US3713201A

US3713201A - Method and apparatus for manufacturing mercury-vapor control assemblies for electric discharge devices

Info

Publication number: US3713201A
Application number: US00143426A
Authority: US
Inventors: G Evans
Original assignee: Westinghouse Electric Corp
Current assignee: Philips North America LLC
Priority date: 1971-05-14
Filing date: 1971-05-14
Publication date: 1973-01-30
Anticipated expiration: 1990-01-30

Abstract

The mercury-vapor pressure within a fluorescent lamp is controlled by an amalgam-forming metal that combines with mercury and is enclosed in a foraminous container disposed at a selected location within the lamp envelope. The vapor-pressure control assembly is fabricated from two strips of wire mesh that are pressed into overlying sandwiched relationship with a strip of amalgam-forming metal by passing the strips between a pair of rollers. Leakage of the amalgam-forming metal (and amalgam) when in a fluid state is prevented by providing a border of overlapped wire mesh that is devoid of metal and extends around the periphery of the assembly. Mass production on a continuous basis is achieved by using two sets of paired rollers, one set of which includes cutting means that severs the strip of amalgam metal and permits segments of the metal to be removed before the second wire mesh strip is pressed into place. The composite mesh-amalgam strip is then severed along the resulting gaps between the enclosed lengths of amalgam metal.

Description

United States Patent 1 Evans 1 Jan. 30, 1973 [54] METHOD AND APPARATUS FOR MANUFACTURING MERCURY-VAPOR CONTROL ASSEMBLIES FOR ELECTRIC DISCHARGE DEVICES [75] Inventor: George S. Evans, Caldwell, NJ.

[73] Assignee: Westinghouse Electric Corporation,

Pittsburgh, Pa.

[22] Filed: May 14, 1971 [21] Appl. No.: 143,426

Related U.S. Application Data [62] Division of Ser. No. 32,924, April 29, 1970, Pat. No.

[52] U.S. Cl ..29/414, 29/200 D, 29/432, 29/521, 313/174 [51] Int. Cl. ....B23p 17/00, B23p 19/00, B23p 11/00 Primary Examiner-Thomas H. Eager Att0rneyA. T. Stratton, W. D. Palmer and D. S. Bleza [57] ABSTRACT The mercury-vapor pressure within a fluorescent lamp is controlled by an amalgam-forming metal that combines with mercury and is enclosed in a foraminous container disposed at a selected location within the lamp envelope. The vapor-pressure control assembly is fabricated from two strips of wire mesh that are pressed into overlying sandwiched relationship with a strip of amalgam-forming metal by passing the strips between a pair of rollers. Leakage of the amalgamforming metal (and amalgam) when in a fluid state is prevented by providing a border of overlapped wire mesh that is devoid of metal and extends around the periphery of the assembly. Mass production on a continuous basis is achieved by using two sets of paired rollers, one set of which includes cutting means that severs the strip of amalgam metal and permits segments of the metal to be removed before the second wire mesh strip is pressed into place. The composite mesh-amalgam strip is then severed along the resulting gaps between the enclosed lengths of amalgam metal.

10 Claims, 6 Drawing Figures METHOD AND APPARATUS FOR MANUFACTURING MERCURY-VAPOR CONTROL ASSEMBLIES FOR ELECTRIC DISCHARGE DEVICES CROSS-REFERENCE TO RELATED APPLICATIONS This application is a division of application Ser. No. 32,924 filed Apr. 29, 1970, now U.S. Pat. No. 3,614,506 and is related to the subject matter of application Ser. No. 381,503, now PAT. No. 3,619,697 entitled MERCURY VAPOR DISCHARGE LAMP AND PRESSURE REGULATING MEANS THEREFOR of George S. Evans, the present inventor, which application was filed July 9, 1964, and is assigned to the same assignee as the present application.

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to electric discharge devices and has particular reference to a method and apparatus for manufacturing mercury-vapor pressure control assemblies for fluorescent lamps.

2. Description of the Prior Art Mercury-vapor discharge lamps having an amalgam which regulates the mercury-vapor pressure within the lamp during operation are, per se, well known in the art. A lamp of this type is disclosed in U.S. Pat. No. 3,007,071 issued Oct. 31, 1961 to A. Lompe et al.

