EP0844081B1 - Method and apparatus for powdering products, in particular printed products - Google Patents

Abstract

The method involves generating (22) a powder gas flow from powder particles and a gas. The powder gas flow is directed towards the surfaces of the products (8) as they are moved along a conveyor surface. A transport gas flow is directed against the surfaces of the products with a speed component tangential to the conveyor surface so that the transport gas flow spatially overlaps the powder gas flow.

Description

The invention relates to a method for dusting Products, especially printed products, according to the generic term of claim 1 and a device for performing such a method according to the preamble of claim 10.

In this known prior art (DE 38 19 203A1) generate transversal to the conveying direction of the printed products Powder dispensing nozzles distributed in the direction together a powder gas cloud through which the products be moved through.

If the products are not rigid Products, e.g. Print sheets, so generate from the dispensing nozzles emitted powder gas jets a transverse channel in the product. This is with regard to a flutter-free Adverse of the products. Through the sharp pressing of the powder gas jets to the surface of the pollinating products also get unstable flow conditions. Another disadvantage of the known arrangement is that the reflected air jets are one larger portion of the powder from the surface of the to carry away pollinating products.

Furthermore, a device is known from US 3,053,180 known for dusting printed products, at which is also guaranteed that the Print products no excess powder remains and no such to the Environment is delivered.

For this purpose, a pollination head is added to powder discharge openings via further, downstream openings open air to the pollinated Blown printed products, creating a sealing air curtain arises, which retains powder particles. An adjustable suction device in the middle of the Pollination head ensures that the excess Powder is transported away.

This arrangement also blows powder particles away from dusted printed sheets and thus reduced the pollination effectiveness.

A method and specified a device for dusting products in which a better efficiency when transferring of powder from the powder gas flow onto the products is guaranteed.

According to the invention, this object is achieved by a method with the features specified in claim 1 or a device with the features specified in claim 10.

In the process according to the invention, the powder gas flow proportions, which from the surface of the printed products be reflected by a transport gas stream fed back to the product surface. This transport gas stream is rubbed against the product surface and is essentially laminar. In the invention One thus obtains a higher process Yield in the transfer of powder to the product surfaces.

Advantageous developments of the invention are in the subclaims specified.

In a method according to claim 2 you have a very intensive flow of powder gas onto the product surfaces.

The development of the invention according to claim 3 is in With regard to good laminar flow conditions for the Transport gas and with a view to extensive recycling powder particles moving away from the product surface beneficial to the product surface.

The development of the invention according to claim 4 allows it, one through the moving products and their conveyor generated air flow, which is dragged in the conveying direction will compensate.

The development of the invention according to claim 5 is in With regard to good laminar flow conditions between Dispensing device and suction device advantageous.

The development of the invention according to claim 6 is in In view of this, it is advantageous for powder particles to escape to keep small or whole from the pollination area to avoid.

It is in accordance with the developments of the invention Claim 7 and 8 achieves that such powder particles after a first impact on the product surface not got stuck on this, again against the Product surface. This is done according to Claim 7 by a counter to the direction of conveyance Products current transport gas flow, according to the training of the invention according to claim 8 by a gentle, to the conveying direction of the products in the same direction transport gas flow.

The further development of the invention according to claim 9 is advantageous in terms of avoiding that powder particles not used up the pollination area leave.

In a device according to claim 12, the powder gas in the part of the transport gas stream adjacent to the conveying surface fed in, which is also possible extensive powder transfer to the product surfaces is an advantage.

In a device according to claim 13, the different interfere Dispensing nozzles for the powder gas the transport gas stream only a little.

The arrangement according to claim 14 is possible with regard to intensive initial contact of the powder gas with the product surface advantageous.

In a device according to claim 15, the powder gas distribution pipe in the slipstream of hub sections of Blower wheels, does not disturb the transport gas flow essential, but you only have small flow paths from the powder gas distributor pipe to the discharge ends of the Dispensing nozzles.

The development of the invention according to claim 16 enables a gentle fluidic deflection of the transport gas stream towards the suction device.

The development of the invention according to claim 17 is used avoiding powder deposits inside yourself extending between the dispensing device and the suction device Housing.

In a device according to claim 18, powder gas escapes not in the area, even if the powder gas delivery is not strictly synchronized with the products to be pollinated is controlled at the powder gas discharge nozzles.

The development of the invention according to claim 19 is with regard to the self-centering of product grippers an advantage when entering the pollination device.

