Patent Publication Number: US-2004045319-A1

Title: Method and device for sealing glass ampoules

Description:
[0001] The invention relates to a method for opening or sealing glass ampoules by melting the glass with the help of a jet of a hot medium, as well as to a device for carrying out the method.  
       [0002] Liquids, which must be protected reliably against contamination, especially serums for medical injections, frequently are filled into glass ampoules, which are then sealed airtight by a melting process. Previously, gas burners were used for this purpose and their flame was directed onto the part of the ampoule, which was to be melted.  
       [0003] When the ampoules are delivered in the sealed state, they must first be opened, by severing a cap of the ampoule, before they can be filled. A gas burner is preferably used also for this purpose, in order to ensure that the sterility of the ampoules is maintained.  
       [0004] However, gas burners can be operated only at a great expense and with high operating costs, since relatively expensive, combustible gases are required. A reliable supply of gases must be maintained and the gas-supplying systems must be protected carefully against leakages, so that there is no danger of explosion.  
       [0005] Frequently, the ampoules must be opened, filled and sealed in clean rooms, in order to avoid contamination of the liquids and the ampoules. The combustion process in the gas burner must therefore be controlled carefully, so that soot is not formed. The waste gases, formed during the combustion, may also prove to be harmful.  
       [0006] It is therefore an object of the invention to indicate a method and a device, with which glass ampoules can be opened and/or sealed easily, relatively inexpensively and without the danger of contamination.  
       [0007] Pursuant to the invention, this objective is accomplished for a method of the type named above, owing to the fact that the medium is an atmospheric plasma, which is produced by an electric discharge.  
       [0008] Since the plasma can be produced simply and energy efficiently by an electric discharge using air as working gas, the operating and equipment costs are reduced. In particular, there is no need to maintain a supply of gaseous fuels and an expensive and leak-proof gas-supplying system is not required. The high-energy efficiency is achieved mainly owing to the fact that the excited free radicals and ions in the plasma lead to a particularly effective transfer of heat from the plasma flame to the glass, which is to be melted. Moreover, the excited free radicals and ions have a sterilizing effect. A further significant advantage is to be seen therein that harmful combustion residues are not formed during the generation of the plasma. The method is therefore particularly suitable for applications, for which the purity and sterility requirements are high. It can, however, also be used advantageously in other applications, in which the glass is to be melted locally.  
       [0009] EP-B-0 761 415 and WO-A-01/43512 disclose plasma nozzles, for which a jet of atmospheric plasma is generated with the help of a high-frequency discharge. These plasma nozzles generate a plasma flame, which can also be expanded fan-shaped as required and which, with regard to its shape and flame temperature, is comparable with the flame of the previously used gas burner. These plasma nozzles are therefore particularly suitable for carrying out the inventive method. The flame configuration can be optimized, as required, by the appropriate choice of nozzle configuration, distance between electrodes, frequency, voltage and air throughput. Since the plasma nozzles also simulate the previously used gas burners in their external shape and their dimensions, already existing installations for opening and sealing glass ampoules can be converted without problems to the inventive method.  
       [0010] The device for carrying out the method is the object of claim  6 .  
       [0011] Advantageous developments of the invention arise out of the dependent claims. 
     
    
    
     [0012] Examples of the invention are explained in greater detail in the following by means of the drawing, in which  
     [0013]FIG. 1 shows a section through a plasma nozzle for carrying out the inventive method,  
     [0014]FIGS. 2 and 3 show diagrammatic representations for explaining a method for opening sealed glass ampoules,  
     [0015]FIG. 4 shows the essential parts of a device for opening and/or sealing glass ampoules in plan view and  
     [0016] FIGS.  5  to  7  show different steps of a method for sealing glass ampoules. 
    
