US3102443A

US3102443A - Mechanism for forming ribbon leads

Info

Publication number: US3102443A
Application number: US649513A
Authority: US
Inventors: Paul A Dell; Elmer G Fridrich
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1957-03-29
Filing date: 1957-03-29
Publication date: 1963-09-03
Anticipated expiration: 1980-09-03

Description

s p 3, 1963 P. A. DELL ETAL 3,102,443

I MECHANISM FOR FORMING RIBBON LEADS Filed March 29, 1957 2 Sheets-Sheet 1 L9 lnvesn tovs'.

PauL A.DeLL, Etmer Gfridrich,

Thai? A b tor'neg.

Sept. 3, 1963 P. A. DELL ETAL MECHANISM FOR FORMING RIBBON LEADS 2 Sheets-Sheet 2 Filed March 29, 1957 lnvavtors:

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This invention relates to lamp making in general, and more particularly to apparatus for cross-rolling a lead-in Lvige to form a flattened portion for sealing .into a vitreous In sealing a metallic conductor or lead-in wire through quartz or quartz-like glass, the very high temperatures necessary for fusing into quartz restricts the choice of metal available for all practical purposes to molybdenum and tungsten. Both of these metals have coeflicients of expansion much greater than that of quartz; molybdenum, which is the metal more commonly used, has a coeflicient of expansion approximately ten times that of quartz. Accordingly, it is necessary to shape or proportion the conductor in such fashion that it will yield to the quartz during their unequal contractions after sealing. This is achieved by shaping a portion of the molybdenum conductor as a thin ribbon or foil, for instance a ribbon not over one mil (.001 inch) thick. The metal in such a lead having become bonded to the quartz at a relatively high temperature will merely go into tension when the quartz cools, but will not rupture nor crack the quartz.

The practice up to the present time in sealing molybdenum conductors through quartz has been to use either Welded ribbon leads or longitudinally rolled, flattened wire leads. The welded leads are made by cutting a piece of molybdenum toil into strips a few millimeters Wide and of the proper length required for the seal and Welding molybdenum wires to each end to provide the current connections. Welded molybdenum ribbon leads require considerable manual labor to manufacture and are comparatively expensive. Moreover, considerable wastage occurs during their manufacture due to the difficul-ty of controlling the welding temperature, and trequently the welded joints contain hidden defects and rupture during assembly into lamps.

Longitudinal-1y rolled one-piece molybdenum wire leads oller a definite advantage over welded ribbon leads. The one-piece leads are described and claimed in Patent 2,667,595Noel et al.,\and may be made by longitudinally rolling a central portion of a length of molybdenum wire back and forth between a pair of hardened cylindrical rolls as described and claimed in my Patent 2,670,- 640. These leads are easier to manufacture than the welded ribbon leads and are not subject to emb-rittlement at the joints. They are extensively used by applicants assignee in the manufacture of high-pressure mercury vapor lamps using quart-z arc tubes and of tubular filament type quartz heat lamps.

In the longitudinally rolled wire leads, the metal of the wire is not only flattened in cross section but is also stretched longitudinally. As a result, the cross sectional area of the conductor is greatly reduced in the flattened portion over what it is in the round wire portions. For instance in longitudinally rolled ribbon leads made from 22 mil molybdenum wire flattened down to .a thickness of approximately 0.6 mil, the cross sectional area in the flattened section may be only about 7 to 8 percent of the original. wire cross section. The current carrying capacity of a lead-in conductor is, of course, limited by the area of the least cross section. For many applications, and particularly in the larger sizes of lamps, it is often desirable to have lead-in conductors with much greater aren't panying drawings.

pacity of the longitudinally rolled ribbon lead in commen use. In cross rolling, as much as 50 to percent of the original wire cross section is retained in the flattened ribbon or foil portion. As a result of the greater cross sectional area of the flattened portion, these leads are much stiffer and less fragile than the longitudinally rolled leads. a

An object of the invention is to provide .an improved method of forming foil portions in metal leads for sealing into vitreous material.

Another object oi the invention is to provide an effective and convenient apparatus for cross rolling a flattened portion in wire or ribbon leads of refractory metals such as molybdenum and tungsten.

Another object of the invention is to provide a mechanism for cross rolling flattened portions having controlled lateral taper and maximum edge thickness for effective sealing into quartz.