In the aforementioned Evans application Ser. No. 381,503, now U.S. Pat. No. 3,619,697 the mercuryvapor pressure within a fluorescent lamp is controlled by an amalgam of a selected parent metal and mercury that is held at a predetermined location .on the lamp stem by a collar which is fabricated from wire cloth or mesh. Since the vapor pressure above the amalgam is less than that above liquid mercury at the same temperature, the use of such an amalgam as the vapor control means permits the lamp to be operated at optimum efficiency over a much wider range of ambient temperatures. This is a distinct advantage in outdoor lighting applications and in applications where the lamp is operated in a totally enclosed fixture.

in accordance with the method of fabricating such collar assemblies disclosed in the aforesaid Evans application, a mercury-amalgamative metal (such as indium) is sandwiched between two pieces of suitable foraminous material, (such as nickel wire mesh) by feeding continuous string of these materials between a pair of rollers. The resulting continuous lamination is then cut into sections of the required length and formed into an annular collar that is attached to one of the lamp stems. The strips of wire mesh are wider than the indium strip and the latter is centrally located between the wire mesh members, thus leaving a border along each side of the resulting lamination that is free of indium. These borders act as buffer zones or barriers which prevent the molten indium from migrating to and leaking" out of the sides of the collar during the sealing-in and other phases of lamp fabrication that heat the stem to a temperature above the melting point of the indium. However, experimental runs in the factory revealed that drops of molten indium would frequently fall off the cut ends of the collar where the indium was exposed. Excessive amounts of such loose indium in the finished lamp would, of course, alter the mercury-vapor pressure during operation and could adversely affect both the performance and quality of the lamps.

OBJECTS AND SUMMARY OF THE INVENTION It is accordingly the general object of the present invention to provide an improved mercury-vapor control assembly for an electric discharge device which obviates the foregoing and other problems associated with the use of an amalgam as the pressure-regulating means in such devices.

Another and more specific object is the provision of the method and apparatus for fabricating such assemblies efficiently on a mass production basis.

Briefly, the foregoing objects (and other advantages which will become apparent as the description proceeds) are achieved in accordance with the present invention by manufacturing the assemblies in such a way that an indium-free border is provided at each end of the assembly as well as along its sides. The sandwiched strip of indium, or other suitable amalgamative metal, is thus completely encircled by a fence of overlapped wire mesh that is free of such metal and thus prevents drops of molten metal from collecting at and dropping off the cut ends of the assembly. The improved leak-proof assemblies are made from continuous strips of wire mesh and amalgamative metal by removing preselected segments of the metal strip during the laminating operation and cutting the lamination along the metal-free regions.

BRIEF DESCRIPTION OF THE DRAWING A better understanding of the invention will be obtained by referring to the accompanying drawing, in which:

Hg. 1 is an elevational fragmentary view of a fluorescent lamp embodying the present invention, a

portion of the bulb being removed for convenience of illustration;

which simultaneously compresses and cuts preselected portions of the strip of amalgam-forming metal;

FIG. 5 is a fragmentary enlarged view of the partlyfabricated lamination illustrating an optional step in the manufacturing process; and

FIG. 6 is a view similar to FIG. 4 illustrating the final pressing operation.

While the present invention can be used with advantage in various types of gaseous discharge devices that require a vapor controlcomponent, it is particularly adapted for use in fluorescent lamps and has accordingly been so illustrated and will be so described.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawing in detail, in FIG. 1 there is shown a fluorescent lamp comprising a vitreous tubular envelope 12 that has the customary coating 14 of suitable ultraviolet-responsive phosphor on its inner surface and the usual electrode mounts l6 sealed into each of its ends. Each of the mounts supports a cathode 18 that is connected by

lead wires

19 and 20 to the terminals of a suitable base member 22 attached to each end of the envelope. One of the mounts 16 is provided with a tubulation that is tipped off in a usual manner after the lamp has been evacuated, dosed with mercury and filled with a suitable inert starting gas such as argon, neon or a mixture thereof. The other mount (located at the left end of the lamp 10 as viewed in Flg. 1) is fitted with a mercury-vapor pressure control assembly 28.

As is illustrated more clearly in FIG. 2, the aforesaid mount 16 consists of the usual flared vitreous stem 24 and

lead wires

19 and 20 which support the cathode l8 and are sealed through a press formed on one end of the stem. A pair of enlarged

metal anode

25, 26 are also disposed on opposite sides of the cathode l8 and are held in this position by the protruding ends of the respective lead wires. The control assembly 28 consists of a strip of suitable amalgamative material, such as indium, that is sandwiched between two strips of foraminous metal, such as nickel wire mesh. The resulting lamination is bent into a collar that is slipped over the stem 24 and held in encircling relationship therewith by a resilient wire clamp 30. A mount of this type and the manner in which the laminated collar assembly 28 controls the mercury vapor pressure within the lamp during operation is described in detail in the aforesaid application Ser. No. 381,503.

