Abstract:
A cleaning device for a dust filter has a flow duct extending between an entry opening and an exit opening. An annular chamber surrounds the flow duct. Gas-inlet connectors are provided for inflow of pressurized gas into the annular chamber. Nozzle gaps delimited by nozzle-gap walls open toward the flow duct. The annular chamber has an upper annular shell and a lower annular shell interconnected pressure-tightly in a connection region. The gas-inlet connectors are molded on the upper annular shell. The lower annular shell is predominantly flat, extends horizontally or downwardly toward the nozzle gaps, and forms the lower nozzle-gap wall. In order to meet highest demands in terms of hygiene, in the connection region the angle at which the annular shells mutually abut in the annular chamber is at least 90°. Gaps and constrictions are thus avoided.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to a cleaning device for a dust filter, having a flow duct which extends between an entry opening and an exit opening, and having an annular chamber which surrounds the flow duct and which is provided with gas-inlet connectors for the inflow of pressurized gas into the annular chamber and, towards the flow duct, is provided with nozzle gaps which are delimited by nozzle-gap walls. The annular chamber is composed of an upper annular shell and a lower annular shell which on the radial outside in a connection region are interconnected in a pressure-tight manner. The gas-inlet connectors are moulded on the upper annular shell; the lower annular shell is designed so as to be predominantly flat, extends horizontally or downwardly towards the nozzle gap and, at the same time, forms the lower nozzle-gap wall. 
     Cleaning devices of this type are known from KR 20/0321528 Y1 and from WO 2009/043332. Said cleaning devices operate based on the Coand{hacek over (a)} principle and are employed for cleaning the filter hoses and filter candles of dust filters, to which end the cleaning device is disposed above the filter hose which is open towards the top, or above the filter candle. A flow duct which is surrounded by an annular chamber extends between an entry opening and an exit opening. The annular chamber is supplied from above from a compressed-air reservoir. Said annular chamber is closed on the external wall and is provided on the internal wall thereof with nozzle gaps which open into the flow duct. The nozzle gaps are upwardly and downwardly delimited by nozzle gap walls. 
     The annular wall is formed and enclosed by two walls which in a connection region which extends along the external periphery are interconnected in a pressure-tight manner. The lower wall runs horizontally or slightly downwardly towards the nozzle gap and, at the same time, forms the lower nozzle gap wall; the upper wall determines substantially the spatial shape of the annular chamber and the volume of the annular chamber. 
     The potential of use of cleaning devices of this type covers all sectors in which dust filters are industrially employed. One of these sectors is the foodstuff industry, for example, the industry processing milk to milk powder. Particularly stringent hygiene requirements apply to the foodstuff industry and also to the pharmaceutical industry. An infestation with germs may arise in the case of cleaning devices for dust filters when, following wet cleaning, residues of cleaning fluid mixed with residue of product remain in individual parts of the plant. It has been observed that in the case of cleaning devices of the generic type, even where these are conceived for increased hygiene requirements, an infestation with germs may still arise under unfavourable circumstances involving tight cavities and in particular gaps. Small residues of cleaning fluid, possibly mixed with residue of product, may remain there for a prolonged time after the cleaning process. 
     Therefore, the object of the invention is to provide a cleaning device for a dust filter which meets even the highest hygiene requirements. 
     SUMMARY OF THE INVENTION 
     This object is achieved by a cleaning device wherein, in the connection region, the angle (W) at which the annular shells mutually abut in the annular chamber is at least 90°. 
     In such a cleaning device the angle at which the periphery of the upper annular shell abuts the periphery of the lower annular shell inside the annular chamber is at least 90°. In this manner, the cleaning device is capable of meeting even the highest hygiene standards since an infestation with germs cannot arise in the annular chamber, for instance following preceding wet purging. This is so because the interior of the annular chamber is free of gaps or regions of constriction, in which in the case of the known cleaning devices minimal residues of fluid may accumulate, thus giving rise to an environment which is conducive to the formation of germs. 
     Advantageous design embodiments of the cleaning device are stated in the dependent claims. Gaps and constrictions in the interior of the annular chamber may be avoided when in the connection region the annular zone of the lower annular shell has a curvature towards the upper annular shell, wherein this curvature is preferably of quarter-circular shape. It is furthermore advantageous when the annular zone of the upper annular shell has a curvature towards the lower annular shell. 
     It is furthermore proposed for the connection region that the peripheries of the two annular shells mutually abut by way of the end faces thereof. In this case, the end faces of the two walls are preferably machined, for example, ground, to be planar, wherein the common end-face plane in which said end faces are located extends perpendicularly to the central axis of the annular chamber. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further details and advantages are derived from the following description with reference to the drawings. 
         FIG. 1  shows in a perspective view a cleaning device as is known from the prior art. 
         FIG. 2  shows in a sectional view a cleaning device according to the invention. 
