Air nozzle for a jet dryer

The invention relates to an air nozzle for a nozzle dryer for drying and floating guiding webs, which is formed as a slot nozzle with transverse to the moving web extending nozzle slot, from which the air is blown out along a curved surface, and having an elongated nozzle lip, which together forms the boundary of the channel for the drying air over a greater length with the material web guided substantially parallel along it.

Such an air nozzle has become known for example from DE-AS 21 56 100. In such known air nozzles, the air is blown out of the nozzle slot along a curved surface by utilizing the Coanda effect. Behind the curved surface of the air flow enters a channel which is bounded on the one hand by the extended nozzle lip and on the other hand by the moving web.

For optimum utilization of the drying air previously had to be made relatively long at high air velocity, the flow channel and thus the extended nozzle lip, which could lead to an unwanted fluttering of the web. The reason for this flutter is the fact that the pressure of the Kanaigömung changes by friction at the Strömungskanalwandung. This leads to a pulsation of the air flow and thus to flutter the web. This fluttering could previously be resolved or reduced only by increased tension of the web, which is neither desirable nor possible with all materials

By AT-PS 1 31 513 a drying device for wet material webs has become known in at least one point transversely to the direction of the guided through a drying chamber material web over the entire width of at least one row of dry air nozzles and in the direction of movement of the web immediately behind at least a series of suction nozzles are provided for quick suction of the inflated air. In an embodiment of the nozzles shown there, the nozzle surface facing the moving web between the blow slot and the suction slot underneath is inflected to form a space lying parallel to the nozzle slots in which the air is caused to swirl so that all the air particles reach the web. A calming of the air should not and will not happen here.

The invention has for its object to provide an air nozzle of the type described above, in which even at very different speeds of the drying air at low tension of the web a smooth running of the web is guaranteed and still the drying air is optimally utilized before leaving the air nozzle and a good heat transfer when operating with hot gases is ensured.

This object is achieved in that the extended nozzle lip has at least one over the entire DüsenUreite extending, the nozzle lip interrupting calming zone for the drying air in the form of at least one open towards the web recess with compensation openings at the bottom of the recess and that the length of the elongated die lip between the die slot and settling zone and the length of the die face following the settling zone is about 30 times the width of the die slot. Such lengths reliably prevent the fluttering of the web even at different flow velocities of the drying air.

With this construction, one zone of a channel flow is followed by a zone of pressure equalization, in which the air is calmed.

The pressure equalization causes a calming and a re-investor for the next following zone of the channel flow; of the air jet. The drying air leaves the entire nozzle after passing through at least two zones of the channel flow for optimum

Utilization.

The air nozzle according to the invention is designed so that, regardless of the flow velocity of the air, can not flutter the web, but on the other hand, the drying air is kept in each case so long on the web that their drying capacity before leaving the web optimally is exploited.

The recess extending parallel to the nozzle slot over the entire nozzle width advantageously has a triangular cross-section with rounded passages to the extended nozzle lip and to the nozzle surface. while the compensation openings are formed as slots. Trained as slots compensating openings ensure pressure equalization and calm the flow without significant amounts of drying air are discharged to the outside. The rounded transitions ensure that no additional, disturbing the flow vortex occur between the nozzle lip and calming zone or calming zone and nozzle surface.

Advantageously, three depressions are provided as a calming zone, and the length of the extended nozzle lip before the calming zone and that of the nozzle face after the calming zone is about the same as that of the calming zone. This gives you a structurally simple air nozzle, which fully meets the requirements placed on them as mentioned above.

The extended nozzle lip is expediently further away from the web than the Düsenfläciie arranged. Thus, the extended nozzle lip after the inflow of air has the greatest distance and the nozzle surface after the calming zone the smallest distance to the web. As a result, a stronger injector effect is achieved when flowing in the air jet. Due to the stronger injector effect, a larger quantity of air is conveyed into the flow channel delimited by the extended nozzle lip or the nozzle surface and the material web, while the outflow velocity at the nozzle remains the same. This in turn results in a larger distance of the nozzle lip to the web.

Expediently, the bottom surfaces of the separating parts extend between a plurality of recesses of the calming zone in the connecting plane between the end of the extended nozzle lip and the beginning of the nozzle surface.