    
     [0017] A plasma nozzle  10 , shown in FIG. 1, has a nozzle tube  12  of metal, which tapers conically toward an outlet opening  14 . At the end, opposite to the outlet opening  14 , the nozzle tube  12  has a twisting device  16  with an inlet  18  for a working gas, such as compressed air. A partition  20  of the twisting device  16  has a wreath of boreholes  22 , which are at an angle to the circumferential direction and by means of which the working gas is twisted. The working gas therefore flows in the form of a vortex  24 , the core of which extends along the longitudinal axis of the nozzle tube, through the downstream, conically tapering part of the nozzle tube.  
     [0018] At the center of the underside of the partition  20 , an electrode  26  is disposed, which protrudes coaxially into the tapered section of the nozzle tube. The electrode  26  is connected electrically with the partition  20  and the remaining parts of the twisting device  16 . The twisting device  16  is insulated electrically from the nozzle tube  12  by a ceramic tube  28 . A high-frequency AC voltage, which is generated by a high-frequency transformer  30 , is applied over the twisting device  16  to the electrode  26 . The primary voltage can be controlled variably and is, for example, 300 to 500 V. the secondary voltage may amount to 1 to 5 kV or more. The frequency is, for example, of the order of the 1 to 50 kHz and can also be controlled. The twisting device  16  is connected with the high-frequency transformer  30  over a flexible high-frequency cable  32 . The inlet  18  is connected over a tube, which is not shown, with a compressed air source with a variable throughput and the compressed air source preferably is combined with the high-frequency generator  30  into a supply unit. The nozzle tube  12  is grounded.  
     [0019] A high-frequency discharge is generated in the form of an electric arc  34  between the electrode  26  and the nozzle tube  12  by the voltage applied. Because of the twisting flow of the working gas, this electric arc is channelized in the vortex core on the axis of the nozzle tube  12 , so that it branches only in the region of the outlet opening  14  to the wall of the nozzle tube 12 . The working gas, which rotates at a high flow velocity in the region of the vortex core and, with that, in the immediate vicinity of the electric arc  34 , comes into intimate contact with the electric arc and, by these means, is converted partly into the plasma state, so that a jet  36  of an atmospheric plasma, approximately in the shape of a candle flame, emerges from the outlet opening  14  of the plasma nozzle  10 . The temperature of the plasma jet  36  is, for example, of the order of 1,600° to 2,500° C. If the plasma jet  36  is directed onto the surface of a glass body, such as an ampoule, the glass, well dosed, can be softened and fused locally.  
     [0020]FIG. 2 shows a glass ampoule  38 , which is to be filled under clean room conditions and then sealed tightly once again. The ampoule has a bulb  40 , which is to be filled with a medicinal fluid and, at the upper end, a constricted neck  42 , which is later on broken off or sawn off when the ampoule is opened. A so-called ampoule lance  44 , which is sealed at the upper end by a cap  46 , consisting of the glass of the ampoule, adjoins the neck  42  at the top. Accordingly the glass ampoule  38  is hermetically sealed in the state as delivered.  
     [0021] The cap  46  must be severed so that the ampoule can be filled. For this purpose, a hole is burned in the glass wall at one place in the periphery of the glass cap  46  with the help of the plasma jet  36  that is generated by the plasma nozzle  10 . Subsequently the glass ampoule  38  is rotated and the cap  46  is cut off with the help of the plasma jet  36 . The result is shown in FIG. 3. The glass ampoule  38 , which is now open at the upper end, can then be transported to a filling station, which is not shown.  
     [0022] In a diagrammatic plan view, FIG. 4 shows a part of a device for opening glass ampoules  38  by the method described above. The glass ampoules  38  are transported in sequence onto a carousel  48 , which is rotated stepwise in the direction indicated by an arrow A. In the example shown, several plasma nozzles  10  are disposed in a stationary manner at the inner periphery of the carousel  48 . Only three plasma nozzles  10  are shown in the drawing. Alternatively, a larger number of plasma nozzles can be used.  
     [0023] The glass ampoules  38 , supplied to the carousel  48 , initially reach a station  52 , in which the first plasma nozzle burns a hole in the glass wall, as shown in FIG. 2. During the next stop of the carousel  48 , the glass ampoule is then rotated with the help, for example, of a friction roller  56  into the next station  54 , so that, with the help of the plasma jet  36 , a slot, extending in the peripheral direction, is produced in the glass wall. In the example shown, the slot produced in the station  54  extends over a peripheral angle of 180°. Subsequently the glass ampoule is transported to a station  58 , in which the cap  46  is cut off completely by a further 180° cut, as shown in FIG. 3. The larger the number of plasma nozzles  10  used, the shorter is the working cycle in the individual stations  52  to  56 , and therefore the higher is the productivity.  
     [0024] A method for sealing filled glass ampoules will now be described by means of FIGS.  5  to  7 .  
     [0025]FIG. 5 shows a freshly filled glass ampoule  38 . While the glass ampoule is being rotated about its central vertical axis, the plasma jet  36 , generated by the plasma nozzle  10 , is directed onto the ampoule lance  44 , in order to soften the glass wall in the region of the ampoule lance.  
     [0026] Subsequently, the expanded part of the ampoule lance  44  is taken hold of by a holder  60  and pulled upward, so that the ampoule lance  44  is drawn down and constricted.  
     [0027] When the ampoule has been severed completely, the upper end of the glass ampoule is fused with the help of the plasma nozzle  36  while the rotation of the glass ampoule  36  is continued.  
     [0028] These processes can also be carried out in several steps and with several plasma nozzles  10  with a device, the construction of which is very similar to that of the device shown in FIG. 4.  
     [0029] For the method described here, the electric arc  34  for producing the plasma jet  36  remains largely within the plasma nozzle  10 . However, when working with types of glass, which have a very high softening or melting temperature, such as when sealing quartz glass bulbs for halogen lamps, a higher plasma temperature can be attained owing to the fact that the electric arc  34  is drawn out of the plasma nozzle. This can be accomplished owing to the fact that a grounded counter electrode is disposed on the side of the glass bulb opposite to the plasma nozzle  10 , so that the electric arc  34  does not jump over to the wall of the nozzle tube  12  and, instead, flows around the glass bulb and arcs over to the counter electrode.