Lamp base inner shell

Abstract: A lamp base inner shell (20) comprising a base (11) and a wall (16,18) extending from the periphery of said base, the wall having a plurality of slots (17) extending from the free end thereof towards the base, the slots defining a number of tabs (18), at least one tab having an inwardly-extending projection (19), characterised in that at least one slot (17') extends substantially to said base (11). The inner shell is used to electrically connect and secure a lamp base shell (21) to a lamp tube (24). The inner shell can facilitate automated production of high intensity arc discharge lamps.

Description: The present invention relates to a lamp base inner shell. More particularly, the present invention relates to a lamp base inner shell for automated production of high intensity discharge lamps. Most lamps utilize lamp base shells to facilitate insertion and removal into a complementary lamp socket and to establish electrical contact between the lamp and the socket. Several structures have been developed to prevent the lamp base shell from separating from the lamp base, particularly when the lamp is removed from the socket at the end of its useful life. One known configuration used to electrically connect a lamp to a base shell, and mechanically secure the base shell, utilizes a threaded inner shell. FIGS 1A-1E show prior art arrangements, in which inner shell has a washer-like base having an outer rim and an inner rim, which define a surface and an opening. The inner shell further includes a cylindrically-shaped body having a screw thread that extends from the base to a plurality of cut-out portions. The cut-out portions define an equal number of tabs. Each tab having an indentation, or dimple, which corresponds with a depression moulded in the neck of the lamp base. The inner shell is secured to the lamp base by manually placing it over the base until the dimples mate with the corresponding depressions in the lamp tube. The lamp base typically extends into the inner shell up to the beginning of the screw threads, about the length of the cut-out portions and the tabs. When the inner shell is in place, a lamp base shell is securely screwed onto the threads and is staked, or pierced, to engage it with the inner shell. The base shell is staked into the threads to prevent inadvertent cracking of the lamp base which does not extend behind the threads. In addition to the initial mating of indentations with the depressions moulded in the lamp base, the tightening of the lamp base shell on the inner shell forces the tabs and indentations closer to the lamp base. Inner shells are typically made from any of the materials including nickel, nickel-iron alloy, cold-rolled steel, or nickel-plated steel to provide a compatible welding surface for two lead wires, typically extending from the lamp base. A side, or ground, lead wire is resistance welded to the outer portion of the surface prior to the securing and staking of the lamp base shell. A center lead wire typically passes through an eyelet in the base portion of the inner shell and the lamp base shell, where it is trimmed, fluxed, and soldered. This configuration, while securing the lamp base shell and providing electrical contact, requires several parts and difficult manual assembly, particularly with respect to welding the side lead wire to the surface of the inner shell. This approach results in costly, time consuming, and inefficient lamp production. A more efficient, automated method to electrically connect the lamp's lead wires to the lamp base shell, and mechanically secure the base shell to the lamp base, uses a lead solder preform. The lead solder preform is typically made from a 10% tin, 90% lead alloy. The solder preform can be formed in a die into a variety of shapes and sizes to conform with a depression that is moulded into the glass neck of the lamp base. The solder preform is first placed into the depression, and the side lead wire is temporarily retained therein by being pressed into the exposed surface of the soft solder preform. The lamp base shell is then placed onto the lamp base, covering the side lead wire and solder preform. The center lead wire is soldered to the lamp base shell as described above. Heat is then applied to the lamp base shell to melt the solder preform. When cooled, the solder secures the side lead wire and the lamp base shell. Although providing a more efficient automated production technique, use of lead solder has several disadvantages. First, lead solder is an environmental pollutant. Therefore, as environmental laws and regulations continue to impose new and increasingly stringent standards, the lamp industry is attempting to phase out the use of lead solder. Second, the use of lead solder increases both direct and indirect costs associated with lamp production. Lead solder is an expensive material and, further, soldering discolours the brass or copper-nickel alloy base shells typically used in high intensity discharge lamp applications. More expensive nickel-plated base shells must be used to maintain good aesthetics, thereby increasing the overall cost of lamp production. Viewed from one aspect the present invention provides a lamp base inner shell comprising a base and a wall extending from the periphery of said base, the wall having a plurality of slots extending from the free end thereof towards the base, the slots defining a number of tabs, at least one tab having a projection which extends inwardly toward the axis of said inner shell, characterised in that at least one slot extends