The present invention is directed to the problem of retaining the amalgam-forming metal within the cellular structure of the assembly during the sealing-in and subsequent phases of lamp manufacture when the metal is in a liquid state. An improved control assembly which overcomes this problem and a method and apparatus for manufacturing it will now be described.

As shown in FIG. 3, the assembly 28 (prior to being bent into collar form) consists of an elongated rectangular strip of indium 32 that is sandwiched and centrally located between two

rectangular strips

34 and 36 of suitable formaninous material such as nickel wire mesh. Since indium is a relatively soft metal at room temperature, the pressure applied to the overlying strips of wire mesh in forming the lamination partly embeds them in the indium. This welds or bonds the various strips together into an integral assembly 28 that can be handled and bent without coming apart.

As will be noted, the wire mesh strips 34 and 36 are wider and longer than the indium strip 32. There is, accordingly, a margin or border B of overlapped wire mesh that extends around the periphery of the assembly and is devoid of indium. This indium-free border serves as a barrier which prevents the leakage of molten indium from the edges of the collar, even though the wire mesh strips may be fabricated from nickel or other suitable material that is wet by the amalgam.

The relative dimensions of the strips are such that the edges of the indium strip 32 are spaced inwardly from the corresponding edges of the aligned overlying wire mesh strips 34 and 36 by at least 1/16 of an inch. The indium, or other amalgam-forming metal that is used, is thus confined within a border B that is defined by contiguous overlapped portions of the wire mesh strips and is of uniform width.

MANUFACTURING METHOD AND APPARATUS (FIGS 4-6) While a vapor-pressure control assembly of the type shown in FIG. 3 can be manufactured by stacking individually cut pieces of wire mesh and amalgam-forming metal in the proper relationship and then compressing them to force the amalgamative metal into the mesh openings, this would be a time-consuming and clostly operation since a soft metal such as indium is very difficult to cut and handle and the severed edges of the mesh members inherently tend to become entangled. A continuous method of fabrication would, of course, be more efficient and practical, especially in view of the fact that fluorescent lamps are manufactured on a mass production basis. Such a method and a preferred apparatus for practicing it are shown in FIGS. 4 and 6.

As shown in FIG. 4, the first step comprises placing a continuous strip 32 of indium in overlying relationship with a continuous strip 34 of wire mesh and feeding the two strips between a pair of smooth-faced rollers 38 and 40 which rotate in opposite direction (as indicated by the arrows) and are so spaced that the wire mesh strip is pressed into and at least partly embedded in the indium strip. The roller 40 which contacts the indium strip 32' is provided with a pair of suitable cutting elements such as

knives

41 and 42 that extend transversely across and protrude from the work face of the roller. The knives project beyond the work face of roller 40 a distance substantially equal to the thickness of the indium strip 32' and are spaced apart a distance equal to approximately twice the width. of the indium-freeborder B desired at the cut ends of the completed assembly 28. The peripheral distance from the knife 41 around the work face of the roller 40 to the other knife 42 is equivalent to the length of the individual pieces 32 of indium required for the assemblies 28.

The rollers 38 and 40 are rotated at a suitable speed by a motor and gear arrangement (not shown) or other means.

Thus, the rollers 38 and 40 press the first wire mesh strip 34 into the indium strip 32 and concurrently form a series of closely-spaced

transverse cuts

43 and 44 in the latter which divides it into altemately-disposed long segments 32 and short segments 45, as shown in FIG. 4. A recess 46 is also provided in the work face of the roller 40 between the

knives

41 and 42, thereby forming a relief cavity or pocket that extends across the roller face. Thus, only the long segments 32 of indium are pressed against the bonded to the wire mesh strip 34 and the short segments 45 merely lie on top of the mesh, as indicated in FIG. 4.

The short segments 45 of indium are then removed from the wire mesh strip 34 by a jet of compressed air or suitable mechanical means (not shown). If desired, such removal can be achieved with the aid of gravity by inverting the lamination produced by the rollers 38 and 40 so that the

indium segments

32 and 45 face downwardly.

Alternatively, the lamination may be bent along an axis located between the pair of

cuts

43 and 44 in the indium strip 32, as shown in F IG. 5, in a direction such that the short segments 45 of indium are bent into an arch and separated from the underlying mesh strip 34. The protruding indium segments are then stripped from the mesh by a suitable tool.

