Abstract:
A powder device comprises a powder container which is formed as an exchangeable container mounted on a container receptacle via a quick-connect means. The inside of the powder container has a dome which extends from the output flow opening into the inside of the powder container. This loosens up the powder and prevents it from adhering to surfaces.

Description:
BACKGROUND OF THE INVENTION 
     The invention concerns a powder device for powdering printed sheets, comprising a powder container containing powder and from which powder is extracted, wherein the powder device is designed as an exchangeable container which can be removed from the powder device and which has an opening at its lower end which can be closed by a closing element. 
     There are a plurality of conventional powder devices of this kind. DE 22 52 474 A discloses e.g. a supply container for powder, wherein the lower opening forming the outlet can be closed by a ball. Containers of this type have, however, the essential disadvantage that they are relatively easily blocked, since the powder sticks to the side walls or powder bridges are formed thus preventing further supply of powder from above. GB 15 88 393 B discloses a container having an elastic bottom which is moved via a vibrator. The powder is not drawn off from this container via a lower flow opening, rather suctioned off using a suction air flow. This also has the above-mentioned disadvantages, since the powder adheres, in particular, to the walls and can no longer continue to flow towards the suction nozzle. U.S. Pat. No. 4,051,981 discloses a powder device having a bellows-like supply container, opening into a pin-cushion from which powder can be blown into a blowpipe by compressing the supply container. This device prevents sticking or formation of powder bridges, since the supply container is continuously elastically deformed. 
     DE 38 11 309 also discloses a supply container for powder, wherein the lower outlet opening is closed by a ball. When powder is required, the ball is pushed into the supply container by an actuating element to loosen up the powder located above the ball which can then flow past the ball in the direction of the outlet opening. Compressed air is blown into the supply container to further loosen up the powder. The container must be sealed in an air-tight manner to prevent the powder from escaping from the supply container. 
     It is the underlying purpose of the invention to provide an exchangeable powder container which reduces powder build-up on the container walls and which reduces powder bridge formation in the container. 
     SUMMARY OF THE INVENTION 
     This object is achieved in accordance with the invention by a finger or dome extending into the inside of the container above the outflow opening. 
     The lower end of the powder container in accordance with the invention has an outflow opening for discharge of the powder. A finger-like dome is disposed above this outlet opening and is rigidly connected to the powder container. This dome protrudes into the powder in the container to substantially prevent formation of bridges and columns in the powder container and to effect uniform flow of the powder. The vibrations occurring during operation normally cause sufficient shaking of the dome, via the powder container housing, to loosen up the powder and maintain free flow thereof. This also prevents sticking of the powder to the inner walls of the container. 
     With containers having a truncated cone-shaped lower end passing over into the outflow opening, the dome preferentially has a length or height which is greater than or equal to the length of the truncated cone. The critical area in which the powder is usually compressed, is thereby penetrated by the dome to assure loosening of the powder in this area. 
     In an advantageous embodiment, the dome has the shape of a sleeve. The dome thereby has a vertical longitudinal axis and extends, in particular, along the axis of the powder container. The sleeve shape has the substantial advantage that the powder can flow through the dome itself. Towards this end, the dome has several transverse bores for passage of the powder into the dome. Powder flow into the dome leads to additional loosening up of the powder supply. The powder in the dome is discharged via the outlet opening. The dome is preferentially disposed such that the powder must initially flow into the dome before reaching the outlet opening. 
     Advantageously, the upper side of the dome has a pointed tip at the end of the upper side of the dome for distributing the powder, in particular, for breaking-up powder clots located above the dome. 
     Advantageously, the dome extends over 10% to 80% of the height of the powder container. The dome can thereby be disposed in the container in an exchangeable fashion. This permits e.g. use of different dome designs for different types of powder. 
     In a further development of the powder container, the closing element is formed as a flap extending away from the output flow opening. This flap closes the container opening from the outside and is withdrawn when the powder container is opened. This has the essential advantage that the powder in the container is not additionally compressed when the powder container is opened and relatively little force is required to open or move the flap. When the container is opened, it can be easily closed again by seating the flap on the outflow opening. 
     In one embodiment in accordance with the invention, the flap is supported pivotably, in particular, on the powder container. It is also feasible to design the closing element as a slide element which opens the container opening via a sliding motion. 
     The flap is preferably disposed on the opening under the force of a restoring spring, wherein the spring force closes the opening. The spring force is thereby sufficiently large that the flap does not open under the weight of the powder. Moreover, the flap prevents outflow of powder, in particular when the container is replaced or filled. 
     In a preferred variant of the invention, the flap can be actuated by means of a drive. This drive is disposed at the powder container receptacle and is designed, in particular, as a tappet drive. Other drives are feasible, e.g. magnetic drives, pneumatic or hydraulic drives or the like. 