         FIG. 3 a    shows the right part of  FIG. 2  in an enlarged view and  FIG. 3 b    shows an even more enlarged detail illustration of the connection region. 
         FIG. 4  shows a horizontal section through the cleaning device. 
         FIG. 5  shows an enlarged section view along section line V-V indicated in  FIG. 4 . 
     
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     The basic construction and the basic operating mode of the compressed-air cleaning device which operates according to the Coand{hacek over (a)} principle is described in U.S. Pat. No. 6,604,694 B1, and reference is being had to the explanations provided therein. 
       FIG. 1  shows a cleaning device for a dust filter according to the prior art, specifically according to KR 20/0321528 A. A Coand{hacek over (a)} injector  1  is connected at two points to a compressed-gas line  2  which is disposed above the Coand{hacek over (a)} injector  1 . The Coand{hacek over (a)} injector  1  is designed so as to be substantially annular such that the central axis A thereof intersects perpendicularly the central axis of the compressed-gas line  2 . An annular chamber  7  which is disposed about the central axis A is a component part of the Coand{hacek over (a)} injector  1 . The annular chamber  7  by way of gas-inlet connectors  10   a ,  10   b  is connected to the interior of the compressed-gas line  2  at two locations which in relation to the central axis A are oppositely positioned at 180°. Compressed air may flow into the annular chamber  7  by way of the two gas-inlet connectors  10   a ,  101   e  at these two locations. During operation, this inflow is performed abruptly since the compressed-gas line  2  by way of a very rapidly switching valve is connected to a compressed-air source having a capacity for very high pressure. When the rapid-action valve is opened, compressed air or another compressed gas abruptly enters the compressed-gas line  2 , enters by way of the two gas-inlet connectors  10   a ,  10   b  the annular chamber  7 , and is distributed across the annular chamber  7 . 
     Self-evidently, a plurality of Coand{hacek over (a)} injectors  1  are simultaneously connected to one and the same compressed-gas line  2 , for example, 10 to 20 Coand{hacek over (a)} injectors of this type, depending on the size of the dust filter. Moreover, a plurality of compressed-gas lines  2  are disposed parallel to each other in the filter housing, so as to direct in this way compressed air also into adjacent rows of Coand{hacek over (a)} injectors of this type. In this manner an entire “field” in the housing of the dust filter may be equipped with Coand{hacek over (a)} injectors of identical type, each such injector being disposed above a filter element of the dust filter. 
     The annular chamber  7  of the Coand{hacek over (a)} injector  1  is assembled from two wall parts  11 ,  12 , which in a connection region  13  which extends along the external periphery of the annular chamber  7 , are interconnected in a pressure-tight manner. The first wall is an annular shell  12  and the already mentioned gas-inlet connectors  10   a ,  10   b  for the connection to the compressed-gas line  2  are moulded thereon. This upper shell  12  is of pronounced three-dimensional shape, having a dome-shaped cross section. The gas-inlet connectors  10   a ,  10   b  are moulded thereon at locations which are located opposite each other at 180°. 
     The other wall is an annular shell  11  which, in radial inward direction, transitions into a tubular piece  30  having a central axis A. 
     As can be seen in  FIG. 1  showing the prior art device, the two annular shells  11 ,  12  in the connection region  13  are interconnected by a flange connection. While a flange connection on the external periphery of the annular chamber  7  is indeed a connection which in terms of production technology is advantageous, small gaps or cavities may form where the peripheral zones of the annular shells  11 ,  12  close in on one another; in Such gaps or cavities, following operation of the cleaning device, residues of cleaning fluid mixed with residues of product may deposit. Therefore, the risk of an infestation with germs cannot be completely excluded. 
     This risk does not exist in the embodiment according to the invention, which is shown in  FIGS. 2 to 5 . This embodiment will be explained in more detail in the following using the reference characters already used in the context of the prior art device shown in  FIG. 1 . Therefore, the explanations which have already been given in the context of the prior art device also apply to the cleaning device according to the invention to the extent that they do not pertain to the connection region  13 . 
     Both walls  11 ,  12  are shells which, in relation to the axis A, are shaped so as to be of annular design and which each are preferably integral press-moulded sheet-metal panel parts. 
     When viewed radially from the outside to the inside, the lower annular shell  11 , which thus is closer to the exit opening  18 , can be subdivided into a total of four portions. The external peripheral zone  20  is a component part of the connection region  13  and is designed so as to be connectible in a pressure-tight manner to the other annular shell  12  by welding. This peripheral zone  20  is adjoined radially inwardly by a larger wall portion  21 , the upper side  24  of which, facing the annular chamber  7 , extends almost horizontally and flat. This flat wall portion  21  extends up to a nozzle gap  25  where the compressed air or the compressed gas, respectively, exits from the annular chamber  7 . The flat upper side  24  of the wall portion  21  at the same time forms the lower nozzle-gap wall of the nozzle gap  25 . 