The further development of the invention according to claim 20 is the best in terms of dynamic sealing Pollination device against the environment is an advantage.

The same applies to the further development of the invention Claim 21.

In an apparatus according to claim 22, this is done automatically an adaptation of the transport gas flow to the conveying speed of the products.

The development of the invention according to claim 23 is with a view to the conveying direction of the products transverse direction uniform supply of transport gas or sealing gas is an advantage.

The development of the invention according to claim 24 ensures one transverse to the product conveying direction Direction of uniform gas extraction, which is not contains used powder particles.

The development of the invention is according to claim 25 advantageous in that the amount of the against the Products escaping transport gas and possibly sealing gas according to the respective funding conditions for the Can set products. So you have e.g. for printed products take into account that these are different from paper Basis weight can be made, and around always the same in the area of the pollination device To have funding, you have to have printed products high basis weight with slightly less transport gas and Apply sealing gas as products with a low basis weight, if despite the different weights of the Products in the same position in front of the powder gas dispenser wants to ensure. Puderabtrenneinrichtungen, e.g. Powder separation cyclones then work with the best Efficiency when the total gas flow through it does not change. The development of the invention according Claim 25 allows the transport gas stream and possibly Varying the sealing gas flow by controlling it in opposite directions the secondary air opening but the total gas flow that the Separation unit is fed to keep constant.

The with the development of the invention according to claim 26 advantage obtained is that the secondary air opening none differ across the width of the pollinated products Creates suction effects.

The development of the invention according to claim 27 is with regard to symmetrical flow conditions in the Inside the suction pipe is an advantage.

The further development of the invention according to claim 28 ensures uniform in the transverse direction of the products Flow conditions.

Figur 1:

einen Längsschnitt durch eine Vorrichtung zum Bestäuben von Druckprodukten sowie ein Blockschaltbild von Ver- und Entsorgungseinrichtungen für diese Vorrichtung;

Figur 2:

eine ähnliche Schnittansicht wie Figur 1, in welcher eine abgewandelte Bestäubungsvorrichtung wiedergegeben ist;

Figur 3:

eine schematische Ansicht des auslaufseitigen Endabschnittes einer Mehrfarben-Druckmaschine, in welcher eine weiter abgewandelte Bestäubungsvorrichtung schematisch wiedergegeben ist;

Figur 4:

eine Aufsicht auf die Bestäubungsvorrichtung nach Figur 3 in vergrößertem Maßstabe nach Abnehmen einer Deckplatte, wobei zusätzlich Verund Entsorgungseinrichtungen gezeigt sind;

Figur 5:

eine Aufsicht ähnlich zu Figur 4, bei welcher jedoch ein größerer Darstellungsmaßstab gewählt ist und die Ver- und Endsorgungseinrichtungen weggelassen sind;

Figur 6:

eine seitliche Ansicht eines steuerbaren Schlitzrohres, welches zur Abgabe von Transportgas oder Sperrgas oder aber auch zum Absaugen von nicht verbrauchte Puderpartikel enthaltendem Gas verwendet werden kann; und

Figur 7:

einen transversalen Schnitt durch das in Figur gezeigte Schlitzrohr.

The invention is explained in more detail below using an exemplary embodiment with reference to the drawing. In this show:

Figure 1:

a longitudinal section through a device for dusting printed products and a block diagram of supply and disposal facilities for this device;

Figure 2:

a sectional view similar to Figure 1, in which a modified pollination device is shown;

Figure 3:

is a schematic view of the outlet end portion of a multicolor printing machine, in which a further modified pollination device is shown schematically;

Figure 4:

a plan view of the pollination device according to Figure 3 on an enlarged scale after removing a cover plate, additional supply and disposal facilities are shown;

Figure 5:

a plan similar to Figure 4, but in which a larger representation scale is selected and the utilities and final supply facilities are omitted;

Figure 6:

a side view of a controllable slotted tube, which can be used for the delivery of transport gas or sealing gas or for the extraction of gas that does not contain powder particles; and

Figure 7:

a transverse section through the slotted tube shown in the figure.

In the drawing, a conveyor level is dotted with 10 referred to, along which print products 8 by a Conveyor device, not shown, from the bottom right can be moved to the top left. This conveyor has a pair of spaced endless ones in a known manner Funding on which the two ends of rod-shaped Bow grippers 6, each carrying the front end of a printed sheet.

