Patent Publication Number: US-9892905-B2

Title: Stranded outer lead wire assembly for quartz pinch seals

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Patent Application No. 62/262,768, filed Dec. 3, 2015, said application hereby incorporated in its entirety by reference herein. 
    
    
     TECHNICAL FIELD OF THE INVENTION 
     The present invention relates to lead-in wire assemblies for use in fused silica pinch seals and, more particularly to connection of an additional wire to the external portion of said assemblies. 
     BACKGROUND OF THE INVENTION 
     Referring to prior art examples shown in  FIGS. 1-3B , lamps  900  such as a 1000 watt double ended horticultural lamp (1000 W DE), e.g., with a high pressure sodium (HPS) arc tube inside a “quartz” (fused silica) outer jacket, have a special “base”  920  (e.g., designated as a K12×30 s base) that interfaces with a corresponding fixture socket (see  FIGS. 3A-3B ) in order to hold the lamp in the fixture while also providing electrical connection to the lamp lead wires. The base  920  comprises an outer lead assembly  932  made from a stranded (a.k.a. “braided”) Ni wire (may be an alloy such as NiMn)  918  that is mechanically and electrically attached to a refractory metal (e.g., molybdenum (Mo) or Mo alloy) outer pinch lead wire  916  that extends out of a “pinch seal”  924  end of the quartz outer jacket  922  of the lamp  900 . 
     As shown in  FIGS. 3A-3B  a typical fixture socket for this K12×30 s base  920  has a pair of flat faced contact plates to clamp the outer lead assembly  932  (should be only the stranded wire lead  918  part of the outer lead assembly  932 ). The socket clamping/contact plates are a fixed longitudinal distance apart, and registered against the pinch seal ends  924  to be a fixed distance away from each pinch  924  (which is why the pinch is considered part of the lamp base  920 , along with the outer lead assembly  932 ). Regarding lamp installation in the fixture/sockets, keep in mind that the lamp  900  is typically pushed upward into an overhead fixture wherein the lamp hangs underneath the sockets. To install a lamp  900 , the lamp body is held and used to push the lamp outer lead assemblies  934  into the “bottom” of the space between opened contact plates, holding the pinch seals  924  against stops in the socket, and sliding the sockets until they lock in a closed position where the contact plates are squeezed together to pinch the lead wire to make a mechanical and electrical connection. The contact plates are only located at the “bottom” of the gap, so if a lead assembly  934  is bent away from the bottom when inserted (e.g., by misalignment or by being dragged by some kind of interference), then the clamping plates may only partly contact the lead wire. Given the high current (e.g., 8 amps) supplying the lamp, and high starting voltages, a poor electrical connection can cause arcing and/or overheating leading to serious consequences. 
     The attachment/connection  932  in the outer lead assembly  934  between two generally round wires is difficult, especially because: they cannot be soldered due to high lamp operating temperature; and a mechanical/compression joint by itself (e.g., using a surrounding sleeve that is crushed around the overlapping ends) is not reliable due to cyclic thermal expansion and contraction of dissimilar metals and further due to surface oxidation developing over time. This connection is even more challenging because the wires are such different metals with different melting points, have different diameters (e.g., 1 mm solid vs. ˜1.5 mm twisted bundle), and different amounts of hardness/compressibility (stranded Ni is more easily deformed by compression, while solid Mo is relatively hard and non-compressible). Furthermore, the stranded wire has, for example, 19 strands that are twisted together like a cable, which makes resistance welding very difficult and inconsistent due to variable resistance between strands. Finally, as further detailed below, the connection  934  must be made after lamp sealing, so the outer pinch lead  116  will generally be oxidized so that it must be cleaned before a connection can be made. 
     The connection method that has been in use in the prior art is a combination of resistance spot welding of various portions of overlapping wire ends and a sleeve that is crimped around one or both of the overlapping wire ends. This prior art connection will be generically referenced herein as a “crimp connection”  932 , even though welding is also typically involved. For example, the sleeve may be crimped around both wire ends to hold them together and the spot weld(s) are made simultaneously through all of the overlapping layers, or separately where the sleeve overlaps each wire. Or, for example, the sleeve may not surround the wires so that the spot welds can be made separately between each lead and the sleeve, thereby passing weld current through only one layer of the sleeve material. Before resistance welding, any oxidation must be cleaned off the wire surface(s), for example by brushing or sand blasting. The longitudinal positioning of the sleeved connection  934  is not precise enough to ensure adequate connection unless there is extra overlapping length (i.e., a larger target) in which the connection can be made. Therefor any solid wire  916  extending beyond the sleeve is usually trimmed off in an attempt to avoid potential interference with the socket clamp (see  FIG. 1A ). 