     Downstream of the nozzle gap  25 , a transition portion  22  is integrally formed in the shape of a rounded portion that establishes the connection to the tubular piece  30 . The tubular piece  30  forms the beginning of a cylindrical flow duct  27  which extends all the way to the exit opening  18 . The flow duct  27  is welded to the transition portion  22  or to the short tubular piece  30  of the wall  11 . 
     The transition portion  22  has a quarter-circular shape in cross section so as to enable an interference-free deflection of the gas jet, exiting from the nozzle gap  25  at high velocity, in the direction toward the exit opening  18  of the flow duct  27 . 
     Corresponding to the pressure supply by way of the valve-controlled compressed-gas line  2 , the exit of gas from the nozzle gap  25  is also performed in a pulsated manner and at high velocity. The gas, after leaving the nozzle gap  25 , follows the profile of the wall (Coand{hacek over (a)} effect) in the region of the curved transition portion  22  resulting in negative pressure at the center of this polydirectional gas flow. Due to the negative pressure, secondary air is drawn in from above by way of the entry opening  17  into the flow duct  27  such that an increased amount of gas exits from the exit opening  18  at a correspondingly high velocity. The inflow of the entrained secondary air into the entry opening  17  of the Coand{hacek over (a)} injector  1  is visualized by means of the flow arrows S in  FIG. 2 . 
     Since the upper side  24  of the lower annular shell  11 , facing the annular chamber  7 , extends substantially horizontally or slightly downwardly at least up to the end of the nozzle gap  25 , fluid cannot accumulate on the upper side  24  and formation of an atmosphere conducive to an infestation with germs is prevented. Rather, any potential residues of fluids can always run off by way of the nozzle gap  25  and thus escape. In order for this effect to be amplified, the wall portion  21  in a radially inward direction, that is to say toward the central axis A, extends slightly downward, e.g. at an angle of less than 3° relative to the horizontal. It is crucial in this context that there is no location within the annular chamber  7  that is disposed lower than the nozzle gap  25 . 
     In order to avoid gaps, joints, or constrictions that bear the risk of an infestation with germs, on the external periphery of the annular chamber, the angle W at which the periphery  12 A of the upper annular shell  12  on the internal side of the annular chamber  7  meets the periphery  11 A of the lower annular shell  11  is at least 90°. This angle W is preferably approximately 180°, as is the case with the embodiment of  FIGS. 2 to 5 . 
     An angle W of approximately 180° in the connection region  13  may be achieved in that the peripheral zone  11 A of the annular shell  11  has a curvature or a bend toward the other annular shell  12 , on the one hand, and the peripheral zone  12 A of the annular shell  12  also has a curvature or bend toward the annular shell  11  on the other hand. In this way, the end faces of the two annular shells  11 ,  12  in the connection region  13  mutually abut in a straight line. In order to provide a connection without gaps or constricting regions, the mutually bearing end faces of the two annular shells  11 ,  12  are moreover ground so as to be planar. Said end faces are located in a common end-face plane E which extends perpendicularly to the central axis A of the annular chamber  7 . 
     For pressure-tight attachment, a weld seam  35  is produced externally on the connection region  13  so as to be level with the end-face plane E, in this way, complete pressure-tightness of the annular chamber  7  is achieved. There are thus no gaps, constrictions, or other small cavities on the inside of the annular chamber wall in which residues of cleaning fluid mixed with residues of product could be deposited following operation of the cleaning device. 
     The nozzle gap  25  may indeed be a single nozzle gap which extends across the entire circumference. However, in order to calibrate the height of the nozzle gap in a simpler and more reliable manner, preferably a plurality of individual nozzle gaps  25  are provided which are regularly distributed across the circumference and from which the pressurized gas exits radially inwardly. The shells  11 ,  12  are directly supported on one another along short circumferential portions  26  between mutually successive nozzle gaps  25 . On account thereof, it is possible for the height of the nozzle gaps  25  to be precisely dimensioned. 
     The specification incorporates by reference the entire disclosure of German priority document 10 2015 111 825.4 having a filing date of Jul. 21, 2015. 
     While specific embodiments of the invention have been shown and described in detail to illustrate the inventive principles, it will be understood that the invention may be embodied otherwise without departing from such principles. 
     LIST OF REFERENCE CHARACTERS 
     
         
           1  Coand{hacek over (a)} injector 
         Compressed-gas line 
           5  Central axis 
           7  Annular chamber 
           10   a  Gas-inlet connector 
           10   b  Gas-inlet connector 
           11  Lower wall, annular shell 
           11 A Periphery 
           12  Upper wail annular shell 
           12 A Periphery 
           13  Connection region 
           17  Entry opening 
           18  Exit opening 
           20  Peripheral zone 
           21  Rat portion 
           22  Transition portion 
           24  Upper side 
           25  Nozzle gap 
           26  Circumferential portion 
           27  Row duct 
           30  Tubular piece 
           35  Weld seam 
         A Central axis 
         S Flow 
         E End-edge plane 
         W Angle