Above the inclined conveyor level 10 is a total arranged with 12 designated pollination box. This has a delivery shaft 14, in which vertically a plurality lying one behind the other at the drawing level of impellers 16 is arranged. These generate together a transport gas flow indicated by arrows 18.

In extension of the hubs of the impellers 16 is a Powder gas manifold 20 arranged, which with the output a powder gas generator 22 is connected. details the construction of such a powder gas generator can can be taken from DE 38 19 203 A1, on which in this regard Reference is made.

The powder gas distributor pipe 20 carries perpendicular to the plane of the drawing spaced and aligned one behind the other A plurality of powder gas discharge nozzles 24 that are tubular and extend into the vicinity of the conveyor level 10. The dispensing nozzles 24 and the powder gas manifold 20 together form a rake-like structure, which is flowed through by the transport gas stream 18.

The dispensing nozzles 24 each give under working conditions a powder gas bundle 26, which powder particles distributed in air having. The powder gas tufts 26 are against Surface of the printed sheets directed. That from the product surface flowing away, containing less powder particles Powder gas becomes tangential through the transport gas stream 18 Direction along the conveyor plane 10 in the drawing moved downwards so that more powder particles continuously against the sticky surface of the printed sheets to be dusted be performed.

To such an effective transfer of powder particles The delivery chute is to ensure the printing sheets 14 for the transport gas stream 16 at an angle w against the conveyor plane 10 inclined, which is considered here Embodiment is about 22 °. The amount of Delivery chute 14 is corresponding to the angle w on the Length of a window 28 matched, which in a to Conveying plane 10 facing wall 30 of a housing 32 is provided is.

The housing 32 carries one at its upstream end Suction shaft 34, via a powder separation cyclone 36 is connected to the inlet of a suction fan 38.

The axis of the suction shaft 34 closes with the conveying plane 10 an angle that is the same amount is like the angle w, but the opposite sign Has.

A sealing air shaft is located below the suction shaft 34 40 arranged in which successively perpendicular to the plane of the drawing a plurality of impellers 42 are arranged is. These generate a sealing air flow 44 which the mixture of transport gas and depleted powder gas in deflects the suction shaft 34 set to the conveying level 10, as shown at 46.

The wall surface of the housing remote from the conveying plane 10 32 is formed by a microporous plate 48, behind which a compressed air box 50 is located. Is similar the wall below the drawing plane in the drawing of the housing 32 formed by a plate 52, which also is made of microporous material, and behind which is also a compressed air box. The above the boundary wall of the housing to be thought of in the drawing plane 32 is designed analogously. The compressed air box 50 and the other compressed air boxes are via a pressure regulator 54 connected to a compressed air line 56. To this Way constantly emerges from the surfaces of the plates 48, 52 air at low speed, which prevents is that powder particles accumulate on the plates 48, 52.

A guide plate 58 is located somewhat behind the conveyor level 10 arranged, which has larger dimensions than the window 28, and at the upstream end with an inlet slope 60 and at the downstream end with an outlet slope 62 is provided. These bevels work with the press sheet gripping bars together.

In the between the entry slope 60 and the conveyor level 10 lying wedge-shaped gap is a compressed air distribution pipe 64 arranged which is a plurality perpendicular to Drawing level successively and in the wedge-shaped Gap-pointing compressed air discharge nozzles 66.

Is similar in that through the conveyor level 10 and the outlet slope 62 limited wedge-shaped space a compressed air manifold 68 with axially spaced compressed air discharge nozzles 70 provided.

The guide plate 58 serves on the one hand as a support for the Sheet against the incoming powder gas and transport gas. The guide plate 58 also serves as a cover for the window 28 on which powder gas and transport gas are retained and are directed back to the suction shaft 34, if there is no printed sheet in front of window 28, or only part of a sheet is there.

The compressed air manifolds 64 and 70 are with the outlet a blower 72 connected by a blower control unit 74 ago is controlled. The latter controls furthermore the suction fan 38 and drive motors 76, 78, which drive the impellers 16 and 42, respectively.

