Abstract:
A device for supplying a large number of consumer stations with a predetermined amount of a process medium, in particular a coating device for containers, has a supply line for the process medium and a connection at the consumer station. In order to make such a device simpler from the structural point of view and less expensive, a unit is used, which keeps a predetermined flow rate constant and which comprises a capillary path extending before each connection and dimensioned in accordance with the predetermined amount of process medium, and a unit which is associated with a plurality of connections and which is used for maintaining a defined flow velocity along the capillary path.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application claims the benefit of priority of German Patent Application No. 102008037160.2, filed Aug. 8, 2008. The entire text of the priority application is incorporated herein by reference in its entirety. 
     FIELD OF THE DISCLOSURE 
     The present disclosure relates to a device for supplying a large number of consumer stations with a predetermined amount of a process medium, in particular a coating device for containers. 
     BACKGROUND 
     Such a device is known from US 2005/0233077. The known device is used for coating inner surfaces of containers, in particular bottles for holding beverages. The device is integrated in a carousel guiding the containers along a process path whose length is adapted to the necessary processing time, in this case coating time. The process medium or the process media required for treating the container is/are supplied via valves. Each consumer station and each process medium requires a valve of its own. In order to reduce the number of valves, it has already been suggested in this reference that, in each consumer station, two containers should be connected to the junction for a process medium, so that only half the number of valves will be required. Nevertheless, a large number of valves is still necessary, which render the system very expensive. 
     SUMMARY OF THE DISCLOSURE 
     It is the object of the present disclosure to provide a structurally simple, reasonably priced device for supplying a large number of consumer stations with a predetermined amount of a process medium. 
     On the basis of the embodiment according to the present disclosure, the use of valves can possibly be dispensed with completely, or only one single process medium valve will be necessary. In this way, the device according to the present disclosure will become much simpler from the structural point of view and its production costs will be reduced substantially. 
     The fact that the capillary path is implemented as a plastic tube simplifies production still further, since appropriate dimensions of plastic tubes can easily be established. 
     In order to maintain defined flow conditions, the temperature of the process medium flowing through the capillary path should be kept constant in a reproducible manner, and this is preferably accomplished by a heat store in which the capillary path is accommodated. In addition, a heating unit can be provided. 
     Defined flow conditions can also be maintained in that the capillary path is connected to a pressure chamber, which acts as a buffer. 
     When the pressure difference is kept constant in a self-regulating manner, the device will be simplified still further. 
     On the basis of the embodiment according to the present disclosure, all consumer stations can be supplied with process medium. It will suffice to provide one capillary path for each consumer station and each process medium. 
     Another very important advantage of using a capillary path is to be seen in that in cases where process media are provided in a liquid state, but are required in a gaseous state, the capillary path acts, at the point where it terminates into the vacuum, as an evaporator which converts a process medium supplied as a liquid into the gaseous state without any necessity of taking special measures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the following, an embodiment of the present disclosure will be explained in more detail on the basis of the drawings, in which: 
         FIG. 1  shows a cross-section through a device according to the present disclosure in a highly schematic representation, 
         FIG. 2  shows a consumer station in its closed condition, and 
         FIG. 3  shows a consumer station for introducing process medium. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       FIG. 1  shows a highly schematic representation of a device  1  for supplying a large number of consumer stations  2  with a predetermined amount of a process medium. In the embodiment shown, the device  1  is implemented as a plasma coating system that serves to provide containers  3  which are arranged in the consumer station  2  with a coating that improves the gas tightness, the UV resistance, the UV shielding effect or the like, the containers shown in  FIG. 1  being plastic bottles. In the embodiment shown, this coating is applied to the inner side of the containers  3 . 
     The device  1  comprises a carousel  4 , i.e. a device conveying the containers  3  about an axis  4 ′ from a pick-up station (not shown) to a delivery station (not shown) along an intermediate treatment path. The carousel  4  comprises a first pressure chamber  5  by means of which the outer side of the container  3  is acted upon, and a second pressure chamber  6  which communicates with the inner side of the container  3  and which is arranged in the first pressure chamber  5 . The pressure chambers  5  and  6  are maintained at different pressures, and they are both configured as vacuum chambers. For coating inner surfaces, the second pressure chamber  6  is maintained at a pressure at which a plasma can easily ignite (normally &lt;1 mbar), whereas a higher or a lower pressure, at which the plasma cannot ignite, prevails in pressure chamber  5 . 
     Each consumer station  2  is provided with a gas pressure valve  7 . In addition, each consumer station  2  is provided with a holder for the containers  3  by means of which the opening of the containers  3  can be pressed against the valve  7 . This movement for closing the opening of the container  3  though the valve  7  is preferably executed via a cam follower or the like, which lifts the container  3  and presses it against the valve located above the container. Each consumer station  2  additionally comprises an electrode  8 , which may e.g. be annular in shape or U-shaped. 