In accordance with the invention, a cross rolled ribbon portion is formed in a length of wire or relatively thick ribbon by placing the piece lengthwise between a pair of hardened rolls, that is in such fashion that the axes of the rolls and the wire are in the same plane. The rolls, are so formed that their centers of curvature are further removed from the working plane where they engage the wire than their respective centers of rotation. The rolls are forced together by .a suitable pressure system and are oscillated a number of times through a small angle. In a preferred arrangement suitable for cross rolling molybdenum wire, tungsten carbide pressure tools having cylindrically formed working faces are mounted in rockers having suitably curved outer rolling surfaces which rock on opposed plane parallel pressure platforms. Only one of the rockers is actuated to oscillate the system, the other rocker being oscillated by friction drive only through the lead wire and the pressure tools. By reason of the location of the centers of curvature of the pressure tools at a greater distance from the working plane than the centers of curvature of the rockers, the pressure tools generate during their oscillations a lead cross section which may be described as double convex, that is thick in the middle and thin at each edge with a controlled taper.

For fuztherobjects and advantages and for a fuller appreciation of the various features of the invention, attention is now directed to the following description of a preferred embodiment taken in conjunction with the accom- The features of the invention believed to be novel will be more particularly pointed out in the appended claims.

In the drawings:

FIG. 1 is a side view of a cross rolling device embodying the invention.

FIG. 2 is a side sectional view of the pressure tool and rocker assemblies.

FIG. 3 is a front sectional view of the pressure tool and rocker assemblies.

FIG. 4 is a diagram of the pressure tool and rocker assemblies illustrating the principles of operation.

FIG. 5 is a much enlarged plan view of a cross rolled molybdenum lead.

"FIGS. 66:, b and c illustrate successive stages in the making of a cross rolled molybdenum lead according to a preferred technique.

Referring to the drawings and more particularly to FIGS. 1 to 3, there are provided upper and lower rocker assemblies 1, 2 arranged to roll on opposed upper and

lower pressure platforms

3, 4 providing plane parallel surfaces. Upper platform 3 is fastened to a top plate 5 rigidly supported by four posts or pillars 6 above a bottom plate 7 which, in' turn, is fastened to a frame member 8. Lower pressure platform 4 is provided as a raised step on a crosshead 9 which is provided on opposite sides with bushings 10 accommodating guide rods 11 fastened into the upper pressure platform 3. The two guide rods make a sliding fit into the bushings and thereby keep the 'lower pressure platform in parallel alignment with the upper. Pressure is applied to cross-head 9 of lower platform 4 through a bumper bar 12 by the piston 13 of a conventional hydraulic jack 14 secured to lower plate '7. The jack is of a conventional kind commonly used with automobiles and is actuated by swinging the lever 15 up and down to work the pump plunger 16. The jack contains the usual check or non-return valve cooperating with the pump plunger 16 to prevent return of fluid so that the spacing of the pressure platforms is rigidly controlled. In the particular jack used, a lever 15 for hanging weights 17 gives a force multiplication of 180 times and allows development of a pressure load of 806 to 1500 pounds with weights of convenient size.

The rocker assemblies, as best seenin FIGS. 2 and 3, each comprise a holder 18 having a curved rolling surface 19 which rolls on the pressure platform. The opposite face of the holder is milled transversely to the axis of rolling to provide a slot 21 accommodating pressure tool 22,. Each pressure tool has a curved forward face 23 and is generally T-shaped in cross section as shown in FIG. 2, being provided with overhanging shoulders 24 which are engaged by clamping plates 25 secured to the holder by screws 26.

necessary to apply force to one only of the rocker assemblies in order to drive both, and to this end there is provided lever 31 secured to one side of rocker assembly 2 by the screws 26. The short shaft ends 32r on the holder body are useful mainly in machining the piece to provide accurate rolling surfaces. In the assembly illustrated in FIG.1, they provide a convenient means for holding the rocker assemblies in place while the machine is at rest and the pressure tools are withdrawn. To this end, the shaft ends are engaged by retaining bars 33 supported by helical springs 34 in the case of upper rocker assembly 1,.

and by coiled springs 35 in the case of lower rocker assembly 2.

Due to the tremendous unit pressures required to work molybdenum, the pressure tools 22 are preferably made of some very hard material suchas tungsten carbide. The working surfaces 23 of the tools are formed as short cylindrical sections the'ends of which are blended into a side radius indicated at 36 in FIG. 3 which form smooth transitions in the lead 37 from the rolled flattened central portion 38 to the thicker ends 39 as shown in FIG. 5.