The blower control unit 74 operates in dependence from the output signal of a speed sensor 80, the one to the conveying speed of the printed sheet gripping bars provides proportional signal. It can this is a tachometer generator that works with a Chain wheel works together, over which one the sheet-grip arms carrying chain is running. The blower control unit Roughly speaking, 74 works in such a way that it Delivery capacity of the various blowers increases when the Conveying speed of the products is increased, vice versa the flow rate of the blower decreases when the products be moved more slowly. To at this speed control from a linear mapping between the Conveying speed of the products and the performance of the To be able to deviate fans is between the exit of the speed sensor 80 and the input of the blower control unit 74 a characteristic curve circle 82 is inserted, e.g. a constant for low conveyor speeds can set small base power of the blower, and a constant upper one for high conveyor speeds Blower performance can specify these areas by a proportional zone are connected. It goes without saying that the total conveying performance of the various blowers are different: The amount of air from the sealing air shaft 40 sealing air emitted is significantly smaller as the amount of transport air discharged from the discharge chute 14, and the amounts of that from the compressed air manifolds 64, 68 released sealing air is again clear less than the amount of sealing air.

In the modified exemplary embodiment according to FIG. 2 are device components referenced above on Figure 1 already in a functionally equivalent manner have been described, again with the same reference numerals Mistake. These components are also not mentioned below described again.

Instead of the row of arranged in the delivery chute 14 Blower wheels 16 is in the discharge shaft 14 downstream of the powder gas discharge nozzles 24 now a discharge pipe 84 for transport gas arranged, which opposes a plurality at the angle w the conveying surface 10 employed discharge nozzles 86 for transport air having. Those emerging from the dispensing nozzles 86 Air jets together form one of the discharge ends of the Powder gas discharge nozzles 24 adjacent air flow 18.

The two ends of the delivery tube 84 are over one controllable current regulator 88 with the output of the fan 72 connected. The current regulator 88 is controlled by the fan control 74 analogous to the control of the drive motor 76 of Figure 1.

Similarly, instead of the set of impellers 42, one Dispensing tube 90 is provided for sealing air, which on average employed at the angle w against the conveyor plane 10 Has discharge nozzles 92 for sealing air.

The dispensing tube 90 has one end at both ends Current regulator 94 connected to the outlet of fan 72, the flow controller 94 through the fan controller 74 is controlled in a similar manner as the drive motor 78 in the exemplary embodiment according to FIG. 1.

In Figure 3 is the course by the dashed line 96 the chains of the printed-sheet conveying device carrying the grippers 6 shown. 98 denotes a printing sheet depositing station. In the ascending section of the funding path between the outlet of the multi-color press and the End of the printed sheet conveying path, which is above the filing station 98 lies, a pollination box 12 is arranged. at These are again components that are listed above Reference to Figures 1 and 2 already described Components functionally corresponding, with the same reference numerals Mistake.

The blower wheels 16 providing transport gas are now arranged upstream of the powder gas distribution pipe 20, while the fan wheels generating the sealing gas flow 42 are located downstream of the pollination area. The fan wheels are designed and operated so that the transport gas stream 18 is smaller than the sealing air flow 44 due to the arrangement described, the transport gas stream runs 18 with a parallel to the product conveying direction Component, while the sealing gas flow one to Product conveying direction has opposite component.

Between the powder gas partial pipe 20 and the sealing air shaft 40 is a large diameter suction pipe 100 provided. This is at its farthest downstream horizontal lines with a large number of suction openings 102 provided in Figures 4 and 5 of the for a better illustration tilted upwards by 90 ° are reproduced, in reality in the drawing levels of Figures 4 and 5, namely on there left or upper side of the suction pipe 100.

The suction pipe 100 has in its from the conveying plane 10 facing away from a central secondary air opening 104, by two oppositely symmetrical control spools 106 can be opened more or less. Moving the spool 106 may e.g. by a transverse actuating rod 108 take place.

In the embodiment shown in FIGS. 4 and 5, which is suitable for installation under particularly narrow spaces Conditions is determined, is compared to the embodiment according to Figure 3, the upstream set of impellers 16 replaced by a dispensing tube 84 as is was explained above with reference to FIG. 2. In the downstream area of the pollination box 12, where there is usually more space available, however, the fan wheels 42 are still provided.

In Figures 6 and 7 is a controllable slotted tube Play 110. This has a plurality along one Surface line successively and only by small Bridges 112 of separate slots 114, which are essentially one continuous axial slot of greater width pretend.

On the outer surface of the support tube 110 is a partially cylindrical one Control spool 116 in the circumferential direction rotatable, the inside diameter of the outside diameter corresponds to the slotted tube 110.