substantially to said base. Viewed from another aspect the invention provides a method of fabricating a high intensity discharge lamp assembly in which a preferred lamp base inner shell is mounted to a base portion of a high intensity discharge lamp tube, comprising the steps of placing the inner shell onto the lamp base, locating said inner shell on said lamp base by said at least one inwardly-extending projection engaging a receiving indentation in said lamp tube, passing a heating means through said slot which extends substantially to the base of the inner shell, and joining a wire from said lamp tube to said inner shell by the application of heat from said heating means. According to a preferred embodiment of the present invention, a lamp base inner shell comprises a washer-like base having a cylindrical wall attached to a first end to an outer periphery of the base. The cylindrical wall includes a threaded portion and a plurality of cut-out portions in a second end thereof which define an equal number of tabs having inwardly-extending indentations forming inwardly-extending projections as claimed. At least one of the cut-out portions extends to the washer-like base. The modified lamp base inner shell according to preferred embodiments of the present invention can be used to electrically connect a lamp to a lamp base shell and to secure the lamp base shell onto a lamp tube. The inner shell may be placed onto the lamp base until the indentations, located on the tabs, mate with depressions typically moulded in the neck of the lamp tube. The lamp base usually extends into the inner shell a distance equivalent to the length of the cut-out portions and tabs. Preferred embodiments have the at least one cut-out portion which substantially extends to the washer-like base to provide access within the inner shell, say while resistance welding the lamp's ground lead wire to the outer portion of the inner shell base. The ground lead wire can extend from the lamp base through an opening in the inner shell's washer-like base where it is folded onto the base and welded. A second lead wire also passes through the opening in the washer-like base. After the ground lead wire is joined to the lamp base inner shell, say by soldering or welding, the lamp base shell can be screwed onto a threaded portion of the inner shell and may cover the tabs and cut-out portions. The lamp base shell may be staked above the threaded portion of the inner shell to secure it to the inner shell. The second lead wire may also pass through an eyelet in the base portion of the lamp base shell, where it can be trimmed, fluxed and soldered. An embodiment of the present invention will now be described by way of example only and with reference to the accompanying drawings in which:- FIG. 1A shows an elevation of a prior art inner shell from one end; FIG. 1B shows a partial cross-sectional view, taken along line 1B-1B of FIG. 1A; FIG. 1C shows a side elevation of the prior art inner shell shown in FIG. 1A; FIG. 1D shows a partial cross-sectional view, taken along line 1D-1D of FIG. 1C; FIG. 1E shows an elevation of the prior art inner shell shown in FIG. 1A from the other end; FIG. 2 is a perspective view of a preferred embodiment of the inner shell of the present invention. FIG. 3 is a partial cross-sectional view of a lamp including a lamp base shell and a lamp tube utilizing a preferred modified inner shell of the present invention. The present invention provides a modified lamp base inner shell that can be used to secure a lamp base shell to a lamp base. A modified lamp base inner shell according to a preferred embodiment of the present invention is shown in FIG. 2. A modified lamp base inner shell 20 includes a washer-like base 11 having an outer rim 12 and an inner rim 13, which define a surface 14 and an opening 15. The inner shell further includes a cylindrically-shaped body having screw threads 16 extending from base 11 to a plurality of cut-out portions 17. Cut-out portions 17 may define an equal number of tabs 18, each having an indentation forming a projection 19 which extends inwardly. One extended cut-out portion 17' extends to the washer-like base 11. The modified lamp base inner shell 20 is typically made from a metal material which may be compatibly welded to a lamp's ground lead wire (not shown in FIG. 2). Preferably, lamp base inner shell 20 is made of the same nickel material used to make the ground lead wire. More preferably, inner shell 20 is made from cold-rolled steel or nickel plated cold-rolled steel, which can be compatibly welded to nickel ground lead wires and is typically less expensive than solid nickel. Inner shell 20 is formed from a sheet of the selected metal having a thickness of between about 0.38mm (0.015 inch) to 0.64mm (0.025 inch). This thickness, however, may vary depending on the size and type of the lamp base. The modified lamp base inner shell 20, as shown in FIG. 2, is similar to inner shell 10 shown in Figures 1A-1E and described above, except for the extended cut-out portion 17' which extends to the outer rim 12 of base 11. Washer-like base 11 includes outer rim 12 and inner rim 13 which define surface 14 and opening 15. Rims 12 and 13 are typically concentric circles forming an annular surface 14 as well as a circular central opening 15. Surface 14 and opening 15, however, may be formed in various shapes and sizes provided that surface 14 has sufficient surface area for attachment of the lamp's ground lead wire, and opening 15 is sufficiently wide to pass the ground lead wire and a second lead wire (not shown in FIG. 