     Although in the depicted embodiment only two consumer stations  2  are shown, it is clearly evident that a large number of consumer stations  2  can be distributed around the axis  4 ′. In addition, each consumer station  2  can accommodate more than one container  3 . 
     The process medium or the process media required for plasma coating are fed to the carousel  4  through a rotary feedthrough  9 , preferably in the area of the axis of rotation  4 ′. The rotary feedthrough  9  is supplied by one or by a plurality of supply sources  10 ,  11 . For providing a coating of silicon oxide, these supply sources are, in the embodiment shown, a first reservoir  10  for a gaseous process medium, in particular oxygen, and a second reservoir  11  for a liquid process medium, e.g. a liquid monomer, such as hexamethyldisiloxane (HMDSO) or some other silane. 
     Each of these reservoirs  10 ,  11  is connected via a respective valve  12 ,  13  to a pressure chamber  9   a  and  9   b , respectively, provided in the rotary feedthrough  9 . The valves  12 ,  13  may be configured e.g. as mass flow controllers. The mass flow controllers are preferably adjusted such that a constant media flow takes place. 
     Each of the pressure chambers  9   a ,  9   b  communicates via a respective line  14  and  15  with all consumer stations  2 . The lines  14 ,  15  terminate in a connection  7   a  of the valve  7 , without any additional process media valve being provided between the connections  7   a  and the respective pressure chambers  9   a  and  9   b . Before the respective connection  7   a  of the valve  7  of each consumer station  2 , the line  14 ,  15  is configured as a respective capillary path  14   a  and  15   a  ( FIGS. 2 and 3 ). The capillary paths  14   a ,  15   a  are preferably configured as capillary tubes which consist of an appropriate plastic material. They can easily be produced with the desired dimensions. Both capillary paths  14   a ,  15   a  terminate jointly into the connection  7   a.    
     The capillaries  14   a ,  15   a  are part of a unit generally designated by reference numeral  16  and used for keeping predetermined flow conditions constant, so as to accomplish and keep constant a predetermined flow rate which replaces the separate process media valves required at each consumer station in the prior art. In addition to the capillary paths  14   a ,  15   a , which provide a defined flow cross-section that is as small as possible, a unit for keeping constant the flow velocity through the capillary paths  14   a ,  15   a  is additionally provided. Depending on the structural characteristics of the device  1 , the unit  16  may, for example, comprise measures for keeping the temperature of the capillary paths  14   a ,  15   a  substantially constant and, where appropriate, also at a value that deviates from the ambient temperature. In the embodiment shown, the capillary paths  14   a ,  15   a  are accommodated in a heat store  17 , which may e.g. be an aluminum block with sufficient heat storage mass. For increasing the temperature, the heat store  17  may contain a heating  18 , e.g. a temperature controller and water as a heat carrier. Although this is not shown in the figures, the heat storage block  17  may be annular in shape and it may comprise a plurality of, preferably all of the capillary paths of all the consumer stations  2 . 
     The unit  16  additionally provides a defined pressure drop in the lines  14 ,  15  between the respective reservoir  10 ,  11  and, as will be explained in more detail hereinbelow, the second pressure chamber  6 . Since the second pressure chamber  6  has established therein a defined pressure, which allows the plasma to be ignited during plasma coating, and since this pressure is maintained, this may also be utilized for keeping the flow velocity constant within the capillary paths  14   a ,  15   a  in that the mass flow controller  12  and  13 , respectively, is set to a predetermined constant flow. This has the effect that a certain media pressure will build up in the respective pressure chamber  9   a ,  9   b , which is in equilibrium with the medium escaping through the capillary paths  14   a ,  15   a  and the medium supplied through the mass flow controller  12  and  13 , respectively. In this way, the system is self-regulating and the process medium introduced in the pressure chamber  9   a ,  9   b  will be distributed uniformly to all the capillary paths  14   a ,  15   a  of all the connected consumer stations  2 . It follows that the pressure chambers  9   a ,  9   b  act as a buffer. 
     In this way, it is guaranteed that the same predetermined amount of process medium will be supplied to all the consumer stations  2 . 
     Another advantage of the use of the capillary paths  14   a ,  15   a  according to the present disclosure will be obtained when a process medium is used, which, though required in a gaseous state, can be handled and stored more effectively and more easily in a liquid state. The unit according to the present disclosure allows transmitting this process medium first in a liquid state through the respective capillary, and, when the process medium is discharged from the capillary into the vacuum (prevailing in the treatment chamber  6 ), it will evaporate and therefore be present in the container  3  in gaseous form. 
     The valve  7  includes a substantially cylindrical valve body  19  in the interior of which a plunger  20  is axially displaceable. A tube  21  is secured in position in said plunger  20  and is movable together therewith. This tube  21  may be implemented e.g. as a tubular microwave conductor or as a tubular electrode. The valve body  19  and the plunger  20  have provided between them a spring  22  whose bias force urges the plunger  20  towards the container  3  so as to close the opening of said container  3 . The tube  21  has formed therein an intake passage  23  having an intake opening  23   a  through which the process medium can enter from the capillary paths  14   a ,  15   a , and an outlet opening  23   b  through which the process medium will flow into the container  3 . 