By turning the control spool 116 on the slotted tube 110 one can thus determine the effective extension of the slots 114 vary in the circumferential direction and so the flow cross section of the slot 114 change. Moving the Control spool 116 can e.g. by an actuator 118 take place with a pinion 120 in one of the spool 116 carried gear ring segment 122 engages.

The slotted tube 110 can both be used to discharge a gas stream as well as for sucking in gas. In both Applications have one in the longitudinal direction of the pipe, i.e. in Product conveying direction transverse direction uniform Gas delivery or gas intake, the strength of the Slits 114 passing current by twisting the Control spool 116 is adjustable.

Claims (28)

1. A process for applying powder to products, in particular printed products, in which

   a) a stream of powder gas is produced from powder particles and a gas; and

   b) the stream of powder gas is directed towards the surface of the products which are moved along a conveying surface,
   characterised in that

   c) a stream of transport gas with a velocity component tangential to the product-conveying surface and directed contrary to the conveying direction is directed towards the surface of the products, with the stream of transport gas spatially overlapping the stream of powder gas.
2. Process according to Claim 1, characterised in that the stream of powder gas and the product-conveying surface together include substantially a right angle.
3. Process according to Claim 1 or 2, characterised in that the setting angle between the stream of carrier gas and the product-conveying surface amounts to between 5° and 60°, preferably between 10° and 45°, still more preferably between 15° and 25°.
4. Process according to one of Claims 1 to 3, characterised in that the magnitude of the stream of transport gas is set as a function of the product-conveying speed.
5. Process according to one of Claims 1 to 4, characterised in that the overlapping region between the stream of powder gas and the stream of transport gas is adjacent to the product-conveying surface.
6. Process according to one of Claims 1 to 5, characterised in that a stream of buffer gas with a velocity component tangential to the product-conveying surface is directed towards the surface of the products, said stream of buffer gas being opposed to the stream of transport gas and, with respect to the stream of powder gas, being situated opposite the stream of transport gas.
7. Process according to Claim 6, characterised in that the stream of transport gas exhibits a tangential component opposed to the product-conveying direction and is larger than the stream of buffer gas, which has a tangential component concurrent with the product-conveying direction.
8. Process according to Claim 6, characterised in that the stream of transport gas exhibits a tangential component concurrent with the product-conveying direction and is smaller than the stream of buffer gas, which has an opposite-sense tangential component relative to the product-conveying direction.
9. Process according to one of Claims 1 to 8, characterised in that transport gas and optionally buffer gas are aspirated out of a chamber region which, viewed in the product-conveying direction, is situated downstream of the overlapping region of the stream of transport gas and the stream of powder gas.
10. A device for implementing the process according to one of Claims 1 to 9, with at least one powder-gas discharge arrangement (24) which extends transverse to the product-conveying direction, preferably exhibits a plurality of discharge nozzles for powder gas which are spaced in the transverse direction, and is connected to a powder-gas generator (22), characterised in that it exhibits: a discharge arrangement (16, 76; 72, 84-88) for transport gas, which extends in the width direction, transverse to the product-conveying direction, and by which a transport-gas stream (18) with a component tangential to the conveying plane (10) of the products (8) and directed contrary to the conveying direction is generated, and a housing (32). surrounding the powder-gas discharge arrangement (24), which extends between the transport-gas discharge arrangement (16, 76; 72, 84-88) and an aspirator (34; 100), the width direction of the aspirator running in the direction transverse to the product-conveying direction and the aspirator (34; 100) being in communication with a suction fan (38); and in that the plane of action of the transport-gas discharge arrangement (16, 76; 72, 84-88) and the plane of action of the aspirator (34; 100) exhibit a component tangential to the product-conveying surface (10).
11. Device according to Claim 10, characterised in that the planes of action of the transport-gas discharge arrangement (16, 76; 72, 84-88) and of the aspirator (34; 100) exhibit substantially oppositely equal setting angles (w) relative to the surface (10) for conveying the products (8).
12. Device according to Claim 10 or 11, characterised in that in the plane of action predetermined by the powder-gas discharge arrangement (24) the discharge ends of powder-gas discharge nozzles (24) exhibit a smaller spacing from the product-conveying surface (10) than the plane of action of the transport-gas discharge arrangement (16, 76; 72, 84-88).