     Other techniques and method variations may be employed to establish the prior art electrical-mechanical connection designated herein as a crimp connection  932 , however they all produce similar results as shown in  FIGS. 2-3  by images of the assembly  934  from three different prior art lamp manufacturers. What the examples show is (a) offset misalignment of the Mo outer pinch lead  916  and the stranded Ni lead  918 , (b) a stranded lead that is offset from the lamp axis in different directions (“crankshaft”—compare ends of the lamp in  FIG. 2 ), (c) a stranded lead  918  that is typically not straight and may also extend outward at an angle to the outer pinch lead  916 , and (d) an irregularly shaped larger diameter portion (a lump or bump) where the sleeve covers the connection  932 . Any of these irregularities can cause serious electrical problems if it interferes with optimum closure of the socket clamps which need to compress and grip a significant length of the stranded lead. 
       FIGS. 1-3  show typical construction details and example images of prior art implementations of this base  920  in a 1000 W DE HPS horticultural lamp  900  as made and sold by three different lamp making companies. The lamp is a high power HID light source (e.g., HPS) sealed in a tubular quartz outer jacket  922 , the quartz material being used to withstand the very high operating temperature imposed on the envelope of a lamp like this, which is a horizontal burning high wattage lamp with a close fitting outer jacket having a gas fill. 
     Also referring to  FIGS. 1-2 , for hermetically sealing a quartz envelope  922  around an electrical lead wire  916 , a quartz pinch seal  924  is made (e.g., prefabricated) using a 3 part foliated lead assembly  910  wherein the inner pinch lead  912  and outer pinch lead  916  are solid wires (typically round) that are welded to the face of a thin foil  914 , all made of refractory metal(s) such as some form of molybdenum (Mo). During the pinch sealing operation the 3 part foliated lead assembly  910  is held in position and the quartz tube end is heated enough for it to be pinched flat into a generally planar shape as shown. 
     Importantly, in the prior art the stranded wire lead can only be added (to complete the lamp “base”) after the pinch seal is completed. This is because the prior art crimp connection  932  between the Mo outer pinch lead and the Ni stranded wire will not survive the extreme heating it would receive during the quartz pinch sealing process (quartz/fused silica “glass” requires the most intense heat of all lampmaking glass materials, e.g., 2,000 C versus around 1500 C for hard glass). As a result of the heating in atmosphere, the outer pinch lead  916  develops an oxide layer that must be removed (e.g., by sand blasting, brushing, etc.) before an acceptable weld connection can be made. Further complicating matters, the heating causes partial recrystallization of the Mo wire, making it somewhat brittle, therefor the crimp connection process must take care to avoid breaking the Mo wire. (The recrystallization may be controlled by using doped moly.) 
     There are many disadvantages and potential problems with this prior art “crimp connection”, including one or more of the following:
         Crimp connection can have a poor (high resistance) electrical connection of Ni to Mo because mixed materials overlapped and wrapped in sleeve do not make a good weld using a resistance welder.   Crimp connection can cause an insecure hold and/or poor (high resistance) electrical connection between the outer lead and the fixture socket due to irregularly shaped crimp connection, inconsistent location, and non-aligned offset wires. (The socket uses a pair of flat faced contact bars to clamp the Ni stranded wire lead at each end. The socket clamps are a fixed longitudinal distance apart so inaccurate crimp connection location can result in a socket clamping onto the crimp sleeve instead of the Ni stranded wire.)   Offset or otherwise misaligned outer leads may tilt the lamp off of the optimum axial location in the fixture reflector. Keeping the arc tube (which is mounted on center axis of the lamp) centered is important for the reflector because all DE reflectors are designed to efficiently reflect the light produced by the lamp based on the arc tube being positioned in the center of the reflector, otherwise this will change the optics and efficiency of the reflector, the fixture, and the overall lighting quality.   Crimp connection is a complicated process that is difficult to automate and is therefor time consuming/expensive.   Quality control issues include: length of connected outer lead, amount of overlap, location of overlap, non-zero angle between wires, and the like.       