The removal of the short segments 45 of indium provides a continuous ribbon or lamination (shown in the left-hand portion of FIG. 6) which consists of a strip 34 of wire mesh that is bonded to a plurality of indium segments 32. These segments are of uniform length and separated by a series of indium-free gaps G. The lamination is then aligned with a second strip 36 of wire mesh and the two components are fed through a second set of pressing rollers 48 and 5t as shown in H6. 6. This completes the basic assembly operation and produces a continuous mesh-indium-mesh lamination having a series of uniformly spaced transversely-extending gaps G that are devoid of indium. The lamination is then out along lines which bisect the aforementioned gaps, thereby producing the desired discrete assemblies 28 of the type shown in FIG. 3.

Since indium is very soft, even at room temperature, it may stick to the roller 40 used in the first pressing operation. Hence, this roller (or at least its work face) is fabricated from a material, such as a suitable plastic, that is harder than and does not adhere to indium or indium-rich alloys at room temperature. An example of a suitable plastic is nylon.

It will be appreciated from the foregoing that the objects of the invention have been achieved in that a simple method and apparatus for efficiently and conveniently making leak-proof vapor control assemblies in mass production quantities have been provided.

While preferred embodiments have been illustrated and described, it will be appreciated that various modifications in the method of and apparatus for manufacturing the mercury-vapor control assemblies can be made without departing from the spirit and scope of the invention.

For example, the

knives

41 and 42 and recess 46 in the roller 40 may be designed in such a manner that roller lifts the severed short segments 45 of indium from the underlying wire mesh strip 34. Also, an additional set or sets of knives spaced predetermined distances peripherally from the first pair can be used, if the diameter of the roller 40 is increased proportionately to prevent shortening the pressed lengths 32 of indium.

Under certain conditions, it may also be desirable to apply half of the required amount of indium to a strip of wire mesh in the manner shown in FIG. 4, and then combine two such laminations in another roll-pressing operation to obtain a composite indium-impregnated mesh ribbon having a larger indium loading.

Space limitations within the lamp may also require that the thickness of the collar assembly be increased by using a plurality of stacked indium-impregnated wire mesh strips. This type of assembly can very readily be made by merely repeating the indium-mesh pressing operation and using additional sets of driven rollers having properly spaced work faces.

I claim as my invention: 1. The method of fabricating mercury-vapor control assemblies for electric discharge devices, which method comprises:

positioning a strip of foraminous material in overlying aligned relationship with a strip of a relatively soft metallic material that has an affinity for and combines with mercury to form an amalgam,

making a pair of closely-spaced cuts across said strip of amalgamative material at predetermined spaced intervals and thereby dividing it into a series of alternately-disposed short and long segments,

pressing only the long segments of amalgamative material against the strip of foraminous material so that the latter is at least partly embedded in the respective pressed segments, removing the short unpressed segments of said amalgamative material from said strip of foraminous material to provide a series of spaced transverselyextending gaps therealong that are devoid of amalgamative material, positioning a second. strip of material in overlying relationship with the pressed segments of amalgamative material and on the side thereof opposite said strip of foraminous material so that the amalgamative material is disposed therebetween,

pressing said second strip of material against said amalgamative material so that the latter holds the resulting continuous lamination together, and then severing the foraminous strip and said second strip along each of said transversely-extending gaps to provide a plurality 'of laminated assemblies wherein the amalgamative material is spaced inwardly from each of the cut ends of the respective assemblies.

2. The method set forth in claim 1 wherein the conjoined foraminous strip and strip of amalgamative material resulting from the first pressing operation is oriented so that the amalgamative material faces downwardly and the removal of the cut unpressed short segments of such material is facilitated by the force of gravity.

3. The method set forth in claim 1 wherein the cut unpressed short segments of amalgamative material are removed from the partly-fabricated laminate by an impinging jet of compressed air.

4. The method set forth in claim 1 wherein;

the conjoined foraminous strip and strip of amalgamative material resulting from the first pressing operation is (a) bent along a plurality of transversely-extending lines that are located between each pair of closely-paced cuts in said amalgamative material and (b) at an angle such that the cut short segments of such material are displaced outwardly away from the underlying segment of the foraminous strip, and the said cut-and-displaced segments of amalgamative material are removed by mechanical means. 5. The method of claim 1 wherein; said strip of formainous material and said second strip of material are both wider than the strip of amalgamative material, and said strip of amalgamative is so positioned during the roll-pressing operations that its side edges are spaced inwardly from the corresponding edges of the overlying strips and the end and side portions of the resulting laminated assemblies are this devoid of amalgamative material.