Finally, advantageously, the edge of the nozzle surface is rounded in the exit of the Luftdüsc. As a result, the occurrence of additional vortices of the air and thus a disturbance of the air is avoided in the output of the air nozzle before exiting the flow channel between the air nozzle and web.

Embodiments of the invention are illustrated in the drawings and will be described in more detail below. In the drawings shows

1 shows a longitudinal section through an embodiment of the air nozzle according to the invention,

F i g. FIG. 2 shows a longitudinal section as in FIG. 1 through a further embodiment of the air nozzle according to the invention,

3 shows a longitudinal section through the air nozzle to F i g. 2. which, however, slightly inclined with respect to the web, and

F i g. 4 shows a longitudinal section through a further exemplary embodiment of the air nozzle according to the invention with a nozzle surface graduated with respect to the extended nozzle lip.

The in F i g. 1 has an air chamber 2, through which the drying air is supplied to a Düsenschli'z 3, which extends over the entire width of the air nozzle 1. The nozzle slot 3 is formed between a rounded wall 4 of the air chamber 2 and an inwardly bent plate 5 of the air chamber 2. The plate 5 extends substantially tangentially to the rounded wall 4. The wall 4 is on the underside of the air nozzle 1 in

eineο a parallel to the web 6 extending extended nozzle lip 7 via. The length of the nozzle lip 7 is about 30 times the width of the nozzle slot 3. By the Coanda effect, the web 6 is held with a small distance to the nozzle lip 7. The web moves against the flow direction of the drying air.

At the end of the extended nozzle lip 7 a extending over the entire width of the air nozzle 1 recess 8 is provided with triangular cross-section and also extending transversely to the nozzle width compensation slot 9. The Vert. "Fung 8 forms a calming zone OK for the drying air due to the possibility of pressure equalization through the compensation slot. 9 After the settling zone 10, the drying air enters a Kannlströmungszone between the web 6 and another nozzle surface 11 substantially without loss of air. The edges on the nozzle lip 7 and on the nozzle surface 11 are rounded so that no additional disturbing disturbing vortex arise.

F i g. 2 shows another embodiment of an air nozzle 1, in which the calming zone 10 has three depressions 8 arranged directly one behind the other. The length of the calming zone 10 corresponds approximately to the length of the extended nozzle lip 7 and the length of the nozzle surface 11 after the settling zone 10. Otherwise, the construction of the nozzle according to FIG. 2 corresponds to that of FIG.

Fig. 3 shows the air nozzle Γ of Fig. 2 arranged slightly inclined so that the greatest distance from the web 6 in the region of the extended nozzle lip 7 is located. By virtue of this arrangement of the air nozzle eine, a stronger injector effect is achieved when the air jet flows into the channel between the moving material web 6 and the extended nozzle lip 7 or the nozzle surface 11. Due to the stronger injector effect, a larger amount of air is conveyed in the mentioned flow channel at the same outflow velocity at the nozzle slot 3, thereby increasing the distance between the extended nozzle rib 7 and the material web 6. The web 6 moves counter to the flow direction of the drying air.

Fig.4 finally shows another Ausführungsfo^rm - "he air nozzle 1" with stronger injector effect when flowing in the air jet. Here, the extended nozzle lip 7 and the nozzle surface Ii are graduated from each other such that a greater distance from the extended nozzle lip 7 to the moving web 6 as from the nozzle surface 11 after the reassurance zone 10 to 6 web 6 is formed. The effect is similar to that in FIG. 3 shown nozzle arrangement.

Furthermore, the calming zone 10 is a modification of the air nozzle according to the figure. 2 and 3 only of two recesses 8. The bottom surface of the separating part 12 between the beideti recesses 8 is at a height between the height of the extended nozzle lip 7 and the nozzle surface! 1 after the Beruhieuneszone 10

arranged.

It is understood that the extended nozzle lip 7 instead of only one nozzle surface Il after a calming zone 10 of a plurality of nozzle surfaces 11 can be arranged, which are each separated by calming ions 10, anyway, the arrangement allows extending over the entire nozzle width calming zones with the following nozzle surfaces one optimal utilization of the drying air and ensures an air nozzle usable at different air speeds.

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