - Process and device for controlling the flow of a fluidised powder from a container - Google Patents

Abstract

The method involves a container (2) with a drain pipe (25). Air is introduced into the pipe through an opening and the adjustable air pressure controls the mass flow through the pipe from zero to a maximum value. The container is part of a powder spraying unit (1) and the powder is removed from a fluidised bed in the middle of it.

Description

The invention relates to a method and a device for controlling the Mass flow of a fluidized solid when it is removed from a container.

The method or the device is generally applicable for closing or partial or completely opening an outlet opening on a container for fluidized Solid, with an increased in the container compared to the ambient air pressure There is pressure.

The method and the device are particularly suitable for use in powder spraying devices for electrostatic painting. Such a powder spraying device is, for example, in the unpublished German patent application P 195 370 89. The structure of this powder spraying device is shown below 1 explained in more detail. With regard to the subject of the invention it is essential that the powder spraying device is a mechanical locking system for the powder outlet.

Such a mechanical locking system is subject to wear. Moreover a small amount of non-fluidized powder occurs at the start of spraying because there is no fluidization in the sampling tube. There may be a problem in the sampling tube Powder deposits are coming.

From WO-A-8704643 an arrangement and a method are known with which the Disadvantages of mechanical locking devices are avoided by using a control air is worked. The control air causes this through a delivery line aspirated powder / air mixture from the delivery line to a spray nozzle and is fed via a return line into a special collecting container, where the filter is used to hold back the powder and blow off air. The order and the physical principle used here requires a relatively high level of effort, a powder deposit in the area of the spray nozzle is not avoided.

WO-A-94/13405 also describes a system for powder spraying in which a control air the fluid mass flow is controlled. With this system is out a pressurized container of fluidized powder by one arranged on the outside of the container Pipe passed. The fluid extraction is based on the principle of a Venturi nozzle creates a negative pressure. To homogeneously fluidized powder from the edge area of the To be able to remove the container, an agitator is arranged in the container. The one used Control air is blown into the pipe against the direction of the mass flow. To avoid an additional cleaning air is used for powder deposits. The arrangement is relatively complex.

The invention is therefore based on the object of a method and a device for Specify control of the exit of a fluidized solid, the aforementioned Disadvantages should be avoided.

This object is achieved in a method for controlling a fluid mass flow, starting from WO-A-94/13405 which in the preamble of the claim 1 has specified features, by its characteristic features solved.

In addition, the task is performed by a device for controlling the exit of a fluidized solid dissolved from a container, the device which in claim 4 indicated features, also starting from WO-A-94/13405.

The method and the device cause that by transverse introduction of closing air in the extraction tube the powder from the tube in a closed, under pressure standing container pushed back and thereby the powder output stopped becomes. This means that the sampling tube is cleaned at the same time with each closing process. No solids are deposited, there are no solids at the start of spraying non-fluidized solid particles and mechanical wear of moving parts is avoided. A nozzle located at the outlet will help with each spray stop the closing air cleaned. The mass flow of the fluidized solid is simple Way through change of the closing air flow controllable. The solids emissions can be adjusted accordingly Pressure ratios also to intermediate values between zero and a maximum value can be set.

A more detailed explanation of the invention follows with reference to one in the drawing illustrated embodiment.

Fig. 1

Prinzipdarstellung einer Pulversprüheinrichtung mit mechanischer Schließvorrichtung am Pulveraustritt,

Fig. 2

Prinzipdarstellung eines Schließsystems mittels Lufteinleitung in ein Entnahmerohr, wobei der geschlossene Zustand gezeigt ist,

Fig. 3

Prinzipdarstellung des Schließsystems entsprechend Fig. 2 im geöffneten Zustand.

Show it:

Fig. 1

Schematic diagram of a powder spraying device with mechanical locking device at the powder outlet,

Fig. 2

Schematic representation of a locking system by means of air introduction into a sampling tube, the closed state being shown,

Fig. 3

Schematic representation of the locking system according to FIG. 2 in the open state.

1 shows a powder spraying device already described in application P 195 370 89 1, which essentially consists of a closed container 2 with a first Chamber 3 and a second chamber 4 exists. In the first chamber 3 opens a compressed air supply line 5. Compressed air 7 passes through a frit 6 into the second chamber 4. In the second chamber 4 there is powder 8 which passes through a powder feed opening 9 can be filled.

The fluidizing air 7, which is passed through the frit 6 into the powder 8 and this fluidized, can through an air outlet 10 on the container 2 above the fluidized Exit powder beds 8 again.

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

In the powder outlet area 12, needles are arranged as corona electrodes 14, which coincide with a high-voltage source, not shown, are connected and charging of the emerging powder particles.

The shape of the emerging powder cloud 15 can by the nozzle 11 and an additional Impact body 16 are determined. The shape and arrangement of the electrodes 14 can be adapted to it.

With the help of a controllable air inlet valve 17, the air supply can be influenced and using a flow meter 18 to measure the air supply rate. The outlet opening 10 for fluidizing air is through a controllable outlet valve 19 completed, 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 with suitable pressure sensors. The ambient air pressure is denoted by p ₀ . P ₂ denotes the air pressure above the frit 6 and thus immediately below the fluidized powder bed. 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 in the fluid bed at the level of the powder removal, which pressure can be adjusted by regulating the pressures p ₁ or p ₄ .