2). Threaded portion 16 extends upwardly from the outer periphery of base 11 approximately one half of the length of inner shell 20. The threads 16 are conventionally rolled or otherwise formed by inward deformation of the inner shell wall so as to establish complementing inner and outer threads in the wall. Cut-out portions 17 extend down to the top of threaded portion 16 and form a plurality of tabs 18. Typically, both cut-outs 17 and tabs 18 are rectangularly shaped. However, various other shapes may be used. Tabs 18 are between about one-third and one-half of the total length of inner shell 20, to provide sufficient contact with the lamp base for lamp stability. Tabs 18 each have an indentation 19 which is typically located at the end of the tab furthest from surface 14. Indentations forming projections 19 extend inwardly toward the axis of inner shell 20. Indentations 19 may be shaped in any configuration, such that they can be placed into depressions which are typically moulded into the lamp base. Preferably, indentations 19 conform with the shape of the moulded depressions to provide a tight fit between the inner shell 20 and the lamp base. In the modified lamp base inner shell 20 according to a preferred embodiment of the present invention, the at least one extended cut-out portion 17' provides access to the interior of the inner shell 20. Due to the placement of inner shell 20 on a lamp base such that only tabs 18 extend over the lamp base surface, the extended cut-out portion 17' provides access to the lamp base as well as the interior of the inner shell. This extended cut-out portion 17' permits the ground lead wire to be resistance welded to the outer surface 14 in an automated manufacturing process. One electrode, typically about 4.75 mm (3/16 inch) in diameter, can easily be placed in cut-out portion 17' while a second electrode is placed above the ground lead wire, which passes through opening 15 and is folded upon surface 14. Formerly, the ground lead wire was resistance welded to the outer portion of base 11 by manually manipulating the electrodes and inner shell. Referring now to FIG. 3, a preferred modified inner shell 20, including base 11 having a cylindrically shaped threaded portion 16 and a plurality of cut-out portions 17, 17', defining a number of tabs 18 having indentations 19 is shown securing a lamp base shell 21 to a lamp base 22. The assembly process includes placing inner shell 20 over lamp base 22 until indentations 19 mate with depressions 23, which are typically moulded into the lamp base 22 of lamp tube 24. After inner shell 20 is in place, a ground lead wire 25, which extends from the bottom portion 26 of lamp tube 24 and passes through inner shell 20 opening 15 (see FIG. 2), is resistance welded to base 11. A second lead wire 27 also passes through opening 15 of inner shell 20. After ground lead wire 25 is welded to base 11, the lamp base shell 21 is screwed onto inner shell 20 such that tabs 18 and indentations 19 are covered by base shell 21. Base shell 21 is then staked above the hollow threaded portion 16 of inner shell 20 to secure the lamp base shell 21 to the inner shell. Lastly, lead wire 27 is trimmed and fluxed and is soldered, as is known to those skilled in the art, to a base 28 of lamp base shell 21. Typically, a modified lamp base inner shell 20 according to a preferred embodiment of the present invention as claimed is used in high intensity arc discharge lamps, including high pressure sodium, mercury, and metal arc lamps. However, as may be apparent to those skilled in the art, the modified lamp base inner shell 20 may also be used with various other metal shell-to-ceramic or glass systems, including, for example, incandescent lamps, fluorescent lamps, flashbulbs, or standard screw-type fuses which utilize various sizes and types of bases. In a preferred embodiment, the modified lamp base inner shell 20 of the present invention as claimed is used to secure a large lamp base shell 21, or mogul, to a high intensity discharge lamp base 22. The lamp base shell 21 is in the form of a thin-walled cylinder, having a diameter of about 38mm (1.50 inches) and a length of about 41mm (1.625 inches), including an inwardly directed flange 29 at one end and screw threads 30 extending from that end toward the other open end into which the high intensity discharge lamp tube 24 and inner shell 20 are inserted. The threads 30 are conventionally rolled or otherwise formed by inward deformation of the shell wall so as to establish complementing inner and outer threads in the wall of the lamp base shell 21. Shell 21 is typically formed from a copper-nickel alloy approximately 0.38mm (0.015 inch) thick. The high intensity discharge lamp base 22 has moulded frusto-conical depressions 23. The depressions 23 are tapered inwardly from approximately 5.08mm (0.20 inch) in diameter at the surface to about 1.91mm (0.075 inch) in diameter, and are approximately 0.51mm (0.02 inch) deep. In a preferred embodiment, lamp base inner shell 20 is made from a 0.51mm (0.02 inch) thick sheet of a nickel plated, cold-rolled steel. Inner shell 20 includes a washer-like base having a cylindrically-shaped threaded portion 16 extending from its outer periphery, and cut-out portions 17 which define coaxial tabs 18, each having a frusto-conical indentation extending inwardly, and one extended cut-out portion 17' which extends to the base 11. The inner shell 20 is approximately 21.8mm (0.860 inch) long, the base has an outside diameter of approximately 36.7mm (1.445 inches) and an inside diameter of about 