     In one embodiment, the flap comprises a spherical body for sealing the opening of the container. This has the essential advantage that the opening can be sealed to an optimum degree and the discharged powder can easily flow around the flap. Powder, which could impair re-sealing of the container, does not remain on the flap. 
     Preferably, the powder device comprises a quick-connect means for securing the powder container. This quick-connect means facilitates easy and fast removal of an empty powder container from the powder device for either re-filling or replacement with a full powder container. The removal or mounting of the powder container can be done without tools. 
     Improved loosening of the powder within the container via the dome can be effected by connecting the powder container to a means for setting it into vibration, in particular a vibrator. This vibrator may be operated either continuously or in defined intervals. The vibrator may thereby comprise e.g. a counterweight or a magnetic oscillator. 
     Further advantages, features and details of the invention can be extracted from the dependent claims and the following detailed description of a particularly preferred embodiment with reference to the drawing. The features shown in the drawing, recited in the claims, and delineated in the description may be essential to the invention either individually or collectively in arbitrary combination. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 shows a side view of an exchangeable container inserted into the container receptacle; 
     FIG. 2 shows a longitudinal section II—II, according to FIG. 1, through the exchangeable container; and 
     FIG. 3 shows a view III onto the container receptacle in accordance with FIG.  1 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 shows a container receptacle  1  for an exchangeable container  2  containing powder. The container receptacle  1  is shown in a longitudinal sectional view. A funnel-shaped connecting piece  3  is disposed below the container receptacle  1  which opens into an intermediate container  4  made from an elastic material e.g. rubber or the like. The container receptacle  1  and the connecting piece  3  are mounted to a mounting plate  5 . 
     A vibrator  6  is mounted to the container receptacle  1  for vibration thereof. The vibrator  6  contains an oscillator driven via magnetic forces. The vibrator  6  may thereby be driven continuously, in predetermined time intervals, or as required. 
     The container receptacle  1  comprises an annular radially inward projecting receiving shoulder  7  onto which the exchangeable container  2  is disposed. A receiving shoulder  7  pin  8  thereby engages into an opening  9  (FIG. 2) disposed in the exchangeable container  2 . The opening  9  is located at a funnel-shaped container neck  10 , in particular, at an annular attachment  11  seating precisely within the annular receiving shoulder  7 . This attachment  11  is furthermore provided with a radially extending opening, disposed, with respect to the longitudinal axis  13  of the exchangeable container  2 , opposite to the opening  9 . A spring-loaded pin  14 , borne for displacement, engages in this opening  12 . This pin  14  is disposed on a tensioning knob  15  for radial withdrawal from the opening  12 . The exchangeable container  2  is thereby fixed in the container receptacle  1  via the two pins  8  and  14 . 
     The upper end  16  of the container neck  10  maps into a container housing  17 , closed by a lid  18 . The upper end of the exchangeable container  2  must not be air-tight. The lower end  19  of the container neck  10  has an outflow opening  20  through which the powder contained in the exchangeable container  2  can flow out of the container in a downward direction. A dome  21  is inserted into the outflow opening  20  and extends upwardly in the direction of the longitudinal axis  13 , i.e. into the inside of the container. The outflow opening  20  is closed by a flap  22  supported for pivoting about an axis  23 . The axis  23  is located at a projection  24  of the container neck  10  and supports a pivoting lever  25  in a rocker-like manner which can be actuated at the upper end via a tappet drive  26 . The other end is offset and comprises a spherical sealing body  27  at its free end which closes the outlet opening  20  from the outside. When the tappet drive  26  actuates the pivoting lever  25  (dotted lines), the spherical sealing body  27  moves away from and opens the outflow opening  20  it so that the powder can flow out. 
     The dome  21  disposed in the outflow opening  20  is formed by a sleeve  28  having four transverse bores  29  distributed about the circumference and disposed in four stacked planes. The upper end of the dome  21  is closed with a pointed tip  30 . The powder contained in the exchangeable container  2  thereby flows through the transverse bores  29  into the sleeve  28  of the dome  21  and exits same downwardly into the intermediate container  4  when the outflow opening  20  is open. 
     As shown in FIGS. 2 and 3, the container receptacle  1  is borne by a pin  32  for pivoting about a vertical axis  31 . A stable seating position of the container receptacle  1  is assured via two horizontally supported pressure springs  33  interposed laterally next to the pin  32  between the mounting plate  5  or a retaining angle  34  and the container receptacle  1 . The vibrator  6  thereby generates vibrational motion to shake the container receptacle  1  about the axis  31 . The powder in the exchangeable container  2  is loosened up by the dome  21  and maintained in a pourable or sprayable state. 
     As shown in particular in FIG. 3, the horizontal longitudinal axis  35  of the vibrator  6 , corresponding to the direction of motion of an oscillator, is perpendicular to the axis of oscillation  31  of the container receptacle  1  and is disposed at a distance therefrom such that the container receptacle  1  is shaken when the vibrator  6  is active.