     BRIEF SUMMARY OF THE INVENTION 
     According to the invention a stranded outer lead wire assembly for a quartz pinch sealed lamp. The stranded outer lead wire assembly is a butt welded connection of a refractory metal outer pinch lead (e.g., molybdenum solid wire) and a stranded soft metal lead wire (e.g., nickel wire strands twisted together). The assembly is prefabricated and then welded to sealing foil to make a four part foliated lead wire assembly for pinch sealing in the quartz outer jacket. The foliated lead wire assembly and a quartz envelope lamp utilizing the stranded outer lead wire assembly are also claimed. The sealing machine is adapted to protect the stranded outer lead assembly with a water cooled sleeve. In an embodiment, the outer end of the stranded lead is fused to prevent fraying. 
     Other objects, features and advantages of the invention will become apparent in light of the following description thereof. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Reference will be made in detail to preferred embodiments of the invention, examples of which are illustrated in the accompanying drawing figures. The figures are intended to be illustrative, not limiting. Although the invention is generally described in the context of these preferred embodiments, it should be understood that it is not intended to limit the spirit and scope of the invention to these particular embodiments. 
       Certain elements in selected ones of the drawings may be illustrated not-to-scale, for illustrative clarity. The cross-sectional views, if any, presented herein may be in the form of “slices”, or “near-sighted” cross-sectional views, omitting certain background lines which would otherwise be visible in a true cross-sectional view, for illustrative clarity. 
       Elements of the figures can be numbered such that similar (including identical) elements may be referred to with similar numbers in a single drawing. For example, each of a plurality of elements collectively referred to as  199  may be referred to individually as  199   a ,  199   b ,  199   c , etc. Or, related but modified elements may have the same number but are distinguished by primes. For example,  109 ,  109 ′, and  109 ″ are three different versions of an element  109  which are similar or related in some way but are separately referenced for the purpose of describing modifications to the parent element ( 109 ). Such relationships, if any, between similar elements in the same or different figures will become apparent throughout the specification, including, if applicable, in the claims and abstract. 
       The structure, operation, and advantages of the present preferred embodiment of the invention will become further apparent upon consideration of the following description taken in conjunction with the accompanying drawings, wherein: 
         FIG. 1  shows a plan view and a side view, with cutaway/cross-section portion indicated by circle “c”, of a prior art lamp having a K12×30 s base exemplifying a prior art outer lead with crimp connection. 
         FIG. 1A  shows a magnified view of a base portion of the prior art lamp of  FIG. 1 . 
         FIG. 2  is a plan view image of an example #1 of the prior art lamp of  FIG. 1 . 
         FIG. 2A  is a perspective view image, with magnified outside end portion (frayed), of a prior art stranded lead wire. 
         FIG. 3  shows images of prior art outer lead assembly portions as implemented in example prior art lamps made and sold by three different lamp making companies. 
         FIGS. 3A and 3B  are perspective views of an example prior art fixture having a typical socket for the K12×30 s base, and illustrating a lamp being installed. 
         FIG. 4  shows a side view and a plan view, with cutaway/cross-section portion indicated by label, of a lamp having a K12×30 s base exemplifying an outer lead with a butt weld connection according to the present invention. 
         FIG. 4A  is a magnified detail view of a portion of  FIG. 4  indicated by circle “A”. 
         FIG. 4B  is a magnified detail view of a portion of  FIG. 4A  indicated by circle “B”. 
         FIG. 4C  is a perspective view image, with magnified connection and fused end portions, of a base portion of a lamp having an outer lead assembly according to the present invention. 
         FIGS. 5A-5D  are side views of steps in a process for prefabricating an outer lead assembly, a 3-part foliated lead, and a 4-part lead wire assembly, all according to the present invention. 
         FIG. 6  is a partial side view image of an outer lead assembly according to the present invention. 
         FIG. 7  is an annotated illustration that describes an outer lead assembly bending test procedure according to the present invention. 
         FIG. 8  shows tabulated results of lead assembly bending tests using the procedure of  FIG. 7  on a prior art assembly (using a crimp connection) compared to an assembly using a butt weld according to the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The following table is a glossary of terms and definitions, particularly listing drawing reference numbers or symbols and associated names of elements (features, aspects) of the invention(s) disclosed herein or of related elements in the prior art. 
     