22.2mm (0.875 inch). The threaded portion 16 is approximately 13.1mm (0.515 inch) long, while the rectangular shape cut-out portion 17 and tabs 18 are approximately 8.76mm (0.345 inch) long. Cut-out portions 17 are also approximately 8.76mm (0.345 inch) in width, while tabs 18 are approximately 14.6mm (0.575 inch) wide. Extended cut-out portion 17' is approximately 21.3mm (0.840 inch) long and 87.6mm (0.345 inch) wide. Indentations 19, which have a frusto-conical shape are centered at the end of tab 18, and decrease in diameter from about 0.51mm (0.20 inch) at the tab surface to about 1.91mm (0.075 inch) at an angle of approximately 35 degrees. FIGS 1A-1E show prior art arrangements, in which inner shell 10 has a washer-like base 11 having an outer rim 12 and an inner rim 13, which define a surface 14 and an opening 15. The inner shell 10 further includes a cylindrically-shaped body having a screw thread 16 that extends from the base 11 to a plurality of cut-out portions 17. The cut-out portions 17 define an equal number of tabs 18. Each tab having an indentation 19, or dimple, which corresponds with a depression moulded in the neck of the lamp base. The inner shell is secured to the lamp base by manually placing it over the base until the dimples mate with the corresponding depressions in the lamp tube. The lamp base typically extends into the inner shell 10 up to the beginning of the screw threads 16, about the length of the cut-out portions 17 and the tabs 18. When the inner shell 10 is in place, a lamp base shell is securely screwed onto the threads 16 and is staked, or pierced, to engage it with the inner shell. The base shell is staked into the threads 16 to prevent inadvertent cracking of the lamp base which does not extend behind the threads 16. In addition to the initial mating of indentations with the depressions moulded in the lamp base, the tightening of the lamp base shell on the inner shell 10 forces the tabs and indentations closer to the lamp base. Inner shells are typically made from any of the materials including nickel, nickel-iron alloy, cold-rolled steel, or nickel-plated steel to provide a compatible welding surface for two lead wires, typically extending from the lamp base. A side, or ground, lead wire is resistance welded to the outer portion of the surface 14 prior to the securing and staking of the lamp base shell. A center lead wire typically passes through an eyelet in the base portion of the inner shell and the lamp base shell, where it is trimmed, fluxed, and soldered. This configuration, while securing the lamp base shell and providing electrical contact, requires several parts and difficult manual assembly, particularly with respect to welding the side lead wire to the surface 14 of the inner shell 10. This approach results in costly, time consuming, and inefficient lamp production. Preferred embodiments of the present invention as claimed may provide an improved lamp base inner shell which is cost effective and provides for an efficient assembly line operation; and even for automated production of high intensity discharge lamps.

Claims: A lamp base inner shell (20) comprising a base (11) and a wall (16,18) extending from the periphery of said base, the wall having a plurality of slots (17) extending from the free end thereof towards the base, the slots defining a number of tabs (18), at least one tab having a projection (19) which extends inwardly toward the axis of said inner shell (20), characterised in that at least one slot (17') extends substantially to said base (11). An inner shell as claimed in claim 1 characterised in that said wall (16,18) is substantially cylindrical and includes a threaded portion (16). An inner shell as claimed in claim 1 or 2 characterised in that there are four slots (17). An inner shell as claimed in claim 1, 2 or 3 characterised in that the inner shell (20) is made from nickel, steel, or nickel-plated steel. An inner shell as claimed in any of the preceding claims characterised in that an indentation forming said projection (19) is frusto-conical shaped. A high intensity discharge lamp assembly comprising a high intensity discharge lamp tube having a base portion (22), a lamp base inner shell (20) mounted on said base portion, and a lamp base shell (21) located on said inner lamp base shell (20), characterised in that said lamp base inner shell (20) is as claimed in any of the preceding claims. A method of fabricating a high intensity discharge lamp assembly in which a lamp base inner shell (20) as claimed in any preceding claims, is mounted to a base portion (22) of a high intensity discharge lamp tube (24), comprising the steps of placing the inner shell (20) onto the lamp base, locating said inner shell on said lamp base by said at least one inwardly-extending projection engaging a receiving indentation in said lamp tube (24), passing a heating means through said slot (17') which extends substantially to the base of the inner shell, and joining a wire (25) from said lamp tube (24) to said inner shell (20) by the application of heat from said heating means. A method as claimed in claim 7 characterised in that said wire (25) is joined to said inner shell (20) by soldering. A method as claimed in claim 7 characterised in that said wire (25) is joined to said inner shell (20) by resistance welding.

Inventors: LILLJEDAHL DONALD W, WILLIAMSON GLEN P, LILLJEDAHL, DONALD W., WILLIAMSON, GLEN P.
Applicants: FLOWIL INT LIGHTING, FLOWIL INTERNATIONAL LIGHTING (HOLDING) B.V.
Application year: 1993
Main classification: H01J61
IPC codes: H01J5, H01J9, H01J61