     The valve block  19  has formed therein an intake passage  19   a  which communicates with the connection  7   a  and which is arranged such that it is in alignment with the inlet  23   a  of the passage  23 , when the plunger  20  occupies its uppermost position. 
     The valve body  19  has additionally formed therein a first discharge passage  19   b  and a second discharge passage  19   c  which both terminate into the treatment chamber  6 . The first discharge passage  19   b  is implemented such that it is in alignment with the intake passage  19   a  for flow communication, when the tube  21  occupies the lowermost position, which is determined by the compression spring  22  (and possibly a stop). The second discharge passage  19   c  is adapted to be brought into alignment with an overflow passage  20   a  which is provided in the plunger  20  and which terminates into the container  3 . When the second discharge passage  19   c  communicates with the overflow passage  20   a , pressure compensation will take place between the process chamber  6  and the container  3 . 
       FIG. 3  shows the position of the valve  7  at the beginning of a plasma coating process. As can be seen from the figure, the container  3  is pressed against the plunger  20  (e.g. by means of a cam follower), the container opening being sealed by a lower surface of the plunger  20  implemented as a sealing surface. The lifting movement is dimensioned such that the plunger  20  is forced into the valve body  19  where it compresses the spring  22 , until the process chamber  6  and the interior of the container  3  communicate via the overflow passage  20   a . Due to the vacuum in the process chamber  6 , the container  3  is evacuated. At the same time, the tube  21  establishes a flow connection from the connection  7   a  via the intake passage  19   a  into the passage  23  and from there into the container  3 , through which the process medium or the process media required for coating is/are introduced in the container  3 . This is accomplished through the pressure difference between the evacuated interior of the container  3  and the pressure chamber  9   a  and  9   b , respectively, whose pressure is, in turn, kept constant via the mass flow controllers  12  and  13  and the reservoirs  10  and  11  in a self-regulating manner. It follows that, when the container  3  is moved, via the cam follower, about the axis  4 ′ by a predetermined length and at a predetermined speed, a predetermined amount of process medium which suffices to build the desired coating is transmitted into the container  3 . 
     When the coating process has been finished, the container  3  is, preferably again by lowering the cam follower, moved downwards, with the plunger  20  still following in sealing contact with the opening of the container through the pressure applied by the spring  22 . This has the effect that the supply via the connection  7   a  is interrupted and the overflow passage is separated from its connection with the process chamber  6  so that the pressure (vacuum) prevailing in the process chamber  6  will again be applied to the end of the capillary paths  14   a ,  15   a  via the passages  19   b  and  19   a , and thus produce a defined pressure difference. This position is shown in  FIG. 2 . Subsequently, the container  3  can be removed from the carousel  4 . 
     When the device  1  according to the present disclosure, which serves to supply consumer stations on a carousel, is used for plasma coating of containers (inner surface), a pressure at which plasma can ignite is established and maintained in process chamber  6 , which can be connected to the interior of the container  3  via the passages  19   c  and  20   a , whereas in process chamber  5 , which communicates with the outer side of the container  3 , a pressure can be established and maintained, at which an ignition of plasma is not possible. When the process is being executed, a pressure of 0.1 mbar should prevail in the interior of the container under a process gas load of approx. 50 sccm. The process media used are oxygen and hexamethyldisiloxane (HMDSO). The HMDSO is present in liquid form, whereas the oxygen is supplied in a gaseous state. In order to accomplish a gas flow of 50 sccm oxygen through the respective capillary path, a pressure difference of approx. 600 mbar is required. The pressure in the pressure chamber with the respective process medium (gas/liquid) is stabilized at 600 mbar relative to the end of the capillaries and, consequently, relative to the pressure in process chamber  6 , so that a plurality of capillaries is supplied from this chamber in parallel. 
     The capillary paths for the gaseous oxygen preferably have a length of 600 mm and an inner diameter of 0.25 mm. The capillary paths for the liquid HMDSO preferably have a length of 1000 mm and an inner diameter of 0.10 mm. The temperature of the capillary paths is stabilized by connecting them to the heat store (heat bath), said heat store being heated to 60° C. and stabilized by the heating means (temperature controller and water as a heat carrier). The mass flow controllers are fed with the respective medium under a pressure of normally 2 bar. This course of action is adopted equally for liquid as well as for gaseous process media, the only difference being that the liquid process medium evaporates when it is discharged into the vacuum in the interior of the container  3  where it will then also be present in a gaseous form. 
     In a modified form of the embodiments described and shown hereinbefore, the present disclosure can also be used for other devices in the case of which a large number of consumers is to be supplied with identical, comparatively small amounts of a process medium. Constructing a carousel for a coating system is not critical either, so that the disclosure can be used in all coating systems.