       
         
           
               
               
             
               
                   
               
               
                 REF. 
                 TERMS AND DEFINITIONS 
               
               
                   
               
             
            
               
                   
                 ELEMENTS OF THE INVENTION(S) 
               
               
                 100 
                 lamp using the disclosed butt welded lead wire assembly 106 
               
               
                   
                 with quartz outer jacket 122 and a pinch seal 124 (e.g., high 
               
               
                   
                 wattage, double ended outer jacket, with one lead-in wire at 
               
               
                   
                 each end) 
               
               
                 102 
                 butt welded connection of outer pinch lead 116 and stranded lead  
               
               
                   
                 wire 118, butt weld nugget 
               
               
                 104 
                 prefabricated outer lead assembly, 116 and 118 joined by butt  
               
               
                   
                 weld connection 102, for inclusion in a 4-part lead wire  
               
               
                   
                 assembly 106; all assembled before sealing in quartz pinch 
               
               
                 106 
                 prefabricated 4-part lead wire assembly for sealing in a quartz 
               
               
                   
                 pinch seal 
               
               
                 108 
                 fused end of stranded lead 118 (e.g., TIG welded) 
               
               
                 110 
                 3-part foliated lead portion of prefabricated 4-part assembly 106 
               
               
                   
                 (inner 112 and outer 116 pinch leads welded to foil 114) 
               
               
                 112 
                 inner pinch lead 
               
               
                 114 
                 quartz pinch sealing foil 
               
               
                 116 
                 outer pinch lead 
               
               
                 118 
                 stranded lead wire 
               
               
                 120 
                 “Base” portion of the pinch sealed lamp 100 that includes a  
               
               
                   
                 stranded lead wire 118 that is connected 102 to the outer pinch 
               
               
                   
                 lead 116 
               
               
                 122 
                 quartz outer jacket of lamp 
               
               
                 124 
                 quartz pinch seal (e.g., double ended with one lead-in wire 
               
               
                   
                 assembly) 
               
               
                   
                 ELEMENTS OF THE PRIOR ART, ILLUSTRATED FOR  
               
               
                   
                 COMPARISON AND CONTRAST WITH ELEMENTS OF  
               
               
                   
                 THE DISCLOSED IMPROVED LAMP 
               
               
                 900 
                 prior art lamp with quartz outer jacket 922 and a pinch seal 924  
               
               
                   
                 (e.g., high wattage, double ended outer jacket, with one lead-in 
               
               
                   
                 wire at each end) 
               
               
                 910 
                 preassembled 3-part foliated lead for sealing in a quartz pinch  
               
               
                   
                 seal 924, a.k.a. lead-in wire assembly (for outer jacket) 
               
               
                 912 
                 inner pinch lead 
               
               
                 914 
                 quartz pinch sealing foil 
               
               
                 916 
                 outer pinch lead 
               
               
                 918 
                 stranded lead wire 
               
               
                 919 
                 outside end of stranded lead 918 (showing fraying) 
               
               
                 920 
                 “Base” portion of the pinch sealed lamp 900 that includes a  
               
               
                   
                 stranded lead wire 918 that is mechanically (e.g., crimp) 
               
               
                   
                 connected 930 to the outer pinch lead 916 
               
               
                 922 
                 quartz outer jacket of lamp 
               
               
                 924 
                 quartz pinch seal (e.g., double ended with one lead-in wire 
               
               
                   
                 assembly) 
               
               
                 932 
                 mechanical (and electrical) connection of stranded lead wire 
               
               
                   
                 918 to the outer pinch lead 916, typically includes a crimped- 
               
               
                   
                 on sleeve plus resistance weld of overlapping ends of the wires 
               
               
                   
                 916, 918 
               
               
                 934 
                 prior art outer lead assembly = 916 and 918 joined by crimp 
               