13. Device according to one of Claims 10 to 12, characterised in that spaced powder-gas discharge nozzles (24) of the powder-gas discharge arrangement are borne by a powder-gas manifold (20), so that a rake-like structure arises, the ends of the prongs of the rake being formed by the ends of the discharge nozzles (24) and being adjacent to the product-conveying surface (10), whereas the powder-gas manifold (20) is remote from the conveying surface (10).
14. Device according to one of Claims 10 to 13, characterised in that the axes of the powder-gas discharge nozzles (24) are perpendicular to the product-conveying surface (10).
15. Device according to Claim 13 or 14, characterised in that the powder-gas manifold (20), viewed in the direction of flow of the transport gas, is arranged downstream of hub sections of impellers (16) which are arranged alongside one another in the transverse direction in a transport-gas discharge shaft (14).
16. Device according to one of Claims 10 to 15, characterised in that between the aspirator (34; 100) and the product-conveying surface (10) there is arranged a buffer-air arrangement (40; 90, 92), the width direction of which runs in the transverse direction relative to the product-conveying direction, and which is acted upon by a fan (42; 72).
17. Device according to one of Claims 10 to 16, characterised in that walls (48, 52) of the housing (32) which connects the transport-gas discharge arrangement (16, 76; 72, 84-88) to the aspirator (34; 100) are manufactured at least partially from microporous material and the rears of said walls are in communication with compressed-air chambers (50).
18. Device according to one of Claims 10 to 17, characterised in that between the transport-gas discharge arrangement (16, 76; 72, 84-88) and the aspirator (34; 100) there extends a guide (58) which predetermines the conveying surface (10) or is adjacent to the latter and in front of which the products pass by.
19. Device according to Claim 18, characterised in that the guide (58) is provided, at least at its upstream end, viewed in the product-conveying direction, preferably also at its downstream end, with a guide incline (60; 62) for product carriers (6).
20. Device according to Claim 18 or 19, characterised in that at the upstream end of the guide (58) an air-discharge arrangement (64, 66) is provided which generates a stream of sealing air directed towards the transport-gas discharge arrangement (14), running substantially parallel to the guide (58) and extending over the width of the aspirator (34; 100).
21. Device according to one of Claims 18 to 20, characterised in that at the downstream end of the guide (58) an air-discharge arrangement (68, 70) is provided which generates a stream of sealing air directed towards the aspirator (34; 100), running substantially parallel to the guide (58) and extending over the width of the transport-gas discharge arrangement (16, 76; 72, 84-88).
22. Device according to one of Claims 10 to 21, characterised in that the various fans (16; 38; 42; 72) are capable of being controlled by a control unit (74), in each case in accordance with the product-conveying speed, to which end a control unit (74) is connected on the input side to a speed sensor (80) which interacts with the product-conveying arrangement.
23. Device according to one of Claims 10 to 22, characterised in that the transport-gas discharge arrangement (72, 84 to 88) and optionally the buffer-gas discharge arrangement (72, 90 to 94) exhibit a discharge pipe (84; 90) which is acted upon from each of the two ends by transport gas and buffer gas, respectively.
24. Device according to Claim 23 for implementing the process according to Claim 9, characterised in that the aspirator exhibits a suction pipe (100) which is connected at both ends to a suction fan.
25. Device according to one of Claims 10 to 24 for implementing the process according to Claim 9, characterised in that the aspirator exhibits a suction pipe (100) transverse to the product-conveying direction, which is connected via a powder-separation unit (36), in particular a powder-separating cyclone, to the inlet of a suction fan (38) and in that the suction pipe (100) exhibits a controllable admixed-air aperture (104), via which it is capable of being brought into communication with the surrounding atmosphere.
26. Device according to Claim 25, characterised in that the admixed-air aperture (104) is provided symmetrically relative to the middle of the suction pipe (100) in a wall region of the suction pipe (100) that is remote from the product-conveying plane.
27. Device according to Claim 26, characterised in that the admixed-air aperture (104) is capable of being controlled by two control slide valves (106) capable of being moved by force in the longitudinal direction of the pipe symmetrically relative to the middle of the suction pipe (100) or by one control slide valve (116) capable of being moved transverse to the longitudinal direction of the pipe.
28. Device according to one of Claims 10 to 27, characterised in that a slotted pipe (110) which is used for discharging or for aspirating gas exhibits an aperture (114) extending substantially over the entire axial length, and on the outer surface of the discharge pipe a control slide valve (116) is arranged so as to be displaceable in the peripheral direction.

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