6. Apparatus for manufacturing laminated mercuryvapor control assemblies that include a strip of relatively soft amalgamative material and are adapted for use in electric discharge devices, said apparatus comprising a pair of rotatable rollers that are disposed to receive and compress therebetween a strip of said amalgamative material and a strip of another material that are arranged in overlapping relationship,

a pair of spaced cutting elements carried by one of said rollers and arranged so that said elements extend across and protrude a predetermined distance beyond the work face thereof, and means for rotating said rollers in opposite directions,

7. The apparatus set forth in claim 6 wherein the work face of the roller with said cutting elements has a recess therein a that is located between and extends along said cutting elements and provides a relief cavity thereatj 8. The apparatus set forth in claim 6 wherein the roller with said pair of cutting elements has at least another pair of cutting elements that protrude from its work face and are spaced a predetermined distance peripherally from the first pair of cutting elements.

9. The apparatus set forth in claim 6 wherein the work face of the roller with said pair of cutting elements is composed of a material which is harder than and does not adhere to indium or indium-rich alloys at room temperature 10. The apparatus set forth in claim 6 wherein;

a second pair of rollers with generally smooth work faces are disposed beyond the first pair of rollers and are arranged to receive the lamination produced thereby, and

said second pair of rollers are coupled to driving means adapted to rotate said second pair of rollers in the same direction and at the same speed as the first pair of rollers.

Claims

1. The method of fabricating mercury-vapor control assemblies for electric discharge devices, which method comprises: positioning a strip of foraminous material in overlying aligned relationship with a strip of a relatively soft metallic material that has an affinity for and combines with mercury to form an amalgam, making a pair of closely-spaced cuts across said strip of amalgamative material at predetermined spaced intervals and thereby dividing it into a series of alternately-disposed short and long segments, pressing only the long segments of amalgamative material against the strip of foraminous material so that the latter is at least partly embedded in the respective pressed segments, removing the short unpressed segments of said amalgamative material from said strip of foraminous material to provide a series of spaced transversely-extending gaps therealong that are devoid of amalgamative material, positioning a second strip of material in overlying relationship with the pressed segments of amalgamative material and on the side thereof opposite said strip of foraminous material so that the amalgamative material is disposed therebetween, pressing said second strip of material against said amalgamative material so that the latter holds the resulting continuous lamination together, and then severing the foraminous strip and said second strip along each of said transversely-extending gaps to provide a plurality of laminated assemblies wherein the amalgamative material is spaced inwardly from each of the cut ends of the respective assemblies.

4. The method set forth in claim 1 wherein; the conjoined foraminous strip and strip of amalgamative material resulting from the first pressing operation is (a) bent along a plurality of transversely-extending lines that are located between each pair of closely-paced cuts in said amalgamative material and (b) at an angle such that the cut short segments of such material are displaced outwardly away from the underlying segment of the foraminous strip, and the said cut-and-displaced segments of amalgamative material are removed by mechanical means.

5. The method of claim 1 wherein; said strip of formainous material and said second strip of material are both wider than the strip of amalgamative material, and said strip of amalgamative is so positioned during the roll-pressing operations that its side edges are spaced inwardly from the corresponding edges of the overlying strips and the end and side portions of the resulting laminated assemblies are this devoid of amalgamative material.

6. Apparatus for manufacturing laminated mercury-vapor control assemblies that include a strip of relatively soft amalgamative material and are adapted for use in electric discharge devices, said apparatus comprising a pair of rotatable rollers that are disposed to receive and compress therebetween a strip of said amalgamative material and a strip of another material that are arranged in overlapping relationship, a pair of spaced cutting elements carried by one of said rollers and arranged so that said elements extend across and protrude a predetermined distance beyond the work face thereof, and means for rotating said rollers in opposite directions.

7. The apparatus set forth in claim 6 wherein the work face of the roller with said cutting elements has a recess therein that is located between and extends along said cutting elements and provides a relief cavity thereat.

8. The apparatus set forth in claim 6 wherein the roller with said pair of cutting elements has at least another pair of cutting elements that protrude from its work face and are spaced a predetermined distance peripherally from the first pair of cutting elements.

9. The apparatus set forth in claim 6 wherein the work face of the roller with said pair of cutting elements is composed of a material which is harder than and does not adhere to indium or indium-rich alloys at room temperature