The invention relates to a method for introducing an accurately dosable amount of mercury into the discharge vessel of a lamp, in particular into a straight fluorescent lamp. The discharge vessel is connected to a lamp receptacle and is charged with a gas stream via the lamp receptacle and is filled, moreover, with a predetermined amount of mercury via a mercury-introducing channel. Furthermore, the invention relates to a suitable device.
Fluorescent lamps are manufactured on fully automated production machines, where the lamp blanks run through a plurality of processes in the horizontal position. These processes include: baking out the fluorescent substances, which are suspended in the discharge vessel, melting an electrode into the ends of the discharge vessel, evacuating the discharge vessel, filling the discharge vessel with an inert fill gas, introducing a predetermined amount of mercury and then sealing air-tight the discharge vessel on both ends of the discharge tube.
The documents U.S. Pat. No. 2,699,279, U.S. Pat. No. 2,842,290 and U.S. Pat. No. 2,726,799 describe how liquid mercury is dosed from a container as a part of a fully automated production machine for evacuating and filling straight discharge vessels with inert fill gas and mercury.
Such fully automated production machines are wide spread and have been used for many years.
An alternative method for introducing mercury into the discharge vessel of fluorescent lamps is disclosed in WO 97/19461. In the method described in that patent, a metal strip, which is coated with a mercury compound is mounted on the electrodes. After the discharge vessel has been sealed air-tight, in particular melt-sealed, the metal strip and the mercury compound on said metal strip are heated inductively; and the mercury is released.
The heating of the mercury strip in the finished lamp has the result that eventually other undesired components, in particular H2, are released from the metal strip; and these components have an extremely negative impact on the igniting and burning properties of the lamp.
In order to absorb at least to some extent these disturbing materials, a getter material is usually also applied on the metal strip. This getter material must also be heated inductively in order to activate itself. The heating that is necessary to activate the getter or rather to release the mercury is achieved by introducing inductive energy. In order to heat the metal strip up to a range between 900° and 1,000° over a period ranging from 10 to 30 seconds, a very strong alternating electromagnetic field must be applied. A certain radiation of the antenna in the factory, which could have a negative impact, for example, on persons with cardiac pacemakers, cannot be avoided. The energy costs for a lamp throughput of 7,000/h is noticeable; and the energy efficiency of this method is extremely low. The production of the metal strip with the mercury and getter compounds that are applied by pressure on said metal strip (usually in the shape of a welded ring) and the manipulation during the lamp production makes the getter strip technology very time-consuming and expensive.
In the aforementioned Hg-liquid dosing method the scattering of the dosed amount is very large. Depending on the type of lamp, the fluorescent material and other specific construction features, there is a consumption of the introduced mercury during the service life, which ought to be in a magnitude of 20,000 hours. Therefore, one usually overdoses in order to make sure that one has the minimum amount of mercury that is necessary for operating the lamp and to guarantee the envisaged average life of the lamp.
In contrast, the object of the present invention is to provide a method for introducing an accurately dosable amount of mercury into the discharge vessel of lamps. This method is to ensure that the dosing can be carried out with significantly higher accuracy than with the prior art methods. Furthermore, a corresponding device shall be provided.
According to a core idea of the invention, this problem is solved in that in a preparation step during or after dosing the amount of mercury to be introduced, the mercury is brought in a dosed volume in the form of a single, coalescing drop or adherent drop. Then in a fill step the entire amount of mercury to be introduced is transported—while still maintaining the previously formed drop—into the discharge vessel. To this end there is a change-over mechanism, which in the preparation step guides the gas stream past the drop via a bypass channel and in a fill step blocks the bypass channel in such a manner that, while the bypass channel is blocked, the gas stream is guided over the dosed volume and drags the drop along with it into the discharge vessel.
Consequently one core consideration consists of bringing the entire gas stream for the process of introducing behind the already pre-dosed drop of mercury in order to let the drop be conveyed by the gas stream into the discharge vessel.
Even though the dosing of the drop could already be carried out spatially separately or temporally far in advance, it is preferred that the dosing be carried out by means of or rather within the dosed volume. However, it is ensured that exactly the pre-dosed amount of mercury is available for filling into the discharge vessel.
According to another preferred aspect of the present invention, the drop is formed as a structure having at least an approximately spherical shape. Correspondingly in another preferred design, the device is provided with a dosing borehole, which is dimensioned in such a manner that in said borehole the drop can form into a single bead, whose predetermined diameter is defined by the circumference of the dosing borehole.
Therefore, the dosing borehole is configured differently than in the state of the art so that the drop has room only as a bead, a feature that is also claimed as an independent idea of the present invention. In the state of the art, on the other hand, the dosing borehole is designed oblong or long stretched-out so that the mercury divides into a plurality of small beads. However, this division is not repeatable; the beads are small and are poorly conveyed.
In the preferred design of the invention, however, the inventive dosing of the mercury so as to form a single bead as well as the process control or process technological adaption with respect to rerouting or bypassing the gas stream interact.
In order to further improve the introduction of the drop of mercury, it is advantageous to avoid bypasses at angles greater than or equal to 90°. For example, the drop may be guided over two bypasses of, for example, 45° each. As an alternative, it is also conceivable to guide the drop in a channel, which exhibits in particular a continuous bend, especially by providing a curved acceleration channel in such a manner that sharp angles are totally avoided. Especially if a curved acceleration channel is provided, it may also be provided that this channel empties without a bend and/or without any steps into the feed channel. The above described aspects are also claimed as independent inventions irrespective of the formation of exactly one drop or the rerouting of the gas stream.
In another preferred design the drop of mercury is guided in such a manner that at transitions steps or rather edges in the direction of introduction are avoided. Corresponding transitions may be designed so as to be either totally flat, or the drop may be guided in such a way that the diameter of the guiding mechanisms is expanded at the transitions so that the drop of mercury does not impinge upon any impediment in the direction of travel.
According to a special aspect of the present invention, the dosed volume may be designed as a dosing borehole and may exhibit a length that is equivalent to approximately the diameter of a circle, inscribed in the cross section of the dosing borehole.
According to another aspect of the present invention, the length of the dosing borehole may also be somewhat shorter than the diameter of a circle, inscribed in the cross section of the dosing borehole, in order to ensure that in cutting off the mercury stream above the dosing borehole just one drop actually forms despite the high surface tension of the mercury in the dosing borehole.