               
                   
                 connection 932 
               
               
                   
               
            
           
         
       
     
     The invention(s) will now be described with reference to the drawings using the reference numbers and symbols listed in the above table. 
     A significant part of the present inventive concept is to replace the crimp connection  932  with a butt weld connection  102  as illustrated in  FIGS. 4-6  The butt weld connection provides many advantages over the crimp connection. For example, it allows consistently optimum clamping in the socket because the butt weld nugget  102  has a relatively uniform shape without any protruding bumps and is always at a fixed distance from the pinch seal end  124 , as determined by the length of the outer pinch lead  116 . Also, the connected conductors are coaxially aligned, thus always placing the full length of the outermost lead (stranded lead  118 ) in the center of the socket clamps, thereby also accurately positioning the lamp  100  (and arc tube) at the focal line of the fixture reflector. 
     In addition to the greatly improved shape, as shown particularly in  FIG. 4B  and more generally in  FIGS. 4A-6 , the weld nugget is formed by a butt welding operation that melts an end portion of the Ni strands  118  such that the molten metal flows around a length of the Mo wire end  116  to form a low electrical resistance, mechanically strong connection more like a braze or arc weld connection. The contact area between the two wires is much larger than for a spot weld even one with a crimped sleeve (e.g., prior art connection  932 ), and furthermore the contact area is substantially sealed against subsequent oxidation. 
     An added advantage of the butt weld is that it is made before lamp sealing, for example by prefabricating an outer lead wire assembly  104  (stranded Ni leadwire  118  plus solid wire (e.g., Mo) outer pinch lead  116 ) as shown in the step of  FIG. 5A to 5B . This may be done on automated welding equipment before the outer pinch lead  116  is welded to the foil  114  as in making a 3 part foliated lead  110  (step of  FIG. 5C to 5D ). In other words, a 4 part lead wire assembly  106  is made (prefabricated) before the pinch seal  124  is formed on it. Previously, only the 3-part foliated lead  110  was prefabricated. In a preferred embodiment, the 4 part lead wire assembly  106  is a prefabricated assembly of the inner pinch lead  112 , the sealing foil  114 , and the outer lead assembly  104 , which can be done on a 3 part lead making machine that is adapted to hold the assembly  104  such that the outer pinch lead wire  116  part of the assembly  104  can be welded to the foil  114  as before. The outer lead assembly  104  is made on a separate butt welding machine, for example one that feeds both the wire  116  and the lead  118  off of reels/spools, pushes the ends together while welding heat is applied, pauses to solidify, and then cuts both outer ends to desired length. (This description may omit other details that are known to be included, e.g., an interface material between the foil and the lead wires welded to it.) 
     An additional feature of the outer lead assembly  104  prefabrication is to create a fused end  108  (see  FIGS. 4A, 4C and 5B ) on the stranded lead  118  outer end to prevent a frayed end (see prior art example frayed end  919  shown in  FIG. 2A ). This may be done using a TIG welder. 
     Prefabricating the entire (4-part) lead wire assembly  106  (using a butt welded connection  102 ) is much easier to do than the prior art crimp connection  930  because all of the (weld) connections can be made on a dedicated purpose machine in a controlled environment on a convenient schedule without having to hold a bulky sealed lamp  100  that may get in the way of the crimp and welding equipment. This is easier to automate thereby avoiding manual operations, and thereby reducing cost. 
     The butt weld equipment and process described here is an adaptation of a process previously used to make a butt weld connection between stranded Ni wire and a round solid tungsten lead wire (not Mo). The prior art lead wire assembly is distinguished by the use of round tungsten wire because it is for sealing in a hard glass stem. Tungsten has a thermal expansion coefficient that is suitable for such seals in “hard glass” so it is used without foil. It is important to note that hard glass sealing is accomplished at much lower temperatures (1500-1600 C) than for quartz glass sealing (approximately 2000 C), therefor the butt weld has never been previously suggested for use with quartz sealing lead wires. It was not obvious to try butt weld connected stranded nickel outer lead wire for quartz pinch seal leads because the general assumption has been that the nickel part of the butt weld would (obviously) soften/melt to fall apart, and/or would become too brittle as a result of the extreme heat of quartz pinch sealing being sufficient to affect the wire microstructure. 
