Abstract:
A device for creating a spread-out stream of tobacco fibers includes a concave-curved guide track along which the fiber stream of tobacco fibers are conveyed. The guide track has a generatrix based on a uniform generating curve. At least one air jet has an air flow opening interrupting the guide track so that air exiting the air flow jet acts in a conveyance direction of the fiber stream for spreading out the tobacco fibers.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
         [0001]    Priority is claimed with respect to German application No. 199 01 087.0 filed in Germany on Jan. 14, 1999, the disclosure of which is incorporated herein by reference.  
         FIELD OF THE INVENTION  
         [0002]    The invention relates to a device for creating a spread-out fiber stream of tobacco fibers along a concave-curved guide track provided with air flow openings acting in the transport direction of the fiber stream.  
         BACKGROUND OF THE INVENTION  
         [0003]    A guide track of the type mentioned at the outset is part of a so-called distributor of a cigarette string machine. The guide track, together with an essentially parallel directed air flow, constitutes a so-called moving bed. Tobacco in the form of a loosened and spread-out tobacco stream is moved along close to the guide track and transferred to a suction string conveyor which forms the tobacco fibers into a tobacco string.  
         SUMMARY OF THE INVENTION  
         [0004]    An object of the invention is to optimize the effectiveness, or respectively the conveying capacity, of the moving bed in respect to the energy outlay for the air flow supplied.  
           [0005]    Moreover, it is an object to improve the guide track constituting the moving bed in respect to its construction, handling and exchangeability, or respectively installation and removal.  
           [0006]    The above and other objects are accomplished in accordance with the invention by the provision of a device for creating a spread-out stream of tobacco fibers, comprising: a concave-curved guide track along which the fiber stream of tobacco fibers are conveyed, the guide track having a generatrix based on a uniform generating curve; and at least one air jet having an air flow opening interrupting the guide track so that air exiting the air flow jet acts in a conveyance direction of the fiber stream for spreading out the tobacco fibers.  
           [0007]    Thus, in accordance with the invention the generatrix of the guide track, which is interrupted by the air flow openings designed as air jets, is based on a uniform generating curve.  
           [0008]    For optimizing the conveying and spreading effect it is another aspect of the invention that the air jets terminating in the sliding surface of the guide track extend continuously over the width of the guide track.  
           [0009]    In accordance with an advantageous embodiment, a close-lying wall flow (Coanda effect) is achieved in that the downstream wall of the air jet, in relation to the conveying direction of the fiber stream, makes a transition in the form of a continuous convex curve into the concave sliding surface of the guide track.  
           [0010]    According to a further feature of the invention, the sliding surface of the guide track is interrupted by several air jets, which follow each other in the conveying direction of the fiber stream, which increases and complements the conveyance by the moving bed.  
           [0011]    Preferably, the air jets are connected to a common pressure chamber.  
           [0012]    In accordance with a preferred embodiment, the guide track is put together from individual segments, whose respectively adjoining border surfaces form nozzle walls of the air jets. In this way it is possible to design and assemble the guide track flexibly, or respectively to replace it in partial areas when it is worn, wherein an optimal orientation of sliding surface walls and air jets is always assured.  
           [0013]    The advantageous effects of the construction of the guide track in segments are further increased by a production-specific further development, in that the guide track segments are embodied as extruded sections, whose wall sections defining the sliding surface of the guide track form an upstream and a downstream located nozzle wall, in respect to the conveying direction of the fiber stream, on two successive air jets.  
           [0014]    The invention presents the advantage that, because of the continuous transition along the sections of the guide track which are interrupted by an air jet, the tobacco meets the air flow directly at the outlet of the air nozzle, i.e. at a location at which the air flow still has its maximum flow speed and can accelerate the tobacco fibers accordingly. In this way it is possible to operate the air supply at a low air pressure, or respectively with a respectively reduced blower output, which improves the effectiveness and the economy of the energy generation and the energy output.  
           [0015]    Furthermore, an economical production-related advantage results from the use of individual segments, which are put together to form a guide track, whose simple exterior contours actually predestine them for being manufactured by means of the efficient extrusion process.  
           [0016]    The invention will be explained in greater detail in what follows by means of an exemplary embodiment represented in the drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]    [0017]FIG. 1 is a schematic longitudinal section through a distributor of a cigarette string machine.  
         [0018]    [0018]FIG. 2 is an enlarged section of the distributor with a conventional guide track for the tobacco.  
         [0019]    [0019]FIG. 3 is a guide track of the distributor embodied in accordance with the invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0020]    [0020]FIG. 1 is a section through that portion of a distributor of a cigarette string machine which is required for understanding the invention. A variety of ways are known for the upstream located tobacco delivery to a reservoir and the removal of the tobacco from the tobacco reservoir, for example by means of a steep conveyor, and need not be described here. Reference is made, by way of example, to U.S. Pat. No. 4,185,644, which is incorporated herein by reference.  
