Patent Publication Number: US-6905385-B2

Title: Method for introducing mercury into a fluorescent lamp during manufacture and a mercury carrier body facilitating such method

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to the manufacture of fluorescent lamps and is directed more particularly to the introduction of a limited amount of mercury into the lamp by way of a lamp exhaust tubulation. The invention further relates to a carrier body for placement in the lamp and which carries thereon a selected amount of mercury to be admitted to the lamp. 
     2. Description of the Prior Art 
     Fluorescent lamps typically include at least one tubulation which provides a conduit extending into the interior of the lamp envelope and which, in construction of the lamp, is used as an exhaust tubulation. At completion of manufacture, the exhaust tubulation is hermetically closed. 
     Before sealing off of the exhaust tubulation open end, a measured amount of mercury is introduced into the lamp. One of the challenges facing lamp manufacturers is to minimize the amount of mercury put into the lamp. It has been found difficult to regulate the introduction of small amounts, such as three milligrams or less, of mercury. 
     There is thus a need for a method for introducing small amounts of mercury into a fluorescent lamp. There is further a need for a device which is structured to facilitate the introduction of limited amounts of mercury and which is easily handled in lamp manufacturing procedures. 
     SUMMARY OF THE INVENTION 
     An object of the invention is, therefore, to provide a method for introducing a limited amount of mercury into an envelope of a fluorescent lamp during manufacture of the lamp. 
     A further object of the invention is to provide a body for placement in the lamp during manufacture, which body is adapted to receive and retain only a selected amount of mercury and serve as a carrier for the mercury introduced into the lamp. 
     With the above and other objects in view, a feature of the present invention is the provision of a method for introducing a limited amount of mercury into an envelope of a fluorescent lamp during manufacture of the lamp. The method includes the steps of forming the fluorescent lamp with an exhaust tubulation therein, the exhaust tubulation being open at an end thereof and being provided with a ball retention structure proximate the open end, exhausting the interior of the lamp envelope through the exhaust tubulation open end, and placing a rigid ball of inert material in the exhaust tubulation between the ball retention structure and the exhaust tubulation open end. The ball is provided with a coating of a metal comprising a selected one of silver, gold, and indium, and alloys thereof, of a selected mass over a selected surface area of the ball, and with mercury on the coated area of the ball, such that a limited and selected amount of the mercury is retained on the ball by the coating metal. The amount of mercury retained on the ball is limited by the selected mass of the coating on the ball. The method further comprises sealing the open end of the exhaust tubulation. 
     In accordance with a further feature of the invention, there is provided a method for introducing a limited amount of mercury into an envelope of a fluorescent lamp during manufacture of the lamp. The method includes the steps of forming the fluorescent lamp with an exhaust tubulation therein, the exhaust tubulation being open at an end thereof, exhausting the interior of the lamp envelope through the exhaust tubulation open end, and placing a rigid ball of inert material in the lamp by way of the exhaust tubulation open end. The ball is provided with a coating of a metal comprising a selected one of silver, gold, and indium, and alloys thereof, of a selected mass, over a selected surface area of the ball, and with mercury on the coated area of the ball, such that a limited and selected amount of the mercury is retained on the ball by the coating metal, and sealing the open end of the exhaust tube. The amount of mercury retained on the ball is limited by the selected mass of the coating on ball. 
     In accordance with a still further feature of the invention, there is provided a carrier body for placement in a fluorescent lamp during manufacture of the lamp. The body comprises a sphere of rigid inert material, a coating of a metal comprising a selected one of silver, gold, and indium, and alloys thereof, of a selected mass, disposed over a selected surface area of the sphere, and mercury disposed on the metal coating and retained thereby in an amount up to that permitted by the selected mass of the metal coating. The body thus carries into the lamp a selected amount of mercury and is adapted for retention in the lamp after sealing of the lamp at completion of manufacture. 
     The above and other features of the invention, including various novel details of construction and combinations of parts and method steps, will now be more particularly described with reference to the accompanying drawings and pointed out in the claims. It will be understood that the particular methods and device embodying the invention are shown by way of illustration only and not as limitations of the invention. The principles and features of this invention may be employed in various and numerous embodiments without departing from the scope of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Reference is made to the accompanying drawings in which are shown illustrative embodiments of the invention, from which its novel features and advantages will be apparent. 