     Thus the herein disclosed butt welded quartz pinch outer leadwire assembly  104 , and the associated lampmaking process/method, is novel in that it is used as a lead wire for a quartz jacket  122  lamp  100  with a quartz pinch seal  124  that exposes the butt weld  102  and the stranded nickel lead wire  118  to much higher temperatures for a longer duration compared to hard glass sealing. Therefor it was not obvious that this would work, and experimentation and testing was needed to address the concerns about weld integrity after quartz pinch sealing. In particular, the quartz pinch operation has been adapted to protect the butt welded outer lead assembly  104  during sealing. Whereas the previous operation did not protect the exposed outer pinch lead  916 , our inventive modifications to the pinch sealing machine add a water cooled sleeve that protectively encloses the assembly  104 , i.e., the stranded lead  118 , the weld connection  102  and an external portion of the outer pinch lead wire  116 . 
     It may be noted that in our lamps, the wire we have labeled as “Mo” (molybdenum, a.k.a. “moly”), especially the outer pinch lead  116  is preferably lanthanated molybdenum (“ML wire”), which is Mo doped with lanthanum oxide LaO3 to increase its recrystallization temperature. (to preserve adequate ductility after being subjected to the extreme heating of the quartz pinch sealing process (˜2000 C). There are other doping agents for refractory metals known to have similar benefits, so the present disclosure is not specifically limited to lanthanated moly outer pinch lead  116 , however that is a preferred (best known mode) embodiment of the outer pinch lead  116  that is butt welded to the stranded Ni lead wire  118 . This is the material that we have tested so far and we know it works in terms of making an adequately flexible, non brittle outer leadwire assembly  104 . We started with the ML wire because we have had a positive experience with its use for at least the sealing foil part of foliated leads in quartz pinch seals. 
     Prior art butt welded stranded Ni lead wire assemblies were designed to be sealed in hard glass which requires tungsten wire in order to seal properly (instead of foil or dumet). Recrystallization embrittlement is not as much a problem for this because hard glass only needs to be heated to about 1500-1600 C during its sealing process. 
     Regarding concerns about the effects of quartz pinch sealing temperature, we examined the structure and microstructure of the weld nugget before and after sealing with our adapted sealing machine.  FIGS. 4C and 6  are magnified views of photos taken after sealing What we see leads to the following conclusions: 
     a) that the “weld nugget”  102  is a tapered volume of melted Ni wire strands that flowed and fused over the unmelted end of the Mo wire. 
     b) that the weld structure is substantially unchanged by the heat from sealing the Mo wire in the quartz pinch. (This is helped by our use of lanthanated moly wire (“ML”) which resists and minimizes recrystallization embrittlement.) 
     In  FIGS. 7-8  our bending test is described and results tabulated. The bending test was performed to determine if the assembly  104  was unacceptably embrittled by the quartz pinch sealing process. For comparison, the bending test was also conducted on a prior art crimp connection (as found in Phillips lamp samples). Unexpectedly, our butt weld connection showed no significant difference in the test results before vs. after pinch sealing. On the other hand, the crimp connections were significantly more brittle than our butt weld connections. 
     Tensile tests were also conducted to determine if weld strength was affected. Since our butt weld tensile strength exceeded the ability of our test machine to measure it, we cannot determine differences, if any, before versus after sealing, however the tester did show that our butt weld connection was significantly stronger than the prior art crimp connection. 
     We concluded that our butt weld connection is better than the prior art connection in every way. 
     Although the invention has been illustrated and described in detail in the drawings and foregoing description, the same is to be considered as illustrative and not restrictive in character—it being understood that the embodiments shown and described have been selected as representative examples including presently preferred embodiments plus others indicative of the nature of changes and modifications that come within the spirit of the invention(s) being disclosed and within the scope of invention(s) as claimed in this and any other applications that incorporate relevant portions of the present disclosure for support of those claims. Undoubtedly, other “variations” based on the teachings set forth herein will occur to one having ordinary skill in the art to which the present invention most nearly pertains, and such variations are intended to be within the scope of the present disclosure and of any claims to invention supported by said disclosure.