         [0021]    [0021]FIG. 1 shows a retaining chute  1  with a tobacco supply  1   a  and a removal device  2  consisting of a removal roller  3  and a beater roller  4 . A batch  6  of tobacco fibers taken out of retaining chute  1  by removal device  2  reaches a delivery chute  7 , which narrows funnel-like into the shape of a conduit, in which an acceleration means  8 , which constitutes a pre-sifter in the form of air jets  11  arranged in a pressure chamber  9 , blows a sifting air flow transversely in respect to the conveying direction of tobacco batch  6 . The sifting air flow separates light tobacco fibers  12  from heavier tobacco fibers  13  (tobacco ribs) and conveys the light tobacco fibers away transversely in the direction of arrow  14 .  
         [0022]    Some of the light tobacco fibers  12   a  drop downwardly along with the heavier tobacco ribs  13 . Through a cellular wheel sluice  16  they reach a sifting chute  17 , in which the heavier tobacco ribs  13  drop further down and are removed. The lighter tobacco fibers  12   a  rise upwardly under an injection effect of an air flow out of a nozzle  18  constituting a post-sifter, and are returned into the stream of the lighter fibers  12 . In the illustrated example, the tobacco fibers  12  and  12   a  are transferred with the aid of further air nozzles  19  of a pressure chamber  19   a  onto a guide track  21  in the form of a sliding surface  21   a . There the tobacco fibers are built up into a tobacco stream  22  of loosened and spread-out tobacco fibers, wherein the air flow and the tobacco particles form a wall flow moving closely along the sliding surface  21   a  of the guide track  21 . To aid in the continued conveyance of the spread-out and loosened tobacco stream  22  along guide track  21 , air flow nozzles  23  supplied with air from a pressure chamber  23   a , and further air flow nozzles (not shown) arranged in the course of the guide track  21  are provided.  
         [0023]    The loosened and spread-out tobacco stream  22  reaches a suction strip conveyor  26  in a strip build-up zone  24 , to which a suction draft for forming and maintaining a tobacco string is applied from the direction of the back by the suction effect of an under pressure chamber  27 . Excess air flow escapes through a screen  28  into an expansion chamber  29 .  
         [0024]    The suction strip conveyor  26  rotates in a tobacco conduit  31 , which is laterally bordered by two conduit cheeks  32  and  32   a . The end section of sliding surface  21   a  of guide track  21  is oriented on one of the conduit cheeks  32 , so that a gap-free smooth transition of guide track  21  into tobacco conduit  31  is assured.  
         [0025]    The end section of the guide track  21  comprises a guide body  34 , which can be pivoted away on a pivot axis  33  in order to assure better access to the device in case of malfunctions.  
         [0026]    [0026]FIG. 2 illustrates a conventional guide track  21  wherein sliding surface  21   a  consists of sliding plates, or respectively sliding bodies  37 , set off in steps in the conveying direction (arrow  36 ) of the tobacco stream. As can be seen, air flow nozzles  23  terminate on the respective steps in guide track  21 . This know construction has the result that in the area of a step, between two sliding plates, the tobacco stream meets the air flow coming from the air flow nozzles only at the end of a relatively long free trajectory, where the air flow has already lost approximately two-thirds of its exit velocity. In order to accelerate the tobacco stream to a predetermined value, the flow speed of the air flow must therefore be increased by an increase in the blower output, which negatively affects the overall power economy of the system.  
         [0027]    Referring to FIG. 3, there is shown an arrangement in accordance with the invention. In FIG. 3 the generatrix of the guide track  21 , or more accurately, the guide surface  21   a , is based on a uniform generating curve, so that individual segments  38  of the guide track adjoin each other continuously. Air flow nozzles  23 , designed as air jets extending vertically in respect to the drawing plan, are formed at the respective joints of the individual segments  38 , whose downstream wall  38   a , in relation to the conveying direction (arrow  36 ) of the fiber stream, makes a transition into the concave sliding surface  21   a  of the guide track  21  in a steady convex curvature, so that an unbroken continuous wall flow of blown air and tobacco is formed on sliding surface  21 . Individual segments  38  have an upstream wall  38   b , in relation to the conveying direction, which forms the opposing wall of each flow nozzle or air jet  23 . The tobacco stream and the air flow meet directly in the area of the outlet openings of the air jets, so that the air flow meets the tobacco stream at its maximum outflow velocity at each air jet.  
         [0028]    The individual segments  38  are produced as extruded sections, whose respectively adjoining border surfaces always assure optimal flow conditions.  
         [0029]    The invention has been described in detail with respect to referred embodiments, and it will now be apparent from the foregoing to those skilled in the art, that changes and modifications may be made without departing from the invention in its broader aspects, and the invention, therefore, as defined in the appended claims, is intended to cover all such changes and modifications that fall within the true spirit of the invention.