       In the drawings: 
         FIG. 1  is a diagrammatic sectional view of one type of fluorescent lamp during manufacture thereof, and illustrative of embodiments of the invention; 
         FIG. 2  is a sectional view of an exhaust tubulation portion of the lamp of  FIG. 1 , the tubulation portion being shown with a pinched portion for retention of a spherical body; 
         FIG. 3  is similar to  FIG. 2 , but further includes a mercury carrier in the form of a spherical body resting on the pinched portion; 
         FIG. 4  is similar to  FIG. 3 , but shows an end of the tubulation closed off; and 
         FIG. 5  is an enlarged side elevational view of one form of mercury carrier illustrative of an embodiment of the invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to  FIG. 1 , it will be seen that a known compact fluorescent lamp  10  is provided with a light-transmissive envelope  12  containing an ionizable gaseous fill for sustaining an arc discharge. In manufacture, the lamp  10  is dosed with the fill via an exhaust tubulation  14  in a known manner. A suitable fill, for example, comprises a mixture of a rare gas (e.g., krypton and/or argon) and mercury vapor. An excitation coil  16  is situated within, and removable from, a re-entrant cavity  18  within the envelope  12 . For purposes of illustration, the coil  16  is shown schematically as being wound about the exhaust tubulation  14 . However, the coil  16  may be spaced apart from the exhaust tubulation  14  and wound about a core of insulating material (not shown), or may be free standing (not shown), as desired. The interior surfaces of the envelope  12  are coated in well-known manner with a suitable phosphor  20 . In the illustrated type of lamp, the envelope  12  fits into one end of a base assembly (not shown) containing a radio frequency power supply with a standard Edison type lamp base. 
     An indentation, or pinched portion  22  (FIG.  2 ), is disposed proximate a tip-off region  24  of the exhaust tubulation  14 . The tip-off region  24  is the area at the free end of the exhaust tubulation  14  which is sealed, or “tipped off” to form the closed end  26  ( FIG. 4 ) of the exhaust tubulation after evacuating the lamp therethrough. 
     After the lamp is evacuated through the exhaust tubulation  14 , an appropriately sized and shaped glass ball  28  is inserted into the exhaust tubulation  14  through an opening  30  at the tip-off region  24 . By virtue of the presence of the pinched portion  22  and the size and shape of the ball  28 , the ball remains on the side of the pinched portion  22  away from re-entrant cavity  18 . Finally, as noted above, the exhaust tubulation  14  is tipped-off at a location proximate the ball  28  to form the tubulation closed end  26 . 
     In operation, current flows in the coil  16  as a result of excitation by the aforementioned radio frequency power supply. A radio frequency magnetic field is thereby established within the envelope  12  which ionizes and excites the gaseous fill contained therein, resulting in a toroidal discharge  32  ( FIG. 1 ) and emitting ultraviolet radiation therefrom. The phosphor  20  absorbs the ultraviolet radiation and emits visible radiation. 
     Referring to  FIG. 4 , it will be seen that in accordance with the present invention there is provided the ball  28  disposed in the glass tubulation  14  and retained by the pinched portion  22  of the tubulation. In accordance with the invention, the ball  28  serves as a mercury carrier. 
     Referring to  FIG. 5 , it will be seen that the ball  28  comprises a sphere of a rigid inert material, usually glass. A coating  34  of a metal is disposed on the ball  28 . The metal is a selected one of silver, gold and indium, and alloys thereof. The mass of the coating metal determines the amount of mercury which will be retained thereby. Once the required mass is computed and the desired thickness of the coating is determined, the surface area of the ball which is to be covered will have been determined. The surface area may comprise the whole of the surface area of the ball, or any portion less than the whole of the ball, the latter being illustrated in FIG.  5 . If the selected surface area is less than the whole, it is preferable that the coating be disposed in a single patch on the surface of the ball. 
     Mercury  36  is applied to the metal coating  34 . The metal coating  34 , by virtue of the selected mass thereof, is operative to retain a predetermined amount of the mercury. In practice, amounts of mercury up to three milligrams are readily obtainable on a typical fluorescent lamp glass ball. A dose of about two milligrams is commonly selected and easily supported by the metal coating. The ball  28 , with the coating  34  and mercury  36  thereon, is placed in the exhaust tubulation  14  and the open end of the tubulation is sealed, as at  26  (FIG.  4 ). 
     The ball  28  thus serves to accurately limit dosing of the lamp with very small amounts of mercury, from about 3 milligrams to well under 1 milligram. 
     The ball  28  may be used in conjunction with one or more additional glass balls for supporting an amalgam and/or for spacing the ball  28  and/or amalgam balls in the exhaust tubulation. 
     The ball  28  need not necessarily be disposed in the exhaust tubulation  14 . Rather, the ball  28  may be fed into the lamp envelope  12  through the exhaust tubulation  14 . In this embodiment, the tubulation is not provided with the pinched portion  22  prior to introduction of the ball, and the ball  28  enters the envelope and resides therein, as at  28 ′ in FIG.  1 . The open end of the exhaust tubulation is thereafter pinched, if amalgam balls are to be used, and thereafter closed. 
     There are thus provided methods for introducing a selected and limited amount of mercury into an envelope of a fluorescent lamp during manufacture of the lamp. There is further provided a mercury carrier body in the form of a ball for placement in the lamp during manufacture, and which is adapted to retain only the selected amount of mercury for dosing the lamp. 
     It will be understood that many additional changes in the details, materials, steps and arrangement of parts, which have been herein described and illustrated in order to explain the nature of the invention, may be made by those skilled in the art within the principles and scope of the invention as expressed in the appended claims.