FIG. 4 illustrates diagrammatically how the rolling and working surfaces of the rocker assemblies provide the desired cross section in the flattened portion of the lead 37. The centers C of the radii of curvature R of the rolling surfaces of the holders are closer to the work ing plane W containing lead 37, than the centers C of the radii of curvature R of the working surfaces of the pressure tools. In this particular embodiment, the radii .R of the rolling surfaces are also shorter than the radii R of the working surfaces, but this is not an essential condition.

When the rocker assemblies are oscillated, the loci of the centers of curvature C of the rolling surfaces are the straight lines L parallel to the surfaces of the

pressure platforms

3, 4. However, the loci of the centers of curvature C of the working surfaces are curved lines L concave towards the working plan-e. Geometrically, the loci L are intermediate cycloids as generated by points intermediate the center and the rim of a rolling wheel. Accordingly, the points of engagement betweenthe working surfaces of the pressure tools and the lead 37 move closer together as the rocker assemblies depart from their rest condition of alignment. The points of engagement also shift laterally slightly less than the centers of rotation C but the extent of lateral shift is of no consequence. The lead wire itself is translated laterally back and forth as the rocker assemblies are oscillated and since thedistance apart of the

pressure platforms

3 and 4 is held substantially constant by the hydraulic jack 14 containing substantially incompressible oil, the lead is constrained into the cross section generated by the working surfaces of the pressure tools.

As illustrated in FIG. 4, the cross section 38 is thick in the middle and thin at each edge and may be described generally as double convex. The appearance of the cross rolled lead in plan View to the same scale as the cross section illustrated in PEG. 4 is shown in FIG. 5.

It will be appreciated that whereas the rocker and plane pressure platform arrangement constitutes the preferred form of the invention, it is possible to use a more conventional arrangement with suitable bearings for the shaft ends 32, enlarged if necessary to Withstand the load. Provided the centers of the bearings are closer to the Working plane W than the centers of curvature of the pressure tools, the required lead cross section can be generated in accordance with the invention.

In making cross. rolled ribbon leads, one may start either with round wire or with ribbon. The use of wire is somewhat more critical as it is necessary to center the wire very accurately between the pressure tools and to start off the oscillations of the rocker assemblies through a very small :arc in order to prevent the wire from being flipped out sideways during rolling. When molybdenum r ribbon instead of wire is used, the rolling operation is not so critical and the ribbon will not be flipped out from between the rolls unless very badly misaligned initially.

The cross roll-ed lead 37 illustrated in FIGS. 4 and 5 was made from molybdenum ribbon approximately 7 wide and 3.5 mils thick, such being the cross section of the unuolled ends 39. After rolling, the thickness at the center T :as indicated in FIG. 4 was approximately 2.5 mils and the thickness at the edges indicated by T was approximately 0.5 mils, the width of the flattened portion being approximately that is double the width of the ribbon previous to rolling. In using the rolled lead of FIG. 5 as a lead-in conductor in 1a discharge-device, if it is necessary to have wire terminals to support the electnodes or to make the current connections, suitable lengths of wire may be welded to the thick ribbon ends 39 of the leads. A preferred technique for making a lead-in conductor consists in starting with a round molybdenum wire 41 as illustrated in FIG. 6(a) and first forming a relatively thick central ribbon portion 42 as illustrated in FIG. 6(b). This may be done :by pressing or :by longitudinal rolling between pressure rolls, using for instance an apparatus such as described in my Patent 2,670,640. If the original wire was 30-mil wire, it may be initially rolled down to a thickness of approximately 3.5 mils and a width of @i In the next step, ribbon portion 42 is cross-rolled using the mechanism illustrated in FIG. 1 herein, producing the crossrolled portion 43 illustrated in FIG. 6(0). The center thickness in portion 43 will be approximately 2.5 mils and the edge thickness approximately 0.5 mils. The taper in thickness to the sidesis important for effective sealing into quartz. In general the angle a of taper ('FIG. 4) should be no great-er than approximately 5 degrees to minimize shalin g off of the quartz and yet assure the maximum current carrying capacity as a result of the greater thickness at the center.

By cross-rolling molybdenum ribbon leads using the mechanism of the present invention, lead-in conductors have been made having 2 /2 to 4 times the current carrying capacity possible with longitudinally rolled ribbon leads. For instance, the maximum capacity of longitudinally rolled ribbon leads made with 22 to 30 -mil molybdenum wire is in the range of 5 to amperes. The same Wires made into cross-rolled ribbon leads following the technique described With reference to FIG. 6 will provide a current carrying capacity upwards of 30 amperes.