The amount of powder flowing out and the speed of the particles as they exit is determined by the differential pressure Δp = p ₃ -p ₀ , by the shape of the nozzle 11, ie by its flow resistance, by the parameters of the powder and by the state of fluidization.

Since on the walls of the chamber, e.g. irregularities caused by bubbles are not to be avoided during the fluidization, is attached to the nozzle 11 Pipe 25 tapped the powder from inside the chamber 4. So that is ensures a high uniformity of the powder output.

2 and 3 each show a schematic diagram of the embodiment according to the invention a locking system for the exit of fluidized powder, which is in place of the mechanical locking system shown in FIG. 1, FIG shows the closed state and FIG. 3 shows the open state. Corresponding with Fig. 1 Reference symbols refer to components of the same type in each case.

FIG. 2 shows a section of the container 2, with the removal tube 25 for fluidized powder 8. At a suitable point, the jacket of the removal tube 25 has an opening 50, into which an air tube 51 opens. Closing air L _{S can be introduced} into the air tube 51. The method for controlling the fluid powder outlet and thus the operation of the device shown in FIGS. 2 and 3 is explained below.

Depending on the amount of closing air L _{S introduced} and other parameters, such as the diameter of the extraction pipe 25, the air pipe 51 and the nozzle 11, ambient air pressure p ₀ and fluid bed pressure p _{3, a} closing air pressure p _R is established in the air pipe 51.

If the closing air pressure p _R in the extraction pipe 25 is greater than the pressure p ₃ in the container 2, powder leakage is prevented; ie at a pressure ratio p _R / p ₃ > 1, the fluid powder 8 is pushed back into the container 2. If the closing air pressure p _R in the extraction pipe 25 is less than the pressure p ₃ in the container 2, that is to say the ratio p _R / p ₃ <1, fluidized powder emerges.

A numerical example can further clarify which air pressures are required for closing. With a sampling pipe diameter of 8 mm, air pipe diameter of 2 mm and a nozzle diameter of 0.8 mm, in the case of a container pressure p ₃ of 2 bar (corresponds to 1 bar overpressure) a closing air pressure p _R of at least 2.1 bar is required to discharge the powder stop completely.

If the nozzle diameter is 1.0 mm, a closing air pressure p _R of at least 2.4 bar is required under otherwise identical conditions as previously mentioned in order to completely stop the powder output.

In the closed state, some closing air is constantly consumed, some of it flows through the pipe 25 into the container 2 and partially through the nozzle 11. In This is a case of application with relatively short pauses between powder spraying processes Compressed air consumption without practical importance.

2 shows a state in which a closing air pressure p _{R that} is greater than the fluid bed pressure p ₃ is set by appropriately introducing closing air L _{S into} the extraction tube 25. There is no powder leakage. The closing air L _S flows partly into the container 2 and partly through the nozzle 11.

Fig. 3 shows a state in which the supply of closing air L _{S is} completely shut off and powder can thereby be ejected.

Claims (5)

1. Method for the continuous control of the mass flow of a fluidized solid (8) during the extraction of the latter by means of an extraction pipe (25) from a fluid bed located in a container (2) by the introduction of closing air (L_S) into the extraction pipe (25), characterized in that

   a) an extraction pipe (25) is used, which projects with its entry side in a middle region of the fluid bed, a nozzle (11) being arranged on the extraction-pipe exit side,

   b) the container (2) used is a closed container with a container internal pressure (p₃) higher than the ambient air pressure (p₀), a counterpressure being capable of being generated in the extraction pipe (25) by means of transverse introduction of closing air (L_S) and having the effect that the fluid powder (8) is forced partially or completely through the extraction pipe (25) back into the container (2).
2. Method according to Claim 1, characterized in that the closing air (L_S) flows out at least partially through the nozzle (11) and, particularly in the case of a ratio, bringing about the closing state, of a closing-air pressure (p_R) prevailing in the pipe (25) to the pressure (p₃) in the container (2), has the effect of cleaning the pipe (25) and the nozzle (11).
3. Method according to Claim 1 or 2, characterized in that the ejection of powder from a powder-spraying device (1) for electrostatic lacquering is thereby controlled.
4. Device for controlling the mass flow of a fluidized solid (8) during the extraction of the latter by means of an extraction pipe (25) from a container (2), control taking place by the introduction of closing air (L_S) into the extraction pipe (25), characterized in that

   a) the extraction pipe (25) ends with its entry side in a middle region of a fluid bed located in the container (2), and a nozzle (11) is arranged on the exit side of the extraction pipe (25),

   b) the container (2) is of closed design, a pressure (p₃) higher than the ambient air pressure (p₀) prevailing in the container (2) during operation, and

   c) the casing of the extraction pipe (25) has an orifice (50), into which issues an air pipe (51), via which closing air (L_S) can be introduced into the extraction pipe (25) at a settable pressure transversely to the solid stream, with the result that the mass flow of the fluidized solid (8) in the extraction pipe (25) can be controlled by a suitable selection of the ratio of closing-air pressure (p_R) in the pipe (25) to the pressure (p₃) in the container (2).
5. Device according to Claim 4, characterized in that the container (2) is part of a powder-spraying device (1) for electrostatic lacquering.

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