While :a certain specific embodiment of the invention has been shown and described, it will of course be understood that various modifications may be made without departing from the invention. The details of mounting of the various components of the mechanism admit of many variations while yet preserving the essential features of the invention. The appended claims are, therefore, intended to cover any such modifications coming within the true spirit :and scope of the invention.

What we claim as new and desire to secure by Letters Patent of the United States is:

1. A mechanism for cross rolling and feathering the edges of a short section of a metal lead comprising a pair of opposed pressure tools having cylindrical Working surfaces adapted to engage the lead on opposite sides of a working plane, a pair of holders for said pressure tools each having :a cylindrical rolling surface on the side opposite from the pressure tool, a pair of opposed plane parallel pressure platforms engaged by the rolling surfaces of said holders, said holders being proportioned for angular oscillation about a rest position on centers of rotation closer to said working plane than the centers of curvature of said working surfaces, and means constraining said pressure platforms together to provide a predetermined gap between the working surfaces of said pressure tools in the rest position of said holders which gap diminishes substantially to zero at the limits of oscillation of said holders.

2. A mechanism for cross rolling and feathering the edges of 'a short section of a metal lead comprising a pair of opposed tungsten carbide pressure tools having cylindrical working surfaces with the ends blended into a side radius and adapted to engage the lead on opposite sides of a working plane, a pair of holders for said pressure tools, each holder accommodating a pressure tool on one side and having a cylindrical rolling surface on the opposite side and being so proportioned that the center of curvature of the Working surface of the pressure tool is located intermediate the rolling surface and its center of curvature, a pair of opposed plane parallel pressure platforms engaged by the rolling surfaces of said holders, said holders being proportioned for angular oscillation about a rest position on centers of rotation closer to said Working plane than the centers of curvature of said working surfaces, gear sectors on the sides of the cylindrical rolling surfaces of said holders engaging gear racks in said pressure platforms for positive alignment of the holders in their rest positions, and means constraining said pressure platforms together to provide a predetermined gap between the working surfaces of said pressure tools in the rest position of said holders which gap diminishes substantially to zero at the limits of oscillation of said holders.

References Cited in the file of this patent UNITED STATES PATENTS 16 ,630 Platt Feb. 10, 1857 74,570 Millard Feb. 18, 1868 88,003 Baker Mar. 23, 1869 146,598 Klein Jan. 20, 1874 1,536,777 Day May 5, 1925 2,291,408 Pearson July 28, 1942 2,667,595 Noel et a1 Jan. 26, 1954 2,670,640 Dell Mar. 2, 1954 FOREIGN PATENTS 13,060 Great Britain June 19, 1908 164,040 Great Britain May 30, 1921 605,660 France Feb. 20, 1926

Claims

1. A MECHANISM FOR CROSS ROLLING AND FEATHERING THE EDGES OF A SHORT SECTION OF A METAL LEAD COMPRISING A PAIR OF OPPOSED PRESSURE TOOLS HAVING CYLINDRICAL WORKING SURFACES ADAPTED TO ENGAGE THE LEAD ON OPPOSITE SIDES OF A WORKING PLANE, A PAIR OF HOLDERS FOR SAID PRESSURE TOOLS EACH HAVING A CYLINDRICAL ROLLING SURFACE ON THE SIDE OPPOSITE FROM THE PRESSURE TOOL, A PAIR OF OPPOSED PLANE PARALLEL PRESSURE PLATFORMS ENGAGED BY THE ROLLING SURFACES OF SAID HOLDERS, SAID HOLDERS BEING PROPORTIONED FOR ANGULAR OSCILLATION ABOUT A REST POSITION ON CENTERS OF ROTATION CLOSER TO SAID WORKING PLANE THAN THE CENTERS OF CURVATURE OF SAID WORKING SURFACES, AND MEANS CONSTRAINING SAID PRESSURE PLATFORMS TOGETHER TO PROVIDE A PREDETERMINED GAP BETWEEN THE WORKING SURFACES OF SAID PRESSURE TOOLS IN THE REST POSITION OF SAID HOLDERS WHICH GAP DIMINISHES SUBSTANTIALLY TO ZERO AT THE LIMITS OF OSCILLATION OF SAID HOLDERS.